FR2556710A1 - Sludge from lime treatment of water - Google Patents

Abstract

The sludge produced as residue in the treatment of seawater or river water with calcined or slaked lime is used, after draining and drying, as a dusty or powdered filler in the production of asphalt surfacings, esp. mastic asphalt surfacings, micro-asphalt and melted asphalt. In particular, the sludge derived from the treatment of nuclear power plant cooling water is used in this way.

Description

USE OF RESULTING DECANTING SLUDGE
TREATMENT OF LACUSTRY OR RIVER WATER
BY MEANS OF CALCINATED AND EXTINGUISHED LIME, AND
PROCESS FOR TREATING THIS SLUDGE
The present invention relates to a use of the settling sludge resulting from the treatment of lake or river water by means of calcined lime and quenched after spinning and drying, as well as to a process for treating this settling sludge.

Pre-treatment of make-up water for cooling towers, particularly in nuclear power plants, produces a large amount of unusable residue in the form of sludge which is wrung to a dry matter content around 60%. This sludge comes from the softening and purification of lake or river water which is used as coolant in secondary circuits, for example in cooling towers, cooling installations or similar installations; . In fact, to prevent lime deposits and / or corr osion damage from occurring in the pipes, it is necessary that the hydrated calcium carbonate contained in the water be removed. For this, calcined lime is used which is transformed into lime hydroxide in primary tanks and which is then introduced in this form into a large clarification tank, which also receives the water to be treated. In this low level of clarification, the chemical reaction of hydrated calcium carbonate in water with calcium hydroxide takes place to form calcium carbonate.

However, in the water to be treated are still other minerals, fine or clayey silts, algae or other organic particles which must be eliminated. For this purpose, ferric chloride is generally used which is also introduced into the clarification tank and which is transformed into iron hydroxide. This iron hydroxide then forms large flakes which capture the aforementioned particles and which are then deposited with the calcium carbonate, while the purified water can be taken from the upper part. The residue consisting of lime, iron hydroxide and decanted impurities is then allowed to sediment, then it is generally wrung in a filter press until a dry matter content of approximately 60 to 65%.

An analysis carried out on this dry matter generally shows a content of 80 to 85% of calcium carbonate and around 7% of iron oxide, the remainder comprising said silts, minerals, clays, algae and other organic materials.

Until now, the settling sludge drained to the wetland state had to be transported and landfilled somewhere, with the costs that this entails. Besides this question of cost, this mud also raised a problem of environmental protection.

Consequently, the object of the present invention is to allow reuse of this settling sludge and to provide a treatment method allowing this reuse.

According to the invention, this object is achieved by the use of said dewatered settling sludge, dried and reduced to powder or flour as mineral flour for the manufacture of bituminous coatings, in particular coatings based on asphalt mastic, bituminous microbétons or poured asphalt.

For the production of such bituminous coatings, minerals have been used up to now, generally crushed gravel, ground limestone and bitumen which are mixed in a mixer at temperatures above 100 C.

The limestone used as mineral flour, extracted in the quarry and finely ground, then formed with the bitumen the means of connection (mortar) between the gravel.

Thanks to the present invention, it is now possible to replace all or part of this limestone mineral flour with said settling mud after having wrung it out, dried and reduced to powder if necessary. Although analysis has shown that this settling sludge has a very high content of calcium carbonate, it has always been considered unsuitable for reuse or further treatment, in particular because of its other components, some of which do not is not well determined.

However, it has surprisingly appeared that, thanks to the present invention, this settling sludge can be enhanced by using it as mineral flour for the manufacture of bituminous coatings. On the one hand, this avoids costly disposal and, on the other hand, savings are made in the manufacture of bituminous coatings.

The decantation sludge used can advantageously consist of the decantation sludge resulting from the treatment of lake or river water intended for cooling in cooling towers, cooling installations or similar installations in nuclear power plants.

According to another aspect of the present invention, the process for treating the settling sludge resulting from the treatment of lake or river water using calcined and slaked lime, after wringing said mud, is characterized in that it is dried the mud to reduce it to powder or flour and it is incorporated as mineral flour in bituminous mixtures intended for bituminous coatings, in particular coatings based on asphalt mastic, bituminous micro-concretes or poured asphalts.

In addition to the advantageous use of this settling sludge for the manufacture of bituminous coatings, the analyzes carried out on these coatings and on the settling sludge treated according to the present invention have led to quite surprising results.

The coatings produced with mineral flour according to the invention are very hard and rigid, and therefore have a large load capacity. In road construction, such bituminous coatings are particularly indicated as a wear layer, as a bonding layer or as a support layer and they are especially advantageous on slow tracks heavily stressed by traffic, in the slowdown zones preceding the signals. bright, crossroads, etc. and in steeply sloping sections, because they have a high roughness. Until now, bituminous coatings of this kind were particularly expensive, and expensive additives had to be incorporated, for example natural asphalt and / or special bitumen, organic or inorganic fibrous materials, kieselguhr and powdered or granulated polymers. . With the use of said settling mud as mineral flour according to the present invention, it is unexpectedly found that it is possible to dispense with such additives in order to increase the rigidity and the resistance to wear of the bituminous coatings. Experiments with this mineral flour have effectively shown that it has an exceptionally strong stiffening effect. Under the microscope, the amorphous structures present striking groupings, in particular of the cottony type, around the isolated grains. 96 below 0.09- mm.

Thanks to its properties, the mineral flour according to the invention is particularly suitable for producing thin and hard bituminous coatings, for example on concrete. It can also be used advantageously in road improvement where very thin coatings are used, for example 1.5 cm thick. Thanks to bituminous coatings made with the flour according to the invention, it is even possible, if necessary, to save planing of the damaged coatings. This is particularly the case when it is only necessary to eliminate ruts. With a bituminous coating manufactured according to the present invention, it suffices simply to combine these ruts, then to apply a thin coating on the entire floor.

According to an advantageous embodiment of the invention, to use in the manufacture of bituminous coatings the decantation sludge drained to a dry matter content of about 60 to 65%, this sludge is dried until the dry matter content exceeds 95 96 and preferably reaches 98 96. This drying can be carried out in different ways. The mud can simply be subjected to drying with hot air, carried out at a temperature above 1500C, in particular between 1800 and 1900C A prior or subsequent mechanical reduction of larger lumps increases the drying efficiency (for example drying in a As a rotary kiln is already used to treat and heat mineral mixtures in the manufacture of bituminous coatings, it is advantageous to dry, in a rotary tubular oven, the settling sludge in the state of damp earth after spinning, to dry it and reduce it to powder or flour. Such a rotary kiln also has the advantage of crumbling coarse or agglomerated elements of the drained mud during drying, an effect which can be further improved by adding coarse elements serving as grinding means. It is possible in particular to introduce a coarse-grained mineral mixture into the rotary kiln during the drying of the mud, for example pebbles which grind the lumps during the rotation of the kiln.

The coarse-grained mineral mixture, removed from the other end of the rotary kiln, can also be used to make the bituminous coating.

Depending on the applications, ground natural limestone can be added to the drained, dried and reduced to powder or flour mud. In particular, a mixture of this kind is indicated if it is desired to reduce the stiffening effect of the mineral flour according to the invention.

The strong stiffening effect of the mineral flour obtained from the above-mentioned landing mud can have several causes. Apart from calcium carbonate, the other components of the residue can contribute to it, as well as the flaky formations on the surface of the grains. In fact, it is possible to obtain rigid and wear-resistant bituminous coatings by means of a high proportion of gravel, but the significant bitumen supplements necessary to fill the resulting amount of vacuum are subject to limits in the conventional processes. Bitumen can only bind to a certain extent, and an excess of free bitumen must therefore be avoided. On the other hand, the mineral flour according to the invention can bind more bitumen, which allows the mentioned advantages to be obtained. above.

The present invention will be better understood using the description in principle of an example of the process for treating the aforementioned settling sludge with reference to the drawing, the single figure of which schematically represents an installation for treating this sludge and for manufacturing bituminous coatings.

The settling sludge is stored in a receiving tank 1, from which it is brought to a rotary tubular furnace 2 by a carrier tape. This rotary kiln is of known type and will therefore not be described here in detail. In general, it comprises a drum mounted on rollers 3 and rotating around a longitudinal axis slightly inclined in the direction of the outlet, in order to ensure the circulation of the material to be treated. Normally, the mineral mixtures are dried in the rotary kiln 2 at temperatures from 180 to 1900C. Such an oven can also be used for drying the settling sludge. Via a line 4, an air supply is introduced countercurrently into the rotary kiln 2, while the dried mineral flour in the form of flour powder is discharged through a line 5 and a filtration installation 6 to a silo 7.For loading into the silo, an extraction screw 8 is provided at the outlet of the filtration installation and an elevator 9. The filtered air is evacuated via a pipe 10.

For the manufacture of bituminous coatings, a mineral mixture is brought by conveyor belts from stock 11 to the rotary kiln 2 and it is heated to a temperature of 180 to 1900C. The mineral mixture is transported upwards by a conveyor 12 and it passes through several stages of sieve 13 to reach a mixer 14. Bitumen is contained in another tank 15 to be introduced according to the desired dosage into the mixer 14, from same as the mineral flour taken from the silo 7. The bituminous mixture prepared in the mixer 14 can be dumped directly into a truck 16 to be transported. An additional silo 17 contains conventional ground limestone which can be brought into the mixer 14 in place of the mineral flour according to the invention or with it as the case may be.

A formulation will also be given below, by way of example, which can be used for the manufacture of an asphalt mastic rich in gravel.

An asphaltic mastic rich in gravel consists of a mixture of mineral materials with discontinuous grain size, bitumen used as binder and homogenization additives. The mixture is kneaded hot and compacted. A high gravel content results in a well-supported stony skeleton, the yides of which are largely filled with asphalt putty.

The proportions of the mixture can be for example the following: a) mineral flour: 8 to 13% by weight b) mineral mixture with large grains (gravel): 70 to 80% by weight c) binder / bitumen: 6 to 7.5 % in weight
It is still possible to add additives in small proportions.

Claims (10)

Claims 1. Use of the settling sludge resulting from the treatment of lake or river water by means of calcined lime and slaked after wringing, drying and reduction into powder or flour as mineral flour for the manufacture of bituminous coatings, in particular base coatings asphalt putty, bituminous micro-concrete or poured asphalt. 2. Use according to claim 1 of the settling sludge resulting from the treatment of lake or river water intended for cooling in cooling towers, cooling installations or similar installations in nuclear power plants. 3. Method for treating the settling sludge resulting from the treatment of lake or river water using calcined lime and quenched after draining said mud, characterized in that the mud is dried to reduce it to powder or in flour and it is incorporated as mineral flour in bituminous mixtures arranged to constitute bituminous coatings, in particular coatings based on asphalt mastic, bituminous microbétons or mastic asphalts. 4. Method according to claim 3, characterized in that the mud is dried until the dry matter content exceeds 95%. 5. Method according to claim 3 or 4, characterized in that the sludge is subjected to drying with hot air. 6. Method according to claim 5, characterized in that the drying is carried out at a temperature above 1500C. 7. Method according to any one of claims 4 to 6, characterized in that the mud is dried in a rotary tubular oven (2), this mud being in the state of wet earth after spinning. 8. Method according to claim 7, characterized in that one crumbles, in the rotary kiln (2), the coarse or agglomerated elements of the drained mud. 9. Method according to any one of claims 3 to 8, characterized in that ground natural limestone is added to the drained, dried and reduced to powder or flour mud. 10. Method according to claim 7, characterized in that a coarse-grained mineral mixture is introduced into the rotary kiln (2) during the drying of the mud.