A stream of Fuel Gas containing Ethane (C_2H_6), Propane (C_2H_B) and Butane (C_

Question

A stream of Fuel Gas containing Ethane (C_2H_6), Propane (C_2H_B) and Butane (C_4 H_10) is fed 10 into a combustion chamber where it is totally combusted with the of atmospheric air consisting of oxygen, Nitrogen and 1 mol% of Carbon Dioxide. Flue Gas is being produced at a rate of3.915 kmol/s with the following composition. (a) Sketch the process and clearly indicating all the known and relevant unknown parameters. (b) Confirm that the molar flow rate of Air entering the combustion chamber is 3628.03 mol s^-1 (c) Determine the mole percentages of Oxygen and Nitrogen in the combustion air. The Butane flow in the Fuel Gas entering the combustion chamber is 3.524 kg s^-1. Determine i) The molar flow rate of Fuel Gas being fed to the combustion chamber ii) The composition of the Fuel Gas expressing your answer as mole percentages.

Explanation / Answer

(a) Fuel gas consists of ethane, propane and butane

Known parameters:

Flow rate of flue gas = 3.915 kmole/s

Composition of carbon dioxide, nitrogen and water in flue gas

Unknown parameters:

Flow rate of fuel gas to the combustor

(b) Flow rate of

Carbon dioxide = 0.1213 * 3.915 = 0.474 kmole/s (composition of carbon dioxide multiplied by flue gas flow rate)

Nitrogen = 0.7321 * 3.915 = 2.866 kmole/s

Water = 0.1466 * 3.915 = 0.573 kmole/s

Since air contains 79 % nitrogen, so air flow rate =(Nitrogen flow rate)/0.79

= 2.866/ 0.79

= 3.67 kmole/s

(c) Since it is mentioned that the combustion air contains atmospheric air containing oxygen, nitrogen and 1 % carbon dioxide

We know that atmospheric air contains 21 % oxygen, 79 % nitrogen and 1 % carbon dioxide

(d) Flow rate of water (H2O) in flue gas = 0.573 kmole/s

Therefore, flow rate of hydrogen (H) = 2 * 0.573 = 1.146 kmole/s

Flow rate of CO2 in flue gas = 0.474 kmole/s

So, flow rate of carbon(C) = 0.474 kmole/s

So, total flow rate of C and H = 0.474 + 1.146 = 1.62 kmole/s

Since, fuel gas contains mixture of hydrocarbons (CxHy), so total molar flow rate of fuel gas = 1.62 kmole/s

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