A system and process for preparing biochar by coupling heavy metal high-enrichment plants with sludge

Abstract

The technical solution of the present invention discloses a process for preparing biochar by coupling heavy metal high-accumulation plants with sludge, including pre-treatment of heavy metal high-accumulation plants and sludge, drying after uniformly mixing sludge, heavy metal high-accumulation plant particles, curing agent, and passivating agent, and then performing staged pyrolysis. At the same time, a preparation system is also disclosed, including a biomass crushing device, a sludge filtering device, a filter press device, a mixing and feeding device, a drying device, a pyrolysis device, a sewage treatment and disposal device, a waste gas treatment device, and a biochar cooling device. The preparation system and process provided by the present invention can more conveniently realize the comprehensive treatment of heavy metal high-accumulation plants and sludge, and its treatment process is relatively simple and has good applicability, and realizes the comprehensive treatment and resource utilization of sludge biomass while effectively treating pollution.

Description

Technical Field

[0001] The present invention relates to the field of environmental protection, and in particular to a system and process for preparing biochar by coupling heavy metal high-enriched plants with sludge. Background Art

[0002] Heavy metal pollution refers to environmental pollution caused by heavy metals or their compounds. It is mainly caused by human factors such as mining, exhaust gas emissions, sewage irrigation and the use of products with excessive heavy metals. Commonly used methods for heavy metal pollution control include physical methods and chemical methods. These methods have problems such as large engineering workload, great impact on the surrounding environment, small treatment area and difficulty in large-scale application. Correspondingly, phytoremediation is widely used in heavy metal pollution control because of its advantages such as environmental friendliness, low cost and ability to achieve large-scale in-situ remediation. In the process of phytoremediation, a large amount of plant harvests containing heavy metals will be produced. If such biomass is not reasonably and effectively disposed of and utilized, it will inevitably cause secondary pollution to the soil environment, water environment, etc., and will further harm the safety of agricultural products and human health. How to efficiently and reasonably treat heavy metal-enriched plants and minimize secondary pollution is the key to the development of soil phytoremediation technology.

[0003] In addition, in recent years, with the rapid development of industrialization and urbanization in my country, the amount of sludge that needs to be treated in my country has gradually increased. Sludge contains a large number of pathogenic microorganisms, heavy metals and other toxic and harmful components that are difficult to degrade. If they are not properly treated, they will cause a lot of environmental problems. Sludge pyrolysis carbonization technology is a common sludge treatment process. It can not only remove viruses, parasites and toxic pollutants in sludge, achieve harmless treatment of sludge, but also realize the resource utilization of sludge and produce biochar. At the same time, sludge biochar can be widely used in soil improvement, heavy metal solidification and other occasions due to its porous characteristics.

[0004] There is some research on the combined treatment of biomass and sludge in academia, which is mainly focused on the combined treatment of crop straw and sludge, generally using the heat from straw combustion to reduce the energy consumption of sludge pyrolysis. There is less research on the combined treatment process of heavy metal-accumulating plants and sludge, and there is a lack of mature processes. A large number of papers remain in the laboratory and small-scale treatment stage, and there is a large gap between the treatment process and treatment system and actual use. Summary of the invention

[0005] The object of the present invention is to provide a system and process for preparing biochar by coupling heavy metal high-enriched plants with sludge, so as to solve the problems existing in the prior art.

[0006] In order to achieve the above-mentioned purpose, the technical solution of the present invention discloses a process for preparing biochar by coupling heavy metal high-enriched plants with sludge, comprising the following steps: step 1, pretreatment, pretreating heavy metal high-enriched plants and sludge to obtain sludge with a water content of 60-80% and heavy metal high-enriched plant particles with a particle size of less than 1 cm; step 2, uniformly mixing the sludge, heavy metal high-enriched plant particles, a curing agent, and a passivating agent; the curing agent is limestone, and the passivating agent is a combination of any one or more of zeolite and calcium-based bentonite; the mass ratio of the sludge, heavy metal high-enriched plant particles, the curing agent, and the passivating agent is 1: (0.5-2): (0.1-0.3): (0.1-0.5); step 3, drying the mixture obtained in step 2, and the moisture content of the mixture after drying is less than 10%; step 4, pyrolyzing the mixture obtained in step 3 to obtain biochar.

[0007] Furthermore, in step 2, the mass ratio of the sludge, heavy metal highly enriched plant particles, solidifying agent, and passivating agent is 1:1:0.2:0.2.

[0008] Furthermore, the pyrolysis treatment in step 4 is carried out in an anaerobic or anoxic environment by heating in stages, and the specific process is as follows: the pyrolysis temperature in the first stage is 300-450 degrees, the heating rate is 10-20°C / min; the insulation time is 3-6h; the pyrolysis temperature in the second stage is 500-800 degrees, the heating rate is 5-15°C / min; the insulation time is 2-5h.

[0009] Furthermore, the heavy metal high-accumulation plants are any one or more combinations of Indian mustard, comfrey, and spatholobi, and the heavy metals are any one or more combinations of Cd, Pd, and Zn.

[0010] Furthermore, the pretreatment of the sludge in step 1 includes filtration, wherein the filtration is performed by mechanical filtration; and the pretreatment of the heavy metal high-accumulation plants in step 1 includes crushing.

[0011] The present invention also discloses a system for preparing biochar from plants with high heavy metal accumulation coupled with sludge, comprising a biomass crushing device, a sludge filtering device, a filter pressing device, a mixing and feeding device, a drying device, a pyrolysis device, a sewage treatment and disposal device, a waste gas treatment device, and a biochar cooling device; the biomass crushing device is used to crush and granulate plants with high heavy metal accumulation to obtain plant particles with high heavy metal accumulation, and is a wet material straw crusher; the sludge filtering device is provided with a metal filter screen for removing large impurities in the sludge; the filter pressing device is The belt filter press; the mixing and feeding device comprises a first mixing component and a spiral feeding component; the first mixing component comprises a transmission belt, a pressing rod and a discharging device; the transmission belt is arranged below the discharging port of the belt filter press; the discharging device is arranged above the transmission belt, between the discharging port of the belt filter press and the pressing rod, and is connected to the discharging port of the biomass crushing device for discharging plant particles with high heavy metal enrichment; the pressing rod is arranged on one side of the transmission belt for discharging plant particles with high heavy metal enrichment and sludge treated by the filter press device; The material is extruded and then enters the spiral feeding assembly through a transmission belt; the spiral feeding assembly comprises an outer tube, a spiral feeding pipe and a preheating assembly; the spiral feeding pipe is arranged inside the outer tube, and at least two feeding ports are arranged on the outer tube for feeding heavy metal highly enriched plant particles and sludge mixture, curing agent and / or passivating agent; the preheating assembly comprises a preheating water pipe; the drying device is a drum drying device; the pyrolysis device comprises a drum pyrolysis furnace and a pyrolysis spiral feeding device; the feeding port of the pyrolysis spiral feeding device is the same as that of the drum drying device. The discharge port of the drying equipment is connected, and the discharge port is connected to the drum pyrolysis furnace; the sewage treatment and waste gas treatment devices are common sewage treatment and waste gas treatment devices; the sewage treatment feed port is connected to the sewage outlet of the filter press device and the drying device; the waste gas treatment device feed port is connected to the waste gas outlet of the drying device and the pyrolysis device; the biochar cooling device includes a spiral discharge component and a water cooling component, the water cooling includes a water cooling pipe and a cooling water circulation system, and the water cooling pipe is connected to the preheating water pipe of the mixing and feeding device.

[0012] Furthermore, the inner wall of the drum pyrolysis furnace body is provided with material guide plates, and the material guide plates include two groups, which are symmetrically distributed on both sides of the center axis of the drum pyrolysis furnace body and are of a spiral structure.

[0013] Furthermore, the drum pyrolysis furnace is also provided with an air flow stirring assembly, which includes at least one group of air inlet pipes, air outlet valves, and a gas pressurizing device, the air inlet pipe is connected with the air outlet of the gas pressurizing device, the air inlet pipe outlet is provided with an air outlet valve, and the air inlet pipe is arranged at an axial position of an opening on one side or both sides of the drum pyrolysis furnace body; the air outlet valve includes a first valve body and a second valve body, the upper valve body and the lower valve body are rotating bodies with through holes arranged inside, the upper valve body and the lower valve body are airtightly connected through a screw structure, the internal through holes of the upper valve body and the lower valve body are coaxial, and an air inlet gap is arranged on the contact surface of the upper valve body and the lower valve body, one side of the air inlet gap is connected with the inner side surfaces of the upper valve body and the lower valve body, and the other side is connected to the air inlet pipe through the air inlet hole arranged on the lower valve body.

[0014] Furthermore, the outlet direction of the air outlet valve is downward, and the angle with the horizontal line is 15-45 degrees.

[0015] The present invention provides a system and process for preparing biochar by coupling heavy metal high-enriched plants with sludge, which can conveniently realize the comprehensive treatment of heavy metal high-enriched plants and sludge. The treatment process is relatively simple and has good applicability, and can be easily modified and upgraded on the basis of the existing sludge pyrolysis treatment system.

[0016] The use of heavy metal-rich plants and sludge coupling treatment is conducive to taking advantage of the high carbon content of plants, and using the pyrolysis gas produced during the pyrolysis process as system energy can significantly reduce system energy consumption. At the same time, biomass and sludge can also work together during the pyrolysis process, which can increase the specific surface area of ​​the final biochar while ensuring the heavy metal solidification effect, and realize the comprehensive disposal and resource utilization of sludge biomass while effectively treating pollution.

[0017] In terms of specific hardware, the mixing effect in a small space can be achieved by setting up a mixing and feeding device. Especially for the belt filter press, the mixing and feeding device can be integrated into the belt filter press. By improving the pyrolysis furnace, the stirring of raw materials during the pyrolysis process can be strengthened, which is beneficial to strengthen the coupling effect in the pyrolysis process of plants and sludge and improve the technical effect.

[0018] In order to make the concept and other purposes, advantages, features and functions of the present invention more clearly understood, preferred embodiments will be specifically cited in the following specific implementation manner and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0020] Figure 1 It is an overall schematic diagram of a preparation system according to an embodiment of the present invention.

[0021] Figure 2 It is a schematic diagram of a mixing and feeding device of a preparation system according to an embodiment of the present invention.

[0022] Figure 3 It is a schematic diagram of a material guide plate of a pyrolysis device of a preparation system according to an embodiment of the present invention.

[0023] Figure 4 It is a schematic diagram of an airflow stirring assembly of a pyrolysis device of a preparation system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] The present invention discloses a process for preparing biochar by coupling heavy metal high-enrichment plants with sludge, comprising the following steps: step 1, pretreatment, pretreatment of heavy metal high-enrichment plants and sludge to obtain heavy metal high-enrichment plant particles with a water content of 60-80% and a particle size of less than 1 cm;

[0026] Step 2: Evenly mix the sludge, heavy metal highly enriched plant particles, a solidifying agent, and a passivating agent; the solidifying agent is limestone, and the passivating agent is a combination of any one or more of zeolite and calcium-based bentonite; the mass ratio of the sludge, heavy metal highly enriched plant particles, a solidifying agent, and a passivating agent is 1: (0.5-2): (0.1-0.3): (0.1-0.5), preferably 1: 1: 0.2: 0.2.

[0027] Step 3, drying the mixture obtained in step 2, wherein the moisture content of the mixture after drying is less than 10%;

[0028] Step 4: Pyrolysis the mixture obtained in step 3 to obtain biochar. The pyrolysis treatment is carried out in an anaerobic or anoxic environment by heating in stages, and the specific process is as follows: the pyrolysis temperature in the first stage is 300-450 degrees, the heating rate is 10-20 degrees Celsius / min, and the insulation time is 3-6 hours; the pyrolysis temperature in the second stage is 500-800 degrees, the heating rate is 5-15 degrees Celsius / min, and the insulation time is 2-5 hours.

[0029] The heavy metal high-accumulation plants are any one or more combinations of Indian mustard, comfrey, and spatholobi, and the heavy metals are any one or more combinations of Cd, Pd, and Zn.

[0030] The pretreatment of the sludge in step 1 includes filtration, wherein the filtration is performed by mechanical filtration; the pretreatment of the heavy metal high-accumulation plants in step 1 includes crushing.

[0031] While calcium-based bentonite acts as a passivator, it can promote the pyrolysis of biomass to produce combustible gas components such as CO and methane during the pyrolysis process, which is beneficial to improving its energy recovery efficiency.

[0032] In view of the above process, the present invention provides the following embodiments:

[0033] Example 1

[0034] The heavy metal highly enriched plant, Pinus armeniaca, is crushed into heavy metal highly enriched plant particles with a particle size of less than 1 cm; the sludge is pretreated to obtain sludge with a water content of 70%. Among them, the heavy metals of the highly enriched plants and sludge are mainly copper. Then the sludge, heavy metal highly enriched plant particles, a solidifying agent, and a passivating agent are evenly mixed; the solidifying agent is limestone, and the passivating agent is calcium-based bentonite; the mass ratio of the sludge, heavy metal highly enriched plant particles, a solidifying agent, and a passivating agent is 1:1:0.2:0.2, and then the obtained mixture is dried, and the moisture content of the mixture after drying is less than 10%; then the obtained mixture is pyrolyzed to obtain biochar. The pyrolysis treatment is carried out in an anaerobic or anoxic environment with a staged heating process, and the specific process is as follows: the pyrolysis temperature in the first stage is 400 degrees, the heating rate is 15°C / min, and the insulation time is 5 hours; the pyrolysis temperature in the second stage is 650 degrees, the heating rate is 10°C / min, and the insulation time is 4 hours.

[0035] Comparative Example 1

[0036] After filtering the sludge with a water content of 70%, the sludge is uniformly mixed with a curing agent and a passivating agent; the curing agent is limestone, and the passivating agent is calcium-based bentonite; the mass ratio of the sludge, curing agent and passivating agent is 1:0.2:0.2, and then the obtained mixture is dried, and the moisture content of the mixture after the drying treatment is less than 10%; and then pyrolysis treatment is performed, and the specific pyrolysis process is consistent with Example 1.

[0037] The copper content in the heavy metal high-accumulation plant Herba Lysimachiae, sludge and the final product biochar used in Example 1 and Comparative Example 1 was measured, and the measurement can be carried out using a common measurement method.

[0038] This application adopts the BCR step-by-step extraction method, and the test results are shown in the table below. It should be noted that copper exists in different forms in the heavy metal high-accumulation plant Pinus sylvestris, sludge and the final product biochar, among which the acid-soluble / exchangeable and reducible states have higher environmental hazards, while the oxidizable and residual states have the lowest hazards.

[0039] Table 1: Copper content in Example 1 and Comparative Example 1

[0040]

[0041]

[0042] From the above table, it can be seen that the proportion of acid-soluble / exchangeable copper in the biochar prepared in Example 1 is significantly lower than that in Comparative Example 1, and the proportion of residual copper is significantly increased, indicating that the coupling treatment has a better fixation effect on heavy metals.

[0043] The specific surface areas of the final product biochar were measured and the specific surface areas of Example 1 and Comparative Example 1 were 98 m 2 / g, 65m 2 / g, indicating that the synergistic treatment can significantly increase the specific surface area of ​​biochar, which is beneficial to improving its performance and product price in subsequent applications.

[0044] The relevant specific process parameters set for this application are experimentally verified by the following examples

[0045] Table 2: Specific conditions of Examples 2-5 and Comparative Example 2

[0046]

[0047] From the above table, it can be seen that the proportion of oxidizable and residual copper in the biochar prepared in Examples 2-5 is more than 80%, compared with 59.73% in Example 1, indicating that the coupling treatment has a better fixation effect on heavy metals.

[0048] By comparing Examples 4 and 5, Comparative Example 2 and Example 1, it can be seen that the addition of curing agent and passivating agent has a good effect on the curing of heavy metals, and also affects the specific surface area of ​​the final biochar. The specific surface areas of the final products in Examples 1, 4, 5 and Comparative Example 2 are 98 m 2 / g, 85m 2 / g、100m 2 / g、104m 2 / g, it can be seen that further increasing the proportion of curing agent and passivating agent, especially the proportion of passivating agent, has limited improvement.

[0049] By comparing Example 3 with Example 1, we can see the influence of different pyrolysis processes on the final product. The staged pyrolysis has a significantly better effect on the solidification of heavy metals.

[0050] As attached Figure 1-4 As shown, the present invention also provides a system for preparing biochar by coupling heavy metal high-enriched plants with sludge, including a biomass crushing device 1, a sludge filtering device 2, a filter pressing device 3, a mixing and feeding device 4, a drying device 5, a pyrolysis device 6, a sewage treatment and disposal device O1, a waste gas treatment device O2, and a biochar cooling device 7;

[0051] The biomass crushing device 1 is used to crush and granulate heavy metal highly enriched plants to obtain heavy metal highly enriched plant particles, and is a wet material straw crusher; the biomass is not required to be in a dry state during the pretreatment stage, which can reduce the biomass pretreatment process and eliminate the need for a drying step.

[0052] The sludge filtering device 2 is provided with a metal filter screen for removing large impurities in the sludge; it can be a common filtering device, which can be set during the sludge collection and loading process, and can also be set in the sludge treatment plant.

[0053] The filter press device 3 is a belt filter press; it is a common belt filter press, which performs preliminary dehydration treatment on the sludge and can generally reduce the water content of the sludge to below 30%.

[0054] As attached Figure 2As shown, the mixing and feeding device 4 includes a first mixing component 41 and a spiral feeding component 42. The first mixing component 41 includes a transmission belt 411, a pressing rod 412, and a discharging device 413. The transmission belt 411 is arranged below the discharging port of the belt filter press 3. The discharging device 413 is arranged above the transmission belt 411, between the discharging port of the belt filter press 3 and the pressing rod 412, and is connected to the discharging port of the biomass crushing device 1, and is used for discharging heavy metal highly enriched plant particles. The pressing rod 412 is arranged on one side of the transmission belt 411, and is used for discharging heavy metal highly enriched plant particles. The high-enriched plant particles and the sludge treated by the filter press are squeezed and then enter the spiral feeding component 42 through the transmission belt; the spiral feeding component includes an outer tube 421, a spiral feeding pipe 422, and a preheating component 423. The spiral feeding pipe 422 is arranged inside the outer tube 421, and at least two feeding ports 421a are arranged on the outer tube 421 for feeding the mixture of heavy metal-rich plant particles and sludge, curing agent and / or passivating agent. The preheating component 423 includes a preheating water pipe, which is arranged on the inner side of the outer tube 421 and arranged in a spiral. The first mixing component 41 and the spiral feeding component 42 also include their own driving components, which are driven by common motors.

[0055] The drying device 5 is a drum drying device;

[0056] The pyrolysis device 6 includes a drum pyrolysis furnace 61 and a pyrolysis screw feeding device; the feeding port of the pyrolysis screw feeding device is connected to the discharge port of the drum drying equipment, and the discharge port is connected to the drum pyrolysis furnace.

[0057] The pyrolysis gas generated by the pyrolysis device 6 is used for heating and temperature raising itself, and can also be used for heating and temperature raising of the drying device 5 .

[0058] The sewage treatment device O1 and the waste gas treatment device O2 are common sewage treatment devices and waste gas treatment devices; the feed port of the sewage treatment device O1 is connected to the sewage outlet of the filter press device 3, the drying device 5, and the pyrolysis device 6; the feed port of the waste gas treatment device O2 is connected to the waste gas outlet of the drying device 5 and the pyrolysis device 6;

[0059] The biochar cooling device 7 includes a spiral discharging component and a water cooling component. The water cooling component includes a water cooling pipe and a cooling water circulation system. The water cooling pipe is connected to the preheating water pipe of the mixing and feeding device 4.

[0060] As attached Figure 3 , 4As shown, the inner wall of the drum pyrolysis furnace body 61 is provided with a material guide plate 611, and the material guide plate 611 includes two groups, namely a left material guide plate 611a and a right material guide plate 611b, which are symmetrically distributed on both sides of the central axis of the drum pyrolysis furnace body, and are both spiral structures. When the drum pyrolysis furnace body 61 rotates, it can drive the materials on both sides to move toward the center in opposite directions, which is conducive to sufficient pyrolysis.

[0061] Attached Figure 3 The material guide plate 611 shown is composed of a plurality of phase-separated material guide sub-plates 611zb, or can be a complete continuous material guide plate. The phase-separated material guide sub-plates 611zb can significantly reduce the manufacturing and processing costs.

[0062] An airflow stirring assembly 612 is arranged inside the drum pyrolysis furnace body 61, and the airflow stirring assembly 612 includes at least one group of air inlet pipes 6121, air outlet valves 6122, and a gas pressurizing device (not shown in the figure). The air inlet pipe 6121 is connected to the air outlet of the gas pressurizing device, and the air outlet of the air inlet pipe 6121 is provided with an air outlet valve 6122. The air inlet pipe 6121 is arranged at the axial position of the opening on one side or both sides of the drum pyrolysis furnace body.

[0063] The outlet valve 6122 includes a first valve body F1 and a second valve body F2. The upper valve body F1 and the lower valve body F2 are rotating bodies with through holes arranged inside. The upper valve body F1 and the lower valve body F2 are connected airtightly through a screw structure. The internal through holes are coaxial. An air intake gap F21 is arranged on the contact surface of the upper valve body F1 and the lower valve body F2. One side of the air intake gap F21 is connected to the inner side of the upper valve body F1 and the lower valve body F2, and the other side is connected to the air intake pipe 6121 through the air intake hole F22 arranged on the lower valve body F2. The internal through holes of the upper valve body F1 and the lower valve body F2 are in a trumpet shape with one end larger and the other end smaller, wherein the inner diameter of the through hole on the side close to the contact surface of the upper valve body F1 and the lower valve body F2 is smaller.

[0064] When in use, the gas pressurizing device allows high-speed compressed gas to enter the air intake gap F21 through the air intake pipe 6121 and the air intake hole F22, and is ejected from the air intake gap F21 port, which can drive the gas inside the drum pyrolysis furnace body 61 to follow the compressed gas and be ejected from the air outlet valve 6122, forming gas turbulence, which is conducive to sufficient pyrolysis.

[0065] The outlet direction of the air outlet valve 6122 is downward, and the angle with the horizontal line is 15-45 degrees, which is more conducive to stirring the lower raw materials.

[0066] The airflow stirring component 612 sprays nitrogen gas to the drum pyrolysis furnace body 61, and its preferred working time is the second half of the second stage pyrolysis. That is, after the second stage pyrolysis is heated to the preset temperature and the insulation time reaches half of the preset insulation time, nitrogen gas is blown in, and the gas purity is greater than 95%. The gas pressure in the pyrolysis furnace is maintained at 1.2-2 times the atmospheric pressure by blowing in nitrogen gas. The carbonization quality is improved by gas stirring and pressurization effect.

[0067] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0068] It should be noted that, unless otherwise clearly specified and limited, the terms such as "install", "connect", "connect", "fix", "set" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0069] In addition, it should be noted that in the description of the present invention, the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present application. In the description of the present invention, unless otherwise stated, the meaning of "multiple" refers to two or more.

[0070] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A process for preparing biochar by coupling heavy metal high-enrichment plants with sewage sludge, characterized in that: The steps include: Step 1: pretreatment, pretreating heavy metal high-accumulation plants and sludge to obtain heavy metal high-accumulation plant particles with a sludge water content of 60-80% and a particle size of less than 1 cm; Step 2, uniformly mix the sludge, heavy metal highly enriched plant particles, a solidifying agent, and a passivating agent; the solidifying agent is limestone, and the passivating agent is a combination of any one or more of zeolite and calcium-based bentonite; the mass ratio of the sludge, heavy metal highly enriched plant particles, the solidifying agent, and the passivating agent is 1: (0.5-2): (0.1-0.3): (0.1-0.5); Step 3, drying the mixture obtained in step 2, wherein the moisture content of the mixture after drying is less than 10%; Step 4, pyrolyzing the mixture obtained in step 3 to obtain biochar; The pyrolysis treatment in step 4 is carried out in an oxygen-free or anoxic environment by heating in stages, and the specific process is as follows: the pyrolysis temperature in the first stage is 300-450 degrees, the heating rate is 10-20 degrees Celsius / min, and the holding time is 3-6 hours; the pyrolysis temperature in the second stage is 500-800 degrees Celsius, the heating rate is 5-15 degrees Celsius / min, and the holding time is 2-5 hours. After the second stage pyrolysis is heated to the preset temperature, nitrogen is blown in when the holding time reaches half of the preset holding time to maintain the pressure in the pyrolysis furnace at 1.2-2 times the atmospheric pressure; The pretreatment of the sludge in step 1 includes filtration, wherein the filtration is performed by mechanical filtration; the pretreatment of the heavy metal high-accumulation plants in step 1 includes crushing.

2. The process for preparing biochar by coupling heavy metal high-accumulation plants with sewage sludge according to claim 1 is characterized by: The mass ratio of the sludge, heavy metal highly enriched plant particles, solidifying agent and passivating agent in step 2 is 1:1:0.2:0.

2.

3. The process for preparing biochar by coupling heavy metal high-accumulation plants with sewage sludge according to claim 1 is characterized by: The heavy metal high-accumulation plants are any one or more combinations of Indian mustard, comfrey, and spatholobi, and the heavy metals are any one or more combinations of Cd, Pd, and Zn.

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