Furnaces – Combined – With boiler
Patent
1988-10-31
1990-06-12
Favors, Edward G.
Furnaces
Combined
With boiler
110245, 110205, 122 2, 122 4D, 122 7R, F23B 700
Patent
active
049323350
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a process for the combustion of coal and/or waste products containing organic substances, such as domestic and industrial waste and the like, by using fluidized bed combustion with a median combustion temperature of approximately 800.degree. C., as well as a furnace for the implementation of the process.
For a considerable time fluidized bed combustion units of the most varied implementation types have been part of the state of technology. Their main advantages may be found in the circumstance that, in contrast to other types of combustion units, one can also burn lower grade fuels with a high contents of ballast, such as, for example, ballast coal or processing waste materials, which are generated as by-products during the processing of bituminous coal, or other organic substances, in particular, domestic and/or industrial waste and similar materials with the most varied compositions.
One advantage of fluidized bed combustion units consists in their relative low environmental pollution effects, since at the relatively low combustion temperatures of approx. 800.degree. C. the production of nitrogen oxides, (or of other toxic substances, such as sulfur oxides), is low due to the addition of appropriate absorption agents, such as limestone. To a great extent this makes it possible to bind these toxic substances within the fluidized bed combustion unit. Beyond this, fluidized bed combustion units have the positive characteristic of a homogeneous temperature distribution within the fluidized bed, so that, particularly when burning waste materials consisting of less homogeneous organic substances, such as domestic waste or industrial waste, favorable combustion is ensured.
In contrast to the above, the emission of toxic substances from traditional steam generation plants with a coal operated steam generator without post-treatment of the flue gases, that is, without secondary measures, generally exceeds the limits established by the legislature. The secondary measures known to be used for this purpose, such as dust removal units, devices to remove sulfur from flue gases and DENOX catalysts, considerably increase investment and operational costs.
Thus, we have established the objective of reducing the emission of toxic substances with the aid of so-called primary measures that concern the combustion unit itself, such as by using NOx-poor burners, or with the aid of fluidized bed combustion units equipped with heat exchanger surfaces.
However, it is unfavorable that the heat exchanger surfaces within fluidized bed combustion units are exposed to increased corrosion and erosion effects. During the combustion of waste matter containing organic substances, such as domestic and industrial waste and the like, due to the relatively low combustion temperatures the fluidized bed has restrictions imposed upon it if the substances to be burned contain organic or inorganic chloride compounds, for example, polychlorated biphenyls (PCB), since in this case highly toxic dioxins, such as polychlorated dibenzodioxin (PCDD) or polychlorated dibenzofuranes (PCDF), may be generated.
The invention is based on developing a process and a unit which, on one hand, will prevent the formation of highly toxic dioxins during the combustion of waste products containing organic substances, and on the other hand, when burning coal, it will also ensure that relative large amounts of nitrogen oxides will not be produced to start with, so that the DENOX units used for flue gas post-processing will become superfluous.
According to the invention, this task is solved by heating the flue gases exiting the fluidized bed combustion unit, together with the airborne dust, to a temperature of at least 900.degree. C. in a heating area. Thus, with the aid of the invention it becomes possible to deactivate highly toxic dioxins which, as is known, are generated at temperatures above 900.degree. C., especially at temperatures between 1,000.degree. C., and 1,200.degree. C., and to convert them into non-toxic organic substances.
The heating
REFERENCES:
patent: 4355601 (1982-10-01), Hattiangadi
patent: 4509437 (1986-04-01), Breidenbach et al.
patent: 4628833 (1986-12-01), O'Hagan et al.
patent: 4656972 (1987-04-01), Shimoda
patent: 4676177 (1987-06-01), Engstrom
Bruckner Hermann
Scholl Gerhard
Stadie Lotbar
Stoll Karl-Ewald
Creighton Wray James
Favors Edward G.
Saarbergwerke Aktiengesellschaft
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