Arrangement for feeding wood particles into an impregnation
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- UPM KYMMENE OYJ
- Filing Date
- 2019-01-29
- Publication Date
- 2026-05-29
Smart Images
Figure CN113348061B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the general technical field of converting biomass into chemical bioproducts on an industrial scale. In particular, this invention relates to techniques for pretreating wood pellets and moving them between different pretreating stages. Background Technology
[0002] The production of biomass-based chemicals can use, for example, wood pellets as a primary raw material. In the biomass-to-sugar process, wood pellets may undergo various pretreatments, such as washing, impregnation with water and / or other liquids, and heating, in preparation for later stages of the process.
[0003] Pretreatment processes may involve soaking wood pellets in steam or hot water, followed by soaking them in dilute acid. The acid-impregnated pellets are then fed into a semi-hydrolysis reactor, where a steam explosion reaction breaks the pellets down into reaction products such as cellulose, hemicellulose (so-called C5 sugars), and lignin. Mechanical conveying devices, such as screw feeders, transport the impregnated wood pellets between the various stages of the pretreatment process.
[0004] A screw feeder is an example of a compression conveyor, which applies compressive force to the material being conveyed. This is a useful characteristic when the liquid content of the material needs to be affected. As the material passes through the screw feeder, it is compressed, removing some of the previously absorbed liquid and causing some compression deformation, at least partially elastic. When the compressed material is released from the screw feeder, this elastic deformation relaxes, allowing it to easily absorb new impregnating liquid (if any).
[0005] Not only the actual pretreatment stage, but also the conveying scheme between stages that move the wood particles forward in this process, all affect how this process works, so they must be designed and sized accordingly. Summary of the Invention
[0006] According to a first aspect, an arrangement is provided for feeding wood pellets into an impregnation stage of a wood processing procedure. The apparatus includes a feed hopper, at least one impregnation container for receiving the wood pellets into the impregnation stage, and two or more conveyors between the feed hopper and the at least one impregnation container. The conveyors are used to convey the wood pellets from the feed hopper to the at least one impregnation container. Each conveyor is a compression conveyor for applying pressure to the wood pellets as they pass through the respective conveyor.
[0007] According to a second aspect, a method is provided for feeding wood pellets from a feed hopper into an impregnation stage of a wood processing procedure. The method includes conveying the wood pellets to at least one impregnation vessel for the impregnation stage using at least two compression conveyors, the compression conveyors applying pressure to the wood pellets as they pass through the at least two conveyors. Attached Figure Description
[0008] The accompanying drawings provide a further understanding of the described embodiments and form part of this specification, illustrating various advantageous features and examples of combinations thereof. In the drawings:
[0009] Figure 1 This illustrates a typical level of chemical refining process.
[0010] Figure 2 An example of a process stage in pretreatment is shown.
[0011] Figure 3 Examples of process stages and equipment are shown.
[0012] Figure 4 Further examples of process stages and equipment are shown.
[0013] Figure 5 Further examples of process stages and equipment are shown, as well as
[0014] Figure 6 Additional examples of process stages and equipment are shown. Detailed Implementation
[0015] Numerical attributes such as first, second, and third are used in this description and the appended claims to give clear names to concepts. Unless otherwise expressly stated, they do not refer to any particular order.
[0016] In the context of this specification, the term wood pellets refers to a material consisting primarily of blocks of wood formed by cutting or shaving larger blocks such as trees, branches, logging residues, stumps, roots, and wood waste. Wood pellets can range in size from a few millimeters to a few centimeters in width, so the term wood pellets generally refers to larger materials than the term sawdust. The wood used to make wood pellets can be debarked or primarily contain bark. For wood sugar production processes, hardwoods are preferred raw materials due to their higher inherent sugar content, but the use of other types of wood is not excluded. The terms wood chips, sawdust, or simply chips can be used to refer to the same thing as wood pellets. For brevity, the term chips is used in the accompanying drawings.
[0017] Figure 1The diagram schematically illustrates a method and arrangement for processing wood particles, where the wood particles may undergo pretreatment, schematically shown as 101. The purpose of pretreatment 101 is to ensure the efficient utilization of the incoming wood particles in the processing steps by removing unwanted impurities, compensating for some natural fluctuations in material properties, and breaking down the natural structure of the wood material. Hemicellulose (C5 sugar) can be collected from pretreatment 101, while cellulose (or lignin-cellulose material) can be further processed into hydrolysis 102 to produce the desired types of carbohydrates.
[0018] Figure 2 Examples of the various stages a product goes through are shown, all of which belong to Figure 1 Pretreatment 101. Washing 201 is performed with water to remove some major inorganic impurities, such as sand. The washed wood pellets are then subjected to steam treatment 202, the purpose of which is to remove air from the wood pellets and preheat them to an elevated temperature. The steam-treated wood pellets are then subjected to dilute acid treatment 203, to impregnate the wood pellets with a dilute acid solution. The purpose of dilute acid treatment 203 is to allow the dilute acid solution to penetrate the wood pellets as evenly as possible.
[0019] Acid-soaked wood particles are carried towards semi-hydrolysis ( Figure 2 (Not shown separately), where it is under high pressure and high temperature. At the semi-hydrolyzed output end, the wood particles undergo steam explosion 204, which breaks down their structure. The output stream from steam explosion 204 proceeds to mixing 205 via steam separation (not shown separately), where water is added and the resulting material is mechanically homogenized to break up agglomerates. The solid and liquid can then be separated at 206 for feeding into subsequent process stages.
[0020] It has been found that feeding wood pellets into the impregnation stage using a known plug screw feeder in a commercially viable pretreatment process can lead to suboptimal impregnation results. This is an important finding because uniform absorption of the dilute acid solution into the wood pellets is highly desirable: this affects the quality of the product in subsequent processes. The flow rates in commercially viable wood sugar production processes are relatively high, meaning that assuming the wood pellets spend more than a few minutes in the impregnation vessel 401 is not feasible. Aiming for a longer time would mean that the impregnation vessel 401 would need to be larger than actually constructed. However, with only a few minutes of exposure to the acidic solution, the wood pellets may not be fully penetrated, or at least the acid spatial distribution within the wood pellets may not be completely uniform. This problem is exacerbated if the wood pellets entering the impregnation stage are not under optimal conditions for absorbing the dilute acid solution (shape, size, amount of bark in unpeeled raw material, insufficient compression).
[0021] Commercially available plug screw feeders have compression ratios between 1.5 and 6, and tend to become lower for larger equipment and larger material flows. This is the root cause of the problem: in commercially viable industrial-scale processes, the work done on the wood pellets in the compression vessel prior to the impregnation stage may be insufficient for effective impregnation.
[0022] It is known that by using two or more conveyors between the pre-steaming chamber and the impregnation vessel, more efficient compression can be achieved, resulting in better initial conditions for the wood pellets used for impregnation. This increases the compression work performed by each individual conveyor on each wood pellet.
[0023] Figure 3 A portion of an arrangement for pre-treating wood pellets in a wood processing step is schematically shown. As part of this arrangement, there is an arrangement for feeding the wood pellets into the impregnation stage of the wood processing step. This arrangement includes a feed hopper, in... Figure 3 In this embodiment, a pre-steaming chamber 301 is used for treating wood pellets with steam. This arrangement includes an impregnation vessel 305 for receiving the wood pellets during the impregnation stage discussed herein. The impregnation vessel 305 includes an inlet for introducing a dilute solution of acid, such as sulfuric acid, to immerse the received wood pellets in said dilute acid solution in preparation for their semi-hydrolysis and steam explosion in reactor 307 downstream of the process. Other acids that can be used for said impregnation include, but are not limited to, nitric acid, phosphoric acid, lactic acid, acetic acid, formic acid, and carbonic acid.
[0024] The arrangement includes two or more conveyors 302, 303, and 304 located between the pre-steaming chamber 301 and the impregnation vessel 305 for conveying wood pellets from the pre-steaming chamber 301 to the impregnation vessel 305. Each of these conveyors is a compression conveyor for applying pressure to the wood pellets as they pass through the respective conveyor.
[0025] Regarding the feed hopper, Figure 3 The middle section is the pre-steaming chamber 301, which is used for pre-steaming and is not a necessary requirement. (See above for reference.) Figure 2 The beneficial effects of pre-steaming, as described, include the removal of air from the interior of the wood particles and preheating. These or related effects can be achieved by means other than applying steam; for example, various vacuum and microwave-related technologies can be used. If the chamber is a pre-steaming chamber, the steam used can be pure water steam or may contain additives, such as acids, to enhance the desired effects. Feeding from the hopper by conveyors 302 to 304 has the advantage of ensuring stable operation and consistent performance of the material conveyed by the forced feeding screw of the plug screw feeder (for example, a compression drive) by using the hopper for feeding and by maintaining a sufficiently high surface level of the material within the hopper.
[0026] Commercially viable wood-based sugar production processes employ relatively high flow rates, making it impractical to assume that the wood particles remain in the impregnation vessel 305 for more than a few minutes. Aiming for a longer time would mean that the impregnation vessel 305 would need to be larger than actually constructed. However, after only a few minutes under the influence of an acidic solution, the acid may not have fully penetrated the wood particles, or at least the spatial distribution of the acid within the wood particles may not be entirely uniform. It is known that providing an impregnation chamber as a temporary reservoir allows time for the acid to achieve a uniform spatial distribution within the wood particles. Figure 3 In the schematic diagram, the soaking chamber appears at block 306. The residence time in the soaking chamber 502 can be on the order of tens of minutes. In one embodiment, the residence time in the soaking chamber 502 does not exceed 60 minutes. In another preferred embodiment, the residence time in the soaking chamber 502 does not exceed 30 minutes.
[0027] exist Figure 3 In this arrangement, two or more conveyors operate in parallel. That is, each of the two or more conveyors 302 to 304 includes a corresponding conveyor input and a corresponding conveyor output, and the conveyor input is connected in parallel with the pre-steaming chamber 301 to receive a corresponding component stream of wood particles from the pre-steaming chamber 301. There is only one common impregnation vessel 305, which is connected to the outputs of at least two (here, all) conveyors for receiving at least two (here, all) component streams.
[0028] Assuming a certain total material flow passes through this process, each of the N parallel compression conveyors (N = 2, 3, ...) must transport 1 / N of the total material flow. In general, the workload of a single compression conveyor is N times that of the material flow. This ensures that at the beginning of the impregnation stage in the impregnation vessel 305, the conditioning of the wood particles is more thorough than if only compression conveyors were used.
[0029] Figure 4 Showing with Figure 3 A similar embodiment, but with a separator 401 provided between the feed hopper (pre-steaming hopper 301) and the conveyor input for separating the wood particles from the feed hopper into constituent streams. Figure 3 It is assumed that the input end of the actuator is simply installed at the bottom of the pre-steaming chamber 301. The separator 401 can be a static, mechanical separator, such as a wedge-shaped barrier that mechanically guides the wood particles from the pre-steaming chamber 301 to the input end of the actuator. Additionally or alternatively, it may include its own actuator, such as a twin-helix feeder, which receives the flow of wood particles from the middle hopper and presents a helix with opposing directions of rotation towards its two ends.
[0030] Figure 5An embodiment in which the compression conveyors operate in series is shown. That is, each of two or more conveyors 501 to 503 includes a corresponding conveyor input and a corresponding conveyor output, wherein only the conveyor input of the first conveyor 501 is connected to the feed hopper (pre-steaming hopper 301) for receiving wood particles from the feed hopper. The conveyor output of the first conveyor 501 is connected to the conveyor input of the second conveyor 502 for conveying wood particles from the feed hopper sequentially through the first conveyor 501 and the second conveyor 502 to the impregnation stage. Figure 5 This schematically illustrates the possibility of having more than two compressor transmitters connected in series (see...). Figure 5 Block 503 in the middle.
[0031] In one embodiment, two or more compression transducers operate in series. To fully realize the beneficial effects of dual compression applied to the wood particles, the compression stages should follow each other directly with minimal delay, so that the mechanical deformation achieved in the earlier compression does not relax too much before the subsequent compression. Therefore, the output of the preceding transducer is directly connected to the input of the following transducer, with little or no interruption in between.
[0032] Figure 6 Other examples with Figure 3 or Figure 4 A similar embodiment (separator 401 is optional) exists, but with separate impregnation containers connected to at least two compression conveyors 302 to 304. That is, a first impregnation container 601 is connected to the conveyor output of a first conveyor 302 to receive a first component stream, and a second impregnation container 602 is connected to the conveyor output of a second conveyor 303 to receive a second component stream. This arrangement includes a combiner stage following the first and second impregnation containers 601 and 602, for combining the outputs of the first and second impregnation containers 601 and 602 into a later stage of the wood processing procedure. Figure 6 In the schematic diagram, the bonding stage is included in block 306.
[0033] When considering some of the further stages of the process in more detail, the additional beneficial effects of using at least two compression conveyors prior to the impregnation stage have been discovered. Figure 7 An apparatus for pre-treating wood pellets is schematically shown. A pre-steaming chamber 701 is configured for treating the wood pellets with steam, i.e., implementing... Figure 2 The diagram shows at least a portion of stage 202. At least two compression conveyors 702 are configured to convey steam-treated wood pellets from a pre-steam chamber 701 to one or more impregnation containers 703, in which the process is carried out. Figure 2The process involves a dilute acid treatment stage 203. Downstream of one or more impregnation vessels 703, one or more soaking chambers 704 may be provided to allow the dilute acid solution more time to penetrate the interior portions of the wood particles. One or more further compression conveyors 705 may be used to convey the acid-impregnated wood particles to a reactor 706, where a semi-hydrolysis reaction takes place, and a steam explosion occurs at the reactor's outlet.
[0034] The dry matter content and acid content of the material entering reactor 706 are important process parameters because they affect how the desired reaction proceeds in reactor 706 and downstream. Reactor 706 is pressurized, and the compression capacity of the adjacent compressor conveyor 705 is used to help deliver the material stream into reactor 706.
[0035] Now, when two or more compressor conveyors 702 are used before impregnation vessel 703, the penetration of the dilute acid solution into the wood particles may be more thorough than when only one compressor conveyor is used at stage 702; the material can be "more wetted" by the dilute acid. The extent to which this occurs can be controlled by regulating the operation of the compressor conveyors 702. To achieve the desired dry matter and acid content at the input of reactor 706, the operation of the subsequent compressor conveyors can be controlled. Because two or more compressor conveyors are used at stage 702, there is a greater range of control, i.e., more precise control possibilities, as described last.
[0036] It will be apparent to those skilled in the art that the above ideas can be implemented in various ways as technology advances. Therefore, the scope of the claims is not limited to the examples listed above.
Claims
1. An apparatus for processing wood pellets, comprising: -Feed hopper, - At least one impregnation container for receiving wood particles entering the impregnation stage of the wood processing procedure, the impregnation stage comprising immersing the wood particles in a dilute acid solution. - Two or more conveyors between the feed hopper and the at least one impregnation vessel for feeding wood pellets into the impregnation stage, and for conveying wood pellets from the feed hopper to the at least one impregnation vessel, and Downstream of the impregnation stage in the process, a reactor is used to perform semi-hydrolysis and steam explosion on the wood particles impregnated in the impregnation stage. Each of the conveyors is a compression conveyor, used to apply pressure to the wood particles as they pass through the corresponding conveyor, and includes a corresponding conveyor input and a conveyor output. a) The input terminals of the two or more conveyors are connected in parallel with the feed hopper for receiving a corresponding component stream of wood particles from the feed hopper. or (b) Each of the two or more conveyors is a plug screw feeder, and the conveyor input of the first conveyor of the two or more conveyors is connected to the feed hopper for receiving the wood particles from the feed hopper, while the conveyor output of the first conveyor is connected to the conveyor input of the second conveyor of the two or more conveyors for sequentially conveying the wood particles through the first conveyor and the second conveyor from the feed hopper to the impregnation stage; In case a), the device includes a separator between the feed hopper and the conveyor input for separating wood particles from the feed hopper into at least two component streams.
2. The apparatus according to claim 1, characterized in that, The feed hopper is a pre-steaming hopper used to treat the wood particles with steam.
3. The apparatus according to claim 1 or 2, characterized in that, In case a), each of the conveyors is a plug screw feeder or a forced feed screw.
4. The apparatus according to claim 1, characterized in that, In case a), an impregnation container is connected to at least two of the transmitter outputs for receiving at least two of the component streams.
5. The apparatus according to claim 1, characterized in that, In case a): - A first impregnation container is connected to the transmitter output of a first transmitter to receive a first component stream of the component stream. - The second impregnation container is connected to the transmitter output of the second transmitter to receive the second component stream of the component stream. - The device includes a joining stage following the first and second impregnation containers for joining the outputs of the first and second impregnation containers.
6. A method for treating wood pellets, comprising: - The wood pellets are fed from the feed hopper into the impregnation stage of the wood processing procedure, the impregnation stage comprising immersing the wood pellets in a dilute acid solution, and - The output of at least one impregnation vessel used in the impregnation stage is transferred to the reactor, and - The reactor is used to perform semi-hydrolysis and steam explosion on the wood particles that have been impregnated in the impregnation stage; The method includes: - The wood particles are conveyed to at least one impregnation vessel for the impregnation stage using at least two compression conveyors, the compression conveyors applying pressure to the wood particles as they pass through the at least two conveyors, such that... a) The at least two conveyors are used in parallel to transport at least two component streams of wood particles from the feed hopper to the impregnation stage. or b) The two or more conveyors are each a plug screw feeder used in series, which receives the wood particles from the feed hopper to the input end of the first conveyor and connects the output end of the first conveyor to the input end of the second conveyor to transport the wood particle stream from the hopper to the impregnation stage through the two conveyors. In case a), wood particles from the feed hopper are separated into the at least two component streams by a separator arranged between the feed hopper and the conveyor input.
7. The method of claim 6, further comprising steam-treating the wood particles in the feed hopper.
8. The method according to claim 6, characterized in that, In case a), at least two of the component streams are fed into a common impregnation container for the impregnation stage.
9. The method according to claim 6, characterized in that, In case a): - The first component stream of the component stream is fed into the first impregnation container for the impregnation stage. - The second component stream of the component stream is fed into the second impregnation container for the impregnation stage. - The output ends of the first and second impregnation containers are combined into a common material flow.