A calcium carbide furnace tail gas deep purification process

Abstract

The application discloses a calcium carbide furnace tail gas deep purification process. The calcium carbide furnace tail gas is firstly subjected to wet desulfurization and dehydrocyanation and TSA treatment, and then sequentially enters a de-fluorine and de-hydrocyanation reactor, a hydrolysis desulfurization reactor, a fine desulfurization reactor, a de-phosphorus and de-arsenic reactor, a de-oxygen reactor and a de-hydrocarbon reactor. After the treatment process, the HCl content in the gas is less than 0.1 ppm, the HF content is less than 0.1 ppm, the HCN content is less than 0.1 ppm, the total sulfur content is less than 0.1 ppm, the AsH3 content is less than 5 ppb, the PH3 content is less than 5 ppb, the oxygen content is less than 10 ppm, and the unsaturated hydrocarbon content is less than 0.1 ppm, thereby meeting the separation and purification requirements of subsequent processes, and the pressure drop of the whole process is not more than 100 kPa. The process can remove oxygen and unsaturated hydrocarbons in the gas under low-temperature conditions, thereby reducing the occurrence of side reactions, and has the characteristics of reasonable process design, high purification precision, low energy consumption and low operation cost.

Description

Technical Field

[0001] This invention relates to the field of chemical technology, and in particular to a deep purification process for calcium carbide furnace tail gas, belonging to the field of coal chemical industry. Background Technology

[0002] Calcium carbide is mainly used as a raw material for the production of acetylene, PVC, and calcium cyanamide, and is widely used in chemical, metallurgical and other fields. The production of 1 ton of calcium carbide generates approximately 400 cubic meters of carbon dioxide. 3 The tail gas from calcium carbide furnaces, with CO accounting for 70-80% and H2 for 5-10%, has a high calorific value and significant added value. Therefore, its comprehensive utilization has become a key development direction for the calcium carbide industry. Using this tail gas as a chemical raw material to produce methanol, acetic acid, ethylene glycol, methyl ester, and other chemical products can greatly increase its fuel value. However, deep purification treatment is necessary before utilizing the tail gas. This is because the tail gas contains impurities such as sulfides, phosphides, arsenides, fluorides, and chlorides, and has an oxygen content of nearly 1%. Sulfides and impurities containing phosphorus, arsenic, fluorine, and chlorine can poison and deactivate the catalyst, while a large amount of oxygen can affect the subsequent CO separation and purification. Therefore, removing sulfur, oxygen, and other impurities from the tail gas is a major challenge for its comprehensive utilization.

[0003] Currently, domestic methods for purifying calcium carbide furnace tail gas all involve pre-purification with activated carbon to remove naphthalene, benzene, tar, and some unsaturated hydrocarbons. Then, the gas undergoes conversion and precious metal deoxygenation, followed by deep purification to remove sulfur and acidic toxic substances such as arsenic, fluorine, and chlorine. During the conversion process, due to the high oxygen content and low sulfide content in the gas, sulfur replenishment is required. Furthermore, these processes all involve deoxygenation and hydrocarbon removal at high temperatures (above 250 °C), resulting in numerous side reactions. Long-term operation can lead to catalyst coking and deactivation. The process is also lengthy and the entire unit consumes a lot of energy.

[0004] Chinese patent CN1024889083B discloses a method for purifying tail gas from a calcium carbide furnace. This method involves dry dust removal, cooling wet desulfurization and decyanation, temperature-switching adsorption, and fine arsenic removal. However, this process can only reduce phosphides and cyanides in the gas to 1 ppm, and the sulfides contain COS, which cannot be completely removed by temperature-switching adsorption. None of these substances are removed to less than 0.1 ppm, thus failing to achieve the goal of deep purification.

[0005] Patents CN104445196B and CN10447195B describe a method for purifying and separating tail gas from a calcium carbide furnace. Both methods involve pre-purification to remove naphthalene, benzene, tar, and unsaturated hydrocarbons, followed by a deep purification stage to remove sulfur, phosphorus, arsenic, fluorine, chlorine, HCN, carbonyl metals, and oxygen. The deoxygenation reaction precision can only reach below 500 ppm, and no detailed technical solution is provided.

[0006] Patent CN102516028B discloses a process where the tail gas from a calcium carbide furnace undergoes wet desulfurization, PSA, TSA, followed by activated carbon desulfurization and catalytic deoxygenation to achieve purified gas sulfur ≤0.1 ppm and oxygen content ≤0.1% (vol%). In this process, the 1-3 ppm organic sulfur present in the deep purification is mainly COS, which is removed by activated carbon alone without hydrolysis. Initially, there will be some removal, but long-term operation will cause COS to exceed the standard, leading to excessive total sulfur. Moreover, the deoxygenation accuracy is only 0.1% (vol%), which cannot achieve the purpose of deep purification.

[0007] The deep purification of calcium carbide furnace tail gas in patent CN10462940B uses hydrolysis to desulfurize the gas before deoxygenating and dehydrating it. The deoxygenation is carried out by adsorption deoxygenation, which can remove oxygen content to below 10 ppm. However, the deoxygenating agent has a certain oxygen capacity, but the oxygen content of calcium carbide furnace tail gas can be as high as 1%, which will lead to frequent replacement of the deoxygenating agent in industrial applications, and the unsaturated hydrocarbons in the gas are not removed.

[0008] Patent CN103072945B discloses a process for producing ethylene glycol synthesis gas from calcium carbide furnace gas via a non-sulfur-resistant shift converter. The purification method sequentially employs crude desulfurization, fine dephosphorization and arsenic removal, and hydrodesulfurization and removal of unsaturated hydrocarbons before entering a sulfur-free shift converter. The oxygen content in the calcium carbide furnace tail gas fluctuates greatly and is high. During hydrodesulfurization, deoxygenation occurs simultaneously, leading to a large temperature rise during hydrodesulfurization. Furthermore, since the CO content in the calcium carbide furnace tail gas is as high as 70% or more, CO undergoes disproportionation side reactions during hydrodesulfurization, resulting in carbon buildup on the hydrodesulfurization catalyst, increased resistance, and premature deactivation. Summary of the Invention

[0009] The purpose of this invention is to achieve deep purification of calcium carbide furnace exhaust gas under low-temperature conditions through a rationally designed process route. A deep purification process for calcium carbide furnace exhaust gas includes the following steps:

[0010] (1) The tail gas from the calcium carbide furnace from the gas holder first undergoes wet desulfurization and decyanation to remove dust, tar and acidic substances. Then it is pressurized to 1.0 MPa by the compressor and enters the TSA temperature-switching adsorption to further remove dust, tar and acidic substances from the gas. Then it enters the defluorination and decyanation reactor to remove HCN, chloride ions and fluoride content in the gas to below 0.1 ppm.

[0011] (2) The gas coming out of the defluorination and decyanation reactor is heated to 50~80℃ by the steam heater and then enters the hydrolysis desulfurization reactor. The hydrolysis catalyst hydrolyzes the COS in the tail gas of the calcium carbide furnace into H2S, and the generated H2S reacts with the desulfurizing agent to be removed.

[0012] (3) After the gas is desulfurized by hydrolysis, it is cooled to about 40°C by a water cooler and then enters the fine desulfurization reactor to remove residual CS2, mercaptan, dimethyl sulfide, thiophene trace organic sulfur from the tail gas of the calcium carbide furnace, ensuring that the total sulfur content after fine desulfurization is less than 0.1 ppm.

[0013] (4) The desulfurized gas enters the dephosphorization and dearsenic removal reactor, which can remove AsH3 and PH3 from the calcium carbide furnace gas. After treatment, the AsH3 content at the outlet of the calcium carbide furnace gas is ≤5 ppb and the PH3 content is ≤5 ppb.

[0014] (5) The tail gas from the calcium carbide furnace from the dephosphorization and dearsenic removal reactor and the gas from the dehydrocarbon removal reactor exchange heat through a heat exchanger, and then mix with the circulating gas from the deoxygenation and deacetylation reactor. The temperature is controlled at 120~140℃, and then enters the deoxygenation and deacetylation reactor after passing through the start-up heater. This reduces the oxygen content in the gas to below 30 ppm and the alkyne content to below 0.1 ppm. The deoxygenation adopts a partial circulation process to control the temperature rise of the deoxygenation reaction.

[0015] (6) The gas coming out of the deoxygenation and deacetylation reactor is divided into two paths: one path of circulating gas is cooled to 40°C by a circulating gas heat exchanger and a circulating gas water cooler, and then pressurized by a circulating fan. The pressurized circulating gas is then heated by a circulating gas heat exchanger and then merged with the calcium carbide furnace tail gas that has been heated by a heat exchanger coming out of the dephosphorization and dearsenic removal reactor and enters the deoxygenation and deacetylation reactor together, thereby controlling the oxygen content at the inlet of the deoxygenation and deacetylation reactor; the other path of gas enters the dehydrocarbon removal reactor, which can remove hydrocarbons from the gas and further remove oxygen from the gas, so that the oxygen content of the gas at the outlet of the dehydrocarbon removal reactor is <10 ppm and the unsaturated hydrocarbon content is <0.1 ppm.

[0016] (7) The gas from the dehydrocarbon reactor and the tail gas from the calcium carbide furnace from the dephosphorization and dearsenic removal reactor are cooled by a heat exchanger and then cooled to room temperature by an outlet water cooler before exiting the unit.

[0017] The defluorination and decyanation reactor is filled in two layers. The upper layer is filled with defluorination and dechlorination agents, with active Ce / Ni / Co metals as the active components. The lower layer is filled with decyanation agents, with alkali metals as the active components. The ratio of the volume of defluorination and dechlorination agents to the volume of decyanation agents is 1:1.

[0018] The hydrolysis desulfurization reactor is packed in two layers. The upper layer contains a hydrolysis catalyst and a desulfurizing agent with iron oxide as the active component. The hydrolysis and fine desulfurization in the upper layer can reduce COS to less than 1 ppm. The lower layer contains a hydrolysis catalyst and a desulfurizing agent with activated carbon as the active component. The hydrolysis and desulfurization in the lower layer can reduce COS to below 0.1 ppm. The upper layer of hydrolysis catalyst and desulfurizing agent accounts for 2 / 3 of the total reactor volume, and the lower layer of hydrolysis catalyst and desulfurizing agent accounts for 1 / 3 of the total reactor volume.

[0019] The aforementioned fine desulfurization reactor is filled with a fine desulfurizing agent, which is an organic sulfur adsorbent using activated carbon as a carrier and metal additives as the active component. Two fine desulfurization reactors are installed, one in operation and one on standby. Each reactor is equipped with a regeneration system for periodic regeneration. The regeneration scheme is as follows: the regeneration gas can be either pressure swing adsorption desorbed gas or nitrogen; the regeneration temperature is 180-200℃; the regeneration cycle is 10-15 days / cycle; and the volumetric hourly space velocity (VHSV) is 100-200 h⁻¹. -1 The regeneration time is 48 hours. After regeneration, the temperature is reduced to room temperature for later use.

[0020] The dephosphorization and dearsenic removal reactor is filled in two layers. The upper layer is filled with dephosphorizing agent, with copper and molybdenum metals as active components. The lower layer is filled with dearsenic removal agent, with CuO-ZnO as active components. The ratio of the dephosphorizing agent volume to the dearsenic removal agent volume is 1:1.

[0021] The deoxygenation and deacetylation reactor is filled with a catalyst containing Pt-Pd noble metals as active components. Under the action of this catalyst, H2 and CO in the raw gas react with O2, thereby removing oxygen from the tail gas of the calcium carbide furnace and simultaneously removing trace amounts of alkynes from the gas. The temperature rise of the deoxygenation reaction is regulated by controlling the inlet oxygen content by returning the recycled gas after the deoxygenation reaction to the raw gas. The circulating fan is frequency-controlled and can automatically adjust the flow rate of the circulating gas according to the inlet oxygen content, controlling the inlet oxygen content of the deoxygenation and deacetylation reactor to not exceed 0.4%.

[0022] The dehydrogenation reactor is filled with a catalyst with low-valence copper as the active component, and the inlet temperature of the dehydrogenation reactor is 170~190℃.

[0023] The pressure drop of the entire process is no greater than 100 kPa.

[0024] The beneficial effects of this invention are:

[0025] (1) The tail gas of the calcium carbide furnace is subjected to fine removal of acidic substances in the defluorination and decyanation reactor, and the acidic ions such as HCN, HF and HCl in the gas are finely removed to below 0.1 ppm, which effectively protects the hydrolysis catalyst from acid poisoning and greatly extends the service life of the hydrolysis catalyst.

[0026] (2) New Multi-stage Hydrolysis Conversion Absorption Desulfurization Process: The traditional desulfurization method for calcium carbide furnace tail gas mainly uses the "sandwich" process, which involves first removing H2S at room temperature, then raising the temperature to 60-90℃ for COS hydrolysis to convert COS into H2S, and then cooling to room temperature to remove the generated H2S. This has a drawback, namely the "heating and cooling problem": raising the temperature first and then lowering it will increase energy consumption and operating costs. By using a multi-functional desulfurizing agent that can be used at higher temperatures, which can be used at the same temperature as the hydrolysis catalyst, a multi-stage hydrolysis desulfurization process is adopted. The operation does not require repeated heating and cooling, which greatly reduces energy consumption. Furthermore, the two-stage hydrolysis desulfurization adopts a graded filling mode in one reactor, which can achieve the hydrolysis desulfurization effect with only one reactor, thereby reducing equipment investment and land occupation.

[0027] (3) A multifunctional adsorbent is used for fine desulfurization to remove other organic sulfur compounds after hydrolysis. This fine desulfurizing agent is used to remove trace amounts of thiols, sulfides, thiophenes, and other sulfides that are difficult to remove from the gas, ensuring that the total sulfur content after fine desulfurization is <0.1ppm, thus avoiding catalyst poisoning and deactivation in subsequent processes. Furthermore, this multifunctional adsorbent can be regenerated and recycled, greatly reducing the amount of catalyst used and saving on equipment operating costs.

[0028] (4) To address the large fluctuations in oxygen content in the tail gas of the calcium carbide furnace, which can reach up to 1%, a partial recirculation process is adopted to control the oxygen content at the inlet of the deoxygenation and deacetylene reactor below 0.4%, thereby controlling the bed temperature of the deoxygenation and deacetylene reactor and preventing overheating. Since copper in the non-precious metal catalyst readily reacts with acetylene in the tail gas of the calcium carbide furnace to produce copper acetylene, which is explosive, this process first uses a platinum-palladium precious metal catalyst to remove oxygen and acetylene from the tail gas of the calcium carbide furnace at a lower temperature. The deoxygenation and deacetylene reaction principle is as follows:

[0029] Deoxygenation: O2 + 2H2 = 2H2O O2 + 2CO = 2CO2

[0030] De-alkyne: C2H2 + H2 = C2H4 C2H2 + 2H2 = C2H6

[0031] (5) Due to the poor olefin removal performance of precious metal catalysts below 200℃ and the tendency for CO disproportionation at high temperatures, a dehydrocarbon removal reactor is connected in series after the deoxygenation and deyneation reactor. A non-precious metal deolefin removal catalyst with low-valence copper as the active component is used to remove olefins from the tail gas of the calcium carbide furnace, while further removing trace amounts of oxygen from the gas. This agent has strong resistance to poisoning and high activity at low temperatures, and its price is only one-tenth that of precious metal deoxidizers, greatly saving on equipment investment. The reaction principle is as follows:

[0032] Alkene saturation: C2H4 + H2 = C2H6 C3H6 + H2 = C3H8

[0033] Deoxygenation: O2 + 2H2 = 2H2O O2 + 2CO = 2CO2

[0034] (6) Make full use of the residual heat from the deoxygenation and dehydrocarbonization of the raw material gas to heat the raw material gas, thus saving heat energy consumption. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the deep purification process for calcium carbide furnace exhaust gas.

[0036] In the diagram, 1 is the defluorination and decyanation reactor; 2 is the defluorination and dechlorination agent; 3 is the decyanation agent; 4 is the steam heater; 5 is the hydrolysis desulfurization reactor; 6 is the hydrolysis catalyst; 7 is the desulfurization agent with iron oxide as the active component; 8 is the desulfurization agent with activated carbon as the active component; 9 is the water cooler; 10 is the fine desulfurization reactor A; 11 is the fine desulfurization reactor B; 12 is the organic sulfur adsorbent; 13 is the dephosphorization and dearsenic removal reactor; 14 is the dephosphorization agent; 15 is the dearsenic removal agent; 16 is the heat exchanger; 17 is the start-up heater; 18 is the deoxygenation and deacetylene reactor; 19 is the catalyst with Pt-Pd precious metals as the active component; 20 is the dehydrocarbon removal reactor; 21 is the catalyst with low-valence copper as the active component; 22 is the circulating gas heat exchanger; 23 is the circulating gas water cooler; 24 is the circulating fan; and 25 is the outlet water cooler. Detailed Implementation

[0037] The following is in conjunction with the appendix Figure 1 The present invention is further illustrated by the embodiments, but the present invention is not limited to the embodiments. Example 1

[0038] The deep purification process for the tail gas from a calcium carbide furnace at a calcium carbide furnace plant in Ningxia is shown in the attached figure. Figure 1 As shown in Table 1, the content of major impurities in the calcium carbide furnace tail gas after TSA is as follows. The specific operating steps are:

[0039] (1) 5000 Nm³ of calcium carbide furnace exhaust gas from the gas holder 3 The gas first undergoes wet desulfurization and decyanation to remove dust, tar, and acidic substances. Then, it is pressurized to 1.0 MPa by a compressor before entering a TSA temperature-switched adsorption system to further remove dust, tar, and acidic substances. Finally, it enters defluorination and decyanation reactor 1, which is filled in two layers with a filling volume of 6 m³. 3 The upper layer is filled with 3m 3 Defluorinating and dechlorinating agent 2 with active Ce / Ni / Co metals as active components, with a lower layer of 3m³ packing. 3After treatment, the cyanide removal agent 3, with alkali metals as the active component, produced a gas containing 0.06 ppm HCl, 0.03 ppm HF, and 0.04 ppm HCN.

[0040] (2) The gas exiting the defluorination and decyanation reactor 1 is heated to 50°C by the steam heater 4 and then enters the hydrolysis desulfurization reactor 5. The hydrolysis desulfurization reactor 5 has a packing volume of 9 m³. 3 The upper layer is filled with 2 m 3 Hydrolysis catalysts 6 and 4 m 3 Desulfurizing agent 7, with iron oxide as the active component, reduces COS to 0.83 ppm in the upper layer through hydrolysis and desulfurization, and the lower layer is filled with 2 m³ of [unclear text - likely referring to a specific material or material]. 3 Hydrolysis catalysts 6 and 1 m 3 Desulfurizer 8, with activated carbon as the active component, reduces COS to 0.04 ppm through lower-layer hydrolysis and desulfurization.

[0041] (3) After hydrolysis and desulfurization, the gas is cooled to about 40°C by water cooler 9 and then enters fine desulfurization reactor A 10 and fine desulfurization reactor B 11. Two fine desulfurization reactors are set up, one in operation and one on standby. Each reactor is filled with 5m³ of water. 3 Using activated carbon as a carrier and adding metal additives as the active component, the organic sulfur adsorbent 12 can further remove trace amounts of organic sulfur compounds such as CS2, thiols, dimethyl sulfide, and thiophene from the tail gas of a calcium carbide furnace. The treated gas showed no detectable H2S, COS of 0.04 ppm, CS2 of 0.01 ppm, C4H4S of 0.03 ppm, and a total organic sulfur content of less than 0.1 ppm. The fine desulfurization reactor is equipped with a regeneration system for periodic regeneration. The regeneration scheme is as follows: nitrogen as the regeneration gas, regeneration temperature of 180℃, regeneration cycle of 10 days / cycle, and volumetric hourly space velocity of 100 h⁻¹. -1 The regeneration time is 48 hours. After regeneration, the temperature is reduced to room temperature for later use.

[0042] (4) The gas after fine desulfurization enters the dephosphorization and dearsenic removal reactor 13. The dephosphorization and dearsenic removal reactor 13 is filled in two layers, with a total filling volume of 6m³. 3 The upper layer is filled with 3m 3 Dephosphorizing agent 14 with copper and molybdenum metals as active components; lower layer packed with 3m 3 Arsenic removal agent 15, with CuO-ZnO as the active component, resulted in a gas concentration of 3.8 ppb of AsH3 and 4.2 ppb of PH3 after treatment.

[0043] (5) The tail gas from the calcium carbide furnace at the dephosphorization and dearsenic removal reactor 13 and the gas from the dehydrocarbon removal reactor 20 exchange heat through heat exchanger 16, and then mix with the circulating gas from the deoxygenation and deacetylene removal reactor 18. The temperature is controlled at 120°C, and then the gas enters the deoxygenation and deacetylene removal reactor 18 after passing through the start-up heater 17. The deoxygenation and deacetylene removal reactor 18 is filled with 1m³ of gas. 3 Catalyst 19, with Pt-Pd precious metals as the active component, can catalyze the reaction of H2 and CO with O2 in the raw gas, thereby removing oxygen from the tail gas of the calcium carbide furnace and simultaneously removing trace amounts of alkynes from the gas. The O2 content in the gas after passing through the deoxygenation and deacetylene reactor 18 is 26 ppm, and the acetylene content is 0.05 ppm. To control the temperature rise of the deoxygenation reaction, a partial circulation process is adopted for deoxygenation. The circulating gas from the deoxygenation and deacetylene reactor 18 is cooled to 40°C through the circulating gas heat exchanger 22 and the circulating gas water cooler 23, and then pressurized by the circulating fan 24. The pressurized circulating gas is then heated again through the circulating gas heat exchanger 22 and merged with the calcium carbide furnace tail gas after heat exchange from the dephosphorization and dearsenic removal reactor 13 before entering the deoxygenation and deacetylene reactor 18. The oxygen content at the inlet of the deoxygenation and deacetylene reactor is controlled at about 0.32%.

[0044] (6) The gas exiting the deoxygenation and deacetylation reactor 18 at a temperature of about 170°C directly enters the dehydrocarbonization reactor 20, which is filled with 5 m³ of gas. 3 Using low-valence copper as the active component catalyst 21, hydrocarbons are removed from the gas, and oxygen content is further removed. The treated gas has an oxygen content of 7 ppm, C2H2 content is undetectable, C2H4 content is 0.02 ppm, C3H6 content is 0.02 ppm, and total unsaturated hydrocarbon content is 0.04 ppm. The gas from the hydrocarbon removal reactor 20 and the calcium carbide furnace tail gas from the phosphorus and arsenic removal reactor 13 are cooled by heat exchanger 16 and then cooled to room temperature by outlet water cooler 25 before exiting the unit.

[0045] The entire process ensures that the gas contains HCl < 0.1 ppm, HF < 0.1 ppm, HCN < 0.1 ppm, total sulfur < 0.1 ppm, AsH3 content < 5 ppb, PH3 content < 5 ppb, oxygen content < 10 ppm, unsaturated hydrocarbon content < 0.1 ppm, and pressure drop not greater than 100 kPa. Example 2

[0046] The deep purification process for the tail gas from a calcium carbide furnace at a calcium carbide furnace plant in Ningxia is shown in the attached figure. Figure 1 As shown in Table 1, the content of major impurities in the calcium carbide furnace tail gas after TSA is as follows. The specific operating steps are:

[0047] (1) 5000 Nm³ of calcium carbide furnace exhaust gas from the gas holder 3The gas first undergoes wet desulfurization and decyanation to remove dust, tar, and acidic substances. Then, it is pressurized to 1.0 MPa by a compressor before entering a TSA temperature-switched adsorption system to further remove dust, tar, and acidic substances. Finally, it enters defluorination and decyanation reactor 1, which is filled in two layers with a filling volume of 6 m³. 3 The upper layer is filled with 3m 3 Defluorinating and dechlorinating agent 2 with active Ce / Ni / Co metals as active components, with a lower layer of 3m³ packing. 3 After treatment, the cyanide removal agent 3, with alkali metals as the active component, produced a gas containing 0.06 ppm HCl, 0.03 ppm HF, and 0.04 ppm HCN.

[0048] (2) The gas exiting the defluorination and decyanation reactor 1 is heated to 65°C by the steam heater 4 and then enters the hydrolysis desulfurization reactor 5. The hydrolysis desulfurization reactor 5 has a packing volume of 9 m³. 3 The upper layer is filled with 2 m 3 Hydrolysis catalysts 6 and 4 m 3 Desulfurizing agent 7, with iron oxide as the active component, reduces COS to 0.67 ppm in the upper layer through hydrolysis and desulfurization, and the lower layer is filled with 2 m³ of [unclear text - possibly a type of material]. 3 Hydrolysis catalysts 6 and 1 m 3 Desulfurizer 8, with activated carbon as the active component, reduces COS to 0.03 ppm through lower-layer hydrolysis and desulfurization.

[0049] (3) After hydrolysis and desulfurization, the gas is cooled to about 40°C by water cooler 9 and then enters fine desulfurization reactor A 10 and fine desulfurization reactor B 11. Two fine desulfurization reactors are set up, one in operation and one on standby. Each reactor is filled with 5m³ of water. 3 Using activated carbon as a carrier and adding metal additives as the active component, the organic sulfur adsorbent 12 can further remove trace amounts of organic sulfur compounds such as CS2, thiols, dimethyl sulfide, and thiophene from the tail gas of a calcium carbide furnace. The treated gas showed no detectable H2S, COS of 0.03 ppm, CS2 of 0.01 ppm, C4H4S of 0.03 ppm, and a total organic sulfur content of less than 0.1 ppm. The fine desulfurization reactor is equipped with a regeneration system for periodic regeneration. The regeneration scheme is as follows: nitrogen as the regeneration gas, regeneration temperature of 190℃, regeneration cycle of 12 days / cycle, and volumetric hourly space velocity (VHSV) of 150 h⁻¹. -1 The regeneration time is 48 hours. After regeneration, the temperature is reduced to room temperature for later use.

[0050] (4) The gas after fine desulfurization enters the dephosphorization and dearsenic removal reactor 13. The dephosphorization and dearsenic removal reactor 13 is filled in two layers, with a total filling volume of 6 m³. 3 The upper layer is filled with 3 m 3 Dephosphorizing agent 14 with copper and molybdenum metals as active components; lower layer packed with 3 m3 Arsenic removal agent 15, with CuO-ZnO as the active component, resulted in a gas concentration of 3.8 ppb for AsH3 and 4.2 ppb for PH3 after treatment.

[0051] (5) The tail gas from the calcium carbide furnace at the dephosphorization and dearsenic removal reactor 13 and the gas from the dehydrocarbon removal reactor 20 exchange heat through heat exchanger 16, and then mix with the circulating gas from the deoxygenation and deacetylene removal reactor 18. The temperature is controlled at 130°C, and then the gas enters the deoxygenation and deacetylene removal reactor 18 after passing through the start-up heater 17. The deoxygenation and deacetylene removal reactor 18 is filled with 1m³ of gas. 3 Catalyst 19, with Pt-Pd precious metals as the active component, can catalyze the reaction of H2 and CO with O2 in the raw gas, thereby removing oxygen from the tail gas of the calcium carbide furnace and simultaneously removing trace amounts of alkynes from the gas. The O2 content in the gas after passing through the deoxygenation and deacetylene reactor 18 is 22 ppm, and the acetylene content is 0.04 ppm. To control the temperature rise of the deoxygenation reaction, a partial circulation process is adopted for deoxygenation. The circulating gas from the deoxygenation and deacetylene reactor 18 is cooled to 40°C through the circulating gas heat exchanger 22 and the circulating gas water cooler 23, and then pressurized by the circulating fan 24. The pressurized circulating gas is then heated again through the circulating gas heat exchanger 22 and merged with the calcium carbide furnace tail gas after heat exchange from the dephosphorization and dearsenic removal reactor 13 before entering the deoxygenation and deacetylene reactor 19. The oxygen content at the inlet of the deoxygenation and deacetylene reactor is controlled at about 0.32%.

[0052] (6) The gas exiting the deoxygenation and deacetylation reactor 18 at a temperature of about 180℃ directly enters the dehydrocarbonization reactor 20, which is filled with 5 m³ of gas. 3 Using low-valence copper as the active component catalyst 21, hydrocarbons are removed from the gas, and oxygen content is further removed. The treated gas has an oxygen content of 4 ppm, C2H2 content is undetectable, C2H4 content is 0.02 ppm, C3H6 content is 0.01 ppm, and total unsaturated hydrocarbon content is 0.03 ppm. The gas from the hydrocarbon removal reactor 20 and the calcium carbide furnace tail gas from the phosphorus and arsenic removal reactor 13 are cooled by heat exchanger 16 and then cooled to room temperature by outlet water cooler 25 before exiting the unit.

[0053] The entire process ensures that the gas contains HCl < 0.1 ppm, HF < 0.1 ppm, HCN < 0.1 ppm, total sulfur < 0.1 ppm, AsH3 content < 5 ppb, PH3 content < 5 ppb, oxygen content < 10 ppm, unsaturated hydrocarbon content < 0.1 ppm, and pressure drop not greater than 100 kPa. Example 3

[0054] The deep purification process for the tail gas from a calcium carbide furnace at a calcium carbide furnace plant in Ningxia is shown in the attached figure. Figure 1 As shown in Table 1, the content of major impurities in the calcium carbide furnace tail gas after TSA is as follows. The specific operating steps are:

[0055] (1) 5000 Nm³ of calcium carbide furnace exhaust gas from the gas holder 3 The gas first undergoes wet desulfurization and decyanation to remove dust, tar, and acidic substances. Then, it is pressurized to 1.0 MPa by a compressor before entering a TSA temperature-switched adsorption system to further remove dust, tar, and acidic substances. Finally, it enters defluorination and decyanation reactor 1, which is filled in two layers with a filling volume of 6 m³. 3 The upper layer is filled with 3 m 3 Defluorinating and dechlorinating agent 2, with active Ce / Ni / Co metals as active components, is packed in a 3 m³ lower layer. 3 After treatment, the cyanide removal agent 3, with alkali metals as the active component, produced a gas containing 0.06 ppm HCl, 0.03 ppm HF, and 0.04 ppm HCN.

[0056] (2) The gas exiting the defluorination and decyanation reactor 1 is heated to 80°C by the steam heater 4 and then enters the hydrolysis desulfurization reactor 5. The hydrolysis desulfurization reactor 5 has a packing volume of 9 m³. 3 The upper layer is filled with 2 m 3 Hydrolysis catalysts 6 and 4 m 3 Desulfurizing agent 7, with iron oxide as the active component, reduces COS to 0.5 ppm in the upper layer through hydrolysis and desulfurization, and the lower layer is filled with 2 m³ of [unclear text - possibly a type of material]. 3 Hydrolysis catalysts 6 and 1m 3 Desulfurizer 8, with activated carbon as the active component, reduces COS to 0.02 ppm through lower-layer hydrolysis and desulfurization.

[0057] (3) After hydrolysis and desulfurization, the gas is cooled to about 40°C by water cooler 9 and then enters fine desulfurization reactor A 10 and fine desulfurization reactor B 11. Two fine desulfurization reactors are set up, one in operation and one on standby. Each reactor is filled with 5m³ of water. 3 Organic sulfur adsorbent 12, using activated carbon as a carrier and adding metal additives as the active component, can further remove trace amounts of organic sulfur such as CS2, thiols, dimethyl sulfide, and thiophene from the tail gas of a calcium carbide furnace. The treated gas showed no detectable H2S, COS of 0.02 ppm, CS2 of 0.01 ppm, C4H4S of 0.03 ppm, and a total organic sulfur content of less than 0.1 ppm. The fine desulfurization reactor is equipped with a regeneration system for periodic regeneration. The regeneration scheme is as follows: the regeneration gas is the desorbed gas from pressure swing adsorption, the regeneration temperature is 200℃, the regeneration cycle is 15 days / cycle, and the volumetric hourly space velocity is 200 h⁻¹. -1 The regeneration time is 48 hours. After regeneration, the temperature is reduced to room temperature for later use.

[0058] (4) The gas after fine desulfurization enters the dephosphorization and dearsenic removal reactor 13. The dephosphorization and dearsenic removal reactor 13 is filled in two layers, with a total filling volume of 6 m³.3 The upper layer is filled with 3 m 3 Dephosphorizing agent 14 with copper and molybdenum metals as active components; lower layer packed with 3 m 3 Arsenic removal agent 15, with CuO-ZnO as the active component, resulted in a gas concentration of 3.8 ppb for AsH3 and 4.2 ppb for PH3 after treatment.

[0059] (5) The tail gas from the calcium carbide furnace at the dephosphorization and dearsenic removal reactor 13 and the gas from the dehydrocarbon removal reactor 20 exchange heat through heat exchanger 16, and then mix with the circulating gas from the deoxygenation and deacetylene removal reactor 18. The temperature is controlled at 140℃, and then the gas enters the deoxygenation and deacetylene removal reactor 18 after passing through the start-up heater 17. The deoxygenation and deacetylene removal reactor 18 is filled with 1 m³ of gas. 3 Catalyst 19, with Pt-Pd precious metals as the active component, can catalyze the reaction of H2 and CO with O2 in the raw gas, thereby removing oxygen from the tail gas of the calcium carbide furnace and simultaneously removing trace amounts of alkynes from the gas. The O2 content in the gas after passing through the deoxygenation and deacetylene reactor 18 is 18 ppm, and the acetylene content is 0.02 ppm. To control the temperature rise of the deoxygenation reaction, a partial circulation process is adopted for deoxygenation. The circulating gas from the deoxygenation and deacetylene reactor 18 is cooled to 40°C through the circulating gas heat exchanger 22 and the circulating gas water cooler 23, and then pressurized by the circulating fan 24. The pressurized circulating gas is then heated again through the circulating gas heat exchanger 22 and merged with the calcium carbide furnace tail gas after heat exchange from the dephosphorization and dearsenic removal reactor 13 before entering the deoxygenation and deacetylene reactor 18. The oxygen content at the inlet of the deoxygenation and deacetylene reactor is controlled at about 0.32%.

[0060] (6) The gas exiting the deoxygenation and deacetylation reactor 18 at a temperature of about 190°C directly enters the dehydrocarbonization reactor 20, which is filled with 5 m³ of gas. 3 Using low-valence copper as the active component catalyst 21, hydrocarbons are removed from the gas, and oxygen content is further removed. The treated gas has an oxygen content of 6 ppm, C2H2 is not detected, C2H4 content is 0.01 ppm, C3H6 content is 0.01 ppm, and total unsaturated hydrocarbon content is 0.02 ppm. The gas from the hydrocarbon removal reactor 20 and the calcium carbide furnace tail gas from the phosphorus and arsenic removal reactor 13 are cooled by heat exchanger 16 and then cooled to room temperature by outlet water cooler 25 before exiting the unit.

[0061] The entire process ensures that the gas contains HCl < 0.1 ppm, HF < 0.1 ppm, HCN < 0.1 ppm, total sulfur < 0.1 ppm, AsH3 content < 5 ppb, PH3 content < 5 ppb, oxygen content < 10 ppm, unsaturated hydrocarbon content < 0.1 ppm, and pressure drop not greater than 100 kPa.

[0062] Table 1. Components and main impurities of calcium carbide furnace exhaust gas (after TSA)

[0063] Component name Content, V% Main impurity content content <![CDATA[H2]]> 9 HCN 1 ppm CO 73 <![CDATA[H2S]]> 1 ppm <![CDATA[CO2]]> 6.7 COS 8 ppm <![CDATA[N2]]> 10 <![CDATA[CS2]]> 0.5 ppm <![CDATA[O2]]> 0.8 <![CDATA[C4H4S]]> 2 ppm <![CDATA[CH4]]> 0.5 HCl 1 ppm HF 0.1 ppm <![CDATA[AsH3]]> 0.3 ppm <![CDATA[PH3]]> 0.1 ppm <![CDATA[C2H2]]> 90 ppm <![CDATA[C2H4]]> 50 ppm <![CDATA[C3H6]]> 44 ppm

Claims

1. A deep purification process for calcium carbide furnace exhaust gas, characterized in that, The process includes the following steps: (1) The tail gas from the calcium carbide furnace from the gas holder first undergoes wet desulfurization and decyanation to remove dust, tar and acidic substances. Then, it is pressurized to 1.0 MPa by a compressor and enters the TSA temperature-switching adsorption to further remove dust, tar and acidic substances from the gas. Then it enters the defluorination and decyanation reactor. The defluorination and decyanation reactor is filled in two layers. The upper layer is filled with defluorination and dechlorination agent and the lower layer is filled with decyanation agent. The ratio of the volume of defluorination and dechlorination agent to the volume of decyanation agent is 1:

1. The HCN, chloride ion and fluoride content in the gas is removed to below 0.1 ppm. (2) The gas coming out of the defluorination and decyanation reactor is heated to 50~80℃ by a steam heater and then enters the hydrolysis desulfurization reactor. The hydrolysis desulfurization reactor is filled in two layers. The upper layer is filled with hydrolysis catalyst and desulfurizing agent with iron oxide as active component, and the lower layer is filled with hydrolysis catalyst and desulfurizing agent with activated carbon as active component. The upper layer of hydrolysis catalyst and desulfurizing agent is 2 / 3 of the total filling volume of the reactor, and the lower layer of hydrolysis catalyst and desulfurizing agent is 1 / 3 of the total filling volume of the reactor. In this way, COS in the tail gas of the calcium carbide furnace is hydrolyzed into H2S, and the generated H2S is then removed by reacting with the desulfurizing agent. (3) After the gas is desulfurized by hydrolysis, it is cooled to about 40°C by a water cooler and then enters the fine desulfurization reactor. The fine desulfurization reactor is filled with fine desulfurizing agent to remove residual CS2, mercaptan, dimethyl sulfide, thiophene trace organic sulfur in the tail gas of the calcium carbide furnace, ensuring that the total sulfur content after fine desulfurization is less than 0.1ppm. (4) The desulfurized gas enters the dephosphorization and dearsenic removal reactor and is filled in two layers. The upper layer is filled with dephosphorizing agent and the lower layer is filled with dearsenic removal agent. The filling volume ratio is 1:

1. AsH3 and PH3 in the calcium carbide furnace gas are removed. After treatment, the AsH3 content in the raw material gas outlet is ≤5 ppb and the PH3 content is ≤5 ppb. (5) The tail gas from the calcium carbide furnace from the dephosphorization and dearsenic removal reactor and the gas from the dehydrocarbon removal reactor exchange heat through a heat exchanger, and then mix with the circulating gas from the deoxygenation and deacetylation reactor. The temperature is controlled at 120~140℃. After passing through the start-up heater, the gas enters the deoxygenation and deacetylation reactor, reducing the oxygen content in the gas to below 30 ppm and the alkyne content to below 0.1 ppm. The deoxygenation adopts a partial circulation process to control the temperature rise of the deoxygenation reaction. (6) The gas coming out of the deoxygenation and deacetylation reactor is divided into two paths: one path of circulating gas is cooled to 40°C by a circulating gas heat exchanger and a circulating gas water cooler, and then pressurized by a circulating fan. The pressurized circulating gas is then heated by a circulating gas heat exchanger and then merged with the calcium carbide furnace tail gas that has been heated by a heat exchanger coming out of the dephosphorization and dearsenic removal reactor and enters the deoxygenation and deacetylation reactor together, thereby controlling the oxygen content at the inlet of the deoxygenation and deacetylation reactor; the other path of gas enters the dehydrocarbon removal reactor, which removes hydrocarbons from the gas and further removes oxygen from the gas, so that the oxygen content of the gas at the outlet of the dehydrocarbon removal reactor is <10 ppm and the unsaturated hydrocarbon content is <0.1 ppm. (7) The gas from the dehydrocarbon reactor and the tail gas from the calcium carbide furnace from the dephosphorization and dearsenic removal reactor are cooled by a heat exchanger and then cooled to room temperature by an outlet water cooler before exiting the unit.

2. The process according to claim 1, characterized in that: The defluorinating and dechlorinating agent uses active Ce / Ni / Co metals as active components; the decyanating agent uses alkali metals as active components.

3. The process according to claim 1, characterized in that: The upper layer of hydrolyzing agent and desulfurizing agent in the hydrolysis desulfurization reactor reduces COS to less than 1 ppm, and the lower layer of hydrolyzing agent and desulfurizing agent reduces COS to less than 0.1 ppm.

4. The process according to claim 1, characterized in that: The aforementioned fine desulfurizing agent is an organic sulfur adsorbent with activated carbon as a carrier and metal additives as active components.

5. The process according to claim 1, characterized in that: The dephosphorizing agent uses copper and molybdenum metals as active components, while the arsenic removal agent uses CuO-ZnO as active components.

6. The process according to claim 1, characterized in that: The deoxygenation and deacetylation reactor is filled with a catalyst containing Pt-Pd noble metals as the active component, which causes H2 and CO in the feed gas to react with O2, thereby removing oxygen from the tail gas of the calcium carbide furnace and simultaneously removing trace amounts of alkynes from the gas. The temperature rise of the deoxygenation reaction is regulated by controlling the inlet oxygen content by returning the recycled gas after the deoxygenation reaction to the feed gas. The circulating fan is frequency-controlled and can automatically adjust the flow rate of the circulating gas according to the inlet oxygen content, controlling the inlet oxygen content of the deoxygenation and deacetylation reactor to not exceed 0.4%. The dehydrocarbonization reactor is filled with a catalyst containing low-valence copper as the active component, and the inlet temperature of the dehydrocarbonization reactor is 170~190℃.

7. The process according to claim 1, characterized in that: The pressure drop of the entire process is no more than 100 kPa.

8. The process according to claim 1, characterized in that: Two fine desulfurization reactors are installed, one in operation and one on standby. Each reactor is equipped with a regeneration system for periodic regeneration. The regeneration scheme is as follows: the regeneration gas is either desorbed gas from pressure swing adsorption or nitrogen; the regeneration temperature is 180-200℃; the regeneration cycle is 10-15 days / cycle; and the volumetric hourly space velocity (VHSV) is 100-200 h⁻¹. -1 The regeneration time is 48 hours. After regeneration, the temperature is reduced to room temperature for later use.

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