Presently, coal gasification provides around 18% of the total hydrogen in the world, and is the second-largest and most cost-effective way of producing hydrogen. In China, the scenario is quite different. There coal gasification is the main production method where 62% of its hydrogen comes through the process. Hydrogen production through coal gasification is considered to have the most climate impact since the process results in 18-20 kg of CO2 emissions per 1 kg of H2 while steam methane reforming emits 8-12 kg per the same. Coal gasification is a thermo-chemical process where coal breaks down into a few gases and particulate matter during the process. Anyway, after 4 major steps, hydrogen and carbon dioxide can be separated out as the final products.
Technology Behind Coal Gasification
Through gasification, coal gets to turn into a very hot synthesis gas (Syngas) at a temperature of around 1800 celsius which is a mixture of carbon monoxide, hydrogen and carbon dioxide along with other trace gases such as Sulfur Dioxide and particulate matter.
In the next stage, syngas is cooled and cleaned to remove trace gases and particles. In this process sulfur, mercury, particulate matter and other contaminations are removed.
Then cleaned syngas is transferred to the shift reactor. Through shift reaction, CO is converted to CO2 and afterwords the product stream is mostly H2 and CO2.
Finally, CO2 and H2 are separated into two streams. If the plant is equipped with CCSU (Carbon Capturing Storage and Utilize) technology, CO2 is captured, stored and utilized.