A boiler plant incorporates an economizer and air preheater, and generates steam at 80 bar and 440 ˚C with fuel of heating value 34500 kJ/kg burned at a rate of 490 kg/h. The temperature of feed water is raised from 32 ˚C to 138 ˚C in the economizer and the flue gases are cooled at the same time from 390 ˚C to 215 ˚C. The flue gases then enter the air preheater in which the temperature of combustion air is raised by 82 ˚C. A forced draught fan delivers the air to the air preheater at a pressure of 1.01 bar and a temperature of 20 ˚C with a pressure rise across the fan of 185 mm of water. The power input to the fun is 6.1 kW and it has a mechanical efficiency of 80%. Neglect heat losses and take Cp=1.01 kJ/kg.K for flue gases and 4.182 kJ/kg.k for water. After the calculation of the mass flow rate of air, gas and of the steam, calculate the efficiency of the boiler. Select one: a. 82% b. 89% c. 94% d. 85%
A boiler plant incorporates an economizer and air preheater, and generates steam at 80 bar and 440 ˚C with fuel of heating value 34500 kJ/kg burned at a rate of 490 kg/h. The temperature of feed water is raised from 32 ˚C to 138 ˚C in the economizer and the flue gases are cooled at the same time from 390 ˚C to 215 ˚C. The flue gases then enter the air preheater in which the temperature of combustion air is raised by 82 ˚C. A forced draught fan delivers the air to the air preheater at a pressure of 1.01 bar and a temperature of 20 ˚C with a pressure rise across the fan of 185 mm of water. The power input to the fun is 6.1 kW and it has a mechanical efficiency of 80%. Neglect heat losses and take Cp=1.01 kJ/kg.K for flue gases and 4.182 kJ/kg.k for water. After the calculation of the mass flow rate of air, gas and of the steam, calculate the efficiency of the boiler. Select one: a. 82% b. 89% c. 94% d. 85%
Elements Of Electromagnetics
7th Edition
ISBN:9780190698614
Author:Sadiku, Matthew N. O.
Publisher:Sadiku, Matthew N. O.
ChapterMA: Math Assessment
Section: Chapter Questions
Problem 1.1MA
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A boiler plant incorporates an economizer and air preheater, and generates steam at 80 bar and 440 ˚C with fuel of heating value 34500 kJ/kg burned at a rate of 490 kg/h. The temperature of feed water is raised from 32 ˚C to 138 ˚C in the economizer and the flue gases are cooled at the same time from 390 ˚C to 215 ˚C. The flue gases then enter the air preheater in which the temperature of combustion air is raised by 82 ˚C. A forced draught fan delivers the air to the air preheater at a pressure of 1.01 bar and a temperature of 20 ˚C with a pressure rise across the fan of 185 mm of water. The power input to the fun is 6.1 kW and it has a mechanical efficiency of 80%. Neglect heat losses and take Cp=1.01 kJ/kg.K for flue gases and 4.182 kJ/kg.k for water. After the calculation of the mass flow rate of air, gas and of the steam, calculate the efficiency of the boiler.
Select one:
a. 82%
b. 89%
c. 94%
d. 85%
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