CN1597155A - Method of treating waste matter using plasma electric arc technology and its device - Google Patents

Abstract

The invention discloses a method for treating hazardous waste using plasma arc, comprising (1)the solid waste to be treated being pre-processed and intermittently or continuously added into plasma arc furnace by transporting system; (2) performing split treatment in plasma arc furnace, wherein the working gas of split treatment is reducing gas or other gas, and the ratio of oxygen content in working gas and oxygen demand in waste complete reaction is less than 0.3, at the split treatment temperature of 1200k-3500k; (3) the exhaust gas after spliting in the plasma arc furnace entering into flare system and being processed by quick cooling and cooling down of convenient tail gas,purifying, treating acid gas and detached process of granule; (4) the detached granule and gas being recovered respectively. The invention also relates to the corresponding device using plasma arc furnace. The investment of the invention and the cost are low, and the wasting gas and tail gas are few. The invention can treat all sorts of waste which is not suitable for burning method.

Description

Method and device for treating waste by using plasma arc technology

technical field

The invention relates to the field of waste treatment, more specifically, the invention relates to a method and a device for treating waste by adopting plasma arc technology.

Background technique

The disposal of hazardous waste has become an important environmental issue, and all walks of life pay great attention to harmless disposal methods. Traditional burial and stacking methods not only take up a lot of land but also often cause hidden dangers due to improper handling. Hazardous wastes that are not biodegradable are especially problematic for the environment. The incineration method will produce harmful substances such as dioxins and become a new source of pollution.

Plasma technology to treat hazardous waste overcomes the shortcomings of traditional landfill and incineration methods, and has the advantages of high efficiency and environmental protection. It can also destroy chemical weapons agents and other contaminated materials, remediate contaminated soil, etc. At present, there are some patented technologies for plasma treatment of waste at home and abroad.

Foreign patented technologies include: the patented direct current plasma technology developed by Startech Environmental Corporation of the United States, which can treat various wastes including chemical weapons, but the technology is complicated and the equipment cost is expensive. Carter (US Patent 5,280,757) uses arc plasma to gasify municipal solid waste; Barton (US Patent 4,644,877) and Bell (US Patent 4,431,612) use arc plasma to destroy polychlorinated biphenyls (PCBs), etc., but both have electrode replacement costs higher question.

The patents applied in China include: German Grima (Chinese patent 89105527.4) patent adopts water vapor plasma atmosphere and direct current plasma technology, Australian Commonwealth Scientific and Industrial Research Organization (Chinese patent 93103682.8) adopts inert gas plasma atmosphere and direct current plasma Bulk technology, but the reaction is only carried out in the ceramic tube, and the reaction space is small, which brings difficulties to industrialization. Zhejiang Jusheng Fluorine Chemical Co., Ltd. (Chinese patent 00128708.7) uses DC plasma to treat organic halides, but it is not suitable for treating medical waste; Wang Zhongyi and Huang Shaoqing (Chinese patent 01206033.X) use DC plasma assisted incineration to treat medical waste.

Also, in the above-cited patents, the plasma technology used generally refers to the use of plasma moments. Plasma moment (also known as plasma generator, arc gas heater, plasma gun, plasma beam, etc.) refers to the use of a large amount of working gas to pass through the arc area, and the energy of the arc is used to heat the gas to form a high-temperature plasma jet. The working gas of the plasma torch can be an oxidizing gas, an inert gas or a reducing gas. If an oxidizing gas is used, the same tail gas problem as that of the incineration method will be produced. If an inert or reducing gas is used, but subsequent incineration is used after the plasma treatment, the same problems exist as incineration. If an inert or reducing gas plasma torch is used, subsequent incineration is not used, but because a large amount of working gas is required to form the ion plasma moment, the amount of tail gas is still relatively large, and the requirements for tail gas treatment are still relatively high. Therefore, it is hoped to propose a device and technical method with low investment, low operating cost, stable operation, simple operation, suitable for disposal of wastes in various forms (solid, semi-solid, liquid, gaseous), and zero discharge.

The applicant discloses an AC plasma arc furnace in Chinese patent ZL96119824.9, which is hereby incorporated by reference together with the aforementioned patent.

During operation of a plasma arc furnace, the electrodes wear out and often require repositioning and re-strikes. However, when dealing with waste, especially when dealing with hazardous waste, the plasma arc furnace generally needs to be closed for operation. Therefore, there is a need for a device capable of positioning the electrodes of the plasma arc furnace and assisting arc starting.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art when treating waste, and use plasma arc technology to process waste under a reducing atmosphere, thereby providing a method and device for using plasma arc technology to treat waste

The method for treating hazardous wastes using plasma arc technology of the present invention comprises following steps in sequence:

(1) Carry out the pretreatment process to the solid waste to be treated, and intermittently or continuously add it to the plasma electric arc furnace through the conveying system;

(2) Carry out cracking treatment in plasma electric arc furnace, wherein the working gas of cracking treatment is reducing gas or other gas, the ratio of the oxygen content in the working gas and the oxygen demand of complete reaction of waste is less than 0.3, and the cracking treatment temperature is 1200K-3500K;

(3) The gas discharged from the pyrolysis of the plasma electric arc furnace enters the tail gas treatment system, and undergoes conventional tail gas quenching and cooling, purification, acid gas treatment, and particle separation treatment processes;

(4) Separately recover the particles and gas separated in step (3).

The pre-treatment process includes performing conventional crushing and/or gasification processes on the solid waste to be treated.

The other gases include: inert gas or water vapor.

The plasma arc furnace adopts AC or DC power supply.

It also includes adding an alkaline substance for neutralizing acidic substances in the tail gas when the gas enters the tail gas treatment system in step (3), and the alkaline substance includes: calcium oxide, sodium hydroxide or potassium hydroxide.

It also includes adding metal oxides, silicon compounds, calcium compounds and iron used to generate the glass body into the plasma arc furnace in step (2), and the added parts by weight are: 20-40 parts of silicon compounds, 30-40 parts of calcium-sodium compounds 50 parts, 20-40 parts of iron and metal oxides.

The silicon compound is silicon dioxide.

The calcium compound is calcium carbonate.

Described sodium compound is sodium carbonate.

The iron and metal oxides include: ferric oxide, ferric oxide, metal iron flakes, aluminum blocks or flakes.

The present invention also provides a special plasma electric arc furnace, which includes a furnace body, the inner side of the furnace body is provided with a refractory material and a heat insulating material lining, and the furnace body is provided with a material inlet, a gas discharge port and a waste material discharge port; A working gas inlet is provided on the top; a crucible is provided at the bottom of the furnace body; at least two electrodes connected to the power supply are obliquely inserted on the top of the furnace body; an electrode positioning and auxiliary arc starting are also included for the at least two electrodes Arc positioning device.

The super-arc positioning device includes a positioning rod and a stepping motor for driving the electrodes. The positioning rod is inserted into an opening on the furnace body and can move radially along the opening. Contact with the electrode during and auxiliary arcing, and keep away from the electrode after arcing. The positioning rod is provided with a sensor.

A crucible is provided at the bottom of the furnace, and a heat shield is provided between the crucible and the inner wall of the furnace.

The power source connected to the electrodes is an AC power source or a DC power source.

The invention adopts plasma electric arc technology, has high energy density, and can operate at a working temperature of 1200K-3500K. Organic matter can be decomposed into elemental structures such as carbon and hydrogen, and metal ores or gaseous metals can be collected after recondensation, and silicates can become harmless glass-like structures. The invention can not only process and dispose various common wastes and hazardous wastes, but also generate reusable by-products, such as carbon black, metal, combustible gas, glassy silica and the like. The amount of tail gas produced is only 5-10% of that of the combustion method, and the volume of organic matter can be greatly reduced after treatment, up to 99.7%. The power consumption of waste treatment is about 0.6-1.3kW-h/kg, which has the characteristics of low investment and low cost. This set of equipment can be used for disposal of waste plastics, animal carcasses, hospital waste, asbestos waste, waste batteries, waste electronic circuit boards, waste display screens and other wastes that are not suitable for incineration.

The arc starting positioning device of the present invention can improve the positioning accuracy of the plasma electric arc furnace and assist the arc generation between the electrodes, thus improving the working performance of the plasma arc.

Description of drawings

Fig. 1 is the process flow sheet of the method for adopting plasma treatment waste of the present invention;

Fig. 2 a is the structural representation of the plasma electric arc furnace of furnace roof feeding arrangement of the present invention;

Fig. 2 b is the structural representation of the plasma electric arc furnace of furnace side feeding arrangement of the present invention;

Fig. 3 is a schematic diagram of electrode positioning and auxiliary arc starting in the plasma arc furnace shown in Fig. 2 .

Detailed ways

Embodiment 1: the method of the present invention is described in further detail with reference to Fig. 1 and specific examples

Apply the method of the present invention to process toxic and harmful solid hazardous waste, and its steps are carried out in the following order:

When the waste to be treated is toxic and hazardous waste, the pretreatment process should be carried out in a sealed system, which maintains a slight negative pressure, and the gas in it is pumped into the plasma arc furnace or burner for heating and disinfection.

(1) Pulverize the toxic and harmful solid waste to be treated, pulverize it into a form suitable for plasma arc furnace treatment, and then transport the waste of different forms to the present invention intermittently or continuously through the conveying system In the plasma electric arc furnace; adopt the plasma electric arc furnace of the present invention, what it produces during operation is plasma arc, and what the plasma furnace that uses when processing waste in the prior art produces generally is plasma moment. It can also include gasifying solid and liquid wastes that can be gasified in the waste and then passing them into the furnace; the gasification system can be heated by electric heating or by using system tail gas;

(2) The cracking treatment is carried out in the plasma electric arc furnace, wherein the working gas for the cracking treatment is hydrogen. In the present invention, the working gas in the plasma electric arc furnace can adopt reducing gas (such as hydrogen) to form a reducing atmosphere, and also can adopt inert gas (such as argon, nitrogen, etc.), or adopt water vapor, in the case of carbon oxidation in waste Form a reducing atmosphere under the environment to ensure high-temperature pyrolysis of the processed material; if the working gas contains oxygen, ensure that the ratio of the oxygen content to the oxygen demand for complete chemical reaction of the waste is less than 0.3. Under a reducing atmosphere, the cracking treatment temperature can be within the range of 1200K-3500K. The material is completely cracked in the plasma arc furnace at 1200K-3500K, in which the organic matter is quickly and completely cracked into gas, and the inorganic matter is smelted into glass in the graphite crucible and Metal, made harmless. For wastes containing harmful elements such as heavy metals that are difficult to form vitreous bodies, especially for poisons containing arsenic, add 20 to 40 parts of silicon dioxide, 30 to 50 parts of calcium carbonate, and 30 to 50 parts of sodium carbonate compounds in the furnace. 20-40 parts of ferric oxide or iron nuggets, all calculated in parts by weight. Containing silicon, calcium, sodium, metal iron and metal oxides, it can form a vitreous body, fix harmful elements such as arsenic in the vitreous body, prevent leaching, and partially reduce to simple substances, and will not form diarsenic trioxide (arsenic) and arsenic trihydride.

The pyrolysis residue and metal are discharged from the slag and metal discharge port for reuse. The tail gas produced by cracking enters the tail gas cooling and purification system through the gas discharge port to obtain combustible gas. It should be noted that in the present invention it is the plasma arc technique employed, an electric arc is formed between the electrode ends within the furnace. Compared with the plasma moment technology adopted in the prior art, the amount of working gas consumed by the present invention is greatly reduced, so the amount of tail gas generated during the actual treatment process is also less than that of the prior art.

(3) The tail gas generated from the pyrolysis of the plasma electric arc furnace enters the tail gas treatment system through the gas discharge port, and undergoes conventional tail gas quenching and cooling, purification, acid gas treatment, and particle separation treatment processes to obtain combustible gas. The tail gas here generally contains one or more of the following gases: hydrogen, carbon monoxide, methane, carbon dioxide. The gas also contains cracked carbon black (nano-scale soot).

As shown in Figure 1, the tail gas discharged from the plasma electric arc furnace first passes through the water system for heat exchange cooling and quenching, so as to ensure that the arsenic contained in it can be crystallized, and arsenic trihydride will not be synthesized, and chlorine-containing gases will not Synthesis of polychlorinated dibenzodioxins and polychlorinated dibenzofurans (dioxins for short). The acid gas containing chlorine, fluorine, sulfur and other elements in the tail gas is neutralized with an alkaline neutralizer, and then the solids are separated and recovered. Tiny solid particles in the gas, such as carbon black, arsenic microcrystals, etc., are collected by the bag dust collector. The remaining gas after separation is generally combustible gas, which can be recycled or burned into an internal combustion engine to generate electricity.

In an application example of the present invention, the meat containing plastic, cotton yarn and other medical waste and simulated limbs are put into the plasma electric arc furnace, hydrogen plasma is used as the working gas, and a large amount of energy carried by the high-temperature gas in the furnace quickly acidifies the waste matter, producing carbon, hydrogen-rich gas, etc. The exhausted gas is monitored, and the exhausted tail gas is tested. The sulfur dioxide is 3.0mg/Nm ³ , the nitrogen oxide is 30-90mg/Nm ³ , and the dust is 0.38-0.69mg/Nm ³ , reaching the relevant national standards. After the test, the furnace was turned on and observed, all the organic substances were gasified, and the volume of medical waste was greatly reduced to less than 2% of the original volume.

In another application example of the present invention, a chemical reagent containing arsenic was tested for cracking treatment, the treatment capacity reached 40 kg per hour, and the power consumption was about 1.0-1.2 kw-h/kg. Tests have shown that more than 70% of the arsenic is solidified in the vitreous.

The method and device of the present invention have no strict requirements on the composition of raw materials, and can process urban solid waste, medical waste, electronic industry waste, chemical reagents, low-radioactive waste and other hazardous waste.

The system for realizing the above process can be placed in a sealed device and run under a slight negative pressure (-10mmH ₂ O) without gas leakage. The method and the plasma electric arc furnace described in the present invention can run continuously or intermittently for 24 hours, which can be selected according to requirements.

Example 2

Referring to Figures 2 and 3, a plasma arc furnace is prepared, as shown in Figure 2a. The upper furnace body 1 and the lower furnace body 3 are steel shells, their insides are provided with refractory and heat insulating material linings 2, and the bottom of the lower furnace body 3 is provided with a crucible 4. A heat shield 15 is added between the crucible 4 and the inner wall of the furnace.

Three electrodes 6 connected to a power source (not shown) are interposed oppositely on the top of the furnace (the sectional view shows only two electrodes). In practical application, more than two electrodes can be symmetrically installed according to the type of power supply. The angle formed between the electrode and the axis of the furnace is between 0 and 90 degrees. The plasma arc furnace can be operated with a DC power supply (voltage 40-500V), or use AC power frequency power supply (frequency 50-60Hz, voltage 40-350V), the power supply has a saturable reactor. AC power can be single-phase or three-phase or three single-phase. This embodiment is a three-phase power frequency power supply. The electrode 6 can be a thermal electrode made of graphite or high-temperature metal, or a water-cooled electrode made of metal such as oxygen-free copper, and this embodiment is a graphite electrode. The plasma is formed by electrical discharges between the electrode ends in the furnace, independent of the electrical conductivity of the charge.

In Fig. 2, the working gas enters through the channel in the central opening 8 of the furnace roof, and is ionized into plasma gas by the arc between the electrode ends. The pre-treated waste (solid and gas) enters the furnace from the feed port 7 located on the upper furnace body 1 or the lower furnace body 3, and is decomposed at high temperature after being contacted with plasma gas. The gas produced after the cracking is discharged from the gas discharge port 9, and the inorganic matter therein forms a metal layer and a slag layer 5 in the graphite crucible and is deposited in the crucible 4, and then is discharged from the slag and metal discharge port 10 at the bottom of the crucible 4. There is no blocking device 11 in the discharge port 10 . The plasma arc furnace can periodically discharge metal and slag during operation from the discharge port 10, from which the metal and glass body can be collected. In Fig. 2a, the feed port 7 and the gas discharge port 9 are arranged on the top of the furnace. In practical application, they can also be arranged on the side of the furnace, as shown in Fig. 2b. The working temperature of the plasma arc furnace is kept at 1200K-3500K.

The plasma electric arc furnace adopts water cooling, as shown in Figure 2, the cooling water enters the furnace body through the inlet 13, and is discharged through the outlet 14. Through this cooling measure, the surface temperature of the furnace body is not higher than the ambient temperature by 50°C.

In order to enable the electrode 6 to be accurately positioned in the furnace body before arcing, and to ensure smooth arcing at the end of the electrode 6 in the furnace body, the present invention provides an arcing positioning device. As shown in FIG. 2 and FIG. 3 , the arcing positioning device includes a positioning rod 16 and a sensor (not shown). The positioning rod 16 can be controlled by a motor (not shown) to move up and down along the central opening 8 . Before the plasma arc furnace is started, the positioning rod 16 is lowered, and the stepping motor 12 transports the electrode 6 to the furnace body until the electrode 6 contacts the positioning rod 16 (as shown in Figure 3), and the positioning of the electrode is completed, and the sensor provides Signal that positioning is complete. After the plasma arc furnace is started, the initial arc is formed between the electrode 6 and the positioning rod 16, and then the positioning rod 16 is lifted under the control of the motor, and the arc is gradually transferred between the electrodes 6 as the positioning rod 16 rises.

Claims (12)

1, a kind of using plasma arc technology is handled the method for hazardous waste, it is characterized in that, comprises that order is carried out according to the following steps:

(1) pending solid waste is carried out pretreatment procedure and intermittently or add in the plasma arc furnace continuously by conveying system;

(2) carry out cracking in plasma arc furnace and handle, wherein the working gas handled of cracking is reducibility gas or other gas, and the oxygen content in the working gas and the ratio of the oxygen demand of refuse complete reaction are less than 0.3, and the cracking treatment temperature is 1200K-3500K;

(3) gas of discharging after the plasma arc furnace cracking enters exhaust treatment system, through conventional tail cold cooling out of breath, purification, sour gas handle, the particulate separation treatment process;

(4) step (3) separated particulate material and gas are reclaimed respectively.

2, using plasma arc technology according to claim 1 is handled the method for hazardous waste, it is characterized in that, described pretreatment procedure comprises pending solid waste is carried out conventional fragmentation and/or gasifying process.

3, using plasma arc technology according to claim 1 is handled the method for hazardous waste, it is characterized in that described other gas comprises: inert gas or steam.

4, using plasma arc technology according to claim 1 is handled the method for hazardous waste, it is characterized in that, also be included in when gas enters exhaust treatment system in the step (3), add the alkaline matter that is used for the tail gas middle acid substance, this alkaline matter comprises: calcium oxide, NaOH or potassium hydroxide.

5, using plasma arc technology according to claim 1 is handled the method for hazardous waste, it is characterized in that, also be included in to add in the step (2) and be used to generate Vitrea silicon compound, calcium compound, sodium compound, iron and metal oxide in plasma arc furnace, its weight portion is: 20～40 parts of silicon compounds, 30～50 parts of calcium sodium compounds, 20～40 parts of iron and metal oxides.

6, using plasma arc technology according to claim 1 is handled the method for hazardous waste, it is characterized in that described silicon compound is a silicon dioxide; Described calcium compound is a calcium carbonate; Described sodium compound is a sodium carbonate; Described iron and metal oxide comprise: di-iron trioxide, tri-iron tetroxide, metal iron block, aluminium block or sheet.

7, the special-purpose plasma arc furnace of the described method of a kind of claim 1 comprises a body of heater, and this furnace body inside is provided with refractory material, heat-barrier material lining and cooling jacket, and body of heater is provided with feeding mouth, gas discharge outlet and waste material outlet; The body of heater top is provided with the working gas import; Bottom of furnace body is provided with crucible; At least two electrode oblique cuttings that are connected with power supply are at the body of heater top; It is characterized in that, also comprise a starting the arc positioner that is used for described at least two electrode is carried out the positioning of electrode and the auxiliary starting the arc.

8, plasma arc furnace according to claim 7, it is characterized in that, described starting the arc positioner comprises backstay and is used for the stepping motor of drive electrode, described backstay is inserted in the perforate on the body of heater, and can move radially along this perforate, described backstay contacts with electrode during with the auxiliary starting the arc at positioning of electrode, and after the starting the arc away from electrode.

9, plasma arc furnace according to claim 8 is characterized in that, described backstay is provided with transducer.

10, plasma arc furnace according to claim 7 is characterized in that, the bottom of burner hearth is provided with crucible, is provided with heat shield between crucible and stove inwall.

11, plasma arc furnace according to claim 7 is characterized in that, the described power supply that is connected with electrode is AC power or DC power supply.

12, using plasma arc technology according to claim 1 is handled the method for hazardous waste, it is characterized in that, described plasma arc furnace adopts and exchanges or DC power supply.

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