CH683325A5 - Methods for immobilizing noxious residues from the flue gas cleaning. - Google Patents

Description

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CH 683 325 A5

description

The invention relates to a method for immobilizing pollutant-containing residues such as filter dust and fly ash from flue gas cleaning.

Various methods for processing combustion residues and converting them to a landfillable form are known from the prior art.

The concept of residue washing with subsequent consolidation is already being used industrially several times. In a first step, the filter dusts are suspended with water in a certain ratio to extract the easily water-soluble substances and mixed intensively during a defined dwell time. After the extraction, the suspension is filtered. Washing on the filtration system ensures that the easily water-soluble substances contained in the mother filtrate are displaced from the residues. The washed filter dusts are fed to a compulsory mixer immediately or after an interim storage, where they are to be homogenized with cement and, if appropriate, further additives.

This is followed either by the production of blocks or the like. after appropriate compression by vibration or by a high pressure press. The mixture can also be built into the landfill without being compacted and only compacted on site.

However, complete homogenization in a compulsory mixer is extremely problematic due to the high fineness of the solids, filter dust and cement involved and the associated very high specific surface area. Another disadvantage is that an additional system with corresponding system and personnel costs is required for the mixing. Furthermore, a reproducible consistency of the mixed product has not yet been achieved.

For the immobilization of the relevant pollutants, a homogeneous distribution of the cement in the residue is of the greatest importance. Low-cement or even cement-free zones prove to be dangerous weak points. Here the toxic components are insufficiently or not at all fixed. Furthermore, due to the large strength gradients, these areas represent zones of increased frequency of cracks. This additionally increases the extent of leaching.

The requirement for homogeneous distribution of the cement is extremely difficult to meet because of the fine-grained, clay-like structure of the filter cake.

The object of the invention is to develop a method for immobilizing pollutant-containing residues from flue gas cleaning with which a high degree of homogenization and thus a permanent landfill body with improved eluate values can be obtained.

Another object of the invention is to achieve a reproducible consistency of the mixed product.

According to the invention the object is achieved by the features of claim 1. The amount of water represents a considerable excess compared to the amount required for the hydration. The easily soluble substances can be separated off with the waste water by means of a filtration system.

Surprisingly, the added solids are largely homogenized in the washing tank, which leads to improved setting and to a more homogeneous landfill body.

Another advantage of the invention lies in the fact that improved eluate values are achieved through the more permanent landfill body. By eliminating the previously required mixing plant, the entire investment costs of the mixing plant including the operating and personnel costs required for this can be saved. The improved degree of homogenization also enables cement to be saved.

Another advantageous feature of the invention is that the hydroxide suspension is fed from the wastewater treatment plant to the washing tank.

By adding the hydroxide suspension from the wastewater treatment plant to the washing tank, the plants previously required for dewatering, e.g. Chamber filter presses can be saved. Furthermore, it is advantageously achieved that only one residual material is combined.

The invention is described in more detail in an exemplary embodiment with reference to a drawing. The drawing shows the process flow diagram in FIG. 1.

The residues from the flue gas cleaning are added with the addition of cement and, if necessary, other additives such as Lime and / or milk of lime are added to the washing tank together with the hydroxide suspension from the wastewater treatment plant and water.

The wash container entry can be composed as follows:

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CH 683 325 A5

% By weight

1.

Filter dust / kettle ash:

10-40

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Suspension from the wastewater treatment plant:

0-20

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Cement:

1-20

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Aggregates:

0-10

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Water:

50-90

The easily soluble components of the residues from the flue gas cleaning (e.g. chlorides) are extracted in the washing tank with simultaneous sufficient homogenization of the input substances in one process step.

The hydroxide suspension from the wastewater treatment plant can be added without prior dewatering. The washing container discharge is then filtered on, for example, vacuum belt filters.

After the filtration, a residual product with a water content that can be set to a lower limit is available.

This residual product can be brought to the landfill and compacted there or processed into blocks directly after the filtration, for example by vibratory compression.

There is also the possibility of pelleting the residues after dewatering, e.g. using a roller press.

For the homogenization, extraction and dewatering only approx. 15 min. needed. Claims

1. A process for immobilizing pollutant-containing residues such as filter dusts and fly ash from flue gas cleaning by adding cement and additives, characterized in that during the washing-out process, the pollutant-containing residues with the cement, the additives and with water compared to the amount required for the hydration represents a considerable excess, are suspended and homogenized in the washing plant and the easily soluble substances are separated off with the waste water by a filtration plant.

2. The method according to claim 1, characterized in that the hydroxide suspension from the wastewater treatment plant is fed to the washing tank.

3. The method according to claim 1 to 2, characterized in that the residual product obtained after the filtration is brought to the landfill and is compacted there by vibration.

4. The method according to claim 1 to 2, characterized in that the residual product is processed into blocks or pellets directly after the filtration.

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