Hydrogen from coal

Hydrogen production from carbonaceous feedstocks requires multiple catalytic reaction steps For the production of high-purity hydrogen, the reforming of fuels is followed by two water-gas shift reaction steps, a final carbon monoxide purification and carbon dioxide removal. Steam reforming, partial oxidation and autothermal reforming of methane are well-developed processes for the production of hydro- 

The second step in the process consists of cleaning and shifting the CO to form hydrogen and CO, by reacting with steam. The overall reaction for converting the CO is the chemical shift reaction  

There are commercial or near commercial technologies for coal gasification processes used for hydrogen production. These are Koppers-Totzek and Texaco gasification processes. 

In the Koppers-Totzek process, the polarized coal is rapidly partially oxidized with oxygen and steam at essentially atmospheric pressure under slogging con- 

The product hydrogen is about 2.8 MPa, with a purity higher than 97.5%. It is more efficient to gasify coal at elevated pressures. 

The gasification process combines the coal with steam in a hot environment to produce a syngas (synthetic gas) composed mostly of carbon monoxide (CO) and hydrogen. In the process, coal is first gasified with oxygen and steam to produce a synthesis gas consisting mainly of carbon monoxide (CO) and hydrogen (H), with some carbon dioxide (COj), sulfur, particulates, and trace elements. 

The coke or char carbon that remains after devolatilization is gasified through reactions with oxygen, steam, and carbon dioxide to form additional amounts of hydrogen and carbon monoxide. 

Once the syngas is produced, it can be burned directly in a turbine to produce power or further reacted with more steam to shift the ranaining carbon monoxide to carbon dioxide and produce 

The carbon dioxide can be stored in oil and gas fields and the hydrogen can be used for the many applications that make up the hydrogen economy—such as to power a car in an engine or a fuel cell, to power a turbine to produce electricity, or to power a stationary fuel cell to make electricity. 

Minerals in the feedstock separate as ash and leave the bottom of the gasifier as an inert slag (or bottom ash), a potentially marketable solid product. The fraction of the ash entrained with the synthesis gas, which is dependent upon the type of gasifier employed, requires ranoval downstream in particulate control equipment, such as filtration and water scrubbers. 

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R. E. Billings, Hydrogen From Coal A Cost Estimation Guidebook, PennWeU Publishing Co., Tulsa, OHa., 1983. 

Imperial Chemical Industries in Great Britain hydrogenated coal to produce gasoline until the start of World War II. The process then operated on creosote middle oil until 1958. As of this writing none of these plants is being used to make Hquid fuels for economic reasons. The present prices of coal and hydrogen from coal have not made synthetic Hquid fuels competitive. Exceptions are those cases, as in South Africa, where there is availabiHty of cheap coal, and fuel Hquids are very important. 

HyPr-RING Process, Direct Production of Hydrogen from Coal.114... 

Production of hydrogen from coal is a well-established technology, in which 02 or steam is passed over coal to produce a mixture of H2, CO, and C02 from which H2 is separated (Figure 3.1). 

Although, producing hydrogen from coal is not as cost effective as producing hydrogen from oil or natural gas, coal can be used where oil or natural gas is not readily available and where coal is abundant. 

Figure 3.5 shows the complete process for the production of hydrogen from coal. The process consists of the following components coal preparation, air separation, coal gasification,... 

Because coal is an important economical source for production of hydrogen, developing new technologies to improve the efficiency of hydrogen production is an important priority. Some new approaches for producing hydrogen from coal are discussed in the following section. 

In conventional production of hydrogen from coal, as described earlier, coal is converted to hydrogen and carbon monoxide (CO) through the water-carbon reaction as shown in reactions 3.9 through 3.11. CO is then converted to hydrogen and carbon dioxide by the water-gas shift reaction as shown in reaction 3.12. 

Concept of AGC project for production of hydrogen from coal. 

Shiying L., Yoshizo S., Hiroyuki H. and Michiaki H., A New Method (HyPr-RING) for Producing Hydrogen from Coals, The 10th International Conference on Coal Science, Sep. 12-17, Taiyuan, China, 1999. 

Collot A.-G., Prospects for Hydrogen from Coal, IEA Clean Coal Center, London, 2004. 

Diho, R. J. Patel, J. G., U-gas process for production of hydrogen from coal. International Journal of Hydrogen Energy 1983, 8(3), 175-182. 

Stiegel, G.J. and Ramezan, M., Hydrogen from coal gasification, An economical pathway to a sustainable energy future, Int.. Coal Geol., 65,173, 2006. 

The practicality and environmental consequences of many sequestration techniques have not yet proven from an engineering or scientific aspect. Sequestration still requires much research and development before generating large volumes of hydrogen from coal and sequestering the C02 produced. C02 sequestration on a massive scale would need to be permanent to be practical. 

However, biomass plants appear earlier than coal and more biomass plants are built, because they are smaller and can become central supplies at smaller market penetration. It is important to note that the delivered cost of hydrogen from coal, biomass and natural gas central plants are typically quite close (within 0.5/kg). Thus, the choice of a feedstock may be determined by other factors, such as state policies favouring renewables and the availability of carbon-sequestration sites. 

Both the production of hydrogen from coal and the production of oil from unconventional resources (oil sands, oil shale, CTL, GTL) result in high C02 emissions and substantially increase the carbon footprint of fuel supply, unless the C02 is captured and stored. While the capture of C02 at a central point source is equally possible for unconventionals and centralised hydrogen production, in the case of hydrogen, a C02-free fuel results, unlike in the case of liquid hydrocarbon fuels. This is all the more important, as around 80% of the WTW C02 emissions result from the fuel use in the vehicles. If CCS were applied to hydrogen production from biomass, a net C02 removal from the atmosphere would even be achievable. 

Hydrogen from coal with CO, removed and stored underground 13.2... 

The German COORETEC CO2 Reduction Technologies) concept favours coal gasification with precombustion capture to introduce COj capture into coal fired power plants. The same capture process is suited to produce hydrogen from coal in an environmentally-friendly way. This technical option is outlined in the recently drawn up national vision on hydrogen technologies. The first projects in this area are to be funded in the near future. 

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