1

FLUIDIZED BED GASIFIER

By

Chirag Patel

13MMET12

DEPARTMENT OF MECHANICAL ENGINEERING

INSTITUTE OF TECHNOLOGY

NIRMA UNIVERSITY

AHMEDABAD-382481

DECEMBER-2013

2

FLUIDIZED BED GASIFIER

Seminar Report

Submitted in partial fulfillment of the requirements

For the Degree of

Master of Technology in Mechanical Engineering

(Thermal Engineering)

Submitted by

Chirag Patel

13MMET12

Guided by

Prof. Darshit Upadhyay

DEPARTMENT OF MECHANICAL ENGINEERING

INSTITUTE OF TECHNOLOGY

NIRMA UNIVERSITY

AHMEDABAD-382481

DECEMBER- 2013

3

Certificate This is to certify that

Mr./Ms. __________________________________________________________ Roll No. ______________________ of Semester __________________________

has satisfactorily completed the course in _________________________________________________________________

_ within four walls of the Institute

Date of Submission: _______________

___________________ _________________ Staff In-charge Head of the Department

4

ACKNOWLEDGEMENT

I feel immense pleasure and privilege to express my deep sense of gratitude and feel indebted

towards all those people who have helped, inspired and encouraged me during the preparation

of this Seminar. I would like to thank Prof. Darshit Upadhyay who gave satisfactory

solution to my queries and doubts related to the Seminar and guided me during the Seminar

I would also like to thank Mr.Jignesh Makwana, Engineer, SPRERI, for his guidance on the

topic& give the opportunity to Visit Sardar Patel Renewable Energy Research Institute

(SPRERI), Vallabh Vidhyanagar, Gujarat.

Thanking you,

Chirag Patel

13MMET12

5

ABSTRACT

A great interest in environment-friendly alternative energy resources that can reduce

dependency on fossil fuels has been growing. In particular, among a number of alternative

energy resources, biomass is seen to play an important role both as chemical feedstock and as

an alternative to fossil fuels. The conversion of biomass to chemicals usually takes place via

thermo-chemical and bio-chemical technologies. Among thermo-chemical conversion,

gasification converts biomass into combustible gases, such as H2, CO, CH4 that can be used in

boilers and in internal combustion engine or turbine to produce electricity generation.

Fluidized beds are used for a broad variety of fuels; this flexibility with respect to dierent

fuels is actually another stronghold of fluidized beds. In terms of the utilized fuels, coal has

been most often applied so far, but also waste and biomass have been utilized and are forecast

to play a more important role in the future. The fluidization principle is straight forward:

passing a fluid upward through a packed bed of solids produces a pressure drop due to fluid

drag. Several researchers had worked on bubbling fluidized bed Gasifier and use sized biomass

like sawdust, rise husk, coir pitch, and olive pits, and coconut shell. But with biomass used as

fuel in fluidized bed Gasifier with good quality of producer gas can be achieve by changing

equivalence ratio and fluidization velocity. By introducing steam gasification produces a

higher energy content Producer gas.

6

CONTENTS

SR.NO. CONTENT PAGE

NO.

1 CERTIFICATE iii

2 ACKNOWLEDGEMENT iv

3 ABSTRACT v

4 LIST OF FIGURES viii

5 LIST OF TABLES ix

CHAPTER 1 INTRODUCTION

1.1. History of gasification

1.2. Gasification process

1.3. Requirement of gasification

1.4. Application of thermochemical conversion

1.5. Biomass pyrolysis

1.6. Biomass gasification

1.7. Biomass combustion

1.8. Mechanism of gasification

1.8.1. Drying zone

1.8.2. Devolatilization zone

1.8.3. Oxidation zone

1.8.4. Ash cooling zone

1.9. Types of Gasifier

1.9.1. Moving bed Gasifier

1.9.2. Fluidized bed Gasifier

1.9.3. Entrained flow Gasifier

1.10 .Principle of fluidization

1.11 .Basic terminology

1.12 .Application of fluidized bed Gasifier

01

01

01

03

03

03

04

05

05

05

06

06

06

07

08

09

09

10

11

CHAPTER 2 LITERATURE REVIEW

2.1 Factors influencing gasification process

14

7

2.1.1. bed temperature

2.1.2. bed height

2.1.3. fluidization velocity

2.1.4. equivalence ratio

2.1.5. moisture content of feed material

2.1.6. fuel particle size

2.1.7. air/steam ratio

2.2 Study of gasification process for different fuel

2.3 Steam gasification

2.4 Gasification of dual fluidized bed Gasifier

14

15

16

16

16

17

17

18

24

26

CHAPTER 3 EXPERIMENTAL STUDY

3.1 Gasifier reactor construction

3.2 Feedstock feeding section

3.3 Air supply section

3.4 Working of fluidized bed Gasifier

30

31

31

31

CHAPTER 4 CONCLUSION 32

REFERENCES

8

LIST OF FIGURES

SR NO FIGURE PAGE NO.

Figure1.1 Thermochemical conversion Process 03

Figure 1.2 Types of Gasifier 07

Figure 1.3 Principle of Fluidization 09

Figure 2.1 Influence of the Temperature on Gasification Efficiency 23

Figure 2.2 Influence of the Equivalence Ratio on L.H.V of Gas 23

Figure 2.3 Influence of the Equivalence Ratio on Gasification Efficiency 24

Figure 2.4 Dual Fluidized Bed Gasification Process 26

Figure 3.1 Fluidized Bed Gasifier Experimental setup Design [SPRERI] 28

Figure 3.1 Photograph of Fluidized Bed Gasifier Experimental setup

[SPRERI]

29

9

LIST OF TABLE

SR NO TABLE PAGE NO

Table 1.1 Producer gas vehicles operated in other countries 13

Table 2.1 Gas composition and energy content of product gas during coir

pitch gasification

19

Table 2.2 Gas composition and energy content of product gas during saw

dust gasification

20

Table 2.3 Gas composition and energy content of product gas during Rice

Husk gasification

21

10

NOMENCLATURE

ER: Equivalence Ratio

H.H.V: Higher Heat Value

L.H.V: Lower Heat Value

11

CHAPTER 1

INTRODUCTION

1.1 History Of Gasification

The process of producing energy using the gasification method has been in use for more

than 180 years. During that time coal and peat were used to power these plants. Initially

developed to produce town gas for lighting & cooking in 1800s.This was replaced by

electricity and natural gas, It was also used in blast furnaces During both world

wars especially the Second World War the need of gasification produced fuel remerged

due to the shortage of petroleum. Wood gas generators, called Gasogene or Gazogne,

were used to power motor vehicles in Europe. By 1945 there were trucks, buses and

agricultural machines that were powered by gasification. It is estimated that there were

close to 9,000000 vehicles running on producer gas all over the world.First practical use

of town gas in modern times was for street lighting the first public street lighting with

gas took place in Pall Mall, London on January 28, 1807. Baltimore, Maryland began the

first commercial gas lighting of residences, streets, and businesses in 1816. [1]

1.2 Gasification Process

Gasification is a process that converts carbonaceous materials such as coal, petroleum

into carbon monoxide (CO) and hydrogen (H2) by reacting with raw material at high

Temperatures with a controlled amount of oxygen (O2) and steam (H2O).The resulting

gas mixture (CO+ H2) is called synthesis gas or syngas. Gasification is a method for

extracting Energy from almost any type of organic materials such as wood, biomass. [1]

1.3 Requirement of gasification

Globally, the accelerating rate of energy consumption leads to emptying of reserves of

Conventional energy sources and also causes major problem of pollution, which

ultimately aects mankind in many ways. These concerns require finding out substitute

or alternative sources of energy in place of non-renewable energy sources. To reduce the

dependency on conventional energy sources and address the environmental issues,

development and promotion of technologies using renewable natural resources such as

biomass are required. Biomass can be converted into gaseous or liquid biofuels such as

biogas, synthetic gas, ethanol/methanol, or used directly as fuel. These can be utilized for

applications like, thermal/heat, mechanical, power generation (standalone/grid

12

connected) including village electrification and industrial applications. Among the

biomaterials considered for energy production, granular biomass such as coir pith, rice

husk, bagasse pith, sawdust, etc. need more attention due to its lesser density and lower

energy content. Feasible technical and economical routes have to be identified for the

ecient and eective energy conversion of such granular materials. Biomass gasification

produces fuel gas or synthesis gas through the chemical conversion of biomass, usually

involving partial oxidation of the feedstock in a reducing atmosphere in the presence of

air, oxygen and/or steam. From the stand point of gas production, fluidized beds are

highly desirable because of their higher heat transfer characteristics and their capabilities

for maintaining isothermal conditions for low dense granular materials .The world is

currently facing an ever-increasing energy demand and together with a largely fossil

fuel-based economy this results a greenhouse eect due to increasing CO2 emissions.

Moreover, political instabilities and economic constraints result in increasing energy

prices and more turbulent energy markets. Various forms of biomass are already used as

a CO2 neutral energy source, despite their generally lower energy density. Although up

until now biomass is mainly used for cooking and heating in developing countries, a

large share of increased biomass usage is anticipated to take place in large-scale heat and

power generation, mainly driven by strong government policies. Here, one of the fastest

growing conversion routes for biomass fuels is the co-combustion in large-scale

fluidized bed installations, having the advantage that existing facilities can be utilized.

Relatively low co-firing shares, in the range of up to about 10% of thermal input, are

now commonly utilized. If that share increases and/or more dicult fuels should be

used, agglomeration phenomena become more likely.[2] The environmental benefits of

adding biomass to coal includes decrease in nitrogen and sulphur oxides which are

responsible for causing smog, acid rain and ozone pollution. In addition, relatively

amount of carbon dioxide is released into the atmospheres.[3] Biomass converted to

energy by three thermo chemical conversion processes: (1) Pyrolysis, (2) Gasification,

(3) Combustion [4]

1.4. Application of thermochemical conversion processes

13

Figure 1.1 Thermochemical conversion processes [4]

1.5 Biomass Pyrolysis

Biomass pyrolysis is defined as the thermal decomposition of biomass in the absence

of an oxidizing agent (air/oxygen) and occurs at temperatures in the range of 400 to

800C. With the addition of heat the biomass breaks down to condensable vapours,

non-condensable gases (pyrolysis gas), and charcoal. In some cases a limited amount

of air, not enough for gasification, may be admitted to promote the Process by heat

generation. The pyrolysis gas contains carbon monoxide, carbon dioxide, hydrogen,

methane and higher hydro Carbons. The condensable vapours form a liquid known as

bio-oil or pyrolysis liquid, which contains a wide range of oxygenated chemicals and

water. All products are combustible. It is possible to some extent to influence the

product mix so that one of the products is promoted. [4]

1.6 Biomass gasification

Gasification Processes convert biomass into combustible gases that ideally contain all

the energy originally present in the biomass. In practice, conversion eciencies

ranging from 60% to 90% are achieved. Gasification Processes can be either direct

(using air or oxygen to generate heat through exothermic reactions) or indirect

(transferring heat to the reactor from the outside). The gas can be burned to

produce industrial or residential heat, to run engines for mechanical or electrical

power, or to make synthetic fuels. [4]

14

1.7 Biomass combustion

Biomass combustion simply means burning organic material. For millennia, humans

have used this basic technology to create heat and, later, to generate power through

steam. While wood is the most commonly used feedstock, a wide range of materials

can be burned eectively. These include residuals and byproducts such as straw, bark

residuals, sawdust and shavings from sawmills, as well as so-called "energy

crops" such as switch grass, poplar and willow that are grown specifically to create

feedstock. Pelletized agricultural and wood residues are also an increasingly popular

option because they are very easy to handle. Farmers and other rural homeowners are

increasingly looking to biomass heat as an economical alternative to propane or

furnace oil. Stoves and fireplaces can provide direct space heating or be hooked up

with a back boiler that feeds heated water to radiators throughout the building. One

recent technology advance is the introduction of pellet stoves, which use an

electrically driven auger to deliver a steady supply of compressed pellets of wood or

other biomass into the fire. These stoves can operate for at least 24 hours without

being tended. On a larger scale, biomass-fed boilers can be used to meet hot water

needs, heat a building or generate steam to power equipment. Many farmers are

choosing to use them as the primary heat source in greenhouses, where they heat

very large spaces.[4]

15

1.8 Mechanism of Gasification

In Gasifier, as air is passed through the fuel bed, fairly discrete drying, pyrolysis,

gasification and oxidation zones develop along the reactor. The location of these zones in

the Gasifier depends on the relative movement of the fuel and air. These zones are mainly

differentiated by the variety of reactions or Processes Occurring and the temperature

regimes at that point. The depth and relative importance of each zone depend on the

chemical composition of the feedstock, its moisture content and particle size, the mass

flow rate of the gasifying agent, and the temperature.[5]

1.8.1 Drying zone

The drying zone receives its energy through heat transfer from other zones. The rate of

drying depends upon the temperature, Velocity, and moisture content of the drying gas, as

well as the external surface area of the feed material, the internal diffusivity of moisture

and the nature of bonding of moisture to that material, and the radioactive heat transfer

as the fuels enter the drying zone, their internal temperature is increased to 100-150C.

Low density materials change dimensions slightly due to shrinkage and compression

whereas negligible size changes are experienced by feedstock with high density.No

chemical reactions take place in this zone.[5]

1.8.2 Devolatilization zone

Heat transfer from the adjacent hot reduction zone causes devolatilization of the feed

difference between the relatively cold feed material and hot gases. The rate of

temperature rise is controlled by heat transfer. As feed material pass through this zone,

rapid charring and reduction in volume transpire, causing considerable variation in the

structure as well as the physical and thermal properties of the material. The

products from the devolatilization zone are gases, liquid (tars and oil), and char. The

production of liquids should be controlled in Gasifiers in which their production

is undesirable. The amounts of each of these products vary depending on the zone

temperature, rate of heating, structure, and composition and size of catalysts. [5]

16

1.8.3 Oxidation zone

In the oxidation zone, physical and chemical changes are inhibited as the oxygen carrier,

which is mostly air, is introduced into the fuel bed material. The oxygen burns a portion

of the carbon in the fuel material until practically all free carbon is exhausted. Oxygen,

however, penetrates the material surface to a small extent because it more readily reacts at

the surface with the formed carbon monoxide and hydrogen gases. When air is used as a

gasifying medium, its oxygen content decreases from 21 to 0%.while the carbon dioxide

percentage increases proportionally. The oxidation zone has the highest temperature due

to the exothermic nature of the reactions.[5]

1.8.4 Ash cooling zone

In the ash cooling zone, the reminder particles start to cool down faster than particles

temperature in other zones. The ash cooling zone formed in fixed bed Gasifiers protects

the grate from intense heat and distributes the air over the bed. Practically no

chemical reaction takes place here, although in some fixed bed designs, this zone acts

as a filter for the resulting. [5]

1.9 Types of Gasifier

Moving Bed Gasifier

Fluidized Bed Gasifier

Entrained Flow Gasifier

17

Figure 1.2: Types of Gasifier [6]

1.9.1 Moving Bed Gasifier

In a moving-bed Gasifier, air flows through a fixed bed of solid fuel Particles as shown in

Fig. Fresh coal is fed from the top, while air or oxygen is injected from the bottom. This

configuration, the steam and oxygen/air feed is counter-current to the coal feed, is

referred to as "updraft" or counter-current moving-bed Gasifier. Coal moves downward

slowly. Its residence time can reach 1 hour. The syngas exits from the upper part of

the Gasifier. Ash and unreacted char are removed from the bottom. The depth of coal

bed is kept constant by adding fresh coal from the top. Another configuration is the

"downdraft" or co-current moving-bed Gasifier, where steam and air/oxygen are fed

from the top, co-current to the coal feed.

A counter-current moving-bed Gasifier can be divided into four zones (from top to

Bottom): (i) the drying/preheating zone, (ii) the de-volatilization zone, (iii) the

gasification zone, and (iv)the combustion zone. The coal in the top zone is

dried/preheated by hot gas that is flowing from the bottom. The coals then moves

down to the de-volatilization zone, where heat from the hot gas drives volatiles out of

coal particles. Gasification Occurs in the next zone and any remaining char is then

reacted in the gasification zone. Syngas produced by an updraft Moving-bed Gasifier

has high tar content because the tar released during the de-volatilization Process is

carried away by the hot gas which is flowing up from gasification zone. Ash can be

18

removed from the bottom in the form of dry ash or slag. If dry ash is desired, the

Gasifier temperature is usually kept below ash fusion temperature.

Moving-bed Gasifiers have advantage of high char conversion, high thermal efficiency,

and low exit gas temperature (450-600 C).

The residence time of the coal within a moving bed Gasifier may be on the order of

hours.

Moving bed Gasifier has the following characteristics:

Low oxidant requirements;

Relatively high methane content in the produced gas;

Production of hydrocarbon liquids, such as tars an oils;

Limited ability to handle fines; and

Special requirements for handling caking coal. [7]

1.9.2 Fluidized Bed Gasifier

A diagram of a generic fluidized bed Gasifier is shown in figure. A fluidized bed Gasifier

is a back-mixed or well-stirred reactor in which there is a consistent mixture of new coal

particles mixed in with older, partially gasified and fully gasified particles. The mixing

also fosters uniform temperatures throughout the bed. The flow of gas into the reactor

(oxidant, steam, recycled syngas) must be sufficient to float the coal particles within

the bed but not so high as to entrained them out of the bed. However, as the

particles are gasified, they will become smaller and lighter and will be entrained out

of the reactor. It is also important that the temperatures within the bed are less than

the initial ash fusion temperature of the coal to avoid particle agglomeration.

Typically a cyclone downstream of the Gasifier will capture the larger particles that are

entrained out and these particles are recycled back to the bed. Overall, the residence time

of coal particles in a fluidized bed Gasifier is shorter than that of a moving bed Gasifier.

Generic characteristics of fluidized bed Gasifier include:

Extensive solids recycling;

Uniform and moderate temperature; and

Moderate oxygen and steam requirements. [7]

19

1.9.3 Entrained Flow Gasifier

A diagram of a generic entrained flow Gasifier is shown in figure 4. Finely-ground coal is

injected in co-current flow with the oxidant. The coal rapidly heats up and reacts with the

oxidant. The residence time of an entrained flow Gasifier is on the order of seconds

or tens of seconds. Because of the short residence time, entrained flow Gasifier must

operate at high temperatures to achieve high carbon conversion. Consequently, most

entrained flow Gasifier use oxygen rather than air and operate above the slagging

temperature of the coal.

Generic characteristics of entrained flow Gasifier include:

High-temperature slagging operation;

Entrainment of some molten slag in the raw syngas;

Relatively large oxidant requirements;

Large amount of sensible heat in the raw syngas; and

Ability to gasify all coal regardless of rank, caking characteristics or amount of fines.[7]

1.10 Principle of fluidization

Figure 1.3: Principle of Fluidization [8]

Fluidization is a Process similar to liquefaction whereby a granular material is converted

From a static solid-like state to a dynamic fluid-like state.This Process Occurs when a

fluid (Liquid or gas) is passed up through the granular (solid) material. When a gas flow

is introduced through the bottom of a bed of solid particles, it will move Upwards

through the bed via the empty spaces between the particles. At low gas Velocity,

Aerodynamic drag force (Fd) on each particle is also low, and thus the bed remains in

a fixed state. Increasing the Velocity, the aerodynamic drag forces (Fd) will begin to

20

counteract the gravitational forces (Fg), causing the bed to expand in volume as the

particles move away from each other. Further increasing the Velocity, it will reach a

critical value at which the upward drag forces will exactly equal the downward

gravitational forces (Fd=Fg), causing the particles to become suspended within the

fluid. At this critical value, the bed is to be fluidized and will exhibit fluidic

behaviour and the Velocity at this critical stage is known as minimum fluidization

Velocity. By further increasing Velocity, the bulk density of the bed will continue to

decrease, and its fluidization becomes more violent, look like as a Red hot Fluid, this

stage is known as Fluidization.[8]

1.11 Basic Terminology

Equivalence Ratio: The equivalence ratio of a system is defined as the ratio of the fuel-

to-oxidizer ratio to the stoichiometric fuel-to-oxidizer ratio.[9]

ER: Fuel to Oxidizer ratio

(Fuel to Oxidizer ratio) stoichiometric

Minimum fluidization Velocity

The superficial fluid Velocity at which the upward drag force exerted by the fluid is equal

to the apparent weight of the particles in the bed". Velocity at which the pressure drop

Reaches to maximum, at that point the Velocity is called as minimum fluidization

Velocity.

For minimum fluidization Velocity we increase the flow of fluid in the bed to be

fluidized.[9]

Efficiency of Gasifier: Gasifier Efficiency is the ratio of total energy in supply fuel and total energy in producer gas. [9]

21

1.12 Application Of Fluidized Bed Gasifier

Direct Heat Applications

Most commercial Gasifier currently in operation are used to produce heat rather than fuel

for internal combustion engine, primarily because the requirements for heating fuel

are less stringent. When the Gasifier is close coupled to a burning system, higher

temperatures can be reached and the efficiency and output of the overall system can

be enhanced.

All Gasifier can be used to provide producer gas for combustion purposes. However, the

updraft is preferred in systems rated below 1 MW thermal power while the fluidized bed

Gasifier are appropriate for ranges above this. Where fuel oil is being used to generate

Process heat, run furnaces or kilns, the gasification technology is a viable option.

The economic and technical problems of using direct heat Gasifier appear to be relatively

minor. With more experience and better design, the range of potential uses will expand.

However, fuel availability constraints will remain and, in the long term, will probably be

the principal limitation on the spread of the biomass gasification technology.

Countries that have large forest and agricultural resources are obviously suitable for the

application of the gasification technology to direct heating.

Currently, electric utilities and various industrial firms have expressed growing interest in

finding economical and environmentally attractive methods of converting coal, wastes,

and renewable fuels into replacement energy sources for use in combined heat and

power applications. Biomass gasification will become significantly more attractive in

industrial shaft power applications in rural area where grid electricity is either

expensive or unavailable. In urban areas, the technology will be unattractive since grid

electricity is usually a cheaper source of energy.

One industry of prime interest is the forest industry, which supplies residues such as off-

cuts, edgings, shavings and sawdust. Exact quantities of these depend upon the tree

species being used the end product of the industry and, the efficiency of equipment

employed to Combined, residues from such sources amount to about 50% of the total

quantity of wood Processed. However, these residues would be utilized by a system

whose end product is producer gas. Another Process of prime interest is the harvesting

from which crop residues such as straw could be obtained. The exact quantities of

these crop residues depend upon the species being harvested, the end product of the

mechanism and the efficiency of equipment used. These residues could be utilized using

a fluidized bed Gasifier to produce gas. The gas could be used for direct burning to

22

produce heat for kiln drying or steam generation. Steam could be used to generate

electricity through turbines or for the production of mechanical power. Alternatively, the

producer gas could be purified and used in internal combustion engines for the generation

of mechanical power or on-site electricity.

SHAFT POWER

Shaft power is significantly demanded in developing countries for irrigation. Currently

many fossil-powered units are in use; thus. Where the interruption of fossil fuel supply is

common, alternative energy sources such as producer gas are being used.

As an alternative to internal combustion engines that use producer gas exclusively, there

are engines that are operated on the dual-more principle. In such systems, the producer

gas is used as a supplement to diesel fuel. Here the consumption of wood would be

approximately 1.4 kg per kWh of shaft power. Where the availability of suitable biomass

is scarce, the possibility always exists for the cultivation of trees that take approximately

three to four years to mature. The possibility of using crop residues in Gasifiers has also

gained great attention. Although the questions about the technical suitability of crop

residues as Gasifier fuel remains to be answered, the concept shows promise.

A practical example of this technology is the use of Gasifier-powered irrigation pumps in

Brazil. The production of shaft power for irrigation pumps sawmills, milling and shelling

of maize in isolated rural communities in developing countries is a promising application

of the producer gas. In these operations, a potential gasification feedstock is produced as

part of the Process.[10]

23

Table 1.1 Producer gas vehicles recently operated in other countries

Australia A small pick-up truck using wood chips as fuel.

Belgium Two trucks, one using charcoal, the other wood or biomass

residues as fuel.

China A logging tractor using wood as fuel.

Finland A farm tractor using wood as fuel.

France Six large trucks using wood as fuel.

Germany At least two farm tractors have been converted to wood gas by

two different manufacturers of Gasifier.

Laos A jeep using a charcoal Gasifier has been operated since 1981.

USA A least three wood powered cars have been driven across the

country. There is also a wood powered motorcycle and a wood

powered farm tractor.

24

CHAPTER 2

LITERATURE REVIEW

Several researchers had worked on bubbling fluidized bed Gasifier.

Experimental investigation has been carried out in a pilot scale fluidized bed rice husk

Gasifier. The study investigated the effect of temperature and the equivalence ratio on

fuel gas composition. Gasifier temperatures were in the range of 600800 C with

equivalence ratios of 0.25, 0.35 and 0.45.The experimental tests were carried out to

determine the influences of equivalence ratio and bed temperature on fuel gas

compositions and gas yields.[11]

2.1 Factors Influencing Gasification Process

Several variables seen to affect the gasification Process, product composition, and

distribution including bed temperature, bed pressure, bed height, fluidization Velocity,

gasifying medium, equivalence ratio, feed material moisture content, particle size, air to

steam ratio, and Presence of catalysts. These parameters are quite interrelated and each of

them affects the gasification rate, Process efficiency, product gas heating value and

product distribution.[11]

2.1.1 Bed temperature

The gasification rate as well as the overall performance of the Gasifier is temperature-

dependent. All gasification reactions are normally reversible and the equilibrium point of

any of the reactions can be shifted by changing the temperature. As part of a wider

investigation, Harris et al. (2005) presented gasification conversion data for a suite of

Australian coals reacting with oxygen/nitrogen mixtures at 2.0 MPa pressure and at

temperatures up to 1773 K. Combustible gas concentration increased with increases in

temperature. Char yield decreased with increases in temperature. Scott et al. (1988)

reported that the product gas yield from maple sawdust (1.4 % ) increased as the reactor

temperature increased whereas the liquid and solid products decreased with increases in

temperature. The decreasing amount of char indicated that the conversion increased with

increases in temperature. Voloch et al. (1983) found the conversion of corncobs to

increase from 94% at 500C to 99% at 900C in air gasification. Elliot and Sealock (1985)

reported 10% and 50% weight basis conversion of lignin at 350 and 450C,

respectively. Alves and Figueiredo (1989) reported that tar production at low

temperatures (below 500C) was found to increase initially with increases in

25

temperature and then drop with further increases in temperature. Utioh et al. (1989)

reported increases in hydrocarbon gases, especially C2H4 (ethylene) with increases in

temperature. The yield of higher hydrocarbons decreased with increases in

temperature above 650C, which indicated the onset of cracking/reforming

reactions. Other gas components (H2 and CO), also increased with increases in

temperature (Font et al., 1988). The heating value of the producer gas is also

influenced by temperature. Sadakata et al. (1987) found the calorific value of crop

residue gasification producer gas increased steadily up to 700C and then decreased. The

increase in the gas heating value is due to the increase in concentrations of CO, H2 and

hydrocarbon gases in the gas mixture. The decline at higher temperatures is probably due

to the cracking of hydrocarbons. The first-order rate constant of gasification was found to

increase with temperature in accordance with the Arrhenius equation (Edrich etal.,

1985). Brink (1981) pointed out that gasification rates are too fast and are controlled by

heat and mass transfer rates above 900C while in the range of 600-900C, the

gasification reactions are rate controlling. Below 600C, the gasification reaction rates are

too slow.[11]

2.1.2 Bed height

At a given reactor temperature, a longer residence time (due to higher bed height)

increases total gas yields. Sadaka et al. (1998) showed that a higher bed height resulted in

greater conversion efficiency as well as a lower bed temperature due to the fly-wheel

effect of the bed material. The fly-wheel effect is significantly reduced when the

amount of bed material is reduced thereby resulting in higher bed temperature. Their

results also reported that increasing the bed height increases the bed pressure drop in the

dense bed but resulted in no significant changes in the freeboard region. Font et al.

(1988) reported increases in H2, CO, CO2, CH4 and C2H4 when the residence time was

increased as a result of increased bed height. A long residence time allows for increased

heat transfer and, hence, increased char and tar conversion to gas. Beaumont and Schwob

(1984) found that at a temperature of 350C, water yield increased with increases in vapor

residence time during the pyrolysis Process of wood in an N2 atmosphere.[11]

26

2.1.3 Fluidization Velocity

Fluidization Velocity plays an important role in the mixing of particles in the fluidized

bed. In air gasification systems, the higher the fluidization Velocity the higher the bed

temperature and the lower the produced gas heating value due to increased amounts of

oxygen and nitrogen in the inlet gas to the system. Sadaka et al. (2002) reported that the

higher heating value reached its peak value at a fluidization Velocity of 0.28 m/s but

remained fairly constant at the fluidization Velocity of 0.33 and 0.37 m/s. However,

Raman et al. (1980) tested the gasification of feedlot manure with different superficial gas

Velocity. They found that the tested range of superficial Velocity did not have a

significant influence on produced gas yield, composition, or heating value due to the

tested small range. [11]

2.1.4 Equivalence ratio

The equivalence ratio has the strongest influence on the performance of Gasifiers because

it affects bed temperature, gas quality, and thermal efficiency. Increasing the equivalence

ratio resulted in lower pressure drops both in the dense bed and the freeboard regions

when the Gasifiers operated at different fluidization Velocity and bed heights.

Schoeters et al. (1989) reported that high equivalence ratios increased the gas production

rate in air gasification. The Gasifier temperature was found to increase with increases in

the equivalence ratio because of increases in the exothermic reactions. On the other hand,

a very low equivalence ratio results in very low bed temperatures, thus producing a lower

gas and higher tar yields. Ergudenler and Ghaly (1992) reported that the combustible

components and the heating value of the produced gas decreased with decreases in the

equivalence ratio. At the equivalence ratios of 0.25, 0.20 and 0.17, the higher heating

value of the produced gas were 6.48, 6.19 and 5.98 MJ/Nm, respectively.[11]

2.1.5 Moisture content of feed material

The moisture content of feed material affects reaction temperature due to the energy

required to evaporate water in the fuel. Therefore, the gasification Process takes place at a

lower temperature. Elliot and Sealock (1985) reported on the conversion of lignin (of less

than 10%wt basis moisture content) at 350C and about 50% weight moisture content at

450C. They found a direct correlation between high moisture content and high volumes

of produced char. They reported a decrease in Gasifier temperature with increases in fuel

moisture content.[11]

27

2.1.6 Fuel Particle size

The feed particle size significantly affects gasification results. The coarser the particles,

the more char and less tar they produce. The rate of thermal diffusion within the particles

decreases with increased particle size, thus resulting in a lower heating rate. For a given

temperature, the produced gas yield and composition increased with a decrease in manure

particle size as reported by Raman et al. (1980). The gas yield for the smallest size

fraction (-14 to +40 mesh) increased from 0.51 m/kg at 900 K to 0.81 m/kg at 1010 K.

For the largest size fraction (-2 to +8 mesh), the gas yield increased from 0.10 to 0.60

m/kg for the same temperature range. The heating value versus temperature plots for

each particle size fraction were parabolic with the maximum heating value aligned with

the smallest particle size fraction (18.0 MJ/m at 1010 K). For the largest particle size

fraction, the heating value increased from 14.3 MJ/m at 900 K to a maximum of 19.8

MJ/m at 980 K and then decreased to 12.0 MJ/m at 1010 K. Edrich et al. (1985) found

the gasification rate to depend on particle size. During the gasification of wood in a

fixed bed Gasifier, the gasification rate increased from 0.1 to 1.0 min-1 when the particle

size was decreased from 19.05 to 5.00 mm.[11]

2.1.7 Air/steam ratio

Increasing the air to steam ratio increases the gas heating value until it peaks. Tomeczek

et al. (1987) used an air-steam mixture in the gasification Process of coal in a fluidized

bed reactor. The results showed that the influence of steam-to-air ratio on char was

particularly strong at lower ratios due to the fact that the steam released at the

devolatilization stage contributed to the gasification Process even in the case when steam

was not added. When the steam-air ratio increased, the heating value increased, reaching

its peak at 0.25 kg/kg. Schoeters et al. (1989) investigated the effect of the air-to-steam

ratio on the gasification of wood shavings. An increase in the steam flow rate resulted in

an increase in the heating value and the energy recovery because the reactor was heated

from outside, which helped to keep the temperature constant without any adjustment of

the flows. Halligan et al. (1975) gasified feedlot manure using a mixture of air and

steam in a bed consisting exclusively of the feed material. Over a temperature range

of 966 to 1069 K, increasing the steam-to-air ratio increased the gas volumetric yield

and the heating value from 0.6 to1.3 m/kg. and from 8.7 to 9.8 MJ/m, respectively.

Energy recovery and carbon conversion also increased with temperature from 23 to 49%

and 20 to 50%, respectively. [11]

28

2.2 Study of Gasification Process for Different Fuel

P. Subramanian (2010) studied the factors affecting fluidized bed gasification of coir pith,

Rice husk and saw dust and Process optimization, experiments were conducted in a 40

kg/h Fluidized bed Gasifier at equivalence ratios of 0.3, 0.4 and 0.5. The hot gas

efficiency of the system was in the range of 41.5982.80%. It is observed that with the

increase of Equivalence ratio, CO2 content was increasing whereas CO was reducing.

The fluidized bed Gasifier system is useful for thermal applications and power

generation in agro industries viz. coir industry, rice mills, timbering and other small-

scale industry. They reported that reduction in carbon monoxide content with increase

of equivalence ratio, whereas CO was increased with increase of gasification Process

time. The value of carbon monoxide was in the range of 8.2412.68%, 9.3219.55% and

12.3917.73% for coir pith, rice husk and sawdust, respectively and carbon dioxide

content indicated that, with the increase of equivalence ratio from 0.3 to 0.5, the

CO2 content was also increasing. The maximum (16.24%) and minimum (11.05%)

value of CO2 was observed at 0.5 and 0.3 ER, respectively, in coir pith gasification.

The minimum (10.21% and 10.78%) and maximum (17.14% and 16.84%) content of CO2

was observed with 0.3 and 0.5 ER for rice husk and sawdust gasification, respectively.

Study on fluidized bed gasification of rice husk reported an increasing trend of CO2 and

decreasing trend of CO with increasing equivalence ratio. The content of hydrogen in the

product gas was in the range of 5.6210.61% (coir pith), 5.348.62% (rice husk) and

5.24 10.14% (sawdust). The overall range of methane content was 0.983.82% in all

the trials of fluidized bed gasification. The results showed that the increase in reaction

time as well as equivalence ratio resulted in increase of gas production during fluidized

bed gasification of coir pith, rice husk and sawdust. The data on gas yield during fluidized

bed gasification of coir pith, rice husk and sawdust were found to be in the range of 1.98

3.24, 1.792.81 and 2.183.70 Nm/kg, respectively. The minimum (2.18 MJ/Nm) and

maximum (4.23 MJ/Nm) value of HHV of coir pith synthetic gas was resulted at 0.5 and

0.3 ER, respectively. It is noted from the data that, at increased values of ER, the higher

heating value of synthetic gas was reduced.[12]

29

Table 2.1: Gas composition and energy content of product gas during coir pitch

gasification [12]

Sr.

No.

ER Time

Minute

CO

%

CO2

%

H2

%

CH4

%

N2

%

O2

%

Gas Yield

Nm/Kg

H.H.V

Nm

1 0.30 10 08.71 14.62 08.49 1.52 66.41 0.25 1.98 2.65

2 20 09.26 14.88 07.89 1.36 66.38 0.23 2.02 2.58

3 30 10.12 12.12 09.54 1.89 66.08 0.25 2.26 3.08

4 40 10.28 11.63 10.17 1.53 66.21 0.18 2.18 3.04

5 50 11.53 11.58 10.55 2.67 63.50 0.17 2.21 3.67

6 60 12.57 11.05 10.61 3.82 61.78 0.17 2.32 4.23

7 0.40 10 08.24 15.61 07.54 1.08 67.21 0.32 2.24 2.31

8 20 09.21 15.22 08.62 1.59 65.12 0.24 2.12 2.75

9 30 10.52 14.17 08.79 1.32 65.00 0.20 2.24 2.82

10 40 11.12 12.83 09.53 2.54 63.77 0.21 2.68 3.44

11 50 10.91 11.69 10.46 2.50 64.25 0.19 2.52 3.52

12 60 12.68 11.83 10.57 3.60 61.14 0.18 2.69 4.16

13 0.50 10 06.54 16.24 05.62 1.91 69.37 0.32 2.73 2.18

14 20 08.94 15.48 06.87 1.21 67.29 0.21 3.14 2.36

15 30 08.31 14.32 07.23 1.86 68.00 0.28 2.83 2.57

16 40 10.52 13.67 09.61 1.33 64.68 0.19 3.24 2.93

17 50 11.61 13.14 09.78 2.42 62.88 0.17 2.90 3.40

18 60 12.47 12.68 09.64 2.91 62.19 0.11 2.84 4.14

30

Table 2.2: Gas composition and energy content of product gas during rise husk

gasification [12]

Sr.

No.

ER Time

Minute

C

O

%

CO2

%

H2

%

CH4

%

N2

%

O2

%

Gas Yield

Nm/Kg

H.H.V

Nm

1 0.30 10 10.54 15.24 6.18 1.04 66.81 0.19 1.86 2.40

2 20 11.26 14.31 7.54 1.25 65.47 0.17 2.14 2.73

3 30 10.12 12.87 6.09 1.49 69.23 0.20 1.79 2.51

4 40 14.67 12.19 7.46 2.88 62.67 0.13 2.18 3.75

5 50 15.42 11.68 8.59 3.21 61.00 0.10 2.25 4.10

6 60 19.55 10.21 8.62 3.24 58.33 0.05 2.31 4.61

7 0.40 10 10.11 16.28 5.54 1.08 66.68 0.31 2.23 2.29

8 20 09.87 15.44 6.65 1.27 65.53 0.24 2.37 2.47

9 30 10.53 13.89 6.78 1.66 65.98 0.16 2.31 2.71

10 40 12.64 12.17 6.59 2.26 66.14 0.20 2.40 3.16

11 50 14.78 10.66 7.42 2.01 65.06 0.07 2.56 3.43

12 60 16.13 10.68 7.77 2.78 62.58 0.06 2.57 3.92

13 0.50 10 09.32 17.14 5.34 1.03 65.90 0.27 2.18 2.15

14 20 10.24 16.82 5.88 1.19 65.62 0.25 2.35 2.39

15 30 10.11 15.96 6.65 1.57 65.52 0.19 2.42 2.61

16 40 12.57 14.56 7.49 1.62 63.64 0.12 2.57 3.02

17 50 15.48 12.92 7.12 1.71 62.71 0.06 2.68 3.36

18 60 15.29 11.76 7.42 2.06 63.43 0.04 2.81 3.51

31

Table 2.3: Gas composition and energy content of product gas during saw dust

gasification [12]

Sr.

No.

ER Time

Minute

CO

%

CO2

%

H2

%

CH4

%

N2

%

O2

%

Gas Yield

Nm/Kg

H.H.V

Nm

1 0.30 10 14.23 14.51 6.54 1.02 63.58 0.12 2.42 2.88

2 20 15.19 12.62 7.54 1.81 62.76 0.08 2.51 3.42

3 30 16.28 13.89 7.98 2.04 59.75 0.06 2.43 3.69

4 40 15.61 12.18 8.23 1.60 62.31 0.07 2.52 3.47

5 50 17.38 11.96 9.98 2.45 58.05 0.18 2.71 4.21

6 60 17.54 10.78 10.14 3.21 58.29 0.04 2.64 4.54

7 0.40 10 13.55 15.31 5.59 1.06 64.31 0.18 2.84 2.70

8 20 14.41 14.87 6.78 1.17 62.70 0.07 2.92 2.99

9 30 15.82 13.25 7.69 1.24 61.91 0.09 2.89 3.29

10 40 15.67 12.55 7.82 1.80 62.12 0.04 3.01 3.50

11 50 16.32 11.16 8.12 2.14 62.14 0.12 3.15 3.75

12 60 17.73 11.87 9.35 2.62 58.29 0.14 3.21 4.24

13 0.50 10 12.62 16.84 5.24 0.98 62.44 0.27 3.01 2.52

14 20 12.39 15.56 5.63 1.25 62.19 0.18 3.41 2.64

15 30 13.42 14.24 6.87 1.62 60.86 0.13 3.61 3.05

16 40 14.56 12.63 7.29 1.24 63.15 0.08 3.57 3.09

17 50 15.85 12.81 7.38 1.82 60.57 0.04 3.64 3.48

18 60 16.48 12.33 8.42 2.18 59.50 0.03 3.70 3.82

32

Maria C. Palancar effects of the moving zone temperature and ER on the

gasification efficiency, flue gas composition and LHV were studied under the

following operating

Conditions:

Equivalent ratio, ER: 0.180.82.

Temperature: in the moving bed, 529848 C; in the fluidized bed, 840860 C.

Superficial air Velocity in the fluidized bed (850 C): around 1 m/s.

Input solid moisture: 8% (wet basis).

Water air ratio (extra water feeding): 0.10.3 kg water/kg air.

The ultimate analysis of Pomace and olive pits shows that both have roughly the

same composition (mean dry ash free analysis: 47% C, 5.7% H, 1.5% N and 0.01% S).

The content of ash is about 3.2%. The LHV of the flue gas is similar to other biomass

gasification Process.(between 4 and 6 MJ/Nm). The effects of the moving bed

temperature, ER and water/air ratio on the composition of the flue gas have been

determined experimentally. The best results obtained for temperatures around 825 C

(805845 C) and ER around 0.2 (0.13 0.26) are: efficiency, 43%, LHV, 5.5

MJ/Nm, and a flue gas with 12% H2 and 18% CO. The production of tar increases

as ER decreases. The concentrations of H2, CO and CH4 increase with the moving

bed temperature, due to an increasing of temperature that enhances the

endothermic and steam reactions. The C2H4 concentration shows a low sensitivity to

the moving bed temperature range used because the temperature in the bed was not

very high. The LHV of the flue gas increases with the moving bed temperature.

The increasing LHV is a direct consequence of the increase of the productions of

and CO. The gasification efficiency, increases with the moving bed temperature.

The same comments made above for the effects of the moving bed temperature on

LHV are applicable to the gasification efficiency. The LHV variation with the

ER for temperatures of 700, 750, 800 and 850 C was studied. The LHV is not

`influenced by ER for values of this parameter less than 0.18. However, for ER

higher than 0.18, the LHV decreases with ER.The variation of LHV decreases

with the bed temperature; this fact can be explained by considering that the thermal

cracking of tar is endothermic and becomes more important as temperature

increases. The concentration of H2 and CO is more sensitive to changes of ER

than the one of CH4 . Approximately, the H2 and CO concentrations are

proportional to ER. The product distribution is more sensitive to changes in the ER

33

than to the moving bed temperature. For moving bed temperatures up to about

800 C and ER up to 0.32, the gasification efficiency, decreases with ER. If the

moving bed temperature is higher than 800 C and the ER is less than 0.32, the

gasification efficiency does not depend on ER. The decrease in the efficiency with ER

can be explained based on the decreasing values of LHV with ER.Consequently,

as the efficiency is proportional to the LHV, the efficiency also decreases with the

ER.[13]

Figure 2.1: Influence of the Temperature on Gasification Efficiency .[13]

Figure 2.2: Influence of the equivalence ratio on the LHV of the flue gas.[13]

34

Figure 2.3: Influence of the equivalence ratio on the gasification efficiency [13]

2.3 Steam gasification

Unlike air gasification, steam gasification requires an external heat source if steam is

used as a sole gasifying agent. Using a mixture of steam and air as a gasifying agent is

not uncommon technology and has, in fact, been studied by several researchers. Oxygen

in the air will help to provide the required energy due to the exothermic nature of burning

biomass. The elevated temperature will help in the devolatilization Process of biomass to

produce various gases. Steam will react with carbon monoxide to produce hydrogen and

carbon dioxide. The principle gas-phase reaction in the steam gasification system is the

water gas-shift reaction:

CO+ H2O CO2+ H2

Compared to air gasification, steam gasification produces a higher energy content

producer gas. Boateng et al. (1992) determined the effects of reactor temperature and

steam to biomass ratio on producer gas composition, heating value and energy recovery.

The produced gas, which is rich in hydrogen, had been found to have a heating value

ranging from 11.1 MJ/m at temperature of 700C to 12.1 MJ/m at temperature of 800C.

Energy recovery varied from 35-59% within the same temperature range. Hoveland et al.

35

(1982) studied corn grain-dust gasification in a 0.05 m I.D. fluidized bed Gasifier using

steam as a fluidizing agent and a mixture of sand and limestone as the bed material. The

produced gas yield increased from 0.13 m/kg at 867 K to 0.73 m/kg at 1033K. The gas

heating value increased from 9.4 to 11.5 MJ/m at the same temperature range.

Steam over a temperature range of 873-1073K. The major components of the produced

gas were H2, CO2, CO, and CH4 and the volumetric gas yield was 0.5-1.4 m/kg. The

average gas higher heating value was 11.8 MJ/m. The energy recovery as well as carbon

conversion were ranged from 32-90%.Walawender et al. (1982) gasified straw with

steam in a 0.23 m diameter fluidized bed reactor over a temperature range of 552-757C.

The fraction of feed converted to gas ranged from 32% at 552C to 73 % at 757C. The

heating value of the gas exhibited a parabolic temperature variation with a maximum

value of 16.3 MJ/m obtained at 672C. There was continuous external energy input to the

system, which resulted in higher than expected heating values. According to Slapak et al.

(2000), steam gasification is one possibility for recycling waste in a bubbling fluidized

bed reactor. The main product is syngas, employable for energy recovery.

The produced syngas has a heating value of 8.6 MJ/Nm. Mermoud et al. (2005) studied

charcoal steam gasification of beech charcoal spheres of different diameters (10-30 mm)

at different temperatures (830-1030C). Their results show a very slow reaction at 830C.

A difference in gasification rate as high 6.5 to 1 was observed between temperatures at

1030 and 830C. Experiments carried out with mixtures of H2O/ O2 at 10%, 20%, and

40% mol of steam confirmed that oxidant partial pressure influences gasification. A

gasification rate of 1.9 was obtained for H2O partial pressure varying from 0.4 to 0.1

atm.The gasification of rice husk was studied by Chen and Day (1982) over a

temperature range of 873-973K. They used an electrically heated 0.05 m I. D. fluidized

bed reactor. The bed consisted of fused alumina sand; the fluidizing medium was super-

heated steam. The gas yield increased from 0.38 to 0.55 m/kg and the heating value

varied from 16.8 to 18.5 MJ/m. Over this temperature range, H2, CH4, CO, and CO2

Concentrations in the produced gas varied from 3.6-13.1%, from 14.4-13.5%, from 52.2-

51.1% and from 23-14.6%, respectively. The balance of the product gas was comprised

of higher hydrocarbons including ethane, ethylene, and propylene. Corella et al. (1989)

reported on steam gasification of four different crop residues (wood chips, thistle, saw-

dust and straw) in a 0.15 m I.D. fluidized bed Gasifier. They determined the gas, char,

and tar yield at temperatures between 650-780C for each type of crop residue. Straw and

sawdust exhibited higher gas and lower tar yields compared to wood chips.[14]

36

2.4 Gasification of lignite in a dual fluidized bed Gasifier Influence of bed

material

Particle size and the amount of steam

The dual fluidized bed steam gasification system, developed by the Institute of Chemical

Engineering at Vienna University of Technology, was originally developed for the

utilization of woody biomass as feedstock, but during practical operation of the industrial

sized plants of this system it turned out that fuel flexibility is the key issue for economic

breakthrough. Therefore, gasification tests were carried out with lignite at different

operating conditions at the dual fluidized bed pilot plant at Vienna University of

Technology. Tests were performed with an input fuel power of 90kw.

Olivine was used as bed material and the applied particle size was 370 and 510 m.

The steam-to-carbon ratio was varied between 1.3 and 2.1 kg H2O/kg carbon. In

Addition to standard online measurements of the permanent gas components of the

product gas, impurities like NH3, H2S and tar were also measured. It turned out that a

lower amount of steam for fluidization caused a better performance of the gasification

reactor in terms of product gas yield, carbon conversion and water conversion.

The high catalytic activity of the lignite ash was also a reason for the high product gas

quality producing low amounts of condensable hydrocarbons, like tar.

Figure 2.4: Dual Fluidized Bed Gasifier

37

Steam gasification of lignite with two different sizes of bed materials and different ratios

of steam in a dual fluidized bed (DFB) Gasifier was successfully carried out with a fuel

power of 90 kW at the DFB pilot Plant at Vienna University of Technology. Variation of

the bed material Particle size and the amount of steam for gasification showed that the

Product gas quality was not affected for the used feedstock, but a noticeable Influence on

the performance for both measures (particle size and steam-to-carbon ratio) was found.

The most significant changes by the smaller olivine particles (OP1 vs. OP2) used in this

study are:

Higher (15.7%) product gas yield, higher cold gas efficiency. Increased carbon and water

conversion in the gasification reactor by increased turbulence in the bubbling bed and

enhanced contact to the bed material particles with larger surface. The reduction of the

bed material particle size offers the possibility to operate the gasification reactor with a

lower amount of steam for fluidization, maintaining a good fluidization regime in the

gasification reactor. [15]

Steam gasification of biomass was carried out at the Institute of Chemical Engineering at

Vienna University of Technology with wood pellets; a fuel power of 90 kW, a

gasification temperature of 850C, and a steam-to-fuel ratio of 0.6 are presented. It was

found that the position of feedstock admission has a significant impact on the product gas

composition, amount, and quality. Also, the energy flow and the temperature profiles in

the gasifiers were affected. The major differences found in the case of feeding the

Feedstock onto the bubbling bed compared to in-bed feeding is significantly higher CO

content and lower H2 content in the Product gas.

Higher amount of product gas.

Higher carbon conversion in the gasification reactor.

Lower water conversion.

Higher tar yields[15]

38

CHAPTER 3

EXPERIMENTAL STUDY

Figure 3.1: Fluidized bed Gasifier Experimental setup Design [S.P.R.E.R.I,V.V Nagar]

39

Figure 3.2: Photograph of Fluidized bed Gasifier Experimental setup [S.P.R.E.R.I,V.V Nagar]

40

The system consists of the following:

o Gasifier Reactor

o Screw feeder

o Blower

o Distributor Plate

o Electric Heater

o Cyclone

o Venturimeter

3.1 Gasifier Reactor Construction

Biomass fuels are processed in an atmospheric bubbling fluidized bed reactor. Because

Fluidized beds can handle a variety of feedstock; they are well suited for this application.

The reactor is made of 3 mm-thick stainless steel with a total height of 1.6 m. The reactor

is 21 cm (8 inches) in diameter and measures 1.6 m (5.2 feet) tall. The Reactor is split

into two sections: a bed section and a freeboard section. The height of the bed section is

0.6 m and Freeboard section is 1 m. In the bottom, perforated plate distributors are used

to ensure good gas distribution for a wide range of operating parameters. The distributor

plate consists of 101 numbers of 2 mm diameter holes spaced intervals. The reactor bed

section is surrounded by one ceramic band heater of 2.5 KW with temperature controller.

The ceramic band heater is 21 cm (8 inches) inside diameter and height of 30 cm (12

inches). Numerous access ports that allow for temperature and pressure monitoring and

temperatures of the different zones. The bed is fluidized with air provided by a

regenerative blower. Bed temperature is of 500 C to 700C. The primary fluidization gas

enters the bottom of the reactor and then flows through a drilled-hole distributor plate.

The distributor plate consists of 101 numbers of 2 mm diameter holes spaced 2 inches

intervals. The fluidization media consists of 14 kg of 0.4 mm to 0.595 mm sized sand

with a bed height of 30 cm. The bed is heated to normal operating temperatures by

ceramic band heater at the bed section of the reactor. After the reactor is heated to

reaction temperatures, solid fuel can be processed. The particulate-laden exhaust stream

exits the reactor through the freeboard and passes through the cyclone. The combustible

gas is ignited at the burner after the cyclone.

41

3.2 Feedstock feeding section

It consists of a frame, a hopper, a stirrer, a screw feeder and a drive system with an

electric motor with gear box and a variable frequency drive. The funnel shaped hopper,

which served as a reservoir for the fuel material, has a capacity of about 15 L. The stirrer

is used to loosen and mix the fuel, in order to prevent it from settling and consolidating to

form a bridge, and to keep the fuel supply homogeneous and consistent. The feedstock is

fed by a variable rotating screw feeder (of 100 mm diameter) from the feedstock storage

hopper. The feeding point is at 50 mm from the distributor plate.

3.3 Air supply section

The air required for fluidization is supplied to the plenum by an air supply unit. The unit

Consists of an air regenerative blower, orifice meter and U-tube manometer. Orifice

meter is fitted at air inlet pipe of the regenerative blower for measurement of the air

Velocity. U-tube manometer pipes are fitted across the distributor plate for measurement

of the pressure drop across the distributor plate.

3.4 Working of Fluidized Bed Gasifier

Fill-up bed material of size 0.4-0.5 mm up to certain depth of Gasifier bed

Section.

To start up each experimental, the heaters were turned on and the controllers were

set at the desired operating temperatures.

Then start up the blower

During Heat up Period Air is used as a Fluidizing agent

Then with help of Screw feeder Biomass In Pulverized form is feed

When bed attain Uniform temperature then Heater was stop

Due to Small amount of Air Available, So Gasification will start

This Producer gas contain some amount of tar also

Tar is separated in cyclone separator

After Removing tar, This Produced gas was clean and cool

After cleaning and cooling of this Producer gas, we can use it in I.C engine for

Power.

42

CHAPTER-4

CONCLUSION

Following are major conclusions on the basis of above study

higher equivalence ratios favoured more conversion of carbon

Compared to air gasification, steam gasification produces a higher energy content

producer gas.

Combustible gas concentration increased with increases in Bed temperature

Heating Value of Produced gas was increased with increased in equivalence ratio

During the gasification of wood in a fixed bed Gasifier, the gasification rate increased,

when the particle size was decreased from 19.05 to 5.00 mm.

43

REFERENCES

[1] Mazumder, AKM Monayem Hossain, "Development of a Simulation Model for Fluidized

Bed Mild Gasifier" (2010). University of New Orleans Theses and Dissertations. Paper

101.

[2] Daizo Kunii and Octave Levwnspeil, Fluidization Engineering, 1969, John Wiley and

Sons,Inc., 2nd edition, Butterworth-Heinemann Series in Chemical Engineering.

[3] Thermo-chemical Conversion Technologies for Woody Biomass Utilization

Written by Salman Zafar, Renewable Energy http://www.alternativeenergy-

news.info/thermo-chemical-conversion-technologies-woody-biomassutilization

[4] P. Abdul Salam, S. Kumar and Manjula Siriwardhana The Status of Biomass

Gasification in Thailand and Cambodia

[5] Dr. SamySadaka, Gasification Associate Scientist, Center for Sustainable

Environmental Technologies

Iowa State University 1521 West F. Ave.

[6] 55th international energy agency-fluidized bed conversion, Maria

Laura Mastelone and Umberto arena, October 2007

[7] http:// www.netl.doe.gov/technologies/coalpower/turbines/refshelf/.../1.2.1.pdf

[8] Geldart, D., Gas Fluidization Technology, John Wiley&Sons, New York, 1986.

[9] Fluidized Bed Gasification by Dr.Bhattacharya and Dr. P.Basu

[10] W.C. Yang, R.A. Newby, D.L. Keairns Large-scale fluidized bed physical model

Elsevier,1994

[11] Baker, E. L. Mudge and W. Wilcox, Fundamentals of Thermochemical Biomass

Conversion Elsevier,1985, Applied Science Publishers, London, UK, pp. 863-874

[12] P. Subramanian, A. Sampathrajan, P. Venkatachalam Fluidized bed gasification

of select granular biomaterials,elsevier,2010.

[13] Mara C. Palancar I, Miguel Serrano, Jose M. Aragn Testing the technological

feasibility of FLUMOV as gasifier, elsevier, 2009

[14] V. Wilk, H. Kitzler, Steam Gasification, Vienna University of Technology, Institute of

Chemical Engineering, Getreidemarkt 9, Wien, Austria

[15] Stefan Kernn, Christoph Pfeifer, Hermann Hofbauer, Gasification of wood in a dual

fluidized bed gasifier: Influence of fuel feeding on process performance

Vienna University of Technology, Institute of Chemical Engineering, Getreidemarkt

9/166, 1060 Vienna