saadurrehmansp11bec114d15ttt

PRODUCTION OF 2000 m3/hr OF SYN GAS FROM CO-GASIFICATION

USING CO2 SORBENT

SAAD UR REHMAN CIIT/SP11-BEC-114/LHR

M. RAHIL IFTIKHAR CIIT/SP11-BEC-098/LHR

SAJJAD AHMED CIIT/SP11-BEC-074/LHR

M. FAIZAN RAZZAQ CIIT/SP11-BEC-048/LHR

This report is submitted in partial fulfillment of

the requirements for the award of the degree of

Bachelor of Science in Chemical Engineering

Department of Chemical Engineering

COMSATS Institute of Information Technology

JANUARY 2

iii

To our Parents and Supervisor, Dr. Zakir Khan

xv

ACKNOWLEDGEMENTS

Firstly, we would like to thank ALLAH ALMIGHTY for providing us the strength and

the tolerance to successfully complete this project.

Next, we would like to thank our parents for providing us their moral support and

guiding us towards the right direction in approaching our task.

We would like to thank our head of department Dr. Asad U. Khan for providing us the

opportunity to complete this project.

We would like to express our great appreciation to Dr . Zaki r Khan for his valuable

and constructive suggestions during the planning and development of this project. His

willingness to give his time so generously has been very much appreciated.

We would also like to thank the supportive faculty of the department of chemical

engineering COMSATS Lahore. Finally, we would like to thank our class fellows for

their helpful suggestions during the course of the entire project.

xv

ABSTRACT

Gasification of carbonaceous solid fuels to convert into syngas for application of

power, liquid fuels and chemicals is practiced worldwide. Coal and biomass are major

feedstock for gasification. The concept of blending of coal and biomass will make the

gasification efficient and profitable. In this project mixture of coal and Sugarcane

Bagasse is used. Coal has high fixed carbon and ash content as compared to Sugarcane

Bagasse whereas Sugarcane Bagasse has high volatile matter as compared to coal.

Gasification with in situ carbon dioxide capture has good prospects for the production

of hydrogen enriched Synthesis gas. In this project, the mixture of coal and biomass is

dried and grinded before being fed to the gasifier. After gasification, the resultant gas

is cooled and cleaned by the help of Cyclone Separator and Scrubber. The resultant

gas has a lower heating value of 39630 KJ/Kg of Synthesis gas and consists of 76% of

Hydrogen on volume basis. There exists high potential for gasification production in

Pakistan due to presence of abundant coal sources and agriculture waste. Due to energy

and environmental issues, Synthesis gas has become a more attractive clean fuel.

Furthermore, gasification has become a sustainable technology for the production of

Synthesis gas.

xv

TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

TABLE OF CONTENTS vi

LIST OF TABLES x

LIST OF FIGURES xi

LIST OF SYMBOLS xii

LIST OF APPENDICES xv

1 LITERATURE REVIEW 1

1.0 Coal 1

1.1. Types of coal 1

1.2. Coal Properties 4

1.2.1. Heating Value 4

1.2.2. Caking and Swelling Properties 4

1.2.3. Hardness 5

1.2.4. Density 5

1.3. Coal Reserves in Pakistan 6

1.4. Biomass 8

1.4.1. Types of biomass in Pakistan 8

1.4.2. Biomass Analysis 9

1.4.3. Production of Crops and their Residue availability in Pakistan 9

1.4.4. Properties of Feed Stock Suitable for Gasification 10

1.4.5. Selection of Feed Stock 13

1.5. Application of Syn Gas 14

1.5.1. Heat 14

1.5.2. Electricity 14

1.5.3. Combined heat and power 14

1.5.4. Transport fuel 15

xv

2 PROCESS SELECTION 16

2.1. Methods of Syn Gas Production 16

2.1.1. Landfill 16

2.1.2. Gasification 17

2.1.3. Pyrolysis 18

2.2. Gasifier Types 18

2.2.1. Counter-current fixed bed ("Up draft") gasifier 19

2.2.2. Co-current fixed bed ("down draft") gasifier 20

2.2.3. Fluidized bed reactor 21

2.2.4. Entrained Flow Gasifier 22

2.3. Gasifier Selection 23

3 PROCESS DESCRIPTION 24

3.1. Description of the Process 24

3.1.1. Feed Treatment 25

3.1.2. Gasification 25

3.1.3. Gas Cleaning 26

3.1.4. Utility Section 27

3.2. Factors Affecting Gasification 27

3.2.1. Temperature 27

3.2.2. Pressure 27

3.2.3. Fuel Bed Height 27

3.2.4. Fluidization Velocity 27

3.2.5. Feed Properties 28

3.3. Block Diagram 29

3.4. Process Flow Diagram 30

4 MATERIAL BALANCE 31

4.1. Material Balance on Dryer 31

4.2. Material Balance on Mill 32

4.3. Material Balance on Gasifier 32

4.3.1. Gasification Reactions 33

4.4. Material Balance on Cyclone Separator 36

4.5. Material Balance on Scrubber 37

4.6. Overall Material Balance 39

5 ENERGY BALANCE 40

5.1. Energy Balance on Dryer 40

5.1.1. Heat Inlet 40

5.1.2. Heat Outlet 41

5.2. Energy Balance on Ball Mill 42

5.3. Energy Balance on Gasifier 42

5.3.1. Heat Inlet 42

5.3.2. Heat involved in Chemical Reactions 43

5.3.3. Heat Outlet 45

xv

5.3.4. Overall Energy Balance 45

5.4. Energy Balance on Cyclone Separator 45

5.5. Energy Balance on Scrubber 46

5.6. Overall Energy Balance 48

6 EQUIPMENT DESIGN 49

6.1. Dryer Design 49

6.1.1. Brief Introduction 49

6.1.2. Classification of Dryers 50

6.1.3. Selection of dryer 50

6.1.4. Direct Heat Rotary Dryer 51

6.1.5. Dryer Design 52

6.2. Gasifier Design 62

6.2.1. Fluidized Bed Reactor 62

6.2.2. Hydro Dynamics 62

6.2.3. Minimum Fluidization Velocity 62

6.2.4. Diameter of Reactor 65

6.2.5. Height of Reactor 67

6.2.6. Volume of Reactor 68

6.2.7. Distributor Plate Design 68

6.2.8. Number of Orifices in the Distributor Plate 69

6.2.9. Gasifier Specification Sheet 70

6.2.10. Gasifier Design Data 70

6.3. Cyclone Separator Design 71

6.3.1. General design procedure 71

6.3.2. Number of Cyclones 71

6.3.3. Inlet Duct area 72

6.3.4. Dimensions of Cyclone 72

6.3.5. Calculation of Scaling Factor 73

6.3.6. Pressure Drop Calculation 74

6.3.7. Cyclone Separator Specification Sheet 75

6.3.8. Cyclone Separator Design Data 75

6.4. Design of Scrubber 76

6.4.1. Designing Steps 76

6.4.2. Calculation of Height of Transfer Units (Onda’s Method) 81

6.4.3. Calculation of Liquid Film Mass Transfer Coefficient 81

6.4.4. Calculation of Gas Film Mass Transfer Coefficient 82

6.4.5. Calculation of Gas-film Transfer Unit Height 82

6.4.6. Calculation of Liquid-film Transfer Unit Height 83

6.4.7. Calculation of Height of Transfer Units 83

6.4.8. Calculation of Height of Tower 83

6.4.9. Pressure Drop Calculations 84

6.4.10. Scrubber Specification Sheet 85

6.4.11. Scrubber Design Data 85

xv

7 INSTRUMENTATION AND PROCESS CONTROL 86

7.1. Instrumentation 86

7.2. The Concept of Measurement in Automation Application 86

7.3. Measurement 87

7.4. Process 87

7.4.1. Process Control 87

7.4.2. Objectives of Process Control 88

7.5. Basic Elements of Process Control 89

7.6. Basics of Process Control 90

7.7. Selection of Controller 90

7.8. Control Loops 92

7.9. Control Schemes of Gasifier 94

7.10. Control Schemes of Scrubber 94

8 COST ESTIMATION 96

8.1. Introduction 96

8.2. Fixed Capital Investment 97

8.3. Working Capital 97

8.4. Cost Index 97

8.5. Purchased Equipment Cost 98

8.5.1. Estimate of Dryer Cost 98

8.5.2. Estimate of Ball Mill Cost 98

8.5.3. Estimate of Gasifier Cost 99

8.5.4. Estimate of Cyclone Separator Cost 100

8.5.5. Estimate of Scrubber Cost 101

8.6. Estimation of Working Capital 104

8.7. Total Investments 104

8.8. Production Costs 104

9 HAZOP STUDY 107

9.1. Introduction 107

9.2. Objectives of Hazop Study 107

9.3. Keywords used in HAZOP STUDY 108

9.4. Primary Keywords 108

9.5. Secondary Keywords 109

9.6. How to Conduct a Hazop Study 109

9.7. HAZOP Method Flow Diagram 111

9.8. Hazop Analysis on Fluidized Bed Reactor 112

9.9. Hazop Analysis on Dryer: 113

REFERENCES 114

APPENDICES 117

xv

LIST OF TABLES

TABLE NO. TITLE PAGE

1.1 Particle and Bulk Density 5

1.2 Ultimate and Proximate Analysis of Biomass 9

1.3 Production of Crops and their Residue availability in Pakistan 10

3.1 Operating Conditions and Process Parameters in the Gasifier 26

4.1 Proximate analysis of Coal and Biomass (Dry Basis) 33

4.2 Gasification Reaction 34

4.3 Gasifier Material 35

4.4 Product Gas Composition of Gasifier 36

4.5 Composition of Gas at Inlet of Scrubber 37

4.6 Outlet composition of Gases of Scrubber 38

4.7 Material Balance on Gasifier 44

5.1 Composition of Inlet Gas of Scrubber 46

5.2 Composition of Outlet Gases of Scrubber 47

6.1 Temperature of Inlet and Outlet Streams 54

6.1 Bed Material Properties 63

6.2 Fluidizing Gas Properties (at 950K and 1 atm) 63

6.3 Fluidizing Gas Properties (at 523K and 2 atm) 63

6.4 Proximate analysis of Coal and Biomass (Dry Basis) 65

6.5 Scrubber Material Balance 76

6.6 Scrubber Top Composition 77

8.1 Total Purchased Cost of Major Equipments 102

8.2 Typical factors for the estimation of project fixed capital cost 103

8.3 Fixed Capital Cost 103

9.1 Primary Keywords 108

9.2 Secondary Keywords 109

xv

LIST OF FIGURES

FIGURE NO. TITLE PAGE

2.1 Counter-current Fixed bed (Up draft) Gasifier 19

2.2 Co-current Fixed bed (Down draft) Gasifier 20

2.3 Fluidized Bed Reactor 21

2.4 Entrained Flow Gasifier 22

3.1 Block Diagram 29

3.2 Process Flow Diagram 30

4.1 Overall Material Balance 39

5.1 Overall Energy Balance 48

6.1 Direct Heat Rotary Dryer 51

6.2 Hydrodynamics Calculations 62

6.3 High through-put Cyclone 71

7.1 Control Schemes of Gasifier 94

7.2 Control Schemes of Scrubber 95

9.1 HAZOP Method Flow Diagram 111

xv

LIST OF SYMBOLS

F Feed

LHV Lower Heating Value

HHV Higher Heating Value

CGR Char Gasification Reaction

SMR Steam Methane Reaction

WGSR Water Gas Shift Reaction

H Humidity

Xa Inlet moisture content

Xb Final moisture content

Ar Archimedes Number

Ƿf Fluid Density

Ƿp Density of the Particle

Ƿb Density of the Bed

Emf Voidage at minimum Fluidization

Øs Sphericity

Dp Particle Diameter

Umf Minimum Fluidization Velocity

Remf Renold Number at minimum fluidization

S/C Steam to Carbon Ratio

Qo Initial Volumatric Flow Rate

Qmf Volumatric Flow Rate at minimum Fluidization

Dbm Bubble Diameter

R Distributor to bed pressure ratio

Δpb Bed pressure drop

Δpd Distributor pressure drop

Cd Drag Coefficient

UOR Velocity at Orifice

NOR Number of Holes at Orifice

xv

Dc Diameter of Cyclone

TH Total Height

AO Outlet Area

DO Outlet Diameter

UT Terminal Velocity

D2/D1 Scaling Factor

Dc2 Diameter of Cyclone

Dc1 Diameter of Standard Cyclone=0.203 m

Q1 Standard Flow Rate=0.0619 m3/sec

Q2 Volumetric Flow Rate

ρ1 Standard solid-fluid density =2000 kg/m3

ρ2 Particle density

μ1 Standard viscosity =0.018 Ns/m2

μ2 Gas viscosity

FC Friction factor, taken as 0.005 for gases

AS Surface area of cyclone exposed to the spinning

AI Area of inlet Duct

RT Radius of circle to which the centre line of the inlet

RE Radius of exit pipe

Δp Pressure Drop

C Porosity of packing factor

a Surface area of packing (m2/m3)

FLV Flooding Ratio of Liquid to Vapor

A Column Area

VW Vapor Mass Flow Rate

HOG Height of Overall Gas-phase transfer units

HG Individual Film Transfer Units for Gas

NOG Number of Overall Gas-phase transfer units

HL Individual Film Transfer Units for Liquid

HOL Height of Overall Liquid-phase transfer units

xv

NOL Number of Overall Liquid-phase transfer units

Gm Molar Gas Flow-Rate per unit cross-sectional area

Lm Molar Liquid Flow-Rate per unit cross-sectional area

αW Effective interfacial area of packing per unit volume

α Actual area of packing per unit volume

δL Surface tension of liquid

DL Diffusivity of liquid

Ф Association factor

xv

LIST OF APPENDICES

APPENDIX TITLE PAGE

A1 Char Gasification Reaction Equilibrium 117

A2 Equilibrium Methane Conversion at S/C =2 117

A3 CO Conversion in Water Gas Shift Reaction 118

A4 Temperature Pattern in Dryer 118

A5 Cyclone Pressure Drop Factor 119

A6 Standard Cyclone Dimension, High Gas Rate Cyclone 119

A7 Performance Curves, High Gas Rate Cyclone 120

A8 Scaled Performance Curve Cyclone 120

A9 Generalized Pressure Drop Correlation 121

A10 Number of Transfer units NOG as a function of y1/y2 121

A11 Installed Cost of Dryer 122

A12 Columns Plates. Time Base mid-2004 122

CHAPTER 1

LITERATURE REVIEW

1.0. Coal

Coal is a fossil fuel formed from plants that were buried millions of years

ago. The high-temperature, high-pressure conditions underground transformed the

plants physically and chemically, forming coal. Coal contains energy that the plants

absorbed from the sun millions of years ago. Burning coal releases this energy [1].

1.1. Types of coal

As geological processes apply pressure to dead biotic material over time,

under suitable conditions it is transformed successively into

Peat

Lignite

Sub-bituminous Coal

Bituminous Coal

Anthracite

2

All coal has been formed from biomass. Over time this biomass has been

turned into peat. When covered under a layer of overburden, the influence of time,

pressure, and temperature converts this material into brown coal or lignite.

Subsequently, the later material will turn into sub-bituminous coal, then into

bituminous coal, and finally into anthracite. Coal is often classified in terms of its

rank, which increases from brown coal to anthracite. Brown coal, lignite, and sub-

bituminous coals are called low-rank coals, whereas higher-rank coals are often

called hard coals. The terms brown coal and lignite are essentially synonymous,

lignite being used more often in the United States and brown coal in Europe and

Australia.

1.1.1. Peat

Peat, considered to be a precursor of coal, has industrial importance as a

fuel in some regions, for example, Ireland and Finland. In its dehydrated form, peat

is a highly effective absorbent for fuel and oil spills on land and water. It is also

used as a conditioner for soil to make it more able to retain and slowly release

water.

1.1.2. Lignite

Lignite is a brownish-black fossil fuel that is used primarily for electric

power generation. Considered to be a low-ranking type of coal, the fuel is usually

categorized by geologists as a recent fuel. Typically, it fits between peat and sub-

bituminous coal on geological solid fuel ranking scales. Lignite coal is burnable

and may also be referred to as brown coal. Geologically, lignite is believed to be

relatively young in age. Some geologists estimate that it formed roughly 251

million years ago.

3

1.1.3. Sub-bituminous coal

Sub-bituminous coal, whose properties range from those of lignite to those

of bituminous coal, is used primarily as fuel for steam-electric power generation

and is an important source of light aromatic hydrocarbons for the chemical

synthesis industry.

1.1.4. Bituminous coal

Bituminous coal or black coal is a relatively soft coal containing a tarlike

substance called bitumen. It is of higher quality than lignite coal but of poorer

quality than anthracite coal. Bituminous coal is an organic sedimentary rock

formed by diagenetic and submetamorphic compression of peat bog material. The

carbon content of bituminous coal is around 60-80%; the rest is composed of water,

air, hydrogen, and sulfur. [2].

1.1.5. Anthracite

Anthracite coal is a form of coal that is almost made entirely of carbon.

Anthracite coal is much harder than other forms of coal such as bituminous, and is

usually found in areas surrounding mountains or deep valleys. Anthracite burns

much cleaner than other forms of coal due to its low pollutant content. In fact,

anthracite may contain 91% to 98% pure carbon, leaving only 2% to 9% of other

elements. Anthracite coal is difficult to ignite and burns with a blue, smokeless

flame [3].

4

1.2. Coal Properties

1.2.1. Heating Value

The heating value is obtained by combustion of the sample in a calorimeter.

If not available, the heating value can be calculated with, for example, the Dulong

formula [4] from the ultimate analysis:

HHV (Btu/lb) = 14,600 C + 62,000 (H –O/8 ) + 4000 S

Where C, H, O, and S are the mass fractions of the elements obtained from

the ultimate analysis. There are other formulae for calculating the heating value

from the ultimate and /or proximate analysis. It is always useful to calculate the

heating value from these analyses, as it is a good cross check on measured values.

If the deviation is more than a few percent, all analyses must be checked.

1.2.2. Caking and Swelling Properties

Another important property of a coal is the swelling index. The swelling

index is determined by heating a defined sample of coal for a specified time and

temperature, and comparing the size and shape taken by the sample with a defined

scale. There are a number of different scales defined in, for example, ASTM D

720-91, BS 1016, or ISO 335. The swelling index is an indicator for the caking

properties of a coal and its expansion on heating. Softening/caking does not occur

at a certain temperature but over a temperature range. It is an important variable

for moving-bed and fluid-bed gasifier. For the gasifier of entrained-flow systems,

the coal softening point has no relevance. However, the softening point may limit

the amount of preheating of the pulverized coal feedstock used in dry coal feed

gasifier.

5

1.2.3. Hardness

Physical properties are not very relevant for the operation of a gasifier as

such. The hardness of the coal is, for example, mainly important for the milling and

grinding up stream of the gasifier. The hardness of a coal is usually dependant on

the nature and quantity of its ash content, although some coals, such anthracites,

are also hard. High ash content or a very high hardness of the ash in the coal can

make a feedstock unattractive for gasification because of the high cost of milling

and grinding. Ashes with high silica and/or alumina contents have a high hardness.

The hardness is generally characterized by the hard grove grind ability index.

1.2.4. Density

The density is primarily of importance for the transport of the coal. In this

connection, it is important to discriminate between the particle density and the bulk

density of the coal. The bulk density is always lower, as is shown in table 1.1:

Table 1.1: Particle and Bulk Density [5]

Fuel Particle (True) Density

(kg/m3)

Bulk (Apparent)

Density (kg/m3)

Anthracite 1450-1700 800-930

Bituminous coal 1250-1450 670-910

Lignite 1100-1250 550-630

6

1.3. Coal Reserves in Pakistan [6]

Coal Reserves of Pakistan and Azad Kashmir (million tons).

Coal Reserves of Balochistan Province (million tons). Only Chamalang, Khost-Shahrig-Harnai, Duki-

anambar, Mach-AbeGum, and Pir Ismail Ziarat-Marwar coalfields are developed so far.

Coalfield Coal Th. M. Moist. V.M. FixCarbon Ash T.

Sulphur

H.V.; BTU/lb Rank

Chamala

ng

0.2-2.5m 6 1.14-4.58 7.68-48.17 0.65-50.05 5.35-84.96 3.44-6.93 1818-13569 LigC to hvBb

Kingri

(K)

0.5-2.5m 3.9 1.64 18.4 25.1 55.2 5.58 2000-10,000 LigC to

SubC

Kingri-hikar

0.2-2.0m 1 Same as Chamalang coalfields

Narwal-

Dab

0.2-2.0m 1 Same as Chamalang coalfields

Toi

Nala/

Ghoze

Ghar

0.3-2.0m 1.2 1.8-1.9 42.3-42.9 32.1-32.9 22.8-23.1 5.8-6.1 9,790-13,000 SubC to

hvBb Khost-

Sharig-

Harnai

0.3-2.3m 20.9 1.7-11.2 9.3-45.3 25.5-43.8 9.3-34.0 3.5-9.5 9,637-15,499 SubC to

hvCb Sor Range- Deghari

0.3-1.3m 9.8 3.9-18.9 20.7-37.5 41.0-50.8 4.9-17.2 0.6-5.5 11,245-13,900 SubA to hvBb

Duki-

Anam

bar

0.2-2.3m 22.8 3.5.11.5 32.0-50.0 28.0-42.0 5.0-38.0 4.0-6.0 10,131-14,164 SubB to

hvAb Mach-

Abegum

0.6-1.3m 9 7.1-12.0 34.2-43.0 32.4-41.5 9.6-20.3 3.2-7.4 11,110-12,937 SubA to

hvCb Pir Ismail

Ziarat

0.4-0.7m 3.6 6.3-13.2 34.6-41.0 19.3-42.5 10.3-37.5 3.2-7.4 10,131-14,164 SubB to

hvAb Johan 0.1-0.3m 0.25 Same as Mach coalfield

Total 79.45

Abbreviations; Coal Th - Cumulative coal thickness, M-measured, Ind-indicated, Hyp-hypothetical, Moist- moisture, T.

sulphur-total sulphur, H.V.-heating value, BTU/lb - British thermal unit/pound, m- metre, lig- lignite, Sub-sub

bituminous, b-bituminous, hv-high volatile.

Coal Reserves of Punjab (million tons). Both coalfields are developed.

Province Measured Indicated Inferred Hypothetical Total Reserves

Sindh 3339 11835 56646 113637 185457

Balochistan 79.45 150.45 183.5 45.3 458.7

Punjab 57 31 2 145 235

Khyber Pakhtunkhwa 3 5.75 109.24 5 122.99

Azad Kashmir 1 1 6.72 - 8.72

Grand Total 3479.45 12023.20 56947.26 113832.30 186282.41

Coalfield Coal Th. M. Moist V.M. FixCarbon Ash T. Sulphur H.V.; BTU/lb Rank

Makerwal

0.3-2.0m

7

2.8-6.0

31.5-48.1

34.9-44.9

6.4-30.8

2.8-6.3

10,688-14,029

SubA to hvAb

Salt Range

0.15-1.2m

50

3.2-10.8

21.5-38.8

25.7-44.8

12.3-44.2

2.6-10.7

10,131-14,164

SubC to hvAb

Total 57

7

Coal Reserves of Sindh Province (million tons). Only Lakhra and Meting-Jhimpir coalfields are

developed.

Coal Reserves of Khyber Pakhtunkhwa Province (million tons). Hangu/Orakzai, Cherat, Gulakhel

and Dara Adamkhel coalfields are developed so far.

Coalfield Coal Th. M. Moist. V.M. Fix Carbon Ash T.Sulphur H.V.; BTU/lb Rank

Hangu 0.4-0.6m 2 0.2-2.5 16.2-33.4 21.8-49.8 5.3-43.3 1.5-9.5 10,500-14,149 SubA- hvAb

Cherat 0.8-1.2m 0.5 0.1-7.1 14.0-31.2 37.0-76.9 6.1-39.0 1.1-3.5 9,386-14,171 SubC- hvAb

Gulakhel 0.3-2.0m - 2.8-6.0 31.5-48.1 34.9-44.9 6.4-30.8 2.8-6.3 10,688-14,029 SubA to hvAb

Shirani 0.1-0.3m 0.25 Same as Toi Nala coalfield

Dara

Adamkhe

l

0.4-0.6 0.25 Same as Hangu / Cherat coalfields

Total 3.00

Coal Reserves of Azad Kashmir (million tonnes). Kotli coalfield is developed so far.

Coalfield Coal

Th.

M. Moist. V.M. Fix Carbon Ash T. Sulphur H.V.; BTU/lb Rank

Kotli 0.2-

1.0m

1 0.2-6.0 5.1-32.0 26.3-69.5 3.3-50.0 0.3-4.8 7,336-12,338 LigA-hvCb

Total 0.2-

1.0m

1

Coalfield Coal Th. M. Moist. V.M. Fix

Carbon

Ash T.Sulphur H.V.; BTU/lb Rank

Lakhra 0.3-3.3m 244 9.7-38.1 18.3-38.6 9.8-38.2 4.3-49 1.2-14.8 5,503-9,158 LigB-SubC

Meting

-

Jhimpi

r

0.3-1.0m 10 26.6-36.6 25.2-34.0 24.1-32.2 8.2-16.8 2.9-5.1 7,734-8,612 LigA-SubC

Sonda- Thatta 0.3-1.5m 60 22.6-48.0 16.1-36.9 8.9-31.6 2.7-52.0 0.2-15.0 8,878-13,555 SubC-hvBb

Jherruck 0.3-6.2m 106 9.0-39.5 20.0-44.2 15.0-58.8 5.0-39.0 0.4-7.7 8,800-12,846 SubC-hvCb

Ongar 0.3-1.5m 18 9.0-39.5 20.0-44.2 15.0-58.8 5.0-39.0 0.4-7.7 5,219-11.172 LigB-SubA

Indus

zast

0.3-2.5m 51 9.0-39.5 20.0-44.2 15.0-58.8 5.0-39.0 0.4-7.7 7,782-8,660 LigA-SubC

Badin 0.5-3.1m 150 9.0-39.5 20.0-44.2 15.0-58.8 5.0-39.0 0.4-7.7 11,415-11,521 LigB-SubA

Thar 0.2-22.8m 2700 29.6-55.5 23.1-36.6 14.2-34.0 2.9-11.5 0.4-2.9 6,244-11,045 LigB-SubA

Total 3339

8

1.4. Biomass

Biomass refers to any organic material derived from plants that use sunlight

to grow. When burned, the energy stored in biomass is released to produce heat or

electricity. Common forms of solid biomass include agricultural crops, crop

residues and forestry products. Using biomass for energy offers potential

advantages:

Biomass is an abundant and renewable source of energy.

Using biomass for energy would diversify the energy supply

and reduce dependency on fossil fuels.

Biomass production may create new jobs for the local

economy.

1.4.1. Types of biomass in Pakistan

Following types of biomass is available in Pakistan.

1. Woody Biomass

2. Crop Residues

I. Rice Straw

II. Rice Husk

III. Rice Stalk

IV. Cotton Stalk

V. Cotton Husk

VI. Wheat Stalk

VII. Sugarcane Bagasse

VIII. Maize Cobs

IX. Maize Stalk

X. Barley Stalk

3. Animal Dung

I. Cattle

9

1.4.2. Biomass Analysis [7]

The Ultimate and proximate analysis of different type of biomass present in

Pakistan is shown in the following table.

Table 1.2: Ultimate and Proximate Analysis of Biomass

Type Of

Biomass

Proximate analysis Ultimate analysis CV

MJ/Kg Volatile

matter

%

FC

%

Ash

%

C

%

H

%

O

%

N

%

S

%

Wood [13] 83.0 7.2 9.8 50.5 6.1 43 0.3 0.1 18.7

Rice Straw [8] 65.5 15.8 18.7 38.2 5.20 36.26 0.87 0.18 15.09

Rice Husk [12] 61.81 16.95 21.24 38.50 5.20 34.61 0.45 14.7

Rice Stalk [13] 63.52 16.22 20.26 39.77 5.53 53.64 0.82 0.24 17.62

Cotton Stalk [10] 73.10 22 4.9 45.2 4.4 14.5 1.0 0.0 17.7

Cotton Husk [15] 72.8 20.59 6.61 47.03 5.96 38.42 1.8 16.9

Wheat Stalk [9] 75.3 17.7 7.0 43.4 6.0 44.5 0.8 0.1 18

Sugarcane

Bagasse [10]

71.9 18.03 10.07 45.58 5.96 45.21 0.15 0.001 18.7

Maize Cobs [12] 87.4 11.5 1.1 49 5.4 44.20 0.4 0.0 16.8

Maize Stalk [12] 73.15 19.2 7.65 44.73 5.87 40.44 0.60 0.07 17.7

Barley Stalk [11] 68.8 20.9 10.3 39.92 5.27 43.81 1.25 - 16.6

Cattle Dung [16] 71.24 15.4 13.38 42.07 5.60 50.0 1.75 17.0

1.4.3. Production of Different Crops and their respective Residue

availability in Pakistan [7]

The production of different crops in Pakistan with respect to their residue

availability is shown in the following table.

10

Table 1.3: Production of Different Crops and their respective Residue availability

in Pakistan

1.4.4. Properties of Feed Stock Suitable for Gasification

The composition of different materials varies significantly. Fuel

performance is related to the composition of the material. Important factors include

Moisture, ash, carbon, hydrogen, nitrogen, sulphur, oxygen and chloride content.

I. Moisture

Moisture content is the key factor determining the net energy content of

biomass material. Dry biomass has a greater heating value (or net energy potential),

as it uses little of its energy to evaporate any moisture. Increased moisture means

less energy available for the boiler.

Moisture content is usually reported on an “as-is” or wet basis in which the

water content is given as a fraction of the total weight. All biomass materials

contain some moisture, from as low as 8% for dried straw to over 50% for fresh-

Name of the crop Annual

production

(thousand MT)

Type of

residue

Crop to residue ratio

(residue/kg crop)

Total available

residue (thousand

MT)

Rice 6883 Husks 0.2 1376.6

Stalks 1.5 10,324.5

Straw 1.5 10,324.5

Cotton 3000 Husk 1.1 3300

Stalks 3.8a 11,802.8

Wheat 23,864 Stalks 1.5 35796

Sugarcane 49,373 Bagasse 0.33 16,293.09

Maize 296 Cobs 0.3 88.8

Stalks 2 592

Barley 82 Stalks 1.3 106.6

Dry chilly 187.7 Stalks 1.5 281.55

11

cut wood. A high moisture content adversely affects the collection, storage, pre-

processing, handling and transportation of biomass. In addition, transporting wet

material costs more.

Moisture content

Increases heat loss, due to evaporation and superheating of vapor

Helps, to a limit, in binding fines.

Aids radiation heat transfer.

The moisture content of raw biomass can be reduced by:

Leaving biomass in the field to dry for several weeks

Storing biomass, sheltered from precipitation

Commercial drying

II. Fixed carbon

Fixed carbon is the solid fuel left in the furnace after volatile matter is

distilled off. It consists mostly of carbon but also contains some hydrogen, oxygen,

sulphur and nitrogen not driven off with the gases. Fixed carbon gives a rough

estimate of heating value of coal.

III. Volatile Matter

Volatile matters are the methane, hydrocarbons, hydrogen and carbon

monoxide, and incombustible gases like carbon dioxide and nitrogen found in coal.

Thus the volatile matter is an index of the gaseous fuels present. Typical range of

volatile matter is 20 to 35%.

Volatile Matter content

Proportionately increases flame length, and helps in easier ignition of coal.

Influences secondary air requirement.

Influences secondary oil support.

12

IV. Ash

The non-combustible content of biomass is referred to as ash. High ash

content leads to fouling problems. Unfortunately biomass fuels, especially

agricultural crops/residues tend to have a high ash with high potassium content. As

a result, the ash melts at lower temperatures, resulting in “clinkers” that can jam

furnace elements. Alternately, slagging and fouling occur when ash is vaporized

and condensed in the boiler, resulting in the production of hard formations on the

heat transfer surfaces.

Wood has less than 3% ash. Agricultural crops have higher ash content,

from 3% and higher. Some boilers/stoves cannot handle fuels with high ash

content. More ash means more maintenance. [9]

Ash content:

Reduces handling and burning capacity.

Increases handling costs.

Affects combustion efficiency and boiler efficiency

Causes clinkering and slagging.

V. Carbon

The carbon content of biomass is around 40%, while coal contains 60% or

greater (Demirbas, 2007). A higher carbon content leads to a higher heating

value. [9]

VI. Hydrogen

The hydrogen content of biomass is around 6% (Jenkins, 1998). A higher

hydrogen content leads to a higher heating value. [9]

13

VII. Nitrogen

The nitrogen content of biomass varies from 0.2% to more than 1%

(Jenkins, 1998). Fuel bound nitrogen is responsible for most nitrogen oxide (NOx)

emissions produced from biomass combustion. Lower nitrogen content in the fuel

should lead to lower NOx emissions. [9]

VIII. Sulphur

Most biomass fuels have a sulphur content below 0.2%, with a few

exceptions as high as 0.5%–0.7%.Coals range from 0.5%–7.5% (Demirbas 2007).

Sulphur oxides (SOx) are formed during combustion and contribute significantly to

particulate matter (PM) pollution and acid rain. [9]

Since biomass has negligible sulphur content, its combustion does not

contribute significantly to sulphur emissions. It:

Affects clinkering and slagging tendencies

Corrodes chimney and other equipment such as air heaters and

economizers

Limits exit flue gas temperature.

1.4.5. Selection of Feed Stock

The selection of an appropriate feed stock is the important step at the initial

stage of gasification. The various samples are analyzed and compared in terms of

their costs and compositions. The comparison is generally made by the percentages

of sulfur content, fixed carbon, oxygen, ash and other volatile content. The Thar

coal and Sugarcane bagasse are selected as a feedstock for Gasification because of

i. High Calorific value

ii. Low Sulphur content

iii. High availability in Pakistan

14

1.5. Application of Syn Gas

Syngas can be used for heat production and for generation of mechanical

and electrical power. Like other gaseous fuels, producer gas gives greater control

over power levels when compared to solid fuels, leading to more efficient and

cleaner operation.

1.5.1. Heat

Gasifiers offer a flexible option for thermal applications, as they can be

retrofitted into existing gas fueled devices such as ovens, furnaces, boilers, etc.

where syngas may replace fossil fuels. Heating values of syngas are generally

around 4-10 MJ/m3.

1.5.2. Electricity

Currently Industrial-scale gasification is primarily used to produce

electricity from fossil fuels such as coal, where the syngas is burned in a gas

turbine. Gasification is also used industrially in the production of electricity,

ammonia and liquid fuels (oil) using Integrated Gasification Combined Cycles

(IGCC), with the possibility of producing methane and hydrogen for fuel cells.

IGCC is also a more efficient method of CO2 capture as compared to conventional

technologies. IGCC demonstration plants have been operating since the early

1970s and some of the plants constructed in the 1990s are now entering commercial

service.

1.5.3. Combined heat and power

In small business and building applications, where the wood source is

sustainable, 250-1000 kW and new zero carbon biomass gasification plants have

been installed in Europe that produce tar free syngas from wood and burn it in

reciprocating engines connected to a generator with heat recovery. This type of

plant is often referred to as a wood biomass CHP unit but is a plant with seven

15

different processes: biomass processing, fuel delivery, gasification, gas cleaning,

waste disposal, electricity generation and heat recovery.

1.5.4. Transport fuel

Diesel engines can be operated on dual fuel mode using producer gas. Diesel

substitution of over 80% at high loads and 70-80% under normal load variations

can easily be achieved. Spark ignition engines and fuel cells can operate on 100%

gasification gas. Mechanical energy from the engines may be used for e.g. driving

water pumps for irrigation or for coupling with an alternator for electrical power

generation.

CHAPTER 2

PROCESS SELECTION

2.1. Methods of Syn Gas Production

Different kinds of processes are involved for production of syngas. They

are

Landfill

Gasification

Pyrolysis

2.1.1. Landfill

The placement of solid waste in landfills is the probably the oldest and

definitely the most prevalent form of ultimate garbage disposal. From the outset, it

must be recognized that many landfills are nothing more than open, sometimes

controlled, dumps. The difference between landfills and dumps is the level of

engineering, planning, and administration involved.

17

Open dumps are characterized by the lack of engineering measures, no leach

ate management, no consideration of landfill gas management, and few, if any,

operational measures such as registration of users, control of the number of tipping

fronts or compaction of waste.

2.1.2. Gasification

Gasification is a process that converts organic or fossil based carbonaceous

materials into carbon monoxide, hydrogen and carbon dioxide. This is achieved by

reacting the material at high temperatures, without combustion, with a controlled

amount of oxygen and/or steam. The resulting gas mixture is called syngas (from

synthesis gas or synthetic gas) or producer gas and is itself a fuel.

The power derived from gasification of biomass and combustion of the

resultant gas is considered to be a source of renewable energy; the gasification of

fossil fuel derived materials such as plastic is not considered to be renewable

energy.

Gasification Reactions

Combustion gases can be produced by the reaction of the coal, char or

volatile matter with oxygen, carbon dioxide, hydrogen or stream. The main

reactions are listed below (for simplicity, only reactions with carbon are shown).

Partial combustion reaction: C + ½ O2 CO

Boudouard reaction: C+CO2 2CO

Hydro gasification reaction C + 2H2 CH4

Char Gasification reaction: C + H2O CO + H2

Combustion reaction C+O2 CO2

Water Gas Shift reaction CO + H2O CO2 + H2

18

Methane Reforming Reaction CH4 + H2O CO + 3H2

Carbonation Reaction CaO + CO2 CaCO3

2.1.3. Pyrolysis

Pyrolysis is a thermo chemical decomposition of organic material at

elevated temperatures without the participation of oxygen. It involves the

simultaneous change of chemical composition and physical phase, and is

irreversible. The word is coined from the Greek-derived elements pyr "fire" and

lysis "separating".

Pyrolysis is a case of thermolysis, and is most commonly used for organic

materials, being, therefore, one of the processes involved in charring. The pyrolysis

of wood, which starts at 200–300 °C (390–570 °F), occurs for example in fires

where solid fuels are burning or when vegetation comes into contact with lava in

volcanic eruptions. In general, pyrolysis of organic substances produces gas and

liquid products and leaves a solid residue richer in carbon content, char. Extreme

pyrolysis, which leaves mostly carbon as the residue, is called carbonization.

2.2. Gasifier Types

Depending upon the gasification medium, gasifiers can be classified into three

groups:

1. Air-blown, where air is the gasification medium

2. Oxygen-blown, where pure oxygen is the gasification medium

3. Steam Blown, where steam is the gasification medium

Air gasification produces a low heating value (5000 to 6000 kJ/kg or 3 to 6

MJ/m3, LHV) gas, which contains about 50% nitrogen and can fuel engines and

furnaces. Oxygen blowing is free from diluents like nitrogen. As a result it produces

higher (15,000 kJ/kg or 10 to 12 MJ/m3, LHV) heating value gas, Steam blown

gasifiers produce Syn gas with high hydrogen content and typically having a

heating value of 50,000 kJ/kg.

19

Depending upon how the gas and fuel contact each other, gasifiers can be

further divided into following types:

2.2.1. Counter-current Fixed bed (Up draft) Gasifier

A fixed bed of carbonaceous fuel (e.g. coal or biomass) through which the

"gasification agent" (steam, oxygen and/or air) flows in counter-current

configuration. The ash is either removed in the dry condition or as a slag. The

slagging gasifiers have a lower ratio of steam to carbon. Achieving temperatures

higher than the ash fusion temperature. The nature of the gasifier means that the

fuel must have high mechanical strength and must ideally be non-caking so that it

will form a permeable bed, although recent developments have reduced these

restrictions to some extent. The throughput for this type of gasifier is relatively low.

Thermal efficiency is high as the temperatures in the gas exit are relatively low.

However, this means that tar and methane production is significant at

typical operation temperatures, so product gas must be extensively cleaned before

use. The tar can be recycled to the reactor

Figure 2.1: Counter-current fixed bed (Up draft) gasifier [17]

20

2.2.2. Co-current Fixed bed (Down draft) Gasifier

Similar to the counter-current type, but the gasification agent gas flows in

co-current configuration with the fuel (downwards, hence the name "down draft

gasifier"). Heat needs to be added to the upper part of the bed, either by combusting

small amounts of the fuel or from external heat sources. The produced gas leaves

the gasifier at a high temperature, and most of this heat is often transferred to the

gasification agent added in the top of the bed, resulting in an energy efficiency on

level with the counter-current type. Since all tars must pass through a hot bed of

char in this configuration, tar levels are much lower than the counter-current type.

Figure 2.2: Co-current fixed bed ("down draft") gasifier [17]

21

2.2.3. Fluidized bed reactor

The fuel is fluidized by oxygen and steam or air. The temperatures are relatively

low in fluidized bed gasifiers, so the fuel must be highly reactive; low-grade coals

are particularly suitable. The agglomerating gasifiers have slightly higher

temperatures, and are suitable for higher rank coals. Fuel throughput is higher

than for the fixed bed, but not as high as for the entrained flow gasifier. The

conversion efficiency is higher than fixed bed. Recycle or subsequent combustion

of solids can be used to increase conversion. Fluidized bed gasifiers offers

improved mass and heat transfer from fuel, higher heating value and higher

efficiency.

The concern for climate change has increased the interest in biomass

gasification for which fluidized bed gasifiers are particularly popular, occupying

nearly 20% of their market. Fluidized bed gasifiers are divided into the following

two major types.

1. Bubbling fluidized bed gasifier

2. Circulating fluidized bed gasifiers

Figure 2.3: Fluidized Bed Reactor [17]

22

2.2.4. Entrained Flow Gasifier

Entrained-flow systems gasify pulverized fuel particles suspended in a

stream of oxygen (or air) and steam. Ash in the coal melts at the high operating

temperature of the gasifier and is removed as liquid slag. A number of

manufacturers offer commercial entrained-bed gasifiers for large-scale

applications, such as Texaco, Shell, and Kopper–Totzek. These gasifiers typically

operate at pressures up to 35 bar and use oxygen as the gasifier medium (William

et al., 2000). Many IGCC plants utilize entrained bed gasifiers.

Entrained bed gasifiers are available in much larger capacities (.100 MWe)

than other types, but these are more commonly used for fossil fuels like coal,

refinery wastes, etc. Their use for gasification is rather limited, as it requires the

fuel particles to be very fine (in the order of 80 to 100 mm).

In entrained flow gasifiers, Gasification occurs at 1600 ºC and the product

gas is taken out through collector pipe at 1000-1300 ºC. Ash is removed from the

bottom in the form of slag.

Figure 2.4: Entrained Flow Gasifier [19]

23

2.3. Gasifier Selection

Fluidized bed gasifier is selected due to its following advantages over other

type of gasifiers.

Short residence time

Uniform temperature distribution and Uniform Particle mixing.

Low char or/and tar contents

High cold gas energy efficiency

Reduced ash-related problems

Low air pollution.

No production of SOx because SO2, SO3 etc. are captured by lime stone.

Higher heating value of Synthesis gas

CHAPTER 3

PROCESS DESCRIPTION

3.1. Description of the Process

A simplified process has been developed for Synthesis gas production from

biomass and coal using pure steam as gasification agent and CaO as CO2 sorbent.

The block diagram of the process is shown. The whole process is consists of four

sections

1. Feed treatment

2. Gasification

3. Gas cleaning section

4. Utility section

The detail of each section is described in next headings. The process flow

diagram (PFD) is shown at the end of this chapter

25

3.1.1. Feed Treatment

Pretreatment of feedstock for gasifier is generally consisting of drying and

size reduction. Drying used to remove the moisture from the coal and biomass

either from flue gases or by air. Usually drying removes the moisture contents from

10-15 % in the biomass.

The best condition of feedstock for fluidized bed gasifier is that the

feedstock must well grind as well. So to achieve such best condition for coal and

biomass feed to gasifier a rotary dryer and ball mill used to remove moisture from

the feedstock and fine grinding respectively shown in PFD. [20]

3.1.2. Gasification

The conversion of feedstock to the Synthesis gas takes place in fluidized

bed gasifier through steam gasification process integrated with CO2 capture. There

are few assumptions were considered in flowsheet development modeling for

gasification process are as follows.

1. The gasifier operates under steady state conditions and atmospheric

pressure.

2. The reactions proceed adiabatically and at constant volume.

3. There is no tar formation in this process.

In the modeling framework, it is assumed that four reactions take place

simultaneously including Char gasification, Methane reforming, Water gas shift

and Carbonation. [22]

Char Gasification reaction

C(s) + H2O CO + H2

Steam Methane Reforming

CH4 + H2O CO + 3H2

Water Gas shift reaction

CO + H2O CO2 + H2

26

Carbonation reaction

CaO + CO2 CaCO3

Table 3.1: Operating Conditions and Process Parameters in the Gasifier

Parameter Value Reason

Temperature 950 K High H2/CO ratio [21]

Pressure 1 atm High H2/CO ratio [20]

Bed Material CaO As a CO2 sorbent [20] [21]

Steam/feed ratio 2 For hydrogen purity. [20]

Sorbent/feed ratio 1 For both hydrogen purity and

hydrogen yield profiles.[20]

Feed Size 2 mm For high fluidization [23]

3.1.3. Gas Cleaning

The product gas produced by the gasification process contained hydrogen,

carbon monoxide, carbon dioxide, methane, steam and fly ash. To get pure

hydrogen as end product, there are several steps involved in product gas cleaning

with different units like Cyclone Seprator and scrubber as shown in PFD. Fly ash

was removed from the system by Cyclone and the steam was removed by passing

through scrubber with fresh water. Along with the steam there are also some others

product gases will be also absorbs in water which was calculated by chart of

solubility of gases in water at atmospheric pressure and different temperature. The

scrubber is also used to cool down the product gas and to remove the remaining

amount of the solid particles. [20]

27

3.1.4. Utility Section

I. Steam Generation

The process design includes a steam generation system that produced steam

by a steam generator/Boiler. Furthermore steam is superheated to 523 K. The steam

is supplied to the gasifier at 2 atm pressure which reduces to 1 atm in the gasifier

due to energy losses. The steam generation system is also shown in PFD.

3.2. Factors Affecting Gasification

The main factors affecting the Gasification are as follows.

3.2.1. Temperature

Increasing the temperature increases the formation of combustible gases, decreases

the yield of char and liquids and leads to more complete conversion of the fuel. The

energy content of the syngas increases steadily up to 700 ºC then decreases at

higher temperatures.

3.2.2. Pressure

The rate of char gasification increase with increasing pressure, and the impacts are

most significant at high temperatures.

3.2.3. Fuel Bed Height

For a given reactor temperature, higher fuel bed heights increase the time fuels are

available for reactions to occur (residence time), which increases total syngas

yields and increases the concentrations of hydrogen, and carbon monoxide in the

syngas.

3.2.4. Fluidization Velocity

Fluidization velocity (fluidization is the processing technique employing a

suspension of a small solid particle in a vertically rising stream of fluid – usually

gas – so that fluid and solid come into intimate contact) affects the mixing of

particles within the reactor. Higher velocities increase the temperature of the fuel

bed and lead to the production of lower energy syngas.

28

3.2.5. Feed Properties

Both chemical reaction rates and diffusion rates are dependent on the

properties of the solid materials. The absolute value of the chemical reaction rate

can vary greatly depending on the reactivity of the material.

29

3.3. Block Diagram

Figure 3.1: Block Diagram

30

3.4. Process Flow Diagram

Figure 3.2: Process Flow Diagram

CHAPTER 4

MATERIAL BALANCE

4.1. Material Balance on Dryer

Total mass entering the dryer = F1 = 1000 kg/hr

Biomass : Coal = 30 : 70

Moisture content in Biomass = 15.3 kg/hr

Moisture content in coal = 333.2 kg/hr

Total moisture content = 348.5 kg/h

Dry Solid leaving dryer = F2 = 683.6 kg/hr

32

(There is only 5% moisture at the outlet of the dryer)

Where outlet of dryer contains

H2O = 32.1 Kg/hr

Coal + Biomass = 651.5 kg/hr

Mass In = Mass Out

Wet Solid In = Dry Solid out + Moisture removed

Moisture removed = 1000-683.6 = 316.4 Kg/hr

4.2. Material Balance on Mill

4.3. Material Balance on Gasifier

33

Table 4.1: Proximate analysis of Coal and Biomass (Dry Basis)

Coal [24] Biomass [10] Combined

Fixed Carbon 37.33% 18.03% 31.54%

Volatile matter 47.81% 71.9% 55.04%

Ash 14.86% 10.07% 13.42%

Total feed entering the gasifier = 683.6 kg/hr

Moisture content present in the feed = 32.1 kg/hr

Total Solid feed ( Coal + Biomass ) = 651.5 kg/hr

Assumptions

i. The gasifier operates under steady state conditions [21].

ii. Four reactions occur simultaneously in the gasifier including char

gasification, methane reforming, water gas shift and carbonation [22]

iii. Product gas consist of H2, CO, CO2 and CH4 [21]

iv. The reactions proceed isothermally and occur at constant volume [21]

v. Tar and ash formation in the process are negligible. As the calculation of

tar content will lead to an increasing amount of error for final product gas

composition [21]

4.3.1. Gasification Reactions

I. Char Gasification Reaction

By balanced chemical equation

Moles of C = 17.12 kmol/hr = 205.44 kg/hr

Moles of H2O = 17.12 kmol/hr = 308.16 kg/hr

Moles of CO = 17.12 kmol/hr = 479.36 kg/hr

Moles of H2 = 17.12 kmol/hr = 34.24 kg/hr

34

II. Steam Methane Reforming Reaction


Moles of CH4 = 22.41 kmol/hr = 358.56 kg/hr




III. Water Gas Shift Reaction




Moles of CO2 = 39.53 kmol/hr = 1732.32 kg/hr


Amount of steam required = 1423.08 Kg/hr (S/C = 1)

For S:C = 2 (for high Hydrogen yield)

Amount of steam = 2846.16 Kg/hr (S/C = 2)

Table 4.2: Gasification Reaction

Name Reaction Conversion %

Char Gasification Reaction C(s) + H2O CO + H2 40 [23]

Methane Reforming Reaction CH4 + H2O CO + 3H2 60 [25]

Water Gas Shift Reaction CO + H2O CO2 + H2 70 [26]

Carbonation Reaction CaO + CO2 CaCO3 85 [20]

35

Table 4.3: Material Balance

Reactant Stream Products Stream Unreacted

C

(kmol/hr)

H2O

(kmol/hr)

CO

(kmol/hr)

H2 (kmol/hr) C (kmol/hr) H2O

(kmol/hr)

17.12 17.12 6.85 6.85 10.27 10.27

CH4

(kmol/hr)

H2O

(kmol/hr)

CO

(kmol/hr)

H2 (kmol/hr) CH4

(kmol/hr)

H2O

(kmol/hr)

22.41 22.41 13.45 40.35 8.96 8.96

CO

(kmol/hr)

H2O

(kmol/hr)

CO2

(kmol/hr)

H2 (kmol/hr) CO

(kmol/hr)

H2O

(kmol/hr)

20.3 20.3 14.21 14.21 6.09 6.09

CaO

(kmol/hr)

CO2

(kmol/hr)

CaCO3

(kmol/hr)

CaO

(kmol/hr)

CO2

(kmol/hr)

12.21 12.21 10.38 1.83 3.84

Total CaO fed = 683.6 kg/hr

Total CaCO3 at outlet = 1038 kg/hr

Unreacted CaO = 102.48 kg/hr

CO2 absorbed = 456.72 kg/hr

36

Table 4.4: Product Gas Composition of Gasifier

Component Molar flow rate (kmol /

hr)

Mass Flow Rate (kg/hr)

CH4 8.96 143.36

CO 6.09 170.52

CO2 3.84 168.96

H2 61.41 122.82

H2O 125.39 2256.55

Ash - 87.43

Unreacted C 10.27 123.24

Mass In = Mass Out

683.6 + 2846.16 + 683.6 = 1038 + 102.48 + 143.36 + 170.52 + 168.96 + 122.82

+ 2256.55 + 87.43 + 123.24

4213.36 = 4213.36

4.4. Material Balance on Cyclone Separator

Solid particles are coming in gas stream at the rate of 210.67 kg/hr. Particle Size

is reduced due to attrition. Assuming average particle size of particles in the Inlet

is 50 μm. From the graph the efficiency is 99%.

F6 = 210×0.99 = 208.56 kg/hr

F4 = F5 + F6

3072.88 = F5 + 208.56

Syn gas Out = F5 = 2864.32 Kg/hr

37

4.5. Material Balance on Scrubber

Table 4.5: Composition of Gas at Inlet of Scrubber

Component Molar flow rate (kmol

/ hr)

Mass Flow Rate

(kg/hr)

CH4 8.96 143.36

CO 6.09 170.52

CO2 3.84 168.96

H2 61.41 122.82

H2O 125.36 2256.55

Solids - 2.107

38

Water required = 33,400 kg/hr = 9.28 kg/s

Inlet temperature of water = 25 °C = 298 K

Outlet temperature of water = 89 °C = 362 K

Average Temperature of the Column = 61.4 °C = 334.4 K

Assuming only CO2 is absorbed in water, because solubility of other gases in

water is very less.

CO2 absorbed in water (At 61.4 °C) = 0.6 g CO2/Kg of water [27]

Total CO2 absorbed in water = 18 Kg/hr

Table 4.6: Outlet composition of Gases of Scrubber

Component Molar flow rate (kmol

/ hr)

Mass Flow Rate

(kg/hr)

CH4 8.96 143.36

CO 6.09 170.52

CO2 3.43 150.96

H2 61.41 122.82

H2O 0.49 8.82

Solids Removed = 2.107 kg/hr

Steam Removed = 2247.73 kg/hr

Total Outlet from the bottom = 33400+2247.73+18+2.107 = 35667.74 kg/hr

Total Gas Out from top = 596.48 kg/hr

Density of gas = 0.2953 kg/m3 [28]

Volumetric flow rate of the gas = 2020 m3/hr

39

4.6. Overall Material Balance

Figure 4.1: Overall Material Balance

CHAPTER 5

ENERGY BALANCE

5.1. Energy Balance on Dryer

5.1.1. Heat Inlet

Air inlet temperature = 385 K

Feed inlet temperature = 305 K

Air In

Air contains 0.01 kg water per kg of air

Q = mCp∆T

Heat Capacity of Air = 1.008 KJ/Kg K

Heat Capacity of Water Vapor = 1.869 KJ/Kg K

Q = 661.19 KW

41

Feed Inlet = Q = mCP∆T

Heat Capacity of Feed Solids = 1.104 KJ/Kg K

Heat Capacity of Water = 4.18 KJ/Kg K

Q = 19.36 KW

Total Heat In = Heat of Air at inlet + Heat of Feed at inlet

Total Heat In = 680.55 KW

5.1.2. Heat Outlet

Air outlet temperature = 327.5 K

Feed outlet temperature = 330 K

Feed Out

Q = mCp∆T

Q = 13.54 KW

Water evaporated = 0.008 Kg/s

Assuming evaporation takes place at 311 K

Latent heat of water vapour (λ) = 2410.8 KJ/Kg

Heat in water vapor = mCP∆T + mλ

= 228.834 KW

Heat in air = mCP∆T

= 321.74 KW

Heat losses = 116.43 KW

Total Heat Out = 564.12 KW

42

5.2. Energy Balance on Ball Mill

Energy In = Energy Out

Energy Out = 14.02 KW

5.3. Energy Balance on Gasifier

5.3.1. Heat Inlet

Solid In

Q = mCp∆T

Cp of feed = 1.1047 KJ/Kg. K

Cp of CaO = 0.7563 KJ/Kg. K

Q = 14.02+ 3.59 = 17.67 KW

Steam Inlet (At 523K and 2 atm)

Q = mCp∆T + mλ

Cp of Steam = 1.92 KJ/Kg. K

Cp of Water = 4.189 KJ/Kg. K

λ = 2200 KJ/Kg

At 2 atm, Steam boils at 393.57 K (120.57 ºC)

= (248.51+2200+505.18)*2846.16/3600

Q = 2335.19 KW

Total Heat In = Heat of Solid inlet + Heat Steam inlet

Total Heat In = 2352.86 KW

43

5.3.2. Heat involved in Chemical Reactions

I. Char Gasification Reaction

C + H2O → CO + H2

∆HºR = +131.5 KJ/mol

∆H = ∆HºR + ∆CP (T-TR)

∆CP = 2.276 KJ/Kmol .K

∆H = 133040.85 KJ/Kmol

II. Methane Reforming Reaction

CH4 + H2O → CO + 3H2

∆HºR = +206 KJ/mol



∆H = 214389.4 KJ/Kmol

III. Water Gas Shift Reaction

CO + H2O → CO2 + H2

∆HºR = -41 KJ/mol



∆H = -34414.14 KJ/Kmol

IV. Carbonation Reaction

CO2 + CaO → CaCO3

∆HºR = -178.3 KJ/mol K


44


∆H = -162451.43 KJ/Kmol

Table 4.7: Material Balance on Gasifier

Reactant Stream Products Stream Unreacted

C (kmol/hr)

H2O (kmol/hr)

CO (kmol/hr)

H2 (kmol/hr) C (kmol/hr) H2O (kmol/hr)

17.12 17.12 6.85 6.85 10.27 10.27

CH4

(kmol/hr) H2O

(kmol/hr) CO

(kmol/hr) H2 (kmol/hr) CH4 (kmol/hr) H2O (kmol/hr)

22.41 22.41 13.45 40.35 8.96 8.96

CO (kmol/hr)

H2O (kmol/hr)

CO2

(kmol/hr) H2 (kmol/hr) CO (kmol/hr) H2O (kmol/hr)

20.3 20.3 14.21 14.21 6.09 6.09

CaO (kmol/hr)

CO2

(kmol/hr) CaCO3

(kmol/hr) CaO (kmol/hr) CO2 (kmol/hr)

12.21 12.21 10.38 1.83 3.84

QR =∑ n∆H

=253.14 + 800.98 -135.84 – 468.40

= 449.88 KW

45

5.3.3. Heat Outlet

Total Heat Out = Qout = Qout (Gas) + Qout (Solids)

Heat Outlet by Gaseous stream = Qout (Gas) = m<Cp>∆T + mλ

λ = 2257 KJ/Kg (At 1 atm)

Mean Cp of Outlet Gaseous stream = 2.417 KJ/Kg K

Qout (Gas) = 2811.44 KW

Heat Outlet by Solids = Qout (Solids) = m<Cp>∆T

Mean Cp of Solids = 1.247 KJ/Kg K

Qout (Solids) = 267.45 KW

Total Heat Out = Qout = 3078.89 KW

5.3.4. Overall Energy Balance

Qin = Qout

QSteam + Qfeed + Qgeneration – Qconsumption + Qheater = Qout

Qheater = 1175.91 KW

Therefore Electric jacketed type heater containing electric wires is used to

maintain the temperature of the reactor.

5.4. Energy Balance on Cyclone Separator:

Energy In = 2811.44 KW

Energy Out = Qgas + Qsolid

Qsolid = m<Cp>∆T

Mean Cp of Solids = 1.252 KJ/Kg K

46

= 49.10 KW

Qgas = m<Cp>∆T

Mean Cp of Outlet Gaseous stream = 2.502 KJ/Kg K

Qgas = 2762.077 KW

Heat Inlet = Heat Outlet

2811.44 = 49.10 + 2762.077

5.5. Energy Balance on Scrubber:

Inlet temperature of gas = 677 ºC

Inlet temperature of water = 25 ºC

Table 5.1: Composition of Inlet Gas of Scrubber

Component Molar flow rate (kmol / hr) Mass Flow Rate (kg/hr)

CH4 8.96 143.36

CO 6.09 170.52

CO2 3.84 168.96

H2 61.41 122.82

H2O 125.39 2256.55

Solids - 2.107

Heat inlet by gas = Qgas= m<Cp>∆T = 2762.077 KW

Heat inlet by water = QWin = m<Cp>∆T

= 978.8 KW

Total Heat Inlet = 3740.88 KW

47

Table 5.2: Composition of Outlet Gases of Scrubber

Component Molar flow rate (kmol / hr) Mass Flow Rate (kg/hr)

CH4 8.96 143.36

CO 6.09 170.52

CO2 3.43 150.96

H2 61.41 122.82

H2O 0.49 8.82

Total 80.38 596.48

Heat out by gas = m<Cp>∆T = 23.44 KW

(Assuming that the scrubber cools the gas to 35 ºC)

Assuming no heat losses

Total Heat Out = 3740.88 KW

Heat Out from bottom = 3717.44 KW

Water required = Q = m<Cp>∆T

Assuming the outlet temperature of water = 95 °C

Water required = 33381.85 kg/hr

Actual flow rate of the water at top of column = 33,400 kg/hr

Outlet temperature of the water = m<Cp>∆T = 89 °C

Mass LHV of gas (KJ/Kg) = 3.963E+04 [28]

LHV of gas (KJ/Kgmol) = 2.959 E+05 [28]

48

5.6. Overall Energy Balance

Figure 5.1: Overall Energy balance

CHAPTER 6

EQUIPMENT DESIGN

6.1. Dryer Design

It includes the following steps:

Brief Introduction

Classification of dryers

Selection of dryer

Brief description of selected dryer

Design considerations

6.1.1. Brief Introduction

In general, drying a solid means the removal of relatively small amounts of

water or other liquid from the solid material to reduce the content of residual liquid

to an acceptably low value. Drying is usually the final step in a series of operations,

and the product from a dryer is often ready for final packaging. In a dryer, Water

or other liquids are removed from solids thermally by vaporization.

50

6.1.2. Classification of Dryers

Drying equipment may be classified in several ways. The two most useful

classifications are based on

1. The method of transferring heat to the wet solids.

2. The handling characteristics and physical properties of the wet material.

The first method of classification reveals differences in dryer operation and

design i.e.; it classifies dryers as direct or indirect, with subclasses of continuous

or batch wise operation. While the second method is most useful in the selection of

a dryer or group of dryers for a given drying problem.

6.1.3. Selection of dryer

From Classification No. 1

A. Direct Heat Dryers are selected, because

1. There is no limitation of reduced pressure in our drying problem.

2. Dusting problem is not serious.

3. The material to be handled is not heat sensitive around 100-150ºC.

B. Continuous Dryers are selected, because

1. For throughputs greater than 10,000 Kg/day, continuous dryers are used.

So Direct Heat Continuous Dryer is selected.

From Classification No. 2

C. Rotary Dryer is selected, because

1. Suitable for granular solids.

2. Used for High capacity/High production rate

3. Thermal Efficiency Range is 55—75%

4. Low operating Cost

5. Most Economical in Construction

51

6. Known as Workhorse of Process Industry

7. Low maintenance cost

So Direct Heat Rotary Dryer Is Selected.

6.1.4. Direct Heat Rotary Dryer

1. It consists of a cylinder, rotated upon suitable bearings and usually slightly

inclined to the horizontal.

2. Wet feed enters one end of the cylinder progress through it by virtue of

rotation and slope of the cylinder and discharge as finished product at the

other end.

3. In this dryer solids are directly exposed to hot gas usually air.

Figure 6.1: Direct Heat Rotary Dryer

A, dryer shell; B, shell-supporting rolls; C, drive gear; D, air-discharge hood; E,

discharge fan; F, feed chute; G ,lifting flights; H, product discharge; J air heater

52

6.1.5. Dryer Design [29]

Total mass entering the dryer = F1 = 1000 kg/hr

Biomass: Coal = 30:70

Moisture content in Biomass = 15.3 kg/hr

Moisture content in coal = 333.2 kg/hr

Total moisture content = 348.5 kg/hr

Solid feed rate leaving dryer = F2 = 684.07 kg/hr

(There is only 5% moisture at the outlet of the dryer)

Where outlet of dryer contains

H2O = 32.575 Kg/hr

Coal + Biomass = 651.5 kg/hr

Water removed =F3= 348.5 - 32.575

= 315.93 Kg/hr

Design Considerations

General design considerations for direct heat Rotary dryer are:

1. Solid Feed Rate and Moisture Content

2. Drum Diameter and Length

3. Drum Slope

4. Rotational Speed

5. Lifting Flights

6. Outlet Humidity

1. Solid Feed Rate and Moisture Content

Solid feed rate

F1=1000 kg/hr

Moisture Contents

Moisture contents=Mass of water/Mass of dry solid

Initial moisture content=348.5/651.5

Xa= 0.5349= 53.5 %

53

Final moisture content= 32.575/651.5

Xb= 0.05 = 5 %

Temperature Selection & Calculations

Temperature of air

1. Inlet air temperature (Ta )

1. Hot air is used for drying purpose and air inlet temperature varies from

100 to 150 oC

2. The higher the temperature of inlet air stream, the higher the

efficiency of the dryer in general. --- (a)

3. So take inlet air temperature= Ta = 112 ºC = 385K

Humidity of Inlet air (H1)

Inlet humidity of air is found with the help of dry bulb temperature

(Room temp) of air and wet bulb temperature of entering air from

Humidity chart.

i.e.; At Tdb = 32oC = 305K

Twb = 21oC = 294K

Humidity of air=H1= 0.01 kg of water/kg of dry air

Now this air is heated from 32oC to 112oC (dry bulb temperature of heated

air) and the wet bulb temperature of heated air is found with the help of dry bulb

& humidity of heated air entering the dryer from humidity chart.

i.e.; At Tdb = 385K

H1= 0.01 kg of water/kg of dry air

Twb = 311K

Outlet air temperature (Tb)

The proper outlet gas temperature is a matter of economics,

54

It is estimated from

---------------- (1)

Where

Nt =No. of transfer units (1.5—2.5 for rotary dryers)

Ta = 385K

TWb = 311K

Take Nt =1.5, putting the values in Eq. (1)

Air outlet temperature =Tb = 327.5K

Temperature of Feed

a) Inlet feed temperature (Tsa)

Feed enters the dryer at Tsa = 305K

b) Outlet Feed temperature (Tsb)

Feed leaves the dryer at Tsb = 330K

Temperature pattern in continuous countercurrent adiabatic dryer:

Feed inlet temperature should be less than gas outlet temperature and it should

also less than wet bulb temperature of air, therefore selected feed inlet

temperature is correct.

Outlet temperature of feed is slightly greater than gas outlet temperature,

therefore selected solid outlet temperature is correct.

Table 6.1: Temperature of Inlet and Outlet Streams

Material

Inlet

Temperature K

Outlet

Temperature K

Feed 305 330

Air 385 327.5

Wbb

Wba

tTT

TTLnN

55

2. Drum Diameter

To calculate diameter of the rotary dryer, following steps must be performed.

i. Calculate heat duty on dryer (qt)

ii. Calculate mass flow rate of air entering (mg )

iii. Choose the air mass velocity (G)

iv. Find the dryer area (A)

i. Calculation of heat load on dryer (qt)

Heat must be supplied to a dryer to accomplish the following

A. Heat the feed (solid & liquid) to the vaporization (wet bulb) temperature

B. Vaporize the liquid.

C. Heat the solids to their final temperature.

D. Heat the vapor to its final temperature.

In general, rate of heat transfer per unit mass can be calculated as follows

----------------- (2)

Where

qt =Rate of heat transfer

ms =1000 kg/hr

Tsa = 305K

Tsb =330K

Ta =385K

Tb =327.5K

TWb = 311K

Xa = 0.5349 = 53.5%

Xb= 0.05= 5 %

)(

)()()(

)()(

wbsblb

wbbvbaba

sawbLasasbss

TTCpX

TTCpXXXX

TTCpXTTCpm

qt

56

From steam tables, latent heat of vaporization (λ) =2410.8 KJ/kg (At 311K)

Heat capacity of feed stock = 0.3 Cp bagasse + 0.7 Cp coal

Heat capacity of bagasse [30] = 0.46KJ/kg K

Heat capacity of coal [31] = 1.381KJ/kg K

Heat capacity of solid feed stock = Cps = 1.104KJ/kg K

Heat capacity of water [32] = CpL = 4.178 KJ/kg K

[At T= (311+305)/2]

Heat capacity of water vapors [33] = Cpv = 1.869 KJ/kg K

[At T= (311+327.5)/2]

Putting these values in Eq. (2),

qt /ms = 1230.41 KJ/kg

qt = 1228.41*0.2777 KJ/s =341.38KW

ii. Calculation for air flow rate (mg)

Mass flow rate of air entering is found from given formula

------ (3)

Where

Csb=Humid Heat = 1.005 + 1.82H KJ/kg K = 1.0232 KJ/kg K

H1=Inlet humidity

Putting the values in Eq. (3),

mg = 5.74 Kg/s

iii. Air mass velocity (G)

The allowable mass velocity of air in direct contact rotary dryer ranges from 2000

to 25000 kg/m2 hr.

Take G = 12000 kg/m2 hr = 3.4 kg/m2 s

)1)(( 1HTTC

qg

absb

tm

57

iv. Area of dryer (A)

It can be found as

Area of dryer = Air mass flow rate = 1.724 m2

Air mass velocity

v. Drum Diameter

Diameter is calculated by equation

D=1.483 m

vi. Drum Length

To calculate Length we have to go through the following procedure

i. Calculate the Volumetric heat transfer coefficient (Ua)

ii. Calculate log mean of drying gas wet bulb depression at inlet & exit end of

dryer (ΔTm)

iii. Calculate the volume of dryer (V)

vii. Volumetric heat transfer coefficient (Ua)

Volumetric heat transfer Coefficient is found from given formula

Ua =0.756 KW/m3 K

5.0*4

AD

D

GaU

67.0^5.0

58

viii. Calculation for log mean of drying gas wet bulb depression at inlet

& exit end of dryer (ΔTm)

Log mean depression Of Wet bulb (ΔTm) is found from the following formula

ΔTm= 38.32K

ix. Volume of dryer (V)

Volume of dryer is found from the given formula

V=11.78 m3

x. Length of dryer

Length of dryer is calculated as

L = volume of dryer / area of dryer

L = 11.78 / 1.72 = 6.83 m

L/D ratio

L/D= 6.83/1.72

= 4.6

As L/D ratio for rotary dryer varies from 1 --- 10, therefore the above values can

be accepted.

)]/()[(

)()(

wbawbb

wbawbb

TTTTLn

TTTTTm

ma

t

TU

QV

*

59

2. Slope of drum

Slope of drum should be kept from 0 to 8 cm/m or 0 to 5°, more the slope of the

drying drum more will be forward driving force but product abrasion will also

increase. The slope is taken as 5 cm/m=3°

3. Rotational Speed

Assume the peripheral speed of rotation to be 06 m/min

Revolutions per minute = Peripheral Speed/Diameter

RPM = 6/1.48 = 4.04

= 4.04

The revolution of a drier varies between 2– 5

Therefore the above value can be accepted.

4. Lifting Flights

No. of Flights

The standard no. of flights is 2 to 4 times the diameter

No. of Flights=3*D

=4.5 ≈ 5

Radial height of the flight

The flight heights in direct rotary dryer will range from 1/12 to 1/8th of dryer

diameter.

Flight heights= 1/8*Diameter

=0.185 m

60

Shape of Flights

The shape of the flights depends upon the handling

characteristics of the solids. For free flowing materials, a radial

flight with a 900 lip is employed. So the flights are of radial

type.

5. Outlet Humidity

The air outlet humidity is found from given formula

Where

H2= Outlet Humidity

H1= Inlet Humidity

=0.01 kg of water/ kg of dry air

ms = 1000 kg/hr

mg =20700 kg/hr

Xa = 0.535

Xb= 0.05

Putting the values in above equation, we get

H2=0.0334 Kg of water/Kg of dry air

g

bas

m

XXmHH

)(12

61

6.1.6. Dryer Specification Sheet

6.1.7. Dryer Design Data

Equipment Dryer

Function To reduce the Water contents

Operation Continuous

Type Direct heated Rotary dryer

Flow rate of Solid entering 1000 Kg/hr

Inlet moisture content 53.5%

Outlet moisture content 5%

Mass flow rate of Air 20700 kg/hr

Total heat requirement 341.38 KW

Air mass velocity 3.33 Kg/s-m2

Area of dryer 1.723 m2

Diameter of dryer 1.48 m

Length of dryer 6.83 m

Volume of dryer 11.78 m3

L/D ratio 4.6

62

6.2. Gasifier Design

6.2.1. Fluidized Bed Reactor [22]

The designing of fluidized bed reactor consists of following steps.

1. Calculation of minimum fluidization velocity (Umf)

2. Calculation of Steam flow rate (Qo)

3. Calculation of Reactor Diameter, height and volume

4. Distributor plate design

6.2.2. Hydro Dynamics

Figure 6.2: Hydrodynamics Calculations [22]

6.2.3. Minimum Fluidization Velocity

Minimum fluidization velocity is calculated from the hydrodynamic study

based on physical properties of bed particles and fluidizing gas particles (Table 6.1

and Table 6.2). Bed particles consists of coal, sugarcane bagasse and CaO, whereas

CaO is used as CO2 sorbent in the bed. CaO is the heaviest among the bed particles

and considered as single bed particle in reactor dimensions evaluation. Moreover,

CaO mean particle diameter is initially taken as a single diameter in the gasifier.

63

Table 6.1: Bed Material Properties [22]

Bed material CaO

Mean particle diameter (dp) 2 mm

Particle density (Ƿs) 2551kg/m3

Bulk density (Ƿ) 1089kg/m3

Bed voidage (Emf) 0.57

Sphericity (Øs) 0.43

Table 6.2: Fluidizing Gas Properties (at 950K and 1 atm)

Fluidizing Gas Steam

Density (Ƿf) 0.2312kg/m3

Viscosity (µ) 0.0000356kg/m.s

At inlet the steam pressure must be 2 atm to maintain 1 atm pressure inside the

reactor (Assume that temperature of steam at the inlet is equal to the temperature

of the steam inside the reactor)

Table 6.3: Fluidizing Gas Properties (at 523K and 2 atm)

Fluidizing Gas Steam

Density (Ƿf) 0.8449kg/m3

Viscosity (µ) 0.00001818kg/m.s

Minimum fluidization velocity can be calculated from the following equation.

------------- (1)

Whereas Reynolds number at minimum fluidization is calculated from Ergun’s

(1952) equation.

------------- (2)

Where Ar is Archimedes number and can be calculated as:

fp

mf

mfd

U

Re

2

332Re

75.1Re

1150mf

mfs

mf

mfs

mfAr

64

------------- (3)

Where

Remf = Reynold’s number at minimum fluidization

g = Gravitational acceleration

By putting the values in Eq. (3)

Ar = 511093

By putting the values in Eq. (2)

Ar = 150(1 – Emf)Remf/Øs2Emf

3 + 1.75 Remf2/ØsEmf

3

511093 = [150(1 – 0.57)Remf / (0.43)2(0.57)3] + [1.75Remf2 / (0.43)(0.57)3]

511093 = 21.976 Remf2 + 1883.64 Remf

0 = Remf2 + 85.714 Remf – 23256.87

By using Quadratic formula

Remf = (-85.714+316.82)/2 Remf =(-85.714-316.82)/2

Remf = 115.55 Remf = -201.27 (not possible)

Using the value of Reynold’s number in Eq. (1)

Umf = 1.24 m/s

2

3

gdAr

fsfp

65

6.2.4. Diameter of Reactor

Reaction based steam Calculations

C(s) + H2O CO + H2 ------------- (4)

(Char Gasification reaction)

CH4 + H2O CO + 3 H2 ------------- (5)

(Steam Methane Reforming)

CO + H2O CO2 + H2 ------------- (6)

(Water Gas shift reaction)

Table 6.4: Proximate analysis of Coal and Biomass (Dry Basis)

Coal [24] Biomass [10] Combined

Fixed Carbon 37.33% 18.03% 31.54%

Volatile matter 47.81% 71.9% 55.04%

Ash 14.86% 10.07% 13.42%

Total feed entering the gasifier = 683.6 kg/hr

Moisture content present in the feed = 32.1 kg/hr

Total Solid feed ( Coal + Biomass ) = 651.5 kg/hr

In 651 kg of feed

C=205.5 kg = 17.12 kmol

CH4 = 358.6 kg = 22.41 kmol (For steam calculations, assume that all VM = CH4)

Ash = 87.43 kg

66

Char Gasification Reaction


Moles of C = 17.12 kmol/hr = 205.44 kg/hr




Steam Methane Reforming Reaction


Moles of CH4 = 22.41 kmol/hr = 358.56 kg/hr




Water Gas Shift Reaction




Moles of CO2 = 39.53 kmol/hr = 1732.32 kg/hr


Amount of steam required = 1423.08 Kg/hr (S/C = 1)

For S:C = 2

Amount of steam = 2846.16 Kg/hr

Density of steam = 0.2312 Kg/hr

67

Volumetric flow rate of steam = Qo = 12310.38 m3/hr ≈ 12310 m3/hr

= 3.42 m3/s

Uo = 4 m/s (Uo = 3—5 Umf)

21

02Re

oU

QIDactor

Reactor ID = 1.043 m ≈ 1.04 m

6.2.5. Height of Reactor

Height of the reactor is calculated as

Total Height = Bed height + TDH

For stable operation

Bed Height = Bed Diameter

Bed Height = 1.04m

Total disengaging Height (TDH)

TDH = 4.47 [Dbm]0.5

Dbm = 0.652 [At (U – Umf)]2/5

Uo = 4 m/s (Uo = 3—5 Umf)

𝐴𝑡 = 𝜋𝐼𝐷2

4

= 0.85 𝑚2

𝐷𝑏𝑚 = 0.652 [ 0.85 (4 − 1.24)]2/5

𝐷𝑏𝑚 = 0.917 𝑚

𝑇𝐷𝐻 = 4.47 [𝐷𝑏𝑚] 0.5

TDH = 4.281 m ≈ 4.28 m

68

Total Height = 1.04 + 4.28 = 5.32 m ≈ 5.3 m

6.2.6. Volume of Reactor

Volume = π*r2*L

= 4.5 m3

6.2.7. Distributor Plate Design [34]

𝑅𝑐 = 𝐷𝑖𝑠𝑡𝑟𝑖𝑏𝑢𝑡𝑜𝑟𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒𝐷𝑟𝑜𝑝

𝐵𝑒𝑑𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒𝐷𝑟𝑜𝑝=0.01+0.2[1 − 𝑒−0.5𝐷/𝑍]

R c =0.01+0.2[1 − 𝑒−0.5×0.9/0.9]

R c=0.089

ΔPb =H (1-ε) (ρs-ρf)

ΔPb = 5.3 (1-0.57)(2551-0.8449)

ΔPb= 5811.80 kg

m2 = 56955.67 Pa

ΔPd= Rc ΔPb = 0.089 x 5811.80 = = 517.25 kg

m2 = 5069.70 Pa

69

6.2.8. Number of Orifices in the Distributor Plate [35]

Vessel Reynold’s number can be calculated by the following formula.

Re = ρfxdxUo

μ

= 0.2312 * 1.04 * 4 / 0.0000356 = 27016.63

Re 100 300 500 1000 2000 >3000

CdOR 0.68 0.70 0.68 0.64 0.61 0.60

From the table CdOR = 0.6

UOR=Cdor(2×∆𝑝𝑑

𝜌𝑓)0.5

= 0.6 (2×5069.7

0.8449)0.5

UOR = 65.73 m/s

𝑈𝑜 = 𝐴𝑜𝑟 ∗ 𝑈𝑜𝑟 ∗ 𝑁𝑜𝑟

Whereas

𝑁𝑜𝑟 =𝑈𝑜

𝐴𝑜𝑟 ∗ 𝑈𝑜𝑟

𝑁𝑜𝑟 =4

𝐴𝑜𝑟 ∗ 65.73

NOR = 0.06/ AOR

Dia of orifice = 2 mm

Area of orifice = 3.1416 E-6

NOR = 19108

70

6.1.9. Gasifier Specification Sheet

Equipment Gasifier

Function To Convert Solid fuel into Gaseous Product


Type Fluidized Bed Gasifier

6.2.10. Gasifier Design Data

Minimum Fluidizing Velocity 1.24 m/s

Volumetric flow rate of steam 3.42 m3/s

Reactor ID 1.04 m

Bed Height 1.04 m

TDH 4.28 m

Total Height 5.3 m

Volume of Reactor 4.5 m3

Diameter of Orifice 2 mm

Area of Orifice 3.1416 E-6

NOR 19108

71

6.3. Cyclone Separator Design [36]

6.3.1. General design procedure

1. Select either the high-efficiency or high-throughput design, depending on

the performance required.

2. Estimate the number of cyclones needed in parallel.

3. Calculate the cyclone diameter for an inlet velocity of 9-27 m/s. Scale the

other cyclone dimensions from Figure.

4. Calculate the scale-up factor.

5. Calculate the cyclone performance and overall efficiency (recovery of

solids). If unsatisfactory try a smaller diameter.

6. Calculate the cyclone pressure drop and, if required, select a suitable blower

6.3.2. Number of Cyclones

Flow rate of the gas entering = 3072.88 kg/hr

Density = 0.1922 [28]

Volumetric flow rate = mass/density

= 15980 m3/hr

= 4.44 m3/s (High throughput design is selected)

Standard velocity taken in cyclone is = u = 9-27 m/s

Figure 5.3: High through-put Cyclone

72

6.3.3. Inlet Duct area

Area= Volumetric Flow rate / Velocity

Area of inlet duct at 20 m/s =4.44/20

Area = 0.2219 m2

DC:

From the Figure

Duct area= 0.75Dc × 0.375 Dc

0.2219 = 0.28125 ×𝐷c2

Dc= 0.888 m

𝑆𝑡𝑎𝑛𝑑𝑎𝑟𝑑 Dc = 0.203 m

0.888/0.203 = 4.37

4 cyclones should be used in parallel.

Flow rate per cyclone = 3995 m3/h

6.3.4. Dimensions of Cyclone

Total Height:

0.888/2=0.444m =Dc

From the figure.

Total height = 1.5×𝐷c + 2.5×𝐷c

= 4×0.444= 1.776m

Outlet Duct Area:

From the figure

Do = 0.75×𝐷c

= 0.75×0.444

= 0.333 m

Ao = 𝜋×(0.333/2)2

= 0.087 m2

73

Dust Exit Diameter:

From the Figure

Dust exit diameter = 0.375 × Dc

= 0.375 ×0.444

= 0.166 m

6.3.5. Calculation of Scaling Factor

d2/d1 = [(𝒅𝒄𝟐/𝒅𝒄𝟏)𝟑×(𝑸𝟏/𝑸𝟐)×(Δ𝝆𝟏/ Δ𝝆𝟐 )×(𝝁𝟐/𝝁𝟏)]𝟎.𝟓

dc2 = Diameter of cyclone=0.444 m

dc1 = Diameter of standard cyclone=0.203 m

Q1 = Standard flow rate= 669 m3/h

Q2 = Volumetric flow rate=3995 m3/h

Δ𝝆𝟏 = standard solid-fluid =2000 kg/m3

Δ𝝆2 = particle density=1642 kg/m3

𝝁1 =standard viscosity =0.018 mNs/m2 (cp)

𝝁𝟐 =gas viscosity = 0.02638 cp (mNs/m2)

By putting these values.

d2/d1 = [(0.444/0.203)𝟑×(669/3995)×(2000/ 1642 )×(0.02638/0.018)]𝟎.𝟓

d2/d1 = 1.75

Therefore it has 99% efficiency when the particle size at the outlet is 0.05 mm

74

6.3.6. Pressure Drop Calculation

ΔP = (𝛒𝐟

𝟐𝟎𝟑) {𝐮𝟏𝟐 [𝟏 + 𝟐𝛗𝟐 ((

𝟐𝐫𝐭

𝐫𝐞) − 𝟏)] + (𝟐𝐮𝟐𝟐)}

ΔP=Cyclone pressure drop, millibars

𝝆f = Gas Density = 0.1790 kg/m3

u1 = 20 m/s

u2 = Volumetric Flow rate / Area of exit pipe = 1.11/0.087 = 12.75 m/s

rt = Radius of the circle to which the center line of the inlet is tangential

= [.444-(.166/2)]/2

= 0.18036 m

= 180.36 mm

re = Radius of the exit pipe = .16648m = 166.48 mm

Ψ = (fc × AS)/Ai

fc=0.005 for gases

Surface area of cyclone = As = Dc×ℎ×𝜋

=0.444×1.776×3.14

=2.47 m2

Ai=0.75 Dc* 0.375 Dc

= 0.051 m2

Ψ = 0.24

From the graph

φ = 1.1

ΔP = (𝟎.𝟏𝟕𝟗

𝟐𝟎𝟑) {(𝟐𝟎)𝟐[𝟏 + 𝟐(𝟏. 𝟏)𝟐(𝟐. 𝟏𝟔𝟔 − 𝟏)] + (𝟐(𝟏𝟐. 𝟕𝟓)𝟐)}

ΔP = 1.63 millibar = 16.72 mm H2O

Pressure drop is reasonable.

75

6.3.7. Cyclone Separator Specification Sheet

Equipment Cyclone Separator

Function To separate undesired particles


Type High Throughput Design Separator

6.3.8. Cyclone Separator Design Data

Flow rate of Entering gas 3072.88 kg/hr

Inlet Velocity 20 m/s

Inlet Duct Area 0.222 m2

Diameter of cyclone 0.444 m

Number of Cyclones 4

Flow Rate of each Cyclone 3995 m3/h

Total Height 1.77 m

Outlet duct Area 0.087 m2

Dust Exit Diameter 0.166 m

Gas Density 0.1790 kg/m3

Radius of Exit Pipe, re 166.48 mm

Pressure Drop 1.63 millibar

76

6.4. Design of Scrubber

6.4.1. Designing Steps

1. Selection of column.

2. Selection of packing and material

3. Calculating the size of packing

4. Determining the no. of transfer units (NOG)

5. Calculating the diameter of column

6. Determining the height of packing

7. Determining the height of the column

8. Determining the Column Pressure drop

Table 6.5: Scrubber Material Balance

Feed composition

Components Molar flow rate

(kmol / hr)

Mass Flow Rate

(kg/hr)

Mole Fraction

CH4 8.96 143.36 0.0436

CO 6.09 170.52 0.0296

CO2 3.84 168.96 0.0187

H2 61.41 122.82 0.2986

H2O 125.36 2256.55 0.6095

Solids - 2.107

Total 205.66 2864.317 1

77

Table 6.6: Scrubber Top Composition

Top Composition

Component Molar flow rate

(kmol / hr)

Mass Flow Rate

(kg/hr)

Mole fraction

CH4 8.96 143.36 0.1115

CO 6.09 170.52 0.0757

CO2 3.43 150.96 0.0427

H2 61.41 122.82 0.7640

H2O 0.49 8.82 0.0061

Total 80.38 596.48 1.00

Gm(y1 – y2) = Lm(x1 – x2) [37]

Gm=flow rate of gas entering (Kg/hr)

Lm = flow rate of solvent entering (Kg/ hr)

Y1=Mole fraction of Steam in entering stream of gas

Y2= Mole fraction of Steam in leaving stream of gas

X1= Mole fraction of Steam in leaving solvent stream

X2= Mole fraction of Steam in entering solvent stream

2864.317(Y-0.0061) = 33400(X-0)

Y= 11.66X +0.0061 ……………… (1)

Equation (1) is the operating line equations.

Equation for Equilibrium Curve:

78

Y1= Mole fraction of Steam in entering stream of gas = 0.61

Y2= Mole fraction of Steam in leaving stream of gas = 0.0061

At Y1= 0.61, using Equation (1) X1= 0.052

Using the figure the equation for equilibrium curve is;

ye= 7.5x ……………… (2)

At X1= 0.052 using equation (2), ye1= 0.39

m Gm′

Lm′ =

ye1

y1 −y2 =

0.39

0.61−0.0061

m Gm′

Lm′ = 0.646

y1

y2 =

0.61

0.0061 = 100

From figure 12.23 [39]

At y1

y2 = 100 and m

Gm′

Lm′ = 0.646

NOG= 10.1

6.4.2. Calculation of Diameter of Column [36]

Flow rate of entering gases = G = 2864.32 Kg/hr = 2864.32

3600 = 0.796 Kg/sec

Flow rate of entering solvent = L = 33400 Kg/hr = 33400

3600 = 9.28 Kg/sec

Temperature of entering gas = Tg = 677 °C = 950K

Temperature of entering Solvent = TL= 25 °C = 298K

Average column temperature = Tavg = TDG + 𝐶𝑝𝑔(𝑇𝑤−𝑇𝑔)+(1−ѡ)∆𝐻𝑎

𝐶𝑝𝑔+𝐶𝑝𝑤

Tavg = 61.4 ºC

Operating pressure of Scrubber = P = 1 atm

79

Average molecular weight of entering gases = 13.96 Kg

Density of gas mixture = ρg = 1.033 Kg/m3 [28]

Density of liquid solvent = ρL = 0.9793 g/cm3 = 979.3 Kg/m3

Viscosity of liquid solvent = µL =0.4534 cp = 4.534 × 10−4 Ns/m2 [28]

Viscosity of Gaseous mixture = µg = 0.0174 cp = 1.74 × 10−5 Ns/m2 [28]

Now

Abscissa of fig 11.44 [36]

Lw

Gw√

ρg

ρL =

9.28

0.796√

1.033

979.3 = 0.378

For pressure drop 40 mm of H2O /m of packing

From fig 11.44 [36]

K4 = 0.7 at 40mm H2O

And

K4 = 1.5 at flooding

% Flooding = √0.7

1.5 × 100 = 68.31 % (Satisfactory)

80

Packing Specifications

Packing Type = Ceramic Intallox Saddles

Packing Size =0 38 mm

Bulk density = 625 kg/m3

Surface area = a = 194m2/m3

Packing factor = Fp = 170 m-1

From equation 11.118

Vm∗ = [

K4 ρv(ρL − ρv)

13.1 FP(μLρL

)0.1 ]

0.5

Vm∗ = [

0.7×1.033(979.3− 1.033)

13.1×170(4.534×10−4

979.3)

0.1]

0.5

Vm∗ = 1.336 Kg/m2.s

As

Column Area required = A = G

Vm∗ =

0.796

1.336 m2 = .595 m2

Diameter of column =D =√ 4A

π

Diameter of column= 0.9 m

Actual Area of column = 0.636 m2

%age flooding (at 0.9m dia) = 73.02 %

81

6.4.2. Calculation of Height of Transfer Units (Onda’s Method)

Equation for calculation of effective interfacial area is given as.

Where

aw = effective interfacial area of packing per unit volume m2/m3

Lw = liquid mass velocity kg/m2s = 14.59 kg/m2s

a = actual area of packing per unit volume m2/m3 = 194 m2/m3

σc = critical surface tension for metal packing material = 61 x 10-3 N/m

σL = liquid surface tension N/m = 65.71 dyne/cm = 65.71 x 10-3 N/m

µL= 4.534 × 10−4 Ns/m2

ρL = 979.3 Kg /m3

By putting these values

aw = 142.71 m2/m3

6.4.3. Calculation of Liquid Film Mass Transfer Coefficient

KL = liquid film coefficient m/s

dp = packing size =38x 10-3 m

DL = diffusivity of liquid = 6.4 x 10-9 m2/s

Then, by substituting the values,

KL = 8.16 x 10-4 m/s

2.02

05.0

2

21.075.0

45.1exp1a

L

g

aL

a

L

a

a

LL

w

L

w

L

w

l

cw

4.02

1

3

2

3

1

0051.0 p

LL

L

Lw

w

L

LL ad

Da

L

gK

82

6.4.4. Calculation of Gas Film Mass Transfer Coefficient

Where KG = Gas film coefficient, kmol/m2s.bar

VW = Gas mass velocity = 1.25 Kg/m2.s

K5= 5.23 (For packing size above 15mm, Coulson & Richardson)

Dv =Diffusivity of gas = 5.43 x 10-5 m2/s

Then, by substituting the values,

KG = 1.85 x 10-3 kmol/m2s.bar

6.4.5. Calculation of Gas-film Transfer Unit Height

Where,

HG = Gas-film transfer unit height

Gm = 1.25/13.96 = 0.089 Kmol/m2.sec

Then,

HG = 0.089

1.85 x 10−3×142.71×1.013

HG = 0.333 m

23

17.0

5

p

gg

g

g

w

g

gGad

Da

VK

aD

RTK

PaK

GH

WG

mG

83

6.4.6. Calculation of Liquid-film Transfer Unit Height

Where

HL= Liquid-film transfer unit height

Lm= 14.59/18 = 0.81 Kmol/m2.s

Ct = Concentration of solvent = 979.3/18 = 54.4 Kmol/m3

Then,

HL = 0.81

8.16x 10−4×142.71×54.4

HL = 0.128 m

6.4.7. Calculation of Height of Transfer Units

As,

HG = 0.333 m

HL = 0.128 m

So,

Height of transfer units=HOG = 0.333 + 0.646 × 0.128

HOG = 0.42 m

6.4.8. Calculation of Height of Tower

Total height of packing = Z = NOG × HOG

Z = 10.1 × 0.42 = 4.242 m = 4.25 m

Allowances for liquid distribution = 1m

Allowances for liquid Re-distribution =1m

Total height of tower = 4.25 + 1 + 1

LHmL

mmGGHoGH

tWL

mL

CaK

LH

84

Total height of tower = Zt = 6.25

6.4.9. Pressure Drop Calculations

Pressure drop in a gas absorber is a function of superficial gas velocity and

properties of the packing used. The Scrubber may be designed for a specific

pressure drop or pressure drop may be estimated using Leva’s correlation.

∆P = c(10𝑗∗𝐿) ∗ ((𝑓 ∗ 𝐺𝑣)2/ρv)

ΔP: Pressure drop in inches water/foot packing

Gv: Superficial gas velocity = 0.256 lb/hr-s2

𝜌v: Gas density in lb/ft3 = 0.064 lb/ft3

L: Liquid superficial velocity = 2.99 lb/hr-s2

𝜌L: Liquid density in lb/ft3 = 61.13 lb/ft3

c = 0.14

j = 0.14

∆P = 0.2 inch of H2O/ft of packing

85

6.4.10. Scrubber Specification Sheet

Equipment Scrubber

Function Removal of Steam


Type Packed Column

Packing Type Ceramic Intallox Saddles

6.4.11. Scrubber Design Data

Flow rate of Entering gas 2864.32 kg/hr

NOG 10.1

Diameter of Column 0.9 m

Percentage Flooding 73.02

Effective Packing Interfacial Area 142.71 m2/m3

Liquid Film Mass Transfer Coefficient 8.16 E-4 m/s

Gas Film Mass Transfer Coefficient 1.85 E-3 kmol/m2 s.bar

HG 0.333 m

HL 0.128 m

HOG 0.42 m

Height of Packing 4.25 m

Height of Column 6.25 m

∆P 0.2 inch H2O/ft of packing

86

CHAPTER 7

INSTRUMENTATION AND PROCESS CONTROL

7.1. Instrumentation

Measurement is a fundamental requisite to process control. Either the

control can be affected automatically, semi-automatically or manually. The quality

of control obtainable also bears a relationship to the accuracy, re-product ability

and reliability of the measurement methods, which are employed. Therefore,

selection of the most effective means of measurements is an important first step in

the design and formulation of any process control system.

7.2. The Concept of Measurement in Automation Application

Measurement is defined as the extraction from physical and chemical

systems or processes of signals, which represent parameters or variable. The

performance of an automation system can never surpass that the associated

measuring devices. A basic example is a human being. The output of a measuring

instrument that has its output compared to an arbitrarily chosen reference of

suitable magnitudes which is normally assumed to be unvarying. “Transducer” or

“Sensor” is a general term for a sensing device.

87

7.3. Measurement

Instrumentation can be used to measure certain field parameters (physical

values). These measured values include:

1. Pressure

2. Flow

3. Temperature

4. Level

5. Density

6. Viscosity

7. Radiation

8. Frequency

9. Current

10. Voltage

7.4. Process

A process is broadly defined as an operation that uses resources to transform

inputs into outputs. It is the resource that provides the energy into the process for

the transformation to occur.

7.4.1. Process Control

Process control is the act of controlling a final control element to change the

manipulated variable to maintain the process variable at a desired Set Point.

88

7.4.2. Objectives of Process Control

Effective process control objective is to maintain safe operations, quality

products, and business viability.

I. Safety

The primary purpose of a Process Control system is safety: personnel safety,

environmental safety and equipment safety. The safety of plant personnel and the

community is the highest priority in any operation. An example of safety in a

common heat exchanger process is the installation of a pressure relief valve in the

steam supply.

II. Quality

In addition to safety, process control systems are central to maintaining

product quality. In blending and batching operations, control systems maintain the

proper ratio of ingredients to deliver a consistent product. They tightly regulate

temperatures to deliver consistent solids in cooking systems. Without this type of

control, products would vary and undermine quality.

III. Business Viability

When safety and quality concerns are met, process control objectives can

be focused on profit. All processes experience variations and product quality

demands that we operate within constraints. A batch system may require +- 0.5%

tolerance on each ingredient addition to maintain quality. A cook system may

require +- 0.5 degrees on the exit temperature to maintain quality. Profits will be

maximized the closer the process is operated to these constraints. The real

challenge in process control is to do so safely without compromising product

quality.

89

7.5. Basic Elements of Process Control

Controlling a process requires knowledge of four basic elements, the

process itself, the sensor that measures the process value, the final control element

that changes the manipulated variable, and the controller.

I. Process

It represents the material equipment together with physical or chemical

operation that occurs.

II. Sensors

Sensors measure the value of the process output that we wish to effect. This

measurement is called the Process Variable or PV. Typical Process Variables that

we measure are temperature, pressure, mass, flow and level.

III. Final Control Element

A Final Control Element is the physical device that receives commands

from the controller to manipulate the resource. Typical Final Control Elements

used in these processes are valves and pumps.

IV. The Controller

This is the hardware element that has “intelligence”. It receives the

information from the measuring device and decides what action must be carried

out. The older controllers were of limited intelligence, could perform very limited

and simple operations and could implement very simple control laws. The use of

digital computers in this field has increased the use of complicated control laws.

90

7.6. Basics of Process Control

1. Open Loop Control

2. Closed Loop Control

I. Open Loop Control

In open loop control we are not concerned that a particular Set Point be

maintained, the controller output is fixed at a value until it is changed by an

operator. Many processes are stable in an open loop control mode and will maintain

the process variable at a value in the absence of a disturbance.

II. Closed Loop Control

In closed loop control the controller output is determined by difference

between the process variable and the Set Point. Closed loop control is also called

feedback or regulatory control.

7.7. Selection of Controller

Actually in industry, only P, PI and PID control modes are the usual

practice. The selection of most appropriate type of controller for any particular

environment is a very systematic procedure. There are many ways and means that

how a particular type of system may be controlled through which type of controller.

Usually type of controller is selected using only quantitative considerations

stemming from the analysis of the system and ending at the properties of that

particular controller and the control objective. Proportional, Integral and Derivative

control modes also affect the response of the system. Following is the summarized

criterion to select that appropriate controller for any process depending upon the

detailed study of the controller and control variable along with process severity.

91

If Possible Use a Simple Proportional Controller

Simple P-controller can be used if we can achieve acceptable off-set with

not too high values of gain. So for gas pressure and liquid level control, usually a

simple proportional controller may be used.

If a Simple P-Controller is not Suitable, Use PI-Controller

A steady-state error always remains for proportional controller so in

systems where this off-set is to be minimized, a PI-controller is incorporated. So in

flow control applications, usually PI-controller is found.

Use PID-Controller to Increase the Speed of the Closed Loop Response

The anticipatory characteristics of the derivative control enables to use

somewhat higher values of proportional gains so that off-set is minimized with

lesser derivations and good response of the system. Also it adds the stability to the

system. So this type of control is used for sluggish multi-capacity processes like to

control temperature and composition.

92

7.8. Control Loops

For instrumentation and control of different sections and equipment’s of

plants, following control loops are most often used.

I. Feed backward control loop

II. Feed forward control loop

III. Ratio control loop

IV. Auctioneering control loop

V. Split range control loop

VI. Cascade control loop

I. Feed Backward Control Loop

Feedback control is a control mechanism that uses information from

measurements to manipulate a variable to achieve the desired result.

II. Feed Forward Control Loop

Feed-forward control, also called anticipative control, is a control

mechanism that predicts the effects of measured disturbances and takes corrective

action to achieve the desired result.

III. Ratio Control Loop

Ratio control loop is used to maintain the flow rate of one (dependent

controlled feed) stream in a process at a defined or specified proportion relative to

that of another (independent wild feed stream) in order to control the composition

of a resultant mixture.

93

IV. Auctioneering Control Loop

Auctioneering is the process of choosing one output signal from a set of

multiple input signals. In order to use auctioneering in your control process, you

will first need to have multiple signals all measuring the same variable. The signals

will then all be sent to a set of selectors aligned in series. For each selector, there

will be two inputs. For the first selector, the two inputs will be the first two signals

from the device being controlled. For each subsequent selector, one signal will be

the output signal from the previous selector, while the other input signal will be the

next signal from the device.

V. Split Range Control Loop

In this loop controller is per set with different values corresponding to

different action to be taken at different conditions. The advantage of this loop is to

maintain the proper conditions and avoid abnormalities at very different levels.

VI. Cascade Control Loop

This is a control in which two or more control loops are arranged so that the

output of, one controlling element adjusts the point of another controlling element.

This control loop is used where proper and quick control is difficult by simple feed

forward or feed backward control. Normally first loop is a feed control loop. We

have selected a cascade control loop for our heat exchanger in order to get quick

on proper control.

94

7.9. Control Schemes of Gasifier

The gasifiers of the past were crude, inconvenient devices. Today's gasifiers

are evolving toward safer, automated processes that make use of a wide range of

present-day instruments and controls.

Thermocouples (such as chromel-alumel type K) should be used to measure

various gasifier temperatures, especially below the grate, as a check for normal or

abnormal operation. Temperatures at the grate should not exceed 950 0K higher

temperatures indicate abnormal function. Consequently, the signal from the

thermocouple can be used by a control system or an alarm system.

For gasification reaction, gasification agent steam is required which must

be enter into gasifier at specific temperature and pressure. Therefore temperature

and pressure of steam must be controlled by the used of thermocouple and pressure

gauge respectively.

Figure 7.1: Control Schemes of Gasifier

95

7.10. Control Schemes of Scrubber

Pressure of entering streams will be sensed by the differential pressure sensor

and temperature of entering streams and exits stream must be noticed by the used

of thermocouple as well as for maximum efficiency of scrubber flow rate of the

water entering the scrubber must be control by the used of flow rate meter and

temperature is controlled by thermocouple.

Figure 7.2: Control Schemes of Scrubber

CHAPTER 8

COST ESTIMATION

8.1. Introduction

Before the plant to be operated, specified money must be supplied to

purchase and install the equipment. The capital needed to supply the necessary

plant facilities is called fixed capital investment while that for the operation of the

plant is called the working capital and sum of two capitals is called total capital

investment.

It is essential that chemical engineer be aware of the many different types

of cost involved in manufacturing processes. Capital must be allocated for direct

plant expenses; such as those for raw materials, labor, and equipment. Besides

direct expenses, many other indirect expenses are incurred, and these must be

included if a complete analysis of the total cost is to be obtained.

97

8.2. Fixed Capital Investment

Manufacturing fixed capital investment represents the capital necessary for

the installed process equipment. With all auxiliaries that are needed for the

complete process operation. Expenses for piping, instruments, installation, and

foundation and site preparation are typical examples of cost included in the

manufacturing fixed capital investment. Fixed capital required for the construction

overhead and for all plant components that are not directly related to the process

operation is designed as the non-manufacturing fixed capital investment.

8.3. Working Capital

The working capital for an industrial plant consists of the total amount of

the money invested in:

Raw material and supplies carried in stock.

Finished products in stock and semi-finished products in the process of

being manufactured.

Accounts receivable.

Cash kept on hand for monthly payments of operating expenses, such as

salaries, wages and raw material purchases.

Accounts payable

Taxes payable

8.4. Cost Index

Is an index value for a given point in time showing the cost at that time

relative to certain base time. If the cost at any time in past is known, the equivalent

cost at the present time can be determined by multiplying the original cost by the

ratio of present of index value to the index value applicable when the original cost

was obtained.

Present cost = Original cost × cost index value at present time/cost index value

at past.

98

8.5. Purchased Equipment Cost

8.5.1. Estimate of Dryer Cost [38]

Surface area of dryer = 2πr (r + h) = 35.2 m2 = 378.86 ft2

From figure 16.29 [41]

Cost of Rotary dryer = $ 55000

CE Plant Cost Index= 356, January 1990

CE Plant Cost Index = 576.2, June 2014

Total Cost of Dryer in 1990 = $ 55000

Total Cost of Dryer in 2014 = (55000)(576.2/356)

Total Cost of Dryer in 2014 = $ 89019.66

8.5.2. Estimate of Ball Mill Cost [39]

Ball mill: C = 50.0 W 0.69, 1 < W< 30 tons/hr

W = 0.6836 ton/hr

For 2 ton / hr

C = 80664.17 $

By Six-tenths-factor rule (Slope 0.6) [38]

Cost of Ball mill (for the required capacity) = 42358.82 $

99

CE Plant Cost Index= 325, Middle 1985


Total Cost of Ball mill in 2014 = (42358.82)(576.2/325)

Total Cost of Ball Mill in 2014 = $ 75098.94

8.5.3. Estimate of Gasifier Cost [38]

Thickness = 𝑃∗𝑅𝑖

𝑆𝐸𝑗−0.6𝑃+ 𝐶𝑐

P = Max allowable internal pressure = 1.2 atm = (20% Design pressure)

Ri = Inner radius= 0.52 m = 1.71 ft

Ej = Efficiency of joint = 0.85

S = Max allowable working stress = 12000 psi = 816.55 atm

Cc = Corrosion allowance = 0.125 in

By putting the values

Thickness = 0.5 in

Weight of Shell = π*ID*H*Thickness*Density

Density = 490.06 lb/ft3


Weight of Shell = 3804.04 lb

Weight of two heads = 2π[(D/2)^2]*Thickness * Density

= 373.22 lb

Total weight including 20% increase = 5012.712 lb

100

Cost = 80W-0.34

= 22137.98 $

Cost factor of stainless steel = 2.5

Total cost = 55344.95 $ (January 1990)

CE Plant Cost Index= 356, Jan 1990


Present cost = $ 89546.89

Cost of distributor plate (2004) = 544 $ [36]

Present cost of distributor plate = 777.79 $

Total Cost of Gasifier in 2014 = $ 90324.69

8.5.4. Estimate of Cyclone Separator Cost [39]

Standard duty Cyclone: C = O.65Q0.91, 2 < Q < 40 KSCFM

Q = 2.351 K SCFM

Cost of Cyclone (for the required capacity) = 1414.9 $



Total Cost of Cyclone in 2014 = (1414.9)(576.2/325)

101

Total Cost of Cyclone in 2014 = $ 2508.67

8.5.5. Estimate of Scrubber Cost [39]

For Packed Towers;

C = f1Cb + VpCp + Cp1

Pressure = 1.013 bar

The design pressure of the vessel should be 10% above the operating pressure

Column Diameter (Di) = 0.9 m

Vessel Length (L) = 6.25 m

Height of packing = 4.25 m

Shell Thickness = 10mm

Column Diameter (Do) = 0.92 m

Density of Stainless Steel (ρss) = 7850 kg/m3

Mass of Top and Bottom Heads = 147 kg each

𝑀𝑎𝑠𝑠 𝑜𝑓 𝐶𝑜𝑙𝑢𝑚𝑛 = (𝜋(𝐷𝑜2 − 𝐷𝑖2)/4)(𝐿)(ρ𝑠𝑠) + 𝑀(𝑡𝑜𝑝 ℎ𝑒𝑎𝑑) +

𝑀(𝑏𝑜𝑡𝑡𝑜𝑚 ℎ𝑒𝑎𝑑)

Mass of Column = 1696.62 kg = 3732.57 lb

Cb = exp[6.629+ 0.1826(1n W) + 0.02297(ln W)2]

Cb = $ 16465.13

Cp1 = 246.4D0.7396L0.7068

Cp1 = $ 4639.66

F1 = 1.7 (For stainless steel)

Vp (packing volume) = Area x Height

Vp (packing volume) = 95.48 ft3

Cp = 16.6 $/ft3 (for 1.5 in Ceramic Intalox Saddles)

C = f1Cb + VpCp + Cp1


102

C = $ 34215.35



Total Cost Scrubber in 1985 = $ 34215.35

Total Cost Scrubber in 2014 = (34215.35)(576.2/325)

Total Cost Scrubber in 2014 = $ 60661.18

Table 8.1: Total Purchased Cost of Major Equipments

Equipment Purchased cost $

Dryer 89019.66

Ball Mill 75098.94

Gasifier 90325.69

Cyclone Separator 10034.68

Scrubber 60661.18

Total $ 325140.15

103

Estimation of Fixed Capital [36]

Table 8.2: Typical factors for the estimation of project fixed capital cost

Physical Plant cost PPC= PCE* (1+f1+f2+….f9)

= 325140.15 (1+0.45+0.45+0.15+0.10+0.10+0.45+0.20+0.05+0.20)

PPC = $1,024,191.473

Table 8.3: Fixed Capital Cost

Fixed capital cost =PPC*(1+F10+F11+F12)

Fixed capital cost = $1,024,191.473 (1+0.25+0.05+0.10)

Fixed capital cost = $1,433,868.06

Items Factors

Equipment erection F1 0 .45

Piping F2 0.45

Instrumentation F3 0.15

Electrical F4 0.10

Buildings, process F5 0.10

Utilities F6 0.45

Storage F7 0.20

Site development F8 0.05

Ancillary buildings F9 0.20

Items Factors

Design and Engineering F10 0 .25

Contractor’s fee F11 0.05

Contingency F12 0.10

104

8.6. Estimation of Working Capital

Working capital = 10% of fixed capital to cover the cost of the fixed capital used

= $1,433,868.06*0.1

= $ 143,386.81

8.7. Total Investments

Total investments required = Fixed capital + Working capital

= $1,433,868.06 + $ 143,386.81

= $ 1577254.87

8.8. Production Costs [36]

I. Variable costs

1. Raw materials

= $ 716335.4 /year

2. Miscellaneous materials

= 10 % of maintenance cost

= $ 14338.68 /year

3. Utilities

= 5% of maintenance cost

= $ 7169.34 /year

Total Variable Cost = $ 737843.42

105

II. Fixed costs

Maintenance Cost

= 10 % of fixed capital

= $ 143,386.81

Operating labor

= 15 % of the total operating cost.

= $ 236,588.23

Laboratory costs

= 20 % of Operating Labor

= $ 47,317.65

Supervision


= $ 47,317.65

Plant overheads


= $ 118,294.11

Capital charges

= 10 % of the fixed capital

= $ 143,386

Insurance 1 per cent of the fixed capital


= $ 14,338.6

12. Local taxes 2 per cent of the fixed capital


= $ 28,677.2

106

13. Royalties 1 per cent of the fixed capital


= $ 14,338.6

Total Fixed Cost = $ 793,644.85

Direct production costs = $ 1,531,488.27

Sales expense + General overheads

= 20% of the direct production cost

= $ 306297.65

Annual production cost = $ 1,837,785.92

Production cost $/kg = 𝐴𝑛𝑛𝑢𝑎𝑙 𝑃𝑟𝑜𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝐶𝑜𝑠𝑡

𝐴𝑛𝑛𝑢𝑎𝑙 𝑃𝑟𝑜𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝑅𝑎𝑡𝑒

= 0.35 $/Kg

CHAPTER 9

HAZOP STUDY

9.2. Introduction

The Hazard and Operability Study (or HAZOP Study) is a standard hazard

analysis technique used in the preliminary safety assessment of new systems or

modifications to existing ones. The HAZOP study is a detailed examination, by a

group of specialists, of components within a system to determine what would

happen if that component were to operate outside its normal design mode. The

effects of such behavior is then assessed and noted down on study forms. The

categories of information entered on these forms can vary from industry to industry

and from company to company.

9.3. Objectives of HAZOP Study

To identify the potential risks

To identify and study features of the design that influence the probability of

a hazardous incident occurring.

To familiarize the study team with the design information available.

108

To ensure that a systematic study is made of the areas of significant hazard

potential.

9.4. Keywords used in HAZOP STUDY

Keywords are used to focus the attention of the team upon deviations and

their possible causes. These keywords are divided into two sub-sets:

Primary Keywords which focus attention upon a particular aspect of the

design intent or an associated process condition or parameter.

Secondary Keywords which, when combined with a primary keyword,

suggest possible deviations.

9.5. Primary Keywords

These reflect both the process design intent and operational aspects of the

plant being studied. Typical process oriented words might be as follows. The list

below is purely illustrative, as the words employed in a review will depend upon

the plant being studied.

Table 2: Primary Keywords

Flow Temperature

Pressure Level

Separate (settle, filter, centrifuge) Composition

React Mix

Reduce (grind, crush, etc.) Absorb

Corrode Erode

109

9.6. Secondary Keywords

Secondary keywords when applied in conjunction with a Primary Keyword,

these suggest potential deviations or problems. They tend to be a standard set as

listed below:

Table 3: Secondary Keywords

Guide Words Meaning

No

Less

More

Part of

As well as

Reverse

Other than

Negation of design intent

Quantitative decrease

Quantitative increase

Qualitative decrease

Qualitative Increase

Logical opposite of the intent

Complete substitution

9.7. How to Conduct a Hazop Study

HAZOP study is conducted in following steps:

1. Specify the purpose, objective, and scope of the study. The purpose may be

the analysis of a new plant or a review of the risk of unexisting unit. Given

the purpose and the circumstances of the study, the objectives listed above

can more specific.

Select the HAZOP study team. The team who will conduct the Hazop study

should consist of personnel with a good understanding of the process and

plant to be reviewed. The group should ideally contain about six members,

with perhaps an absolute upper limit being set at nine. In a study in which

both contractor and client are participating, it is desirable to maintain a

balance between the two in terms of team membership so that neither side

feels outnumbered.

2. Make a preparatory work. It is most important that, before a study

commences, work that can be conveniently done beforehand is carried

110

out. This is not only essential in some respects for the proper structuring of

the study and the team, but will also greatly increase the efficiency of the

Hazop and thus retain the interest and enthusiasm of the participants.

3. This preparatory work will be the responsibility of the Chairman, and the

requirements can be summarized as follows:

Assemble the data

Understand the subject

Subdivide the plant and plan the sequence

Mark-up the drawings

Devise a list of appropriate Keywords

Prepare Node Headings and an Agenda

Prepare a timetable.

Select the team.

111

9.8. HAZOP Method Flow Diagram

Figure 9.1: HAZOP Method Flow Diagram

112

9.9. Hazop Analysis on Fluidized Bed Reactor

Node: Fluidized Bed Reactor

Parameter: Temperature of bed

Hazards and Operability Study Worksheet

HAZARD AND OPERABILITY STUDY

NODE: FLUIDIZED BED REACTOR

PROCESS PARAMETER: FLOW OF STEAM

No. Guide

Word

Cause Consequences Actions

1. No Boiler is not

working.

Gasifier will not

work.

Boiler should

work

properly.

2. Less Less water flow

rate inside the

boiler / Boiler

Inefficiency

Gasifier will not

work properly.

(Incomplete

reaction)

Flow rate of

steam must

be

maintained.

3. More Steam flow rate

is not controlled.

Product not

obtained in desired

form.

Steam inlet

flow rate

must be

controlled

4. Other than Minerals present

in water.

Formation of

undesired products

Water must

be treated

properly

113


NODE: FLUIDIZED BED REACTOR

PROCESS PARAMETER: TEMPERATURE OF BED

No. Guide

Word

Cause Consequences Safeguards

1. Less Inefficiency of

boiler.

Gasifier will not

work properly.

Boiler should

work properly.

2. More Poor

temperature

control system.

Desired yield is

not obtained.

Temperature

of steam must

be maintained.

9.10. Hazop Analysis on Dryer:

Node: Dryer

Parameter: Temperature of Inlet air


NODE: DRYER

PROCESS PARAMETER: TEMPERATURE OF INLET AIR

No. Guide

Word

Cause Consequences Safeguards

1. Less Air heater is not

working

properly

Proper drying will

not take place.

Steam heater

must be

repaired.

2. More Temperature of

air is not

controlled

Combustion of

Coal and

Sugarcane

bagasse.

Air inlet

temperature

must be

controlled

114

REFERENCES

1. Fossil fuels (2011). Retrieved from:

http://www.edfenergy.com/energyfuture/coal

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ml

3. Anthracite Coal. Retrieved from:

http://www.tech-faq.com/what-is-anthracite-coal.html

4. GutenbergInstitute (Ohio, United States), Properties of particles (June 05, 2007)

5. Anval data about particle properties, USA Preston press 2007.

6. M. Sadiq Malkani “A review of Coal and Water resources of Pakistan”

7. Abdul Waheed Bhutto, Aqeel Ahmed Bazmib, Gholam reza Zahedi “Greener

energy: Issues and challenges for Pakistan—Biomass energy prospective”

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fuels”

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review on biomass as a fuel for boilers”

13. Tomasz Chmielniak, Marek Sciazko “Co-gasification of biomass and coal for

methanol synthesis”

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http://www.edfenergy.com/energyfuture/coal

http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Bituminous_coal.html

http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Bituminous_coal.html

http://www.tech-faq.com/what-is-anthracite-coal.html

http://www.fao.org/docrep/t0512e/t0512e0a.htm

http://www.safewasteandpower.com/process_plasma-gasification.html

115

19. Entrained Flow Gasifier. Retrieved from

http://www.energy.kth.se/compedu/webcompedu/S4_Combustion/B10_Ther

mochemical_Conversion/C1_Introduction_to_Gasification/ID55_files/Pressurize

d_entrained_flow_gasifier.htm

20. Abrar Inayat, Murni M Ahmad*, M I Abdul Mutalib, Suzana Yusup “Flowsheet

Modelling of Biomass Steam Gasification System with CO2 Capture for

Hydrogen Production“

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Mutalib. “Biomass Steam Gasification with In-Situ CO2 Capture for Enriched

Hydrogen Gas Production: A Reaction Kinetics Modelling Approach”

22. Zakir Khan, Suzana Yusup etal “Evaluation of reactor Dimensions through

Hydrodynamics study in a fluidized bed gasifier”.

23. P. Basu “Combustion and Gasification in Fluidized beds”

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Mining Company Report. Pp 10

25. Marcello De Falco, Luigi Marrelli, Gaetano Iaquaniello “Membrane Reactors for

Hydrogen Production Processes” pp-105

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gas-shift reaction at short contact times”

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28. Aspen Hysys

29. Warren L . McCabe, Julian C. smith, Peter Harriott, Unit Operations of chemical

engineering, 7th ed.

30. Sankalp Shrivastav, Ibrahim Hussain “Design of Bagasse Dryer to Recover

Energy of Water Tube Boiler in a Sugar Factory”

31. Alan J. Rindels, John S. Gulliver, Joseph M. Wetzel, and Vaughan Voller

“Analysis of the Elfuel, Coal Drying Facility”

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http://www.engineeringtoolbox.com/water-vapor-d_979.html

116

35. D. Kunii and O. Levenspiel, Fluidization Engineering, 2nd edition, Butterworth-

Heinemann, MA, 1991, pp95-106.

36. R.K. SINNOTT “Coulson & Richardson's Chemical Engineering Design” Vol 6.

37. Coulson & Richardson's, “Particulate Technology and separation process” Vol 2.

pp 698-699

38. P. Timmerhaus “Plant Design and Economics for Chemical Engineers”

39. Stanlay M. Walas “Chemical Process Equipment- Selection and Design”

117

APPENDIX A

A1: Char Gasification Reaction Equilibrium with Temperature at Pressure

of 1 atm.

A2: Equilibrium Methane Conversion at S/C =2

118

A3: CO Conversion in Water Gas Shift Reaction

A4: Temperature Pattern in Dryer

119

A5: Cyclone Pressure Drop Factor

A6: Standard Cyclone Dimension, High Gas Rate Cyclone

120

A7: Performance Curves, High Gas Rate Cyclone

A8: Scaled Performance Curve Cyclone

121

A9: Generalized Pressure Drop Correlation

A10: Number of Transfer units NOG as a function of y1/y2 with mGm/Lm as

Parameter

122

A11: Installed Cost of Dryer

A12: Columns Plates. Time Base mid-2004

Installed Cost = (Cost From Figure) * Material Factor

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