Chemical apparatus and process disinfecting – deodorizing – preser – Control element responsive to a sensed operating condition – Control element is fluid pressure sensitive
Patent
1995-05-11
1997-08-26
Bhat, Nina
Chemical apparatus and process disinfecting, deodorizing, preser
Control element responsive to a sensed operating condition
Control element is fluid pressure sensitive
422168, 422177, 122 7R, 122470, 60 395, 60 39182, F01N 502, G05D 1600, B01D 5356, F23J 1500
Patent
active
056607997
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to exhaust gas boilers having a denitrator incorporated therein which are characterized in that, even if sulfur oxides are contained in the combustion gas, high degree of heat recovery can be achieved by decomposing the surplus ammonia present on the downstream side of the denitrator almost completely and thus preventing the occurrence of trouble due to the deposition of acid ammonium sulfate on the low-temperature heating tubes.
BACKGROUND ART
FIG. 4 is a heat transfer surface arrangement diagram illustrating one example of a conventional exhaust gas boiler. In this figure, reference numeral 1 represents an exhaust gas flow path; 2, a high-pressure superheater; 3, a high-pressure evaporator; 5, a high-pressure economizer; 6, a low-pressure evaporator; 7, a low-pressure economizer; 8, a high-pressure steam drum; 13, a denitrator; 15, an ammonia injection nozzle; 16, a high-pressure feed water pump; 17, a low-pressure feed water pump; 18, a low-pressure steam drum; and 19, a stack. The fluid temperatures inside the various heat transfer surfaces of this exhaust gas boiler and the gas temperatures outside them are distributed as shown by solid lines in FIG. 5.
In the above-described conventional exhaust gas boiler, if sulfur oxides are contained in the combustion gas, acid ammonium sulfate may be deposited on the low-temperature heating tubes disposed in a gas temperature region located downstream of the denitrator 13 and having temperatures of 200.degree. C. or below. If so, the increase in gas-side draft loss caused by corrosion of the tubes or clogging of the tubes (especially of the finned tubes) presents a problem. For this reason, heat transfer surfaces cannot be disposed in low-temperature regions (i.e., regions B and C in FIG. 5). Consequently, the heat transfer surface arrangement of FIG. 4 which permits highly efficient heat recovery cannot be employed, and a simpler heat transfer surface arrangement as illustrated in FIG. 6 must be employed. Thus, the outlet gas temperature can only be reduced to a level of as high as 200.degree. C.
Even where a clean gas such as LNG is burned, the surplus ammonia level at the outlet of the denitrator usually needs to be reduced to 10 ppm or less. For this reason, it has been difficult to enhance the efficiency of the denitrator.
As a countermeasure to the above-described deposition of acid ammonium sulfate, there is known a method for suppressing the growth of acid ammonium sulfate in which part of the high-temperature gas on the upstream side of the denitrator is suitably supplied to the heat transfer surfaces located downstream of the denitrator and subject to the deposition of acid ammonium sulfate so as to raise the gas temperature around the heating tubes. However, this method is impractical because a complicated arrangement of high-temperature ducts is required and such a high effect as enables the removal of already deposited acid ammonium sulfate cannot be expected. Moreover, if the high-temperature gas is always made to flow, heat absorption in the upstream high-temperature section is decreased and heat absorption in the entire exhaust gas boiler is also decreased. Thus, this method cannot be regarded as suitable even from the viewpoint of plant efficiency.
Furthermore, in the case of clean gases, there has been proposed a method for removing the surplus ammonia by adsorption at the outlet of the denitrator. However, this method has the disadvantage, for example, of increasing the size of the equipment.
DISCLOSURE OF THE INVENTION
In order to solve the above-described problems of the prior art, the present invention provides exhaust gas boilers as described below.
First, there is provided an exhaust gas boiler having a denitrator incorporated therein, characterized in that a residual ammonia decomposer is disposed at a location downstream of said denitrator and between two divided high-pressure evaporators.
Secondly, there is provided an exhaust gas boiler having a denitrator incorporated therein, characteriz
REFERENCES:
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patent: 4891937 (1990-01-01), Noguchi et al.
patent: 4944252 (1990-07-01), Motai et al.
patent: 5282355 (1994-02-01), Yamaguchi
patent: 5336081 (1994-08-01), Saito et al.
patent: 5449495 (1995-09-01), Goto
Development of NOx Removal Processes with Catalyst for Stationary Combustion Facilities; Mitsubishi Technical Bulletin No. 124; May 1977.
Kobayashi Norihisa
Motai Toshiki
Bhat Nina
Mitsubishi Jukogyo Kabushiki Kaisha
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