Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Fluidized bed
Patent
1991-12-12
1994-05-31
Warden, Robert J.
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Fluidized bed
422146, 422147, 422141, 110245, F27B 1508
Patent
active
053167368
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to apparatus for performing an exothermal or an endothermal reaction inside an enclosure (referred to below as a "reactor") between at least one gas and at least one particulate material, the apparatus comprising at least one means for introducing particulate material, at least one means for introducing reaction and fluidization gas, with the respective introduced flow rates of the particulate material and of the fluidization gas being such that they enable a fast upward flow of gas and particulate material to be established within fast circulating fluidized bed zones, means for directing a mixture of the reaction gas and the particulate material reaching the top of the reactor into a separator, means for exhausting the gas produced by the reaction, and means for recycling the particulate material from the separator to the bottom of the reactor.
BACKGROUND OF THE INVENTION
There are essentially two groups of known similar techniques for performing chemical reactions in a fluidized bed.
A first group uses a dense fluidized bed [also called a "bubbling" bed] characterized by the existence of two zones having distinct particle concentrations within the reaction enclosure, with particle concentration being high in a first zone, e.g. 1,000 kg/m.sup.3 for a combustion fluidized bed, and much lower, less than 1 kg/m.sup.3 in a second zone above the first and separated therefrom by a relatively well-defined surface. The velocity difference between the gases and the solid particles is not large. In combustion reactors, combustion efficiencies are low, e.g. 85% to 95%, and the rates at which sulfur oxides and nitrogen oxides are rejected are significant, thereby limiting this technique to small plants.
Within this first group of techniques, a proposal has been made in patent document GB-A-No. 1 412 033 to split up a dense fluidized bed combustion reactor by means of an annular dividing wall, with the lower edge of the dividing wall being spaced apart from the fluidization grid, thereby obtaining a central dense bed region in which combustion takes place, and an annular dense bed region in which solid particles flow downwards, solely for the purpose of exchanging heat with a jacket surrounding the reactor. Some of the solid particles in the central dense bed region overflow the top of the annular dividing wall and move down in the annular dense bed region to return to the central combustion zone beneath the lower edge of the annular dividing wall. This type of apparatus suffers from the above-mentioned drawbacks of dense fluidized bed reactors, mainly the existence of a reaction zone having a very low concentration of particles above the dense bed. Further, it recirculates particulate matter taken solely from the upper part of the dense fluidized zone in the same manner as would a cyclone if located at the outlet from a circulating fluidized bed of the type described below.
A second group of known techniques makes use of a "circulating" fluidized bed of a type described in an article by REH published in the journal Chemical Engineering Progress, February 1971. This is described, in particular, in French Pat. Nos. 2 323 101 and 2 353 332 (Metallgesellschaft) [corresponding to U.S. Pat. No. 4,165,717]. It differs from the first group in particular by the lack of any separation surface between two zones and by the existence of a uniform reaction temperature throughout the reactor. The concentration or suspension density of particulate material varies substantially continuously from the bottom to the top of the reactor body, and the difference between the velocities of the gases and of the solid particles is much higher. For combustion reactors, combustion efficiencies are improved and the rates at which sulfur oxides and nitrogen oxides are rejected are lower. This technique is suitable for application to large plants, but it nevertheless suffers from drawbacks.
These may be observed, in particular, when the reaction is a combustion reaction. It is observed that t
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Morin Jean-Xavier
Payen Philippe
Semedard Jean-Claude
Vidal Jean
Stein Industrie
Tran Hien
Warden Robert J.
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