Reference no: EM133025086

COMBINED MASS AND ENERGY BALANCE

Question: 1. A fuel gas has the following volumetric composition:

It is burned to produce a flue gas which contains on a dry basis by volume:

Calculate:
(i) the theoretical air supply
(ii) the actual air supply(iii) the % excess air.

Question 2. A fuel consists of carbon and hydrogen only. When completely burned in air the flue gas on a dry basis has the following analysis:

The temperature of the flue gases produced is 1600°C and these are fed to a boiler used to raise steam. 15% of the heat available at 1600°C is lost to the surroundings and the flue gases leave the boiler at 300°C.
Calculate:
(i) the amount of air supplied
(ii) the composition of the fuel
(iii) the amount of steam raised per hour if the enthalpy change from water feed to steam product is 2490 kJ kg^-1 and the flow of wet flue gas = 100 kmol h^-1.

Question 3. A power plant burns 100% methane (CH4), supplied at 25°C and
1 atmosphere pressure. 20% excess air is supplied at the same conditions. (a) Write a balanced equation for the reaction.
(b) Calculate the heat of combustion of methane at 25°C and1 atmosphere from the data given below.
(c) Assuming complete combustion of the methane to carbondioxideand water and no heat loss to the surroundings, confirm that the theoretical flame temperature will be approximately 2070 K.
(d) State, without calculation, the effect on flame temperature of using:
(i) less excess air
(ii) more excess air.
Data:
Standard heat of formation of CH₄ (g) = -74 900 kJ kmol^-1
Standard heat of formation of H₂O(g) = -242 100 kJ kmol^-1 Standard heat of formation of CO₂ (g) = -393 000 kJ kmol^-1 For enthalpy values use the table in lesson MAEB - 4 - 3.

Question 4. In the production of chlorosilanes, chloromethane gas (CH₃Cl) is produced as a by-product. This needs to be removed and treated to prevent potential hazardous material entering the atmosphere. This is achieved by continuously dissolving and reacting it with the stoichiometric quantity of potassium hydroxide (KOH) solution in a continuous scrubbing tower according to the reaction:
CH Cl₃ (g) + KOH(aq) → KCl(aq) + CH OH₃ (l)ΔHr° = -167 7. kJ mol-1

It is important that the reaction temperature is maintained below 22°C to ensure maximum removal of the chloromethane. Cooling water at 10°C is available and the maximum rise in water temperature should be 5°C.

Calculate:
(i) the amount of KOH solution required per hour
(ii) the adiabatic temperature of the reaction (no cooling is used)
(iii) the minimum amount of cooling water required to maintain the temperature at 22°C, if no heat is lost to the surroundings.

Data:

Temperature of chloromethane  =  195°C

Molar heat capacity of chloromethane  =  31.4 kJ kmol^-1 K^-1

Flow rate of chloromethane  =  101 kg h^-1

Concentration of KOH solution  =  4% w/w KOH in water

Inlet temperature of KOH  =  25 °C

Specific heat capacity of reaction mixture  =  3.5 kJ kg^-1 K^-1

Specific heat capacity of water  =  4.18 kJ kg^-1 K^-1

Relative atomic mass of  K  =  39, C  =  12, H  =  1, O  =  16 and Cl  =  35.5.

Attachment:- COMBINED MASS AND ENERGY BALANCE.rar