SE534709C2 - Process for plasma treatment of waste - Google Patents

Description

Another type of waste is ion exchange materials and other materials used in the operation of nuclear power plants, such as decontaminants and other chemicals in liquid form.

One problem is that the composition of the waste from nuclear power plants changes from year to year, depending on the chemicals used in cleaning, decontamination and washing procedures, as well as depending on the type of maintenance performed. Another problem is that the solid phase of the wastewater can vary from 1-2% up to 25%.

A further problem is that, even if the volume of the wastewater is reduced by evaporation, the volume of evaporator concentrate is still very large.

Today, one way to dispose of such evaporator concentrate is to mix it with cement and thus produce concrete, thereby binding the contaminants.

SUMMARY OF THE INVENTION The object of the invention is to provide a method by means of which it is possible to reduce the volume of liquid waste in an economical and environmentally friendly manner, and in particular to minimize the remaining volume / amount of such treated waste, which waste, after treatment, preferably is bound in the form of a leach-proof glass matrix / slag.

This object is achieved by means of the method according to the invention by plasma treatment of liquid waste, comprising the steps: - supplying and heating an oxidizing gas in a plasma generator, - supplying the thus heated oxidizing gas and the waste to a plasma mixing zone, - evaporation of any water in the waste, - oxidation of the organic / organic materials in the waste to carbon monoxide, carbon dioxide, hydrogen and water vapor, - melting and oxidation of inorganic / inorganic material in the waste to the corresponding oxide (s) to form a slag product, - separation and collecting the slag product, - rapid cooling of the gases from the separator in a rapid cooler, the molten salt particles in the gases being cooled by cooling gas so rapidly and to such an extent that they do not stick to the walls of the rapid cooling chamber, - removal of particles, especially salts, and dust the rapidly cooled gases in at least one filter, and - cooling any vapor formed to v eighteen in at least one condenser.

Preferred embodiments are described in the dependent claims.

Brief Description of the Drawings The invention is described below with reference to the drawing, in which Fig. 1 shows a flow chart for plasma treatment of evaporator concentrate.

Description of the Preferred Embodiment In the following description, the invention is described with reference to a process for plasma treatment of a liquid waste in the form of evaporator concentrate from nuclear power plants, but it is obvious to the person skilled in the art that other types of liquid waste can be treated.

Liquid waste means a waste which is liquid at room temperature and which can be pumped by means of a suitable pump, such as, but not limited to, sludge comprising organic, inorganic compounds and solid particles.

For example, the evaporator concentrate, as a non-limiting example, comprises about 15% organic and inorganic material and about 25% salts. As an example, the chemical composition of the liquid phase of the evaporator concentrate may be: case., 2.5 kg / m 2 Mg 50, 10.1 kg / m 2 K 2 50, 10.5 kg / m Nacl 54 kg / mß Nazso. 1.6 kg / ma NaoH 7.0 kg / ma Surfactants 20 kg / ma co-so 2.21 E + oa Bq / m * cs-134 8.31 E + o7 Bq / ma cs-iav 4.84 E + oe Bq / në As shown in the drawing provided a plasma generator.

Oxidizing gas, preferably air, and electricity are fed to the plasma generator to thereby form a plasma mixing zone with a controlled oxidizing atmosphere and a temperature of about 800-1800 ° C, preferably 1200-1500 ° C.

Evaporator concentrate or any liquid material is fed from a storage tank (not shown) to the plasma mixing zone. In said zone, the evaporator concentrate is mixed / heated whereby the water evaporates, the organic component or components are completely decomposed and partially burned, and the inorganic material or materials are melted and oxidized, forming three main components, namely gas, glass matrix / slag. and salts. The gases include carbon monoxide, carbon dioxide, hydrogen and water vapor, the glass matrix / slag comprises metals and oxides and the salts include various salts such as NaCl, Na 2 SO 4 and CaSO 4.

After the plasma mixing zone, a separator is arranged in which liquid inorganic / inorganic material, in addition to, for example, NaCl, is separated from the gas stream. The inorganic material or materials from the separator are preferably bound in a leach-proof silicate slag. The glass / slag can then be transported to final disposal, possibly without any further treatment. This means that it is no longer necessary to remove any radioactive cesium and / or strontium.

The gas stream depleted in glass / slag is fed to a rapid cooling stage, where the gas stream is cooled to a temperature at which the salts solidify while the water remains in the form of steam. The gas is then filtered, preferably by means of a hose filter, and is preferably passed to at least one condenser, where the steam is condensed to water.

Salts in the form of dust and other particles from the filter will be compacted by granulation and / or melting before final disposal.

The water that collects in the condenser is evaporated in an evaporator.

The gas leaving the condenser is recycled to the rapid cooling stage and excess gas is burned in a burner to burn CO and H2 to CO2 and Hg). The gas leaving the burner can be cooled and filtered in an additional cooling / filtration step after which the gas is released into the atmosphere.

This means that an organic constituent / constituents are completely decomposed into carbon dioxide and water vapor, and thus, for example, a complexing agent, which is very suitable for a particular field of application, can be used without having to take into account any storage restrictions.

By treating the waste in accordance with the method according to the invention, it is possible to reduce the amount of waste that requires special regulations with regard to final disposal.

The formed glass matrix / silicate slag is also water-resistant and thus leach-proof, which has great advantages with regard to long-term storage. If necessary, a suitable slag-forming material, such as broken glass, sand / quartz, etc., can be added to the plasma mixing zone or the liquid waste to increase the formation of leach-safe glass matrix / slag.

A special feature of the invention is that the molten salt particles, which are formed in the plasma mixing zone and which are not soluble in the glass / slag, are separated from the gas flow by rapid cooling by means of cooling gas so quickly and to such an extent that they form a dust without sticking to the walls. in the rapid cooling chamber. More specifically, the molten salt particles are cooled to such an extent that they no longer have a tendency to stick, while still floating, and thus will not stick to the walls of the rapid cooling chamber.

It should be mentioned that the concentration of salts in the incoming evaporator concentrate is about 45,000 times higher than the concentration of salts in the water leaving the condenser.

Claims (10)

10 l5 20 25 30 534 709 Patent claims Process for plasma treatment of liquid waste, characterized by the steps: - supply and heating of an oxidizing gas in a plasma generator, - supply of the thus heated oxidizing gas and the waste to a plasma mixing zone, - evaporation of any water in the waste, - oxidation of organic / organic material in the waste to carbon monoxide, carbon dioxide, hydrogen and water vapor, - melting and oxidation of inorganic / inorganic material in the waste to the corresponding oxide (s) to form a slag product, - separation and collection of the slag product in a separator, - rapid cooling of the gases from the separator in a rapid cooling chamber, the molten salt particles in the gases being cooled by means of cooling gas so rapidly and to such an extent that they do not stick to the walls of the rapid cooling chamber, - removal of particles, especially salts, and dust from the rapidly cooled gases in at least one filter , and - cooling any water vapor formed into water in at least one condenser. Method according to claim 1, characterized by the further step: - binding of the slag product in the form of a leach-proof slag. A method according to claim 2, characterized in that the bonding is achieved by adding to the plasma mixing zone or the liquid waste of a material selected from the group consisting of crushed glass and sand / quartz to form a leach-safe silicate slag. 10 15 20 25 534 709 Process according to one of the preceding claims, characterized in that the gases from the separator are cooled to a temperature where the salts are solid and the water is evaporated. S. A method according to any one of the preceding claims, characterized by compaction by granulation and / or melting of the salts and other particles obtained by means of said at least one filter. Process according to any one of the preceding claims, characterized by the further steps: - combustion of the gases originating from the condenser to eliminate carbon monoxide and hydrogen, and - cooling and filtering of the combusted gases before they are released into the atmosphere. Process according to any one of the preceding claims, characterized in that the waste is produced during operation and maintenance of nuclear power plants, except with respect to the nuclear fuel. Process according to Claim 7, characterized in that the waste consists of evaporator concentrate. Method according to claim 7, characterized in that the waste is sludge of ion exchange material. Method according to one of the preceding claims, characterized in that the liquid waste is liquid at room temperature.