N5 Power Machines BOILER CALCULATIONS

ialegodi@gmail.com 082 396 7717 BOILER CALCULATIONS A boiler (evaporator) is a device in which the steam is generated The five auxiliaries in a steam plant: I. Economizer II. Evaporator III. Superheater IV. Air-pre-heater SUPERHEATER V. Turbine Superheated steam h4  hg  Cp s (t ss  t s ) hsup from sup erheatedsteam EVAPORATOR h3  hf  xhfg Wet steam h2  hf @tw2 ECONOMISER h1  hf @tw1 h1  hf @tw1 = the enthalpy of steam entering the plant or economizer h2  hf @tw2 = the enthalpy of steam entering the evaporator or leaving the economizer h3  hf  xhfg = the enthalpy of the steam leaving the evaporator or entering the superheater h4  hg  Cp s (t ss  t s ) = the enthalpy of the steam produced by the plant or enthalpy leaving the superheater, superheated enthalpy of the steam ms h4  h1  E.E  = equivalent evaporation from and at 100 C m f  2257 ms h4  h1   thermal   100 = the thermal efficiency of the boiler m f  CV If the plant doesn’t have the superheated meaning superheated part is not given which means h3  hf  xhfg is the final enthalpy of the steam, then Downloaded from hlayiso.com

ialegodi@gmail.com 082 396 7717 ms h3  h1  ms h3  h1  E.E  And  thermal   100 m f  2257 m f  CV msteam h2  h1  Qecon  = heat absorbed by the economizer m fuel msteam h3  h2  Qevap  = heat absorbed by evaporator m fuel msteam h4  h3  Qsup er  = heat absorbed by superheater m fuel POSSIBLE QUESTIONS: 1. A boiler has a pressure of 1 400 kPa evaporates 8 kg of water per kg of coal burnt from the feed water temperature entering the plant at 39 C , while the dryness fraction of steam leaving the evaporator is 95% dry Calculate the following: 1.1. The thermal efficiency of the plant 1.2. The equivalent evaporation from and at 100 C 2. A boiler must supply 2 200 kg of steam per hour, at a pressure of 1 000 kPa and the temperature of 350 C . The feed water temperature enters the economizer at 26, 7 C and the thermal efficiency of the boiler is 72%. The calorific value of the coal burnt is 35 MJ/kg. Calculate the following: 2.1. The mass of coal used per hour 2.2. The equivalent evaporation from and at 100 C 3. A boiler generates 2 400 kg of steam every hour at the pressure of 1 250 kPa and a temperature of 400 C . The temperature of the feed water is 26, 7 C and the thermal efficiency of the boiler is 68%. The S.H.C of superheated steam is 2, 312 kJ/kg. C and the calorific value of coal is 36, 4 MJ/kg Calculate the following: Downloaded from hlayiso.com

ialegodi@gmail.com 082 396 7717 3.1. The mass of coal which will be consumed every minute 3.2. The equivalent evaporation from and at 100 C 4. The equivalent evaporation from and at 100 C of a boiler plant is 10, 05. The pressure in the plant is 2 MPa and the temperature of the steam leaving the plant is 250 C . The temperatures at the inlet and outlet of economizer are 43, 8 C and 81, 4 C respectively. The calorific value of the fuel is 32 MJ/kg and the dryness fraction of the steam entering the superheater is 0, 948. Calculate the following: 4.1. The mass of steam generated per kg of steam 4.2. The thermal efficiency of the plant 4.3. The heat absorbed by: 4.3.1. Economizer 4.3.2. Evaporator 4.3.3. Superheater 5. A boiler plant supplies 5 600 kg of wet steam every hour at a pressure of 800 kPa. The steam is 9% wet and the supply water enters the boiler at 29 C . The boiler consumes 11 kg of coal every minute, which has the heat value of 35 MJ/kg Calculate the efficiency of the boiler 6. Feed water with a temperature of 40, 3 C enters a boiler which is processing steam with a dryness fraction of 93% at a pressure of 2 300 kPa. The steam flows through a superheated at a constant pressure while the temperature increases to 260 C - The steam delivery is 8, 5 kg/kg of fuel - The coal has the calorific value of 33 MJ/kg - The specific heat capacity of superheated steam is 2, 14 kJ/kg.K Calculate the following: 6.1. The heat absorbed by evaporator 6.2. The heat absorbed by superheater Downloaded from hlayiso.com

ialegodi@gmail.com 082 396 7717 6.3. The equivalent evaporation from and at 100 C 6.4. The efficiency of the installation 7. A boiler plant supplies 5 200 kg of wet steam is at pressure of 780 kPa every hour. The steam is 3% wet and the feed water temperature is 40, 3 C . The boiler uses 660 kg of fuel to supply 5 200 kg steam and the fuel has the heat value of 30 MJ/kg. Calculate the following: 7.1. The boiler efficiency 7.2. The equivalent evaporation from and at 100 C 7.3. An economizer is installed and the feed water temperature in QUESTION 7.2 is increased by 28, 8 C . The efficiency of the boiler increases by 7, 25% and all other conditions remain the same. Calculate the mass of fuel saved every hour 8. A boiler produces 18 000 kg steam every hour at a pressure of 2, 5 MPa. The feed water to the boiler has a temperature of 37, 7 C . Fuel which has a calorific value of 30 MJ/kg, is consumed at a rate of 1 775 kg every hour. The equivalent evaporation of the boiler from and at 100 C is 11, 2 kg steam/ kg fuel. Calculate the following: 8.1. The efficiency of the boiler 8.2. The conditions of the steam produced and state the reason based on the calculations 8.3. The dryness fraction percentage of the steam 9. The feed water to the boiler enters the economizer at 26, 7 C and leaves at 98, 2 C and enters evaporator. The pressure of steam is 3 000 kPa and has the quality of 0, 97. The steam then enters superheater where its temperature is increases to 350 C at constant pressure. The boiler produces 10 kg steam for every kg fuel burnt and heat value of fuel is 32 MJ/kg. Calculate the following: 9.1. The energy absorbed by: 9.1.1. Economizer 9.1.2. Evaporator 9.1.3. Superheater 9.2. The equivalent evaporation from and at 100 C 9.3. The efficiency of the boiler Downloaded from hlayiso.com