A method and device for rapid charring detoxification of contaminated straw

Abstract

The present application relates to a kind of contaminated straw fast carbonization detoxification method, comprising the following steps: S1: collecting contaminated straw;S2: contaminated straw is chopped to less than 2cm;S3: chopped straw is dried to moisture content is less than 15%;S4: drying straw is carried out first fast pyrolysis and obtains carbonized straw, flue gas is handled after passing through front condensation recovery purification system by fan and is recycled in second heating device;S5: carbonized straw is carried out second fast pyrolysis and obtains detoxification carbonized straw, flue gas is handled after passing through rear condensation recovery purification system;S6: front condensation recovery purification system and rear condensation recovery purification system collect heavy metal in flue gas and reuse flue gas.The present application also relates to a kind of contaminated straw fast carbonization detoxification equipment.The present application realizes the efficient detoxification recovery of heavy metal in straw by two high-temperature fast pyrolysis, belongs to the technical field of agricultural and forestry waste resource utilization.

Description

Technical Field

[0001] This invention relates to the field of agricultural and forestry waste resource utilization technology, specifically to a method and equipment for rapid carbonization and detoxification of contaminated straw. Background Technology

[0002] Current research on "straw carbonization technology" focuses on the application of carbonized straw as a soil conditioner or carbon-based fertilizer in improving acidic and heavy clay soils, enhancing the utilization efficiency of chemical fertilizers, and expanding the carbon pool in farmland. However, the issue of heavy metal residues after carbonization of contaminated straw has not received sufficient attention. This has resulted in existing straw carbonization technologies failing to strictly differentiate between contaminated and uncontaminated straw, and lacking specific process designs for the harmless treatment of contaminated straw. Traditional straw carbonization technologies typically employ slow heating and long-duration single-stage pyrolysis, which not only leads to the "concentration" of heavy metals in the carbonized straw, posing environmental risks and threatening human health, but also results in decreased straw char yield and increased energy consumption. For example, using traditional straw carbonization technology, contaminated rice straw with a cadmium content of 0.95 mg / kg was pyrolyzed and carbonized at 500℃ for 1 h with a heating rate of 10℃ / min (it takes as long as 47.5 min to heat from room temperature 25℃ to the specified temperature 500℃). The resulting carbonized straw had a cadmium content of 2.67 mg / kg (concentrated by 2.8 times) and a carbon yield of 21.9%. When the pyrolysis and carbonization time was extended to 12 h, the cadmium content in the carbonized straw reached as high as 16.4 mg / kg (concentrated by 17.3 times), and the carbon yield was only 4.1% (Wang Yuefeng, Dong Zhiying, Chen Zaiming, Shi Zhihua, Study on cadmium content and leaching properties in pyrolysis products of contaminated rice straw, Journal of Ningbo University, 2021, 34(3), 54-59).

[0003] Secondly, there is currently a lack of specialized "carbonization and detoxification equipment" for treating straw contaminated with heavy metals. Existing carbonization equipment is typically designed for large-scale, ground-level factories, resulting in high costs, complex structures, large footprints, and difficult maintenance. Furthermore, the lightweight, bulky, and widely distributed nature of crop straw further complicates its collection, transportation, and storage. While mobile / vehicle-mounted straw carbonization equipment promises to significantly reduce the costs and labor intensity of straw collection, transportation, and storage, currently available mobile / vehicle-mounted straw carbonization equipment still employs traditional straw carbonization technology principles (slow heating and long-term single-stage pyrolysis), failing to address the problem of heavy metal concentration during the carbonization process of contaminated straw. Moreover, its structural design and functionality have numerous shortcomings.

[0004] Currently, the mobile / vehicle-mounted straw carbonization equipment with published patents can be roughly divided into two categories: The first category consists of equipment with complex structures and large size, requiring large trucks for transportation. These devices have multiple motors, high energy consumption, and high operating and maintenance costs. Examples include Chinese invention patents such as "Mobile Straw Carbonization and Pyrolysis Device (Patent No. 202010558396.7)," "A Mobile Agricultural Straw Integrated Treatment System and Method (Patent No. 201811580823.0)," "Mobile Continuous Multi-Tube Biomass Pyrolysis Charcoal Making Integrated Machine (Patent No. 201911041310.7)," and "Mobile Biomass Catalytic Pyrolysis Reactor (Patent No. 201610757281.4)." The second category consists of equipment with complex structures. Simple, but with long carbonization time, low production efficiency, and uneven carbonization; for example, Chinese utility model patent "Mobile Portable Carbonization Furnace (Patent No. 201520506969.6)", Chinese invention patent "Mobile Straw Carbonization and Return to Field Carbonization Furnace and its Carbonization Method (Patent No. 201310339328.1)", "A Mobile Straw Biochar Preparation Device and Method (Patent No. 201510170153.5)", "Biomass Moving Bed Internal Heating Continuous Carbonization Method and Device (Patent No. 201310616167.6)", and "A Mobile Internal and External Combined Heating Biomass Pyrolysis Carbon Oil Co-production System (Patent No. 201710530833.2)".

[0005] Therefore, in order to solve the problem of concentrating heavy metals in traditional carbonization equipment, as well as the defects in its structural design and function, carbonization equipment must be redesigned based on new technological principles. Summary of the Invention

[0006] To address the technical problems existing in the prior art, the purpose of this invention is to provide a rapid carbonization and detoxification method for contaminated straw that achieves efficient detoxification and recovery of heavy metals from contaminated straw, and results in low heavy metal residual concentration and high carbon yield in carbonized straw.

[0007] Another objective of this invention is to provide a rapid carbonization and detoxification device for contaminated straw with high heavy metal detoxification efficiency.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for rapid carbonization and detoxification of contaminated straw includes the following steps: S1: Collect straw and test it for heavy metal content to identify contaminated straw; S2: Chop the contaminated straw into chopped straw with a length less than 2 cm; S3: Air-dry the chopped straw to obtain dried straw with a moisture content below 15%; S4: Transport the dried straw to a first heating device for first-stage pyrolysis to obtain carbonized straw. The flue gas generated during the first pyrolysis is treated by a pre-cooling and recovery purification system and then drawn into a second heating device for recycling by a cross-flow fan; S5: Transport the carbonized straw to the second heating device for a second-stage pyrolysis. The detoxified carbonized straw is obtained. The flue gas generated during the second pyrolysis process is treated by a post-condensation recovery and purification system and then recycled. S6: The steps of the pre-condensation recovery and purification system and the post-condensation recovery and purification system for treating the flue gas are as follows: a: The pre-condensation recovery and purification system collects heavy metals from the flue gas generated during the first pyrolysis process to obtain purified first combustible flue gas, which is then sent to the second heating device for ignition and recycling; b: The post-condensation recovery and purification system collects heavy metals from the flue gas generated during the second pyrolysis process to obtain purified second combustible flue gas, which is then sent to the second heating device for ignition and recycling.

[0010] As a preferred embodiment, in step S4, the first heating device is a heating furnace, the temperature of the first pyrolysis is 600-700℃, and the duration of the first pyrolysis is 0.8-3min.

[0011] As a preferred embodiment, in step S5, the second heating device is a combustion chamber, the temperature of the second pyrolysis is 500-600℃, and the duration of the second pyrolysis is 0.4-0.8 min.

[0012] As a preferred option, in step S1, the straw includes rice straw, corn straw, and cassava straw.

[0013] A rapid carbonization and detoxification device for contaminated straw includes a material conveying system, a temperature control system, and a ventilation control system. The material conveying system includes a feed pipe, a screw feeder, and a collection chamber. The two ends of the screw feeder's feed pipe are sealed to the feed pipe and the collection chamber, respectively. The temperature control system includes a first heating device and a second heating device. The screw feeder's feed pipe passes sequentially through the interiors of the first and second heating devices. The ventilation control system includes a cross-flow fan, a pre-condensation recovery and purification system, and a post-condensation recovery and purification system. One end of the inlet pipe of the pre-condensation recovery and purification system is connected to the starting end of the feed pipe, and the outlet pipe of the pre-condensation recovery and purification system is connected to the cross-flow fan. One end of the inlet pipe of the post-condensation recovery and purification system is connected to the top of the collection chamber, and the outlet pipe of the post-condensation recovery and purification system is connected to the cross-flow fan. The cross-flow fan is located outside the second heating device and is connected to a strip-shaped multi-hole flue gas nozzle inside the second heating device via a pipe.

[0014] As a preferred embodiment, the first heating device is an intelligent digital display heating furnace, and the second heating device is a combustion chamber; the furnace, combustion chamber, and collection chamber are set at the same height.

[0015] As a preferred embodiment, both the pre-condensation recovery and purification system and the post-condensation recovery and purification system are equipped with valves in their outlet pipes. The middle sections of both systems are set at the same height as the top of the second heating device, and the cross-flow fan is set at the same height as the strip-shaped multi-hole flue gas nozzle. The condensation pipes of both systems are equipped with stainless steel baffles.

[0016] As a preferred option, the combustion chamber has a double-layer box structure, with an ignition window on the front and an exhaust gas chimney on the top.

[0017] As a preferred embodiment, the inner wall of the collection chamber is provided with a semi-open interlayer for assisting in the collection of heavy metal condensate in the flue gas, the outer wall of the collection chamber is provided with a collection chamber drain valve, the top of the collection chamber is provided with a collection chamber outlet pipe, the bottom of the collection chamber is provided with a discharge port, and the top of the feed pipe is provided with a cover plate; when the collection chamber is unloading, the cover plate and the cross-flow fan are in the closed state.

[0018] As a preferred option, a rapid carbonization and detoxification device for contaminated straw also includes a transport vehicle, on which the material conveying system, temperature control system, and air control system are all installed.

[0019] In summary, the present invention has the following advantages:

[0020] 1. Compared with existing technologies, the carbonization detoxification method provided by this invention adopts a new technical principle of "rapid secondary pyrolysis-condensation recovery." It mainly uses two short-duration, high-temperature pyrolysis carbonization processes to allow heavy metals in contaminated straw to escape with the flue gas and be rapidly condensed and recovered. By adjusting the pyrolysis temperature, pyrolysis time, and flue gas flow rate, the amount of heavy metals released and the carbon yield are controlled, ensuring that the heavy metal residue in the carbonized straw meets national safety standards. This invention provides a method specifically for the "rapid carbonization detoxification" of contaminated crop straw. It not only solves the environmental risk of heavy metal pollution caused by the current practice of returning contaminated straw to the field through carbonization and ensures a high carbon yield, but also simultaneously achieves the "harmless treatment," "resource utilization," and "in-situ carbon sequestration" of contaminated straw. It has a clear application, innovative technical principles, economical and efficient detoxification effect, and urgent and important environmental significance.

[0021] 2. Compared with existing straw carbonization equipment, the rapid carbonization and detoxification equipment for straw provided by this invention is specifically designed for the rapid carbonization and detoxification of contaminated straw and its safe return to the field nearby. It not only boasts high detoxification efficiency, high carbon yield, and low heavy metal residue concentration in the carbonized straw, but also features a simple structure and operation, and low manufacturing and operating costs. Furthermore, the main components of the rapid carbonization and detoxification equipment provided by this invention are all box-shaped structures, tightly assembled, with feeding pipes running through the interior of each box. Therefore, the overall equipment is small in size, easy to install on transport vehicles, and can be directly driven into the field for use. This significantly reduces the costs of straw collection, transportation, and storage, achieving one-stop "harmless treatment," "resource utilization," and "in-situ carbon sequestration" of contaminated straw, possessing significant environmental importance and enormous application and promotion value. Attached Figure Description

[0022] Figure 1 This is a flowchart of a method for rapid carbonization and detoxification of contaminated straw.

[0023] Figure 2 This is a schematic diagram of a device for the rapid carbonization and detoxification of contaminated straw.

[0024] Figure 3 This is a front view of a device for the rapid carbonization and detoxification of contaminated straw.

[0025] Figure 4 This is a rear view of a device for the rapid carbonization and detoxification of contaminated straw.

[0026] Figure 5 This is a schematic diagram of the collection chamber in a rapid carbonization and detoxification device for contaminated straw.

[0027] Figure 6 This is a schematic diagram of the combustion chamber in a rapid carbonization and detoxification device for contaminated straw.

[0028] Figure 7This is a schematic diagram of the pre-condensation recovery and purification system in a rapid carbonization and detoxification device for contaminated straw.

[0029] The system includes: 1. Feed pipe; 2. Drive motor; 201. Spiral auger; 202. Feeding pipe; 3. Intelligent digital display heating furnace; 301. Heating wire; 4. Combustion chamber; 401. Exhaust gas chimney; 402. Box interlayer; 403. Ignition window; 5. Collection chamber; 501. Semi-open interlayer; 502. Collection chamber drain valve; 503. Discharge port; 6. Air control system; 601. Pre-condensate recovery and purification system; 6011. Pre-baffle; 6012. Pre-condensate drain valve; 602. Pre-gas valve; 603. Post-gas valve; 604. Post-condensate recovery and purification system; 6041. Rear partition, 6042 rear condensate drain valve, 605 cross-flow fan, 606 strip-shaped multi-hole flue gas nozzle, 7 base, 6021 exhaust pipe of pre-condensate recovery and purification system, 6031 exhaust pipe of post-condensate recovery and purification system, 6051 sealing protective cover, 6052 air duct, 6053 air duct motor, 6013 stainless steel hollow square tube, 6014 air inlet pipe of pre-condensate recovery and purification system, 6015 stainless steel connecting pipe, 6016 exhaust pipe of pre-condensate recovery and purification system, 6043 exhaust pipe of collection chamber. Detailed Implementation

[0030] The present invention will now be described in further detail with reference to specific embodiments.

[0031] Example 1

[0032] This embodiment describes a rapid carbonization and detoxification device for contaminated straw, such as... Figures 2-7 As shown, the system includes a material conveying system, a temperature control system, and a ventilation control system. The material conveying system includes a feed pipe, a screw feeder, and a collection chamber. The two ends of the screw feeder's feed pipe are sealed to the feed pipe and the collection chamber, respectively. The temperature control system includes a first heating device and a second heating device. The screw feeder's feed pipe passes sequentially through the interiors of the first and second heating devices. The ventilation control system includes a cross-flow fan, a pre-condensation recovery and purification system, and a post-condensation recovery and purification system. One end of the inlet pipe of the pre-condensation recovery and purification system is connected to the starting end of the feed pipe, and the outlet pipe of the pre-condensation recovery and purification system is connected to the cross-flow fan. One end of the inlet pipe of the post-condensation recovery and purification system is connected to the top of the collection chamber, and the outlet pipe of the post-condensation recovery and purification system is connected to the cross-flow fan. The cross-flow fan is located outside the second heating device and is connected to the strip-shaped multi-hole flue gas nozzle inside the second heating device through a pipe. In this embodiment, both the first and second heating devices are located between the feed pipe and the collection chamber.

[0033] In this embodiment, the material conveying system includes a feed pipe, a screw feeder, and a collection chamber. A drive motor is installed outside the feed pipe of the screw feeder, and the drive motor is connected to a spiral auger inside the feed pipe. Both ends of the feed pipe are connected to the feed pipe and the collection chamber respectively, and are sealed and welded together. The drive motor drives the spiral auger inside the feed pipe to rotate, thereby propelling the straw forward.

[0034] The drive motor outside the screw feeder's feeding pipe is connected to the screw auger inside the feeding pipe; a cover plate is installed at the top of the feeding pipe; the inner wall of the collection chamber has a semi-open jacket for assisting in the collection of heavy metal condensate from the flue gas, reducing contamination of the detoxified carbonized straw product. A drain valve is installed on the outer wall of the collection chamber, a discharge port is located at the bottom of the collection chamber, and an exhaust pipe is installed at the top of the collection chamber. Figure 5 During unloading, the feed pipe cover and the ventilation duct motor are closed. The feed pipe is protected from rainwater entry by opening and closing the cover. The discharge port has a funnel-like structure; during unloading, the feed pipe cover and ventilation duct motor must be closed to reduce gas flow within the collection chamber.

[0035] Temperature control system: Includes a first heating device and a second heating device. The first heating device is an intelligent digital display heating furnace, and the second heating device is a combustion chamber. The feeding pipe of the screw feeder passes sequentially through the furnace cavity of the intelligent digital display heating furnace and the interior of the combustion chamber, but the interior of the feeding pipe is isolated from and not connected to the interior of the heating furnace cavity and the combustion chamber. The intelligent digital display heating furnace can precisely control the temperature inside the furnace cavity. The heating wire inside the furnace cavity heats the outer wall of the feeding pipe. The space between the heating wire and the outer shell of the heating furnace is filled with insulation material to maintain a high-temperature environment inside the feeding pipe. Because the screw auger obstructs the gas flow inside the feeding pipe, when the feeding pipe is continuously fed, it becomes an oxygen-deficient environment filled with straw and the screw auger. Under the action of the drive motor, the screw auger propels the contaminated straw forward. When the contaminated straw passes through the interior of the heating furnace cavity, it rapidly heats up and undergoes its first pyrolysis and carbonization, releasing heavy metals from the straw and producing a large amount of flue gas containing heavy metals. The flue gas generated from the first pyrolysis is treated by a pre-cooling and recovery purification system to obtain the first combustible flue gas. This first combustible flue gas is then transported to the combustion chamber for ignition, used to heat the outer wall of the feeding pipe and maintain a high temperature inside the pipe. The carbonized straw undergoes a second pyrolysis and carbonization as it passes through the combustion chamber, and any heavy metals remaining on the surface of the carbonized straw escape with the flue gas. The flue gas generated from the second pyrolysis is treated by a post-cooling and recovery purification system to obtain the second combustible flue gas, which is then transported to the combustion chamber for ignition.

[0036] The screw feeder (including the drive motor, screw conveyor, and feeding pipe), the first heating device (intelligent digital display heating furnace), and the cross-flow fan (including the air duct and air duct motor) are existing products that can be purchased and used directly, and will not be described in detail here. The remaining devices, including the feed pipe, the combustion chamber housing, the collection chamber housing, the pre-condensation recovery and purification system, and the post-condensation recovery and purification system, are all made of stainless steel plates or steel pipes through cutting, drilling, and welding. Finally, the various devices are assembled and welded together to form a rapid carbonization and detoxification equipment.

[0037] The combustion chamber has a double-layered box structure. An ignition window is located on the front of the combustion chamber for igniting the flame and observing its condition. A chimney is located at the top of the combustion chamber, from which the clean exhaust gas from the combustion process is discharged. Figure 6 The combustion chamber's casing is filled with insulating cotton to maintain a high-temperature environment. A feeding pipe passes through the inside of the combustion chamber, and a strip-shaped multi-hole flue gas nozzle is located below the feeding pipe. Combustible flue gas, after being treated by the pre-condensation recovery and purification system and the post-condensation recovery and purification system, is ejected from the strip-shaped multi-hole flue gas nozzle. The ejected combustible flue gas is ignited and used to heat the feeding pipe inside the combustion chamber. The size of the flame is controlled by the air control system.

[0038] The air control system includes a pre-cooled condensate recovery and purification system, a post-cooled condensate recovery and purification system, and a cross-flow fan. The pre-cooled and post-cooled condensate recovery and purification systems have identical structures, each consisting of three stainless steel hollow square tubes, two stainless steel connecting pipes, an inlet pipe, and an outlet pipe welded together. Figure 7 Each stainless steel hollow square tube is equipped with a condensate drain valve at the bottom. The condensate drain valve of the pre-condensate recovery and purification system is the pre-condensate drain valve, and the drain valve of the post-condensate recovery and purification system is the post-condensate drain valve.

[0039] Among them, the stainless steel hollow square tubes are welded together by stainless steel connecting pipes to form condensate pipes. Figure 7The middle sections of both the pre-condensation recovery and purification system and the post-condensation recovery and purification system are set at the same height as the top of the second heating device (i.e., the middle of the condensation pipe is set at the same height as the top of the second heating device), and the cross-flow fan is set at the same height as the strip-shaped multi-hole flue gas nozzle. Stainless steel baffles are installed inside the condensation pipes of both the pre-condensation recovery and purification system; the stainless steel baffles of the pre-condensation recovery and purification system are pre-mounted baffles, and the stainless steel baffles of the post-condensation recovery and purification system are post-mounted baffles. One end of the inlet pipe of the pre-condensation recovery and purification system is connected to the starting end of the feeding pipe, and the outlet pipe of the pre-condensation recovery and purification system is connected to the cross-flow fan. It is used to condense and recover heavy metals in the flue gas generated during the first pyrolysis, and simultaneously transport the purified combustible flue gas to the combustion chamber for ignition and reuse. One end of the inlet pipe of the post-condensation recovery and purification system is connected to the outlet pipe of the collection chamber, and the outlet pipe of the post-condensation recovery and purification system is connected to the cross-flow fan. It is used to condense and recover heavy metals in the flue gas generated during the second pyrolysis, and simultaneously transport the purified combustible flue gas to the combustion chamber for ignition and reuse. During the first and second pyrolysis processes, heavy metals from the straw and carbonized straw escape along with the flue gas. The flue gas containing heavy metals is quickly drawn by cross-flow fans to the pre-condensation recovery and purification system and the post-condensation recovery and purification system, respectively. Due to the temperature difference, the heavy metals in the flue gas are condensed and collected along with water vapor. The collected heavy metal condensate can be discharged through the collection chamber drain valve, the pre-condensation drain valve, and the post-condensation drain valve.

[0040] The flow of flue gas is driven by a small cross-flow fan, and the flow rate and flame size in the combustion chamber are mainly controlled by the fan's rotation speed. Both the pre-cooling and post-cooling condensate recovery purification systems have valves in their outlet pipes. The valve in the pre-cooling system is the pre-valve, and the valve in the post-cooling system is the post-valve. These valves are used to assist in regulating the flue gas flow rate and flame size in the combustion chamber. The cross-flow fan consists of a duct and a motor. A sealed protective cover surrounds the duct, and the motor is located outside the cover, connected to the duct inside. Under the action of the cross-flow fan, the purified combustible flue gas enters the second heating device (combustion chamber) through a strip-shaped multi-hole flue gas nozzle and is ignited. The exhaust gas is then discharged from the exhaust chimney at the top of the combustion chamber.

[0041] A rapid carbonization and detoxification device for contaminated straw also includes a transport vehicle. The material conveying system, temperature control system, and air control system are all mounted on a base, which is then mounted on the transport vehicle. In this embodiment, the collection chamber, temperature control system, and air control system are all box-shaped structures, tightly arranged and assembled. The feeding pipes of the material conveying system run through the interior of each box. Therefore, the overall equipment is small in size, easy to install on a transport vehicle, and can be driven directly into the field for use, significantly reducing the costs of straw collection, transportation, and storage.

[0042] The principle is as follows: The crushed, contaminated straw falls into the feeding pipe of the screw conveyor through the feed pipe. Driven by the screw conveyor, the contaminated straw first passes through the first heating device (heating furnace), where it rapidly heats up and undergoes its first pyrolysis and carbonization, resulting in carbonized straw. Heavy metals in the straw escape with the flue gas and are quickly drawn away by a cross-flow fan to the pre-cooling and recovery purification system for recycling. Subsequently, the carbonized straw passes through the second heating device (combustion chamber) for a second pyrolysis and carbonization. Residual heavy metals on the surface of the carbonized straw escape with the flue gas and are quickly drawn away by a cross-flow fan to the post-cooling and recovery purification system for recycling, resulting in detoxified carbonized straw. Finally, the detoxified carbonized straw falls into the collection chamber. In the cooling and recovery purification system, heavy metals in the flue gas are condensed and recovered along with water vapor. The purified combustible flue gas is then transported to the second heating device (combustion chamber) for combustion and reuse. This equipment controls the heavy metal residue in carbonized straw to meet national safety standards by adjusting the pyrolysis temperature, pyrolysis time, and flue gas flow rate, while ensuring a high carbon yield.

[0043] Example 2

[0044] In this embodiment, as Figure 1 As shown, a method for rapid carbonization and detoxification of contaminated straw includes the following steps: S1: Collect straw and test it for heavy metal content to obtain contaminated straw; S2: Chop the contaminated straw to obtain chopped straw with a length of less than 2 cm; S3: Air-dry the chopped straw to obtain dried straw with a moisture content of less than 15%; S4: Transport the dried straw to a first heating device for the first pyrolysis to obtain carbonized straw. The flue gas generated during the first pyrolysis is treated by a pre-condensation recovery and purification system and then drawn into a second heating device for recycling by a cross-flow fan; S5: Transport the carbonized straw to the second heating device for the second pyrolysis. Pyrolysis yields detoxified carbonized straw. The flue gas generated during the second pyrolysis process is treated by a post-condensation recovery and purification system for recycling. S6: The steps of the pre-condensation recovery and purification system and the post-condensation recovery and purification system for treating the flue gas are as follows: a: The pre-condensation recovery and purification system collects heavy metals from the flue gas generated during the first pyrolysis process to obtain purified first combustible flue gas, which is then sent to the second heating device for ignition and recycling; b: The post-condensation recovery and purification system collects heavy metals from the flue gas generated during the second pyrolysis process to obtain purified second combustible flue gas, which is then sent to the second heating device for ignition and recycling.

[0045] In step S4, the first heating device is a heating furnace, the temperature of the first pyrolysis is 600-700℃, and the duration of the first pyrolysis is 0.8-3min.

[0046] In step S5, the second heating device is a combustion chamber, the temperature of the second pyrolysis is 500-600℃, and the duration of the second pyrolysis is 0.4-0.8 min.

[0047] In step S1, the straw includes rice straw, corn straw and cassava straw.

[0048] Principle: The contaminated straw undergoes two short-duration, high-temperature, and intense pyrolysis processes. The heavy metals in the straw escape with the flue gas and are quickly condensed and recovered. By adjusting the pyrolysis temperature, pyrolysis time, and flue gas flow rate, the residual amount of heavy metals in the carbonized straw is controlled to meet national safety standards, while ensuring a high carbon yield.

[0049] The specific steps of the method in this embodiment are as follows:

[0050] Rice straw grown in actual cadmium-contaminated paddy fields was collected, and the cadmium content of the contaminated rice straw was measured to be 0.43 mg / kg, which exceeds the risk screening value (0.3 mg / kg) of the Agricultural Land Soil Risk Control Standard (GB15618-2018) and the limit value (0.3 mg / kg) of the Edible Agricultural Product Production Area Environmental Quality Evaluation Standard (HJ / T 332-2006).

[0051] First, chop the collected cadmium-contaminated rice straw into pieces less than 2cm in length and air-dry it until the moisture content is below 15% (Note: a moisture content above 20% will make the recovered combustible gas difficult to ignite). Set the heating furnace temperature to 600℃. For the first start-up, wait until the temperature inside the heating furnace reaches 600℃ before starting the drive motor of the screw feeder and setting the conveying speed to low. The rice straw will then enter the screw feeder's feeding pipe from the inlet pipe. Figure 2When cadmium-contaminated rice straw passes through the first heating device (heating furnace), the straw rapidly heats up and undergoes a first short-term, intense pyrolysis to produce carbonized rice straw. This generates a large amount of flue gas, with heavy metals from within the straw escaping with the gas. The flue gas gradually diffuses into the collection chamber and the post-condensation recovery and purification system. Once flue gas can be observed emerging from the strip-shaped porous flue gas nozzles in the second heating device (combustion chamber) (at which point the air in the collection chamber has been largely exhausted), the flue gas is ignited through the ignition window. Then, the drive motor speed is immediately increased to ensure continuous flue gas production; simultaneously, the cross-flow fan is activated to ensure the generated flue gas is quickly extracted, and the flame size is adjusted via pre- and post-valve valves to maintain the temperature in the second heating device (combustion chamber) at 500-600℃. The carbonized rice straw then passes through the combustion chamber, undergoing a second short-term, high-temperature pyrolysis. Residual heavy metals on the surface of the carbonized straw escape with the flue gas, resulting in detoxified carbonized rice straw. Finally, the detoxified and carbonized rice straw falls into the collection chamber. Heavy metals in the flue gas produced by the first and second pyrolysis are collected along with water vapor by the pre-condensation and post-condensation recovery purification systems. The purified combustible flue gas is then transported to the combustion chamber for combustion and reuse. Once the equipment is running stably, only straw needs to be continuously added.

[0052] When the equipment is operating stably, the technical parameters are as follows: For rice straw with excessive cadmium, the temperature of the first heating device (heating furnace) is set to 600℃, and the first pyrolysis carbonization time is 2.0 min (the total time for the straw to pass through the heating furnace, during which the screw conveyor runs continuously). The temperature of the second heating device (combustion chamber) is maintained at 500-600℃, and the second pyrolysis carbonization time is 0.5 min (the total time for the straw to pass through the combustion chamber, during which the screw conveyor runs continuously). Under these technical parameters, the average carbon yield is 36% (after deducting moisture content), and the cadmium content in the detoxified carbonized rice straw is 0.08 mg / kg, which is far below the national standard limit. Specific parameter information is shown in Table 1.

[0053] The parts not mentioned in this embodiment are the same as in Embodiment 1.

[0054] Example 3

[0055] First, the collected cadmium-contaminated corn stalks are chopped to a length of less than 2cm and air-dried until the moisture content is below 15%. The temperature of the first heating device (heating furnace) is set to 600℃. For the first start-up, wait until the temperature inside the heating furnace reaches 600℃ before starting the drive motor of the screw feeder and setting the conveying speed to low. The cadmium-contaminated corn stalks enter the feeding pipe of the screw feeder from the feed pipe. Figure 2When cadmium-contaminated corn stalks pass through the heating furnace, the stalks rapidly heat up and undergo a first short-term pyrolysis to produce carbonized corn stalks. This generates a large amount of flue gas, with heavy metals from within the stalks escaping with the gas. The flue gas gradually diffuses into the collection chamber and the post-condensation recovery and purification system. Once flue gas can be observed emerging from the strip-shaped porous flue gas nozzles in the second heating device (combustion chamber) (at which point the air in the collection chamber has been largely exhausted), the flue gas is ignited through the ignition window. Then, the drive motor speed is immediately increased to ensure continuous flue gas production; simultaneously, the cross-flow fan is activated to ensure the generated flue gas is quickly extracted, and the flame size is adjusted via pre- and post-valve valves to maintain the temperature in the combustion chamber at 500-600℃. The carbonized stalks then pass through the combustion chamber, undergoing a second short-term high-temperature pyrolysis carbonization. Residual heavy metals on the surface of the carbonized stalks escape with the flue gas, resulting in detoxified carbonized corn stalks. Finally, the detoxified and carbonized corn stalks fall into the collection chamber. Heavy metals in the flue gas produced by the first and second pyrolysis are collected along with water vapor by the pre-condensation recovery and purification system and the post-condensation recovery and purification system. The purified combustible flue gas is then transported to the combustion chamber for combustion and reuse. Once the equipment is running stably, only the straw needs to be continuously added.

[0056] When the equipment is operating stably, the technical parameters are as follows: For corn stalks with excessive cadmium, the temperature of the first heating device (heating furnace) is set to 600℃, and the first pyrolysis carbonization time is 2.0 min (the total time for the straw to pass through the heating furnace, during which the feeder runs continuously). The temperature of the second heating device (combustion chamber) is maintained at 500-600℃, and the second pyrolysis carbonization time is 0.5 min (the total time for the straw to pass through the combustion chamber, during which the feeder runs continuously). Under these technical parameters, the average char yield is 33% (after deducting moisture content), and the cadmium content in the detoxified carbonized corn stalks obtained is 0.16 mg / kg, which is far below the national standard limit. Specific parameter information is shown in Table 1.

[0057] The parts not mentioned in this embodiment are the same as in Embodiment 2.

[0058] Example 4

[0059] Cassava straw grown in actual cadmium-contaminated farmland was collected, and the cadmium content of the contaminated cassava straw was measured to be 0.56 mg / kg, which exceeds the risk screening value (0.3 mg / kg) of my country's Agricultural Land Soil Risk Management Standard (GB15618-2018) and the limit value (0.3 mg / kg) of my country's Edible Agricultural Product Origin Environmental Quality Evaluation Standard (HJ / T 332-2006).

[0060] First, the collected cadmium-contaminated cassava stalks are chopped to less than 2cm in length and air-dried until the moisture content is below 15%. The temperature of the first heating device (heating furnace) is set to 700℃. For the first start-up, wait until the temperature inside the heating furnace reaches 700℃ before starting the drive motor of the screw feeder and setting the conveying speed to low. The cadmium-contaminated cassava stalks enter the feeding pipe of the screw feeder from the feed pipe. Figure 2 When cadmium-contaminated cassava straw passes through the heating furnace, the straw rapidly heats up and undergoes a first short-term pyrolysis to produce carbonized cassava straw. This process generates a large amount of flue gas, with heavy metals from within the straw escaping with the gas. The flue gas gradually diffuses into the collection chamber and the post-condensation recovery and purification system. Once flue gas can be observed emerging from the strip-shaped porous flue gas nozzles in the second heating device (combustion chamber) (at which point the air in the collection chamber has been largely exhausted), the flue gas is ignited through the ignition window. Then, the drive motor speed is immediately increased to ensure continuous flue gas production; simultaneously, the cross-flow fan is activated to ensure the generated flue gas is quickly extracted, and the flame size is adjusted via pre- and post-valve valves to maintain the combustion chamber temperature at 500-600℃. The carbonized cassava straw then undergoes a second short-term high-temperature pyrolysis and carbonization in the combustion chamber, with residual heavy metals on the surface of the carbonized straw escaping with the flue gas, resulting in detoxified carbonized cassava straw. Finally, the detoxified and carbonized cassava straw falls into the collection chamber. Heavy metals in the flue gas produced by the first and second pyrolysis are collected along with water vapor by the pre-condensation recovery and purification system and the post-condensation recovery and purification system. The purified combustible flue gas is then transported to the combustion chamber for combustion and reuse. Once the equipment is running stably, only straw needs to be continuously added.

[0061] When the equipment is operating stably, the technical parameters are as follows: For cassava straw with excessive cadmium, the temperature of the first heating device (heating furnace) is set to 700℃, and the first pyrolysis carbonization time is 0.85 min (the total time for the straw to pass through the heating furnace, during which the feeder runs continuously). The temperature of the second heating device (combustion chamber) is maintained at 500-600℃, and the second pyrolysis carbonization time is 0.4 min (the total time for the straw to pass through the combustion chamber, during which the feeder runs continuously). Under these technical parameters, the average carbon yield is 40% (after deducting moisture content), and the cadmium content in the obtained detoxified carbonized cassava straw is 0.17 mg / kg, which is far below the national standard limit. Specific parameter information is shown in Table 1.

[0062] Table 1. Technical parameters and cadmium content of rapid carbonization detoxification technology for straw with excessive cadmium levels.

[0063]

[0064] The parts not mentioned in this embodiment are the same as in Embodiment 2.

[0065] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for rapid charring and detoxification of contaminated straw, characterized by, The method comprises the following steps: S1: collecting straws, and detecting heavy metal content of the straws to obtain contaminated straws; S2: chopping the contaminated straws to obtain chopped straws, the length of the chopped straws being less than 2 cm; S3: naturally airing the chopped straws to obtain dried straws, the water content of the dried straws being less than 15%; S4: conveying the dried straws into a first heating device to perform first pyrolysis to obtain carbonized straws, flue gas generated in the first pyrolysis being treated by a front condensation recovery and purification system and then being drawn into a second heating device by a cross-flow fan for recycling; S5: conveying the carbonized straws into the second heating device to perform second pyrolysis to obtain detoxified carbonized straws, flue gas generated in the second pyrolysis being treated by a rear condensation recovery and purification system for recycling; S6: the front and rear condensation recovery and purification systems treat the flue gas in the following steps, a: the front condensation recovery and purification system collects heavy metals in the flue gas generated in the first pyrolysis to obtain purified first combustible flue gas, and the first combustible flue gas is conveyed into the second heating device to be ignited for recycling; b: the rear condensation recovery and purification system collects heavy metals in the flue gas generated in the second pyrolysis to obtain purified second combustible flue gas, and the second combustible flue gas is conveyed into the second heating device to be ignited for recycling; In step S4, the first heating device is a heating furnace, the temperature of the first pyrolysis is 600-700℃, and the duration of the first pyrolysis is 0.8-3 min; In step S5, the second heating device is a combustion chamber, the temperature of the second pyrolysis is 500-600℃, and the duration of the second pyrolysis is 0.4-0.8 min.

2. A method for quick charring and detoxification of contaminated straw as claimed in claim 1, wherein: In step S1, the straws include rice straw, corn straw and cassava straw.

3. A device for rapid charring and detoxification of contaminated straw, characterized in that: The system comprises a material conveying system, a temperature control system and an air control system, the material conveying system comprises a feeding pipe, a screw feeder and a collection chamber, the feeding pipe and the collection chamber are sealingly connected to two ends of the feeding pipe of the screw feeder; The temperature control system comprises the first heating device and the second heating device, the feeding pipe of the screw feeder passes through the first heating device and the second heating device in sequence; The air control system comprises a cross-flow fan, the front condensation recovery and purification system and the rear condensation recovery and purification system, one end of an air inlet pipe of the front condensation recovery and purification system is communicated with a starting end of the feeding pipe, an air outlet pipe of the front condensation recovery and purification system is connected to the cross-flow fan, one end of an air inlet pipe of the rear condensation recovery and purification system is communicated with the top of the collection chamber, an air outlet pipe of the rear condensation recovery and purification system is connected to the cross-flow fan, and the cross-flow fan is located outside the second heating device and connected to a strip-shaped porous flue gas nozzle in the second heating device through a pipe; The first heating device is an intelligent digital display heating furnace, and the second heating device is a combustion chamber; the box bodies of the heating furnace, the combustion chamber and the collection chamber are arranged at the same height. The gas outlet pipeline of the front condensation recovery and purification system and the rear condensation recovery and purification system is provided with a valve, the middle part of the front condensation recovery and purification system and the rear condensation recovery and purification system is arranged at the same height as the top of the second heating device, and the cross-flow fan is arranged at the same height as the strip-shaped porous flue gas nozzle; the inside of the condensation pipeline of the front condensation recovery and purification system and the rear condensation recovery and purification system is provided with a stainless steel partition plate.

4. The apparatus for quick charring and detoxification of contaminated straw according to claim 3, characterized in that: The combustion chamber is a double-layer box structure, the front face of the combustion chamber is provided with an ignition window, and the top of the combustion chamber is provided with a tail gas chimney.

5. The apparatus for quick charring and detoxification of contaminated straw according to claim 3, characterized in that: The inner wall of the collection chamber is provided with a semi-open interlayer for assisting in collecting heavy metal condensed water in flue gas, the outer wall of the collection chamber is provided with a collection chamber drain valve, the top of the collection chamber is provided with a collection chamber gas outlet pipeline, the bottom of the collection chamber is provided with a discharge port, and the top of the feeding pipeline is provided with a cover plate; when the collection chamber is discharged, the cover plate and the cross-flow fan are in a closed state.

6. The apparatus for quick charring and detoxification of contaminated straw according to claim 3, characterized in that: The transport vehicle, the material conveying system, the temperature control system and the air control system are all installed on the transport vehicle.

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