Water gas

Water gas is a synthesis gas, containing carbon monoxide and hydrogen. It is a useful product but requires careful handling because of the risk of carbon monoxide poisoning. The gas is made by passing steam over red-hot coke:


 * C + H2O → CO + H2

The reaction is endothermic so the coke must be continually re-heated to keep the reaction going. This was usually done by alternating the steam stream with an air stream.

Variations
Water gas had a lower calorific value than coal gas so the calorific value was often boosted by passing the gas through a heated retort into which oil was sprayed. The resulting mixed gas was called carburetted water gas.

Semi-water gas is a mixture of water gas and producer gas made by passing a mixture of air and steam through heated coke. The heat generated when producer gas is formed keeps the temperature of the coke high enough to allow water gas to be formed.

Pure hydrogen can be obtained from water gas by using the Water gas shift reaction.