Generating stations 5

 Question = the relation between water evaporated (w kg) , coal consumption ( c kg) and kWh generated per 8 hours shift for a steam generating station is as follows : 

W = 13500 + 7.5 kWh  (1) 

C = 5000 + 2.9 kWh (2) 

(1) To what limiting value dose the water evaporating per kg of coal consumed approach as the station output increases ? 

(2) how much coal per hour would be required to keep the station running on no load ? 

Solution = (1) For an 8 hours shift , weight of water evaporated per kg of coal consumed is = w/c = 13500 +7.5 kWh / 5000 + 2.9 kWh , 

» as the station output ( kWh) increases towards infinity , the limiting value of w/c approaches 7.5/2.9 = 2.6 . Therefore, the weight of water evaporated per kg of coal consumed approaches a limiting value of 2.6 kg as the kWh output increases . 

(2) At  no load , the station output is zero . kWh = 0 , therefore , from expression (2) we get , coal consumption at no Load = 5000 + 2.9  × 0 = 5000 kgs ,

So , consumption/hour = 5000 ÷ 8 = 625 kgs , answer ✓