Apparatus, method and system for increasing the yield of a sulfate pulping facility

Abstract

Apparatus, methods, and systems for improving the yield of a kraft cooking facility provide synergistic benefits for at least two parallel cooking facilities. For example, one cooking facility produces dissolving pulp in a prehydrolysis kraft process, while another cooking facility produces kraft pulp via a kraft pulping process. By recovering hemicellulose dissolved in the acidic hydrolyzate of the prehydrolysis kraft process, the cooking yield of the kraft cooking facility producing the kraft pulp can be improved. In some embodiments, a cold caustic extraction step can be eliminated in the dissolving pulp line because only the prehydrolysis step is required to achieve the target pulp purity, and the acidic hydrolyzate stream can be reused in the kraft pulp line.

Description

[0001] This patent application disclosure describes inventive aspects that include various novel innovations (hereinafter referred to as the "disclosure") and contains material that is protected by copyright, mask work, and / or other intellectual property rights. The respective owners of such intellectual property have no objection to the facsimile reproduction by anyone of the disclosure as it appears in published Patent Office file / records, but otherwise reserve all rights whatsoever. Technical Field

[0002] The innovation relates to pulp production and, more particularly, to improving the pulp yield of the kraft cooking process. Background Art

[0003] In recent years, the use of biomass as a raw material for various industries and products has increased. In this context, the pulp and paper industry provides low-carbon footprint materials, including dissolving pulp, which can supply a large number of industries, such as regenerated cellulose (such as viscose and lyocell fibers, glass paper and sponge), cellulose acetate, cellulose nitrate and some other celluloses.

[0004] Wood and other materials used in the pulp and paper industry are composed of four primary chemical components: cellulose, hemicellulose, lignin, and extractives. Dissolving pulp is characterized by higher purity compared to paper-grade pulp, for example, with a higher cellulose content and lower hemicellulose content. The challenge with dissolving pulp is to remove the majority of the lignin and extractives during the cooking and bleaching reactions, while retaining the majority of the cellulose and hemicellulose. The challenge with dissolving pulp is also to remove the hemicellulose, resulting in a product with an α-cellulose purity of at least 90%.

[0005] Wood, both softwood and hardwood, is the primary raw material used in the pulp industry. Although the macromolecular composition of all species is similar, the ratios between the components can vary, as shown in Table 1 (Sixta, 2006).

[0006] Table 1 Composition (%)

[0007]

[0008]

[0009] Wood costs influence the cost of pulp production, so pulp yield is an important economic factor and an area of development and research. Because most of the wood components other than cellulose are removed, dissolving pulp processes can achieve yields of 35% to 38%, lower than paper-grade manufacturing processes, where yields typically exceed 50%.

[0010] The kraft process (KP) and the prehydrolysis kraft cooking (PHK) process or prehydrolysis sulfate cooking have been described in the literature, for example in Sixta, H., Handbook of Pulp, and are used to produce paper grade pulp and dissolving pulp, respectively, from lignocellulosic material.

[0011] The prehydrolysis step applied before the kraft cooking process can selectively break down and solubilize short-chain molecules such as hemicellulose, producing an aqueous phase rich in acidic carbohydrates. The severity of the prehydrolysis is controlled by the so-called P factor, a single parameter that combines the reaction temperature and retention time of the prehydrolysis stage and is manipulated to control the pulp purity. The pulp purity can be determined, for example, by the alpha cellulose test (Tappi T-203) or the alkali solubility method (Tappi T-235) or other standard similar methods.

[0012] During the prehydrolysis process, acetyl groups are released into the aqueous phase due to the cleavage reactions of hemicellulose chains (primarily (glucuronic acid) xylan in hardwood and (galacto) glucomannan in softwood), typically lowering the pH to a range of 3-4. Furthermore, with the addition of catalysts such as mineral acids, the pH can be further lowered to below 2.0, increasing the reaction rate. Garrote (1999) reported that up to 95% of the original hemicellulose content of the wood source can be removed during the prehydrolysis process, with little effect on the lignin and cellulose molecules. The hemicellulose removed from the wood source can be present in the aqueous solution as oligomers or monomers or converted into byproducts such as furfural or acetic acid. The resulting acid solution containing dissolved hemicellulose is referred to as a hydrolysate or acidic hydrolysate.

[0013] To terminate the pre-hydrolysis reaction, in a step called neutralization, the wood chips are alkalized at a lower temperature than that of the pre-hydrolysis stage by adding a strongly alkaline solution, such as white liquor, black liquor or other alkali-rich filtrate, such as the filtrate from the subsequent cold caustic extraction (CCE) stage, thereby raising the pH to above 11.

[0014] Several implementations of the PHK process have been more extensively discussed in batch cookers and their variations, such as the Continuous Batch Cooking process and the Superbatch process.

[0015] In a batch system, wood chips are added through an opening in the top of the vessel to fill the batch digester for each cooking cycle. The chips can be fed into the digester via screw and / or belt conveyors and passed through a packing device as they enter the digester to help increase the amount of wood loaded in each batch. The packing device can include a set of low-pressure steam nozzles to push and distribute the stream of chips downward. The steam displaces air from the spaces between the chips, and the air is continuously exhausted from the digester.

[0016] When the digester is completely filled, the top opening is closed and more steam is injected into the vessel to heat the chips to the target prehydrolysis temperature, for example above 150°C. When the target temperature is reached, the steam valve is closed and the digester is kept open for a period of time until the target P factor is reached.

[0017] In a batch system, as wood chips and steam are fed into the digester, a pre-hydrolysis step is carried out in the "steam stage" until the pre-hydrolysis is complete. During this stage, the liquid medium in the vessel is a mixture of wood moisture and steam condensate, which is mainly located in the interstices of the wood chips, with a negligible amount of free liquid between the chips. After the pre-hydrolysis reaction, as acetic acid is formed and hemicellulose is dissolved in the liquid phase, the total liquid volume per dry metric ton of wood may not exceed 1 cubic meter (m3). 3 / BDtw).

[0018] After pre-hydrolysis, a neutralization step is performed by injecting a strong alkaline solution into the bottom of the digester. As more liquor is added, the neutralizing solution is displaced through the digester. As the neutralizing solution impregnates the wood chips, it simultaneously displaces and mixes with the acid hydrolysis solution that forms in the interstices within the chips. As a result, the PHK batch system produces virtually no acid stream that can be separated and reused for other purposes.

[0019] The PHK cooking process may also include embodiments comprising a continuous cooking system, and more particularly, a system in which the pre-hydrolysis step is performed in a separate vessel from the alkaline cooking stage.

[0020] In such systems, lignocellulosic material, such as wood chips, and water / condensate are continuously fed into the top of a vessel (e.g., a prehydrolysis vessel or PHV) capable of maintaining its contents at the required time and temperature to achieve the desired prehydrolysis reaction intensity.

[0021] The initial pre-hydrolysis step can be carried out in the steam phase, for example at the top of the PHV, while the biomass is heated by direct steam injection, but the majority of the pre-hydrolysis reactions are carried out in the water phase in such a way that the amount of water present in the vessel is typically 2-5 m3 relative to the amount of wood chips. 3 / BDTw. This water volume is significantly higher than in, for example, a batch digester, where the water volume is usually no more than 1m 3 / BDTw, because at this stage most of the water in the digester is simply due to wood moisture and condensate from direct steam heating.

[0022] Neutralization is usually performed inside the PHV (lowest area / bottom of the vessel) or in the top of a subsequent digester, or even in the pipes that transfer the chips from the prehydrolysis vessel to the digester.

[0023] Before the neutralization stage begins, a portion of the free acidic hydrolysate can be partially extracted from the PHV vessel through one or more screens (filters). This early extraction serves several purposes, such as removing dissolved hemicellulose from the process to improve pulp purity or to produce hemicellulose-derived byproducts such as xylitol or furfural. The extracted acidic hydrolysate can be neutralized with white liquor, mixed with spent cooking liquor, and then sent to a heat recovery system (flash tank or heat exchanger). It is then sent to the recovery island where the hemicellulose is burned along with other organic compounds in a recovery boiler to generate steam.

[0024] The amount of hydrolysate available for extraction depends on several factors, such as chip moisture, water intake with chips, steam condensate generated during direct steam heating of the PHV vessel top, PHV degassing, prehydrolysis strength coefficient, prehydrolysis yield, and whether PHV bottom displacement washing is performed.

[0025] The remaining free and bound hydrolysate fractions in the PHV are neutralized together with the wood chips and conveyed to the digester via a transfer circulation line.

[0026] The chips are transferred from the bottom of the PHV to the top of a cooking vessel (e.g., a digester) for the alkaline kraft cooking process. There are many different digester configurations that differ in, for example, the number of recirculation zones, liquid addition, extraction points, number / location of filters, and whether the digester is a hydraulic or steam-liquid phase type.

[0027] Some mills have already undergone expansion projects and now have more than one cooking unit on the same site. In addition, many of these existing installations have been converted from paper-grade pulp mills to dissolving pulp mills, either permanently or on a flexi- / fluctuating basis.

[0028] Adjacent parallel production lines that produce both paper-grade pulp and dissolving pulp allow the integration of the two lines. Side streams, such as liquid extracted from one digester, can be used at strategic locations in the other line to improve pulping yield and / or quality. As an example, BOGREN et al. (WO / 2013 / 178608) disclose a system using such integration. In this system, cold alkali extract filtrate (CCE filtrate) containing high molecular weight xylan is extracted from a pre-hydrolysis kraft pulp line producing dissolving pulp and sent to a parallel kraft pulp line producing conventional kraft pulp to increase kraft pulp yield and improve the process economy and mechanical properties of the final kraft pulp. After the alkali impregnation of the wood is completed, the CCE filtrate is added to form the residual cooking liquor. SUMMARY OF THE INVENTION

[0030] The apparatus, methods, and systems disclosed herein for increasing the yield of a kraft cooking facility, in various embodiments, provide synergistic effects for at least two parallel cooking facilities, for example, one cooking facility producing dissolving pulp in a pre-hydrolysis kraft process and another cooking facility producing kraft pulp via a kraft pulping process. Some embodiments can increase the cooking yield of a kraft cooking facility producing kraft pulp by recovering hemicellulose dissolved in an acidic hydrolyzate. In some embodiments, a hydrolyzate stream that might otherwise be placed in a recovery island for steam generation and / or extraction for the production of by-products is reused in an adjacent kraft pulp line for the production of kraft pulp. In embodiments of the disclosed apparatus, methods, and systems, a cold caustic extraction step can be eliminated from the dissolving pulp line because only a pre-hydrolysis step is required to achieve the target pulp purity and reuse the acidic hydrolyzate stream in the kraft pulp line.

[0031] Under certain conditions, some of the hemicellulose and other organic compounds dissolved in the acidic hydrolysate may precipitate onto the fibers, thereby increasing the cooking yield, thereby reducing overall specific wood consumption and / or increasing pulp throughput. Embodiments of the disclosed apparatus, methods, and systems may also increase the hemicellulose content of the final bleached pulp, thereby providing, for example, improved beating properties, mechanical properties, and / or the like.

[0032] Embodiments of the disclosed apparatus, methods, and systems may include two methods for reusing acidic hydrolyzate in a kraft cooking process of kraft slurry.

[0033] One method (A) includes a pretreatment step in which the wood chips are sent to an acid impregnation stage before the alkaline cooking process. The steamed wood chips are mixed with cooled acidic hydrolysate extracted from an adjacent PHK line, thereby soaking and saturating the wood chips with the hydrolysate, and the dissolved hemicellulose is precipitated onto the fibers. The acidic hydrolysate is cooled to such an extent that the temperature of the resulting mixture of wood chips and hydrolysate becomes 70°C to 125°C or 100°C. After this step, any kraft cooking process can be carried out to produce pulp, such as conventional cooking or other modified cooking methods, such as ITC cooking, low-solids process, compact cooking process, super batch cooking and / or similar methods.

[0034] The acid impregnation stage can be performed in a continuous digester with or without providing substantial retention time. In other words, the chips can be fed directly to the digester using only the chip feed system, with a short retention time (<5 minutes) during the impregnation stage, or alternatively the digester top can be used to provide a longer retention time, or another arrangement could be to use a separate vessel for the acid impregnation step.

[0035] For batch cooking facilities, the acid chip impregnation and subsequent alkaline kraft cooking steps can be performed in the same digester (e.g., between the digester chip filling sequence and the kraft cooking stage).

[0036] In different embodiments, the degree of hemicellulose recovery can depend on several factors, such as, but not limited to, the wood species and the applied process conditions, with retention time having a significant impact on the results obtained. The effect of this retention time has been demonstrated in the laboratory by pilot-scale cooking with Eucalyptus urophylla (Eucalyptus Urograndis). The pulp yields at different acid impregnation times were compared with reference cookings without a hydrolyzate recovery step and with the same kappa number level. It was found that the retention time that maximized the hemicellulose recovery was 40-100 minutes, as shown in Table A. However, due to the lower implementation costs, a process with the shortest impregnation time (without additional containers or areas) is also economically feasible.

[0037] The second method (B) involves injecting the acidic hydrolysate into the alkaline cooking zone within the digester, rather than having a dedicated acid impregnation vessel or area. Continuous digester embodiments may include various cooking zones separated by filters in the vessel wall, where liquor circulation, liquid extraction and injection, temperature and alkaline profile changes occur.

[0038] According to the second method (B), the acidic hydrolysate is added to a low alkali concentration cooking zone, for example to the last cooking zone, where the residual effective alkali is less than 10 g EA / l, so that hemicellulose is precipitated onto the fiber surface during the cooking reaction.

[0039] For batch digesters and process (B), the acidic hydrolysis liquor is introduced at the end of the digestion cycle and / or during the subsequent cold displacement phase.

[0040] In one embodiment, a process for increasing pulp yield in a kraft cooking facility is disclosed comprising utilizing an acidic hydrolyzate stream from an adjacent pre-hydrolysis kraft process producing dissolving wood pulp.

[0041] In another embodiment, a method for producing kraft pulp is disclosed, comprising: extracting acidic hydrolysate from a prehydrolysis kraft process for producing dissolving wood pulp; and applying the acidic hydrolysate to a kraft cooking process of a kraft cooking facility.

[0042] In another embodiment, a system for producing a sulfate slurry is disclosed, comprising: a sulfate cooking facility; and an acidic hydrolyzate source that provides acidic hydrolyzate to a sulfate cooking process of the sulfate cooking facility.

[0043] BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The appendices and / or accompanying drawings illustrate various non-limiting, exemplary, innovative aspects according to this specification:

[0045] Figure 1 A flow diagram of a PHK cooking facility is shown, representing a two-vessel continuous digester for dissolving grade pulp production, wherein a side stream of acidic hydrolysate is generated containing the dissolved hemicellulose;

[0046] Figure 2 A flow diagram showing an embodiment of Process A for kraft pulping in a kraft cooking facility, the flow diagram representing a two-vessel continuous digester configuration with a separate acid chip impregnation vessel;

[0047] Figure 3 A flow diagram showing an embodiment of Method A for grading kraft pulp in a kraft cooking facility is shown, the flow diagram representing one vessel configuration (continuous or batch digester);

[0048] Figure 4 A flow chart showing an embodiment of Method B for a kraft slurry in a kraft cooking facility (continuous or batch digester); and

[0049] Figure 5Shown is a comparison of the cooking screened yields for both Methods A and B for kraft pulps over a wide range of Kappa numbers, in one embodiment, with a reference cooking process.

[0050] Detailed description of the accompanying drawings

[0051] Embodiments of the disclosed apparatus, method, and system include two parallel continuous cooking facilities, one line producing pre-hydrolyzed kraft dissolving pulp (PHK) and a second line producing kraft pulp (KP) via a kraft process (KP). An alternative embodiment includes two parallel production lines in which dissolving pulp is produced in a continuous PHK process and kraft pulp is produced in a batch kraft process. The PHK process may include one or more vessels.

[0052] Figure 1 The configuration of a continuous prehydrolysis kraft (PHK) cooking facility for dissolving grade pulp production is shown in one embodiment. In this embodiment, wood chips 101, water 105 and steam 110 are fed into a vessel 115 where the prehydrolysis reaction takes place. Water and / or evaporation facility clean condensate is added, for example, in an amount of 0.5-5 m³ / min relative to the wood input flow. 3 / BDtw, or 1-3m 3 The prehydrolysis temperature in the PHV vessel can be controlled by steam flow to achieve a target prehydrolysis strength (P factor) at a given chip retention time, for example, a temperature range of 140-175°C for a P factor in the range of 50-1000 units.

[0053] As the hemicellulose is gradually degraded and dissolved, the liquid phase of the reactor is converted into a hydrolyzate. Under the above conditions, up to 5 m3 of hemicellulose can be separated from the wood chip stream, for example, by a filter on the pre-hydrolysis vessel 115. 3 / BDtw or up to 2m 3 The hydrolyzate of BDtw is then sent to a parallel kraft pulping line for recovery. The wood chips are transferred to a second vessel (digester) 120 where they are cooked to produce dissolving grade pulp 125.

[0054] Embodiments of the disclosed apparatus, methods, and systems include implementing methods A and / or B to reuse the hydrolyzed liquid in a second parallel production line, which can help reduce overall specific wood consumption.

[0055] Figure 2This represents one embodiment of method A. The wood chips 201 and the hydrolyzed liquid 205 can be continuously fed into a vessel 210 and acid impregnated at a temperature of 70-125°C for up to 180 minutes or 40-100 minutes. In some embodiments, the hydrolyzed liquid can be fed in a manner that includes up to 5 m 3 / BDtw or 0.5-2m 3 The amount of wood impregnated with hydrolysate 215 is adjusted to the desired impregnation temperature and / or cooled in an indirect heat exchanger. The hydrolysate impregnated wood chips 215 are transferred from the vessel outlet to a subsequent digester 220 for continuous kraft cooking to produce papermaking grade wood pulp 225.

[0056] Figure 3 This represents another variation of Method A. In this embodiment, the chips and hydrolyzed liquor 301 are fed directly into the top of the digester 305, rather than into separate vessels. In this embodiment, acid impregnation occurs in the topmost region of the digester, using the same mass quantities, impregnation times, and temperatures as described above. At the start-up of the designed section of the alkaline cooking process, excess hydrolyzed liquor can be extracted and replaced with white liquor 310 and / or other alkaline liquor to neutralize and alkalize the acidic chips and remaining hydrolyzed liquor. Following neutralization, the subsequent cooking zone is typical of any kraft cooking process and will not be further described.

[0057] The above method A can be further derived into embodiments in which the KP production line includes a batch cooking system. In these embodiments, the hydrolyzed liquid can be, for example:

[0058] - cooled and fed into the top of the digester simultaneously with the chips; or

[0059] - After being loaded with chips, they are injected into the bottom of the digester and further displaced through the digester by injecting liquid (such as white liquor and / or other alkali liquor) to neutralize and alkalize the acidic chips and remaining hydrolyzate.

[0060] Figure 4 An embodiment of method B is shown. In a continuous cooking digester 401 comprising multiple zones, the dry wood input flow is up to 2 m 3 In an embodiment, the hydrolyzed liquor 405 is added to, for example, the lowest cooking zone (e.g., the final cooking zone) in an amount of 100 / bdt. A matching amount of black liquor 410 can be withdrawn from the digester so that the liquor-to-wood flow ratio is not adversely affected by the addition of the hydrolyzed liquor. In this embodiment, the retention time in the combined precipitation / cooking stage can be 30-90 minutes, the residual available alkali calculated as NaOH is less than 10 g / l, and the temperature is typical of a kraft cooking process (140-170°C).

[0061] In an alternative embodiment of method B for a batch cooking system, the hydrolyzed liquor 405 can be added to the digester 401 at an intermediate time during the cooking phase, for example, mixed with the cooking liquor in the digester and circulated for the remaining cooking time, displaced through the digester (in a system without a circulation pump), and / or the like.

[0062] Figure 5 Shown is a comparison of the cooking screen yield 501 for embodiments of methods A and B for kraft pulp over a wide range of kappa numbers 505, in one embodiment, to a reference cooking process.

[0063] Table 2 shows the absolute increase in screen cook yield for embodiments of Method A over a wide range of retention times and at comparable Kappa numbers.

[0064] Table 2

[0065] Method A - Screening for Increased Cooking Yield at Different Retention Times

[0066]

Claims

1. A method for increasing pulp yield in a kraft cooking facility, comprising: Utilizing an acidic hydrolysate stream from an adjacent pre-hydrolysis kraft process producing dissolving wood pulp, wherein the kraft cooking facility is a parallel cooking facility producing conventional kraft pulp, wherein the acidic hydrolysate stream containing dissolved hemicellulose and produced by pre-hydrolyzing wood chips in an aqueous phase is reused in the kraft cooking facility; and The acidic hydrolysis solution is used to pre-treat and impregnate wood chips in the kraft cooking facility prior to the alkaline cooking process.

2. The method according to claim 1, wherein the acid impregnation is carried out in a vessel located before the alkali digester.

3. The process according to claim 1, wherein the acid impregnation is carried out in an alkali digester.

4. The method of claim 1, wherein the sheet is impregnated with the acidic hydrolysis solution for 2 to 180 minutes.

5. The method of claim 1, wherein the sheets are impregnated with the acidic hydrolysis solution at a temperature of 70-125°C.

6. The method according to claim 5, wherein the sheets are impregnated with the acidic hydrolysis solution at a temperature of 90-100°C.

7. The method of claim 1, wherein the acidic hydrolyzate is injected into the cooking zone of a digester.

8. The method of claim 7, wherein the acidic hydrolyzate is injected into the last of a plurality of cooking zones.

9. The method according to claim 7, wherein the residual effective alkali concentration in the cooking zone is 10 g / l or less.

10. The method of claim 7, wherein the slice retention time in the cooking zone is 30-90 minutes.

11. A method for producing a sulfate slurry, comprising: extracting an acidic hydrolysate from a prehydrolysis kraft process for producing dissolving wood pulp, wherein the acidic hydrolysate is produced by prehydrolyzing wood chips in an aqueous phase; The acidic hydrolysis solution is applied to a parallel kraft cooking process of a kraft cooking facility for producing conventional kraft pulp, including acid impregnation of wood chips with the acidic hydrolysis solution in the kraft cooking facility prior to an alkaline cooking process.

12. The method according to claim 11, wherein the wood chips are acid impregnated in a vessel located before the alkali digester.

13. The method of claim 11, wherein the wood chips are acid impregnated in an alkali digester.

14. The method of claim 13, wherein the acid pickling is performed in an acid pickling zone near the top of the alkali digester.

15. The method according to claim 11, wherein the acid impregnation is performed for a duration of 2 to 180 minutes.

16. The method of claim 11, wherein the acid impregnation is performed at a temperature of 70-125°C.

17. The method according to claim 16, wherein the acid impregnation is performed at a temperature of 90-100°C.

18. The method of claim 11, wherein applying the acidic hydrolyzate to the parallel kraft cooking process further comprises: The acidic hydrolyzate is injected into the cooking zone of the alkaline digester.

19. The method of claim 18, wherein the acidic hydrolyzate is injected into the last of a plurality of cooking zones of the alkali digester.

20. The method of claim 18, wherein the residual effective alkali concentration in the cooking zone is 10 g / l or less.

21. The method of claim 18, wherein the slice retention time in the cooking zone is 30-90 minutes.

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