A method and apparatus for rapid drying of activated carbon

Abstract

This invention discloses a method and apparatus for rapid drying of activated carbon. Utilizing a stirrer, the resistivity of the activated carbon particles within the drying furnace is effectively reduced. Furthermore, the collisions and friction between the activated carbon particles remove surface impurities, enhance conductivity, and generate numerous electric arcs. These arcs further promote current flow between the activated carbon particles, reducing their apparent resistivity and accelerating heat and mass transfer during the drying process. This invention also provides a feasible condition for drying activated carbon using low voltage, significantly reducing energy consumption. The invention constructs a regional arc-starting voltage calculation model adaptable to different activated carbon properties and drying furnace shapes, providing accurate guidance on the minimum voltage required to generate a stable arc at the start of drying. Under the coordinated action of stirrer operation, fan drive, and a DC voltage input to the two electrode plates that is greater than but less than 1.5 times the regional arc-starting voltage, the drying time of activated carbon is greatly shortened, and the drying efficiency is improved.

Description

Technical Field

[0001] This invention belongs to the field of activated carbon drying technology, specifically relating to a method and apparatus for rapid drying of activated carbon. Background Technology

[0002] Activated carbon, as one of the most common adsorbents in water treatment, often contains a large amount of moisture on its surface and in its pores. During regeneration, this moisture must be removed first. Natural air drying is not only affected by weather conditions but also requires a significant amount of time. For large-scale production of activated carbon, this requires a large area and a large workforce. Traditional industrial methods use high-temperature flue gas from natural gas combustion or heat generated by resistance heating to heat the activated carbon. The former is an indirect heating method, generating a large amount of waste gas and consuming a lot of energy, as seen in various types of hot air drying equipment and fluidized bed drying equipment. The latter, based on heat generated by resistance heating, heats the activated carbon particles through heated pipes or a shell, and then through heat conduction and radiation, as seen in rotary drying equipment. However, this method also suffers from multiple heat transfer stages and high heat loss during the heat and mass transfer process. Furthermore, both methods involve heating the activated carbon particles from the outside in, requiring a long time to evaporate the moisture from the pores, resulting in low production efficiency.

[0003] In addition, some literature proposes utilizing the electrical conductivity of activated carbon to directly heat and dry static activated carbon electrothermally, causing the activated carbon to spontaneously heat up to 800-900 degrees Celsius, thereby completing the drying and regeneration of saturated activated carbon. However, this method has the following two problems: 1. Because activated carbon adsorbs a large amount of organic matter, static activated carbon has a high resistance, almost like an insulator, requiring several thousand or even tens of thousands of volts of high voltage to break it down. This is not only dangerous, but also because the breakdown arc of the corresponding high voltage short circuit can only achieve localized electric heating, the temperature is difficult to control and the heating is not uniform (see Table 1). 2. Placing drying and regeneration together can easily cause water vapor to react with activated carbon to produce water gas, generating large amounts of H2 and CO, which may even lead to an explosion in severe cases.

[0004] In conclusion, current activated carbon drying methods cannot achieve rapid, uniform, and low-energy drying of activated carbon. Summary of the Invention

[0005] This invention addresses the problems of low and uneven drying efficiency of activated carbon in existing technologies, as well as uneven regeneration, H2 and CO pollution, and even explosions when directly regenerating activated carbon with excessive moisture using high-voltage electricity. It provides a method and apparatus for rapid drying of activated carbon.

[0006] This invention discloses a method for rapid drying of activated carbon, as detailed below:

[0007] Step 1: Input the activated carbon with the surface moisture removed into the drying furnace until the activated carbon is higher than the two electrode plates that are directly opposite each other and spaced apart inside the drying furnace.

[0008] Step 2: Connect the two electrode plates to the positive and negative terminals of the DC power supply respectively; start the fan connecting the exhaust vent at the top of the drying furnace to the exhaust gas treatment device, and start the stirrer inside the drying furnace; turn on the DC power supply and input a DC voltage greater than U and less than 1.5U to the two electrode plates, where U is the regional arc ignition voltage. The formula for calculating the regional arc ignition voltage U is as follows:

[0009]

[0010] Where C1 is the specific heat capacity of activated carbon, C2 is the specific heat capacity of water, and ρ m ρ is the packing density of activated carbon. 水 Where ρ is the density of water, T0 is the current temperature of the activated carbon before drying, ρ is the resistivity of the activated carbon at the current temperature, n is the initial moisture content of the activated carbon before drying, D is the diameter of the drying furnace, ω is the angular velocity of the stirrer, and the proportionality coefficient η ranges from 0.3 to 1.

[0011] Step 3: Activated carbon generates Joule heat under the DC voltage applied to the electrode plates. Stirred by the agitator, the activated carbon rotates, reducing the overall resistance of all activated carbon within the drying furnace. The agitator ensures uniform heating and also causes collisions and friction between adjacent activated carbon particles, removing impurities from their surface, enhancing conductivity, and promoting the formation of electric arcs between adjacent activated carbon particles. These arcs further promote current flow between the activated carbon particles, ultimately desorbing the adsorbed moisture. The desorbed moisture is then discharged from the furnace's exhaust vent by the fan, flowing into the exhaust gas treatment device to remove impurities before being released into the atmosphere. The coordinated action of the agitator, the fan, and the DC voltage input to the two electrode plates (greater than U and less than 1.5U) shortens the activated carbon drying time.

[0012] Step 4: After reaching the target drying temperature and maintaining it for the set time, the activated carbon drying is complete. Turn off the DC power and the stirrer, and let the dried activated carbon flow out from the activated carbon outlet at the bottom of the drying furnace.

[0013] Preferably, the drying time is shortened by increasing the angular velocity of the stirrer, which increases the regional arc ignition voltage and the DC voltage value.

[0014] Preferably, during the drying process, after successful arc ignition, the angular velocity of the stirrer is adjusted according to the humidity in the pipe connecting the exhaust port at the top of the drying furnace and the fan. The angular velocity of the stirrer increases as the humidity in the pipe increases; wherein, a humidity sensor is installed on the pipe.

[0015] More preferably, the angular velocity of the stirrer first increases and then decreases, and the range of the angular velocity of the stirrer is 0.2 to 0.7 rad / s.

[0016] Preferably, the DC voltage input to the DC power supply box is in the range of 50 to 200V.

[0017] Preferably, the target drying temperature is set to 120–200°C.

[0018] This invention discloses a rapid activated carbon drying device, comprising a silo, a primary valve, a conveying pipe, a stirrer, a fan, a drying furnace body, electrode plates, a temperature sensor, a secondary valve, and a tail gas treatment device. The activated carbon outlet of the silo is connected to the activated carbon inlet at the top of the drying furnace body via the conveying pipe, and a primary valve and a flow meter are installed at the activated carbon outlet of the silo; a secondary valve is installed at the activated carbon outlet at the bottom of the drying furnace body; two electrode plates are fixed to the inner wall of the drying furnace body, facing each other and spaced apart; the terminals connected to the electrode plates extend outside the drying furnace body; the exhaust vent at the top of the drying furnace body is connected to the tail gas treatment device via the fan; the stirrer is fixed inside the drying furnace body and positioned between the two electrode plates; a temperature sensor is installed on the stirrer.

[0019] Preferably, the agitator is a screw agitator, and the lead of the screw is 0.5 to 1 cm.

[0020] Preferably, the diameter to height ratio of the drying furnace body is 1:0.5 to 1.

[0021] Preferably, the electrode plate is arc-shaped.

[0022] The beneficial effects of this invention are:

[0023] 1. This invention utilizes the electrical conductivity of activated carbon. By inputting a low voltage into the drying furnace, the activated carbon, which is forced to rotate, becomes conductive, generating Joule heat and electric arc heating. Under the action of Joule heat and electric arc heat release between carbon particles, the activated carbon can be dried quickly, reducing the energy consumption during the drying process.

[0024] 2. This invention utilizes a screw-type agitator to not only rotate the activated carbon, effectively reducing the overall resistance of all activated carbon within the drying furnace, but also to facilitate collisions and friction between activated carbon particles. This removes impurities from the activated carbon surface, enhances its conductivity, and generates numerous electric arcs. These arcs further promote current flow between the activated carbon particles, and the heat generated accelerates the drying efficiency, reduces the apparent resistance, and facilitates the rapid escape of water vapor generated inside the activated carbon. This accelerates heat and mass transfer during the drying process and creates feasible conditions for low-voltage drying of activated carbon, significantly reducing energy consumption. Furthermore, the screw-type agitator allows the activated carbon to undergo an upward throwing motion, enabling the desorbed water vapor to exit the drying furnace more quickly. Simultaneously, the agitation prevents the accumulation of activated carbon, ensuring uniform heating and guaranteeing effective drying, thus improving the drying efficiency.

[0025] 3. This invention achieves rapid moisture removal from activated carbon through Joule heating and an electric arc. The generation of the electric arc and the Joule heating of the activated carbon itself are related to its moisture content, resistivity, packing density, movement speed, the shape of the drying furnace, and the voltage of the applied DC power supply. Based on the shape of the drying furnace, the moisture content, resistivity, and packing density of the activated carbon, and by inducing movement of the static activated carbon (i.e., introducing an activated carbon movement parameter), a regional arc-ignition voltage calculation model is constructed to adapt to different activated carbon properties and drying furnace shapes. This provides accurate guidance on the minimum voltage required to generate a stable arc at the beginning of drying, thus reducing energy consumption. Furthermore, this invention significantly shortens the drying time of activated carbon and improves drying efficiency through the coordinated action of agitator stirring, fan drive, and a DC voltage input to two electrode plates that is greater than but less than 1.5 times the regional arc-ignition voltage.

[0026] 4. In the process of drying activated carbon, the electric arc generated by the activated carbon particle group can effectively decompose some of the low-boiling-point harmful gases desorbed from the activated carbon, thus avoiding the emission of harmful gases. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the activated carbon rapid drying device of the present invention.

[0028] Figure 2 This is the external shape and AA cross-sectional view of the drying furnace body in this invention.

[0029] Figure 3 The graph shows a comparison of the resistivity of coconut shell activated carbon particles and coal-based activated carbon particles under static and dynamic states with moisture content at a stirring angular velocity of 0.3 rad / s.

[0030] Figure 4 This is a graph showing the resistivity of coconut shell activated carbon particles as a function of stirring angular velocity. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and specific examples.

[0032] like Figure 1 and Figure 2 As shown, a rapid activated carbon drying device includes a hopper 1, a first valve 2, a conveying pipe 3, a stirrer 4, a fan 6, a drying furnace body 7, electrode plates 8, a temperature sensor 10, a second valve 11, and a tail gas treatment device 13. The activated carbon outlet of the hopper 1 is connected to the activated carbon inlet at the top of the drying furnace body 7 via the conveying pipe 3, and the activated carbon outlet of the hopper 1 is equipped with a first valve 2 and a flow meter; the activated carbon outlet at the bottom of the drying furnace body 7 is equipped with a second valve 11; two electrode plates 8 are fixed to the inner wall of the drying furnace body 7, facing each other and spaced apart; the terminals 9 connected to the electrode plates 8 extend outside the drying furnace body 7; the exhaust port 5 at the top of the drying furnace body 7 is connected to the tail gas treatment device 13 via the fan 6; the stirrer 4 is fixed inside the drying furnace body 7 and placed between the two electrode plates 8; the stirrer 4 is equipped with a temperature sensor 10 (preferably an NTC temperature sensor) for detecting the temperature of the activated carbon inside the drying furnace body 7. The temperature sensor 10 communicates wirelessly with a host computer.

[0033] The activated carbon drying method of this rapid activated carbon drying device is as follows:

[0034] Step 1: Close valve 11 (second valve) and open valve 2 (first valve). Place the activated carbon (after removing surface moisture) into hopper 1. The activated carbon in hopper 1 flows into the drying furnace 7 through conveying pipe 3 until the activated carbon is higher than the electrode plate 8. Then close valve 2. The flow rate of the activated carbon in conveying pipe 3 is measured by a flow meter to determine the volume of activated carbon entering the drying furnace 7. Combined with the volume of activated carbon in the drying furnace 7 at the height of the electrode plate 8, it can be determined whether the activated carbon is higher than the electrode plate 8.

[0035] Step 2: Connect the terminals 9 of the two electrode plates 8 to the positive and negative terminals of the DC power supply 12 respectively; start the fan 6 and stirrer 4, turn on the DC power supply 12, and input a DC voltage greater than U and less than 1.5U to the two electrode plates, where U is the regional arc ignition voltage. When the target drying temperature is high (greater than or equal to 100℃), the DC voltage is the higher value (greater than or equal to 1.3U) between U and 1.5U. When the target drying temperature is low (less than 100℃), the DC voltage is the lower value (greater than U and less than 1.3U) between U and 1.5U.

[0036] The formula for calculating the regional arc-starting voltage U designed in this invention is as follows:

[0037]

[0038] Where C1 is the specific heat capacity of activated carbon, C2 is the specific heat capacity of water, and ρ m ρ is the packing density of activated carbon. 水 Let T0 be the density of water, T0 be the current temperature of the activated carbon (initially room temperature; this invention only studies the initial regional arc-ignition voltage, because once the arc is successfully ignited, the resistivity of the activated carbon gradually decreases, making it easier to generate an arc), ρ be the resistivity of the activated carbon at the current temperature, n be the initial moisture content of the activated carbon (moisture content at the current temperature before drying), D be the diameter of the drying furnace, ω be the angular velocity of the stirrer, and the proportionality coefficient η range from 0.3 to 1. The packing density ρ of the activated carbon... m The measurement is as follows: Place the activated carbon sample into a 100ml graduated cylinder, gently tap the bottom of the cylinder with an eraser, and add more activated carbon sample while continuing to tap until the volume of the activated carbon sample reaches 100ml and no longer decreases. At this point, calculate... Where m is the mass of activated carbon in the graduated cylinder; the bulk density of activated carbon is related to the type of activated carbon, and the packing density of granular activated carbon is generally between 450 and 650 kg / m³. 3 The packing density of powdered activated carbon is approximately 380–450 kg / m³. 3 about.

[0039] The formula for calculating the regional arc ignition voltage U in this invention is based on different activated carbon properties and drying furnace shapes. The value calculated according to this formula accurately gives the minimum voltage required to generate a stable arc at the beginning of drying under different activated carbon properties and drying furnace shapes. However, the DC voltage input to the two electrode plates must be less than 1.5U, because if it is higher than this voltage value, it is easy to cause local drying or even breakdown of the drying furnace.

[0040] Step 3: Activated carbon generates Joule heat under the DC voltage applied to electrode plate 8. Stirred by stirrer 4, the activated carbon is forced to rotate, reducing the overall resistance of all activated carbon within the drying furnace 7. The stirrer 4 also ensures uniform heating of the activated carbon and causes collisions and friction between adjacent activated carbon particles, removing impurities from the activated carbon surface. This enhances the conductivity of the activated carbon and promotes the formation of electric arcs between adjacent activated carbon particles. The generation of these arcs further promotes current conduction between the activated carbon particles, ultimately causing the adsorbed water to desorb rapidly. The desorbed water is discharged from the exhaust port 5 of the drying furnace 7 by the fan 6, flowing into the exhaust gas treatment device 13 to remove impurities before being discharged, reducing environmental pollution from exhaust gas. The coordinated action of stirrer 4, fan 6, and the DC voltage input to the two electrode plates (greater than U and less than 1.5U) significantly shortens the drying time of the activated carbon and improves drying efficiency.

[0041] Step 4: After reaching the target drying temperature and maintaining it for the set time, the activated carbon drying is complete. At this time, turn off the DC power supply and stirrer 4, open valve 11, and let the dried activated carbon flow out from the activated carbon outlet at the bottom of the drying furnace 7. The dried activated carbon flowing out of the outlet can directly enter the regeneration furnace for regeneration, which greatly improves the regeneration efficiency and uniformity, and can greatly reduce the occurrence of H2 and CO pollution or even explosions during regeneration.

[0042] Taking a saturated coconut shell activated carbon granule as an example, its initial moisture content at room temperature is 40%, its resistivity at room temperature is 8 Ω·m, and its packing density is 500 kg / m³. 3 The specific heat capacity is 840 J / (kg·℃); while the specific heat capacity of water is 4200 J / (kg·℃); the diameter of the drying furnace is designed to be 1 m, the angular velocity ω is 0.3 rad / s, and η is 0.7. According to the formula for calculating the regional arc ignition voltage, the regional arc ignition voltage is calculated to be U = 106 V; the target drying temperature is designed to be 200℃, so the DC voltage is taken as 1.4U; of course, if you want to shorten the drying time, you can increase the angular velocity of the stirrer. At this time, the regional arc ignition voltage will increase accordingly, and the DC voltage value should also be increased accordingly.

[0043] This invention mainly utilizes the overall regional low-voltage electric arc generated when activated carbon particles move in a low-voltage electric field to dry the activated carbon particles, which is quite different from high-voltage electric arc drying of activated carbon, as shown in Table 1.

[0044] Table 1 Comparison of Low-voltage Arc and High-voltage Arc Drying of Activated Carbon

[0045] Arc type Voltage range Range of electric arc generation range of heat release low-voltage electric arc 50～200V Local Uniform heat release High voltage arc 1000V or more Single-path penetration Local heat release

[0046] During the drying process, after successful arc ignition, the angular velocity of the stirrer can be adjusted based on the humidity in the pipe connecting the exhaust port 5 at the top of the drying furnace body 7 and the fan 6. A humidity sensor can be installed on this pipe to detect the humidity inside. When the humidity inside the pipe increases, the angular velocity of the stirrer increases, accelerating the dissipation of water vapor. At the same time, since a screw stirrer is used, the activated carbon can also generate upward movement during the stirring process, which further facilitates the dissipation of moisture. During the drying process of activated carbon, the humidity inside the pipe first increases and then decreases, so the angular velocity of the stirrer can also be set to first increase and then decrease.

[0047] This invention utilizes the electrical conductivity of activated carbon. When energized, the activated carbon removes its own moisture through Joule heating. Simultaneously, a stirrer forces the activated carbon to rotate, reducing the overall resistance of all activated carbon within the drying furnace and ensuring uniform heating. The collisions and friction between activated carbon particles remove impurities from their surface, enhance conductivity, and generate numerous electric arcs. These arcs further promote current flow between the activated carbon particles. The heat generated by the arcs accelerates the drying process, reduces the apparent resistance of the activated carbon, and facilitates the rapid escape of water vapor generated internally, thus speeding up heat and mass transfer during drying. Therefore, this invention achieves rapid moisture removal from activated carbon through the combined effects of Joule heating and electric arcs. The generation of an electric arc and the Joule heat of activated carbon are both related to the activated carbon's moisture content, resistivity, packing density, movement speed, shape of the drying furnace, and the voltage of the applied DC power supply. Based on the shape of the drying furnace, the activated carbon's moisture content, resistivity, and packing density, and by inducing movement of the static activated carbon (i.e., adding an activated carbon movement parameter), a regional arc-ignition voltage calculation model is constructed to adapt to different activated carbon properties and drying furnace shapes. This provides accurate guidance on the minimum voltage required to generate a stable arc at the beginning of drying. Based on this, this invention, through the coordinated action of agitator stirring, fan drive, and a DC voltage input to two electrode plates that is greater than but less than 1.5 times the regional arc-ignition voltage, significantly shortens the drying time of activated carbon and improves drying efficiency.

[0048] To demonstrate the effect of the agitator forcibly rotating the activated carbon, thereby reducing the overall resistance of all activated carbon particles in motion within the drying furnace, a comparison graph was plotted showing the conductivity changes of coconut shell activated carbon particles at different moisture contents under static and dynamic states when the agitator angular velocity is 0.3 rad / s. Similarly, a comparison graph was plotted showing the conductivity of coal-based activated carbon particles at different moisture contents under static and dynamic states. (See figures below.) Figure 3As shown in (a) and (b), it is evident that the overall electrical conductivity of the activated carbon particle group is significantly reduced under dynamic conditions compared to the static state. Furthermore, the curve showing the overall electrical conductivity of the coconut shell activated carbon particle group as a function of the stirring angular velocity is shown below. Figure 4 As shown, the overall conductivity of the coconut shell activated carbon particle group gradually decreases as the stirring angular velocity of the stirrer increases, indicating that forced rotation of the activated carbon does indeed reduce the overall resistance of the activated carbon particle group.

Claims

1. A method for rapid drying of activated carbon, characterized in that: The method is as follows: Step 1: Input the activated carbon with the surface moisture removed into the drying furnace until the activated carbon is higher than the two electrode plates that are directly opposite each other and spaced apart inside the drying furnace. Step 2: Connect the two electrode plates to the positive and negative terminals of the DC power supply respectively; start the fan connected to the exhaust port and tail gas treatment device at the top of the drying furnace, and start the stirrer inside the drying furnace. Turn on the DC power supply and input a voltage greater than [value missing] to the two electrode plates. and less than The DC voltage input to the DC power supply ranges from 50 to 200V; among which, Design the regional arc-starting voltage; The calculation formula is as follows: Where C1 is the specific heat capacity of activated carbon, C2 is the specific heat capacity of water, and ρ m ρ is the packing density of activated carbon. 水 The density of water, ρ is the current temperature of the activated carbon before drying, n is the resistivity of the activated carbon at the current temperature, and D is the initial moisture content of the activated carbon before drying. The angular velocity of the stirrer during stirring is η, and the value of the proportionality coefficient η ranges from 0.3 to 1. Step 3: Activated carbon generates Joule heat under the DC voltage applied to the electrode plates. Under the stirring action of the stirrer, the activated carbon rotates, reducing the overall resistance of all activated carbon within the drying furnace. The stirrer ensures uniform heating of the activated carbon and also causes collisions and friction between adjacent activated carbon particles, removing impurities from the activated carbon surface, enhancing its conductivity, and promoting the formation of electric arcs between adjacent activated carbon particles. The generation of these arcs further promotes current conduction between the activated carbon particles, ultimately causing the adsorbed water to desorb, thus enabling the application of the designed regional arc-ignition voltage. The conditions are created for drying activated carbon; the moisture desorbed from the activated carbon is discharged from the exhaust port of the drying furnace by the action of the fan, flows into the tail gas treatment device to remove impurities in the moisture, and is then discharged into the atmosphere; the agitator stirs, the fan drives, and the input of the two electrode plates is greater than and less than The coordinated action of the DC voltage and three other factors shortens the drying time of activated carbon. Step 4: After reaching the target drying temperature and maintaining it for the set time, the activated carbon drying is complete. Turn off the DC power and the stirrer, and let the dried activated carbon flow out from the activated carbon outlet at the bottom of the drying furnace. The agitator is a screw agitator, and the screw lead is 0.5 to 1 cm.

2. The method for rapid drying of activated carbon according to claim 1, characterized in that: The drying time is shortened by increasing the angular velocity of the stirrer. At this time, the arc ignition voltage in the region is increased, and the DC voltage value is also increased.

3. The method for rapid drying of activated carbon according to claim 1, characterized in that: During the drying process, after successful arc ignition, the angular velocity of the stirrer is adjusted according to the humidity in the pipe connecting the exhaust port at the top of the drying furnace to the fan. The angular velocity of the stirrer increases as the humidity in the pipe increases; a humidity sensor is installed on the pipe.

4. The method for rapid drying of activated carbon according to claim 3, characterized in that: The angular velocity of the stirrer first increases and then decreases, and the range of the stirrer angular velocity is 0.2 to 0.7 rad / s.

5. The method for rapid drying of activated carbon according to claim 1, characterized in that: The target drying temperature is set to 120–200°C.

6. The activated carbon rapid drying device used in any one of claims 1 to 5, comprising a silo, a first valve, a conveying pipeline, a drying furnace body, an electrode plate, a temperature sensor, and a second valve, characterized in that: It also includes a stirrer, a blower, and an exhaust gas treatment device; the activated carbon outlet of the silo is connected to the activated carbon inlet at the top of the drying furnace body through a conveying pipe, and a first valve and a flow meter are provided at the activated carbon outlet of the silo; a second valve is provided at the activated carbon outlet at the bottom of the drying furnace body; two electrode plates facing each other and spaced apart are fixed on the inner wall of the drying furnace body. The terminals of the electrode plates extend out of the drying furnace body; the exhaust vent at the top of the drying furnace body is connected to the exhaust gas treatment device via a fan; the stirrer is fixed inside the drying furnace body and placed between the two electrode plates; a temperature sensor is installed on the stirrer.

7. The activated carbon rapid drying device according to claim 6, characterized in that: The diameter to height ratio of the drying furnace body is 1:0.5 to 1.

8. The activated carbon rapid drying device according to claim 6, characterized in that: The electrode plate is arc-shaped.

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