A method of biomass pyrolysis
By designing a rotating shaft, connecting rod, scraper, and counterweight structure in the biomass pyrolysis reactor, the problem of coking in the reactor was solved, the stability of heat transfer efficiency and the improvement of pyrolysis efficiency were achieved, and the continuous operation time of the system was extended.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- GREEN HARVEST ENERGY (BEIJING) TECHNOLOGY CO LTD
- Filing Date
- 2023-11-28
- Publication Date
- 2026-05-29
Smart Images
Figure CN117736757B_ABST
Abstract
Description
Technical Field
[0001] This application belongs to the field of biomass pyrolysis technology, specifically relating to a biomass pyrolysis method. Background Technology
[0002] Biomass pyrolysis refers to the thermal decomposition of biomass under completely oxygen-free or oxygen-deficient conditions, ultimately producing biochar, biomass liquid fuel, and non-condensable gases. The proportions of these three products depend on the type of pyrolysis process and reaction conditions. Due to the unique and complex structure of biomass, its pyrolysis systems often employ indirect heating reactors such as rotary kilns or rotary furnaces. However, these methods inevitably lead to reactor coking problems caused by the high oxygen content and poor stability of biomass, thus affecting the long-term continuous operation of the system and resulting in low system energy efficiency and poor economic performance.
[0003] Biomass pyrolysis heating methods are mainly divided into direct heating and indirect heating. Direct heating gas-carrier circulating fluidized bed pyrolysis reactors are used in biomass pyrolysis. Their main advantages are: compact reactor structure, extremely high heat transfer rate, and short gas phase residence time within the reactor, effectively suppressing secondary cracking reactions. The disadvantage is the need for a large amount of circulating carrier gas. Indirect heating rotary kiln (rotating bed) pyrolysis reactors are similar to fixed-bed reactors in their advantages and disadvantages; they also suffer from low heat transfer efficiency and reactor coking, resulting in short continuous operating times. Summary of the Invention
[0004] The purpose of this application is to provide a biomass pyrolysis method that can better remove the deposits generated during pyrolysis on the reactor wall, especially coking deposits, thereby improving the pyrolysis efficiency of biomass pyrolysis while improving the heat transfer efficiency of the reactor.
[0005] To achieve this objective, in a basic implementation scheme, this application provides a biomass pyrolysis method, wherein the pyrolysis method involves feeding biomass raw materials into a pyrolysis reactor for pyrolysis;
[0006] The pyrolysis reactor includes a rotating shaft, connecting rod, scraper limiting baffle, and counterweight.
[0007] The rotating shaft is arranged on the central axis of the pyrolysis reactor;
[0008] One end of the connecting rod is fixedly connected to the rotating shaft, and the other end of the connecting rod is connected to the scraper, and the scraper can rotate at the end of the connecting rod;
[0009] The limiting baffle is arc-shaped, with one side of the arc connected to the middle of the connecting rod, and the other side of the arc used to control the rotation angle β of the scraper by stopping it after contacting the surface of the scraper. β is 6-15°.
[0010] The counterweight is disposed on the plate surface on the other side of the scraper;
[0011] When the rotating shaft drives the scraper to rotate, the scraper continuously contacts the inner wall of the pyrolysis reactor and scrapes off the deposits on the inner wall.
[0012] In one implementation, the counterweight satisfies the following conditions: Let the weight of each scraper be w1, the width of each scraper be m, the weight of each counterweight be w2, and the distance from the connection point between the counterweight and the scraper surface to the connecting sleeve be L, then the following conditions are met:
[0013] (w2×L+0.5w1×0.5m) / (0.5w1×0.5m)=2~3.
[0014] In one embodiment, the scraper is connected to the connecting rod via a connecting sleeve, wherein the scraper is rotatable about the central axis of the connecting sleeve.
[0015] In one embodiment, the angle α between each of the connecting rods and the axis of rotation is independently 45-90°.
[0016] In one embodiment, the end of the scraper that contacts the inner wall of the pyrolysis reactor is fan-shaped.
[0017] In one embodiment, the pyrolysis reactors are included in a plurality of the pyrolysis reactors, and the pyrolysis reactors are connected in series and / or in parallel.
[0018] In one embodiment, the biomass raw material is selected from one or more of sawdust, straw, bamboo waste, and rice husks.
[0019] In one implementation, the pyrolysis temperature remains stable at 500℃-600℃ for more than 30 days.
[0020] In one embodiment, the pyrolysis reactor is indirectly heated by flue gas.
[0021] In one embodiment, the biomass feedstock undergoes pretreatment involving crushing and / or drying before being fed into the pyrolysis reactor.
[0022] Preferably, the size of the crushed biomass raw material is less than 30 mm, and more preferably 5-10 mm;
[0023] Preferably, the water content of the dried biomass raw material is less than 10% by weight, preferably in the range of 3-8% by weight, for example less than 5% by weight.
[0024] The beneficial effect of this application is that the biomass pyrolysis method of this application adopts a pyrolysis reactor with a specific structural design, which can scrape off the attached substances, especially coke, on the inner wall in real time during the biomass pyrolysis process, thereby ensuring the continuous and stable heat transfer efficiency of the pyrolysis reactor and avoiding the decrease in heat transfer efficiency due to the accumulation of coke. This extends the continuous operation time of the pyrolysis method and improves the pyrolysis efficiency. Attached Figure Description
[0025] Figure 1 This is an exemplary structural diagram of the biomass pyrolysis system of this application, used in the biomass pyrolysis method of this application.
[0026] Figure 2 This is a schematic diagram of the axial angle α between the connecting rod and the rotating shaft in the biomass pyrolysis system of this application, which is an exemplary method for biomass pyrolysis in this application.
[0027] Figure 3 This is an exemplary diagram of the biomass pyrolysis system of this application, showing connecting rods connected in different directions from a point along the axial direction of the rotation axis.
[0028] Figure 4 for Figure 1 Diagram showing the positions and connections of the central rotating shaft, connecting rod, scraper, connecting sleeve, limit baffle, and counterweight.
[0029] Figure 5 for Figure 4 Schematic diagram of medium dimensions and angles.
[0030] Figure 6 This is a schematic diagram illustrating the principle of connecting the connecting rod and the scraper for connecting the sleeve.
[0031] Figure 7 This is a schematic diagram illustrating the principle of connecting the sleeve and the connecting rod.
[0032] Figure 8 A top view showing the assembly of the scraper, connecting sleeve, connecting rod, and counterweight.
[0033] Figure 9 A side view showing the assembly of the scraper, connecting sleeve, connecting rod, and counterweight.
[0034] Figure 10 This is a schematic diagram of two pyrolysis reactors connected in series.
[0035] Figure 11 This is a schematic diagram illustrating the connection principle of a two-stage pyrolysis reactor.
[0036] Figure 12 The flowchart of the biomass pyrolysis method of this application is an example.
[0037] The meanings of the labels in the above figure are as follows: 1. Inlet; 2. Outlet; 3. Pyrolysis gas outlet; 4. Rotating shaft; 5. Connecting rod; 6. Scraper; 7. Reactor shell; 8. Connecting sleeve; 9. Limiting baffle; 10. Counterweight; 11. Outer sleeve tube; 12. Inner sleeve tube; 13. First stage first reactor 1-1; 14. First stage second reactor 1-2. Detailed Implementation
[0038] Biomass feedstocks include sawdust, straw, bamboo waste, rice husks, etc., involving garden waste and agricultural waste. The biomass feedstocks in this application undergo pyrolysis first through crushing and drying, then are fed into a pyrolysis reactor via a feeding device for pyrolysis at a temperature of 450℃-600℃. The pyrolysis reactor typically uses external flue gas heating, isolating the flue gas from the biomass feedstock, thus employing indirect heating. The high-temperature pyrolysis oil and gas produced by the pyrolysis reactor are discharged and then enter a condenser for cooling and separation, yielding liquid bio-oil and biomass fuel gas. The pyrolysis solids produced are discharged via a cooling conveyor device, yielding biochar.
[0039] The aforementioned biomass raw materials have a dry basis oxygen content of 35%-45%, indicating a high oxygen content. Therefore, the pyrolysis of these biomass raw materials generates a large amount of heat-labile oxygen-containing organic matter. This organic matter is prone to secondary decomposition on the heated surfaces of the pyrolysis reactor, producing coking deposits. When these coking deposits accumulate and adhere to the heated surfaces of the pyrolysis reactor, the heat transfer efficiency of the reactor decreases, leading to unstable pyrolysis temperatures. Consequently, the chance of secondary decomposition of the biomass increases, and the quality of the obtained pyrolysis product deteriorates. Furthermore, the crushed biomass raw materials have low bulk density and fibrous particle structure (lightweight, resulting in low heat transfer efficiency between naturally packed, loose materials). Therefore, considering the physical and pyrolysis characteristics of biomass raw materials, this application provides a biomass pyrolysis method.
[0040] The biomass pyrolysis method of this application involves a pyrolysis reactor with a specific structural design, the composition and structure of which are as follows: Figure 1 As shown, it includes a feed inlet 1, a discharge outlet 2, a pyrolysis gas outlet 3, a rotating shaft 4, a connecting rod 5, a scraper 6, and a reactor shell 7.
[0041] Biomass enters the pyrolysis reactor through feed inlet 1 for pyrolysis.
[0042] The pyrolysis solids produced after biomass pyrolysis are discharged from the pyrolysis reactor through the discharge port 2, and the pyrolysis oil and gas produced are discharged from the pyrolysis gas outlet 3.
[0043] The rotating shaft 4 is located at the center of the pyrolysis reactor, and one or more connecting rods 5 are connected along the axial direction of the rotating shaft 4. Each connecting rod 5 is then connected to a scraper 6.
[0044] The scraper 6 rotates under the drive of the rotating shaft 4. The scraper keeps in contact with the inner wall of the pyrolysis reactor while rotating and scrapes off the deposits on the inner wall of the pyrolysis reactor, especially the coking material.
[0045] Furthermore, such as Figure 2 As shown, the angle α between each connecting rod 5 and the axis of rotation 4 is independently 45-90°, preferably 75-85°.
[0046] Furthermore, such as Figure 3 As shown, 2-4 connecting rods 5 are connected in different directions from a point on the axis of rotation 4, and the included angle between any two adjacent connecting rods 5 formed therefrom is equal (the included angle is 180° for the scheme of 2 connecting rods 5, 120° for the scheme of 3 connecting rods 5, and 90° for the scheme of 4 connecting rods 5).
[0047] Furthermore, the scraper 6 is rotatably connected to the end of the connecting rod 5 via a connecting sleeve. A counterweight 10 is fixedly arranged on the panel of the scraper 6, and a limit baffle 9 is fixed on the connecting rod. The limit baffle 9 and the counterweight 10 work together to adjust the rotation angle of the scraper 6. In one embodiment, such as Figure 4 , Figure 6 , Figure 7 , Figure 8 As shown, the connecting sleeve 8 includes an outer sleeve 11 and an inner sleeve 12.
[0048] The middle part of the scraper 6 is connected to the connecting rod 5 through the connecting sleeve 8, so that the scraper 6 can rotate about the central axis of the connecting sleeve 8.
[0049] The limiting baffle 9 is arc-shaped, with one side of the arc connected to the middle of the connecting rod 5, and the other side of the arc used to control the rotation angle β of the scraper 6 by stopping after it passes through the plate surface on one side of the contact scraper 6. β is 6-15°.
[0050] The counterweight 10 is set on the plate surface on the other side of the scraper 6.
[0051] Furthermore, such as Figure 5 As shown, the distance from the connection point between the limiting baffle 9 and the middle part of the connecting rod 5 to the connecting sleeve 8 is d, the arc of the limiting baffle 9 is θ, the distance from the connection point between the counterweight 10 and the surface of the scraper 6 to the connecting sleeve 8 is L, and the height of the counterweight 10 is h.
[0052] Furthermore, such as Figure 9 As shown, the end of the scraper 6 that contacts the inner wall of the reactor is fan-shaped, and the radius R of the fan-shaped area is 0.5-1 times the thickness of the scraper 6.
[0053] Furthermore, let the weight of each scraper 6 be w1, the width of each scraper 6 be m, the weight of each counterweight 10 be w2, and the distance from the connection point of the counterweight 10 to the surface of the scraper 6 to the connecting sleeve 8 be L. Then, the following condition is satisfied: (w2×L+0.5w1×0.5m) / (0.5w1×0.5m)=2~3.
[0054] In this application, the design of scraper 6 and its supporting structure is the key point of the entire pyrolysis reactor design. Its design focuses on how to achieve better contact with the inner wall of the pyrolysis reactor under hot conditions to remove the coking produced by pyrolysis. In addition, scraper 6 should make the scoopable material roll and be heated evenly, and push the material towards the discharge port 2.
[0055] In the above structure, the scraper 6 rotates under the drive of the connecting rod 5. During the rotation, the scraper 6 itself rotates around the axis of the connecting sleeve 8 under the action of the counterweight 10. Under the action of the counterweight 10, the scraper 6 can rotate and abut against the inner wall of the reactor when it comes into contact with the inner wall of the reactor. Under the drive of the connecting rod 5, the scraper 6 continues to rotate while abutting against the inner wall of the reactor until the scraper 6 leaves the inner wall of the reactor under the action of the counterweight 10.
[0056] The scraper 6 is kept in contact with the inner wall of the reactor within the range of β of 6-15°, preferably within the range of 10°, which can achieve a better descaling effect.
[0057] Due to gravity, the material is at the bottom of the pyrolysis reactor. After being lifted to a certain height by the scraper, it falls back to the bottom of the reactor. Therefore, the volumetric filling degree of the biomass feedstock inside the pyrolysis reactor is generally 20-60%. When the scraper 6 rotates to near the lower part of the pyrolysis reactor, the resistance of the limiting baffle 9 and the material will allow the scraper 6 to make better contact with the lower reactor wall, thus achieving a descaling effect.
[0058] Furthermore, such as Figure 10-11 As shown, the biomass pyrolysis method of this application may include multi-stage pyrolysis reactors, which are connected in series and / or in parallel. Series and / or parallel connections are achieved by connecting the outlet of one stage pyrolysis reactor to the inlet of the next stage pyrolysis reactor.
[0059] In one implementation scheme, when the particle size of the lignocellulosic biomass raw material is less than 20 mm after pulverization, a pyrolysis reactor with 2-3 stages connected in series and / or in parallel can be used.
[0060] In one implementation scheme, when the particle size of straw-based biomass raw materials is less than 30 mm after crushing, a pyrolysis reactor with 4-5 stages connected in series and / or in parallel can be used. This is because, compared to wood-based biomass, straw-based biomass is more difficult to crush into smaller particle sizes, and straw-based biomass has a lower bulk density and a longer reaction heat transfer time.
[0061] Furthermore, in the biomass pyrolysis method of this application, the pyrolysis reactor can be heated by flue gas. In one embodiment, a flue gas channel is arranged around the outer shell 7 of the pyrolysis reactor for circulating high-temperature flue gas. Preferably, the flow direction of the high-temperature flue gas is opposite to the flow direction of the biomass feedstock in the pyrolysis reactor to achieve sufficient heat exchange. To ensure that the temperature of the pyrolysis reaction remains stable at 500℃-600℃, the flue gas inlet temperature of the flue gas channel is controlled at 650-800℃, and the flue gas outlet temperature is controlled not to exceed 450℃.
[0062] The process flow of the exemplary biomass pyrolysis method of this application using the above-described exemplary biomass pyrolysis system is as follows: Figure 12 As shown.
[0063] The present application will be described in detail below with reference to the accompanying drawings and embodiments.
[0064] In the following example, the biomass feedstock is rice husks with a moisture content of 10-15 wt%. The husks are crushed to an average particle size of 5-10 mm and dried until the moisture content is below 5% by weight. The biomass feedstock is continuously pyrolyzed at a rate of 10 tons / hour. The pyrolysis reactor is heated by high-temperature flue gas. The flue gas inlet temperature is controlled at 700-800℃, and the flue gas outlet temperature is controlled not to exceed 450℃. The pyrolysis temperature is maintained stably at 500-550℃, and the residence time of the rice husks in each stage of the pyrolysis reactor is 30 minutes.
[0065] Example 1:
[0066] In the pyrolysis method of this embodiment, the pyrolysis reactor is as follows: Figure 10 As shown.
[0067] Rice husks enter the first-stage pyrolysis reactor through inlet 1 and are propelled towards outlet 2 by scraper 6. The pyrolysis gas produced from rice husk pyrolysis exits through outlet 3 and enters the condensation unit for separation. The pyrolysis char produced from rice husk pyrolysis enters the second-stage pyrolysis reactor through outlet 2 and is propelled towards outlet 2 by scraper 6. The pyrolysis gas outlet 3 of the second-stage pyrolysis reactor is connected to the pyrolysis gas outlet 3 of the first-stage pyrolysis reactor and leads to the condensation unit. The pyrolysis char produced in the second-stage pyrolysis reactor exits through outlet 2.
[0068] Each pyrolysis reactor has an inner diameter of 1.5m and a length of 9m. Twenty rows of connecting rods 5 are arranged parallel to each other at equal intervals of 0.4m on the rotating shaft 4 of each pyrolysis reactor. Each connecting rod 5 is connected to a scraper 6 at its end, and the scrapers 6 are arranged axially around the rotating shaft 4.
[0069] Three connecting rods 5 with equal included angles are arranged on the same circumference. The included angle α between the connecting rods 5 and the rotation axis 4 is 80°. Each connecting rod 5 is 0.6m long and 20cm in diameter. Each scraper 6 is a square scraper with a weight w1 of 7612g, a short side (i.e., width) m of 8cm, a long side of 20cm, a thickness of 8cm, and a fan-shaped arc edge radius R = 6cm.
[0070] The distance L = 8cm from each counterweight 10 to the connecting sleeve 8, and the weight w2 of each counterweight 10 is 2100g. Where d = 10cm, θ = π / 3, h = 4cm, and β = 10°.
[0071] Wherein, (w2×L+0.5w1×0.5m) / (0.5w1×0.5m)=2.
[0072] After 60 days of continuous operation of the biomass pyrolysis method, the furnace was shut down to check the coking condition of each stage of the pyrolysis reactor. It was found that there was a thin layer of black coking material on the walls of each stage of the pyrolysis reactor. The average thickness of the coking material on the inner wall of the first stage pyrolysis reactor was 0.1 mm, and the average thickness of the coking material on the inner wall of the second stage pyrolysis reactor was 0.1 mm. After cleaning, the coking material was discharged with the pyrolysis char.
[0073] During the continuous 60-day operation of the pyrolysis method, the flue gas outlet temperature did not fluctuate significantly. In the first 15 days of operation, the flue gas outlet temperature remained at 400℃. In the middle stage, around day 40, the temperature fluctuated slightly, ranging between 420-430℃. In the later stage, from day 55 to 60, the temperature fluctuated between 440-450℃. These temperature fluctuations indicate that coking has begun to accumulate on the inner wall of the pyrolysis reactor, slightly affecting the heat transfer efficiency.
[0074] The analysis of the pyrolysis products after shutdown is shown in Table 1 below.
[0075] Table 1
[0076]
[0077]
[0078] Example 2:
[0079] This embodiment is carried out in the same manner as Example 1, except that d, θ, h, β, w1, w2, L, and m are adjusted to d = 10cm, θ = π / 3, h = 4cm, β = 10°, w1 = 7612g, w2 = 3806g, L = 8cm, and m = 8cm, respectively, where (w2×L+0.5w1×0.5m) / (0.5w1×0.5m) = 3.
[0080] After 60 days of continuous operation of the biomass pyrolysis method, the furnace was shut down to check the coking condition of each stage of the pyrolysis reactor. It was found that there was a thin layer of black coking material on the walls of each stage of the pyrolysis reactor. The average thickness of the coking material on the inner wall of the first stage pyrolysis reactor was 0.1 mm, and the average thickness of the coking material on the inner wall of the second stage pyrolysis reactor was 0.2 mm. The coking material was cleaned and discharged with the pyrolysis char.
[0081] The analysis of the pyrolysis products after shutdown is shown in Table 2 below.
[0082] Table 2
[0083] Content (by weight %) pyrolysis oil 36％ Pyrolysis gas 32％ pyrolytic carbon 22％
[0084] Comparative Example 1:
[0085] This example is conducted in accordance with Example 1, except that a two-stage spiral pyrolysis reactor is used for the pyrolysis reaction. Each spiral pyrolysis reactor has an inner diameter of 1.5m, a length of 9m, a spiral blade diameter of 1.2m, and a pitch of 20cm.
[0086] After 60 days of continuous operation of the biomass pyrolysis method, the furnace was shut down to check the coking condition of each stage of the spiral pyrolysis reactor. It was found that there was a thin layer of black coking material on the inner wall and spiral blades of each stage of the spiral pyrolysis reactor. The average thickness of the coking material in the first stage spiral pyrolysis reactor was 1.0 cm, and the average thickness of the coking material in the second stage spiral pyrolysis reactor was 1.4 mm. The coking material was cleaned and discharged with the pyrolysis char.
[0087] The analysis of the pyrolysis products after shutdown is shown in Table 3 below.
[0088] Table 3
[0089] Content (by weight %) pyrolysis oil 30％ Pyrolysis gas 25％ pyrolytic carbon 35％
[0090] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations. The above embodiments or implementations are merely illustrative examples of this application, and this application can also be implemented in other specific ways or forms without departing from the gist or essential characteristics of this application. Therefore, the described implementations should be considered illustrative rather than limiting in any respect. The scope of this application should be defined by the appended claims, and any changes equivalent to the intent and scope of the claims should also be included within the scope of this application.
Claims
1. A biomass pyrolysis method, characterized in that: The pyrolysis method involves feeding biomass raw materials into a pyrolysis reactor for pyrolysis. The pyrolysis reactor includes a rotating shaft, connecting rod, scraper, limiting baffle, and counterweight. The rotating shaft is arranged on the central axis of the pyrolysis reactor; One end of the connecting rod is fixedly connected to the rotating shaft, and the other end of the connecting rod is connected to the scraper, and the scraper can rotate at the end of the connecting rod; The limiting baffle is arc-shaped, with one side of the arc connected to the middle of the connecting rod, and the other side of the arc used to control the rotation angle β of the scraper by stopping it after contacting the surface of the scraper. β is 6-15°. The counterweight is disposed on the plate surface on the other side of the scraper; When the rotating shaft drives the scraper to rotate, the scraper continuously contacts the inner wall of the pyrolysis reactor and scrapes off the deposits on the inner wall. The scraper is connected to the connecting rod via a connecting sleeve, wherein the scraper is capable of rotating about the central axis of the connecting sleeve. Let the weight of each scraper be w1, the width of each scraper be m, the weight of each counterweight be w2, and the distance from the connection point of the counterweight and the scraper surface to the connecting sleeve be L. Then the following condition is satisfied: (w2×L+0.5 w1×0.5m) / (0.5 w1×0.5m)=2~3; The angle α between each of the connecting rods and the axis of rotation is independently 45-90°.
2. The pyrolysis method according to claim 1, characterized in that: The end of the scraper that contacts the inner wall of the pyrolysis reactor is fan-shaped.
3. The pyrolysis method according to claim 1, characterized in that: It includes multiple pyrolysis reactors, and the pyrolysis reactors are connected in series and / or in parallel.
4. The pyrolysis method according to any one of claims 1-3, characterized in that: The biomass raw materials are selected from one or more of sawdust, straw, bamboo waste, and rice husks.
5. The pyrolysis method according to any one of claims 1-3, characterized in that: The pyrolysis temperature remained stable at 450℃-600℃ for more than 30 days.
6. The pyrolysis method according to any one of claims 1-3, characterized in that: The pyrolysis reactor is indirectly heated by flue gas.
7. The pyrolysis method according to any one of claims 1-3, characterized in that: The biomass feedstock is further pretreated by crushing and / or drying before being fed into the pyrolysis reactor.
8. The pyrolysis method according to claim 7, characterized in that: The size of the crushed biomass raw material is less than 30 mm.
9. The pyrolysis method according to claim 8, characterized in that: The size of the crushed biomass raw material is 5-10 mm.
10. The pyrolysis method according to claim 7, characterized in that: The biomass raw material has a water content of less than 10% by weight after drying.
11. The pyrolysis method according to claim 10, characterized in that: The water content of the dried biomass raw material is in the range of 3-8% by weight.