Method and system for preparing biochar and co-producing carbon dioxide through internal heating type pyrolysis

Abstract

The invention belongs to the field of energy and environmental protection, and discloses a method and system for preparing biochar and co-producing carbon dioxide through internal heating type pyrolysis. The preparation method comprises the following steps: providing a medium-temperature oxygen-carrying heat carrier to be in contact with a solid organic fuel and pyrolyzing the medium-temperature oxygen-carrying heat carrier and the solid organic fuel to obtain a pyrolysis gas-phase product and a pyrolysis solid-phase product; separating the pyrolysis solid-phase product to obtain a low-temperature oxygen-carrying heat-carrying body and biochar; the pyrolysis gas-phase product makes contact with a high-temperature oxygen-carrying heat carrier and is oxidized, and a high-temperature gas product and a medium-temperature oxygen-carrying heat carrier are obtained; carrying out first cooling separation on the high-temperature gas product to obtain high-concentration carbon dioxide; the obtained medium-temperature oxygen-carrying heat carrier can be used for pyrolytic reaction of solid organic fuel. By utilizing the method and the system, high-concentration carbon dioxide and high-concentration nitrogen can be obtained while pyrolysis of the solid organic fuel is realized to produce the biochar, and the effect of controlling pollutant and carbon emission is achieved while effective utilization of resources is realized.

Description

Technical Field

[0001] The invention provides a method and system for preparing biochar by endothermic pyrolysis and co-producing carbon dioxide, belonging to the field of energy and environmental protection. Background Art

[0002] By using solid organic fuels such as coal, petroleum coke or biomass, high-carbon products such as coke, charcoal or biochar can be obtained through pyrolysis at high temperature. Coke, charcoal, biochar, etc. are widely used in steel, non-ferrous metal smelting, soil, water and atmospheric environmental governance, electrochemical electrodes and other materials. Pyrolysis is the process of achieving high-temperature decomposition of solid fuels and further transformation of decomposition products under high-temperature and oxygen-deficient conditions. While obtaining solid carbon products with high carbon content, small molecular gas products such as carbon monoxide, hydrogen, methane, carbon dioxide and liquid products such as hydrocarbons, acid aldehydes, alcohols and ketones and aromatic compounds are produced. The gaseous products and liquid products can be used as fuels to provide heat energy for the pyrolysis process, or as raw materials for gas or chemical extraction.

[0003] The pyrolysis process and device generally adopt a fixed bed or rotary kiln reactor, using external heat sources such as fuel combustion or electric heating to increase the temperature of the pyrolysis reactor through indirect heating to provide heat for the pyrolysis reaction. The heat transfer efficiency and heating effect of this external heating pyrolysis method are limited by the space and materials of the device. At the same time, the pyrolysis process and fuel combustion process must also consider the emission of pollutants such as gas and liquid.

[0004] In response to the above problems, the present invention aims to provide a method of utilizing metal oxides or metal oxide minerals as solid oxygen and heat carriers to prepare biochar under endothermic pyrolysis conditions while obtaining high-concentration carbon dioxide, thereby reducing carbon emissions and achieving effective utilization of resources. Summary of the invention

[0005] The purpose of the present invention is to provide a method and system for producing biochar and co-producing carbon dioxide by pyrolyzing solid organic pollutants using metal oxides or metal oxide minerals as oxygen carriers and heat carriers. By using the method and system, high-concentration carbon dioxide and high-concentration nitrogen can be obtained while producing biochar by pyrolyzing solid organic fuels, thereby achieving effective resource utilization and controlling pollutants and carbon emissions.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] The present invention provides a method for preparing biochar and co-producing carbon dioxide by endothermic pyrolysis, comprising the following steps:

[0008] Providing a medium-temperature oxygen-carrying heat carrier to contact with a solid organic fuel and pyrolyze the fuel to obtain a pyrolysis gas phase product and a pyrolysis solid phase product; the pyrolysis solid phase product is separated to obtain a low-temperature oxygen-carrying heat carrier and biochar;

[0009] The pyrolysis gas phase product is contacted with a high temperature oxygen-carrying heat carrier and oxidized to obtain a high temperature gas product and a medium temperature oxygen-carrying heat carrier; the high temperature gas product is subjected to a first cooling separation to obtain high concentration carbon dioxide;

[0010] The obtained medium-temperature oxygen-carrying heat carrier can be used for the pyrolysis reaction of solid organic fuel.

[0011] In some embodiments, the oxygen-carrying heat carrier is a metal oxide or a metal oxide mineral;

[0012] Preferably, the metal oxide is a variable valence iron oxide, and the metal oxide mineral is at least one of hematite or ilmenite materials;

[0013] Preferably, the medium-temperature oxygen-heat carrier is mainly composed of a low-valent metal oxide or a mixture containing at least one element of a low-valent metal oxide, such as ferrosoferric oxide.

[0014] In some embodiments, the temperature of the medium-temperature oxygen-carrying heat carrier is 500-700°C, the temperature of the high-temperature oxygen-carrying heat carrier is 700-900°C, the temperature of the low-temperature oxygen-carrying heat carrier is controlled below 400°C, and the temperature of the pyrolysis is above 400°C;

[0015] Preferably, the low-temperature oxygen-carrying heat carrier is at least one of ferroferric oxide, ferrous oxide, elemental iron and ferric oxide;

[0016] Preferably, the high-temperature oxygen-carrying heat carrier is a high-valent metal oxide or a mixture containing at least one element of a high-valent metal oxide, such as ferric oxide or hematite, ilmenite material, and the like.

[0017] In some embodiments, the mass ratio of the high temperature oxygen-carrying heat carrier to the solid organic fuel is 1:18-1:40;

[0018] Preferably, the solid organic fuel is at least one of wood or crop straw.

[0019] In some embodiments, the high-temperature gas products are mainly high-temperature carbon dioxide and water vapor, and also contain a small amount of sulfur oxides, nitrogen oxides or tar, carbon monoxide, methane and other substances.

[0020] In some embodiments, the first cooling and separating step comprises:

[0021] The high-temperature gas product is in direct contact with cooling water, the gas product is cooled down, and at the same time, the components in the gas product that are soluble in water or in liquid form at low temperature are absorbed by the water flow, releasing a gas product with carbon dioxide as the main component.

[0022] The present invention also provides a method for co-producing nitrogen, the method comprising:

[0023] Providing high-temperature nitrogen gas to contact and exchange heat with the low-temperature oxygen-carrying heat carrier to obtain medium-temperature nitrogen gas and preheated oxygen-carrying heat carrier;

[0024] Providing hot air to contact and react with the preheated oxygen-carrying heat carrier to obtain high-temperature nitrogen that can be used to contact and exchange heat with the low-temperature oxygen-carrying heat carrier and high-temperature oxygen-carrying heat carrier that can be used to contact and oxidize the pyrolysis gas phase product;

[0025] In some embodiments, the oxygen in the hot air reacts with one of the oxygen-carrying heat carriers, iron oxide or ilmenite, in an exothermic reaction, and ferroferric oxide is converted into ferrous oxide while releasing a large amount of heat, and high-temperature nitrogen and high-temperature oxygen-carrying heat carriers can be obtained at the same time.

[0026] Providing air to contact and exchange heat with the medium-temperature nitrogen to obtain low-temperature nitrogen and hot air that can be used to contact and oxidize the preheated oxygen-carrying heat carrier;

[0027] The low-temperature nitrogen is subjected to a second cooling separation to obtain high-concentration nitrogen.

[0028] In some embodiments, the temperature of the high-temperature nitrogen is above 700°C, the temperature of the medium-temperature nitrogen is controlled below 600°C, the temperature of the low-temperature nitrogen is controlled below 350°C, the temperature of the hot air is above 350°C, and the temperature of the preheating oxygen-carrying heat carrier is above 500°C.

[0029] In some embodiments, the second cooling and separating step comprises:

[0030] The low-temperature nitrogen is in direct contact with cooling water to reduce the temperature and wash out impurities, and high-concentration nitrogen is obtained after gas and water separation.

[0031] The present invention also provides a system for preparing biochar by endothermic pyrolysis and co-producing carbon dioxide.

[0032] include:

[0033] A low-temperature solid-phase pyrolysis device is used to contact the reduced medium-temperature oxygen-carrying heat carrier with the solid organic fuel for pyrolysis to obtain a pyrolysis gas phase product and a pyrolysis solid phase product;

[0034] A separation device, used to separate the pyrolysis solid phase product obtained by the reaction of the low-temperature solid phase pyrolysis device to obtain a low-temperature oxygen-carrying heat carrier and biochar;

[0035] A high-temperature gas phase oxidation device, used to contact and oxidize the pyrolysis gas phase product obtained by the reaction of the low-temperature solid phase pyrolysis device with a high-temperature oxygen-carrying heat carrier to obtain a high-temperature gas product and a medium-temperature oxygen-carrying heat carrier, and the medium-temperature oxygen-carrying heat carrier can be transported to the low-temperature solid phase pyrolysis device for pyrolysis reaction with solid organic fuel;

[0036] A first cooling device, used for cooling and separating the high-temperature gas product obtained from the high-temperature gas-phase oxidation device to obtain high-concentration carbon dioxide;

[0037] A carrier-nitrogen heat exchanger is used to bring high-temperature nitrogen into contact with the low-temperature oxygen-carrying heat carrier and exchange heat to obtain medium-temperature nitrogen and preheated oxygen-carrying heat carrier;

[0038] A gas-solid oxidation separation device, used to contact and oxidize and separate the hot air with the preheated oxygen-carrying heat carrier obtained from the carrier-nitrogen heat exchanger, to obtain high-temperature nitrogen that can be used to contact and exchange heat with the low-temperature oxygen-carrying heat carrier in the carrier-nitrogen heat exchanger and a high-temperature oxygen-carrying heat carrier that can be used to contact and oxidize the pyrolysis gas phase product in the high-temperature gas phase oxidation device;

[0039] An air-nitrogen heat exchanger, used to contact and exchange heat between air and the medium-temperature nitrogen obtained from the carrier-nitrogen heat exchanger, to obtain low-temperature nitrogen and hot air that can be used to contact and oxidize with the preheated oxygen-carrying heat carrier in the gas-solid oxidation separation device;

[0040] The second cooling device is used for separating the low-temperature nitrogen obtained from the air-nitrogen heat exchanger through a second cooling process to obtain high-concentration nitrogen.

[0041] The equipment used in the system may be equipped with adjustment, detection, control and protection implementation and automatic control instruments to meet the needs of continuous production.

[0042] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0043] The present invention utilizes metal oxides or their minerals as oxygen-carrying and heat-carrying media, which are in direct contact with solid organic fuels, to achieve rapid heating of the solid organic fuels and initiate a pyrolysis reaction. While achieving pyrolysis of the solid organic fuels to produce biochar, high-concentration carbon dioxide and high-concentration nitrogen are obtained. Compared with traditional pyrolysis methods, this method achieves the effect of controlling pollutants and carbon emissions.

[0044] Other features and beneficial effects of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other beneficial effects of the present invention can be realized and obtained by the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 Schematic diagram of the process for preparing biochar and co-producing carbon dioxide by endothermic pyrolysis. DETAILED DESCRIPTION

[0046] The present invention provides a method for preparing biochar and co-producing carbon dioxide by endothermic pyrolysis. Figure 1 As shown, the following steps are included:

[0047] Step 1: providing a medium-temperature oxygen-carrying heat carrier to contact with a solid organic fuel and pyrolyze the fuel to obtain a pyrolysis gas phase product and a pyrolysis solid phase product; the pyrolysis solid phase product is separated to obtain a low-temperature oxygen-carrying heat carrier and biochar;

[0048] Specifically, a medium-temperature oxygen-carrying heat carrier with a temperature of 500-700°C and containing ferrosoferric oxide as its main component is brought into full contact and heat exchange with at least one solid organic fuel selected from wood or crop straw, so that the temperature of the solid organic fuel is raised to above 400°C for pyrolysis, thereby forming pyrolysis solid phase products and pyrolysis gas phase products. At the same time, the medium-temperature oxygen-carrying heat carrier is cooled due to heat exchange to form a low-temperature oxygen-carrying heat carrier with a temperature below 400°C.

[0049] It should be noted that the present invention can use copper oxide, manganese oxide, ferric oxide, ilmenite and ferromanganese compounds as oxygen-carrying heat carriers, among which ferric oxide, ilmenite and ferromanganese compounds have the advantages of being cheap and readily available, and can be separated from biochar by magnetic separation. In addition, the type of oxygen-carrying heat carrier and the operating temperature at each stage are key factors that determine the operating effect, and the type of oxygen-carrying heat carrier and the operating temperature need to match each other.

[0050] Step 2: contacting the pyrolysis gas phase product with a high temperature oxygen-carrying heat carrier and oxidizing it to obtain a high temperature gas product and a medium temperature oxygen-carrying heat carrier; the high temperature gas product is subjected to a first cooling separation to obtain high concentration carbon dioxide;

[0051] Specifically, the pyrolysis gas phase product is contacted with a high-temperature oxygen-carrying heat carrier with a temperature of 700-900°C and a main component of ferric oxide and completely oxidized, wherein the mass ratio of the high-temperature oxygen-carrying heat carrier to the mass ratio of the solid organic fuel is 1:18-1:40, and a high-temperature gas product and a medium-temperature oxygen-carrying heat carrier are obtained. In this process, materials such as ferric oxide undergo a reduction reaction and are converted into ferric oxide and the like, and the temperature is reduced to form a medium-temperature oxygen-carrying heat carrier with a temperature of 500-700°C, and the pyrolysis gas phase product is completely oxidized to produce high-temperature gas products and water, wherein the high-temperature gas product is mainly high-temperature carbon dioxide and water vapor, and there are also a small amount of sulfur oxides, nitrogen oxides or tar, carbon monoxide, methane and other substances. The high-temperature gas product is subjected to a first cooling separation to obtain a high-concentration carbon dioxide, wherein the first cooling separation method is:

[0052] Preferably, the high-temperature gas product is in direct contact with cooling water at a temperature below 40°C, the gas product is cooled, and at the same time, the components in the gas product that are soluble in water or in liquid form at low temperature are absorbed by the water flow, releasing a gas product with carbon dioxide as the main component.

[0053] It should be noted that in the present invention, a small amount of sulfur oxides, nitrogen oxides or tar in the high temperature gas will be absorbed by water, and a small amount of carbon monoxide, methane and other gases that are insoluble in water may be discharged together with carbon dioxide, so the obtained carbon dioxide is high-concentration rather than pure carbon dioxide. In addition, the cooling water mainly plays the role of cooling and washing impurities, and can remove water vapor, macromolecular organic matter, particulate matter and some water-soluble impurities in the gas. The temperature of the cooling water cannot be too high, otherwise it will affect the washing effect on the gas.

[0054] The present invention also provides a method for co-producing nitrogen, comprising the following steps:

[0055] Providing high-temperature nitrogen gas to contact and exchange heat with the low-temperature oxygen-carrying heat carrier to obtain medium-temperature nitrogen gas and preheated oxygen-carrying heat carrier;

[0056] Specifically, the high-temperature nitrogen with a temperature above 700°C is brought into contact with the low-temperature oxygen-carrying heat medium and heat-exchanges are performed to obtain the medium-temperature nitrogen with a temperature below 600°C and the preheated oxygen-carrying heat medium with a temperature above 500°C.

[0057] It should be noted that the purity of the high-temperature nitrogen used in the present invention is higher than the nitrogen content in the air, but lower than the purity of more than 99% required for industrial nitrogen, and still contains a small amount of oxygen and other impurities. Because the temperature of the low-temperature oxygen-carrying heat carrier is relatively low, below 400°C, and the oxygen content is relatively low, the reaction between the oxygen-carrying heat carrier and oxygen is not significant, and the high-temperature nitrogen mainly plays a role in heat exchange.

[0058] Providing hot air to contact and react with the preheated oxygen-carrying heat carrier to obtain high-temperature nitrogen that can be used to contact and exchange heat with the low-temperature oxygen-carrying heat carrier and high-temperature oxygen-carrying heat carrier that can be used to contact and oxidize the pyrolysis gas phase product;

[0059] Specifically, the hot air with a temperature above 350°C is contacted and reacted with the preheated oxygen-carrying heat carrier with a temperature above 500°C to obtain high-temperature nitrogen with a temperature above 700°C and a high-temperature oxygen-carrying heat carrier with a temperature of 700-900°C.

[0060] Providing room temperature air to contact and exchange heat with the medium temperature nitrogen to obtain low temperature nitrogen and hot air that can be used to contact and oxidize the preheated oxygen-carrying heat carrier;

[0061] Specifically, the air at room temperature is brought into contact with the medium-temperature nitrogen at a temperature below 600° C. and heat-exchanged to obtain low-temperature nitrogen at a temperature below 350° C. and hot air at a temperature above 350° C.

[0062] The low-temperature nitrogen is subjected to a second cooling separation to obtain high-concentration nitrogen.

[0063] Specifically, the low-temperature nitrogen with a temperature below 350° C. is subjected to a second cooling separation to obtain high-concentration nitrogen, wherein the second cooling separation method is:

[0064] The low-temperature nitrogen gas flow is in direct contact with cooling water below 40°C, the nitrogen gas is cooled to below 50°C and some impurities in the gas are washed away to obtain hot water and high-concentration nitrogen gas.

[0065] The present invention also provides a system for preparing biochar by endothermic pyrolysis and co-producing carbon dioxide.

[0066] include:

[0067] A low-temperature solid-phase pyrolysis device is used to contact the reduced medium-temperature oxygen-carrying heat carrier with the solid organic fuel for pyrolysis to obtain a pyrolysis gas phase product and a pyrolysis solid phase product;

[0068] A separation device, used to separate the pyrolysis solid phase product obtained by the reaction of the low-temperature solid phase pyrolysis device to obtain a low-temperature oxygen-carrying heat carrier and biochar;

[0069] A high-temperature gas phase oxidation device, used to contact and oxidize the pyrolysis gas phase product obtained by the reaction of the low-temperature solid phase pyrolysis device with a high-temperature oxygen-carrying heat carrier to obtain a high-temperature gas product and a medium-temperature oxygen-carrying heat carrier, and the medium-temperature oxygen-carrying heat carrier can be transported to the low-temperature solid phase pyrolysis device for pyrolysis reaction with solid organic fuel;

[0070] A first cooling device, used for cooling and separating the high-temperature gas product obtained from the high-temperature gas-phase oxidation device to obtain high-concentration carbon dioxide;

[0071] A carrier-nitrogen heat exchanger is used to bring high-temperature nitrogen into contact with the low-temperature oxygen-carrying heat carrier and exchange heat to obtain medium-temperature nitrogen and preheated oxygen-carrying heat carrier;

[0072] A gas-solid oxidation separation device, used to contact and oxidize and separate the hot air with the preheated oxygen-carrying heat carrier obtained from the carrier-nitrogen heat exchanger, to obtain high-temperature nitrogen that can be used to contact and exchange heat with the low-temperature oxygen-carrying heat carrier in the carrier-nitrogen heat exchanger and a high-temperature oxygen-carrying heat carrier that can be used to contact and oxidize the pyrolysis gas phase product in the high-temperature gas phase oxidation device;

[0073] An air-nitrogen heat exchanger, used to contact and exchange heat between air and the medium-temperature nitrogen obtained from the carrier-nitrogen heat exchanger, to obtain low-temperature nitrogen and hot air that can be used to contact and oxidize with the preheated oxygen-carrying heat carrier in the gas-solid oxidation separation device;

[0074] The second cooling device is used for separating the low-temperature nitrogen obtained from the air-nitrogen heat exchanger through a second cooling process to obtain high-concentration nitrogen.

[0075] The equipment used in the system may be equipped with adjustment, detection, control and protection implementation and automatic control instruments to meet the needs of continuous production.

[0076] It should be noted that the system startup process for preparing biochar and co-producing carbon dioxide by internal pyrolysis described in the present invention requires external energy to heat the oxygen-carrying heat carrier to a high temperature, but no external energy input is required during the operation of the system, and it relies on the energy carried by the solid organic fuel and the heat released by the oxidation reaction of the hot air and the oxygen-carrying heat carrier to achieve self-heating balance.

[0077] Since the type of solid organic fuel and the process operating temperature affect the energy consumption of the process, the energy consumption can be adjusted by adjusting the proportion of solid organic fuel participating in the reaction. That is, solid organic fuel with low calorific value and high energy consumption can achieve energy balance by increasing the degree of reaction and reducing the biochar yield.

[0078] The present invention is further described in detail in conjunction with specific embodiments. The following embodiments can enable those skilled in the art to more fully understand the present invention, but do not limit the present invention in any way.

[0079] Embodiment 1:

[0080] The sawdust is used as the raw material, and the iron oxide powder with a particle size of less than 1mm is used as the high-temperature oxygen carrier. The mass ratio of the two is 1:30. The inlet working temperature of the medium-temperature oxygen carrier of the low-temperature solid-phase pyrolysis device is about 580℃. The medium-temperature oxygen carrier is in contact with the added room-temperature sawdust raw material in the low-temperature solid-phase pyrolysis device and undergoes a pyrolysis reaction. The pyrolysis gas product is fully contacted with the 800℃ high-temperature oxygen carrier in the high-temperature gas phase oxidation device and reacts to produce a high-temperature gas product and enters the water washing cooling device. The room temperature 25℃ cooling water is used to produce CO with a temperature of 40℃ and a concentration of 95%. 2 The solid phase product of pyrolysis with a temperature of about 380°C is sent to the magnetic separation device, and the solid biochar with a temperature below 350°C and a low-temperature oxygen carrier and heat carrier are produced respectively by the on-off and magnetic separation effects of the electromagnetic device. The solid biochar is stored in a closed container and cooled to below 40°C by external air cooling to obtain a biochar product with a biochar yield of 42%.

[0081] The low-temperature oxygen-carrying heat carrier is transported into the carrier-nitrogen heat exchanger, and is fully contacted with the high-temperature nitrogen with an inlet temperature of 820°C to obtain a preheated oxygen-carrying heat carrier with a temperature of more than 550°C and a medium-temperature nitrogen with a temperature of about 570°C. The preheated oxygen-carrying heat carrier is transported into the gas-solid oxidation separation device, and after being fully contacted with 430°C hot air, the temperature is raised to more than 860°C to obtain a high-temperature oxygen-carrying heat carrier, and a high-temperature nitrogen with a temperature of more than 820°C is generated. The high-temperature oxygen-carrying heat carrier is transported to the high-temperature gas-phase oxidation device to contact and react with the pyrolysis gas phase product, and the high-temperature nitrogen is transported to the carrier-nitrogen heat exchanger to exchange heat with the low-temperature oxygen-carrying heat carrier to obtain a medium-temperature nitrogen with a temperature of about 550°C. The medium-temperature nitrogen flows into the air-nitrogen heat exchanger, and is fully heat-exchanged with the room-temperature air supplied from the outside to produce a low-temperature nitrogen with a temperature of 290°C and a hot air with a temperature of about 430°C. The hot air is sent to the gas-solid oxidation separation device. The low-temperature nitrogen enters the water cooling device and is fully contacted with the cooling water with an inlet temperature of 25°C, generating nitrogen with a temperature of 40°C and a concentration of 87% and 40°C hot water.

[0082] Embodiment 2:

[0083] Sawdust is used as raw material, and iron oxide powder with a particle size of less than 1.5mm is used as high-temperature oxygen carrier. The mass ratio of the two is 1:18. The inlet working temperature of the medium-temperature oxygen carrier of the low-temperature solid-phase pyrolysis device is about 700℃. The medium-temperature oxygen carrier is in contact with the added room-temperature sawdust raw material in the low-temperature solid-phase pyrolysis device and undergoes pyrolysis reaction. The pyrolysis gas product is fully contacted with the 890℃ high-temperature oxygen carrier in the high-temperature gas phase oxidation device and reacts to produce high-temperature gas products and enter the water washing cooling device. The room temperature 25℃ cooling water is used to produce CO with a temperature of 40℃ and a concentration of 98.5%. 2 The solid phase product of pyrolysis with a temperature of about 400°C is sent to the magnetic separation device, and the magnetic separation produces solid biochar with a temperature below 380°C and a low-temperature oxygen carrier and heat carrier. The solid biochar is stored in a closed container and cooled to below 40°C by external air cooling to obtain a biochar product with a biochar yield of 37%.

[0084] The low-temperature oxygen-carrying heat carrier is transported into the carrier-nitrogen heat exchanger, and is fully contacted with the high-temperature nitrogen with an inlet temperature of 880°C to obtain a preheated oxygen-carrying heat carrier with a temperature of more than 580°C and a medium-temperature nitrogen with a temperature of about 587°C. The preheated oxygen-carrying heat carrier is transported into the gas-solid oxidation separation device, and is fully contacted with 410°C hot air and heated to above 890°C to obtain a high-temperature oxygen-carrying heat carrier and high-temperature nitrogen. The high-temperature oxygen-carrying heat carrier is transported to the high-temperature gas-phase oxidation device to contact and react with the pyrolysis gas phase product, and the high-temperature nitrogen is transported to the carrier-nitrogen heat exchanger to exchange heat with the low-temperature oxygen-carrying heat carrier to obtain medium-temperature nitrogen with a temperature of 587°C. The medium-temperature nitrogen flows into the air-nitrogen heat exchanger, and is fully heat-exchanged with the room-temperature air supplied from the outside to produce low-temperature nitrogen with a temperature of 270°C and hot air with a temperature of about 410°C. The hot air is sent to the gas-solid oxidation separation device. The low-temperature nitrogen enters the water cooling device and is fully contacted with the cooling water with an inlet temperature of 25°C, producing nitrogen with a temperature of 40°C and a concentration of 91% and 40°C hot water.

[0085] Embodiment 3:

[0086] Corn stalk powder is used as raw material, and iron oxide powder with a particle size of less than 1mm is used as high-temperature oxygen carrier. The mass ratio of the two is 1:24. The inlet working temperature of the medium-temperature oxygen carrier of the low-temperature solid-phase pyrolysis device is about 550°C. The medium-temperature oxygen carrier is contacted with the added room-temperature corn stalk powder raw material in the low-temperature solid-phase pyrolysis device and a pyrolysis reaction occurs. The generated pyrolysis gas phase product is fully contacted with the 820°C high-temperature oxygen carrier in the high-temperature gas phase oxidation device and reacts to generate high-temperature gas products and enter the water washing cooling device. The cooling water with a temperature of 30°C is used to generate CO with a temperature of 43°C and a concentration of 97%. 2 The solid phase product of pyrolysis at a temperature of about 410°C enters the magnetic separation device, and the solid biochar and low-temperature oxygen carrier are produced respectively by the on-off and magnetic separation of the electromagnetic device. The solid biochar is stored in a closed container and cooled to below 40°C by external air cooling to obtain a biochar product with a biochar yield of 30%.

[0087] The low-temperature oxygen-carrying heat carrier is transported into the carrier-nitrogen heat exchanger, and is fully contacted with the high-temperature nitrogen with an inlet temperature of 823°C to obtain a preheated oxygen-carrying heat carrier with a temperature of about 580°C or more and a medium-temperature nitrogen with a temperature of about 600°C. The preheated oxygen-carrying heat carrier is transported into the gas-solid oxidation separation device, and after being fully contacted with the 410°C hot air, the temperature is raised to above 850°C to obtain a high-temperature oxygen-carrying heat carrier, and a high-temperature nitrogen with a temperature of more than 820°C is generated. The high-temperature oxygen-carrying heat carrier is transported to the high-temperature gas phase oxidation device to contact and react with the pyrolysis gas phase product, and the high-temperature nitrogen is transported to the carrier-nitrogen heat exchanger to exchange heat with the low-temperature oxygen-carrying heat carrier to obtain medium-temperature nitrogen with a temperature of about 600°C. The medium-temperature nitrogen flows into the air-nitrogen heat exchanger, and is fully heat-exchanged with the room-temperature air supplied from the outside, to produce low-temperature nitrogen with a temperature of about 330°C and hot air with a temperature of about 410°C. The hot air is sent to the gas-solid oxidation separation device. The low-temperature nitrogen enters the water cooling device and is fully contacted with 30°C cooling water, producing nitrogen with a temperature of 38°C and a concentration of 91% and 38°C hot water.

[0088] Embodiment 4:

[0089] Corn stalk powder is used as raw material, and ilmenite powder with a particle size of less than 0.5 mm is used as high-temperature oxygen carrier. The mass ratio of the two is 1:35. The inlet working temperature of the medium-temperature oxygen carrier of the low-temperature solid-phase pyrolysis device is about 520°C. The medium-temperature oxygen carrier is contacted with the added room-temperature corn stalk powder in the low-temperature solid-phase pyrolysis device and a pyrolysis reaction occurs. The generated pyrolysis gas phase product is fully contacted with the 870°C high-temperature oxygen carrier in the high-temperature gas phase oxidation device and reacts to generate high-temperature gas products and enter the water washing cooling device. Using 38°C cooling water, CO with a temperature of 46°C and a concentration of 96% is generated. 2 The solid phase product of pyrolysis at a temperature of about 375°C enters the magnetic separation device, and the solid biochar and low-temperature oxygen carrier are produced respectively by the on-off and magnetic separation of the electromagnetic device. The solid biochar is stored in a closed container and cooled to below 40°C by external air cooling to obtain a biochar product with a biochar yield of 33%.

[0090] The low-temperature oxygen-carrying heat carrier is transported into the carrier-nitrogen heat exchanger, and is fully contacted with the high-temperature nitrogen with an inlet temperature of 850°C to obtain a preheated oxygen-carrying heat carrier with a temperature of more than 610°C and a medium-temperature nitrogen with a temperature of about 580°C. The preheated oxygen-carrying heat carrier is transported into the gas-solid oxidation separation device, and after being fully contacted with the 420°C hot air, the temperature is raised to more than 880°C to obtain a high-temperature oxygen-carrying heat carrier, and a high-temperature nitrogen with a temperature of more than 850°C is generated. The high-temperature oxygen-carrying heat carrier is transported to the high-temperature gas-phase oxidation device to contact and react with the pyrolysis gas phase product, and the high-temperature nitrogen is transported to the carrier-nitrogen heat exchanger to exchange heat with the low-temperature oxygen-carrying heat carrier to obtain a medium-temperature nitrogen with a temperature of about 580°C. The medium-temperature nitrogen flows into the air-nitrogen heat exchanger, and is fully heat-exchanged with the external normal-temperature air to produce a low-temperature nitrogen with a temperature of about 350°C and a hot air with a temperature of about 420°C. The hot air is sent to the gas-solid oxidation separation device. The low-temperature nitrogen enters the water cooling device and is fully contacted with 38°C cooling water, producing nitrogen with a temperature of 40°C and a concentration of 94% and 40°C hot water.

[0091] Embodiment 5:

[0092] Corn stalk powder is used as raw material, and ilmenite powder with a particle size of less than 0.5 mm is used as high-temperature oxygen carrier. The mass ratio of the two is 1:40. The inlet working temperature of the medium-temperature oxygen carrier of the low-temperature solid-phase pyrolysis device is about 516°C. The medium-temperature oxygen carrier is contacted with the added room-temperature corn stalk powder in the low-temperature solid-phase pyrolysis device and a pyrolysis reaction occurs. The generated pyrolysis gas phase product is fully contacted with the 704°C high-temperature oxygen carrier in the high-temperature gas phase oxidation device and reacts to generate high-temperature gas products and enter the water washing cooling device. Using 35°C cooling water, CO with a temperature of 42°C and a concentration of 91% is generated. 2 The solid phase product of pyrolysis at a temperature of about 355°C enters the magnetic separation device, and the magnetic separation produces solid biochar and low-temperature oxygen-carrying heat carrier at a temperature below 330°C. The solid biochar is stored in a closed container and cooled to below 40°C by external air cooling to obtain a biochar product with a biochar yield of 42%.

[0093] The low-temperature oxygen-carrying heat carrier is transported into the carrier-nitrogen heat exchanger, and is fully contacted with the high-temperature nitrogen with an inlet temperature of 710°C to obtain a preheated oxygen-carrying heat carrier with a temperature of 520°C and a medium-temperature nitrogen with a temperature of about 513°C. The preheated oxygen-carrying heat carrier is transported into the gas-solid oxidation separation device, and is fully contacted with 350°C hot air and heated to above 720°C to obtain a high-temperature oxygen-carrying heat carrier and high-temperature nitrogen. The high-temperature oxygen-carrying heat carrier is transported to the high-temperature gas-phase oxidation device to contact and react with the pyrolysis gas phase product, and the high-temperature nitrogen is transported to the carrier-nitrogen heat exchanger to exchange heat with the low-temperature oxygen-carrying heat carrier to obtain a medium-temperature nitrogen with a temperature of about 513°C. The medium-temperature nitrogen flows into the air-nitrogen heat exchanger, and is fully heat-exchanged with the room-temperature air supplied from the outside to produce a low-temperature nitrogen with a temperature of about 275°C and a hot air with a temperature of about 350°C. The hot air is sent to the gas-solid oxidation separation device. The low-temperature nitrogen enters the water cooling device and is fully contacted with 38°C cooling water, producing nitrogen with a temperature of 44°C and a concentration of 86% and 44°C hot water.

[0094] Comparative Example:

[0095] Sawdust is used as raw material, and iron oxide powder with a particle size of less than 1mm is used as oxygen carrier and heat carrier. The mass ratio of the two is 1:30. They are added to a pyrolysis device with an operating temperature of about 800℃. The device uses external electric heating. The fuel stays in the pyrolysis device for about 480 seconds. High-temperature gas products are generated and enter the water washing cooling device. Cooling water at room temperature of 25℃ is used to generate CO with a temperature of 40℃ and a concentration of 45%. 2 Air flow and hot water at 40°C. The pyrolysis solid phase product with a temperature of about 760°C is air-cooled in a closed container for 12 hours, and then sent to a magnetic separation device after cooling to below 200°C. The solid biochar and low-temperature oxygen-carrying heat carrier are separated by the on-off and magnetic separation of the electromagnetic device. The solid biochar is stored in a closed container and cooled to below 40°C by external air cooling to obtain a biochar product with a biochar yield of 16%.

[0096] The low-temperature oxygen-carrying heat carrier is transported to the air oxidation device, heated to above 500°C by electric heating, and then fully contacted with air to react, thereby obtaining a high-temperature oxygen-carrying heat carrier at 820°C and high-temperature nitrogen. The high-temperature nitrogen is transported to the water cooling device, fully contacted with cooling water at an inlet temperature of 25°C, and produces nitrogen at a temperature of 40°C and a concentration of 89% and hot water at 40°C.

[0097] It can be seen from the above embodiments and comparative examples that providing an external heat source can also produce biochar and carbon dioxide, but the carbon dioxide concentration and biochar yield are both low. The main advantage of the internal heat method of the present invention is that during internal heating, the oxygen-carrying heat carrier directly contacts the raw material and heats it. Compared with the indirect heating of the raw material by the external heat source through the reactor wall, the heating is more uniform and the heat transfer efficiency is higher. At the same time, when the internal heat method is adopted, the system dissipates less heat to the outside world, and the energy utilization efficiency is higher. In addition, under the external heat method, the solid organic fuel and the oxygen carrier mixture are heated at the same time, and the oxygen carrier will react with the solid fuel to reduce the biochar yield, and the reaction of the oxygen carrier with the gas phase product produced by the decomposition of the solid fuel will be affected and the reaction is insufficient, resulting in a more complex gas product composition and a lower carbon dioxide concentration in the produced gas product. In the internal heat method of the present invention, the high-temperature oxygen-carrying heat carrier only reacts with the gas phase product to produce a high concentration of carbon dioxide, while the medium-temperature oxygen-carrying heat carrier contacts the solid organic fuel and only plays a heating role without reaction, which has little effect on the biochar yield. At the same time, the internal heating method segments the system's heat transfer through high, medium and low temperature oxygen-carrying heat carriers and high, medium and low temperature nitrogen, making full use of energy and improving energy efficiency.

[0098] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A method for preparing biochar and co-producing carbon dioxide by endothermic pyrolysis, characterized in that: include: Providing a medium-temperature oxygen-carrying heat carrier to contact with a solid organic fuel and pyrolyze the fuel to obtain a pyrolysis gas phase product and a pyrolysis solid phase product; the pyrolysis solid phase product is separated to obtain a low-temperature oxygen-carrying heat carrier and biochar; The pyrolysis gas phase product is contacted with a high temperature oxygen-carrying heat carrier and oxidized to obtain a high temperature gas product and a medium temperature oxygen-carrying heat carrier; the high temperature gas product is subjected to a first cooling separation to obtain carbon dioxide with a concentration of more than 90%; The obtained medium-temperature oxygen-carrying heat carrier can be used for the pyrolysis reaction of solid organic fuel.

2. The method according to claim 1, characterized in that: The oxygen-carrying heat carrier is a metal oxide or a metal oxide mineral.

3. The method according to claim 1, characterized in that The temperature of the medium-temperature oxygen-carrying heat carrier is 500-700°C, the temperature of the high-temperature oxygen-carrying heat carrier is 700-900°C, the temperature of the low-temperature oxygen-carrying heat carrier is controlled below 400°C, and the temperature of the pyrolysis is above 400°C.

4. The method according to claim 1, characterized in that The mass ratio of the high temperature oxygen-carrying heat carrier to the solid organic fuel is 1:18-1:40; Preferably, the solid organic fuel is at least one of wood or crop straw.

5. The method according to claim 1, characterized in that: The first cooling and separation step comprises: The high-temperature gas product is contacted with cooling water at a temperature below 40° C. to reduce the temperature of the high-temperature gas to below 50° C., and carbon dioxide with a concentration of more than 90% is obtained after gas-water separation.

6. The method according to claim 1, characterized in that Also included is a method for co-producing nitrogen, the method comprising: Providing high-temperature nitrogen gas to contact and exchange heat with the low-temperature oxygen-carrying heat carrier to obtain medium-temperature nitrogen gas and preheated oxygen-carrying heat carrier; Providing hot air to contact and react with the preheated oxygen-carrying heat carrier to obtain high-temperature nitrogen that can be used to contact and exchange heat with the low-temperature oxygen-carrying heat carrier and high-temperature oxygen-carrying heat carrier that can be used to contact and oxidize the pyrolysis gas phase product; Providing air to contact and exchange heat with the medium-temperature nitrogen to obtain low-temperature nitrogen and hot air that can be used to contact and oxidize the preheated oxygen-carrying heat carrier; The low-temperature nitrogen is subjected to a second cooling separation to obtain nitrogen.

7. The method according to claim 6, characterized in that The temperature of the high-temperature nitrogen is above 700°C, the temperature of the medium-temperature nitrogen is controlled below 600°C, the temperature of the low-temperature nitrogen is controlled below 350°C, the temperature of the hot air is above 350°C, and the temperature of the preheating oxygen-carrying heat carrier is above 500°C.

8. The method according to claim 6, characterized in that The second cooling and separation step comprises: The low-temperature nitrogen is contacted with cooling water at a temperature below 40° C. to reduce the temperature of the low-temperature nitrogen to below 50° C., and nitrogen with a concentration of more than 85% is obtained after gas-water separation.

9. A system for preparing biochar and co-producing carbon dioxide by endothermic pyrolysis, characterized in that: include: A low-temperature solid-phase pyrolysis device is used to contact the reduced medium-temperature oxygen-carrying heat carrier with the solid organic fuel for pyrolysis to obtain a pyrolysis gas phase product and a pyrolysis solid phase product; A separation device, used to separate the pyrolysis solid phase product obtained by the reaction of the low-temperature solid phase pyrolysis device to obtain a low-temperature oxygen-carrying heat carrier and biochar; A high-temperature gas phase oxidation device, used to contact and oxidize the pyrolysis gas phase product obtained by the reaction of the low-temperature solid phase pyrolysis device with a high-temperature oxygen-carrying heat carrier to obtain a high-temperature gas product and a medium-temperature oxygen-carrying heat carrier, and the medium-temperature oxygen-carrying heat carrier can be transported to the low-temperature solid phase pyrolysis device for pyrolysis reaction with solid organic fuel; The first cooling device is used to cool and separate the high-temperature gas product obtained from the high-temperature gas-phase oxidation device to obtain high-concentration carbon dioxide.

10. The system according to claim 9, characterized in that Also includes: A carrier-nitrogen heat exchanger is used to bring high-temperature nitrogen into contact with the low-temperature oxygen-carrying heat carrier and exchange heat to obtain medium-temperature nitrogen and preheated oxygen-carrying heat carrier; A gas-solid oxidation separation device, used to contact and oxidize and separate the hot air with the preheated oxygen-carrying heat carrier obtained from the carrier-nitrogen heat exchanger, to obtain high-temperature nitrogen that can be used to contact and exchange heat with the low-temperature oxygen-carrying heat carrier in the carrier-nitrogen heat exchanger and a high-temperature oxygen-carrying heat carrier that can be used to contact and oxidize the pyrolysis gas phase product in the high-temperature gas phase oxidation device; An air-nitrogen heat exchanger, used to contact and exchange heat between air and the medium-temperature nitrogen obtained from the carrier-nitrogen heat exchanger, to obtain low-temperature nitrogen and hot air that can be used to contact and oxidize with the preheated oxygen-carrying heat carrier in the gas-solid oxidation separation device; The second cooling device is used for separating the low-temperature nitrogen obtained from the air-nitrogen heat exchanger through a second cooling process to obtain high-concentration nitrogen.

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