RU2775593C1 - Method for melting ash and slag from waste incineration plants - Google Patents

Abstract

FIELD: processing municipal solid waste.

SUBSTANCE: invention relates to the field of processing municipal solid waste (MSW) at incineration plants (WEP). The method for melting fly ash and slag formed during incineration (MSW) at (WEP) includes starting the furnace, heating the furnace, loading material into the furnace volume, remelting the material, draining the resulting slag melt into a water bath, cooling the slag melt and granulation. To start the furnace, an arc discharge is used, the arc is ignited between the graphite and bottom electrodes, the melt pool is obtained by melting the fly ash and slag from MSW combustion at the WEP pre-loaded into the furnace, the remelting of fly ash and MSW combustion slag at WEP is carried out at the expense of resistive heating from the flow of current through the electrodes, electric arc, melt and melted fly ash and slag.

EFFECT: long and continuous melting of fly ash and slag formed during the combustion of MSW at waste incineration plants, with an insignificant specific power consumption not exceeding 0.8-1.0 kW⋅h/kg of ash.

1 cl, 2 dwg

Description

The invention relates to the field of processing municipal solid waste (MSW) at incineration plants (MSZ), namely, for melting fly ash and slag resulting from the combustion of MSW, with the production of environmentally friendly chemically inert slag suitable for use in the construction industry. The invention is also applicable in other industries where smelting of ore material is required.

Ash and slag waste after incineration is usually toxic and has a hazard class 3. Distinguish between fly and hearth ash. Fly ash is carried away from the flue gas chamber and retained by bag filters. It contains an increased amount of volatile and heavy metals and dioxins absorbed on its particles. In the hearth ash, which is discharged from the grate of the furnace, heavy metals are also present, but less than in the volatile one. They are also found in slags, but are present in a slightly soluble form (oxides and silicates) [V.P. Lukashov, S.P. Vashchenko, G.I. Bagryantsev, H.S. Pak, Plasma-thermal processing of solid waste // Ecology and industry of Russia, 2005; H.S. Pak Investigation of the composition and properties of slag during plasma remelting of waste incineration plant ash // Thermophysics and Aeromechanics T18, No. 2, 2011 p. 325-333; Ariake K., KogaA., MatsuokaY. et. al. Plasma slagging system for incineration of ash // FAPJG, 1995, N144, P. 3-8].

One of the effective ways to solve the problem of processing ash and slag wastes is their melting, which leads to a significant reduction in the volume of ash and its transfer to inert (vitrified) slag. This technology eliminates the subsequent leaching of toxic substances from the molten slag. Low-boiling ash components evaporate from the melt and are trapped in bag filters or on cooled surfaces. Particularly dangerous toxicants, namely, dioxins and furans, can be easily removed only by raising the temperature to 1200-1400°C.

Known laboratory plasma melting plant and method of plasma remelting of incinerator ash (H.S. Pak. Study of the composition and properties of slag during plasma remelting of incinerator ash // Thermophysics and Aeromechanics, 2011, vol. 18, No. 2, pp. 325-334 ). The melting plant consists of a melting chamber, a plasma torch, a plasma torch power source and a system for its launch, systems for analyzing, cleaning and removing gas generated during the melting process. The smelting chamber has a refractory bottom wall lining and is designed to rotate 180 degrees to drain the molten slag. For melting ash, a jet-type plasma torch with a power of up to 70 kW is used. As a result of plasma remelting of ash, a dioxin-free, environmentally friendly slag is obtained.

Known installation has a small capacity, since the processing of ash is carried out by a discrete method of 500 g. The cleaning system of the installation does not allow to achieve environmental standards for harmful emissions.

A known ash disposal unit is used as part of an integrated district thermal station for processing and neutralizing industrial and household waste of the city [RU 2502017, 10.05.2012, F23G 5/00; RU 2502018, 05/10/2012, F23G 5/00], containing a melting reactor lined from the inside, a plasma torch, an ash bin with an ash input mechanism, a melt drain and slag granulation system. To start and subsequent melting of ash and slag waste, an electric arc plasma torch is used.

The duration of continuous operation of the installation depends on the service life of the electrodes of the plasma torch used and is no more than 500 hours.

Thus, in the known solutions, in which electric arc plasma torches are used to start devices and subsequent melting of ash and slag waste, the duration of continuous operation of the devices depends on the service life of the electrodes of the plasma torch used. The service life of known plasma torches ranges from 100 to 1000 hours [I.A. Sharina, L.N. Perepechko, P.V. Domarov. Development of technology of plasma processing of technogenic wastes (brief review). Journal of Physics: Conference Series. 2019 J. Phys.: Conf. Ser. 1261012031], and, therefore, every 100-1000 hours it is necessary to change the electrodes or the plasma torch and start the device.

Ore-thermal furnaces are known and widely used in metallurgy. (RTP), which are designed to carry out reducing electrothermal processes, with the help of which pure metals or metal alloys are obtained from ores containing these metals in the form of oxides or sulfur compounds. In the RTP, the processed materials are heated by resistive heating of the charge. The temperature in the reaction zone is 1500-2000°C. Ready metal and slag melts are periodically drained through holes in the bath lining (“taps”). RTP is characterized by continuous operation for 1-2 years and high specific electricity consumption per unit of output, which requires a powerful energy economy. The specific consumption of electrical energy, depending on the energy intensity of the technological process, is 2.5-13 MW h/t of the alloy.

It is known to use RTP for melting a mixture consisting of ash from coal combustion in the combustion chambers of boilers and a solid reducing agent (lignite) in order to obtain foam silicate [A.V. Proshkin, V.F. Pavlov, O.G. Egorova, D.S. Kalinovsky. Fly ash is a raw material base for new heat-insulating materials. Energy and resource saving. https://www.lib.tpu.ru/fulltext/v/Bulletin_TPU/2002/v305/i2/39.pdf]

Information on the use of RTP for melting ash and slag waste from MSW incineration was not found.

Known furnace plasma-arc type for melting ash [JP 2001324124 (A) - 2001-11-22, F23J 1/00; F27B 3/08; F27D 11/08]. The furnace is equipped with two electrodes, the lower one, located at its bottom, and the main one, passing through the furnace cover. At the bottom of the furnace, there is a metal material on the bottom electrode, and slag on the metal material. This invention is aimed at solving the problem of extending the service life of the electrodes by providing a more accurate and faster start of the furnace.

It should be noted the complexity of the start-up system of the specified furnace, since start-up requires the presence of molten metal on the hearth and slag on the metal material. In addition, before starting this furnace, it is required to melt the metal, which requires additional energy and time.

The objective of the invention is to create a simple technology for the implementation of a long, continuous and energy-efficient mode of melting fly ash and slag generated during the combustion of MSW in waste incineration plants, with the production of an environmentally friendly chemically inert slag suitable for use in the construction industry.

EFFECT: long-term and continuous melting of fly ash and slag formed during the combustion of MSW at waste incineration plants, with an insignificant specific power consumption not exceeding the values known from literary sources, 0.8-1.0 kWh / kg of ash.

The result is achieved due to the fact that for the melting of fly ash and slag formed during the combustion of MSW at the incinerator, I use resistive heating of fly ash and slag, which ensures the continuity and duration of the furnace up to 2 years.

A method is proposed for melting fly ash and slag formed during the combustion of MSW at the MSZ, including starting the furnace, heating the furnace, loading material into the furnace volume, remelting the material, draining the resulting slag melt into a water bath, cooling the slag melt and granulation. According to the invention, an arc discharge is used to start the furnace, the arc is ignited between the graphite and bottom electrodes, the melt pool is obtained by melting the fly ash and slag from MSW incineration preliminarily loaded into the furnace at the MSZ, the fly ash and slag are remelted by resistive heating from the flow of current through the electrodes, electric arc, melt and melted fly ash and slag. The arc discharge is used to start the furnace when organizing the primary channel for the passage of current, then they switch to resistive heating of fly ash and slag from MSW incineration at the incinerator.

To implement the method of melting fly ash and slag formed during the combustion of MSW at the MSZ, a plasma-thermal furnace similar to a single-electrode RTP is used.

In FIG. 1 shows a diagram of a plasma-thermal furnace, where: 1 - graphite electrode (cathode); 2 - bottom electrode (anode); 3 - furnace body; 4 - power supply of electric current, including a rectifier and a transformer; 5 - permanent melt (swamp or melt bath); 6 - ash and slag melt; 7 - mold (container for draining remelted slag). The plasma thermal furnace also includes, not shown in FIG. 1, a unit for loading processed material from bunkers through pipes, a gas cleaning unit, including a gas cooler, filters and an exhaust pipe; ash utilization unit, including the remelted slag discharge system, mold, tap-hole.

The body 3 of the furnace is a metal water-cooled casing, lined from the inside (walls and under) with high-temperature material. In the working space of the furnace there is a graphite electrode 1, held by an electrode holder, immersed in the ash and slag melt 6. The bottom electrode 2 is located in the furnace bottom under the constant melt 5.

The ignition of the arc is carried out between the graphite electrode 1 and the bottom electrode 2. The furnace is heated on fly ash and slag from MSW incineration at the MSZ until a melt pool 5 is obtained. After heating, the material is loaded, namely fly ash and slag from MSW combustion at the MSZ , in the volume of the furnace. The remelting of recyclable fly ash and slag is carried out due to the heat that occurs when current flows through the electrodes, electric arc, melt and melted material. The melting time of the processed material depends on the volume of the furnace and the amount of fly ash and slag.

Flue gases are removed by a smoke exhauster through filters into an exhaust pipe (not shown in the figure). From remelted fly ash and slag, volatile components (K, Na, C, Cl, S) and heavy metals (Zn, Cu, Cd, Pb) go into the gas cleaning system. Secondary dust with a high content of heavy and non-ferrous metals is also captured here.

The resulting melt is poured into the mold 7 (water bath) through the tap-hole punched as the melt accumulates. In the water bath, the slag melt is cooled and granulated. The temperature of the ash melt on the drain t melt. _drain =1350°C.

Granulated slag in the form of particles up to several mm in size has a high resistance to dissolution in water and weak acids. Such slag belongs to the 4th hazard class and is suitable for the construction of roads, the production of building materials.

In general, the method provides continuous processing of up to 90% of the initial mass of fly ash and slag, formed during the combustion of MSW at the incinerator, into environmentally friendly products. The dioxins contained in the original material are completely absent in the resulting vitrified slag.

The duration of the continuous operation of the plasma-thermal furnace is 1-2 years. The specific power consumption for melting fly ash and slag does not exceed 0.8-1.0 kWh per kilogram of fly ash and slag.

To confirm the implementation of the invention, an experimental melting of the ash from an incineration plant in the RTP was carried out. As a result of the remelting of the ash from the incineration plant, small particles of vitrified slag were obtained in the form of coarse sand (Fig. 2).

For the entire remelting cycle of 320 kg of incinerator ash and 50 kg of limestone, 402 kWh of electricity was spent to obtain vitrified slag. Specific energy consumption was 1.08 kWh per kilogram of ash.

According to the literature, the specific energy consumption for melting ash is 0.8-1.0 kWh per kilogram of ash [V.P. Lukashov, S.P. Vashchenko, G.I. Bagryantsev, H.S. Pak, Plasma-thermal processing of solid waste // Ecology and industry of Russia, 2005; H.S. Pak Investigation of the composition and properties of slag during plasma remelting of waste incineration plant ash // Thermophysics and Aeromechanics T18, No. 2, 2011 p. 325-333; Ariake K., Koga A., Matsuoka Y. et al. Plasma slagging system for incineration of ash // FAPJG, 1995, N144, P. 3-8].

Thus, the possibility of using a furnace similar to the ore-thermal furnace known from the field of technology for remelting MSZ ash with a new technical result is shown. At the same time, the main advantage of using such a furnace remains, namely, long-term continuous operation up to 2 years, and the specific energy costs are reduced by 2-3 times and correspond to known technologies based on the use of electric arc plasma torches. It should be noted that the duration of operation of known installations based on the use of electric arc plasma torches for melting ash and slag waste from the MSZ depends on the service life of the electrodes of the used electric arc plasma torches, which currently ranges from 100 to 1000 hours according to open data.

Claims (1)

A method for melting fly ash and slag generated during the combustion of municipal solid waste (MSW) at waste incineration plants (MSW), including starting the furnace, heating the furnace, loading material into the furnace volume, remelting the material, draining the resulting slag melt into a water bath, cooling the melt slag and granulation, characterized in that an arc discharge is used to start the furnace, the arc is ignited between graphite and hearth electrodes, the melt bath is obtained by melting fly ash and slag from MSW incineration at the incinerator pre-loaded into the furnace, remelting of fly ash and slag from incineration of MSW at the MSZ is carried out due to resistive heating from the flow of current through the electrodes, electric arc, melt and melted fly ash and slag.

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