RU2650558C1 - Method of thermal neutralizing of mineral building materials and soils polluted by highly toxic organochlorine compounds - Google Patents

Abstract

FIELD: ecology.

SUBSTANCE: invention relates to ecology, in particular to methods for neutralizing in loose form mineral building materials and soils contaminated with highly toxic organochlorine compounds: products of incomplete decomposition of poisonous substances, pesticides, polychlorinated biphenyls, etc., and can be effectively used in the implementation of measures to protect the environment from pollution. Mineral building materials and soils contaminated with highly toxic organochlorine compounds, are successively placed in a tumble dryer and oven, heated by flue gases through the enclosing bodies of the dryer and furnace external chambers, while spraying into the volume of the dryer the chopped hydrated lime with a particle size of less than 30 mcm. Process is carried out at a temperature of 200–750 °C for 1 hour. Chlorine content of neutralized mineral building materials and soils is less than 360 mg/kg, and the weight ratio of hydrated lime: contaminated building materials/soils is 0.11÷0.2.

EFFECT: invention provides a simple process from the point of view of hardware design, technologically and environmentally safe, the neutralization of hydrogen chloride, formed during thermal detoxification of mineral building materials and soils contaminated with highly toxic organochlorine compounds, directly in the volume of drum dryers and furnaces.

3 cl, 1 dwg, 1 tbl

Description

The invention relates to ecology, in particular to methods for the neutralization in bulk of mineral building materials and soils contaminated with highly toxic organochlorine compounds: products of incomplete decomposition of toxic substances, pesticides, polychlorinated biphenyls, etc., and can be effectively used in the implementation of protective measures environmental pollution.

A known method for the disposal of organochlorine wastes, including their supply to the combustion zone of a shaft-type furnace and thermal decomposition with subsequent passage through charge materials, while calcium compounds are additionally introduced into the initial charge as a chlorine-binding additive [RU 2502922].

The main disadvantages of this method are the high temperature of the process (1700-1900 ° C), as well as the need to use a mixture and chlorine-binding additives in quantities many times greater than the mass of loaded organochlorine waste.

A known method for the destruction and disposal of toxic organic waste containing polychlorinated biphenyls or unsuitable pesticides, which includes two stages: the first stage, during which the reagent, useful additives and waste are preliminarily prepared, after which the waste is subjected to a chemical reduction reaction to low toxic combustible and non-combustible compounds with the release of toxic volatile substances, and the second stage, during which low toxic compounds and toxic volatile substances are subjected to high thermal oxidation followed by cooling of the exhaust gases in the heat exchanger and their wet cleaning [RU 2480260].

The main disadvantage of this method is the use of highly toxic monoethanolamine as one of the reagents. In addition, the application of this technology is not economically feasible on an industrial scale for the disposal of contaminated soils. [Lucian Vasile Pavel, Maria Gavrilescu. Overview of ex situ decontamination techniques for soil cleanup. // Environmental engineering and management journal. 7 (6), 2008, pp. 815-834.]

The closest technical solution, selected as a prototype of the present invention, is a method for thermal neutralization of solid waste, which includes placing solid waste in a drum dryer, drying solid waste in a drum dryer, moving solid waste from a drum dryer to a drum furnace, calcining them in a drum furnace, removal of gases generated during the neutralization process from a drum dryer and a drum furnace and unloading of neutralized solid waste, and drying and calcining solid waste they are constructed by transferring heat from the drum dryer and drum furnace bodies to them, and the bodies are heated in external heating chambers covering the drum dryer and drum furnace case from the outside [RU 2552831, IPC B09B 3/00, F23G 5/04, 06/10/2015 ].

The disadvantage of this method is that, for example, when calcining solid chlorine-containing wastes, hydrogen chloride is present in the gases discharged from the drum furnace, high concentrations of which, especially in the presence of moisture, without special anti-corrosion protection measures, such as lining, can lead to premature destruction of the process equipment [I.Ya. Klinov, P.G. Udyma, A.V. Molokanov, A.V. Goryainova. Chemical equipment in corrosion resistant design. Directory. M .: Mechanical Engineering, 1970, p. 5]. As a rule, to capture hydrochloric acid vapors in the exhaust flue gases, installation of specialized equipment (absorber) with the organization of a cooling system is required, since the absorption of hydrochloric acid vapor is accompanied by the release of a large amount of heat [Straus V. Industrial gas cleaning: Trans. from English - M., Chemistry, 1981. p. 140]. All this, obviously, complicates and increases the cost of gas cleaning.

The technical result from the use of the invention is to reduce the concentration of hydrogen chloride in the gas mixture leaving the furnace during thermal neutralization of mineral building materials and soils contaminated with highly toxic organochlorine compounds.

The essence of the proposed method is as follows.

The method of thermal neutralization of mineral building materials and soils contaminated with highly toxic organochlorine compounds, including their sequential placement in a drum dryer and furnace heated by flue gases through the external chambers of the dryer and furnace, sequential drying and calcination in a drum dryer and furnace, removal of gases generated as a result of neutralization, unloading of neutralized mineral building materials and soils from a drum furnace. Unlike the prototype, to reduce the concentration of hydrogen chloride in the gases discharged from the drum furnace, crushed slaked lime (reagent) is additionally introduced into the volume of the drum dryer. In this case, the reagent is introduced by direct spraying it in the form of particles with a size of less than 30 microns in the volume of a drum dryer over a layer of neutralized mineral building materials and soils, and the weight ratio of reagent: contaminated building materials / soils is 0.11 ÷ 0.2.

The maximum chlorine content in the neutralized mineral building materials and soils is less than 360 mg / kg. Subject to the specified condition, the maximum possible amount of water-soluble calcium chloride formed as a result of the neutralization of hydrogen chloride in the composition of neutralized mineral building materials and soils does not exceed 560 mg / kg, which corresponds to the established sanitary and hygienic standards for the content of chloride ions in the soil.

The invention is illustrated in the drawing, where in Fig. 1 shows a schematic diagram of the implementation of the claimed method.

The crushed mineral building materials and soils contaminated with highly toxic organochlorine compounds 1 are fed into the rotary drum dryer 7 heated by flue gases 3 through the external chamber 5 surrounding the dryer body using a screw feeder 2. Exhaust flue gases 4 from the external chamber 5 are released into the atmosphere. During drying, reagent 9 is additionally sprayed into the volume of the drum dryer 7 over the materials to be treated 6 using a pneumatic spraying device 8. From the drum dryer 8, the materials to be neutralized 6 are fed through a pipe 10 to a rotary drum furnace 14, heated by flue gases 11 through an external chamber enclosing the dryer body 13. Exhaust flue gases 12 from the external chamber 13 enter the atmosphere. The resulting gas mixture during calcination through the duct 16 is sent to the gas cleaning system. Calcined mineral building materials and soils 15 through the pipeline 17 are sent to the discharge system.

Shredded slaked lime (particle size less than 30 microns) in the amount of 11 ÷ 20 kg / h is sprayed into the volume of the dryer in the direct-flow mode by means of a pneumatic device. As you move the bulk mixture through the pipeline enters a drum furnace heated to a temperature of 700 ÷ 750 ° C, where it is calcined. The total residence time of the thermally treated mixture in the drum dryer and furnace is 1 hour. The exhaust gas velocity in the dryer and furnace is 0.5 ÷ 1.5 m / s. The volume of exhaust gases is 40 m ³ / h due to air leaks in the dryer and oven.

The gas mixture formed as a result of thermal neutralization is discharged from the furnace and fed to the gas purification system, and the thermally treated bulk mixture is sent to the cooling and unloading system.

To determine the concentration of hydrogen chloride in the exhaust gases, a gas analyzer is mounted in the duct after the drum furnace.

The test results are shown in table 1.

The use of particles larger than 30 μm led to inefficient atomization due to their high deposition rate in the exhaust gas stream, which ultimately led to an increase in the concentration of hydrogen chloride (example 2).

At a flow rate of the sprayed reagent G _p less than 11 kg / h, an increase in the concentration of hydrogen chloride in the exhaust gases was observed (Example 3), and at a flow rate of more than 20 kg / h the concentration remained practically unchanged, which makes a further increase in the flow rate of the reagent impractical (Example 4).

A residence time of t 1 hour in the temperature range T 200 ÷ 750 ° C ensures the completeness of thermal treatment of mineral building materials and soil. With a decrease in the residence time in the material discharged from the furnace, trace amounts of organochlorine compounds were detected (Example 5).

A comparative analysis of the proposed solution with the prototype shows that the proposed method is characterized by the use of slaked lime sprayed into the volume of a drum dryer to transfer hydrogen chloride formed during the thermal treatment of mineral building materials and soils contaminated with highly toxic organochlorine compounds into inorganic salts with their subsequent discharge in the composition of the neutralized solid waste.

Claims (3)

1. The method of thermal neutralization of mineral building materials and soils contaminated with highly toxic organochlorine compounds, including their sequential placement in a drum dryer and furnace, heated by flue gases through the outer chambers of the dryer and furnace, drying and calcination in a drum dryer and furnace, exhaust gases, formed as a result of neutralization, unloading of neutralized solid waste from a drum furnace, characterized in that pulverized pulverized into the volume of the drum dryer constant prices slaked lime. 2. The method according to p. 1, characterized in that the particle size of the ground slaked lime is less than 30 microns. 3. The method according to p. 1, characterized in that the weight ratio of slaked lime: contaminated building materials / soils is 0.11 ÷ 0.2.

Images