acads (08-006) covered keywords boiler, efficiency, blowdown, assessment, boiler feedwater....
TRANSCRIPT
Boilers & Thermic Fluid Heaters
ACADs (08-006) Covered
KeywordsBoiler, efficiency, blowdown, assessment, boiler feedwater.
Description
Supporting Material
1.3.4.1 5.2.1.9.c 5.2.2.2 5.2.2.2
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Training Session on Energy Equipment
Boilers & Thermic Fluid Heaters
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1. Describe the theory, construction, and applications of boilers
2. Describe the common type of boilers
3. Explain how to assess the performance and efficiency of a boiler
4. Describe methods to improve boiler efficiency
5.List energy efficiency opportunities
Objectives
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Introduction – Purpose?
Type of boilers
Boiler Assessment
Energy efficiency opportunities
Objectives
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What is a Boiler?
Introduction
• 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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Introduction
BURNERWATER
SOURCE
BRINE
SOFTENERSCHEMICAL FEED
FUELBLOW DOWN SEPARATOR
VENT
VENTEXHAUST GASSTEAM TO PROCESS
STACK DEAERATOR
PUMPS
Figure: Schematic overview of a boiler room
BOILER
ECO-NOMI-ZER
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Introduction
Type of boilers
Assessment of a boiler
Energy efficiency opportunities
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Types 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
What Type of Boilers Are There?
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Type 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 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 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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Type 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
• 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 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 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 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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Independence Steam Electric Station - Newark, AR
Operation: Unit 1 - January 1983/Unit 2 - December 1984Fuel: Low-sulfur coal mined near Gillette, Wyoming Capability: 1,678 megawatts
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Type 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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Introduction
Type of boilers
Boiler Assesment
Energy efficiency opportunities
Training Agenda: Boiler
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1. Boiler
2. Boiler blow down
3. Boiler feed water treatment
Boiler Assessment
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Assessment 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 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 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 Boiler
Heat BalanceGoal: improve energy efficiency by reducing avoidable lossesAvoidable 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 Boiler
1. Boiler EfficiencyThermal efficiency: % of (heat) energy input that is effectively useful in the generated steam
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Assessment 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 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 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 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 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 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 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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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
Energy Efficiency Opportunities
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1. Stack Temperature Control• Keep as low as possible• If >200°C then recover waste heat
Energy 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 Opportunities
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Energy 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 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 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 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 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 Equipment
Boilers & Thermic Fluid Heaters
THANK YOUFOR YOUR ATTENTION
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