Consider a coal fired plant converting fuel energy into mechanical energy and th

Question

Consider a coal fired plant converting fuel energy into mechanical energy and then to electrical energy. In a typical day, the plant uses 800 ton of coal. The coal energy value is 25000 kj/kg.

a). Only 30% of burning coal energy is converted to the electrical energy; Calculate it.

b). 80% of the wasted energy(heat) is used by cooling water taken from a nearby river. The cooling water temperature rises 12 degrees celcius during the cooling process.Compute the flow rate of the water taken from the lake.

c). The temperature of water in the river upstream and downstream of the plant are 15 and 20 degrees celcius respectively. Determine the flow rate of the river.

Explanation / Answer

A) coal = 800 tons

Energy given by coal = 25000 kj/kg

Total energy for 800 tons i.e 800×1000 kgs is (25000)(800)(1000) = 200*10^8 kj

Electrical energy produced is only 30% = (200)(0.3) 10^8

= 60 * 108 kj

B) energy removed as heat = (200 - 60) = 140*10^8 kj

80% of wasted energy = 140 × 0.8 = 112*10^8 kj

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