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discussion on fuels and combustion
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1
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
© UNEP 2006© UNEP 2006
Ther m
al System
s/ Fuels
2
© UNEP 2006© UNEP 2006
Training Agenda: Fuels & Training Agenda: Fuels & CombustionCombustion
Introduction
Type of fuels
Performance evaluation
Energy efficiency opportunities
Ther m
al System
s/ Fuels
3
© UNEP 2006© UNEP 2006
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 Fuels
Ther m
al System
s/ Fuels
4
© UNEP 2006© UNEP 2006
Training Agenda: Fuels & Training Agenda: Fuels & CombustionCombustion
Introduction
Type of fuels
Performance evaluation
Energy efficiency opportunities
Ther m
al System
s/ Fuels
5
© UNEP 2006© UNEP 2006
Type of FuelsType of Fuels
Liquid FuelsTher m
al System
s/ Fuels
Usage• Used extensively in industrial applications
Examples• Furnace oil
• Light diesel oil
• Petrol
• Kerosine
• Ethanol
• LSHS (low sulphur heavy stock)
6
© UNEP 2006© UNEP 2006
Type of FuelsType of Fuels
Liquid Fuels
Ther m
al System
s/ Fuels
Density
• Ratio of the fuel’s mass to its volume at 15 oC,
• kg/m3
• Useful for determining fuel quantity and quality
7
© UNEP 2006© UNEP 2006
Type of FuelsType of Fuels
Liquid FuelsTher m
al System
s/ Fuels
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.)
8
© UNEP 2006© UNEP 2006
Type of FuelsType of Fuels
Liquid Fuels
Ther m
al System
s/ Fuels
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
9
© UNEP 2006© UNEP 2006
Type of FuelsType of Fuels
Liquid FuelsTher m
al System
s/ Fuels
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
10
© UNEP 2006© UNEP 2006
Type of FuelsType of Fuels
Liquid FuelsTher m
al System
s/ Fuels
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
11
© UNEP 2006© UNEP 2006
Type of FuelsType of Fuels
Liquid FuelsTher m
al System
s/ Fuels
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
12
© UNEP 2006© UNEP 2006
Type of FuelsType of Fuels
Liquid Fuels
Ther m
al System
s/ Fuels
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
13
© UNEP 2006© UNEP 2006
Type of FuelsType of Fuels
Liquid Fuels
Ther m
al System
s/ Fuels
Storage of fuels
• Store in cylindrical tanks above or below the ground
• Recommended storage: >10 days of normal consumption
• Cleaning at regular intervals
14
© UNEP 2006© UNEP 2006
Type of FuelsType of Fuels
Liquid FuelsTher m
al System
s/ Fuels
Properties Fuel Oils
Furnace Oil L.S.H.S L.D.ODensity (Approx. g/cc at 150C)
0.89-0.95 0.88-0.98 0.85-0.87
Flash Point (0C) 66 93 66
Pour Point (0C) 20 72 18
G.C.V. (Kcal/kg) 10500 10600 10700
Sediment, % 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.)
15
© UNEP 2006© UNEP 2006
Type of FuelsType of Fuels
Solid Fuels
Ther m
al System
s/ Fuels
Coal classification
• Anthracite: hard and geologically the oldest
• Bituminous
• Lignite: soft coal and the youngest
• Further classification: semi- anthracite, semi-bituminous, and sub-bituminous
16
© UNEP 2006© UNEP 2006
Type of FuelsType of Fuels
Solid FuelsTher m
al System
s/ Fuels
Physical properties
• Heating or calorific value (GCV)
• Moisture content
• Volatile matter
• Ash
Chemical properties
• Chemical constituents: carbon, hydrogen, oxygen, sulphur
17
© UNEP 2006© UNEP 2006
Type of FuelsType of Fuels
Solid Fuels (Physical properties)Ther m
al System
s/ Fuels
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
18
© UNEP 2006© UNEP 2006
Type of FuelsType of Fuels
Solid Fuels (Physical properties)Ther m
al System
s/ Fuels
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
19
© UNEP 2006© UNEP 2006
Type of FuelsType of Fuels
Solid Fuels (Physical properties)Ther m
al System
s/ Fuels
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 +
ash)
• Carbon + hydrogen, oxygen, sulphur, nitrogen residues
• Heat generator during combustion
20
© UNEP 2006© UNEP 2006
Type of FuelsType of Fuels
Solid Fuels (Physical properties)Ther m
al System
s/ Fuels
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
21
© UNEP 2006© UNEP 2006
Type of FuelsType of Fuels
Solid Fuels (Physical properties)
Ther m
al System
s/ Fuels
Proximate analysis
Typical 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
22
© UNEP 2006© UNEP 2006
Type of FuelsType of Fuels
Solid Fuels (Chemical Properties)
Ther m
al System
s/ Fuels
Ultimate analysis
Typical 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
23
© UNEP 2006© UNEP 2006
Type of FuelsType of Fuels
Solid Fuels (Chemical Properties)
Ther m
al System
s/ Fuels
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
24
© UNEP 2006© UNEP 2006
Type of FuelsType of Fuels
Gaseous Fuels
Ther m
al System
s/ Fuels
Advantages of gaseous fuels
• Least amount of handling
• Simplest burners systems
• Burner systems require least maintenance
• Environmental benefits: lowest GHG and other emissions
25
© UNEP 2006© UNEP 2006
Type of FuelsType of Fuels
Gaseous FuelsTher m
al System
s/ Fuels
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
26
© UNEP 2006© UNEP 2006
Type of FuelsType of Fuels
Gaseous Fuels
Ther m
al System
s/ Fuels
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
27
© UNEP 2006© UNEP 2006
Type of FuelsType of Fuels
Gaseous Fuels
Ther m
al System
s/ Fuels
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
28
© UNEP 2006© UNEP 2006
Type of FuelsType of Fuels
Gaseous Fuels
Ther m
al System
s/ Fuels
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
29
© UNEP 2006© UNEP 2006
Type of FuelsType of Fuels
Comparing Fuels
Ther m
al System
s/ Fuels
Fuel Oil Coal Natural Gas
Carbon 84 41.11 74
Hydrogen 12 2.76 25
Sulphur 3 0.41 -
Oxygen 1 9.89 Trace
Nitrogen Trace 1.22 0.75
Ash Trace 38.63 -
Water Trace 5.98 -
30
© UNEP 2006© UNEP 2006
Training Agenda: Fuels & Training Agenda: Fuels & CombustionCombustion
Introduction
Type of fuels
Performance evaluation
Energy efficiency opportunities
Ther m
al System
s/ Fuels
31
© UNEP 2006© UNEP 2006
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 m
al System
s/ Fuels
32
© UNEP 2006© UNEP 2006
Performance EvaluationPerformance Evaluation
• 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 m
al System
s/ Fuels
1T) Temperature
2T) Turbulence
3T) Time
33
© UNEP 2006© UNEP 2006
Performance EvaluationPerformance Evaluation
Oxygen is the key to combustion
Principle of Combustion
Ther m
al System
s/ Fuels
Bureau of Energy Efficiency, India, 2004
34
© UNEP 2006© UNEP 2006
Performance EvaluationPerformance Evaluation
Stochiometric calculation of air required
Ther m
al System
s/ Fuels
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
35
© UNEP 2006© UNEP 2006
Performance EvaluationPerformance Evaluation
• Measure CO2 in flue gases to estimate excess air level and stack losses
Concept of Excess AirTher m
al System
s/ Fuels
Carbon dioxide (%)
Exc
ess
air
(%)
Source: Bureau of Energy Efficiency, India, 2004
36
© UNEP 2006© UNEP 2006
Performance EvaluationPerformance Evaluation
Concept of Excess AirTher m
al System
s/ Fuels
Residual oxygen (%)
Ex
ces
s a
ir (
%)
Bureau of Energy Efficiency, India, 2004
• Measure O2 in flue gases to estimate excess air level and stack losses
37
© UNEP 2006© UNEP 2006
Performance EvaluationPerformance Evaluation
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 m
al System
s/ Fuels
38
© UNEP 2006© UNEP 2006
Training Agenda: Fuels & Training Agenda: Fuels & CombustionCombustion
Introduction
Type of fuels
Performance evaluation
Energy efficiency opportunities
Ther m
al System
s/ Fuels
39
© UNEP 2006© UNEP 2006
Energy Efficiency OpportunitiesEnergy Efficiency Opportunities
Preheating of combustion oil
Temperature control of combustion oil
Preparation of solid fuels
Combustion controls
Four main areasTher m
al System
s/ Fuels
40
© UNEP 2006© UNEP 2006
Energy Efficiency OpportunitiesEnergy Efficiency Opportunities
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 Oil
Ther m
al System
s/ Fuels
41
© UNEP 2006© UNEP 2006
Energy Efficiency OpportunitiesEnergy Efficiency Opportunities
To prevent overheating
• With reduced or stopped oil flow
• Especially electric heaters
Using thermostats
Temperature Control of Combustion Oil
Ther m
al System
s/ Fuels
42
© UNEP 2006© UNEP 2006
Energy Efficiency OpportunitiesEnergy Efficiency Opportunities
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 Fuels
Ther m
al System
s/ Fuels
43
© UNEP 2006© UNEP 2006
Energy Efficiency OpportunitiesEnergy Efficiency Opportunities
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
Ther m
al System
s/ Fuels
Preparation of Solid Fuels
44
© UNEP 2006© UNEP 2006
Energy Efficiency OpportunitiesEnergy Efficiency Opportunities
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
Ther m
al System
s/ Fuels
Preparation of Solid Fuels
45
© UNEP 2006© UNEP 2006
Energy Efficiency OpportunitiesEnergy Efficiency Opportunities
• 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 m
al System
s/ Fuels
46
Training Session on Energy Training Session on Energy EquipmentEquipment
Fuels & CombustionFuels & Combustion
THANK YOUTHANK YOU
FOR YOUR ATTENTIONFOR YOUR ATTENTION
© UNEP GERIAP© UNEP GERIAP
Ther m
al System
s/ Fuels
47
Ther m
al System
s/ Fuels
© UNEP 2006© UNEP 2006
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