A fuel gas consists of 75% butane (C4H10), 10% propane (C3H8) and 15% butene (C4H8) by volume. It is to be fed to the
Posted: Sat May 21, 2022 4:21 pm
A fuel gas consists of 75% butane (C4H10), 10% propane (C3H8) and 15%
butene (C4H8) by volume.
It is to be fed to the combustion chamber in 10% excess air at 25ºC, where
it is completely burnt to carbon dioxide and water. The flue gases
produced are to be used to generate 5 bar steam from water at 90ºC.
With the aid of the data at the end of the question, steam/ enthalpy tables.
(a) Write balanced equations for the combustion of each component of the fuel gas.
(b) Explain the need for excess air.
(c) Determine the actual fuel:air ratio (i) by volume (ii) by mass.
(d) Calculate:
(i) the net calorific value (CV) per m3 of the fuel/air mix at 25ºC (ii) the net calorific
value (CV) per kmol of the fuel/air mix at 25ºC.
(e) Determine the composition of the flue gases by volume (assuming the inlet air is dry):
(i) on a wet basis
(ii) on a dry basis.
(f) Determine the ‘furnace efficiency’ if the flue gases leave the boiler at 300ºC.
(g) Give two advantages of preheating the water in this way and one disadvantage.
(h) Give two reasons why the presence of any sulphur in the fuel mix would be undesirable.
Data:
Net calorific value (MJ m–3) at 25ºC of:
Butane (C4H10) = 111.7 MJ m–3
Butene (C4H8) = 105.2 MJ m–3
Propane (C3H8) = 85.8 MJ m–3
Air is 21% oxygen, 79% nitrogen by volume and 23.3% oxygen and
76.7% nitrogen by mass.
Atomic mass of C = 12, O = 16, N=14 and H = 1.
butene (C4H8) by volume.
It is to be fed to the combustion chamber in 10% excess air at 25ºC, where
it is completely burnt to carbon dioxide and water. The flue gases
produced are to be used to generate 5 bar steam from water at 90ºC.
With the aid of the data at the end of the question, steam/ enthalpy tables.
(a) Write balanced equations for the combustion of each component of the fuel gas.
(b) Explain the need for excess air.
(c) Determine the actual fuel:air ratio (i) by volume (ii) by mass.
(d) Calculate:
(i) the net calorific value (CV) per m3 of the fuel/air mix at 25ºC (ii) the net calorific
value (CV) per kmol of the fuel/air mix at 25ºC.
(e) Determine the composition of the flue gases by volume (assuming the inlet air is dry):
(i) on a wet basis
(ii) on a dry basis.
(f) Determine the ‘furnace efficiency’ if the flue gases leave the boiler at 300ºC.
(g) Give two advantages of preheating the water in this way and one disadvantage.
(h) Give two reasons why the presence of any sulphur in the fuel mix would be undesirable.
Data:
Net calorific value (MJ m–3) at 25ºC of:
Butane (C4H10) = 111.7 MJ m–3
Butene (C4H8) = 105.2 MJ m–3
Propane (C3H8) = 85.8 MJ m–3
Air is 21% oxygen, 79% nitrogen by volume and 23.3% oxygen and
76.7% nitrogen by mass.
Atomic mass of C = 12, O = 16, N=14 and H = 1.