Hydromethanation
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Hydromethanation, Hy-dro-meth-an-a-tion [hahy-droh- meth-uh-ney-shuhn], n. 1. [Hydromethanation] is the process by which methane (the main constituent of natural gas) is produced through the combination of steam, carbonaceous solids and a catalyst in a fluidized bed reactor. The process, developed over the past 60 years by multiple research groups, enables the highly efficient conversion of coal, petroleum coke and biomass (e.g. switchgrass or wood waste) into clean, pipeline quality methane.[citation needed]
Chemistry
The chemistry of catalytic hydromethanation involves reacting steam and carbon to produce methane and carbon dioxide, according to the following reaction:
2C + 2H2O -> CH4 + CO2
The process utilizes a specially designed reactor and depends upon a proprietary metal catalyst to promote chemical conversion at the low temperatures where the water gas shift reaction and methanation take place.
When a feedstock treated with the catalyst is introduced into this reactor and mixed with steam, three reactions occur that efficiently convert the feedstock into methane.
Hydromethanation reactions
- Steam carbon
C + H2O -> CO + H2
- Water-gas shift
CO + H2O -> H2 + CO2
- Hydro-gasification
2H2 + C -> CH4
The combination of carbon (C) from the carbon feedstock, water (H2O) from steam, and the catalyst, produces pure methane and a pure stream of carbon dioxide (CO2) which is 100% captured in the system and available for sequestration. The overall reaction is thermally neutral, requiring no addition or removal of heat, making it highly efficient.
The development of hydromethanation is an example of process intensification, where several operations are combined into a single step to improve overall efficiency, reduce maintenance and equipment requirements, and lower capital costs.
Other technologies
- Main article: Coal gas
Coal gasification has a history that dates back to the 19th century with the production of “town gas,” or “coal gas”. Traditionally, the production of any gas from carbon feedstocks has been an inefficient and capital intensive process. Conventional gasification technologies produce synthesis gas (or syngas), a combination of hydrogen and carbon monoxide which has a significantly lower energy value than natural gas and which generates far more carbon dioxide when burned [citation needed]. Syngas also cannot be transported in natural gas pipelines, and is not compatible with existing power facilities, industrial plants, and commercial/residential heating systems. Although syngas can be further upgraded into methane (pipeline quality natural gas), it currently can only be done through the addition of multiple, complex, higher cost and lower efficiency processing plants. The result is a far more expensive end product.
Byproducts
In addition to methane, hydromethanation produces a high-purity stream of carbon dioxide (CO2), an odorless colorless gas that is also considered a greenhouse gas. This CO2 stream is fully captured in the process and prevented from entering the atmosphere using a process called sequestration. The CO2 can be injected into underground oil reserves, through a process called enhanced oil recovery (“EOR”), or geologically sequestered.
Because hydromethanation is a catalytic process that does not rely on the combustion of carbonaceous solids to capture their energy value, it does not produce the nitrogen oxides (NOx), sulfur oxides (SOx) and particulate emissions typically associated with the burning of carbon feedstocks, including certain types of biomass. Due to this quality, it intrinsically captures nearly all of the impurities found in coal and converts them into valuable chemical grade products. Ash, sulfur, nitrogen, and trace metals are all removed using commercial gas clean-up processes and are either safely disposed of or used as raw materials for other products such as sulfuric acid and fertilizer.
See also
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