Module 1: Fuels characterization and energy balance
  Lecture 7:Production of Gaseous Fuel
 
   2.   With air + steam

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 H2 << volume of N2.
  • Excessive heat in the producer is utilized since decomposition of steam is endothermic.

Consider the following gasification reaction
 
In the gasification of coal or coke with a mixture of air and steam, it is important to know how much amount of steam can be fed without supplying any heat from outside. Heat balance can yield the amount of steam which can be fed.

Consider gasification of 1 Kg mole of C with a mixture air and steam under adiabatic conditions:Let X Kg mole of C reacts with air. Assuming that all steam decomposes to H2 and carbon forms CO.