Combustion Numerical

Engr. Ghulam Abbas

Numerical 01

A fuel gas behaving the following analysis is burned with air; CO2 = 2%; O2 = 1%; N2 = 12%; CO = 7%; H2 = 46%; CH4 = 30% AND C2H2 = 2%. The flue gas issuing from the combustion chamber contained; H2 = 18%; CO = 10%; CO2 = 3% and H2O = 6%.

Compute the following;• The volume of flue gas produced per M3 fuel

gas burned.• The percentage air deficiency.

Numerical 02

A coal containing 84% C and 10% ash is burned in a furnace leaving an ash which contains 25% C.

Estimate;• The mass of carbon lost in the ash per Kg coal

burned.• The percentage if the carbon burned.• The heat lost due to the loss of carbon in ash.

Calculate value of Carbon = 33.96 MJ/Kg

Numerical 3. An oil fuel, containing carbon and hydrogen only is burned to produce the following flue gas (dry basis);CO2 = 10.5%; O2 = 7.5%; N2 = 82.0% Estimate the gravimetric analysis of the fuel and the excess air supplied.

Numerical 04

The following producer gas;CO = 25%; CO2 = 5%; H2 = 12%; CH4 = 4% N2 =

54%; (CV 5.9 MJ/M3)Is manufactured from coke, containing 84% C and

12% ash on a producer gas plant. If the ash leaving the plant contains 13% C,

Estimate on the basis of 1Kg coke fired.• The weight of carbon gasified• The make of gas• The heat available; in the gas.

Numerical 05

1. A coal of the following analysis on the dry, ash free basis: Carbon = 89.3%; Hydrogen = 5%; Nitrogen = 1.5%; Sulpher = 0.8%; and Oxygen = 3.4% by weight is used with 8% ash and 7% moisture. Gross calorific value of the d.a.f. coal in 15650 BTU/lb (36,000 KJ/Kg). Compute the following:

• Air required for combustion of 1 Kg coal as fired.• Analysis of dry flue gas resulting from the

combustion.• Analysis of flue gas (i.e. wet flue gas) resulting from

the combustion.• Total volume of flue gases leaving the chimney at

120oC per Kg coal as fired.

•

Numerical 06A gas of the following composition by volume is burned with air: CH4 =

25%; H2 = 45%; CO2 = 3%; CO = 10%; O2 = 1%; C2H2 = 1%; N2 = 15%. Calculate:

• The theoretical air requirement.• Composition of the dry fuel gas produced when the gas is burned

with (a) the theoretical and (b) 50% excess air.• Composition and mass of the wet fuel gas produced when the

gas is burned with 50% excess air.• If the fuel gas burns to give a flue gas (dry basis) containing CO2

= 7.35%; O2 = 7.33% and N2 = 85.3%, what is the volume of dry flue gas and the total mass of flue gas produced.

• If the dry flue gas contains CO2 = 7.35%; O2 = 7.33% and N2 = 85.3%, what is the actual air and excess air used.

Solution

Numerical 07

• Assignment

Numerical 07A coal has the following analysis on the dry, ash free basis; C = 88.3%; H2 = 5.3%; N2 = 1.7%; S = 1%; O2 = 3.7%; by weight.

As fired, it contains 9% ash and 8% moisture. Gross calorific value of the dry ash free coal is 36,000 KJ/Kg. This coal is on combustion gives rise to smoke. The volumetric dry flue gas analysis is;

CO2 = 11.2%; CO = 1.4%; N2 = 80.5%; O2 = 6.9%. Calculate;• The amount of carbon lost in the smoke.• Percentage excess air used for combustion.• Heat lost due to un burnt carbon in the smoke expressed as

percentage of the Net calorific value of the coal as fired.• The calorific value of carbon may be taken as 33000 KJ/Kg while

heat of condensation of moisture as 2454 KJ/Kg.

• In a petroleum refinery the steam boiler plant has an overall thermal efficiency on gross calorific value of the fuel of 85% and an output of 200,000 lb of steam per hour. The steam is generated at a pressure of 250 lb/in2g, and superheated to 450oF from feed at 120oF

Refinery gas of the following volumetric composition is used to fire the plant; N2 = 9% H2 = 21%; CO = 1%; CO2 = 1%; H2S = 2; CH4 = 15%; C2H6 = 15%; Hydrocarbons as C3H6 = 36%;

From the information given below, Calculate the quantity of gas necessary to fire the

plant.

• If the exit gas temperature from the plant is 400oF calculate the capacity of the induced draught fan in cubic/feet per minute assuming the gas is burned with 20% excess air.

Calorific value at NTP, gross Btu/ft3; CO = 340; CH4 = 1000; H2 = 340; C2H6 = 1930; H2S = 703; C3H6 = 2300;

• Heat required to raise steam is;• 1 lb steam at 250 lb/in2.g and superheated to

450oF = 1230 Btu.

THE END

Numerical 4

A coal containing 84% C, is burned to produce a flue gas of the following composition (dry basis)

• CO2 = 12.5%; CO = 1.5%; O2 = 5.5%; N2 = 80.5%

• Estimate the mass of carbon converted to carbon monoxide per Kg coal burned

• Also estimate the heat lost by the incomplete combustion due to the formation of CO. Calorific value of carbon = 33.96 MJ/Kg and calorific value of CO = 10.23 MJ/Kg.