Gas separation: apparatus – Gas and liquid contact apparatus for gas separation... – Heating or cooling means
Reexamination Certificate
2000-03-22
2001-05-22
Chiesa, Richard L. (Department: 1724)
Gas separation: apparatus
Gas and liquid contact apparatus for gas separation...
Heating or cooling means
C422S198000, C585S015000
Reexamination Certificate
active
06235091
ABSTRACT:
INTRODUCTION
1. Field of the Invention
The field of this invention is selective absorption of CO
2
gas.
2. Introduction
In many applications where mixtures of two or more gaseous components are present it is often desirable to selectively remove one or more of the component gases from the gaseous stream. Of increasing interest in a variety of industrial applications, including power generation, chemical synthesis, natural gas upgrading, and conversion of methane hydrates to hydrogen and CO
2
, is the selective removal of CO
2
from multicomponent gaseous streams.
An example of where selective CO
2
removal from a multicomponent gaseous stream is desirable is the processing of synthesis gas or syngas. Syngas is a mixture of hydrogen, carbon monoxide and CO
2
that is readily produced from fossil fuels and finds use both as a fuel and as a chemical feedstock. In many applications involving syngas, the carbon monoxide is converted to hydrogen and additional CO
2
via the water-gas shift process. It is then often desirable to separate the CO
2
from the hydrogen to obtain a pure H
2
stream for subsequent use, e.g. as a fuel or feedstock.
As man made CO
2
is increasingly viewed as a pollutant, another area in which it is desirable to separate CO
2
from a multicomponent gaseous stream is in the area of pollution control. Emissions from industrial facilities, such as manufacturing and power generation facilities, often comprise CO
2
. In such instances, it is often desirable to at least reduce the CO
2
concentration of the emissions. The CO
2
may be removed prior to combustion in some cases and post combustion in others.
A variety of processes have been developed for removing or isolating a particular gaseous component from a multicomponent gaseous stream. These processes include cryogenic fractionation, selective adsorption by solid adsorbents, gas absorption, and the like. In gas absorption processes, solute gases are separated from gaseous mixtures by transport into a liquid solvent. In such processes, the liquid solvent ideally offers specific or selective solubility for the solute gas or gases to be separated.
Gas absorption finds widespread use in the separation of CO
2
from multicomponent gaseous streams. In CO
2
gas absorption processes that currently find use, the following steps are employed: (1) absorption of CO
2
from the gaseous stream by a host solvent, e.g monoethanolamine; (2) removal of CO
2
from the host solvent, e.g. by steam stripping; and (3) compression of the stripped CO
2
for disposal, e.g. by sequestration through deposition in the deep ocean or ground aquifers.
Although these processes have proved successful for the selective removal of CO
2
from a multicomponent gaseous stream, they are energy intensive. For example, using the above processes employing monoethanolamine as the selective absorbent solvent to remove CO
2
from effluent flue gas generated by a power plant often requires 25 to 30% of the available energy generated by the plant. In most situations, this energy requirement, as well as the additional cost for removing the CO
2
from the flue gas, is prohibitive.
Accordingly, there is continued interest in the development of less energy intensive processes for the selective removal of CO
2
from multicomponent gaseous streams. Ideally, alternative CO
2
removal processes should be simple, require inexpensive materials and low energy inputs, and be low in cost for separation and sequestration of the CO
2
. For applications in which it is desired to effectively sequester the separated CO
2
, of particular interest would be the development of alternative CO
2
absorbents or adsorbents from which the absorbed or adsorbed CO
2
could be effectively and efficiently stripped at high pressure prior to further compression and sequestration. Of particular interest would be the development of a system which minimizes parasitic energy losses for all process steps necessary to produce a high pressure CO
2
gas stream for disposal (sequestration and utilization).
Relevant Literature
Patents disclosing methods of selectively removing one or more components from a multicomponent gaseous stream include: U.S. Pat. Nos. 3,150,942; 3,838,553; 3,359,744; 3,479,298; 4,253,607; 4,861,351; 5,387,553; 5,434,330; 5,562,891 and 5,600,044.
Reports summarizing currently available processes for reducing the CO
2
content of multicomponent gaseous streams, such as coal fired power plant emissions, include: Smelser, S.C. et al., “Engineering and Economic Evaluation of CO
2
Removal From Fossil-Fuel-Fired Powerplants, Vol. 1: Pulverized -Coal-Fired Powerplants,” EPRI IE-7365Vol. 1 and Vol. 2; Coal Gasification-Combined Cycle Power Plants, EPRI IE-7365, Vol. 2.
Other publications discussing CO
2
clathrate formation include Japanese unexamined patent application 3-164419, Nishikawa et al., “CO
2
Clathrate Formation and its Properties in the Simulated Deep Ocean,” Energy Convers. Mgmt. (1992) 33:651-657; Saji et al., “Fixation of Carbon Dioxide by Clathrate-Hyrdrate,” Energy Convers. Mgmt. (1992) 33: 643-649; Austvik & Løken, “Deposition of CO
2
on the Seabed in the Form of Clathrates,” Energy Convers. Mgmt. (1992) 33: 659-666; Golumb et al., “The Fate of CO
2
Sequestered in the Deep Ocean,” Energy Convers. Mgmt. (1992) 33: 675-683; Spencer, “A Preliminary Assessment of Carbon Dioxide Mitigation Options,” Annu. Rev. Energy Environ. (1991) 16: 259-273; Spener & North, “Ocean Systems for Managing the Global Carbon Cycle,” Energy Convers. Mgmt. (1997) 38 Suppl.: 265-272; and Spencer & White, “Sequestration Processes for Treating Multicomponent Gas Streams,” Proceedings of 23
rd
Coal and Fuel Systems Conference, Clearwater, Florida (March 1998).
SUMMARY OF THE INVENTION
Methods are provided for the selective removal of CO
2
from a multicomponent gaseous stream. In the subject methods, a multicomponent gaseous stream comprising CO
2
is contacted with CO
2
nucleated water in which hydrate precursors are contained under conditions of selective CO
2
clathrate formation, conveniently in a reactor. The CO
2
nucleated water (hydrate precursor water) employed in the subject invention comprises dissolved CO
2
in the form of CO
2
hydrate or clathrate precursors, where the precursors are in metastable form. The CO
2
nucleated water (hydrate precursor water) may either be formed in situ in the reactor or in a separate reactor, where the water may be fresh or salt water. Once the CO
2
nucleated water is formed, it serves as a selective CO
2
liquid absorbent or adsorbent. Upon contact of the gaseous stream with the CO
2
nucleated water, CO
2
is selectively absorbed or adsorbed from the gaseous stream by the CO
2
nucleated water and concomitantly fixed as CO
2
clathrates to produce a CO
2
depleted multicomponent gaseous stream and a slurry of CO
2
clathrates. The resultant CO
2
depleted multicomponent gaseous stream is then separated from the CO
2
clathrate slurry, either in the reactor itself or in a downstream separator. In a preferred embodiment, the resultant slurry is then treated in a manner sufficient to decompose the CO
2
hydrates to produce a moderate to high pressure CO
2
gas and CO
2
nucleated water. The process is suitable for use with a wide variety of multicomponent gaseous streams.
REFERENCES:
patent: 3150942 (1964-09-01), Vasan
patent: 3359744 (1967-12-01), Bolez et al.
patent: 3479298 (1969-11-01), Sze et al.
patent: 3838553 (1974-10-01), Doherty
patent: 4235607 (1980-11-01), Kinder et al.
patent: 4861351 (1989-08-01), Nicholas et al.
patent: 5397553 (1995-03-01), Spencer
patent: 5434330 (1995-07-01), Hnatow et al.
patent: 5562891 (1996-10-01), Spencer et al.
patent: 5600044 (1997-02-01), Colle et al.
patent: 5700311 (1997-12-01), Spencer
patent: 6106595 (2000-08-01), Spencer
patent: 3-164419 (1991-07-01), None
Austvick et al. (1992). “Deposition of CO2On the Seabed in the Form of Hydrates”Energy Convers. Mgmt., vol. 33(5-8): 659-666.
Golomb et al. (1992). “The Fate of CO2Sequestered in the Deep Ocean”Energy Convers. Mgmt., vol. 33(5-8): 675-683.
Bozicevic, Field & Francis
Chiesa Richard L.
Field Bret E.
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