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1 Training Session on Energy Equipment Boilers & Thermic Fluid Heaters Presentation from the “Energy Efficiency Guide for Industry in Asia” www.energyefficiencyasia.org © UNEP 2006 Thermal Equipment/ Boilers

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2 Thermal Equipment/ Boilers Introduction Type of boilers Assessment of a boiler Energy efficiency opportunities © UNEP 2006 Training Agenda: Boiler

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3 Thermal Equipment/ Boilers What is a Boiler? © UNEP 2006 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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4 Thermal Equipment/ Boilers © UNEP 2006 Introduction BURNER WATER SOURCE BRINE SOFTENERS CHEMICAL FEED FUEL BLOW DOWN SEPARATOR VENT VENT EXHAUST GAS STEAM TO PROCESS STACK DEAERATOR PUMPS Figure: Schematic overview of a boiler room BOILER ECO-NOMI-ZER

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5 Thermal Equipment/ Boilers Introduction Type of boilers Assessment of a boiler Energy efficiency opportunities © UNEP 2006 Training Agenda: Boiler

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6 Thermal Equipment/ Boilers © UNEP 2006 Types of Boilers Fire Tube Boiler Water Tube Boiler Packaged Boiler Fluidized Bed (FBC) Boiler Stoker Fired Boiler Pulverized Fuel Boiler Waste Heat Boiler Thermic Fluid Heater (not a boiler!) What Type of Boilers Are There?

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7 Thermal Equipment/ Boilers © UNEP 2006 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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8 Thermal Equipment/ Boilers © UNEP 2006 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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9 Thermal Equipment/ Boilers © UNEP 2006 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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10 Thermal Equipment/ Boilers © UNEP 2006 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 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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11 Thermal Equipment/ Boilers © UNEP 2006 Type 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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12 Thermal Equipment/ Boilers © UNEP 2006 Type 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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13 Thermal Equipment/ Boilers © UNEP 2006 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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14 Thermal Equipment/ Boilers © UNEP 2006 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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15 Thermal Equipment/ Boilers © UNEP 2006 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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16 Thermal Equipment/ Boilers © UNEP 2006 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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17 Thermal Equipment/ Boilers © UNEP 2006 Type 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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18 Thermal Equipment/ Boilers © UNEP 2006 Type 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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19 Thermal Equipment/ Boilers Introduction Type of boilers Assessment of a boiler Energy efficiency opportunities © UNEP 2006 Training Agenda: Boiler

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20 Thermal Equipment/ Boilers Boiler Boiler blow down Boiler feed water treatment © UNEP 2006 Assessment of a boiler

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21 Thermal Equipment/ Boilers © UNEP 2006 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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22 Thermal Equipment/ Boilers © UNEP 2006 Assessment of a Boiler 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 FUEL INPUT STEAM OUTPUT Stack Gas Ash and Un-burnt parts of Fuel in Ash Blow Down Convection & Radiation

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23 Thermal Equipment/ Boilers © UNEP 2006 Assessment of a Boiler Heat Balance Balancing 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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24 Thermal Equipment/ Boilers © UNEP 2006 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

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25 Thermal Equipment/ Boilers © UNEP 2006 Assessment of a Boiler Boiler Efficiency Thermal efficiency: % of (heat) energy input that is effectively useful in the generated steam The efficiency is the different between losses and energy input The energy gain of the working fluid (water and steam) is compared with the energy content of the boiler fuel.

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26 Thermal Equipment/ Boilers © UNEP 2006 Assessment of a Boiler h g -the enthalpy of saturated steam in kcal/kg of steam h f -the enthalpy of feed water in kcal/kg of water Boiler Efficiency: Direct Method Boiler efficiency (  ) = Heat Input Heat Output x 100 Q x (hg – hf) Q x GCV x 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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27 Thermal Equipment/ Boilers © UNEP 2006 Assessment 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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28 Thermal Equipment/ Boilers © UNEP 2006 Assessment 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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29 Thermal Equipment/ Boilers © UNEP 2006 Assessment of a Boiler Boiler Efficiency: Indirect Method Required 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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30 Thermal Equipment/ Boilers © UNEP 2006 Assessment 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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31 Thermal Equipment/ Boilers 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 © UNEP 2006

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32 Thermal Equipment/ Boilers © UNEP 2006 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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33 Thermal Equipment/ Boilers © UNEP 2006 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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34 Thermal Equipment/ Boilers © UNEP 2006 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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35 Thermal Equipment/ Boilers © UNEP 2006 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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36 Thermal Equipment/ Boilers © UNEP 2006 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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37 Thermal Equipment/ Boilers © UNEP 2006 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 Ion exchange Demineralization De-aeration Reverse osmoses Boiler Feed Water Treatment

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38 Thermal Equipment/ Boilers © UNEP 2006 Assessment 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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39 Thermal Equipment/ Boilers © UNEP 2006 Assessment 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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40 Thermal Equipment/ Boilers © UNEP 2006 Assessment of a Boiler External Water Treatment Steam Storage Section De-aerated Boiler Feed Water Scrubber Section (Trays) Boiler Feed Water Vent Spray 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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41 Thermal Equipment/ Boilers © UNEP 2006 Assessment 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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42 Thermal Equipment/ Boilers © UNEP 2006 Assessment 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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43 Thermal Equipment/ Boilers © UNEP 2006 Assessment 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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44 Thermal Equipment/ Boilers Introduction Type of boilers Assessment of a boiler Energy efficiency opportunities © UNEP 2006 Training Agenda: Boiler

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45 Thermal Equipment/ Boilers 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 © UNEP 2006 Energy Efficiency Opportunities

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46 Thermal Equipment/ Boilers © UNEP 2006 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 o C 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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47 Thermal Equipment/ Boilers © UNEP 2006 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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48 Thermal Equipment/ Boilers © UNEP 2006 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 %CO 2 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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49 Thermal Equipment/ Boilers © UNEP 2006 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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50 Thermal Equipment/ Boilers © UNEP 2006 Energy Efficiency Opportunities 9. Reduced Boiler Steam Pressure 8. Scaling and Soot Loss Reduction Every 22 o C 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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51 Thermal Equipment/ Boilers © UNEP 2006 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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52 Thermal Equipment/ Boilers © UNEP 2006 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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53 Training Session on Energy Equipment Boilers & Thermic Fluid Heaters THANK YOU FOR YOUR ATTENTION © UNEP GERIAP Thermal Equipment/ Boilers

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54 Thermal Equipment/ Boilers © UNEP 2006 Disclaimer 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

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