Method for preparing sulfuric acid from coking flue gas

Abstract

The invention provides a method for preparing sulfuric acid from coking flue gas, which comprises the following steps of: at the start-up temperature rise stage of a system, forming gas circulation temperature rise in the system through a temperature rise internal circulation pipeline, concentrating and drying dilute sulfur foam sent by a coking desulfurization unit to obtain sulfur-containing mixed salt, incinerating the sulfur-containing mixed salt to generate high-temperature SO2-containing flue gas, and recycling the high-temperature SO2-containing flue gas. The method comprises the following steps: cooling high-temperature SO2-containing flue gas, purifying to obtain SO2 flue gas, dehydrating and drying the SO2 flue gas, and absorbing the dehydrated and dried SO2 flue gas in a conversion unit by adopting a five-section conversion two-stage absorption process to prepare sulfuric acid. Through the five-stage conversion and two-stage absorption process, temperature heat exchange of gas among multiple conversion procedures is realized, and heat energy generated by conversion is always circulated and utilized in the system, so that the reaction heat is completely utilized, the heat energy efficiency of the whole process is improved, and the energy consumption is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for preparing sulfuric acid, in particular a method for preparing sulfuric acid from coking flue gas, and belongs to the technical field of recycling. BACKGROUND

[0002] The acid production from coking plant flue gas is a technology for realizing resource recycling and environmental protection and emission reduction by converting the sulfur-containing waste gas (such as hydrogen sulfide and sulfur dioxide) generated in the coking process into chemical products such as sulfuric acid. The main recycling process is to burn the sulfur-containing waste gas at high temperature to generate sulfur dioxide, and then oxidize it into sulfur trioxide through a vanadium catalyst, and finally generate sulfuric acid. The oxidation of sulfur dioxide into sulfur trioxide is an exothermic reaction. The conventional conversion process is to connect multiple conversion processes in series, and when the temperature rises to a certain extent, the temperature is lowered, so as to improve the conversion efficiency through multiple conversion. This is easy to waste the heat generated by the conversion exothermic reaction. SUMMARY

[0003] The technical problem to be solved by the present application is to provide a method for preparing sulfuric acid from coking flue gas, and to improve the heat utilization efficiency of acid production from coking plant flue gas.

[0004] To solve the above technical problems, the technical solution adopted by the present application is: A method for preparing sulfuric acid from coking flue gas, characterized by comprising the following steps: S1. During the system start-up and temperature rising stage, the gas circulation and temperature rising in the system are formed through the temperature rising internal circulation pipeline; S2. The dilute sulfur foam concentrated and dried in the coking desulfurization unit is obtained as a sulfur-containing mixed salt; S3. The sulfur-containing mixed salt is incinerated to generate high-temperature SO2-containing flue gas, and the SO2-containing flue gas is purified after being cooled to obtain SO2 flue gas; S4. The SO2 flue gas is dehydrated and dried; S5. The SO2 flue gas after dehydration and drying is absorbed in the conversion unit by using a five-stage conversion and two-stage absorption process to prepare sulfuric acid.

[0005] Further, the step S1 is specifically: connecting a temperature rising internal circulation pipeline between the gas inlet of the drying tower and the tail gas outlet of the second absorption tower, closing the electric precipitator outlet valve and the tail gas exhaust valve during the system start-up and temperature rising stage, opening the valves at both ends of the temperature rising internal circulation pipeline, and making the SO2 fan directly suck the gas at the outlet of the second absorption tower to form the gas circulation and temperature rising in the system around the drying process, the conversion process and the absorption process.

[0006] Further, the step S2 is specifically: concentrating the dilute sulfur foam from the coking desulfurization unit to form concentrated sulfur foam with a total solid content of 35% to 45%, and sending the concentrated sulfur foam to the dryer by screw pump for evaporation and drying to solidify into powder and granular sulfur-containing mixed salt.

[0007] Further, the step S3 is specifically: the sulfur-containing mixed salt is sent to a furnace hopper by a pipe chain conveyor, sent to a sulfur-burning furnace by a belt conveyor, and burned in the sulfur-burning furnace to generate high-temperature SO2-containing flue gas at 800-1150°C; the high-temperature SO2-containing flue gas is cooled to 230-350°C by heat exchange in a waste heat boiler; the flue water in the waste heat boiler is vaporized by heat exchange with the high-temperature SO2-containing flue gas to recover the waste heat of the high-temperature SO2-containing flue gas; the low-temperature SO2-containing flue gas from the waste heat boiler enters a purification process, is humidified, cooled, and preliminarily washed and purified by a dynamic wave scrubber; then the low-temperature SO2-containing flue gas enters a cooling tower and is countercurrently contacted with cooling circulating dilute acid sprayed from the top of the tower, is again cooled, condensed, washed and purified, and removes water vapor and impurities therefrom, and then enters an electric demister to remove acid mist, to obtain SO2 flue gas.

[0008] Further, the step S4 is specifically: the SO2 flue gas enters a drying tower from a bottom gas inlet of the drying tower, is countercurrently contacted with 93% concentrated sulfuric acid sprayed from the top of the tower in the drying tower, and removes water in the flue gas, so that the water content in the SO2 flue gas out of the tower is ≤0.1 g / Nm 3 The SO2 flue gas out of the tower is pressurized by a sulfur dioxide blower and sent to a conversion unit.

[0009] Further, the concentrated sulfuric acid circulating in the drying tower is reduced in concentration after absorbing water in the SO2 flue gas, and the concentration is maintained by adding 98% concentrated sulfuric acid; the increased low-concentration sulfuric acid is sent to a sulfuric acid storage tank for temporary storage, and is sent to the absorption process to increase the concentration after normal production.

[0010] Further, the step S5 is specifically: the dehydrated and dried SO2 flue gas is pressurized by a SO2 blower and sequentially passes through the shell side of a three-stage heat exchanger and a one-stage heat exchanger, is indirectly heat-exchanged with respective high-temperature conversion gas, is gradually heated to 420°C, and then enters a first conversion bed of a converter for conversion reaction; the flue gas after the conversion reaction in the first conversion bed is heated to 585°C, enters the tube side of the one-stage heat exchanger, and is indirectly heat-exchanged with hot SO2 flue gas from the third heat exchanger, is cooled to 460°C, enters a second conversion bed of the converter for further catalytic reaction, is heated to 510°C, enters the tube side of a two-stage heat exchanger, and is indirectly heat-exchanged with hot SO2 flue gas from the fourth heat exchanger and the fifth heat exchanger, is cooled to 440°C, enters a third conversion bed of the converter for further reaction, enters the tube side of a three-stage heat exchanger from the third conversion bed of the converter, is heat-exchanged with cold SO2 flue gas from the SO2 blower, is cooled to 175°C, and then enters a primary absorption tower. The flue gas from the first-stage absorption tower is sequentially subjected to indirect heat exchange with high-temperature conversion gas in the shell side of five-stage heat exchangers, four-stage heat exchangers and two-stage heat exchangers, heated to 420 DEG C and then enters the four-stage conversion bed of the converter for second conversion; the gas from the four-stage conversion bed enters the tube side of the four-stage heat exchanger for heat exchange with the cold flue gas from the first-stage absorption tower, cooled to 415 DEG C and then enters the five-stage conversion bed of the converter for continuous reaction, and the outlet gas from the five-stage conversion bed is subjected to heat exchange and cooling with the cold flue gas from the first-stage absorption tower in the tube side of the five-stage heat exchanger, and then enters the second-stage absorption tower for secondary absorption after the temperature is reduced to 165 DEG C; The conversion gas from the three-stage conversion bed of the converter is cooled to 175 DEG C by the three-stage heat exchanger and then enters the first-stage absorption tower, and after countercurrent contact with 98% concentrated sulfuric acid sprayed from the top of the tower and absorption of SO3 in the flue gas, the remaining gas is removed from the acid mist by the demister at the top of the first-stage absorption tower and is sent back to the four-stage conversion bed for continuous conversion, and the sulfuric acid absorbing SO3 flows from the bottom of the first-stage absorption tower into the absorption circulating tank, is sent to the absorption acid cooler by the absorption circulating pump for cooling, and the cooled concentrated sulfuric acid is circulated and sprayed by the acid distributor at the upper part of the first-stage absorption tower and the second-stage absorption tower; The gas from the five-stage conversion bed is cooled by the five-stage heat exchanger and then enters the second-stage absorption tower, and after countercurrent contact with 98% concentrated sulfuric acid sprayed from the top of the tower and absorption of SO3 in the flue gas.

[0011] Further, a 1# electric heating furnace is arranged at the gas inlet of the first-stage heat exchanger, and a 2# electric heating furnace is arranged at the gas inlet of the second-stage heat exchanger.

[0012] Compared with the prior art, the present application has the following advantages and effects: 1. The conversion process of the present application realizes heat exchange of the gas between multiple conversion processes by the five-stage conversion two-stage absorption process, the heat energy generated by conversion is always circulated and utilized within the system, so that the reaction heat is also completely utilized, the heat energy efficiency of the whole process is improved, and the energy consumption is reduced; 2. In the system start-up and temperature rising stage, the temperature rising internal circulation pipeline is used to shorten the temperature rising time, save the temperature rising energy consumption, and isolate the external air to reduce the corrosion rate of the equipment. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 is a flow chart of a method for preparing sulfuric acid from coking flue gas. DETAILED DESCRIPTION

[0014] In order to describe the technical solutions adopted by the present application in detail to achieve the predetermined technical objectives, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments, and the technical means or technical features in the embodiments of the present application can be replaced without creative labor. The present application will be described in detail below with reference to the drawings and in conjunction with the embodiments.

[0015] As shown in the figure, the method for preparing sulfuric acid from coking flue gas of the present application comprises the following steps: Figure 1 S1, in the system start-up temperature rising stage, the gas circulation temperature rising in the system is formed through the temperature rising internal circulation pipeline. S1, in the system start-up temperature rising stage, the gas circulation temperature rising in the system is formed through the temperature rising internal circulation pipeline.

[0016] A temperature rising internal circulation pipeline is connected between the gas inlet of the drying tower and the tail gas outlet of the secondary absorption tower. In the system start-up temperature rising stage, the outlet valve of the electric precipitator and the tail gas exhaust valve are closed, the valves at both ends of the temperature rising internal circulation pipeline are opened, the SO2 fan directly sucks the gas at the outlet of the secondary absorption tower, and the gas circulation temperature rising in the system is formed around the drying process, the conversion process and the absorption process.

[0017] In the initial stage of system start-up, the process temperature at each point of the system is low, and the conversion process needs to be preheated. The traditional heating method is to close the outlet valve of the electric precipitator, open the inlet valve connected to the atmosphere in front of the drying tower, start the sulfur dioxide fan, directly suck air into the system, and start two electric heating furnaces to heat the air flowing through the conversion process, thereby driving the overall temperature rising of the conversion process.

[0018] When the temperature of the first-stage conversion bed layer reaches 450℃, the temperature of the fourth-stage conversion bed layer reaches 400℃, the temperature of the second-stage conversion bed layer reaches 380℃ or above, and the outlet temperatures of the third-stage and fifth-stage conversion bed layers reach 280℃ or above, it can be considered that the temperature rising is mature, and the system can be started with air.

[0019] Due to the long process flow of the conversion process, the system temperature rising time is about 72 hours, which will cause the following problems in the process: 1. Energy waste problem: the power of the first electric heater in the system is 480KW / h, the power of the second electric heater is 240KW / h, and the total power of the heater is 720KW / h. The daily power consumption of the conversion process during the temperature rising stage reaches 17280KW. During the temperature rising stage, due to the continuous suction of the ambient temperature air into the system, the temperature rising time is prolonged, and the power consumption is high.

[0020] 2. Material waste problem: During the heating stage, air is continuously sucked into the system, and this part of air will pass through the drying tower to be washed and dehydrated by spraying 93% concentrated sulfuric acid. During the dehydration process, the 93% concentrated sulfuric acid will be diluted to between 80-90%. The entire heating process will cause about 200 tons of concentrated sulfuric acid to be diluted by water. This part of diluted sulfuric acid needs to be re-concentrated during the later production period, causing double waste of materials and energy.

[0021] 3. Equipment corrosion problem: During the system heating stage, with the continuous intake of external air, although the drying tower sprays sulfuric acid to absorb the moisture in the air, the drying effect gradually decreases as the acidity in the drying tower continues to decrease. At this time, the moisture brought into the conversion process will increase. The moisture reacts with the sulfur dioxide flue gas in the heat exchanger before the flue gas enters the conversion bed, generating a certain amount of dilute acid. Since dilute acid has strong corrosive properties, it will cause strong corrosion when it comes into contact with the metal material of the heat exchanger, and even can corrode and perforate the tube and shell materials of the heat exchanger, causing flue gas overflow. This phenomenon poses a hidden danger to the safe and stable operation of the production, environmental protection, and increases the frequency of equipment maintenance.

[0022] In the internal gas circulation heating process of the present application, as the temperature of the circulating gas gradually rises, the temperature of the gas after the second absorption tower gradually rises to 60-80℃, and after being introduced into the drying tower, the temperature of the gas is reduced to 45-60℃ by the drying acid circulating in the tower. This can improve the basic temperature of the gas, shorten the heating time by about 24 hours compared to using air at room temperature continuously, and save about 17,000 KW of power consumption.

[0023] After the external air is isolated, the water content in the internal circulating gas continues to decrease, and in the absence of external water intake, the concentration of the drying acid remains stable, and there is no need to produce a large amount of low-concentration sulfuric acid, reducing the subsequent production steps of re-concentrating the acid concentration, stabilizing the yield and quality of the product. At the same time, the water entering the heat exchanger is reduced, the corrosion rate of the equipment is reduced, and the service life of the equipment is improved.

[0024] S2, the dilute sulfur foam sent by the coking desulfurization unit is concentrated and dried to obtain a sulfur-containing mixed salt.

[0025] The dilute sulfur foam sent by the coking desulfurization unit is concentrated to form a concentrated sulfur foam with a total solid content of 35%-45%. The concentrated sulfur foam is sent to a dryer by a screw pump for evaporation drying and solidification into a powder-particle-shaped sulfur-containing mixed salt.

[0026] S3, the sulfur-containing mixed salt is incinerated to generate high-temperature SO2-containing flue gas, and the high-temperature SO2-containing flue gas is cooled and purified to obtain SO2 flue gas.

[0027] Sulfur-containing mixed salts are conveyed to the furnace hopper via a tubular chain conveyor, and then to the sulfur incinerator via a belt conveyor. There, they undergo combustion to generate high-temperature SO2-containing flue gas at 800–1150°C. This high-temperature SO2-containing flue gas is cooled to 230–350°C via a waste heat boiler. The boiler water in the waste heat boiler exchanges heat with the high-temperature SO2-containing flue gas, vaporizing to generate steam and recovering the waste heat. The low-temperature SO2-containing flue gas exiting the waste heat boiler enters the purification process. It is humidified, cooled, and pre-washed by a dynamic wave scrubber. Afterward, the low-temperature SO2-containing flue gas enters a cooling tower where it comes into counter-current contact with the cooling circulating dilute acid sprayed from the top of the tower. The low-temperature SO2-containing flue gas is cooled, condensed, and washed again to remove water vapor and impurities. Finally, it enters an electrostatic precipitator to remove acid mist, yielding SO2 flue gas.

[0028] S4. Dehydrate and dry the SO2 flue gas.

[0029] The SO2 flue gas exiting the electrostatic precipitator contains a certain amount of water vapor, which must be dehydrated and dried before entering the conversion system. Since concentrated sulfuric acid has strong hygroscopic and dehydrating properties, it is used in the process to dehydrate and dry the SO2 flue gas.

[0030] SO2 flue gas enters the drying tower through the bottom inlet. Inside the drying tower, it comes into countercurrent contact with 93% concentrated sulfuric acid sprayed from the top, removing moisture from the flue gas and ensuring that the moisture content of the SO2 flue gas exiting the tower is ≤0.1g / Nm³. 3 The SO2 flue gas exiting the tower is pressurized by a sulfur dioxide blower and sent to the conversion unit.

[0031] The concentration of concentrated sulfuric acid circulating in the drying tower decreases after absorbing moisture from the SO2 flue gas. The concentration is stabilized by adding 98% concentrated sulfuric acid. The increased low-concentration sulfuric acid is temporarily stored in the sulfuric acid storage tank and sent to the absorption process to increase the concentration again after normal production resumes.

[0032] S5. The dehydrated and dried SO2 flue gas is absorbed in the conversion unit using a five-stage conversion and two-stage absorption process to prepare sulfuric acid.

[0033] After dehydration and drying, the SO2 flue gas is pressurized by an SO2 blower and then passes sequentially through the shell side of a three-stage heat exchanger and a first-stage heat exchanger, where it undergoes indirect heat exchange with the corresponding high-temperature converted gas. Gradually heated to 420°C, it enters the first conversion bed of the converter for conversion reaction. After conversion in the first conversion bed, the flue gas temperature rises to 585°C and enters the tube side of the first-stage heat exchanger, where it undergoes indirect heat exchange with the hot SO2 flue gas from the third heat exchanger. The flue gas temperature drops to 460°C and enters the second conversion bed of the converter for further catalytic reaction. The temperature rises to 510°C and exits the converter, entering the tube side of the second-stage heat exchanger where it undergoes indirect heat exchange with the hot SO2 flue gas from the fourth and fifth stage heat exchangers. The flue gas is cooled to 440°C and enters the third conversion bed of the converter for further reaction. The flue gas exiting the third conversion bed enters the tube side of the third-stage heat exchanger where it undergoes heat exchange with the cold SO2 flue gas from the SO2 blower for cooling. The flue gas is cooled to 175°C and then enters the first-stage absorption tower.

[0034] The flue gas exiting the primary absorption tower passes sequentially through the shell side of the five-stage heat exchanger, the four-stage heat exchanger, and the two-stage heat exchanger, where it undergoes indirect heat exchange with the corresponding high-temperature converted gas. After being heated to 420°C, it enters the fourth-stage conversion bed of the converter for a second conversion. The gas exiting the fourth-stage conversion bed enters the tube side of the fourth-stage heat exchanger and exchanges heat with the cold flue gas from the primary absorption tower. After being cooled to 415°C, it enters the fifth-stage conversion bed of the converter to continue the reaction. The gas exiting the fifth-stage conversion bed passes through the tube side of the fifth-stage heat exchanger and exchanges heat with the cold flue gas from the primary absorption tower, where it is cooled to 165°C before entering the secondary absorption tower for a second absorption.

[0035] The converted gas from the three-stage conversion bed of the converter is cooled to 175°C by the three-stage heat exchanger and then enters the first-stage absorption tower. In the first-stage absorption tower, it comes into countercurrent contact with 98% concentrated sulfuric acid sprayed from the top of the tower and absorbs SO3 in the flue gas. The remaining gas passes through the demister at the top of the first-stage absorption tower to remove acid mist and is returned to the fourth-stage conversion bed for further conversion. The sulfuric acid that has absorbed SO3 flows from the bottom of the first-stage absorption tower into the absorption circulation tank and is then pumped to the absorption acid cooler for cooling. The cooled concentrated sulfuric acid enters the acid separator at the top of the first-stage and second-stage absorption towers for circulating spraying. The gas from the five-stage conversion bed is cooled by the five-stage heat exchanger and then enters the secondary absorption tower. Inside the secondary absorption tower, it comes into countercurrent contact with 98% concentrated sulfuric acid sprayed from the top of the tower to absorb SO3 in the flue gas.

[0036] To facilitate flue gas heating during startup, an electric heater (No. 1) was installed at the inlet of the first-stage heat exchanger, and an electric heater (No. 2) was installed at the inlet of the second-stage heat exchanger. Necessary process piping bypasses and regulating valves were installed to adjust and control the appropriate operating temperatures of each stage of the converter.

[0037] The conversion process mainly involves reacting sulfur dioxide flue gas with a catalyst (vanadium pentoxide) to convert it into sulfur trioxide flue gas, allowing the sulfur in the flue gas to be directly absorbed and converted into sulfuric acid.

[0038] The conversion process of this invention achieves temperature heat exchange between multiple conversion processes through a five-stage conversion and two-stage absorption process. The heat energy generated by the conversion is always circulated and utilized within the system, thereby fully utilizing the heat of reaction, improving the thermal efficiency of the entire process and reducing energy consumption. During the system start-up and heating stage, this invention shortens the heating time and saves heating energy consumption through the heating internal circulation pipe, and also isolates external air, reducing the rate of equipment corrosion.

[0039] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent substitutions, and improvements made to the above embodiments without departing from the scope of the present invention, based on the technical essence of the present invention and within the spirit and principles of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing sulfuric acid from coking flue gas, characterized in that... Includes the following steps: S1. During the system start-up and heating phase, the gas inside the system is circulated and heated through the heating internal circulation pipe. S2. Concentrate and dry the dilute sulfur foam from the coking desulfurization unit to obtain sulfur-containing mixed salt; S3. The combustion of sulfur-containing mixed salts generates high-temperature SO2-containing flue gas. After cooling and purification, the high-temperature SO2-containing flue gas is purified to obtain SO2 flue gas. S4. Dehydrate and dry the SO2 flue gas; S5. The dehydrated and dried SO2 flue gas is absorbed in the conversion unit using a five-stage conversion and two-stage absorption process to prepare sulfuric acid.

2. The method for preparing sulfuric acid from coking flue gas according to claim 1, characterized in that: Specifically, step S1 involves connecting a heating internal circulation pipe between the air inlet of the drying tower and the tail gas outlet of the secondary absorption tower. During the system start-up and heating phase, the outlet valve of the electrostatic precipitator and the tail gas exhaust valve are closed, and the valves at both ends of the heating internal circulation pipe are opened, allowing the SO2 fan to directly draw in the gas from the outlet of the secondary absorption tower, forming a gas circulation heating system around the drying process, conversion process, and absorption process.

3. The method for preparing sulfuric acid from coking flue gas according to claim 1, characterized in that: Specifically, step S2 involves concentrating the dilute sulfur foam from the coking desulfurization unit to form concentrated sulfur foam with a total solids content of 35% to 45%. The concentrated sulfur foam is then pumped to a dryer via a screw pump for evaporation, drying, and solidification into a powdery sulfur-containing mixed salt.

4. The method for preparing sulfuric acid from coking flue gas according to claim 1, characterized in that: Step S3 specifically involves: sulfur-containing mixed salts being conveyed to the furnace hopper via a tubular chain conveyor, then to the sulfur incinerator via a belt conveyor, where they undergo combustion to generate high-temperature SO2-containing flue gas at 800–1150°C. The high-temperature SO2-containing flue gas is cooled to 230–350°C by a waste heat boiler. The boiler water in the waste heat boiler exchanges heat with the high-temperature SO2-containing flue gas to generate steam, recovering the waste heat of the high-temperature SO2-containing flue gas. The low-temperature SO2-containing flue gas exiting the waste heat boiler enters the purification process, where it is humidified, cooled, and pre-washed by a dynamic wave scrubber. Afterward, the low-temperature SO2-containing flue gas enters a cooling tower and comes into countercurrent contact with the cooling circulating dilute acid sprayed at the top of the tower. The low-temperature SO2-containing flue gas is cooled, condensed, and washed again to remove water vapor and impurities. Then, it enters an electrostatic precipitator to remove acid mist, yielding SO2 flue gas.

5. The method for preparing sulfuric acid from coking flue gas according to claim 1, characterized in that: Step S4 specifically involves: SO2 flue gas entering the drying tower through the bottom inlet, where it comes into countercurrent contact with 93% concentrated sulfuric acid sprayed from the top of the tower, removing moisture from the flue gas and ensuring that the moisture content of the SO2 flue gas exiting the tower is ≤0.1g / Nm³. 3 The SO2 flue gas exiting the tower is pressurized by a sulfur dioxide blower and sent to the conversion unit.

6. The method for preparing sulfuric acid from coking flue gas according to claim 5, characterized in that: The concentration of concentrated sulfuric acid circulating in the drying tower decreases after absorbing moisture from the SO2 flue gas. The concentration is stabilized by adding 98% concentrated sulfuric acid. The increased low-concentration sulfuric acid is temporarily stored in the sulfuric acid storage tank and sent to the absorption process to increase the concentration again after normal production resumes.

7. The method for preparing sulfuric acid from coking flue gas according to claim 1, characterized in that: Step S5 specifically involves the following steps: After dehydration and drying, the SO2 flue gas is pressurized by an SO2 blower and then sequentially passes through the shell side of a three-stage heat exchanger and a first-stage heat exchanger, where it undergoes indirect heat exchange with the corresponding high-temperature converted gas. Gradually heated to 420°C, it enters the first conversion bed of the converter for conversion reaction. After conversion reaction in the first conversion bed, the flue gas temperature rises to 585°C and enters the tube side of a first-stage heat exchanger, where it undergoes indirect heat exchange with the hot SO2 flue gas from the third heat exchanger. The flue gas temperature decreases to 460°C and enters the second conversion bed of the converter for further catalytic reaction. The temperature rises to 510°C and exits the converter, entering the tube side of a second-stage heat exchanger where it undergoes indirect heat exchange with the hot SO2 flue gas from the fourth and fifth stage heat exchangers. The flue gas is cooled to 440°C and then enters the third conversion bed of the converter for further reaction. The flue gas exiting the third conversion bed enters the tube side of a third-stage heat exchanger where it undergoes heat exchange with the cold SO2 flue gas from the SO2 blower for cooling. After cooling to 175°C, the flue gas enters the first-stage absorption tower. The flue gas exiting the primary absorption tower passes sequentially through the shell side of the five-stage heat exchanger, the four-stage heat exchanger, and the two-stage heat exchanger, where it undergoes indirect heat exchange with the corresponding high-temperature converted gas. After being heated to 420°C, it enters the fourth-stage conversion bed of the converter for a second conversion. The gas exiting the fourth-stage conversion bed enters the tube side of the fourth-stage heat exchanger and exchanges heat with the cold flue gas from the primary absorption tower. After being cooled to 415°C, it enters the fifth-stage conversion bed of the converter to continue the reaction. The gas exiting the fifth-stage conversion bed passes through the tube side of the fifth-stage heat exchanger and exchanges heat with the cold flue gas from the primary absorption tower, where it is cooled to 165°C before entering the secondary absorption tower for a second absorption. The converted gas from the three-stage conversion bed of the converter is cooled to 175°C by the three-stage heat exchanger and then enters the first-stage absorption tower. In the first-stage absorption tower, it comes into countercurrent contact with 98% concentrated sulfuric acid sprayed from the top of the tower and absorbs SO3 in the flue gas. The remaining gas passes through the demister at the top of the first-stage absorption tower to remove acid mist and is returned to the fourth-stage conversion bed for further conversion. The sulfuric acid that has absorbed SO3 flows from the bottom of the first-stage absorption tower into the absorption circulation tank and is then pumped to the absorption acid cooler for cooling. The cooled concentrated sulfuric acid enters the acid separator at the top of the first-stage and second-stage absorption towers for circulating spraying. The gas from the five-stage conversion bed is cooled by the five-stage heat exchanger and then enters the secondary absorption tower. Inside the secondary absorption tower, it comes into countercurrent contact with 98% concentrated sulfuric acid sprayed from the top of the tower to absorb SO3 in the flue gas.

8. The method for preparing sulfuric acid from coking flue gas according to claim 7, characterized in that: Electric heating furnace #1 was installed at the air inlet of the first-stage heat exchanger, and electric heating furnace #2 was installed at the air inlet of the second-stage heat exchanger.

Images