RU2722937C1 - Method for thermal processing of solid wastes - Google Patents

Abstract

FIELD: processing of solid wastes.SUBSTANCE: invention relates to solid wastes processing and can be used in metallurgical, chemical, construction and other industries. Method of thermal processing of solid wastes involves preliminary crushing wastes to particle size "-150 mm". Solid wastes, fluxes and solid fuel are continuously supplied to the molten slag bath, which is blown through the side buried and unloaded tuyeres with oxygen-containing gas supplied together with gaseous or solid fuel, at excess of oxygen in comparison with stoichiometric required for complete oxidation of all types of hydrocarbon fuel. Into melt with temperature of 1,200–1,700 °C and above the melt is added the oxygen-containing blowing enriched in oxygen in range of 65–100 %. Outgoing gas before outlet from furnace is pressed with partitions to melt and filtered through area of gas space saturated with spray and melt splashes. When exhaust gas gets into gas cleaning system, it is subjected to high-speed cooling from temperature over 850 °C with aqueous solution with the intensity of irrigation within 0.01–0.03 mof solution/nmof cooled gas providing cooling gas in less than 1 second up to ≤200 °C, excluding repeated formation of organic toxic compounds.EFFECT: method provides neutralization of all harmful and toxic compounds, organic and inorganic volatile substances.5 cl, 4 dwg

Description

The invention relates to a method for processing solid waste, including stale and medical, and can be used in the household, chemistry, metallurgy, energy, construction and other industries.

A known method of thermal processing of solid waste in a furnace with lateral submersible blasting (AS USSR No. 1315738). Together with the waste, fuel, metal oxides and scrap metal are charged into the slag bath, purged with an oxygen-containing gas in the bubbling mode. The amount of fuel loaded provides a carbon content in the mixture of 2-25%. When the carbon content in the charge is more than 10%, for each percent increase in its content, metal oxides or scrap metal are introduced in an amount of 0.25–5.0 and 0.5–15%, respectively, of the charge charge. Purge the bath with an intensity of 150-2200 nm ³ / m ² * hour. The disadvantages of this method are that there is no control over the oxygen potential of the method (process) and, as a result, it is possible to burn toxic compounds or reoxidize the slag melt. The method does not guarantee the absence of re-formation of toxic compounds, since the gas purification system has not been considered, and its operation parameters have not been determined to guarantee the absence of toxic components in the exhaust gases after their purification and cooling. When using a blast with low oxygen enrichment, a large amount of nitrogen oxides (NO _x ) is formed. Measures to neutralize (clean) the exhaust gases from nitrogen oxides are not considered.

A known method of thermal processing of solid waste in a furnace with lateral submerged blasting (RF Patent No. 2030684). Waste, fuel and fluxes are loaded onto the surface of a slag bath sparged with oxygen-containing blast. The loading is carried out dispersed over the surface area of the slag bath. The removal of gaseous products of processing is carried out outside the loading zone. The total amount of oxygen in the blast supplied to the slag bath is 1.2-2.2 from the charge theoretically necessary for the oxidation of carbon to CO, hydrogen to H ₂ O. An oxygen-containing blast is fed over the melt, in which the total amount of oxygen is 0.05 -0.8 from theoretically necessary for the oxidation of carbon loading to CO ₂ and hydrogen to H ₂ O. Liquid slag is released from the furnace and used for the production of building materials. Process gases of the process do not contain toxic substances and after dust collection can be released into the atmosphere. According to a variant of the method, the process is carried out with the loading of calcium-containing flux at a CaO / FeO ratio in the loading of 0.2-0.6: 1. In order to reduce dust extraction, solid waste can be loaded into a slag bath in a combustible container. The disadvantages of the method are that it provides only the use of solid fuel loaded onto the surface of the bubbled bath and does not provide solutions to minimize dust removal and re-formation of polychlorinated dibenzo-n-dioxins and dibenzofurans in the treatment of exhaust gases. When using blast with low oxygen enrichment, a large amount of NO _{x is formed} . Measures to neutralize (clean) the exhaust gases from nitrogen oxides are also not considered.

Also known is a method of thermal disposal of solid municipal waste in a slag melt and a furnace for its implementation (RF Patent No. 2623394). In the method, including loading the prepared charge into the working chamber, burning it with the formation of a slag melt bath, bubbling the melt with natural gas combustion products through immersion tuyeres, discharging melting products and purifying gases after thermal decomposition of the charge, and waste heat treatment are carried out directly in the slag melt bath for by loading the charge directly to the level of the molten slag bath and supplying air heated to 500 ° C to the melt with an excess air coefficient α≤1.3 through tuyeres located on the side walls of the working chamber, while the temperature of the slag bath is maintained in the range of 1400- 1600 ° С, natural gas is burned in remote combustion chambers at α≤0.9, and natural gas combustion products for bubbling the slag bath and maintaining its temperature are fed to the melt level through nozzles installed on the combustion chambers located on the side walls of the working chamber in staggered relative to nozzles, races laid on the opposite wall. The disadvantages of the method are that the use of external furnaces and air blasting in bubble-type furnaces indicates the inevitable in this case, the low rate of interaction of oxygen of the blast with hydrocarbon compounds. The hydrocarbon portion of the waste will slowly interact with the combustion products formed in the remote furnaces. Therefore, there is great doubt that with air blasting it will be possible to guarantee the decomposition of all toxic organic compounds. In addition, with air blasting and high process temperatures, the formation of large amounts of NO _{x is} inevitable. The known technical solution does not reflect in any way how the issue of neutralizing gases from NO _x will be solved. Measures to prevent the re-formation of polychlorinated dibenzo-n-dioxins and dibenzofurans during gas cooling are not reflected either.

The closest analogue to the proposed invention is a method of processing solid waste in slag melt in a multi-zone furnace (RF Patent No. 2451089). The method involves drying and feeding the mixture in minimal portions to different places in the bath, where it is burned and melted in a bubbling slag melt. The combustion products are thermally decomposed and washed under a cowl using gas washers of a multi-zone furnace at a temperature of 1350 ° C, which allows you to get rid of halogens in the waste and dissociated chlorine along the path to gas turbine cooling. The washing of the furnace gas is carried out by a gas-liquid medium ejected by bubbling melt, which contains excess hydrogen and CO. Due to controlled synthesis, new substances are created in the furnace zones that neutralize the dry gas purification in the spray absorber. Flue gas cooling is carried out in 3 stages and ends in an electrostatic precipitator, smoke exhaust and chimney. The disadvantages of the closest analogue are as follows:

1. When using portable furnaces, there is no guarantee of the complete decomposition of organic toxic compounds due to the low rate of interaction of oxygen from the air blast with hydrocarbon compounds of the organic component of solid waste.

2. Remote furnaces reduce the reliability of operation of the furnace, since the use of inlets (plugs blocking the mouth of the blowing channels to prevent the melt from leaving the furnace in an emergency) is impossible and the termination of purging for any reason leads to the failure of the furnace for a long time.

3. The proposal to prevent the secondary formation of polychlorinated dibenzo-n-dioxins and dibenzofurans by increasing the gas passage through the waste heat boiler by limiting the number of working sections of the boiler and using the maximum draft of the smoke exhauster is doubtful from the standpoint of guaranteeing the absence of these toxic compounds in the exhaust gases at the outlet of gas treatment systems, since the forced-draft regime of the furnace depends on many factors, including the composition of the waste received for processing, which, due to its specific formation characteristics, cannot have a constant composition. The gas purification system is designed in such a way that it is divided into sections, on one of which the gas is cooled in a waste heat boiler from 950 ° С to 500 ° С, and then in a smoke exhaust mixer, where it is mixed with air - from 500 ° С to 200 ° C. However, the research results (Ladygin K.V., Osvetitskaya N.D., Rakhmanov Yu.A. On the preliminary assessment and methods for reducing the dioxin content in the exhaust gases of thermal oxidative treatment units for medical waste // Scientific journal NRU ITMO. Economics and Environmental Management ”No. 2, 2014, pp. 14-19) show that in order to prevent the re-formation of dibenzo-n-oxins and dibenzofurans, it is important to have a high cooling rate in the temperature range of ~ 850 ° C to ~ 230 ° C. Thus, the proposed phased cooling scheme cannot guarantee the re-formation of highly toxic compounds.

The objective of the proposed method is to develop a technology - a method for the thermal processing of solid waste, which guarantees the environmental safety of all melting products formed during processing: exhaust gases, slag and metal alloy.

The technical result in the implementation of the proposed method of thermal processing of solid waste is to guarantee the neutralization of all harmful and toxic compounds, organic and inorganic volatile substances due to oxidation by oxygen blasting in a high-temperature melt, subsequent high-speed cooling of hot gases and the return of the solid residue of neutralization of wet gas cleaning to smelting, and inorganic non-volatile harmful and toxic substances - due to their occlusion of the glassy slag mass formed during water granulation of slag melt.

The technical result is achieved by the fact that in the method of thermal processing of solid waste, including pre-grinding waste to particles with a size of "-150 mm", a continuous supply of solid waste, fluxes and solid fuel to a molten slag bath, blown through lateral buried and non-immersed tuyeres with oxygen-containing gas, supplied with a gaseous or solid fuel, an excess of oxygen compared with stoichiometrically necessary for the complete oxidation of all types of hydrocarbon fuel, according to the method, an oxygen-containing blast enriched in oxygen in the range of 65 is supplied to the melt having a temperature of 1200-1700 ° C. -100%. To ensure complete oxidation, an oxygen-air mixture is additionally supplied to the furnace above the melt level, afterburning the remaining organic substances and providing a free oxygen content in the exhaust gas at the furnace outlet of at least 6 vol. %

According to the method, the exhaust gas is pressed against the melt by means of special baffles before exiting the furnace and filtered through a region of gas space saturated with splashes and splashes of the melt. This provides an additional reduction in the already low level of dust extraction in the smelting furnace in a liquid bath, and is also an additional guarantee that there will be no breakthrough of unreacted solid and gaseous organic substances into the gas duct system of the furnace.

According to the method, when the exhaust gas enters the gas treatment system, it is subjected to rapid cooling (quenching) from a temperature exceeding 850 ° C with an aqueous solution with an irrigation rate in the range of 0.01-0.03 m ^{3 of} solution / nm ^{3 of the} gas to be cooled. Quenching provides gas cooling in less than 1 second to a temperature of ≤200 ° C, which, in turn, guarantees the impossibility of re-formation of organic toxic compounds.

According to the method, the slag basicity coefficient (K = (CaO + MgO + Me _x O _y ) / (SiO ₂ + Al ₂ O ₃ ); where: Me - Fe, Cr, Ni, Cu, Co, Zn, Pb, Sn, V) should be maintained in the range of 0.5-1.2. This is necessary to ensure a high rate of hardening of glassy slag and a high degree of its monolithicity, which guarantees the safe storage of toxic inorganic compounds.

According to the method, the total content in the slag of iron and other heavy ferrous and non-ferrous metals (chromium, nickel, copper, cobalt, zinc, lead, tin, vanadium) should be maintained at a level of not more than 28% of the mass, which under the oxidizing conditions of smelting higher metals form refractory spinels, the high concentration of which leads to foaming of the bath and the creation of an emergency.

According to the method, part of the slag can be returned to the furnace in the range from 0 to 90% by weight of the loaded flux components. Slag turnover is advisable from the point of view of saving flux, oxygen and fuel consumption for smelting, and the share of the turnover will be determined by its degree of saturation with spinels based on iron and other heavy ferrous and non-ferrous metals.

According to the method, together with the waste, it is possible to load scrap metal into the furnace or return the polymetallic alloy to the furnace in an amount necessary to maintain the presence of the metal bath in the furnace within 500-1000 mm from the level of the furnace hearth.

Below the invention will be described in more detail with reference to the attached graphic materials.

In FIG. 1 schematically shows a General view of the pilot pilot furnace Vanyukov, which is explained in more detail:

- 1 - furnace frame;

- 2 - cooling the hole;

- 3 - furnace lining;

- 4 - caissons of the shaft of the furnace;

- 5 - hatch window of the furnace;

- 6 - vaulted caisson;

- 7 - upper loading door of the furnace.

In FIG. 2, table 1 presents the composition of a representative sample of solid waste.

In FIG. 3, table 2 presents the composition of the process gas samples according to the content of toxic substances, depending on the method of gas cooling.

In FIG. 4, table 3 presents the results of sanitary-epidemiological studies of slag.

The method is as follows

Testing of the method for processing solid waste was carried out on a pilot experimental Vanyukov furnace. An explanation of the general view of the furnace is shown in FIG. 1.

For research, a representative sample of solid waste was compiled as shown in Table 1. The composition of solid waste for processing in the Vanyukov pilot furnace was adopted based on the analysis of existing solid waste streams generated in the municipal sector of St. Petersburg (Decree of the Government of St. Petersburg of May 29 2012 No. 544 “On the Program“ Regional Targeted Program for Solid Waste Management in St. Petersburg for the period 2012-2020 ”.

The composition of a representative sample of solid waste is given in table 1, FIG. 2.

The test procedure for processing solid waste in the Vanyukov furnace was as follows.

After drying and heating the lining, a mixture of low-quality quartzite (with a high content of Al ₂ O ₃ ) and limestone was initially loaded into the furnace based on the production of slag containing 50% SiO ₂ , 35% CaO, 15% Al ₂ O ₃ and having a melting point of ~ 1330 ° C. Fluxing components were loaded until the slag bath was 200 mm higher than the tuyeres — the standard melt level in the pilot furnace for normal melting. Then, solid waste pre-packed ~ 1/3 of the volume into nets with a size of not more than 200 × 500 mm and weighing ~ 5-10 kg was loaded into the slag melt through the upper loading door of the furnace. The furnace capacity for loaded solid waste was 220 kg / h. Solid waste was loaded in the steady-state operating mode of the Vanyukov pilot furnace on the surface of the slag melt for 4 hours. The melting temperature was maintained in the range 1350-1370 ° C. In the process of loading, the composition of the exhaust gases was monitored for the content of toxic compounds. At the end of the loading of solid waste, the melt was downloaded from the furnace, samples of hardened slag were transferred for sanitary and epidemiological studies.

To represent the proposed method conducted swimming trunks, including:

- smelting No. 1 - slagging of the furnace, preparation for testing;

- Smelts No. 2 and No. 3 are the main ones, in one of which (smelting No. 2) the exhaust gas was not quenched, and in the other (heat No. 3) - the exhaust gas was quenched by irrigation with water, providing a quenching rate from 1200 to 200 ° C within - 0.5-0.7 seconds.

Since the main purpose of the tests was to confirm the environmental friendliness of the proposed processing method, the main attention was paid to the study of the composition of the exhaust gas and slag.

The selection and analysis of process gas was carried out by specialists of the St. Petersburg organization CJSC CIKV, which has certification for the analysis of toxic substances.

Slag obtained during testing to determine the class of environmental hazard was also sent to the certified organization - FBUZ “Center for Hygiene and Epidemiology in the City of St. Petersburg” for research. The acute toxicity of the slag was evaluated using biotesting methods using granulated semen of bull and daphnia (Daphnia Magna) as test objects.

The research results are presented in the following tables:

- table 2, FIG. 3 - Composition of process gas samples according to the content of toxic substances, depending on the method of gas cooling;

- table 3, FIG. 4 - The results of sanitary-epidemiological studies of slag.

According to regulatory documents, the maximum permissible level of toxic toxic substances of polychlorinated dibenzo-n-dioxins and dibenzofurans in industrial emissions is in a toxic equivalent of 100 pg / m ³ . As can be seen from table 2 (Fig. 3), the use of high-speed cooling (quenching) of the exhaust process gas during the processing of solid waste in the Vanyukov furnace reduces the total content of dibenzo-n-dioxins and dibenzofurans in the exhaust process gas from 173.217 to 30.388 pg / m ³ , which corresponds to a decrease in toxic substances by 5.7 times. The achieved result during gas quenching by water irrigation is 3.3 times lower than the established standard. This suggests that the implementation of the method of processing solid waste in the Vanyukov furnace with quenching of the waste process gas is an environmentally friendly option for processing solid waste.

As shown by the research results (table 3, Fig. 4), the slag toxicity index is within the established norm (80≤It≥120) and is equal to 94.1. During biotesting using Daphnia Magna without dilution, the death of daphnia is not observed, which confirms the performed control measurement.

Thus, on the basis of sanitary and epidemiological studies of slag, it was found that:

- slag hardened in accordance with SP 2.1.7.2570-10 “Change No. 1”, SP 2.1.7.2850-11 “Changes and Additions No. 2” in SP 2.1.7.1386-03 should be classified as hazard class IV - low hazard;

- slag hardened in accordance with the Order of the Ministry of Natural Resources of the Russian Federation dated June 15, 2001 No. 511 can be attributed to class V hazard for the environment (OPS) - practically not dangerous.

It should be noted that one of the important results of tests performed on the processing of solid waste in the experimental Vanyukov furnace of Gipronickel Institute LLC is the high reliability of the Vanyukov furnace design for implementing this method. During the tests, all the main components of the experimental furnace worked normally, including cooled elements - caissons and tuyeres, whose operation is associated with direct contact with the melt in the furnace.

Thus, the combination of the claimed features allows the proposed method to achieve the claimed technical result, namely: to guarantee the neutralization of all harmful and toxic compounds, organic and inorganic volatile substances by oxidation with oxygen blast in a high-temperature melt, subsequent high-speed cooling of hot gases and the return of solid neutralization residue wet cleaning of gases into smelting, and inorganic non-volatile harmful and toxic substances - due to their occlusion with a glassy slag mass formed during water granulation of slag melt.

Claims (7)

1. The method of thermal processing of solid waste, including pre-grinding waste to a particle size of "-150 mm", a continuous supply of solid waste, fluxes and solid fuel to a molten slag bath, blown through side buried and non-immersed tuyeres with oxygen-containing gas supplied together with gaseous or solid fuel, with an excess of oxygen compared with stoichiometrically necessary for the complete oxidation of all types of hydrocarbon fuel, characterized in that an oxygen-containing blast enriched in oxygen in the range of 65-100% is supplied to the melt having a temperature of 1200-1700 ° C. in this case, the exhaust gas is pressed into the melt with the help of baffles before exiting the furnace and filtered through the region of gas space saturated with splashes and bursts of the melt, and when the exhaust gas enters the gas purification system, it is subjected to rapid cooling from a temperature exceeding 850 ° С with an aqueous solution of irrigation intensity in in the range of 0.01-0.03 m ³ solution / nm ^{3 of the} gas to be cooled, which provides gas cooling in less than 1 s to a temperature of ≤200 ° C, excluding the re-formation of organic toxic compounds. 2. The method according to p. 1, characterized in that the basicity coefficient of slag K = (CaO + MgO + Me _x O _y ) / (SiO ₂ + Al ₂ O ₃ ), where Me - Fe, Cr, Ni, Cu, Co, Zn, Pb, Sn, V, maintain in the range of 0.5-1.2, with the possibility of ensuring a high cooling rate of the silicate melt and a high degree of solidity of glassy slag, guaranteeing the safe storage of toxic inorganic compounds. 3. The method according to p. 1, characterized in that the total content in the slag of iron and other heavy ferrous and non-ferrous metals of chromium, nickel, copper, cobalt, zinc, lead, tin, vanadium is maintained at a level of not more than 28 wt.%. 4. The method according to p. 1, characterized in that part of the slag is returned to the furnace in an amount excluding the excess of the degree of saturation with spinels based on iron and other ferrous and non-ferrous metals, up to 90% by weight of the loaded flux components. 5. The method according to p. 1, characterized in that, together with the waste, metal scrap is loaded into the furnace or the polymetallic alloy is returned to the furnace in an amount necessary to maintain the presence of the metal bath in the furnace within 500-1000 mm from the level of the furnace hearth.

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