Pulping system and pulping method

Abstract

A pulp system and a pulp method, comprising a first washing device, an oxygen deprivation feed tank, a second washing device, an oxygen deprivation device and a third washing device; a pulp outlet of the first washing device is communicated with the oxygen deprivation feed tank, along a pulp conveying direction, the third washing device is arranged downstream of the oxygen deprivation device; the pulp system has a first pulp passage and a second pulp passage, the first pulp passage communicates an outlet of the oxygen deprivation feed tank with a pulp inlet of the oxygen deprivation device; the second pulp passage sequentially communicates the outlet of the oxygen deprivation feed tank, the second washing device and the pulp inlet of the oxygen deprivation device; the pulp system comprises a first operation mode and a second operation mode, in the first operation mode, the first pulp passage is communicated, and the second pulp passage is disconnected; in the second operation mode, the first pulp passage is disconnected, and the second pulp passage is communicated.

Description

Technical Field

[0001] This application relates to the field of pulping technology, and more specifically, to a pulping system and a pulping method. Background Technology

[0002] In the sulfate pulping process, the pulp after cooking and screening typically requires washing to remove impurities such as black liquor, dissolved lignin, and organic acids. The washed pulp is then transported to an oxygen delignin unit for oxygen delignin treatment. Existing pulping systems usually utilize a single-stage washing unit to wash the pulp before it enters the oxygen delignin process. However, under high production loads, single-stage washing has limited ability to remove impurities from the pulp, leaving the pulp entering the oxygen delignin unit still carrying a significant amount of impurities. These impurities consume additional oxygen and sodium hydroxide, increasing the unit pulp reagent consumption in the oxygen delignin process and further limiting the pulp processing capacity and efficiency of the oxygen delignin process. Summary of the Invention

[0003] The purpose of this invention is to provide a pulping system and a pulping method. The pulping system includes a first washing device, an oxygen descaling feeder, a second washing device, an oxygen descaling device, and a third washing device. The pulp outlet of the first washing device is connected to the oxygen descaling feeder. Along the pulp conveying direction, the third washing device is located downstream of the oxygen descaling device. The pulping system has a first pulp passage and a second pulp passage. The first pulp passage connects the outlet of the oxygen descaling feeder and the pulp inlet of the oxygen descaling device. The second pulp passage sequentially connects the outlet of the oxygen descaling feeder, the second washing device, and the pulp inlet of the oxygen descaling device. The pulping system includes a first operating mode and a second operating mode. In the first operating mode, the first pulp passage is connected and the second pulp passage is disconnected. In the second operating mode, the first pulp passage is disconnected and the second pulp passage is connected.

[0004] On the one hand, this application further incorporates a second washing unit between the first washing unit and the oxygen desulfurization unit, allowing the pulp already washed by the first washing unit to be washed again before entering the oxygen desulfurization unit. This secondary washing and concentration of the pulp by the second washing unit further separates black liquor and soluble impurities such as lignin and organic acids from the pulp, reducing the chemical oxygen demand (COD) carried by the pulp entering the oxygen desulfurization unit. This reduces the additional consumption of oxygen and sodium hydroxide by these impurities, thus lowering the amount of oxygen and sodium hydroxide required per unit of pulp to achieve the target oxygen desulfurization level. Given a fixed oxygen and sodium hydroxide supply capacity, this application also allows the same reagent supply capacity to meet the oxygen desulfurization needs of more pulp, thereby improving the processing capacity of the pulping system.

[0005] On the other hand, this solution does not simply connect the second washing unit directly after the first washing unit. Instead, it sets up an oxygen descaling feeder between the first and second washing units, and positions the second washing unit between the oxygen descaling feeder and the oxygen descaling unit. Thus, the oxygen descaling feeder can serve as a common upstream supply node for both the first and second pulp paths: in the first operating mode, the pulp output from the oxygen descaling feeder can bypass the second washing unit and be directly transported to the oxygen descaling unit; in the second operating mode, the pulp output from the oxygen descaling feeder first enters the second washing unit for secondary washing before being transported to the oxygen descaling unit. Through the aforementioned coordination of the positions of the oxygen descaling feeder and the second washing unit, the pulping system can select different pulp transport paths based on the operating status of the second washing unit. Therefore, this application improves the pre-oxygen descaling washing effect while preventing the second washing unit from becoming the only path for pulp to enter the oxygen descaling unit, thus improving the adaptability of the pulping system to different operating conditions and the continuity of production.

[0006] Optionally, the pulping system further includes a first filtrate passage and a second filtrate passage. The first filtrate passage is configured to transport the filtrate generated by the third washing device to the first washing device. The second filtrate passage includes a first filtrate conveying section and a second filtrate conveying section. The first filtrate conveying section is configured to transport the filtrate generated by the third washing device to the second washing device. The second filtrate conveying section is configured to transport the filtrate generated by the second washing device to the first washing device. In the first operating mode, the first filtrate passage is connected and the second filtrate passage is disconnected; in the second operating mode, the first filtrate passage is disconnected and the second filtrate passage is connected.

[0007] Optionally, the first pulp passage and the second pulp passage are each provided with a shut-off valve; the first filtrate passage and the second filtrate passage are each provided with a shut-off valve, so that the pulping system can be switched between the first operating mode and the second operating mode by opening and closing each shut-off valve.

[0008] Optionally, the second washing device is a two-roll washing machine.

[0009] Optionally, the first washing device is an airless vacuum drum washing machine, and the third washing device is a drum displacement washing machine.

[0010] Optionally, a double roller riser is provided between the thick pulp outlet of the double roller washer and the oxygen descaling unit, and the double roller riser is configured to store the pulp output from the double roller washer.

[0011] Optionally, the third washing device is connected to a third filtrate tank, which is connected to the first washing device via a first filtrate passage.

[0012] It is connected to the second washing device through the second filtrate passage.

[0013] Optionally, in the second operating mode, the chemical oxygen demand (COD) of the filtrate produced by the third washing device is less than that of the filtrate produced by the second washing device, and the COD of the filtrate produced by the second washing device is less than that of the filtrate produced by the first washing device.

[0014] A pulping method employs a pulping system and includes a first operating mode and a second operating mode; In the first operating mode, the pulp washed by the first washing device is transported to the oxygen descaling device via the oxygen descaling feed tank, and the pulp bypasses the second washing device; the filtrate produced by the third washing device is transported to the first washing device. In the second operating mode, the pulp washed by the first washing device is transported to the second washing device via the oxygen descaling feed tank, and after being washed again by the second washing device, it is transported to the oxygen descaling device; the filtrate produced by the third washing device is transported to the second washing device, and the filtrate produced by the second washing device is transported to the first washing device. When switching between the first and second operating modes, the slurry processing volume entering the oxygen descaling unit and the dosing parameters of oxygen and sodium hydroxide are switched accordingly.

[0015] Optionally, the oxygen dosage per unit of oven-dry slurry in the second operating mode is less than the oxygen dosage per unit of oven-dry slurry in the first operating mode, and the sodium hydroxide dosage per unit of oven-dry slurry in the second operating mode is less than the sodium hydroxide dosage per unit of oven-dry slurry in the first operating mode.

[0016] Optionally, the dosage of oxygen and sodium hydroxide is adjusted according to the kappa number of the deoxygenated pulp. In the second operating mode, the chemical oxygen demand (COD) carried by the pulp entering the deoxygenation unit is reduced by the second washing device, thereby reducing the amount of oxygen and sodium hydroxide required per unit of oven-dry pulp to achieve the target kappa number. Furthermore, the pulp processing capacity in the second operating mode is greater than that in the first operating mode. Attached Figure Description

[0017] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments of this specification and, together with their description, serve to explain the principles of this specification.

[0018] Figure 1 This is a schematic diagram of the pulping system in the embodiment of this application.

[0019] Figure label: 100 Pulping system; 10 First washing unit; 11 First filtrate tank; 20 Oxygen desulfurization feed tank; 30 Second washing unit; 31 Double roller riser; 32 Second filtrate tank; 40 Oxygen desulfurization unit; 41 First oxygen desulfurization tower; 42 Second oxygen desulfurization tower; 43 Oxygen desulfurization spray boiler; 50 Third washing unit; 51 Third filtrate tank; 81 Spray boiler; 82 De-icing feed pump; 83 De-icing machine; 84 First stage screen feed pump; 85 First stage pressure screen; 86 Cooking section; 90 Pre-bleaching tower; 91 Fourth washing unit; 92 Fourth filtrate tank; 93 Secondary condensate unit; 94 Bleaching section. Detailed Implementation

[0020] The pulping system 100 and pulping method of this application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the following embodiments and their technical features can be combined with each other. The directions shown in the accompanying drawings, such as up, down, left, right, front, and rear, are only used to illustrate the relative positional relationships between components and are not intended to limit the scope of protection of this application. When the absolute installation posture of related components changes, the corresponding connection relationships, mating relationships, and achieved technical effects do not change.

[0021] See Figure 1 In some specific embodiments of this application, the pulping system 100 may include, from front to back, a spraying pot 81, a de-straining feed pump 82, a de-straining machine 83, a first-stage screen feed pump 84, a first-stage pressure screen 85, a first washing device 10, an oxygen destraining feed tank 20, a second washing device 30, a double-roller riser 31, an oxygen destraining device 40, a third washing device 50, and a pre-bleaching tower 90 along the main pulp flow direction; wherein, in some embodiments, the oxygen destraining device 40 may include a first oxygen destraining tower 41, a second oxygen destraining tower 42, and an oxygen destraining spraying pot 43. In coordination with the main pulp flow, the pulping system 100 may also include a first filtrate tank 11, a second filtrate tank 32, a third filtrate tank 51, a cooking section 86, a fourth washing device 91, a fourth filtrate tank 92, a secondary condensate unit 93, and a bleaching section 94 to form a complete pre- and post-washing, filtrate reuse, and subsequent bleaching process.

[0022] Specifically, the second filtrate tank 32 cooperates with the second washing device 30. The second filtrate tank 32 is located on the filtrate outlet side of the second washing device 30, and not in the main pulp flow path. The filtrate generated after washing the pulp by the second washing device 30 can first enter the second filtrate tank 32, and then be transported from the second filtrate tank 32 to the first washing device 10 through the second filtrate flow path. The cooking section 86 is connected to the first filtrate tank 11. At least a portion of the filtrate generated by the first washing device 10 and collected in the first filtrate tank 11 can be returned to the cooking section 86 to form a filtrate reuse process that cooperates with the main pulp flow.

[0023] In some specific embodiments of this application, the first washing device 10 is preferably an airless vacuum drum washer, the third washing device 50 is preferably a drum displacement washer, and the second washing device 30 is preferably a twin-roll washer. However, under a broader perspective, the first washing device 10 can also be a vacuum drum washer, a pressure washer, or a belt washer, and the third washing device 50 can also be a displacement drum washer, a diffusion washer, or other washing equipment capable of end-of-pipe washing and filtrate recovery. In addition to a twin-roll washer, the second washing device 30 can also, under broader perspective, be a roller press washer, a squeeze washer, or a press-concentration washer. Of course, using a twin-roll washer is more advantageous for achieving higher deliquescence efficiency and a more stable pulp concentration before oxygen desulfurization.

[0024] According to some specific embodiments of this application, the pulping system 100 includes a first washing device 10, an oxygen descaling feeder 20, a second washing device 30, an oxygen descaling device 40, and a third washing device 50; the pulp outlet of the first washing device 10 is connected to the oxygen descaling feeder 20, and the third washing device 50 is located downstream of the oxygen descaling device 40 along the pulp conveying direction; the pulping system 100 has a first pulp passage and a second pulp passage, the first pulp passage connecting the outlet of the oxygen descaling feeder 20 to the pulp inlet of the oxygen descaling device 40; the second pulp passage sequentially connects the outlet of the oxygen descaling feeder 20, the second washing device 30, and the pulp inlet of the oxygen descaling device 40; the pulping system 100 includes a first operating mode and a second operating mode, in the first operating mode, the first pulp passage is connected and the second pulp passage is disconnected; in the second operating mode, the first pulp passage is disconnected and the second pulp passage is connected.

[0025] Specifically, the first washing device 10 can be arranged downstream of a pressure screen 85, and its outlet is connected to the inlet of the oxygen descaling feed trough 20 via a slurry conveying pipe. The oxygen descaling feed trough 20 can adopt a trough-type, bucket-type, horizontal box-type, or vertical buffer tank-type structure, and its interior can have a free liquid surface area, a buffer zone, and a slurry outlet area to temporarily store, homogenize, and continuously supply the slurry from the first washing device 10. The second washing device 30 is arranged between the oxygen descaling feed trough 20 and the oxygen descaling device 40, so that the oxygen descaling feed trough 20 becomes the common upstream node of the first and second slurry paths. The oxygen descaling device 40 can include a first oxygen descaling tower 41 and a second oxygen descaling tower 42 arranged in series, and if necessary, an oxygen descaling spray pot 43 can also be arranged downstream of it. In the first operating mode, the slurry in the oxygen descaling feed tank 20 is directly fed into the oxygen descaling unit 40 via the first slurry passage. In the second operating mode, the slurry in the oxygen descaling feed tank 20 first enters the second washing unit 30 via the second slurry passage, and then enters the oxygen descaling unit 40 after further washing and concentration. By placing the second washing unit 30 between the oxygen descaling feed tank 20 and the oxygen descaling unit 40, the buffering and homogenizing functions of the oxygen descaling feed tank 20 can be used to stably supply slurry to the second washing unit 30, and the direct oxygen descaling path can be retained when the second washing unit 30 is not in use, thus improving the adaptability of the existing production line after modification.

[0026] Therefore, by adding a second washing device 30 between the first washing device 10 and the oxygen desulfurization device 40, secondary washing and further concentration of the pulp before it enters the oxygen desulfurization device 40 are achieved. This reduces the content of impurities such as black liquor, leached lignin, and organic acids carried in the pulp, thus mitigating their interference with the subsequent oxygen desulfurization reaction. At the same time, by setting the second washing device 30 between the oxygen desulfurization feed trough 20 and the oxygen desulfurization device 40, and connecting the oxygen desulfurization feed trough 20 to both the first and second pulp passages, the oxygen desulfurization feed trough 20 and the second washing device 30 form a synergistic relationship of "buffered pulp supply - selective secondary washing - stable oxygen desulfurization." This not only allows the second washing device 30 to operate under more stable conditions but also prevents it from becoming the only passage, thus balancing the improvement of washing effect with the needs of continuous production.

[0027] According to some specific embodiments of this application, the pulping system 100 further includes a first filtrate passage and a second filtrate passage. The first filtrate passage is configured to transport the filtrate generated by the third pulp washing device 50 to the first pulp washing device 10. The second filtrate passage includes a first filtrate conveying section and a second filtrate conveying section. The first filtrate conveying section is configured to transport the filtrate generated by the third pulp washing device 50 to the second pulp washing device 30. The second filtrate conveying section is configured to transport the filtrate generated by the second pulp washing device 30 to the first pulp washing device 10. In the first operating mode, the first filtrate passage is connected and the second filtrate passage is disconnected. In the second operating mode, the first filtrate passage is disconnected and the second filtrate passage is connected.

[0028] Specifically, the filtrate from the third washing device 50 can first flow into the third filtrate tank 51, and then the third filtrate tank 51 supplies filtrate to the first filtrate passage and the second filtrate passage respectively. The first filtrate passage is used to directly return the filtrate from the third washing device 50 to the first washing device 10 under the original operating conditions to meet the washing liquid circulation requirements. The second filtrate passage includes a first filtrate conveying section and a second filtrate conveying section: the first filtrate conveying section conveys the cleaner filtrate in the third filtrate tank 51 to the second washing device 30 for secondary washing of the pulp that has already been washed by the first washing device 10; the second filtrate conveying section conveys the filtrate produced by the second washing device 30 back to the first washing device 10 for further washing of the preceding coarse pulp. In the second operating mode, the filtrate is reused step by step in the direction opposite to the mainstream direction of the pulp, thus forming a stepped reuse path of "third washing device 50 → second washing device 30 → first washing device 10". To ensure the stability of reuse, a transfer pump, buffer tank, filter, or throttling device can be installed in the first and second filtrate passages to regulate the flow rate and prevent particle blockage.

[0029] Furthermore, the second filtrate tank 32 can be arranged below, to the side, or adjacent to the second washing device 30. It can be a vertical tank, a horizontal tank, a box-type tank, or a tank structure with a conical bottom. The second filtrate tank 32 can have an inlet, an outlet, a drain outlet, an overflow outlet, and a liquid level detection unit. The inlet is connected to the filtrate outlet of the second washing device 30, and the outlet is connected to the second filtrate passage. The filtrate produced by the second washing device 30 is first temporarily stored and buffered in the second filtrate tank 32 before being transported to the first washing device 10, thereby reducing the impact of instantaneous fluctuations in the output of the second washing device 30 on the washing liquid supply of the first washing device 10.

[0030] Therefore, by setting up a first filtrate path and a second filtrate path, the same production line can have a filtrate reuse path that matches its different operating modes. In the first operating mode, the filtrate generated by the third washing unit 50 is directly returned to the first washing unit 10, which helps maintain the filtrate circulation mode of the process. In the second operating mode, the filtrate from the third washing unit 50 is first used in the second washing unit 30, and then the filtrate from the second washing unit 30 is returned to the first washing unit 10. This allows the relatively clean filtrate to be used preferentially for the relatively clean pulp, while the filtrate with increased contamination is then used for the upstream coarse pulp, thereby improving the utilization level and washing matching of the filtrate.

[0031] According to some specific embodiments of this application, the first slurry passage and the second slurry passage are respectively provided with shut-off valves; the first filtrate passage and the second filtrate passage are respectively provided with shut-off valves, so that the pulping system 100 can switch between the first operating mode and the second operating mode by opening and closing each of the shut-off valves.

[0032] Specifically, the shut-off valve can be installed after the outlet of the oxygen descaling feed tank 20, before and after the inlet of the second slurry washing device 30, and at key nodes in the first and second filtrate passages. The shut-off valve can be any one or more of a gate valve, ball valve, butterfly valve, globe valve, or diaphragm valve. If necessary, it can also be used in conjunction with an electric actuator, pneumatic actuator, or hydraulic actuator to achieve remote switching. By installing shut-off valves on the slurry passage and the filtrate passage respectively, in the first operating mode, the shut-off valves on the first slurry passage and the first filtrate passage can be opened, while the shut-off valves on the second slurry passage and the second filtrate passage can be closed; in the second operating mode, the reverse operation is performed. Since passage switching is achieved around existing nodes without disassembling equipment or temporarily replacing pipelines, it facilitates rapid switching of operating conditions during normal production, maintenance, repair, or fault response. Of course, in some embodiments, the shut-off valve can also be used in conjunction with a flow meter, pressure gauge, or level gauge, but its core function remains the selective connection and disconnection of different passages.

[0033] Therefore, by installing shut-off valves on the first pulp path, the second pulp path, the first filtrate path, and the second filtrate path, the pulping system 100 can switch between the two operating modes in a relatively simple and reliable manner. The pulp path and the filtrate path can be switched synchronously, avoiding mismatches where the pulp has been switched but the filtrate has not, thereby improving the operational stability and controllability of the second pulp washing device 30 when it is put into operation or taken out of operation.

[0034] According to some specific embodiments of this application, the second pulp washing device 30 is a two-roller pulp washing machine.

[0035] Specifically, a two-roll washer typically includes a frame, a pair of opposing roller assemblies, a pressing zone, a spray zone, a filtrate collection chamber, and a discharge section. The roller assembly can consist of a driving roller and a driven roller, or two synchronously driven pressing rollers; the roller surface can be smooth, textured, porous, or coated with a wear-resistant layer. After the pulp enters from the inlet end of the two-roll washer, it is squeezed and deliquified under the action of the roller gap, and displacement washing and concentration are achieved with the assistance of the spray liquid. Compared with screw press equipment, belt press equipment, or disc washer equipment, the two-roll washer is more likely to form a stable mechanical deliquescence zone and a higher discharge pulp concentration in the pre-oxygen desulfurization stage, and it is also beneficial to concentrate and discharge the separated filtrate. Of course, in the superior claim, the second washing device 30 can also adopt a squeeze washing equipment, a roller press thickening equipment, or other deliquescence washing equipment; however, the scheme of using a two-roll washer is more conducive to quickly achieving secondary washing and deliquescence enhancement before oxygen desulfurization.

[0036] Therefore, by defining the second washing device 30 as a double-roller washer, its combined effects of double-roller pressing, spray replacement, and simultaneous filtrate discharge can be utilized to further deliquulate, concentrate, and remove soluble impurities from the pulp after preliminary washing by the first washing device 10 before it enters the oxygen desulfurization device 40. The double-roller washer has a simple mechanical structure and a clear pressing path, making it particularly suitable for placement in the limited space between the oxygen desulfurization feed tank 20 and the oxygen desulfurization device 40, thus balancing the convenience of modifying existing production lines with the effectiveness of secondary washing.

[0037] According to some specific embodiments of this application, the first washing device 10 is an airless vacuum drum washing machine, and the third washing device 50 is a drum displacement washing machine.

[0038] Specifically, the airless vacuum drum washer, as the first washer unit 10, is responsible for the initial washing of the coarse pulp after cooking. Structurally, it can include a rotating drum, a filter cloth layer, a vacuum suction zone, a washing liquor distribution zone, and a discharge zone, making it suitable for processing front-end pulp with high impurity content and large flow rates. The drum displacement washer, as the third washer unit 50, is located downstream of the oxygen desulfurization unit 40, and can further wash the pulp after oxygen desulfurization and recover the relatively clean filtrate. The double-roll washer, as the second washer unit 30, is positioned between the two. On the one hand, it receives the pre-washed pulp from the airless vacuum drum washer, and on the other hand, it provides a secondary utilization location for the filtrate from the drum displacement washer, thus enabling the three washer units with different characteristics to perform the functions of coarse washing, fine washing, and final washing liquor return, respectively. To adapt to different production lines, the first washing unit 10 and the third washing unit 50 can also adopt the same or similar types of washing equipment; of course, it is more conducive to making full use of their respective functions by adopting a combination of airless vacuum drum washing machine, double roller washing machine and drum displacement washing machine.

[0039] Furthermore, the cooking section 86 may include cooking equipment for cooking the pulping raw materials and a liquid recycling pipeline connected to the cooking equipment. The filtrate produced by the first washing device 10 can flow into the first filtrate tank 11. At least one outlet of the first filtrate tank 11 is connected to the cooking section 86 through the liquid recycling pipeline, so as to return at least a portion of the filtrate in the first filtrate tank 11 to the cooking section 86. Thus, while setting up the second washing device 30 before oxygen desulfurization and changing part of the filtrate recycling path, the filtrate recycling relationship between the first washing device 10 and the cooking section 86 can be maintained, so that the newly added second washing device 30 and second filtrate tank 32 can cooperate with the front-end cooking and washing processes.

[0040] Therefore, by defining the first washing unit 10, the second washing unit 30, and the third washing unit 50 as an airless vacuum drum washer, a double-roller washer, and a drum displacement washer, respectively, a clear division of labor is achieved between the initial coarse washing, the intermediate secondary intensified washing, and the final washing liquor recovery. This combination not only facilitates the use of more suitable equipment in pulp sections with different levels of contamination, but also allows the filtrate output from the third washing unit 50 to preferentially serve the second washing unit 30 before serving the first washing unit 10, thereby improving the washing efficiency and filtrate utilization efficiency of the entire pulping line. Simultaneously, the pulp concentration after washing by the second washing unit 30 is higher than that after washing by the first washing unit 10, and the impurity content is lower.

[0041] According to some specific embodiments of this application, a double roller riser 31 is provided between the thick pulp outlet of the double roller washer and the oxygen descaling device 40. The double roller riser 31 is configured to store the pulp output from the double roller washer and supply pulp to the oxygen descaling device 40.

[0042] Specifically, the twin-roll riser 31 can adopt a vertically arranged tubular structure, cylindrical structure, box-type riser structure, or a buffer riser structure that is larger at the top and smaller at the bottom. Its inlet end is connected to the concentrated pulp outlet of the twin-roll washer, and its outlet end is connected to the inlet of the first oxygen stripper 41. The main body of the twin-roll riser 31 can be cylindrical, elliptical, square, or prismatic with guide rounded corners. Since the pulp concentration output by the twin-roll washer under pressing conditions is high, and the instantaneous flow rate may fluctuate, by setting up the twin-roll riser 31, at least a portion of the high-concentration pulp can be temporarily stored inside it, and a relatively continuous pulp supply can be achieved by means of liquid level height, gravity, or cooperation with subsequent conveying devices. If necessary, the twin-roll riser 31 can also be equipped with observation ports, maintenance ports, exhaust ports, or anti-bridging guides. In addition to the twin-roll riser 31, other forms of vertical buffer containers can also be used; of course, the twin-roll riser 31 is more convenient for direct connection with the twin-roll washing machine and oxygen descaling device 40.

[0043] Therefore, by installing a double-roller riser 31 between the double-roller washer and the oxygen desulfurization unit 40, the flow fluctuations at the pulp outlet of the double-roller washer can be effectively absorbed, allowing the high-concentration pulp to be buffered and homogenized briefly before entering the oxygen desulfurization unit 40. This avoids the impact of high-concentration pulp pulsation after secondary washing on the feeding stability of the oxygen desulfurization unit 40. At the same time, the double-roller riser 31 and the second washer 30 form a tight fit, ensuring that the enhanced deliquescence effect of the second washer 30 can be stably transferred to the oxygen desulfurization process.

[0044] According to some specific embodiments of this application, the third washing device 50 is connected to a third filtrate tank 51, which is connected to the first washing device 10 through a first filtrate passage and to the second washing device 30 through a second filtrate passage.

[0045] Specifically, the third filtrate tank 51 can be arranged in a low-lying area below, to the side, or near the third washing device 50. It can be a horizontal tank, a vertical tank, a box-type tank, or a buffer tank structure with a conical bottom drainage section. The filtrate discharged from the third washing device 50 first enters the third filtrate tank 51 for collection, and then is transported forward through the first and second filtrate passages respectively. The third filtrate tank 51 facilitates the temporary storage, pressure stabilization, and flow equalization of the filtrate generated by the third washing device 50, and allows for liquid supply to different passages in both the first and second operating modes. To ensure stable filtrate delivery, the third filtrate tank 51 can be coordinated with a delivery pump, a level gauge, and an overflow return pipe to prevent instantaneous fluctuations in the incoming liquid from being directly transmitted to the upstream washing process. In some embodiments, the third filtrate tank 51 can also be divided into multiple functional areas, such as an inlet buffer zone, a settling zone, and an outlet zone, but its overall function remains the collection and distribution of filtrate.

[0046] Therefore, by setting a third filtrate tank 51 after the third washing device 50, the filtrate output from the third washing device 50 is no longer directly dispersed into the upstream section, but is first uniformly collected and then distributed to the first filtrate passage or the second filtrate passage. On the one hand, this helps to stabilize the filtrate supply and reduce the risk of the upstream washing process being affected by instantaneous fluctuations; on the other hand, it also facilitates switching the filtrate destination under different operating modes, thereby making the switching between the first filtrate passage and the second filtrate passage smoother and more reliable.

[0047] According to some specific embodiments of this application, in the second operating mode, the chemical oxygen demand (COD) of the filtrate produced by the third washing device 50 is less than that of the filtrate produced by the second washing device 30, and the COD of the filtrate produced by the second washing device 30 is less than that of the filtrate produced by the first washing device 10.

[0048] Specifically, in an exemplary operating condition of this application, the filtrate produced by the third washing device 50, i.e. the filtrate from the downstream section of the drum displacement washing machine, can have a chemical oxygen demand of approximately 30 mg / L; the filtrate produced by the second washing device 30 can have a chemical oxygen demand of approximately 45 mg / L; and the filtrate produced by the first washing device 10 can have a chemical oxygen demand of approximately 180 mg / L.

[0049] The filtrate produced by the second washing device 30 can be collected in the second filtrate tank 32. In the above exemplary operating condition, the chemical oxygen demand (COD) of the filtrate in the second filtrate tank 32 can be approximately 45 mg / L, the COD of the filtrate in the third filtrate tank 51 can be approximately 30 mg / L, and the COD of the filtrate corresponding to the first filtrate tank 11 can be approximately 180 mg / L. Because the second filtrate tank 32 is located on the filtrate outlet side of the second washing device 30, it can independently collect the intermediate filtrate with increased contamination after the filtrate from the third washing device 50 has undergone secondary washing by the second washing device 30, facilitating its subsequent directional transport to the first washing device 10.

[0050] This demonstrates a gradient characteristic: the filtrate from the later stages is cleaner, the filtrate from the middle stages has a moderate level of contamination, and the filtrate from the earlier stages has a higher level of contamination. It should be understood that specific values ​​can vary depending on the type of wood pulp, cooking conditions, and testing procedures. However, the general rule is that the chemical oxygen demand (COD) of the filtrate from the third washing unit 50 is lower than that from the second washing unit 30, and the COD of the filtrate from the second washing unit 30 is lower than that from the first washing unit 10. Based on this COD gradient, the cleaner later-stage filtrate is best supplied to the second washing unit 30 first, and the filtrate discharged from the second washing unit 30 is then supplied to the first washing unit 10, thus forming a filtrate utilization relationship that matches different washing stages.

[0051] Therefore, by defining the chemical oxygen demand (COD) patterns of the filtrates corresponding to the third washing unit 50, the second washing unit 30, and the first washing unit 10, the basic conditions for the cascaded utilization of filtrate under the second operating mode can be clearly defined. Specifically, filtrate with lower COD is preferentially used for the later, more refined secondary washing, while filtrate with increased contamination after secondary washing is then used for the earlier coarse washing. This improvement ensures that the filtrate reuse pathway matches the filtrate quality, which is beneficial for improving reuse efficiency and reducing the pressure of replenishing fresh washing liquid.

[0052] According to some specific embodiments of this application, the aforementioned pulping system 100 is adopted, including a first operating mode and a second operating mode. In the first operating mode, the pulp washed by the first washing device 10 is conveyed to the oxygen descaling device 40 via the oxygen descaling feed tank 20, and the pulp bypasses the second washing device 30. The filtrate generated by the third washing device 50 is conveyed to the first washing device 10. In the second operating mode, the pulp washed by the first washing device 10 is conveyed to the second washing device 30 via the oxygen descaling feed tank 20, washed again by the second washing device 30, and then conveyed to the oxygen descaling device 40. The filtrate generated by the third washing device 50 is conveyed to the second washing device 30, and the filtrate generated by the second washing device 30 is conveyed to the first washing device 10. When switching between the first operating mode and the second operating mode, the pulp processing volume entering the oxygen descaling device 40 and the addition parameters of oxygen and sodium hydroxide are switched accordingly.

[0053] Specifically, after passing through the first washing unit 10, the slurry directly enters the oxygen desulfurization unit 40 via the oxygen desulfurization feed tank 20 and the first slurry passage. The filtrate from the third washing unit 50 is returned to the first washing unit 10 via the first filtrate passage. The second operating mode corresponds to the operation mode after the addition of the second washing unit 30. In this mode, the slurry after the first washing unit 10 first enters the oxygen desulfurization feed tank 20, and then is sent to the second washing unit 30 via the second slurry passage for further washing and concentration. Subsequently, it enters the oxygen desulfurization unit 40 via the double roller riser 31. At the same time, the filtrate from the third washing unit 50 is first sent to the second washing unit 30 via the second filtrate passage, and the filtrate discharged from the second washing unit 30 is then sent back to the first washing unit 10. Since the slurry contamination load entering the oxygen desulfurization unit 40 is reduced in the second operating mode, the set values ​​of the oxygen dosing component and the sodium hydroxide dosing component can be adjusted accordingly, and the slurry processing capacity can also be increased simultaneously. In other words, the method of this application does not simply switch a slurry pipeline, but rather switches the slurry path, filtrate path, and oxygen removal dosing parameters in a coordinated manner.

[0054] In the second operating mode, the second washing unit 30 and the second filtrate tank 32 can operate together: the filtrate in the third filtrate tank 51 is transported to the second washing unit 30, the filtrate produced by the second washing unit 30 enters the second filtrate tank 32, and is then transported by the second filtrate tank 32 to the first washing unit 10; in the first operating mode, the branch containing the second washing unit 30 and its associated second filtrate tank 32 can be disconnected, allowing the filtrate produced by the third washing unit 50 to be directly transported to the first washing unit 10 through the first filtrate passage. Regardless of whether the first or second operating mode is used, the filtrate produced by the first washing unit 10 and entering the first filtrate tank 11 can be returned to the cooking section 86 according to process requirements.

[0055] Therefore, by defining a first operating mode and a second operating mode and switching between them, the pulping method of this application can correspond to the logic of existing production line modification. The first operating mode facilitates maintaining production line operation, while the second operating mode utilizes the second pulp washing device 30 to achieve secondary washing before oxygen desulfurization and cascaded reuse of filtrate. More importantly, when switching operating conditions, the pulp processing volume and the addition parameters of oxygen and sodium hydroxide are simultaneously switched accordingly, so that the added washing effect can be directly reflected in the operation control of the oxygen desulfurization process, thereby more fully releasing the value of the modification.

[0056] According to some specific embodiments of this application, the oxygen dosage per unit of oven-dry slurry in the second operating mode is less than the oxygen dosage per unit of oven-dry slurry in the first operating mode, and the sodium hydroxide dosage per unit of oven-dry slurry in the second operating mode is less than the sodium hydroxide dosage per unit of oven-dry slurry in the first operating mode.

[0057] Specifically, in this application, the oxygen dosage per unit of oven-dry pulp refers to the ratio of the mass of oxygen added during oxygen removal to the mass of oven-dry pulp treated accordingly; the sodium hydroxide dosage per unit of oven-dry pulp refers to the ratio of the mass of sodium hydroxide added during oxygen removal to the mass of oven-dry pulp treated accordingly. Here, "dosage per unit of oven-dry pulp" can be measured in the form of kg / adt, where adt represents oven-dry pulp tons.

[0058] In the first operating mode, since the pulp only undergoes one washing in the first washing unit 10 before entering the oxygen descaling unit 40, the pulp entering the oxygen descaling unit 40 carries a lot of soluble impurities. Therefore, the amount of oxygen added per unit of oven-dry pulp and the amount of sodium hydroxide added per unit of oven-dry pulp required to achieve the target oxygen descaling degree are relatively high. In the second operating mode, after the second washing unit 30 washes the pulp again, the amount of black liquor and chemical oxygen demand carried by the pulp before oxygen descaling decreases, thereby reducing the demand for oxygen and sodium hydroxide per unit of oven-dry pulp.

[0059] In actual operation, the oxygen and sodium hydroxide dosages in the second operating mode can be lower than those in the first operating mode, and the specific reduction can be determined based on the type of wood pulp, the target kappa number, and the capacity of the equipment. This method allows for a redundancy in dosage for higher pulp processing volumes without increasing the total supply capacity of oxygen and sodium hydroxide.

[0060] Therefore, by limiting the oxygen and sodium hydroxide dosage per unit of oven-dry pulp in the second operating mode to be lower than in the first operating mode, the direct technical benefits brought by the second washing unit 30 can be reflected from a methodological perspective. Specifically, after improving the pre-oxygen descaling washing effect, less chemicals are required per unit of oven-dry pulp to achieve the target oxygen descaling level. This improvement not only reduces chemical consumption costs but also allows the existing oxygen and sodium hydroxide delivery capacity to serve a larger pulp processing volume, thus providing conditions for increasing production capacity.

[0061] According to some specific embodiments of this application, the dosage of oxygen and sodium hydroxide is adjusted according to the kappa number of the deoxygenated pulp; in the second operating mode, the chemical oxygen demand carried by the pulp entering the deoxygenation device 40 is reduced by the second pulp washing device 30, so as to reduce the amount of oxygen and sodium hydroxide required per unit of oven-dry pulp to achieve the target kappa number; and the pulp processing capacity in the second operating mode is greater than that in the first operating mode.

[0062] Specifically, the kappa number can be used as an important characterization parameter for oxygen removal efficiency.

[0063] In some embodiments of this application, the dosage of the oxygen dosing component and the sodium hydroxide dosing component can be adjusted in a closed-loop or semi-closed-loop manner based on the kappa value of the slurry after oxygen deoxygenation. For example, when the kappa value is too high, the dosage of oxygen and sodium hydroxide can be appropriately increased; when the kappa value is too low, the dosage of oxygen and sodium hydroxide can be appropriately decreased.

[0064] In the second operating mode, the second washing unit 30 performs secondary washing on the slurry entering the oxygen removal unit 40, which significantly reduces the chemical oxygen demand carried by the slurry, thereby reducing the amount of oxygen and sodium hydroxide required per unit of oven-dry slurry to achieve the same target kappa number.

[0065] By adopting the scheme in this application, in the second operating mode, the pulp concentration of the washer can be increased from 15% to 35% in the original process, the chemical oxygen demand load carried by the pulp can be reduced from 180 to 45, the oxygen deoxygenation consumption can be reduced from 32 kg / adt to 18 kg / adt, the oxygen desodium hydroxide consumption can be reduced from 28 kg / adt to 15 kg / adt, the total available chlorine consumption for bleaching can be reduced from 54 kg / adt to 42 kg / adt, and the daily production capacity of the production line can be increased from 950 adt / d to 1100 adt / d. Regarding the pulp concentration of the second pulp washing unit 30, in some embodiments it is preferably stabilized at 25% to 35%, for example, it can be 25%, 27%, 29%, 31%, 33%, or 35%.

[0066] If the concentration is below 25%, it indicates that the deliquescence effect of the second washing unit 30 is insufficient, and the pulp entering the oxygen desulfurization unit 40 still carries a large amount of free water and black liquor. If it is above 35%, the pulp is too thick, which may lead to decreased fluidity in the twin-roll riser 31, poor stable pulp supply capacity, and fluctuations in the feed to the oxygen desulfurization unit 40. Controlling it within the range of 25% to 35% can balance the concentration effect with the stability of subsequent conveying.

[0067] Therefore, by using the kappa number as the adjustment basis and combining it with the improvement of the second washing unit 30 to reduce the chemical oxygen demand of the pulp before oxygen desulfurization, the oxygen desulfurization control strategies of the first and second operating modes can be clearly distinguished. In the second operating mode, because the second washing unit 30 removes more soluble impurities in advance, oxygen and sodium hydroxide are no longer consumed in large quantities in ineffective side reactions, but are used more for the target oxygen desulfurization reaction. Thus, while reducing the amount of oxygen and sodium hydroxide added per unit of oven-dry pulp, the oxygen desulfurization process has a higher pulp processing capacity, ultimately achieving a balance between increased production capacity and reduced chemical consumption.

[0068] To more clearly illustrate the impact of the second washing unit 30 on the washing effect of pre-oxygen descaling pulp, consumption of oxygen descaling agents, and capacity improvement under the second operating mode, typical operating data based on the statistical caliber of oven-dry pulp per ton are provided below. This data can be used to illustrate the differences between the first and second operating modes.

[0069]

[0070] Specifically, the parameters in the aforementioned data table, such as "slurry concentration from the washing machine," "chemical oxygen demand load carried by the slurry," "oxygen consumption per unit of oxygen in oxygen removal," "sodium hydroxide consumption per unit of sodium hydroxide in oxygen removal," "total effective chlorine consumption per unit of bleaching," and "daily production capacity of the production line," collectively reflect the comprehensive effect produced by placing the second washing unit between the oxygen removal feed tank and the oxygen removal unit. In particular, in the second operating mode, the second washing unit first receives the slurry stably output from the oxygen removal feed tank, and then sends the further washed high-concentration slurry into the oxygen removal unit. This allows the secondary washing effect to work in conjunction with the feed stability of the oxygen removal unit, thereby optimizing the dosage and processing load of subsequent oxygen removal agents.

[0071] It should be noted that the above values ​​are data from a set of typical embodiments and do not constitute a limitation on the scope of protection. Under different wood pulp varieties, cooking conditions, equipment scale, and production line capacity, the specific values ​​corresponding to the first and second operating modes may vary, but as long as they meet the technical concept of this application regarding the first pulp passage, the second pulp passage, the first filtrate passage, the second filtrate passage, and their inter-passing relationships, they should all be considered to fall within the scope of protection of this application.

[0072] The foregoing embodiments are merely illustrative. Those skilled in the art can make various improvements and modifications to the invention without departing from its principles, and these improvements and modifications also fall within the scope of the claims. Furthermore, those skilled in the art can combine the various embodiments in part or in whole, and all technical solutions derived from such combinations fall within the scope of this patent.

Claims

1. A pulping system, characterized in that, It includes a first washing device (10), an oxygen descaling feeder (20), a second washing device (30), an oxygen descaling device (40), and a third washing device (50); The pulp outlet of the first pulp washing device (10) is connected to the oxygen descaling feed trough (20). Along the pulp conveying direction, the third pulp washing device (50) is located downstream of the oxygen descaling device (40). The pulping system (100) has a first pulp passage and a second pulp passage. The first pulp passage connects the outlet of the oxygen descaling feed tank (20) to the pulp inlet of the oxygen descaling device (40). The second pulp passage connects the outlet of the oxygen descaling feed tank (20), the second pulp washing device (30), and the pulp inlet of the oxygen descaling device (40) in sequence. The pulping system (100) has a first operating mode and a second operating mode. In the first operating mode, the first pulp passage is connected and the second pulp passage is disconnected. In the second operating mode, the first slurry path is disconnected, and the second slurry path is connected.

2. The pulping system according to claim 1, characterized in that, The pulping system (100) further includes a first filtrate passage and a second filtrate passage. The first filtrate passage is configured to transport the filtrate generated by the third pulp washing device (50) to the first pulp washing device (10). The second filtrate passage includes a first filtrate conveying section and a second filtrate conveying section. The first filtrate conveying section is configured to transport the filtrate generated by the third pulp washing device (50) to the second pulp washing device (30). The second filtrate conveying section is configured to transport the filtrate generated by the second pulp washing device (30) to the first pulp washing device (10). In the first operating mode, the first filtrate passage is connected, and both the first filtrate delivery section and the second filtrate delivery section are disconnected; in the second operating mode, the first filtrate passage is disconnected, and both the first filtrate delivery section and the second filtrate delivery section are connected.

3. The pulping system according to claim 2, characterized in that, The first slurry passage and the second slurry passage are each provided with a shut-off valve; the first filtrate passage and the second filtrate passage are each provided with a shut-off valve, so that the pulping system (100) can switch between the first operating mode and the second operating mode by opening and closing each of the shut-off valves.

4. The pulping system according to claim 1, characterized in that, The second washing device (30) is a double roller washing machine.

5. The pulping system according to claim 4, characterized in that, The first washing device (10) is an airless vacuum drum washing machine, and the third washing device (50) is a drum displacement washing machine.

6. The pulping system according to claim 4, characterized in that, A double roller riser (31) is provided between the thick pulp outlet of the double roller washer and the oxygen descaling device (40), and the double roller riser (31) is configured to store the pulp output by the double roller washer.

7. The pulping system according to any one of claims 2 to 6, characterized in that, The third washing device (50) is connected to a third filtrate tank (51), which is connected to the first washing device (10) via a first filtrate passage. It is connected to the second washing device (30) through the second filtrate passage.

8. The pulping system according to any one of claims 2 to 6, characterized in that, In the second operating mode, the chemical oxygen demand of the filtrate produced by the third washing device (50) is less than that of the filtrate produced by the second washing device (30), and the chemical oxygen demand of the filtrate produced by the second washing device (30) is less than that of the filtrate produced by the first washing device (10).

9. A pulping method, characterized in that, The pulping system according to any one of claims 1 to 6 is used, and includes a first operating mode and a second operating mode; In the first operating mode, the pulp washed by the first pulp washing device (10) is transported to the oxygen descaling device (40) through the oxygen descaling feed tank (20), and the pulp bypasses the second pulp washing device (30); the filtrate generated by the third pulp washing device (50) is transported to the first pulp washing device (10); In the second operating mode, the pulp washed by the first pulp washing device (10) is transported to the second pulp washing device (30) through the oxygen descaling feed tank (20), and after being washed again by the second pulp washing device (30), it is transported to the oxygen descaling device (40); the filtrate generated by the third pulp washing device (50) is transported to the second pulp washing device (30), and the filtrate generated by the second pulp washing device (30) is transported to the first pulp washing device (10); When switching between the first operating mode and the second operating mode, the slurry processing volume entering the oxygen removal device (40) and the addition parameters of oxygen and sodium hydroxide are switched accordingly.

10. The pulping method according to claim 9, characterized in that, The oxygen dosage per unit of oven-dry slurry in the second operating mode is less than that in the first operating mode, and the sodium hydroxide dosage per unit of oven-dry slurry in the second operating mode is less than that in the first operating mode.

11. The pulping method according to claim 9 or 10, characterized in that, The dosage of oxygen and sodium hydroxide is adjusted according to the kappa number of the slurry after oxygen desulfurization; in the second operating mode, the chemical oxygen demand carried by the slurry entering the oxygen desulfurization device (40) is reduced by the second slurry washing device (30) to reduce the amount of oxygen added per unit of oven-dry slurry and the amount of sodium hydroxide added per unit of oven-dry slurry required to reach the target kappa number; and the slurry processing volume in the second operating mode is greater than that in the first operating mode.

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