Fuels and Combustion

transcript

Training Session on Energy Training Session on Energy EquipmentEquipment

Fuels & CombustionFuels & Combustion

Presentation from the

“Energy Efficiency Guide for Industry in Asia”

www.energyefficiencyasia.org

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Training Agenda: Fuels & Training Agenda: Fuels & CombustionCombustion

Introduction

Type of fuels

Performance evaluation

Energy efficiency opportunities

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IntroductionIntroduction

• Solar energy is converted to chemical energy through photo-synthesis in plants

• Energy produced by burning wood or fossil fuels

• Fossil fuels: coal, oil and natural gas

The Formation of FuelsTher mal S

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Introduction

Type of fuels

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Type of FuelsType of Fuels

Liquid FuelsTher mal S

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Usage• Used extensively in industrial applications

Examples• Furnace oil

• Light diesel oil

• Petrol

• Kerosine

• Ethanol

• LSHS (low sulphur heavy stock)

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Density• Ratio of the fuel’s mass to its volume at 15 oC,

• kg/m3

• Useful for determining fuel quantity and quality

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Specific gravity• Ratio of weight of oil volume to weight of same water volume at a given temperature

• Specific gravity of water is 1

• Hydrometer used to measure

Fuel oil type

LDO(Light Diesel Oil)

Furnace oil LSHS (Low SulphurHeavy Stock)

Specific Gravity

0.85-0.87 0.89-0.95 0.88-0.98

Table 1. Specific gravity of various fuel oils (adapted from Thermax India Ltd.)

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Viscosity• Measure of fuel’s internal resistance to flow

• Most important characteristic for storage and use

• Decreases as temperature increases

Flash point• Lowest temperature at which a fuel can be heated so that the vapour gives off flashes when an open flame is passes over it

• Flash point of furnace oil: 66oC

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Pour point• Lowest temperature at which fuel will flow

• Indication of temperature at which fuel can be pumped

Specific heat• kCal needed to raise temperature of 1 kg oil by

1oC (kcal/kgoC)

• Indicates how much steam/electricity it takes to heat oil to a desired temperature

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Calorific value• Heat or energy produced

• Gross calorific value (GCV): vapour is fully condensed

• Net calorific value (NCV): water is not fully condensed

Fuel Oil Gross Calorific Value (kCal/kg)Kerosene 11,100Diesel Oil 10,800L.D.O 10,700Furnace Oil 10,500LSHS 10,600

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Sulphur content• Depends on source of crude oil and less on the refining process

• Furnace oil: 2-4 % sulphur

• Sulphuric acid causes corrosion

Ash content• Inorganic material in fuel

• Typically 0.03 - 0.07%

• Corrosion of burner tips and damage to materials /equipments at high temperatures

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Carbon residue• Tendency of oil to deposit a carbonaceous solid residue on a hot surface

• Residual oil: >1% carbon residue

Water content• Normally low in furnace oil supplied (<1% at

refinery)

• Free or emulsified form

• Can damage furnace surface and impact flame

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Storage of fuels• Store in cylindrical tanks above or below

the ground

• Recommended storage: >10 days of normal consumption

• Cleaning at regular intervals

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Properties Fuel OilsFurnace Oil L.S.H.S L.D.O

Density (Approx. g/cc at 150C)

0.89-0.95 0.88-0.98 0.85-0.87

Flash Point (0C) 66 93 66Pour Point (0C) 20 72 18G.C.V. (Kcal/kg) 10500 10600 10700Sediment, % Wt. Max.

0.25 0.25 0.1

Sulphur Total, % Wt. Max.

< 4.0 < 0.5 < 1.8

Water Content, % Vol. Max.

1.0 1.0 0.25

Ash % Wt. Max. 0.1 0.1 0.02

Typical specifications of fuel oils (adapted from Thermax India Ltd.)

Solid FuelsTher mal S

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Coal classification• Anthracite: hard and geologically the

oldest

• Bituminous

• Lignite: soft coal and the youngest

• Further classification: semi- anthracite, semi-bituminous, and sub-bituminous

Solid FuelsTher mal S

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Physical properties• Heating or calorific value (GCV)

• Moisture content

• Volatile matter

• Ash

Chemical properties• Chemical constituents: carbon, hydrogen,

oxygen, sulphur

Solid Fuels (Physical properties)Ther mal S

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Heating or calorific value• The typical GVCs for various coals are:

Parameter Lignite(Dry

Basis)

Indian Coal

Indonesian Coal

South African Coal

GCV (kCal/kg)

4,500 4,000 5,500 6,000

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Moisture content• % of moisture in fuel (0.5 – 10%)

• Reduces heating value of fuel

• Weight loss from heated and then cooled powdered raw coal

Volatile matter• Methane, hydrocarbons, hydrogen, CO, other

• Typically 25-35%

• Easy ignition with high volatile matter

• Weight loss from heated then cooled crushed coal

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Ash• Impurity that will not burn (5-40%)

• Important for design of furnace

• Ash = residue after combustion

Fixed carbon• Fixed carbon = 100 – (moisture + volatile matter +

• Carbon + hydrogen, oxygen, sulphur, nitrogen residues

• Heat generator during combustion

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Proximate analysis of coal• Determines only fixed carbon, volatile matter,

moisture and ash

• Useful to find out heating value (GCV)

• Simple analysis equipment

Ultimate analysis of coal• Determines all coal component elements: carbon,

hydrogen, oxygen, sulphur, other

• Useful for furnace design (e.g flame temperature, flue duct design)

• Laboratory analysis

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Proximate analysisTypical proximate analysis of various coals

(%)Indian Coal

Indonesian Coal

South African Coal

Moisture 5.98 9.43 8.5

Ash 38.63 13.99 17

Volatile matter

20.70 29.79 23.28

Fixed Carbon 34.69 46.79 51.22

Solid Fuels (Chemical Properties)Ther mal S

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Ultimate analysisTypical ultimate analysis of coal (%)

Parameter Indian Coal, % Indonesian Coal, % Moisture 5.98 9.43 Mineral Matter (1.1 x Ash) 38.63 13.99 Carbon 41.11 58.96 Hydrogen 2.76 4.16 Nitrogen 1.22 1.02 Sulphur 0.41 0.56 Oxygen 9.89 11.88 GCV (kCal/kg) 4000 5500

Solid Fuels (Chemical Properties)Ther mal S

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Storage, Handling & Preparation• Storage to minimize carpet loss and loss due

to spontaneous combustion

• Reduce carpet loss: a) a hard surface b) standard concrete/brick storage bays

• Coal preparation before use is important for good combustion

Gaseous FuelsTher mal S

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Advantages of gaseous fuels• Least amount of handling

• Simplest burners systems

• Burner systems require least maintenance

• Environmental benefits: lowest GHG and other emissions

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Classification of gaseous fuels (A) Fuels naturally found in nature-Natural gas-Methane from coal mines(B) Fuel gases made from solid fuel-Gases derived from coal-Gases derived from waste and biomass-From other industrial processes (C) Gases made from petroleum-Liquefied Petroleum gas (LPG)-Refinery gases-Gases from oil gasification(D) Gases from some fermentation

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Calorific value• Fuel should be compared based on the net calorific value (NCV), especially natural gas

Typical physical and chemical properties of various gaseous fuelsFuel Gas

Relative Density

Higher Heating Value kCal/Nm3

Air/Fuel ratio m3/m3

Flame Temp oC

Flame speed m/s

Natural Gas

0.6 9350 10 1954 0.290

Propane 1.52 22200 25 1967 0.460

Butane 1.96 28500 32 1973 0.870

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Liquefied Petroleum Gas (LPG)• Propane, butane and unsaturates, lighter C2 and heavier C5 fractions

• Hydrocarbons are gaseous at atmospheric pressure but can be condensed to liquid state

• LPG vapour is denser than air: leaking gases can flow long distances from the source

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Natural gas• Methane: 95%

• Remaing 5%: ethane, propane, butane, pentane, nitrogen, carbon dioxide, other gases

• High calorific value fuel

• Does not require storage facilities

• No sulphur

• Mixes readily with air without producing smoke or soot

Comparing FuelsTher mal S

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Fuel Oil Coal Natural Gas

Carbon 84 41.11 74Hydrogen 12 2.76 25

Sulphur 3 0.41 -Oxygen 1 9.89 TraceNitrogen Trace 1.22 0.75Ash Trace 38.63 -Water Trace 5.98 -

Introduction

Type of fuels

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Performance EvaluationPerformance Evaluation

• Combustion: rapid oxidation of a fuel

• Complete combustion: total oxidation of fuel (adequate supply of oxygen needed)

• Air: 20.9% oxygen, 79% nitrogen and other

• Nitrogen: (a) reduces the combustion efficiency (b) forms NOx at high temperatures

• Carbon forms (a) CO2 (b) CO resulting in less heat production

Principles of CombustionTher mal S

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• Control the 3 Ts to optimize combustion:

• Water vapor is a by-product of burning fuel that contains hydrogen and this robs heat from the flue gases

Principles of CombustionTher mal S

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1T) Temperature

2T) Turbulence

3T) Time

Oxygen is the key to combustion

Principle of CombustionTher mal S

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Bureau of Energy Efficiency, India, 2004

Stochiometric calculation of air required

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Stochiometric air needed for combustion of furnace oil

Theoretical CO2 content in the flue gases Actual CO2 content and % excess air Constituents of flue gas with excess air Theoretical CO2 and O2 in dry flue gas by

volume

• Measure CO2 in flue gases to estimate excess air level and stack losses

Concept of Excess AirTher mal S

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Carbon dioxide (%)

Source: Bureau of Energy Efficiency, India, 2004

Concept of Excess AirTher mal S

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Residual oxygen (%)

Bureau of Energy Efficiency, India, 2004

• Measure O2 in flue gases to estimate excess air level and stack losses

To exhaust combustion products to atmosphere

Natural draft:• Caused by weight difference between the hot gases

inside the chimney and outside air

• No fans or blowers are used

Mechanical draft:• Artificially produced by fans

• Three types a) balanced draft, b) induced draft and c) forced draft

Draft SystemTher mal S

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Introduction

Type of fuels

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Energy Efficiency OpportunitiesEnergy Efficiency Opportunities

Preheating of combustion oil Temperature control of combustion

oil Preparation of solid fuels Combustion controls

Four main areasTher mal S

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Purpose: to make furnace oil easier to pump

Two methods:• Preheating the entire tank

• Preheating through an outflow heater as the oil flows out

Preheating of Combustion OilTher mal S

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To prevent overheating• With reduced or stopped oil flow

• Especially electric heaters

Using thermostats

Temperature Control of Combustion Oil

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Sizing and screening of coal• Important for efficient combustion

• Size reduction through crushing and pulverizing (< 4 - 6 mm)

• Screen to separate fines and small particles

• Magnetic separator for iron pieces in coal

Preparation of Solid FuelsTher mal S

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Conditioning of coal:• Coal fines cause combustion problems

• Segregation can be reduced by conditioning coal with water • Decrease % unburnt carbon

• Decrease excess air level required

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Preparation of Solid Fuels

Blending of coal• Used with excessive coal fines

• Blending of lumped coal with coal containing fines• Limits fines in coal being fired to <25%

• Ensures more uniform coal supply

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Preparation of Solid Fuels

• Assist burner to achieve optimum boiler efficiency through the regulation of fuel supply, air supply, and removal of combustion gases

• Three controls:• On/Off control: burner is firing at full rate or it is

turned off

• High/Low/Off control: burners with two firing rates

• Modulating control: matches steam pressure demand by altering the firing rate

Combustion ControlsTher mal S

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Training Session on Energy Training Session on Energy EquipmentEquipment

Fuels & CombustionFuels & Combustion

THANK YOUTHANK YOU

FOR YOUR ATTENTIONFOR YOUR ATTENTION

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Disclaimer and ReferencesDisclaimer and References

• This PowerPoint training session was prepared as part of the project “Greenhouse Gas Emission Reduction from Industry in Asia and the Pacific” (GERIAP). While reasonable efforts have been made to ensure that the contents of this publication are factually correct and properly referenced, UNEP does not accept responsibility for the accuracy or completeness of the contents, and shall not be liable for any loss or damage that may be occasioned directly or indirectly through the use of, or reliance on, the contents of this publication. © UNEP, 2006.

• The GERIAP project was funded by the Swedish International Development Cooperation Agency (Sida)

• Full references are included in the textbook chapter that is available on www.energyefficiencyasia.org

Fuels and Combustion

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