A pulping system

Abstract

The invention relates to the field of pulping, and discloses a pulping system, comprising a pulping workshop, the pulping workshop comprising a cooking system, a screening system, a bleaching system and a pulp washing system, the screening system comprising a knot remover and a multi-stage fine screening system, the pulp washing system comprising a coarse screening section pulp washer, a fine screening section pulp washer, a screening pulp washer, an oxygen descaling section pulp washer, a D0 section pulp washer, an EOP section pulp washer, a D1 section pulp washer and a reflux pipe, the knot remover, the coarse screening section pulp washer, the multi-stage fine screening system, the fine screening section pulp washer and the bleaching system are connected in sequence, the filtrate outlet of the coarse screening section pulp washer is connected to the cooking system, and the filtrate outlet of the fine screening section pulp washer is connected to the multi-stage fine screening system, so as to improve the pulping rate of bamboo pulp and reduce resource waste.

Description

Technical Field

[0001] The invention relates to the field of pulping, and in particular to a pulping system. Background Art

[0002] The pulping process mainly includes the steps of material preparation, cooking, screening, bleaching, pulp washing, papermaking, recycling, etc. However, the pulping methods in the prior art generally follow the process flow of wood pulping, and the bamboo pulp preparation process is not as mature as the wood pulp preparation process. In fact, there are many essential differences between bamboo pulping and wood pulping. Since the chemical structure uniformity of bamboo is much lower than that of wood, the lignin content of bamboo is lower than that of wood, and the hemicellulose content of bamboo is much higher than that of wood, how to improve the bamboo pulp preparation method according to the characteristics of bamboo, improve the pulping rate, and reduce resource waste is a key issue in the domestic pulping industry. Summary of the invention

[0003] The invention aims to provide a pulping system to improve the bamboo pulp yield and reduce resource waste.

[0004] To achieve the above-mentioned object, the present invention adopts the following technical scheme: a pulping system, including a pulping workshop, the pulping workshop includes a cooking system, a screening system, a bleaching system and a pulp washing system, the screening system includes a knot remover and a multi-stage fine screening system, the pulp washing system includes a coarse screening section pulp washer, a fine screening section pulp washer, a screening pulp washer, an oxygen desorption section pulp washer, a D0 section pulp washer, an EOP section pulp washer, a D1 section pulp washer and a return pipe, the knot remover, the coarse screening section pulp washer, the multi-stage fine screening system, the fine screening section pulp washer The pulp machine and the bleaching system are connected in sequence, the filtrate outlet of the coarse screening section pulp washer is connected to the cooking system; the filtrate outlet of the fine screening section pulp washer is connected to the multi-stage fine screening system, the bleaching system includes an oxygen desorption bleaching device, a D0 section bleaching device, an EOP section bleaching device and a D1 bleaching device, and the screening pulp washer, oxygen desorption bleaching device, oxygen desorption section pulp washer, D0 section bleaching device, D0 section pulp washer, EOP section bleaching device, EOP section pulp washer, D1 bleaching device and D1 section pulp washer are connected in sequence.

[0005] The beneficial effects of this program are:

[0006] 1. After the cooking system cooks the bamboo chips into bamboo pulp, the bamboo pulp enters the screening system. The knot remover removes the large bamboo knots in the pulp, and then the pulp is washed by the coarse screen section washer. At this time, since the pulp has just come out of the cooking pot, the filtrate generated by the coarse screen section washer has a higher temperature, more residual alkali, and contains some unscreened fibers. At this time, the filtrate of the coarse screen section washer is recovered and used in the cooking system, which can reuse the heat energy, residual alkali and unscreened fibers in the filtrate, thereby improving the bamboo pulp yield and reducing resource waste.

[0007] 2. The impurities in the slurry are screened out through the multi-stage fine screening system. The slurry screened by the multi-stage fine screening system enters the fine screening section pulp washer. The fine screening section pulp washer adjusts the concentration of the slurry to meet the concentration requirements of the bleaching system. After the screening of the multi-stage fine screening system, the temperature of the slurry drops after contacting multiple screening devices. At this time, the filtrate produced by the fine screening section pulp washer has a lower temperature. The filtrate of the fine screening section pulp washer is used in the multi-stage fine screening system and the filtrate of the fine screening section pulp washer is recycled to save water resources, protect the environment, and reduce emissions.

[0008] The filtrate from the fine screening section pulp washer is used in the multi-stage fine screening system, which further reduces the temperature of the pulp in the multi-stage fine screening system, thereby improving the screening and bleaching efficiency. Specifically, after the pulp is cooked, the temperature is high, and the material of small and medium-sized impurities is soft. When screening, the impurities are easily broken by collision and passed through the screening; after the temperature is lowered, the impurities become compact and hard, and are not easy to break, and are easier to be screened out, thereby preventing impurities from affecting the bleaching effect, thereby improving the screening and bleaching efficiency.

[0009] 3. The pulp flows back and forth in the bleaching system and the pulp washing system, and bleaching and pulp washing are carried out alternately. The bleaching system heats up according to the temperature required for bleaching at different stages, and adds different bleaching agents for bleaching. The pulp washing system controls the pulp concentration at a higher concentration to ensure the reaction rate during bleaching. Specifically, after the oxygen stripping stage is completed, the pulp is cleaned by the oxygen stripping section pulp washer to wash away the removed lignin to prevent the lignin from affecting the reduction reaction in the D0 stage, so that the reaction in the D0 stage is more sufficient and faster, thereby improving the bleaching efficiency. After the D0 stage is completed, the pulp is cleaned by the D0 pulp washer to wash away the acidic substances generated in the D0 stage to prevent the acidic substances from reacting with the alkaline substances in the EOP stage, thereby strengthening the bleaching effect of the oxidation reaction in the D1 stage, thereby improving the bleaching efficiency. After the D1 stage is completed, the pulp is cleaned by the D1 section pulp washer to wash away the residual alkaline substances in the D1 stage, and then the pulp is stored to improve the bleaching efficiency.

[0010] Preferably, as an improvement, the multi-stage fine screening system includes a first-stage fine screening device, a desander, a second-stage fine screening device, a third-stage fine screening device, a slag washer and a dilution riser, the screening outlet of the first-stage fine screening device is connected to the pulp washing system, the screening outlet of the first-stage fine screening device is connected to the desander, the screening outlet of the desander is connected to the second-stage fine screening device, the screening outlet of the second-stage fine screening device is connected to the first-stage fine screening device, the screening outlet of the second-stage fine screening device is connected to the third-stage fine screening device, the screening outlet of the third-stage fine screening device is connected to the second-stage fine screening device, the screening outlet of the third-stage fine screening device is connected to the slag washer, the screening outlet of the slag washer is connected to the third-stage fine screening device, the filtrate outlet of the fine screening section pulp washer is connected to the dilution riser, and the dilution riser is simultaneously connected to the first-stage fine screening device, the desander, the second-stage fine screening device and the third-stage fine screening device. Such an arrangement has the following effects:

[0011] 1. The first-stage good pulp screened by the first-stage fine screening equipment enters the next process, the first-stage tailings screened by the first-stage fine screening equipment enters the desander, the good pulp screened by the desander enters the second-stage fine screening equipment, the second-stage good pulp screened by the second-stage fine screening equipment enters the first-stage fine screening equipment, the second-stage tailings screened by the second-stage fine screening equipment enters the third-stage fine screening equipment, the good pulp screened by the third-stage fine screening equipment enters the second-stage fine screening equipment, the tailings screened by the third-stage fine screening equipment enters the slag washer, the good pulp washed by the slag washer enters the third-stage fine screening equipment, and the filtrate of the pulp washer in the fine screening section can enter the dilution riser.

[0012] 2. After the slurry enters the first stage fine screening equipment, some fibers are attached to the impurities and form blocks, which cannot pass through the screen plate. They can only enter the desander with the first stage tailings. At this time, the liquid in the dilution riser dilutes the first stage tailings and enters the desander. The first stage tailings rotate at high speed in the desander, and the heavier impurities and fibers are separated under the action of centrifugal force. The heavier impurities are discharged downward, and the lighter fibers are discharged upward and enter the second stage fine screening equipment. If the slurry enters the desander first and then the first stage fine screening equipment, there will be more fibers in the slurry at this time, and the fibers attached to the impurities are not easy to disperse. After entering the desander, most of the fibers are discharged downward with the impurities, resulting in large fiber loss and low pulp yield. In this scheme, after screening by the first stage fine screening equipment, most of the fibers have been screened out and enter the fine screening section pulp washer. The remaining fibers are diluted by liquid, and the combination of fibers and impurities is no longer tight. The desander can more easily separate impurities and fibers, thereby reducing fiber loss and improving pulp yield.

[0013] 3. Let the second-stage fine pulp screened by the second-stage fine screening equipment enter the first-stage fine screening equipment for screening again to form the first screening cycle, and let the good pulp screened by the third-stage fine screening equipment enter the second-stage fine screening equipment to form the second screening cycle. For some workshops with limited space, the first-stage fine screening equipment, the sand remover, the second-stage fine screening equipment, and the third-stage fine screening equipment are usually connected in sequence. The first-stage fine screening equipment and the third-stage fine screening equipment are the farthest apart. Compared with the good pulp screened by the three-stage fine screening equipment directly entering the first-stage fine screening equipment to form a large screening cycle, the length of each screening cycle in this solution is shorter, the total pipeline length used is shorter, the process is shorter, the cycle time is shorter, and the screening efficiency is higher.

[0014] 4. Finally, the tailings screened out by the three-stage fine screening equipment are cleaned to wash out the remaining fibers in the tailings to avoid wasting fibers. The good pulp washed out by the slag washer enters the three-stage fine screening equipment to form the third screening cycle with a short cycle length and a short cycle time. The fast cycle is used to make up for the low screening efficiency of low-concentration tailings.

[0015] 5. In the subsequent process of the multi-stage fine screening system, the fine screening section pulp washer is further away from the cooking process, so the filtrate temperature produced by the fine screening section pulp washer is lower. Using this filtrate in the multi-stage fine screening system can effectively reduce the system temperature and thus improve the screening efficiency.

[0016] The filtrate from the fine screening section pulp washer can enter the dilution riser for storage and be used in the three fine screening devices respectively to dilute the slurry at each stage and control the slurry concentration to achieve the best screening efficiency. At the same time, since the three fine screening devices all use the liquid in the dilution riser for dilution, the temperature difference is not large, so that the concentration can be adjusted at any time according to the properties of the slurry.

[0017] 6. The temperature of the knot removal stage is relatively high because it has just been cooked; the temperature of the bleaching stage is also certain to ensure the reaction efficiency of the bleaching agent; and in the fine screening stage, cooling can improve the screening efficiency, so heating is not required. A separate liquid circulation system is required to maintain room temperature, and the filtrate of the fine screening section pulp washer flows back to the dilution riser to form such a liquid circulation system.

[0018] Preferably, as an improvement, the cooking system comprises a cooking pot, a pumping unit and a holding tank, the holding tank comprises a white liquid tank, a warm black liquid tank and a hot black liquid tank, the white liquid tank holds white liquid, the warm black liquid tank holds warm black liquid, the hot black liquid tank holds hot black liquid, the cooking pot is connected to the white liquid tank, the warm black liquid tank and the hot black liquid tank respectively; the cooking pot is connected to the white liquid tank, the warm black liquid tank and the hot black liquid tank, a heating and heat preservation unit is provided on the cooking pot, and the cooking pot is divided into a first cooking pot and a second cooking pot according to the cooking stage;

[0019] The first cooking pot can pre-soak bamboo chips, the first cooking pot can replace warm black liquor with hot black liquor, and the first cooking pot can replace part of the hot black liquor with white liquor; the second cooking pot can cook bamboo chips, and the heating and insulation unit can heat the second cooking pot to 140-154°C; the second cooking pot can convert black liquor into pulp washing liquid, and according to the temperature of the replaced black liquor, the pumping unit can discharge the hot black liquor into the hot black liquor tank and the warm black liquor into the warm black liquor tank.

[0020] This setting has the following effects:

[0021] 1. Due to the compact structure of bamboo chips, after loading them into the first cooking pot, they are pre-soaked with warm black liquid so that the warm black liquid is in full contact with the bamboo chips and penetrates into the inside of the bamboo chips, thus opening up the heat transfer channel inside the bamboo chips, making the subsequent heating faster, using less steam, and having a higher pulp yield. Based on a cooking pot of 400m3, 15 pots of pulp can be produced per day.

[0022] 2. Compared with gradually heating up the first cooking pot, in this scheme, the first cooking pot directly replaces the warm black liquor with hot black liquor, the temperature rises faster, the temperature difference at the contact point between the hot black liquor and the warm black liquor is the largest, the wax layer on the surface of the bamboo knot is removed faster and more thoroughly, and the wax layer and the warm black liquor are also replaced together to complete the cleaning of impurities; at the same time, since part of the warm black liquor penetrates into the bamboo chips during the pre-impregnation process, the warm black liquid inside the bamboo chips cannot be replaced immediately, and can only be gradually heated up to become hot black liquid through heat exchange, thereby avoiding the fibers inside the bamboo chips from being damaged by the temperature difference caused by the rapid heating, thereby improving the pulping rate.

[0023] 3. In the first cooking pot, part of the hot black liquor is replaced with white liquor to maintain the pH value.

[0024] 4. In the second cooking pot, the cooking pot can be heated to 140-150°C by the heating and insulation unit and maintained for 1 hour. According to the temperature of the displaced black liquor, the pumping unit can discharge the hot black liquor into the hot black liquor tank and the warm black liquor into the warm black liquor tank.

[0025] 5. Compared with washing the bamboo chips with pulping liquid after they come out of the second cooking pot, in this scheme, the black liquor is directly replaced by pulping liquid in the second cooking pot, and the bamboo chips are washed by utilizing the high temperature remaining in the second cooking pot. The adhesion of impurities is lower at high temperature, and the bamboo chips are easier to be rinsed clean. At the same time, directly replacing the black liquor with pulping liquid can quickly terminate the reaction between the black liquor and the bamboo chips, and prevent the excessive reaction from causing a low pulping rate.

[0026] 6. According to the temperature of the black liquor displaced by the second cooking pot, the hot black liquor is discharged into the hot black liquor tank, and the warm black liquor is discharged into the warm black liquor tank, so that the alkali and temperature in the black liquor are recycled, which saves energy and protects the environment and improves production efficiency; at the same time, the black liquor is discharged into different tanks according to the temperature so that the black liquor forms a temperature gradient for use by the next batch of the first cooking pot.

[0027] Preferably, as an improvement, a recovery workshop is also included, and the recovery workshop includes an evaporation workshop, an alkali furnace workshop and a calcination workshop which are connected in sequence, the filtrate outlet of the coarse screen section pulp washer of the screening system is connected to the evaporation workshop and the warm black liquor tank, the calcination workshop is connected to the white liquor tank, the evaporation workshop can evaporate and concentrate the black liquor, the alkali furnace workshop can burn the black liquor to obtain green liquor, and the calcination workshop can make the green liquor undergo a calcination reaction to obtain white liquor. In this arrangement, the black liquor is the waste liquid formed after bamboo chips are boiled. In this scheme, the black liquor is evaporated, burned and calcined to obtain white liquor, and the white liquor is reused for bamboo chips to boil, thereby recovering the alkali in the black liquor, so as to save costs, reduce emissions, and be green and environmentally friendly.

[0028] Preferably, as an improvement, the alkali furnace workshop includes an alkali ash treatment system, which includes a stirring tank, a crystallization tank, a centrifuge and an evaporator connected in sequence, and a recirculation unit is provided on the crystallization tank, and the recirculation unit includes a circulation pipeline, a steam pipeline and a heat exchanger, and the circulation pipeline passes through the heat exchanger, and the steam pipeline communicates with the top of the crystallization tank and the heat exchanger, and the steam pipeline and the circulation pipeline are connected in the heat exchanger. Such a configuration has the following effects:

[0029] 1. Stir the alkali ash and water in a stirring tank to form a slurry, and pass the slurry into a crystallization tank. The slurry continuously enters the heat exchanger through a circulation pipeline for heat exchange and cooling. Since mirabilite is easy to crystallize at high temperatures, and potassium chloride is more likely to crystallize at low temperatures, the crystals precipitated in the crystallization tank are mainly potassium chloride. The remaining slurry after passing through the centrifuge contains a large amount of mirabilite. The remaining slurry after passing through the centrifuge may also contain potassium chloride and needs to be recrystallized. The solution containing a large amount of mirabilite enters the evaporator for evaporation and crystallization, thereby achieving the purpose of recovering potassium chloride and mirabilite in the alkali ash respectively.

[0030] 2. The higher temperature steam rises to the top of the crystallizer, then merges with the slurry in the steam pipe and the circulation pipe, and then cools down through the heat exchanger and returns to the crystallizer, thereby improving the efficiency of cooling the slurry, thereby accelerating the crystallization speed and improving the recovery efficiency.

[0031] Preferably, as an improvement, the crystallizer includes an upper cone, a cylinder, a lower cone and a salt leg from top to bottom, a demister is arranged in the upper cone, a flushing pipe is arranged horizontally at the upper end of the cylinder, one end of the flushing pipe is connected to the outside of the cylinder, the other end of the flushing pipe is located directly below the demister, a vertical upward nozzle is arranged at the other end of the flushing pipe, and the spraying range of the nozzle covers the demister; one end of the circulation pipe is connected to the cylinder, and the other end of the circulation pipe is connected to the lower cone. Such an arrangement has the following effects:

[0032] 1. If the mist and other particles entrained by the steam enter the steam pipe and the heat exchanger, it is easy to cause blockage, scaling or corrosion of the equipment. Therefore, a demister is set in this scheme. When the steam passes through the demister, due to the inertial impact of the steam, the mist collides with the corrugated plate and the gathered droplets are so large that the gravity generated by itself exceeds the combined force of the gas rise force and the liquid surface tension. The droplets are separated from the surface of the corrugated plate, thereby avoiding blockage, scaling or corrosion of the equipment.

[0033] 2. After long-term use, steam causes slurry or crystallization in the demister, which can easily cause the demister to become blocked, thereby reducing the gas-liquid separation effect of the demister. In this solution, the demister is sprayed under the flushing pipe to avoid blockage.

[0034] Preferably, as an improvement, a transition portion is provided at the lower end of the lower cone, and the transition portion is inserted into the upper end of the salt leg. The salt leg is provided with a drain port, a discharge port and three feed ports. The drain port is located at the bottom of the salt leg. The three feed ports are respectively an upper feed port, a middle feed port and a lower feed port. The upper feed port is horizontally arranged between the outer wall of the transition portion and the inner wall of the salt leg. The middle feed port, the discharge port, the lower feed port and the drain port are vertically aligned from top to bottom and are all located on the central axis of the salt leg. The middle feed port and the lower feed port are both facing downward. Such an arrangement has the following effects:

[0035] 1. The slurry enters the salt leg through multiple feed ports at the same time, collides with the side wall of the salt leg to form a vortex, which spreads upward, thereby evenly distributing the slurry in the crystallization tank.

[0036] 2. The slurry entering the circulation pipeline is continuously cooled, potassium chloride crystals are precipitated and slide down the side wall of the lower cone into the salt leg. However, the side wall of the lower cone is an inclined surface, and some crystals expand at low temperatures and combine with the side wall of the lower cone without sliding into the salt leg. After a long time, the surface of the side wall of the lower cone will become rough, and more crystals cannot slide into the salt leg, making it difficult to collect the crystals. In this scheme, a transition part is provided, and the slurry entering the salt leg from the upper feed port cannot directly enter the lower cone upward, and cannot exchange temperature with the slurry in the lower cone. Therefore, the slurry between the salt leg and the transition part cools down slowly, and the slurry is horizontally ejected from the upper feed port to impact the outside of the transition part. When the transition part contacts the slurry of this part, the temperature is higher than that of the lower cone. Therefore, when the crystal passes through the transition part, the expansion effect is small and it is easier to slide into the salt leg. The lower cone is also connected to the lower end of the circulation pipe. Since the part connected to the lower end of the circulation pipe has greater fluidity, there is no need to consider the problem that the crystal is not easy to slide into the salt leg.

[0037] 3. After the slurry sprayed from the upper feed port collides with the transition part, it flows in the annular space on the outer wall of the transition part, thereby driving the slurry in the salt leg to form a vortex. After the middle feed port and the lower feed port spray downward, they rush upward in the opposite direction, and rush into the crystallization tank under the drive of rotation, so that the slurry is more evenly distributed in the crystallization tank.

[0038] 4. The slurry enters from the middle feed port to continuously flush the discharge port to prevent it from being blocked; the slurry enters from the lower feed port to continuously flush the drain port to prevent it from being blocked, so as to remove the crystals at the bottom of the salt leg. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic diagram of the overall process of the embodiment;

[0040] Figure 2 A schematic diagram of a cooking system according to an embodiment;

[0041] Figure 3 Schematic diagram of a screening system, a bleaching system and a pulp washing system of an embodiment;

[0042] Figure 4 A schematic diagram of a multi-stage fine screening system of an embodiment;

[0043] Figure 5 It is a schematic diagram of the oxygen debleaching device of the embodiment;

[0044] Figure 6 This is a schematic diagram of the D0 stage bleaching device of the embodiment;

[0045] Figure 7 It is a schematic diagram of the EOP section bleaching device of the embodiment;

[0046] Figure 8 This is a schematic diagram of the D1 stage bleaching device of the embodiment;

[0047] Fig. 9 It is a front view of the desander of the embodiment;

[0048] Fig.10 A top view of a desander according to an embodiment;

[0049] Fig.11 A schematic diagram of an alkali ash treatment system in an embodiment;

[0050] Fig.12 It is the crystallization tank structure diagram of embodiment. DETAILED DESCRIPTION

[0051] The following is further described in detail through specific implementation methods:

[0052] The reference numerals in the drawings of the specification include:

[0053] Material preparation workshop a, pulping workshop b, pulp board workshop c, recycling workshop d,

[0054] Cooking pot 1, heat exchanger 2, warm black liquor tank 3, hot black liquor tank 4, pulp washing liquid tank 5, cold white liquor tank 6, hot white liquor tank 7, water pump 8, pumping valve 9, spray pot 10,

[0055] coarse screen washer 111, fine screen washer 112, first oxygen descaling stage washer 121, second oxygen descaling stage washer 122, D0 stage washer 130, EOP stage washer 140, D1 stage washer 150, reflux pipe 160, oxygen descaling bleaching device 210, oxygen descaling medium-consistency riser 211, oxygen descaling medium-consistency pump 212, first oxygen mixer 213, oxygen pre-reaction pipe 214, oxygen descaling steam ejector 215, second oxygen mixer 216, oxygen reaction tower 217, oxygen descaling feeding pump 218, pre-bleaching riser 221, pre-bleaching feeding trough 222, pre-bleaching feeding pump 223, pre-bleaching feeding pump 224, D0 stage bleaching device 230, D0 medium-consistency riser 231, D0 medium-consistency pump 232, D0 steam ejector 233, D0 mixer 234, D0 reaction tower 2 35. D0 feeding pump 236, EOP section bleaching device 240, EOP medium-consistency riser 241, EOP medium-consistency pump 242, EOP mixer 243, EOP reaction tower 244, EOP feeding pump 245, D1 section bleaching device 250, D1 medium-consistency riser 251, D1 medium-consistency pump 252, D1 mixer 253, D1 reaction tower 254, pulping tower 260, de-knot machine 300, filtrate tank 400, multi-stage fine screening system 500, buffer riser 510, first-stage fine screening equipment 520, desander 530, pulp inlet pipe 531, pulp outlet pipe 532, conical cyclone 533, connecting branch pipe 534, frame 535, slag discharge tank 536, second-stage fine screening equipment 540, third-stage fine screening equipment 550, slag washer 560, dilution riser 570,

[0056] Stirring tank 610, centrifuge 620, evaporator 630, crystallizer 700, upper cone 711, cylinder 712, lower cone 713, transition portion 714, salt leg 715, demister 721, flushing pipe 722, nozzle 723, pressure gauge 731, liquid level gauge 732, sight glass 733, steam outlet 741, population 742, recycling inlet 743, recycling outlet 744, drain port 745, feed pipe 750, upper feed port 751, middle feed port 752, lower feed port 753, discharge pipe 760, discharge port 761, circulation pipeline 771, steam pipeline 772, heat exchanger 773.

[0057] Example

[0058] The embodiment is basically as follows Figure 1-Figure 12 As shown: A pulping system, including Figure 1The material preparation workshop, pulping workshop, pulp board workshop and recycling workshop are shown. The material preparation workshop, pulping workshop and pulp board workshop are connected in sequence. The material preparation workshop is equipped with a re-crusher, a washing machine and a dehydrator connected in sequence. The bamboo chips are transported between the material preparation workshop and the pulping workshop through a transportation device; the pulping workshop and the recycling workshop are connected to each other to form a circulation of black liquid and white liquid. The pulp board workshop can make pulp into paper. The recycling workshop includes an evaporation workshop, an alkali furnace workshop and a condensation workshop ( Figure 1 The evaporation workshop can evaporate and concentrate the black liquor, the alkali furnace workshop can burn the black liquor to obtain green liquor, and the alkali chemical workshop can subject the green liquor to a alkali chemical reaction to obtain white liquor.

[0059] The pulping workshop includes the cooking system, screening system, bleaching system and pulp washing system, such as Figure 2 As shown, the cooking system includes a cooking pot 1, a pumping unit, a heat exchanger 2 and a holding tank. The holding tank has a heat preservation and heat insulation function. The side wall of the holding tank is provided with heat insulation cotton. The holding tank includes a white liquid tank, a black liquid tank and a pulp washing liquid tank 5. The white liquid tank includes a cold white liquid tank 6 and a hot white liquid tank 7. The cold white liquid tank 6 contains cold white liquid, and the hot white liquid tank 7 contains hot white liquid. The black liquid tank includes a warm black liquid tank 3 and a hot black liquid tank 4. The warm black liquid tank 3 contains warm black liquid, the hot black liquid tank 4 contains hot black liquid, and the pulp washing liquid tank 5 contains pulp washing liquid. The cooking pot 1 is provided with a cooking liquid inlet pipe at the upper end, and a grate and a cooking liquid outlet pipe at the lower end. All liquids must be filtered through a grate before entering the cooking liquid inlet pipe. The cooking liquid inlet pipe is connected to the cold white liquor tank 6, the hot white liquor tank 7, the warm black liquor tank 3, the hot black liquor tank 4 and the pulp washing liquid tank 5 respectively, and the cooking liquid outlet pipe is connected to the warm black liquor tank 3 and the hot black liquor tank 4 respectively; the heat exchanger 2 is provided with a first heat exchange tube and a second heat exchange tube capable of heat exchange. The first heat exchange tube is connected to the hot black liquor tank 4, the heat exchanger 2 and the warm black liquor tank 3 in sequence, the second heat exchange tube is connected to the chemical workshop in the recovery workshop d, the heat exchanger 2 and the hot white liquor tank 7 in sequence, and the cold white liquor tank 6 is directly connected to the chemical workshop in the recovery workshop d.

[0060] The temperature of hot black liquor is 80℃-90℃, and the temperature of warm black liquor tank 3 and hot white liquor are both 50℃-55℃; a heating and heat preservation unit is provided on the cooking pot 1, and the heating and heat preservation unit includes steam, a circulation pipe and a heater on the circulation pipe. The circulation pipe is connected to the cooking pot 1, and high-pressure steam circulates between the circulation pipe and the cooking pot 1. The cooking pot 1 is divided into a first cooking pot and a second cooking pot according to the cooking stage. In this embodiment, the first cooking pot and the second cooking pot use the same cooking pot 1. The first cooking pot 1 can use a mixed liquid to pre-soak bamboo chips. The mixed liquid includes cold white liquor and warm black liquor. The ratio of cold white liquor and warm black liquor can maintain the pH value of the mixed liquid at a stable value. Using the mixed liquid at a stable value to soak bamboo chips can prevent the precipitation of fibers in the bamboo chips; the first cooking pot 1 can replace the warm black liquor with hot black liquor, and can also replace part of the hot black liquor with hot white liquor;

[0061] The second cooking pot 1 can cook bamboo chips, and the heating and insulation unit can heat the second cooking pot 1 to 150°C-154°C; the second cooking pot 1 can convert black liquor into pulp washing liquid, and according to the temperature of the replaced black liquor, the pumping unit can discharge the hot black liquor into the hot black liquor tank 4 and discharge the warm black liquor into the warm black liquor tank 3.

[0062] The volume of the cooking pot 1 is 400m 3 , a vertical pot with a height of 10-20m, a pot top valve is provided on the cooking pot 1, and the pumping unit includes a plurality of pumping pipes, a water pump 8 and a valve. In this embodiment, the pumping of the liquid is completed by controlling the water pump 8 and the valve switch by the pumping unit. The cooking liquid inlet pipe, the cooking liquid outlet pipe, the first heat exchange pipe and the second heat exchange pipe are all pumping pipes. In this embodiment, the liquid is replaced by pumping the liquid into the cooking pot 1 from the cooking liquid inlet pipe and pumping the liquid out of the cooking pot 1 from the cooking liquid outlet pipe.

[0063] like Figure 3 As shown, the pulp washing system includes a coarse screen pulp washer 111, a fine screen pulp washer 112 and a return pipe 160, the screening system includes a knot remover 300, a knot washer, a filtrate tank 400 and a multi-stage fine screening system 500, the cooking pot 1, the spray pot 10 and the knot remover 300 are connected in sequence, the bamboo chips cooked by the cooking system are sprayed into pulp by high pressure in the spray pot 10, and then enter the knot remover 300, the knot remover 300 model is FCJ-4, the knot remover 300 removes the bamboo knots and lumps in the slurry that cannot be pulped, and the slurry obtained at this time is coarse pulp, the knot remover 300, the coarse pulp washer 111 and the multi-stage fine screening system 500 are connected in sequence, the coarse pulp enters the coarse screen pulp washer 111 for cleaning, and the coarse pulp cleaned by the coarse screen pulp washer 111 enters the multi-stage fine screening system 500.

[0064] On this basis, a knot removal cycle is formed: the bamboo knots and lumps removed by the knot remover 300 enter the knot washer for cleaning, the coarse pulp obtained after cleaning by the knot washer enters the knot remover 300 again, and the remaining bamboo knots and lumps after cleaning by the knot washer enter the previous cooking process for cooking again.

[0065] On this basis, the first filtrate cycle is formed: the filtrate of the fine screen washer 112 is heated and used for the coarse screen washer 111 to wash the coarse pulp. The filtrate generated after washing the coarse pulp in the coarse screen washer 111 enters the filtrate tank 400 for buffering. A part of the filtrate in the filtrate tank 400 is refluxed and recycled by the coarse screen washer 111 itself, and the other part flows into the filtrate tank 400 of the coarse screen washer 111. The filtrate tank 400 is connected to the warm black liquor tank 3 and the evaporation workshop of the recovery workshop d to be used in the cooking system or to recover black liquor.

[0066] like Figure 4As shown, the multi-stage fine screening system 500 includes a buffer riser 510, a first-stage fine screening device 520, a desander 530, a second-stage fine screening device 540, a third-stage fine screening device 550, a slag washer 560 and a dilution riser 570. The screening outlet of the first-stage fine screening device is connected to the pulp washing system, the screening outlet of the first-stage fine screening device is connected to the desander, the screening outlet of the desander is connected to the second-stage fine screening device, the screening outlet of the second-stage fine screening device is connected to the first-stage fine screening device, the screening outlet of the second-stage fine screening device is connected to the third-stage fine screening device, the screening outlet of the third-stage fine screening device is connected to the second-stage fine screening device, the screening outlet of the third-stage fine screening device is connected to the slag washer, the screening outlet of the slag washer is connected to the third-stage fine screening device, and the filtrate outlet of the fine screening section pulp washer is connected to the dilution riser.

[0067] The desander includes a slurry inlet pipe 531, a slurry outlet pipe 532, a frame 535 and a plurality of conical cyclones 533. Fig. 9 , Fig.10 As shown, the pulp inlet pipe 531 is arranged in parallel directly below the pulp outlet pipe 532, and the pulp inlet pipe 531 and the pulp outlet pipe 532 are both bolted to the frame 535, and a plurality of conical cyclones 533 are evenly distributed on both sides of the pulp inlet pipe 531 and the pulp outlet pipe 532, as shown in FIG. Fig.10 As shown, a plurality of conical cyclones 533 are arranged in a plum blossom shape in the horizontal direction, such as Fig. 9 As shown, a plurality of conical cyclones 533 are arranged in a staggered manner in the vertical direction, a slag discharge groove 536 is opened on the frame 535, and the slag discharge groove 536 is located below the conical cyclone 533. Connecting branch pipes 534 are horizontally welded on both sides of the slurry inlet pipe 531 and the slurry outlet pipe 532. The connecting branch pipes 534 are made of steel. The lower ends of the conical cyclones 533 are connected to the connecting branch pipes 534 on the side of the slurry inlet pipe 531, and the upper ends of the conical cyclones 533 are connected to the connecting branch pipes 534 on the side of the slurry outlet pipe 532. After a section of tail slurry enters the conical cyclone 533, the conical cyclone 533 causes the tail slurry to rotate at a high speed, and the lighter material (good slurry) is discharged upward, and the heavier material (impurities, etc.) is discharged downward from the bottom along the inner wall of the conical cyclone tube under the action of centrifugal force and discharged into the slag discharge groove 536.

[0068] The coarse pulp after cleaning by the coarse screen washer 111 is buffered by the buffer riser 510 and then enters a first-stage fine screening device 520. The good pulp screened by the first-stage fine screening device 520 enters the fine screen washer 112 for cleaning.

[0069] On this basis, the first screening cycle is formed: the tailings screened out by the first-stage fine screening device 520 enters the desander 530, the good slurry screened by the desander 530 enters the second-stage fine screening device 540, the impurities screened out by the desander 530 are discharged into the ditch, and the second-stage good slurry screened by the second-stage fine screening device 540 enters the first-stage fine screening device 520.

[0070] On this basis, a second screening cycle is formed: the second-stage tail pulp screened out by the second-stage fine screening device 540 enters the third-stage fine screening device 550 , and the good pulp screened by the third-stage fine screening device 550 enters the second-stage fine screening device 540 .

[0071] On this basis, a third screening cycle is formed: the tailings screened out by the three-stage fine screening equipment 550 enters the slag washer 560, the good slurry washed out by the slag washer 560 re-enters the three-stage fine screening equipment 550, and the impurities washed out by the slag washer 560 are collected and discharged for treatment.

[0072] On this basis, a second filtrate cycle is formed: the slurry needs to be diluted before entering the first-stage fine screening equipment 520, the desander 530, the second-stage fine screening equipment 540 and the third-stage fine screening equipment 550, the fine screening pulp washer 112, the return pipe 160 and the dilution riser 570 are connected in sequence, the dilution riser 570 is simultaneously connected to the first-stage fine screening equipment 520, the desander 530, the second-stage fine screening equipment 540 and the third-stage fine screening equipment 550, the filtrate of the fine screening pulp washer 112 enters through the return pipe 160 and is contained in the dilution riser 570, the dilution riser 570 provides dilution liquid for the first-stage fine screening equipment 520, the desander 530, the second-stage fine screening equipment 540 and the third-stage fine screening equipment 550.

[0073] The slurry in the multi-precision screen system is pumped. Figure 4 The delivery pump is omitted, and the first-stage fine screening device 520, the second-stage fine screening device 540 and the third-stage fine screening device 550 are all vibrating screens.

[0074] like Figure 3 As shown, the pulp washing system also includes an oxygen desorption pulp washer, a D0 section pulp washer 130, an EOP section pulp washer 140 and a D1 section pulp washer 150. The pulp washers in the pulp washing system are all double-roll pulp washers or vacuum pulp washers. The bleaching area includes an oxygen desorption bleaching device 210, a buffer device, a D0 section bleaching device 230, an EOP section bleaching device 240, a D1 section bleaching device 250 and a pulping tower 260. The fine screening pulp washer 112, the oxygen desorption bleaching device 210, the oxygen desorption section pulp washer, the D0 section bleaching device 230, the D0 section pulp washer 130, the EOP section bleaching device 240, the EOP section pulp washer 140, the D1 section bleaching device 250, the D1 section pulp washer 150 and the pulping tower 260 are connected in sequence, and the pulping tower 260 is connected to the pulp board workshop.

[0075] like Figure 5As shown, the oxygen desiccant bleaching device 210 includes an oxygen desiccant medium-concentration riser 211, an oxygen desiccant medium-concentration pump 212, a first oxygen mixer 213, an oxygen pre-reaction tube 214, an oxygen desiccant steam ejector 215, a second oxygen mixer 216, an oxygen reaction tower 217 and an oxygen desiccant feeding pump 218 which are connected in sequence. The fine screening section pulp washer 110 is connected to the oxygen desiccant medium-concentration riser 211. The oxygen desiccant medium-concentration riser 211 is provided with a NaOH feeding port and a MgOH feeding port. The first oxygen mixer 213 and the second oxygen mixer 216 can both mix O2 and slurry.

[0076] like Figure 3 As shown, the oxygen desorption section washer includes a first oxygen desorption section washer 121 and a second oxygen desorption section washer 122, and a steam inlet is provided on the second oxygen desorption section washer 122; the buffer device includes a pre-bleaching riser 221, a pre-bleaching feeding trough 222 and a pre-bleaching feeding pump 223, and the oxygen desorption feeding pump 218, the first oxygen desorption section washer 121, the pre-bleaching riser 221, the pre-bleaching feeding trough 222, the pre-bleaching feeding pump 223 and the second oxygen desorption section washer 122 are connected in sequence.

[0077] like Figure 6 As shown, the D0 stage bleaching device 230 includes a D0 medium-consistency riser 231, a D0 medium-consistency pump 232, a D0 steam ejector 233, a D0 mixer 234, a D0 reaction tower 235 and a D0 feeding pump 236 which are connected in sequence, the second oxygen desorption stage pulp washer 122 is connected to the D0 medium-consistency riser 231, the D0 feeding pump 236 is connected to the D0 stage pulp washer 130, the D0 medium-consistency riser 231 is provided with an H2SO4 feeding port, and the D0 mixer 234 is provided with a ClO2 feeding port.

[0078] like Figure 7 As shown, the EOP section bleaching device 240 includes an EOP medium-consistency riser 241, an EOP medium-consistency pump 242, an EOP mixer 243, an EOP reaction tower 244 and an EOP feeding pump 245 which are connected in sequence, the D0 section pulp washer 130 is connected to the EOP medium-consistency riser 241, the EOP feeding pump 245 is connected to the EOP section pulp washer 140, a steam inlet, a NaOH feeding port and a H2O2 feeding port are provided on the EOP medium-consistency riser 241, and the EOP mixer 243 mixes O2 and pulp.

[0079] like Figure 8 As shown, the D1 section bleaching device 250 includes a D1 medium-consistency riser 251, a D1 medium-consistency pump 252, a D1 mixer 253 and a D1 reaction tower 254 which are connected in sequence, the EOP section pulp washer 140 is connected to the D1 medium-consistency riser 251, the D1 reaction tower 254 is connected to the D1 section pulp washer 150, the D1 medium-consistency riser 251 is provided with a NaOH feeding port, the D1 mixer 253 is provided with a ClO2 feeding port, and the D1 section pulp washer 150 is provided with a Na2S2O3 feeding port.

[0080] Excess filtrate in the pulp washer in the pulp washing system is recycled using a circulating pump for multiple pulp washings; steam can be introduced into the steam inlet.

[0081] The alkali furnace workshop includes the alkali ash handling system, such as Fig.11 As shown, the alkali ash treatment system includes a stirring tank 610, a crystallization tank 700, a centrifuge 620 and an evaporator 630 which are connected in sequence, and the warm black liquor tank 3 is connected to the evaporator 630.

[0082] like Fig.12 As shown, the crystallizer 700 includes an upper cone 711, a cylinder 712, a lower cone 713 and a salt leg 715 from top to bottom, a demister 721 is bolted in the upper cone 711, a steam outlet 741 and two pressure gauges 731 are provided on the upper left side of the upper cone 711, an inlet 742 and a pressure gauge 731 are provided on the upper right side of the upper cone 711, the demister 721 is a plate demister 721, a flushing pipe 722 is horizontally welded on the upper end of the cylinder 712, the right end of the flushing pipe 722 is connected to the outside of the cylinder 712, the left end of the flushing pipe 722 is located directly below the demister 721, and the left end of the flushing pipe 722 is located directly below the demister 721. A vertically upward nozzle 723 is integrally formed, and the spraying range of the nozzle 723 covers the lower surface of the wave plate of the demister 721. A sight glass 733 and two liquid level gauges 732 are provided on the left side of the cylinder 712, a recirculation inlet 743 is provided on the upper right side of the cylinder 712, a population 742 is provided on the lower right side of the cylinder 712, a recirculation outlet 744 is provided on the lower left side of the lower cone, and a vertically arranged cylindrical transition portion 714 is provided at the lower end of the lower cone. The diameter of the transition portion 714 is smaller than the diameter of the cylindrical salt leg 715, and the transition portion 714 is inserted from above the salt leg 715, and the upper end of the salt leg 715 is welded to the outer side of the lower cone.

[0083] The lower end of the salt leg 715 is provided with a drain port 745, the right side of the salt leg 715 is provided with a discharge pipe 760, the left end of the discharge pipe 760 is a discharge port 761, the discharge port 761 is inclined to the upper left, and the discharge port 761 is connected to the centrifuge 620. Three feed pipes 750 are horizontally arranged on the left side of the salt leg 715, and the discharge pipe 760 and the three feed pipes 750 are provided with branch pipes for flushing. The angle between the uppermost feed pipe 750 and the side wall of the salt leg 715 is less than °, and the three feed pipes are arranged at the same time. The right end of the material pipe 750 has, from top to bottom, an upper feed port 751, a middle feed port 752 and a lower feed port 753. The upper inlet is located on the side wall of the salt leg 715, horizontally to the right and located between the outer wall of the transition portion 714 and the inner wall of the salt leg 715; the middle feed port 752 and the lower feed port 753 are both facing downward, and the middle feed port 752, the discharge port 761, the lower feed port 753 and the drain port 745 are vertically aligned from top to bottom and are all located on the central axis of the salt leg 715.

[0084] like Fig.11As shown, a recirculation unit is provided on the crystallizer 700, and the recirculation unit includes a circulation pipeline 771, a steam pipeline 772 and a heat exchanger 773, and one end of the circulation pipeline 771 is connected to the recirculation inlet 743, and the other end of the circulation pipeline 771 is connected to the recirculation outlet 744, and the circulation pipeline 771 passes through the heat exchanger 773, and the steam pipeline 772 communicates with the steam outlet 741 and the heat exchanger 773, and the steam pipeline 772 and the circulation pipeline 771 are communicated in the heat exchanger 773, and the solution separated by the centrifuge 620 is communicated with the circulation pipeline 771. The quantity of the crystallizer 700 can be adjusted according to actual demand, and multiple crystallizations are carried out by connecting a plurality of crystallizers 700 in series, and the amount of potassium chloride crystallization can be increased.

[0085] The specific implementation steps of the cooking system are as follows:

[0086] 1. Loading the pot: Put the bamboo chips from the bamboo and wood yard into the cooking pot 1, and evenly distribute the bamboo chips in the cooking pot 1.

[0087] 2. Warm charging, warm black liquor pre-soaking: pump warm black liquor into the cooking pot 1, close the valve on the top of the pot, and continue to pump warm black liquor until the pressure in the pot rises to the specified pressure value, which is the best pressure value that the cooking pot 1 can withstand. When fresh bamboo chips come into contact with warm black liquor, the residual alkali is quickly consumed. For this reason, a portion of cold white liquor needs to be added to maintain a certain pH value to prevent the fiber in the bamboo chips from precipitating. At the same time, low-pressure steam is passed into the circulation pipe and heated by the heater.

[0088] 3. Hot charging: first replace the warm black liquor in the cooking pot 1 with hot black liquor, the replaced warm black liquor enters the warm black liquor tank 3 through the grate, and then part of the hot black liquor in the cooking pot 1 is replaced with hot white liquor.

[0089] 4. Heating and keeping warm: While replacing the liquid in step 2-3, the low-pressure steam in the cooking pot 1 has been heated to medium-pressure steam, and the temperature in the cooking pot 1 has reached about 140°C. The temperature is further increased by 10-15°C to make the temperature in the cooking pot 1 reach 150°C-154°C. In this embodiment, it is more suitable to reach 150°C. The temperature is maintained at 150°C for 1 hour, and the pressure in the pot is controlled at 0.5 MPa.

[0090] 5. Replacement: Open the valve on the top of the pot to release the pressure, and the temperature in the cooking pot 1 drops to 100°. The black liquor in the cooking pot 1 is replaced with pulp washing liquid. The hot black liquor with a higher temperature replaced in the early stage is pumped to the hot black liquor tank 4, and the warm black liquor with a lower temperature replaced in the later stage is pumped to the warm black liquor tank 3. The excess warm black liquor is pumped to the recovery workshop d. The recovery workshop d converts the black liquor into white liquor through evaporation, combustion and causticization reactions. A part of the white liquor and the hot black liquor are heat exchanged in the heat exchanger 2 and then enter the hot white liquor tank 7, and the remaining white liquor enters the cold white liquor tank 6. The hot black liquor after heat exchange becomes warm black liquor and enters the warm black liquor tank 3.

[0091] 6. Pot: Pump the softened bamboo slurry into the spray pot for 10 ( Figure 2 (not shown) and proceed to the next process.

[0092] The specific implementation steps of the screening system, bleaching system and pulp washing system are as follows:

[0093] 1. The pulp after cooking passes through the knot remover, coarse screen washer, multi-stage fine screening system and fine screen washer in turn.

[0094] 2. The pulp enters the pulp washing and bleaching system, and is washed and bleached back and forth between the pulp washing system and the bleaching system. Finally, the pulp enters the pulping tower 260 for storage.

[0095] The specific implementation steps of the alkali ash treatment system are as follows:

[0096] 1. Soda ash and water are stirred in a stirring tank 610 to form a slurry, and the slurry is passed into a crystallization tank 700. The slurry continuously enters a heat exchanger 773 through a circulation pipe 771 for heat exchange and cooling. The crystals precipitated in the crystallization tank 700 are mainly potassium chloride, so as to achieve the purpose of recovering potassium chloride. After the remaining slurry passes through the centrifuge 620, the remaining solution contains a large amount of sodium sulfate. After the remaining slurry passes through the centrifuge 620, the remaining slurry may also contain potassium chloride, and returns to the crystallization tank 700 through the circulation pipe 771 for recrystallization. Since the black liquor contains sodium sulfate, the solution containing a large amount of sodium sulfate passing through the centrifuge 620 and the black liquor in the warm black liquor tank 3 enter the evaporator 630 together for evaporation and crystallization, thereby achieving the purpose of recovering sodium sulfate separately.

[0097] 2. The steam with a higher temperature rises to the top of the crystallization tank 700, then merges with the slurry in the circulation pipe 771 through the steam pipe 772, and then cools down through the heat exchanger 773 and returns to the crystallization tank 700, thereby improving the efficiency of cooling the slurry, thereby accelerating the crystallization speed and improving the recovery efficiency.

[0098] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions and / or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A pulping system, characterized in that: It includes a pulping workshop, which includes a cooking system, a screening system, a bleaching system and a pulp washing system. The screening system includes a knot remover and a multi-stage fine screening system. The pulp washing system includes a coarse screen section pulp washer, a fine screen section pulp washer, a screening pulp washer, an oxygen desorption section pulp washer, a D0 section pulp washer, an EOP section pulp washer, a D1 section pulp washer and a return pipe. The knot remover, the coarse screen section pulp washer, the multi-stage fine screening system, the fine screen section pulp washer and the bleaching system are connected in sequence. The coarse screen The filtrate outlet of the section washer is connected to the cooking system, the filtrate outlet of the fine screening section washer is connected to the multi-section fine screening system, the bleaching system includes an oxygen desorption bleaching device, a D0 section bleaching device, an EOP section bleaching device and a D1 bleaching device, and the screening washer, the oxygen desorption bleaching device, the oxygen desorption section washer, the D0 section bleaching device, the D0 section washer, the EOP section bleaching device, the EOP section washer, the D1 bleaching device and the D1 section washer are connected in sequence; The multi-stage fine screening system includes a first-stage fine screening device, a desander, a second-stage fine screening device, a third-stage fine screening device, a slag washer and a dilution riser. The screening outlet of the first-stage fine screening device is connected to the pulp washing system, the screening outlet of the first-stage fine screening device is connected to the desander, the screening outlet of the desander is connected to the second-stage fine screening device, the screening outlet of the second-stage fine screening device is connected to the first-stage fine screening device, the screening outlet of the second-stage fine screening device is connected to the third-stage fine screening device, the screening outlet of the third-stage fine screening device is connected to the second-stage fine screening device, the screening outlet of the third-stage fine screening device is connected to the slag washer, and the screening outlet of the slag washer is connected to the third-stage fine screening device. The filtrate outlet of the fine screening section pulp washer is connected to the dilution riser, and the dilution riser is connected to the first-stage fine screening equipment, the desander, the second-stage fine screening equipment and the third-stage fine screening equipment at the same time. The filtrate of the fine screening section pulp washer enters the dilution riser for storage and is then used in the three fine screening equipments to dilute the slurry at each stage and control the slurry concentration. After the slurry enters the first-stage fine screening equipment, some fibers are attached to the impurities and form blocks, which cannot pass through the screen plate and can only enter the desander with the first-stage tail slurry. At this time, the liquid in the dilution riser dilutes the first-stage tail slurry and enters the desander; The desander includes a slurry inlet pipe, a slurry outlet pipe, a frame and a number of conical cyclones. The slurry inlet pipe is arranged in parallel and just below the slurry outlet pipe. The slurry inlet pipe and the slurry outlet pipe are bolted to the frame. A number of conical cyclones are evenly distributed on both sides of the slurry inlet pipe and the slurry outlet pipe. A number of conical cyclones are arranged in a plum blossom shape in the horizontal direction, and a number of conical cyclones are arranged in a staggered manner in the vertical direction.

2. A pulping system according to claim 1, characterized in that: The cooking system includes a cooking pot, a pumping unit and a holding tank, the holding tank includes a white liquid tank, a warm black liquid tank and a hot black liquid tank, the white liquid tank contains white liquid, the warm black liquid tank contains warm black liquid, the hot black liquid tank contains hot black liquid, the cooking pot is connected with the white liquid tank, the warm black liquid tank and the hot black liquid tank respectively; the cooking pot is connected with the white liquid tank, the warm black liquid tank and the hot black liquid tank, the cooking pot is provided with a heating and heat preservation unit, and the cooking pot is divided into a first cooking pot and a second cooking pot according to the cooking stage; The first cooking pot can pre-soak bamboo chips, the first cooking pot can replace warm black liquor with hot black liquor, and the first cooking pot can replace part of the hot black liquor with white liquor; the second cooking pot can cook bamboo chips, and the heating and insulation unit can heat the second cooking pot to 140-154°C; the second cooking pot can convert black liquor into pulp washing liquid, and according to the temperature of the replaced black liquor, the pumping unit can discharge the hot black liquor into the hot black liquor tank and the warm black liquor into the warm black liquor tank.

3. A pulping system according to claim 2, characterized in that: It also includes a recovery workshop, which includes an evaporation workshop, an alkali furnace workshop and a causticizing workshop connected in sequence. The filtrate outlet of the coarse screen section pulp washer of the screening system is connected to the evaporation workshop and the warm black liquor tank. The causticizing workshop is connected to the white liquor tank. The evaporation workshop can evaporate and concentrate the black liquor, the alkali furnace workshop can burn the black liquor to obtain green liquor, and the causticizing workshop can subject the green liquor to a causticizing reaction to obtain white liquor.

4. A pulping system according to claim 3, characterized in that: The alkali furnace workshop includes an alkali ash treatment system, which includes a stirring tank, a crystallization tank, a centrifuge and an evaporator connected in sequence. The crystallization tank is provided with a recycling unit, which includes a circulation pipe, a steam pipe and a heat exchanger. The circulation pipe passes through the heat exchanger, and the steam pipe connects the top of the crystallization tank and the heat exchanger. The steam pipe and the circulation pipe are connected in the heat exchanger.

5. A pulping system according to claim 4, characterized in that: The crystallization tank includes an upper cone, a cylinder, a lower cone and a salt leg from top to bottom. A demister is arranged in the upper cone. A flushing pipe is arranged horizontally on the upper end of the cylinder. One end of the flushing pipe is connected to the outside of the cylinder. The other end of the flushing pipe is located directly below the demister. A vertically upward nozzle is arranged at the other end of the flushing pipe. The spraying range of the nozzle covers the demister. One end of the circulation pipe is connected to the cylinder, and the other end of the circulation pipe is connected to the lower cone.

6. A pulping system according to claim 5, characterized in that: A transition portion is provided at the lower end of the lower cone portion, and the transition portion is inserted into the upper end of the salt leg. A drain port, a discharge port and three feed ports are provided on the salt leg. The drain port is located at the bottom of the salt leg, and the three feed ports are respectively an upper feed port, a middle feed port and a lower feed port. The upper feed port is horizontally arranged between the outer wall of the transition portion and the inner wall of the salt leg. The middle feed port, the discharge port, the lower feed port and the drain port are vertically aligned from top to bottom and are all located on the central axis of the salt leg, and the middle feed port and the lower feed port are both facing downward.

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