Furnaces – Refuse incinerator – For liquid refuse
Reexamination Certificate
1999-12-08
2001-05-22
Ferensic, Denise L. (Department: 3749)
Furnaces
Refuse incinerator
For liquid refuse
C431S004000, C431S009000, C431S010000, C431S190000
Reexamination Certificate
active
06234092
ABSTRACT:
The invention relates to a process and an apparatus for the thermal treatment of incombustible liquids.
For the purposes of the invention, thermal treatment means that combustible constituents of an incombustible liquid (for example a waste water) are chemically converted, while incombustible constituents are generally evaporated.
To treat contaminated waste waters or low heating value liquid wastes, various processes have proved useful in practice. In addition to what are termed generative processes (for example distillation, extraction, adsorption), oxidative waste water treatment processes (for example wet oxidation, ozonolysis, evaporation/combustion) are used especially to treat organically polluted waste waters.
The focus hereinafter will be on the process evaporation/combustion—usually also called “waste water incineration”. This process is used when highly polluted waste water streams (contaminant content greater than 50 g/l) are to be disposed of. A waste water incineration plant generally consists of the waste water pretreatment stage (neutralization, concentration), the high-temperature part (combustion apparatus) and the downstream flue gas clean-up devices (quench, electrostatic precipitators). The waste water composition, in particular the type and level of loading, determines the processing design of the individual apparatuses. It must be noted here that even waste water contaminants in the trace region (for example compounds of S, N, P or Cl) can lead to operating problems.
For this reason, particular care must be devoted to the design of the combustion part. However, before the combustion part is considered in more detail, some important terms which are used below are to be defined. The processes which can take place during waste water combustion in the combustion part are especially chemical reactions, for example combustions, gasifications, oxidations or pyrolyses. All of these chemical processes are summarized hereinafter as combustion. In addition to incombustible liquids, liquids which burn poorly or are of low flammability under atmospheric conditions at temperatures of up to about 1000° C., and also nonflammable liquids, are also termed incombustible liquids. Incombustible liquids contain (within the meaning of the waste water combustion principle) combustible components. The word gas is used as a collective term for gases or gas mixtures. For the purposes of the patent, the term mixing also means blending below. Inert gases generally mean those gases which cannot react chemically or only react under extreme conditions (for example temperatures higher than 2000° C. and/or pressures higher than 1000 bar) with a fuel used, However, in an individual case inert gases can also comprise components which can react chemically as such with the fuel used. Vice versa, a fuel can be burned in the presence of a reactive gas. Reactive gases are especially gaseous oxidizing agents, for example oxygen or ozone-containing gases. In contrast, inert gases contain at most an amount of oxidizing agent such that on mixing with the supplementary fuel at combustion space temperature ignition and thus combustion do not occur.
In the combustion of an incombustible liquid, a fuel, what is termed a supplementary fuel, is required. The incombustible part of the incombustible liquid is evaporated and combustible constituents are chemically reacted. Generally, substances which are more environmentally compatible are obtained in the process. It is particularly important to minimise the content of carbon monoxide, soot and nitrogen oxides. In addition, there is the aim of optimizing the ratio of incombustible waste water liquid and supplementary fuel required, i.e., as little fuel as possible is to be used in the combustion. The recovery of the energy supplied for the combustion is generally made problematic, since the components present in the incombustible liquid (chiefly comprising water), for example salts or halogens, would strongly attack the material of heat exchanger apparatuses. A minimum temperature and a corresponding minimum residence time generally ensures sufficient conversion of pollutant. The unwanted formation of nitrogen oxides can be minimized by generating a certain temperature profile and oxygen concentration profile in the combustion space or in the flame. The technical procedure of the combustion is critical for the environmental compatibility and economic efficiency of the combustion. It has been found here, for example, that the atomization of a mixture of supplementary fuel and incombustible liquid (for example using a nozzle) is advantageous prior to the combustion. Correct design of the nozzle/burner/combustion chamber system, ie. matching atomization and combustion, is of particular importance here if waste waters having a high loading of organically bound carbon are also to be worked up by combustion. Care must be taken especially to ensure that the combustion temperature is neither too high nor too low. At too high a temperature the formation of nitrogen oxides is promoted, while at too low a temperature incomplete combustion, soot formation and carbon monoxide formation occur. In addition, care must be taken to ensure that the combustion takes place in the presence of sufficient quantities of reactive gas in order to counteract especially the formation of carbon monoxide and soot. In industry, for waste water incineration (incineration of incombustible liquids), what are termed combination burners are used which use heating oil, natural gas or high-energy wastes as supplementary fuel. These burners are constructed in such a manner that a stabilized flame is generated by the supplementary fuel and an incombustible-liquid spray produced (produced by atomization in a gas) is mixed with this flame or with the complete-combustion region of the flame.
There is particular interest in industry in also using liquid supplementary fuels. However, the disadvantage is that, when many burners used in the industry are employed, there is severe soot formation, since the hot supplementary fuel flame is quenched by the incombustible liquid.
EP-B-0 463 218 describes a process and an apparatus in which the formation of a stabilized flame is avoided. In this process, the fuel is fed at high velocity (high axial momentum) into a combustion space separately from the combustion air, so that the combustion air is mixed with relatively large amounts of exhaustively burnt flue gas prior to fuel contact. Liquid fuels can also be reacted in this case by “flameless oxidation”. However, if a waste water combustion is also to be carried out by this process, incombustible liquid and liquid supplementary fuel must be miscible with one another (which is not usually the case, however) or supplementary fuel and incombustible liquids must be separately atomized in the center of the burner prior to being fed into the burner. There is the disadvantage here that waste water droplets and supplementary fuel droplets, prior to complete vaporization, penetrate into injected combustion air jets and thus water droplets (or other droplets consisting of incombustible liquids) impact on ignited supplementary fuel droplets, soot formation thus occurring.
It is an object of the present invention to provide a more economical and more environmentally compatible process for the combustion of incombustible liquids. In this process, the amount of supplementary fuel required is to be minimized and especially liquid supplementary fuels having high contents of high-boilers (for example fuel oil) shall also be usable. In the combustion it is of importance that minimum pollutant loads of carbon monoxide, nitrogen oxides and soot are formed. In addition, as complete a conversion as possible of the combustible contents in the incombustible liquid is to be achieved.
We have found that this object is achieved by the process for the thermal treatment of incombustible liquids in a combustion space of a combustion apparatus by contacting the incombustible liquid with a supplementary fuel in the combustion space in the pr
Domschke Thomas
Joa Andreas
Steinebrunner Klaus
BASF - Aktiengesellschaft
Ferensic Denise L.
Keil & Weinkauf
Rinehart K. B.
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