The following data is collected from a boiler trial. Feed water = 680 kg/hr at 20°C. Steam generated at 15 bar and 300°C. Coal used=95 kg/hr with C.V.= 26.5 MJ/kg. Ash and unburned coal collected=4 kg/hr whose C.V.- 2.2 MJ/kg. Flue gas formed = 18 kg per kg of coal. Flue gas temp. 300°C and ambient temp = 28°C. Take C 1.025 kJ/kg-"C. Determine (a) Boiler efficiency (b) Equivalent evaporation from and at 100°C. (c) % of unaccounted heat (d) Draught produced in em of water if the chimney height = 50 m.
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Boiler efficiency is 71%
Explanation:
(a) Heat supplied to the boiler per hour = 95 x 26500
= 25,17,500
At 8 bar, h = 721-1 kJ/kg, L = 2,048 kJ/kg (from steam tables)
Enthalpy of wet steam,
H1= hy * xL1
= 721-1 + 0-97 x 2,048
= 2,707.67 kJ/kg'
Enthalpy of feed water at 20°C, = 20 x 4.187 = 83.74 kJ/kg
Heat utilised in steam formation per hour
= mass of steam produced per hr. x (H1 - h2)
= 680(2,707.67 - 83.74)
= 17,84,272.4kJ/hr
Boiler efficiency = Heat utilized in steam formation per hr./Heat supplied
= 17,84,272.4/25,17,500
= 0.708
= 70.8%
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