Deep cooling and adsorption denitration purification process coupled with tail gas of organic fluorine compound AHF synthesis

Abstract

The application discloses a kind of organic fluorinated compound AHF synthesis tail gas cryogenic coupling adsorption denitration purification process, including the synthesis tail gas generated in the process of organic fluorinated compound synthesis, the cryogenic tail gas formed after the deep cooling heat exchanger of the synthesis tail gas enters activated carbon adsorption tower, residual HF in the cryogenic tail gas, organic fluorinated compound and other VOCs components are adsorbed, and the adsorption tail gas of activated carbon adsorption tower is discharged after entering SCR denitration unit denitration purification.The process route of the present application is simple, clean and environmentally friendly, stable and efficient, and the pollution components are recycled.

Description

Technical Field

[0001] This invention belongs to the field of chemical waste gas treatment, and relates to the treatment of waste gas pollutants generated in the production process of the organic fluorine chemical industry. Specifically, it is a cryogenic coupling adsorption denitrification purification process for waste gas from the synthesis of organic fluorine compounds using the AHF method. Background Technology

[0002] Organofluorine chemicals occupy the top of the entire fluorochemical industry value chain. With the development of the new energy vehicle industry, the demand for organofluorine compounds is rapidly increasing. Currently, there are two main industrial production methods for organofluorine compounds: the Schiemann reaction and the anhydrous hydrogen fluoride (AHF) method. Among them, the AHF method is widely used due to its high yield and simple process control. For example, in the production process of fluorobenzene: aniline, hydrogen fluoride, and nitrite are added to a reactor, and the reaction produces aniline diazonium salt. After thermal decomposition, alkali washing, drying, and distillation, the product is obtained, and the inorganic fluoride is recovered and reused after treatment. Early synthesis of fluorinated organic compounds paid little attention to the purification of synthesis tail gases. The waste gas treatment scheme adopted was to convert them into the liquid phase as much as possible, and then use the process route of "neutralization-sedimentation-hydrogen peroxide-activated carbon adsorption" for treatment [Wang Zhijian, Miao Runchun, Lin Sen, et al. Synthesis and application of fluorobenzene [J]. Liaoning Chemical Industry, 1996; Weng Xingyuan, Dong Qingguo. Synthesis and application of fluorobenzene [J]. Journal of Liaoning University of Engineering and Technology, August 2003]. The waste gas purification effect was poor.

[0003] With technological advancements, HF in synthesis waste gas is removed through absorption with water and alkaline solutions. There are also technical solutions that use hot sulfuric acid to dry and dehydrate the tail gas, followed by condensation and recovery of anhydrous hydrogen fluoride [Lü Zhimin, Zhang Yuqing, Tang Anping, et al. Clean Production Process of Fluorobenzene [J]. Chemical World, December 2002]. In general, to date, there are very few reports on comprehensive treatment schemes for synthesis tail gas from the AHF method for synthesizing organofluorine compounds. The treatment of HF and NOx in the tail gas has been impacting the development of the organofluorine chemical industry.

[0004] This invention addresses the aforementioned problems by developing a cryogenic coupling adsorption denitrification purification process for the tail gas from the AHF synthesis of organofluorine compounds. Summary of the Invention

[0005] The purpose of this invention is to solve the above-mentioned technical problems and provide a cryogenic coupling adsorption denitrification purification process for the tail gas of the AHF synthesis of organofluorine compounds that is simple in process route, clean and environmentally friendly, stable and efficient, and allows for the recovery and utilization of pollutant components.

[0006] The method of the present invention includes the synthesis tail gas generated during the synthesis of organofluorine compounds. The synthesis tail gas is cryogenically cooled by a cryogenic heat exchanger to form cryogenic tail gas, which enters an activated carbon adsorption tower. The residual HF, organofluorine compounds and other VOCs in the cryogenic tail gas are adsorbed. The adsorbed tail gas exiting the activated carbon adsorption tower enters an SCR denitrification unit for denitrification and purification before being discharged.

[0007] The activated carbon adsorption towers consist of at least three connected in parallel to form an adsorption unit, which performs adsorption and desorption respectively, and are used alternately. By setting an alternation cycle, the towers are switched periodically. Superheated steam is used to desorb the activated carbon adsorption towers after completing one adsorption cycle. The desorption tail gas is returned to the synthesis reactor after being condensed and dehydrated, or it enters the cryogenic heat exchanger for defrosting and then enters the synthesis reactor to participate in the synthesis reaction.

[0008] The condensation and dehydration process is as follows: the desorption tail gas enters the low-temperature water spray cooling tower, and after being cooled by low-temperature water spray, the condensate returns to the spray cooling tower. The desorption tail gas cooled by the low-temperature water spray is sent to the desorption tail gas condenser for condensation and dehydration, and then returned to the synthesis reactor to participate in the synthesis reaction, or it enters the cryogenic heat exchanger for defrosting and then enters the synthesis reactor to participate in the synthesis reaction.

[0009] Based on the mass of hydrogen fluoride adsorbed by the activated carbon adsorption tower, the temperature of the superheated steam is controlled, the regeneration time is controlled, and the amount of superheated steam used for regeneration is controlled; the amount of condensate introduced by the superheated steam for desorption is controlled to ensure that the mass concentration of hydrogen fluoride in the low-temperature water is above 40%.

[0010] The activated carbon adsorption tower after desorption is cooled by the adsorption tail gas, and the heated adsorption tail gas enters the SCR denitrification unit.

[0011] The SCR denitrification unit consists of a denitrification heat exchanger, a heater, and a denitrification reactor connected in sequence. After the adsorption tail gas enters the SCR denitrification unit, it exchanges heat with the purified tail gas exiting the denitrification reactor through the denitrification heat exchanger, and the temperature rises to 120-140℃. It then enters the heater and is heated to above 170℃ before entering the denitrification reactor for denitrification and purification. According to the concentration of nitrogen oxides in the adsorption tail gas, a certain amount of ammonia gas is injected into the adsorption tail gas pipeline to mix with the adsorption tail gas and then enter the denitrification heat exchanger together.

[0012] The purified exhaust gas is cooled to 120-150℃ after heat exchange, and is drawn out by a circulating fan and divided into two parts. One part is discharged after heat exchange with the desorbed exhaust gas in the purified exhaust gas heat exchanger to dehydrate and cool down and recover residual heat; the other part is re-entered into the denitrification unit and mixed with the adsorbed exhaust gas through the exhaust gas circulation regulating valve.

[0013] The synthesis tail gas is indirectly cooled to below -50°C via a cryogenic heat exchanger using a low-temperature refrigerant below -70°C. More than 99.9% of the organic fluorine compounds, nitrogen dioxide, and more than 70% of the hydrogen fluoride are condensed and intercepted, and returned to the synthesis reactor to continue participating in the synthesis reaction. The cryogenic tail gas from the cryogenic heat exchanger enters the activated carbon adsorption unit to adsorb and remove hydrogen fluoride, and then enters the SCR unit for denitrification before being discharged.

[0014] Before entering the cryogenic heat exchanger, the synthesis exhaust gas first exchanges heat with the cryogenic exhaust gas, and the temperature drops to -8 to -12°C, while the temperature of the cryogenic exhaust gas rises to -20 to -30°C.

[0015] The cryogenic heat exchangers are configured in groups of at least three to form a cryogenic unit. The three cryogenic heat exchangers are used alternately for condensation-condensation-defrosting in sequence. The condensation-condensation-defrosting process is controlled by setting upper and lower limits for the pressure difference between the inlet and outlet exhaust gases of the cryogenic heat exchanger. When the pressure difference between the inlet and outlet exhaust gases of the cryogenic heat exchanger is higher than the upper limit, the refrigerant is cut off, and the cryogenic heat exchanger enters the defrosting stage. When the pressure difference between the inlet and outlet exhaust gases of the cryogenic heat exchanger is lower than the lower limit, the refrigerant is introduced, and the cryogenic heat exchanger enters the cryogenic working stage. This process is repeated alternately.

[0016] The refrigerant in the shell side of the cryogenic heat exchanger is enhanced by a refrigerant circulation pump, forming three enhanced cooling sections within the cryogenic heat exchanger. These sections respectively enhance the condensation of hydrogen fluoride, organic fluorinated compounds, and nitrogen dioxide components, thereby improving the condensation and interception effect of pollutants in the synthetic exhaust gas.

[0017] After the cryogenic exhaust gas is adsorbed by the activated carbon adsorption tower, more than 99.99% of the hydrogen fluoride, organic fluorine compounds, and some nitrogen oxides are adsorbed.

[0018] In the cryogenic exhaust gas, HF has the highest polarity and has a competitive adsorption advantage, followed by NO, then organofluorine compounds, NO2, and nitrogen is hardly adsorbed.

[0019] HF, NO, and organofluorine compounds are adsorbed and concentrated using an activated carbon adsorption unit. The desorption tail gas after adsorption contains almost no nitrogen. After dehydration, it is introduced into the synthesis reactor and then cryogenically recovered.

[0020] During the cryogenic process, most of the nitrogen dioxide condenses back into the synthesis reactor, increasing the nitrogen dioxide concentration in the reactor liquid, inhibiting the occurrence of the side reaction <2HNO2→NO+NO2+water>, and improving the utilization rate of HNO2.

[0021] Because the composition of pollutants in synthesis tail gas is complex and the concentration of pollutants is high, simply using a pollutant component purification treatment scheme would result in significant resource waste and high treatment costs. This invention, combined with the production process, employs activated carbon adsorption followed by SCR denitrification purification of the synthesis tail gas after cryogenic treatment. Specifically, the following improvements are adopted: (1) Cooling the adsorption tail gas. 20-30% of the adsorption tail gas from another activated carbon adsorption tower is refluxed back into the activated carbon adsorption tower after desorption to cool the activated carbon adsorption layer. The adsorption tail gas, after being heated by heat exchange in the activated carbon layer, is mixed with the remaining 80-90% of the adsorption tail gas and enters the subsequent denitrification unit. The reason for cooling the activated carbon adsorption layer after desorption is that the lower the temperature of the activated carbon during adsorption, the better the adsorption. This avoids the situation where, in the early stage of adsorption, the temperature of the activated carbon adsorption layer is high, and the adsorption tail gas is heated when it enters, resulting in a fast tail gas flow rate, short adsorption time, and a decrease in adsorption rate. The reason for using 20-30% of the adsorption tail gas for reflux cooling is to cool the activated carbon at a lower cooling rate to avoid rapid cooling affecting the service life of the activated carbon.

[0022] (2) After the desorption tail gas (mainly composed of organic fluorine compounds and nitrogen oxides) is dehydrated by activated carbon, it is then heated by heat exchange with the purified tail gas after SCR denitrification, and then returned to the synthesis reactor for stirring and temperature adjustment.

[0023] The technical effects of this solution are as follows: (1) The high concentration of nitrogen oxides in the tail gas is partially recycled through adsorption, thereby improving the conversion rate of sodium nitrite raw material. There is a side reaction in the synthesis process: 2HNO2→NO+NO2+water. Through the activated carbon adsorption tower, trace amounts of hydrogen fluoride, organic fluorinated compounds and other components in the tail gas are adsorbed, while nitric oxide is also partially adsorbed. After desorption in the activated carbon adsorption tower, the desorbed tail gas is returned to the cryogenic heat exchanger for defrosting. The defrost contains a large amount of nitrogen dioxide. The temperature of the solution after defrosting is low. After returning to the reactor, the occurrence of side reactions can be suppressed. At the same time, there is also the possibility of reversible side reactions, which can effectively improve the conversion rate of sodium nitrite raw material.

[0024] (2) Reduce the operating cost of denitrification and mitigate the impact of high concentrations of nitrogen oxide tail gas on the denitrification catalyst. Due to the non-selective adsorption of activated carbon, although the polarity of nitric oxide is lower than that of HF, it will be partially adsorbed due to its high concentration, thereby reducing the concentration of nitrogen oxides entering the denitrification reactor and promoting the stable operation of the denitrification reaction.

[0025] (3) Achieve maximum recovery of organofluorine compounds. By recycling the desorption tail gas into the synthesis reaction system, the pollutants such as organofluorine compounds and nitrogen oxides contained in the desorption tail gas are fully recovered and utilized.

[0026] (4) The system makes full use of the cold and heat sources of the internal medium. By cooling the activated carbon adsorption tower after desorption through the reflux of the adsorption tail gas, the cold energy of the adsorption tail gas at a lower temperature is recovered; by exchanging heat with the desorption tail gas and the purified tail gas after SCR denitrification, the enthalpy of the purified tail gas at a higher temperature is recovered; by defrosting the desorption tail gas after heat exchange and heating it up, the enthalpy required for defrosting is saved.

[0027] Furthermore, due to the complex composition and high concentration of pollutants in the synthesis tail gas, this invention, combined with the production process, breaks through traditional treatment concepts by proposing a deep cryogenic condensation solution that directly reuses the condensate. The synthesis tail gas is cooled to below -50°C using a -70°C low-temperature refrigerant, recovering nitrogen dioxide, organofluorine compounds, hydrogen fluoride, etc., which are then returned to the production process to participate in the synthesis reaction again, achieving resource utilization. The reason for cryogenic condensation to below -50°C is that at this temperature, almost all nitrogen dioxide is condensed, more than 70% of hydrogen fluoride is also condensed, and more than 90% of organofluorine compounds are also condensed.

[0028] Deep cryogenic treatment enables timely and on-site resource utilization of pollutants, resulting in high efficiency and low cost. The condensed pollutants originate from raw materials, reaction products, or byproducts required in the synthesis of organofluorine compounds. Returning these condensed components to the reaction system effectively inhibits side reactions and improves the conversion rate of reactants.

[0029] In addition to HF components, the tail gas from fluorobenzene synthesis also contains a large amount of organic fluorine compounds, nitrogen oxides, and small amounts of VOCs. To remove or recycle these pollutants and obtain anhydrous HF at the source, this invention, based on the physical properties and characteristics of these components, creatively proposes a cryogenic heat exchanger refrigerant internal circulation scheme, forming an enhanced cooling section within the cryogenic heat exchanger. By adjusting the circulation rate, different cooling effects are obtained, achieving different condensation rates for pollutants and improving the condensation and interception effect of pollutants in the synthesis tail gas.

[0030] Among these pollutants, nitrogen dioxide has a melting point of -11℃ and a boiling point of 21℃; nitric oxide has a melting point of -163.6℃ and a boiling point of -151℃; HF has a melting point of -83℃ and a boiling point of 19.54℃; and organofluorine compounds generally have melting points below -40℃. When the exhaust gas is cryogenically cooled to -50℃, nitrogen dioxide and some organofluorine compounds condense, and more than 70% of HF also condenses. During the condensation process, nitrogen dioxide and organofluorine compounds will frost up inside the cryogenic heat exchanger, blocking the exhaust gas flow channels. To mitigate the frost clogging problem, this invention makes the following improvements: (1) The exhaust gas enters the cryogenic heat exchanger and exchanges heat with the refrigerant in the opposite direction. The refrigerant is forced to circulate back in the cryogenic heat exchanger, forming enhanced cooling sections corresponding to hydrogen fluoride, organic fluorinated compounds and nitrogen dioxide respectively. By setting up a refrigerant circulation pump, the refrigerant with a higher temperature downstream is returned to the upstream, forming a condensation section with a small temperature difference corresponding to the melting point temperature of the pollutant components, so as to ensure that the pollutant components are fully condensed and do not solidify and blockage.

[0031] (2) Utilize the high-temperature gas circulation defrosting in the exhaust gas purification system. First, the high-temperature desorbed exhaust gas desorbed from the activated carbon adsorption unit is used as the defrosting heat source, which not only recovers the organic fluorine compounds in the desorbed exhaust gas, but also defrosts efficiently; second, the original synthesis exhaust gas is used as the defrosting heat source, which not only initially cools the synthesis exhaust gas and recovers the frost cooling capacity, but also achieves the defrosting effect. Part of the original synthesis exhaust gas is introduced into the cryogenic heat exchanger that needs to be defrosted, and after defrosting, it returns to the cryogenic heat exchanger for further condensation.

[0032] The effects of this improvement are as follows: (1) Stepwise condensation and recovery of contaminant components reduces frost blockage during the cryogenic process and improves system operational stability.

[0033] (2) Forced circulation of refrigerant is carried out to make full use of the cold energy of refrigerant, increase the temperature of refrigerant exiting the cryogenic heat exchanger, and then exchange heat with the cryogenic tail gas at a lower temperature (-50℃) after cryogenic cooling, thereby improving the efficiency of refrigerant cold energy utilization.

[0034] (3) Fully recover the cold energy from frost formation.

[0035] (4) No external defrosting medium is required to achieve efficient defrosting.

[0036] (5) During the cryogenic process, most of the nitrogen dioxide condenses back into the synthesis reactor, which increases the concentration of nitrogen dioxide in the reactor liquid, inhibits the occurrence of the side reaction <2HNO2→NO+NO2+water>, and improves the utilization rate of HNO2.

[0037] Furthermore, this invention innovatively proposes a purified exhaust gas recirculation technology for SCR denitrification treatment of the adsorption exhaust gas after activated carbon adsorption. Specifically, the purified exhaust gas from the denitrification heat exchanger is divided into two parts. One part is directly mixed with the heated adsorption exhaust gas and participates in the exhaust gas recirculation. The other part is cooled and dehydrated by exchanging heat with the desorbed exhaust gas in a purified exhaust gas heat exchanger before being discharged through a chimney. The effects of this technology are as follows: (1) In terms of system operation stability, by circulating the purified tail gas, the fluctuation range of NOx content in the adsorbed tail gas entering the SCR denitrification reactor is reduced, the impact of NOx concentration fluctuation in the inlet gas on the catalyst is mitigated, which is conducive to the stability of the SCR denitrification reaction process.

[0038] (2) Through the circulating dilution effect of the purified tail gas, the temperature fluctuation of the adsorbed tail gas entering the reactor will also be reduced, thereby improving the system's operational stability. The improved system operational stability can effectively reduce the system's operating costs and extend the catalyst's service life.

[0039] (3) By monitoring the NOx concentration in the purified tail gas online and adjusting the amount of ammonia injected into the adsorbed tail gas, the circulation of the purified tail gas also controls the fluctuation of ammonia content in the tail gas entering the SCR denitrification reactor, which is conducive to the stability of the SCR denitrification reaction process, improves the denitrification effect, and reduces ammonia escape.

[0040] (4) The exhaust gas is heated by exchanging heat with the desorbed gas at a lower temperature, so that some of the water in the exhaust gas is condensed. The condensation process also absorbs the ammonia component in the flue gas, reducing ammonia escape.

[0041] (5) By circulating the purified exhaust gas, the concentration of nitrogen oxides is diluted, thus avoiding violent local reactions in the reactor and damage to the catalyst.

[0042] This invention enables the recovery and utilization of pollutant components in synthesis tail gas, fully recovers waste heat and waste cooling capacity, has a relatively simple process route, is environmentally friendly, has high pollutant purification efficiency, and low operating costs. Attached Figure Description

[0043] Figure 1 A schematic diagram of the process of this invention.

[0044] Among them, SL1-synthesis tail gas pipe; SL2-cryogenic tail gas pipe; SL3-desorption tail gas pipe; SL4-primary cooling tail gas pipe; SL6-primary condensate tank; SL7-primary cooling heat exchanger; SL8-cryogenic heat exchanger A / B / C; SL11-deep condensate tank; SL12-refrigerant circulation pump; SL13-purified tail gas heat exchanger; SL14-cryogenic induced draft fan; SL15-adsorption tail gas pipe; HX1 - Activated carbon adsorption tower; HX2 - Control valve; HX3 - Reflux cooling fan; HX4 - Spray cooling tower; HX7 - Desorption tail gas condenser; HX6 - Condensation tail gas fan; HX5 - Low-temperature water heat exchanger; HX8 - Low-temperature water circulating pump; HX9 - Hydrofluoric acid product tank; HX10 - High-concentration hydrofluoric acid product tank; HX14 - Desorption tail gas induced draft fan; XT1 - Denitrification induced draft fan; XT2 - Primary ammonia adder; XT3 - Denitrification heat exchanger; XT4 - Circulating fan; XT5 - Tail gas circulation control valve; XT6 - Expansion joint; XT8 - Tail gas heater; XT9 - Denitrification reactor; XT10 - Pipeline mixer; XT11 - Ammonia addition device; XT18 - External exhaust tail gas control valve; XT19 - Start-up and shutdown control valve. Detailed Implementation

[0045] The main processes for synthesizing organofluorine compounds include salt formation, diazotization, and pyrolysis, all of which are completed in a synthesis reactor.

[0046] Each reaction step is accompanied by the generation of a large amount of tail gas. The salt formation stage produces tail gas containing hydrogen fluoride and a small amount of aniline; the diazotization stage produces tail gas containing hydrogen fluoride, nitrogen dioxide, nitric oxide, and aniline; and the pyrolysis stage produces tail gas containing nitrogen, hydrogen fluoride, aniline, and organic fluorinated compounds.

[0047] The reaction temperature varies at different stages of the reaction and needs to be adjusted according to the reaction time.

[0048] The following explanation, in conjunction with the accompanying diagram, further illustrates the process of cryogenic coupled adsorption denitrification purification of tail gas from the AHF synthesis of organofluorine compounds: See appendix Figure 1 Taking a factory's production line with an annual output of 4,000 tons of organofluorine compounds as an example, the synthesis tail gas volume is 1,000 to 2,000 Nm³. 3 / h, the main components of the exhaust gas are: HF: 160~170g / Nm 3 Organofluorine compounds: 1000–2000 mg / Nm 3 NOx: 12000–20000 mg / Nm³ 3 It contains a small amount of VOCs; the rest is nitrogen.

[0049] Synthesis tail gas from the AHF process for producing organofluorine compounds enters the primary cooling heat exchanger SL7 through the synthesis tail gas pipe SL1. After exchanging heat with the cryogenic tail gas from the cryogenic heat exchanger SL8, the temperature drops to -10 to -15°C. It then enters the cryogenic heat exchanger SL8 through the primary cooling tail gas pipe SL4 for further cooling and condensation. More than 99.9% of the organofluorine compounds, nitrogen dioxide, and more than 70% of the hydrogen fluoride are condensed and intercepted, and are recycled into the cryogenic condensate tank SL11. The temperature of the cryogenic tail gas exiting the cryogenic heat exchanger SL8 drops to below -50°C.

[0050] The cryogenic exhaust gas, below -50℃, is heated to -20℃ after passing through the primary cooling heat exchanger SL7. It then enters the activated carbon adsorption tower HX1 in the adsorption stage of the adsorption unit. Under the adsorption action of the activated carbon adsorption tower HX1, more than 99.99% of the hydrogen fluoride, organic fluorine compounds, and some nitrogen oxides in the cryogenic exhaust gas are adsorbed. The adsorbed exhaust gas exiting the activated carbon adsorption tower HX1 enters the SCR denitrification unit.

[0051] The adsorption unit consists of three activated carbon adsorption towers HX1 connected in parallel, which perform adsorption and desorption respectively, and are used alternately. The adsorption-desorption cycle of the activated carbon adsorption towers HX1 is set and switched periodically.

[0052] When the adsorption time of the carbon adsorption tower HX1 reaches the adsorption cycle, it enters the desorption stage. Superheated steam is used to desorb the carbon adsorption tower HX1 after completing one adsorption cycle. The desorption tail gas is condensed and dehydrated before entering the cryogenic heat exchanger SL8 and the primary cooling tail gas pipe SL4 for defrosting.

[0053] The condensation and dehydration process is as follows: the desorption tail gas enters the low-temperature water spray cooling tower HX4, and after being cooled by low-temperature water spray, the condensate returns to the spray cooling tower. The desorption tail gas exiting the low-temperature water spray cooling tower HX4 is sent to the desorption tail gas condenser HX7 for condensation and dehydration, and then returns to the synthesis reactor CH1 to participate in the synthesis reaction, or enters the cryogenic heat exchanger CH3 for defrosting and then enters the synthesis reactor CH1 to participate in the synthesis reaction.

[0054] The adsorption tail gas from the activated carbon adsorption tower HX1 is drawn by the denitrification induced draft fan XT1, and then enters the denitrification heat exchanger XT3 to exchange heat with the purified tail gas exiting the denitrification reactor XT9, raising its temperature to 100-120℃. It then enters the tail gas heater XT8 to be heated to 180℃, and then enters the ammonia addition device XT11 to mix a certain amount of ammonia and oxygen. After being mixed by the pipeline mixer XT10, it enters the denitrification reactor XT9 for denitrification and purification.

[0055] The purified exhaust gas from the denitrification reactor XT9 has a temperature of approximately 260°C. After heat exchange in the denitrification heat exchanger XT3, the temperature drops to 160-170°C. Part of this purified exhaust gas participates in the circulation within the denitrification reactor XT9, while the remaining part exchanges heat with the desorbed exhaust gas in the purified exhaust gas heat exchanger SL13 and the desorbed exhaust gas condenser HX7, reducing the temperature to 80-110°C before being discharged.

[0056] Through the implementation of the cryogenic coupled adsorption denitrification purification scheme for synthesis tail gas of this invention, the HF recovery rate is above 99.99%; the organic fluorine compound recovery rate is above 99.9%; the NOx removal rate is above 99.95%, and the outlet NOx is below 100 mg / Nm³. 3 It recovers approximately 2,000 tons of HF and about 10 tons of organofluorine compounds annually.

Claims

1. A cryogenic coupled adsorption denitrification purification process for tail gas from the AHF synthesis of organofluorine compounds, comprising the synthesis tail gas generated during the synthesis of organofluorine compounds, characterized in that... The synthesis tail gas is cryogenically cooled by a cryogenic heat exchanger to form cryogenic tail gas, which then enters an activated carbon adsorption tower. The residual HF, organic fluorine compounds, and other VOCs in the cryogenic tail gas are adsorbed. A portion of the adsorbed tail gas exiting the activated carbon adsorption tower is sent to the activated carbon adsorption tower after desorption to cool the activated carbon adsorption tower. This portion of the adsorbed tail gas, after being heated, enters the SCR denitrification unit together with the remaining adsorbed tail gas for denitrification and purification before being discharged. The activated carbon adsorption towers consist of at least three connected in parallel to form an adsorption unit. By setting an alternating usage cycle and switching periodically, superheated steam is used to desorb the activated carbon adsorption towers after completing one adsorption cycle. The desorption tail gas enters a low-temperature water spray cooling tower, where it is cooled by low-temperature water spray. The condensate returns to the low-temperature water spray cooling tower. The desorption tail gas exiting the low-temperature water spray cooling tower is sent to a desorption tail gas condenser for condensation and dehydration before returning to the synthesis reactor to participate in the synthesis reaction. Alternatively, the desorption tail gas exiting the low-temperature water spray cooling tower can enter a cryogenic heat exchanger for defrosting before entering the synthesis reactor to participate in the synthesis reaction.

2. The cryogenic coupled adsorption denitrification purification process for tail gas from the AHF synthesis of organofluorine compounds as described in claim 1, characterized in that, Based on the mass of hydrogen fluoride adsorbed by the activated carbon adsorption tower, the temperature of the superheated steam is controlled, the desorption time is controlled, and the amount of superheated steam used for desorption is controlled; the amount of condensate introduced by the superheated steam used for desorption is controlled to ensure that the mass concentration of hydrogen fluoride in the low-temperature water is above 40%.

3. The cryogenic coupled adsorption denitrification purification process for tail gas from the AHF synthesis of organofluorine compounds as described in claim 1, characterized in that, The SCR denitrification unit consists of a denitrification heat exchanger, a heater, and a denitrification reactor connected in sequence. After the adsorption tail gas enters the SCR denitrification unit, it exchanges heat with the purified tail gas exiting the denitrification reactor through the denitrification heat exchanger, and the temperature rises to 120-140℃. It then enters the heater and is heated to above 170℃ before entering the denitrification reactor for denitrification and purification. According to the concentration of nitrogen oxides in the adsorption tail gas, ammonia gas is injected into the adsorption tail gas pipeline to mix with the adsorption tail gas and then enter the denitrification heat exchanger together.

4. The cryogenic coupled adsorption denitrification purification process for tail gas from the AHF synthesis of organofluorine compounds as described in claim 3, characterized in that, The purified exhaust gas is cooled to 120-150℃ after heat exchange, and is then drawn out by a circulating fan and divided into two parts. One part is dehydrated, cooled, and discharged after recovering residual heat; the other part is regulated by the exhaust gas circulation regulating valve and re-enters the denitrification unit to mix with the adsorbed exhaust gas.

5. The cryogenic coupled adsorption denitrification purification process for tail gas from the AHF synthesis of organofluorine compounds as described in claim 1, characterized in that, The synthesis tail gas is indirectly cooled to below -50°C via a cryogenic heat exchanger using a low-temperature refrigerant below -70°C. More than 99.9% of the organic fluorine compounds, nitrogen dioxide, and more than 70% of the hydrogen fluoride are condensed and intercepted, and returned to the synthesis reactor to continue participating in the synthesis reaction. The cryogenic tail gas from the cryogenic heat exchanger enters the activated carbon adsorption unit to adsorb and remove hydrogen fluoride, and then enters the SCR denitrification unit for denitrification before being discharged.

6. The cryogenic coupled adsorption denitrification purification process for tail gas from the AHF synthesis of organofluorine compounds as described in claim 1, characterized in that, Before entering the cryogenic heat exchanger, the synthesis exhaust gas first exchanges heat with the cryogenic exhaust gas, and the temperature drops to -8 to -12°C, while the temperature of the cryogenic exhaust gas rises to -20 to -30°C.

7. The cryogenic coupled adsorption denitrification purification process for tail gas from the AHF synthesis of organofluorine compounds as described in claim 1, characterized in that, The cryogenic heat exchangers are grouped into three units to form a cryogenic unit. The three cryogenic heat exchangers alternately perform condensation-condensation-defrosting in sequence. The condensation-condensation-defrosting process is controlled by setting upper and lower limits for the pressure difference between the inlet and outlet exhaust gases of the cryogenic heat exchanger. When the pressure difference between the inlet and outlet exhaust gases of the cryogenic heat exchanger is higher than the upper limit, the refrigerant is cut off, and the cryogenic heat exchanger enters the defrosting stage. When the pressure difference between the inlet and outlet exhaust gases of the cryogenic heat exchanger is lower than the lower limit, the refrigerant is introduced, and the cryogenic heat exchanger enters the cryogenic working stage. This process is repeated alternately.

8. The cryogenic coupled adsorption denitrification purification process for tail gas from the AHF synthesis of organofluorine compounds as described in claim 1 or 7, characterized in that, The refrigerant in the shell side of the cryogenic heat exchanger is enhanced by a refrigerant circulation pump, forming three enhanced cooling sections within the cryogenic heat exchanger. These sections respectively enhance the condensation of hydrogen fluoride, organic fluorinated compounds, and nitrogen dioxide components, thereby improving the condensation and interception effect of pollutants in the synthetic exhaust gas.

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