RU2353857C1 - Method for recycling of liquid wastes - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: method for recycling of liquid wastes includes their evaporation in evaporator and supply directly to jet of plasma-forming gas of reactor. Wastes comprising polychlorinated biphenyls, are supplied to jet of plasma-forming gas together with neutralising agent, wastes are thermally decomposed, and products of recycling are made. At that neutralising agent used is quicklime crushed down to size of less than 74 mcm. Produced recycling products in the form of gas mixture via tuyers are blown into lower part of furnace for lime annealing, temperature of which is equal to 700-750°C.

EFFECT: increased efficiency and ecological effectiveness of method.

2 cl, 1 ex

Description

The invention relates to the field of environmental protection, and in particular to methods for the disposal and disposal of gaseous and liquid organohalogen wastes, in particular liquid polychlorinated biphenyls (PCBs, C ₁₂ H _X Cl _Y ) using low-temperature plasma.

The problem of utilization and neutralization of polychlorinated biphenyls is included in the list of global environmental problems, since they belong to the group of persistent organic pollutants that have toxic effects on the human body. In addition, improper storage or destruction of PCBs leads to the formation of polychlorinated dibenzodioxins and dibenzofurans.

A known method of fire neutralization of liquid halogen-containing wastes, including mixing them with a neutralizing agent in a disintegrator with a collision speed of 75-350 m / s to obtain a stable emulsion or suspension, feeding it into a furnace where their high-temperature products of fuel combustion occurs at a temperature of 1400-1700 ° C processing together with a neutralizing agent, and removal of heat treatment products from the furnace (USSR AS No. 1101623, publ. 07.07.84. Bull. No. 25).

The following disadvantages are inherent in this method: high costs for the alkali used, a large amount of the resulting aqueous salt solution, the need for its disposal.

A known method of pyrolytic decomposition of waste, preferably liquid (US Pat. US No. 4644877, MKI F23G 5/10, 5/12, publ. 02.24.1987), in which PCB waste and a small amount of air is fed into the discharge chamber of the arc plasma torch, which at a temperature of 5000 ° C, the destruction of PCB molecules and air to atoms and ions occurs. Then the resulting mixture enters the reactor, where it is cooled to a temperature of 900-1200 ° C with the formation of synthesis gas and solid particles of soot. At the outlet of the reactor, these components are additionally cooled with an aqueous alkaline solution to 80 ° C, while the hydrogen chloride is neutralized to sodium chloride.

This method has the same drawbacks as the previous one: high costs for the alkali used, a large amount of the formed aqueous salt solution, the need for its disposal, in addition, a large amount of soot is formed, which complicates the process of quenching and neutralization of products, and the temperature regime adopted in the reactor does not guarantee the absence of highly toxic substances, such as dioxins, furans, in pyrolysis products.

A known method of plasma-chemical neutralization of gaseous and liquid organohalogen substances and waste containing them, described in patent RU 2105928, publ. 1998.02.27. Its essence lies in the fact that organohalogen waste is preheated to a temperature not exceeding the limit of their thermal stability, and sprayed with a stream of hot air. The resulting vapor-air mixture is sent to a plasma jet, where pyrolysis is carried out at a temperature of at least 1500 ° C, a residence time of 2-10 ms and an excess of oxidizing agent sufficient to completely oxidize the carbon contained in the waste. Further, the pyrolysis products are quenched and neutralized with an aqueous alkali solution, which is used repeatedly, periodically adding alkali to it until the initial concentration is restored and removing salts formed during neutralization.

The method has the following disadvantages. Since pyrolysis is carried out with atmospheric oxygen, a large amount of energy will be spent on heating the nitrogen contained in it. The use of air as a plasma-forming gas reduces the service life of the plasma torch in comparison with units operating on neutral gases, such as nitrogen. The pyrolysis products are neutralized with an aqueous alkali solution of high cost. The salts formed during the neutralization process precipitate, which requires a shutdown of the process to remove them. Periodic shutdown of the process under these operating conditions is undesirable. Removed salts require additional means for their disposal. The method is complex and requires a large number of devices for its implementation. Thus, this method does not allow for a long and reliable operation of the plants with the necessary process efficiency.

The closest in technical essence and the achieved result is a method of disposing of liquid waste in the evaporator and feeding directly into the plasma plasma gas of the reactor (patent RU 2288407 C2, CL G 7/04, publ. 11/27/2006), where due to the secondary air at high temperature, they are oxidized. The method has disadvantages similar to those inherent in the previous method. When using this method for the disposal of PCBs as a result of the destruction of chemical bonds between the atoms of the substance being utilized, a large number of chlorine ions are formed in the plasma, which, when the gas cools, interact with carbon, oxygen and hydrogen ions, forming various organochlorine compounds, including dioxins and furans.

The technical result of the invention is the creation of an economical and environmentally efficient method for the disposal of PCB waste on existing equipment with a slight modernization, as a result of which the exhaust gases do not contain toxic organochlorine compounds.

The specified technical result is achieved by the fact that in a method for the disposal of liquid waste, providing for their evaporation in an evaporator, feeding directly into the plasma plasma gas of the reactor, according to the invention, the waste containing polychlorinated biphenyls (PCBs), fed into the plasma plasma gas stream together with a neutralizing reagent, carry out thermal decomposition of waste and receive recycling products, while quicklime is used as a neutralizing agent, crushed to a particle size of less than 74 microns in the amount of 1.02-1.04 of the stoichiometrically necessary for the binding of chlorine, and the resulting waste products in the form of a gas mixture are blown through the tuyeres into the lower part of the limestone kiln, the temperature of which is 700-750 °.

The particle size of quicklime should not exceed 74 microns. With a larger size, the interaction of quicklime with PCB is not complete, therefore, excess quicklime and harmful organochlorine enter the furnace.

The temperature of the zone of the furnace into which the mixture is blown must not exceed 700-750 ° C. At these temperatures, condensation of calcium chloride (t _PL = 774 ° C) occurs on pieces of calcined limestone and at the same time the combustion of carbon and hydrogen.

The amount of quicklime supplied is 1.02-1.04 of the stoichiometrically necessary for the binding of PCB chlorine in CaCl ₂ . Putting more quicklime will lead to an increase in dust removal, a decrease in the gas permeability of the layer. When you enter a smaller amount of quicklime, the formation of undesirable, very dangerous organochlorine compounds.

Example. Raw materials (spent transformer oil) from the tank through the evaporator was introduced directly into the plasma-forming gas (nitrogen) stream into the reactor, and quicklime powder was also fed from the batcher. The nitrogen flow rate of 10 l / min, the temperature of the plasma jet 5000 ° C. PCB consumption 2.5 l / min. Quicklime consumption 15 g / min. Heat treatment products entered the furnace, filled with calcined limestone with a particle size of 5-10 mm. Layer thickness 900 mm. The temperature of the furnace is 700 ° C. To burn soot carbon and hydrogen, oxygen (20 l / min) was blown into the furnace. The composition of the gas leaving the furnace (vol.%): N ₂ - 24; СО ₂ - 62; H ₂ O - 14. Toxic organochlorine compounds in the gas are absent. Calcium chloride precipitates in the layer.

This method allows efficient disposal of PCB wastes using existing equipment. It is technically simple, not expensive and does not create problems with the disposal of products resulting from its implementation.

Claims (2)

1. A method of disposing liquid waste, including evaporating it in an evaporator and feeding directly into the plasma plasma gas stream of the reactor, characterized in that the waste containing polychlorinated biphenyls is fed into the plasma gas stream together with a neutralizing agent, thermal decomposition of the waste is carried out, and waste products are obtained, in this case, quicklime, crushed to a particle size of less than 74 microns, is used as a neutralizing agent, and the resulting products of utilization in the form of a gas mixture through blowing tuyeres They are pressed into the lower part of the limestone kiln, the temperature of which is 700–750 ° С. 2. The method according to claim 1, characterized in that the neutralizing agent is supplied in an amount of 1.02-1.04 from stoichiometrically necessary for the binding of chlorine contained in polychlorinated biphenyls to calcium chloride.