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7.1. Why Hydrogen?

Syngas derived from most high pressure gasification processes already contains a significant amount of hydrogen (H2), which can be increased through water gas shift (WGS) and be readily separated into a pure H2 product meeting industry product quality standards. There are several conventional H2 separation processes, but modern installations preferentially choose pressure swing adsorption (PSA), which is a well-proven technology offering high availability and low cost. PSA has the ability to produce high purity (99.9%) hydrogen at near feed pressure; however, relatively high H2 concentration in feed gases is required for its economics to remain favorable. New technologies are being developed to increase the efficiency and reduce the costs associated with H2 production from coal gasification.

Although most hydrogen is produced by steam reforming of natural gas (95% of world totals), hydrogen production or co-production from syngas generated by liquid or solid gasification is commercially practiced as well. This is mainly based on gasification of residuals, heavy oil or petcoke from refinery operations, with the hydrogen helping to satisfy the in-house demand for hydrotreating, hydrodesulfurization, hydrogenation, and hydrocracking. Many studies and demonstrations on producing H2 from coal have been completed, but there is currently no commercial coal gasification plant producing significant quantities of H2 as a final product. Even so, in the case of a number of large-scale ammonia and fertilizer-producing gasification plants in China, which is lacking low-cost sources of natural gas, coal is first converted to H2 before reacting with nitrogen to form ammonia.

In fact, any scenario in which high cost of natural gas would occur concurrently with low cost of coal, will provide impetus for production of hydrogen from coal feedstock. Moreover, H2 production technologies are gaining attention because hydrogen is predicted by some to be the energy carrier of the future, as it is extremely clean when reacted with oxygen (producing water) and has a high energy density by mass. Hydrogen can be used to feed fuel cells or combusted in a hydrogen turbine to generate electricity. Hydrogen could also power fuel cell vehicles. Although there are technical challenges to overcome, a clean coal gasifier to produce H2 would be a key component of a hydrogen economy and hydrogen-based power generation as envisioned.



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