RU2700424C1 - Method for utilization of solid chlorine-containing medical waste - Google Patents

Abstract

FIELD: waste processing and disposal.

SUBSTANCE: invention relates to the field of thermal recycling of medical wastes, including chlorine-containing wastes. Waste is subjected to thermal decomposition in two thermal decomposition chambers (TDC) placed in the heating chamber and located above each other low-temperature and high-temperature chambers under conditions of a layer of solid material moving from top to bottom, the speed of which is set by the motion controller. Both TDC are heated by heat from combustion of gaseous pyrolysis products. Temperature in low-temperature TDC, which does not exceed 350 °C is controlled by the air flow supplied to the upper part of the heating chamber. Gaseous products extracted from low-temperature TDC are washed with an aqueous alkaline solution, and gaseous products which are not washed during flushing are burnt together with the main part of gaseous pyrolysis products. Fumes gases formed during combustion of gaseous pyrolysis products are cooled in a heat exchanger, purified in a gas cleaning system and discharged to atmosphere. Solid residue is removed from high-temperature TDC separately from gaseous products, inorganic inclusions are separated, and coke residue is gasified by superheated steam at atmospheric pressure and temperature of 800–900 °C to complete or partial exhaustion of carbon. Activated carbon formed after partial gasification of carbon is used for additional cleaning of flue gases, and combustible water (synthesis) gas is released from water vapor, compressed and directed for combustion into electric power generator.

EFFECT: creation of conditions that minimize possibility of formation of dioxins, provision of ecologically safe emissions, production of materials for additional cleaning of flue gases and provision of autothermal process.

4 cl, 2 tbl, 1 dwg

Description

The invention relates to the field of disposal of medical waste containing organic materials, including chlorine-containing and infected.

The most radical and universal methods of disposal of infected medical waste, guaranteeing the complete elimination of infectious hazards, include high-temperature disposal, which is provided by various processes: burning, pyrolysis, gasification.

One of the main requirements for high-temperature neutralization of chlorine-containing waste is to ensure conditions that maximally prevent the formation of polychlorinated dibenzo-para-dioxins and dibenzofurans (dioxins and furans), which are highly toxic persistent organic pollutants. Of the above technologies for the high-temperature disposal of medical waste, pyrolysis technologies have the least potential for the formation of dioxins and furans.

A known method of disposal of medical and biological waste, comprising loading the waste into the combustion chamber with a mechanized loading device through a rotary lock tray, combining the drying, thermal decomposition and burning processes due to the fact that the waste is dried and partially pyrolyzed on the rotary tray in the upper part of the recycling chamber, at the same time burning solid residue at the bottom of the chamber. Emissions safety is provided due to fire neutralization of gaseous products in the afterburner, their subsequent cleaning from solid inclusions in a cyclone and washing in a wet scrubber [1].

The disadvantage of this method is that with the joint combustion of gaseous and solid pyrolysis products, the possibility of the formation of dioxins remains. This is because in the products of combustion with the simultaneous presence of oxygen, chlorine compounds and coke particles, the conditions for the repeated formation of dioxins and furans in the low-temperature region (250-450 ° C) on the surface of particles and equipment by heterogeneous catalytic and non-catalytic mechanisms are preserved [2, 3 ].

Therefore, one of the key measures to prevent the very possibility of the formation of dioxins is the most complete exclusion from the process of thermal decomposition of the main component - chlorine.

Studies are known that have shown that removal of chlorine from polyvinyl chloride (PVC plastics) is possible during its melting and the first stage of pyrolysis in the temperature range 280-320 ° C [4].

In these studies, a laboratory gas-liquid reactor was used with a fluidized bed of a portion of shredded PVC by a stream of heated nitrogen. The research results are of scientific interest and can be partially used in the implementation of the present invention, but the use of such a dechlorination method for the disposal of large amounts of medical and biological waste in an industrial environment is almost impossible due to the impossibility of organizing fluidization of heavy multicomponent waste with a large amount of heated inert gas.

Closest to the claimed invention is a method of thermal decomposition of waste containing polyvinyl chloride [5]. The method involves grinding the waste, feeding it into a dehalogenation reactor together with a heavy fraction of pyrolysis oil, heating the reaction mixture to a temperature of 210-250 ° C, at which gaseous halogenated hydrogen (HCl) is released and removed from the process, feeding the mixture remaining in the chamber into the reactor, the temperature of which rises to 480-600 ° C, the extraction of the resulting gaseous mixture of hydrocarbons, its separation into fractions, condensation and the return of part of the heavy oil fraction to a dehalogenation reactor to obtain mixture of crumbs of polymer waste and heavy oil.

The disadvantage of this method is that it provides for a cyclic process with a long stay of substances at different stages of the process, the need to use condensation and fractionation systems to obtain a heavy oil fraction and the orientation of the whole process, primarily to obtain a product intended for energy, and not for waste disposal.

The disadvantages of the method is the need to use "external" fuel for the process, the lack of fire neutralization systems and additional purification of flue gases.

The technical result to which this invention is directed is to create conditions that exclude the possibility of the formation of dioxins (PCDD / F) as much as possible, ensure environmentally friendly emissions, obtain materials suitable for flue gas purification, and ensure the process is autothermal due to its own energy resources.

The technical result is achieved due to the fact that the waste is subjected to thermal decomposition in two low-temperature and high-temperature thermal decomposition chambers (KTR) located in the heating chamber and located one above the other under conditions of a layer of solid material moving from top to bottom, the speed of which is set by the motion controller of the solid material . The regulator of the movement of material located under the lower CTE can be continuous or discrete mechanisms. Both thermal decomposition chambers are heated from the outside by heat from the combustion of gaseous pyrolysis products removed from the high-temperature KTP, the temperature in which does not exceed 600 ° C. The temperature in the low-temperature KTP does not exceed 350 ° C. Gaseous products removed from the low-temperature KTP are washed with an aqueous alkaline solution, and gaseous products that are not condensed during washing are burned together with the main part of the gaseous pyrolysis products. The flue gases generated during the combustion of gaseous pyrolysis products are cooled in a heat exchanger, cleaned in a gas purification system and vented to the atmosphere. The solid residue is removed from the high-temperature KTP separately from the gaseous products, inorganic inclusions are separated, and the coke residue is gasified with water vapor superheated at atmospheric pressure at a temperature of 800-900 ° С until the carbon is completely or partially exhausted. The activated carbon remaining after gasification of approximately 50% of carbon is used for the post-treatment of flue gases, and the combustible water (synthesis) gas formed during gasification is freed from water vapor, compressed and sent to the electric power generator for burning.

The essence of the proposed technical solution is illustrated by the drawing in FIG. 1, which shows a schematic diagram of a process and a drawing of an installation that implements the method.

The installation comprises a lock loading device 1, a loading hopper 2, a low-temperature thermal decomposition chamber (KTP) 3 and a high-temperature KTP 4, equipped with an external spiral gas duct 5 and placed in a heating chamber 6 with a burner device 7, an ignition burner 8 and an air temperature regulator 9, a regulator movement of solid material 10; a wet scrubber 11, a combustion chamber 12, a solid separator 13, a gasifier 14, a heat exchanger 15 with a superheater 16 and a heat removal system 17, an electric power generator 18, a gas purification system 19, a smoke exhauster 20. The gasifier 14 is equipped with a water vapor condenser 21.

The technological process is carried out as follows: At the first start-up, the entire system, starting from the regulator of movement of solid material 10 to a predetermined level in the loading hopper 2, is filled with inert material (sand), which is subsequently replaced during the technological process with solid pyrolysis products (semi-coke) and waste . The movement of the material in the direction from top to bottom is carried out and regulated by the motion controller of the solid material 10.

The heating chamber 6 and KTR 3, 4 are preheated using an ignition burner 8. Medical waste (MO) is fed through a lock loading device 1 to a loading hopper 2 from which it enters the low-temperature KTP 3, the temperature of which is maintained at a level not exceeding 350 ° With a change in the air flow rate supplied by the air temperature controller 9 to the upper part of the heating chamber 6. As the waste moves from top to bottom, it heats up and steam-gas mixture PGS1 is released, including water vapor, gases (СО ₂ , СО, H ₂ S, NH ₃ ) and g halogenated hydrogen gas (HCl). Gaseous products removed from section 3 are neutralized with an aqueous alkaline solution (SHR) in a scrubber 11, and gaseous products non-condensable during washing are burned together with the main part of the steam-gas mixture ПГС2, formed in the high-temperature section 4, in the torch of the burner device of the combustion chamber 12 at a temperature of 1000 -1350 ° C. Another part of the gaseous vapor-gas products formed in the high-temperature section 4 is burned in the burner 7 of the heating chamber 6 at a temperature of 1000-1350 ° C, ensuring the maintenance of the heat balance of the pyrolysis process. The gaseous pyrolysis products from the high-temperature section 4 are burned in the burner 7 and the combustion chamber 12. The solid pyrolysis residue (TH) is removed separately from the gaseous products, inorganic inclusions (BUT) are isolated from it, and the remaining coke residue (KO) is subjected to steam gasification at atmospheric pressure in the gasifier 14 at a temperature of 800-900 ° C until the carbon is completely or partially exhausted. The high-temperature steam (VP) required for gasification is obtained in a flow-through steam generator 16 located in the heat exchanger 15. The moist combustible gas (SHG) generated during gasification is dehydrated in the condenser 21, compressed and sent to the electric power generator 18. For coke pyrolysis, as an option the remainder (KO) is gasified by VP at a temperature of 800-900 ° C and atmospheric pressure until only half of the carbon is exhausted, and the remaining activated carbon (AC) is used to clean the flue gases (DG). DG formed during the combustion of gaseous products of pyrolysis is cooled in a heat exchanger 15, cleaned in a gas purification system 19 and, with the help of a smoke exhauster 20, is discharged into the atmosphere.

The practical reachability of the proposed method is illustrated by the following examples:

1. An example of dechlorination [4].

The experiments were carried out in an experimental setup consisting of a fluidized bed reactor with electric heating, temperature control systems and N ₂ gas supply and an absorber of evolved gas with a NaOH solution. The samples used for the study were granules of PVC with a diameter of 2-3 mm. To check the effect of additives, we also studied the trimming of PVC pipes 2-3 mm in size.

The elemental composition of the feedstock is presented in table 1.

According to the results of studies, it was concluded that when heated to 350 ° C, the mass loss is 65%, including 86.4% of the initial mass of HCl.

2. An example of dechlorination (JSC ENIN).

Thermogravimetric experiments on PVC in an inert gas (nitrogen) were carried out on a Netzsch STA 449 F3 thermochemical analysis device.

Polyvinyl chloride tubes (TU 9393-018-00149535-2003) included in blood transfusion systems, which are an integral part of class B medical waste, were selected as samples for research. Polyvinyl chloride tubes are made of granular plastic compound, including stabilizers and modifying additives containing calcium compounds , zinc and proprietary plasticizers.

The sample was heated in the experiment in stages: up to 250, 300, and 350 ° C. At each stage, the pyrolysis gases were passed through a system of absorbers, in which the amount of absorbed hydrogen chloride was then determined and the amount of chlorine was calculated. It was found that when heated to 250 ° C, about 10% of the total chlorine content in the initial sample is released, 37% of chlorine is released in the temperature range 250-300 ° C, and when the temperature reaches 350 ° C, the total mass of chlorine released corresponds to 88.4% of initial content in the sample.

3. An example of gasification of semicoke with obtaining activated carbon from it (JSC "ENIN").

Gasification was carried out in the mode of a layer suspended by a "sharp" stream of superheated water vapor. A portion of the semi-coke was placed in a gasifier placed in a heating furnace, which was heated to a temperature of 500-600 ° C and a stream of water vapor heated to 800-900 ° C at atmospheric pressure was supplied from above to the semi-coke layer. The supply of a jet of water vapor to the surface of the semicoke layer ensures its transfer to the state of the suspended layer, which creates conditions for intense heat and mass transfer. Particles of semicoke quickly warm up to the required temperature, carbon interacts with water vapor by the reaction C + H ₂ O = CO + H ₂ to produce water (synthesis) gas. The duration of the gasification process depends on temperature and the vapor / semi-coke ratio.

The results of the experiments are presented in table 2.

Legend:

α - degree of gasification during activation;

P - strength;

ρ _us - bulk density;

V _∑ is the total pore volume;

W _S is the volume of sorbing pores;

V _MA - micropore volume.

From the analysis of the results it follows that when the process is terminated at a level of gasification degree of ~ 50%, the coke residue is a fairly high-quality activated carbon. With further heating, the proportion of macropores increases due to the burning of the walls of the porous structure of the coke particle, and with a certain duration of the process, the degree of carbon gasification will be 100%.

In this way:

The task of ensuring environmental safety of the environment in the proposed method is achieved due to the fact that:

- In the first stage of pyrolysis, preceding the thermal decomposition of the bulk of solid organics from waste into the gas phase, in addition to water vapor and inorganic gases (CO ₂ , CO, H ₂ S, NH ₃ ), the bulk of chlorine is discharged in the form of HCl, which, to a large extent, degree, eliminates the possibility of the formation of PCDC / F in the subsequent stages of the process and enriches the CBC obtained in the second stage of pyrolysis. With further pyrolysis in the temperature range 350-600 ° C, the remaining chlorine leaves with the bulk of the volatile combustible products that burn in the torch of the burner, and the chlorine compounds are trapped and neutralized with an alkaline solution in a scrubber.

- Gaseous hydrocarbon products released in the second stage of waste pyrolysis in the form of concentrated ASG are burned at a temperature of 1000-1350 ° C, which ensures fire neutralization of combustion products.

- It is fundamentally important that the maximum dechlorinated solid pyrolysis residue containing carbon and the waste products organic matter compaction is separated from the vapor-gas mixture, and therefore the base for the formation of dioxins during cooling of the combustion products in the temperature range of 250-450 ° C is eliminated. FROM;

- Integrated flue gas treatment in the gas cleaning system ultimately ensures their environmental safety.

Steam gasification of the coke residue of pyrolysis at a temperature of 800-900 ° C and the required duration allows the coke residue to be completely consumed by the reaction C + H ₂ O = CO + H ₂ to produce water (synthesis) gas, which after purification from water vapor is used to generate electricity .

Incomplete steam gasification allows to obtain coke residue in the form of activated carbon, which can be used for post-treatment of flue gases.

The objective of obtaining an economic effect is achieved by using the heat potential of utilized waste as an energy carrier, which allows for the process to be autothermal, since the use of external fuel is necessary only for starting and heating the installation. The economic effect is also achieved by producing water (synthesis) gas, which, after purification from water vapor, is used to generate electricity. The economic effect is also achieved by reducing the metal consumption of the heat exchanger and lowering the cost of the gas cleaning system by using its own activated carbon, as well as by increasing the service life of the equipment due to a decrease in the corrosion activity of gas flows.

Thus, the combination of these essential features ensures an environmentally friendly thermal disposal of chlorine-containing medical waste by creating conditions that exclude the possibility of the formation of dioxins (PCDD / F) as much as possible, makes it possible to obtain one’s own agent (activated carbon) for the post-treatment of flue gases and ensures the process is autothermal due to its own energy resources.

Information sources:

1. RF patent No. 2645057. The method of disposal of medical and biological waste.

2. Ballschmiter K., Swerev M. // Z. Anal. Chem. - 1987. - V. 328. - R. 125-127.

3. Shaub W. M., Tsang W. Physical and Chemical Properties of Dioxins in Relation to the their Disposal. // Human and Environmental Risks of Chlorinated Dioxins and Related Compounds. - N-Y: Plenum Press, 1983. - P. 731-748.

4. G. Yan, D. Chen, L. In, Z. Wang, L. Zhao, J. Y. Wang. High efficiency chlorine removal from polyvinyl chloride (PVC) pyrolysis with a gas-liquid fluidized bed reactor. // Waste Manag., 2014, Jun 14, 34 (6), pp. 1045-1050.

5. RF patent No. 2556934. The method of thermal decomposition of waste containing polyvinyl chloride.

Claims (4)

1. The method of disposal of solid chlorine-containing medical waste, including their thermal decomposition without air (pyrolysis) with the formation of gaseous and solid products, burning of pyrolysis products, cooling and purification of flue gases, characterized in that the waste is subjected to thermal decomposition in successively located low-temperature and high-temperature thermal decomposition chambers (CTE), heated externally by heat from the combustion of gaseous pyrolysis products removed from high-temperature CTE, the temperature at which does not exceed 600 ° C, and the temperature in the low-temperature KTP does not exceed 350 ° C, the gaseous products removed from the low-temperature KTP are washed with an aqueous alkaline solution, the gaseous products that are not condensed during washing are burned together with the main part of the gaseous pyrolysis products formed during combustion gaseous pyrolysis products, flue gases are cooled in a heat exchanger, purified in a gas purification system and vented to the atmosphere, solid pyrolysis products are removed from the high-temperature section KTP is separate from gaseous products, inorganic inclusions are isolated from them, and the coke residue is subjected to steam gasification in a separate device. 2. The method according to p. 1, characterized in that the pyrolysis process is carried out in two heat decomposition chambers located in the heating chamber and located one above the other, in the conditions of a moving layer of solid material, the speed of which is set by the material movement regulator. 3. The method according to PP. 1, 2, characterized in that the temperature in the upper low-temperature KTP is controlled by changing the amount of air supplied by the air temperature controller to the upper part of the heating chamber. 4. The method according to PP. 1-3, characterized in that the coke residue formed during pyrolysis is gasified with superheated water vapor at atmospheric pressure at a temperature of 800-900 ° C until about half of the carbon is exhausted, the activated carbon formed is used to purify flue gases, and the combustible water formed during gasification (synthesis ) gas is freed from water vapor, compressed and sent for combustion in an electric power generator.

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