Heat exchange system and method for pulping liquid

Abstract

The invention discloses a heat exchange system of liquid for pulping, which comprises a first heat exchanger for cooling dilute black liquor flowing into a cooking tower, and further comprises a second heat exchanger for carrying out heat exchange on white water of a pulp machine and the dilute black liquor, the first heat exchanger is used for carrying out heat exchange on the dilute black liquor subjected to heat exchange by the second heat exchanger and factory water; and the pulp machine white water subjected to heat exchange by the second heat exchanger is used for diluting and heating pulp flowing into the slushing tank. According to the heat exchange system for the liquid for pulping, the steam consumption is reduced, the production cost is reduced, the yield of hot water is reduced, heat waste is reduced, and water resources are saved. The invention further provides a heat exchange method of the liquid for pulping.

Description

Technical Field

[0001] The invention relates to the technical field of pulp and paper production, and in particular to a system and method for heat exchange of pulping liquid. Background Art

[0002] Pulping is the process of separating fibers from plant fiber raw materials to obtain pulp. During the pulping process, the hot water generated in each section needs to be sent to the cooling tower for cooling and then sent back to the water purification station for reuse. The heat of the hot water is not fully utilized, resulting in heat waste. At the same time, the section that needs to be heated uses other heat for heating, which increases energy consumption. In addition, the evaporation cooling process of hot water at the cooling tower will cause a large amount of water loss, wasting water resources. Summary of the invention

[0003] In view of this, the present invention provides a heat exchange system for pulping liquid, which saves steam usage, reduces production costs, reduces hot water output, reduces heat waste, and saves water resources.

[0004] The invention also provides a heat exchange method for pulping liquid.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A heat exchange system for pulping liquid comprises a first heat exchanger for cooling dilute black liquor flowing into a cooking tower, and also comprises a second heat exchanger, wherein the second heat exchanger is used for heat exchange between pulp machine white water and dilute black liquor, and the first heat exchanger is used for heat exchange between dilute black liquor and factory water after heat exchange through the second heat exchanger; the pulp machine white water after heat exchange through the second heat exchanger is used for diluting and heating pulp flowing into a pulping tank.

[0007] Optionally, a plant water supply system is further included, the plant water supply system comprising a first water inlet branch and a second water inlet branch arranged in parallel, the first water inlet branch is used to provide normal temperature plant water to the first heat exchanger, and the second water inlet branch is used to provide heated plant water to the first heat exchanger;

[0008] When the temperature of the plant water is higher than a set value, the first water inlet branch provides the first heat exchanger with plant water, and when the temperature of the plant water is lower than the set value, the second water inlet branch provides the first heat exchanger with plant water.

[0009] Optionally, a third heat exchanger is provided on the second water inlet branch, and the third heat exchanger utilizes bleaching alkaline wastewater to heat the factory water flowing through.

[0010] Optionally, the factory water heated by the first heat exchanger flows into a hot water tank, and the hot water tank provides hot water for the bleaching stage.

[0011] Optionally, the first heat exchanger includes a first heat exchange chamber and a second heat exchange chamber, and the second heat exchanger includes a third heat exchange chamber and a fourth heat exchange chamber;

[0012] The inlet of the third heat exchange chamber is connected to the weak black liquor input pipe, and the outlet is connected to the inlet of the first heat exchange chamber, and the outlet of the first heat exchange chamber is connected to the cooking tower; the inlet of the fourth heat exchange chamber is connected to the pulp machine white water, and the outlet is connected to the high concentration tower; the inlet of the second heat exchange chamber is connected to the factory water, and the outlet is connected to the hot water tank.

[0013] Optionally, the outlet of the second heat exchange chamber is also connected to a cooling water tower.

[0014] Optionally, the third heat exchanger includes a fifth heat exchange chamber and a sixth heat exchange chamber, the inlet of the fifth heat exchange chamber is connected to the ends of the first water inlet branch and the second water inlet branch, and the outlet is connected to the inlet of the second heat exchange chamber of the first heat exchanger; the inlet of the sixth heat exchange chamber is connected to the bleaching alkaline wastewater, and the outlet is connected to the sewage treatment device.

[0015] Optionally, a first conductivity meter is provided at an inlet end of the pulp machine white water of the second heat exchanger, and a second conductivity meter is provided at an outlet end of the pulp machine white water of the second heat exchanger.

[0016] It can be seen from the above technical scheme that the heat exchange system for pulping liquid provided by the present invention performs heat exchange and cooling of the input dilute black liquor in sequence by arranging a second heat exchanger and a first heat exchanger. At the position of the second heat exchanger, the pulp machine white water is heated by the high-temperature dilute black liquor, so that the outlet temperature of the pulp machine white water is increased to a preset temperature. The pulp machine white water increased to the preset temperature dilutes the slurry, and the temperature of the diluted slurry is reduced to the temperature required by the pulping tank, thereby saving the low-pressure steam that needs to be introduced into the pulping tank for heating in the prior art, saving the steam consumption, and reducing the production cost. After the dilute black liquor is cooled by heat exchange in the second heat exchanger, it is further cooled by the factory water at the first heat exchanger. Since the dilute black liquor has been cooled by heat exchange in the second heat exchanger, the temperature of the dilute black liquor entering the first heat exchanger is relatively low, so the demand for cooling the dilute black liquor can be met by reducing the flow rate of the factory water entering the first heat exchanger. The factory water flowing out of the first heat exchanger is hot water, thereby reducing the amount of hot water generated by the first heat exchanger. Most of the hot water generated by the first heat exchanger flows to the storage device for storage to provide hot water for other processes. Since the total amount of hot water generated is small, only a small amount of hot water flows out, which reduces heat waste and saves water resources.

[0017] The present invention also provides a heat exchange method for pulping liquid, which is applied to the heat exchange system for pulping liquid, and comprises the following steps:

[0018] Using dilute black liquor to heat the pulp machine white water so that the pulp machine white water reaches a first preset temperature, and the pulp machine white water reaching the first preset temperature is used to dilute and heat the slurry in the high-concentration tower;

[0019] The dilute black liquor cooled by the pulp machine white water is further cooled by factory water to a second preset temperature, and the dilute black liquor cooled to the second preset temperature enters the cooking tower.

[0020] Optionally, the factory water is water at room temperature or water heated by bleaching alkaline wastewater;

[0021] When the temperature of the factory water is higher than the set value, the factory water uses normal temperature water. When the temperature of the factory water is lower than the set value, the factory water uses bleaching alkaline wastewater for heat exchange heating.

[0022] Optionally, by detecting the difference in conductivity between the inlet and outlet of the pulp machine white water of the heat exchanger, it is determined whether the pulp machine white water is contaminated by the dilute black liquor.

[0023] The heat exchange method for pulping liquid provided by the present invention is applied to the heat exchange system for pulping liquid mentioned above, and thus has the advantages of the heat exchange system for pulping liquid mentioned above, which will not be described in detail herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 A schematic structural diagram of a heat exchange system for pulping liquid provided in one embodiment of the present invention;

[0026] Figure 2 A schematic structural diagram of a heat exchange system for pulping liquid provided in another embodiment of the present invention.

[0027] in:

[0028] 1. Slurry trough,

[0029] 2. Second temperature sensor,

[0030] 3. High concentration tower,

[0031] 4. Thin black liquor inlet pipe,

[0032] 5. The first temperature sensor,

[0033] 6. Second conductivity meter,

[0034] 7. Second heat exchanger,

[0035] 8. The first conductivity meter,

[0036] 9. The third temperature sensor,

[0037] 10. The fourth pipeline,

[0038] 11. The first heat exchanger,

[0039] 12. The fourth temperature sensor,

[0040] 13. The eighth pipeline,

[0041] 14. Alkaline wastewater pipe,

[0042] 15. The third heat exchanger,

[0043] 16. Sewage delivery pipes,

[0044] 17. Input pipeline,

[0045] 18. The first pipeline,

[0046] 19. The seventh pipeline,

[0047] 20. Hot water tank,

[0048] 21. The first water inlet branch,

[0049] 22. Second water inlet branch,

[0050] 23. Second pipeline,

[0051] 24 Ninth pipeline. DETAILED DESCRIPTION

[0052] The invention discloses a heat exchange system for pulping liquid, which saves steam usage, reduces production costs, reduces hot water output, reduces heat waste, and saves water resources.

[0053] The invention also provides a heat exchange method for pulping liquid.

[0054] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0055] Reference Figure 1 and Figure 2 The heat exchange system for pulping liquid of the present invention comprises a first heat exchanger 11 and a second heat exchanger 7 for cooling the dilute black liquor flowing into the digester, the second heat exchanger 7 is used for heat exchange between the pulp machine white water and the dilute black liquor, and the first heat exchanger 11 is used for further heat exchange between the dilute black liquor and the factory water after heat exchange through the second heat exchanger 7. The pulp machine white water after heat exchange through the second heat exchanger 7 is used for diluting and heating the pulp flowing into the pulping tank 1, so that the pulp flowing into the pulping tank 1 reaches the required concentration and temperature.

[0056] The white water from the pulp machine heated by the second heat exchanger 7 flows into the high-concentration tower 3 for diluting the slurry. The temperature of the diluted slurry meets the temperature in the pulping tank 1, so the pulping tank 1 does not need to be heated by low-pressure steam. The temperature of the white water from the pulp machine rises after passing through the second heat exchanger 7. At the same time, the temperature of the dilute black liquor after passing through the second heat exchanger 7 decreases. The dilute black liquor after the temperature is reduced flows into the first heat exchanger 11 and is further cooled to meet the temperature requirement of the cooking tower for the washing slurry.

[0057] The heat exchange system for pulping liquid of the present invention sequentially exchanges heat and cools down the input dilute black liquor by arranging a second heat exchanger 7 and a first heat exchanger 11. At the position of the second heat exchanger 7, the pulp machine white water is heated by the high-temperature dilute black liquor, so that the outlet temperature of the pulp machine white water is increased to a preset temperature. The pulp machine white water increased to the preset temperature dilutes the slurry, and the temperature of the diluted slurry is reduced to the temperature required by the pulping tank 1, thereby saving the low-pressure steam that needs to be introduced into the pulping tank 1 for heating in the prior art, saving the steam consumption, and reducing the production cost. After the dilute black liquor is cooled by heat exchange once in the second heat exchanger 7, it is further cooled by the factory water at the first heat exchanger 11. Since the dilute black liquor has been cooled by heat exchange once in the second heat exchanger 7, the temperature of the dilute black liquor entering the first heat exchanger 11 is relatively low, so the demand for cooling the dilute black liquor can be met by reducing the flow rate of the factory water entering the first heat exchanger 11. The factory water flowing out of the first heat exchanger 11 is hot water, thereby reducing the amount of hot water generated by the first heat exchanger 11. Most of the hot water generated by the first heat exchanger 11 flows to the storage device for storage to provide hot water for other processes. Since the total amount of hot water generated is small, only a small amount of hot water flows out, thereby reducing heat waste and saving water resources.

[0058] The heat exchange system for pulping liquid of the present invention also includes a factory water supply system, which is used to provide the required factory water for the first heat exchanger 11, and specifically includes a first water inlet branch 21 and a second water inlet branch 22 arranged in parallel, the first water inlet branch 21 is used to provide the first heat exchanger 11 with normal temperature factory water, and the second water inlet branch 22 is used to provide the first heat exchanger 11 with heated factory water. When the temperature of the factory water is higher than the set value, the first water inlet branch 21 provides factory water for the first heat exchanger 11, and when the temperature of the factory water is lower than the set value, the second water inlet branch 22 provides factory water for the first heat exchanger 11. The temperature setting value of the factory water is set by the technician according to the needs. The input pipeline 17 is connected with the inlet end of the first water inlet branch 21 and the second water inlet branch 22, and provides factory water for the first water inlet branch 21 or the second water inlet branch 22.

[0059] In order to ensure the inlet temperature of the factory water under different ambient temperatures, a third heat exchanger 15 is provided on the second inlet branch 22 , and the third heat exchanger 15 uses the bleaching alkaline wastewater to heat the factory water flowing through. Specifically, the bleaching alkaline wastewater is transported to the third heat exchanger 15 by the alkaline wastewater pipe 14 .

[0060] In order to facilitate the control of water inflow from different water inlet branches, a first valve is provided on the first water inlet branch 21, and the first valve is used to control whether liquid is inflowed into the first water inlet branch 21. A third heat exchanger 15 and a second valve are provided on the second water inlet branch 22, and the second valve is used to control whether liquid is inflowed into the second water inlet branch 22. The ends of the first water inlet branch 21 and the second water inlet branch 22 are both connected to the first heat exchanger 11. The first water inlet branch 21 is used to directly transport the factory water at room temperature transported by the input pipeline 17 to the first heat exchanger 11, and the second water inlet branch 22 is used to transport the factory water after heat exchange in the third heat exchanger 15 to the first heat exchanger 11. When the temperature of the factory water is high, the factory water flows into the first heat exchanger 11 through the first water inlet branch 21; in winter, the temperature of the factory water directly transported by the input pipeline 17 is low, and the factory water flows into the first heat exchanger 11 after heat exchange and temperature increase through the third heat exchanger 15 on the second water inlet branch 22. When in use, the opening and closing of different water inlet branches are controlled by controlling the opening and closing of the first valve and the second valve, or the opening of the two water inlet branches is adjusted. The factory water heated by the first heat exchanger 11 flows into the hot water tank 20, and the hot water tank 20 provides hot water for the bleaching stage.

[0061] Specifically, the first heat exchanger 11 includes a first heat exchange chamber and a second heat exchange chamber, and the second heat exchanger 7 includes a third heat exchange chamber and a fourth heat exchange chamber. The inlet of the third heat exchange chamber is connected to the weak black liquor input pipe 4, and the outlet is connected to the inlet of the first heat exchange chamber, and the outlet of the first heat exchange chamber is connected to the cooking tower. The inlet of the fourth heat exchange chamber is connected to the white water of the pulp machine, and the outlet is connected to the high-concentration tower 3, and the outlet of the high-concentration tower 3 is connected to the pulping tank 1. The inlet of the second heat exchange chamber is connected to the factory water, and the outlet is connected to the hot water tank 20.

[0062] In one embodiment, the third heat exchange chamber of the second heat exchanger 7 is a tube chamber, that is, the thin black liquor runs the tube side of the second heat exchanger 7, and the fourth heat exchange chamber is a shell chamber, that is, the pulp machine white water runs the shell side of the second heat exchanger 7. Because there are fine fibers in the pulp machine white water, the fine fibers will adhere to the heat exchange tube wall in actual operation, which will cause the heat exchanger efficiency to decrease over time. Therefore, a floating head heat exchanger is selected in the selection of the heat exchanger, which can achieve high-pressure cleaning of the shell side of the heat exchanger. In addition, the pH value of the pulp machine white water is about 5.0, and it contains trace amounts of chloride ions. The corrosion problem of the equipment must be considered in the selection of materials, and duplex steel or more corrosion-resistant materials must be selected. One of the first heat exchange chamber and the second heat exchange chamber of the first heat exchanger 11 is a tube chamber, and the other is a shell chamber. Preferably, the first heat exchange chamber is a tube chamber.

[0063] Furthermore, the outlet of the second heat exchange chamber of the first heat exchanger 11 is also connected to the cooling water tower through the first pipeline 18. The outlet of the fourth heat exchange chamber is connected to the hot water tank 20 through the second pipeline 23, and the hot water in the hot water tank 20 flows to the bleaching section through the seventh pipeline 19. The first pipeline 18 and the second pipeline 23 are arranged in parallel, the second pipeline 23 transports the hot water to the hot water tank 20 to meet the needs of the bleaching section, and the first pipeline 18 is used to transport a small amount of excess hot water to the cooling water tower for cooling so as to be recycled.

[0064] Furthermore, the third heat exchanger 15 includes a fifth heat exchange chamber and a sixth heat exchange chamber, the inlet of the fifth heat exchange chamber is connected to the ends of the first water inlet branch 21 and the second water inlet branch 22, and the outlet is connected to the inlet of the second heat exchange chamber of the first heat exchanger 11. The inlet of the sixth heat exchange chamber is connected to the alkaline wastewater pipe 14, which is used to transport bleaching alkaline wastewater, and the outlet of the sixth heat exchange chamber is connected to the sewage treatment device. The outlet of the sixth heat exchange chamber is connected to the sewage treatment device through the sewage delivery pipe 16. At the location of the third heat exchanger 15, the factory water is heated by heat exchange with the alkaline wastewater. By recovering the heat of alkaline wastewater, alkaline wastewater can provide warm water of 15-25 degrees in winter, and the factory water can be heated to warm water in winter, thereby avoiding the situation where the temperature of the factory water flowing into the first heat exchanger 11 is too low, and the requirement for increasing the temperature and flow rate of the factory water at the outlet of the first heat exchanger 11 is avoided. It is not necessary to increase the temperature of the dilute black liquor flowing into the first heat exchanger 11 to meet the requirement of increasing the factory water temperature, so that even in winter, the second heat exchanger 7 can ensure continuous heat exchange of the pulp board white water, and meet the temperature requirements of the subsequent process for the pulp board white water. At the same time, after heat exchange, the temperature of the bleaching alkaline wastewater is also reduced, thereby reducing the impact of the high temperature of the sewage in the sewage treatment workshop on microorganisms.

[0065] Specifically, the second heat exchanger 7 is connected to the high-concentration tower 3 through the third pipeline, and the second heat exchanger 7 is connected to the white water tower of the pulp machine through the fourth pipeline 10. The fourth pipeline 10 is used to transport the white water of the pulp machine to the second heat exchanger 7. The dilute black liquor and the white water of the pulp machine exchange heat in the second heat exchanger 7. If the dilute black liquor enters the white water of the pulp machine during operation, it will cause immeasurable losses. In order to monitor whether the third heat exchange chamber and the fourth heat exchange chamber of the second heat exchanger 7 leak and mix water, a first conductivity meter 8 is arranged on the fourth pipeline 10, and a second conductivity meter 6 is arranged on the third pipeline. The first conductivity meter 8 and the second conductivity meter 6 are both connected to the DCS for monitoring, and the corresponding alarm threshold is connected. The second conductivity meter 6 is used to monitor the conductivity of the white water of the pulp machine flowing out of the second heat exchanger 7, and the first conductivity meter 8 is used to monitor the conductivity of the white water of the pulp machine flowing into the second heat exchanger 7. By comparing the difference in the conductivity of the pulp machine white water flowing into and out of the second heat exchanger 7, it is determined whether the heat exchanger has mixed water with the dilute black liquor and the pulp machine white water, thereby avoiding the occurrence of abnormal conditions. In order to facilitate monitoring whether the water temperature of the pulp machine white water flowing into the high-concentration tower 3 is within a preset range, a first temperature sensor 5 is also provided on the third pipeline.

[0066] In one embodiment, the high-concentration tower 3 is connected to the slurry tank 1 through a fifth pipeline, and a second temperature sensor 2 is provided on the fifth pipeline. The second temperature sensor 2 is used to monitor the temperature of the white water in the fifth pipeline. Similarly, the second heat exchanger 7 is connected to the first heat exchanger 11 through a sixth pipeline, and a third temperature sensor 9 is provided on the sixth pipeline. The first heat exchanger 11 is connected to the cooking tower through an eighth pipeline 13, and a fourth temperature sensor 12 is provided on the eighth pipeline 13.

[0067] In order to cope with the situation that the temperature of the white water of the pulp machine flowing into the high-concentration tower 3 cannot meet the standard, the weak black liquor input pipe 4 is connected to the sixth pipe through a ninth pipe 24, such as Figure 2 When the temperature of the white water from the pulp machine flowing into the high-concentration tower 3 cannot reach the preset temperature range, more high-temperature dilute black liquid is allowed to enter the second heat exchanger 7 to provide heat by closing the valve on the ninth pipeline 24, so that the temperature of the white water in the third pipeline reaches the standard.

[0068] Compared with the prior art that uses only one first heat exchanger 11 for heat exchange of the dilute black liquor, the heat exchange system of the pulping liquid of the present invention is provided with two heat exchangers, the second heat exchanger 7 and the first heat exchanger 11, for step-by-step heat exchange, that is, the dilute black liquor first enters the second heat exchanger 7 before entering the first heat exchanger 11, and the dilute black liquor exchanges heat with the white water of the pulp board machine in the second heat exchanger 7. The temperature of the white water entering the fourth pipeline 10 from the white water tower of the pulp board machine is about 68°C. The white water is first sent to the pulping workshop for heat exchange with the second heat exchanger 7. The temperature of the dilute black liquor in the second heat exchanger 7 is about 90°C. After the heat exchanger selection calculation, the temperature of the white water outlet of the second heat exchanger 7 can reach 80°C, and then enter the high-concentration tower 3 to dilute the pulp, so that the temperature of the pulp in the pulp board machine pulping tank 1 meets the required temperature of 72°C, and the low-pressure steam of the pulping tank 1 is then stopped or used less, saving steam.

[0069] Among them, the temperature requirement of the dilute black liquor washed by the first heat exchanger 11 entering the bottom of the cooking tower through the eighth pipeline 13 is about 70°C. Since the dilute black liquor is firstly heat-exchanged with white water by the second heat exchanger 7, the inlet temperature of the dilute black liquor entering the first heat exchanger 11 is greatly reduced, thereby achieving a decrease in the flow rate of factory water flowing into the first heat exchanger 11 for heat exchange, that is, compared with the prior art, the use of factory water is reduced, and the total amount of factory water for heat exchange is reduced. Since the total amount of hot water obtained is reduced, in addition to meeting the hot water demand of the hot water tank 20, the flow rate of the heated factory water (i.e., hot water) diverted to the cooling water tower is reduced, thereby reducing the evaporation loss of water. At the same time, due to the drop in factory water temperature in winter, the amount of hot water produced is insufficient, which reduces the heat intake of white water. In order to solve this problem, a second water inlet branch 22 for heat exchange of bleaching alkaline wastewater is added. Because the temperature of the alkaline wastewater used for bleaching is low, the temperature of the factory water after heat exchange is low, generally 40-50°C, and cannot be directly used for hot water. Therefore, the factory water adopts a two-stage heat exchanger 15 and a first heat exchanger 11. First, the cold water is converted into warm water through the alkaline wastewater of bleaching, and then the warm water is used to exchange heat with the dilute black liquor of the first heat exchanger 11 to become hot water. At the same time, the ratio of cold water and warm water in winter is adjusted by the valve on the first water inlet branch 21. This not only ensures the heat intake of the pulp machine white water, but also achieves a balanced hot water supply.

[0070] Since the solid content (fine fibers and lignin dissolved substances) in the dilute black liquor is about 10%, the pH is 12-13, and the residual alkali is 0-1g / l in terms of NaOH, the dilute black liquor needs to run in the tube side of the heat exchanger so that it can be cleaned regularly with high-pressure water.

[0071] The heat exchange system for pulping liquid of the present invention adds a white water heat exchanger, i.e., the second heat exchanger 7, in the cooking section. The 90°C dilute black liquor first enters the white water heat exchanger (the second heat exchanger 7) to exchange heat with white water. After the dilute black liquor exchanges heat with the white water, it is cooled by the first heat exchanger 11 to reach the temperature required for cooking and cold spraying. The flow direction of the white water of the pulp board machine is modified. The original white water flow is directly sent from the white water tank to the high-concentration tower for dilution. The white water is first sent from the white water tank to the pulping workshop for heat exchange with the dilute black liquor to increase the temperature of the white water. Then the white water enters the high-concentration tower 3 to dilute the pulp. Since the temperature of the diluted white water is increased, the temperature of the pulp entering the pulping tank 1 is increased accordingly, thereby closing or reducing the use of the low-pressure steam of the pulping tank 1. By recovering the heat from the bleaching alkaline wastewater, warm water can be provided in winter. The cooking section uses heated water instead of cold factory water in winter, ensuring the production of hot water in the pulping workshop, thereby achieving continuous heat exchange between the black liquor and the pulp board white water, and also reducing the impact of the high sewage temperature on microorganisms in the sewage treatment workshop.

[0072] The present invention also provides a heat exchange method for pulping liquid, which is applied to the heat exchange system for pulping liquid, and includes the following steps: using dilute black liquor to heat pulp machine white water, so that the pulp machine white water reaches a first preset temperature, the pulp machine white water reaching the first preset temperature is used to dilute and heat the slurry in the high-concentration tower 3, and after the pulp machine white water dilutes and heats the slurry in the high-concentration tower 3, the slurry enters the pulping tank 1. The dilute black liquor cooled by the pulp machine white water is further cooled by factory water to a second preset temperature, and the dilute black liquor cooled to the second preset temperature enters the cooking tower. The first preset temperature is higher than the required temperature of the pulping tank 1, so that a higher pulp temperature is obtained when diluting the low-temperature pulp from bleaching at the high-concentration tower 3. In a specific embodiment, the first preset temperature is 80°C, and the required temperature of the pulping tank 1 is 72°C. The second preset temperature is about 70°C.

[0073] In order to be applicable to factory water of different temperatures, the factory water is water at room temperature or water heated by alkaline wastewater used for bleaching, which is selected by those skilled in the art according to actual needs. When the temperature of the factory water is higher than the set value, the factory water uses water at room temperature, and when the temperature of the factory water is lower than the set value, the factory water uses heat exchange heating of bleaching alkaline wastewater.

[0074] In order to conveniently monitor whether the pulp machine white water is contaminated by the dilute black liquor, the difference in the conductivity of the pulp machine white water at the inlet and outlet of the heat exchanger is detected to determine whether the pulp machine white water is contaminated by the dilute black liquor. Specifically, since the second heat exchange chamber of the second heat exchanger 7 is used to transport the pulp machine white water, the conductivity of the inlet and outlet of the second heat exchange chamber of the second heat exchanger 7 is detected respectively, and whether the pulp machine white water is contaminated by the dilute black liquor is determined according to whether the difference between the two detected conductivities is within the set range. If the difference between the two conductivities exceeds the set range, it is determined that the pulp machine white water is contaminated by the dilute black liquor, otherwise, it is not contaminated.

[0075] In the description of this solution, it should be understood that the terms "upper", "lower", "vertical", "inside", "outside", etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this solution.

[0076] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of this solution, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0077] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0078] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A heat exchange system for pulping liquid, comprising a first heat exchanger for cooling weak black liquor flowing into a cooking tower, characterized in that: It also includes a second heat exchanger, which is used for heat exchange between pulp machine white water and dilute black liquor, and the first heat exchanger is used for heat exchange between dilute black liquor and factory water after heat exchange through the second heat exchanger; the pulp machine white water after heat exchange through the second heat exchanger is used for diluting and heating the slurry flowing into the pulp flushing tank.

2. The heat exchange system for pulping liquid according to claim 1, characterized in that: The invention also includes a plant water supply system, wherein the plant water supply system includes a first water inlet branch and a second water inlet branch arranged in parallel, wherein the first water inlet branch is used to provide the first heat exchanger with normal temperature plant water, and the second water inlet branch is used to provide the first heat exchanger with heated plant water; When the temperature of the plant water is higher than a set value, the first water inlet branch provides the first heat exchanger with plant water, and when the temperature of the plant water is lower than the set value, the second water inlet branch provides the first heat exchanger with plant water.

3. The heat exchange system for pulping liquid according to claim 2, characterized in that: The second water inlet branch is provided with a third heat exchanger, and the third heat exchanger utilizes bleaching alkaline wastewater to heat the factory water flowing through.

4. The heat exchange system for pulping liquid according to claim 2, characterized in that: The factory water heated by the first heat exchanger flows into the hot water tank, which provides hot water for the bleaching stage.

5. The heat exchange system for pulping liquid according to claim 1, characterized in that: The first heat exchanger includes a first heat exchange chamber and a second heat exchange chamber, and the second heat exchanger includes a third heat exchange chamber and a fourth heat exchange chamber; The inlet of the third heat exchange chamber is connected to the weak black liquor input pipe, and the outlet is connected to the inlet of the first heat exchange chamber, and the outlet of the first heat exchange chamber is connected to the cooking tower; the inlet of the fourth heat exchange chamber is connected to the pulp machine white water, and the outlet is connected to the high concentration tower; the inlet of the second heat exchange chamber is connected to the factory water, and the outlet is connected to the hot water tank.

6. The heat exchange system for pulping liquid according to claim 5, characterized in that: The outlet of the second heat exchange chamber is also communicated with a cooling water tower.

7. The heat exchange system for pulping liquid according to claim 3, characterized in that: The third heat exchanger includes a fifth heat exchange chamber and a sixth heat exchange chamber, the inlet of the fifth heat exchange chamber is connected to the ends of the first water inlet branch and the second water inlet branch, and the outlet is connected to the inlet of the second heat exchange chamber of the first heat exchanger; the inlet of the sixth heat exchange chamber is connected to the bleaching alkaline wastewater, and the outlet is connected to the sewage treatment device.

8. The heat exchange system for pulping liquid according to claim 1, characterized in that: A first conductivity meter is provided at the inlet end of the pulp machine white water of the second heat exchanger, and a second conductivity meter is provided at the outlet end of the pulp machine white water of the second heat exchanger.

9. A method for heat exchange of pulping liquid, characterized in that: The heat exchange system for pulping liquid according to any one of claims 1 to 8 comprises the following steps: Using dilute black liquor to heat the pulp machine white water so that the pulp machine white water reaches a first preset temperature, and the pulp machine white water reaching the first preset temperature is used to dilute and heat the slurry in the high-concentration tower; The dilute black liquor cooled by the pulp machine white water is further cooled by factory water to a second preset temperature, and the dilute black liquor cooled to the second preset temperature enters the cooking tower.

10. The heat exchange method for pulping liquid according to claim 9, characterized in that: The factory water is water at room temperature or water heated by bleaching alkaline wastewater; When the temperature of the factory water is higher than the set value, the factory water uses normal temperature water. When the temperature of the factory water is lower than the set value, the factory water uses bleaching alkaline wastewater for heat exchange heating.

11. The heat exchange method for pulping liquid according to claim 9, characterized in that: By detecting the difference in conductivity between the inlet and outlet of the pulp machine white water of the heat exchanger, it is determined whether the pulp machine white water is contaminated by dilute black liquor.

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