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13th National Certification Exam Energy Managers & Auditors SEPTEMBER 2012 Paper 2

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Click Here & Upgrade PDF Complete Expanded Features Unlimited Pages Documents Paper 2 - Set A Solutions 13th NATIONAL CERTIFICATION EXAMINATION FOR ENERGY MANAGERS & ENERGY AUDITORS - September 2012 PAPER 2: Energy Efficiency in Thermal Utilities Date: 15.9.2012 Timings:14:00-17:00Hrs Duration:3 Hrs Section I: OBJECTIVE TYPE (i) (ii) 1. Marks: 50 x 1 = 50 Answer all 50 questions Each question carries one mark Steam mains are run with a slope primarily to a) avoid water hammer c) avoid condensation of steam 2. 2 2 less than the saturation temperature at 3 kg/cm g 2 more than the saturation temperature at 3 kg/cm g 2 equal to the saturation temperature at 3 kg/cm g equal to the saturation temperature at 3.3 kg/cm2 g The mineral matter in coal after combustion mostly becomes a) carbon dioxide 5. b) reduces fuel costs d) increases boiler blow down If 10% air is entrained in a steam system at 3 kg/cm g then the saturation temperature of steam will be a) b) c) d) 4. b) increase the velocity of steam d) reduce radiation and convection losses Which of the following is not true of condensate recovery? a) reduces water charges c) increases boiler output 3. b) carbon monoxide c) nitrous oxide d) ash Conditioning of coal with water in certain boilers is done to a) increase unburnt losses c) minimize losses of fine coal particles 6. Max.Marks:150 b) increase GCV d) increase convection heat transfer Which of the following is false? a) LPG vapour is twice as light as air b) LPG is a mixture of propane and butane c) LPG is a gas at normal atmospheric pressure d) LPG is required to be odorized 7. , Of the following fuels which will have the highest carbon content? a) furnace oil _________________________ Bureau of Energy Efficiency b) coal c) natural gas d) paddy husk 1 Click Here & Upgrade PDF Complete Expanded Features Unlimited Pages Documents 8. 100 kg of a fuel contains 2% sulphur. For complete combustion of sulphur it will require _________kg of oxygen a) 2 9. Paper 2 - Set A Solutions b) 4 c) 50 d) 200 In the direct method of efficiency evaluation of boilers which of the following is not required? a) enthalpy of steam c) O2 in flue gas 10. b) calorific value of fuel d) mass flow rate of steam Select the incorrect statement with respect to steam a) evaporation is a constant temperature process b) higher the pressure higher is the steam saturation temperature c) higher the pressure higher is the latent heat d) latent heat at critical point is zero 11. The amount of flash steam generated from the condensate mainly depends on _____ a) sensible heat of high pressure condensate c) latent heat of flash steam 12. b) sensible heat of flash steam d) all of the above Tuyeres is a terminology associated with a) induction furnace 13. b) boiler efficiency b) SOx b) light weight d) thermal shock resistant c) CO d) CO2 b) back pressure steam turbine d) all of the above Power is to be generated from a cement kiln exhaust gas. The applicable type of cogeneration is called a) topping cycle 19. b) refractoriness under load (RUL) d) cold crushing strength An axial compressor is used in conjunction with which of the following a) gas turbine c) condensing steam turbine 18. d) heat content of fuel Low combustion temperature in FBC boilers results in the reduced formation of a) NOx 17. c) steam pressure Which of the following is not a property of ceramic fibre ? a) low thermal conductivity c) high heat capacity 16. d) cupola The softening temperature of a refractory is indicated by a) Pyrometric cone equivalent (PCE) c) creep 15. c) arc furnace In determining the economic thickness of steam pipe insulation which of the following is not required? a) cost of fuel 14. b) pusher type furnace b) trigeneration c) bottoming cycle d) none of the above The effectiveness of a heat exchanger does not depend on _________________________ Bureau of Energy Efficiency 2 Click Here & Upgrade PDF Complete Expanded Features Unlimited Pages Documents Paper 2 - Set A Solutions a) specific heat of hot fluid c) inlet temperature of hot fluid 20. An element in fuel oil responsible for corrosion in exhaust system of a boiler is a) carbon 21. b) specific heat of cold fluid d) LMTD b) hydrogen d) chlorine c) sulphur The presence of calcium and magnesium bicarbonates in feedwater to a boiler would form: a) acidic solution c) neutral solution 22. b) alkaline solution d) none of the above Turn down ratio of a burner is the ratio of a) maximum to minimum fuel input without affecting optimum excess air levels b) minimum to maximum fuel input without affecting optimum excess air levels c) maximum to average fuel input d) average to minimum fuel input 23. Comparatively, lowest excess air is required in a a) coal burner c) high pressure gas burner 24. b) low pressure oil burner d) high pressure oil burner The velocity of steam in steam pipe is directly proportional to a) number of bends in pipe c) length of pipe 25. b) specific volume of steam d) diameter of the pipe The emissivity of ceramic coatings used in furnace a) decreases with increase in furnace temperature b) Increases with increase in furnace temperature c) remains constant d) decreases with increase in furnace pressure 26. Scale losses in reheating furnaces will a) increase with excess air c) have no relation with excess air 27. b) decrease with excess air d) increase with CO in combustion gases Instrument used for measuring billet temperature in a reheating furnace is ___. a) thermograph c) Pt/Pt-Rh thermocouple with indicator 28. b) infrared pyrometer d) chrome alumel thermocouple with indicator Glass mineral wool can be applied for temperature range application upto o a) 950 C 29. o d) 750 C b) Convection c) Radiation d) All of the above The storage heat losses in a batch type furnace can be best reduced by a) insulating brick 31. o c) 1200 C Heat transfer in a reheating furnace is achieved by a) Conduction 30. o b) 500 C b) ceramic fibre c) cold face insulation d) fire brick The cogeneration system which has high overall system efficiency is a) back pressure steam turbine _________________________ Bureau of Energy Efficiency b) combined cycle 3 Click Here & Upgrade PDF Complete Expanded Features Unlimited Pages Documents Paper 2 - Set A Solutions c) extraction condensing steam turbine 32. The Brayton cycle is a characteristic of a) steam turbine 33. d) reciprocating engine b) petrol engine c) gas turbine Recuperator as a waste heat recovery system is used mainly in a a) boiler c) compressor 34. d) regenerator b) 15 C c) 25 C d) 30 C b) water content c) sulphur content d) volatile matter In the context of cogeneration turbine, the thermodynamic process taking place is a) expansion 38. c) economizer Which of the following contributes to erosive effect on burner tips during combustion? a) ash content 37. b) recuperator Density of liquid fuels are measured at a reference temperature of a) 0 C 36. b) reheating furnace d) gas turbine The device used for recovering waste heat from the textile drier exhaust a) heat wheel 35. d) none of the above b) condensation c) contraction d) both (a) & (c) Reduction of steam pressure will increase a) sensible heat c) saturation temperature 39. b) enthalpy of steam d) specific volume Ten meter lift of condensate in a distribution pipe work will result in a) 0.1 bar back pressure c) 10 bar back pressure 40. b) 1 bar back pressure d) none of the above ____________ is predominantly used as a medium for soot blowing in boilers . a) compressed air c) high pressure water 41. b) steam d) all of the above The recommended TDS level for package fire tube boilers is a) 10,000 ppm 42. b) 5,000 ppm c) 2,000 ppm d) 3,000 ppm Ideal furnace for melting & alloying is a) induction furnace c) rotary hearth 43. b) cupola furnace d) recirculating bogie furnace Commonly used flux medium in a cupola furnace a) calcium carbide b) fluorspar c) calcium carbonate d) sodium carbonate _________________________ Bureau of Energy Efficiency 4 Click Here & Upgrade PDF Complete Expanded Features Unlimited Pages Documents 44. Paper 2 - Set A Solutions Dolomite is a ________ type of refractory a) acidic 45. b) basic 3 c) gm/cc 3 b) m /kg d) none of the above Insulation used for temperatures more than 350 C is a) polyurethane 47. d) none of the above The unit of specific gravity in SI system is a) kg/ m 46. c) neutral b) polystyrene c) calcium silicate d) wood Time dependent property that determines the deformation of a refractory is a) creep c) porosity 48. b) refractoriness under load d) crushing strength Capillary wick is a part of a) heat pump 49. b) heat wheel c) heat pipe The working fluid for thermo compressor is a) low pressure steam c) compressed air 50. d) heat recovery steam generator b) high pressure steam d) waste heat from chimney Fly ash in a FBC boiler is in the range of a) 20% Section - II: b) 30% c) 40% d) none of the above SHORT DESCRIPTIVE QUESTIONS Marks: 8 x 5 = 40 (i) Answer all 8 questions (ii) Each question carries 5 marks S-1 In a paper industry, 35,000 kg/hr of soda liquor with specific heat of 0.38 kCal/kg C is heated using saturated steam at 8 bar in a heat exchanger from 65 C to 115 C. Calculate the LMTD of the exchanger & the amount of steam required for heating : using the following data Enthalpy kcal/kg Steam Pressure (bar) Steam Temperature C Water Evaporation Steam 8.0 170 170 490 660 _________________________ Bureau of Energy Efficiency 5 Click Here & Upgrade PDF Complete Expanded Features Unlimited Pages Documents Ans Paper 2 - Set A Solutions a) Heat gain by soda liquor = 35000 x 0.38 x (115-65) = 665000 Kcal/hr Heat lost by saturated steam = 665000 Kcal/hr Steam required for heating = 665000 / 490 = 1357 Kg/hr Amount of steam required for heating is 1.36 Ton/hr b)LMTD calculation = (170-115)-(170-65) Ln (170-115) (170-65) = (55-105)/ln(55/105) = 77.3 C S-2 A process requires 5.5 tonnes/hr of dry saturated steam at 7 kg/cm2g having specific volume of 0.28 m3/kg. For the flow velocity not to exceed 25 m/s, determine the pipe diameter. Ans Volumetric flow rate = 5500 x 0.28 = 1540 m3/hr = 1540/3600 = 0.43 m3/s Cross sectional area = volumetic flow rate / velocity = 0.43 / 25 = 0.017 = 0.0217 = 0.149 m (or) 150 mm 3.14 x D2/4 D2 Diameter, D S-3 a) 230 kg/hr of hot condensate from a heat exchanger is coming out at 6 bar(g) with a sensible heat of 166 kCal/kg. Using a flash vessel, the condensate is flashed to 1 bar(g) with a sensible heat of 120 kCal/kg and latent heat of 526 kCal/kg. Find out the flash steam generation in kg/hr. b) The flash steam produced above is used to heat water from 30oC to 80oC by direct injection. Calculate the quantity of hot water in that can be obtained per hour. Ans a) Flash steam available % =( S1 - S2 ) / L2 S1 = is the sensible heat of higher pressure steam S2 = is the sensible heat of the steam at lower pressure L2 = is the latent heat of flash steam (at lower pressure) Flash Steam generated = ( 166 120) x 230 526 = 20.11 Kg/hr. b) Quantity of hot water generated _________________________ Bureau of Energy Efficiency 6 Click Here & Upgrade PDF Complete Expanded Features Unlimited Pages Documents Paper 2 - Set A Solutions m x cp x (80-30) = 20.11 x (120+526) m = 260 kg/hr S-4 The evaporation ratio of a coal fired boiler is 4.50. A quantity of 600 kCal/kg of heat is added to the feed water in the boiler to produce the steam. a) If the GCV of coal is 3800 kCal/kg, find out the efficiency. b) Find out the total enthalpy of the steam as per the details of the data given below Saturation temperature = 143 oC Sensible heat = 143.7 kCal/kg Latent heat = 509.96 kCal/kg Specific volume = 0.47 m3/kg Dryness fraction of steam = 96% Ans a) Boiler efficiency (%) = Evaporation ratio x enthalpy added x 100 GCV of coal Boiler efficiency = 4.5 x 600/3800 = 71 % b) Total enthalpy of steam = 143.7 + (0.96 x 509.96 ) = 633.26 kCal/kg S-5 a. Steam should be used in the process at the lowest acceptable pressure . Explain the significance of the terms lowest and acceptable b. Explain briefly about turbine heat rate . How is it related to turbine efficiency ? Ans a. lowest : Lower the pressure higher is the latent heat which is primarily used in the process. Hence the lowest pressure would be desirable. acceptable : However the lower the steam pressure lower will be the steam temperature. Since the temperature is the driving force for heat transfer, rate of heat transfer reduces and increases process time. Therefore there is a limit to the reduction in steam pressure. b. Heat rate is the heat input to turbine, needed to produce 1 kWh of electricity Turbine efficiency is the ratio useful heat and power output, to the heat input to the turbine in Kcal or KJ, expressed as a percentage. Performance of steam turbine is also expressed as heat rate, which is the quantity of heat in kCal or KJ required to generate 1 kWh of electrical power output. Turbine heat rate is expressed in kJ/kWh. The inverse relation between heat rate and efficiency is applicable only to a power plant, since all the input energy is deployed for power generation alone. _________________________ Bureau of Energy Efficiency 7 Click Here & Upgrade PDF Complete Expanded Features Unlimited Pages Documents Paper 2 - Set A Solutions S-6 Write short notes on factors affecting wall losses in batch type reheating furnaces? Ans a) Emissivity of walls : Emissivity of fire brick refractory should be high Emissivity of most of the refractory bricks decreases with increase in temperature. High emissivity coatings whose emissivity increases with temperature can be used to increase emissivity and decrease wall losses. b) Conductivity of refractories: The refractory and insulating bricks should have low thermal conductivity. Chosing low thermal conductivity bricks will reduce wall losses. Conductivity raises with rise in temperature. Batch type furnaces can use ceramic fibre to reduce storage losses. c) Wall thickness of batch furnaces: Heat losses can be reduced by increasing the wall thickness, or through the application of insulating bricks. Outside wall temperature and heat losses for a composite wall of a certain thickness of firebrick and insulation brick are much lower due to lesser conductivity of may be worked out to reduce the heat storage. S-7 Explain any two proven methods of testing steam traps? ANS There are two proven methods of testing of steam traps: - Sound method and Temperature method. 1.Sound Method : Mechanisms within steam traps and the flow of steam and condensate through steam traps generate sonic (audible to the human ear) and supersonic sounds. Proper listening equipment, coupled with the knowledge of normal and abnormal sounds, can yield reliable assessments of steam trap working condition. Listening devices range from a screwdriver or simple mechanic's stethoscope that allow listening to sonic sounds. 2.Temperature Method: Saturated steam and condensate exist at the same temperature. So it's not possible to distinguish between the two based on temperature. Still, temperature measurement provides important information for evaluation purposes. A cold trap (i.e., one that is significantly cooler than the expected saturated steam temperature) indicates that the trap is flooded with condensate, assuming the trap is in service. On the other hand, the temperature downstream of the trap will be nearly constant if significant steam is getting past the trap. At the low-end, spitting on the trap and watching the sizzle provides a general indication of temperature. _________________________ Bureau of Energy Efficiency 8 Click Here & Upgrade PDF Complete Expanded Features Unlimited Pages Documents Paper 2 - Set A Solutions Finally, non-contact (i.e., infrared) temperature measuring devices provide the precision of thermometers and thermocouples without requiring physical contact. Non-contact temperature measurement makes it easier to evaluate traps that are relatively difficult or dangerous to access closely. S-8 Ans A vessel has to be cooled from 90 C to 55 C. The mass of the vessel is 2 tonnes. The specific heat of vessel material is 0.18 kCal/kg C. The vessel is cooled with water which is available at 28 C. The maximum allowed increase in water temperature is 5 C. Calculate the quantity of water required for vessel cooling. Mass of vessel (m) = 2000 kg Specific heat (Cp) = 0.18 kCal/kg C Initial vessel temperature (T1) = 90 C Desired vessel temperature (T2) = 55 C Total heat that has to be removed from the vessel = m x Cp x (T1 - T2) = 2000 x 0.18 x (90-55) = 12600 kCal Quantity of water required = M kg Specific heat of water = 1 kCal/kg C Inlet cooling water temperature (T3) = 28 C Maximum cooling water outlet temperature (T4) = 33 C Heat removed by water, 12600 = M x 1 x (33 - 28) Quantity of water required , M = 12600/5 = 2520 kg ------- End of Section - II --------- Section - III: LONG DESCRIPTIVE QUESTIONS Marks: 6 x 10 = 60 (i) Answer all 6 questions (ii) Each question carries 10 marks L-1 Paddy husk is being used as a fuel in a water tube boiler. The ultimate analysis of fuel is given below. Calculate the theoretical quantity of air required for complete _________________________ Bureau of Energy Efficiency 9 Click Here & Upgrade PDF Complete Expanded Features Unlimited Pages Documents Paper 2 - Set A Solutions combustion and also compute the quantity of CO2, H2O and SO2 generated per 100 kg of fuel. The ultimate analysis of paddy husk is given below. Ultimate analysis of paddy husk Moisture Mineral Matter Carbon Hydrogen Nitrogen Sulphur Oxygen GCV (kCal/kg) ANS % 10.8 16.7 34.0 5.0 0.9 0.1 32.5 3570 Considering a sample of 100 kg of paddy husk. The chemical reactions are: Oxygen required for complete combustion of carbon: CO2 124.78 CO2 C+ O2 (34.0) C + (34 x 2.67) O2 90.78 Oxygen required for complete combustion of hydrogen: (5) H2 + (5 x 8) O2 H2O H2 + O2 45 H2O 40 Oxygen required for complete combustion of sulphur: S (0.1) S + O2 + (0.1 x 1) O2 SO2 0.2 SO2 0.1 Total Oxygen required = 90.78 + 40 + 0.1 = 130.88 Oxygen already present in 100 kg fuel (given) Additional Oxygen Required = 130.88 -32.5 Therefore quantity of dry air reqd. = (98.38) / 0.23 CO2 generated per 100 kg of fuel H2O generated per 100 kg of fuel L-2 = 124.78 kg = 45 kg SO2 generated per 100 kg of fuel = 32.5 kg = 98.38 = 427 kg = 0.2 kg In a crude distillation unit of a refinery, furnace is operated to heat 500 m3/hr of crude oil from 255 C to 360 C by firing 3.4 tons/hr of fuel oil having GCV of 9850 kcal/kg. As an energy conservation measure, the management has installed an air preheater _________________________ Bureau of Energy Efficiency 10 Click Here & Upgrade PDF Complete Expanded Features Unlimited Pages Documents Paper 2 - Set A Solutions (APH) to reduce the flue gas heat loss. The APH is designed to pre-heat 57 tonnes/hr of combustion air to 195 C. Calculate the efficiency of the furnace before & after the installation of APH. Consider the following data: Specific heat of crude oil Specific heat of air Specific gravity of Crude oil Ambient temperature ANS = 0.6 kcal/kg C = 0.24 kcal/kg C = 0.85 = 28 C. Before the installation of APH Heat gain by the crude Heat input to the furnace Efficiency of the furnace = 500 x 1000 x 0.85 x 0.6 x (360-255) = 26775000 Kcal/hr = 3.4 x1000x 9850 = 33490000 kcal/hr = 26775000 / 33490000 = 80 % After the installation of APH Heat gain by the crude = 500 x 1000 x 0.85 x 0.6 x (360-255) = 26775000 Kcal/hr Heat gain by Air-preheater = 57 x 1000 x 0.24 x (195-28) = 2284560 Kcal/hr Heat reduction in input to the furnace = Heat gain by Air-preheater New Heat input to the furnace= 33490000 2284560 = 31,205,440 Efficiency of furnace after installation of APH = 26775000 / 31,205,440 = 85.8 % L3 The management of a foundry is considering retrofitting the existing heat treatment furnace with hot face insulation of 75 mm ceramic fibre. (Note: Hot face insulation is known as veneering: ie over the existing refractory lining, ceramic fibre modules are applied to reduce the heat loss during operation and heat storage loss in refractory structure). Furnace Operating data: Heat Treatment furnace Furnace Capacity Fuel type : : : (Bogey Type) Batch Operation 5 Ton (per batch) Furnace Oil Surface Area of Side walls Back Wall : : (1.4 x 4.5) x 2 = 12.6 m2 0.95 x 1.4 = 1.33 m2 _________________________ Bureau of Energy Efficiency 11 Click Here & Upgrade PDF Complete Expanded Features Unlimited Pages Documents Paper 2 - Set A Solutions Roof Refractory Type : : 0.95 x 4.5 = 4.3 m2 Fire Bricks Wall Thickness Side walls : Arch : Number of cold starts per month: Number of batches per month : Fuel Cost : 18 inches 13.5 inches 5 Nos. 15 Nos. Rs 48/ kg GCV of furnace oil 10200 kCal/kg : Heat Storage (kCal /m2) for batch operation and cold start from walls and roof area are given below. For batch operation Cold Start Existing(with only fire bricks) Wall 79480 75 mm Veneering+ fire bricks 45350 Roof 74770 31,401 Existing(with only fire bricks) 116697 75 mm Veneering+ fire bricks 23,964 97,236 16,438 For batch operation furnace is heated from 300oC to 850oC For cold start up furnace is heated from ambient 30 oC to 850oC Calculate the following due to veneering a) Total heat loss reduction per month from wall and roof during batch operation. b) Total heat loss reduction per month from wall and roof during cold starts. Ans Heat loss calculation for batch operation Heat reduction from Wall per m2 = 79480-45350 =34130 Kcal Heat reduction from total side wall & back wall = 34130 x13.93 =475430.90 Kcal Heat reduction from roof per m2 = 74770- 31401 =43369 Kcal Heat reduction from total roof area = 43369 x 4.3 = 186486.7 Kcal Total heat reduction per batch from wall& roof = 475430. 90 + 186486.7 = 661917.60 Number of batches per month = 15 Nos Total heat reduction per month from wall& roof = 661917.6 x15 = 9928764 Kcals/month Heat loss calculation for Cold Start Heat reduction from Wall per m2 _________________________ Bureau of Energy Efficiency = 116697.5- 23,964.50 = 92733 Kcal 12 Click Here & Upgrade PDF Complete Expanded Features Unlimited Pages Documents Paper 2 - Set A Solutions Heat reduction from total side wall & back wall = 92733 x13.93 = 1291770.69 Kcal Heat reduction from roof per m2 = 97,236 - 16,438.00 = 80798 Kcal Heat reduction from total roof area = 80798 x 4.3 = 347431.4 Kcal Total heat reduction per batch from wall& roof =1291770.69 + 347431.4 =1639202 Number of cold starts per month =5 Nos. Total heat reduction per month from wall& roof = 8196010 Total heat reduction per month from operation and cold start =1,81,24,774kCal/month L-4 a) Find out the efficiency of the furnace oil fired boiler by direct method in a agro product manufacturing plant with the data given below: Type of boiler Quantity of steam (dry) generated Steam pressure / temp Quantity of oil consumed Feed water temperature GCV of Furnace oil Enthalpy of saturated steam at 10 kg/cm2 Enthalpy of feed water : Furnace oil fired : 5 Ton per hour (TPH) : 10 kg/cm2(g)/ 180 oC : 0.350 TPH : 75 oC : 10400 kCal/kg : 665 kCal/kg : 75 kCal/kg b) The above furnace oil fired boiler was converted to coconut shell firing. Determine the boiler efficiency by direct method after conversion. GCV of coconut shell fuel : 4565 kCal/kg Quantity of coconut shell consumed for the same steam demand and pressure. : 850 kg/hr c) The cost of fuel and operating hour of boiler are given below. Operating hour/ year = 5000 hr Cost of furnace oil per ton = Rs 40000/ton Cost of coconut per ton = Rs 5000/ton Find out the annual cost saving due to the fuel substitution fuel in the above boiler? a)Boiler efficiency with furnace oil firing : ANS Boiler Efficiency ( ) Boiler efficiency = 5000 x (665-75) x 100 / (350 x 10400) = 81% (on GCV basis) b)Boiler efficiency with coconut shell fuel firing : Boiler Efficiency ( ) = 5000 x (665-75) x 100/ (850 x 4565) Boiler efficiency = 76% (on GCV basis) c) Annual cost saving Annual furnace oil cost _________________________ Bureau of Energy Efficiency = 5000Hr x 0.35 x Rs 40000 13 Click Here & Upgrade PDF Complete Expanded Features Unlimited Pages Documents Paper 2 - Set A Solutions = Rs.7.0 crore Annual coconut shell Cost Annual cost saving L5 = 5000 hrs x 0.85x Rs.5000 = Rs. 2.125 crore = 7.0- 2.125= Rs 4.875 Crore Explain briefly any two of the following a) Heat Wheel b) Topping and bottoming cycles for cogeneration with examples c) Economic thickness of insulation Ans a) Heat wheel Widely used in low to medium temperature waste heat recovery systems. A disk rotates between two side-by-side ducts: one a cold gas duct, the other a hot gas duct. As the disk slowly rotates, sensible heat (moisture that contains latent heat) is transferred to the disk by the hot air and, as the disk rotates, from the disk to the cold air. b) Topping and bottoming cycles for cogeneration with examples In a topping cycle, the fuel supplied is used to first produce power and then thermal energy, which is the by-product of the cycle and is used to satisfy process heat or other thermal requirements ex. steam turbine, Diesel engine, Gas turbine etc. In a bottoming cycle, the primary fuel produces high temperature thermal energy and the heat rejected from the process is used to generate power through a recovery boiler and a turbine generator Power production from waste heat of cement plant, sponge iron plant etc c) Economic thickness of insulation As the insulation thickness increases heat loss cost reduces, At the same time insulation cost increases. Hence there is an optimum limit to thickness. The economic thickness of insulation is the thickness at which the combined cost is least. _________________________ Bureau of Energy Efficiency 14 Click Here & Upgrade PDF Complete Expanded Features Unlimited Pages Documents L6 Paper 2 - Set A Solutions List five energy conservation measures in ANY TWO of the following: a) Furnaces b) Steam distribution systems c) Boilers a) Furnaces Ans 1) 2) 3) 4) 5) 6) 7) 8) 9) Complete combustion with minimum excess air Correct heat distribution Operating at the desired temperature Reducing heat losses from furnace openings Maintaining correct amount of furnace draught Optimum capacity utilization Waste heat recovery from the flue gases Minimum refractory losses Use of Ceramic Coatings b) Steam Distribution systems 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Monitoring Steam Traps Avoiding Steam Leakages Providing Dry Steam for Process Utilising Steam at the Lowest Acceptable Pressure for the Process Minimising Heat Transfer Barriers Proper Air Venting Condensate Recovery Insulation of Steam Pipelines and Hot Process Equipments Flash Steam Recovery Reducing the Work to be done by Steam c) Boilers 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. Reduce Stack Temperature Feed Water Preheating using Economiser Combustion Air Preheating Ensure complete Combustion Control excess air Radiation and Convection Heat Loss Automatic Blowdown Control Reduction of Boiler Steam Pressure Variable Speed Control for Fans, Blowers and Pumps Ensure boiler Loading for Efficiency Boiler Replacement for efficiency _________________________ Bureau of Energy Efficiency 15

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