Mineral oils: processes and products – Chemical conversion of hydrocarbons – Cracking
Reexamination Certificate
2001-07-31
2003-06-03
Griffin, Walter D. (Department: 1764)
Mineral oils: processes and products
Chemical conversion of hydrocarbons
Cracking
C208S108000, C208S112000, C210S237000, C210S345000, C210S346000
Reexamination Certificate
active
06572761
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an improved method for using biomass and fossil fuels, such as coal, in order to power gas turbine engines using unmixed combustion of solid fuels. The invention also relates to a process for separating the products of unmixed combustion, including pollutants such as carbon dioxide, sulfur compounds, nitrogen compounds, and volatile metals (e.g., mercury) into a separate stream available for subsequent treatment and ultimate sequestration.
One of the major problems in modern industrial society is the production of air pollution by conventional combustion systems based on biomass and fossil fuels. The oldest recognized air pollution problem is the emission of smoke. In modern boilers and furnaces, smoke emissions could be eliminated or at least greatly reduced by the use of Over Fire Air (“OFA”) technology. Other types of air pollution produced by combustion include particulate emissions such as fine particles of ash from pulverized coal firing, oxides of sulfur (SO
2
and SO
3
), carbon monoxide emissions, volatile hydrocarbon emissions and the release of two oxides of nitrogen, NO and NO
2
. More recently, the problem of global warming due to greenhouse gas emissions of CO
2
from power plants and other combustion systems have become a matter of serious environmental concern.
Another major technological problem concerns the use of coal as a fuel for powering gas turbines. Gas turbines are the lowest capital cost systems available for generating electrical power. Since the thermodynamic efficiency of gas turbines increases with increasing turbine inlet temperature, efforts to improve turbine efficiency generally involve increasing the turbine inlet temperature to higher levels. As a result, turbine blades and other components have been engineered to tolerate increasing high inlet temperatures.
It is well known that the hot gases produced by coal firing contain fly ash (which is erosive to turbine blades). In the presence of this erosive fly ash the maximum service temperature at which turbine blades can operate is less than it would be otherwise. This limitation significantly decreases the overall process efficiency and lowers the competitiveness of coal as a gas turbine fuel. These and other disadvantages have also prevented lower cost (and abundant) coal from being considered an attractive gas turbine fuel. If a process were developed whereby coal could be burned in a manner that produced hot gases that were not erosive or corrosive, the need for temperature reduction would be eliminated and coal would become a much more economically viable gas turbine fuel.
With respect to global warming, coal has the further disadvantage that its CO
2
emissions per BTU released are significantly higher than those of most ashfree fuels. Again, however, if coal could be burned in a manner that did not cause the emission of CO
2
and/or other pollutants, this known disadvantage would disappear, making coal a much more environmentally acceptable fuel for existing uses and new uses such as fueling gas turbines.
U.S. Pat. Nos. 5,339,754, 5,509,362 and 5,827,496 (incorporated herein by reference) disclose a new method of burning fuels using a catalyst that is readily reduced when in an oxidized state and readily oxidized when in a reduced state, with the fuel and air being alternatively contacted with the catalyst. The fuel reduces the catalyst and is oxidized to CO
2
and water vapor. In turn, the air oxidizes the catalyst and becomes depleted of oxygen. Combustion can thereby be effected without the need of mixing the fuel and air prior to or during the combustion process. If means are provided whereby the CO
2
and water vapor and the oxygen depleted air can be directed in different directions as they leave the combustion process, the mixing of fuel and air can be completely avoided. This particular method of combustion has become known in the art as “unmixed combustion.” In one embodiment disclosed in the '362 patent, the CO
2
produced by the combustion process is separated from the water vapor and disposed of by conventional means. The '362 patent also removes the acid gases such as SO
2
, HCl and HF.
It is well known that the total volume of combustion gases produced by unmixed combustion is comparable to that produced in conventional combustion. It is also well known that the cost of removing acid gases from combustion effluents by scrubbing increases with the volume of gas being scrubbed. The '362 patent recognize that if unmixed combustion is carefully controlled such that the acid gases leave the combustion process as part of the CO
2
and water vapor steam, the volume of gas that must be scrubbed can be greatly reduced, as well as the cost of scrubbing.
The subject matter of the '362 patent is discussed in greater detail in paper 98F36, presented at the October 1998 meeting of the Western States Section of the Combustion Institute (hereafter referred to as the “Combustion Institute paper”). The authors of the paper include R. K. Lyon (the inventor of U.S. Pat. No. 5,509,362 and the inventor of the present invention) and J. A. Cole. The paper discloses a conceptual process for using coal to power a gas turbine and reports on a series of experiments illustrating certain aspects of the proposed process.
The reported experiments used an atmospheric pressure fluid bed of powdered, chemically pure iron oxide (i.e., FeO/Fe
2
O
3
). In the experimental setup, the gas being used to fluidize the bed could be switched from air to 5% SO
2
+95% N
2
and back again. The basic experiments as reported in the paper involved two steps. First, a bed fully oxidized to Fe
2
O
3
was fluidized with the 5% SO
2
+95% N
2
at a temperature of 857 @ C. A small amount of coal was injected into the bed while the gases leaving the bed were continuously analyzed. In a second step, the fluidizing gas was switched to air while the gases leaving the bed were analyzed. Based on available data, the paper concludes that coal is readily oxidized in the presence of SO
2
and that the chief carbon containing product of the oxidation is CO
2
, with little or no CO being produced. The paper attributes the ability of the solid particles of Fe
2
O
3
to rapidly oxidize the coal to a catalytic action by the SO
2
used in the fluidizing gas. That is, the SO
2
reacts with the coal, converting it into to CO
2
, CO, CS
2
, COS, and sulfur vapor. The CO, CS
2
, COS, and sulfur vapor are, in turn, oxidized by the Fe
2
O
3
to CO
2
and SO
2
. Thus, the SO
2
serves as a catalyst, allowing the solid Fe
2
O
3
to oxidize the solid coal char. The first half of this process, the gasification of coal char by SO
2
, is described by J. D. Blackwood and D. J. McCarthy in the Australian J. Chem. P. 723, 1973.
The initial experiments reported in the Combustion Institute paper indicate that the gases exiting the bed after being fluidized with air contain little or no SO
2
and little or no CO and CO
2
. Thus, the paper concludes that the Fe
2
O
3
oxidized the coal to completion during the first step, i.e., while the bed was fluidized with 5% SO
2
+95% N
2
. The oxidation converted all the sulfur in the coal to SO
2
and other volatile species which exited the bed during the first step of the experiment.
Another series of two-step experiments discussed in the paper used a bed fluidized with N
2
. Like the experiments conducted with coal, when the amount of thiophene injected was small, all of the sulfur left the bed as SO
2
and other volatile species during the first step. Conversely, none of the sulfur was retained in the bed during the first step and exited during the second air fluidization step. Increasing the amount of injected thiophene changed that situation. That is, injecting thiophene in excess of a threshold amount caused some of the sulfur to be retained in the bed during the first step and to be released as SO
2
during the second air fluidization step. The paper speculates that this threshold is a result of FeS, i.e., after thiophen
General Electric Company
Griffin Walter D.
Nguyen Tam M.
Nixon & Vanderhye P.C.
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