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Boilers & Thermic Fluid Heaters

Boilers & Thermic Fluid Heaters. ACADs (08-006) Covered Keywords Boiler, efficiency, blowdown , assessment, boiler feedwater . Description Supporting Material. Training Session on Energy Equipment. Boilers & Thermic Fluid Heaters. Objectives.

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Boilers & Thermic Fluid Heaters

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  1. Boilers & Thermic Fluid Heaters ACADs (08-006) Covered Keywords Boiler, efficiency, blowdown, assessment, boiler feedwater. Description Supporting Material

  2. Training Session on Energy Equipment Boilers & Thermic Fluid Heaters

  3. 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

  4. Objectives • Introduction – Purpose? • Type of boilers • Boiler Assessment • Energy efficiency opportunities

  5. 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

  6. Introduction STEAM TO PROCESS VENT EXHAUST GAS STACK DEAERATOR PUMPS ECO-NOMI-ZER Thermal Equipment/ Boilers BOILER VENT BURNER WATER SOURCE BLOW DOWN SEPARATOR FUEL BRINE CHEMICAL FEED SOFTENERS Figure: Schematic overview of a boiler room

  7. Introduction Type of boilers Assessment of a boiler Energy efficiency opportunities Thermal Equipment/ Boilers

  8. Types of Boilers What Type of Boilers Are There? • Fire Tube Boiler • Water Tube Boiler • Packaged Boiler • Fluidized Bed (FBC) Boiler • Stoker Fired Boiler • Pulverized Fuel Boiler • Waste Heat Boiler Thermal Equipment/ Boilers

  9. Type of Boilers 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 Thermal Equipment/ Boilers (Light Rail Transit Association)

  10. Type of Boilers 2. Water Tube Boiler • 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 Thermal Equipment/ Boilers (Your Dictionary.com)

  11. To Chimney Oil Burner Type of Boilers 3. Packaged Boiler • 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 Thermal Equipment/ Boilers (BIB Cochran, 2003)

  12. 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 Thermal Equipment/ Boilers

  13. 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 Thermal Equipment/ Boilers

  14. Type of 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 Thermal Equipment/ Boilers (University of Missouri, 2004)

  15. Type of Boilers 6. Pulverized Fuel Boiler • Pulverized coal powder blown with combustion air into boiler through burner nozzles Thermal Equipment/ Boilers • Combustion temperature at 1300 -1700 °C • Benefits: varying coal quality coal, quick response to load changes and high pre-heat air temperatures Tangential firing

  16. 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

  17. Type of 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 • Used in heat recovery from exhaust gases from gas turbines and diesel engines Thermal Equipment/ Boilers Agriculture and Agri-Food Canada, 2001

  18. Training Agenda: Boiler Introduction Type of boilers Boiler Assesment Energy efficiency opportunities Thermal Equipment/ Boilers

  19. Boiler Assessment • Boiler • Boiler blow down • Boiler feed water treatment Thermal Equipment/ Boilers

  20. 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 Thermal Equipment/ Boilers

  21. FUEL INPUT Stochiometric Excess Air Un burnt Stack Gas STEAM OUTPUT Convection & Radiation Blow Down Ash and Un-burnt parts of Fuel in Ash Assessment of a Boiler Heat Balance An energy flow diagram describes geographically how energy is transformed from fuel into useful energy, heat and losses Thermal Equipment/ Boilers

  22. Assessment of a Boiler Heat Balance Balancing total energy entering a boiler against the energy that leaves the boiler in different forms 12.7 % Thermal Equipment/ Boilers Heat loss due to dry flue gas BOILER 8.1 % Heat loss due to steam in fuel gas 1.7 % 100.0 % Heat loss due to moisture in fuel 0.3 % Fuel Heat loss due to moisture in air 2.4 % Heat loss due to unburnts in residue 1.0 % Heat loss due to radiation & other unaccounted loss 73.8 % 73.8 % Heat in Steam

  23. Assessment 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 Thermal Equipment/ Boilers

  24. Assessment of a Boiler 1. Boiler Efficiency Thermal efficiency: % of (heat) energy input that is effectively useful in the generated steam Thermal Equipment/ Boilers

  25. Blow down (%) = Feed water TDS x % Make up water Maximum Permissible TDS in Boiler water Assessment of a Boiler 2. Boiler Blow Down • 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: Thermal Equipment/ Boilers

  26. Assessment of a Boiler 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 Thermal Equipment/ Boilers

  27. Assessment of a Boiler Boiler Blow Down • Benefits • Lower pretreatment costs • Less make-up water consumption • Reduced maintenance downtime • Increased boiler life • Lower consumption of treatment chemicals Thermal Equipment/ Boilers

  28. Assessment of a Boiler 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 Thermal Equipment/ Boilers

  29. Assessment of a Boiler Boiler Feed Water Treatment • 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 Thermal Equipment/ Boilers

  30. Assessment of a Boiler Boiler Feed Water Treatment • 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 Thermal Equipment/ Boilers

  31. Assessment of a Boiler Boiler Feed Water Treatment • External water treatment: • Removal of suspended/dissolved solids and dissolved gases • Pre-treatment: sedimentation and settling • First treatment stage: removal of salts • Processes • Ion exchange • Demineralization • De-aeration • Reverse osmoses Thermal Equipment/ Boilers

  32. Energy Efficiency Opportunities • 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 Thermal Equipment/ Boilers

  33. Energy Efficiency Opportunities • 1. Stack Temperature Control • Keep as low as possible • If >200°C then recover waste heat Thermal Equipment/ Boilers • 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

  34. Energy Efficiency Opportunities • 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 Thermal Equipment/ Boilers

  35. 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 Thermal Equipment/ Boilers

  36. Energy Efficiency Opportunities 6. Radiation and Convection Heat Loss Minimization • Fixed heat loss from boiler shell, regardless of boiler output • Repairing insulation can reduce loss Thermal Equipment/ Boilers 7. Automatic Blow Down Control • Sense and respond to boiler water conductivity and pH

  37. Energy Efficiency Opportunities 8. Scaling and Soot Loss Reduction • Every 22oC increase in stack temperature = 1% efficiency loss • 3 mm of soot = 2.5% fuel increase Thermal Equipment/ Boilers 9. Reduced Boiler Steam Pressure • Lower steam pressure • = lower saturated steam temperature • = lower flue gas temperature • Steam generation pressure dictated by process

  38. Energy Efficiency Opportunities 10. Variable Speed Control for Fans, Blowers and Pumps • Suited for fans, blowers, pumps • Should be considered if boiler loads are variable Thermal Equipment/ Boilers 11. Control Boiler Loading • Maximum boiler efficiency: 65-85% of rated load • Significant efficiency loss: < 25% of rated load

  39. Energy Efficiency Opportunities 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 Thermal Equipment/ Boilers 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

  40. Training Session on Energy Equipment Boilers & Thermic Fluid Heaters THANK YOU FOR YOUR ATTENTION Thermal Equipment/ Boilers

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