Options to Produce Syngas and Hydogen Overview

For natural gas, partial oxidation is usually not an economical option as the investment costs for the required cryogenic air separation are high. Only in cases where syngas with a high CO content is needed is partial oxidation of natural gas - mostly then in combination with a steam reformer - an option. Thus partial oxidation is mostly applied where steam-reformable feeds are not available and where local conditions provide relatively cheap heavy feedstocks such as coal or heavy oil. 

The feed for steam reforming, typically natural gas, usually has to be desulfurized. If only small amounts of sulfur are present as H2S, the reaction with ZnO (to ZnS) is used. For a high content of H2S, scrubbing (absorption) with a solvent is usually the method of choice if the feed also contains organic sulfur compounds, hydrotreatment is needed as the primary treatment step (Section 6.8). 

For coal and heavy oil based syngas production, feedstock purification is, to date, not possible. Hence during partial oxidation the organic sulfur compounds are converted into H2S as we have a reducing atmosphere, at least after the oxygen has been consumed. Thus, H2S and other unwanted impurities like ash, tar, and solid carbon (soot) have to be separated from the raw syngas before it can be used further. 

Even if all these unwanted impurities have been removed, extended treatment steps are still required such as the water-gas shift reaction, CO2 removal, and 

Ammonia production requires a gas phase with hydrogen and nitrogen present in a ratio of 3 1 (Section 6.1), and the ammonia syngas must be free of CO and CO2 because these compounds poison the iron catalyst used in the ammonia synthesis reactor. 

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