AU736661B2 - Process for treating waste gases produced in an organic waste incineration plant - Google Patents

Description

P:AOPERAxd 2142146- I.doc- 1506/01 -1- The invention concerns a process for treating waste gases arising in a combustion facility for wastes containing toxic organic compounds.

A series of processes in the area of pyrolysis, gasification and in particular of the combustion of wastes for thermal processing of organic waste substances such as, for example, household and/or commercial garbage, have become known.

In practise, thermal waste processing chiefly takes place now in combustion facilities, and in particular in combustion facilities outfitted with a grate firing.

The waste gases arising in these facilities are subjected to dust separation, 10 desulfurization and usually also to denitrification similar to the flue gases from fossil firings of industrial boiler facilities, such as, for example, coal power plants.

In this connection, it is a disadvantage that organic hydrocarbon compounds o* .usually still contained in the waste gases from waste combustion facilities owing to the S inhomogeneous composition of the waste, among them highly toxic furans and dioxins, are 15 not picked up by the cleansing facilities mentioned, or lead to a contamination of the separated flue dust. In addition to impairing dust processing, it is thus necessary to provide additional, generally very expensive separation facilities (usually activated charcoal facilities) in waste combustion facilities to separate the hydrocarbon compounds still

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present in the waste gas.

Advantageously, the invention provides a means for significantly reducing the technical and economic expense of the separation of toxic hydrocarbon compounds from waste gases of trash burning facilities.

According to the present invention there is provided a process for treating waste gases containing harmful substances produced in a waste incineration plant comprising leading the waste gases into a fossil fired industrial boiler facility without prior segregation of harmful substances, mixing hot emissions from the plant with combustion air from a furnace necessary to fire burners of the facility, leading the hot emissions together with the Sfurnace air into the facility, and heating to a temperature higher than 1200'C.

P:\OPER\Ad214246-i.doe-I5/6/01 -2- The organic compounds still contained in the waste gas are either afterburned or even cleaved through the heating of the waste gases of a trash burning facility to temperatures above 1200'C. As experiments have shown, highly toxic dioxins and furans are no longer detectable in the flue gas of fossil industrial boiler facilities to which the waste gas of the combustion facility was admixed. At the same time it has surprisingly also become apparent that neither dioxins nor furans form again when the flue gas is cooled.

The admixed waste gases from trash burning facilities can henceforth be subjected to the usual toxic substance separation (dust removal, desulfurization, denitrification) and then be dissipated into the atmosphere.

According to a further feature of the process of the invention, it proves to be especially advantageous to admix the combustion facility waste gases to the hot flue gas of o. :the furnace of a cement facility.

With flue gas temperatures in the cement facility of up to 2000 0 C, it will henceforth create no problems of any kind to heat the waste gases from the trash burning facility as well up to the required temperature of 1200'C.

Secondly, and herein lies a special economic advantage, the heat content even of untreated, that is, not prepared waste, can be directly used in a cement facility.

While with previous methods for the joint use of waste as a fuel in cement facilities, the waste was directly admixed with the operating fuel (which imposes very high standards on the quality of waste preparation and basically permits only the use of about of the waste arising in order to avoid processing engineering-related impairment of cement manufacture). Now a complete disconnection of the combustion of waste and fossil fuel is taking place in the area of the cement facility. The heat content of the waste is henceforth being injected into the cement manufacturing process through the hot waste gas, which as a rule permits temperatures between 800 and 1000 0 C in trash burning facilities. The residues arising from waste combustion, as for example, the preponderant P:\OPER\A d2142146- I .do- I5A(610I -3part of slag, thereby remain in the trash burning facility and cannot prove to be harmful in respect to the operating parameters to be maintained in cement production.

Appropriately, the waste gas arising in the waste combustion facility is here admixed directly to the furnace air required for fossil firing of the cement facility. In this way, a homogenous mixture of waste gas and flue gas is guaranteed directly behind the burner.

Of course, the waste gas can also be directly introduced into the cement furnace at an appropriate place.

According to a further feature of embodiments of the process of the invention, it also proves practical in connection with cement facilities to use the hot cooling air from the clinker cooler as furnace air for the waste combustion facility. Owing to the high temperature of exhaust air from the clinker cooler of approx. 800'C, optimal firing conditions are herewith created in the trash burning facility. In the event that the waste combustion facility is to be operated under reducing conditions, that is, as a waste gasification facility, at least one part of the heat required for the gasification can also be

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injected from the hot flue gas of the cement furnace. In this case, the waste gas from the trash burning facility still contains chemically bound heat which is released by combustion in the cement furnace.

The residues arising in waste combustion or gasification can be used in the usual manner, for example for road construction and building or, however, in prepared form, for the cement process itself as additives.

According to a further feature of embodiments of the invention, the hot waste gas of the trash combustion facility can also appropriately be admixed to the even hotter flue gas of a coal power plant. With coal-fired power plants with coal dust firing as well as with melt firing, thus with dry as well as in connection with wet-deslagged coal-fired boilers, the temperature level of the flue gas arising is sufficient for attaining the minimum temperature of 1200'C requisite for eliminating toxic hydrocarbon compounds, such as ,oxins and furans, for example, after mixing with the waste gas of trash burning facilities.

P:\OPERMAxd2 142146- I.d.--I5/06/01 -4- Appropriately, in this connection the waste gas from the trash burning facility is admitted to the lower area of the boiler of the coal-fired power plant, due to which particularly long holding times and consequently heating times of the waste gas are attained in the coal-fired boiler.

In coal-fired power to which a trash burning facility is being retroactively connected up on the waste gas end as a so-called satellite facility, it may also prove to be appropriate to admix the waste gases from the waste combustion facility directly to the furnace air for the coal burner of the coal-fired boiler and to feed it with these into the power plant boiler.

It is also possible, however, to introduce the waste gases from the trash burning facility into the boiler together with the fresh coal over the grinding-drying facility. This method has the further advantage that thereafter the heat content of the hot waste gases :from the trash burning facility can be used for drying the fresh coal.

Further variants for introducing the waste gases from trash burning facilities into 15 the boiler of the coal power plant are: introducing them into the coal drop chute of the coal grinder, into the return feed shaft of the flue gas used for grinding-drying, thus before the i: coal grinder as well as in connection with grinder air compressors present in the air duct in front of or behind the grinder air duct.

In the event that, due to the existing infrastructure, the trash burning facility can only be erected at a great distance from the power plant boiler, it may also prove appropriate to cool the hot flue gases of the waste gases, for example in direct or indirect heat exchange with furnace air for the coal-fired boiler, to the extent that an expensive brick lining of the waste gas connection conduit between the trash burning facility and the power plant boiler can be dispensed with.

It also proves appropriate according to a further feature of embodiments of the process of the invention to separate the waste intended for the waste combustion facility into a coarse fraction richer in heat value which is then fed into the combustion facility, and into a fine fraction poorer in heat value which is first subjected to a steeping process P:\OPER\Ad2 142 146-I.dc-I15A6)01 and subsequently burned together with fossil fuel in an industrial boiler, preferably a coalfired power plant boiler.

In particular, household waste, for example, is separated by a trommel revolving screen with a cross section of ca.± 40 mm into a fraction rich in heat value and into a fraction poor in heat value. The latter contains much organic material with great moisture (food residues) and largely inert fine waste. The fraction rich in heat value consists to a large part of wood, cardboard, paper, foils, textiles, and is contaminated with coarse impurities.

The fraction rich in heat value is burned either directly or after transportation with the press container in grate firing after sorting out the largest impurities and running through magnetic separation. Transport in press balls is also possible, for which, of course, a crushing process is also necessary. The flue gas of grate firing is also conducted to the coal-fired large boiler and passes through the boiler together with the flue gas from S* its firing. Harmful substances are destroyed or vaporized owing to the high combustion chamber temperatures of far above 1200'C and separated by condensation or sublimation on flue dust together with this in a filter or washer.

The fraction poor in heat value is transformed into a biologically stable state in an intensive steeping, whereby a steeping loss by carbon dioxide and water vapor of about *30% arises. The steeped material is not pathogenic, its odor is minor, and its residual .oo.oi moisture amounts to 10-15%. The formation of gas deposits and seepage water are minimized and the material can be used for constructing deposits, covering deposits, or for soil amelioration in certain areas. Even in this material about 30% heat value-rich substance is still present, which can be separated by sieving at about 40 20 mm. In accordance with the invention, the fraction so obtained is conducted directly, [or] with container or press ball transport, to a coal-fired power plant, for example, placed together with the intended fuel into the grinder-dryer, and subsequently burned in the large boiler.

SAlthough, about 55% of household waste is thermally processed with high power ant efficiency with the process variants for the invention. A remaining residue of about P:\OPER\AxdU2142146-rsL.doc-15/06/1 -6is a gassed out, seepage water-poor material suited for building deposits. The remaining 20% represents the steeping loss. The quality of the stepped material allows improving the quality of the steepage material on compost quality in setting up a resteeping, which considerably expands the area of application as a soil improver.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

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Claims (9)

1. Process for treating waste gases containing harmful substances produced in a waste incineration plant comprising leading the waste gases into a fossil fired industrial boiler facility without prior segregation of harmful substances, mixing hot emissions from the plant with combustion air from a furnace necessary to fire burners of the facility, leading the hot emissions together with the furnace air into the facility, and heating to a temperature higher than 1200 0 C.

2. The process of claim 1, wherein the step of leading the waste gases to the facility comprises leading the gases to burners or boilers of cement plants or coal power plants.

3. The process of claim 2, wherein the mixing comprises mixing at least a part of the emissions with the combustion air and directing the mixed emissions and air into the boiler via a milling and drying facility for the raw coal. 11 S.

4. The process of claim 1, further comprising supplying waste into the waste incineration plant and processing the waste into fine fractions with less heat values and coarse fractions with high heat values.

5. The process of claim 4, further comprising allowing the fine fractions to go through a rotting process.

6. The process of claim 5, further comprising directing the fine fractions from the rotting process to coal mills of a coal power plant.

7. The process of claim 4, wherein the fine fractions have a particle size smaller than about 60 mm.

8. The process of claim 4, further comprising directing the coarse fractions into and burning in the industrial boiler facility with fossil fuels of the boiler facility.

9. The process of claim 4, wherein the coarse fractions have a particle size greater 3 N" han about 60 mm. PAOPERkAxdfU 142 M46-Ldc- 1/6/01 -8- The process of claim 9, wherein the particle size is from about 60 to 140 mm. Process for treating waste gases substantially as hereinbefore described. DATED this 14th day of JUNE, 2001 HEINZ HOLTER by DAVIES COLLISON CAVE Patent Attorneys for the Applicant(s) 9 S S S S. 59 S S S S. SW S S. 5 9 9 *SS. S S S. S 9 *SS**9 9