Why and to What Extent Is Gas Purification Required

All raw gases produced by gasifying coal require purification and, under certain circumstances, additional conditioning before they are used as synthesis gas for methanol synthesis. The task of the purification unit is to remove gas components which are detrimental to the process route or harmful to methanol synthesis, whereas gas conditioning has the purpose of providing the proper stoichiometric conditions for producing methanol from carbon monoxide, carbon dioxide and hydrogen, expressed by the formula 

This condition, also termed the stoichiometric number, has its optimum for methanol synthesis at about 2.02 to 2.1, depending upon the concentration of inert gases such as methane, nitrogen, and argon. 

The gas purification procedure downstream of coal gasification is by its very nature considerably more difficult and complex than purifying gases produced from gaseous or liquid hydrocarbons. Basically, it can be said that the fewer the molecules of the raw material from which synthesis gas is produced, the smaller will be the size of the gas purification and conditioning units. However, for the same raw material, namely coal, there are also considerable difrerences in the requirements for gas purification and conditioning, dependent upon the type of gasification processes applied. 

In regard to purifying coal gases, the following impurities must be considered  

In addition to the aforegoing components which are usually present in such quantities that they can be easily determined analytically, there are still a number of impurities which normally occur only in traces but can have a damaging in- 

---