Low-carbon strength chemimechanical non-wood pulp, by-product desilication and production

Abstract

A system and process for producing pulp and other bioproducts from non-wood raw materials are described. The non-wood raw materials are screened, desilicated, impregnated, mechanically refined to obtain a pulp stream, and then subjected to oxygen-alkali treatment. Lignin and silica are separated from the pulp stream to obtain pulp. Desilication is carried out at a first temperature using warm water, an alkaline solution, and / or an alkaline liquor with a low alkali charge to selectively separate silica from the non-wood raw materials. Impregnation is carried out at a second temperature using an alkaline solution with a low alkali charge to selectively separate lignin from the non-wood raw materials and prepare the pulp for mechanical refining. The oxygen-alkali treatment is carried out at a third temperature to separate more lignin from the pulp stream.

Description

Technical Field

[0001] The present invention generally relates to pulp production, and more particularly to producing pulp and other by-products from non-wood raw materials.

[0002] (Related Application) This application claims the priority of U.S. Application No. 63 / 350,276, filed on June 8, 2022, entitled "Low Carbon Intensity Chemi-Mechanical Non-Wood Pulp, Silica Removal and Production of By-Products". For the purposes of the United States, this application claims the benefit of U.S. Application No. 63 / 350,276, filed on June 8, 2022, entitled "Low Carbon Intensity Chemi-Mechanical Non-Wood Pulp, Silica Removal and Production of By-Products", under 35 USC §119, the entire text of which is incorporated herein by reference.

Background Art

[0003] Pulp is an important material used in the industrial production of paper products. In conventional pulp production, wood is decomposed by chemical or mechanical means to separate lignin from cellulose fibers. Next, the cellulose fibers are screened, washed, dried, and collected as pulp in preparation for papermaking. Conventional pulp production processes contribute to problems such as climate change and pollution and may have an adverse impact on the environment. Sustainability in the paper industry is required by finding ways to reduce industrial pressure on forests, excessive water use, and fossil fuel consumption. For example, various non-wood raw materials are being considered as candidate materials for pulp production. Unlike wood-based raw materials typically obtained through environmentally harmful practices such as deforestation, non-wood raw materials can be obtained from by-products (e.g., wheat straw, which is a by-product of wheat grain harvesting).

[0004] However, although desirable from an environmental perspective, non-wood raw materials can be difficult to process for several reasons compared to conventional wood-based raw materials. First, non-wood raw materials tend to be less uniform (e.g., straw raw materials are overly long) and have a lower bulk density compared to wood raw materials, resulting in potential equipment clogging and operational losses. Second, non-wood raw materials tend to have a high fines content, which adversely affects the properties of the pulp and reduces the productivity of the mill due to pulp discharge limitations. Third, non-wood raw materials tend to have a high silica content, which fouls process equipment and reduces its efficiency. The high silica content also impairs the lignin precipitation process necessary to improve the treatability of the waste liquor (i.e., high levels of silica present in the process liquor can co-precipitate colloidal-ly, thereby impairing filtration and making lignin removal difficult). In some cases, the lignin precipitation process is further impaired by the presence of hemicellulose in the by-product stream (e.g., black liquor), which can contribute to the formation of hydrogels. The above problems generally result in a process with limited advantages and poor energy efficiency compared to conventional wood pulp production.

[0005] Furthermore, pulp manufactured from non-wood raw materials using existing technologies tends to have a slower drainage rate compared to conventional wood-derived pulp. Due to the slow drainage rate, it is necessary to process non-wood pulp in larger equipment. Also, non-wood pulp typically has a lower tensile strength compared to wood pulp. High-kappa (value) chemi-mechanical non-wood pulp generally has a higher lignin content compared to low-kappa (value) chemical non-wood pulp. The increase in lignin content and keratinization (i.e., inhibition of re-swelling of the pulp fibers after drying) that occurs during flash drying of non-wood pulp can potentially reduce the strength properties of the pulp.

[0006] There is a need for methods and systems to address the aforementioned challenges associated with manufacturing pulp from non-wood raw materials. There is a need for methods and systems that can efficiently process pulp filtrate from non-wood raw materials. systems are needed. SUMMARY OF THE INVENTION

[0007] Generally, this specification describes systems and processes for manufacturing pulp and other bioproducts from non-wood raw materials.

[0008] One aspect relates to a method for manufacturing pulp from non-wood raw materials. This method includes a step of desilicating the non-wood raw material to selectively remove silica, a step of impregnating the desilicated non-wood raw material to selectively separate lignin, a step of mechanically refining the impregnated non-wood raw material to obtain a pulp stream, a step of subjecting the pulp stream to an oxygen-alkali treatment to separate additional lignin from the pulp stream, and a step of removing the separated lignin from the pulp stream. The desilication step is carried out at a first temperature. The impregnation step is carried out at a second temperature using an alkali solution with a low alkali charge. The oxygen-alkali treatment is carried out at a third temperature.

[0009] In some embodiments, the non-wood raw material is desilicated with a compound solution. The compound solution may be sodium carbonate, sodium hydroxide, or potassium hydroxide. In some embodiments, the non-wood raw material is mechanically desilicated with a mechanical pulper. The concentrated filtrate containing the separated silica may be removed from the flow of the non-wood raw material with a mechanical press.

[0010] In some embodiments, the first temperature ranges from 50°C to 100°C. In some embodiments, the second temperature ranges from 100°C to 130°C. In some embodiments, the third temperature ranges from 95°C to 130°C. The second temperature may be higher than the first temperature. The third temperature may be lower than the second temperature. The third temperature may be higher than the first temperature.

[0011] In some embodiments, the impregnated non-wood raw material is mechanically refined at a medium to high concentration. For example, the impregnated non-wood raw material may be mechanically refined at a concentration level in the range of 8% to 40%. In some embodiments, water is removed from the pulp stream after completion of the oxygen-alkali treatment. To remove water from the pulp stream, the pulp stream may be dried with superheated steam.

[0012] In some embodiments, the method includes decomposing a non-wood raw material, cutting the decomposed non-wood raw material to a nominal length, and then desilicating the cut non-wood raw material. The nominal length can be in the range of 40 mm to 100 mm. In some embodiments, the cut non-wood raw material can be screened to remove fines before and / or before impregnating the screened non-wood raw material with an alkaline solution. The cut non-wood raw material can be screened by a primary screen and a secondary screen. The primary screen and the secondary screen can be pyramid screens. The primary screen has a set of slots spaced between a set of rolls, and the width of each slot of the set of slots defines a set of internal roll openings. The secondary screen has a second set of slots spaced between a second set of rolls, and the width of each slot of the second set of slots defines a second set of internal roll openings. The first internal roll opening can be about 1 mm, and the second internal roll opening can be about 2 mm. In some embodiments, the screened non-wood raw material is washed before being desilicated.

[0013] Another aspect relates to a method for producing pulp from a non-wood raw material, the method comprising chemically treating a stream of the non-wood raw material with a first alkaline solution, performing an oxygen-alkaline treatment on the stream of the desilicated non-wood raw material, and removing separated silica and separated lignin from the stream to obtain pulp. The desilication is carried out at a first temperature. The delignification is carried out at a second temperature. The second temperature may be higher than the first temperature.

[0014] Another aspect relates to a system for manufacturing pulp from non-wood raw materials. The system includes an apparatus for desilicating non-wood raw materials at a first temperature to selectively remove silica, and an impregnation tube for impregnating non-wood raw materials with an alkaline solution at a second temperature to selectively separate silica. The alkaline solution has a low alkaline charge. The system includes a mechanical refining apparatus for refining the impregnated non-wood raw materials into a pulp stream, and a reaction tower for receiving the pulp stream. The reaction tower is configured to receive oxygen and steam and perform an oxygen-alkaline treatment on the pulp stream to separate lignin. The system may also include a post-treatment apparatus connected to the reaction tower for removing the lignin separated from the pulp stream.

[0015] A further aspect of the present invention will become apparent from the following description.

[0016] The features and advantages of embodiments of the present invention will become apparent from the following detailed description when taken in conjunction with the accompanying drawings.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

[0018] Description paragraph of FIG. 2

[0019] Description paragraph of FIG. 3

Examples

[0020] The following description and the embodiments described therein are provided to illustrate examples of specific embodiments of the principles of the present invention. These examples are provided to explain those principles and the present invention and are not limiting.

[0021] Aspects of the present invention relate to systems and processes for manufacturing pulp and, optionally, by-products (e.g., bioproducts) from non-wood raw materials. For ease of explanation, in this specification, the term "non-wood" is used to refer to products such as straw and / or other agricultural residues remaining after harvesting. The term "straw" as used in this specification includes, but is not limited to, wheat straw, barley straw, oat straw, flax straw, rice straw, hemp, bamboo, pampas grass, sorghum, switchgrass, ryegrass, corn stover, bagasse, and banana trees.

[0022] The system and process can include treating the non-wood raw material with an alkaline solution and / or an alkaline liquor in one or more steps. For ease of explanation, in this specification, the term "alkaline solution" is used to refer to a solution containing only inorganic dissolved solids of a compound (e.g., Na 2 CO 3 , NaOH, KOH, etc.). For ease of explanation, in this specification, the term "alkaline liquor" is used to refer to a solution containing both inorganic dissolved solids of a compound (e.g., Na 2 CO 3 , NaOH, KOH, etc.) and organic dissolved solids (e.g., lignin, cellulose, hemicellulose, etc.).

[0023] Exemplarily, the systems and processes described herein overcome issues associated with increasing the silica level of non-wood raw materials to provide a low-carbon intensity solution for the manufacture of non-wood pulp. It can be done. For example, the systems and processes described herein can overcome problems related to keratinization during the pulp manufacturing process. By overcoming such problems, the non-wood pulp produced has a reduced fines content and / or improved material properties. Further, the systems and processes described herein can provide improved drainage treatability, lignin precipitation, and filterability. This can help facilitate the valorization of straw fines, sulfur-free lignin, and silica as by-products such as biofuel pellets, sodium silicate, etc. Also, the systems and processes described herein can increase the drainage rate of non-wood pulp and enable the miniaturization of the equipment necessary to efficiently process non-wood pulp.

[0024] Figure 1 is a flowchart of a process 10 for manufacturing pulp 4 from a non-wood raw material 2 (e.g., straw raw material) according to one embodiment. Process 10 is a hybrid pulping process that manufactures pulp 4 from raw material 2 using a combination of chemical and mechanical means. Such a hybrid process provides a relatively low carbon intensity solution for the manufacture of non-wood pulp by leveraging both the advantages of chemical pulping (e.g., selectivity and pulp strength) and the advantages of mechanical pulping (e.g., high yield). Process 10 can be utilized to manufacture pulp 4 from various different types of straw raw materials 2 and other types of non-wood raw materials. For ease of explanation herein, process 10 is described in relation to straw raw material 2.

[0025] Process 10 begins with an optional straw preparation step 20. Straw preparation step 20 consists of separating fines 6 from straw raw material 2 and removing the separated fines 6 as a dry material. To remove fines 6 in step 20, straw raw material 2 can be screened or passed through one or more screens. The fines 6 removed from straw raw material 2 can optionally be converted into useful by-products such as pellet fuel products in an auxiliary process. (See, for example, Figure 3).

[0026] In one embodiment, step 20 includes pretreating the straw raw material 2 before passing it through the screen. The pretreatment of the straw raw material 2 may include releasing the stacking, releasing the bundling, and / or decomposing large bundles of straw. The loose straw is then cut into a relatively uniform length, either individually or in batches. For example, the loose straw may be cut to a length in the range of about 40 mm to about 100 mm (50 mm in certain embodiments). Long bundles of straw can cause operational problems in the non-wood pulping operation. Therefore, in order to reduce such problems, it may be desirable to cut long bundles of straw to a more nominal length. Cutting long bundles of straw to a more nominal length can reduce the variation in the final pulp product, increase the bulk density of the raw material 2, and / or improve the reliability of the overall pulping process 10.

[0027] To prepare the straw in step 20, the pretreated raw material 2 is transferred to the screening system. The pretreated raw material 2 may be transferred to the screening system via, for example, a belt conveyor system. The belt conveyor system may include a detection system that rejects the pretreated straw raw material 2 if there are residual twist yarns present. If the pretreated straw raw material 2 is rejected (failed) by the detection system, it may be returned for further pretreatment before being transferred to the screening system.

[0028] The screening system may include one or more layers or stages of screens. Each layer of the screen may have openings for removing the straw fines 6 from the supply stream of the raw material 2 (i.e., the straw fines 6 are removed from the raw material 2 as they pass through the openings). Each layer of the screen may have openings of different sizes.

[0029] The screening system may optionally include a dust collection system for collecting dust in the raw material 2. The dust collection system may include dust hoods disposed at various transfer points of the raw material 2. The dust hoods may be connected to one or more draft fans, etc. The draft fan may operate to draw dust into a baghouse or the like, where the dust is filtered from the air. The dust collection system can help prevent the accumulation of straw dust and fine powder 6 in the factory for housekeeping and fire prevention purposes.

[0030] In one embodiment, the screening system includes two levels of screens (i.e., a primary screen and a secondary screen). Each level of the screen includes slots spaced between rolls. Each level of the screen may be, for example, a pyramid roll screen. Each level of the screen may be configured to classify the raw material 2 into an acceptable stream (e.g., a stream containing straw longer than a threshold length) and a reject stream (e.g., a stream containing fine powder of straw) based on length or other dimensions. The screen may be configured, for example, by adjusting the size of the gap between slots or the spacing between rolls. The size of the gap between slots or the spacing between rolls may be referred to herein as the internal roll opening (IRO). The IRO may be adjusted before or during operation of the screening system. In certain embodiments, this feature allows optimization of the screening process during operation. For example, the IRO may be varied to control the amount or size of the fine powder 6 filtered from the raw material 2.

[0031] In one embodiment, the fine powder 6 of the first screening level falls from between the slots of the rolls, for example, onto a fine powder belt conveyor and enters the reject stream, while the "overs" (i.e., straw longer than the threshold length) are discharged from the first level to one or more subsequent screen levels. One or more subsequent screen levels may be configured to screen relatively large fine powder 6 or fine powder 6 not screened by the previous screen level. For example, the IRO of the first level screen may be set to about 1 mm, and the IRO of the next or second level screen may be set to about 2 mm.

[0032] In one embodiment, relatively large fines 6 in the second-level screening fall from between the roll-to-roll slots, for example, onto a fines belt conveyor, while the oversize is discharged from the second-level screen.

[0033] The fines 6 removed from the feed by the second-level screen may be collected together with the fines 6 removed by the first-level screen. The collected fines 6 may be stored for further processing or provided to a separate or auxiliary system. For example, the collected fines 6 may be transported to a straw pellet factory for producing biofuel pellets.

[0034] Since non-wood raw materials such as straw raw material 2 essentially have a high concentration of fines 6 that add little value to pulp properties, it may be desirable to pretreat the straw raw material 2 by the above-described method during any preparation step 20. By removing fines 6 and / or straw dust as dry materials from the straw raw material 2, it can be more efficiently converted into value-added by-products (such as biofuel pellets) that can be used, for example, for power generation.

[0035] The flow of straw raw material 2 output by the screening system may be washed by a straw washing system (e.g., by a belt conveyor) before being transported to the next process stage. The washing system may be included as part of the screening system or provided as a separate system. The washing system may wash the straw with warm water. Agricultural raw materials typically have a high concentration of sand, gravel, and rock due to the nature of the harvesting operation, so it may be desirable to wash the raw material 2 before the pulping operation to remove debris and contaminants. Further, the washed straw can absorb alkaline cooking chemicals more uniformly, as described elsewhere in this specification, and the properties of the pulp become more consistent (i.e., lower variability in kappa number).

[0036] ​Optionally, the allowable flow of the straw raw material 2 may pass through a mass meter before being desilicated in step 25. The mass meter may be configured to monitor the total mass flow rate of the straw raw material 2.

[0037] After completing the straw preparation step 20, the process 10 proceeds to step 25, where the allowable flow of the raw material 2 is treated with warm water or a chemical solution (e.g., an alkaline solution) to pre-filter or otherwise separate a portion of the silica 7 from the flow of the raw material 2. The chemical treatment may be carried out over a period of 10 minutes to 30 minutes or more. In some embodiments, the flow of the raw material 2 is heated and chemically desilicated with compounds such as sodium carbonate, sodium hydroxide, potassium hydroxide. The raw material 2 may be treated with warm water without adding an alkaline chemical in step 25. In contrast to organic compounds such as weak black liquor that cause lignin to co-precipitate with silica during pH adjustment, the compounds used in the desilication step 25 can preferentially separate the silica 7 from the flow of the raw material 2.

[0038] To preferentially separate the silica 7 from the raw material 2, the desilication step 25 may be carried out at a temperature in the range of 50°C to 100°C under atmospheric pressure. When a strong alkali (e.g., NaOH) is used in step 25, silica removal can be prioritized over the delignification reaction at a relatively low reaction temperature (e.g., about 60°C or lower). When a weak alkali (e.g., Na 2 CO 3 ) or warm water is used, a relatively high reaction temperature (e.g., about 90°C or lower) may be required to prioritize silica removal over the delignification reaction. In some embodiments, the desilication step 25 is carried out at a relatively low concentration level or a concentration in the range of 1% to 5%.

[0039] In some embodiments, mechanical desilication is added to the chemical desilication of the raw material 2 to provide a chemical-mechanical process in step 25. In such embodiments, the desilication step 25 may include mechanically pulping the flow of the raw material 2 after a chemical reaction (e.g., in an alkaline solution) that is heated to mechanically separate more silica 7 from the raw material 2.

[0040] When the desilication step 25 is completed, a relatively large amount of silica 7 is dissolved in the alkaline desilication liquid and selectively removed from the flow of the raw material 2 as shown in FIG. 1. The silica concentrated filtrate (i.e., the liquid containing dissolved silica) may be removed from the flow of the raw material by a mechanical press. Furthermore, trace metals (e.g., copper, iron, nickel, manganese, and other transition metals, etc.) may also be separated from the flow of the raw material 2 upon completion of step 25 and removed together with the silica concentrated filtrate.

[0041] Generally, it is difficult to precipitate or separate lignin from the raw material 2 in the presence of silica (i.e., silica can act as a protective barrier for lignin that hinders the delignification process), so it is desirable to remove silica 7 from the flow of the raw material 2 (e.g., as a sodium silicate solution) before delignification. Furthermore, generally, a mixture of lignin and silica may be difficult to manage in an auxiliary process, so it is desirable to avoid mixing lignin and silica in the black liquor (i.e., a by-product obtained from the process of digesting the raw material into pulp by removing lignin and other extracts from the raw material to liberate cellulose fibers) as much as possible. By performing the desilication step 25 before the impregnation step 30, the drainage property of the final pulp product can also be improved.

[0042] After completing the desilication step 25, the process 10 proceeds to the impregnation step 30, where the raw material 2 is heated and impregnated with compounds such as sodium carbonate, sodium hydroxide, potassium hydroxide, etc. In some embodiments, the impregnation step 30 is optional.

[0043] In contrast to conventional processes operated at high temperatures with strong alkalis to directly remove lignin from the raw material, the impregnation step 30 is typically carried out at a relatively low temperature (e.g., 130 °C or lower) using an alkaline impregnation solution having a relatively low alkali charge (e.g., low alkali soda). Thereby, in step 30, priority is given to selectively removing lignin 8A from the raw material 2 and preparing fibers for further downstream processing.

[0044] Compared with the desilication step 25, the impregnation step 30 is typically carried out under a relatively high pressure and / or at a relatively high temperature. In some embodiments, the impregnation step 30 is carried out under a pressure in the range of 1 bar to 11 bar. In some embodiments, the impregnation step 30 is carried out at a temperature of 100 °C to 130 °C. In some embodiments, the impregnation step 30 is carried out at a concentration in the range of 8% to 30%. The alkali compound used in step 30 can swell the fibers of raw material 2, making it more accessible for further purification and delignification downstream.

[0045] In addition to selective lignin removal and fiber preparation, the impregnation step 30 may also result in further separation and removal of trace metals (including but not limited to transition metals such as copper, iron, nickel, manganese, etc.) from raw material 2. This can be advantageous since high levels of transition metals in the pulp can negatively affect the performance and selectivity of the oxygen-alkali-based delignification step 50.

[0046] In some embodiments, the impregnation step 30 is carried out in an impregnation tube. The impregnation tube may be connected to a digestion blow tank. In some embodiments, the impregnation step 30 is carried out for about 15 to 25 minutes. In some embodiments, the impregnation step 30 consists of heating, immersing in an alkali solution, or mechanically pressurizing raw material 2 after squeezing or mechanically removing lignin 8A from raw material 2. When the impregnation step 30 is completed, a relatively large amount of lignin 8A dissolves in the alkali impregnation liquid and is removed as black liquor 8 from the flow of raw material 2 (see Figure 1). For example, 60% to 70% of the lignin originally contained in raw material 2 may be removed therefrom upon completion of step 30.

[0047] After the impregnation step 30, the process 10 proceeds to the purification step 40. In the purification step 40, the desilicated and impregnated raw material 2 is subjected to medium to high concentration purification. Here, the concentration is defined as the mass percentage of solids in the pulp slurry mixture (in other words, the ratio of solids in the pulp slurry mixture measured by mass). The purification level of the desilicated and impregnated raw material 2 may be, in certain embodiments, medium concentration purification (e.g., 8% - 12% concentration), medium to high concentration purification (e.g., 13% - 19% concentration), or high concentration purification (e.g., 20% - 40% concentration). Medium to high concentration purification may be carried out by a mechanical purification device. The mechanical purification device may be, for example, a roller line purification device. The mechanical purification device may include a stator and a rotor operable to move a set of one or more plates in a synchronized manner. The plates may be made of metal or other suitable materials. In some embodiments, the purification step 40 is carried out for about 1 - 3 minutes. The purification operation can be used to defibrate the chemically treated raw material 2 before additional lignin 8B is removed from the pulp stream purified in the delignification step 50.

[0048] In contrast to conventional mechanical pulping techniques carried out at low concentrations (e.g., 3% - 4% concentration), the medium to high concentration purification step 40 can promote fiber - to - fiber contact and reduce fiber - to - metal contact. This allows the desilicated and impregnated raw material 2 to be purified in the pulp stream in a gentler manner.

[0049] After the purification step 40, the process 10 proceeds to a further delignification step 50. Delignification The delignification process 50 is typically carried out at a temperature in the range of 95°C to 130°C, although other temperatures are possible. The delignification process 50 includes performing an oxygen-alkali treatment on the pulp stream formed from the raw material 2 mechanically refined in process 40 to separate more lignin 8B therefrom. The oxygen-alkali treatment is carried out by adding oxygen, alkali, and steam to the refined pulp stream. In one embodiment, the amount of oxygen added is about 1% to 3% by mass, and the amount of alkali added is about 2% to 10% by mass. Examples of suitable alkali compounds include, but are not limited to, sodium hydroxide, potassium hydroxide, and other strong alkali compounds. In one embodiment, an auxiliary compound such as hydrogen peroxide is added to the oxygen and alkali streams during process 50. Additional compounds such as magnesium sulfate may also be utilized to enhance the selectivity of the oxidation reaction.

[0050] Compared with the impregnation process 30, the delignification process 50 is typically carried out at a lower temperature, a lower pressure level (e.g., 2 bar to 7 bar), and a lower concentration (e.g., 8% to 12%). Generally, the delignification process 50 removes lignin more selectively than other carbohydrates (e.g., cellulose and hemicellulose) that may remain in the non-wood fibers contained in the raw material 2. Performing the delignification process 50 can, in some cases, help produce a final pulp product 4 with a brighter and / or improved color characteristic of L*a*b* (i.e., lightness, red / green value, blue / yellow value).

[0051] The oxygen-alkali treatment carried out in process 50 can also move the silica remaining in the pulp (i.e., the residual silica not removed in process 25) onto the pulp fibers and remove it from the alkaline process liquid. The oxygen-alkali treatment may be carried out in a reaction tower or the like. In a particular embodiment, the oxygen-alkali treatment is carried out for about 30 to 60 minutes.

[0052] In one embodiment, an in-line booster pump or the like is configured to maintain the pressure in stages and transport the refined pulp to a downstream blow tank or the like, where a chemical / vapor mixer facilitates the addition of oxygen and steam to the refined pulp stream before entering the reaction tower. The pressure may be maintained, for example, at about 4 bar to 6 bar.

[0053] After the delignification step 50, the process 10 proceeds to the post-treatment step 60. In the post-treatment step 60, the lignin 8B separated from the pulp stream during the step 50 is removed from the pulp stream. In one embodiment, the step 60 includes washing the pulp stream to remove the black liquor 8 containing the lignin 8B from the pulp. In one embodiment, the ratio of the amount of lignin removed in the step 30 to the amount of lignin removed in the step 60 is about 2:1. For example, at the completion of the step 50, 20% to 30% of the lignin originally contained in the raw material 2 may be removed therefrom.

[0054] The lignins 8A, 8B removed from the pulp stream may be collected for use in one or more supplementary processes (e.g., the supplementary process 80 in FIG. 3). The post-treatment step 60 may also include one or more pulp screening stages. Pulp screening includes the removal of fines from the pulp produced in the step 50. By removing the primary and secondary fines after the oxygen-alkali treatment, the drainage rate of the pulp is improved, and the surface area of the dewatering device required for pulp treatment is reduced. This saves capital costs and improves pulp properties.

[0055] When the process 60 is completed, typically a high kappa (value) pulp stream (e.g., a pulp stream with a kappa value exceeding 30) is obtained. In the pulp and paper industry, the kappa value is a dimensionless indicator showing the bleachability of the pulp. The kappa value is approximately proportional to the residual lignin content of the pulp. The kappa value can be defined as the product of a constant and the percentage of lignin content (e.g., the kappa value is approximately equal to 6.578×L. Here, L is the percentage of lignin content). In some embodiments, the kappa value of the pulp stream exceeds 30. For example, the kappa value of the pulp stream is in the range of 4 to 50 in some applications (e.g., unbleached paper towels). A low standard deviation and a high kappa value are good indicators showing high uniformity of the pulp stream.

[0056] Since values higher than the pulp kappa value of the pulp stream and silica 7, lignin 8A, and 8B are removed independently (i.e., silica 7 is removed in process 25, and lignin 8A, 8B are removed in processes 30 and 50), the discharge characteristics of the black liquor 8 can be improved and can be improved to a reduced level in terms of biochemical oxygen demand (BOD), chemical oxygen demand (COD), and toxicity.

[0057] The above processes of process 10 can, alone or in combination, help to enhance the selective removal of lignin 8A, 8B from the straw while reducing the amount of silica 7 in the impregnating liquid and the oxygen-alkali cooking liquor. For example, combining the targeted delignification in process 50 and the fines removal in the filtrate in process 60 improves the drainage characteristics of the pulp stream and the pulp properties. Furthermore, the reduced processing temperature requirements (e.g., both the impregnation process 30 and the delignification process 50) reduce the carbon intensity required to produce non-wood fibers with properties suitable for use as pulp.

[0058] After the post-treatment step 60, the pulp stream is dried in step 70 to form the final pulp product 4. In some embodiments, the pulp stream is moved to a high-density storage before being transported to the pulp drying and final area. The pulp drying and final area may include one or more drying sections (e.g., those equipped with fans and cyclone separators), a pulp cooling stage, an exhaust scrubber, a gas burner, a reboiler, and a superheater. In such embodiments, the pulp stream may be supplied from the high-density storage to a press (e.g., a twin roll press (TRP)) that operates in parallel to dewater the pulp stream. The dewatered pulp (e.g., pulp with a concentration exceeding 48%) from each TRP is metered by a pressure specified sensor device (PSSD) by a rotary valve.

[0059] In some embodiments, the drying of the pulp in step 70 is performed using superheated steam. The water evaporated from the pulp stream by the superheated steam treatment is removed from the dryer and can be used for heating the process. For example, the water may be used to heat the stream of the raw material 2 in the impregnation step 30 and / or the delignification step 50. Under steady-state operating conditions, the superheated steam dryer used in step 70 can generate steam at about 2.8 bar. This steam can replace boiler steam, low-quality steam, and high-quality warm water (e.g., heated to 130°C). Integrating these energy streams into the pulping process can reduce the carbon footprint compared to other thermal drying processes. Furthermore, using superheated steam can improve the pulp properties of high-kappa (value) pulp. For example, high-kappa (value) pulp dried with superheated steam is generally bulkier, stronger, tougher, and more rigid than conventional flash-dried pulp. High-kappa (value) pulp dried with superheated steam can also have a more desirable color (e.g., a darker or richer color) compared to conventional flash-dried pulp.

[0060] Process 10 may be implemented by various devices that collectively form a chemo-mechanical system for manufacturing pulp 4 from non-wood raw material 2. This system may be installed within pulp manufacturing plant 200 or otherwise provided (see, for example, FIG. 3).

[0061] FIG. 2 is a schematic diagram of an exemplary embodiment of a system 100 that can be used to implement a process of the type shown in FIG. 1. System 100 includes an impregnation tube 102 located upstream of blow tank 104. Impregnation tube 102 may be designed or adapted to perform step 30 of process 10. Impregnation tube 102 has a chamber for impregnating washed straw or other raw material 2 prepared in step 20 and desilicated in step 25 with steam and one or more alkali compounds. Blow tank 104 may be operated to transfer desilicated and impregnated raw material 2 from the chamber of impregnation tube 102 to refining device 106 at a desired pressure and / or concentration level.

[0062] Press 105 is disposed between impregnation tube 102 and refining device 106. Press 105 may be disposed upstream or downstream of blow tank 104. In some cases, it may be advantageous to dispose press 105 upstream of blow tank 104, thereby reducing the energy consumption required to treat black liquor 8 in subsequent processes. In the embodiment shown in FIG. 2, press 105 is provided between blow tank 104 and refining device 106 and squeezes or mechanically removes the press liquor carrying separated lignin 8A from the remainder of the stream carrying desilicated and impregnated raw material 2. The press liquor may be stored in tank 107 before being transferred to an auxiliary system for further processing (see, for example, process 80 of FIG. 3).

[0063] Refining device 106 receives desilicated and impregnated raw material 2 from blow tank 104. Refining device 106 can be designed to perform step 40 of process 10. In the example shown in FIG. 2, refining device 106 also receives one or more alkali compounds to support mechanical refining. The alkali compound supplied to the refining device 106 may be the same compound as that supplied to the impregnation tube 102, or may be a different compound in other embodiments. The refining device 106 can be appropriately configured to refine the impregnated raw material 2 at a medium to high concentration.

[0064] The dilution conveyor 108 is disposed downstream of the refining device 106. The dilution conveyor 108 can be operated to transfer the refined pulp stream to the oxygen-alkali reactor 110 and perform step 50 therein. In one embodiment, the system 100 includes a mixer 109 disposed between the dilution conveyor 108 and the reactor 110. The mixer 109 can be operated to mechanically mix the pulp stream with steam and / or oxygen and send the mixture to the reactor 110.

[0065] The downflow tower 112 is disposed downstream of the oxygen-alkali reactor 110. The downflow tower 112 is designed to function as a storage buffer between the reactor 110 and additional screening and pulp washing devices (not shown) disposed further downstream. The downflow tower 112 includes a port for receiving the dilution filtrate and a chamber for mixing the dilution filtrate with the pulp. Since it may be difficult to pump the pulp at a higher concentration, the downflow tower 112 can provide additional reaction time necessary to dilute the pulp to a relatively low concentration before pumping the diluted pulp to the screening and pulp washing devices.

[0066] Within the scope of the present invention, a wide range of variations and additions are possible. These include supplementary processes that can be carried out in conjunction with the main process 10 for manufacturing the pulp 4 described herein. FIG. 3 shows some exemplary supplementary processes 80, 82, 84 that can be incorporated into or combined with the process 10 to produce useful by-products from the non-wood raw material 2.

[0067] In one exemplary auxiliary process, a lignin precipitation step 80 is incorporated to convert the black liquor 8 produced in process 10 into materials useful for electronic device applications (e.g., supercapacitors) and / or chemical applications (e.g., chemical emulsions, chemical adhesives, etc.). In another exemplary supplementary process, a thermal process 82 (e.g., hydrothermal liquefaction process) is incorporated to produce low-carbon transport fuels from the fines 6 and the black liquor 8. In another exemplary supplementary process, a pelletization process 84 is incorporated to produce biofuel pellets from the fines 6. In another exemplary supplementary process, a silica precipitation process 90 is incorporated to convert the silica compound (e.g., sodium silicate) produced in the desilication step 25 into materials such as silicic acid for use in additional high-value products. for use in materials such as silicic acid.

[0068] The examples and corresponding figures used herein are for illustrative purposes only. Different configurations and terms can be used without departing from the principles represented herein.

[0069] Although the present invention has been described with reference to specific embodiments, various changes will be apparent to those skilled in the art without departing from the scope of the present invention. The scope of the claims should not be limited by the exemplary embodiments described in the examples, but the broadest interpretation consistent with the entire description should be given. For example, in this specification, various features are described as being present in "some embodiments" or "an embodiment". Such features are not essential and may not be present in all embodiments. Embodiments of the present invention may include such features in any combination of 0, 1, or 2 or more. This is provided that no particular one of such features is limited to the extent that it is incompatible with other ones of such features and it is not possible for a person skilled in the art to construct a practical embodiment combining such incompatible features. Thus, the description that "some embodiments" have feature A and "some embodiments" have feature B should be interpreted as explicitly indicating that the inventor has also contemplated embodiments combining feature A and feature B (except where the description states otherwise or where feature A and feature B are fundamentally incompatible).

Claims

1. A method for producing pulp from non-wood raw materials, The non-wood raw material is desilicated at a first temperature, and silica is selectively removed therefrom. The desilicated non-wood raw material is impregnated in an alkaline solution with a low alkali charge at a second temperature to selectively separate lignin from the desilicated non-wood raw material. The impregnated non-wood raw material is mechanically purified to obtain a pulp stream. The pulp stream is subjected to oxygen-alkali treatment at a third temperature to separate lignin from the pulp stream, and A method comprising removing lignin separated from the desilicatenated non-wood raw material and lignin separated from the pulp flow.

2. The method according to claim 1, wherein the non-wood raw material is desilicated with a compound solution.

3. The method according to claim 2, wherein the compound solution comprises sodium carbonate, sodium hydroxide, or potassium hydroxide.

4. The method according to claim 1, wherein the non-wood raw material is mechanically desilicated by a mechanical pulper.

5. The method according to claim 1, wherein the first temperature is in the range of 50°C to 100°C.

6. The method according to claim 1, wherein the second temperature is in the range of 100°C to 130°C.

7. The method according to claim 1, wherein the third temperature is in the range of 95°C to 130°C.

8. The method according to claim 1, wherein the second temperature is higher than the first temperature.

9. The method according to claim 1, wherein the third temperature is lower than the second temperature.

10. The method according to claim 1, wherein the third temperature is higher than the first temperature.

11. The method according to claim 1, wherein the impregnated non-wood raw material is mechanically purified to a medium to high concentration.

12. The method according to claim 1, wherein the impregnated non-wood raw material is mechanically purified to a concentration in the range of 8% to 40%.

13. The method according to claim 1, comprising decomposing the cut non-wood material before desilicatering the cut non-wood material, and cutting the decomposed non-wood material to a nominal length.

14. The method according to claim 13, wherein the nominal length is in the range of 40 mm to 100 mm.

15. The method according to claim 13, wherein the cut non-wood material is screened to remove fine powder before desilicatering the screened non-wood material.

16. The cut non-wood raw materials are screened by primary and secondary screens. The primary screen has a set of first slots arranged at intervals between the first rolls, The secondary screen has a set of second slots spaced apart between the second rolls, The width of each slot in the first set of slots defines the first internal roll opening, The method according to claim 15, wherein the width of each slot in the set of second slots defines a second internal roll opening.

17. The method according to claim 16, wherein the primary screen and the secondary screen are pyramidal screens.

18. The method according to claim 16, wherein the first internal roll opening is approximately 1 mm and the second internal roll opening is approximately 2 mm.

19. The method according to claim 15, comprising washing the screened non-wood raw material before desilicatering the washed non-wood raw material.

20. The method according to claim 1, comprising removing water from the pulp stream.

21. The method according to claim 1, comprising removing moisture from the pulp stream by drying the pulp stream with superheated steam.

22. A method for producing pulp from non-wood raw materials, The non-wood raw material is chemically treated with a first alkaline solution at a first temperature, and the first alkaline solution selectively separates silica from the non-wood raw material. To separate lignin from desilicified non-wood raw materials, The desilicated non-wood raw material is chemically treated with a second alkaline solution at a second temperature. The second temperature is higher than the first temperature, and A method comprising removing the separated silica and separated lignin from the flow.

23. A system for producing pulp from non-wood raw materials, An apparatus for desilicate non-wood raw materials at a first temperature and selectively remove silica therefrom. An impregnation tube is used to impregnate the desilicified non-wood raw material at a second temperature and selectively separate lignin therefrom. A mechanical refining apparatus that receives the impregnated non-wood raw material and refines the impregnated non-wood raw material into a pulp flow. A reaction tower configured to receive the pulp stream, receive oxygen and steam, and subject the pulp stream to oxygen-alkali treatment to separate lignin therefrom, and A system connected to the reaction tower, including a post-treatment device for removing separated lignin from the pulp flow.

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