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14th National Certification Exam Energy Managers & Auditors AUGUST 2013 Paper 2

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Paper 2 - Set A Key 14th NATIONAL CERTIFICATION EXAMINATION FOR ENERGY MANAGERS & ENERGY AUDITORS August, 2013 PAPER 2: Energy Efficiency in Thermal Utilities Date: 24.8.2013 Max.Marks:150 Timings:14:00 -17:00 Hrs Duration:3 Hrs Section I: OBJECTIVE TYPE 50 x 1 = 50 Marks: (i) Answer all 50 questions (ii) Each question carries one mark (iii) Please hatch the appropriate oval in the OMR answer sheet with Black Pen or HB pencil 1. In coal fired combustion, the flame length is influenced by a) moisture carbon 2. c) remains same d) none of the b) 6 c) 30 d) 103 b) pour point c) specific heat d) specific Which of the following contributes to spluttering of flame at burner tip during combustion of fuel oil ? a) ash content air 6. b) decreases Which property indicates the lowest temperature at which fuel oil is readily pumpable? a) flash point volume 5. d) fixed 100 kg of a fuel contains 3% sulphur. For complete combustion of sulphur in the fuel it will require _________kg of oxygen a) 3 4. c) volatile matter With increase in the percentage of excess air for combustion of coal, percentage of CO2 in flue gas a) increases above 3. b) ash content b) water content c) sulphur content d) humidity of In an oil fired steam boiler the air to fuel ratio is 15:1 & evaporation ratio is 14:1. The flue gas to fuel ratio will be _________________________ Bureau of Energy Efficiency 1 Paper 2 - Set A Key a) 29:1 7. b) 16:1 c) 14:1 d) 15:1 Which among the following fuels, on combustion ,has higher tendency towards acid corrosion in the flue gas path? a) a) LSHS d) kerosene 8. b) furnace oil c) Diesel The balanced draft furnace is one that is operated with a) a) positive pressure draft fan b) c) negative pressure 9. b) induced and forced d) Natural draft The factor that influences atomisation of fuel oil is a) viscosity 10. b) density c) flash point d) pour point Which of the following is not measured in ultimate analysis ? a) carbon moisture 11. b) sulphur c) hydrogen d) In flue gas, the oxygen measured is 4% by volume. The percentage excess air will be a) a) 23.5% d) 36% 12. b) 40% c) 21% A boiler generates 5 TPH of steam at an efficiency of 78 %. The enthalpy added to steam in the boiler is 580 kcal/kg. The fuel consumption with a GCV of 4200 kcal/kg is a) 885 kg/hr kg/hr 13. b) 985 kg/hr c) 1038 kg/hr d) 1200 Automatic blowdown controls for boilers work by sensing a) dissolved gases and pH 14. b) dissolved solids c) pH d) conductivity Dissolved CO2 in boiler feed water when left untreated would result in occurrence of _____in boiler tubes a) creep hammer b) water side corrosion c) scale d) water Recommended boiler feed water pH value at 25 oC is --------- 15. a) 8.0 - 9.0 16. b) 5.2 - 6.2 c) 9.8-10.2 d) 10-10.5 Which of the following is not applicable in the preservation of boiler by dry method ? a) un-slacked lime c) anhydrous calcium cloride 2 b) activated alumina d) hydrazine Paper 2 - Set A Key 17. Which one of the following is true of a water softening process? a) It reduces hardness but not TDS c) It reduces TDS but not hardness 18. Soot deposit in boiler tubes is predominantly due to a) poor water treatment c) incomplete combustion 19. b) low steam pressure d) high excess air Which of the following will be the most suitable heating medium for heat transfer in indirect heating? a) dry saturated steam water 20. b) 1 bar b) thermostatic trap c) orifice type trap b) 0.94 m/s b) bimetallic c) 1.88 m/s d) 3.7 m/s c) inverted bucket used d) float trap b) specific volume of steam d) fifth power of pipe diameter b) partly convert to flash steam d) convert to superheated steam Steam at 4 bar has sensible heat of 144 kcal/kg and latent heat of 510 kcal/kg. If the steam is 90% dry than the total enthalpy of steam in kcal/kg is a) 588 27. d) float trap Condensate, at 3 bar pressure & 160 C, when exposed to atmosphere will a) fully convert to flash steam c) remain as condensate 26. d) The velocity of steam in steam pipe is directly proportional to a) number of bends in pipe c) length of pipe 25. c) 10 bar To drain condensate from tracer steam lines , the most common trap is_________ a) thermodynamic 24. d) hot Water flows at a rate of 30 m 3/hr. at 15oC in a 150 mm bore pipe horizontally. What is the velocity of water flow in the pipe? a) 0.47 m/s 23. c) wet steam The difference in temperature between steam and condensate is the principle of operation of a) thermodynamic trap 22. b) superheated steam Ten meter lift of condensate in a distribution pipe will result in a back pressure of a) 0.1 bar 1.1 bar 21. b) It reduces both hardness and TDS d) None of the above b) 654 c) 603 d) 459 For transporting steam to a long distance, the most suitable among the following will be a) slightly superheated steam _________________________ Bureau of Energy Efficiency b) dry saturated steam 3 Paper 2 - Set A Key c) mildly wet steam 28. d) high pressure steam Heat transfer in a reheating furnace is achieved by a) conduction 29. b) convection c) radiation d) all of the above Which of the following is not a property of ceramic fibre ? a) low thermal conductivity c) high heat capacity 30. b) light weight d) thermal shock resistant The unit of overall heat transfer coefficient is a) kcal/m-hr- C kcal/ m- C 31. b) kcal/ m -hr- C c) kcal/m - C d) Which property of ceramic coating influences energy savings in furnaces? a) emissivity c) conductivity 32. b) coating thickness d) convective heat transfer coefficient In a CFBC boiler the capture and recycling of bed materials is accomplished by a) elecrostatic precipitator 33. b) bag filter c) cyclone d) scrubber What is the most effective way to avoid ambient air infiltration into a continuous furnace? a) close all openings b) increase the chimney height c) operate at about 90% capacity d) maintain slightly positive pressure inside the furnace 34. The storage heat losses in a batch type furnace can be best reduced by use of a) hot face insulating bricks c) cold face insulating bricks 35. b) hot face ceramic fibre d) cold face ceramic fibre Tuyeres is a terminology associated with a) forging furnace furnace 36. b) cupola c) open hearth furnace d) heat treatment Which of the following is a synthetic refractory? a) MgO 37. b) Al2O3 c) SiC d) SiO2 Alumina is a __________________ type of refractory a) basic 38. b) acidic c) neutral d) none of the above An increase in bulk density of a refractory increases its a) volume stability c) resistance to slag penetration 4 b) heat capacity d) all of the above Paper 2 - Set A Key 39. Which of these is used in a fluidised bed boiler to control sulphur dioxide emissions? a) charcoal 40. b) limestone c) sand d) silica In FBC boiler the combustion is carried out at a temperature a) closer to steam temperature b) at adiabatic combustion temperature c) at and above ash fusion temperature d) below ash fusion temperature of fuel used 41. Low combustion temperature minimises___ in FBC boilers a) NOx 42. b) SOx c) CO A chemical plant needs steam at 3 bar and 10 bar in addition to electric power. The most suitable co-generation choice among the following will be a) extraction cum condensing c) back pressure turbine 43. b) Carnot cycle b) heat wheel c) heat pump b) recuperator d) b) forward movement of hot liquid d) return of hot vapors b) heat pump c) heat pipe d) The exhaust from which of the following is not suitable for waste heat boiler application? a) gas turbine 49. c) economizer Which of the following requires electrical energy for equipment operation? a) thermo compressor economizer 48. d) thermo compressor Wick in heat pipe is provided to facilitate a) forward movement of hot vapors c) return of condensed liquid 47. d) Brayton Which of these devices can be used for recovering waste heat from the textile drier exhaust? a) heat wheel regenerator 46. c) bottoming cycle Which of the following works on a refrigeration cycle? a) heat pipe 45. b) condensing turbine d) extraction cum back pressure turbine Power is to be generated from a cement kiln exhaust gas. The applicable type of cogeneration is called a) topping cycle cycle 44. d) Suspended particulate matter b) hot air dryer c) diesel engine d) furnace Pinch analysis of process streams depicts the plot of a) temperature vs entropy c) temperature vs specific heat _________________________ Bureau of Energy Efficiency b) temperature vs area d) temperature vs enthalpy 5 Paper 2 - Set A Key 50. Correction factor for LMTD calculation is applicable for a) parallel flow & (b) b) counter current flow . End of Section I . 6 c) cross flow d) both (a) Paper 2 - Set A Key Section - II: 40 (i) (ii) S-1 SHORT DESCRIPTIVE QUESTIONS Marks: 8 x 5 = Answer all Eight questions Each question carries Five marks The following are the parameters obtained from a steam audit of a cylindrical dryer used for drying cloth. Cloth Throughput = 20 m/minute Cloth Density = 9.8 m/kg Measured Condensate Rate = 135 kg/hour Calculate the specific steam consumption per kg of cloth. Cloth throughput per hour = 20 x 60 = 1200 m/hr Weight of cloth = 1200 / 9.8 = 122.45 kg/hr Steam consumption = condensate collected Specific steam consumption = 135/122.45 =1.1 kg of steam per kg of cloth S-2 In a crude distillation unit of a refinery, furnace is operated to heat 300 kilo Litres/hr of crude oil at an inlet temperature of 255 C by firing 2.5 kilolitres/hr of furnace oil having GCV of 9880 kcal/kg. If the efficiency of the furnace is 82% ,calculate the outlet temperature of the crude oil from the furnace. Consider the following data: Specific heat of Crude Oil = 0.65 kcal/kg C Specific gravity of Crude Oil = 0.86 Specific gravity of furnace Oil = 0.98 Solution: Furnace oil consumption = 2.5 X 0.98 = 2.45 TPH Heat input to the furnace = 2.45 x 1000 x 9880 = 24.2 x 10 6 Kcal/hr Heat absorbed by the crude = 24.2 x 106 x 0.82 = 19.85x 106 Kcal/hr Q = m * Cp * Del T 19.85 * 106 = 300 * 0.86 * 1000 * 0.65 * T T = 118 C T out = 255 + 118 = 373 C _________________________ Bureau of Energy Efficiency 7 Paper 2 - Set A Key Temperature of crude at furnace outlet is 373 C S-3 In a process plant, 20 TPH of steam after pressure reduction with pressure reducing valve to 20 kg/cm2 gets superheated. The temperature of steam is 280oC. The management wants to install a de-superheater to convert superheated steam into saturated steam at 20 kg/cm 2 for process use, and its saturation temperature is 210oC. Calculate quantity of water at 30oC to be injected in de-superheater to get the desired saturated steam using the following data. Specific heat of superheated steam Latent heat of steam at 20kg/cm2 = 0.45 kcal/Kg oC = 450 kcal/kg Answer Quantity of heat available above saturation Quantity of water required in de-superheater S-4 = 20,000 x 0.45 x (280-210) = 6,30,000 kCal = Q x{1x (210-30) + 450}= 630000 = 1000 Kg/hr A 5 TPH capacity boiler is generating saturated steam at 8 kg/ cm2g .The following operating parameters was measured during the survey. Furnace oil consumption - 200 kg/hr. GCV of furnace oil - 10,500 kcal/kg Qty of steam generation - 3000 kg/hr Feed water temperature - 60 oC Enthalpy of dry saturated steam - 660 kcal/kg Dryness fraction - 0.9 Saturation temperature of steam - 170 oC Calculate the boiler efficiency by direct method. Boiler Efficiency = 2700 kg x (660-60) kcal/kg + 300 x (170-60) x 200 kg x 10500 kcal/kg = 78.7% S-5 In a pharma industry, a chemical process requires 5000 kg/hr of dry saturated steam at 7 kg/cm 2 (g). Specific volume of steam at 7 kg/cm 2g is 0.24 m3/kg . Determine the pipe diameter size for a steam flow velocity of 25 m/s. The velocity of steam Specific volume at 7 kg/cm2 g Mass flow rate of steam 8 100 = 25 m/s = 0.24 m3/kg = 5000 kg/hr Paper 2 - Set A Key Volumetric flow of steam = 5000/3600 = 1.389 kg/sec = 1.389 x 0.24 =0.333 m3/sec Therefore, using formula: S-6 Ans Distinguish between plate heat exchanger and shell and tube heat exchanger ? Shell and Tube heat Exchangers Shell-and-tube heat exchangers consist of a bundle of parallel tubes that provide the heat-transfer surface separating the two fluid streams. The tube-side fluid passes axially through the inside of the tubes; the shell-side fluid passes over the outside of the tubes. Baffles external and perpendicular to the tubes direct the flow across the tubes and provide tube support. Tube sheets seal the ends of the tubes, ensuring separation of the two streams. The process fluid is usually placed inside the tubes for ease of cleaning or to take advantage of the higher pressure capability inside the tubes. The thermal performance of such an exchanger usually surpasses a coil type but is less than a plate type. Pressure capability of shell-and-tube exchangers is generally higher than a plate type but lower than a coil type. Plate Heat Exchangers Plate heat exchangers consist of a stack of parallel thin plates that lie between heavy end plates. Each fluid stream passes alternately between adjoining plates in the stack, exchanging heat through the plates. The plates are corrugated for strength and to enhance heat transfer by directing the flow and increasing turbulence. These exchangers have high heat-transfer coefficients and area, the pressure drop is also typically low, and they often provide very high effectiveness. However, they have relatively low pressure capability. The biggest advantage of the plate and frame heat exchanger, and a situation where it is most often used, is when the heat transfer application calls for the cold side fluid to exit the exchanger at a temperature significantly higher than the hot side fluid exit temperature i.e. temperature cross . This would require several shell and tube exchangers in series due to the lack of purely counter-current flow. The overall heat transfer coefficient of plate heat exchangers under favorable circumstances can be as high as 8,000 W/m2 C. With traditional shell and tube heat exchangers, the U-value will be below 2,500 W/m2 C. S-7 Give reasons for the following a) Explain why natural gas requires less amount of excess air compared to solid/liquid fuels b) Why steam is to be used at the lowest practicable pressure for indirect process heating ? Ans a) Natural gas requires less amount of excess air compared to solid/liquid fuels Natural gas is in the gaseous form and lighter than air, it mixes with air readily (intimate mixing of air (oxygen) and fuel takes place) and aids to complete combustion with less amount of excess air. It does not produce smoke or soot. It has no sulphur content. It is lighter than air and disperses into air easily in case of leak. Natural gas is also free of ash. Solid or liquid fuels must be changed to a gaseous form before they will burn. Hence it requires more excess air compared to natural gas for complete combustion. Solid fuels need to be pulverized properly to get uniform sizes and liquid fuels need to be preheated and atomized _________________________ Bureau of Energy Efficiency 9 Paper 2 - Set A Key properly for intimate mixing with air to ensure complete combustion. Hence more excess air is provided for solid and liquid fuels. b) Steam is to be used at the lowest practicable pressure for indirect process heating A study of the steam tables would indicate that the latent heat in steam reduces as the steam pressure increases. It is only the latent heat of steam, which takes part in the heating process when applied to an indirect heating system. Thus, it is important that its value be kept as high as possible. This can only be achieved if we go in for lower steam pressures. As a guide, the steam should always be generated and distributed at the highest possible pressure, but utilized at as low a pressure as possible since it then has higher latent heat. However, it may also be seen from the steam tables that the lower the steam pressure, the lower will be its temperature. Since temperature is the driving force for the transfer of heat at lower steam pressures, the rate of heat transfer will be slower and the processing time greater. In equipment where fixed losses are high (e.g. big drying cylinders), there may even be an increase in steam consumption at lower pressures due to increased processing time. There are, however, several equipment in certain industries where one can profitably go in for lower pressures and realize economy in steam consumption without materially affecting production time. Therefore, there is a limit to the reduction of steam pressure. Depending on the equipment design, the lowest possible steam pressure with which the equipment can work should be selected without sacrificing either on production time or on steam consumption. S-8 List down five major advantages of waste heat recovery in rolling mill furnace 1. 2. 3. 4. 5. 6. 7. 8. Fuel economy Improved combustion/less excess air/reduction in stack losses Increased output Reduction in scale losses Uniform temperature across the material Reduced pollution Less auxiliary energy consumption Reduction in equipment sizes ------- End of Section - II --------- Section - III: LONG DESCRIPTIVE QUESTIONS Marks: 6 x 10 = 60 (i) Answer all Six questions (ii) Each question carries Ten marks L-1 An oil fired reheating furnace has an operating temperature of around 1000 oC. Average furnace oil consumption is 440 litres/hour. The flue gas exit temperature after the air preheater is 300 oC. Combustion air is preheated from ambient temperature of 35oC to 200oC through the air preheater. The other data are as given below. Specific gravity of oil = 0.92 Calorific value of oil = 10,200 kcal/kg Average O2 percentage in flue gas = 14% Theoretical air required = 14 kg of air per kg of oil 10 Paper 2 - Set A Key Specific heat of air = 0.24 kcal/kgoC Specific heat of flue gas = 0.23 kcal/kgoC Find out the sensible heat carried away by the exhaust gases and heat recovered by the combustion air in kcal/hr as a percentage of the energy input. Ans Energy input = 440 litres/hr = 440 x 0.92 kg/hr = 404.80 kg/hr = 404.80 x 10,200 = 41,28,960 kCal/hr : Excess air = ( %O2 ) x 100 (21-O2%) = 14 x 100 (21-14) = 200% Theoretical air required = 14 kg of air to burn 1 kg of oil Actual mass of air required = 14 x (1 + 200/100) kg/kg of oil = 42 kg/kg of oil Sensible heat loss in the flue gas = m x Cp x T m = mass of flue gas = 42 + 1 = 43 kg/kg of oil Cp = Specific heat of flue gas = 0.23 T = Temperature of flue gas Ambient Temperature = 300oC 35oC = 265 oC Heat loss = 43 x 0.23 x (300-35) = 43 x 0.23 x 265 = 2620.85 kCal/kg of oil = 2620.85 x 404.80 Kcal/hr = 10,60,920 Kcal/hr Sensible heat loss in the flue gas as % heat loss to input energy = 10,60,920 x 100 41,28,960 = 25.7 % Heat gained by combustion air = 42 x 0.24 x (200-35) = 1663.2 kCal/kg of oil = 1663.2 x 404.80 Kcal/hr = 673263.36 Kcal/hr _________________________ Bureau of Energy Efficiency 11 Paper 2 - Set A Key Heat gained by combustion air as % of input energy = 673263.36 x 100 41,28,960 = 16.3 % L-2 Describe briefly any two of the following a) Mechanical de-aeration and chemical de-aeration b) Functions of a steam trap c) Describe the operation of regenerator for high temperature furnace An s a) Mechanical de-aeration and chemical de-aeration In de-aeration, dissolved gases, such as oxygen and carbon dioxide, are expelled by preheating the feed water before it enters the boiler. Mechanical de-aeration Mechanical de-aeration for the removal of these dissolved gases is typically utilized prior to the addition of chemical oxygen scavengers. Mechanical de-aeration is based on Charles' and Henry's laws of physics. Simplified, these laws state that removal of oxygen and carbon dioxide can be accomplished by heating the boiler feed water, which reduces the concentration of oxygen and carbon dioxide in the atmosphere surrounding the feed water. Mechanical de-aeration can be the most economical. They operate at the boiling point of water at the pressure in the de-aerator. They can be of vacuum or pressure type. Chemical de-aeration While the most efficient mechanical deaerators reduce oxygen to very low levels (0.005 mg/litre), even trace amounts of oxygen may cause corrosion damage to a system. Consequently, good operating practice requires removal of that trace oxygen with a chemical oxygen scavenger such as sodium sulfite or hydrazine. Sodium sulphite reacts with oxygen to form sodium sulphate, which is removed through blow down. Hydrazine reacts with oxygen to form nitrogen and water. It is invariably used in high pressures boilers when low boiler water solids are necessary, as it does not increase the TDS of the boiler water. b) Functions of a steam trap The three important functions of steam traps are: 1 To discharge condensate as soon as it is formed in the steam line / pipes. 2 3 Not to allow steam to escape. To be capable of discharging air and other incondensable gases from the steam pipe. c) Operation of regenerator for high temperature furnace There are two sets of regenerators consisting of refractory bricks. In one path, the flue gases flow heating up the chequered refractory bricks on one side, while through the 12 Paper 2 - Set A Key other path, air for combustion flows which picks up the heat from heated chequered refractory bricks on the other side. The cycle reverses with the time interval. A heat exchanger is to be designed to condense the hydrocarbon vapor mixture from a distillation column at the rate of 11.0 kg/sec which is available at its saturation temperature of 120 C. The latent heat of condensation of the hydrocarbon vapor mixture is 450 kJ/kg. The cooling water at 32 C is used in counter-current direction at the rate of 58 kg/sec to condense the vapor mixture. The specific heat of cooling water is 4.18 kJ/kg oC. Determine LMTD and area of the heat exchanger surface if the overall heat transfer co-efficient is 550 J/m 2s C. Heat loss in hydrocarbon vapour mixture = heat gain in cooling water Ans 11 * 450 = 58 * 4.18 * (T 32) T = 52.4 C L-3 Water leaves the exchanger at 52.4 C LMTD = (120-32)-(120-52.4)/ln(120-32)/(120-52.4) LMTD of counter flow pattern = 77.4 C Q = m*Cp* T = U * A * LMTD 58 * 4.18 * (52.4 32) * 1000 = 550 * A * 77.4 A = 116.3 m2 L-4 Area of the heat exchanger surface is 116.3 m2 A steam pipeline of 250 mm outer diameter & 100 meters long is insulated with 150 mm Mineral wool insulation. As an energy conservation measure, the management has upgraded the existing Mineral wool insulation with efficient calcium silicate insulation. Calculate the economics in terms of payback if the insulation is upgraded at a cost of 20 lakhs. Given: Operating hours : 8000 Boiler efficiency : 87 % Fuel Oil Cost : Rs. 45,000 per ton GCV of the fuel : 10,200 kcal/kg Thickness of Mineral wool insulation : 150 mm Thickness of Calcium Silicate insulation : 100 mm Surface temperature with Mineral wool insulation : 70 C Surface temperature with Calcium silicate insulation : 55 C Ambient temperature : 30 C _________________________ Bureau of Energy Efficiency 13 Paper 2 - Set A Key Ans Heat loss with Mineral wool insulation = {10 + (Ts Ta)/20} x (Ts Ta) = ( 10 + (70 30)/20 } x (70 30) = 480 kCal/hr per Square meter Heat loss with Calcium silicate insulation = ( 10 + (55 30)/20 } x (55 30) = 281.25 kCal/hr Sq. m Surface Area with Mineral wool = 3.14 D L = 3.14 x 0.550 x 100 = 172.7 Square meter Surface Area with Calcium Silicate= 3.14 x 0.450 x 100 = 141.3 Square meter Heat loss with Mineral wool Heat loss with Calcium silicate = 480 x 172.7 = 82896 kCal/hr = 281.25 x 141.3 = 39741 kCal/hr (82,896 - 39,741) x 8,000 x 45,000 10,200 x 1000 x 0.87 Annual savings = = Payback period L-5 14 = = Rs. 17.5 Lakhs / year 20 / 17.5 1.14 years = 13.7 months The energy flow diagram in a cogeneration plant in paper industry is given below. Paper 2 - Set A Key Calculate the following i) Input coal consumption per hour if feed water temperature is 50 oC ii) Heat to power ratio of cogeneration plant iii) % turbine and generator losses Ans Input coal consumption = Q=50,000 x(770-50) / (0.8 x 4000) =11.25 Tons/ hr Heat to power ratio = (50,000 x 660) / (4600 x 860) = 8.34 Turbine and generator loss = 50000 x 770 (4600 x 860 +50,000 x 660)/10 6 = 1.544 Million kCal % loss = 1.544 x 106 x 100 / (50,000 x 770) =4% L-6 List down any ten points that need attention while selecting biomass fluidised bed combustion boiler The following areas need attention with biomass fed boilers: Uneven spreading of biomass fuel on boiler grate can lead to secondary combustion in the super-heater zone, resulting in overheating of super heater tubes and fluctuations in steam pressure. Frequent erosion of super-heater and economizer coils can occur, due to high silica content in the biomass, especially in rice husk. High extraneous matter in biomass (sand and mud) causes tube fouling and fluidized bed to be drained more frequently, with resultant heat loss. Carbon and dust coating of boiler tubes results in lowering of steam temperatures, especially during soot blowing. Presence of Pesticides (used during farming) adds to tube failure frequencies; mainly due to potassium constituents. Corrosive constituents in biomass adversely affect boiler internals, especially the superheater tubes. Chloride content in certain types of biomass (like cotton stalk, 8 9%) can combine _________________________ 15 Bureau of Energy Efficiency Paper 2 - Set A Key with sodium and potassium in high temperature regime to aggravate the corrosion process. Some boilers which use Red Gram husk/twigs as fuel pose corrosion problems at the cold end (i.e., secondary super-heater and economizer tubes), due to the sulfur content. The biomass fuel mix fed to the boiler, in quite a few cases, contains a combination of 6 to 7 biomass types. Each biomass has a separate air-to fuel ratio, and it is difficult to set a workable air fuel ratio. High moisture content in the biomass causes frequent jamming of the fuel in feeders, leading to fluctuations in steam pressure and temperature. High moisture content in the biomass also leads to plugging and choking of closely spaced heating surfaces. This situation is further aggravated by the super-heater tube coil with very close spacing, often the result of a desire to achieve a compact design. Due to biomass fuel size variation, occurance of unburnts in flue gases and bottom ash is high, resulting in lower efficiency and also variation in steam pressure and temperature. Absence of biomass feed rate measurement mechanism leaves little room for accurate assessment of heat rate/efficiency. Providing a weighing mechanism is difficult on account of different biomass fuel combinations being used, with different (and low) bulk densities. Degradation of biomass during storage in exposed ambient wet atmosphere leads to loss of heat value. Loss of material due to windage and carpet loss, coupled with loss of heat value on account of decay (inherent biomass characteristics), can cause an error in assessment of input fuel energy (as the input heat is customarily evaluated based on received biomass quantities and GCV). ------- End of Section - III --------- 16

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