RU2478169C1 - Plasma-chemical method of processing solid domestic and industrial wastes - Google Patents

Abstract

FIELD: chemistry.SUBSTANCE: method of processing domestic and industrial wastes involves loading the wastes with preliminary separation by separating glass, concrete, ceramics and metal; drying with partial pyrolysis of organic matter in a shaft furnace; agitation of the processed wastes with further pyrolysis thereof. Temperature of said process is reduced to 500-850°C as a result of the action of reducing plasma-chemical components obtained by steam-oxygen conversion of methane with increase in consumption of steam fed by the counter-current of the moving wastes. Recycled process gas coming from the shaft furnace is cleaned in scrubbers and is divided into fuel gas which is fed into both the methane converter and the exhaust-heat boiler when producing reducing gas with partial addition of natural gas and oxygen. Exhaust gases from the exhaust-heat boiler are cleaned in an adsorber via contact with fine-grained lime. Also, a portion of the formed reducing gases is consumed in the bottom part of the reactor during an instantaneous thermal shock which results from burning soot-dust particles coming from a hot gas cyclone with deposition thereon of dioxins, furans and other harmful components in an atmosphere of oxygen, wherein the formed reducing gases can also be fed as synthesis gas for production of methanol, dimethyl ether, engine fuel and other products.EFFECT: invention reduces power consumption of the method.1 dwg

Description

The invention relates to a method for processing waste from processing, municipal (MSW), industrial and other industries containing organic matter.

A known method of plasma gasification and devices for its implementation (see Kumkova II. Plasma gasification. Business, engineering and technical journal on mechanical engineering, No. 2, 2007, p. 84-87), including high-temperature plasma gasification with the possibility of obtaining electrical energy, residual heat recovery and subsequent multi-stage cleaning of flue gases, while the plasma installation includes a gasification reactor, a plasma generator (up to 50 kW), an afterburner, a plasma generator (6 kW), a spray scrubber, and a nozzle scrubber th, exhaust fan.

The disadvantage is the significant energy intensity, due to the need for a plasmatron, and the associated electrical costs, as well as the formation of huge quantities of exhaust gases, requiring significant costs for their cleaning and disposal.

A known method of processing household and industrial wastes (see RF patent No. 2349654, IPC C22B 7/00, F23G 5/00. Published on March 20, 2009), including loading them with fluxing additives into a bubble bath of slag melt in an electric furnace with an immersed furnace into the slag melt with an electrode; at a specific power of 400-1500 kW / m ³ , a blast intensity of 0.3-0.5 nm ³ / t and a melt temperature of 1450-1600 ° C, the combustion of emitted combustible components occurs, the dust and heat of the exhaust gases are utilized, and the volume of the near-electrode zone support in the range from 5 to 25% of the volume of the bath of the slag melt, and the gas enters the slag melt at a speed in the range of 50-150 nm / s.

The disadvantage of this method is the need to maintain the temperature up to 1600 ° C, which leads to high energy consumption due to the presence of high-voltage alternating current plasma generators, the use of an afterburner and a complex gas cleaning system.

The technical task is to reduce the energy intensity of the method of processing household and industrial waste by reducing the burning temperature, through the use of reduced gases (CO + H ₂ ) obtained by the method of steam, carbon dioxide or oxygen conversion of methane, and the presence of afterburning products.

The solution of the technical problem when implementing the proposed method is as follows:

- instead of plasma gasification with a temperature of 1200 ° C and higher, reduced gases containing CO + H _{2 are used} , obtained in the converter by steam and steam-oxygen catalytic conversion, which allows to reduce the temperature to 500-850 ° C;

- the use of reducing gas with a partial addition of oxygen and natural gas will dramatically reduce the use of natural gas in the reactor and in general in the process of plasma-chemical processing of municipal solid waste, and ash and slag are an environmentally friendly product;

- the implementation of the cleaning of flue gases in contact with finely ground lime before being fed into the exhaust pipe practically ensures the environmentally necessary parameters of the stream emitted into the atmosphere in the industrial zone.

The technical result is achieved by a method of processing household and industrial waste, including loading with preliminary separation by separating glass, concrete, ceramics and metal; drying with partial pyrolysis of organics in a furnace shaft; mixing the recyclable waste mass with further pyrolysis and characterized in that the methane conversion temperature is reduced to 500-850 ° C as a result of exposure to gasified components with an increased steam flow rate countercurrent to the moving waste, and the circulating process gas leaving the shaft furnace is cleaned in scrubbers and is divided into fuel gas supplied to both the converter and the recovery boiler, upon receipt of the reducing gas, with a partial addition of natural gas and acid ode, while the exhaust gases from the recovery boiler are cleaned in the adsorber by contact with fine-grained lime, in addition, part of the resulting reducing gases is consumed in the lower part of the reactor during an instant heat stroke by burning soot and dust particles coming from a cyclone for hot gas with the dioxins, furans and other harmful components deposited on them in an oxygen atmosphere, and the resulting reducing gases are sent as synthesis gas to the production of methanol, methyl ester, motor fuels.

The originality of the proposed method consists in organizing a continuous process of drying and gasification of wastes (MSW) in the atmosphere of reducing gases, which allows you to maintain a stable process of the high-power circuit of incinerator plants (MSZ), and the gas flows circulating in the reverse technological circuit are easily regulated by changing their ratio quantities and burning of harmful impurities in the reactor system in the recirculation stream of the reducing gas, as a result of which solid and gaseous products You low-flame gasification process are cleaned of harmful impurities to environmentally acceptable standards.

The technological scheme (Fig. 1) of the proposed plasma-chemical method for processing municipal solid waste (MSW) allows the production of secondary synthesis gas from biomass waste, denoted by a circulating process gas in a schematic diagram, with its subsequent use for the conversion of methane, steam, hot water and electricity . At the same time, solid products in the form of environmentally friendly ash or slag are part of the high-temperature pyrolysis process, and non-condensable CO and H ₂ gases with high calorific value are used as renewable fuel.

The proposed method is as follows.

Household waste, undergoing preliminary separation (not shown in Fig. 1) with the separation of glasses, concrete, ceramics and metals, and in the form of gasification material (see Fig. 1) enter the mine 1 in the wet state, where under the influence of reducing gas opposite to the moving solid waste, the organics are dried and partially pyrolyzed by reactions (4) and (5). Then, with a screw (not shown in Fig. 1), the MSW is sent to reactor 2 (the gasifier itself), followed by stirring, which improves the pyrolysis process under the influence of the gasifying components of the reducing gas obtained earlier by the method of carbon dioxide or oxygen methane conversion.

The gases leaving the reactor 2 enter a cyclone for hot gas 4 and, after a shaft furnace 1 and a scrubber 5, are sent as a component of the mixture to a converter 3 and a waste heat boiler 7.

The stirred reaction mass in the lower part of the reactor 2 is subjected to thermal shock resulting from the ingress of dust, soot and oxygen; the main quantities of dioxins, furans and other environmentally harmful components adsorbed onto particles in the whole mass immediately burn out upon contact with oxygen. Ash and slag become environmentally friendly and can be used, for example, in road construction, etc.

The gases leaving the shaft furnace 1 form a circulating process gas, which is sent to the scrubber 5 for cleaning by means of a gas blower 6, and after gas blowing 6 is divided into two streams. The first stream with the partial addition of both oxygen and natural gas (GHG), as well as dust and gas from cyclone 4 is sent to the converter 3, which simultaneously receives atmospheric air and fuel gas for heating the converter 3. The second stream of circulating process gas in the form of "fuel gas" partially sent to converter 3, and partially to the waste heat boiler 7, where it mixes up with air and burns up to form steam, which is used both for the conversion of hydrocarbon in converter 3 and is supplied to consumers for domestic and industrial needs, whether as synthesis gas is sent to the methanol production process, dimethyl ether, and other motor fuels.

The waste gases from the recovery boiler 7 enter the adsorber 8, where they are in contact with finely ground lime, as a result of which residues of dioxins and furans are captured. Flue gases after cleaning in the adsorber 8, as well as after the converter enter the exhaust pipe 9, after which they are released into the atmosphere in an environmentally friendly state.

Example 1 practical implementation of the proposed method, developed according to the quality criteria of gas products

The mechanism of carbon pyrolysis in a reducing environment

Household waste is pre-separated with the separation of inorganic components in the form of glass, concrete, ceramics and metal, and then loaded into a shaft furnace 1 (see the schematic diagram of the plasma chemical processing of solid household waste), where under the influence of hot reducing gases obtained by mixed steam-carbon catalytic methane conversion:

or oxygen conversion of methane

(see, for example, Atroshchenko V.I. et al. Bound Nitrogen Technology Course / Ed. by Corresponding Member of the Ukrainian Academy of Sciences Atroshchenko V.I. in a shaft furnace 1 mass with partial pyrolysis of organics. After which, with a screw (not shown in Fig. 1), the MSW is moved into the reactor 2 with stirring, which improves the process of further pyrolysis under the influence of gasification components supplied by the counterflow to the MSW and organizing the regime of carbon thermolysis:

The choice of oxidizing agents and their combination are determined both by the intended purpose of the CH ₄ and CO conversion process, as well as by kinetic and technical and economic solutions.

So an increase in superstoichiometric water vapor consumption

allows you to shift the equilibrium of the reaction (1) to the right, which increases the efficiency of using the proposed method by lowering the temperature to 500-800 ° C. Consequently, relatively low temperatures of homogeneous conversion reactions of methane and carbon monoxide are allowed:

which occur not only in a separate converter apparatus (reformer) (2), but partially in a shaft furnace 1 (reactions (1), (2) and (3)).

The use of reducing gas obtained in accordance with reactions (4) and (5) for the formation of CO ₂ in apparatuses 1 and 2 due to the gasification of organic components of garbage, followed by their supply to scrubbers for purification and further mixing with natural gas, allows partially or in its entirety, the dependence of the garbage plant (MRZ) on natural gas sources.

Initial data for the calculation of solid waste gasification processes

When calculating gas-generating processes, we use the following assumptions.

1) The gasification temperature in the upper part of the reactor 2, where absolutely dry solid waste substances come from the shaft furnace 1 and where guaranteed suppression of harmful substances, including chlorine-containing dioxides and furans, is achieved, is 1000 ° C.

2) Received commercial products - thermal energy in an amount of not less than 12.0 Gcal / h and quicklime in an amount of up to 150 kg / h - is released to consumers, which dips the spent funds.

3) The capacity of the incineration plant (MSZ) for solid municipal waste (MSW) entering the MSZ is 10 t / h.

4) MSW arriving at the MRZ have the following average morphological composition (% by weight):

- paper - 35.1; - textiles - 7.6; - food waste - 18.5; - skin - 2.8; - wood - 2.2; - rubber - 3.3; - metals - 11.5; - plastics 8.7; - glass, concrete, ceramics - 10.3

The average design humidity of solid waste is 32%.

5) Inorganic waste (glass, concrete, ceramics, metals) is separated at the separation stage, in total - 21.8% of the mass. For these purposes, magnetic, mechanical, air and partially manual separation equipment is used.

6) The average elemental composition of absolutely dry organic components of solid waste is:

6.1 (in% of mass): C - 44.0; H - 5.2; O - 28.5; S is 0.1; Cl - 0.3; N - 4.4; ash - 17.5.

6.2 (in t): C - 2.34; H 0.28; O - 1.52; S 0.053; Cl - 0.016; N 0.23; ash - 0.93. In total - 5.32 tons.

7) The organic part of solid waste with a moisture content of 32% is subjected to grinding to fragments with sizes not exceeding 100 mm. Grinding occurs, for example, in gear crushers. Next, the crushed organic components are included in the corresponding schemes for gasification of solid waste.

8) Gaseous blast carried out in the reactor (1) and (2) is heated to 300-400 ° C.

Gas phase calculation results

Case 1. Air blast

Since the energy-material balance calculations of gas-generating processes are very complicated and cumbersome (a joint solution of the systems of material and heat engineering equations is required), in our case we will simplify by using the results of the already performed operations of process modeling in air gasification of solid waste of a given composition (L. Kalinin , Kalinina O.V., Tikhonov A.V., Tikhonova E.V. Method for burning solid household other organic waste and device for its implementation / Invention. eration RU 2249766 of 05.08.2002).

Recalculations in our case show that the burning of 5.32 tons of absolutely dry solid waste requires an amount of air determined by stoichiometric ratios of oxidative reactions

C + O ₂ = CO ₂ ,

H ₂ + 0.5O ₂ = H ₂ O,

S ₂ + 2O ₂ = 2SO ₂ ,

and preset values of the coefficient of excess oxidizer equal to 1.4, as well as the ratio of oxygen content in 1 kg of air equal to 0.233. It was found that 44.5 tons of air must be supplied to the gas generator 2. The following gaseous product contents are obtained (see table 1).

Table 1 Component Wet gas Dry gas t thousand nm ³ % vol. t thousand nm ³ % vol. CO ₂ 8.79 4.47 21.45 8.79 4.47 30.64 H ₂ O 5.02 6.25 30.00 - - - SO ₂ 0.01 0.00 0.00 0.01 0.00 0.00 O ₂ 1.88 1.32 6.33 1.88 1.32 Cl 0.016 0.01 0.05 0.016 0.01 0.05 N 35,677 8.79 42.18 35,674 8.79 60.25 Ash 0.93 - - 0.93 - - Total: 52.32 20.84 100.00 47.30 14.60 100.00

As a result of the combustion of carbon, hydrogen and sulfur, the actual release of thermal energy was (minus 20% heat loss) 26.0 Gcal / h.

Case 2. Steam-air blast

The calculations of the inventors of RU 2249766 show that when using a catalytic afterburner, the temperature of the combustion products reaches 1385-1400 ° C. The calculations of other authors (Beskov SD Technochemical calculations. - M .: Higher school., 1965. - P.265-316) reveal that when coal is gasified with clean air, a temperature of 1498 ° C can be reached inside the gas generator. We, under the conditions of the problem, accepted that the gasification temperature should be equal to 1000 ° C. Lowering the temperature to a predetermined limit can be achieved through the use of steam-air blast in the reaction zone:

C + 0.5 O ₂ + 1.88 N ₂ = CO + 1.88 N ₂ ,

C + H ₂ O = CO + H ₂

According to Beskov S.D. to ensure a temperature of 1000 ° C in the generator, a steam-air mixture is blown in the ratio: 0.129 nm ³ steam 1 nm ³ air. Or recalculated: 3.81 nm ³ steam-air mixture is consumed per 1 kg of coal (p.273). Therefore, during the gasification of 2.34 tons of elemental coal, the volume of dry generator gas is: 2.34 × 3.84 = 10 nm ³ / h. Its composition will be as follows (% vol.):

СО - 34.4; N ₂ - 53.8; H ₂ - 8.9.

Steam supply reaches:

или 3,56 т/ч, где 29 - молярная масса воздуха, моль^-1.

or 3.56 t / h, where 29 is the molar mass of air, mol ^-1 .

Case 3. Reductive plasma blast

The effect of oxygen supply on the change in the volume of the gas phase is not taken into account due to the insignificance of the impact of this factor. We also do not take into account the influence on the same process of supply factors of chlorine, sulfur with the initial fuel.

MSW is gasified with the following elemental composition (t):

C 2.34; O - 1.52; H 0.28; N 0.23; H ₂ O - 2.5 t (physical water).

1) Oxygen consumption for hydrogen combustion:

;

;

where 2 t, 8 t and 18 t are the molar masses of hydrogen, oxygen and water vapor.

Oxygen Remaining: 1.52-1.12 = 0.4 t

2) Burns carbon:

;

;

where 12 t, 8 t and 28 t are the molar masses of carbon, oxygen and carbon monoxide

Remaining carbon: 2.34-0.60 = 1.74 t

3) Carbon steam conversion:

Water consumption:

;

;

;

;

4) The gas phase contains water:

2.5 + x ₂ -x ₅ = 2.5 + 2.52-2.61 = 2.41 t / h = 3000 nm ³ / h

CO was released into the gas phase:

1.40 + 4.06 = 5.46 t / h or 4370 nm ³ / h

Hydrogen formed: 0.29 t or 3.250 nm ³ / h

5) Goes into the gas phase of nitrogen (0.23 t) or 370 nm ³ / h

6) The composition of the dry generator gas during plasma gasification of solid waste (see table 2)

table 2 Component m ³ / h % vol. CO 4370 54.69 H ₂ 3250 40.68 N ₂ 370 4.63 Total 7990 one hundred

findings

1. The ratio between the volumes of dry generator gases:

V _{air blast} : V is _{steam. blast} : V _{plasma. ghazif.} = 14600: 9000: 8000 = 1.83: 1.13: 1

Obviously, the expenditure coefficients for moving and cleaning the generator gases will be the smallest for the option with plasma gasification of solid waste.

2. The ratio between the quantities of chemically and energetically valuable reducing components (CO and H ₂ denote their sum by a ₁ , and ₂ and a ₃ in% of the volume of dry generator gases):

a ₁ : a ₂ : a ₃ = 0: 46.30: 95.37 = 0: 1: 2.06

It can be seen that the most valuable products are formed in the variant of plasma reduction gasification of solid waste, which indicates its technical, economic and environmental advantages.

Example 2 assessment of the degree of environmental safety of the claimed method for in-plant suppression of dioxins and furans

In the aforementioned invention RU 2249766, for conditions similar to ours, an example of sanitary cleaning of exhaust gases from these environmentally extremely hazardous components by treating combustion products (52320 kg / h) in a decarbonization chamber (vertical shaft, counterflow from bottom to top) is considered. Lime flour (CaCo ₃ ) in the amount of 220 ct / h with an average particle diameter of 15 mm is sprayed towards the gas stream. At temperatures of 1100-1200 ° C, the time of complete dissociation of particles of this component does not exceed 0.12 s, i.e. almost instantly. It was experimentally proved that the chlorine-containing components that make up dioxins and furans (Cl - 16 kg) (see above) are almost completely environmentally deactivated with the formation of quicklime in an amount of up to 150 kg / h, which is released to consumers (in our case, the decontamination process combustion products is carried out in the apparatus 8).

However, taking into account the special environmental hazard of the above-mentioned supertoxicants belonging to the classes of polychlorodibenzodioxins and polychlorobenzofurans, the simplest of which is 2,4-dichlorophenoxyacetic acid

,

,

We have envisaged a number of in-house measures for their decontamination:

1) Replacing the oxidizing medium in reactor 1 and 2 (see diagram) with a reducing one. As a result, the formation of toxins is suppressed due to the occurrence of a chlorine deactivation reaction:

Cl ₂ + H ₂ = 2Cl ^- + 2H ⁺

2) Organization of recycling through the line of apparatuses 2, 1, 6, 3, which minimizes the removal of toxicants from the circuit.

3) The possible incompleteness of combustion of toxicants generated during the fire processing of organochlorine wastes is suppressed by supplying oxygen and natural gas to the lower part of the reactor 2, where dust and soot are burned at temperatures of 1000-1100 ° C, on which harmful substances are adsorbed. It produces environmentally friendly solid (ash, slag) and gaseous products (recycled process gas, fuel gas and converted gas). In addition, the delivery of oxygen and natural gas by 15-20% intensifies the pyrolysis processes in reactor 2.

4) Organization of sanitary cleaning of exhaust gases in the apparatus 8.

The originality of the proposed method consists in organizing a continuous process of drying and gasification of wastes (MSW) in the atmosphere of reducing gases, which allows you to maintain a stable process of the high-power circuit of incinerator plants (MSZ), and the gas flows circulating in the reverse technological circuit are easily regulated by changing their ratio quantities and burning of harmful impurities in the reactor system in the recirculation stream of the reducing gas, as a result of which solid and gaseous products You low-flame gasification process are cleaned of harmful impurities to environmentally acceptable standards.

Claims (1)

A method for processing household and industrial wastes, including loading them with preliminary separation by separating glass, concrete, ceramics and metal; drying with partial pyrolysis of organic matter in a shaft furnace; mixing the processed mass of waste with their further pyrolysis, characterized in that a reduction in the temperature of this process to 500-850 ° C is achieved as a result of exposure to reducing plasma-chemical components obtained by steam-oxygen conversion of methane with increased steam flow, countercurrent to moving waste, and recycled process gas , leaving the shaft furnace, is cleaned in scrubbers and separated into fuel gas supplied to both the methane converter and the recovery boiler, upon receipt reducing gas, with the partial addition of natural gas and oxygen, while the exhaust gases from the recovery boiler are cleaned in the adsorber by contact with fine-grained lime, in addition, part of the resulting reducing gases is consumed in the lower part of the reactor during instantaneous heat stroke by combustion soot and dust particles coming from a cyclone for hot gas with dioxins, furans and other harmful components deposited on them in an oxygen atmosphere, and the resulting Emulsified gases can also be sent as synthesis gas to the production of methanol, dimethylether, motor fuel and other products.

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