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Title:
PROCESS FOR STABILIZING RESIDUES RESULTING FROM COMBUSTION OF WASTE
Document Type and Number:
WIPO Patent Application WO/2017/194490
Kind Code:
A1
Abstract:
Process for stabilizing residues resulting from combustion of waste In this process a cement-free mixture is prepared by placing in contact via mixing first solid residues comprising filter residues collected by a flue gas cleaning filter to which flue gases produced by combustion of the waste are sent, second solid residues comprising clinker fines produced by combustion of the waste, the fines having a size of less than 10 mm, and water, so that in the mixture each kilogram of the first solid residues is combined with between 0.15 and 0.5 kg of the second solid residues and with between 0.5 and 1.2 kg of water.

Inventors:
SIRET, Bernard (1 rue Jean Duclos, VENISSIEUX, 69200, FR)
TABARIES, Frank (15 rue de l'Officier Challier, SAINT MANDRIER SUR MER, 83430, FR)
Application Number:
EP2017/060971
Publication Date:
November 16, 2017
Filing Date:
May 09, 2017
Export Citation:
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Assignee:
LAB GEODUR GMBH (Bludenzer Str. 6, STUTTGART, 70469, DE)
International Classes:
B09B3/00; B09B5/00
Foreign References:
EP0389328A11990-09-26
JPH09327680A1997-12-22
EP0545804A11993-06-09
EP0389328A11990-09-26
JPH09327680A1997-12-22
Attorney, Agent or Firm:
GRAND, Guillaume et al. (LAVOIX, 62 rue de Bonnel, LYON CEDEX 03, 69448, FR)
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Claims:
CLAIMS

1 . - Process for stabilizing residues resulting from combustion of waste,

wherein a mixture is prepared by placing in contact via mixing:

- first solid residues comprising filter residues that are collected by a flue gas cleaning filter to which flue gases produced by combustion of the waste are sent;

- second solid residues comprising clinker fines produced by combustion of the waste, the fines having a size of less than 10 mm; and

- water,

so that, in the mixture, each kilogram of the first solid residues is combined with between 0.15 and 0.5 kg of the second solid residues and with between 0.5 and 1 .2 kg of water.

2. - The process according to claim 1 , wherein the clinker fines have a size of less than 4 mm.

3. - The process according to one of claims 1 or 2, wherein the mixture, after mixing, is compacted.

4. - The process according to any of the preceding claims, wherein the filter residues comprise residues which result from flue gas cleaning with lime and which are collected by a bag filter.

5. - The process according to any of claims 1 to 3, wherein the filter residues consist of residues which result from flue gas cleaning with lime and which are collected by a bag filter.

6. - The process according to any of the preceding claims, wherein the water of the mixture comprises boiler purges. 7.- The process according to any of the preceding claims, wherein the water of the mixture comprises recycled water, run-off water, waste water and/or liquid sludge derived from waste water treatment.

8.- The process according to any of the preceding claims, wherein the first solid residues consist of filter residues.

9. - The process according to any of claims 1 to 7, wherein the first solid residues, in addition to filter residues, comprise ash collected from a boiler through which the waste combustion flue gases transit before reaching the filter.

10. - The process according to any of the preceding claims, wherein the second solid residues consist of clinker fines.

1 1 . - The process according to any of claims 1 to 9, wherein the second solid residues, in addition to the clinker fines, comprise ash collected from a boiler through which the waste combustion flue gases transit before reaching the filter.

Description:
Process for stabilizing residues resulting from combustion of waste

The present invention concerns a process for the stabilization of residues resulting from combustion of waste.

The combustion or incineration of waste, and energy-producing facilities which use all or part of waste or other refuse as fuel, produce various residues i.e. clinker, fly ash, residues generated by flue gas cleaning, and liquid effluent.

Solid residues, in particular fly ash and the fine fraction of clinker have marked toxicity and therefore need to be stabilized.

These solid residues can be made inert by mixing with cement in a cementing process. However, usually between 30 and 50 % cement must be added which increases the mass to be disposed of and increases the amount of water required for mixing. It is also possible to treat solid residues by washing with water or acidic water but these processes are complex and are not well integrated if the flue gases of the waste are not treated with wet scrubbers. These processes are therefore ill-adapted for dry systems which use bag filters or electrostatic precipitators, and are associated with the injection of an alkaline reagent such as lime to neutralise the acid pollutants of the flue gases.

EP 0 389 328 proposes stabilizing fly ash resulting from waste incineration by mixing this fly ash with small amounts of water, not necessarily clean water, in a proportion of between 10 % and 35 weight %, and optionally with small amounts of lime to which a silica and/or alumina-based product is optionally added. The paste obtained can be compacted, extruded or used in concretes.

For its part, JP H09 327680 discloses a process for stabilizing combustion residues wherein fly ash previously moistened with a little water is mixed with clinker, also previously moistened with a little water. The respective proportions of moistened fly ash and moistened clinker are such that the pH of the mixture obtained after mixing is between 9 and 1 1 .

It is the objective of the present invention to propose a process for stabilizing solid residues resulting from the combustion of waste, the process being economical, practical to implement and in particular does not have recourse to some extra cement.

For this purpose, the subject of the invention is a process for stabilizing residues resulting from combustion of waste, as defined in claim 1 .

The invention therefore allows « co-stabilisation » of the two main streams of solid residues produced by the combustion of waste, namely clinker and residues from flue gas cleaning. To do so, according to the invention, clinker fines i.e. a clinker fraction having elements less than 10 millimetres in size preferably less than 4 millimetres, act as a hydraulic binder whilst the residues from flue gas cleaning contain excess alkaline reagent non-used in the neutralisation of flue gas acid pollutants, as well as salts resulting from the reaction of this reagent with the acid pollutants such as chlorides, calcium sulfates and sulfites when this reagent is lime: by mixing the clinker fines with these flue gas cleaning residues and with water, in proportions set by the invention, a mixture is produced which sets without the addition of any cement, and has favourable mechanical properties for long-term storage thereof.

Additional, advantageous characteristics of the process conforming to the invention are specified in the dependent claims. It will be noted that in the claims the term « consist of » is to be construed as meaning « exclusively comprising », in other words « solely containing ».

The invention will be better understood on reading the following description given solely as an example.

When treating waste by combustion or incineration, the waste is burnt in a furnace and flue gases are released which generally, after passing through an energy recovery boiler, are mixed with an alkaline reagent to neutralise the acid pollutants thereof, and are then sent to a flue gas cleaning filter e.g. a bag filter or electrostatic precipitator. Said treatment generates several types of solid waste namely clinker, boiler ash and filter residues.

The filter residues correspond to the solid residues collected by the flue gas cleaning filter, whether this filter is a bag filter or electrostatic precipitator. These filter residues are composed of a mixture of:

- fly ash;

- the non-used excess neutralisation reagent which is, but not limited thereto, slaked lime, quick lime, magnesium oxide or sodium bicarbonate or carbonate; and

- salts derived from the reaction of the reagent with the acid pollutants of the flue gases, such as chlorides, calcium sulfates and sulfites when lime is used as reagent.

The filter residues may also contain unburned residues, activated carbon, heavy metals and many other toxic compounds. They cannot therefore be directly disposed of.

Also, it will be noted that the bulk density of these filter residues is low, usually being between 400 and 800 kg/m 3 , which means that they have a large storage volume at corresponding high cost.

Clinker, which is solid combustion residue remaining at the bottom of the furnace and regularly evacuated from the base thereof, is less toxic and can be recovered after maturing. However, the fines of this clinker i.e. the fraction having a size of less than 10 millimetres, also have a concentration of pollutants. For example, up to 80 % of heavy metals are concentrated in these clinker fines. The boiler ash collected under the above-mentioned boiler corresponds to solid residues that are sufficiently fine to have been entrained by the flue gases out of the furnace but that are too heavy to reach the flue gas cleaning filter.

Additionally, as in any plant, the installation implementing waste treatment by combustion in some way or another generates liquid effluent, either directly through flue gas treatment or else via scrubbing or collection of run-off water. This water must generally be treated before being discharged.

According to the invention, first solid residues which comprise either solely filter residues or a mixture of these filter residues at least with boiler ash, are mixed at the same time with water and second solid residues which comprise either solely clinker fines or a mixture of these fines at least with boiler ash. The mixture of the first and second residues is proportioned so that each kilogram of the first residues is combined with between 0.15 and 0.5 kg of the second residues and with between 0.5 and 1 .2 kg of water. To put the first residues, second residues and water in contact with each other, they are mixed and the mixture obtained sets thereby imparting favourable mechanical properties thereto for long-term storage. In particular, the bulk density of this mixture is far higher than that of some of the initial residues, and is advantageously between 1 100 and 1600 kg/m 3 , compared with the previously indicated bulk density of the filter residues.

It is to be understood that the clinker fines i.e. the clinker fraction having a screening size of less than 10 millimetres, even preferably less than 4 millimetres, provide a hydraulic binder which, when combined with both the excess alkalinity of the aforementioned neutralisation reagent and with the chlorides, sulfates and/or sulfites of the filter residue salts, allow rapid setting of the mixture without any cementitious addition. The mixture is therefore cement-free.

In addition, since the solid residues of the mixture already contain all kinds of pollutants, it is not particularly necessary for the water of the mixture to be clean water. Therefore, for mixing of the mixture, the water used may advantageously comprise purge water from the above-mentioned boiler, this purge water contributing sodium phosphate which will react with the calcium-containing grains thereby coating the latter and reducing the pH of interstitial solutions, hence also improving the retention of metals. Similarly, the water used for mixing may comprise recycled water, run-off water, waste water and/or liquid sludge derived from waste water treatment.

In practice, the mixing operation is known per se, being performed using mixers for example and lasts a few minutes to allow the water and various solid residues to be placed in contact and the chemical reactions to take place. According to one optional embodiment, after mixing, the mixture is compacted in particular for forming thereof. Extrusion, press or compression equipment can be used for this purpose.

At all events, the solidification of the mixture via hydraulic setting occurs within a few minutes, typically in less than one hour, even in less than thirty minutes, and after setting the mixture can be handled for disposal thereof. After one to seven days, the mixture has sufficient mechanical strength to withstand the circulation of material handling equipment. Maximum mechanical strength is generally only obtained after more than seven days as is the case with cement. In this respect, it is noted that the clinker fines, on account of their particle size and composition, also contribute a filler content which acts as mortar for this ultimate mechanical strength.

Optionally, to delay the setting of the mixture during mixing, it is possible to have recourse to a mixing device taking advantage of the thixotropic properties of the mixture.

The process conforming to the invention notably brings the following advantages: - several streams containing toxics are stabilized at the same time, namely the clinker fines, filter residues and optionally liquid sludge or waste or recycled water, with or without matter in suspension in this water;

- the mixture of the first and second solid residues has a bulk density which is much higher than that of the filter residues, these being the majority solid constituents thereof, and which correspond to the most problematic constituents regarding storage on account of their low bulk density;

- the mixture obtained is moist and does not generate any dust; it can therefore be laid in successive layers, the surface of these layers allowing the movement of vehicles and material handling equipment;

- no extra cement such as Portland cement and no additional binder are used; and

- the process in itself does not generate any liquid effluent but, on the contrary, may make good use of one and thereby reduce the amounts to be discharged into the natural environment.

The implantation of the process conforming to the invention may therefore globally be considered to be ecological since this process favourably combines several residues and effluents and is particularly well adapted for units having a storage or discharge site in the vicinity.

Worked example:

150 g of filter residues from a municipal waste incineration plant, collected by a bag filter using lime for flue gas cleaning, and containing calcium chloride, calcium sulfate, fly ash and excess lime, were mixed with 45 g of clinker fines having a screen size of less than 4 mm, and 100 g of water. This mixture was triturated in a small mixer for about ten minutes until a paste was formed. The mixture was poured into a concrete test-piece mould of diameter 40 mm and height of 105 mm. Hydraulic setting of the mixture was effective after fifteen minutes. After twenty-four hours, the bulk density was 1 .57 g/cm 3 .