Desiliconization and manufacture of low carbon strength chemical mechanical non-wood pulp and co-products

Abstract

Systems and methods for producing pulp and other biological products from non-wood feedstock are described. Non-wood feedstock is sieved, desiliconized, impregnated, and mechanically refined to obtain a pulp stream, which is then subjected to an oxygen-alkali treatment. Lignin and silica are separated from the pulp stream to obtain pulp. Desiliconization is carried out at a first temperature with hot water, an alkaline solution, and / or an alkaline solution having a low amount of alkali to selectively separate silica from the non-wood feedstock. Impregnation can be performed at a second temperature with an alkaline solution having a low amount of alkali to selectively separate lignin from the non-wood feedstock and produce pulp for mechanical refining. The oxygen-alkali treatment is performed at a third temperature to separate more lignin from the pulp stream.

Description

Technical Field

[0001] The present disclosure relates generally to pulp production, and more particularly to the production of pulp and other co-products from non-wood feedstocks.

[0002] Related Applications

[0003] This application claims priority to U.S. Application No. 63 / 350,276, filed on June 8, 2022, entitled “DESILICATION AND MANUFACTURE OF LOW CARBON INTENSITY CHEMI-MECHANICAL NON-WOOD PULP AND CO-PRODUCTS.” For U.S. purposes, this application claims the benefit of U.S. Application No. 63 / 350,276, filed on June 8, 2022, entitled “DESILICATION AND MANUFACTURE OF LOW CARBON INTENSITY CHEMI-MECHANICAL NON-WOOD PULP AND CO-PRODUCTS,” under 35 U.S.C. §119, which is incorporated herein by reference in its entirety. Background Art

[0004] Pulp is an important material used in the industrial production of paper products. In traditional pulp production, wood is decomposed by chemical or mechanical means to separate lignin from cellulose fibers. These cellulose fibers are then screened, cleaned, dried and collected as pulp to prepare for papermaking. Traditional pulp production processes may have an adverse impact on the environment due to problems such as climate change and pollution. It is necessary to reduce industrial pressure on forests, excessive water use and fossil fuel consumption by finding ways to make the papermaking industry sustainable. For example, various non-wood raw materials are considered as candidate materials for pulp production. Unlike wood-based raw materials typically obtained by harmful environmental practices like deforestation, non-wood raw materials can be obtained from by-products (e.g., wheat straw, by-products of harvesting wheat grains).

[0005] However, although it is desirable from an environmental point of view, non-wood raw materials may be difficult to process due to multiple reasons compared to traditional wood-based raw materials. First, compared to wood-based raw materials, non-wood raw materials tend to have less uniformity (e.g., straw raw materials may be too long) and lower bulk density, which may cause equipment clogging and operating losses. Second, non-wood raw materials tend to have increased fine powder content, which may adversely affect pulp properties and reduce mill productivity due to pulp drainage restrictions. Third, non-wood raw materials tend to have increased silica content, which may pollute process equipment and damage its efficiency. The increased silica content also damages the lignin precipitation process required for the treatability of the effluent (that is, the increased level of silica present in the process liquor can be co-precipitated in colloidal form, thereby damaging filtration and making lignin difficult to remove). In some cases, the lignin precipitation process is further damaged by the presence of hemicellulose in the by-product stream (e.g., black liquor), which may contribute to the formation of hydrogels. The above problems usually lead to a method with low energy efficiency, which has limited advantages compared to traditional wood-based pulp production.

[0006] In addition, compared with traditional wood-based pulp, pulp produced by non-wood raw materials using prior art tends to have a slower drainage rate. Slower drainage rate will require larger equipment to process non-wood pulp. Non-wood pulp also typically has lower tensile strength than wood-based pulp. High κ chemical mechanical non-wood pulp typically has higher lignin content than low κ chemical non-wood pulp. The increased lignin content and the hornyization (that is, the suppressed re-swelling of pulp fibers after drying) caused during flash drying of non-wood pulp may reduce the strength properties of pulp.

[0007] There is a need for methods and systems that address the above challenges associated with producing pulp from non-wood feedstocks. There is a need for methods and systems that can efficiently process pulp filtrate from non-wood feedstocks. Summary of the invention

[0008] In general, this specification describes systems and methods for producing pulp and other bioproducts from non-wood feedstocks.

[0009] One aspect relates to a method for producing pulp from a non-wood feedstock. The method comprises the steps of desiliconizing the non-wood feedstock to selectively remove silica therefrom, impregnating the desiliconized non-wood feedstock to selectively separate lignin therefrom, mechanically refining the impregnated non-wood feedstock to obtain a pulp stream, subjecting the pulp stream to an oxygen-alkali treatment to separate additional lignin from the pulp stream, and removing the separated lignin from the pulp stream. The desiliconization step is performed at a first temperature. The impregnation step is performed at a second temperature with an alkaline solution having a low alkali dosage. The oxygen-alkali treatment is performed at a third temperature.

[0010] In some embodiments, the non-wood feedstock is desiliconized with a compound solution. The compound solution can be sodium carbonate, sodium hydroxide, or potassium hydroxide. In some embodiments, the non-wood feedstock is mechanically desiliconized with a mechanical pulper. The enriched filtrate containing separated silica can be removed from the non-wood feedstock stream with a mechanical press.

[0011] In some embodiments, the first temperature is in the range of 50°C to 100°C. In some embodiments, the second temperature is in the range of 100°C to 130°C. In some embodiments, the third temperature is in the range of 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.

[0012] In some embodiments, the impregnated non-wood feedstock is mechanically refined at medium to high consistency. For example, the impregnated non-wood feedstock can be mechanically refined at a consistency level in the range of 8% to 40%. In some embodiments, water is removed from the pulp stream after the oxygen-alkali treatment is completed. Water can be removed from the pulp stream by drying the pulp stream with superheated steam.

[0013] In some embodiments, the method includes deconstructing the non-wood raw material and cutting the deconstructed non-wood raw material into a nominal length, and then desiliconizing the cut non-wood raw material. The nominal length can be in the range of 40mm to 100mm. In some embodiments, the cut non-wood raw material can be screened to remove fine powder, and then the screened non-wood raw material is desiliconized and / or the screened non-wood raw material is then impregnated 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 conical screens. The primary screen can have a first group of slots spaced apart between a first group of rollers, wherein the width of each slot in the first group of slots defines a first internal roller opening. The secondary screen can have a second group of slots spaced apart between a second group of rollers, wherein the width of each slot in the second group of slots defines a second internal roller opening. The first internal roller opening can be about 1mm, and the second internal roller opening can be about 2mm. In some embodiments, the screened non-wood raw material is washed before desiliconization.

[0014] Another aspect relates to a method for producing pulp from non-wood raw materials, the method comprising the steps of chemically treating a non-wood raw material stream with a first alkaline solution, oxygen-alkali treating the desiliconized non-wood raw material stream, and removing separated silica and separated lignin from the stream to obtain pulp. Desiliconization is performed at a first temperature. Delignification is performed at a second temperature. The second temperature may be higher than the first temperature.

[0015] Another aspect relates to a system for producing pulp from non-wood raw materials. The system includes a device for desiliconizing the non-wood raw material at a first temperature to selectively remove silica therefrom, and an impregnation tube for impregnating the non-wood raw material with an alkaline solution at a second temperature to selectively separate silica therefrom. The alkaline solution has a low alkali dosage. The system includes a mechanical refiner for refining the impregnated non-wood raw material into a pulp stream, and a reaction tower for receiving the pulp stream. The reaction tower is configured to receive oxygen and steam to perform an oxygen-alkali treatment on the pulp stream to separate lignin therefrom. The system may also include a post-treatment device connected to the reaction tower to remove the separated lignin from the pulp stream.

[0016] Further aspects of the invention will be apparent in view of the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Features and advantages of embodiments of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0018] Figure 1 is a flow chart of a method for producing pulp from non-wood feedstock according to an exemplary embodiment.

[0019] Figure 2 It can be used for implementation Figure 1 Schematic diagram of an exemplary embodiment of a system for various aspects of the method.

[0020] Figure 3 Describes the Figure 1 Exemplary complementary methods of combining or combining methods to produce other bioproducts from non-wood feedstocks. DETAILED DESCRIPTION

[0021] The following description and the embodiments described therein are provided by way of illustration of examples of specific embodiments of the principles of the present invention. These examples are provided for the purpose of explaining, rather than limiting, these principles of the present invention.

[0022] Aspects of the present invention relate to systems and methods for producing pulp and optionally co-products (e.g., bioproducts) from non-wood raw materials. For purposes of facilitating description, the term "non-wood" is used herein to refer to products remaining after harvest, such as straw and / or other agricultural residues. As used herein, the term "straw" includes, but is not limited to, wheat straw, barley straw, oat straw, flax straw, rice straw, hemp, bamboo, Miscanthus, sorghum, switchgrass, ryegrass, corn stover, bagasse, and banana trees.

[0023] These systems and methods may involve treating the non-wood feedstock with an alkaline solution and / or alkaline liquor in one or more steps. For the purpose of facilitating description, the term "alkaline solution" is used herein to refer to a solution containing only inorganic dissolved solids of a compound (e.g., Na2CO3, NaOH, KOH, etc.). For the purpose of facilitating description, the term "alkaline liquor" is used herein to refer to a solution containing both inorganic dissolved solids of a compound (e.g., Na2CO3, NaOH, KOH, etc.) and organic dissolved solids (e.g., lignin, cellulose, hemicellulose, etc.).

[0024] Illustratively, the system and method described herein can overcome the challenges associated with the silica levels of non-wood raw materials that increase to provide a low carbon intensity solution for producing non-wood pulp. For example, the system and method described herein can overcome the problems associated with keratinization during the pulp production process. By overcoming such problems, the non-wood pulp produced will have reduced fine powder content and / or improved material properties. In addition, the system and method described herein can provide improved effluent treatability, lignin precipitation, and filterability. This can help promote the added value of straw fine powder and sulfur-free lignin and silica as co-products (like biofuel pellets, sodium silicate, etc.). The system and method described herein can also increase the water filtration rate of non-wood pulp to allow the size of the equipment required for efficient processing of non-wood pulp to be reduced.

[0025] Figure 1 1 is a flow chart of a method 10 for producing pulp 4 from a non-wood raw material 2 (e.g., a straw raw material) according to one embodiment. Method 10 is a hybrid pulping method for producing pulp 4 from a raw material 2 using a combination of chemical and mechanical means. Such a hybrid method utilizes both the benefits of chemical pulping (e.g., selectivity and pulp strength) and the benefits of mechanical pulping (e.g., high yield) to provide a relatively low carbon intensity solution for producing non-wood pulp. Method 10 can be used to produce pulp 4 from various different types of straw raw materials 2 and other types of non-wood raw materials. For the purpose of facilitating description, method 10 is described herein with respect to straw raw materials 2.

[0026] The method 10 begins with an optional straw preparation step 20. The straw preparation step 20 includes separating fine powder 6 from the straw raw material 2 and removing the separated fine powder 6 as a dry material. To remove the fine powder 6 in step 20, the straw raw material 2 can be sieved or otherwise passed through one or more screens. The fine powder 6 removed from the straw raw material 2 can optionally be used in a supplementary method (e.g., see Figure 3 ) into useful co-products, such as pellet fuel products.

[0027] In one embodiment, step 20 comprises pre-treating straw raw material 2, and then makes pre-treated straw raw material 2 pass one or more screens.Pre-treatment of straw raw material 2 can comprise unstacking, unwinding and / or deconstructing one or more in straw bundle to provide loose straw.These loose straws can then be cut into relatively uniform lengths individually or in batches.For example, these loose straws can be cut into lengths (for example, in a particular embodiment, 50mm) within the range of about 40mm to about 100mm.In non-wood pulping operations, long straw bundles may cause operational problems.Therefore, it may be desirable to cut long straw bundles into more nominal lengths to alleviate such problems.Cutting long straw bundles into more nominal lengths can reduce the variability of final pulp products, increase the bulk density of raw material 2, and / or improve the reliability of whole pulping method 10.

[0028] To prepare the straw in step 20, the pre-treated raw material 2 is transferred to the screening system. The pre-treated raw material 2 can be transferred to the screening system, for example, by a conveyor belt system. The conveyor belt system can include a detection system that will reject the pre-treated straw raw material 2 if there is residual rope. If the pre-treated straw raw material 2 is rejected by the detection system, it can be returned for further pre-treatment before being transferred to the screening system.

[0029] The screening system may include one or more layers or one or more stages of screens. Each layer of the screen may have openings that remove the straw fines 6 from the feed stream of the raw material 2 (i.e., the straw fines 6 will be removed from the raw material 2 as they fall through the openings). Each layer of the screen may have openings of different sizes.

[0030] The screening system may optionally include a dust collection system for collecting dust from the raw material 2. The dust collection system may include dust hoods located at various transfer points of the raw material 2. The dust hoods may be connected to one or more ventilation fans, etc. The one or more ventilation fans may be operated to draw dust into a bag filter, etc., where the dust is filtered from the air. The dust collection system may help prevent straw dust and fines 6 from accumulating in the factory for housekeeping and fire prevention purposes.

[0031] In one embodiment, the screening system includes two levels of screens (i.e., primary screen and secondary screen). The screen of each level can include slots spaced apart between rollers. The screen of each level can be, for example, a tapered roller screen. The screen of each level can be configured to sort raw material 2 into an accepted stream (e.g., a straw stream with a length greater than a threshold length) and a rejected stream (e.g., a stream with straw fines) based on length or other dimensions. The screen can be configured, for example, by adjusting the gap size between the slots or the spacing between the rollers. The gap size between the slots or the spacing between the rollers can be referred to as an internal roller opening (IRO) in this article. IRO can be adjusted before or during the screening system operation. In a specific embodiment, this feature enables the screening process to be optimized during operation. For example, IRO can be changed to control the amount or size of the fines 6 filtered out from raw material 2.

[0032] In one embodiment, the fine powder 6 screened at the initial level will fall between the roller grooves onto, for example, a fine powder conveyor belt to enter the rejected stream, while the "overs" (i.e., straw with a length greater than a threshold length) will be discharged from the initial level to the screens of one or more subsequent levels. The screens of one or more subsequent levels can be configured to screen relatively large fine powders 6 or fine powders 6 that will not be screened out by the screens of the previous levels. For example, the IRO of the screen of the first level can be set to about 1 mm, and the IRO of the screen of the next level or the second level can be set to about 2 mm.

[0033] In one embodiment, the relatively large fine powder 6 screened at the second stage will fall between the roller grooves onto, for example, a fine powder conveyor belt, and the screened rejects will be discharged from the screen of the second stage.

[0034] The fine powder 6 removed from the feed by the second level screen can be collected together with the fine powder 6 removed by the first level screen. The collected fine powder 6 can be stored or provided to a separate or supplementary system for further processing. For example, the collected fine powder 6 can be transported to a straw pellet plant to produce biofuel pellets.

[0035] Since non-wood feedstocks like straw feedstock 2 inherently have high concentrations of fines 6 that do not add anything to pulp properties, it may be desirable to pretreat the straw feedstock 2 in the manner described above during the optional preparation step 20. By removing the fines 6 and / or straw dust from the straw feedstock 2 as a dry material, they can be more efficiently converted into value-added co-products (e.g., biofuel pellets) that can be used, for example, to generate electricity.

[0036] The stream of straw raw material 2 output by the screening system can be washed by a straw washing system and then transported (e.g., by a conveyor belt) to the next processing stage. The washing system can be included as part of the screening system or provided as a separate system. The washing system can wash the straw in hot water. Since agricultural raw materials typically have high concentrations of sand, gravel, and rocks due to the nature of the harvesting operation, it may be desirable to wash the raw material 2 before the pulping operation to remove debris and contamination. In addition, as described elsewhere herein, the washed straw can absorb alkaline cooking chemicals more evenly during the desiliconization and digestion processes, resulting in more consistent pulp properties (i.e., lower κ variability).

[0037] Optionally, the flow of the received straw feedstock 2 may be passed through a weight scale and then desiliconized in step 25. The weight scale may be configured to monitor the total mass flow of the straw feedstock 2.

[0038] After completing the straw preparation step 20, the method 10 proceeds to step 25, wherein the received stream of the raw material 2 is treated with hot water or a chemical solution (e.g., an alkaline solution) to pre-filter or otherwise separate some silica 7 from the stream of the raw material 2. The chemical treatment can be carried out for a period of ten to thirty minutes or longer. In some embodiments, the stream of the raw material 2 is heated and chemically desiliconized with compounds such as sodium carbonate, sodium hydroxide, potassium hydroxide, etc. The raw material 2 can also be treated with hot water in step 25 without adding alkaline chemicals. Compared with organic compounds (like dilute black liquor) that cause lignin to co-precipitate with silica when pH is adjusted, the compounds used in the desiliconization step 25 can preferentially separate silica 7 from the stream of the raw material 2.

[0039] In order to preferentially separate silica 7 from feedstock 2, desiliconization step 25 may be performed at a temperature in the range of 50°C to 100°C at atmospheric pressure. If a strong base (e.g., NaOH) is used in step 25, a relatively low reaction temperature (e.g., about 60°C) may be sufficient to preferentially remove silica over delignification. If a weak base (e.g., Na2CO3) or hot water is used in step 25, a relatively high reaction temperature (e.g., about 90°C) may be required to preferentially remove silica over delignification. In some embodiments, desiliconization step 25 is performed at a relatively low consistency level or at a consistency in the range of 1% to 5%.

[0040] In some embodiments, chemical desiliconization of feedstock 2 is supplemented with mechanical desiliconization to provide a chemical mechanical process in step 25. In such embodiments, desiliconization step 25 can include mechanically slurrying the stream of feedstock 2 to mechanically separate more silica 7 from feedstock 2 after the stream of feedstock 2 has been heated and chemically reacted (e.g., in an alkaline solution).

[0041] After the desiliconization step 25 is completed, a relatively large amount of silicon dioxide 7 will be dissolved in the alkaline desiliconization liquid and selectively removed from the stream of feedstock 2, such as Figure 1 As shown. The silica-rich filtrate (i.e., the liquid containing dissolved silica) can be removed from the feed stream by a mechanical press. In addition, trace metals (e.g., copper, iron, nickel, manganese, other transition metals, etc.) can also be separated from the feed stream 2 and removed with the silica-rich filtrate after step 25 is completed.

[0042] Because it is generally difficult to precipitate or separate lignin from the feedstock 2 in the presence of silica (i.e., silica can act as a protective barrier to lignin to hinder the delignification process), it may be desirable to remove silica 7 (e.g., as a sodium silicate liquor) from the stream of feedstock 2 prior to delignification. In addition, because mixtures of lignin and silica can be difficult to manage in a replenishment process, it is generally desirable to avoid mixing lignin with silica in black liquor (i.e., a byproduct obtained during the digestion of feedstock into pulp by removing lignin and other extractives from the feedstock to release cellulose fibers) as much as possible. Performing the desiliconization step 25 prior to the impregnation step 30 can also help improve the drainage characteristics of the final pulp product.

[0043] After completing the desiliconization step 25, the method 10 proceeds to the impregnation step 30, where the feedstock 2 is heated and impregnated with a compound such as sodium carbonate, sodium hydroxide, potassium hydroxide, etc. In some embodiments, the impregnation step 30 is optional.

[0044] Compared to conventional processes that operate at high temperatures and use aggressive alkalis to directly remove lignin from the feedstock, the impregnation step 30 is typically performed at relatively low temperatures (e.g., less than 130° C.) and with an alkaline impregnation solution having a relatively low alkali dosage (e.g., low alkali soda). This is in preference to selectively removing lignin 8A from the feedstock 2 at step 30 and preparing the fiber for further downstream processing.

[0045] The impregnation step 30 is typically carried out at a relatively high pressure and / or a relatively high temperature compared to the desiliconization step 25. In some embodiments, the impregnation step 30 is carried out at a pressure in the range of 1 bar to 11 bar. In some embodiments, the impregnation step 30 is carried out at a temperature between 100° C. and 130° C. In some embodiments, the impregnation step 30 is carried out at a consistency in the range of 8% to 30%. The alkali compound used in step 30 can swell the fibers of the feedstock 2 to make them more susceptible to further refining and delignification downstream.

[0046] In addition to selective lignin removal and fiber preparation, the impregnation step 30 can also result in further separation and removal of trace metals (e.g., transition metals including but not limited to copper, iron, nickel, manganese, etc.) from the feedstock 2. This can be advantageous because high levels of transition metals in the pulp can adversely affect the performance and selectivity of the oxygen-alkali based delignification step 50.

[0047] In some embodiments, the impregnation step 30 is performed in an impregnation tube. The impregnation tube can be connected to a digester blowdown tank. In some embodiments, the impregnation step 30 is performed for about fifteen (15) to twenty-five (25) minutes. In some embodiments, the impregnation step 30 includes mechanically pressing the feedstock 2 after the feedstock 2 has been heated and impregnated in the alkaline solution to squeeze or mechanically remove the lignin 8A from the feedstock 2. After the impregnation step 30 is completed, a relatively large amount of the lignin 8A will be dissolved in the alkaline impregnation solution and removed from the stream of feedstock 2 as black liquor 8 (e.g., Figure 1 For example, after step 30 is completed, between 60% and 70% of the lignin originally found in feedstock 2 may be removed therefrom.

[0048] After the impregnation step 30, the method 10 proceeds to the refining step 40. In the refining step 40, the desiliconized and impregnated raw material 2 is subjected to medium to high consistency refining, wherein the consistency is defined as the weight percentage of solids in the pulp slurry mixture (or in other words, the proportion of solids in the pulp slurry mixture, as measured by weight). In a particular embodiment, the refining level of the desiliconized and impregnated raw material 2 can be medium consistency refining (e.g., 8% to 12% consistency), medium-high consistency refining (e.g., 13% to 19% consistency), or high consistency refining (e.g., 20% to 40% consistency). The medium to high consistency refining can be implemented by a mechanical refiner. The mechanical refiner can be, for example, a blowline refiner. The mechanical refiner can include a stator and a rotor, which are operable to drive one or more pairs of plates to move in a synchronized manner. The plates can be made of metal or other suitable materials. In some embodiments, the refining step 40 is performed for about one to three minutes. The refining action may help defibrillate the chemically treated feedstock 2 prior to removing additional lignin 8B from the refined pulp stream in the delignification step 50 .

[0049] The medium to high consistency refining step 40 can promote more fiber-to-fiber contact and less fiber-to-metal contact than conventional mechanical pulping techniques performed at low consistency (e.g., 3% to 4% consistency). This allows the desiliconized and impregnated stock 2 to be refined into a pulp stream in a gentler manner.

[0050] After the refining step 40, the method 10 proceeds to another delignification step 50. The delignification step 50 is typically carried out at a temperature in the range of 95°C to 130°C, but other temperatures are also possible. The delignification step 50 includes an oxygen-alkali treatment of the pulp stream formed from the mechanically refined feedstock 2 in step 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 weight, and the amount of alkali added is about 2% to 10% by weight. Examples of suitable alkali compounds include, but are not limited to, sodium hydroxide, potassium hydroxide, and other strong alkali compounds. In one embodiment, a supplemental compound such as hydrogen peroxide is added to the oxygen and alkali streams during step 50. Additional compounds like magnesium sulfate can also be used to enhance the selectivity of the oxidation reaction.

[0051] Compared to the impregnation step 30, the delignification step 50 is typically performed at a lower temperature, a lower pressure level (e.g., 2 bar to 7 bar), and a lower consistency (e.g., 8% to 12%). Generally, the delignification step 50 is more selective in removing lignin than other carbohydrates (e.g., cellulose and hemicellulose) that may remain in the non-wood fibers contained in the feedstock 2. In some cases, performing the delignification step 50 can help produce a final pulp product 4 that is brighter and / or has enhanced L*a*b* (i.e., lightness, red / green values, blue / yellow values) color attributes.

[0052] The oxygen-alkali treatment performed in step 50 can also transfer silica remaining in the pulp (i.e., residual silica not removed in step 25) to the pulp fibers and out of the alkaline process liquor. The oxygen-alkali treatment can be performed in a reaction tower, etc. In a particular embodiment, the oxygen-alkali treatment is performed for a duration of about thirty (30) to sixty (60) minutes.

[0053] In one embodiment, an inline booster pump or the like is configured to maintain stage pressure and transport the refined pulp to a downstream blow tank or the like, wherein a combined chemical / steam mixer facilitates the addition of oxygen and steam to the refined pulp stream before it enters the reaction tower. The pressure may be maintained, for example, at about 4 to 6 bar.

[0054] After the delignification step 50, the method 10 proceeds to a post-processing step 60. In the post-processing step 60, the lignin 8B separated from the pulp stream during step 50 is removed from the pulp stream. In one embodiment, step 60 includes washing the pulp stream to remove black liquor 8 containing lignin 8B from the pulp. In one embodiment, the ratio between the amount of lignin removed in step 30 and the amount of lignin removed in step 60 is about 2:1. For example, after step 50 is completed, between 20% and 30% of the lignin originally found in the feedstock 2 may be removed therefrom.

[0055] The lignin 8A, 8B removed from the pulp stream can be collected for use in one or more supplementary processes (e.g., Figure 3 The post-treatment step 60 may also include one or more pulp screening stages. Pulp screening may include removing fines from the pulp produced in step 50. Removal of both primary and secondary fines improves the drainage rate of the pulp after the oxygen-alkali treatment and reduces the surface area of ​​the dewatering equipment required to process the pulp. This may result in capital cost savings and improved pulp properties.

[0056] After step 60 is completed, a high κ pulp stream (e.g., a pulp stream having a κ value greater than 30) is typically obtained. In the pulp and paper industry, the κ value is a dimensionless indicator of the bleachability of the pulp. The κ value is roughly proportional to the residual lignin content of the pulp. The κ value can be defined as the product of a constant and the percentage of lignin content (e.g., κ value ≈ 6.578*L, where L is the percentage of lignin content). In some embodiments, the pulp stream has a κ value greater than 30. For example, for some applications (e.g., unbleached tissue paper), the pulp stream can have a κ value in the range of 40 to 50. A high κ value with a low standard deviation can be a good indicator of high uniformity in the pulp stream.

[0057] Due to the higher pulp kappa value of the pulp stream and the independent removal of silica 7 and lignin 8A, 8B (i.e., removal of silica 7 in step 25 and removal of lignin 8A, 8B in steps 30, 50), the effluent characteristics of the black liquor 8 can be improved, with reduced biochemical oxygen demand (BOD), chemical oxygen demand (COD) and toxicity levels.

[0058] The above steps of method 10 can help enhance the selective removal of lignin 8A, 8B from the straw, either alone or in combination, while reducing the amount of silica 7 in the steeping and oxygen-alkali cooking liquors. For example, the targeted delignification in step 50 combined with the removal of fines in the filtrate in step 60 provides a pulp stream having an increased freeness characteristic and improved pulp properties. In addition, the reduced processing temperature requirements (e.g., in both the steeping step 30 and the delignification step 50) reduce the carbon intensity required to produce non-wood fibers having acceptable properties for use as pulp.

[0059] After the post-processing 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 and then transported to a pulp drying and finishing area. The pulp drying and finishing area may include one or more of the following: one or more drying sections (e.g., completed with fans and cyclone separators), a pulp cooling stage, an exhaust air scrubber, a gas burner, a reboiler, and a superheater. In such embodiments, the pulp stream can be fed 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 having a consistency greater than 48%) from each TRP can be metered into a specified pressure sensing device (PSSD) through a rotary valve.

[0060] In some embodiments, the drying of the pulp in step 70 is accomplished using superheated steam. Water evaporated from the pulp stream by superheated steam treatment can be removed from the dryer and used for process heating. For example, water can be used to heat the stream of 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 produce steam at about 2.8 bar. The steam can replace boiler steam, low-grade steam and high-grade hot water (e.g., heated to 130°C). Integrating these energy flows into the pulping process can help reduce the carbon footprint relative to other thermal drying processes. In addition, the use of superheated steam can provide improvements in the pulp properties of high κ pulp. For example, high κ pulp dried by superheated steam is typically more fluffy, stronger, tougher and harder than conventional flash-dried pulp. Compared with conventional flash-dried pulp, high κ pulp dried by superheated steam can also have a more desirable color (e.g., a darker or richer color).

[0061] Method 10 can be implemented by various devices that together form a chemical mechanical system for producing pulp 4 from non-wood raw materials 2. The system can be located or otherwise provided within a pulp production plant 200 (e.g., see Figure 3 ).

[0062] Figure 2 It can be used for implementation Figure 1 Schematic diagram of an exemplary embodiment of a system 100 for a method of the type shown in . System 100 includes a steeping pipe 102 located upstream of a blow tank 104. The steeping pipe 102 can be designed or otherwise adapted to perform step 30 in method 10. The steeping pipe 102 has a chamber for impregnating the washed straw or other feedstock 2 prepared in step 20 and desiliconized in step 25 with steam and one or more alkaline compounds. The blow tank 104 can be operated to transfer the desiliconized and impregnated feedstock 2 from the chamber of the steeping pipe 102 to a refiner 106 at a desired pressure and / or consistency level.

[0063] The press 105 is located between the impregnation tube 102 and the refiner 106. The press 105 can be located upstream or downstream of the blow tank 104. In some cases, it may be advantageous to locate the press 105 upstream of the blow tank 104 to reduce the energy consumption required to treat the black liquor 8 in subsequent processes. Figure 2 In the illustrated embodiment, a press 105 is disposed between the blow tank 104 and the refiner 106 to squeeze or mechanically remove the pressate carrying the separated lignin 8A from the remainder of the stream carrying the desiliconized and impregnated feedstock 2. The pressate may be stored in a tank 107 which is then transferred to a supplementary system for further processing (e.g., see Figure 3 process 80).

[0064] The refiner 106 receives the desiliconized and impregnated feedstock 2 from the blow tank 104. The refiner 106 can be configured to perform step 40 of the method 10. Figure 2 In the exemplary embodiment illustrated in , the refiner 106 also receives one or more alkali compounds to support mechanical refining. The alkali compounds provided to the refiner 106 can be the same compounds as those provided to the impregnation tube 102, or in other embodiments they can be different compounds. The refiner 106 can be suitably configured to refine the impregnated feedstock 2 at medium to high consistency.

[0065] A dilution conveyor 108 is located downstream of the refiner 106. The dilution conveyor 108 can be operated to transfer the refined pulp stream to the oxygen-alkali reactor 110, where step 50 is performed. In one embodiment, the system 100 includes a mixer 109 located 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 deliver the mixture to the reactor 110.

[0066] Downflow tower 112 is located downstream of oxygen-alkali reactor 110. Downflow tower 112 is designed to act as a storage buffer between reactor 110 and additional screening and pulp washing equipment (not shown) located further downstream. Downflow tower 112 includes a port for receiving dilution filtrate and a chamber for mixing the dilution filtrate with pulp. Since pulp may be difficult to pump at a higher consistency, downflow tower 112 can provide additional reaction time required to dilute the pulp to a relatively lower consistency before pumping the diluted pulp to the screen and pulp washing equipment.

[0067] A wide range of variations and additions are possible within the scope of the present invention. These include supplementary methods which can be carried out together with the main method 10 of producing pulp 4 described herein. Figure 3 Depicted are some exemplary supplemental methods 80 , 82 , 84 that may be coupled or combined with the method 10 to produce useful co-products from the non-wood feedstock 2 .

[0068] In one exemplary supplemental process, a lignin precipitation process 80 is incorporated to convert the black liquor 8 produced in process 10 into useful materials for electronic applications (e.g., supercapacitors) and / or chemical applications (e.g., chemical emulsions, chemical adhesives, etc.). In another exemplary supplemental process, a thermal process 82 (e.g., a hydrothermal liquefaction process) is incorporated to produce low-carbon transportation fuels from fines 6 and black liquor 8. In another exemplary supplemental process, a pelletizing process 84 is incorporated to produce biofuel pellets from fines 6. In another exemplary supplemental process, a silica precipitation process 90 is incorporated to convert silica compounds (e.g., sodium silicate) produced in the desiliconization step 25 into materials like silicic acid for additional high-value products.

[0069] The examples and corresponding figures used herein are for illustrative purposes only. Different configurations and terminologies may be used without departing from the principles expressed herein.

[0070] Although the present invention has been described with reference to certain specific embodiments, various modifications thereof 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 illustrative embodiments set forth in the examples, but should be given the broadest interpretation consistent with the entire specification. For example, various features are described herein as being present in "some embodiments" or in "one embodiment". Such features are not mandatory and may not be present in all embodiments. Embodiments of the present invention may include zero, any one, or any combination of two or more of such features. This is limited to the extent that some of such features are incompatible with other features of such features in the sense that it is impossible for a person of ordinary skill in the art to construct an actual embodiment combining such incompatible features. Therefore, the description that "some embodiments" have feature A and "some embodiments" have feature B should be understood as a clear indication that the inventors also envision an embodiment combining features A and B (unless the description states otherwise or features A and B are fundamentally incompatible).

Claims

1. A method for producing pulp from non-wood raw materials, the method comprising: desiliconizing the non-wood feedstock at a first temperature to selectively remove silicon dioxide therefrom; impregnating the desiliconized non-wood raw material with an alkaline solution having a low alkali dosage at a second temperature to selectively separate lignin from the desiliconized non-wood raw material; mechanically refining the impregnated non-wood feedstock to obtain a pulp stream; subjecting the pulp stream to an oxygen-alkaline treatment at a third temperature to separate lignin from the pulp stream; as well as Lignin separated from the desiliconized non-wood feedstock and lignin separated from the pulp stream are removed.

2. The method of claim 1 or any other claim herein, wherein: The non-wood feedstock is desiliconized using a solution of a compound.

3. The method of claim 2 or any other claim herein, wherein: The compound solution includes sodium carbonate, sodium hydroxide or potassium hydroxide.

4. The method of claim 1 or claim 2, or any other claim herein, wherein: The non-wood raw material is mechanically desiliconized using a mechanical pulper.

5. The method of claim 1 or any other claim herein, wherein: The first temperature is in the range of 50°C to 100°C.

6. The method of claim 1 or any other claim herein, wherein: The second temperature is in the range of 100°C to 130°C.

7. The method of claim 1 or any other claim herein, wherein: The third temperature is in the range of 95°C to 130°C.

8. The method of claim 1 or any other claim herein, wherein: The second temperature is higher than the first temperature.

9. The method of claim 1 or any other claim herein, wherein: The third temperature is lower than the second temperature.

10. The method of claim 1 or any other claim herein, wherein: The third temperature is higher than the first temperature.

11. The method of any one of claims 1 to 10 or any other claim herein, wherein: The impregnated non-wood raw material is mechanically refined at medium to high consistency.

12. The method of claim 11 or any other claim herein, wherein: The impregnated non-wood raw material is mechanically refined at a consistency ranging from 8% to 40%.

13. The method of any one of claims 1 to 12 or any other claim herein, comprising deconstructing the non-wood feedstock and cutting the deconstructed non-wood feedstock into nominal lengths and then desiliconizing the cut non-wood feedstock.

14. The method of claim 13 or any other claim herein, wherein: The nominal length is in the range of 40 mm to 100 mm.

15. The method of claim 13 or any other claim herein, comprising screening the cut non-wood feedstock to remove fines and then desiliconizing the screened non-wood feedstock.

16. The method of claim 15 or any other claim herein, wherein: The cut non-wood raw material is screened through a primary screen and a secondary screen, wherein the primary screen has a first set of grooves spaced between a first set of rollers, and the secondary screen has a second set of grooves spaced between a second set of rollers, the width of each groove in the first set of grooves defining a first internal roller opening, and the width of each groove in the second set of grooves defining a second internal roller opening.

17. The method of claim 16 or any other claim herein, wherein: The primary screen and the secondary screen are conical screens.

18. The method of claim 16 or any other claim herein, wherein: The first inner roller opening is about 1 mm, and wherein the second inner roller opening is about 2 mm.

19. The method of claim 15 or any other claim herein, comprising washing the screened non-wood feedstock and then desiliconizing the washed non-wood feedstock.

20. The method of any one of claims 1 to 19 or any other claim herein, comprising removing water from the pulp stream.

21. The method of claim 20 or any other claim herein, comprising removing water from the pulp stream by drying the pulp stream with superheated steam.

22. A method for producing pulp from non-wood raw materials, the method comprising: chemically treating the non-wood feedstock stream with a first alkaline solution at a first temperature, the first alkaline solution selectively separating silica from the non-wood feedstock; chemically treating the desiliconized non-wood feedstock stream with a second alkaline solution at a second temperature to separate lignin from the desiliconized non-wood feedstock, wherein the second temperature is higher than the first temperature; as well as The separated silica and the separated lignin are removed from the stream.

23. A system for producing pulp from non-wood raw materials, the system comprising: means for desiliconizing the non-wood feedstock at a first temperature to selectively remove silicon dioxide therefrom; an impregnation tube for impregnating the desiliconized non-wood feedstock at a second temperature to selectively separate lignin therefrom; a mechanical refiner for receiving the impregnated non-wood feedstock and refining the impregnated non-wood feedstock into a pulp stream; a reaction tower for receiving the pulp stream and configured to receive oxygen and steam to perform an oxygen-alkaline treatment on the pulp stream to separate lignin therefrom; and A post-processing device is connected to the reaction tower to remove the separated lignin from the pulp flow.

24. A device having any new and inventive feature, combination of features, or sub-combination of features as herein described.

25. A method having any new and inventive step, action, combination of steps and / or actions, or sub-combination of steps and / or actions as described herein.

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