What are the advantages of combined drying equipment?

What is a combined drying equipment?

Due to the different nature of various materials, drying materials in a single form of drying equipment often does not achieve the purpose of drying. If two or more drying equipments are used, they are joined together, or special equipment is added to the machine to make new In the drying process, the device has the performance of different forms of drying equipment, which can not be achieved by a single drying device, which is called a combined drying device. The combined drying may be a series connection of the same type of equipment, or a series of different types of equipment, but the materials are successively passed through different drying equipment in series, and the drying medium may pass through in series or through the drying equipment in parallel.

Combination drying is roughly:

(1) A combination of various drying methods, such as spray drying equipment;

(2) Combination of various heat transfer processes, such as film. Fluidized bed drying equipment, etc.;

(3) Combination of multi-stage drying equipment of the same type, such as multi-stage air drying equipment.

For example, a film-flow drying device is equipped with a high-speed scraper in a drying device, and the added slurry is smashed to the wall of the airflow pipe, and the outer wall of the airflow pipe is covered with a heat-insulating jacket, which will be smashed to the pipe wall. The material is dried. Due to the small distance between the scraper and the pipe wall, the dried material on the pipe wall is scraped by the impact of the airflow, and the pipe is taken out with the airflow to become the required dry material.

For another example, the spiral airflow drying device passes through the spiral pre-drying section before the material inlet flow drying device, and then is sent to the blower impeller to enter the airflow drying. This combined drying device is beneficial for reducing the moisture content of the material. When entering the blower impeller, it is easy to knead into fine powder, thus facilitating the drying process.

For another example, generally, it is stationary or simply performing a simple rotation or linear motion, and the flowability of the material is poor. If the bulk material is dried, the unevenness of the material drying will increase. We can make full use of the characteristics of the conventional dry fluidization effect to make the material evenly heated, so the advantages of the combination: short drying time (drying time is 1/4 of the time required for convection drying), high product quality, equipment integration system Compact and reduced in size, resulting in a smaller footprint and lower operating costs.

Combined drying equipment advantages

In recent years, one of the development of drying equipment direction has turned to the development of combined drying, in an effort to optimize the combination of existing drying equipment to take advantage of each drying equipment.

Advantages of combined drying compared to single stage drying:

(1) Combined drying makes it easier to save energy;

(2) Combination drying makes it easier to ensure product quality, and the drying process can be subjected to classification, pulverization, etc., and the heat sensitive material can be cooled in time after drying;

(3) The operation is more flexible, and various drying equipments can be scientifically combined according to the specific law of material drying.

Combined drying can fully utilize the characteristics of two or more drying equipment to complete a drying task. For example, the centrifugally dehydrated polyvinyl chloride resin is dried from a moisture content of 7.6% to a water content of 0.3% or less, and can be dried to a moisture content of 0.82% by a gas flow drying apparatus. If the horizontal fluidized bed drying equipment is used again, the combined moisture in the material can be removed, and the moisture content of the product can reach 0.2%, and a good effect is obtained. This is a gas-one-flow fluidized bed combined drying device.

Now, there is a trend in the combination process, that is, the use of microwave pair flow, spout, convection, and spout. The combination mode of microwave, but should consider the characteristics of various drying methods and the characteristics of materials, analyze the comprehensive factors, and determine the optimal combination process. It can be said that a reasonable combination of drying can obtain high quality products, improve the production capacity of the equipment, and obtain better economic effects.

How to treat combined drying equipment from the drying process

Most materials are dried in both constant and deceleration stages. In the constant-speed drying stage, a large amount of water is removed, and the drying rate depends on the gasification rate of the surface water of the material. The high-wind speed and large air volume are used to take the dried vaporized water vapor away from the surface of the material to improve the drying rate. In the slow-drying drying stage, the drying rate depends on the nature of the material, the mass transfer rate and the thermal driving force, and is limited by the outward migration rate of the internal moisture of the material. Increasing the hot air temperature is an important way to increase the drying rate.

Because the tail gas in the constant-speed drying stage is a low-temperature and high-humidity gas, close to saturation, it has no desiccant capacity, no drying driving force, and can no longer dry. In the slow-drying stage, the tail gas is high-temperature and low-humidity gas. How to recover this part of gas? It is used for drying at a constant speed drying stage and still functions as a drying agent. As one of the combined drying methods, the two-pole drying equipment utilizes this rule to carry out the two drying stages of the material in two drying equipments, that is, the constant-speed drying exhaust gas is discharged, and the tail gas recovery in the slow-down drying stage makes the system The discharged gas is close to saturation, thus achieving energy saving, especially for continuous drying in large quantities.

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What are the differences between drying equipment and drying equipment?

Drying equipment and drying equipment are the equipment we often mention, but the difference between drying equipment and drying equipment seems to be unclear. When we want to dehydrate a product, we will think of drying equipment or drying equipment. We will look for information about drying equipment and drying equipment. Because of the special information about this type of product, many times we will Mix the drying equipment with the drying equipment. I don’t know how to distinguish between drying equipment and drying equipment.

For example, we say that food drying equipment can generally be understood as a device that can dry food. It is concerned with the result of “drying”, not the drying process, such as microwave dryer, which emphasizes the result of drying with microwave instead of the process. Therefore, drying equipment can be understood in a broad sense as any equipment that can “dry” the product, including “low temperature drying equipment”, “high temperature drying equipment”, “air drying equipment”, “dewatering equipment”, “drying equipment”, “freeze drying” Equipment”, in any case, any method, any method that can dry the product can be called a drying device.

What is the difference between drying equipment? It emphasizes “drying”, which is a dry method or process, that is, placing the product in a certain temperature environment, allowing it to “bake” the ambient temperature and obtain The result of drying. For example, heat pump drying equipment, which emphasizes the use of heat pump to generate temperature to dry the product, it emphasizes the process of “drying”.

Drying is a method of obtaining the drying result, and the drying equipment is only one type of drying equipment that uses a drying method for drying. It can be said that the drying equipment comprises drying equipment, and the drying equipment is only one type of drying equipment commonly used in many drying equipments, and they are related and affiliated.

Drying equipment on the market can generally be divided into five broad categories from dry form:

 

Static drying equipment:

Hot air circulation oven (room), high temperature sterilization oven, circular vacuum dryer, square vacuum dryer

Continuous drying equipment:

Belt dryer, dehydrated vegetable dryer, roller scraper wafer dryer, rotary drum dryer, disc continuous dryer, vacuum tray dryer

Stirring drying equipment:

Vacuum dryer, double cone rotary vacuum dryer, horizontal vacuum ribbon dryer, LHG vertical vacuum ribbon dryer, Openable vacuum sputum mixing dryer, hollow blade dryer, high efficiency boiling dryer;

Fluidized dryer:

Rotary flash dryer, spiral vibration dryer, horizontal boiling dryer, pulse airflow dryer, enhanced airflow dryer, linear vibration fluidized bed dryer;

Spray dryer:

High-speed centrifugal spray dryer, Chinese medicine extract centrifugal spray dryer, pressure spray dryer, pressure spray granulation dryer;

In addition, according to the difference of the heat source of the drying equipment, the difference of the drying process principle and the application industry, there are many other different classifications.

With the continuous improvement of production processes in various specific fields, the selection and application of drying equipment has become more and more rational; a variety of combined drying equipment (systems) have emerged, and drying equipment has become more energy-saving and environmentally friendly.

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Blade dryer structure description

Both the agitator shaft of the paddle dryer and the blades welded to the shaft are hollow structures. The shape of the blade is a wedge-shaped hollow semi-circular shape, which can be passed into the heat transfer medium. In addition to stirring, it is also the heat transfer surface of the device. The blade is triangular, and the sides of the two main heat transfer surfaces are inclined. When the material is in contact with the inclined surface, the material quickly slides off the inclined surface as the surface of the surface rotates, resulting in a self-cleaning effect, so that the heat transfer surface is continuously updated. , thus enhancing heat transfer efficiency. A scraper is arranged at the bottom of the triangle of the blade to scrape the material deposited on the bottom of the shell to prevent the material in the drying chamber from forming a dead angle and to make the product moisture uniform.

Hollow paddle dryer structure

The structure of the hollow blade dryer is mainly composed of a transmission mechanism part, a box part, a main shaft stirring part, a bearing body part, a discharge adjusting mechanism, a rotary joint and the like.
Power transmission part: mainly composed of electric motor, reducer, drive gear, driven gear, inter-shaft gear, etc. Its main function is to transmit the power of the motor to the agitating part of the main shaft to make it run within the rated speed range. It can also be equipped with variable frequency speed regulation or electromagnetic speed regulation configuration for variable speed operation.

The main shaft stirring part is mainly composed of two hollow shafts and a plurality of wedge-shaped hollow blades on the surface thereof. The hollow shaft has a heating medium (steam) return pipe. Single-ended swivel joints are the interface for these media to enter and exit. During the operation, the spindle agitating part stirs, pushes and heats the material.

The bearing body part is at both ends of the main shaft, and the power end bearing body and the non-power end bearing body. Mainly by bearings, bearing blocks, bearing caps, sealing packing, packing gland, inspection cover, etc.
The hollow double-shaft paddle dryer has a jacketed end face of a W-shaped housing, an upper cover, two bladed hollow shafts, end caps at both ends, a rotary joint with a heat medium, a metal hose and a gear included , the transmission mechanism of the sprocket and other components.

The drying heating medium may be steam or hot oil or hot water, but the structure of the shaft is different depending on the phase of the heat carrier. The heat required for drying relies on the jacket and the wall surface of the blade for heat transfer, rather than direct heat transfer by gas convection. The amount of air used during the drying process is small, and a small portion of the air used is simply to remove the moisture from the material. The paddle dryer avoids the loss of heat and the thermal efficiency is as high as 80% to 90%. The heat transfer surface of the paddle dryer consists of several parts such as blades, agitator shaft and wall surface. Moreover, the blade is the main heat transfer surface, so the device has a compact structure and a large heat transfer area per unit volume. In addition, stirring and mixing make the material violently turn, thereby obtaining a high heat transfer coefficient, generally reaching 120-350 W/m2•K. Therefore, the floor space and space are small, saving the capital cost of the plant.

In the drying process, the gas consumption is small, the flow rate is low, and the amount of dust carried away by the gas is small, so that the gas dust is easily recovered after drying, and the recycling equipment is small in size, which can save equipment investment. For the drying process that requires recovery of the solvent, the solvent concentration can be greatly increased, which is advantageous for the recovery of the solvent. Due to the special structure of the blade, the material is alternately squeezed and relaxed during the drying process, strengthening the drying process. The filling degree of the material in the drying chamber is very high, and can reach 80% to 90%. The residence time of the material is completed by adjusting parameters such as feeding speed, stirring shaft speed and material fullness, and can be arbitrarily adjusted from several minutes to several hours. In addition, the movement of the material in the dryer from the feeding port to the discharge port is basically a piston movement, and the residence time is narrowly distributed, so that the product has a uniform water content.

Sludge dryer structure

The sludge dryer is a kind of drying equipment for sludge drying, which is suitable for the treatment of various materials, sludge discharged from sewage plants, chemical gypsum, carbide slag, and dregs.

The sludge dryer has a compact internal structure and almost no auxiliary equipment, so the heat loss is also relatively small, the heat utilization rate can reach 80% to 90%; the single unit can process about 10 tons of sludge per hour. Multi-machine and various multi-effect evaporation principles and structures, so in operation, it is the same as the hollow blade dryer. We can change the number of layers of the sludge dryer according to the actual situation. The blades of each level are adjusted according to various variables of the material.

The improved design of the sump condensate discharge system inside the blade shaft of the sludge paddle dryer is designed according to the large amount of sludge dewatering, and the condensate drain system inside the blade shaft is designed. A device is added inside the blade to increase the drainage time during the rotation of the blade; the condensate drain pipe is increased to increase the discharge of the condensed water. Improve the structure of the original siphon to make the condensate discharge more thorough, thus increasing production.

Jaw dryer structure

The dry material is added from the upper part of the top of the vacuum squeezing dryer. When the material is in contact with the shell wall under the stirring of the rotating dent, the surface is continuously updated, and the dried material is subjected to steam (or hot water, heat transfer oil). Indirect heating, but the moisture of the material is vaporized, and the vaporized water is pumped away by the vacuum pump in time. The material to be dried is indirectly heated by the heat carrier to vaporize the water in the material, and the vaporized water is discharged by the vacuum pump in time.

Due to the high degree of operating vacuum, generally in the range of 400-700 mmHg, the water vapor pressure on the surface of the dried material is much larger than the water vapor pressure in the evaporation space in the dryer housing. Thereby, it is beneficial to discharge the internal moisture and surface moisture of the material to be dried, and is beneficial to the movement of water molecules of the dried material to achieve the purpose of drying. The vacuum kneading dryer is suitable for heat sensitive materials that are easily oxidized at high temperatures or materials that are easy to be kneaded during drying, and materials that must be recovered from steam discharged during drying. Typical dry materials are sodium propylene sulfonate, CMC, phthalocyanine blue, dye intermediates, carboxymethyl starch, maltodextrin, hydrazine sulfonic acid and the like.

The jaw dryer is suitable for drying heat sensitive, organic solvent-containing materials under vacuum conditions. It is characterized by low energy consumption and high thermal efficiency, which can reach 80%. It is easy to operate and has a wide range of adaptability.

Under the action of the circulating fan, the air as the carrier gas flows through the dryer quickly, carrying moisture, ensuring the evaporation rate and diffusion speed of the water; the carrier gas is discharged from the dryer and processed by the washing tower to remove the carrier gas. It contains a large amount of water vapor and a small amount of dust; most of the treated carrier gas is passed to the dryer for recycling, and the other part enters the deodorization system.

The paddle dryer is an indirect heating low speed agitating dryer. There are two or four hollow rotating shafts inside the equipment. The hollow shafts are densely arranged in parallel with the fan-shaped wedge-shaped hollow blades. The structural design is particularly clever. The relative rotation of the shaft body, using the principle and structure of the same angular velocity and different linear velocity, skillfully achieves the self-cleaning effect of the sludge on the shaft body, and largely prevents the axle-holding phenomenon during the sludge drying process. With rapidity, the sludge quickly rushes through the adhesive phase during the drying process.

At the same time, the ingenious structure makes the sludge reach the bidirectional shear state during the drying process. The dried sludge is continuously and continuously fed into the feeding port of the dryer by the screw feeder. After the sludge enters the body, the sludge is turned over and stirred by the rotation of the blade, and the heating interface is continuously updated to contact the body and the blade. It is heated sufficiently to evaporate the surface moisture contained in the sludge. At the same time, the sludge is conveyed in the direction of the discharge port with the rotation of the blade shaft in a spiral path, and the stirring is continued during the transportation, so that the water oozing out from the sludge continues to evaporate. Finally, a uniform product that is evenly dried is discharged from the discharge port.

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Study on steam hydrophobic structure of steam tube rotary dryer

Project project:

The introduction of steam from the steam tube and the discharge of condensed water directly affect the efficiency of the dryer. The traditional steam tube rotary dryer or steam calciner has a steam drum at one end and the steam heat exchange tubes in the dryer are connected. The steam drum is steam-distributed and hydrophobic by a steam drum. The connection between the steam heat exchange tube and the steam drum is subject to inspections such as hydrostatic tests, which are generally carried out at the factory. It is more difficult to complete these tasks on site, that is, complete machine manufacturing, overall transportation, and overall installation are required at the factory. Due to the application and development of coal chemical industry, a large-scale steam tube rotary dryer is required. Due to the large volume of the equipment, heavy weight, and overall transportation, the overall installation is difficult. However, the existing steam tube rotary dryer is difficult to manufacture on site due to the actual structure.

In order to solve the problem of processing and manufacturing and on-site assembly of steam tube rotary dryer parts factory, the project has been carried out to study related technical solutions.

Project achievement:

1. The steam hydrophobic structure of the steam tube rotary dryer can solve the problems of processing, manufacturing and on-site assembly of the steam tube rotary dryer parts factory, thereby avoiding the problems of transportation, on-site installation and inspection;

2. The basic structure includes a heat exchange tube for the dryer, a nozzle, a circular loop tube, a connecting tube, a steam distribution package, a rotary joint, and an equal blocking plate;

3. The rotary joint is sealed and communicated with one end of the connecting pipe uniformly arranged on the circumference of the inserted steam drum by the rotating steam separator, and the other section is connected with the circular ring tube arranged in the radial direction; the arc of the circular ring tube The section is connected to the rotating dryer heat exchange tube through the take-over; each circular loop tube and the circumferentially arranged connecting pipe are arranged with an aliquot blocking plate;

4. The rotating sub-pack is provided with a fixed elbow, one end of the elbow is downward, and the other end of the elbow is connected to the condensate outlet pipe of the rotary joint through the steam separator;

5. The connecting pipe is composed of two arranged pipes, one end of the two arranged pipes is radially inserted into the steam drum for a length; the other connecting pipe is provided with a connecting hole corresponding to the circular ring pipe arranged in the radial direction;

6. The circular ring tube is concentric, and is provided with a communication hole corresponding to the connecting pipe uniformly arranged in the circumference; a plurality of connecting pipes are arranged on the arc segment of the circular ring pipe, and the connecting pipe is connected to the heat exchange tube of the dryer through the flange;

7. The rotary center end of the steam drum is provided with a rotary joint, the steam distribution package is arranged on the axial center of the rotary dryer end, and the split steam center line is concentric with the axial line of the rotary dryer end;

8. The working steps are as follows: the pressure steam sent from the pipeline enters the steam drum through the steam inlet of the rotary joint; the circular pipe arranged in the radial uniform arrangement is connected through the connecting pipe arranged uniformly on the circumference of the steam drum; The loop pipe introduces pressure steam into each heat exchange tube of the dryer through the nozzle; the indirect heat exchange between the heat exchange tube and the material of the dryer according to the concentric circle is evaporation and drying of the material; the pressure steam in the heat exchanger tube of the dryer is heated by the steam The steam is condensed into condensed water; the condensed water is discharged to the circular ring pipe, and each round ring pipe and the circumferentially arranged connecting pipe are arranged with an equal dividing plate, when located between the two equal dividing plates of the annular pipe When the segment is higher than the rotary axis of the dryer, the condensed water in the heat exchange tube reaches the connecting pipe; with the rotation of the steam drum, the condensed water in the connecting pipe flows into the steam distribution bag by gravity; the condensation in the steam drum The water is discharged from the condensate outlet of the rotary joint by steam pressure through a fixed elbow;

9. On-site assembly, each dryer heat exchange tube can be independently assembled and flanged to connect with water pressure test. The steam drum and round ring tube can be factory-made, assembled on site and welded in place; steam hydrophobic structure is completely externally placed. In addition to the cylinder, it is separated from the material and evaporated moisture, and can be installed, inspected, repaired and maintained outside the cylinder;

10. The overall structure is a parallel connection of a plurality of concentric circular heat exchanger tubes and a plurality of circular loop tubes arranged in a concentric circle, and the connection mode is through the nozzles and the flanges. Each of the plurality of circular loop tubes arranged in a concentric circle may be equally divided into six equal parts, seven equal parts or eight equal parts in the circumferential direction, and is equally divided by the blocking plate. Each segment of the circular ring tube is open at both ends and connected to the steam distribution bag through the nozzle. And a split steam package of the steam hydrophobic structure is installed on the axial center of the rotary dryer;

11. The overall structure has the following advantages: the complex steam drum structure manufactured by the factory is simplified into a pipe connection structure that can be constructed and inspected on site. Therefore, the steam tube rotary dryer is simplified from the whole factory manufacturing, transportation and installation to factory parts manufacturing, split transportation, on-site assembly; large-scale manufacture of steam tube rotary dryer can be realized to meet the demand of large processing capacity; Other parts such as steam heat exchange tubes can be inspected and replaced separately; the steam distribution and hydrophobic structure can be easily observed and maintained; the manufacturing cost and transportation cost are reduced.

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What are the operating steps of the freeze drying equipment?

First, preparation stage:

Check the venting valve and butterfly valve at the bottom of the drying box, the upper water valve of the condenser, the intermediate overflow valve, the bottom drain valve, the hot air blower butterfly valve and the vacuum line venting valve, all should be in the closed position. Check if the oil level of the refrigeration unit and vacuum pump is normal and check if the Freon in the refrigerator is normal. Check that the submersible pump in the reservoir is completely submerged in water, if not immediately added water. Check the fuses and wiring screws for looseness.

Second, the operation phase:

1. Pre-cooling and pre-freezing:

Turn on the main power gate and turn on the water pump switch. Press the drying box cooling button on the drying device for 5 minutes, then press the drying box solenoid valve switch to gradually open the infusion main valve (red). When the temperature of the partition plate meets the temperature requirement of the product (below -30 °C), the product is quickly placed in the box, and each resistance thermometer is inserted into the sample at each position of the layer, and the door is pre-cooled. Generally, the temperature of the separator can be maintained below -30 ° C for stability, and the time is 2 to 3 hours to freeze and transfer to dryness.

2, dry:

Press the condenser refrigeration button to turn on the refrigeration unit (run for 2 minutes), dial the condenser solenoid valve switch, and gradually open the low pressure hand valve. The pressure of the low pressure gauge should not exceed 2Pa, and then open the high pressure hand valve to see that the pressure gauge cannot be greater than 2Pa. If the pressure is too high, close the solenoid valve or the hand valve to lower the pressure. After the condenser temperature is low below -50 °C, wait for 30 to 60 minutes, that is, press the vacuum pump button to start the vacuum pump. Before opening the vacuum pump, first turn off the dry box infusion main valve solenoid valve (wait 5 minutes), and the dry box cooling button is also turned off. System check on the condenser and vacuum line, then plug in the solenoid valve power, press the vacuum pump button, turn on the vacuum pump, slowly open the large butterfly valve between the drying box and the condenser to avoid a large amount of exhaust, and then turn on the vacuum pump set and The butterfly valve between the condensers, wait for the vacuum pressure to rise to 760mmHg and then open the two valves of the vacuum pump group every 1-2 minutes, unplug the power supply, and turn on the Roots pump. When the vacuum in the box meets the heating of the product, the vacuum is generated at 6 or more. After the moisture of the product is also drained, the circulation pump is gradually turned on to observe whether the vacuum is lowered, and then the fuel tank is heated. After the product temperature reaches 32 ° C ~ 35 ° C stability, the insulation is dried for 2 to 3 hours, the drying process can be ended.

3, stop deflation:

Close the tank heating, circulating oil pump, Roots pump, vacuum pump. Turn off the condenser solenoid valve, high pressure hand valve, make the machine run for 10 minutes, close the low pressure hand valve, and close the condenser button. Close the pump valve between the condenser and the pump set; turn on the condenser drain valve to deflate; open the intake valve at the front of the pump, vacuum the pump; remove the product.

4, defrosting:

When defrosting, the overflow valve and drain valve on the condenser must be opened first. The defrosting generally uses tap water, and flows into the condenser from the inlet valve to perform the rinsing. The defrosting is completed. After the water is discharged, the fan butterfly valve is opened and the fan is heated. Dry the water and cut off the total power.

Remark: The button on the console is turned on in green and disconnected in red; the small switch is up and down, and the down is off.

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Steam calciner maintenance

The steam calciner in the drying equipment is a type of drum type reaction equipment for indirect heating of steam in the production of soda ash to decompose the material. The second furnace body consists of a furnace body, an alkali, an alkali, a heating and a transmission device. The second furnace body is a cylinder welded by a steel plate. The furnace body has two rolling rings on the front and rear sides of the furnace body. The furnace body is inclined backward by 1.5% to 2%. A gear ring is arranged near the end of the furnace ring, and the motor rotates through the reducer, the floating coupling and the gear ring. A screw conveyor is used for both the alkali and the alkali. The heating pipes in the furnace are arranged in a concentric circle and supported by the pipe rack. The outer wall of the heating tube has a spiral fin, and the end of the furnace is 2 to 4 m at the end of the furnace. The heavy alkali (sodium bicarbonate) and the return alkali are added to the furnace by the feeder, and are heated indirectly by the medium pressure steam in the heating tube as the furnace body rotates, and the heavy alkali is decomposed into soda ash. The produced soda ash mountain screw conveyor is discharged, and a part is returned to the furnace as a return alkali. At present, the emergence of self-back alkali, throwing and alkali steam forging furnace has made new progress in steam satin furnace.

First, the precautions for the use of steam calciner:

1. Always check the temperature of the 驮 wheel bearing and the sound of the bearing and the rotation of the bearing. If abnormal conditions are found, open the side cover to check the inside. If the problem is serious, stop the furnace for maintenance.

2. The friction surfaces should be kept well lubricated, and the lubricating oil and grease that meet the requirements for drying equipment should be used.

3. When the furnace is shut down, the furnace material should be cleaned, the condensed water should be drained and the steam valve should be cut off to prevent steam leakage.

4. After stopping the furnace, the manhole should be opened and enter the furnace to check whether there is any blockage of the block and whether the inner part is misplaced or fallen off.

5. It is strictly forbidden to beat the furnace and the rotary joint.

6. Regularly check the foundation sinking situation and adjust the height of the base of the 驮 wheel bearing according to the sinking value.

7. Keep the equipment clean and tidy, the insulation layer is complete, and the coating layer should not fall off.

8. Always check and tighten various connecting bolts.

Second, common faults of steam calcining furnaces and their treatment methods

The reason for the large amount of up and down movement of the furnace body is as follows:

1. The position of the wheel is not adjusted well; 2. The lubricating oil changes between the wheel and the ring; 3 the foundation sinks unevenly.

Approach:

1. Adjust the position of the wheel; 2. Check the oiling condition of each wheel and solve it; 3. Adjust the bearing seat gasket after the measurement.

Causes of furnace vibration:

1. The surface of the wheel and the raceway has a concave surface; 2. The gear ring and the pinion gear mesh poorly; 3. The wheel is worn or moved; 4. The connecting bolt of the bearing seat is loose.

Approach:

1. Repair or update; 2. Check and tighten the ring gear bolts; 3. Update or align; 4. Fasten.

Causes of difficulty in starting the furnace:

1. The furnace body is bent; 2. The end face seal is not disengaged; 3. The furnace has many materials and poor fluidity.

Approach:

1. Use the lifting tool to drive the car; 2. Disengage the moving and static sealing rings; 3. Use the lifting tool to drive the car.

Bearing temperature is too high:

1, lack of oil or oil is too dirty; 2, bearing damage; 3, the load of the wheel is too large; 4, the furnace body radiation and conduction heat is large; 5, the bearing clearance is small, the axial force is too large.

Approach:
1. Refueling or oil change; 2. Checking and updating; 3. Adjusting the wheel and feeding amount; 4. Preventing heat and increasing cooling water; 5. Improving the amount of clearance.

Seal ring wear is fast:

1, poor lubrication, into the debris; 2, the sealing surface pressure is too large; 3, the sealing ring is misaligned or skewed.

Approach:
1. Clean the oil hole and surface; 2. Reduce the pressure; 3. Try to adjust.

Causes of leakage of the rotary joint

1. The seal ring is worn or broken;
2, the filler is aging or insufficient pressure;
3. The central axis and the central axis of the furnace are misaligned.

Treatment method: 1. Replace the new one; 2. Replace the packing or tighten the gland bolt; 3. Adjust the suspension spring and the bellows to tighten the bar.

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Select drying equipment according to material form

The method of dryer selection involves the use of past experience. The initial method of selecting the dryer is based on the nature of the material. The equipment selected for handling the liquid material is usually limited to spray drying equipment, drum drying equipment and stirred intermittent vacuum drying. device. It is also suitable for drying liquid materials which are not very viscous, rotary flash drying equipment and inert carrier drying.

Other factors affecting the final choice include low product loss, equipment condition, solvent recovery or the need to use an inert environment and the sensitivity of the material to temperature. In this case, the agitation vacuum drying equipment is preferred, and the residence time of the vacuum drying equipment is stirred. It is very long, while the circulating drying equipment has moderate temperature and moderate residence time. Drum drying equipment has a shorter drying time (residence time) but higher average temperature; spray drying equipment has a shorter contact time and a wider operating temperature range. The above selection is suitable for pumpable suspensions containing fine particles. Liquid, not including paste material.

For continuous drying of pastes and sludge, the most common is a rotary flash drying apparatus. The dust problem is a major consideration because the material is in the state of fine particle dispersion. However, it is therefore difficult to make a choice between intermittent and continuous operation. The intermittent drying equipment usually used is a normal pressure or vacuum tray drying device, a batch normal pressure or vacuum stirring drying device, and a normal pressure or vacuum drum drying device. Vacuum operation is preferable when solvent recovery, fire, danger of toxicity, or when temperature limitation is required.

Drying equipment for continuous operation is:

1. Spray, atomization is the key at this time, which is a problem that should be considered;
2, fluidized bed, but the material is evenly dispersed in the deep bed layer is more difficult;
3. Continuous belt circulating drying equipment, suitable for products requiring dust free;
4, air flow drying, sometimes requires mixing of raw materials and dry products to promote the dispersion of wet materials in the gas entering the drying equipment;
5. Continuous twisting cylinder Direct (heating) or indirect (heating), it is beneficial to operate the wet material and dry material in this equipment.

Indirect heat transfer is usually better if the raw material contains fine particles. For wet powders, pastes and sludges with a particle size of less than 3005 m, drying equipment with vertical tumbling frame can be used; for granular crystal materials with particle size greater than 3005 m, direct heating tumbling drying equipment is usually used. The crystallization of the drying equipment is a problem, but it can be overcome by a suitable tumbling structure; for particles larger than 25 mesh, a through-flow drying equipment with a moving belt or a vibrating perforated plate can be used; the fiber material contains a large amount of moisture, but is dry. It is quite easy because these materials have a large specific surface area, and the fiber material is usually heat sensitive, so care should be taken to maintain a low air temperature, and the operating conditions for avoiding overheating are determined by a penetration cycle test at various temperatures.

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Drying equipment in the chemical industry

In order to increase the drying rate and prevent uneven drying, mechanical agitation or the rotation of the container itself is usually used to increase or continuously update the heat transfer surface of the material, so it is necessary to further study the adhesion problem of the heat transfer mechanism. The drying unit itself is expensive, but it is characterized by a small load on the dust collecting system, high thermal efficiency, easy recovery of the solvent, and the total cost is much cheaper than the direct drying method.

(1) Belt dryer

The belt dryer consists of several independent unit sections. Each unit section includes a circulating fan, a heating device, a separate or common fresh air intake system, and an exhaust gas exhaust system. The operating parameters of the amount of drying medium, temperature, humidity and tail gas circulation can be independently controlled to ensure the reliability of the operation of the dryer and the optimization of operating conditions. The operation with the dryer is flexible, the wet material is fed, and the drying process is carried out in a completely sealed box, and the labor conditions are good, and the leakage of dust is avoided. It is used for the drying of flake, strip and granular materials with good gas permeability. It is especially suitable for materials such as dehydrated vegetables and traditional Chinese medicine decoction pieces with high water content and high material temperature.

(2) Roller scraper dryer

The drum scraper dryer is a continuous operation device for drying a liquid material or a strip material attached to the outer wall of the cylinder by means of a rotating cylinder in a heat conduction manner. The liquid to be dried is flowed from the high level tank into the receiving tank of the drum dryer. The drying drum is driven by the transmission and rotates at a specified speed. The material is formed by a film coating device to form a film on the wall surface of the drum. The heating medium is continuously introduced into the cylinder, and the cylinder body is heated, and the moisture of the film is vaporized by the heat transfer of the cylinder wall, and then the material which meets the drying requirement is scraped off by a scraper, and is spirally conveyed into the storage tank for packaging. The moisture removed by evaporation can be introduced into the corresponding treatment device through a closed cover depending on its nature; it is generally water vapor, which can be directly discharged into the atmosphere by the exhaust pipe at the top of the cover. The machine is mainly used for the treatment of liquid materials, which can be heated and dried by steam, hot water or hot oil, and can be cooled by cold water. Immersion, spray, and milled auxiliary feeding methods can be used according to different material properties and process requirements.

(3) Hollow paddle dryer (blade dryer)

The hollow blade dryer, also known as the blade dryer, is mainly composed of a W-shaped casing with a jacket and two hollow blade shafts and a transmission device. Hollow blades are arranged on the shaft, and the rotary end of the heat medium is introduced at the shaft end. The heat required to dry the water is conducted to the material by the inner wall of the jacketed W-shaped groove and the hollow blade wall. During the drying process, the hollow shaft with hollow blades agitates the material while heating the material, thereby updating the heating surface. It is a continuous conduction heating dryer. The heating medium is steam, hot water or heat transfer oil. The heating medium is introduced into the casing jacket and the two hollow blade shafts to heat and dry the materials in a conductive manner, and the hollow shaft structure of the different materials is different.

The machine is suitable for processing various materials with good thermal stability such as paste, granules and powder. Under special conditions, the heat sensitive material can be dried and the solvent can be recovered during the drying process. It is commonly used for drying or cooling materials such as carbon black, light calcium carbonate, titanium dioxide, barium carbonate, nitrile uric acid, gypsum, clay, manganese dioxide, nylon and polyester chips, polyethylene, polypropylene (recovery solvent).

(4) Vacuum dryer

The dry material is added from the upper part of the top of the vacuum squeezing dryer. When the material is in contact with the shell wall under the stirring of the rotating dent, the surface is continuously updated, and the dried material is subjected to steam (or hot water, heat transfer oil). Indirect heating, but the moisture of the material is vaporized, and the vaporized water is pumped away by the vacuum pump in time. The dried material is indirectly heated by the heat carrier to vaporize the water in the material, and the vaporized water is discharged by the vacuum pump in time.

Due to the high operating vacuum, generally in the range of 400-700 mmHg, the water vapor pressure on the surface of the dried material is much larger than the water vapor pressure in the evaporation space in the dryer housing. Thereby, it is beneficial to the discharge of the internal moisture and the surface water of the material to be dried, which is beneficial to the movement of the water molecules of the dried material to achieve the purpose of drying. The vacuum kneading dryer is suitable for heat-sensitive materials that are easily oxidized at high temperatures or materials that are easily smeared during drying, and materials that must be recovered from steam discharged during drying. Typical dry materials are sodium propylene sulfonate, CMC, phthalocyanine blue, dye intermediates, carboxymethyl starch, maltodextrin, hydrazine sulfonic acid and the like.

(5) Double cone rotary vacuum dryer

The double-cone rotary vacuum dryer has a slightly olive-like shape with a cover at both ends, and two shafts are arranged in the middle to support the body. The body has a jacket for heating, and the body can be rotated when dry, so that the material and the wall are frequently replaced, which overcomes the disadvantage that the material in the vacuum oven is mainly guided by the heating cylinder and has low thermal efficiency. Rotary vacuum dryers have been widely used in fine chemicals and medicines, and are not suitable for materials with high viscosity or strong adhesion during the turning process. The equipment is mainly used for concentrating, mixing, drying and low-temperature drying materials (such as biochemical products) of powder, granular and fibrous materials in the pharmaceutical, chemical and food industries, and is more suitable for oxidizing, volatile and heat sensitive. Strongly irritating, toxic materials and drying of materials that do not allow damage to the crystals.

(6) Spray dryer

Spray drying is the most widely used process in the liquid process forming and drying industry. It is most suitable for the production of powdery, granular solid products from solutions, emulsions, suspensions and paste liquid materials. Therefore, spray drying is an ideal process when the particle size distribution, residual moisture content, bulk density and particle shape of the finished product must meet exact standards.

(7) Vacuum oven

Since the evaporation temperature of the volatile matter contained in the evaporation of the material can be reduced after decompression, it is suitable for drying various heat sensitive and easy oxide materials. This device is often a cylinder or other vacuum-operated outer casing. It is heated by electric heating or hot water or heat-conducting oil through a heating plate or a heating pipe, and is suitable for batch production in small batches.

The oven is a general-purpose drying equipment with a wide application surface. It is a tray-type intermittent drying equipment and is used in pharmaceutical, chemical and food. Heat curing, drying and dehydration of materials and products in light industry, heavy industry and other industries. Such as raw materials, biopharmaceuticals, Chinese herbal medicines, extracts, powders, granules, granules, water pills, packaging bottles, pigment dyes, dehydrated vegetables, dried fruits, sausages, plastic resins, electrical components, baking varnishes, etc.

(8) Rotary flash dryer

The material to be dried enters the drying chamber through the screw input device, and is pulverized by the stirring paddle at the lower part of the dryer. The pulverized material is in full contact with the hot air, flows upward and is dried under the double action of the stirring paddle and the airflow distributor, and passes through the classifier. Screen the material with acceptable particle size and humidity and spin it down until it is qualified.

Product features: fast drying speed. The dryer can be completed in 1-10 seconds; the material residence time can be adjusted. It can be adjusted between 1-500s, suitable for drying of heat-sensitive materials; a variety of feeding devices are available for selection, the feeding is continuous and stable, and no bridging phenomenon occurs; the circumferential air velocity in the drying chamber is high, the material residence time is short, and the material is effectively prevented. The sticky wall and the heat sensitive material are deteriorated; the drying chamber is equipped with a grading ring and a swirling sheet, and the material fineness and the final moisture are adjustable and controllable; the drying strength is high.

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Lignosulfonate obtained after drying

Lignosulfonate, also known as sulfonated lignin, is a by-product of sulfite process paper pulp and can be used as concrete water reducer, refractory material, ceramics, etc. Precipitating agent such as lime, calcium chloride or basic lead acetate is obtained by a process such as precipitation, separation and drying. This week, I will share with you the lignosulfonate product obtained by drying it through drying equipment and its use.

First, the dispersant for making coal water slurry In the industrial preparation of coal water slurry, a certain amount of additives must be added to mix the coal powder and water into a suspension, thereby having good stability and fluidity. Additives include two major categories of dispersants and stabilizers. At present, the domestic industrial coal slurry is naphthalene sulfonate (code 2024), the price is about 4500~5000 yuan / ton, the cost of dispersant per ton of coal water slurry is about 45~5 yuan due to the high cost of dispersant, the impact Development and promotion of coal water slurry industry. The lignosulfonate extracted by the black liquor of papermaking has good dispersibility and stability. After modification, it can be made into a dispersing agent and a stabilizer for coal water slurry, and the cost per ton of coal slurry is about 31 yuan. Lignosulfonate is cheap, and the current price is about 1500~2000 yuan/ton. Instead of naphthalene sulfonate, it can reduce the cost of coal water slurry.

Second, the use of water reducing agent in the production of cement water reducing agent cement can improve the quality of concrete and reduce the amount of cement. Lignosulfonate products can be used to make good water reducing agents. The active group on the alkali lignin benzene ring in the black liquor can be chemically modified to obtain a water-reducing agent with good performance. The most common method is the sulfonation method to produce a lignosulfonate product. An anionic surfactant with semi-colloidal properties that can produce monolayer adsorption at the interface. When the sulfonate product is incorporated into the cement slurry, it can promote the dispersion of the cement particles and release the moisture contained in the gel. The free water is increased to increase the fluidity and retardation of the cement slurry, and the product has a good water reducing effect at a low incorporation amount. The sulfonation process can be carried out in a special reaction tank before entering the drying tower and then dried to obtain a lignosulfonate product.

Third, the granulation of binders and metal ore fines used in industrial briquette production. The boiled industrial coal includes boiler briquette and gasified briquette, that is, pulverized coal and powder coke. The pulverized coal (coke) is added to the binder and cold-formed to produce boiler briquette and industrial briquette for gasification. The boiler briquette is tested in a 4T/hour boiler, the total suspended solids (TSP) is reduced by 80%, the thermal efficiency is increased by 20%~25%, the industrialized burning of gasified coal (coke), the furnace condition is normal, and the gas composition The calorific value and gas production are equivalent to the corresponding lump coal (coke), which can be used as a gas generator for fertilizer, metallurgy and machinery industries. Due to the increasing degree of mechanization of coal mining in China, the amount of coal powder produced during the coal mining process is increasing, causing the long-term backlog of pulverized coal to be untreated. The use of briquette technology can not only alleviate the contradiction between supply and demand of lump coal, but also fully utilize coal resources, and its market prospect is broad.
In addition, metallurgical vertical tank zinc smelting and the like use concentrated black liquor as a binder, but liquid transportation is inconvenient. If the black liquor is made into a lignosulfonate, it is easy to transport and more convenient to use.

Fourth, the alkali lignin extracted from the alkali-pulping black liquor extracted by the petroleum extraction aid is reacted with phenol to obtain a lignin phenolic resin, which is then compounded with a saponified product obtained by hydrolysis of oil to form a paste. Dark brown oily water coagulant. The product is an excellent emulsifier and surfactant, which can be used as a cleaning agent for oil pipelines, a heavy oil viscosity reducer for oil field production and water injection emulsification to increase oil recovery.

Fifth, the lignin sulfonate product used for the production of straw feed has a certain alkalinity and contains a large amount of polypentose, and the polypentose is the nutrient component required by the livestock, and its chemical composition conforms to the feed hygiene standard (GB13078-9C). ), can be used as a straw feed admixture. Lignosulfonate is a resource-based product for treating papermaking waste liquid, which is cheap, and the technology of composite processing of straw with lignosulfonate and urea is simple and the technology is easy to grasp. The use of lignosulfonate to alkalinize straw as a feed has obvious advantages over ordinary ammoniated straw and other ammoniated straws in improving the digestibility of livestock and increasing nutritional value.

Sixth, the production of asphalt emulsifier utilizes lignosulfonate as a basic raw material, and can be processed into LCO-1 asphalt emulsifier. The technical index of the emulsifier fully meets the requirements of domestic commonly used asphalt emulsifier, and Compared with similar products, the production cost is low, about 1/3~1 / 2 of the price of other products, and it can improve the performance of asphalt, and is suitable for the inferior asphalt with high wax content, so that the ductility is improved. The asphalt emulsion produced by the emulsifier can withstand high temperature of 100 ° C, has good storage stability, and has a stable period of up to half a year, and can better meet the construction requirements. This emulsifier is not only suitable for asphalt operations in construction projects such as roads and railways, but also a good waterproof, anti-seepage and anti-corrosion agent. It can be used for waterproofing, leak-proof coating and wood anti-corrosion of houses and buildings.

Seventh, the product used as the water treatment agent for the black liquor extraction by alkali method contains a large amount of alkali lignin, which has the property of anionic polymer coagulant, has good reactivity, and is easy to destabilize under acidic conditions, and has agglomeration characteristics. It is especially suitable for the treatment of acidic wastewater. Alkali lignin is an effective coagulant for charged proteins, bacteria, dyes and other colloids and suspensions in acidic wastewater.

Eighth, other uses of the water solubility and surface activity of lignosulfonate products, can be used as a release agent for building components, and also used in refractory production and sand molding operations. It can be used as a flotation agent for metal ore beneficiation operations by utilizing its surface activity and adsorption properties. The use of lignin contains a variety of living genes, which are slowly degraded by soil organisms in the soil and converted into humic substances. Lignosulfonate products can be used as fertilizer additives. For ammonium lignin products extracted from black liquor by cooking with ammonium sulfite, because it contains more than 5% organic potassium, more than 7% of nitrogen, the product humus content is as high as 84%, and can be compounded with other fertilizers. Produce high-efficiency compound fertilizer. Lignin powder is widely used as a pesticide dispersant, a nitrogen fertilizer slow release agent, a phosphate fertilizer to produce a grinding aid, and a wood binder.

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Resource management of papermaking black liquor

China has a lot of small and medium-sized paper mills with straw as raw material, but the problem of black liquor pollution has not been solved very well. The previously proposed alkali recovery black liquor treatment measures, due to large investment, are generally difficult for medium and small paper mills to bear. In addition, there are many processes, complicated operation and operation, and it is difficult to meet environmental emission standards. The practical results show that it is difficult to promote and apply.

In recent years, Wuxi Linzhou Drying Machine Factory, China Academy of Forestry Science and Technology Research Institute and Nanjing Forestry University have been working hard to explore and introduce the black liquor resource utilization method, that is, to separate the black liquor solid and liquid into lignin. Dry powder of sulfonate. The technology is characterized by high technology content, advanced engineering technology, simple process flow, low investment, and the recycled lignosulfonate has a wide range of uses and good economic benefits. After the completion of the project, not only can the papermaking black liquor be converted into products, but there is no wastewater discharge port in the project area, no secondary pollution, good pollution control effect, good environmental and economic benefits. In particular, due to the current black liquor pollution can not be resolved, a number of small paper mills have been forcibly shut down, and many existing paper mills are facing a production crisis due to pollution problems. The application of pulping black liquor resource treatment engineering technology will undoubtedly bring hope for re-survival to these plants.

The preparation of lignosulfonate from black liquor is technically mature. There are fifteen paper mill users in Wuxi Linzhou Drying Machine Factory, and there is no problem in equipment manufacturing supply. Many paper mills now want to solve the problem of black liquor pollution as soon as possible, but it is difficult to solve problems due to funding and other issues, resulting in the failure of the governance project. Now with the black liquor resource management method, the by-product lignosulfonate produced at the same time can obtain good economic benefits, and the equipment investment cost can be recovered within a few years. Therefore, if the financing channels can be properly solved and the cooperation between the factory and the technical design parties and equipment manufacturers, this will be a very good and promising investment project.

Black liquor resource management technology program

 

First, the cause of papermaking black liquor

The wastewater produced during the non-wood fiber (straw) papermaking process is:
1. The waste liquid (ie black liquor) remaining after the steamed pulp stock solution is subjected to pressure filtration. 2. Separate the rinse water produced by the concentrate.
3. White water produced by the paper machine.

The white water produced by the paper machine can be reused after treatment, but the black liquor and rinse water cannot be recycled. This part of the water accounts for more than 90% of the total discharge of pollutants in the paper mill. After the waste liquid is discharged, it will seriously pollute the environment, so direct discharge is strictly prohibited.

Second, black liquor ingredients

The straw used in papermaking raw materials contains cellulose, lignin and hemicellulose (glycans). The paper is only used for cellulose (about 40%), and about 25% of the lignin and About 28% of hemicellulose and xylose, potassium, nitrogen, phosphorus, etc., are discarded with black liquor. The lignin, hemicellulose, and xylose, potassium, nitrogen, and phosphorus contained in the black liquor are highly valuable in industrial and agricultural production.

Third, technical scheme for recycling black liquor of papermaking

Slurry separation→Evaporation and concentration (middle stage sulfonation reaction)→Spray drying Slurry separation: After removing the impurities from the original slurry, the double-layer slurry extruder with “three-crush and two-replacement” function makes the black liquor extraction rate ≥90 %, the concentration of black liquor is about 8~10%, and the black liquor is extracted ≤10m3/t pulp;

Evaporation and concentration: the black liquor after slurry separation has a concentration of about 8~10%. The concentration after evaporation and concentration by the high-efficiency energy-saving horizontal spray evaporation device is about 40%. During the evaporation process, the steam condensation water generated by the evaporator heat source can be used. The boiler is replenished with water or used in production. The evaporating condensed water in the concentration process can be reused without sewage discharge; the middle part of the evaporation and concentration is subjected to sulfonation reaction through a high pressure reaction kettle;

Spray drying: The concentrated black liquor is spray-dried by a high-speed centrifugal spray dryer to obtain a lignosulfonate product, which has a wide range of uses.

Fourth, the status quo of other papermaking black liquor treatment technology

1.1 alkali recovery method
The traditional alkali recovery technology uses a concentration-combustion-caustic process to recover the alkali and recycle it. The alkali recovery rate of large wood pulp and paper mills is up to 90%, and the alkali recovery rate of non-wood raw material pulp mills (rice, wheat straw, reed, sucrose residue, etc.) can reach more than 70%. The use of alkali recovery can greatly reduce the high-load pollution of black liquor, BOD5 can be reduced by 80% to 85%, in addition to the recovery of thermal chemicals to reduce costs and increase economic benefits.

The advantage of this method is that the organic matter in the black liquor is burned to produce steam for use by the factory, there is no market sales problem; the pollution load of about 80% of the whole plant can be reduced; more than 50% of caustic soda can be recovered, which is a thorough pollution. Governance technology. For small and medium-sized straw pulp enterprises, this method has certain shortcomings: the project investment and operation cost are high, and the pulp mill with an annual output of more than 17,000 tons can achieve low profit operation; wheat straw black liquor has low calorific value, high viscosity and silicon content. The high volume makes the alkali recovery cost high, the alkali recovery rate is low, the operation is difficult, and the processes such as causticization and combustion still need to be improved, otherwise it will not operate normally.

1.2 Physical Chemistry
1.2.1 Acid precipitation method
After extracting the black liquor through the microfilter to remove the fine fibers, the lignin separator is added to the acid solution to control the pH value, and the lignin is precipitated and dehydrated by heating and pressure filtration to become a lignin product. The method has a CODCr removal rate of 80%, an SS removal rate of about 85%, a chroma removal rate of 95%, and a lignin recovery rate of about 80%, which has a significant effect on reducing organic dye loading. The advantage of this method is that the process is simple, the investment is small, and the lignin is recovered while reducing the dyeing load of the organic matter. At the same time, there are a series of shortcomings: technically, the equipment is seriously corroded, lignin is difficult to filter and dehydrate; the residual liquid after the process can not meet the discharge standard, and it is acidic and needs further treatment; economically, the cost of acid must be reduced, and at the same time There are sales problems in the products.

1.2.2 Coagulation sedimentation method
After the black liquor is acidified, the flocculant is added to the coagulation and sedimentation. After the solid-liquid separation, the sediment is incinerated as a fuel, and the filtrate is partially adsorbed and filtered for reuse in the pulping section, and the rest is discharged into the middle section wastewater. The initial investment of this method is relatively low, and it is suitable for small paper mills with an annual output of less than 10,000 tons. However, there are many shortcomings: the treatment is not complete, the treatment rate of BOD5 is only about 20%; the amount of sludge generated is large, the dehydration is difficult, and the treatment is Difficult, it is actually a method of pollution transfer; operating costs are sensitive to flocculant prices, and annual operating costs are high.

1.3 Anaerobic biological treatment
After the pretreatment of the straw black liquor, the anaerobic treatment process is used to reduce the CODCr and recover some of the biogas energy. Anaerobic processes generally use more efficient AFB (anaerobic fluidized bed), UASB (anaerobic sludge bed) or ABR (anaerobic baffled reactor) with two-phase anaerobic characteristics, CODCr removal rate is generally It is about 50%. When the conditions are met, the papermaking black liquor can be mixed with other wastes and liquids to achieve the effect of mutual utilization and waste disposal. Compared with the aerobic biological method, the anaerobic treatment of high-concentration organic wastewater has its unique advantages: it can recover energy in the form of biogas, the sludge production is low, and the initial degradation of complex organic matter is beneficial to the subsequent process. The main disadvantages are: sensitive to toxic substances in the wastewater; the treatment is not thorough enough, there must be a follow-up process to enable the sewage to reach the standard discharge; the operation management is relatively complicated, and the alkali cannot be recovered.

1.4 Comprehensive utilization method

1.4.1 Resource Management
The lignin is extracted by acid precipitation and the lignin product is obtained. The supernatant is lime-calculated to separate the calcium salt and the alkaline solution, the calcium salt is used as a building material raw material, and the alkaline solution is concentrated by evaporation to obtain a sugar slurry product. The evaporated condensed water is completely recovered and used for vacuum washing, so that the black liquor is all utilized to achieve zero discharge. Resource management has the advantages of turning waste into treasure, the equipment is simpler, and the system operation is relatively stable; but in order not to affect the pulp quality, the alkaline liquid reuse rate cannot exceed 25%, resulting in a corresponding alkali recovery rate of only 5%. The various products generated during the process have more impurities and no comprehensive utilization value, and need to be further processed.

1.4.2 Resource utilization

Directly use black liquor of straw pulp to produce black liquor coal water slurry, obtain thermal energy through combustion, exhaust gas after combustion reaches the standard, residue can be used as building materials; or black liquor can be changed by chemical method Sex, used as a drilling mud viscosity reducer; another research direction is to extract lignin in black liquor, which is chemically modified to become a chemical raw material, which can be made into water reducing agent, asphalt emulsifier and water treatment agent. Etc. There have been a lot of research results on this.

The resource utilization of black liquor has broadened the thinking of black liquor pollution control, and enterprises can fully apply it according to actual conditions. Annual production of 10,000 tons of pulp and paper enterprises, using traditional alkali recovery technology, annual loss of 110-1.4 million yuan; scale expansion to annual output of more than 17,000 tons, can maintain low-profit operation; scale greater than 25,000 tons, alkali recovery process The annual profit for the enterprise is more than 2 million yuan, and the economic benefit of alkali recovery is positively related to the scale of the enterprise. The benefits of SO2 acid precipitation, acid precipitation + anaerobic process and resource management all depend on the sales and price of lignin produced. It is of great significance to develop and promote the market application of lignin. Although the LB_1 alkali precipitation method is simple in equipment and convenient in operation, the alkali recovery rate is only 5%, and the recovered lignin impurities are numerous, and there is no comprehensive utilization value, and it can only be used as a transitional measure for reducing the black liquor of the straw pulp.

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