Chemistry: electrical current producing apparatus – product – and – Having magnetic field feature
Reexamination Certificate
1998-11-05
2001-02-13
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Having magnetic field feature
C429S010000
Reexamination Certificate
active
06187465
ABSTRACT:
This invention relates generally to a process and system for the elimination of carbon dioxide and other greenhouse gas emissions from conventional coal, oil, and natural gas power plants.
BACKGROUND OF THE INVENTION
The burning of fossil fuels in boilers to raise high temperature, high pressure steam that can be used to power turbo-electric generators produces a problem source of carbon dioxide and other greenhouse gases, e.g. methane, ozone and fluorocarbons. This fossil fuel combustion, especially of coal, needs a technological fix to avoid the emission of carbon dioxide and other greenhouse gases with their attendant undesirable release to the earth's atmosphere resulting in the absorption of solar radiation known as the greenhouse effect. Much of the world depends on coal for power. There have been significant efforts to develop clean coal technologies to greatly reduce the release of acid gases, such as sulfur oxides and nitrogen oxides. However, to date none of these clean coal programs aim to eliminate the emissions of carbon dioxide and other greenhouse gases. Efforts to use pure oxygen in power plants and gasification systems to avoid the diluting effects of nitrogen and to achieve higher efficiency suffers from the unacceptable cost of requiring an air separation plant and the problems of excessive temperatures in oxygen-fed turbo-generators.
There is also widespread effort to increase the efficiency of power plants by utilizing advanced thermodynamic combined cycles, more efficient turbo-generators, improved condensers and cooling towers, and similar systems. A small portion of this effort involves the use of fossil fuel gasification processes, which are higher efficiency because they avoid combustion and large combustion product emissions. Finally there is an effort by Westinghouse (Corporate literature, “SureCell®” 1996) and others to combine the use of advanced high temperature turbo-generators and fuel cells to accomplish conversion to electricity at about 70% instead of current conventional power plants of about 47%.
Today there is worldwide concern that the atmospheric buildup of carbon dioxide and other greenhouse gases will start to have serious environmental consequences for the earth's tropospheric temperature, global rainfall distribution, water balance, severe weather storms, and similar consequences. Technological solutions are being demanded throughout the world.
The worldwide research establishment, encouraged by government funding from various agencies, continues to be focused on identifying commercially attractive gas separation technologies to remove carbon dioxide from stack gases and also attractive chemistry that will utilize this carbon dioxide as a raw material to manufacture useful products. This has, indeed, been a very large challenge with poor successes as summarized by the review papers; see Michele Aresta, and Eugenio Quaranta, “
Carbon Dioxide: A Substitute for Phosgene
,” Chem.Tech. pp. 32-40, March 1997. and Bette Hileman, “
Industry Considers CO
2
Reduction Methods
”, Chem & Engr. News, pg. 30, Jun. 30, 1997. Trying to scrub the CO
2
from stack gases and trying to chemically react the recovered CO
2
clearly is not the right path of research because of the technical difficulty and the process expense of reacting carbon dioxide.
SUMMARY OF THE INVENTION
The process and system of the invention converts carbonaceous feedstock from fossil fuels and other combustible materials into energy without the production of unwanted greenhouse emissions. The present process comprises the following steps:
(a) converting a carbonaceous feedstock and a greenhouse gas stream in a gasification unit to synthesis gas comprising carbon monoxide and hydrogen;
(b) electrochemically oxidizing at least a portion of the synthesis gas from the gasification unit in a first half-cell of a fuel cell to produce a first half-cell exit gas comprising carbon dioxide and water;
(c) recovering the carbon dioxide from the first half-cell exit gas to serve as at least a portion of the greenhouse gas stream in step (a); and
(d) electrochemically reducing an oxygen-containing gas in a second half-cell of the fuel cell completing the circuit and resulting in the production of electrical energy.
The present system comprises the following:
(a) the gasification unit having inlet means for the carbonaceous feedstock and the greenhouse gas stream, a catalyst or other means for converting the combined feedstock into the synthesis gas;
(b) the fuel cell for the production of electrical energy comprising the first half-cell having an inlet in fluid communication with the synthesis gas and a first means or anode for electrochemically oxidizing synthesis gas into the first half-cell exit gas, a second half-cell having a second means or cathode for electrochemically reducing the oxygen-containing gas, and a membrane separating the first and second half cells that will not allow passage of the gaseous components from the respective half-cells; and
(c) passage means for passing the carbon dioxide from the first half-cell to serve as at least a portion of the greenhouse gas stream for the gasification unit.
The present process avoids the difficult path of attempting to strip and capture the carbon dioxide from stack gases and without attempting to carry out separate chemical reactions of carbon dioxide to attempt to produce useful products. The process and system of the present invention uses commercially available gasification technology combined with fuel cells to generate electricity at high efficiency. This is accomplished by taking advantage of a very unique property of fuel cells—namely, the two anodic and cathodic reactions are separated by an electronically conducting membrane that keeps the product gases separate. In this way, a combustible feed gas can be fully oxidized in the first half-cell of the fuel cell without being commingled with the final products of the air in the second half-cell electrode, i.e., N
2
. For example, in coal gasification, synthesis gas is formed consisting predominantly of hydrogen and carbon monoxide. This synthesis gas is fed into the first half-cell, i.e., the anode or negative terminal side, of the fuel cell, such as the solid oxide or molten carbonate types, where it is oxidized to water and carbon dioxide. These gases are not diluted by the typical nitrogen from combustion air used on the second or remaining half-cell, i.e., the cathode side or positive terminal, of the fuel side. Nitrogen and combustion gases are commingled when combustion air is used in boilers or furnaces. Thus, in the fuel cell, the synthesis gas (syngas) is oxidized without being combusted with air and without being diluted by other gases. The fuel cell-produced water and carbon dioxide are simply separated from each other by condensing the liquid water and allowing the carbon dioxide to return to the gasifier. The carbon dioxide being injected into the high temperature gasifier undergoes a reaction with the high temperature carbonaceous feed to form more carbon monoxide, repeating the cycle.
By means of the present process and system, the carbon dioxide in the fuel cell is easily kept separate from the air side and any nitrogen. This carbon dioxide can be recycled back to the gasifier in nearly pure form. Likewise water in pure form can be recycled as well in different amounts under gasifier control system requirements to maintain the ideal hydrogen to carbon monoxide ratio of in the range of about 1.75 to about 2.25. This helps maintain a high hydrogen content in the gasifier so that the gasifier-produced syngas can be used downstream in a chemical reactor such as a Fischer-Tropsch reaction system for the production of a variety of useful chemicals ranging from methanol to paraffin waxes. These in turn are used to make useful chemicals such as naphtha, gas oil, and kerosine. Thus, the carbon monoxide is used to produce useful chemicals instead of discarding the valuable carbon source in the carbon dioxide. The carbon balance of the plant is maintained such tha
Coudert Brothers
Kalafut Stephen
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