Question

Calculate the amount of CO2 (in kg) released when 1 kg coal is burnt. Assume that carbon content of the coal is 50% by mass. 4. Calculate the CO2 production in kg/MJ if a coal fired power plant (efficiency - 30%) is used to produce electricity. Assume energy density of coal - 24 MJ/kg and assume the coal is

Answer 1

Step-by-step explanation:

(a) Here, the assumption is that complete combustion of carbon is taking place. This means that there is no CO formation

Reaction equation when carbon is burning is as follows.

`C + O_(2) \rightarrow CO_(2)`

Molar mass of C = 12 kg/kmol

Molar mass of
`CO_(2)` = 44 kg/kmol

Hence, according to the stoichiometry,

1 Kmol of C reacted = 1 kmol of
`CO_(2)` produced

Therefore, 12 kg of C reacted = 44 kg
`CO_(2)` produced

It is given that coal contains 50 mass % Carbon

So, 1 kg of coal contains (0.50 × 1)kg Carbon

Carbon in 1 kg Coal = 1 × 0.5 = 0.5 kg

As per the stoichiometry,

12 kg of C reacted = 44 kg
`CO_(2)` produced

0.5 kg of C reacted = x kg
`CO_(2)` produced

Therefore, value of x can be calculated as follows.

x =
`\frac{\text{44 kg of CO_(2) produced} * \text{0.5 kg of C reacted}}{\text{12 kg of C reacted}}`

= 1.83 kg

This means that amount of
`CO_(2)` released is 1.83 kg.

(b) It is assumed that coal contains 50 mass % carbon and 1 kg of coal burnt.

Since, it is given that energy density of coal is 24 Mj and efficiency of the power plant is 30%.

After burning 1 kg of coal amount of energy released = 24 Mj

Amount of energy converted to electricity =
`24 Mj * 0.3` = 7.2 Mj

It is calculated that amount of
`CO_(2)` released per 1 kg of coal = 1.83 kg

Therefore, calculate the amount of
`CO_(2)` released in kg/Mj as follows.

amount of
`CO_(2)` released in kg/Mj =
`\frac{\text{Amount of CO_(2) released in kg}}{\text{amount of energy converted to electricity}}`

=
`(1.83 kg)/(7.2 mJ)`

= 0.2541 kg/Mj

Hence, the production of
`CO_(2)` in kg/MJ is 0.2541 kg/Mj.