7.3. Technologies for Hydrogen Production
Technologies for hydrogen (H2) production fall into three main categories:
- 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 known 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 water-gas shift (WGS) is performed to increase the amount of H2 in the product gas as much as possible.
- 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 H2via electrolytic processes is directly dependent on the cost and efficiency of the electricity used in the process.
- 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.
| Table 1: Efficiency/Cost Comparison to Competing Technologies 1 |
|
Process
|
Energy Required (kWh/Nm3)
|
Status of Tech.
|
Efficiency
[%]
|
Costs Relative
to SMR
|
|
Ideal
|
Practical
|
|
Steam methane reforming (SMR)
|
0.78
|
2-2.5
|
mature
|
70-80
|
1
|
|
Coal gasification (GE Energy)
|
1.01
|
8.6
|
mature
|
60
|
1.4-2.6
|
|
Partial oxidation of coal
|
|
|
mature
|
55
|
|
|
H2S methane reforming
|
1.5
|
|
R&D
|
50
|
<1
|
|
Landfill gas dry reformation
|
|
|
R&D
|
47-58
|
~1
|
|
Partial oxidation of heavy oil
|
0.94
|
4.9
|
mature
|
70
|
1.8
|
|
Naphtha reforming
|
|
|
mature
|
|
|
|
Steam reforming of waste oil
|
|
|
R&D
|
75
|
<1
|
|
Steam-iron process
|
|
|
R&D
|
46
|
1.9
|
|
Chloralkali electrolysis
|
|
|
mature
|
|
by-product
|
|
Grid electrolysis of water
|
3.54
|
4.9
|
R&D
|
27
|
3-10
|
|
Solar & PV-electrolysis of water
|
|
|
R&D to mature
|
10
|
>3
|
|
High-temp. electrolysis of water
|
|
|
R&D
|
48
|
2.2
|
|
Thermochemical water splitting
|
|
|
early R&D
|
35-45
|
6
|
|
Biomass gasification
|
|
|
R&D
|
45-50
|
2.0-2.4
|
|
Photobiological
|
|
|
early R&D
|
<1
|
|
|
Photolysis of water
|
|
|
early R&D
|
<10
|
|
|
Photoelectrochemical decomp. of water
|
|
|
early R&D
|
|
|
|
Photocatalytic decomp. of water
|
|
|
early R&D
|
|
|
|
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.
Coal-to-Hydrogen Process Description
The U.S. Department of Energy (DOE) has sponsored many design studies on the production of H2 from coal, with or without the co-production of power.
Recent DOE studies presented the following four process design schemes as possible options for centralized-large-scale H2 production from coal, and discussed their performance and efficiency:2
- Co-producing H2 and power in today's coal-based integrated gasification combined cycle (IGCC) plants
- Co-producing H2 and power in coal-based IGCC with carbon capture
- H2 production from coal without power export
- Co-producing H2 and power in future IGCC based on advanced warm gas clean-up and advanced membrane (combined shift and H2 separation) technologies
|
1.
|
Hydrogen: Automotive Fuel of the Future, by FSEC's Ali T-Raissi and David Block, IEEE Power & Energy, Vol. 2, No. 6, page 43, Nov-Dec 2004. |
|
2.
|
Hydrogen from Coal, D. Gray & G. Tomlinson, Mitretek Technical Paper (Nov 2001) |
Hydrogen
