RU2770298C1 - Method for vitrifying high-ash toxic waste - Google Patents

Abstract

FIELD: disposal of waste.

SUBSTANCE: invention relates to the field of disposal of non-combustible toxic waste with high ash content and can be used to dispose of fly ash from waste incineration plants, sludge and sediments from the category of accumulated environmental damage. The method for vitrifying high-ash toxic waste includes: preparing the high-ash waste prior to supplying into the melting chamber in the pre-processing unit; loading the preliminarily prepared high-ash waste into the melting chamber; melting the high-ash waste in the melting chamber; vitrifying. Pellets in the form of spherical granules are formed from the high-ash waste in the pre-processing unit, the pellets are then supplied into the melting chamber. The temperature required for melting the resulting pellets is therein maintained in the volume of the melting chamber, the exhaust gas is evacuated from the melting chamber, the molten ash is poured from the melting chamber, followed by cooling to produce a chemically stable inert material.

EFFECT: increase in the environmental safety, reduction in dust loss, and increase in the yield of vitrified material.

9 cl, 1 dwg

Description

The invention relates to the field of disposal of non-combustible toxic waste with a high ash content, and can be used for the disposal of fly ash from waste incineration plants (Incineration Plants), sludge and sediments from the category of accumulated environmental damage.

The burning of human waste products inevitably leads to the formation of secondary waste: hearth and fly ash. Fly ash is a toxic waste, belongs to the 3rd hazard class (FKKO Code 7 47 110 00 00 0), requires special handling and disposal. Also, at present, many problems of accumulated environmental damage remain unresolved in Russia, for example, toxic sludge from stopped chemical and pulp and paper industries. There remains a need for environmentally friendly, efficient and cost effective solutions to the problem of high ash toxic waste.

The following solutions are known in the art for the disposal or processing of fly ash from incinerators and other hazardous wastes with a high ash content.

A method is known for reducing the concentration of toxic organic substances in volatile dusts (RF patent RU2323387), characterized in that the return of volatile dusts is carried out during or after cleaning the boiler of the combustion plant after ascertaining special combustion conditions. This method allows to reduce the amount of toxic compounds in flying dust, but does not provide complete utilization of fly ash.

A method is known for immobilizing radioactive waste into a mineral matrix block (RF patent RU2189652), which can be used in the processing of ash residues resulting from the incineration of radioactive waste, which includes pre-mixing of radioactive waste with mineral additives followed by vitrification. The disadvantages of this invention include a limited scope, as well as the fact that immobilization by pre-mixing with mineral additives followed by vitrification can lead to an increase in the volume of waste, and that the use of electrical heating can lead to high operating costs.

A known method of vitrification of radioactive ash and a device for its implementation (RF patent RU2152652). Said method includes mixing radioactive ash with an oxidizing agent, powdered aluminum, silicocalcium and an accelerator, preparing a glass melt in a container from a portion of the above mixture and batch feeding a mixture of radioactive ash with an oxidizing agent, powdered aluminum, silicocalcium and an accelerator to the surface of the melt until the container is completely filled. The known method is intended for batch processing of radioactive waste. The disadvantages of the known method include its low productivity, which limits the possibility of its application on an industrial scale.

A known method of waste localization by vitrification in metal containers (RF patent RU2523844). In a known manner, such wastes as residues in the form of furnace ash, fly ash and filter sludge from the neutralization and purification of exhaust gases from waste incineration plants can be processed. At the same time, at least one oxidizing agent is additionally introduced into the metal container. The concentration of oxidizing agent on an oxide basis in the molten glass is 0.1 to 20% by weight, preferably 4 to 20% by weight, more preferably 5 to 15% by weight, and most preferably 10 to 13% by weight of masses of molten glass. The vitrifying additive includes at least one oxide selected from SiO2 (silicon dioxide), B2O3 (boron oxide), Al2O3 (alumina), Na2O (sodium oxide), Fe2O3, CaO, Li2O, ZnO, ZrO2. The invention makes it possible to localize undesirable chemical compounds, such as cadmium, in waste in a simple way, to completely eliminate or limit the release of volatile reaction products in reduced form and the accompanying degassing and foaming phenomena, to limit, if possible, the corrosion of a metal vessel and thereby preserve its integrity. The known invention has limited applicability, as it involves a batch mode of operation. If it is used, it is advisable to send vitrified waste for disposal in metal containers, which will lead to an increase in operating costs in the processing of fly ash. Heating in the known invention is carried out indirectly through the wall of the container using electricity, which reduces the energy efficiency of the process.

A known method of processing bottom ash and fly ash incineration plant (RF patent RU2595747). The method comprises the steps of collecting ash from the incinerator, supplying the collected ash and additional feed material to the gasification/glassification reactor, vitrification of the ash and additional feed material in the gasification/glassification reactor to form slag of the molten material, ensuring the flow of slag from the gasification/glassification reactor/ glass transition and its solidification outside the gasification/glass transition reactor, gasify the volatiles in the ash and additional feed, supply air to the secondary combustion zone in the gasification/glass transition reactor, and combust the synthesis gas generated in the gasification/glass transition reactor in the secondary combustion zone to improving the thermal environment of the combustion plant. In the known method, a plasma torch is used as a heating source, which leads to high operating costs, since the efficiency of plasma torches is limited and electrical energy is required to produce thermal energy. Also, the method does not involve the recovery of thermal energy for heating the plasma-forming gas to improve energy efficiency.

A known method of vitrification of sludge or other organic sludge and waste and a device for its implementation. (RF patent RU2704398). SUBSTANCE: method includes waste drying before being fed into the melting chamber, loading them into the melting chamber, burning organic components on the surface of the molten slag obtained from the mineral components of the waste in the melting chamber, the body of which is cooled with a coolant, heat recovery of the produced gases and their purification. At the same time, the dried sludge is fed to pelletization, after which it is fed into the accumulator hopper, from which it is fed into the melting chamber in a distributed manner to the surface of the slag melt, which is located at the bottom of the melting chamber, while the temperature in the volume of the melting chamber must be at least 1200 ° C and not more than 1600°C without cooling the body of the melting chamber with a coolant, the level of liquid slag is maintained inside the melting chamber due to the mineral fraction of the feedstock re-entering the surface of the melt, distributed blowing into the melting chamber is carried out, the oxidizer is introduced, preheated by the exhaust gas on the heat exchangers, excess stoichiometric ratio of the oxidizing agent/organic component of the raw material, while the excess over the stoichiometric ratio of the oxidizing agent/organic component of the raw material for complete oxidation of organic matter should be 1.5-2 for air, 1.1-1.3 for oxygen (by weight), carry out draining the melt from the melting chamber, from the exhaust gas is evacuated from the volume of the melting chamber through an opening in the melting chamber using a smoke removal system, while the exhaust gas at the outlet of the afterburning zone is diluted with cold air to a temperature of 1000-1100 ° C, the exhaust gas enters the NO reduction cyclone reactor, where it is mixed with urea solution and the content of thermal nitrogen oxides is suppressed, after which the exhaust gas is sent to the blast heating heat exchanger and to the waste heat boiler, after cooling in which the exhaust gas is sent to gas cleaning.

The disadvantages of the known method include a narrow focus, is intended only for processing sludge or other organic sludge and waste. The described invention is not adapted to work with such a type of waste as fly ash, the composition of which is typical for waste with a high ash content. Proposed in a known invention, the method of sludge granulation by extrusion on press granulators with an annular or flat matrix is not appropriate for waste with a high ash content. Wastes with a high ash content are difficult to compact, as they mainly contain a mineral fraction, their extrusion will lead to premature wear of the matrix, an increase in operating costs. For wastes such as fly ash, it is more appropriate to use other methods of forming granules of a given shape.

A known method for the detoxification of asbestos (Japanese patent application JP2011136320A), which is the closest analogue of the claimed method. The known method includes the step of impregnating asbestos waste with an alkali metal silicate solution, the step of granulating asbestos waste impregnated with alkali metal silicate, the step of curing the granules and mixing and heating the hardened granules and thermite agent, then the asbestos detoxification step, including the step of melting and vitrification. In contrast to the claimed invention, in the stage of preparing waste for processing in a known method, asbestos waste impregnated with alkali metal silicate is fed to granulation in a wet, soft form, and after granulation, a curing stage is required, that is, drying, as indicated in the description of a well-known invention - drying in one of the examples occurred at 200°C. According to the well-known invention, the curing of the granules (their drying) will require thermal energy, which will lead to an increase in operating costs and a complication of the technological process. In the claimed invention, waste with a high ash content is proposed to bring a spherical shape with a diameter of 3-20 mm in one stage of pelletizing on equipment mastered by the industry, for example, a plate granulator. If the waste has a moisture content of 10-40%, then the addition of binders is not required. If the humidity is low, then the binder is added in a percentage of 10-40% directly at the pelletizing stage in a plate granulator, drying the pellets for curing is not required. The resulting granule of spherical formula in the claimed method is hard enough to be loaded into the melting chamber without a curing stage, additional curing occurs when the pellets enter the volume of the melting chamber. Also, as a binder in the claimed invention, in contrast to the known method, water, an aqueous solution of molasses or other known aqueous solutions are used, which is simpler and in many cases cheaper than alkali metal silicate. The known method has a narrow focus, is intended only for the processing of asbestos waste. The known invention is not adapted to work with this type of waste, such as fly ash, from which pollutants such as mercury and arsenic can sublimate during heating, and measures for their capture and neutralization are accordingly not provided.

The technical problem to be solved by the claimed invention is to develop an efficient and environmentally friendly thermal technology for the processing of toxic wastes with a high ash content, in particular, fly ash.

The technical result achieved by using the claimed invention is to increase the environmental safety and efficiency of the method, namely, to reduce dust entrainment and increase the yield of vitrified material.

An additional technical result is to reduce operating costs by increasing the life of the matrix.

The specified technical problem is solved and the specified technical result is achieved due to the fact that in the method of vitrification of toxic wastes with a high ash content, including the preparation of wastes with a high ash content before being fed into the melting chamber in the preliminary preparation unit, loading the prepared wastes with a high ash content into the melting chamber, melting the waste with a high ash content inside the melting chamber, vitrification, pellets are formed from the waste in the form of spherical granules in the preliminary preparation unit, they are fed into the melting chamber, in which the temperature necessary for melting the obtained pellets is maintained, the exhaust gas is evacuated from the melting chamber, the molten substance drained and vitrified.

In the case of vitrification of wastes with a moisture content below 10%, such as fly ash from waste incinerators, the pre-treatment of the waste includes the step of adding an aqueous solution in an amount of 10-40% by weight of the dry component.

As an aqueous solution, water or an aqueous solution of molasses is used. The aqueous solution promotes adhesion of the waste. The chemical composition of the aqueous solution is chosen in accordance with the chemical composition of the waste experimentally with the achievement of the degree of adhesion, which ensures the preservation of the spherical shape of the granules when they are loaded into the melting chamber.

Granulation avoids dusting of ash when fed into the melting chamber and reduces dusting in the melting chamber. When entering the high-temperature zone, the pellets are sintered, which also reduces dusting and increases the yield of vitrified material.

The process of forming pellets in the form of granules of a spherical shape is the least energy-consuming, since it allows not to significantly increase the moisture content of the waste, which eliminates the stage of drying or solidifying the pellets. The use of a spherical shape increases the performance of the equipment used. When using pellets of a spherical shape, compared to using pellets of a different shape, the service life of the die increases, since the extrusion process is excluded.

Pellets from feedstock (waste) are formed using a plate granulator.

Auxiliary mineral substances (for example, based on silicon, calcium, potassium, sodium or magnesium) are added to the feedstock (waste) to reduce the melting point or obtain a product with desired properties.

As a heating source of the melting chamber, burners on hydrocarbon gas or liquid fuels are used, or the temperature required for melting is maintained using an electric arc through which air preheated using the heat of the flue gas is supplied, or the temperature required for melting is maintained using using plasmatrons, through which air preheated using the heat of the flue gas is supplied as a plasma gas.

Air preheated using the heat of the flue gas is fed into the melting chamber, which ensures complete oxidation of the residual organic component of the ash.

Additionally, maintaining the temperature required for melting is carried out by the method of ohmic heating of the molten ash in the melting chamber.

The melt is drained from the melting chamber into the glass mass granulator.

The exhaust gas after the recovery of thermal energy is cleaned of mechanical impurities and the collected dust is re-formed into pellets and returned to the melting chamber.

Combustible waste with a low ash content can be added to non-combustible waste. The addition of such waste leads to a decrease in fuel consumption in the melting chamber and, as a result, to a decrease in operating costs, which increases the efficiency of the proposed method. Also, for an enterprise implementing the claimed method, the acceptance of combustible waste, for example, fuel from waste tires, will lead to an increase in revenue due to a fee for receiving another type of waste. As a result, a complex effect will be obtained from the joint processing of waste with a high ash content and waste with a low ash content: a reduction in the consumption of thermal energy from the main source of heat in the melting chamber and the solution of auxiliary environmental problems.

Low dust entrainment in the claimed invention is achieved by forming pellets (granules of a spherical shape) from fly ash before being fed into the melting chamber. Thermal processing of fly ash pellets at a temperature of at least 1400 ° C and above in the melting chamber allows you to convert the original ash into a chemically resistant inert matrix that reliably encapsulates heavy metals. Some heavy metals (for example, mercury, arsenic) are sublimated inside the melting chamber in the specified temperature range and then removed in the gas cleaning system by known methods. The temperature regime inside the melting chamber in the claimed invention makes it possible to obtain a vitreous matrix from fly ash. Heavy metals and radioactive substances are known to have extremely low leachability from chemically resistant glassy materials, which makes the vitrification method group applicable to various hazardous, toxic and industrial wastes. For example, the chemical stability of the vitrified material was very high in the processing of radioactive waste [IAEA-TCS-27, Technological and organizational aspects of radioactive waste management, International Atomic Energy Agency, Vienna, 2005], so the normalized cesium leaching rate did not exceed in order values are 10-5 g/(cm2 ⋅ day), while strontium and α-emitters are 1–3 orders of magnitude smaller. Similar high indicators of chemical resistance of vitrified materials are known from the literature regarding the low leaching of heavy metals according to the results of relevant tests, for example, the results of a test for the leaching of a fly ash melt quenched with water: Zn - 2.7 10-2, Cd - 1.1 ∙10-3, Cr - 8.1∙10-4, Pb - 2.3∙10-2, As - 6∙10-2, Hg - <5.0∙10-4 [Plasma Science and Technology, Vol .14, No.9, Sep. 2012, https://doi.org/10.1088/1009-0630/14/9/08]. Thus, as a result of the application of the claimed method, it is possible to reduce the hazard class of fly ash, use the final product in construction, and safely dispose of it at a landfill.

The essence of the claimed method is illustrated by the drawing (Fig. 1), which shows a diagram of the claimed method of vitrification of toxic waste with a high ash content.

The claimed method can be carried out in the following way.

The pretreatment unit 1 is fed with high ash content wastes such as fly ash. After that, in the pretreatment block 1, pellets are formed from fly ash (granules of a spherical shape with a diameter of 3-20 mm). The formation of pellets is carried out using equipment that has been mastered by the industry, for example, a plate granulator. When forming pellets, the addition of a binder is acceptable if the initial fly ash has a low moisture content (less than 10%), for example, water, various aqueous solutions (for example, an aqueous solution of molasses). In some cases, water (10-40% by weight) is preliminarily added to fly ash before transportation from the incinerator to disposal sites for ease of transportation. In this case, the moisture already contained in the ash acts as a binder during the production of pellets. The chemical composition of the aqueous solution is chosen in accordance with the chemical composition of the waste experimentally with the achievement of the degree of adhesion, which ensures the preservation of the spherical shape of the granules when they are loaded into the melting chamber.

Auxiliary mineral substances (for example, based on silicon, calcium, potassium, sodium or magnesium) can be added to the feedstock (waste) to reduce the melting point or obtain a product with desired properties.

Ash pellets through the loading system 2 are fed into the melting chamber 3, the temperature in the volume of the melting chamber using, for example, hydrocarbon fuel burners 4, is maintained necessary for melting the ash pellets, but not less than 1400 ° C, this temperature may exceed 1600 ° C, depending on composition of the mineral fraction of ash.

In the heat recovery unit 5, air is heated using the thermal energy of flue gases. The air heating temperature in the recovery unit 5 can reach 500-1200 °C. The heated air is directed to the burner device on hydrocarbon fuel 4. In this case, the excess over the stoichiometric ratio of air/hydrocarbon fuel is at least 1.05-1.2 (by weight). The specified ratio is optimal to ensure the completeness of combustion.

Heated air is directed to the melting chamber 3 for complete oxidation of the residual organic component of the ash.

The melt is drained from the melting chamber 3 into a glass granulator (not shown in the figure). The molten ash is drained from the melting chamber 3 with subsequent cooling to obtain a chemically resistant inert material, the exhaust gas is evacuated from the melting chamber 3 through a hole in the melting chamber designed for this purpose using a vacuum maintenance system 7. The exhaust flue gas is sent to the recovery unit 5 and after recovery thermal energy in block 5 is sent to gas cleaning 6, where it is cleaned using known methods. The exhaust gas at the gas cleaning stage is subjected to cleaning using known methods from mechanical impurities, acidic components, heavy metals (for example, mercury, arsenic), the concentration of thermal nitrogen oxides NOx can also be reduced: in the temperature zone of 950-1050 ° C by non-catalytic methods or after cooling the exhaust gas using catalytic methods. From the captured dust, pellets are re-formed and returned to the melting chamber 3. The exhaust gas resulting from the application of the method meets the regulatory requirements.

Claims (19)

1. Method for vitrification of toxic waste with high ash content, including preparation of waste with a high ash content before being fed into the melting chamber in the pretreatment unit, loading pre-prepared waste with a high ash content into the melting chamber, melting waste with high ash content inside the melting chamber, vitrification, characterized in that in the pre-treatment unit, waste with a high ash content is used to form pellets in the form of spherical granules, the pellets are fed into the melting chamber, in the volume of the melting chamber, the temperature necessary for melting the obtained pellets is maintained, evacuate the exhaust gas from the melting chamber, molten ash is drained from the melting chamber, followed by cooling to obtain a chemically resistant inert material. 2. The method according to claim 1, characterized in that for waste with a moisture content below 10%, waste preparation includes the stage of pellet formation with the addition of an aqueous solution in an amount of 10-40% by weight of the dry component. 3. The method according to p. 1, characterized in that auxiliary minerals are added to the waste. 4. The method according to p. 1, characterized in that burners on hydrocarbon gas or liquid fuel are used as a source of heating for melting. 5. The method according to claim 1, characterized in that the maintenance of the temperature required for melting is carried out using an electric arc, through which air preheated using the heat of the flue gas is supplied. 6. The method according to claim 1, characterized in that the maintenance of the temperature required for melting is carried out using plasma torches, through which air preheated using the heat of the flue gas is supplied as a plasma gas. 7. The method according to p. 1, characterized in that the maintenance of the temperature required for melting is carried out by the method of ohmic heating of the molten ash in the melting chamber. 8. The method according to p. 1, characterized in that combustible waste with a low ash content is added to the waste. 9. The method according to p. 1, characterized in that the melt is drained from the melting chamber into a glass granulator.

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