A RDH cooking pulping process and system

Abstract

The present invention relates to an RDH cooking pulping process and a system thereof. An RDH cooking pulping process comprises the following steps: (1) adding SO2 chemicals and black liquor 1 to fiber raw materials, keeping the raw materials at 100-110°C for 25-35 minutes, and then using black liquor 2 to replace the black liquor 1 after the insulation; (2) keeping the raw materials at 140-150°C for 90-130 minutes, and then using black liquor 3 to replace the black liquor 2 after the insulation; the black liquor 3 is the black liquor 1 after the insulation replaced by the black liquor 2; (3) using dilute alkali solution to replace the warm black liquor 3, keeping the raw materials at 105-115°C until the pulp kappa number reaches 17-20; (4) using dilute black liquor to replace the dilute alkali solution after the insulation to obtain a coarse pulp. The RDH cooking pulping process and the system thereof of the present invention use SO2 as the cooking chemical and ethanol as the organic solvent medium, which significantly reduces environmental pressure while reducing costs and improving extraction efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of fiber raw material processing, and in particular relates to an RDH cooking pulping process and a system thereof. Background Art

[0002] Traditional pulping and cooking processes include alkaline pulping, neutral sulfite pulping, acid sulfite pulping, and kraft pulping. Large and medium-sized alkaline and kraft pulping companies are equipped with alkali recovery facilities to recover some of the heat generated by chemicals and lignin, thereby reducing pulping costs and environmental pressures. Although the lignin sulfonates produced by neutral and acid sulfite pulping are excellent organic fertilizers, large-scale production is rare due to environmental pressures and high costs.

[0003] Considering the high cost and high environmental pressure of the traditional pulping process, the present invention proposes a new pulping process and system thereof, which uses SO2 as a cooking agent and ethanol as an organic solvent medium. Summary of the Invention

[0004] The purpose of the present invention is to provide an RDH cooking pulping process, which uses SO2 as a cooking agent and ethanol as an organic solvent medium, thereby significantly reducing environmental pressure while reducing costs and improving extraction efficiency.

[0005] In order to achieve the above objectives, the technical solutions adopted are:

[0006] An RDH cooking pulping process is a liquid phase multi-stage displacement cooking process, comprising the following steps:

[0007] (1) adding SO2 chemicals and black liquor 1 to the fiber raw material, keeping it warm at 100-110°C for 25-35 minutes, and then replacing the black liquor 1 after the insulation with black liquor 2;

[0008] The black liquor 2 contains SO2 and ethanol, with an alcohol content of 45-55° and a mass concentration of SO2 of 5-6%;

[0009] (2) keeping the temperature at 140-150° C. for 90-130 minutes, and then replacing the heat-maintained black liquor 2 with black liquor 3; the heat-maintained black liquor 3 is the heat-maintained black liquor 1 replaced by the black liquor 2;

[0010] (3) replacing the warm black liquor 3 with a dilute alkali solution and keeping the temperature at 105-115° C. until the slurry has a kappa number of 17-20;

[0011] (4) using dilute black liquor to replace the dilute alkali liquor after heat preservation to obtain a coarse pulp.

[0012] Furthermore, the temperature of the black liquor 1 and black liquor 3 is 120-130°C.

[0013] The temperature of the black liquor 2 is 140-150°C;

[0014] The temperature of the dilute black liquor is 70-80°C;

[0015] The dilute alkali solution is a 0.5-1.5wt% sodium hydroxide solution with a temperature of 105-115°C.

[0016] Furthermore, in the step (1), the mass ratio of cellulose, SO2, and black liquor 1 is 100:4-6:600-800.

[0017] Furthermore, in the step (1), the mass ratio of cellulose to SO2 is 100:5.

[0018] Furthermore, in the step (3), the temperature is kept at 45-75 minutes.

[0019] Another object of the present invention is to provide a system for an RDH cooking and pulping process, which can be used for the RDH cooking and pulping process.

[0020] In order to achieve the above objectives, the technical solutions adopted are:

[0021] A RDH cooking pulping process system includes: a cooking unit, a warm black liquor unit, a hot black liquor unit, a dilute alkali liquor unit, a cold black liquor unit, and a drug dispensing unit;

[0022] The warm black liquor unit, hot black liquor unit, dilute alkali liquor unit, and cold black liquor unit are respectively connected to the cooking unit;

[0023] The medicine configuration unit is communicated with the hot black liquor unit.

[0024] Furthermore, the cooking unit includes: a cooking pot, a cooking pot heater, and a cooking pot circulation pump;

[0025] The warm black liquor unit comprises: a warm black liquor tank, a warm black liquor tank heater, a warm black liquor tank circulation pump, and a warm black liquor tank pump;

[0026] The hot black liquor unit comprises: a hot black liquor tank, a hot black liquor tank heater, a hot black liquor tank circulation pump, and a hot black liquor tank pump;

[0027] The dilute alkali liquid unit comprises: a dilute alkali liquid tank, a dilute alkali liquid tank heater, a dilute alkali liquid tank circulation pump, and a dilute alkali liquid tank pump;

[0028] The cold black liquor unit comprises: a cold black liquor tank and a cold black liquor tank pump;

[0029] The medicine configuration unit includes a sulfur dioxide unit, an ethanol unit, and a mixing unit.

[0030] Furthermore, the cooking pot is an intermittent vertical steamer, comprising a pot cover, a pot loader, an upper filter screen, a middle filter screen, a cross joint and a discharge port.

[0031] Furthermore, the volumes of the warm black liquor tank, the hot black liquor tank, the diluted alkali tank, and the cold black liquor tank are greater than the volume of the cooking pot.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The technical solution of the present invention uses SO2 as a cooking agent, which prevents metal salts from entering the pulp and black liquor, and can significantly reduce environmental pressure. The low price of SO2 can greatly reduce the cost of chemicals per ton of pulp.

[0034] 2. The technical solution of the present invention can produce high-purity cellulose and generate high-quality organic fertilizer of sulfonated lignin during the pulping process. Its low cost, low pollution and product quality all show extremely high economic and social value.

[0035] 3. The technical solution of the present invention uses ethanol as the extraction solvent, which can significantly improve the extraction efficiency of lignin, hemicellulose, pectin and other components in the fiber raw material, with an extraction rate of over 90%, while the extraction rate without ethanol is only 30-40%. It also facilitates the production of high-purity cellulose. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Simple diagram of a steam cooking pot

[0037] Figure 2 A simplified diagram of the system;

[0038] Figure 3 This is a simplified diagram of the cooking process. DETAILED DESCRIPTION

[0039] To further illustrate the RDH cooking pulping process and system and achieve the intended purpose of the present invention, the following describes the RDH cooking pulping process and system according to the present invention, including its specific implementation, structure, features, and effectiveness, in conjunction with preferred embodiments. In the following description, different references to "one embodiment" or "embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics of one or more embodiments may be combined in any suitable manner.

[0040] The following will further introduce the RDH cooking pulping process and system of the present invention in detail with reference to specific embodiments:

[0041] The technical solution of the present invention is:

[0042] An RDH cooking pulping process is a liquid phase multi-stage displacement cooking process, comprising the following steps:

[0043] (1) adding SO2 chemicals and black liquor 1 to the fiber raw material, keeping it warm at 100-110°C for 25-35 minutes, and then replacing the black liquor 1 after the insulation with black liquor 2;

[0044] The black liquor 2 contains SO2 and ethanol, with an alcohol content of 45-55° and a mass concentration of SO2 of 5-6%;

[0045] (2) keeping the temperature at 140-150° C. for 90-130 minutes, and then replacing the heat-maintained black liquor 2 with black liquor 3; the heat-maintained black liquor 3 is the heat-maintained black liquor 1 replaced by the black liquor 2;

[0046] (3) replacing the warm black liquor 3 with a dilute alkali solution and keeping the temperature at 105-115° C. until the slurry has a kappa number of 17-20;

[0047] (4) using dilute black liquor to replace the dilute alkali liquor after heat preservation to obtain a coarse pulp.

[0048] Preferably, the temperature of the black liquor 1 and black liquor 3 is 120-130°C.

[0049] The temperature of the black liquor 2 is 140-150°C;

[0050] The temperature of the dilute black liquor is 70-80°C;

[0051] The dilute alkali solution is a 0.5-1.5wt% sodium hydroxide solution with a temperature of 105-115°C.

[0052] Preferably, the discharged warm black liquor and hot black liquor are subjected to SO2 and ethanol recovery, the sulfonated lignin after drug recovery is evaporated and concentrated to prepare high-efficiency organic fertilizer, and the cellulose is screened and bleached to obtain high-quality cellulose.

[0053] In the above technical solution, there is a recovery device for SO2 and ethanol, which can avoid the ineffective loss of drugs, make full use of drugs, and reduce the consumption of drugs per ton of pulp to the greatest extent.

[0054] Preferably, in step (1), the mass ratio of cellulose, SO2, and black liquor 1 is 100:4-6:600-800.

[0055] Further preferably, in the step (1), the mass ratio of cellulose to SO2 is 100:5.

[0056] Preferably, in step (3), the temperature is kept at 45-75 minutes.

[0057] A RDH cooking pulping process system includes: a cooking unit, a warm black liquor unit, a hot black liquor unit, a dilute alkali liquor unit, a cold black liquor unit, and a drug dispensing unit;

[0058] The warm black liquor unit, hot black liquor unit, dilute alkali liquor unit, and cold black liquor unit are respectively connected to the cooking unit;

[0059] The medicine configuration unit is communicated with the hot black liquor unit.

[0060] Preferably, the cooking unit comprises: a cooking pot, a cooking pot heater, and a cooking pot circulation pump;

[0061] The warm black liquor unit comprises: a warm black liquor tank, a warm black liquor tank heater, a warm black liquor tank circulation pump, and a warm black liquor tank pump;

[0062] The hot black liquor unit comprises: a hot black liquor tank, a hot black liquor tank heater, a hot black liquor tank circulation pump, and a hot black liquor tank pump;

[0063] The dilute alkali liquid unit comprises: a dilute alkali liquid tank, a dilute alkali liquid tank heater, a dilute alkali liquid tank circulation pump, and a dilute alkali liquid tank pump;

[0064] The cold black liquor unit comprises: a cold black liquor tank and a cold black liquor tank pump;

[0065] The medicine configuration unit includes a sulfur dioxide unit, an ethanol unit, and a mixing unit.

[0066] Further preferably, the cooking pot is an intermittent vertical steamer, comprising a pot cover, a pot loader, an upper filter screen, a middle filter screen, a cross joint and a discharge port.

[0067] In the above technical solution, the two filter screens, the upper and the middle, make the filtrate circulation path shorter and the circulation temperature rise faster.

[0068] Further preferably, the volumes of the warm black liquor tank, the hot black liquor tank, the diluted alkali tank, and the cold black liquor tank are greater than the volume of the cooking pot.

[0069] The present invention discloses a process and apparatus for producing high-purity cellulose and its black liquor resource utilization by boiling fiber raw materials, which can realize high-value resource utilization of fiber raw materials while significantly reducing costs and reducing environmental pollution, and can greatly improve the technical level in the field of fiber raw material resource utilization at home and abroad.

[0070] Black liquor: The liquid used to wash the pulp after cooking during the kraft or soda pulping process. Black liquor is black and contains inorganic substances from the cooking liquor, as well as lignin, hemicellulose, cellulose degradation products, and organic acids dissolved from the plant fiber raw materials. Approximately 10 tons of black liquor are produced during the production of one ton of pulp.

[0071] Thin black liquor refers to black liquor with low solids content.

[0072] Example 1: A system for RDH cooking pulping process

[0073] Combine Figure 1-2 The system includes: a cooking unit, a warm black liquor unit, a hot black liquor unit, a dilute alkali liquor unit, a cold black liquor unit, and a drug configuration unit.

[0074] The warm black liquor unit, the hot black liquor unit, the diluted alkali liquor unit and the cold black liquor unit are respectively connected to the cooking unit to transport the impregnation liquid to the cooking unit for impregnation treatment.

[0075] The drug dispensing unit is connected to the hot black liquor unit and is used to transport sulfur dioxide and ethanol to the hot black liquor unit.

[0076] (1) The cooking unit includes a cooking pot 7, a hopper 8, a cooking pot heater 9, a cooking pot circulation pump 10 (variable frequency), and a cooking pot slurry pump 37. The cooking pot heater 9 and the cooking pot circulation pump 10 are used to heat the cooking pot 7.

[0077] Cooking pot Figure 1 As shown, an intermittent vertical steamer includes an automatic pot cover 1, a pot loader 2, an upper filter 3, a middle filter 4, a cross joint 5 and a discharge port 6.

[0078] (2) Warm black liquor unit, comprising: a warm black liquor tank 11, a warm black liquor tank heater 12, a warm black liquor tank circulation pump 13, and a warm black liquor pump 14. The warm black liquor unit is used to store black liquor. The warm black liquor tank heater 12 and the warm black liquor tank circulation pump 13 are used to heat the warm black liquor tank 11, and the warm black liquor tank pump 14 delivers the warm black liquor to the cooking pot 7.

[0079] (3) Hot black liquor unit, including: hot black liquor tank 15, hot black liquor tank heater 16, hot black liquor tank circulation pump 17, hot black liquor pump 18. The hot black liquor unit is used to store black liquor, and the hot black liquor tank heater 16 and hot black liquor tank circulation pump 17 are used to heat the warm black liquor tank 15.

[0080] (4) A dilute alkali solution unit, comprising a dilute alkali solution tank 19, a dilute alkali solution tank heater 20, a dilute alkali solution tank circulation pump 21, and a dilute alkali solution pump 22. The dilute alkali solution unit is used to store dilute alkali solution, and the dilute alkali solution tank heater 20 and the dilute alkali solution tank circulation pump 21 are used to heat the dilute alkali solution tank 19.

[0081] The purchased alkali is transported to the dilute alkali liquid tank 19 in sequence through the alkali unloading tank 33, the alkali unloading pump 34, the alkali tank 35, and the alkali pump 36.

[0082] (5) Cold black liquor unit, including: cold black liquor tank 23, cold black liquor pump 24.

[0083] (7) Chemical preparation unit, including sulfur dioxide unit, ethanol unit, and mixing unit. After sulfur dioxide and ethanol are mixed in the mixing unit, they are transported to the hot black liquor tank.

[0084] The sulfur dioxide unit includes a sulfur dioxide storage tank 25 and a sulfur dioxide pump 26 .

[0085] The ethanol unit includes an ethanol storage tank 27 , an ethanol pump 28 , an ethanol recovery tank 29 , and an ethanol recovery pump 30 . The recovered ethanol is transported from the ethanol recovery tank 29 to the ethanol storage tank 27 via the ethanol recovery pump 28 .

[0086] The mixing unit includes an ethanol mixing tank 31 and an ethanol metering pump 32 .

[0087] The volumes of the warm black liquor tank 11 , the hot black liquor tank 15 , the diluted alkali tank 19 , and the cold black liquor tank 23 are greater than the volume of the cooking pot 7 .

[0088] Example 2.

[0089] Combine Figure 2-3 , using the system of Example 1, the specific operation steps are as follows:

[0090] 1) After cutting and screening, qualified fiber raw materials enter the cooking pot 7 through the automatic metering device, and SO2 chemicals and warm black liquor are added for pre-soaking and extraction. The clean chopped fiber raw materials are rotated into the pot loader under a certain pressure, and are evenly filled in the cooking pot 7 through the impregnation and dispersion of warm black liquor. The temperature rises rapidly to 100-110℃, and is kept warm for 25-35 minutes. Figure 3 -(1). After the fiber raw materials are loaded, the pot lid is closed and the warm black liquor is added to fill the pot according to the volume V of the cooking pot (the mass ratio of the fiber raw materials to the warm black liquor is 1:6-8).

[0091] Pre-soaking extraction can effectively extract impurities such as pectin and inorganic salts from fiber raw materials, which can significantly reduce the subsequent cooking chemical consumption and increase the solid content of black liquor.

[0092] Among them, the mass ratio of fiber raw material and SO2 is 100:4-6.

[0093] Warm black liquor is pumped from the warm black liquor tank 11 into the boiler 7 through the warm black liquor pump 14, and the temperature of the warm black liquor tank 11 is maintained at 120-130°C.

[0094] 2) The hot black liquor in the hot black liquor tank 15 is discharged from the bottom cross joint 5 of the cooking pot 7 (see Figure 1 ) is pumped in to displace the warm black liquor in the cooking pot 7 from the top of the cooking pot 7 to the warm black liquor tank 11. Figure 3 -(2). When the output of warm black liquor is not less than volume V, the replacement is stopped and the cycle heating and heat preservation phase begins. Figure 3-(3).

[0095] The temperature of the hot black liquor tank is 140-150°C, the SO2 mass concentration in the hot black liquor is 5-6%, and the alcohol content is 45-55°.

[0096] After the replacement is completed, the temperature is kept at 140-150°C for 90-130 minutes. At this time, more than 90% of the lignin, hemicellulose, pectin, salts, and other impurities in the fiber raw material are dissolved, and only a negligible amount of cellulose is dissolved.

[0097] 3) At this time, warm black liquor is used to replace the hot black liquor with a volume not less than V, and the drugs in the hot black liquor are protected. Figure 3 -(4).

[0098] The warm black liquor is the warm black liquor displaced in step (2), which is pumped from the warm black liquor tank 11 through the warm black liquor pump 14 and from the bottom cross joint 5 (see FIG. Figure 1 ) is pumped into the pot 7.

[0099] 4) Replace the warm black liquor with dilute alkali solution to protect the drugs in the warm black liquor. Figure 3 -(5). Extract the slurry with alkali for 45-75 minutes at 105-115℃ to reduce the kappa value of the slurry to 17-20. Figure 3 -(6).

[0100] The dilute alkali solution is a 0.5-1.5wt% sodium hydroxide solution at 105-115°C.

[0101] 5) Finally, replace the dilute alkali solution with cold dilute black liquor at 70-80℃. Figure 3 -(7), after the replacement is completed, cold spraying is achieved, and the pulp yield is more than 30%, see Figure 3 -(8).

[0102] After spraying, the pulp lignin, hemicellulose and other non-cellulose substances are almost all dissolved by the cooking liquid. The output cellulose has extremely high purity, which can reach more than 94%. After washing, screening and bleaching, high-quality high-purity cellulose is obtained. The fiber washing, screening and bleaching processes are traditional processes.

[0103] During the above cooking process, as non-fiber substances are continuously dissolved, the solid content of hot black liquor and warm black liquor will gradually increase. In order to ensure the subsequent pulp washing effect and process water balance, it is necessary to continuously discharge the black liquor. After the discharged black liquor is recycled through liquid-liquid heat exchange and SO2 and ethanol recovery systems, it is discharged to the sulfonated lignin treatment system. SO2 and ethanol are returned to the drug recovery tank for reuse. The total amount of alkali extract is very small and can be concentrated and added to the sulfonated lignin system or used to produce alkali lignin separately. Figure 2 .

[0104] After recovering SO2 and ethanol, the black liquor needs to be processed through a black liquor filter or plate and frame to remove insoluble suspended impurities in the black liquor. It is then evaporated and concentrated to a solid content of about 50% through an evaporator and stored as a waste base liquid. It is then compounded with other nutrients required for the growth of different plants to produce different types of high-end liquid organic fertilizers. Alternatively, it can be evaporated and concentrated before being sprayed with powder and compounded to produce various solid fertilizers, turning waste into treasure and achieving comprehensive and high-value utilization of fiber raw materials. The sulfonated lignin evaporation and concentration process is a traditional process.

[0105] Example 3.

[0106] Combine Figure 2-3 , using the system of Example 1, the specific operation steps are as follows:

[0107] 1) After cutting and screening, qualified fiber raw materials enter the cooking pot 7 through the automatic metering device, and SO2 chemicals and warm black liquor are added to soften them. Clean chopped fiber raw materials are rotated into the pot under a certain pressure, and are evenly filled in the cooking pot 7 through the impregnation and dispersion of warm black liquor. The temperature rises rapidly to 100℃ and is kept warm for 35 minutes. Figure 3 -(1). After the fiber raw materials are loaded, the pot lid is closed and the warm black liquor is added to fill the pot according to the volume V of the cooking pot (the mass ratio of the fiber raw materials to the warm black liquor is 1:8 at this time).

[0108] The mass ratio of fiber raw material to SO2 is 100:4.

[0109] Warm black liquor is pumped from the warm black liquor tank 11 into the boiler 7 through the warm black liquor pump 14, and the temperature of the warm black liquor tank 11 is maintained at 120°C.

[0110] 2) The hot black liquor in the hot black liquor tank 15 is discharged from the bottom cross joint 5 of the cooking pot 7 (see Figure 1 ) is pumped in to displace the warm black liquor in the cooking pot 7 from the top of the cooking pot 7 to the warm black liquor tank 11. Figure 3 -(2). When the output of warm black liquor is not less than volume V, the replacement is stopped and the cycle heating and heat preservation phase begins. Figure 3 -(3).

[0111] The temperature of the hot black liquor tank is 140°C, the SO2 mass concentration in the hot black liquor is 5%, and the alcohol content is 45°.

[0112] After the replacement is completed, the temperature is kept at 140°C for 130 minutes. At this time, more than 90% of the lignin, hemicellulose, pectin, salts, and other impurities in the fiber raw material are dissolved, and only a negligible amount of cellulose is dissolved.

[0113] 3) At this time, use 120℃ warm black liquor to replace the hot black liquor with a volume of not less than V, and protect the drugs in the hot black liquor. Figure 3 -(4).

[0114] The warm black liquor is the warm black liquor displaced in step (2), which is pumped from the warm black liquor tank 11 through the warm black liquor pump 14 and from the bottom cross joint 5 (see FIG. Figure 1 ) is pumped into the pot 7.

[0115] 4) Replace the warm black liquor with dilute alkali solution to protect the drugs in the warm black liquor. Figure 3 -(5). Alkali extraction was performed at 105°C for 75 minutes to reduce the kappa number of the slurry to 17-20. Figure 3 -(6).

[0116] The dilute alkali solution is a 1.5wt% sodium hydroxide solution at 105°C.

[0117] 5) Finally, replace the dilute alkali solution with 70℃ cold dilute black liquor. Figure 3 -(7), after the replacement is completed, cold spraying is achieved, and the pulp yield is 34%, see Figure 3 -(8). Cellulose purity is 96%

[0118] Example 4.

[0119] Combine Figure 2-3 , using the system of Example 1, the specific operation steps are as follows:

[0120] 1) After cutting and screening, qualified fiber raw materials enter the cooking pot 7 through the automatic metering device, and SO2 chemicals and warm black liquor are added to soften them. The clean chopped fiber raw materials are rotated into the pot under a certain pressure, and are evenly filled in the cooking pot 7 through the impregnation and dispersion of warm black liquor. The temperature rises rapidly to 110℃ and is kept warm for 25 minutes. Figure 3 -(1). After the fiber raw materials are loaded, the pot lid is closed and the warm black liquor is added to fill the pot according to the volume V of the cooking pot (the mass ratio of the fiber raw materials to the warm black liquor is 1:6 at this time).

[0121] The mass ratio of fiber raw material and SO2 is 100:6.

[0122] Warm black liquor is pumped from the warm black liquor tank 11 into the boiler 7 through the warm black liquor pump 14, and the temperature of the warm black liquor tank 11 is maintained at 130°C.

[0123] 2) The hot black liquor in the hot black liquor tank 15 is discharged from the bottom cross joint 5 of the cooking pot 7 (see Figure 1 ) is pumped in to displace the warm black liquor in the cooking pot 7 from the top of the cooking pot 7 to the warm black liquor tank 11. Figure 3 -(2). When the output of warm black liquor is not less than volume V, the replacement is stopped and the cycle heating and heat preservation phase begins. Figure 3 -(3).

[0124] The temperature of the hot black liquor tank is 150°C, the SO2 mass concentration in the hot black liquor is 6%, and the alcohol content is 55°.

[0125] After the replacement is completed, the temperature is kept at 150°C for 90 minutes. At this time, more than 90% of the lignin, hemicellulose, pectin, salts, and other impurities in the fiber raw material are dissolved, and only a negligible amount of cellulose is dissolved.

[0126] 3) At this time, use 130℃ warm black liquor to replace the hot black liquor with a volume of not less than V, and protect the drugs in the hot black liquor. Figure 3 -(4).

[0127] The warm black liquor is the warm black liquor displaced in step (2), which is pumped from the warm black liquor tank 11 through the warm black liquor pump 14 and from the bottom cross joint 5 (see FIG. Figure 1 ) is pumped into the pot 7.

[0128] 4) Replace the warm black liquor with dilute alkali solution to protect the drugs in the warm black liquor. Figure 3 -(5). Alkali extraction at 115℃ for 45min to reduce the kappa number of the slurry to 17-20. Figure 3 -(6).

[0129] The dilute alkali solution is a 0.5wt% sodium hydroxide solution at 115°C.

[0130] 5) Finally, replace the dilute alkali solution with 80℃ cold dilute black liquor. Figure 3 -(7), after the replacement is completed, cold spraying is achieved, and the pulp yield is 36%. Figure 3 -(8). Cellulose purity is 95%.

[0131] Example 5.

[0132] Combine Figure 2-3 , using the system of Example 1, the specific operation steps are as follows:

[0133] 1) After cutting and screening, qualified fiber raw materials enter the cooking pot 7 through the automatic metering device, and SO2 chemicals and warm black liquor are added to soften them. The clean chopped fiber raw materials are rotated into the pot under a certain pressure, and are evenly filled in the cooking pot 7 through the impregnation and dispersion of warm black liquor. The temperature rises rapidly to 105℃ and is kept warm for 30 minutes. Figure 3 -(1). After the fiber raw materials are loaded, the pot lid is closed and the warm black liquor is added to fill the pot according to the volume V of the cooking pot (the mass ratio of the fiber raw materials to the warm black liquor is 1:7 at this time).

[0134] The mass ratio of fiber raw material to SO2 is 100:5.

[0135] Warm black liquor is pumped from the warm black liquor tank 11 into the boiler 7 through the warm black liquor pump 14, and the temperature of the warm black liquor tank 11 is maintained at 125°C.

[0136] 2) The hot black liquor in the hot black liquor tank 15 is discharged from the bottom cross joint 5 of the cooking pot 7 (see Figure 1 ) is pumped in to displace the warm black liquor in the cooking pot 7 from the top of the cooking pot 7 to the warm black liquor tank 11. Figure 3 -(2). When the output of warm black liquor is not less than volume V, the replacement is stopped and the cycle heating and heat preservation phase begins. Figure 3 -(3).

[0137] The temperature of the hot black liquor tank is 145°C, the SO2 mass concentration in the hot black liquor is 5.5%, and the alcohol content is 50°.

[0138] After the replacement is completed, the temperature is kept at 145°C for 120 minutes. At this time, more than 90% of the lignin, hemicellulose, pectin, salts, and other impurities in the fiber raw material are dissolved, and only a negligible amount of cellulose is dissolved.

[0139] 3) At this time, warm black liquor is used to replace the hot black liquor with a volume not less than V, and the drugs in the hot black liquor are protected. Figure 3 -(4).

[0140] The warm black liquor is the warm black liquor displaced in step (2), which is pumped from the warm black liquor tank 11 through the warm black liquor pump 14 and from the bottom cross joint 5 (see FIG. Figure 1 ) is pumped into the pot 7.

[0141] 4) Replace the warm black liquor with dilute alkali solution to protect the drugs in the warm black liquor. Figure 3 -(5). Alkali extraction was performed at 110°C for 60 min to reduce the kappa number of the slurry to 17-20. Figure 3 -(6).

[0142] The dilute alkali solution is a 1.0 wt% sodium hydroxide solution at 110°C.

[0143] 5) Finally, replace the dilute alkali solution with 75℃ cold dilute black liquor. Figure 3 -(7), after the replacement is completed, cold spraying is achieved, and the pulp yield is 38%, see Figure 3 -(8). Cellulose purity 97%.

[0144] The above is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the embodiments of the present invention. Any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the embodiments of the present invention are still within the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A RDH cooking pulping process, characterized in that: The RDH cooking pulping process is a liquid phase multi-stage displacement cooking process, comprising the following steps: (1) adding SO2 chemicals and black liquor 1 to the fiber raw material, keeping it warm at 100-110°C for 25-35 minutes, and then replacing the black liquor 1 after the insulation with black liquor 2; The black liquor 2 contains SO2 and ethanol, with an alcohol content of 45-55° and a mass concentration of SO2 of 5-6%; (2) keeping the temperature at 140-150° C. for 90-130 minutes, and then replacing the heat-maintained black liquor 2 with black liquor 3; the heat-maintained black liquor 3 is the heat-maintained black liquor 1 replaced by the black liquor 2; (3) replacing the black liquor 3 with a dilute alkali solution and keeping the temperature at 105-115° C. until the slurry has a kappa number of 17-20; (4) using dilute black liquor to replace the dilute alkali liquor after heat preservation to obtain a coarse pulp.

2. The RDH cooking pulping process according to claim 1, characterized in that: The temperature of the black liquor 1 and black liquor 3 is 120-130°C The temperature of the black liquor 2 is 140-150°C; The temperature of the dilute black liquor is 70-80°C; The dilute alkali solution is a 0.5-1.5wt% sodium hydroxide solution with a temperature of 105-115°C.

3. The RDH cooking pulping process according to claim 1, characterized in that: In the step (1), the mass ratio of cellulose, SO2 and black liquor 1 is 100:4-6:600-800.

4. The RDH cooking pulping process according to claim 3, characterized in that: In the step (1), the mass ratio of cellulose to SO2 is 100:

5.

5. The RDH cooking pulping process according to claim 1, characterized in that: In the step (3), the temperature is kept at 45-75 minutes.

6. A system for RDH cooking pulping process, characterized in that: The system is used to implement the RDH cooking pulping process according to any one of claims 1 to 5, comprising: a cooking unit, a warm black liquor unit, a hot black liquor unit, a dilute alkali liquor unit, a cold black liquor unit, and a drug configuration unit; The warm black liquor unit, hot black liquor unit, dilute alkali liquor unit, and cold black liquor unit are respectively connected to the cooking unit; The medicine configuration unit is communicated with the hot black liquor unit.

7. The system according to claim 6, characterized in that The cooking unit includes: a cooking pot, a cooking pot heater, and a cooking pot circulation pump; The warm black liquor unit comprises: a warm black liquor tank, a warm black liquor tank heater, a warm black liquor tank circulation pump, and a warm black liquor tank pump; The hot black liquor unit comprises: a hot black liquor tank, a hot black liquor tank heater, a hot black liquor tank circulation pump, and a hot black liquor tank pump; The dilute alkali liquid unit comprises: a dilute alkali liquid tank, a dilute alkali liquid tank heater, a dilute alkali liquid tank circulation pump, and a dilute alkali liquid tank pump; The cold black liquor unit comprises: a cold black liquor tank and a cold black liquor tank pump; The medicine configuration unit includes a sulfur dioxide unit, an ethanol unit, and a mixing unit.

8. The system according to claim 7, characterized in that The cooking pot is an intermittent vertical steamer, comprising a pot cover, a pot loader, an upper filter screen, a middle filter screen, a cross joint and a discharge port.

9. The system according to claim 7, wherein: The volumes of the warm black liquor tank, the hot black liquor tank, the diluted alkali tank and the cold black liquor tank are greater than the volume of the cooking pot.

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