Integrated air separation process

Details Integrated air separation process Integrated air separation process

2000-07-19

2001-09-04

Nguyen, Hoang (Department: 3748)

Power plants

Motive fluid energized by externally applied heat

Process of power production or system operation

C060S651000, C060S671000

Reexamination Certificate

active

06282901

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an integrated air separation process. More specifically, the present invention relates to a process for separating at least oxygen and nitrogen from air and integrating the use of oxygen and nitrogen into a process for efficiently generating steam and electrical power.
BACKGROUND DISCUSSION
Cogeneration involves using a single fuel source to simultaneously produce, in the same facility, thermal energy, usually in the form of steam, and electric energy. Since the Public Utility Regulatory Policy Act of 1978, owners of cogeneration facilities have been given a financial incentive to sell excess electrical power to utility companies, while utilities are encouraged to purchase that electrical power. Consequently, there has been a continuing effort to improve the energy efficiency of cogeneration plants, particularly in the United States. Moreover, the rising and volatile costs of natural gas have increased the economic incentive for many cogeneration plants to use other fuel sources, such as coal, for example.
Many cogeneration processes use an integrated, high-efficiency combined cycle to increase efficiency. Typically, a combined cycle is a steam turbine (i.e., Rankine-cycle) thermodynamically coupled with a gas turbine (i.e., Brayton-cycle). Steam and gas turbine combined cycle systems are often used where natural gas is the fuel source because natural gas tends to have a lower concentration of impurities that can cause hot corrosion, fouling and rapid deterioration in the gas turbine parts, particularly gas turbine blade surfaces. Therefore, historically, use of high-efficiency steam/gas combined cycle systems has been discouraged where coal is used as a fuel source due to the various impurities in coal that can cause gas turbine corrosion. Consequently, when using a steam/gas combined cycle in a coal combustion cogeneration process, it is important to limit the gas turbine's exposure to flue gas impurities and temperatures significantly exceeding the maximum admissible value (i.e., in a range of from about 1000° C. to about 1450° C.) for the gas turbine's materials of construction and its other operating conditions. This method will help forestall significant corrosion problems with the gas turbine and, thereby, keep equipment maintenance costs down.
U.S. Pat. No. 4,116,005 by Willyoung proposes using a fluidized combustor bed containing sulfur-sorbing particles that are fluidized by a gas turbine's air exhaust, at about atmospheric pressure, which also provides an O
2
source for the coal's combustion. However, Willyoung's proposed system fails to further enhance the inherent efficiency of using a steam/gas combined cycle in a cogeneration process. Also, Willyoung's modification of the combustion chamber with a fluidized bed requires significant expense and upkeep for limiting gas turbine corrosion.
Another factor challenging many coal fired cogeneration processes are gaseous emissions into the atmosphere, particularly nitrogen oxides (NO
x
), such as nitrogen oxide (NO), nitrogen dioxide (NO
2
) and nitrous oxide (N
2
O), sulfur oxides (SO
x
), such as sulfur dioxide (SO
2
) and sulfur trioxide (SO
3
), and carbon dioxide (CO
2
). Some global warming proponents relate excess N
2
O and CO
2
emissions to climatological change. Also, NO
x
emissons, such as NO or NO
2
, in sufficient concentration, can be toxic to health and the environment. Additionally, SO
x
emissions, in sufficient concentration, can contribute to the production of “acid rain,” which can have a detrimental effect on various plant and aquatic life. Thus, it is possible that many or all of these gases could become more stringently regulated, at least in certain market-developed countries or regions, such the United States, Canada, Japan and Europe. Consequently, this prospect of increasing regulatory stringency for some or all gaseous emissions that are typically coal combustion byproducts has made coal-fueled cogeneration processes less attractive from an operational cost standpoint.
For instance, various countries, including, among others, France, Germany, the United Kingdom, Australia, the United States, Canada and Japan have elected to adopt the Kyoto Protocol, which ensued from the United Nations Framework Convention on Climate Change, held in December, 1997 at Kyoto, Japan. Under the Kyoto Protocol each participant agreed in principle to “implement and/or further elaborate policies and measures in accordance with its national circumstances” to, among other things, enhance energy efficiency and protect reservoirs of certain atmospheric gases not controlled by the Montreal Protocol (e.g., CO
2
).
Generally, under the Kyoto Protocol the participating countries agreed to limit emissions of greenhouse gases specified under the Protocol, including CO
2
, methane (CH
4
), N
2
O, hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulfur hexafluoride (SF
6
), as well as work towards reducing the overall emissions of these gases by at least 5 percent below 1990 levels in the target period of 2008 to 2012. To date, no legislative amendments to the U.S. Clean Air Act Amendments of 1990 (CAAA) have been passed that would require facilities operating in the U.S. to comply with the Kyoto Protocol greenhouse gas emissions target. Nonetheless, the present U.S. administration has made a policy decision to adopt and promote the Kyoto Protocol. Accordingly, companies operating in the U.S. that have significant CO
2
emissions have been encouraged to voluntarily work towards the Kyoto Protocol's target level for the greenhouse gases specified. Also, if good progress towards the Protocol's goals is not shown, it is possible that some further amendments to the CAAA could flow from the Kyoto Protocol. CAAA amendments conforming with the Kyoto Protocol could also be motivated if models are developed to more definitively measure and predict the extent of global climate changes based on current and projected gaseous emissions. Thus, limiting the gaseous emissions, particularly from coal-fueled power generation plants, while maintaining an energy efficient power generation process is becoming a more important commercial objective.
For example, U.S. Pat. No. 5,937,652 by Abdelmalek proposes to produce energy more efficiently and reduce CO
2
emissions from a combined coal gasification and synthesis gas (i.e., a carbon monoxide (CO) and hydrogen gas (H
2
) mixture) combustion process. The coal gasification step is conducted under an oxygen (O
2
) free atmosphere, while using CO
2
and steam as oxidants for the coal fuel. The heat from the coal/CO
2
gasification reaction is used to produce steam for driving a steam turbine/generator that produces electricity. Also, Abdelmalek separates CO
2
from sulfur dioxide (SO
2
) and other gases discharged from a boiler using a cyclone separator system disclosed in U.S. Pat. Nos. 5,403,569 and 5,321,946.
Abdelmalek indicates that the process has a higher efficiency because the gasification reaction is run without O
2
, while the separated CO
2
, which is recycled back to the gasification chamber for reacting with coal, produces a nitrogen (N
2
) free synthesis gas, namely a CO and H
2
mixture. This CO/H
2
mixture is then combusted with O
2
to generate heat. According to Abdelmalek, the gross heat value of his combined coal gasification, where little to no O
2
is present, and synthesis gas combustion process, where CO and H
2
are reacted with O
2
to produce the principle heat, is 20% greater versus conventional coal combustion processes, where coal is burned using O
2
as a principle oxidant. Abdelmalek also contends that his process reduces CO
2
emissions by 20%. Moreover, Abdelmalek teaches that the combustion reaction chemistry, particularly where coal is a fuel source (e.g., coal+O
2
), makes conventional combustion type reactions inherently limited in the extent to which they can be made any more efficient, even in the context of a cogeneration process. Consequently, Abdelmale

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