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16th National Certification Exam Energy Managers & Auditors SEPTEMBER 2015 Paper 2

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Paper 2 Set A REGULAR Regn No: __________________ Name : __________________ (To be written by the candidate) 16th NATIONAL CERTIFICATION EXAMINATION FOR ENERGY MANAGERS & ENERGY AUDITORS September, 2015 PAPER 2: Energy Efficiency in Thermal Utilities Date: 19.09.2015 Timings: 1400-1700 HRS Duration: 3 HRS Max. Marks: 150 General instructions: o o o o o Please check that this question paper contains 8 printed pages Please check that this question paper contains 64 questions The question paper is divided into three sections All questions in all three sections are compulsory All parts of a question should be answered at one place Section I: a) b) c) 1. Answer all 50 questions Each question carries one mark Please hatch the appropriate oval in the OMR answer sheet with Black Pen or HB pencil Which one of the following is not true with respect to the role of nitrogen in the combustion of any fuel a) b) c) d) 2. produces oxides of nitrogen reduces the volume of combustion by-products dilutes the flue gases carries useful heat in flue gases Which one of the following fuel has the highest hydrogen content and lowest sulphur content a) coal 3. b) fuel oil c) natural gas d) LSHS Which of the following yields a low CO2 reading a) soot deposits on boiler tubes c) proper air-fuel mixture 4. Marks: 50 x 1 = 50 OBJECTIVE TYPE b) flue gas bypass in air pre-heater d) air ingress in flue gas duct Which of the following salt causes temporary hardness in water a) calcium sulphate c) calcium chloride _________________________ Bureau of Energy Efficiency b) calcium bicarbonate d) calcium nitrate 1 Paper 2 Set A REGULAR 5. Which of the following requires the largest amount of oxygen/kg of substance for combustion a) carbon 6. b) carbon c) sulphur b) low fixed carbon b) activated carbon c) un-slaked lime b) softening c) de-aeration b) water walls d) all of the above c) diesel oil d) kerosene What happens when the float in a float trap develops a puncture b) loss of live steam c) fails to open d) fails to close Transfer of heat without a conveying medium is possible with b) radiation c) convection d) none of the above The velocity of steam in steam pipe is directly proportional to a) number of bends in pipe c) length of pipe 18. c) re-heaters b) furnace oil a) conduction 17. b) packaged boiler d) pulverized fuel boiler Which fuel among the following needs temperature control during storage a) loss of condensate 16. d) all of the above Which of the component is common to supercritical boiler and sub critical boiler for power generation a) coal 15. d) all of the above Which of the following boiler utilizes the combination of suspension firing and great firing a) economizer 14. d) none of the above Which of the following boiler water treatment ensures complete removal of salts a) traveling grate stoker boiler c) spreader stoker boiler 13. c) less ash Which of the following can be used as desiccant in boiler preservation a) demineralization 12. b) fouling coefficient d) effectiveness Which of the following contribute to spontaneous combustion of coal a) silica gel 11. d) methane Which of the following depends on physical properties of fluids as well as geometry of the heat exchanger a) low Volatile matter 10. d) calorific value of fuel Which of the following has the lowest stoichiometric oxygen demand (kg/kg of fuel) a) overall heat transfer coefficient c) LMTD (Log Mean Temperature Difference) 9. d) nitrogen b) boiler efficiency c) enthalpy of steam a) hydrogen 8. c) sulphur Which of the following is not required for determining economic thickness of steam line a) cost of fuel 7. b) hydrogen b) 5th power of the diameter of pipe d) specific volume of steam The unit of overall heat transfer coefficient is a) W/m2 K _________________________ Bureau of Energy Efficiency b) W 2/m2 K c) W 2 /m3 K d) W/m3 K 2 Paper 2 Set A REGULAR 19. The thermal resistance of an insulation a) decreases with increased thermal conductivity b) increases with increased thermal conductivity c) decreases with decreased thermal conductivity d) has no relation with thermal conductivity 20. The stoichiometric amount of air required to burn 1 kg of methane is a) 69.57 21. b) 4 c) 17.39 The parameter assumed to remain constant during LMTD calculation of a Heat exchanger is a) temperature drop c) specific heat of fluids 22. b) heat transfer area d) none of the above The material used to control SOx in the FBC boiler is a) limestone 23. b) alumina c) silica b) conductivity of refractory d) all of the above The chemical used to prevent oxidation in boiler feedwater is a) sodium sulphite c) calcium phosphate 25. b) sodium phosphate d) magnesium phosphate The best time for intermittent blow down in a boiler a) High load under full pressure c) high load under partial pressure 26. b) low load under full pressure d) low load under partial pressure The amount of CO2 produced in complete combustion of 18 Kg of carbon a) 50 27. b) 44 c) 66 b) air locking b) NOx c) SOx d) all of the above d) all of the above Portable fyrite is used for the measurement of a) CO2 content in flue gas c) stack temperature 31. c) water hammer Presence of _____ in flue gas confirms incomplete combustion in furnace a) CO 30. b) decrease with excess air d) increase with CO in combustion gases Removal of condensate from main steam line is done to prevent a) steam locking 29. d) 792 Scale losses in reheating furnaces will a) increase with excess air c) have no relation with excess air 28. d) fly ash The heat loss in a furnace depends on a) emissivity of walls c) wall thickness 24. d) 16 b) O2 content in flue gas d) both (a) & (b) On an inverted bucket trap, what happens to the bucket as the trap fills with water a) it rises b) it inclines _________________________ Bureau of Energy Efficiency c) it sinks d) it remains stationary 3 Paper 2 Set A REGULAR 32. NOx formation in FBC boilers is minimised because of a) higher velocity of flue gas in combustion chamber b) higher pressure of the air supplied c) lower temperatures in the bed and combustion chamber d) higher contact of solid particles in the flue gas 33. In which zone of cupola furnace does the conversion of CO2 to CO take place? a) combustion zone 34. b) melting zone c) reduction zone d) preheating zone In a fire-tube boiler, soot forms on a) outside tube surface c) waterside surface 35. If the volatile matter in coal is low, which of the following equipment is the best waste heat recovery option in a boiler a) economiser 36. b) air preheater b) density b) dry steam d) high pressure steam Furnace wall heat loss depends on b) velocity of air around the furnace d) all of the above For flash steam calculation, flash steam quantity available depends upon a) condensate pressure and flash steam pressure c) steam enthalpy at atmospheric pressure 40. d) unpredictable b) ash content in fuel d) all of the above b) partly convert to flash steam d) fully convert to flash steam Coal size of 75% below 75 micron is required for use in a) spreader stoker boiler c) fluidized bed boiler 44. c) less than zero Condensate at pressure of 4 kg/cm2 and 160oC temperature when exposed to atmosphere will a) become super heated c) remain as condensate 43. b) zero Corrosion in chimney, air pre-heater and economizer is mainly influenced by a) sulphur content in fuel c) moisture content in fuel 42. b) steam pressure d) total heat of flash steam Enthalpy of evaporation of any vapour at its critical point will be a) more than zero 41. d) humidity Heat transfer rate for indirect heating application will be less if we heat with a) temperatures of external wall surfaces c) thermal conductivity of wall brick 39. d) heat pipe c) water content a) saturated steam c) superheated steam 38. c) deaerator Hydrometer is used for the measurement of a) viscosity 37. b) inside tube surface d) water wall surface b) chain grate stoker boiler d) pulverized fuel boiler Ceramic coating is used in furnaces because it enhances _________________________ Bureau of Energy Efficiency 4 Paper 2 Set A REGULAR a) conductivity c) emissivity 45. b) convective heat transfer coefficient d) radiation factor As the pressure of water increases from 1kg/cm 2 to 8 kg/cm2, the values of enthalpy of steam and enthalpy of evaporation respectively a) increases & remains the same c) decreases & increases 46. b) increases & decreases d) decreases & remains the same An increase in bulk density of a refractory increases its a) volume stability c) Resistance to slag penetration 47. A small quantity of leakage of stored Liquid LPG evaporates to produce about ____ times of volume of gas. a) 100 48. b) heat capacity d) all of the above b) 150 c) 250 d) 350 A high carbon monoxide reading indicates a) moisture in the fuel c) high excess air 49. 2 m lift of condensate in steam pipe will result in back pressure of a) 0.02 bar 50. b) high furnace temperature d) none of the above b) 0.2 bar c) 2 bar d) 20 bar _____ gives an estimate of heating value of coal a) ash content b) moisture content c) fixed carbon d) volatile matter -------- End of Section Section - II: SHORT DESCRIPTIVE QUESTIONS Marks: 8 x 5 = 40 (i) Answer all eight questions (ii) Each question carries five marks S-1 Determine the Energy Utilization Factor (EUF) from the following back pressure cogeneration plant diagram and data given. Back Pr.Steam P =4 kg/cm2 T =165 C Q =12MT/hr H =650kcal/kg Process Plant Condensate P= 4 kg/cm2 T= 165oC Inlet Steam P = 42 kg/cm2 T = 410 C Q = 12 MT/hr H = 760kcal/kg BPT Alternator Power 0.7 MW Back Pr Turbine Cogeneration Plant _________________________ Bureau of Energy Efficiency 5 Paper 2 Set A REGULAR Solution: Input heat to turbine = 12,000 x 760 = 91,20,000 Kcal/hr .(1 mark) Useful heat to process Plant = 12,000 x 650-165 = 5820,000 Kcal/hr .(1 mark) .(1 mark) Useful Electrical output in alternator = 700x860= 602000 Kcal/hr Energy Utilization Factor (EUF) = [(602000+5820,000) /91,20,000] x 100 = 70.42% .(2 marks) S-2 For combustion of 500 kg/hr of natural gas containing 100% methane, calculate the percentage of CO2 in the flue gas while 15% excess air is supplied. Ans: CH4 + 2 O2 CO2 + 2H2O 1 mole of Methane requires 2 moles of Oxygen. 16 Kg of Methane requires 64 Kg of Oxygen. 16 Kg of Methane produces 44 Kg of CO 2. 500 Kg/hr of Methane requires 2000 Kg/hr of Oxygen. 500 Kg/hr of Methane produce 1375 Kg/hr of CO2. . (1 mark) Theoretical air required for combustion = 2000 / 0.23 = 8696 Kg/hr . (1 mark) Considering 15% excess air, Actual air supplied for combustion is = 8696 * 1.15 = 10,000.4 Kg/hr of air . (1 mark) Flue gas generation with 15% excess air = 500 + 10,000.4 = 10,500.4 Kg/hr . (1 mark) % CO2 in the flue gas = (1375 / 10,500.4)x 100 = 13.1 % . (1 mark) _________________________ Bureau of Energy Efficiency 6 Paper 2 Set A REGULAR S-3 In a sugar mill, a process requires 5000 kg/hr of dry saturated steam at 7 kg/cm2 (g). For the flow velocity not to exceed 28 m/s, determine the pipe diameter size for distribution of steam. Specific volume at 7 kg/cm2 = 0.24 m3/kg. Ans: The velocity of steam maximum = 28 m/s Specific volume at 7 kg/cm2 = 0.24 m3/kg Mass flow rate Volumetric flow = 5000 kg/hr = 5000/3600 = 1.389 kg/sec = 1.389 x 0.24 = 0.333 m3/sec . (1 mark) Therefore, using: Volumetric flow rate(m3/s) = Velocity (m/s) x Cross sectional area (m2) . (1 mark) D 4 Volumetric flowrate Flow velocity D 4 0.333 28 D 0.123 m or 123 mm . (3 marks) Since the steam velocity must not exceed 28 m/s, the pipe size must be at least 123 mm; the nearest commercially available size, 150 mm, would be selected. S-4 Paddy husk is being used as a combustion fuel in a water tube boiler. The ultimate analysis of fuel is given below. Calculate theoretical amount of air required per 100 kg of husk for the combustion from the following data. Ultimate Analysis of Typical Agro Residues Moisture Mineral Matter Carbon Hydrogen Nitrogen Sulphur Oxygen _________________________ Bureau of Energy Efficiency % 10.8 16.7 34.0 5.0 0.9 0.1 32.5 7 Paper 2 Set A REGULAR Ans: Considering a sample of 100 kg of paddy husk. Component in fuel % (wt) in fuel Equation Specific stoichiometric oxygen required Actual stoichiometric oxygen required Carbon 34 C + O2 = CO2 2.67 90.78 12 + 32 = 44 (32/12) (34 x 2.67) H2 + 0.5 O2 = H2O 8.0 40.0 2 + 16 = 18 (16/2) (5 x 8) S + O2 = SO2 1.0 0.1 32 + 32 = 64 (32/32) (0.1 x 1) Hydrogen Sulphur 5 0.1 Oxygen 32.5 (-)32.5 Nitrogen 0.9 - Moisture 10.8 - Mineral matter 16.7 - Total 100 98.38 .. (4 marks) Total Oxygen required = 98.38 kg oxygen / 100 kg fuel Therefore theoretical quantity of dry air reqd. = 98.38 / 0.23 =427.7 kg air / 100 kg fuel (air contains 23% oxygen by wt.) .. (1 mark) S-5 (a) Why should LPG cylinders not be stored in basements or cellars? (b) Why should the stack temperature of furnace oil fired boilers not be maintained below 160-170 C? Ans: (a) LPG is a predominant mixture of propane and butane. Both propane and butane are denser than air. Consequently, the vapour flows along the ground into drains and sinks to the lowest level of the surroundings and gets ignited at a considerable distance from the source of leakage. Escape of even small quantities of LPG can give rise to large volume of vapour mixture and can cause considerable hazard. Hence there should be adequate _________________________ Bureau of Energy Efficiency 8 Paper 2 Set A REGULAR ground level ventilation where LPG cylinders are stored. For this reason LPG cylinders should not be stored in cellars or basements, which have no ventilation at ground levels. .(2.5 marks) (b) For fuels containing sulphur, low temperatures (below 160-170 C) of stack can lead to sulphur dew point corrosion. The main disadvantage of sulphur is the risk of corrosion by sulphuric acid formed during and after combustion, and condensing on cool parts of the chimney or stack, air preheater and economiser. .(2.5 marks) S-6 Calculate the electricity consumption in an induction melting furnace from the following melt cycle data Mild steel (MS) scrap charged : 1250 kg Specific heat of MS : 0.68 kJ/kg 0C Latent heat of MS : 270 kJ/kg MS melting temperature : 1450 0C Inlet MS charge temperature : 35 0C Efficiency of furnace : 70% Ans: Theoretical energy required for melting = 1250 (0.68 x (1450 35) + 270)/3600 = 427.8 kWh . (3 marks) Actual energy input to the furnace = 427.8 / 0.7 Electricity consumption = 611.2 kWh . (2 marks) S-7 Feed water is provided to a boiler from the feed water tank at 60oC, temperature of condensate water returning to the tank is 80oC, and temperature of makeup water is 27 oC. What is the amount of condensate recovered? Solution: _________________________ Bureau of Energy Efficiency 9 Paper 2 Set A REGULAR 27x + (1 x) 80 =60 Therefore x = 0.37 (37 percent makeup water or only 63 per cent of condensate is recovered). .(5 marks) S-8 Milk is flowing in a pipe cooler at a rate of 0.95 kg/sec. Initial temperature of the milk is 55 C and it is cooled to 18 C using a stirred water bath with the constant temperature of 10 C around the pipe. Specific heat of milk is 3.86 KJ/kg C. Calculate the heat transfer rate (kcal/hr) and also LMTD of the exchanger. Ans: Heat transfer in cooling milk = 0.95 * 3.86 * (55 18) = 135.7 KJ/sec =135.7 /4.18 = 32.46 kcal/sec =(32.46*3600)= 116856 kCal/hr . (2.5 marks) LMTD: DT1 = 55 10 = 45 C DT2 = 18 10 = 8 C LMTD of the heat exchanger = (45 8) / ln (45 / 8) LMTD of the heat exchanger = 21.4 C . (2.5 marks) -------- 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 a) Find out the efficiency of the furnace oil fired boiler by the direct method in an agro product manufacturing plant given the following data: Type of boiler Quantity of steam (dry) generated Steam pressure / temp _________________________ Bureau of Energy Efficiency : Furnace oil fired : 5 TPH : 10 kg/cm2(g)/ 180 0C 10 Paper 2 Set A REGULAR Quantity of oil consumed Feed water temperature GCV of Furnace oil Enthalpy of saturated steam at 10 kg/cm2 pressure Enthalpy of feed water Cost of furnace oil Annual operating hours : 0.350 TPH : 75 0C : 10400 kCal/kg : 665 kCal/kg : 75 kCal/kg : Rs 32/kg : 7200 hrs /year b) The oil fired boiler was converted to coconut shell firing maintaining the same steam and feed water parameters. i) Determine the fuel consumption per hour ii) Return on investment for the conversion scheme. Fuel fired in the boiler GCV of coconut shell Efficiency with coconut shell firing Cost of coconut shell Annual interest on capital Annual operating hours Investment towards boiler conversion : coconut shell fuel : 4200 kCal/kg : 76% : Rs 12/kg : Rs 6 lakhs /yr : 7200 hrs /year : Rs 50 lakhs Solution: a) Efficiency of furnace oil fired boiler (Direct method) Boiler Efficiency ( ) = 5000 x (665-75) / (350 x 10400) = 81% (on GCV basis) . (2.5 marks) b) i) Coconut shell fuel consumption after conversion: Fuel consumption = 5000 x (665-75) / (0.76 x 4200) = 924.2 kg/hr . (2.5 marks) ii) ROI for the conversion scheme: Annual fuel cost of furnace oil fired boiler = 350 x 7200 x 32 = Rs 8,06,40,000 /year .. (1 mark) Annual fuel cost of coconut shell fired boiler = 924.2 x 7200 x 12 = Rs 7,98,50,880/year .. (1 mark) Annual net monetary savings after conversion = [(8,06,40,000 - 7,98,50,880) 6,00,000] 50,00,000 = 3.8 % x 100 . (3 marks) _________________________ Bureau of Energy Efficiency 11 Paper 2 Set A REGULAR L-2 A liquid waste stream has a flow rate of 3.5 kg/s and a temperature of 70o C with a specific heat capacity of 4190 J/kgK. Heat recovered from the hot waste stream is used to pre-heat boiler make-up water. The flow rate of the make-up water is 2 kg/s, its temperature is 10 oC and its specific heat capacity is 4190 J/kg/K. The overall heat transfer coefficient of the heat exchanger is 800 W/m2K. If a make-up water exit temperature of 50 oC is required, and assuming that there is no heat losses from the exchanger, determine 1) The heat transfer rate 2) The exit temperature of the effluent and 3) The area of the heat exchanger required Solution : i) Heat gained by makeup water = Qc= mc cc T = 2 x 4190 x (50-10) = 335200 W = 335.2 kW ..(2 marks) ii) mh ch (th1 th2) = mc cc (tc1 tc2) 3.5 x 4190 x (70 - th2) = 2 x 4190 x (50 -10) th2 = 47.14 o C ..(3 marks) iii) Now because the water outlet temperature is above the outlet temperature of the effluent a counter-flow heat exchanger is required. LMTD = t1 t2 ln ( t1/ t2) = ((70-50)-(47.14-10) ln (70-50)/(47.14-10) LMTD = 27.69oC ..(2.5 marks) Q = UA (LMTD) A= 335200 800 x 27.69 Area = 15.13 m2 ..(2.5 marks) _________________________ Bureau of Energy Efficiency 12 Paper 2 Set A REGULAR L-3 Write short notes on any two of the following: (5 marks each) a) Plate heat exchanger (page 242 of book-2) b) Multiple effect evaporator (page 247-248 of book-2) c) Gas turbine cogeneration system L-4 (page 192 of book-2) a) In a typical fertiliser manufacturing plant, the quantity of 133200 Ton of Ammonia is produced annually, using naphtha as fuel as well as raw material (feed) and electricity from captive power plant. Naphtha as fuel Naphtha as feed raw material Electricity Ammonia production plant Ammonia Production The quantity of annual raw material consumption and its heating values are given in table. Raw material Quantity Heating Value consumption 1.Naphtha - feed 2.Naphtha - fuel 3.Electricity 66800 Ton 31200 Ton 1180 x Lakh kWh 10650 kCal / kg 10650 kCal / kg 2500 kCal/kWh Calculate the specific energy consumption of ammonia production in Gcal / Ton. b) Sketch the schematic diagram of Back Pressure Turbine and Extraction Condensing Turbine Cogeneration systems (Note: no explanation required). Answer : a) Specific Energy Consumption(SEC) of Ammonia Raw material consumption 1.Naphtha - feed 2.Naphtha - fuel 3.Electricity Quantity 66800 Ton 31200 Ton 1180 x Lakh kWh Heating Value Gcal 10650 kCal / kg 10650 kCal / kg 2500 kCal/kWh 711420 332280 295000 1338700 1 mark 1 mark 1 mark 10.05 Gcal per Ton 2marks Ammonia 133200 Ton production Specific Energy Consumption(SEC) of Ammonia production = _________________________ Bureau of Energy Efficiency 13 Paper 2 Set A REGULAR b) Schematic diagram of (i) Back Pressure Turbine and (ii) Extraction Condensing Turbine Cogeneration systems (2.5 marks for each schematic) L-5 As a part of energy conservation measure, APH (Air Pre-heater) is installed in a fired heater. The APH is designed to pre-heat 240 m3/min of combustion air to 250 C. Flue gas enters the APH at 375 C. Calculate the flue gas leaving the stack and also determine the improvement in furnace efficiency after the installation of APH with the following data Density of air : 1.15 kg/m3 Specific heat of air : 0.23 Kcal/kg C Specific heat of flue gas : 0.26 Kcal/kg C Calorific value of fuel : 9850 Kcal/kg Air to fuel ratio : 18 Efficiency of furnace : 73 % Ambient temperature : 30 C Solution: Amount of Air flow = 240 * 60 * 1.15 = 16560 Kg/hr . (1mark) Amount of fuel = 16560 / 18 = 920 Kg/hr Amount of flue gas = 16560 + 920 = 17480 Kg/hr Heat absorbed by combustion air = 16560 * 0.23 * (250 30) = 837936 Kcal/hr . (1mark) . (1mark) . (1.5 marks) _________________________ Bureau of Energy Efficiency 14 Paper 2 Set A REGULAR Temperature difference in flue gas = 837936 / (17480 * 0.26) = 184 C . (1.5 mark) = 375 184 = 191 C Flue gas leaves the stack at temp L-5 . (1 mark) Efficiency of APH = Heat absorbed by air / Heat input * 100 = 837936 * 100 / (920* 9850) = 9.2 % ..(2 marks) Overall efficiency after APH = 73 + 9.2 % = 82.2 % .. (1 mark) A process industry is equipped with a steam power plant generating 1,00,000 units/day and a separate low-pressure boiler generating at an average steam production of 8.3 Tons of steam/hour at enthalpy of 630 kcal/kg for process heating. The feed water temperature to the boiler is 70oC. The efficiencies of the steam power plant and boiler are 29% and 75% respectively. Coal is used in both cases and calorific value of coal is 3800 kcal/kg. The management proposes to commission a cogeneration plant retaining the coal as fuel. The expected energy utilization factor of the cogeneration plant is 75%. Calculate coal savings with the new cogeneration plant. SOLUTION: Heat input for separate production of power and useful heat = = = Heat input with cogeneration plant = = = Coal savings = = (100000 x 860) / (24 x 0.29) + (8.3 x (630-70) x 1000))/0.75 12356321 + 6197333 18553654 kcal/hr ..(4 marks) [(100000 x 860) /24 + (8.3 x (630-70) x 1000)] / 0.75 (3583333 + 4648000) / 0.75 10975111 kcal/hr ..(4 marks) (18553654 10975111) / 3800 1995 kg/h .. .(2 marks) . . End of Section III .. . _________________________ Bureau of Energy Efficiency 15

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