Boilers & Thermic Fluid Heaters ACADs (08-006) Covered 126.96.36.199 188.8.131.52.c 184.108.40.206 220.127.116.11 Keywords Boiler, efficiency, blowdown, assessment, boiler feedwater. Description Supporting Material Training Session on Energy Equipment Boilers & Thermic Fluid Heaters
2 Objectives 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 3 Objectives Introduction Purpose? Type of boilers
Boiler Assessment Energy efficiency opportunities 4 Introduction What is a Boiler? 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 5 Introduction STEAM TO PROCESS
EXHAUST GAS Thermal Equipment/ Boilers STACK VENT DEAERATOR PUMPS ECONOMIZER VENT BOILER BLOW DOWN SEPARATOR BURNER
WATER SOURCE FUEL BRINE CHEMICAL FEED SOFTENERS Figure: Schematic overview of a boiler room 6 Thermal Equipment/ Boilers Introduction Type of boilers Assessment of a boiler Energy efficiency opportunities
7 Types of Boilers Thermal Equipment/ Boilers What Type of Boilers Are There? 1. 2. 3. 4. 5. 6. 7. Fire Tube Boiler Water Tube Boiler Packaged Boiler Fluidized Bed (FBC) Boiler Stoker Fired Boiler
Pulverized Fuel Boiler Waste Heat Boiler 8 Type of Boilers Thermal Equipment/ Boilers 1. Fire Tube Boiler (Light Rail Transit Association) Relatively small steam capacities (12,000 kg/hour)
Low to medium steam pressures (18 kg/cm2) Operates with oil, gas or solid fuels 9 10 11 Type of Boilers Thermal Equipment/ 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 12 Type of Boilers Thermal Equipment/ Boilers 3. Packaged Boiler To Chimney Oil Burner (BIB Cochran, 2003)
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 13 Type of Boilers Thermal Equipment/ 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 14 Type of Boilers Thermal Equipment/ 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 15 Type of Boilers Thermal Equipment/ Boilers
5. Stoke Fired Boilers b) Chain-grate or traveling-grate stoker Coal is burnt on moving steel grate Coal gate controls coal feeding rate Uniform coal size for complete combustion (University of Missouri, 2004) 16 Type of Boilers Thermal Equipment/ Boilers 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 preheat air temperatures Tangential firing 17 Independence Steam Electric Station - Newark, AR
Operation: Unit 1 - January 1983/Unit 2 - December 1984 Fuel: Low-sulfur coal mined near Gillette, Wyoming Capability: 1,678 megawatts 18 Type of Boilers Thermal Equipment/ Boilers 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 Agriculture and Agri-Food
Canada, 2001 Used in heat recovery from exhaust gases from gas turbines and diesel engines 19 Training Agenda: Boiler Thermal Equipment/ Boilers Introduction Type of boilers Boiler Assesment Energy efficiency opportunities 20 Boiler Assessment
Thermal Equipment/ Boilers 1. Boiler 2. Boiler blow down 3. Boiler feed water treatment 21 Assessment of a Boiler Thermal Equipment/ Boilers 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 22 Assessment of a Boiler Thermal Equipment/ Boilers Heat Balance An energy flow diagram describes geographically how energy is transformed from fuel into useful energy, heat and losses Stochiometric Excess Air Un burnt
Stack Gas FUEL INPUT STEAM OUTPUT Convection & Radiation Blow Down Ash and Un-burnt parts of Fuel in Ash 23 Assessment of a Boiler Thermal Equipment/
Boilers Heat Balance Balancing total energy entering a boiler against the energy that leaves the boiler in different forms 12.7 % 8.1 % 100.0 % Fuel 1.7 % BOILER 0.3 % 2.4 % 1.0 % 73.8 %
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 moisture in air Heat loss due to unburnts in residue Heat loss due to radiation & other unaccounted loss Heat in Steam Assessment of a Boiler Thermal Equipment/ Boilers 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 25 Assessment of a Boiler Thermal Equipment/ Boilers 1. Boiler Efficiency Thermal efficiency: % of (heat) energy input that is effectively useful in the generated steam 26 Assessment of a Boiler 2. Boiler Blow Down Thermal Equipment/ Boilers
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: Blow down (%) =
Feed water TDS x % Make up water Maximum Permissible TDS in Boiler water 28 Assessment of a Boiler Thermal Equipment/ Boilers Boiler Blow Down 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 29
Assessment of a Boiler Thermal Equipment/ Boilers Boiler Blow Down Benefits Lower pretreatment costs Less make-up water consumption Reduced maintenance downtime Increased boiler life Lower consumption of treatment chemicals 30 Assessment of a Boiler Thermal Equipment/ Boilers
3. Boiler Feed Water Treatment 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 31 Assessment of a Boiler Boiler Feed Water Treatment Thermal Equipment/ Boilers 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 32 Assessment of a Boiler Boiler Feed Water Treatment Thermal Equipment/ Boilers 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 33 Assessment of a Boiler Boiler Feed Water Treatment Thermal Equipment/ Boilers 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 34 Energy Efficiency Opportunities
Thermal Equipment/ Boilers 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. Stack temperature control Feed water preheating using economizers Combustion air pre-heating
Incomplete combustion minimization Excess air control Avoid radiation and convection heat loss Automatic blow down control Reduction of scaling and soot losses Reduction of boiler steam pressure Variable speed control Controlling boiler loading Proper boiler scheduling Boiler replacement 38 Energy Efficiency Opportunities 1. Stack Temperature Control Thermal Equipment/ Boilers Keep as low as possible If >200C then recover waste heat
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 20C = 1% improve thermal efficiency 39 Energy Efficiency Opportunities 4. Minimize Incomplete Combustion Thermal Equipment/ Boilers 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 40 Energy Efficiency Opportunities 5. Excess Air Control Thermal Equipment/ Boilers 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 41 Energy Efficiency Opportunities Thermal Equipment/ Boilers 6. Radiation and Convection Heat Loss Minimization
Fixed heat loss from boiler shell, regardless of boiler output Repairing insulation can reduce loss 7. Automatic Blow Down Control Sense and respond to boiler water conductivity and pH 42 Energy Efficiency Opportunities 8. Scaling and Soot Loss Reduction Thermal Equipment/ Boilers
Every 22oC increase in stack temperature = 1% efficiency loss 3 mm of soot = 2.5% fuel increase 9. Reduced Boiler Steam Pressure Lower steam pressure = lower saturated steam temperature = lower flue gas temperature Steam generation pressure dictated by process 43 Energy Efficiency Opportunities
Thermal Equipment/ Boilers 10. Variable Speed Control for Fans, Blowers and Pumps Suited for fans, blowers, pumps Should be considered if boiler loads are variable 11. Control Boiler Loading Maximum boiler efficiency: 65-85% of rated load Significant efficiency loss: < 25% of rated load
44 Energy Efficiency Opportunities 12. Proper Boiler Scheduling Thermal Equipment/ Boilers Optimum efficiency: 65-85% of full load Few boilers at high loads is more efficient than large number at low loads 13. Boiler Replacement 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 45 Training Session on Energy Equipment Thermal Equipment/ Boilers Boilers & Thermic Fluid Heaters THANK YOU FOR YOUR ATTENTION 46
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