Paper pulp black liquor wastewater resourceful treatment process and device

Abstract

The invention discloses a resourceful treatment process and device for paper pulp black liquor wastewater. The resourceful treatment process comprises the steps that the paper pulp black liquor wastewater is subjected to primary filtration, suspended solids are removed, primary filtrate and primary concentrated water are obtained, the primary concentrated water flows back to a pulping system and continues to be used for pulping, and the primary filtrate continues to be subjected to secondary filtration; second-stage filtrate and second-stage concentrated water are obtained through second-stage filtration, third-stage filtration continues to be conducted on the second-stage filtrate, and pH adjustment is conducted on the second-stage concentrated water to separate out lignin; xylose and inorganic salt in the liquid are separated through third-stage filtration, third-stage filtrate and third-stage concentrated water are obtained, the third-stage filtrate is subjected to high-power concentration, concentrated concentrated water and concentrated produced water are obtained, the concentrated produced water is used for recycling pulp washing, the concentrated concentrated water is subjected to first-stage filtration after being subjected to evaporation treatment, and the third-stage concentrated water is used for furfural preparation. The comprehensive energy consumption is reduced by more than 50%; two chemical biomass raw materials with high value are separated through simple treatment, and the effective utilization rate of the black liquor value is increased.

Description

Technical Field

[0001] The present application relates to the technical field of pulp black liquor wastewater treatment, and specifically to a pulp black liquor wastewater resource treatment process and device and application thereof. Background Art

[0002] At present, the mainstream pulp manufacturing in the world generally adopts the kraft chemical pulping process, of which the Kraft pulping accounts for more than 70%. The Kraft process uses alkaline sulfate as the cooking liquid to dissolve and separate the lignin and hemicellulose components in the wood chips. The waste liquid generated during the cooking process is called black liquor; the main components of black liquor are organic components, accounting for 60-65%, mainly soluble lignin salts, hemicellulose and cellulose hydrolyzed pentose and oligosaccharides, and oligosaccharides are mainly xylose and xylan; inorganic components account for 35-40%, mainly residual cooking agents such as sodium sulfate, sodium sulfide, etc.

[0003] The pollutants in black liquor account for about 80%-90% of the total pollution in paper mills. Due to the large amount of black liquor, extremely high COD and low B / C ratio, it brings great inconvenience to conventional biochemical treatment. The conventional method for treating black liquor is alkali recovery, that is, evaporating and concentrating the black liquor and igniting it to recover energy, then adding sodium carbonate and sodium sulfide to causticize it to form green liquor, and finally adding calcium hydroxide to achieve sodium hydroxide recovery. However, this treatment process still has the following problems: 1) The alkali recovery system has high technical requirements and high equipment investment. Small and medium-sized paper mills are generally unable to afford the high cost of building an alkali recovery system. Currently, it is mainly used in large paper mills. 2) The black liquor concentration process uses high-temperature evaporation, and the temperature is generally above 150°C, which can easily cause equipment scaling and affect operation; 3) The content of inorganic components in black liquor is relatively high, resulting in incomplete combustion; 4) Alkali recovery requires that the dry solid content in black liquor must reach more than 80%, while the dry solid content of black liquor is usually only about 15%, which will consume huge energy; 5) The causticizing process of alkali recovery produces a large amount of waste solids, resulting in a very high content of suspended solids in the causticizing liquid, which is difficult to handle; 6) Black liquor contains a large amount of biomass effective components. Simply burning and recovering alkali cannot fully realize the value of black liquor. Summary of the invention

[0004] The present application provides a process and device for resource recovery treatment of pulp black liquor wastewater to solve the problems in the above-mentioned background technology.

[0005] The technical solution adopted by the present application to solve the technical problem is: a process for resource treatment of pulp black liquor wastewater, comprising the following steps: S1. Perform primary filtration on the pulp black liquor wastewater to remove 99% of the suspended solids to obtain primary filtrate and primary concentrated water. The primary concentrated water is returned to the pulping system for continued pulping, and the primary filtrate is further subjected to secondary filtration; S2, secondary filtration to obtain secondary filtrate and secondary concentrated water, the secondary filtrate continues to be filtered for tertiary filtration, and the secondary concentrated water is pH adjusted to precipitate lignin; S3. The three-stage filtration separates the xylose and inorganic salts in the liquid to obtain the third-stage filtrate and the third-stage concentrated water. The salt removal rate reaches 98% and the xylan retention rate is 95%. The third-stage filtrate is highly concentrated to obtain concentrated concentrated water and concentrated produced water. The concentrated produced water is used for reuse in pulp washing. The concentrated concentrated water is evaporated and then refluxed for primary filtration. The third-stage concentrated water is used for furfural production and further used for the production of high-value chemicals such as furan and PHA.

[0006] The pulp black liquor wastewater resource treatment process of the present application does not require high-temperature treatment, and the comprehensive energy consumption is reduced by more than 50%; it can separate two high-value chemical biomass raw materials through simple treatment, and the effective utilization rate of the black liquor value is increased; the whole process realizes the resource recovery of black liquor and the reuse of produced water without the need for additional processes.

[0007] Preferably, the first stage filtration, the second stage filtration and the third stage filtration all adopt tubular membrane filtration.

[0008] Preferably, the cut-off pore size of the tubular membrane for primary filtration is 0.1-0.5 μm, the secondary filtration uses a tubular membrane with a molecular weight cut-off of 5000-10000 MW, and the tertiary filtration uses a tubular membrane with a molecular weight cut-off of 2000-5000 MW.

[0009] Preferably, the concentration of lignin in the secondary concentrated water is above 35%, and the pH value of the secondary concentrated water is adjusted to 8-9 to precipitate the lignin for separation. Lignin is often used as a water reducer, a synthetic raw material for cosmetics and other chemical products.

[0010] Preferably, the high-concentration uses DTRO or STRO high-pressure reverse osmosis membrane components.

[0011] Preferably, the pH of the secondary concentrated water is adjusted with an organic acid to precipitate lignin.

[0012] Preferably, the evaporation treatment adopts MVR evaporation, and the energy source of MVR evaporation is the waste heat of the pulp black liquor wastewater after passing through the heat exchanger.

[0013] Preferably, the tertiary concentrated water is concentrated to obtain a xylose concentrate, and the xylose component is extracted with an organic solvent, and then the pH is adjusted to 4-5 with an acid to convert the xylose into furfural.

[0014] A pulp black liquor wastewater treatment device, used in any of the above-mentioned pulp black liquor wastewater resource treatment processes, comprising: Primary filtration component: The pulp black liquor wastewater is filtered in the primary stage to remove suspended matter to obtain primary filtrate and primary concentrated water. The primary concentrated water is returned to the pulping system for continued pulping, and the primary filtrate is further filtered in the secondary stage; Secondary filtration component: The secondary filtration obtains secondary filtrate and secondary concentrated water, the secondary filtrate continues to be filtered at the third stage, and the secondary concentrated water is pH-adjusted to precipitate lignin; Three-stage filtration component: The three-stage filtration separates the xylose and inorganic salts in the liquid to obtain the three-stage filtrate and the three-stage concentrated water. The three-stage filtrate is highly concentrated to obtain concentrated concentrated water and concentrated produced water. The concentrated produced water is used for reuse in pulp washing. The concentrated concentrated water is evaporated and then refluxed for the first-stage filtration. The three-stage concentrated water is used for furfural production.

[0015] Preferably, the primary filtration component comprises a tubular membrane, which performs primary filtration on the pulp black liquor wastewater to remove suspended matter to obtain primary filtrate and primary concentrated water; The secondary filtration component includes a tubular membrane and a pH adjustment tank. The tubular membrane performs secondary filtration to obtain a secondary filtrate and secondary concentrated water. The secondary concentrated water is pH-adjusted in the pH adjustment tank to precipitate lignin. The tertiary filtration component includes a tubular membrane, a high-multiple concentration component and an MVR system. The tubular membrane separates the xylose and inorganic salts in the tertiary filtration liquid to obtain a tertiary filtrate and a tertiary concentrated water. The high-multiple concentration component highly concentrates the tertiary filtrate to obtain a concentrated concentrated water and concentrated produced water. The concentrated produced water is used for reuse in pulp washing. The MVR system evaporates the concentrated concentrated water and refluxes it for primary filtration. The tertiary concentrated water is used for furfural production.

[0016] The substantial effects of the present application are as follows: the pulp black liquor wastewater resource treatment process of the present application does not require high-temperature treatment, and the comprehensive energy consumption is reduced by more than 50%; it is possible to separate two high-value chemical biomass raw materials through simple treatment, and the effective utilization rate of the black liquor value is increased; the entire process realizes black liquor resource recovery and produced water reuse, without the need for additional processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a process flow chart of Example 1 of the present application. DETAILED DESCRIPTION

[0018] The technical solution of the present application is further described below through specific embodiments.

[0019] Embodiment 1

[0020] like Figure 1 As shown, a process for resource treatment of pulp black liquor wastewater comprises: S1. Perform primary filtration on the pulp black liquor wastewater to remove 99% of the suspended solids to obtain primary filtrate and primary concentrated water. The primary concentrated water is returned to the pulping system for continued pulping, and the primary filtrate is further subjected to secondary filtration; S2, secondary filtration to obtain secondary filtrate and secondary concentrated water, the secondary filtrate continues to be filtered for tertiary filtration, the lignin concentration in the secondary concentrated water is more than 35%, the pH value of the secondary concentrated water is adjusted to 8-9 with acetic acid or citric acid to precipitate lignin for separation, organic acid can prevent xylan from being hydrolyzed into small molecular organic acid, lignin is often used as a water reducer, synthetic raw material for cosmetics and other chemical products; S3. The three-stage filtration separates the xylose and inorganic salts in the liquid to obtain the third-stage filtrate and the third-stage concentrated water. The salt removal rate reaches 98%, and the xylan retention rate is 95%. The third-stage filtrate is highly concentrated to obtain concentrated concentrated water and concentrated produced water. The concentrated produced water is reused for pulp washing. The concentrated concentrated water is evaporated and then refluxed for primary filtration. The third-stage concentrated water is concentrated to obtain xylose concentrate. The xylose component is extracted with dichloromethane or tetrahydrofuran, and the pH is adjusted to 4-5 with acetic acid to convert xylose into furfural. Furfural is further used to prepare high-value chemicals such as furan and PHA.

[0021] Embodiment 2

[0022] A pulp black liquor wastewater treatment device, comprising: Primary filtration component: The primary filtration component includes a tubular membrane. The cutoff pore size of the tubular membrane of the primary filtration component is 0.1-0.5μm. The tubular membrane performs primary filtration on the pulp black liquor wastewater to remove suspended matter to obtain primary filtrate and primary concentrated water. The primary concentrated water is returned to the pulping system for continued pulping, and the primary filtrate continues to undergo secondary filtration; Secondary filtration component: The secondary filtration component includes a tubular membrane and a pH adjustment tank. The secondary filtration component uses a tubular membrane with a molecular weight cutoff of 5000-10000MW. The tubular membrane performs secondary filtration to obtain secondary filtrate and secondary concentrated water. The secondary filtrate continues to undergo tertiary filtration, and the secondary concentrated water is pH-adjusted in a pH adjustment tank to precipitate lignin. Three-stage filtration component: The three-stage filtration component includes a tubular membrane, a high-concentration component and an MVR system. The three-stage filtration component adopts a 2000-5000MW tubular membrane. The tubular membrane separates the xylose and inorganic salts in the three-stage filtration separation liquid to obtain a three-stage filtrate and a three-stage concentrated water. The high-concentration component adopts a high-pressure reverse osmosis membrane component DTRO or STRO to highly concentrate the three-stage filtrate to obtain concentrated concentrated water and concentrated produced water. The concentrated produced water is used for reuse in pulp washing. The MVR system evaporates the concentrated concentrated water and refluxes it for primary filtration. The three-stage concentrated water is used for furfural production. The energy source of MVR evaporation is the waste heat of pulp black liquor wastewater after passing through the heat exchanger.

[0023] Embodiment 3

[0024] S1. The black liquor produced in the pulping process is first pumped through a pipeline to a tubular microfiltration membrane system with a pore size of 0.2 microns for filtration. The primary filtrate and primary concentrated water are obtained by setting a constant flux of 150 LMH through pressure regulation. The recovery rate of primary filtrate water is 90%. 98% of the suspended solids are retained in the primary concentrated water. The primary concentrated water is returned to the pulping section through the reflux system. The primary filtrate water is transported to the secondary tubular ultrafiltration system through a pipeline for further secondary filtration.

[0025] S2. Use an ultrafiltration tubular membrane system with a molecular weight cutoff of 10,000 MW to treat the primary filtrate to produce water to obtain a secondary filtrate and secondary concentrated water. The pressure is adjusted to set a constant flux of 80LMH for operation, and the secondary filtrate water recovery rate is 90%. The lignin concentration in the secondary concentrated water is about 25-30%. By introducing the secondary concentrated water into the sedimentation tank and adding a regulating liquid such as acetic acid to reduce the pH to 8, lignin crystals with a purity of 95%-98% are precipitated. Lignin of this purity can be fermented into PDA by Pseudomonas bacteria, which is further used to produce degradable plastics; or degraded into PDC by Sphingomonas, which is a mild chemical engineering oxidant; S3, the secondary filtrate water is further treated with an ultrafiltration membrane system with a molecular weight cutoff of 2000MW to obtain a tertiary filtrate and tertiary concentrated water. The pressure is adjusted to set a constant flux of 40LMH for operation, and the recovery rate of the tertiary filtrate water is 50%. The concentrated water of the three-stage tubular ultrafiltration membrane system is introduced into the fermentation tank for further conversion to increase the xylose content through biological enzymatic hydrolysis, and then the pH is adjusted to 4-5 with acetic acid. The reaction is 12-24h to convert xylose into furfural, and furfural is extracted by 2-methyltetrahydrofuran, and then further catalytic hydrogenation is performed to obtain tetrahydrofuran. The tertiary filtrate water is highly concentrated by a DTRO membrane system, with a set flux of 10LMH and a recovery rate of 60%. The concentrated concentrated water is evaporated by the MVR system, and the concentrated filtrate water is returned to the pulping system for pulp washing.

[0026] Embodiment 4

[0027] S1. The black liquor produced in the pulping process is first pumped through a pipeline to a tubular microfiltration membrane system with a pore size of 0.2 microns for filtration. The pressure is adjusted to set a constant flux of 150 LMH and the water recovery rate is 90%. 98% of the suspended solids are retained in the primary concentrated water, which is returned to the pulping section through the reflux system, and the primary filtrate water is transported to the secondary tubular ultrafiltration system through a pipeline.

[0028] S2. Use an ultrafiltration tubular membrane system with a molecular weight cutoff of 10,000 MW to treat the primary filtrate water production. Set a constant flux of 80LMH through pressure regulation, and the secondary filtrate water production recovery rate is 90%. The lignin concentration in the secondary concentrated water is about 25-30%. The pH is lowered to 8 by introducing the secondary concentrated water into the sedimentation tank and adding a regulating liquid such as acetic acid. Then, the lignin crystals are separated by a centrifuge at a speed of 10,000 r / min to improve the lignin separation efficiency. The lignin crystals with a purity of 95%-98% are precipitated. The lignin of this purity can be fermented into PDA by Pseudomonas bacteria, which is further used to produce degradable plastics; or degraded into PDC by Sphingomonas, which is a mild chemical engineering oxidant; S3, the secondary filtrate water is further treated with an ultrafiltration membrane system with a molecular weight cutoff of 2000MW, and the pressure is adjusted to set a constant flux of 40LMH for operation, and the recovery rate of the tertiary filtrate water is 50%. The concentrated water of the three-stage tubular ultrafiltration membrane system is introduced into the fermentation tank for further conversion to increase the xylose content through biological enzymatic hydrolysis, and then the pH is adjusted to 4-5 with acetic acid, and the reaction is 12-24h to convert xylose into furfural, and furfural is extracted by 2-methyltetrahydrofuran, and then further catalytic hydrogenation is performed to obtain tetrahydrofuran. The tertiary filtrate water is highly concentrated by the DTRO membrane system, with a set flux of 10LMH and a recovery rate of 60%. The concentrated concentrated water is evaporated by the MVR system, and the concentrated filtrate water is returned to the pulping system for pulp washing.

[0029] Embodiment 5

[0030] S1. The black liquor produced in the pulping process is first pumped through a pipeline to a tubular microfiltration membrane system with a pore size of 0.2 microns for filtration. The pressure is adjusted to set a constant flux of 150 LMH and the water recovery rate is 90%. 98% of the suspended solids are retained in the primary concentrated water, which is returned to the pulping section through the reflux system, and the primary filtrate water is transported to the secondary tubular ultrafiltration system through a pipeline.

[0031] S2. Use an ultrafiltration tubular membrane system with a molecular weight cutoff of 5000MW to treat the primary filtrate water production. Set a constant flux of 60LMH through pressure regulation, and the secondary filtrate water production recovery rate is 80%. The lignin concentration in the secondary concentrated water is about 25-30%. Use sodium hydroxide to adjust the pH to 11, add coking sodium bisulfite, and the product is precipitated, washed, sprayed and dried to obtain wood sulfonate, which is a concrete water reducer; S3, the water produced by the secondary filtrate is further treated with an ultrafiltration membrane system with a molecular weight cutoff of 2000MW, and the pressure is adjusted to set a constant flux of 40LMH for operation, and the recovery rate of the water produced by the tertiary filtrate is 50%. The concentrated water of the three-stage tubular ultrafiltration membrane system is introduced into the fermentation tank for further conversion to increase the xylose content through biological enzymatic hydrolysis, and then the xylose solution is extracted with 2-methyltetrahydrofuran, and the pH is adjusted to 4-5 with acetic acid. After reacting for 12 hours, furfural solution is obtained, and further catalytic hydrogenation is performed to obtain tetrahydrofuran. The water produced by the tertiary filtrate is highly concentrated by the DTRO membrane system, with a set flux of 10LMH and a recovery rate of 60%. The concentrated concentrated water is evaporated through the MVR system, and the concentrated filtrate water is returned to the pulping system for pulp washing.

[0032] The above-described embodiment is only a preferred solution of the present application and does not limit the present application in any form. There are other variations and modifications without exceeding the technical solution described in the claims.

Claims

1. A process for resource treatment of pulp black liquor wastewater, characterized in that: The following steps are involved: S1. Perform primary filtration on the pulp black liquor wastewater to remove suspended solids to obtain primary filtrate and primary concentrated water, the primary concentrated water is returned to the pulping system for continued pulping, and the primary filtrate is further subjected to secondary filtration; S2, secondary filtration to obtain secondary filtrate and secondary concentrated water, the secondary filtrate continues to be filtered for tertiary filtration, and the secondary concentrated water is pH adjusted to precipitate lignin; S3. The xylose and inorganic salts in the liquid are separated by three-stage filtration to obtain a third-stage filtrate and a third-stage concentrated water. The third-stage filtrate is highly concentrated to obtain a concentrated concentrated water and a concentrated produced water. The concentrated produced water is used for pulp washing. The concentrated concentrated water is evaporated and then refluxed for primary filtration. The third-stage concentrated water is used for furfural production.

2. The process for recycling pulp black liquor wastewater according to claim 1, characterized in that: The first stage filtration, second stage filtration and third stage filtration all adopt tubular membrane filtration.

3. The process for recycling pulp black liquor wastewater according to claim 2, characterized in that: The cut-off pore size of the tubular membrane for primary filtration is 0.1-0.5 μm, the secondary filtration uses a tubular membrane with a molecular weight cut-off of 5000-10000 MW, and the tertiary filtration uses a tubular membrane with a molecular weight cut-off of 2000-5000 MW.

4. The process for recycling pulp black liquor wastewater according to claim 1, characterized in that: The lignin concentration in the secondary concentrated water is above 35%, and the pH value of the secondary concentrated water is adjusted to 8-9 to allow the lignin to precipitate and separate.

5. The process for resource recovery of pulp black liquor wastewater according to claim 1, characterized in that: High concentration uses DTRO or STRO high pressure reverse osmosis membrane components.

6. The process for resource recovery of pulp black liquor wastewater according to claim 1 or 4, characterized in that: The pH of the secondary concentrated water is adjusted with organic acid to precipitate lignin.

7. The process for recycling pulp black liquor wastewater according to claim 1, characterized in that: The evaporation treatment adopts MVR evaporation, and the energy source of MVR evaporation is the waste heat of pulp black liquor wastewater after passing through the heat exchanger.

8. The process for recycling pulp black liquor wastewater according to claim 1, characterized in that: The tertiary concentrated water is concentrated to obtain a xylose concentrate, and the xylose component is extracted using an organic solvent, and then the pH is adjusted to 4-5 with acid to convert the xylose into furfural.

9. A pulp black liquor wastewater treatment device, used in the pulp black liquor wastewater resource treatment process according to any one of claims 1 to 8, characterized in that: include: Primary filtration component: The pulp black liquor wastewater is filtered in the primary stage to remove suspended matter to obtain primary filtrate and primary concentrated water. The primary concentrated water is returned to the pulping system for continued pulping, and the primary filtrate is further filtered in the secondary stage; Secondary filtration component: The secondary filtration obtains secondary filtrate and secondary concentrated water, the secondary filtrate continues to be filtered at the third stage, and the secondary concentrated water is pH-adjusted to precipitate lignin; Three-stage filtration component: The three-stage filtration separates the xylose and inorganic salts in the liquid to obtain the three-stage filtrate and the three-stage concentrated water. The three-stage filtrate is highly concentrated to obtain concentrated concentrated water and concentrated produced water. The concentrated produced water is used for reuse in pulp washing. The concentrated concentrated water is evaporated and then refluxed for the first-stage filtration. The three-stage concentrated water is used for furfural production.

10. The pulp black liquor wastewater treatment device according to claim 9, characterized in that: The primary filtration component includes a tubular membrane, which performs primary filtration on the pulp black liquor wastewater to remove suspended matter to obtain primary filtrate and primary concentrated water; The secondary filtration component includes a tubular membrane and a pH adjustment tank. The tubular membrane performs secondary filtration to obtain a secondary filtrate and secondary concentrated water. The secondary concentrated water is pH-adjusted in the pH adjustment tank to precipitate lignin. The tertiary filtration component includes a tubular membrane, a high-multiple concentration component and an MVR system. The tubular membrane separates the xylose and inorganic salts in the tertiary filtration liquid to obtain a tertiary filtrate and a tertiary concentrated water. The high-multiple concentration component highly concentrates the tertiary filtrate to obtain a concentrated concentrated water and concentrated produced water. The concentrated produced water is used for reuse in pulp washing. The MVR system evaporates the concentrated concentrated water and refluxes it for primary filtration. The tertiary concentrated water is used for furfural production.

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