TABLE OF CONTENTS Historically, moving-bed processes are the oldest processes, and two processes in particular, the producer gas process and the water gas process, have played an important role in the production of synthesis gas from coal and coke. The preferred feedstocks are in general coke or anthracite, as otherwise the gas needs extensive cleaning to remove tars from the gas. Both processes operate at atmospheric pressure.
In the producer gas process, humidified air is blown upward through a deep bed of coal or coke. The coal is fed from the top and moves slowly downwards as it is consumed. Ash is drawn off at the bottom of the reactor from a rotating grate. The air reacts with the coal, thereby producing a gas with a lower heating value of about 6500 kJ/Nm 3. The presence of about 50% nitrogen in the product gas is the main cause for this low value. The advantage of this process is that it is continuous. The main drawback is that because of its low heating value, producer gas cannot be transported economically over long distances. When using low-rank feedstocks such as wood, the heating value of the gas can be as low as 3500 kJ/Nm 3. Gas producers continue to be built in small numbers today where gas is required locally for firing industrial furnaces, particularly in locations where coal is the only available energy form as in parts of China (Wellman, undated).
The water gas...
