Question

Calculate weight of air needed for complete combustion of 2kg of coal containing C=70%, H=10%, O=10%, N=5% and remaining ash.

Answer 1

1kg of coal contains 0.7kg C,0.1kg H & 0.1kg O₂

Combustion reactions	Weight of O2 required(kg)
1) C + O → CO2	`0.7xx32/12=1.86`
2) H2+12O2 → H2O	`0.1xx16/1=0.8`

Weight of O₂ = 1.86+0.8=2.66
Available O₂ = 0.10
Total O₂ = 2.56
Air contains 23% O₂ by weight
∴Min quantity of air required = 2.56`xx100/23`

= 11.13 kg.

For 2kg of coal air needed = 11.32 × 2
= 22.26kg.