Method and device for producing activated carbon

Abstract

The invention relates to a method for preparing activated carbon from wastes in grain processing and wood industry. The method comprises the following steps: performing extrusion treatment on the wastes, granulating the wastes to obtain particles, drying, conveying the particles to the lower part of a carbonization furnace through a horizontal screw conveyor, and heating, and separating the mixture of the gas and the coke into coke and pyrolysis gas in a cyclone separator, conveying the coke to the lower part of a hot steam activation furnace, heating to 700-900 DEG C to obtain activated carbon, cooling the activated carbon to 30-40 DEG C, and packaging. The technical result is obtaining activated carbon having high porosity and a larger adsorption surface area, while reducing energy consumption and increasing the efficiency of a carbonization furnace and an activation furnace.

Description

[0001] The invention relates to a method for the thermal treatment of bulk organic waste, such as waste from the grain processing industry (buckwheat, sunflower, rice, straw, etc.) and waste from the forestry industry (wood chips) and the preparation of activated carbon with an increased adsorption surface. All the listed materials have a similar chemical composition: lignin 20-35%, cellulose 30-50%, so the method and equipment for processing these materials into high-strength granules are the same.

[0002] Methods and devices for processing organic matter and waste are known from the prior art.

[0003] From the description of patent RU2749665Cl (published on June 16, 2021), a method for pyrolysis of organic matter and waste is known, which comprises the following steps: the raw material with a fraction size of 1-5 mm and a humidity of 4-12% is supplied in each step by a screw conveyor equipped with a variable frequency drive into a vertical reactor, which comprises a shell sewn from metal plates, which are in contact with the flue gases and pyrolysis products at the same time, and comprises a rotor with blades arranged at the same pitch from the bottom to the top. By the rotational movement of the blades, the raw material moves from bottom to top, passing through a chamber heated to 750-850 ° C, where it is decomposed into char and gas components. Further, the coke is mixed with gas and conveyed to the upper part of the reactor heated to 980-1000°C, i.e. the cracking zone. The residence time of the mixture in the cracking zone is 0.5-1.5 seconds. After that, the gas mixture enters cooling and purification through a pipeline before further use. The coke is conveyed downward along the storage through the discharge port by gravity to a screw conveyor equipped with a water jacket and installed at an angle of 45° to the horizontal plane, and then discharged into the storage hopper.

[0004] The main disadvantages of this method are:

[0005] The extracted coke is totally unsuitable for obtaining activated carbon due to the complete absence of volatiles and carbon sintering, and the high temperature is not sufficient to open the pores during activation;

[0006] Using stitched reactor bodies to increase heat transfer while contacting heat elements with the combustion chamber gases and products inside the reactor increases both surfaces by 40%, which cannot be increased further;

[0007] Since the flue gas moves from top to bottom, the heat loss is large, the fuel consumption is too large, and the temperature difference between the furnace inlet and outlet gases does not exceed 150°C.

[0008] Furthermore, from the description of patent RU2721696Cl (published on May 21, 2020), a method and device for preparing activated carbon from coal residues obtained after a thermochemical pyrolysis process when processing organic raw materials in a pyrolysis device are known. A method for processing carbon material, comprising the following steps: supplying the carbon material to the inlet of an activation chamber with blades by means of a horizontal screw conveyor, the blades moving the carbon material to a steam activation zone under the action of steam, steam at a temperature of 900-1000°C is delivered by nozzles at the bottom of the steam activation chamber at a pressure of 5 to 20 bar, and through a rotating rotor with blades, the carbon material moves to the top of the steam activation chamber, from which the loose carbon material descends through a gravity pipe to the inlet of a screw conveyor cooled by a water jacket, the screw conveyor being mounted in such a way that the material moves from bottom to top at an angle of 28-32° to the horizontal, after cooling to 30-50°C, the activated carbon material is conveyed to the outlet of the spiral cooling screw conveyor and supplied to a storage hopper.

[0009] The main disadvantages of this solution are:

[0010] Since the steam superheater is located in a separate shell, heat losses increase and there are technical difficulties in operating the device to transport superheated steam at 1000°C;

[0011] The process is inefficient because the reactor shell is heated by superheated steam as a transport link, which results in significant losses of water and fuel.

[0012] Due to the imperfect heating surface of the reactor shell, the inefficient use of superheated steam, water and fuel leads to a low heating efficiency of the coke in the activator.

[0013] From the description of patent RU 2776051 (published on July 12, 2022), a method for preparing activated carbon from food processing industry waste is known, which includes carbonization and activation, and the carbonization and activation are carried out simultaneously in a sealed volume without the entry of oxygen. The carbon product is activated by evaporating water in the raw material flowing to the side of the space zone where the hot carbon is formed due to the pyrolysis zone. At all stages of the process, continuous forced movement and mixing of the material are carried out.

[0014] The main disadvantage of the known methods is that activated carbon cannot be obtained under the conditions described due to insufficient steam. For example, 4 to 6 kg of steam are required for activation in a horizontal reactor per 1 kg of activated carbon, 2 to 4 kg of steam are required in a vertical reactor, and in the known methods the internal moisture of the grain processing waste is used, i.e. a maximum of 0.3 kg of steam per kg of coal, and activation cannot be achieved at such ratios.

[0015] At the same time, in the case of combined reactors, the consumption of superheated steam increases threefold, since, first of all, the volatile substances, whose volume in the cereal waste exceeds 70%, are cracked, and only then does the solid carbon activation occur. The steam consumption of the combined vertical reactor is 6-12 kg of steam per kg of activated carbon.

[0016] These conclusions are based on the experiments performed and the laws of chemistry.

[0017] The technical problem solved by the present invention is to develop a method and a device that ensure the use of a new and more economical technology to obtain shaped activated carbon with given properties from cereal processing and forestry waste (including buckwheat husks).

[0018] The technical result achieved by the solution described is that it is possible to obtain shaped activated carbon with given properties, namely high strength, given shape and size, increased adsorption surface of the carbon, increased efficiency of the process and reduced energy consumption compared to known methods.

[0019] The technical achievement is achieved by implementing a method for producing activated carbon from food processing and forestry waste, comprising the following steps:

[0020] The waste is squeezed into a powder with a dispersion of 1-3 mm and a moisture content of 11-16%.

[0021] Then, the crushed waste is fed into a granulator, and high-strength whole granules with a diameter of 4-8 mm and a density of 500-750 g / l are obtained at its outlet.

[0022] The granules are then dried at a temperature of 120-180°C to a humidity of 3-7%;

[0023] Then, the waste is moved to the lower part of the carbonization furnace by a horizontal screw conveyor. In the carbonization furnace, the raw materials are moved upward by the horizontal screw conveyor and the pressurization generated by the pyrolysis airflow released from the raw materials. In the absence of oxygen, the raw materials are heated to 300-850℃ due to the direct contact between the inner wall of the carbonization furnace and the vertical plates in its shell. The 650-850℃ temperature airflow passes up and down along the multi-turn spiral in the plate fin space, thereby removing 60-80% of the volatile substances.

[0024] The mixture of gas and coke is sent from the activation furnace to the cyclone separator, where it is separated into coke and pyrolysis gas.

[0025] The coke is fed into the lower part of the hot steam furnace by a horizontal screw conveyor. Since the inner wall of the activation furnace and the vertical plates in its shell are in direct contact with the steam superheated to 1000°C, the coke is heated to 700-900°C. At the same time, the coke moves upward from the center of the shaft to the outer wall of the furnace, and returns to the center of the free space due to the pressure increase caused by the horizontal screw conveyor and the superheated steam flow supplied to the bottom of the inner space of the steam superheater activation furnace, while removing the remaining volatiles and opening the pores to obtain activated carbon.

[0026] The activated carbon is cooled to 30°-40°C and sent for packaging.

[0027] Grain and / or sawdust, and fuel pellets made from grain and / or sawdust are used as waste from grain processing and wood industry.

[0028] The hardness of the shaped activated carbon is determined in the pretreatment (extrusion) stage, whereby two densities of shaped particles can be obtained at this stage - high density (620-750 g / L) and medium density (500-600 g / L).

[0029] To improve the efficiency of the method and reduce energy consumption:

[0030] The pyrolysis gas after the cyclone separator is sent to the burner for combustion. The flue gas produced by the combustion of the pyrolysis gas is used in the entire thermal process in sequence - steam superheating, carbonization, activation and drying of raw materials;

[0031] The exhaust gas discharged from the cyclone separator after the activation furnace is sent to the furnace of the steam boiler to burn all the gas and other activation products therein and make full use of the heat energy. This will reduce fuel consumption by nearly 50%.

[0032] In particular, in order to reduce energy consumption, the waste gas of the carbonization furnace is used to dry the raw materials. In order to heat the carbonization furnace raw materials, the waste gas of 650℃-850℃ of the activation furnace is used. In the drying, carbonization, activation and steam superheating stages, the flue gas generated by burning the pyrolysis gas released by the carbonization furnace in the burner is used.

[0033] In addition, in order to reduce the heat loss caused by the flow of combustion gas and superheated steam, a steam superheater is installed above the activation furnace to heat the steam to 950-1000℃.

[0034] If nut shells and kernels are used as waste, then granular activated carbon is obtained from them, in the first stage, before drying, they are crushed to 3-5 mm, then the process is the same as in the above method.

[0035] Furthermore, technical results were achieved when using an apparatus for producing activated carbon from waste from food processing and forestry industries, the apparatus consisting of hoppers connected in series, an extruder with variable pressure, a granulator with variable particle size and density, a dryer connected to the bottom of a carbonizing furnace via a horizontal screw conveyor, connected to a cyclone separator for separating coke from pyrolysis gases, a horizontal screw conveyor for feeding the coke into an activation furnace, a cyclone separator installed behind the activation furnace for separating steam from activated carbon, and an activated carbon cooling device connected to an activated carbon packaging hopper.

[0036] To improve installation efficiency and reduce energy consumption:

[0037] The carbonizing furnace and the activation furnace include a shaft with blades to ensure uniform mixing and upward movement of the raw materials, the shaft is located in the shell and can rotate, the outer surfaces of the carbonizing furnace and the activation furnace are both plate fins in the form of multiple turns of spirals from top to bottom, and the inner surfaces of the carbonizing furnace and the activation furnace are covered with vertically placed plates, which have gaps along the shell radius of the carbonizing furnace and the activation furnace for the vertical shaft blades to pass through;

[0038] A cyclone separator for separating coke from the pyrolysis gas is connected to a burner for burning the pyrolysis gas;

[0039] The apparatus also includes a steam superheater mounted in a housing directly above the activation furnace.

[0040] In order to reduce the pressure of the pyrolysis gas in the carbonization furnace and the steam pressure in the activation furnace to atmospheric pressure (0.1 bar), the cross-section of the steam and gas pipes is large and selected according to the performance of the device. This will avoid the use of gas filling equipment and gates.

[0041] If nut shells and fruit shells are used as waste, install a pulverizer before the dryer instead of the extruder and granulator.

[0042] By implementing the method of producing activated carbon from food processing and forestry waste, energy and fuel consumption are significantly reduced, which is achieved by effectively using the heat released during the pyrolysis of gases and steam, by increasing the inner and outer surfaces of the carbonization furnace and the activation furnace, because the increased outer surface transfers more heat energy to the inner surface and plates of the furnace, ensuring the enthalpy of the superheated steam in the furnace, at the same time, the multi-turn spiral of the carbonization furnace and the activation furnace increases the outer heat transfer surface three times and ensures that the flue gas moves from top to bottom along the spiral, thereby increasing the contact time of the flue gas with the furnace and the maximum heat transfer of the furnace flue gas, the vertical plate doubles the inner (ablation) surface of the furnace and ensures the maximum heat transfer from the spiral plate located on the outer surface of the furnace to the processed material in the furnace to the space between the furnace lining and the furnace body. In addition, due to the countercurrent movement of the raw materials to be treated in the carbonization furnace and the activation furnace and the air flow used for heating, the carbonization and activation time is reduced, thereby improving the effectiveness coefficient. In this case, the pyrolysis gases released in the carbonization furnace and the superheated steam in the activation furnace move in the same direction as the raw materials, which accelerates the movement of the raw materials in the furnace and ensures high efficiency of the pyrolysis gases and steam for additional heating, which also ensures high efficiency of the device, accelerates the start of the carbon activation reaction, and correspondingly shortens the time to obtain the final product without losing its quality.

[0043] Further, the solution is explained by the example of processing buckwheat husks into shaped activated carbon, which example does not limit the patented solution, as the parameters described for buckwheat husks will apply to the processing of all other claimed crops.

[0044] In the first step of buckwheat husk processing, it is fed into an extruder, where it is deformed to a given dispersion (particle size 1-3 mm) and humidity 11-16%, depending on the requirements for the activated carbon variety. After extrusion, the treated material is fed into a granulator and pressed into high-hardness granules with activated carbon quality of 500-600 g / L with charcoal parameters and activated carbon quality of 750 g / L with bituminous coal indicators.

[0045] In the second step, the solid particles are fed into a carbonization furnace where they undergo an ablation-pyrolysis process.

[0046] In the third step, the coke obtained is fed into an activation furnace.

[0047] In the fourth step, the activated carbon is cooled and sent to the hopper for packaging.

[0048] Furthermore, the present invention is explained in detail with reference to the accompanying drawings, which show a process flow chart of a buckwheat hull processing device under the method.

[0049] As shown in the figure, buckwheat husks are loaded into a hopper 1 and sent from the hopper to an extruder 2. Under the action of a pressure of 3-4 MPa, the temperature in the extruder rises to 120-180°C, and the buckwheat husks are extruded and ground to 1-3 mm and 11-16% humidity. The dispersibility of the powder is adjusted by the speed of the extruder shaft, and the particle density and integrity depend on the degree of grinding of the buckwheat husks in the extruder. Then, the extruded powder enters a granulator 3 and is granulated under a pressure of 3-4 MPa. At the outlet of the granulator, particles with a diameter of 4-8 mm are obtained according to the size of the established mold and the given size to obtain activated carbon. Then, the particles are sent to a carbonization furnace 6. The waste flue gas is heated and diluted to 130°C in the conveyor dryer 4. The particles in the dryer 4 are dried to 3-7% humidity and sent to the bottom of the lower carbonization furnace 6 through the screw conveyor 5. Then, under the action of the vertical shaft blades of the carbonization furnace 6, the particles move from the axis center to the outer wall of the furnace, and return to the center of the free space under the pressure generated by the screw conveyor 5. The entire stirring layer moves upward, and this movement is enhanced by the pyrolysis airflow released from the particles. The waste gas discharged from the activation furnace 9 with a temperature of 650°-850°C enters the flue at the top of the carbonization furnace 6, and passes through the furnace plate fin space limited by the large furnace wall from top to bottom along the multi-turn spiral. This design ensures that the flue gas temperature difference between the furnace inlet and outlet is 350°C, and the waste gas with a temperature of 300-400°C is discharged from the carbonization furnace 6 through the flue located at the bottom. The heat energy of the furnace gas transferred to the furnace shell with plate fins is transferred to the particles by ablation (through contact with the inner wall of the furnace and the vertical plates located in the furnace shell), thus ensuring that the particles are uniformly heated to a temperature of 550°-700°C in the furnace shell. In this case, the uniform heating and simultaneous mixing of the particles lead to the active release of volatiles (pyrolysis process occurs), while the presence of free oxygen in the volatile components ensures the passage of the exothermic reaction, significantly reducing the energy consumption in the carbonization furnace 6. Passing through the entire furnace body from bottom to top, 60-70% of the particles are released from the volatiles and converted into formed coke (hereinafter referred to as coke), which enters the cyclone separator 7 at a temperature of 550-700°C, where it is separated into pyrolysis gas and coke. The pyrolysis gas of the cyclone separator 7 enters the burner 13 through the insulated gas duct. The furnace gas with a temperature of 1050-1150°C from the burner 13 enters the upper flue of the activation furnace 9, passes through the steam superheater 16 to raise the steam temperature from 200°C to 950-1000°C, and then passes from top to bottom along the multi-turn spiral of the plate fins of the activation furnace 9 with a large furnace wall, ensuring that the furnace gas temperature difference between the furnace inlet and outlet is 350°C. The waste furnace gas with a temperature of 800°C-650°C is discharged from the activation furnace through the flue located at the bottom of the activation furnace 9.

[0050] The coke from the cyclone separator 7 is supplied to the lower part of the activation furnace 9 through the horizontal screw conveyor 8. At the bottom of the activation furnace, the coke moves from the center of the shaft to the outer wall of the furnace under the action of the blades of the vertical shaft, and returns to the center to the free space. When there is a pressure increase generated by the horizontal screw conveyor 8, the entire stirring layer moves upward, and this movement is enhanced by the superheated steam flow entering the manifold 17 from the steam superheater 16 just above the furnace 9. The superheated steam enters the inner space of the activation furnace 9 from the manifold 17 through the disperser 18. On the basis of the indication of the flow meter 15, the steam consumption is adjusted according to the specified parameters of the activated carbon, that is, when the steam consumption is increased to 4 kg per 1 kg of carbon, the adsorption surface area increases to 1100 square meters / gram, but the strength of the carbon decreases to 45%, and when the steam consumption is reduced to 2 kg per 1 kg of carbon, the strength reaches 90% and the surface area decreases to 500 square meters / gram. Through direct contact between the inner wall of the activation furnace 9 and the vertical plates in its shell, the heat energy transferred by the furnace gas to the furnace shell with plate fins is transferred to the coke and steam in a burning manner, whereby the coke in the furnace body is heated to a temperature of 700-900°C transferred by the furnace wall and water vapor superheated to 1000°C, and volatile residues are removed and pores are opened, and the carbon material acquires a high adsorption capacity.

[0051] Thus, the activation process is more efficient and the activation process time is reduced by half by heating the coke from the inner shell, the furnace itself and the superheated steam. In this case, the temperature (enthalpy) of the steam is kept at the same level throughout the activator volume due to its contact with the plates and the outer shell.

[0052] Further, the mixture of steam and activated carbon is separated in the cyclone separator 10. The exhausted steam is conveyed to the furnace of the steam boiler 14 for calcining and burning all gases and other activation products therein, thereby reducing the fuel consumption in the steam boiler 14 by 50%, improving the boiler efficiency factor, and reducing CO2 emissions by reducing fuel consumption.

[0053] The shaped activated carbon from the cyclone separator 10 is conveyed to a screw conveyor 11 with a water-cooling jacket, cooled to 30° C.-40° C., and then sent to a hopper 12 for packaging.

[0054] In order to prepare carbon having the characteristics of biological activated carbon with high porosity of 1200 m2 / g and low strength (not exceeding 55%), particles with a bulk density of 500-600 g / l are produced by reducing the pressure in the extruder, which is achieved by reducing the rotation speed of the extruder shaft, and in order to obtain AR, SK-AG grade coal, when the rotation speed of the extruder shaft is increased to the nominal value, the pressure in the extruder is increased to the maximum value, the bulk density of the particles is 620-750 g / l, and the activated carbon obtained from such particles has a porosity of 700 m2 / g and a strength of more than 90%.

[0055] Thus, the use of the patented method and the device for implementing the method makes it possible to produce high-strength pellets made from grain processing and forestry waste, as well as to process organic waste fuel pellets into activated carbon.

[0056] Furthermore, since pellets are easy to transport, while shells with a mass of 140 g / l are difficult to transport, i.e. a 20 ton vehicle can only transport a maximum of 5 tonnes of shells, the proposed solution allows the production activities to be carried out anywhere, without being restricted to the origin of the raw materials.

Claims

1. A method for producing activated carbon from food processing and forestry waste, characterized in that The properties of activated carbon are controlled during the production of shaped granules through the following stages: The waste is squeezed into powder with a dispersion of 1-3 mm and a humidity of 11-16%. Then, the crushed waste is fed into a granulator, and high-strength monolithic granules with a diameter of 4-8 mm and a density of 500-750 g / l are obtained at its outlet. After this, the granules are dried at a temperature of 120-180°C to a humidity of 3-7%; Then, the waste is moved to the lower part of the carbonization furnace by a horizontal screw conveyor, in which the raw material is moved upward by the pressurized gas flow generated by the horizontal screw conveyor and the pyrolysis gas flow released from the raw material, and the raw material is heated to a temperature of 300-850°C by direct contact between the inner wall of the carbonization furnace and the vertical plate in its shell without the entry of oxygen, and with the help of a gas flow of 650-850°C, it passes from top to bottom along the multi-turn spiral in the plate fin space of the carbonization furnace, with the aim of removing 60-80% of volatile substances, The mixture of gas and coke is supplied from the carbonization furnace to the cyclone separator, where it is separated into coke and pyrolysis gas. With the help of a horizontal screw conveyor, the coke is conveyed to the bottom of a hot steam-gas activated furnace, and is heated to 700-900°C in the activated furnace through direct contact with steam superheated to 1000°C on the inner wall of the activated furnace and the vertical plates in its shell, and is moved from the center of the shaft upward to the outer wall of the furnace and back to the center of the free space by the superheated steam flow supplied to the bottom of the inner space of the activated furnace by the pressure increase generated by the horizontal screw conveyor and the steam superheater, thereby removing volatile residues and opening the pores to obtain activated carbon, The activated carbon is cooled to 30-40°C and sent for packaging.

2. The method according to claim 1, characterized in that The waste used is rice husks and / or sawdust, and fuel pellets made from the rice husks and / or sawdust.

3. The method according to claim 1, characterized in that After the cyclone separator, the pyrolysis gases are sent to the burner for combustion.

4. The method according to claim 3, characterized in that The flue gas produced by the combustion of pyrolysis gases is used in the entire thermal process in sequence, namely steam superheating, carbonization, activation, and raw material drying.

5. The method according to claim 1, characterized in that: The waste steam from the cyclone separator installed after the activation furnace is sent to the furnace of the steam boiler to burn all the gases and other activation products therein and make full use of the thermal energy.

6. A device for producing activated carbon from food processing and forestry waste, characterized in that It consists of hoppers connected in series, an extruder with variable pressure, a granulator with variable particle size and density, a dryer connected to the bottom of the carbonization furnace through a horizontal screw conveyor, connected to a cyclone separator that separates the coke from the pyrolysis gases, a horizontal screw conveyor for feeding the coke into the activation furnace, a cyclone separator installed behind the activation furnace, An activated carbon cooling device connected to the activated carbon packaging hopper is used to separate steam from the activated carbon.

7. The device according to claim 6, characterized in that The carbonization furnace and the activation furnace comprise a shaft with blades, which ensure uniform mixing and upward movement of the raw materials, and the shaft is located in a housing and is rotatable.

8. The device according to claim 6, characterized in that The outer surface of the carbonization furnace and the activation furnace is made of plate fins in the form of multiple turns of spirals from top to bottom.

9. The device according to claim 8, characterized in that The inner surfaces of the carbonization furnace and the activation furnace are covered with vertically arranged plates having gaps along the radius of the carbonization furnace and the activation furnace body for the vertical axis blades to pass through.

10. The device according to claim 6, characterized in that The cyclone separator for separating coke from the pyrolysis gas is connected to a burner for burning the pyrolysis gas.

11. The device according to claim 6, characterized in that It also includes a steam superheater installed on the integral shell just above the activation furnace.

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