System and method for recycling carbon dioxide in carburizing waste gas

Abstract

The invention discloses a system and a method for recycling carbon dioxide in carburizing waste gas, and belongs to the technical field of industrial waste gas recycling. The method mainly comprises the following steps: 1, preliminary process: treating carburizing waste gas in a combustion manner, and pretreating the combusted waste gas to remove impurities; 2, methanol preparation process: adding hydrogen into the carbon dioxide waste gas obtained after pretreatment to reduce the carbon dioxide waste gas into methanol; and 3, a methanol recycling process: the generated methanol is directly conveyed into a carburizing atmosphere after being subjected to a rectification purification process. The technology is a green transformation technology, waste gas can be reasonably reutilized, in summer, the heat loss of the environment temperature rising, the pipeline conveying process and the pretreatment link can be greatly reduced, waste heat in the waste gas can also be utilized, and the energy consumption of the technological process can also be greatly reduced. Meanwhile, the method has the advantage of reducing direct carbon emission of carbon dioxide in the production and operation process, and double benefits of energy conservation, emission reduction and efficient utilization of resources are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial waste gas recycling, and more specifically, to a system and method for recycling carbon dioxide in carburizing waste gas. Background Art

[0002] During the heat treatment process, the carburizing atmosphere containing methanol enters the quenching furnace. Due to the high temperature in the resistance furnace (about 800℃), the outside air is isolated when the carburizing atmosphere burns, and the oxygen in the furnace is consumed to prevent the surface oxidation of the workpiece. The amount of oxygen in the resistance furnace is insufficient, and since the carburizing process is not directly ignited and burned, the carburizing atmosphere will be decomposed, and its decomposition products are mainly CH, [C], H2 and CO. The decomposed active carbon atoms are absorbed by the metal workpiece as a carburizing agent, and the remaining components are discharged as carburizing waste gas. In order to meet the emission standards permitted by the environment, general enterprises will use a burner at the exhaust outlet of the furnace body to burn the remaining CO, CH, and H2, and then discharge them at high altitude through the exhaust pipe. The waste gas here has the following characteristics: 1. There are fewer impurities, and the combustion products are mainly CO2 and H2O, as well as a small amount of smoke. The correlation coefficient can refer to the "Manual of Emission Source Statistical Survey and Pollution Emission Accounting Methods and Coefficients", "33-37, 431-434 Mechanical Industry Coefficient Manual", where the industrial waste gas coefficient is 500 cubic meters / ton-product, and the volatile organic matter is 0.01 kg / ton-product. 2. The waste gas is generated by direct combustion, but the temperature is difficult to reach above 200°C and is unstable. It is difficult to use the existing waste heat utilization technology, and waste heat cannot be recovered, resulting in a certain waste of resources.

[0003] According to the existing technology, the operating temperature of carbon dioxide hydrogenation to methanol is generally 240~250℃, and the operating pressure is 6~8MPa. During the period when green methanol has not yet been commercialized, how to use the existing technology to effectively reduce the emission of carbon dioxide from thermal treatment is a problem that needs to be solved at present. Summary of the invention

[0004] In order to solve the above problems, the actual carbon emissions in the production process are reduced by reusing the carbon dioxide in the exhaust gas, and the generated carbon dioxide is converted into methanol in the carburizing atmosphere on site, and the purchased clean energy hydrogen is used instead of the purchased methanol to reduce the carbon emissions of traditional energy from the source. It should be noted that the equipment and raw materials not specifically mentioned in the present invention are all purchased from outside.

[0005] To achieve the above purpose, the present invention improves the original waste gas treatment process. In order to meet the emission standards permitted by the environment, general enterprises will use a burner at the tail gas outlet of the furnace to burn the remaining CO, CH, and H2. The combustion products are mainly CO2 and H2O, as well as a small amount of smoke. The mixed gas is collected by the waste gas collection hood, and the impurities in the waste gas are removed by the waste gas pretreatment device. A tapered pipe is installed on the pipeline leading to the pretreatment device, the purpose of which is to make the waste gas flow at a uniform speed as much as possible, so as to achieve a better pretreatment effect.

[0006] Furthermore, the obtained carbon dioxide and hydrogen are compressed to 6-8 MPa by corresponding compressors respectively and then mixed as inlet gas.

[0007] Furthermore, the inlet gas is first heated to a reaction temperature of 240-250°C by the heat exchanger and the residual heat in the outlet gas of the methanol synthesis tower. The mixed gas enters the catalyst bed of the methanol synthesis tower for reaction. The outlet mixed gas temperature is about 240°C. After the intermediate heat exchanger preheats the inlet gas, the temperature drops to about 90°C, at which time a small amount of methanol condenses. Then it enters the cooler and is further cooled to about 40°C, at which time most of the methanol can be condensed.

[0008] Furthermore, most of the insoluble gases are removed by high-pressure flash evaporators and low-pressure flash evaporators. The mixture coming out of the cooler first enters the high-pressure flash evaporator to remove some gaseous impurities in the product, such as unreacted hydrogen, carbon dioxide, and other low-boiling point gases that may be generated. Then enter the low-pressure flash evaporator to reduce the pressure to achieve a more thorough separation of low-boiling point components. Considering the low conversion rate of the one-way CO2 hydrogenation to methanol reaction, most of the unreacted gas needs to be recycled. The unreacted gas is discharged from the upper part of the high-pressure flash evaporator and the low-pressure flash evaporator, and is returned as a circulating gas through the circulating compressor for recycling. The addition of circulating materials will cause the purge gas to accumulate, and the purge gas needs to be discharged separately.

[0009] Furthermore, the crude liquid methanol obtained at the bottom of the low-pressure flash evaporator enters the preheater through a methanol pump, and then the liquid directly enters the distillation tower, the waste water generated is discharged from the bottom of the distillation tower, and the methanol vapor generated flows into the methanol storage tank through the condenser from the top. The carburizing atmosphere generally enters the quenching furnace by dripping, so the refined methanol generated needs to enter the condenser from the top and condense it into liquid and send it to the methanol storage tank.

[0010] Furthermore, the produced refined methanol can be directly transported from the methanol storage tank to the carburizing atmosphere pipeline of the quenching furnace and recycled as the carburizing atmosphere.

[0011] Furthermore, the exhaust gas of the workshop heat treatment furnace line can be centrally treated and individually controlled by valves. When the quenching furnace is working, the valve is opened; when the quenching furnace is stopped, the valve is closed.

[0012] The above-mentioned system and method for recycling carbon dioxide in heat treatment carburizing waste gas disclosed in the present invention have the following advantages: First, the waste gas can be reasonably reused. At the same time, the direct use of carbon dioxide can reduce the additional energy consumption caused by transportation needs, greatly reducing the CO2 disposal cost.

[0013] Second, in summer, due to the increase in ambient temperature, the heat loss in the pipeline transmission process and pretreatment links will be greatly reduced, the waste heat in the exhaust gas can also be utilized, and the energy consumption of the process will be greatly reduced.

[0014] Third, the one-step method for producing methanol is simple in process and takes up little space.

[0015] Replacing purchased methanol with purchased hydrogen effectively reduces direct carbon dioxide emissions during production operations, helps create zero-carbon steel products, avoids green trading barriers that may be encountered in future product exports, and achieves the dual benefits of energy conservation and emission reduction and efficient resource utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a work flow chart of the present invention; Figure 2 It is a schematic diagram of the overall structure of the present invention; Figure 3 This is a scenario application diagram of the present invention.

[0017] In the figure: 1. Burner; 2. Waste gas collection device; 3. Valve; 4. Waste gas pretreatment device; 5. Carbon dioxide compressor; 6. Hydrogen compressor; 7. Heat exchanger; 8. Methanol synthesis tower; 9. Cooler; 10. High-pressure flash evaporator; 11. Low-pressure flash evaporator; 12. Circulation compressor; 13. Methanol pump; 14. Preheater; 15. Distillation tower; 16. Condenser; 17. Methanol storage tank. DETAILED DESCRIPTION

[0018] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. The same parts are represented by the same reference numerals. It should be noted that the words "front", "rear", "left", "right", "upper" and "lower" used in the following description refer to directions in the accompanying drawings, and the words "bottom surface" and "top surface", "inner" and "outer" refer to directions toward or away from the geometric center of a specific component, respectively.

[0019] like Figure 1-3 As shown, a method for recycling carbon dioxide in carburizing waste gas includes the following steps: S1. Preliminary process: carburizing waste gas is treated by combustion, and the waste gas after combustion is pre-treated to remove impurities; S2, methanol production process: adding hydrogen to the carbon dioxide waste gas obtained after pretreatment to reduce it into methanol; S3, methanol recycling process: the generated methanol is directly transported into the carburizing atmosphere after the distillation purification process.

[0020] Furthermore, the preliminary process includes the following steps: S1, the tail gas of the quenching furnace enters the burner 1 for combustion treatment; S2, the exhaust gas is collected by the exhaust gas collecting device 2; S3, the collected waste gas enters the waste gas pretreatment device 4 for pretreatment; S4, the pretreated gas enters the carbon dioxide compressor 5.

[0021] In order to meet the emission standards permitted by the environment, general enterprises will use burner 1 at the tail gas outlet of the furnace to burn the remaining CO, CH, and H2. The carburizing process in the process refers to the carburizing atmosphere containing methanol entering the quenching furnace. Since the temperature in the quenching furnace is relatively high at about 800°C, the outside air is isolated when the carburizing atmosphere is high, and the oxygen in the furnace is consumed to prevent the surface oxidation of the workpiece. The amount of oxygen in the quenching furnace is insufficient, and since the carburizing process is not directly ignited and burned, the carburizing atmosphere will be decomposed. At this time, the carburizing atmosphere will be decomposed into CH, [C], H2 and CO, and the decomposed active carbon atoms [C] are absorbed by the metal workpiece as a carburizing agent. The remaining components are directly burned as carburizing waste gas through the burner 1 at the end of the quenching furnace and then discharged, that is, the burner 1 is used for combustion treatment, and the combustion products are mainly CO2 and H2O, as well as a small amount of smoke.

[0022] The exhaust gas after combustion is collected by the exhaust gas collection device 2, and after passing through the pipeline containing the tapered pipe, it passes through the exhaust gas pretreatment device 4 at a nearly uniform speed to remove impurities in the exhaust gas. The main components of the impurities are H2O and a small amount of smoke. Considering that not only the carburizing process is applied in the production process, but also the carbonitriding process is required, the N content in the exhaust gas will increase at this time, and NOx will exist in the exhaust gas after combustion. The membrane separation technology can be used in the exhaust gas pretreatment device to separate the NOx component.

[0023] Further, the methanol production process includes the following steps: S1, the waste gas enters the carbon dioxide compressor 5, and the hydrogen enters the hydrogen compressor 6 for separate treatment; S2, the treated gas enters the heat exchanger 7 to be heated; S3, the heated gas enters the methanol synthesis tower 8; S4, the product outlet of the methanol synthesis tower 8 enters the cooler 9 after passing through the heat exchanger 7; S5, the cooled gas is purified by a high-pressure flash evaporator 10 and a low-pressure flash evaporator 11 to obtain liquid crude methanol; S6. Most of the gas produced after purification in the high-pressure flash evaporator 10 and the low-pressure flash evaporator 11 re-enters the heat exchanger 7 as circulating gas through the circulating compressor 12, and a small amount of gas is discharged as purge gas.

[0024] The obtained waste gas carbon dioxide and hydrogen are compressed to 6~8MPa by the corresponding carbon dioxide compressor 5 and hydrogen compressor 6 respectively, and then mixed to obtain the inlet gas. In order to save the space cost of the workshop, the source of hydrogen is purchased from outside. The inlet gas is first heated to a reaction temperature of 240~250℃ by the heat exchanger 7. The mixed gas enters the catalyst bed of the methanol synthesis tower 8 for reaction. At this time, the temperature of the outlet mixed gas is about 243℃. In order to effectively utilize this part of the heat energy, the outlet gas is preheated to the inlet gas through the heat exchanger 7, and the temperature of the mixed gas drops to about 90℃. At this time, a small amount of methanol condenses. Then it enters the cooler and is further cooled to about 40℃, at which time most of the methanol can be condensed.

[0025] The hydrogen gas enters the heat exchanger 7 together with the compressed carbon dioxide through the hydrogen compressor 6, and after the gas temperature is increased, it enters the methanol synthesis tower 8 for reaction. The mixture of methanol and other substances produced after cooling is separated into gas and liquid by the high-pressure flash evaporator 10 and the low-pressure flash evaporator 11, and the crude methanol liquid is obtained from the bottom of the low-pressure flash evaporator 11.

[0026] The mixture coming out of the cooler 9 first enters the high-pressure flash evaporator 10 to remove some gaseous impurities in the product, such as unreacted hydrogen, carbon dioxide and other low-boiling point gases that may be generated. The generated gaseous substances are discharged from the top, and the liquid enters the low-pressure flash evaporator 11 from the bottom to reduce the pressure, so that the low-boiling point components can be separated more thoroughly. Similarly, the separated gas is discharged from the top and the liquid is discharged from the bottom. Considering the low conversion rate of the single-pass CO2 hydrogenation to methanol reaction, most of the unreacted gas needs to be recycled. The unreacted gas discharged from the upper part of the high-pressure flash evaporator 10 and the low-pressure flash evaporator 11 is returned as a circulating gas through the circulating compressor 12 and then enters the heat exchanger 7 for recycling. In this process, the addition of circulating materials will cause the purge gas to accumulate, and the purge gas needs to be discharged separately.

[0027] Further, the methanol recycling process includes the following steps: S1, liquid crude methanol is first preheated by preheater 14 through methanol pump 13; S2, the liquid crude methanol after preheating treatment enters the distillation tower 15 for purification; S3, the methanol vapor generated in the distillation tower 15 flows into the methanol storage tank from the top through the condenser 16, and the waste water generated in the distillation tower 15 is discharged from the bottom of the distillation tower 15; S4. The refined methanol in the methanol storage tank is connected to the carburizing atmosphere delivery pipeline, and its flow rate is controlled by a flow meter.

[0028] The liquid crude methanol obtained from the lower part of the low-pressure flash evaporator 11 is firstly sent to the methanol pump 13, and then preheated to 80°C by the preheater 14, and then sent to the distillation tower 15 for separation and purification. The waste water generated is discharged from the lower end of the distillation tower, and the methanol vapor flows out from the upper end. The carburizing atmosphere generally enters the quenching furnace by dripping, so the generated refined methanol needs to enter the condenser 16 from the top, condensed and converted into liquid and sent to the methanol storage tank 17.

[0029] The obtained refined methanol can be transported to the carburizing atmosphere pipeline for recycling. Considering that there are multiple furnace lines in the heat treatment workshop, the tail gases of multiple furnace lines can be connected in series and then processed centrally. Figure 3 As shown, the exhaust gas of the workshop heat treatment furnace line can be centrally treated. For the exhaust gas emission of each furnace line, an independent valve 3 is equipped for control. When the quenching furnace stops working, the corresponding valve can be closed separately. In summer, due to the increase in ambient temperature, the heat loss in the pipeline transmission process and pretreatment links will be greatly reduced, the waste heat in the exhaust gas can also be utilized, and the energy consumption of the process will be greatly reduced.

[0030] The present invention is a green transformation process that can reasonably recycle waste gas. In summer, when the ambient temperature rises, the heat loss in the pipeline transmission process and pretreatment link will be greatly reduced, the waste heat in the waste gas can also be utilized, and the energy consumption of the process will be greatly reduced. At the same time, the present invention has the advantage of reducing direct carbon emissions of carbon dioxide during production and operation, achieving the dual benefits of energy conservation and emission reduction and efficient resource utilization.

[0031] By reusing the carbon dioxide in the waste gas, the actual carbon emissions in the production process are reduced. At the same time, the generated carbon dioxide is converted into methanol in the carburizing atmosphere on site. By purchasing clean energy hydrogen instead of methanol, the carbon emissions of traditional energy are reduced from the source. It should be noted that the equipment and raw materials not specifically mentioned in the present invention are all purchased from outside.

[0032] A carbon dioxide recycling system in carburizing waste gas comprises a waste gas collecting device 2, a waste gas pretreatment device 4, a carbon dioxide compressor 5, a hydrogen compressor 6, a heat exchanger 7, a methanol synthesis tower 8 and a distillation tower 15, a converging pipe and a valve 3 are installed between the waste gas collecting device 2 and the waste gas pretreatment device 4, the waste gas pretreatment device 4 is connected to the carbon dioxide compressor 5, the methanol synthesis tower 8 is connected to a cooler 9, a high-pressure flash evaporator 10 and a low-pressure flash evaporator 11 are both connected to the same circulation compressor 12 above, and a methanol pump 13 and a preheater 14 are sequentially connected below the low-pressure flash evaporator 11; The waste gas collection device 2 is used to collect waste gas and transfer the waste gas to the waste gas pretreatment device 4 through a tapered pipe. The waste gas pretreatment device 4 is used to remove impurities in the waste gas. The valve 3 is used to control tail gas emissions. The carbon dioxide compressor 5 is used to compress the waste gas. The hydrogen compressor 6 is used to compress hydrogen. The heat exchanger 7 is used to heat the compressed waste gas and hydrogen mixed gas. The methanol synthesis tower 8 and the cooler 9 cooperate and are used to convert the mixed gas into methanol. The high-pressure flash evaporator 10 and the low-pressure flash evaporator 11 cooperate and are used to preliminarily purify methanol. The circulating compressor 12 is used to transfer the excess unreacted gas after purification by the high-pressure flash evaporator 10 and the low-pressure flash evaporator 11 to the heat exchanger 7 and recycle the gas. The methanol pump 13 is used to transfer the preliminarily purified methanol to the distillation tower 15, and the distillation tower 15 is used to purify the methanol again.

[0033] The purpose of installing a tapered pipe on the pipe leading to the pre-treatment device is to make the exhaust gas flow at a uniform speed as much as possible, so as to achieve a better pre-treatment effect.

[0034] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for recycling carbon dioxide in carburizing waste gas, characterized in that: The following steps are included: S1. Preliminary process: carburizing waste gas is treated by combustion, and the waste gas after combustion is pre-treated to remove impurities; S2, methanol production process: adding hydrogen to the carbon dioxide waste gas obtained after pretreatment to reduce it into methanol; S3, methanol recycling process: the generated methanol is directly transported into the carburizing atmosphere after the distillation purification process.

2. The method for recycling carbon dioxide in carburizing waste gas according to claim 1, characterized in that: The initial process includes the following steps: S1, the tail gas from the quenching furnace enters the burner for combustion treatment; S2. The waste gas is collected by a waste gas collection device; S3, the collected waste gas enters the waste gas pretreatment device for pretreatment; S4. The pretreated gas enters the carbon dioxide compressor.

3. The method for recycling carbon dioxide in carburizing waste gas according to claim 1, characterized in that: The methanol production process includes the following steps: S1, the waste gas enters the carbon dioxide compressor, and the hydrogen enters the hydrogen compressor for separate treatment; S2, the treated gas enters the heat exchanger for heating; S3, the heated gas enters the methanol synthesis tower; S4, the product outlet of the methanol synthesis tower enters the cooler after passing through the heat exchanger; S5, the cooled gas is purified by a high-pressure flash evaporator and a low-pressure flash evaporator to obtain liquid crude methanol; S6. Most of the gas produced after purification in the high-pressure flash evaporator and the low-pressure flash evaporator re-enters the heat exchanger as circulating gas through the circulating compressor, and a small amount of gas is discharged as purge gas.

4. The method for recycling carbon dioxide in carburizing waste gas according to claim 1, characterized in that: The methanol recycling process includes the following steps: S1, liquid crude methanol is first preheated by a preheater through a methanol pump; S2, the liquid crude methanol after preheating treatment enters the distillation tower for purification; S3, the methanol vapor generated in the distillation tower flows into the methanol storage tank from the top through the condenser, and the waste water generated in the distillation tower is discharged from the bottom of the distillation tower; S4. The refined methanol in the methanol storage tank is connected to the carburizing atmosphere delivery pipeline, and its flow rate is controlled by a flow meter.

5. A system for recycling carbon dioxide in carburizing waste gas, characterized in that: It includes a waste gas collection device, a waste gas pretreatment device, a carbon dioxide compressor, a hydrogen compressor, a heat exchanger, a methanol synthesis tower and a distillation tower. A reduction pipe and a valve are installed between the waste gas collection device and the waste gas pretreatment device. The waste gas pretreatment device is connected to the carbon dioxide compressor. The methanol synthesis tower is connected to a cooler. The high-pressure flash evaporator and the low-pressure flash evaporator are both connected to the same circulation compressor above. The low-pressure flash evaporator is sequentially connected to a methanol pump and a preheater below. The waste gas collection device is used to collect waste gas and transfer it to the waste gas pretreatment device through a tapered pipe. The waste gas pretreatment device is used to remove impurities in the waste gas. The valve is used to control tail gas emissions. The carbon dioxide compressor is used to compress the waste gas. The hydrogen compressor is used to compress hydrogen. The heat exchanger is used to heat the compressed waste gas and hydrogen mixed gas. The methanol synthesis tower and the cooler are used to convert the mixed gas into methanol. The high-pressure flash evaporator and the low-pressure flash evaporator are used to preliminarily purify the methanol. The circulating compressor is used to transfer the excess unreacted gas after purification by the high-pressure flash evaporator and the low-pressure flash evaporator to the heat exchanger for gas recycling. The methanol pump is used to transfer the preliminarily purified methanol to the distillation tower, and the distillation tower is used to purify the methanol again.

Images