Catalyst – solid sorbent – or support therefor: product or process – Solid sorbent – Free carbon containing
Patent
1997-04-22
2000-10-03
Griffin, Steven P.
Catalyst, solid sorbent, or support therefor: product or process
Solid sorbent
Free carbon containing
502432, C01B 3108
Patent
active
061273120
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to the removal of nitrogen oxides present in combustion exhaust gases discharged from boilers, engines, turbines and the like, and more particularly to an exhaust gas denitration technique in which cold to hot nitrogen oxides can be efficiently reduced and thereby decomposed to nitrogen and water.
This invention is especially suitable for the denitration of cold exhaust gases discharged from the outlets of existing exhaust gas denitration apparatus, boilers and the like.
Moreover, this invention also relates to the removal of nitrogen oxides present in ventilation gases produced in road tunnels, underground parking spaces, street crossings and the like, and more particularly to a low-temperature denitration technique in which nitrogen oxides having a lower concentration (typically about 15 ppm or less) and a low temperature (typically ordinary temperature to about 50.degree. C.) as compared with exhaust gases from boilers and the like can be efficiently reduced and thereby decomposed to nitrogen and water.
Furthermore, this invention also relates to denitration systems using a heat-treated active carbon for the removal of nitrogen oxides (NO.sub.x) present in exhaust gases discharged from boilers, gas turbines, engines and combustion furnaces for burning various types of fuel. The present invention can be suitably used for the removal of nitrogen oxides present in tunnels and for the removal of nitrogen oxides present in exhaust gases from nitric acid production plants.
BACKGROUND ART
For the denitration of exhaust gases from stationary nitrogen oxide-producing sources such as boilers, a method for reducing nitrogen oxides selectively by using vanadium oxide as a catalyst and ammonia as a reducing agent (i.e., the SCR method) has conventionally been known and is widely employed for practical purposes ("Techniques and Regulations for the Prevention of Environmental Pollution", Volume on the Atmosphere, p. 130, Maruzen Co., Ltd.). However, in this method using the vanadium oxide catalyst, the temperature of exhaust gas needs to be raised to 300.degree. C. or above in order to achieve a practically sufficient degree of denitration. Consequently, it is necessary to install a denitrator containing a catalyst bed in the high-temperature section of the boiler (e.g., just behind the outlet of the boiler or in the heat transfer section of the boiler), or reheat cold exhaust gas and thereby raise its temperature. However, these techniques involve the following problems.
When the denitrator is installed in the high-temperature section of the boiler, various problems arise in that the overall equipment becomes complicated, the use of a heat-resisting material causes an increase in equipment cost, and workability for replacement of the catalyst bed is reduced. When cold exhaust gas is reheated, an additional heater is required, resulting in an increase in equipment cost.
Accordingly, a first object of the present invention is to provide a technique by which the denitration of exhaust gases from stationary nitrogen oxide-producing sources such as boilers can be performed at low temperatures ranging from ordinary temperature (about 5 to 20.degree. C.) to about 150.degree. C.
On the other hand, exhaust gases from road tunnels and the like are characterized in that they have a much lower NO concentration of about 10 ppm or less as compared with the concentration of nitrogen oxides in exhaust gases from boilers and the like, their temperature is in the vicinity of ordinary temperature, and they are produced in enormous volumes. Consequently, in order to remove denitrate gases from road tunnels and the like according to the conventional SCR method, the temperature of the gases must be raised to 300.degree. C. or above. This requires a huge amount of thermal energy and is unprofitable from an economical point of view.
In Japanese Patent Publication No. 41142/195, Japanese Patent Provisional Publication No. 47227/'95 and the like, there has been proposed a process in which low-concent
REFERENCES:
patent: 4855116 (1989-08-01), Richter et al.
patent: 5172307 (1992-12-01), Tabuchi et al.
Kasuh Takahiro
Kobayashi Norihisa
Mochida Isao
Setoguchi Toshihiko
Yasutake Akinori
Griffin Steven P.
Hendrickson Stuart L.
Osaka Gas Company Ltd.
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