Preamble

Gaseous fuel is produced by gasifying coal or coke in a reactor called gas producer. Gaseous fuels have several advantages like

• It is easy to handle.
• Combustion is rapid in comparison to coal or fuel oil.
• Less excess air for combustion is required than for combustion of fuel oil and coke.

Thermodynamics of Gasification:

Thermodynamics deals with the conversion of carbon of fuel to gaseous product at equilibrium, which means thermodynamics deals with initial and final states.

Consider gasification of 1 mole of carbon with air. Stoichiometrically ½ mole of oxygen is required to produce 1 mole of CO. One mole of oxygen is obtained from 4.76 moles of air, which means that every  mole of oxygen carries 3.76 moles of   with it. Thus if the initial state of reactants is  and  and final state is  and  the following gasification reaction can be written: 
                                                                                           (1)  

Gaseous fuel produced by gasification of carbon consists of CO and  in which

 

One can also use a mixture of air + steam to gasify the fuel. Now suppose we gasify carbon with a mixture of air + steam. Note that reaction 1 generates  Kcal of heat per Kg of carbon. This excessive amount of heat can generate a very high temperature in the gasifier, if the excessive amount of heat  is not  properly managed.  In large sized gas producers heat losses are very small and there occurs substantial rise in temperature. Steam is utilized to use the heat produced by reaction 1. Steam usage brings the following advantages:

• Decomposition of steam produces hydrogen and thereby producer gas is enriched in calorific value.

• Gaseous fuel is enriched per unit volume since volume of  of

• Excessive heat in the producer is utilized since decomposition of steam is endothermic.