Editing Gasification (section)

==Chemical reactions==
In a gasifier, the carbonaceous material undergoes several different processes:
[[File:pyrolysis.svg|frame|Pyrolysis of carbonaceous fuels]]
[[File:gasification.gif|frame|Gasification of char]]
# The [[dehydration reaction|dehydration]] or drying process occurs at around 100&nbsp;°C.  Typically the resulting steam is mixed into the gas flow and may be involved with subsequent chemical reactions, notably the water-gas reaction if the temperature is sufficiently high (see step #5).
# The ''[[pyrolysis]]'' (or devolatilization) process occurs at around 200–300&nbsp;°C.  Volatiles are released and [[charring|char]] is produced, resulting in up to 70% weight loss for coal. The process is dependent on the properties of the carbonaceous material and determines the structure and composition of the char, which will then undergo gasification reactions.
# The ''[[combustion]]'' process occurs as the volatile products and some of the char react with oxygen to primarily form carbon dioxide and small amounts of carbon monoxide, which provides heat for the subsequent gasification reactions. Letting '''C''' represent a carbon-containing [[organic compound]], the basic reaction here is C + O<sub>2</sub> → CO<sub>2</sub>.
# The ''gasification'' process occurs as the char reacts with steam and carbon dioxide to produce carbon monoxide and hydrogen, via the reactions C + H<sub>2</sub>O → H<sub>2</sub> + CO and  C + CO<sub>2</sub> → 2CO.
# In addition, the [[reversible reaction|reversible]] gas phase [[water-gas shift reaction]] reaches [[chemical equilibrium|equilibrium]] very fast at the temperatures in a gasifier. This balances the concentrations of carbon monoxide, steam, carbon dioxide and hydrogen: CO + H<sub>2</sub>O ⇌ CO<sub>2</sub> + H<sub>2</sub>.

In essence, a limited amount of oxygen or air is introduced into the reactor to allow some of the organic material to be "burned" to produce carbon dioxide and energy, which drives a second reaction that converts further organic material to hydrogen and additional carbon dioxide. Further reactions occur when the formed carbon monoxide and residual [[water]] from the organic material react to form methane and excess carbon dioxide (4CO + 2H<sub>2</sub>O → CH<sub>4</sub> + 3CO<sub>2</sub>). This third reaction occurs more abundantly in reactors that increase the [[Residence time distribution|residence time]] of the reactive gases and organic materials, as well as heat and pressure. [[Catalysts]] are used in more sophisticated reactors to improve reaction rates, thus moving the system closer to the reaction equilibrium  for a fixed residence time.

Hydrogasification is a gasification process where hydrogen is used in place of oxygen to produce methane/natural gas from coal or biomass.<ref>{{cite web |url= https://www.mdpi.com/2073-4344/13/2/417 |title=A Review of Coal and Biomass Hydrogasification: Process Layouts, Hydrogasifiers, and Catalysts|access-date=31 May 2025}}</ref><ref>{{cite web |url=https://link.springer.com/article/10.1007/s40789-024-00677-x |title= A critical review on direct catalytic hydrogasification of coal into CH4: catalysis process configurations, evaluations, and prospects) |access-date=31 May 2025}}</ref><ref>{{cite web |url= http://www.hceco.com/HCEI105001.pdf |title= Conversion of Coal to Substitute Natural Gas (SNG) |access-date=31 May 2025}}</ref><ref>{{Cite journal |last=Sasidhar |first=Nallapaneni |date=May 2025 |title=In-situ and Ex-situ Conversion of Coal to Methane using Hydrogen |url=https://www.ijeer.latticescipub.com/wp-content/uploads/papers/v4i3/C104404030525.pdf |access-date=2025-05-28 |journal=Indian Journal of Energy and Energy Resources |issn=2583-1186|volume=4 |issue=3|pages=1–5 |doi=10.54105/ijeer.C1044.04030525 |s2cid=258753397}}</ref>