Trace Components in Gasifier Syngas

In high temperature processes all sulfur components in the feed are converted to H2S or COS. Other compounds such as SOx or CS2 are essentially absent. This is not the case in low temperature processes, where tars and other species have not been completely cracked. 

The H2S COS ratio of a raw gas is determined by the hydrogenation and hydrolysis reactions. Under typical gasification conditions H2S is the dominant species and approximately 93-96% of the sulfur is in this form, the rest being COS. 

Chlorine compounds are present in most coals. They will react with ammonia in the raw gas to form ammonium 

Metals in the feedstock will also form chlorides (e.g., sodium chloride). Many of these have melting points in the range 350-800°C and represent a fouling risk in heat exchangers. 

The existence of unsaturated hydrocarbons in the raw synthesis gas varies widely. In low temperature processes, there will, in general, be significant quantities of aromatics and other unsaturates in the volatiles and tars, though the exact amount also will depend heavily on the feedstock. For high-temperature-entrained flow processes including oil gasification, the presence of any hydrocarbon other than methane, whether saturated or unsaturated, is minimal. 

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