Coal-to-Hydrogen Efficiency and Performance

Technologies for Hydrogen Production

Technologies for hydrogen (H₂) production fall into three main categories:

1. Thermal Processes: Some thermal processes use the energy in various feedstocks (natural gas, coal, biomass, etc.) to release the H₂ that is part of their molecular structure.  Other thermal processes, know as thermo chemical processes use heat in combination with a closed chemical cycle to produce H₂ from feedstocks such as water. 
   
   In addition to gasification, the main thermal process technology which is available for production of H₂ is steam reformation of natural gas. It is a well established technology that produces about 95% of the H₂ produced in the United States.  Steam reforming involves the reaction of natural gas and steam over a nickel based catalyst.  This breaks the methane component of the natural gas into carbon monoxide (CO) and H₂ gas, similar to synthesis gas (syngas) produced via gasification.  Then a water-gas shift (WGS) is performed to increase the amount of H₂ in the product gas as much as possible.
2. Electrolytic Processes: These processes use electricity to split water into its two chemical constituents, oxygen (O₂) and H₂, using an electrolyzer.  The cost and efficiency of producing H₂ via electrolytic processes is directly dependent on the cost and efficiency of the electricity used in the process. 
3. Photolytic Processes: These processes use light energy to also split water into H₂ and O₂.  These processes are currently in the early stages of development and currently are not viable for large scale production.

Efficiency/Cost Comparison to Competing Technologies
Table 1 presents the cost and performance characteristics of various H₂ production pathways, as of 2004.  Many of the technologies that are in the research and development (R&D) stage will require years of improvements before becoming a commercial reality.

The cost of H₂ production depends heavily on the cost of fuel or electricity from which it is produced.  As the market price for these inputs to the H₂ production system fluctuate, one given technology may become more attractive economically compared to others.

Efficiency of H₂ Production for Various Coal Plant Schemes

There are several gasification plant layouts which produce H₂ from coal, as discussed in the Coal to Hydrogen Processes page.  The following sections describe the efficiency and performance of these different plant schemes.  The data in the following sections is taken from references 2 through 4 at the bottom of this page. 

IGCC and H₂ Co-Production
Table 2 lists the published overall performance and efficiency of a typical IGCC/H₂ co-production plant using Illinois No. 6 coal as feed.  The plant design is based on advanced dry feed entrained flow gasification technology with conventional acid gas removal (AGR) and pressure swing absorption (PSA) H₂ separation technology.   Performance and efficiency shown are for maximum power co-production.

IGCC and Hydrogen Co-Production with CO₂ Capture
Table 3 lists some of the typical coal-to-H₂ plant performance and efficiency. The designs used different coal feed and gasifiers. The performance and efficiency shown include carbon dioxide (CO₂) compression for sequestration, and are for maximum power co-production with the use of gas turbine.

Hydrogen Production Only
Table 4 lists some of the published overall performance and efficiency values for coal-to-H₂ production only design studies. Results are shown for both with and without CO₂ capture scenarios, and are for minimal power co-production without the use of gas turbines.

IGCC/H₂ Co-Production with WGCU and Advanced WGS Membrane
Table 5 shows the reported overall performance and efficiency of an IGCC/H₂ co-production plant, equipped with a warm gas cooling unite and  WGS membrane.  Performance and efficiency are shown for both with and without CO₂ capture scenarios, and for with and without co-producing significant amount of power for export.

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