Post on 31-Mar-2015
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Training Session on Energy Training Session on Energy EquipmentEquipment
Boilers & Thermic Boilers & Thermic Fluid HeatersFluid Heaters
Presentation from the“Energy Efficiency Guide for Industry in Asia”
www.energyefficiencyasia.org
©© UNEP 2006 UNEP 2006
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Introduction
Type of boilers
Assessment of a boiler
Energy efficiency opportunities
©© UNEP 2006 UNEP 2006
Training Agenda: BoilerTraining Agenda: Boiler
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What is a Boiler?
©© UNEP 2006 UNEP 2006
IntroductionIntroduction
• Vessel that heats water to become hot water or steam
• At atmospheric pressure water volume increases 1,600 times
• Hot water or steam used to transfer heat to a process
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©© UNEP 2006 UNEP 2006
IntroductionIntroduction
BURNERBURNERWATER WATER
SOURCESOURCE
BRINEBRINE
SOFTENERSSOFTENERSCHEMICAL FEEDCHEMICAL FEED
FUELFUELBLOW DOWN BLOW DOWN SEPARATORSEPARATOR
VENTVENT
VENTVENTEXHAUST GASEXHAUST GASSTEAM TO STEAM TO PROCESSPROCESS
STACKSTACK DEAERATORDEAERATOR
PUMPSPUMPS
Figure: Schematic overview of a boiler room
BOILERBOILERE
CO
-E
CO
-N
OM
I-N
OM
I-Z
ER
ZE
R
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Introduction
Type of boilers
Assessment of a boiler
Energy efficiency opportunities
©© UNEP 2006 UNEP 2006
Training Agenda: BoilerTraining Agenda: Boiler
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Types of BoilersTypes of Boilers
1. Fire Tube Boiler
2. Water Tube Boiler
3. Packaged Boiler
4. Fluidized Bed (FBC) Boiler
5. Stoker Fired Boiler
6. Pulverized Fuel Boiler
7. Waste Heat Boiler
8. Thermic Fluid Heater (not a boiler!)
What Type of Boilers Are There?
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©© UNEP 2006 UNEP 2006
Type of BoilersType of Boilers
(Light Rail Transit Association)
1. Fire Tube Boiler
• Relatively small steam capacities (12,000 kg/hour)
• Low to medium steam pressures (18 kg/cm2)
• Operates with oil, gas or solid fuels
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Type of BoilersType of Boilers
2. Water Tube Boiler
(Your Dictionary.com)
• Used for high steam demand and pressure requirements
• Capacity range of 4,500 – 120,000 kg/hour
• Combustion efficiency enhanced by induced draft provisions
• Lower tolerance for water quality and needs water treatment plant
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Type of BoilersType of Boilers
(BIB Cochran, 2003)
3. Packaged Boiler
Oil Burner
To Chimney
• Comes in complete package
• Features• High heat transfer• Faster evaporation • Good convective
heat transfer• Good combustion
efficiency• High thermal
efficiency
• Classified based on number of passes
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©© UNEP 2006 UNEP 2006
Type of BoilersType of Boilers
4. Fluidized Bed Combustion (FBC) Boiler• Particles (e.g. sand) are suspended in high
velocity air stream: bubbling fluidized bed
• Combustion at 840° – 950° C
• Capacity range 0,5 T/hr to 100 T/hr
• Fuels: coal, washery rejects, rice husk, bagasse and agricultural wastes
• Benefits: compactness, fuel flexibility, higher combustion efficiency, reduced SOx & NOx
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Type of BoilersType of Boilers
4a. Atmospheric Fluidized Bed Combustion (AFBC) Boiler
• Most common FBC boiler that uses preheated atmospheric air as fluidization and combustion air
4b. Pressurized Fluidized Bed Combustion (PFBC) Boiler
• Compressor supplies the forced draft and combustor is a pressure vessel
• Used for cogeneration or combined cycle power generation
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Type of BoilersType of Boilers
(Thermax Babcock & Wilcox Ltd, 2001)
4c. Atmospheric Circulating Fluidized Bed Combustion (CFBC) Boiler
• Solids lifted from bed, rise, return to bed
• Steam generation in convection section
• Benefits: more economical, better space utilization and efficient combustion
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Type of BoilersType of Boilers
5. Stoke Fired Boilers
a) Spreader stokers
• Coal is first burnt in suspension then in coal bed
• Flexibility to meet load fluctuations
• Favored in many industrial applications
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Type of BoilersType of Boilers
5. Stoke Fired Boilers
b) Chain-grate or traveling-grate stoker
(University of Missouri, 2004)
• Coal is burnt on moving steel grate
• Coal gate controls coal feeding rate
• Uniform coal size for complete combustion
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Type of BoilersType of Boilers
Tangential firing
6. Pulverized Fuel Boiler
• Pulverized coal powder blown with combustion air into boiler through burner nozzles
• Combustion temperature at 1300 -1700 °C
• Benefits: varying coal quality coal, quick response to load changes and high pre-heat air temperatures
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Type of BoilersType of Boilers
Agriculture and Agri-Food Canada, 2001
7. Waste Heat Boiler• Used when waste heat
available at medium/high temp
• Auxiliary fuel burners used if steam demand is more than the waste heat can generate
• Used in heat recovery from exhaust gases from gas turbines and diesel engines
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Type of BoilersType of Boilers
8. Thermic Fluid Heater
• Wide application for indirect process heating
• Thermic fluid (petroleum-based) is heat transfer medium
• Benefits:
• Closed cycle = minimal losses
• Non-pressurized system operation at 250 °C
• Automatic controls = operational flexibility
• Good thermal efficiencies
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Type of BoilersType of Boilers
(Energy Machine India)
8. Thermic Fluid Heater
Control panel
Blower motor unit
Fuel oil filter
Exhaust
Insulated outer wall
1. Thermic fluid heated in the heater
2. Circulated to user
equipment
User equipment
3. Heat transfer through heat exchanged
4. Fluid returned to
heater
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Introduction
Type of boilers
Assessment of a boiler
Energy efficiency opportunities
©© UNEP 2006 UNEP 2006
Training Agenda: BoilerTraining Agenda: Boiler
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1. Boiler
2. Boiler blow down
3. Boiler feed water treatment
©© UNEP 2006 UNEP 2006
Assessment of a boilerAssessment of a boiler
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Assessment of a BoilerAssessment of a Boiler
1. Boiler performance• Causes of poor boiler performance
-Poor combustion-Heat transfer surface fouling-Poor operation and maintenance-Deteriorating fuel and water quality
• Heat balance: identify heat losses
• Boiler efficiency: determine deviation from best efficiency
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Assessment of a BoilerAssessment of a Boiler
Heat BalanceAn energy flow diagram describes geographically how energy is transformed from fuel into useful energy, heat and losses
StochiometricExcess AirUn burnt
FUEL INPUT STEAM OUTPUT
Stack Gas
Ash and Un-burnt parts of Fuel in Ash
Blow Down
Convection & Radiation
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Assessment of a BoilerAssessment of a Boiler
Heat BalanceBalancing total energy entering a boiler against the energy that leaves the boiler in different forms
Heat in Steam
BOILER
Heat loss due to dry flue gas
Heat loss due to steam in fuel gas
Heat loss due to moisture in fuel
Heat loss due to unburnts in residue
Heat loss due to moisture in air
Heat loss due to radiation & other unaccounted loss
12.7 %
8.1 %
1.7 %
0.3 %
2.4 %
1.0 %
73.8 %
100.0 %
Fuel
73.8 %
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Assessment of a BoilerAssessment of a Boiler
Heat Balance
Goal: improve energy efficiency by reducing avoidable losses
Avoidable losses include:
- Stack gas losses (excess air, stack gas temperature)
- Losses by unburnt fuel
- Blow down losses
- Condensate losses
- Convection and radiation
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Assessment of a BoilerAssessment of a Boiler
Boiler EfficiencyThermal efficiency: % of (heat) energy input that is effectively useful in the generated steam
BOILER EFFICENCY CALCULATION
1) DIRECT METHOD: 2) INDIRECT METHOD:
The efficiency is the different between lossesand energy input
The energy gain of theworking fluid (water and steam) is compared with the energy content of the boiler fuel.
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Assessment of a BoilerAssessment of a Boiler
hg -the enthalpy of saturated steam in kcal/kg of steam
hf -the enthalpy of feed water in kcal/kg of water
Boiler Efficiency: Direct Method
Boiler efficiency () = Heat Input
Heat Outputx 100 Q x (hg – hf)
Q x GCVx 100=
Parameters to be monitored: - Quantity of steam generated per hour (Q) in kg/hr - Quantity of fuel used per hour (q) in kg/hr- The working pressure (in kg/cm2(g)) and superheat
temperature (oC), if any - The temperature of feed water (oC) - Type of fuel and gross calorific value of the fuel (GCV) in
kcal/kg of fuel
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Assessment of a BoilerAssessment of a Boiler
Advantages• Quick evaluation• Few parameters for computation • Few monitoring instruments• Easy to compare evaporation ratios with
benchmark figures
Disadvantages• No explanation of low efficiency• Various losses not calculated
Boiler Efficiency: Direct Method
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Assessment of a BoilerAssessment of a Boiler
Efficiency of boiler () = 100 – (i+ii+iii+iv+v+vi+vii)
Boiler Efficiency: Indirect Method
Principle losses:i) Dry flue gas
ii) Evaporation of water formed due to H2 in fuel
iii) Evaporation of moisture in fuel
iv) Moisture present in combustion air
v) Unburnt fuel in fly ash
vi) Unburnt fuel in bottom ash
vii) Radiation and other unaccounted losses
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Assessment of a BoilerAssessment of a Boiler
Boiler Efficiency: Indirect MethodRequired calculation data• Ultimate analysis of fuel (H2, O2, S, C, moisture
content, ash content)
• % oxygen or CO2 in the flue gas
• Fuel gas temperature in ◦C (Tf)
• Ambient temperature in ◦C (Ta) and humidity of air in kg/kg of dry air
• GCV of fuel in kcal/kg
• % combustible in ash (in case of solid fuels)
• GCV of ash in kcal/kg (in case of solid fuels)
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Assessment of a BoilerAssessment of a Boiler
Boiler Efficiency: Indirect Method
Advantages• Complete mass and energy balance for each
individual stream• Makes it easier to identify options to improve
boiler efficiency
Disadvantages• Time consuming• Requires lab facilities for analysis
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Assessment of a BoilerAssessment of a Boiler
• Controls ‘total dissolved solids’ (TDS) in the water that is boiled
• Blows off water and replaces it with feed water
• Conductivity measured as indication of TDS levels
• Calculation of quantity blow down required:
2. Boiler Blow Down
Blow down (%) = Feed water TDS x % Make up water
Maximum Permissible TDS in Boiler water
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Assessment of a BoilerAssessment of a Boiler
Two types of blow down
• Intermittent• Manually operated valve reduces TDS• Large short-term increases in feed water• Substantial heat loss
• Continuous• Ensures constant TDS and steam purity• Heat lost can be recovered• Common in high-pressure boilers
Boiler Blow Down
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Assessment of a BoilerAssessment of a Boiler
Benefits
• Lower pretreatment costs
• Less make-up water consumption
• Reduced maintenance downtime
• Increased boiler life
• Lower consumption of treatment chemicals
Boiler Blow Down
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Assessment of a BoilerAssessment of a Boiler
• Quality of steam depend on water treatment to control• Steam purity
• Deposits
• Corrosion
• Efficient heat transfer only if boiler water is free from deposit-forming solids
3. Boiler Feed Water Treatment
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Assessment of a BoilerAssessment of a Boiler
Deposit control
• To avoid efficiency losses and reduced heat transfer
• Hardness salts of calcium and magnesium• Alkaline hardness: removed by boiling
• Non-alkaline: difficult to remove
• Silica forms hard silica scales
Boiler Feed Water Treatment
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Assessment of a BoilerAssessment of a Boiler
Internal water treatment
• Chemicals added to boiler to prevent scale
• Different chemicals for different water types
• Conditions:
• Feed water is low in hardness salts
• Low pressure, high TDS content is tolerated
• Small water quantities treated
• Internal treatment alone not recommended
Boiler Feed Water Treatment
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Assessment of a BoilerAssessment of a Boiler
External water treatment:
• Removal of suspended/dissolved solids and dissolved gases
• Pre-treatment: sedimentation and settling
• First treatment stage: removal of salts
• Processes
a) Ion exchange
b) Demineralization
c) De-aeration
d) Reverse osmoses
Boiler Feed Water Treatment
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Assessment of a BoilerAssessment of a Boiler
a) Ion-exchange process (softener plant)• Water passes through bed of natural zeolite of
synthetic resin to remove hardness
• Base exchange: calcium (Ca) and magnesium (Mg) replaced with sodium (Na) ions
• Does not reduce TDS, blow down quantity and alkalinity
b) Demineralization• Complete removal of salts
• Cations in raw water replaced with hydrogen ions
External Water Treatment
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Assessment of a BoilerAssessment of a Boiler
c) De-aeration
• Dissolved corrosive gases (O2, CO2) expelled by preheating the feed water
• Two types:
• Mechanical de-aeration: used prior to addition of chemical oxygen scavangers
• Chemical de-aeration: removes trace oxygen
External Water Treatment
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Assessment of a BoilerAssessment of a Boiler
External Water Treatment
Steam
Storage Section
De-aerated Boiler Feed Water
Scrubber Section (Trays)
Boiler Feed Water
VentSpray Nozzles
( National Productivity Council)
Mechanical de-aeration• O2 and CO2 removed by
heating feed water
• Economical treatment process
• Vacuum type can reduce O2 to 0.02 mg/l
• Pressure type can reduce O2 to 0.005 mg/l
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Assessment of a BoilerAssessment of a Boiler
External Water Treatment
Chemical de-aeration
• Removal of trace oxygen with scavenger
• Sodium sulphite:
• Reacts with oxygen: sodium sulphate
• Increases TDS: increased blow down
• Hydrazine
• Reacts with oxygen: nitrogen + water
• Does not increase TDS: used in high pressure boilers
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Assessment of a BoilerAssessment of a Boiler
d) Reverse osmosis
• Osmosis
• Solutions of differing concentrations
• Separated by a semi-permeable membrane
• Water moves to the higher concentration
• Reversed osmosis
• Higher concentrated liquid pressurized
• Water moves in reversed direction
External Water Treatment
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Assessment of a BoilerAssessment of a Boiler
d) Reverse osmosis
External water treatment
More Concentrated
Solution
Fresh Water
Water Flow
Semi Permeable Membrane
Feed Water
Concentrate Flow
Pressure
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Introduction
Type of boilers
Assessment of a boiler
Energy efficiency opportunities
©© UNEP 2006 UNEP 2006
Training Agenda: BoilerTraining Agenda: Boiler
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1. Stack temperature control2. Feed water preheating using
economizers3. Combustion air pre-heating4. Incomplete combustion
minimization5. Excess air control6. Avoid radiation and convection
heat loss7. Automatic blow down control8. Reduction of scaling and soot
losses9. Reduction of boiler steam
pressure10. Variable speed control11. Controlling boiler loading12. Proper boiler scheduling13. Boiler replacement
©© UNEP 2006 UNEP 2006
Energy Efficiency OpportunitiesEnergy Efficiency Opportunities
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1. Stack Temperature Control
• Keep as low as possible
• If >200°C then recover waste heat
Energy Efficiency OpportunitiesEnergy Efficiency Opportunities
2. Feed Water Preheating Economizers
• Potential to recover heat from 200 – 300 oC flue gases leaving a modern 3-pass shell boiler
3. Combustion Air Preheating• If combustion air raised by 20°C = 1% improve
thermal efficiency
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4. Minimize Incomplete Combustion• Symptoms:
• Smoke, high CO levels in exit flue gas
• Causes: • Air shortage, fuel surplus, poor fuel distribution
• Poor mixing of fuel and air
• Oil-fired boiler: • Improper viscosity, worn tops, cabonization on
dips, deterioration of diffusers or spinner plates
• Coal-fired boiler: non-uniform coal size
Energy Efficiency OpportunitiesEnergy Efficiency Opportunities
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Energy Efficiency OpportunitiesEnergy Efficiency Opportunities
5. Excess Air Control• Excess air required for complete combustion
• Optimum excess air levels varies
• 1% excess air reduction = 0.6% efficiency rise
• Portable or continuous oxygen analyzers
Fuel Kg air req./kg fuel %CO2 in flue gas in practice
Solid Fuels Bagasse Coal (bituminous) Lignite Paddy Husk Wood
3.3 10.7 8.5 4.5 5.7
10-12 10-13 9 -13 14-15 11.13
Liquid Fuels Furnace Oil LSHS
13.8 14.1
9-14 9-14
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Energy Efficiency OpportunitiesEnergy Efficiency Opportunities
7. Automatic Blow Down Control
6. Radiation and Convection Heat Loss Minimization• Fixed heat loss from boiler shell, regardless of
boiler output
• Repairing insulation can reduce loss
• Sense and respond to boiler water conductivity and pH
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Energy Efficiency OpportunitiesEnergy Efficiency Opportunities
9. Reduced Boiler Steam Pressure
8. Scaling and Soot Loss Reduction
• Every 22oC increase in stack temperature = 1% efficiency loss
• 3 mm of soot = 2.5% fuel increase
• Lower steam pressure
= lower saturated steam temperature
= lower flue gas temperature
• Steam generation pressure dictated by process
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Energy Efficiency OpportunitiesEnergy Efficiency Opportunities
11. Control Boiler Loading
10. Variable Speed Control for Fans, Blowers and Pumps• Suited for fans, blowers, pumps
• Should be considered if boiler loads are variable
• Maximum boiler efficiency: 65-85% of rated load
• Significant efficiency loss: < 25% of rated load
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Energy Efficiency OpportunitiesEnergy Efficiency Opportunities
13. Boiler Replacement
12. Proper Boiler Scheduling• Optimum efficiency: 65-85% of full load
• Few boilers at high loads is more efficient than large number at low loads
Financially attractive if existing boiler is
• Old and inefficient
• Not capable of firing cheaper substitution fuel
• Over or under-sized for present requirements
• Not designed for ideal loading conditions
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Training Session on Energy Training Session on Energy EquipmentEquipment
Boilers & Thermic Boilers & Thermic Fluid HeatersFluid Heaters
THANK YOUTHANK YOUFOR YOUR ATTENTIONFOR YOUR ATTENTION
©© UNEP GERIAP UNEP GERIAP
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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