1. Screening and drying of chips
The wood chips are sent to the vibrating screen by the bucket elevator, and the 6-40 mesh wood chips are selected and sent to the cyclone separator by the air blower. The separated wood chips fall into the silo. Then, the airflow is dried, and the wood chips are continuously dropped into the spiral feeder by the disc feeder under the silo, and the hot air duct is added, and the hot air from the hot air furnace is taken away and dried by the high-speed air, and the moisture content of the wood chips is 40. The % drops to 15%-20%, and the dry wood chips fall into the dry sawdust silo after the cyclone separator is separated.
2. Preparation of zinc solution
The zinc chloride solution is prepared according to the requirements of the production, and a zinc chloride solution of a predetermined concentration is prepared. During the preparation, the concentration of 40 US cents of zinc recovered in the recovery process is pumped into the zinc bath, and then fixed zinc chloride and hydrochloric acid are added to prepare a zinc chloride solution of the specified concentration and pH, or directly prepared with water. Alternatively, then pump it into the concentrated zinc bath for use.
3. pinch and
Pump the zinc chloride solution of the concentrated zinc pool into the high-concentration tank of the concentrated zinc solution. Since the wood chips under the wood chip silo are lifted to the metering tank by the bucket elevator, a certain amount of wood chips is put into the kneading machine, and the high level is from the high position. After mixing the concentrated zinc solution in the tank, it is poured into the hopper of the rotary kiln.
4. Activation
The wood chips are added to the rotary kiln by the disc feeder and the screw feeder at the lower part of the hopper, and the hot flue gas is introduced from the other end of the furnace to carbonize and activate the wood chips, and the activated material falls into the discharge chamber and is periodically taken out, using the trolley. Push to the bucket elevator feeding point in the recycling process.
5. Recycling, rinsing
Start the bucket elevator and add the activated material to the recovery tank to recover zinc chloride. First wash with 25-30 Baumezinc zinc chloride solution, the concentrated zinc solution is sent to prepare zinc chloride solution, then washed with dilute zinc solution, add appropriate amount of hydrochloric acid during washing, and heat the solution to 70 degrees Celsius In the above, zinc oxide is converted into zinc chloride. Finally, the concentration of the washing liquid is required to be below 1 Baume. The recovered charcoal is flushed into the rinsing tank with water, rinsed with hot water of 90 degrees Celsius or higher, and an appropriate amount of hydrochloric acid is added during the second rinsing, and heated to boiling to remove iron from the charcoal until the washing liquid contains no iron.
6. Centrifugal dehydration, drying and grinding
The activated carbon is dehydrated in a centrifuge and then dried in an external thermal rotary dryer to a moisture content of 4 to 6%, which is then sent to a ball mill for grinding.
In addition, a special exhaust gas and wastewater treatment system is attached to recover zinc chloride and hydrochloric acid in the flue gas to eliminate pollution.
Requirements for raw materials for zinc chloride activation
The raw material for producing powdered activated carbon by zinc chloride method is mainly wood chips. When producing carbon for sugar, it is better to use chopped wood chips and pine wood chips, and pure fir chips are better. Fresh pine chips contain more turpentine, which is not conducive to the infiltration of zinc chloride solution. If stored for a period of time, it is more beneficial to use the volatile components to self-evaporate and oxidize. However, the storage time should not be too long, so as to prevent the wood chips from decaying and deteriorating. When producing other activated carbon varieties, mixed wood chips of various tree species can be used. The requirements for wood chips are: particle size 6-40 mesh, without plate skin, wood block, sediment and iron filings, etc., the water content is 15%-20%.
In order to stabilize the process operation, the wood chips need to be screened with a vibrating screen, and the wood chips that meet the requirements are selected and impurities are removed to avoid affecting the product quality.
The selected wood chips have a moisture content of about 40%. Drying is generally carried out using a gas flow dryer. It consists of a hot blast stove, a fan and a drying tube. The drying tube is made of steel plate with a diameter of 300 mm and a height of about 20 m. The wood chips are sent to the drying pipe, and the hot air of 120-150 degrees Celsius sent by the hot air furnace drives the wood chips to pass through the drying pipe at a speed of 8 meters per second. The moisture content of the dried wood chips is reduced to 15%-20%, and separated by cyclone. Recycling.
The wood chips are dried, and some factories use rotary kiln. Wood chips are indirectly heated by the flue gas and dried. During production, the wood chips enter the cylinder body from one end of the feeding port, and slowly move forward with the rotation of the cylinder body and a certain slope, and the dried wood chips are continuously discharged from the discharging port. The flue gas generated by the combustion of the combustor first flows through the outside of the cylinder, heats the cylinder, and then enters the tobacco pipe inside the cylinder to fully exchange heat and finally discharge into the chimney. When operating, the amount of feed should be controlled according to the furnace temperature. At the same time, the furnace temperature should not be too high to prevent wood chips from burning.
Preparation of zinc chloride solution
The concentration of the zinc chloride solution varies depending on the type of activated carbon produced. The preparation of the zinc chloride solution refers to a zinc chloride solution formulated to a predetermined concentration, which is an important factor in ensuring the zinc-to-chip ratio. Industrial zinc chloride which is white, easy to absorb and deliquesce, and has a content of more than 96% should be used.
Due to the different uses of activated carbon, the requirements for using zinc chloride to make carbon are different, as follows:
The formulation requirements for activated carbon for sugar are:
The zinc chloride solution has a concentration of 50-57 Baume at 60 degrees Celsius and a pH of 3.0-3.5.
The formulation requirements for medicinal activated carbon are:
The zinc chloride solution has a concentration of 45-47 Baume at 60 degrees Celsius and a pH of 1.0-1.5.
In the preparation, in the zinc bath, the solid zinc chloride is dissolved in the zinc chloride solution recovered in the recovery process. If the recovered zinc solution is not enough, it can also be prepared with water. When the required Baume degree is reached, the pH of the solution is adjusted with hydrochloric acid.
Baume concentration is a widely used means of indicating the concentration of a solution in a zinc chloride process plant. The concentration measured by the Baume pycnometer immersed in the solution indicates the concentration.
The concentration of Baume in zinc chloride solution has a certain relationship with temperature. When the percentage concentration is constant, the concentration of Baume decreases with the increase of temperature. Therefore, for the Baume concentration of the zinc chloride solution, the temperature of the solution must be indicated. For example, to prepare a zinc chloride solution with a concentration of 45-46 Baume at 60 degrees Celsius, if it is at 30 degrees Celsius, it should be formulated with a concentration of 46-47 Baume.
The concentration of Bomei chloride solution (0Be?FONTFONT-SIZE: 14pt;">宋体" LANG="ZH-CN">) and temperature (degrees Celsius), the concentration and relative density of zinc chloride solution The relationship between the percent concentration can be found in the relevant chart.
Purpose and process conditions of the kneading process
The purpose of the kneading process is to continuously stir the wood chips and the zinc chloride solution by means of a pair of zigzag stirring blades in the kneader, repeatedly pressurizing them to uniformly mix them, and accelerate the penetration of the zinc chloride solution into the wood chips.
Kneading is carried out in a kneader. The kneading machine is made of acid-resistant steel, which is a horizontal semi-circular groove. The groove has a pair of zigzag agitators. The volume is generally 0.5 cubic meters, and the operation is intermittent. The kneading machine is provided with a transmission mechanism, and pressing the button of the mechanism enables the kneading machine to rotate the semicircular groove by an angle to pour the zinc scrap into the hopper of the rotary kiln.
For ease of operation, the kneading process also sets up a wood chip metering device and a zinc chloride solution high level tank and metering device. The wood chip metering device consists of a bucket elevator, scale and hopper that transports wood chips, which accurately controls the weight of each pinch and wood chip. A tube is connected to the upper part of the kneader in the lower part of the zinc chloride solution to uniformly spray the quantitative zinc chloride solution into the kneader and mix with the wood chips.
When kneading, the ratio of the weight of the process wood chips to the weight of the zinc chloride solution is called the ratio of the material to the liquid, sometimes referred to as the impregnation ratio.
The process conditions for kneading are:
1. Production of industrial activated carbon
Wood chip moisture content (%) 15-20
Concentration of zinc chloride solution at 60 degrees Celsius (Pomez) 45-47
Zinc chloride solution pH 1-1.5
Material to liquid ratio 1:3
Kneading time (minutes) 10-15
2. Production of activated carbon for sugar
Wood chip moisture content (%) 15-20
Concentration of zinc chloride solution at 60 degrees Celsius (Pomez) 50-57
Zinc chloride solution pH 3 - 3.5
Material to liquid ratio 1:4-5
Kneading time (minutes) 10-15
How does the rotary furnace operate? What are the process conditions for carbonization and activation?
Rotary furnace is a key equipment for carbonization and activation of zinc scrap. The rotary kiln is horizontal, with an inner diameter of 1 meter and a length of 13 meters. The cylinder is made of steel plate and lined with refractory bricks. A large gear is mounted on the outside of the middle of the cylinder to push the cylinder to rotate. There are a pair of rollers at each end to support the weight of the cylinder. There are seals on the burner and the furnace. The installation has an inclination of 2-4 degrees.
The rotary kiln is operated continuously, and the zinc scrap is fed into the furnace tail by a disc feeder and a screw feeder. The material moves slowly to the burner by the rotation and inclination of the cylinder. A combustion chamber is arranged in the burner to burn crude oil or gas, and the generated high-temperature flue gas directly enters the furnace, flows from the burner head to the furnace tail, and is in direct contact with the material countercurrent. In the carbonization process, a viscous plastic material is formed, adhered to the furnace wall, and agglomerated into a crucible to block the furnace. In order to prevent clogging, a chain-shaped star-shaped scraper is installed in the furnace, so that it will continuously hit the furnace wall as the cylinder rotates, and the agglomerated material stuck on the furnace wall is scraped off.
The activated material is called the activated material, which falls from the burner into the discharge chamber and is periodically taken out and sent to the recycling process. Waste flue gas enters the exhaust gas recovery system from the end of the furnace through the flue.
When the furnace is started, the converter is started first, and then the temperature is raised by the ignition. When the temperature of the furnace tail rises to about 300 degrees Celsius, the feeding is started. If it is necessary to stop the furnace, first stop the feeding, continue to maintain a certain furnace temperature, and wait until the materials in the furnace are completely discharged, and then stop the furnace. Before the furnace is not completely cooled, the cylinder is rotated once every few minutes to 20 minutes to prevent deformation of the cylinder.
The process conditions for carbonization and activation of rotary kiln are as follows:
Activation zone material temperature (degrees Celsius) 500-600
Charring, activation time (minutes) about 40
Furnace filling coefficient (%) 15-20
Cylinder speed (rev / min) 1-3
The pressure in the furnace is slightly negative
Furnace flue gas temperature (degrees Celsius) 700-800
Furnace flue gas temperature (degrees Celsius) 200-300
Discharge interval (minutes) 20
The purpose of the process of producing activated carbon by zinc chloride method
The activated material contains 70% to 90% zinc chloride and a zinc-containing compound. The purpose of recycling is to recover this part of zinc chloride and zinc-containing compounds, reducing the consumption of zinc chloride in the production of activated carbon, in order to reduce the cost of the product.
The recovery operation of zinc chloride belongs to the extraction method, that is, zinc chloride solution (zinc water for short) and a small amount of industrial hydrochloric acid are added to the activated material to dissolve zinc chloride and zinc oxide, and then separated by filtration.
The recycling is carried out in a recycling bin. The recycling bin is made of steel plate and is a cylindrical body. The inside and outside of the barrel are painted with diabase clay. A diabase plate is lined on the inside of the barrel. The lower part of the barrel is made of steel and diabase powder cast filter plates.
In operation, the activated material is added to the recovery tank, firstly added with the higher concentration of recovered zinc water to the activated material, and about 5% by weight of hydrochloric acid is added to convert the zinc oxide formed during activation into zinc chloride.
Stir well during the reaction. After the reaction is completed, let it stand for a few minutes, open the vacuum suction valve, draw the zinc chloride solution in the recovery tank into the vacuum drum, and then put it into the acid-resistant cylinder. Generally, the concentration of the zinc chloride solution recovered for the first time can reach 40 or more, and can be sent to prepare a zinc chloride solution. After the first recovery, the low-concentration zinc water is pumped into the recovery tank in turn, so that the zinc water covers the carbon surface, so that the recovery is repeated several times, and the recovered zinc water with different concentration is obtained, and respectively placed in the acid-resistant cylinder. Medium, for the next recycling. Until the various concentrations of zinc water left last time are used up, they are washed with hot water, and the washing liquid is also collected in the acid-resistant cylinder. Until the zinc chloride content in the char is less than 1%.
What is the purpose of rinsing? How to rinse?
The purpose of rinsing is to remove various impurities from the raw materials and processing, so that the content of chloride, total iron, ash and the like of the activated carbon and the pH are all up to the specified indexes. Rinsing is carried out in two steps. First, hydrochloric acid is added to remove iron.
The compound, which is called acid pickling, is also called acid treatment or "boiled iron"; the second is to neutralize the acid with alkali, remove the chloride root, and wash it repeatedly with hot water, so it is called water washing.
Both steps of rinsing are carried out in the same rinsing tank. The rinsing bucket is made of steel plate and has a cylindrical shape. The inside and outside of the barrel of the barrel are coated with several layers of glass fiber cloth with epoxy resin mud, and the inner side is lined with an acid-resistant ceramic tile, and a filter plate is installed at the bottom of the barrel.
During rinsing, the activated carbon is washed from the recovery tank into the rinsing tank by using the difference in the installation position of the recycling tub and the rinsing tub. After releasing some water, close the bottom drain valve, then add hydrochloric acid with a 5% activation amount, open the open steam, and boil for 2 hours. At this time, impurities mixed in the carbon react with hydrochloric acid, and impurities such as iron oxide and calcium oxide which are insoluble in water become water-soluble substances of ferric chloride and calcium chloride, and are removed with water.
After the acid treatment, the acid water in the barrel is discharged, and the water is continuously rinsed several times with hot water, and the water temperature is kept above 60 degrees Celsius. Since excess hydrochloric acid is not easily washed by water, an appropriate amount of soda ash is added to neutralize, and the pH of the aqueous solution in the barrel is adjusted to 7-8. Heat it with open steam for about 15 minutes to release the water. The mixture is further washed with hot water until the chlorine content in the carbon is less than 0.16%. The total washing time is 4-6 hours.
Centrifugal dehydration, drying and grinding?
Centrifugation
The rinsed charcoal is flushed from the rinse tank into the charcoal tank. The horizontal piston pusher centrifuge is used to reduce the moisture content of the activated carbon to 60%-65%. In operation, the sand pump is first actuated, and the rinsing charcoal in the carbon storage tank is pumped together with the water into the high carbon tank, and then the mixer of the high carbon tank is activated to mix the carbon with the water. Then start the centrifuge. After the centrifuge runs smoothly, open the bottom valve of the high tank and let the charcoal enter the centrifuge for dehydration. The charcoal is sent to dryness, and the water that is extracted contains a lot of fine carbon, and the fine carbon is recovered by precipitation to discharge the waste water.
dry
The purpose of drying is to reduce the moisture content of the activated carbon to less than 10%. There are many drying methods, and the rotary drying oven is more commonly used. The rotator is made of steel plate. The cylinder has a diameter of about 1 meter and a length of 7 meters. It is installed in a heating furnace and indirectly heated by flue gas. The wet charcoal enters the cylinder body from one end of the feeding port, and the material moves forward due to the inclination and rotation of the cylinder body, and the discharging port is continuously discharged. The temperature of the material in the rotary drying furnace is required to be 120-130 degrees Celsius. When operating, it is necessary to control the amount of feed according to the furnace temperature to prevent the occurrence of Mars on dry charcoal. The drying furnace can be turned in the cylinder due to the carbon particles, and the drying speed is faster. In addition, the drying furnace uses indirect heating to avoid direct contact between the charcoal and the drying medium, thus reducing the possibility of carbon contamination.
Grinding
The purpose of the grinding is to increase the external surface area of ​​the activated carbon. Commonly used ball mill to smash to 120 mesh - 200 mesh. The shaped ball mill is continuously fed and discharged, and the feed amount is generally adjusted according to the particle size of the product. In order to avoid the increase of iron content in the ball milling process, the ball mill is usually lined with a layer of hard wood and pulverized with pebbles or porcelain balls. Some factories also use Raymond shredders for grinding.
Process for intermittent production of powdered activated carbon from zinc chloride
Take a production plant as an example, the process is as follows:
The raw wood chips are sent to the vibrating screen through the belt conveyor to be screened through the 8-16 mesh screen. The qualified wood chips fall into the feeding hopper, and then sent to the rotary dryer for drying by another belt conveyor. After drying, the wood moisture content is 10%. —15%. The dry wood chips are transported by the feed fan to the cyclone, and the wood chips fall into the storage bin for use.
The solid zinc chloride is placed in an underground zinc bath, dissolved in the concentrated zinc solution or water, and is prepared into a zinc chloride solution that meets the requirements, and then pumped into the dip tank to mix with the wood chips.
The wood chips are placed in the dip tank from the storage bin, and then pumped into the prepared zinc chloride solution, and uniformly stirred and impregnated in the dip tank. The impregnated zinc scraps are sent to the carbonization furnace by a belt conveyor and scooped into a carbonization furnace for carbonization. After the carbon waste material is carbonized, it is called the carbonized material, which is pushed by the trolley to the activation furnace for activation. The activated material is called the activated material.
After the activator is weighed into the hopper, it is lifted by a hoist and poured into a recovery tank, and hot water and hydrochloric acid are added for recovery. The concentration of the first recovery liquid is relatively high, and it is placed in a concentrated zinc pool, and flows from the underground channel to the underground zinc pool with the zinc chloride solution process for use as a ingredient. The low-concentration zinc chloride liquid recovered several times later will be placed in different concentrations of zinc water tank for the next recycling. The recycled charcoal is flushed into the soaking bucket, heated and steamed for steaming. It is called “boiled ironâ€. The iron salt is removed. After cooking, the waste acid water is discharged into the underground ditch, and the charcoal is flushed into the washing bucket to heat the water. It is steamed for washing.
The rinsing qualified activated carbon is placed in a three-legged centrifuge to dry, and the dried charcoal is concentrated in a hopper and sent to a rotary dryer for drying through a belt conveyor.
The dried charcoal is lifted by a hoist and poured into a ball mill for grinding. Finally packaged into the warehouse.
What is the purpose of the impregnation process and how is it handled?
The zinc chloride method is used to batchly produce powdered activated carbon. In order to reduce the investment in mechanical equipment, the mixing of wood chips and zinc chloride solution is not carried out by a kneading machine, but a dip tank is used, and zinc chloride is dipped. It penetrates into the wood chips and acts as a kneading machine.
The operation method of impregnation is slightly different from different manufacturers, but they are all similar.
Impregnation generally uses an impregnation tank, also known as a dip tank. It is a pool made of brick and acid-resistant cement on the ground. The pool is 3 meters long, 2 meters wide and 1 meter deep. The outer surface of the tank is covered with acid-proof porcelain sheets to prevent corrosion, and a drain pipe is arranged at the bottom of the tank for discharging excess zinc chloride solution after immersion.
During immersion, the wood chips that meet the requirements are put into the immersion tank, and then the zinc water pump is started, and the prepared and tested zinc chloride solution is evenly poured on the wood chips until the zinc chloride solution covers the wood chips, impregnation After 8-12 hours, open the drain port at the bottom of the immersion tank, and let the excess zinc chloride solution flow into the zinc pool. After 2 hours, the zinc scrap material can be transported to the carbonization process for carbonization.
In some factories, the mixture is mixed with a certain solid-liquid ratio. After mixing, the mixture is flooded for 8-10 hours, and it needs to be mixed occasionally to obtain uniform mixing of the zinc chips. It is not necessary to add zinc solution to the zinc crumb mixture, and it is suitable to knead the cake by hand without dripping. The production process of the activated carbon for different uses is as follows:
Sugar activated carbon
Zinc chloride solution concentration (Pomet) 53-54
The temperature (in degrees Celsius) of the zinc chloride solution is higher than 40
pH of zinc chloride solution (pH) 3 - 3.2
Sawdust and zinc chloride solution weight ratio 1:4
Dipping time (hours) 8 or more
Medicinal activated carbon
Zinc chloride solution concentration (Pomet) 46-47
The temperature (in degrees Celsius) of the zinc chloride solution is higher than 50
pH of zinc chloride solution (pH) 1-1.5
Sawdust and zinc chloride solution weight ratio 1:3
Dipping time (hours) 8 or more
Carbonization of zinc scrap
The carbonization of the zinc crumb is carried out in an open flat-bottom carbonization furnace. This carbonization furnace is operated intermittently.
The carbonization furnace is spliced ​​into a flat-bottomed carbonized bed by cast iron plates or 6.5 cm thick refractory ceramic plates, so it is called a flat plate furnace. Below the carbonized bed, there is a uniform distribution of refractory brick walls for support, and cast iron plates or refractory ceramic plates are placed over these supports. There is a combustion chamber in the lower front of the flat-bottom carbonized bed, where the fuel is burned, and the flue gas generated after combustion is uniformly distributed on the heated cast iron plate or the temperature-resistant ceramic plate under the flat-bottomed carbonized bed, and then the chimney is led to the chimney by the rear collecting flue. . Immediately above the flat carbonized bed, an exhaust hood is installed, and the exhaust gas generated during the carbonization process is led to the outside.
When carbonizing, put the zinc scrap into the carbonization furnace, the furnace temperature is required to be 400-600 degrees Celsius, and the material temperature is 200-300 degrees Celsius. The furnace fire should be kept even and the material should be turned over regularly to prevent agglomeration. When the carbonized material becomes loose, does not agglomerate, and when black and black is light, it can be discharged, and the charcoal in the furnace can be quickly taken out. The carbonization time is 30-60 minutes.
The flat-plate furnace is simple to build, but the cast iron plate is in contact with zinc chloride, which is prone to corrosion, and the surface of the plate is uneven, warped or even burned, and the service life is short. At the same time, the contact of the zinc flakes with the iron plate will have the disadvantage of increasing the iron content of the material. In order to avoid the above disadvantages, some manufacturers use refractory ceramic plates instead of cast iron plates. In addition, since the carbonization furnace is open, toxic zinc chloride gas can overflow and fill the workshop, seriously affecting the working environment.
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