Replacement type continuous cooking method and device

Abstract

The invention belongs to the pulping and papermaking industry, and particularly relates to a replacement type continuous cooking method and device, which is characterized in that when a fiber raw material is cooked and pulped, firstly, raw material fibers are subjected to single-stage or multi-stage preimpregnation by using cooked concentrated black liquor, so that residual liquor and heat in the black liquor are fully utilized; and then replacing the black liquor carried by the pre-impregnated raw material fiber by using a cooking liquid medicine with relatively high medicine concentration, rapidly cooking the replaced raw material fiber into pulp under relatively high medicine concentration, pressure and temperature, and sending the pre-impregnated black liquor to a black liquor treatment process. According to the method and the device, residual liquid medicine and heat in the black liquor after cooking can be fully utilized, energy consumption and medicine consumption generated in the fiber cooking stage can be greatly reduced, the concentration of the black liquor subjected to black liquor removal treatment can be improved, the method and the device particularly accord with pulping characteristics of non-wood fibers, and the fiber cooking cost, especially the pulping cost of the non-wood fibers, can be greatly reduced.

Description

Technical Field

[0001] The present invention relates to the technical fields of pulping, papermaking, biosynthesis, etc. In particular, it relates to a method and device for producing high-quality, low-energy-consumption, and low-chemical fiber pulp by using fiber raw materials and changing the traditional cooking system, specifically a displacement continuous cooking method and device. Background Art

[0002] Fiber raw materials for pulping can be divided into two categories: wood fiber (including bamboo fiber) and non-wood fiber. For wood fiber (including bamboo fiber), due to its good water filtration, there are relatively mature and reliable cooking methods, such as the modified continuous cooking process (MCC) in Camille vertical continuous cooking, extended modified continuous cooking technology (EMCC), low solid cooking (LSC) and rapid displacement cooking (RDH), super cooking and displacement cooking (DDS) in vertical pot intermittent cooking. For non-wood fiber, due to the small average fiber length and high content of impurities in non-wood fiber raw materials, the filter plates of super displacement intermittent cooking devices and isothermal tower cooking devices are very easy to clog in the cooking device, and cannot be used for non-wood fiber, such as wheat straw, reed, bagasse, kenaf, dragon beard grass, cotton stalks and other raw materials.

[0003] There are two types of pulping and cooking methods for non-wood fiber raw materials: traditional intermittent cooking such as steaming ball and steamer, and continuous cooking in tubular continuous steaming system. Traditional steaming ball and steamer are rarely used due to energy consumption and environmental protection issues. The tubular continuous cooking system can use steam phase high-temperature cooking, which has high production efficiency, mature technology, convenient control, compact equipment structure, and short cooking time. It is currently a non-wood raw material pulping and cooking technology commonly used at home and abroad. The tubular continuous cooking system can also be used for pulping and cooking of wood fiber.

[0004] Compared with RDH and DDS, the tubular continuous steaming system has a high pulp output per unit volume, low investment, and wide adaptability to raw materials. However, this technology also has its shortcomings: compared with displacement cooking, the steam consumption is relatively high and the utilization rate of chemicals is relatively low; moreover, due to the low liquid ratio and intense cooking reaction during the cooking process, the cooked straw pulp has low strength and poor water filterability.

[0005] Some scholars and enterprises have used RDH intermittent cooking technology and super cooking methods in intermittent displacement cooking systems to test and produce non-wood fibers such as rice straw and wheat straw fibers using large liquid ratio cooking processes. This process and equipment can achieve the layered removal of lignin under mild reaction conditions, and can produce grass pulp with light color, good water filtration, high yield and good strength. However, this series of processes is a wood pulp process. Due to the poor water filtration and fluidity of non-wood fibers, when using this process to cook non-wood fibers, the filter screen is easily blocked and the fibers are not cooked evenly.

[0006] ZL201010227189.X "Non-wood fiber continuous cooking method and device" provides a cooking method that combines intermittent displacement cooking with horizontal tube continuous cooking. Its characteristics are: a suction filter plate is set on the cooking tube of the traditional horizontal tube continuous cooking device, so that the cooking liquid can be extracted through the filter plate and then heated by an external heat exchanger before being re-injected into the cooking device to achieve the purpose of displacement heating cooking. This energy-saving non-wood fiber continuous cooking device can reduce the steam consumption, energy consumption, and chemical consumption per ton of pulp, and improve the quality of the pulp. However, this patent invention heats the black liquor through an external tank and heater for recycling, which is similar to the intermittent displacement cooking process of RDS, DDS, etc., and the equipment matching and control are complicated.

[0007] Experimental and actual results show that although intermittent displacement cooking has been widely used on wood pulp and bamboo pulp fibers, it can improve the quality of pulp and reduce the hardness of pulp when used for non-wood fiber cooking. The black liquor can be reused repeatedly during the steaming process, and it can save energy, reduce pollution and is beneficial to the environment. However, due to the small size of grass raw materials, poor water filterability, and premature softening during the cooking temperature increase process, the stacking density increases, and the filtration resistance increases, making it difficult to displace. The cooking liquid will short-circuit at low density locations, resulting in a series of problems such as uneven raw material temperature and poor cooking uniformity. Therefore, large-scale continuous production is still not possible at present.

[0008] At the same time, the high investment costs, complex automation control and subsequent high maintenance costs of displacement cooking technologies such as Camille vertical continuous cooking and DDS cooking make it difficult for small and medium-sized pulping enterprises to bear them. They have no choice but to choose traditional intermittent cooking methods such as steaming balls and steamers with high energy consumption and open exhaust gas emissions, or tubular continuous cooking methods, which restricts the development of enterprises. Summary of the invention

[0009] In order to overcome the defects of the above pulping methods, the present invention proposes a countercurrent displacement continuous cooking method and device, which retains the advantages of the tubular continuous cooking system while fully absorbing the pulping characteristics of the cooking systems such as RDS and DDS, and can achieve the removal of lignin in layers under mild reaction conditions. That is, a pre-impregnation device is set in the tubular continuous cooking system, and the fiber raw material is firstly impregnated and pre-extracted with the concentrated black liquor after cooking, and then steam-phase cooking is carried out, so that the black liquor is recycled and reused, and the lignin can be removed in layers under mild reaction conditions. While producing continuously with high efficiency, it can greatly reduce the consumption of steam and chemicals, reduce the pressure of black liquor treatment on environmental protection, improve the quality of pulp, and produce pulp with light color, good filterability, high yield and good strength. At the same time, because the cooking device is continuous, compared with intermittent cooking, under the same scale, the required pumps and tanks, pumps, heat exchangers and other equipment can be greatly saved.

[0010] The countercurrent displacement continuous cooking method and device of the present invention are realized by the following technical solutions:

[0011] The structure and cooking process of the conventional tubular continuous steaming device are completely redesigned, that is, one or more prepreg tubes are installed in series between the feeder and the cooking tube in the conventional tubular continuous steaming device according to the needs of different fiber raw materials and different cooking processes, and a conveying chain plate or spiral is configured in each prepreg tube, so that the cooking process of the continuous cooking system is divided into two parts: the prepreg section and the cooking section. The stage in which the raw material fiber enters the continuous steaming system and begins to contact with the cooking liquid or black liquor, absorb the liquid, and the fiber extract is dissolved is the prepreg section of the cooking process, and the stage in which the raw material fiber is cooked into pulp at high temperature and high liquid concentration is the cooking section of the cooking process. When the raw fiber is cooked, the raw fiber is first pre-impregnated with the concentrated black liquor after cooking to make full use of the residual liquid and heat in the black liquor. Then, the black liquor carried by the pre-impregnated raw fiber is replaced with the cooking liquid with a higher concentration at the rear of the pre-impregnation section. The raw fiber after the cooking liquid is replaced enters the cooking section of the cooking process. The raw fiber in the cooking section is quickly cooked into pulp at a higher temperature and liquid concentration. Two-stage or multi-stage cooking is performed according to the needs of the cooking process.

[0012] During two-stage cooking, the concentrated black liquor produced in the cooking section is sent to the continuous steaming equipment in the pre-impregnation section, and the heat and residual effective liquid medicine in the black liquor are used to pre-impregnate the fibers entering the continuous steaming system. The black liquor after pre-impregnation of the fiber raw material is filtered by the filter screen attached to the continuous steaming equipment in the pre-impregnation section and then discharged from the continuous steaming system and sent to the black liquor treatment or recycling process; cooking liquor with a higher drug concentration is added to the rear part of the pre-impregnation section to replace the black liquor carried by the raw material fibers after pre-impregnation, and the raw material fibers carrying a higher drug concentration enter the cooking section and are cooked into pulp in the cooking section. The concentrated black liquor produced after cooking into pulp is sent to the continuous steaming equipment in the pre-impregnation section to start the next black liquor cycle.

[0013] In case of multi-stage cooking, the prepreg section is composed of two or more prepregs. First, the black liquor produced by cooking in the cooking section is sent to the prepreg equipment of the last stage of the prepreg section, and the heat and residual effective liquid medicine in the black liquor are used to prepreg the fibers in the last stage of the prepreg equipment. After being filtered through the filter screen of the prepreg equipment, the black liquor is sent to the fibers in the previous stage of the prepreg equipment for prepreg. By analogy, the black liquor after multiple prepregs is finally discharged from the prepreg equipment of the prepreg section and sent to the black liquor treatment or recycling process; cooking liquid with a higher drug concentration is added to the raw fiber at the rear of the prepreg section to replace the black liquor carried by the raw fiber. The raw fiber carrying a higher drug concentration enters the cooking section and is cooked into pulp in the cooking section. The concentrated black liquor produced after cooking into pulp is sent to the continuous steaming equipment of the last stage of the prepreg section of the prepreg section to start the next black liquor cycle.

[0014] The above two-stage or multi-stage steaming can be connected in series with a pre-extraction device before pre-soaking. Hot water or a certain concentration of liquid medicine is introduced into the pre-extraction device to pre-extract the raw material fibers entering the continuous steaming device, and the extract is sent to the extract treatment process.

[0015] The cooking method adopts a tubular continuous steaming device, which is mainly composed of a feeding device, two or more interconnected tubular steamers installed in series, and a discharger; according to the needs of the cooking raw materials and the process, the steamer can be equipped with a liquid inlet, a steam inlet, a liquid discharge port, a temperature and pressure instrument interface.

[0016] The cooking method adopts a tubular continuous steaming device, which is mainly composed of a feeding device, two or more tubular steamers connected to each other and installed in series, an intermediate pipe, and a discharger. The tubular steamer is equipped with a conveying chain plate or spiral, and the steamer with a continuous discharge port is equipped with a filter plate with mesh or a grate at the position of the continuous discharge port. The black liquor or cooking liquor in adjacent steamers is directly connected or indirectly connected through pipelines and delivery pumps.

[0017] During cooking, the pre-impregnated fiber raw materials are firstly pre-impregnated in a single or multiple stages using the residual alkali and heat in the concentrated black liquor, and then the black liquor adsorbed on the raw fiber is replaced by the cooking liquid; the raw fiber after the cooking liquid is replaced enters the digester, and is quickly cooked into pulp at a higher temperature and pressure. The pulped fiber is discharged through the intermediate pipe and the discharger or directly through the discharger. After the pre-impregnation of the raw fiber, the concentrated black liquor with a high solid content is filtered through the digester filter plate or grate, and then discharged under the pressure in the system and sent to evaporation or other black liquor treatment processes.

[0018] The basic structure of the digester is basically the same as the horizontal tube or inclined tube of the conventional tubular continuous steaming system. Both are shell and tube pressure vessels with stirring and conveying functions, and a conveying screw or conveying chain plate is installed in the pressure shell; the difference from the horizontal tube or inclined tube of the conventional tubular continuous steaming system is that some or all of the digesters of this technical solution are equipped with continuous drainage ports, and the drainage ports of the digesters with continuous drainage ports are equipped with filter plates or filter grates, and the periphery of the grates or filter holes is connected to the drainage pipe. According to the type of fiber and the needs of the cooking process, the prepreg section and cooking section digesters in the continuous cooking device can all adopt horizontal tube or inclined tube digesters, or a combination of some horizontal tubes and some inclined tubes; the number of digesters can be configured in series from two to more according to the needs of the specific process.

[0019] Taking advantage of the fact that non-wood fiber absorbs liquid medicine quickly, most of the lignin and extracts can be removed at a temperature of 80-100°C and a low liquid medicine concentration in the early stage of cooking, and a relatively high concentration of medicine is required in the later stage of cooking to prevent the removed lignin from being re-adsorbed; combining the pulping advantages of wood chip (including bamboo chip) super displacement intermittent cooking device and isothermal tower cooking device; adding concentrated black liquor after cooking in the pre-impregnation stage to pre-impregnate and pre-extract the raw material fiber. After the concentrated black liquor after pre-impregnation and extraction of the raw material fiber is filtered through a filter plate or grate with mesh, it is sent to the black liquor treatment or reuse process.

[0020] During pre-preg, the fiber raw material from the feeder is transported in the pre-preg tube while removing lignin and other extracts. The pre-preg fiber raw material is first pre-extracted using the residual alkali and heat in the concentrated black liquor, and then the black liquor adsorbed on the raw material fiber is replaced by the cooking liquid after dissolving part of the extract. In this process, the concentrated black liquor in the front section of the pre-preg and the cooking liquid in the back section are gradually mixed, the concentration of the liquid in the mixed liquid gradually increases, and the content of lignin and other solubles in the fiber gradually decreases. After removing most of the lignin and extracts, the cooking liquid replaces the black liquor adsorbed by the fiber in the back section of the pre-preg. Then, the raw material fiber adsorbing the higher concentration cooking liquid enters the horizontal tube for the next step of the vapor phase cooking process. After the vapor phase cooking in the horizontal tube, the raw material fiber is discharged through the intermediate tube and the discharger.

[0021] After pre-impregnation and extraction of raw material fibers, concentrated black liquor with a high extract content is filtered through a filter plate or grate with meshes and then sent to evaporation or other black liquor treatment processes under the pressure in the system. The conveying direction of the raw materials in the pre-impregnation section is opposite to the flow direction of the black liquor, so as to consume the liquid medicine in the black liquor as much as possible and increase the concentration of the extract discharged from the black liquor.

[0022] The filter plate or grate on the prepreg tube needs special design, and the filter hole area is calculated and determined according to the pulp type, process and cooking liquid ratio. The interval between the filter plate or grate and the chain plate or spiral outer diameter in the prepreg tube is small, and the filter plate or grate is self-cleaned by the moving chain plate or rotating spiral. If necessary, a backwash pipe can be arranged for forced backwashing and cleaning. The cycle and time of forced cleaning of each filter plate can be set in the automatic control system.

[0023] The present invention uses concentrated black liquor after cooking to pre-impregnate the raw materials in the pre-impregnation tube in the early stage of the cooking process, and uses cooking liquor with a higher drug concentration to remove residual lignin in the later stage of the cooking process. The liquid ratio during pre-impregnation is relatively large, which is conducive to the dissolution of extracts in the fiber, and can recover and consume a large amount of residual drugs and heat in the black liquor, effectively reducing the drug consumption and steam consumption in the entire cooking process; at the same time, the extracted black liquor concentration is relatively high, which is conducive to reducing the cost of black liquor treatment. After uniform and gentle impregnation and low-temperature pre-cooking of black liquor and mixed liquor, the quality of the fiber after cooking is better and more uniform. The continuous cooking device can be applied to pulping and cooking of various fiber raw materials, especially non-wood fiber, by selecting different feeding devices.

[0024] The countercurrent displacement continuous cooking method and device of the present invention have main and auxiliary equipment of the dry and wet material preparation and metering systems that are completely the same as those of the traditional tubular continuous cooking device. The automatic control system is expanded on the DCS control system of the tubular continuous cooking device. The liquid ratio in the early pre-impregnation stage of the cooking process is equivalent to the pulping method of the super-displacement intermittent cooking device and the isothermal tower cooking device, which is beneficial to the dissolution of lignin and other extracts in the raw material fiber. The later cooking stage of the cooking process can adopt a liquid ratio of about 1:3.5 similar to that of the tubular continuous cooking device. Since most of the lignin and extracts have been removed in the pre-impregnation stage, the consumption of steam and cooking liquid can be greatly reduced in the cooking stage.

[0025] The present invention combines displacement cooking with tubular continuous cooking technology to form a new industrial method for continuous cooking of plant fiber raw materials. The process device has a compact structure, a reasonable layout, and a high degree of automation. It combines the technical advantages of various cooking processes, and can not only improve the uniformity of cooking and the quality of pulp, improve the hardness and bleachability of the pulp, but also reuse the chemical components and cooking heat in the black liquor, reduce the amount of alkali and steam consumption, and extract the black liquor with a high concentration, which is beneficial to the production and operation of the liquid medicine recovery system. The cooking energy consumption is low, the investment is low, and it has good energy-saving and environmental protection effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0027] Figure 1 It is a structural schematic diagram of a specific embodiment of the present invention.

[0028] Figure 2 It is a structural schematic diagram of specific embodiment 2 of the present invention.

[0029] Figure 3 It is a structural schematic diagram of specific embodiment 3 of the present invention.

[0030] Figure 4 It is a structural schematic diagram of specific embodiment 4 of the present invention.

[0031] Figure 5 It is a structural schematic diagram of specific embodiment 5 of the present invention.

[0032] Figure 6 It is a structural schematic diagram of specific embodiment 6 of the present invention.

[0033] Figure 7 It is a structural schematic diagram of specific embodiment 7 of the present invention.

[0034] Figure 8 It is a structural schematic diagram of specific embodiment 8 of the present invention.

[0035] In the figure:

[0036] 1. T-tube, 2. screw feeder, 3. pre-preg tube, 4. pre-preg tube, 5. pre-preg tube, 6. cooking tube, 7. intermediate tube, 8. circulation pump, 9. filter screen, 10. cooking liquid pump, 11. cooking liquid tank, 12. discharger, 13. weak black liquor pump, 14. weak black liquor tank, 15. circulation pump, 16. circulation pump;

[0037] 21. Rotary feeder;

[0038] 31. Intermediate pipe, 32. Concentrated black liquor tank, 33. Concentrated black liquor pump;

[0039] 41. Spiral T-tube, 42. Prepreg tube, 43. Circulation pump, 44. Circulation pump, 45. Prepreg tube, 46. Prepreg tube;

[0040] 61. oblique pipe, 62. oblique pipe, 63. oblique pipe, 64. circulating pump; DETAILED DESCRIPTION

[0041] like Figures 1 to 8 The specific embodiments of the present invention shown are some typical applications of the present invention.

[0042] like Figure 1In the specific embodiment 1 shown, the prepreg section of the tubular continuous cooking device is composed of three inclined prepreg tubes installed in series, and a conveying and stirring screw is installed in the prepreg tube. The raw material passes through the screw feeder 2 and enters the three prepreg tubes via the T-tube 1 for three-stage countercurrent displacement prepreg, and then enters the cooking tube 6 of the cooking section for cooking into slurry, and then the slurry is discharged through the intermediate tube 7 and the discharger 12. The three prepreg tubes are equipped with a filter screen. The intermediate tube 7 is equipped with a filter screen 9. The weak black liquid from the weak black liquid tank 14 enters the intermediate tube 7 to replace the high-temperature concentrated black liquid carried by the slurry in the intermediate tube. The replaced concentrated black liquid is discharged from the intermediate tube 7 through the filter screen 9 and sent to the prepreg tube 5 through the circulation pump 8 to prepreg and extract the raw material fiber in the prepreg tube 5. The cooking liquid from the cooking liquid tank 11 replaces the black liquid in the fiber at the rear section of the prepreg tube 5. The raw material fiber carrying the cooking liquid enters the cooking tube 6 under the push of the spiral, and the cooking tube 6 is steamed by passing high-temperature steam. The concentrated black liquor after pre-impregnation and extraction of the fibers in the pre-impregnation tube 5 is mixed with a portion of the cooking liquid, filtered through a filter screen in the pre-impregnation tube 5, and then pumped into the pre-impregnation tube 4 by a circulation pump 15.

[0043] In the prepreg tube 4 , the concentrated black liquor from the prepreg tube 5 prepregs and extracts the fiber raw material. After the prepreg and extraction, the concentrated black liquor is filtered through the filter screen in the prepreg tube 4 and then pumped into the prepreg tube 3 by the circulation pump 16 .

[0044] In the prepreg tube 3, the concentrated black liquor from the prepreg tube 4 pre-impregnates and extracts the fiber raw materials from the T-tube 1 and the screw feeder 2. The concentrated black liquor after pre-impregnation and extraction is filtered through the filter net in the prepreg tube 3 and then sent to the black liquor treatment process under the pressure in the system.

[0045] The concentrated black liquor from the intermediate pipe 7 is discharged from the prepreg pipe 3 after the above-mentioned three-stage countercurrent replacement, which can maximize the use of the residual heat in the black liquor after cooking and the residual effective cooking liquid, greatly reduce the steam and cooking liquid consumption in the cooking process, and increase the concentration of black liquor sent to the black liquor treatment process.

[0046] like Figure 2 The specific embodiment 2 shown has the same system configuration as the pre-impregnation and cooking parts of the specific embodiment 1, and is composed of three-stage pre-impregnation and a cooking tube. The difference is that: the specific embodiment 1 adopts a spiral feeder 2 for feeding, which is suitable for the cooking of non-wood fibers; the specific embodiment 2 adopts a rotary feeder 21 for feeding, which is suitable for the continuous cooking of wood chips (including bamboo chips), and the countercurrent replacement process of the concentrated black liquor after cooking into pulp is consistent with the specific embodiment 1.

[0047] like Figure 3The specific embodiment 3 shown is configured the same as the feeding and pre-impregnation cooking parts of the specific embodiment 1, except that: the intermediate pipe 7 after cooking in the specific embodiment 1 adopts a filter screen structure, and the concentrated black liquor carried in the slurry after cooking is filtered through the filter screen of the intermediate pipe 7, and then sent to the pre-impregnation section by the circulating pump 5, and after three-stage countercurrent displacement pre-impregnation, it is discharged from the continuous steaming device and sent to the black liquor treatment process; the intermediate pipe 31 of the specific embodiment 2 does not have a filter screen, and after the slurry after cooking is discharged and sprayed by the discharger, the concentrated black liquor is extracted by special equipment and enters the concentrated black liquor tank 32, and then sent to the pre-impregnation section through the circulating pump 33, and after three-stage countercurrent displacement pre-impregnation, it is discharged from the continuous steaming device and sent to the black liquor treatment process.

[0048] like Figure 4 In the fourth embodiment shown, a screw feeder and a T-tube 41 are used for feeding, and an intermediate tube 7 with a filter screen is used for filtering and extracting black liquor to be sent to the prepreg section. The prepreg section is composed of three prepreg tubes connected in series. Different from the first embodiment, the T-tube 41 of the fourth embodiment is equipped with a press screw to press the raw fiber from the screw feeder down into the prepreg tube. The liquids in the three prepreg tubes installed in series are interconnected, while the liquid levels in the three prepreg tubes of the cooking system shown in the first to third embodiments are independent of each other. Figure 4 In this way, the hot concentrated black liquor from the intermediate tube 7 is sent to the prepreg tube 46 by the circulation pump 8, and the raw material fiber in the prepreg tube 46 is prepreg and extracted. The cooking liquid from the cooking liquid tank 11 replaces the black liquor in the fiber at the rear section of the prepreg tube 46, and the raw material fiber carrying the cooking liquid enters the cooking tube 6 under the push of the spiral, and the cooking tube 6 is steamed by passing high-temperature steam. After the concentrated black liquor after prepreg and extraction of the fiber in the prepreg tube 46 is mixed with part of the cooking liquid, it is filtered through the filter net in the prepreg tube 46 and then pumped into the prepreg tube 45 by the circulation pump 44. In the prepreg tube 45, the concentrated black liquor from the prepreg tube 46 prepregs and extracts the fiber raw material, and the concentrated black liquor after prepreg and extraction is filtered through the filter net in the prepreg tube 45 and then pumped into the prepreg tube 42 by the circulation pump 43. In the prepreg tube 42, the concentrated black liquor from the prepreg tube 45 pre-impregnates and extracts the fiber raw materials from the T-tube 41 and the screw feeder 2. The concentrated black liquor after pre-impregnation and extraction is filtered through the filter net in the prepreg tube 42 and then sent to the black liquor treatment process under the pressure in the system.

[0049] like Figure 5The specific embodiment 5 shown has the same system configuration as the pre-impregnation and cooking parts of the specific embodiment 4, both of which are composed of three-stage pre-impregnation with liquids interconnected and a cooking tube. The difference is that: the intermediate tube 7 after cooking in the specific embodiment 4 adopts a filter screen structure, and the concentrated black liquor carried in the slurry after cooking is filtered by the filter screen of the intermediate tube 7, and then sent to the pre-impregnation section by a circulation pump, and after three-stage countercurrent displacement pre-impregnation, it is discharged from the continuous steaming device and sent to the black liquor treatment process; the intermediate tube 31 of the specific embodiment 5 does not have a filter screen. After the slurry after cooking is discharged and sprayed by the discharger, the concentrated black liquor is extracted by a special equipment and enters the concentrated black liquor tank 32, and then sent to the pre-impregnation section through the circulation pump 33, and after three-stage countercurrent displacement pre-impregnation, it is discharged from the continuous steaming device and sent to the black liquor treatment process.

[0050] like Figure 6 The specific embodiment 6 is basically similar to the specific embodiment 1, and is composed of three-stage prepreg and a cooking tube. The prepreg liquids in the three prepreg tubes are not interconnected. The difference is that: the specific embodiment 1 uses an inclined horizontal tube as the prepreg tube; the specific embodiment 6 uses inclined tubes 61, 62, and 63 with filters as three-stage prepreg tubes, and a scraper conveying device is installed in the inclined tubes. The countercurrent replacement process of the concentrated black liquor is consistent with the specific embodiment 1.

[0051] like Figure 7 The specific embodiment 7 shown has the same system configuration as the prepreg and cooking parts of the specific embodiment 6, both of which are composed of three-stage prepreg inclined tubes and a cooking horizontal tube. The difference is that: the specific embodiment 6 uses a spiral feeder 2 for feeding, which is suitable for the cooking of non-wood fibers; the specific embodiment 7 uses a rotary feeder 21 for feeding, which is suitable for the continuous cooking of wood chips (including bamboo chips), and the countercurrent replacement process of the concentrated black liquor is consistent with that of the specific embodiment 6.

[0052] like Figure 8 The specific embodiment eight shown is configured the same as the feeding and pre-impregnation and cooking parts of the specific embodiment six, except that: the intermediate pipe 7 after cooking in the specific embodiment six adopts a filter screen structure, and the concentrated black liquor carried in the slurry after cooking is filtered through the filter screen of the intermediate pipe 7, and then sent to the pre-impregnation section by the circulation pump 64, and after three-stage countercurrent displacement pre-impregnation, it is discharged from the continuous steaming device and sent to the black liquor treatment process; the intermediate pipe 31 of the specific embodiment eight does not have a filter screen, and after the slurry after cooking is discharged and sprayed by the discharger, the concentrated black liquor is extracted by special equipment and enters the concentrated black liquor tank 32, and then sent to the pre-impregnation section through the circulation pump 33, and after three-stage countercurrent displacement pre-impregnation, it is discharged from the continuous steaming device and sent to the black liquor treatment process.

[0053] Obviously, the above embodiments are only examples for clear explanation, and are not intended to limit the implementation methods. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from them are still within the protection scope of the invention.

Claims

1. A displacement continuous cooking method and device, characterized in that: (1) A new design is made for the structure and cooking process of the conventional tubular continuous steaming device, that is, one or more prepreg tubes are installed in series between the feeder and the cooking tube in the conventional tubular continuous steaming device according to the needs of different fiber raw materials and different cooking processes, and a conveying chain plate or spiral is configured in each prepreg tube, so that the cooking process of the continuous cooking system is divided into two parts: the prepreg section and the cooking section. The stage in which the raw material fiber enters the continuous steaming system and contacts with the cooking liquid or black liquor, absorbs the liquid, and the fiber extract is dissolved is the prepreg section of the cooking process, and the stage in which the raw material fiber is cooked into pulp at high temperature and high liquid concentration is the cooking section of the cooking process. When the raw fiber is cooked, the concentrated black liquor after cooking is first used to pre-impregnate the raw fiber to make full use of the residual liquid and heat in the black liquor. Then, at the rear of the pre-impregnation section, the black liquor carried by the pre-impregnated raw fiber is replaced with cooking liquid with a higher concentration. The raw fiber after the cooking liquid is replaced enters the cooking section of the cooking process. The raw fiber in the cooking section is quickly cooked into pulp at a higher temperature and liquid concentration. According to the needs of the cooking process, two-stage or multi-stage cooking is carried out. (2) During two-stage cooking, the concentrated black liquor produced in the cooking section is sent to the continuous steaming equipment in the pre-impregnation section, and the heat and residual effective liquid medicine in the black liquor are used to pre-impregnate the fibers entering the continuous steaming system. The black liquor after pre-impregnation of the fiber raw material is filtered by the filter screen attached to the continuous steaming equipment in the pre-impregnation section and then discharged from the continuous steaming system and sent to the black liquor treatment or recycling process; cooking liquor with a higher drug concentration is added to the rear part of the pre-impregnation section to replace the black liquor carried by the raw material fiber after pre-impregnation. The raw material fiber carrying a higher drug concentration enters the cooking section and is cooked into pulp in the cooking section. The concentrated black liquor produced after cooking into pulp is sent to the continuous steaming equipment in the pre-impregnation section to start the next black liquor cycle. (3) In case of multi-stage steaming, the pre-impregnation section is composed of two or more pre-impregnation stages. First, the black liquor produced by steaming in the steaming section is sent to the pre-impregnation equipment at the last stage of the pre-impregnation section. The heat and residual effective liquid medicine in the black liquor are used to pre-impregnate the fibers in the last stage of the pre-impregnation equipment. After being filtered through the filter screen of the continuous steaming equipment, the fibers are then sent to the pre-impregnation equipment at the previous stage of the pre-impregnation section for pre-impregnation. By analogy, the black liquor after multiple pre-impregnations is finally discharged from the pre-impregnation equipment and sent to the black liquor treatment or recycling process. At the rear of the prepreg section, cooking liquid with higher drug concentration is added to the raw fiber to displace the black liquor carried by the raw fiber. The raw fiber carrying higher drug concentration is cooked into pulp in the cooking section. The concentrated black liquor produced after cooking into pulp is sent to the last stage prepreg equipment of the prepreg section to start the next black liquor cycle. (4) For the above two-stage or multi-stage steaming, a pre-extraction device can be installed in series before pre-soaking. Hot water or a certain concentration of liquid medicine is introduced into the pre-extraction device to pre-extract the raw material fibers entering the continuous steaming device, and the extract is sent to the extract treatment process. (5) The cooking method described in (1) to (4) above adopts a tubular continuous steaming device, which is mainly composed of a feeding device, two or more interconnected tubular steamers installed in series, and a discharger; according to the needs of the cooking raw materials and process, the steamer can be equipped with a liquid inlet, a steam inlet, a liquid discharge port, temperature and pressure instrument interfaces. (6) The cooking method described in (1) to (4) above adopts a tubular continuous steaming device, which is mainly composed of a feeding device, two or more tubular steamers connected to each other and installed in series, an intermediate pipe, and a discharger. A conveying chain plate or spiral is arranged in the tubular steamer, and a steamer with a continuous discharge port is provided with a filter plate or grate with a mesh at the position of the continuous discharge port. (7) The black liquor or cooking liquor in adjacent digesters are directly connected or indirectly connected through pipelines and transfer pumps. (8) During cooking, the pre-impregnated fiber raw materials are firstly pre-impregnated in a single or multiple stages using the residual alkali and heat in the concentrated black liquor, and then the black liquor adsorbed on the raw fiber is displaced by the cooking liquid; the raw fiber after the cooking liquid is displaced enters the digester and is quickly cooked into pulp at a relatively high pressure and temperature. The pulped fiber is discharged through an intermediate pipe and a discharger or directly through a discharger. (9) After pre-impregnation of the raw material fibers, the concentrated black liquor with a high solid content is filtered through the digester filter plate or grate, discharged under the pressure in the system, and sent to evaporation or other black liquor treatment processes.

2. The displacement continuous cooking method and device according to claim 1, characterized in that: The basic structure of the pre-impregnation section and cooking section digesters is basically the same as the horizontal tube or inclined tube of the conventional tubular continuous steaming system. Both are shell and tube pressure vessels with stirring and conveying functions, and a conveying screw or conveying chain plate is installed in the pressure shell; the difference from the horizontal tube or inclined tube of the conventional tubular continuous steaming system is that some or all of the digesters of the present technical solution are provided with continuous drainage ports, and the drainage ports of the digesters with continuous drainage ports are provided with filter plates or filter grates, and the periphery of the grates or filter holes are connected to the drainage pipe.

3. The displacement continuous cooking method and device according to claim 1, characterized in that: According to the fiber type and the requirements of the cooking process, the prepreg section and cooking section cookers in the continuous cooking device can all adopt horizontal tube or inclined tube cookers, or a combination of some horizontal tubes and some inclined tubes; the number of cookers can be configured in series from two to more according to the requirements of the specific process.

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