Incineration plant with heat exchanger

Details Incineration plant with heat exchanger Incineration plant with heat exchanger

1995-07-14

1997-10-07

Bennett, Henry A.

Furnaces

Combined

With boiler

110302, 60 39182, 60 39512, 122 1C, F23B 700

Patent

active

056736347

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to an incineration plant with a heat exchanger for the return transfer of the flue gas waste heat. The heat recovery from the flue gases by means of such a heat exchanger usually has the purpose of preheating the combustion air required for the incineration plant and/or the boiler feed water of a steam producer heated by the incineration plant.
2. Description of the Related Art
Such incineration plants are equipped subsequently or when newly constructed with catalytic or non-catalytic reduction stages for the nitrogen oxides and with a flue gas desulfurization plant. For economical reasons, i.e., because of low efficiency losses and because of significantly lower investment costs, the catalytic or non-catalytic reduction stage for the nitrogen oxides is preferably arranged in the flue gas flow upstream of the heat recovery. This reduction stage is then also located upstream of a dust collector which is always required in incineration plants heated by coal.
In this arrangement, the low temperatures of the pipe walls of a feed water or condensate preheater arranged downstream of the reduction stage for the nitrogen oxide poses difficulties because deposits of ammonium bisulfate and dust occur on the heating surfaces due to the ammonia slippage present following the reduction stage or at the end of the steam producer and due to the sulfur oxides. These deposits are corrosive, reduce the heat transfer and lead to clogging. Therefore, the deposits must be removed by suitable methods. It is possible to remove the deposits by washing, however, the heat exchanger surfaces must be constructed accordingly.
In the case of a feed water preheater, another possibility of removing deposits from the heat exchanger heating surfaces is to empty the heat exchanger heating surfaces and to conduct hot flue gas or steam to the heat exchanger heating surfaces. In that case, the temperature of the flue gas or steam must be above the sublimation temperature of the ammonium salts. A boiler stoppage is also required in this case, wherein no information exists with respect to frequency and duration of the stoppage.
Finally, it is also possible to dimension the heat exchanger surfaces so large that, in spite of the deposits, the heat transfer is sufficient until a boiler stoppage which is usually necessary occurs. In that case, subsequently arranged heating surfaces would be required that are so large that such a construction would be uneconomical.


SUMMARY OF THE INVENTION

The invention is based on the object of providing an incineration plant with a heat exchanger in the flue gas flow, wherein the heat exchanger surfaces of the heat exchanger have a temperature at which an increased danger of deposits does not yet exist or which can be easily freed from the deposits and wherein the heat exchanger makes it possible to operate the heat exchanger for the return transfer of the waste heat in the flue gases to portions of the steam producer of the incineration plant at a very low temperature, without the danger of deposits and corrosion of these heat exchanger surfaces.
Starting from this object, in an incineration plant of the above-mentioned type, the invention proposes to arrange a heat exchanger in the flue gas flow following, for example, a catalytic reduction stage for nitrogen oxides and in front of a flue gas dust remover, to admit a circulated heat transfer medium to this heat exchanger for absorbing heat from the heat exchanger in the flue gas flow, and to arrange at least one heat exchanger in the heat transfer medium for absorbing heat from the heat transfer medium.
Since the heat transfer medium can be kept free of the components contained in the flue gases, such as, dust, ammonium sulfate and sulfur oxides, the second heat exchanger can be operated at very low pipe wall temperatures without producing the danger of falling below the dew point and the formation of ammonium bisulfate. The first heat exchanger in the flue gas flow can be easily const

REFERENCES:
patent: 4739713 (1988-04-01), Vier et al.
patent: 5175993 (1993-01-01), Raiko et al.
patent: 5367870 (1994-11-01), Vollmer
patent: 5435123 (1995-07-01), Scholl et al.
patent: 5509264 (1996-04-01), Ito et al.

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