Question

A boiler plant incorporates an economizer and air preheater and generates steam at 40 bar and 300°C with a fuel heating value of 33000 kg/hr. The temperature of the feedwater is raised from 40°C to 125°C in the economizer, and the flue gases are cooled at the same time from 395°C to 225°C. The flue gas then enters the air preheater at a pressure of 1.2 bar and 16°C with a pressure rise across the fan of 18 mm of water. The power input to the fan is 5 kW, and it has a mechanical efficiency of 78%. Neglecting heat losses and assuming the flue gases as an ideal gas with a constant specific heat of Cp = 1.01 kJ/kg-K, calculate: (a) the mass flow rate of the air, (b) the temperature of the flue gases leaving the plant, (c) the mass flow rate of the steam, and (d) the efficiency of the boiler.

          A boiler plant incorporates an economizer and air preheater and generates steam at 40 bar and 300°C with a fuel heating value of 33000 kg/hr. The temperature of the feedwater is raised from 40°C to 125°C in the economizer, and the flue gases are cooled at the same time from 395°C to 225°C. The flue gas then enters the air preheater at a pressure of 1.2 bar and 16°C with a pressure rise across the fan of 18 mm of water. The power input to the fan is 5 kW, and it has a mechanical efficiency of 78%. Neglecting heat losses and assuming the flue gases as an ideal gas with a constant specific heat of Cp = 1.01 kJ/kg-K, calculate: (a) the mass flow rate of the air, (b) the temperature of the flue gases leaving the plant, (c) the mass flow rate of the steam, and (d) the efficiency of the boiler.

Added by Keith H.

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