Carbon dioxide fixation system

Details Carbon dioxide fixation system Carbon dioxide fixation system

1998-07-08

2001-08-07

Knode, Marian C. (Department: 1764)

Chemical apparatus and process disinfecting, deodorizing, preser

Chemical reactor

Waste gas purifier

C422S169000, C422S173000, C422S150000, C422S158000

Reexamination Certificate

active

06270731

ABSTRACT:

The present invention relates to a carbon dioxide fixation system for retrieving carbon dioxide gas existing in the atmosphere or contained in an exhaust gas emitted from factories or industrial plants.
BACKGROUND OF THE INVENTION
The global warming is known to be mainly caused by carbon dioxide gas which is emitted through human activities into the atmosphere from factories, industrial plants, thermal power plants, automobiles and so on. Reduction of carbon dioxide gas emission or retrieval of carbon dioxide gas existing in the atmosphere is thus recognized as one of the most important measures for protecting the environment.
Numerous systems have been proposed to reduce the emission or content of carbon dioxide gas. One of these such systems is shown in FIG.
5
. The carbon dioxide fixation system of
FIG. 5
is composed substantially of a CO
2
isolator
6
, an H
2
producer
8
and a reactor
9
. The CO
2
isolator
6
isolates CO
2
from the exhaust gas of a CO
2
source
1
, which is typically an industrial plant or a thermal plant, and concentrates the CO
2
gas by eliminating impurities therefrom. The H
2
producer
8
produces H
2
gas by a known method such as electrolytic water decomposition. In the reactor
9
, the CO
2
gas and H
2
gas react so that CO
2
-fixing products such as methanol (CH
3
0
H), for example, are produced. Thus the CO
2
gas retrieved from the atmosphere is fixed to a state harmless to the global warming, and, further, is changed to methanol which can be used as a fuel.
The above conventional CO
2
fixation system has a serious drawback, that is, a large amount of electric energy is required to produce hydrogen gas by the electrolytic process. It is estimated that more than 90 percent of the total operational energy of the conventional CO
2
fixation system is consumed in the hydrogen producer
8
. Except in the case where the price of electricity is very low, the running cost of such CO
2
fixation system is normally very high. The system has another disadvantage in that it does not reduce the CO
2
emission so much as a whole. In some countries, a large part of electricity is generated thermally. In a thermal power plant, fossil fuel such as oil, coal or natural gas is burned to generate high temperature steam, through which a large amount of CO
2
gas is inevitably generated.
Thus the following system is proposed. A part of the CO
2
fixation system including the hydrogen producer is installed in a place (or country) where there is a stable supply of electricity at low cost and where it is generated by a method other than burning fossil fuel, such as by a hydraulic generator or by solar batteries. CO
2
gas retrieved from the atmosphere and liquefied in other areas is transported by tankers or other carriers to the place, where the liquefied CO
2
is reacted with hydrogen to produce methanol. The methanol is then usually transported back to the areas of the CO
2
source.
The above separating system is difficult to visualize practically because the CO
2
is not processed near its emission source but the liquefied CO
2
, and its fixed product, must be transported to a remote place, which increases the processing cost.
SUMMARY OF THE INVENTION
An object of the present invention is therefore to provide an energy efficient, low cost CO
2
fixation system having a high overall CO
2
reducing performance.
The system according to the present invention is a system for fixing CO
2
gas in an atmosphere or in an exhaust gas, which includes:
fermentor for anaerobically fermenting organic wastes and for isolating methane gas;
hydrogen producing reactor for decomposing the methane gas produced by the fermentor and for producing hydrogen gas; and
fixing reactor for allowing a reaction between the hydrogen gas produced in the hydrogen producing reactor and the CO
2
gas in the atmosphere or in the exhaust gas and for producing solid state carbon and water.
In the inventive CO
2
fixation system described above, the hydrogen gas necessary to fix CO
2
gas is produced not by electrolytical means but by decomposing methane which is obtained through an anaerobic fermentation of organic wastes. Thus the electric power needed by the system is greatly decreased, so that the system can be installed close to the sites of CO
2
source even though the electric cost is high in such areas.
Since the electric power consumed by the system is greatly reduced, the overall efficiency of CO
2
reduction is considerably improved. It also reduces other harmful substances inherently emitted from thermal plants when fossil fuels are burned in generating electricity.
The CO
2
fixation system may further include a first heat exchanger in which heat is retrieved from the exhaust gas. The retrieved heat can be given to the fermentor for enhancing the fermenting reaction.
The CO
2
fixation system may further include a second heat exchanger in which heat is retrieved from the hydrogen producing reactor. The heat retrieved here can also be given to the fermentor.
The heat obtained in the first or second heat exchanger may also be used to generate electricity, where the electricity can be used to operate the system.


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patent: 3962411 (1976-06-01), Setzer et al.
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Database WPI; Section Ch, Week 9930; Derwent Publications Ltd., London, GB; An 99-351055;XP002114544 & JP 11 128682 A (Shimadzu Corp), May 18, 1999.
Chemical Abstracts, vol. 119, No. 22, Nov. 29, 1993; Columbus, Ohio, US; abstract No. 229398, Uetake Naoto et al.: “Method and apparatus for converting carbon dioxide into carbon or methane”; XP002114644 & JP 05 193920 (Hitachi Ltd.) Aug. 3, 1993.

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