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Lecture20 Exercises on heat recovery

Decrease in gah is

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Unformatted text preview: to 1400K decreases GAH by 19%. Decrease in GAH is followed by increase in fuel consumption in the same proportion Exercise‐II Effect of excess air (self study) Now consider that the above fuel is combusted with excess air to arrive at a furnace temperature of 1100K. Calculate GAH when a) excess air is 20% and b) when excess air is 50% Calculations can be performed in a way similar to the above. The readers may do these calculations. The calculations show that increase in excess air decreases GAH from 7339 kcal at theoretical air to 6284 kcal at 20% excess air and 5561kcal at 50% excess air. This decrease in 14% at 20% and 24% at 50% excess air. Decrease in GAH will increase in fuel consumption Calculations show further that preheating of theoretical amount of air to 500K will add 510 kcal sensible heat in air. As a result GAH will increase at all furnace temperatures. Exercise‐3 The heat requirement of a process is 1.5 10 kW. The furnace is fired with coal which has 70% C. The NCV of coal is 27900 kJ/kg. The process is carried out at 1600K. Products of combustion analyse 76% N 7 % O 5% H O and 12 %CO Calculate fuel consumption Solution : Solution is presented in brief. The readers should calculate the values given Since the POC temperature is not given. It is assumed that POC exit t...
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