Gas: heating and illuminating – Processes – Coal
Reexamination Certificate
2002-06-24
2004-02-03
Langel, Wayne A. (Department: 1754)
Gas: heating and illuminating
Processes
Coal
C252S372000, C252S373000, C252S376000, C423S359000, C518S704000
Reexamination Certificate
active
06685754
ABSTRACT:
STATEMENT REGARDING FEDERALLY FUNDED RESEARCH
None
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a method for the production of valuable hydrocarbon products by reacting a carbonaceous material and steam in a molten metal to form a synthesis gas that can be used to produce high-value hydrocarbon products. More particularly, the present invention is directed to a method for the production of a synthesis gas that includes a controlled ratio of hydrogen to carbon monoxide by contacting a carbonaceous material and a reactive metal with steam, wherein a portion of the steam reacts with the carbonaceous material and a portion of the steam reacts with the reactive metal. The synthesis gas can be used to form high-value hydrocarbon products, such as methane or methanol.
2. Description of Related Art
Recently, the United States and other countries have experienced a shortage of natural gas and as a result, natural gas prices for consumers have increased substantially. Accordingly, there is a pressing need for economic methods for the manufacture of a high-value heating gas that can be used in place of natural gas. Natural gas has a composition that includes from about 80 percent to 93 percent methane (CH
4
), the balance including ethane (C
2
H
6
), propane (C
3
H
8
), butane (C
4
H
10
) and nitrogen (N
2
). Methane, the primary component of natural gas, has a heating value of about 21,520 Btu/lb. Thus, an economic method for the production of methane would supplement the use of non-renewable natural gas.
There are many natural resources in addition to natural gas that are utilized to produce energy. For example, coal can be burned in conventional boilers to generate steam, which is converted to energy through steam turbines. 85 percent of the electricity in the United States is generated by combusting fossil fuels, namely coal, oil and natural gas. Coal however, because of its high carbon content, generates large quantities of carbon dioxide (CO
2
), and the use of coal for electricity generation is a major contributor to the 5.5 billion tons of CO
2
emitted by the United States per annum. The 5.5 billon tons of CO
2
amounts to one-fourth of the world emissions. Coal combustion is also responsible for other pollution, most notably sulfur dioxide (SO
2
) and nitrogen oxides (NO
x
), both of which are now regulated.
Furthermore, only 30 percent of the heat generated by burning coal is converted into electricity and 70 percent is wasted to the atmosphere. In contrast, electrical generation in modern plants burning natural gas is about 50 percent efficient and natural gas produces only about 60 percent of the CO
2
that coal produces.
As an alternative to simply burning high carbon containing materials, such as coal, the materials can be converted to a synthesis gas in a gasifier. Synthesis gas includes five major gaseous components—carbon monoxide (CO), hydrogen (H
2
), methane, carbon dioxide and steam (H
2
O). These gases are derived from the carbon (C), hydrogen, and oxygen (O
2
) molecules found in the high carbon containing material and steam used to convert the high carbon containing material to synthesis gas. Other elements, designated impurities, typically found with carbonaceous materials include sulfur (S), nitrogen (N
2
), chlorine (Cl
2
) and fluorine (F). These impurities can form minor amounts of other gaseous species. Taken together the major and minor gases constitute a “raw” synthesis gas stream. As used herein, synthesis gas refers to the gas mixture after the minor gases have been removed. Nitrogen, steam and carbon dioxide do not contribute to the heating value and therefore typically are reduced or eliminated from the gas stream. The term “syngas” refers to a gaseous mixture that includes only hydrogen and carbon monoxide.
Synthesis gas has numerous applications, including the conversion of the synthesis gas into valuable hydrocarbons. In one application, the synthesis gas can be converted to methane, which is burned in a combined cycle power plant to generate electricity. The combined cycle gas turbines can be located at coal-fired generating stations thereby taking advantage of existing coal-handling infrastructure and electrical transmission lines. Most importantly, compared to coal-fired electrical generators, the conversion efficiency of thermal to electrical energy increases by about 67 percent. Concomitantly, there is a reduction in carbon dioxide emissions per unit of electricity.
For a gas turbine, gas is input to the turbine and the output is thermal energy. For increased efficiency, a gas with a high thermal energy per cubic foot is desirable. The net heating value (heat of combustion) of the three major components of synthesis gas are illustrated in Table 1 below. These values assume that the heat contained in the steam, the combustion product of hydrogen, is not recovered.
TABLE 1
Net Heats of Combustion
Synthesis Gas
Component
Btu/lbs
Btu/ft
3
Carbon Monoxide
4,347
322
Hydrogen
51,623
275
Methane
21,520
913
As is illustrated in Table 1, methane releases more than three times the amount of heat that hydrogen releases on a per cubic foot basis. The reason for this is that hydrogen occupies more cubic feet on a per pound basis, even though hydrogen has more Btu on a per pound basis. Due to its clean burning nature and high heat content, methane is the preferred fuel. Consequently, syngas (H
2
and CO) is more economically burned after it is converted to methane.
Syngas can be used to form other hydrocarbons in addition to methane. Since 1955, SASOL, a South African entity has been producing a waxy synthetic crude from syngas. Some transportation fuel, about 11 percent gasoline, is extracted from the synthetic crude. However, due to the large portion of hydrocarbons having a high molecular weight and oxygenated organics that are also produced, other approaches have been investigated for making specific materials from syngas.
There are well known processes for producing methanol (CH
3
OH) and acetic acid (CH
3
COOH) from syngas, for example. Typically, methanol is produced using syngas derived from natural gas, which exerts further pressure on the price and availability of natural gas. At least one major US oil company has developed a family of catalysts that produce a mixture of hydrocarbons in the gasoline range with high selectivity from methanol. Because methanol can be readily made from syngas, and catalysts are available for converting methanol into gasoline with great selectivity, coal-derived syngas affords the US an opportunity to achieve energy independence.
Methanol is also a chemical building block for manufacturing a wide array of other products, including: MTBE (methyl tertiary butyl ether) used in reformulated gasoline; formaldehyde resins, used in engineered wood products and products such as seat cushions and spandex fibers; acetic acid used to make PET (polyethylene terepthalate) plastic bottles and polyester fibers; and windshield wiper fluid. Additionally, methanol is relatively environmentally benign, is less volatile than gasoline and is a leading candidate to power fuel cell vehicles.
There are known processes for converting coal into gaseous products. Hydrogasification converts coal and steam into a raw synthesis gas. Gasification, a companion process, employs coal, steam and oxygen and produces hydrogen, carbon monoxide and carbon dioxide, but no methane. Pyrolysis, which utilizes heat alone, partitions coal into volatile matter and a coke or char. The volatile matter includes hydrogen, oxygen, some portion of the carbon (volatile carbon), organic sulfur and trace elements. The coke or char includes the balance of the (fixed) carbon and the ash derived from the mineral matter accompanying the organics.
Heat by itself disproportionates gaseous volatile matter, derived from coal, into methane and carbon as is illustrated by Equation 1.
CH
x
→(
x/
4)CH
4
+[1−(
x/
4)]C (1)
(where the value of x must be less than 4)
The hydropyrolysis reaction combi
Kindig James Kelly
Weyand Thomas E.
Alchemix Corporation
Langel Wayne A.
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