CN1297781C - Method for treating solid organic waste substance using high frequency plasma - Google Patents

Abstract

The invention provides a method for treating solid organic waste with high-frequency plasma, which is characterized in that it includes a spouted bed composed of two-stage plasma regions. The method steps include generating a first plasma region and a second plasma region under low pressure conditions, a spouted bed is formed by the first plasma region and the second plasma region, water vapor is mainly used as a plasma working gas, And the solid material is supplied to the second plasma region. The invention overcomes the limitations of the prior art, has good operation stability and continuity, can handle large particles and massive solid materials, and can obtain valuable syngas with high efficiency.

Description

A method for treating solid organic waste using high-frequency plasma

technical field

The invention relates to the technical field of solid waste treatment, in particular to the technology of pyrolysis and gasification of solid organic waste using high-frequency plasma in the electrical category.

Background technique

Solid organic waste includes municipal solid waste, polymer waste such as plastic, rubber, and some agricultural and forestry production waste and industrial waste. In recent years, the national economy has developed rapidly, and the amount of solid organic waste has increased greatly. In 2000, the amount of waste plastics in my country reached 3.7 million tons, and waste rubber reached 850,000 tons, causing increasingly serious "white pollution" and "black pollution". And other issues. At present, the treatment technologies for solid waste at home and abroad are mainly landfill, incineration, mechanical or chemical recycling. For example, at present, a small part of waste plastics in my country has been recycled for recycling, but most of the recycled products are of low grade and the market demand is not large. Most of the discarded plastic products in the garbage are still treated as landfills together with the garbage. Due to the light weight and large volume of plastics, landfills occupy a lot of land, and plastic macromolecules cannot degrade by themselves and will not rot for a long time. This not only wastes resources, but also destroys land. Pollution of ground water. The incineration treatment method has good volume reduction and volume reduction effects, but the incineration of waste plastics often produces a large amount of smoke containing toxic pollutants, causing serious air pollution. Recently, chemical recycling methods such as catalytic cracking of waste plastics to produce gasoline and diesel have also received great attention. Waste plastic cracking to oil needs to be carried out under the conditions of pressure 0.2-0.5MPa, temperature 500-800°C and catalyst action. Under the action of catalyst and heat, waste plastic raw materials undergo thermal cracking reaction and catalytic cracking reaction, and the carbon and hydrogen elements are composed of The high molecular material is converted into low molecular fuel oil, and after fractional distillation and condensation, products similar to gasoline and diesel are obtained. The main problem of the current waste plastic pyrolysis technology is that it is difficult to control the product quality to produce gasoline and diesel oil that meet the national standards, the reaction effect of the catalyst is poor, the oil yield is low, and the energy consumption is high.

Plasma is an excited ionized gas, which is composed of negatively charged particles such as electrons, positively charged particles such as positive ions, and neutral particles such as atoms. The number of positive and negative charges in the ionized gas is equal, and its overall charge neutrality remains Conductive. Plasma can provide a reaction environment with concentrated energy and high temperature, which can not only greatly increase the chemical reaction rate, but also produce chemical reactions that are difficult to occur in other reaction systems. Therefore, plasma technology has been gradually applied to many industrial fields such as chemical industry, Metallurgy, electronics, energy, materials, etc. In terms of energy and environmental protection, there are many reports on the plasma pyrolysis gasification technology of solid waste.

The technology of using DC arc plasma to treat solid organic waste can be found in Chinese patents 01129931 and 02250661. Usually, the working gas is ionized into high-temperature plasma in the DC arc plasma generator, and injected into the plasma gasification reactor to form a high-temperature environment of 3000-10000K; solid organic waste is carried by the carrier gas through the screw feeder and injected into the plasma The pyrolysis zone of the solid gasification reactor forms a high-temperature reaction environment in which a large number of active ions exist; solid organic waste undergoes rapid pyrolysis and gasification reactions in the high-temperature zone of the reactor to generate chemical synthesis gas with recycling value. At present, the application of DC arc plasma to treat solid organic waste has some technical limitations, for example: (1) DC arc discharge is a large current and strong discharge, the electrode is easy to ablate, and the service life is short. When using inert gas (Ar, He) , reducing gas (H ₂ ) or neutral gas (N ₂ ) as the working gas, the electrode life is generally 600 hours; when using oxidizing gas (O ₂ , air, H ₂ O), the electrode life is only 200 hours about. (2) The DC arc plasma temperature is as high as 3000-10000K, and the reactor wall material is difficult to withstand for a long time. (3) Solid materials can only be introduced in the downstream of the plasma jet, and it is difficult to enter the central area of the plasma. The plasma gasification reactor adopts the form of a flow-filled bed, and the residence time of the reactants is short (0.2~2ms), resulting in pyrolysis gas incomplete.

The technology of using high-frequency plasma to treat solid organic waste is represented by Chinese patent 93102963. High-frequency plasma is generated by high-frequency coupling electrodeless discharge. According to different coupling methods, high-frequency plasma is divided into capacitively coupled plasma and inductively coupled plasma. If the energy coupling in the plasma is mainly composed of radio frequency Generated by the voltage of the antenna/electrode (static charge), the coupling method is capacitive coupling, and the generated plasma is capacitively coupled plasma (CCP); if the energy coupling in the plasma is mainly caused by the radio frequency antenna/electrode Generated by the magnetic field (moving charge), the corresponding coupling method is inductive coupling, and the generated plasma is inductively coupled plasma (ICP). High-frequency plasma has many advantages, such as: (1) Other plasma torches must use inert gas as the working gas to prevent ablation of electrodes, while high-frequency plasma can work under air or oxygen conditions, which greatly saves Operating costs. (2) The high-frequency plasma area is large, the air velocity is small, and it is easy to supply powder at the center. The powder stays in the high-temperature area for a long time, and the plasma torch has a long high-temperature jet tail flame. (3) Due to the skin effect of the high-frequency current, the high-frequency plasma can be in the form of a ring, and the carrier gas can form a channel in the center of the plasma, and the solid powder can be rapidly decomposed under the action of the ring-shaped high-temperature plasma.

The infinite plasma injection device proposed in Chinese patent 93102963 is mainly used to dissociate harmful wastes. A radio frequency plasma nozzle is used to excite free electrons. The waste materials are combined with a controllable free electron source, and the collision and ultraviolet radiation generated by electrons and molecules are used. Enabling free electrons to dissociate waste materials into simple compounds that can be safely discharged and are not harmful to the environment. In particular, the dissociation process adopts a non-heating method and relies on the bond cracking effect of excited electrons. The degree of dissociation of the waste is affected by the density and temperature of the free electrons and the residence time of the waste in the plasma. The electron density can be controlled by the flow rate of the carrier gas. , changing the RF power can control the temperature. The inventor once proposed that the device can be expanded to the MW level of radio frequency power, and the waste processing rate can be used on a scale of 500kg/h. However, the main problems to be improved are: (1) The temperature of the radio frequency plasma nozzle operated under the atmospheric pressure is still relatively high, and additional water cooling is required. (2) The radio frequency plasma nozzle is sensitive to external interference. When the supply of solid material is increased, the plasma is unstable and the arc is easily extinguished. (3) The solid material to be processed must be in the form of powder, while large particles and blocky materials are difficult to handle.

Contents of the invention

The purpose of the present invention is to overcome the limitations of the prior art and provide a method for pyrolysis and gasification of solid organic waste using high-frequency plasma, which has good operational stability and continuity, and can handle large particles and massive solids materials, and can efficiently obtain valuable syngas.

First of all, high-frequency plasma state parameters (such as electron density, electron temperature, and gas temperature) are greatly affected by operating pressure. If the discharge is carried out under high-pressure conditions close to atmospheric pressure, electrons, ions, and neutral particles will pass through the intense Collisions fully exchange energy, so that the plasma reaches or is close to a thermal equilibrium state; on the contrary, hundreds of Pa or thousands of Pa low-pressure plasmas are often in a non-thermal equilibrium state. At this time, the number density of gas particles is low, and electrons and ions or neutral The collision probability of particles is very small, and the difference between the temperature of electrons and the temperature of heavy particles is relatively large. The temperature of electrons can be as high as tens of thousands of degrees, while the temperature of heavy particles is only a few hundred degrees. Our experimental results show that: for a radio frequency plasma torch with an inner diameter of 30mm, when the working gas pressure in the torch is 50Pa (absolute pressure), the high-frequency power required for plasma ignition is 50W, and the temperature measured by a thermocouple is 150°C When the gas pressure is 3000Pa, the ignition power is 700W, and the temperature measured by the thermocouple is 500°C; when the gas pressure is 5000-10000Pa, the ignition power is about 1-2kW, and the temperature is 1000-1500°C. When using high-frequency plasma to pyrolyze and gasify solid organic wastes such as plastics and rubber, the preferred operating pressure is 5000-10000Pa and the temperature is 1000-1500°C.

Second, regarding the stability of high-frequency plasma, it is mainly caused by the influence of the difference between the properties of the plasma working gas and the processed solid material on the high-frequency energy coupling process. This patent adopts the following two-stage plasma to improve the stability of high-frequency plasma: (1) use the first plasma torch with a smaller diameter, the plasma working gas is passed through inside, and the first inductive coupling coil is used to generate the first plasma torch. A plasma area, the high-temperature jet tail flame enters the second plasma area from the outlet of the first plasma torch. (2) Using a second plasma torch with a larger diameter, with the assistance of the high-temperature jet tail flame of the first plasma torch, a second plasma region is generated through a second inductively coupled coil. (3) The solid material is supplied to the second plasma area, and is pyrolyzed and gasified in the plasma high-temperature reaction atmosphere. In the above two-stage plasma, the first plasma region is not affected by solid materials, and it is easy to maintain stable operation; when the second plasma region is affected by the supply of solid materials and becomes unstable, due to the first plasma torch The high-temperature jet plume contains various active particles such as high-energy electrons, ions, excited atoms, molecules, and free radicals. Under the joint action of the second inductively coupled coil, the second plasma torch can not be easily extinguished.

Third, in order to deal with large particles and massive solid materials, the first plasma zone and the second plasma zone form a spouted bed form, the method is as follows: a semi-conical air distribution plate is arranged at the lower part of the second plasma zone, The bottom of the semi-conical air distribution plate is connected to the outlet of the first plasma torch, and the high-temperature jet tail flame of the first plasma torch becomes the central jet flow of the spouted bed in the second plasma area, and the corresponding part of the semi-conical air distribution plate The part of the second plasma area becomes the downward recirculation area of the spouted bed; after the solid material is supplied to the second plasma area, it will be entrained by the central jet flow and spray upward, and then the coarse particles will be separated from the jet due to gravity out, return to the downflow area, and then enter the next injection cycle. In this way, large particles and massive solid materials have sufficient residence time in the spouted bed until the pyrolysis and gasification reaction is completed, and become small particle ash, which reaches the ash removal system with the airflow.

Fourth, in order to make full use of the organic components of solid waste to produce synthesis gas, the plasma working gas can be superheated steam, or a mixture of superheated steam and air, oxygen or other gases. Water vapor and oxygen are dissociated into O and OH radicals under the action of high-frequency plasma, so in this method, the pyrolysis gasification reaction of solid waste is essentially an oxidation reaction. Active particles such as high-energy electrons and ions contained in the plasma also have a bond-cleaving effect on high-molecular organic matter. The overall reaction formula for producing synthesis gas by reacting organic components of solid waste with superheated steam is: . When the plasma working gas contains air and oxygen, some organic components also participate in the oxidation reaction: , so as to provide part of the energy required for pyrolysis and gasification.

Based on the above points, this patent proposes a method for treating solid organic waste using high-frequency plasma, which consists of the following steps:

(1) Under low pressure conditions, the first plasma region is generated by the first inductively coupled coil, and its high-temperature jet tail flame enters the second plasma region;

(2) Under the auxiliary effect of the first plasma high-temperature jet tail flame, the second plasma region is generated through the second inductively coupled coil;

(3) The first plasma region and the second plasma region constitute a spouted bed, wherein the high-temperature jet tail flame of the first plasma is the central jet flow of the second plasma region, and the other regions of the second plasma are Downward recirculation zone of the spouted bed;

(4) The solid material is supplied to the second plasma area, and the pyrolysis and gasification reaction is completed under the action of the plasma.

Among them, the preferred operating pressure of the first plasma region and the second plasma region is 5000-10000Pa, and the temperature is 1000-1500°C; the plasma working gas adopts superheated steam, or superheated steam and air, oxygen Mixtures or other gases and their mixtures.

Compared with the prior art, the present invention has the following outstanding advantages: (1) Due to the low-pressure operating conditions, the high-frequency plasma temperature can be controlled below 1500 ° C, and the plasma reactor can be manufactured using conventional materials (such as cast ceramics) , and is conducive to long-term continuous operation of the device. (2) Due to the use of dual-stage plasma, the stability of high-frequency plasma has been greatly improved, and the plasma ignition process is also easier. (3) Due to the spouted bed form, large particles and massive solid materials can also be processed. (4) The plasma working gas mainly uses water vapor, which is beneficial to the preparation of synthesis gas from the organic components of solid waste.

Description of drawings

Below in conjunction with accompanying drawing, the substantive content of this patent is described in further detail.

Figure 1 is a schematic diagram of an embodiment of this patent. In the figure: 1, the first plasma area, 2, the second plasma area, 3, the first inductively coupled coil, 4, the first plasma torch, 5, the semi-conical air distribution plate, 6, the second inductance Coupling coil, 7, second plasma torch, 8, steam generator, 9, screw feeder, 10, feed bin, 11, first matching network, 12, first crystal-controlled RF high-frequency power supply, 13 , the second matching network, 14, the second crystal-controlled RF high-frequency power supply, 15, the ash removal system, 16, the ash bin, 17, the air extraction system.

Detailed ways

Embodiment one

As shown in Figure 1, the water steam generator (8) generates superheated steam, which is supplied to the first plasma area (1) after metering and adjustment. The semi-conical air distribution plate (5) of the hole is provided to the second plasma area (2); the model of the first crystal-controlled RF high-frequency power supply (12) is JG-2K-B, the output power is 0-2kW, and the output frequency It is a high-frequency 13.56MHz dedicated to industry; the first matching network (11) is JG-2KW, equipped with a forward power meter and a reverse power meter; the first inductive coupling coil (3) is wound with a copper tube and is in a spiral shape Surrounded by the outer wall of the first plasma torch (4) cast from high-temperature-resistant ceramics; the second crystal-controlled RF high-frequency power supply (14) is JG-10K-B, with an output power of 0-10kW and a frequency of 13.56MHz, and The model of the second matching network (13) is JG-10KW, and it is equipped with a forward power meter and a reverse power meter; the second inductive coupling coil (6) is wound with a copper tube, and is wound in a spiral shape and is casted with high temperature resistant ceramics. The outer wall of the second plasma torch (7); the pumping system (17) is a water ring vacuum pump, the pumping rate is 12L/s, and the ultimate pressure is 4000Pa, and the plasma reactor gas is extracted through the ash removal system (15), so that The pressure of the first plasma region and the second plasma region is about 5000Pa; start the first crystal-controlled RF high-frequency power supply (12), adjust the first matching network (11), so that the first plasma region (1) glows; Then start the second crystal-controlled RF high-frequency power supply (14), adjust the second matching network (13), so that the second plasma region (2) glows; adjust the crystal-controlled RF high-frequency power supply (12,14) output power and matching network (11, 13), so that the temperature of the first plasma zone and the second plasma zone reaches above 1000°C; start the screw feeder (9), and add the polypropylene PP plastic particles stored in the silo (10) Plasma reactor, under the high temperature of plasma, polypropylene PP plastic particles are pyrolyzed and gasified, and the gas is discharged through the ash removal system (15) and the exhaust system (17). The gas is sampled and analyzed by chromatography. The main components are H _2. CO, CH ₄ , C ₂ H ₄ , C ₂ H ₂ , CO ₂ , C ₂ H ₆ , C ₃ H ₆ , C ₃ H ₈ , etc., the gas calorific value is about 22MJ/Nm ³ , suitable for chemical synthesis gas, raw material gas or fuel gas, etc. The ash bin (16) can collect a very small amount of ash.

Embodiment two

Same as embodiment one, adjust the pumping system (17), so that the pressure of the first plasma region and the second plasma region is about 10000Pa; adjust the output power of the crystal-controlled RF high-frequency power supply (12,14) and the matching network (11 , 13), so that the temperature of the first plasma region and the second plasma region is about 1300 ° C; polypropylene PP plastic particles are pyrolyzed and gasified, and the gas is sampled and analyzed by chromatography. The main components are the same as in Example 1.

Embodiment Three

Same as Example 1, when the solid material feed is waste tire crushed particles, the main components of gas production are H ₂ , CO, CH ₄ , C ₂ H ₄ , C ₂ H ₂ , CO ₂ , C ₂ H ₆ , C ₃ H ₆ , C ₃ H ₈ , etc., and hydrogen sulfide H ₂ S, the gas calorific value is about 20MJ/Nm ³ . Ash bin (16) can collect solid product, i.e. pyrolysis carbon black, and its elemental analysis is: 85%C, 0.5%H, 12%O, 0.4%N, 1.9%S; Its ash of industrial analysis is 16.2%, Calorific value is 28500kJ/kg, BET specific surface area is 70m ² /g; scanning electron microscope analysis (SEM) shows that pyrolytic carbon black particles form a primary particle aggregate structure with a size of 50-2000μm; photoelectron spectroscopy (XPS) shows that thermal The carbon in pyrolysis carbon black mainly exists as graphite structure carbon, and the form of sulfur is similar to _FeS2 and ZnS; nuclear magnetic resonance spectroscopy (NMR) shows that the main chemical property of pyrolysis carbon black is aromatic carbon C=C bond structure. Therefore, these solid products can be used as industrial semi-reinforcing carbon black and can also be used as activated carbon after further processing.

Claims (2)

1. A method for treating solid organic waste by using high-frequency plasma, comprising the following steps:

(1) under the condition of low pressure, a first plasma area is generated through a first inductive coupling coil, and a high-temperature jet flow tail flame enters a second plasma area;

(2) generating a second plasma area through a second inductive coupling coil under the auxiliary action of the first plasma high-temperature jet flow tail flame;

(3) the first plasma area and the second plasma area form a spouted bed, wherein the high-temperature jet tail flame of the first plasma is the central spouted air flow of the second plasma area, and the other areas of the second plasma are downward reflux areas of the spouted bed;

(4) solid materials are supplied to the second plasma area, and pyrolysis and gasification reactions are completed under the action of plasmas; wherein, the operating pressure of the first plasma area and the second plasma area is 5000-10000 Pa.

2. The method for treating solid organic waste with high-frequency plasma according to claim 1, wherein: the plasma working gas adopts superheated steam.

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