Gas separation: processes – Liquid contacting – Hydrate inhibitor
Reexamination Certificate
2002-12-27
2004-09-28
Smith, Duane S. (Department: 1724)
Gas separation: processes
Liquid contacting
Hydrate inhibitor
C095S236000, C096S243000, C423S220000, C423S437100, C585S015000
Reexamination Certificate
active
06797039
ABSTRACT:
FIELD OF THE INVENTION
The field of this invention is selective absorption of CO
2
gas.
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 nearly 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 include 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 and expensive in terms of cost per ton of CO
2
removed or sequestered. 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 expensive and/or 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
. Of particular interest would be the development of a process which provided for efficient CO
2
separation at low temperature (e.g., 0 to 10° C.) from low to moderate CO
2
partial pressure multicomponent gaseous streams.
Relevant Literature
U.S. Patents of interest include U.S. Pat. Nos.: 5,700,311; 6,090,186; 6,106,595; 6,235,091; 6,235,092 and 6,352,576.
SUMMARY OF THE INVENTION
Methods are provided for the selective removal of CO
2
from a multicomponent gaseous stream to provide a CO
2
depleted gaseous stream. In practicing the subject methods, an initial multicomponent gaseous stream that includes a gaseous CO
2
hydrate promoter is contacted with an aqueous fluid, e.g., CO
2
nucleated water, in a hydrate formation reactor under conditions of selective CO
2
clathrate formation to produce a CO
2
clathrate slurry and CO
2
depleted gaseous stream. In certain embodiments, a feature of the subject invention is that additional gaseous CO
2
hydrate promoter is introduced into the process stream at some point prior to the output of the hydrate reactor. In certain embodiments, a feature of the subject invention is that the hydrate formation reactor is a tubular finned reactor. Also provided are systems that find use in practicing the subject methods. The subject methods and systems find use in a variety of applications where it is desired to selectively remove CO
2
from a multicomponent gaseous stream.
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Bozicevic Field & Francis LLP
Field Bret E.
Smith Duane S.
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