Method for processing ash from waste incineration plants by means of wet classification

Abstract

A method for processing ash from waste incineration plants by wet classification includes mixing the ash with a liquid in a mixing hopper. After screening, the mixture is fed to a first classifying stage, including an upflow classifier and an upstream hydrocyclone, where it is separated into a good fraction and a residual fraction. The residual fraction is drawn off as a suspension on an upper side of a fluidized bed of the upflow classifier. The good fraction is drawn off on an underside of the fluidized bed. A pass through fraction is fed back into the hydrocyclone installation and a material flow containing particles which are smaller than a separation particle size is separated as cyclone overflow. The cyclone overflow is separated in a second classifying stage into a fine particle mineral fraction and a residue which has a grain size upper limit between 20 m and 50 m.

Claims

1. A method for processing ash from waste incineration plants by wet classification comprising: mixing ash with liquid in a mixing hopper; screening a coarse fraction from the ash; feeding the ash as a feed flow to a first classifying stage which comprises an upflow classifier and an upstream hydrocyclone installation; separating the feed flow in the first classifying stage into a good fraction free of harmful substances and a residual fraction contaminated with harmful substances; drawing off the residual fraction as a suspension on an upper side of a fluidized bed contained in the upflow classifier; drawing off the good fraction on an underside of the fluidized bed; dewatering the good fraction by means of a screening device; feeding a pass-through fraction of the dewatered good fraction in the screening device back into the upstream hydrocyclone installation; separating, in the upstream hydrocyclone installation, at least one material flow containing substantially only particles which are smaller than a separation particle size of the screening process as a cyclone overflow; and separating the cyclone overflow in a second classifying stage into a fine particle mineral fraction with a grain spectrum between 20 m and 250 m and a fine particle residue contaminated with harmful substances, wherein the fine particle residue has a grain size upper limit between 20 m and 50 m.

2. The method as claimed in claim 1, wherein the hydrocyclone installation comprises two hydrocyclones connected in parallel, wherein the feed flow is fed to a first hydrocyclone of the hydrocyclone installation and the pass-through fraction of the screening device is fed to the second hydrocyclone of the hydrocyclone installation and wherein the cyclone overflows of the hydrocyclones connected in parallel are fed to the second classifying stage and substantially only contain particles which are smaller than the separation grain size of the screening carried out in the screening device.

3. The method as claimed in claim 1, wherein a screening residue of the screening device has a lower grain size of more than 150 m and wherein the cyclone overflow of the hydrocyclone installation substantially only entrains particles having a grain size of less than 100 m.

4. The method of claim 3 wherein the lower grain size is about 250 m.

5. The method as claimed in claim 1, wherein metals are separated from the screening residue.

6. The method as claimed in claim 1, wherein light organic substances are separated from the residual fraction drawn off from the upflow classifier and wherein the residual fraction is then fed together with the cyclone overflow to the second classifying stage.

7. The method as claimed in claim 1, wherein a hydrocyclone installation is used in the second classifying stage, wherein the mineral fraction is drawn off as cyclone underflow and the cyclone overflow entrains the fine-particle residue contaminated with harmful substances.

8. The method as claimed in claim 7, wherein the cyclone underflow is dewatered by means of a screening device.

9. The method as claimed in claim 8, wherein metals are separated from a screening residue of the screening device used in the second classifying stage.

10. The method as claimed in claim 7, wherein the cyclone overflow of the hydrocyclone installation used in the second classifying stage is concentrated in a thickener, wherein clarified liquid is drawn off from the thickener and returned into the process.

11. The method as claimed in claim 10, wherein a liquid return comprises a liquid tank to which a water treatment plant is connected.

12. The method as claimed in claim 10, wherein a suspension having a high solid content is drawn off from the thickener and then dewatered.

13. The method as claimed in claim 12, wherein a pressure filtration is used for dewatering the residue.

14. The method of claim 1 further comprising separating, in the second classifying stage, metals in fine particle form.

15. The method of claim 14 further comprising recycling the fine particle metals.

16. The method of claim 1 further comprising separating, in the second classifying stage, metal oxides together with the fine particle residue.

17. A method for processing ash from waste incineration plants by wet classification comprising: mixing ash with liquid in a mixing hopper; feeding the ash as a feed flow to a first classifying stage which comprises an upflow classifier and a first hydrocyclone installation; separating the feed flow in the first classifying stage into a good fraction free of harmful substances and a residual fraction contaminated with harmful substances; drawing off the residual fraction as a suspension on an upper side of a fluidized bed contained in the upflow classifier; drawing off the good fraction on an underside of the fluidized bed; feeding a pass-through fraction of the good fraction flowing through a screening device back into the first hydrocyclone installation; separating, in the first hydrocyclone installation, at least one material flow containing substantially only particles which are smaller than a separation particle size of the screening device as a cyclone overflow; and separating the cyclone overflow in a second classifying stage, which comprises a second hydrocyclone installation, into a fine particle mineral fraction with a grain spectrum between 20 m and 250 m and a fine particle residue contaminated with harmful substances, wherein the fine particle residue has a grain size upper limit between 20 m and 50 m.

18. The method of claim 17, wherein the first hydrocyclone installation comprises two hydrocyclones connected in parallel, wherein the feed flow is fed to a first hydrocyclone of the first hydrocyclone installation and the pass-through fraction of the screening device is fed to the second hydrocyclone of the first hydrocyclone installation and wherein the cyclone overflows of the two hydrocyclones are fed to the second classifying stage and substantially only contain particles which are smaller than the separation grain size of the screening carried out in the screening device.

19. The method of claim 17, wherein in the second hydrocyclone installation, the fine particle mineral fraction is drawn off as a cyclone underflow and a cyclone overflow entrains the fine-particle residue contaminated with harmful substances.

20. The method of claim 17 further comprising: separating, in the second classifying stage, metals in fine particle form; and recycling the fine particle metals.

Description

(1) The invention will be explained hereinafter with reference to a drawing showing merely one exemplary embodiment. The SINGLE FIGURE shows as a highly simplified block diagram a system for the processing of ash by wet classification.

(2) The ash 1 comes from a waste incineration plant, in particular a domestic waste incineration plant, and is mixed with liquid 3 in a mixing hopper 2 and after screening a coarse fraction 4, is fed to a classifying stage 5. The coarse fraction 4 comprises a grain spectrum between 4 mm and 60 mm and can optionally be divided into two or more coarse fractions. The screening devices used for this purpose can be fitted with metal separators to separate non-ferrous metals or iron.

(3) The classifying stage 5 comprises an upflow classifier 6 and an upstream hydrocyclone installation 7. The feed flow is separated in the classifying stage 5 into a good fraction 8 free from harmful substances and a residual fraction 9 contaminated with harmful substances, wherein the residual fraction 9 is drawn off as a suspension on the upper side of a fluidized bed produced in the upflow classifier 6 and wherein the good fraction 8 drawn off on the underside of the fluidized bed is dewatered by means of a screening device 10. The screening residue 11 of the screening device 10 expediently has a lower grain size of more than 150 m. Preferably the classifying stage 5 is operated so that the screening residue 11 of the screening device 10 has a grain spectrum between 250 m and 4 mm. Metals 12 separated from the screening residue can be recycled as valuable materials. The screening residue 11 having a grain spectrum between 0.25 mm to 4 mm is free from harmful substances and can be recycled economically.

(4) The pass-through fraction 13 of the screening device 10 is fed back to the hydrocyclone installation 7, which in the exemplary embodiment comprises two hydrocyclones 14, 14 connected in parallel. The feed flow is fed to a first hydrocyclone 14 of the hydrocyclone installation 7. The pass-through fraction 13 of the screening device 10 enters as feed into the second hydrocyclone 14 of the hydrocyclone installation 7. The cyclone overflows 15, 15 of the hydrocyclones 14, 14 connected in parallel substantially only contain particles which are smaller than the separation grain of the screening device 10. In the exemplary embodiment, the screening residue 11 of the screening device 10 has a lower grain size of more than 150 m, preferably a lower grain size of about 250 m. The cyclone overflows 15, 15 are designed for a separating section of about 60 to 70 m and substantially only entrain particles having a grain size of less than 100 m.

(5) Light organic substances, in particular fibrous substances, are separated from the residual fraction 9 drawn off from the upflow classifier 6, wherein the separation of light substances can be accomplished, for example, by means of a tumbler screen 16. The residual fraction 9 is then fed together with the cyclone overflows 15, 15 to a second classifying stage 17, in which the material flows are separated into a fine-particle mineral fraction 18 as well as a residue 19 contaminated with harmful substances. The second classifying stage 17 is operated so that the residue 19 has a grain-size upper limit between 20 and 50 m. Preferably a grain-size upper limit of the residue 19 is about 25 m.

(6) In the second classifying stage 17, a hydrocyclone installation 20 is used wherein the fine-particle mineral fraction 18 is drawn off as cyclone underflow and the cyclone overflow entrains the fine-particle residue 19 contaminated with harmful substances. The cyclone underflow is dewatered by means of a screening device 21, wherein metals 23 are expediently separated from the screening residue 22. A fine-particle mineral valuable product accumulates, which has a grain spectrum between 20 and 250 m. In addition, metals 23 accumulate in fine-particle form, which can also be recycled as valuable substances.

(7) The hydrocyclone installation 20 comprises two hydrocyclones 29, 29 connected in parallel, wherein the feed flow is fed to a first hydrocyclone 29 of the hydrocyclone installation 20 and the pass-through fraction 30 of the screening device 21 is fed to the second hydrocyclone 29 of the hydrocyclone installation. The cyclone overflows 31, 31 of the hydrocyclones 29, 29 connected in parallel are fed to a thickener 24.

(8) The cyclone overflow of the hydrocyclone installation used in the second classifying stage 17 is concentrated in the thickener 24, wherein clarified liquid 25 is drawn off from the thickener 24 and fed back into the process. The liquid return comprises a liquid tank 26, to which a water treatment system is connected. A suspension 28 having a high solid content is drawn off from the thickener 24, which suspension is then dewatered by a pressure filtration 27. The fine-particle residue has a grain spectrum with a grain upper limit between 20 and 50 m, wherein preferably a grain upper limit of about 25 m is selected. The residue consisting exclusively of very fine particles has a large surface area to which the harmful substances contained in the ash are effectively bound. Metal oxides are also separated with the fine-particle residue.