Moderator
The most common moderator used in gasification processes is steam. The steam must have a minimum temperature corresponding to that of saturated steam at the pressure prevailing in the gasifier, otherwise condensation in the lines to the gasifier will occur. In general, steam is used that is superheated to a temperature of 30CM-00°C. At pressures above 40 bar this superheat is mandatory, since otherwise the steam becomes wet on expansion.
The use of carbon dioxide as a moderator is unusual but not entirely unknown. Some plants use it to influence the H2/CO ratio of the synthesis gas where carbon monoxide or a СО-rich gas is the product. A process has been published using an oxygen-blown gasifier for the production of pure carbon monoxide from coke, incorporating carbon dioxide as a moderator (Lath and Herbert 1986).
Where C02 is used as a transport gas for pulverized coal in entrained gasifiers, it will also act as moderator or part thereof.
