Chemistry of inorganic compounds – Carbon or compound thereof – Oxygen containing
Reexamination Certificate
2000-08-08
2001-12-25
Langel, Wayne (Department: 1754)
Chemistry of inorganic compounds
Carbon or compound thereof
Oxygen containing
C423S418200
Reexamination Certificate
active
06333015
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of synthesis gas production and to the field of synthesis gas combustion for the generation of power (e.g., generation of electricity) with little or no environmental pollution. In particular, the invention pertains to a closed loop system for the generation and use of synthesis gas for electric power production with zero emissions.
2. Background Information
It is well known in the art that a combustible gas mixture can be produced by the pyrolytic decomposition of a carbonaceous material such as wood, organic refuse, coal and coke. Typically the carbonaceous material is pyrolytically decomposed by contacting hot carbonaceous material with steam under pyrolizing conditions in a vessel. The products of pyrolytic decomposition are mainly hydrogen and carbon monoxide.
It is known to produce a combustible gaseous product which comprises hydrogen and carbon monoxide by the water gas system wherein water or steam is reacted with incandescent carbonaceous material. It is known to use a two-step operation wherein a bed of carbonaceous material, such as coke, is first oxidized by passing air therethrough until the material becomes incandescent and, in the second step, passing steam through the incandescent material to yield the product gasses, including hydrogen and carbon monoxide according to the following chemical equation:
H
2
O+C→H
2
+CO
The bed of coke is cooled during the second step, and the first step of air oxidation must be repeated in order to reheat the bed.
It is also known to heat the bed of carbonaceous material electrothermally by using carbon or graphite electrodes. Electrothermic gasification is accomplished by placing the electrodes in contact with the material and applying a sufficient electrical potential to the electrodes, thereby causing resistive heating of the material to sufficiently elevated temperatures which result in the gasification reactions. Water required for the gasification reactions is provided in the form of injected steam or as water vapor from a reservoir located in the bottom of the reactor vessel. In addition to utilizing electrodes for resistive heating, it is also known to carry out the water gas reaction by utilizing an electric arc for heating the material to the required elevated temperatures.
Various technical and economic deficiencies have been noted with respect to the aforementioned prior art technology. U.S. Pat. No. 5,069,765, the specification of which is incorporated herein by reference, is said to provide a more energy efficient and environmentally acceptable method for manufacturing combustible gases from a wide variety of carbonaceous materials. The process described in the aforementioned patent uses a primary reactor, a secondary reactor and optionally a tertiary reactor which are connected in series. A charge of carbonaceous material is fed into the primary reactor which contains electrodes therein for creating an electric arc zone. A constant level of charge is maintained in the reactor and a supply of water for vaporization by the arc is maintained at a level just below the arc zone. When a continuous electric arc is maintained at the electrodes, the intense heat of the arc creates an “arc pocket” in the feed charge at the arc zone, thereby exposing the downwardly feed charge at the periphery of the pocket and the gases and vapors within the pocket to the thermal and photochemical effects of the arc. The primary reactor produces a raw product gas which contains mainly hydrogen and carbon monoxide. It is said that the raw product gas produced in the primary reactor is generally unsuitable for direct use because of its high (approximately 10%) carbon dioxide content.
In order to deal with the undesirable high level of carbon dioxide, the raw product gas is sent to a secondary reactor for reaction with a bed of coke contained therein. The top of the secondary reactor is provided with a single carbon electrode which is positioned within the bed so that the terminal end of the electrode is spaced from the upper level of the coke bed a desired distance in order to permit the creation of an arc between the electrode and the coke bed. In operation, arcing and resistance heating occurs throughout the height of the coke bed which causes the bed to be heated to incandescence. Raw product gas in the secondary reactor is first subjected to the electrothermal and photochemical effects of the arc and thereafter the gas passes downwardly through the incandescent coke bed for further reaction. This results in a reduction in the carbon dioxide content of the product gas. As noted above, it is desired to reduce the carbon dioxide content of the product gas because the gas coming from the primary reactor is unsuitable for direct use because of its high carbon dioxide content. It is said that the refined product gas having a low carbon dioxide content is suitable for combustion in a power generating plant. Thus, it is clear from the disclosure of this patent that the carbon dioxide content of the gas which is burned in the power plant must be minimized.
All gasification processes such as mass burn, incineration, fluidized bed as well as the process described in U.S. Pat. No. 5,069,765 must deal with the problem of removing the inert ash products from the gasifier. In all of the gasification processes in use today, large amounts of ash products, clinkers, etc., fall down onto a metal conveyor or screw system. This allows the removal of the ash from the gasifier to an ash holding compartment where the products are allowed to cool. Costly equipment is generally required to remove pollutants from the ash. After the removal of pollutants from the ash, the ash may then be disposed of in a landfill. Often, the ash products are not completely reacted and there can be as much as about 37% by weight of these ash products left over from the un-reacted feed material.
It is known to remove the ash products from the gasifier and then convey the ash to another vessel that is equipped with electrodes which are adapted to heat the ash to form a molten product which is poured into molds where it is allowed to cool into a glass-like substance. This process is called “vitrification”. However, this process is quite cumbersome and there is a possibility that pollutants can be released into the atmosphere unless costly additional equipment is used during the vitrification process. It would therefore be highly desirable to adapt the primary reactor, such as the primary reactor of U.S. Pat. No. 5,069,765 so that the desired vitrification process can be conducted within the gasification vessel so that all potential pollutants which are released from the ash during the vitrification process can remain in the system for further breakdown when subjected to the high temperature pyrolysis conditions. It would also be highly desirable to provide a primary gasifier which avoids the problems associated with clinkers which fall down onto the aforementioned metal conveyor or screw system.
Although the refined product gas produced in accordance with U.S. Pat. No. 5,069,765 is highly refined, the power plants in which this type of gas is combusted typically use air to support the combustion. It is well known that when ambient air or atmospheric air is used for combustion, various types of pollutants such as oxides of nitrogen (NO
x
), carbon monoxide and huge amounts of CO
2
are released into the atmosphere. These unwanted pollutants can be removed by the use of various types of catalytic converters or by the use of other costly gas cleaning equipment to meet EPA standards. Thus it would be highly desirable to produce synthesis gas and burn it for the production of power without releasing these or other pollutants into the environment.
In most combustion processes where ambient air or atmospheric air is used, the combustion mixture includes a mixture of gases which are naturally found in the atmosphere. These gases include nitrogen, oxygen, argon and other small amounts
Bacon & Thomas
Langel Wayne
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