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16th National Certification Exam Energy Managers & Auditors SEPTEMBER 2015 Paper 4

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Paper 4 Set B REGULAR 16th NATIONAL CERTIFICATION EXAMINATION FOR ENERGY MANAGERS & ENERGY AUDITORS September, 2015 PAPER 4:Energy Performance Assessment for Equipment and Utility Systems Date: 20.09.2015 Timings: 14:00-16:00 HRS Duration: 2 HRS Max. Marks: 100 o Section - I: BRIEF QUESTIONS Marks: 10 x 1 = 10 (i) Answer all Ten questions (ii) Each question carries One mark S-1 Ans S-2 Ans S-3 Ans S-4 Ans The Net present value of a Energy Conservation Project is Rs.38784/- and the initial capital investment Rs 1,50,000/- calculate the Profitability Index of the project. PI = 38784 = 0.258 1,50,000 Between a natural gas fired boiler and oil fired boiler which will have a higher percentage of hydrogen loss in flue gas? Why? Gas fired boiler. Because the hydrogen percentage is more in natural gas compared to oil. If the condenser back pressure is 82 mm Hg, calculate the condenser vacuum if the atmospheric pressure is 755 mmHg. Condenser vacuum, mmHg = (Atmospheric pressure, mmHg - Condenser back pressure, mmHg) = (755 - 82) = 673 mmHg. For a process requiring indirect heating to 200 oC, thermic fluid is preferred to steam as a heat carrier. Why ? Because for steam to be heated to high temperatures, the pressure required will be very high. S-5 Ans After cleaning of choked AHU filter, AHU fan power increased. Why? Due to less resistance, the air flow increased. S-6 Ans S-7 Why is the exhaust temperature of furnace oil fired systems limited to about 170 0C? Acid dew point due to presence of sulphur Other than exhaust gas what is the major source of waste heat recovery in a water _______________________ Bureau of Energy Efficiency 1 Paper 4 Set B REGULAR Ans S-8 Ans S-9 Ans cooled DG set? Engine jacket cooling water In poorly loaded motor, current measurements are not a right indicator of motor loading. Why? PF will be low. If the coal GCV is 4500 kcal/kg and specific coal consumption is 0.60 kg/kWh, what is the Power station Gross efficiency? (860 /(4500 x 0.60)) x100 = 31.85% S-10 The dry bulb and wet bulb temperatures of air entering an air washer are 35 and 28 0 C respectively. If the saturation efficiency is 90 %, calculate the air temperature leaving the air washer. Ans 90% = 35 -Tout 35-28 Tout = 28.7oC . End of Section - I . Section - II: SHORT NUMERICAL QUESTIONS Marks: 2 x 5 = 10 (i) Answer all Two questions (ii) Each question carries Five marks L-1 A luxury hotel is using a diesel fired heater with an efficiency of 70% for supplying hot water at 60oC from an initial temperature of 20oC. The hot water requirement is 24,000 litres per day. The management is considering to install a specially designed electric heat pump for the specific high hot water temperature requirement with a heat pump coefficient of performance (C. O. P.) of 2.5. Find out the reduction in daily operating cost with heat pump in place of diesel fired heater ignoring auxiliary energy consumption. The following data are given. Electricity cost Diesel cost G.C.V. of diesel = = = Rs.10/kWh Rs.50/litre 9100 kcal/litre Ans Diesel required _______________________ Bureau of Energy Efficiency 2 Paper 4 Set B REGULAR For hot water heater = [24000 LitHotwater/ day ) x (60-20oC) x (1 kca/LitoC)] (0.7 Effy x 9100 kcal/Lit diesel ) 1 Mark = 150.7 Lit diesel /day Diesel cost / day = 150.7 x 50 = 7535 Rs./day 1 Mark COP = Heat pump refrigeration effect / input electrical energy or Input electrical energy , kW = Heat pump refrigeration effect, kcal COP x 1 kW or Input electrical energy , kW = Heat pump refrigeration effect, kcal COP x 860 kcal/hr Electrical energy required with heat = 24000 x 1 x (60 20) (2.5 x 860)(1 Mark) pump of COP = 2 Energy input with heat pump = 446.51 Kwh/day Operating cost with heat pump = 446.51 x 10 = 4465.1 Rs./day .. 1 mark Reduction in operating cost = 7535 4465.1 = Rs.3069.9 /day .. 1 mark L-2 A pump is drawing water through a 150 mm diameter pipe with a suction head of 3 m below the pump centre line. Find out the pump efficiency if the actual power input the motor is 16.7 kW at a motor efficiency of 90 %. The discharge pressure is 4.5 kg/cm2 and the velocity of water through the pipe as measured by an ultrasonic flow meter is 1 m/s. _______________________ Bureau of Energy Efficiency 3 Paper 4 Set B REGULAR Ans Discharge Head, kg/cm2 Suction Head, m Total Head Flow rate Hydraulic Power = 4.5 = -3 = 45 - (-3) 48 m = (22/7 x D2/4) x 1 m/s = (22/7 x 0.152 / 4) x 1 m/s = 0.0177 m3/sec .. 2 marks = 0.0177 x 1000 x 9.81 x 48/1000 = 8.33 kW Pump Efficiency .. 1 mark 8.33/(16.7x0.9) = 55.2 % .. 2 marks . End of Section - II . Section - III: LONG NUMERICAL QUESTIONS Marks: 4 x 20 = 80 (i) Answer all Four questions (ii) Each question carries Twenty marks N-1 In an organic chemical industry 15 Tonne per hour steam is generated at 10 kgf/cm2 in a 18 TPH natural gas fired smoke tube boiler. The % oxygen in the exit flue gas was 3.1% and the flue gas temperature was 190oC. The following data have been provided. Ultimate analysis of natural gas per kg, Carbon = 0.72 kg/kg; Hydrogen = 0.236 kg/kg; Nitrogen = 0.03 kg/kg; Oxygen = 0.011 kg/kg; Specific heat of flue gas = 0.297 kcal/kgoC Specific heat of superheated water vapor = 0.45 kcal/kgoC G.C.V. of natural gas = 9100 kcal/m3 Density of natural gas = 0.7 Density of air = 1.12 kg/m3 Enthalpy of steam at 10 kg/cm2 = 665 kcal/kg Temperature of feed water at inlet to boiler = 95oC Yearly hours of operation = 8000 hours _______________________ Bureau of Energy Efficiency 4 Paper 4 Set B REGULAR a. Find out the S/F (steam to fuel) ratio in kg steam/m3 gas b. Estimate the annual reduction in carbon dioxide emission in tones/year compared to the furnace oil fired boiler of 83% efficiency on G.C.V. which was earlier used for delivering the same steam load. Assume G.C.V. of furnace oil as 10300 Kcal/kg and 0.86 carbon per kg furnace oil. Ans Ultimate analysis of natural gas per kg. of gas Carbon = 0.72 kg/kg; Hydrogen = 0.236 kg/kg; kg/kg; Oxygen = 0.011 kg/kg; Nitrogen = 0.03 Theoretical air required = 11.6C + [34.8 (H2 O2/8)] + 4.35S, = 11.6 X 0.72 + [34.8 (0.236 0.011/8)] (note S= sulfur in above composition is nil) = 16.524 kg air/kg gas (1 Mark) % Excess Air = [% O2 / (21 - % O2)] x 100 = [3.1 / (21 3.1)] x 100 = 17.3% (1 Mark) Actual Air Supplied (AAS) = [1 + 0.173] x 16.524 = 19.38 kg air / kg gas . (1 mark) Mass of dry flue gas; mdfg = mass of combustion gases due to presence C, N2,S in the fuel+mass of residual O2 in flue gas + mass of N2 supplied with air = 0.72 X 44/12 + 0.03 + (19.38 16.524) x 0.23 + 19.38 x 0.77 = 18.24 kg dfg / kg gas . (1.5 mark) L1 = % heat loss due to dry flue gases = mdfg x cpfg x (Tg Ta) ------------------------------ X 100 G.C.V. of gas Kcal / m3 9100 G.C.V. of gas = ----------- = --------- = 13000 Kcal/kg Density 0.7 _______________________ Bureau of Energy Efficiency 5 Paper 4 Set B REGULAR = 18.24 x 0.297 x (190 - 30) -------------------------------- X 100 = 6.67 % 13000 . (2 marks) L2 = Loss due to presence of hydrogen forming water vapor = 9H [584 + Cps x (Tg Ta) ---------------------------------- X 100 G.C.V. 9 x 0.236 [584 + 0.45 (190 30) = --------------------------------------------- x 100 13000 L2 = 10.72 % . (2 marks) Radiation and unaccounted losses in the boiler (given) = 1.45% Total losses = 6.67 + 10.72 + 1.45 = 18.84% Efficiency of natural gas fired boiler on G.C.V. by indicated method = 100 18.84 = 81.16% . (1.5 marks) Steam to fuel ratio in kg steam/m3 gas= 0.8116 x 9100 / (665 95) = 12.96 . (2 marks) Amount of gas required for generation 15 tonne/hr of steam = (15,000 / 12.96) x 0.7 = 810.19 kg/hour (1.5 Marks) CO2 emission with natural gas firing = 0.72 x 3.67 x 810.19 (1 kg carbon gives 44/12 i.e. 3.67 kg CO2) = 2140.77 kg/hr . (1.5 marks) Furnace oil required for 15TPH steam = (15,000 x 570) / (0.83 x 10,300) = 1000.12 kg/hr (1.5 Marks) CO2 emission with furnace oil firing = 0.86 x 3.67 x 1000.12 = 3156.58 kg/hr (1.5 Marks) _______________________ Bureau of Energy Efficiency 6 Paper 4 Set B REGULAR Net reduction in CO2 emission with natural gas compared to furnace oil firing = 3156.58 2140.77 = 1015.81 kg/hr . (1 mark) Annual reduction in CO2 for 8000 hrs. = 1015.81 x 8000 operation = 8126.140 Tonnes . (1 mark) N-2 A gas engine-based trigeneration plant operates in two modes: Power and heating mode (10 hours per day) : Pel= 650 kW of electricity and 325 kg/h of steam with enthalpy addition of 530 kcal/kg of steam EUFheat = 0.85 Power and cooling mode (14 hours per day) : Pel = 650 kW of electricity and chilling load of 250 TR for absorption chillers EUFcool= 0.73 Calorific value of natural gas = 8500 kcal/Sm3 Average operating days/year = 330 Alternator efficiency = 0.95 The energy loss in the flue gas and that in the cooling water is same as engine power output and other losses are negligible Answer the following: (1) What is the average plant energy utilization factor (2) Calculate the useful energy produced daily by the trigeneration plant in Gcal (3) Determine the daily plant natural gas requirements based on average energy utilization factor (4) The plant proposes to install a 60 TR hot water driven Vapour absorption chiller with a COP of 0.5 using waste heat from jacket cooling water. Check if it is feasible with supporting calculations. _______________________ Bureau of Energy Efficiency 7 Paper 4 Set B REGULAR Ans 1) Plant average energy utilization factor Plant average energy utilization factor = (0.85 x 10 + 0.73 x 14)/24 = 0.78 ---- (3 marks) 2) The useful energy produced daily by the trigeneration plant in Gcal PEle QHeat QCool = = = = = 650 KW 325 x 530 172250 kcal/h 250 x 3024 756000 kcal/h ---- (2 marks) Total daily useful energy production of the plant The useful energy produced daily The useful energy produced in Gcal/year (650 x 860 x 24 +172250 x 10 + 756000 x 14) 13416000 + 1722500 + = 10584000 = 25722500 kcal/day (2 Marks) 6 25722500x 330 / 10 = = = 8488.43 Gcal ---- (2 marks) 3)The daily plant natural gas requirements = Input heat 25722500/ 0.78 Natural gas requirements = 32977564 kcal/day = 32977564/ 8500 = 3879.7 (2 Marks) Sm3/day ---- (2 marks) 4) Justification for a 60 TR Vapour Absorption chiller from waste heat of the jacket cooling water Heat required for operating 60 TR at = 60 x 3024/0.5 (2 Marks) COP of 0.5 = 362880 Kcal/hr Power output of the engine = 650 /0.95 684.2 KW (2 Marks) _______________________ Bureau of Energy Efficiency 8 Paper 4 Set B REGULAR Heat in the jacket cooling water = 684.2 x 860 = 588412 kcal/hr (2 Marks) Since the heat requirement (362880 Kcal/hr) is much less than heat available (588412 kcal/hr) the proposal is feasible. ---- (1 mark) N-3 Hot effluent having a flow rate of 56789 Kg/hr at 85OC from the process is sent to a heat exchanger for cooling. The outlet temperature of effluent in the heat exchanger is 38 OC. Air having a flow rate of 370057 Kg/hr enters the heat exchanger at a temperature of 30 OC and leaves at 60 OC. Power drawn by the fan is 30 KW. The plant works for 16 hours a day for 300 days per year. Now plant has decided to replace air cooled heat exchanger with a water cooled counter current Heat Exchanger. Given that Pump Efficiency = 80%, Motor efficiency = 90 %, Effectiveness of water cooled heat exchanger is 0.4 water is available at 25 OC & Pressure drop in plate heat exchanger is 1.2 kg/cm2 , Over all heat transfer coefficient of heat exchanger is 22300 Kcal/m2/OC. Ans 1. Calculate the savings due to replacement by water cooled heat exchanger 2. Calculate the heat transfer area of heat exchanger. Heat Duty Heat duty in hot fluid = M x Cph x (Ti - To) = 56789 x 1 x (85 38) = 2669083 Kcal / Kg . (2 marks) Heat duty in cold Air = M x Cpair x (to ti) = 370057 x 0.24 x (60 30) = 2664410 Kcal / Kg . (2 marks) In heat exchanger, Heat duty in hot fluid = Heat duty in cold Air Effectiveness of water cooled heat exchanger = 0.4 Cold Water outlet Cold water inlet Effectiveness = Hot effluent inlet Cold water inlet Cold Water Outlet = (0.4 x (85 25)) + 25 _______________________ Bureau of Energy Efficiency 9 Paper 4 Set B REGULAR = 49 OC . (2.5 marks) Mass flow rate of cooling water (M) =Heat duty in hot fluid Cpx(Cold Water outlet Cold water inlet) = 2669083 1 x (49 25) x 1000 = 111.21 m3 /Hr . (2.5 marks) Pressure drop in Plate Heat exchanger = 12 m Hydraulic Power Requirement for one Cooling Water Pump: = (Flow in m3/Hr x Head in m x Density in Kg/m3 x g in m/s2) (1000 x 3600) = (111.21 x 12 x 1000 x 9.81) (1000 x 3600) = 3.64 KW . (3 marks) Pump Power Requirement at 80% pump efficiency = 3.64 KW 0.8 = 4.55 KW . (1 mark) Motor Input Power Required at 90% Efficiency = 4.55 0.9 = 5.06 KW . (1 mark) Thus savings = Power consumption by fans Water Pumping Power = 30 5.06 = 24.94KW Annual Saving in kWh = 24.94 KW x 16 Hrs x 300 Days = 119712 kWh/Annum . (2 marks) _______________________ Bureau of Energy Efficiency 10 Paper 4 Set B REGULAR Calculations for LMTD for Proposed HEx: LMTD for counter current flow in HEx = {(85-49) (38-25)} / ln {(85-49) / (38-25)} = 22.5 Deg C . (2 marks) Considering overall heat transfer coefficient (U) = 22300 kW/m2/0C Heat transfer Area = Q (U x Tlm) = 2669083 (22300 x 22.5) = 5.32 m2 (Say 6 m2) . (2 marks) N-4 Answer ANY ONE OF THE FOLLOWING among A, B, C and D A) A steam power plant consisting of high pressure Turbine(HP Turbine) and low pressure Turbine(LP Turbine) is operating on Reheat cycle(schematic of power plant is represented below).Steam from Boiler at a pressure of 150 bar(a) and a temperature of 5500C expands through the HP Turbine. The exhaust steam from HP Turbine is reheated in a Reheater at a constant pressure of 40 bar (a) to 5500C and then expanded through LP Turbine. The exhaust steam from LP Turbine is condensed in a condenser at a pressure of 0.1 bar (a).The isentropic efficiency of HP Turbine and LP Turbine is same and is 0.9. Generator efficiency is 95% _______________________ Bureau of Energy Efficiency 11 REGULAR Paper 4 Set B The other data of the power plant is as given below: Main steam flow rate : 228 TPH Enthalpy of main steam : 3450 KJ/kg Enthalpy of feed water : 990.3KJ/kg Isentropic Enthalpy of cold reheat steam : 3050 KJ/kg Enthalpy of hot reheat steam : 3560 KJ/kg Condenser pressure and temperature : 0.1 bar(a) and 45.80C Isentropic enthalpy of LP Turbine exhaust steam : 2300 KJ/kg Enthalpy of dry saturated steam at 0.1 bar(a) and 45.80C : 2584.9KJ/kg Enthalpy of water at 0.1 bar(a) and 45.80C:191.9 KJ/kg Based on the above data calculate the following parameters (a) Power developed by the Generator (b) Turbine heat rate (c) Turbine cycle efficiency (d)Dryness fraction of LP Turbine Exhaust steam (e) Specific steam consumption of turbine cycle. _______________________ Bureau of Energy Efficiency 12 REGULAR Ans Paper 4 Set B (a) Power developed by the Generator: Turbine output x Generator efficiency--(1) Turbine out put = Q1 (H1 h2) + Q2(H3 h4)/860 MW ----------- (2) Where, Q1=main steam flow rate =228 TPH H1=main steam enthalpy=3450 KJ/Kg h2=actual enthalpy at HP Turbine outlet= ?=cold reheat enthalpy Q2=steam flow through reheater=228TPH H3=enthalpy of hot reheat steam=3560 KJ/kg h4= actual enthalpy of LP turbine exhaust steam=? . (1 mark) HP Turbine isentropic efficiency= Actual enthalpy drop/isentropic enthalpy drop 0.9= (H1- h2)/(H1-h2is) , h2is=isentropic enthalpy of cold reheat steam = 3050 KJ/kg 0.9= (3450 h2)/(3450 3050) h2= 3090KJ/kg . (3 marks) LP Turbine isentropic efficiency= (H3 h4)/(H3 h4is), h4is=isentropic enthalpy of LP Turbine Exhaust steam=2300KJ/kg 0.9=( 3560-h4)/(3560 2300) h4= 2426 KJ/kg . (3 marks) Substituting the values in equation-2,we get Turbine output = 228(3450 3090) + 228(3560 2426)/860 =75.73MW Generator output= 75.73 x 0.95= 71.5 MW . (3 marks) (b) Turbine heat rate=Q1 (H1 hfw) +Q2(H3 h2)/Generator output =KJ/kwhr------------(3) hfw=enthalpy of feed water=990.3KJ/kg Substituting the values in the above equation-3, we get Turbine heat rate=228 (3450 990.3) + 228(3560 3090)/71.5 =9342 KJ/kWhr . (3 marks) (C) Turbine cycle efficiency= 860/Turbine heat rate =860/9342=38.5% . (2 marks) (d)Dryness fraction of steam at 0.1 bar(a) and 45.8C _______________________ Bureau of Energy Efficiency 13 Paper 4 Set B REGULAR Actual enthalpy of LP Exhaust steam= enthalpy of water + dryness fraction of steam x L.H of vaporisation of steam 2426 = 191.9+ dryness fraction of steam x(2584.9 191.9) Dryness fraction of steam= 93.35% . (3 marks) (e) Specific steam consumption of cycle =Steam flow/generator output =228/71.5=3.19 tons/MW hr . (2 marks) Or B) Stenter operations in a textile process were significantly improved to reduce inlet moisture from 60% to 55% in wet cloth while maintaining the same outlet moisture of 7% in the dried cloth . The Stenter was operated at 80 meters/min in both the cases. The dried cloth weighs 0.1 kg /meter. Further steps were taken to improve the efficiency of the fuel oil fired thermic fluid heater from 80% to 82%, which was supplying heat energy to the dryer. The other data and particulars are Latent heat of water evaporated = 540kcal/kg, Inlet temperature of wet cloth = 28 oC , Outlet temperature of dried cloth = 80 oC, Dryer efficiency = 50% , G.C.V of fuel oil = 10,300 kcal/kg, Yearly operation of the stenter = 7000 hours a) Find out the % reduction in Dryer heat load , b) Estimate the overall yearly fuel savings in tonnes by reducing moisture and efficiency improvement compared to the initial case. Assume only energy for moisture evaporation for dryer heat load Ans Initial case: inlet moisture, 60%, outlet moisture 7%, dryer efficiency 50%,thermic fluid heater efficiency 80% Output of stenter = = 80 mts/min x 0.1 x 60 480 Kg/hr (1 Mark) Moisture in the dried output cloth = 7% Wt. of bone- dry cloth,W = 480 X (1 0.07) = 446.4 Kg/hr ---- (1 mark) mo = moisture in outlet cloth = (480 446.4) /446.4 = 0.0753 Kg/Kg bone dry cloth (1 Mark) _______________________ Bureau of Energy Efficiency 14 Paper 4 Set B REGULAR Inlet moisture Wt of inlet cloth = 60% = 446.4 / (1 0.60) = 1116.00 Kg./hr. mi = moisture in inlet cloth = ((60/40) x 446.4)/446.4 = 1.5 Kg./Kg. bone- dry cloth ---- (1 mark) Inlet temperature of cloth Tin = Final temperature of clothTout = 28oC 80oC Heat load on the dryer . . . Heat load on the dryer = w x (mi mo) X [(Tout Tin) + 540] Kcal/hr. = = 446.4 (1.5 0.0753) X [(80 28) + 540] 3,76,503.76 Kcal/hr ---- (2.5 marks) Efficiency of the dryer is 50%, Efficiency of the thermic fluid heater is 80% Fuel oil consumption in the thermic fluid heater =3,76503.76/( 0.5x 0.8x10300) = 91.40 kg/hr ---- (2.5 marks) Improve case: inlet moisture, 55%, outlet moisture 7%, dryer efficiency 50%,thermic fluid heater efficiency 82% Inlet moisture Wt of inlet cloth mi = 55% = 446.4 / (1 0.55) = 992.00 Kg./hr. (1 Mark) = moisture in inlet cloth = ((55/45) x 446.4)) / 446.4 = 1.22 Kg./Kg. bone-dry cloth ---- (1 mark) Heat load on the dryer = w x (mi mo) X [(Tout Tin) + 540] Kcal/hr. Heat load on the dryer = = 446.4 (1.22 0.0753) X [(80 28) + 540] 3,02508.00 Kcal/hr ---- (2.5 marks) Efficiency of the dryer is50%, Efficiency of the thermic fluid heater is 82% Fuel oil consumption in the thermic fluid heater in impoved case = 3,02,508.00/( 0.5x 0.82x10300) _______________________ Bureau of Energy Efficiency 15 Paper 4 Set B REGULAR = 71.63 kg/hr (2.5 Marks) % reduction in dryer load due to reduction inlet moisture (3,76,504-3,02,508) x 100 = ----------------------------------------(3,76,504) = 19.65% ---- (2 marks) Saving in fuel oil consumption in improved case = 91.4 - 71.63 = 19.77 kg/hr Yearly fuel oil savings =19.77x7000 x1/1000 =138.390 tonnes ---- (2 marks) or C) In a steel industry, the composition of blast furnace gas by volume is as follows CO 27%, H2 - 2%, CO2 11%, N2 - 60%. i) ii) iii) iv) Ans Calculate the stoichiometric air for combustion Calculate the gross calorific value of gas in kcal/m3 Calculate the net calorific value of gas in kcal/Nm 3 If 3,00,000 Nm3/hr of gas is available and is to be co-fired in a coal fired boiler. How much coal it can replace if the GCV of coal is 4300 kcal/kg. (i) Stoichiometric air for combustion: C + O2 ------ CO2 + 8,084 kcal/kg Carbon 2C + O2 ------ 2 CO + 2,430 kcal/kg Carbon H2 + O2 -------H2O + 28,922 kcal/kg Hydrogen CO + O2 -------CO2 + 5,654 kcal/kg Carbon ---- (2 marks) 1 mole CO + 0.5 mole O2 ------ 1 mole CO2 + 5654 kCal/kg For 27% CO, O2 required is (0.5/1) x 0.27 = 0.135 O 2 ---- (2 marks) 1 mole H2 + 0.5 mole O2 ------ 1 mole H2O + 28922 Kcal/kg For 2 % of H2, O2 required is (0.5/1) x 0.02 = 0.01 O2 _______________________ Bureau of Energy Efficiency 16 Paper 4 Set B REGULAR ---- (2 marks) Total stoichiometric oxygen required = 0.135 + 0.01 = 0.145 O2 Stoichiometric air required = 100 x 0.145 = 0.690 m3 air / m3 blast furnace gas 21 ---- (3 marks) (ii) Gross calorific value of gas: 1 kg mole of any gas at STP occupies 22.4 m3 of volume. ---- (1 mark) Therefore, ((5654 x 12) / 22.4) x 0.27 = 817,83 kCal/m3 (molecular weight of Carbon = 12) ---- (2 marks) ((28922 x 2) / 22.4) x 0.02 = 51.64 kCal/m3 (molecular weight of Hydrogen = 2) ---- (2 marks) Gross Calorific Value = 817.83 + 51.64 = 869.5 kcal/m3 ---- (1 mark) (iii) Replacement of coal by blast furnace gas: Gross calorific value of coal = 4300 kcal/kg (given) Blast furnace gas available = 3,00,000 m3/hr (given) Heat content available from gas = 3,00,000 m3/hr x 869.5 kcal/m3 = 2608.5 x 105 kcal/hr ---- (2.5 marks) If X is the coal quantity to be replaced, then 4300 kcal/kg x X = 2608.5 x 105 kcal/hr X = 60663 kg/hr of coal can be replaced by gas of 3,00,000 m3/hr. ---- (2.5 marks) or D) As an energy auditor, auditing a cement plant, it is essential to assess the specific coal consumption for the production of the clinker. With the following data available, calculate the specific coal consumption (kgCoal/ KgClinker). S.No Parameter 1. Reference temperature Value 20Oc _______________________ Bureau of Energy Efficiency 17 REGULAR Paper 4 Set B 2. Barometric pressure 10329 mmWC 3. Density of the Pre-heater at NTP 1.436kg/m3 4. Density of Air 1.293Kg/m3 5. Pitot Tube Constant 0.85 6. Clinker production rate 4127 TPD 7. Static Pressure of the Pre-heater gas in the pre-heater duct 640mmWC 8. Dynamic pressure of the pre-heater gas in the duct 15.8mmWC 9. Temperature of the Pre-heater gas 320OC 10. Specific heat of the Pre-heater gas 0.247kCal/kg 0C 11. Area of the Pre-heater Duct 8.5 m2 12. Temperature of the exit clinker 128OC 13. Specific heat of the clinker 0.193 kCal/kg 0 C 14. Static Pressure of the Cooler Exhaust gas in the duct 42mmWC 15. Dynamic pressure of the Cooler Exhaust gas in the duct 15.5mmWC 16. Temperature of the Cooler Exhaust gas gas 290 17. Specific heat of the Cooler Exhaust gas 0.247kCal/kg 0C 18. Area of the Cooler exhaust duct 7.1m2 19. Heat of Formation of Clinker 405 Kcal/KgClinker 20. All other heat loss except heat loss through Pre-heater gas, exiting clinker and cooler exhaust gases 84.3 Kcal/KgClinker 21. All heat inputs except heat due to Combustion of fuel (Coal) 29 Kcal/KgClinker 22. GCV of the Coal 6200Kcal/Kg _______________________ Bureau of Energy Efficiency 18 Paper 4 Set B REGULAR Ans Solution: Heat Lost in the along with the Exiting pre-heater gases: QPH Gas = mphgas Cpphgas (tephgas-tr) mphgas = VphgasX Phgas Vphgas = vph gas X A Corrected density of the pre-heater gas: 10329 640 273 = 1.436 Phgas 10334 273 320 = 0.6198 kg/ m3 Velocity (v) (1 Mark) =Pt (2g( Pdynamic)avg / Phgas) m/sec 2 9.81 15.8 = 0.85 = 19.0 m/sec 0.6198 m/sec (2 Marks) VPH gas = 19.0m3/s X 8.5 m2 = 161.5 m3/sec = 5,81,400m3/hr (1 Mark) Mph gas = 581400 m3/hr X 0.6198 kg/m3 =3,60,351/72 Kg/hr (1 Mark) mphgas = 3,60,351 kg/hr / 1,71,958 kg/hr =2.095Kgph gas/ Kg clinker (1 Mark) QPH Gas = 2.095 X 0.247 X (320 -20) = 155.24Kcal/KgClinker (1 Mark) Heat Lost in the along with the Exiting Hot Clinker: QHot clinker = mclinker Cpclinker ( tclinker- tr) = 1 x 0.193 x (128 20), = 20.84 kCal/kgClinker ---- (2 marks) Heat Lost in the along with the Exiting Cooler Exhaust gases: QCooler Exhaust Gas = mCooler Exhaust Gas CpCooler Exhaust Gas (tCooler Exhaust Gas-tr) _______________________ Bureau of Energy Efficiency 19 Paper 4 Set B REGULAR = VCooler Exhaust Gas X Cooler Exhaust Gas = vCooler Exhaust Gas X A mCooler Exhaust Gas VCooler Exhaust Gas Corrected density of the pre-heater gas: 10329 42 273 = 1.293 Cooler Exhaust gas 10334 273 290 = 0.624 kg/ m3 Velocity (v) (1 Mark) =Pt (2g( Pdynamic)avg / Cooler Exhausts) m/sec 2 9.81 15.5 = 0.85 = 18.76 m/sec 0.624 m/sec (2 Marks) VcoolerExhaustgas = 18.76m/s X 7.1 m2 = 133.196 m3/sec = 4,79,505m3/hr (1 Mark) McoolerExhaustgas = 479505 m3/hr X 0.624 kg/m3 =2,99,211 Kg/hr (1 Mark) mcoolerExhaustgas = 2,99,211 kg/hr / 1,71,958 kg/hr =1.74 KgcoolerExhaustgas/ Kg clinker (1 Mark) QcoolerExhaustgas = 1.74 X 0.244 X (290 -20) = 114.63Kcal/KgClinker (1 Mark) Heat Input = Heat output Heat Inputcoal + Heat inputothers = HeatClikerfrmtn+ HeatPH gas + HeatCliker+ Heatcooler exhaust gas + Heatothers GCVcoalX m coal + 29 = 405 + 155.24 + 20.84 +114.63 + 84.3 mcoal = 751 / 6200 = 0.121 Kgcoal/Kgclinker ---- (4 marks) -------- End of Section - III --------- _______________________ Bureau of Energy Efficiency 20 REGULAR Paper 4 Set B _______________________ Bureau of Energy Efficiency 21

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