A physical desulfurization device and method for flue gas of a crude benzol hydrogenation gas boiler

Abstract

The present application belongs to the technical field of coke crude benzene hydrogenation device fuel gas boiler flue gas treatment, and particularly relates to a crude benzene hydrogenation fuel gas boiler flue gas physical desulfurization device and method. The present application uses hot water heat exchanger and air cooler to cool and condense, and liquefies, recycles and reuses water vapor in flue gas. The water solubility of harmful component SO2 in flue gas is used, and in the water vapor liquefaction process, a self-designed gas-liquid separator is used to increase the dissolution power of SO2 in flue gas, efficiently solubilize gaseous SO2, achieve flue gas desulfurization effect, realize the operation requirements of efficient and low-consumption environmental protection facilities, and ensure that flue gas meets the emission standard. In combination with the process particularity of the crude benzene hydrogenation device provided with the fuel gas boiler, the chemical properties of the flue gas recycling soft water and the sulfur-containing wastewater after crude benzene hydrogenation are the same, the flue gas recycling soft water is used to replace externally supplied soft water, production cost is saved, and it is a new solution for the energy-saving and environment-friendly operation of the fuel gas boiler of the crude benzene hydrogenation device.

Description

Technical Field

[0001] This invention belongs to the technical field of flue gas treatment for gas-fired boilers in coking crude benzene hydrogenation units, and particularly relates to a physical desulfurization device and method for flue gas from crude benzene hydrogenation gas-fired boilers. Background Technology

[0002] Most domestic coking crude benzene hydrogenation units employ a two-stage hydrogenation process, involving hydrorefining and extractive distillation. This process removes impurities such as sulfur (S), nitrogen (N), and oxygen (O) from the coking-produced light crude benzene feedstock. Aromatic hydrocarbons are extracted via extractive distillation. The main products are coking benzene, coking toluene, and coking xylene, with byproducts including C5 and smaller non-aromatic hydrocarbons, C8+ fractions, and heavy benzene. The yields of each product are as follows: coking benzene 70-75%, coking toluene 11-15%, coking xylene 3-5.5%, heavy benzene 4-8%, and other fractions 2-4%.

[0003] Due to the inherent characteristics of the industry, the main heating energy media are natural gas, steam, and coke oven gas. To improve processing efficiency, coke oven gas is mostly used, and organic heat carrier gas-fired boilers are installed. These coke oven gas boilers heat heat transfer oil, which is then used as the heat carrier to provide a heat source for the crude benzene hydrogenation unit.

[0004] The main components of coke oven gas are: H2 (54-59%), CH4 (23-28%), O2 (0-0.7%), N2 (0-5%), CO2 (2-3%), CO (5.5-7%), and C. m H n (2-3%). The content of harmful components is: H2S (≤20mg / Nm³). 3 Naphthalene ≤ (5mg / Nm 3 ), tar ≤ (2mg / Nm 3 Input pressure 5-10 kPa. The main products of a gas-fired boiler after burning coke oven gas are: air (80%), CO, CO2, H2O (>10%), carbon black, and SO2 (100-200 mg / Nm³). 3 NO X According to the "Emission Standard for Air Pollutants from Boilers", the SO2 content in flue gas should be ≤50 mg / Nm³. 3 NOx ≤ 100 mg / Nm 3 Particulate matter ≤10mg / Nm 3 Ringelmann blackness ≤ 1.

[0005] In existing processes, the control of flue gas environmental indicators relies entirely on desulfurization and denitrification facilities, and the operating efficiency of these facilities determines whether flue gas emissions meet standards. On the other hand, flue gas desulfurization uses chemical methods, resulting in high operating costs for these facilities, typically accounting for 10-15% of production costs, which significantly restricts processing efficiency.

[0006] For example, Chinese patent CN213942628U discloses a high-temperature flue gas desulfurization system for an incinerator in the hydrogenation refining of crude benzene. This system includes an incinerator, a heat exchanger, a primary desulfurization unit, and a secondary desulfurization unit. The primary desulfurization unit includes a quench tower for cooling and desulfurization, while the secondary desulfurization unit includes a reaction tower with packing material in the middle and a spray pipe at the top. Sodium hydroxide solution atomizing nozzles are installed on the spray pipe for desulfurization. However, in this process, the desulfurization effect is significantly affected by the quality and quantity of the desulfurization reactants, reaction conditions, and reaction equipment, resulting in considerable limitations in environmental protection control. After desulfurization, secondary treatment of the reaction products and wastewater is required, making the process relatively complex. Furthermore, the continuous addition of desulfurization reactants, mostly involving acid-base neutralization reactions, leads to high operating costs, significantly restricting economic efficiency.

[0007] In existing equipment, the flame inside the boiler transfers most of the heat to the heat carrier through conduction and radiation. Currently, the heating efficiency of domestic gas-fired boilers is 60-80%, and 20-40% of the heat in the flue gas is still wasted. Although the flue gas is used to preheat the combustion air, very little heat is recovered, which cannot meet the requirements of energy conservation and environmental protection in my country's future industrial development. Therefore, flue gas waste heat recovery has become an important issue in the development of energy-saving technologies for gas-fired boilers.

[0008] Existing domestic equipment and processes mostly meet the energy-saving and environmental protection requirements of gas-fired boilers by adding environmental protection facilities and air preheating facilities. This approach is generally inefficient and basically meets my country's current energy-saving and environmental protection requirements, but it is insufficient to fully address the new requirements for high-quality development in the future. Summary of the Invention

[0009] To address the aforementioned problems, this invention provides a physical desulfurization device and method for flue gas from a crude benzene hydrogenation gas-fired boiler. This device and method utilize waste heat recovery technology for physical dehydration, simultaneously desulfurizing and producing soft water and hot water for the plant's own use.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A physical desulfurization device for flue gas from a gas-fired boiler undergoing crude benzene hydrogenation is disclosed. The device comprises a heating unit, a heat exchange unit, a desulfurization and soft water collection unit, and a crude benzene hydrogenation unit, connected sequentially by pipelines. The heating unit is a gas-fired boiler. The heat exchange unit includes a hot water heat exchanger and an air cooler connected by pipelines. The desulfurization and soft water collection unit includes a gas-liquid separator and a chimney connected by pipelines, a water pump connected to the gas-liquid separator via a soft water pipeline, and a soft water tank connected to the water pump via a pipeline. The crude benzene hydrogenation unit includes a hydrogenation reactor and a cold water separator connected by pipelines.

[0012] The gas-liquid separator includes a gas-liquid separator body. The inner cavity of the gas-liquid separator body is divided into a front chamber and a rear chamber by a vertical partition. The tops of the front chamber and the rear chamber are connected, and the volume of the rear chamber is larger than that of the front chamber. The gas-liquid separator also has a flue gas inlet and a flue gas outlet. The flue gas inlet is located in the middle of the lower wall of the front chamber and is connected to the flue gas outlet of the air cooler through a flue gas inlet pipe. The flue gas outlet is located in the middle of the side wall of the rear chamber and is connected to the chimney through a flue gas outlet pipe. The gas-liquid separator also has a one-chamber demister and a two-chamber demister. The one-chamber demister is located at the top of the front chamber, and its height is lower than the height of the vertical partition. The two-chamber demister is located in the middle of the side wall of the rear chamber and is connected to the flue gas outlet of the gas-liquid separator.

[0013] Preferably, the gas-fired boiler includes an air duct, a coke oven gas duct, a thermal oil furnace, and a thermal oil duct. The air inlet of the thermal oil furnace is connected to the air duct, and a blower is installed on the air duct. The coke oven gas duct is connected to the gas inlet of the thermal oil furnace. The thermal oil outlet of the thermal oil duct is connected to the crude benzene hydrogenation unit through a pipeline to form a circulation loop. The thermal oil is used as a heat carrier to provide a heat source for the crude benzene hydrogenation unit. The generated flue gas is transported to the heat exchange unit through a pipeline. The gas-fired boiler also has a flue gas outlet, which is connected to the flue gas inlet of the hot water heat exchanger of the heat exchange unit through a pipeline.

[0014] Preferably, in the heat exchange unit, the flue gas inlet of the hot water heat exchanger is connected to the flue gas outlet of the gas-fired boiler via a pipe, the flue gas outlet of the hot water heat exchanger is connected to the flue gas inlet of the air cooler via a pipe, and the flue gas outlet of the air cooler is connected to the flue gas inlet of the gas-liquid separator via a flue gas inlet pipe.

[0015] More preferably, the hot water heat exchanger has an inlet at the bottom and an outlet at the top, and the tube bundle of the hot water heat exchanger uses large-diameter finned tubes.

[0016] More preferably, the heat exchange unit further includes a pipeline heat tracing system for the crude benzene hydrogenation unit, wherein the top outlet of the hot water heat exchanger is connected to the pipeline heat tracing system for the crude benzene hydrogenation unit via an outlet pipe for pipeline heat tracing.

[0017] In a further preferred embodiment, the gas-liquid separator body is also provided with a soft water outlet, which is located at the bottom of the rear chamber side wall and is 5cm higher than the lower wall. The soft water outlet is connected to a water pump through a soft water pipe. The gas-liquid separator is also provided with a first-chamber water level gauge and a second-chamber water level gauge for monitoring the water level. The first-chamber water level gauge is located at the lower part of the front chamber side wall, and the second-chamber water level gauge is located at the lower part of the rear chamber side wall.

[0018] More preferably, the lower walls of the front and rear chambers of the gas-liquid separator body are provided with connecting ports, which are connected by pipes and equipped with connecting pipe regulating valves; the soft water pipe connecting the soft water outlet and the water pump is equipped with a soft water priming pump and a soft water outlet regulating valve, the inlet of the soft water priming pump is connected to the soft water outlet by a pipe, the outlet of the soft water priming pump is connected to the inlet of the soft water outlet regulating valve by a pipe, and the outlet of the soft water outlet regulating valve is connected to the inlet of the water pump by a pipe.

[0019] The bottom of both the front and rear chambers is a liquid layer. The liquid layer in the front chamber is controlled between 2-5cm by a level gauge in the first chamber and a regulating valve in the connecting pipe. The liquid layer in the rear chamber is controlled by a level gauge in the second chamber and a soft water outlet regulating valve. The soft water outlet in the rear chamber is 5cm higher than the bottom to ensure water replenishment to the front chamber.

[0020] Preferably, in the desulfurization and soft water collection unit, the flue gas inlet of the gas-liquid separator is connected to the flue gas outlet of the air cooler through a flue gas inlet pipe, and the flue gas outlet of the gas-liquid separator is connected to the chimney through a flue gas outlet pipe; the soft water outlet regulating valve of the gas-liquid separator is connected to the water pump inlet through a pipe, the water pump outlet is connected to the water inlet on the side wall of the soft water tank through a pipe, and the outlet at the bottom of the soft water tank is connected to the crude benzene hydrogenation unit through a pipe.

[0021] In a further preferred embodiment, the side wall of the soft water tank is also connected to an external soft water pipe, and the flue gas outlet pipe of the gas-liquid separator is equipped with a frequency-controlled induced draft fan.

[0022] Preferably, the crude benzene hydrogenation unit further includes a hydrogenation process soft water injection pump, the inlet of which is connected to the outlet at the bottom of the soft water tank via a pipeline, and the outlet of which is connected to the pipeline connecting the hydrogenation reactor and the cold separator via a pipeline.

[0023] Preferably, the device further includes a sulfur-containing wastewater purification device, which is connected to the liquid outlet of the cold low-temperature separator of the crude benzene hydrogenation unit via a pipeline.

[0024] This invention also provides a method for physical desulfurization of flue gas from a crude benzene hydrogenation gas-fired boiler, specifically:

[0025] The high-temperature flue gas generated by the gas-fired boiler that provides heat for the crude benzene hydrogenation process is cooled to low-temperature flue gas. The low-temperature flue gas is then condensed by a hot water heat exchanger and an air cooler, and the temperature drops to below 90°C. It is then dehydrated and desulfurized by a gas-liquid separator, and the desulfurized flue gas is discharged. The soft water produced after desulfurization is used in the crude benzene hydrogenation unit.

[0026] Preferably, the high-temperature flue gas is cooled to low-temperature flue gas by an air preheater.

[0027] Preferably, the condensation via the hot water heat exchanger and air cooler can be achieved through the following three condensation methods:

[0028] a. The hot water heat exchanger is used for condensation only, while the air cooler is shut down;

[0029] b. The hot water heat exchanger stops operating, and forced condensation is achieved only through the air cooler;

[0030] c. The hot water heat exchanger and air cooler start simultaneously to perform two-stage condensation.

[0031] More preferably, when the low-temperature flue gas is cooled by condensation using method a, the latent heat generated is used for pipeline heating in the crude benzene hydrogenation unit; when the low-temperature flue gas is cooled by condensation using method b, the latent heat generated is used as air distribution for the gas-fired boiler; more preferably, when the heat recovery of the hot water heat exchanger is insufficient when condensing and cooling the low-temperature flue gas using method a, method c is adopted, in which the hot water heat exchanger and the air cooler condense simultaneously to ensure the normal use of the co-produced soft water.

[0032] More preferably, in the method, a hot water heat exchanger is used to condense and cool the low-temperature flue gas in winter, and the latent heat generated is used for pipeline heat tracing in the crude benzene hydrogenation unit; in non-winter periods, the pipeline heat tracing system of the crude benzene hydrogenation unit is shut down, the hot water heat exchanger is not used for heat exchange, and an air cooler is used to force condense and cool the low-temperature flue gas, and the latent heat generated is used as air distribution for the gas boiler.

[0033] Preferably, in the method, if the heat recovery of the hot water heat exchanger is insufficient in winter, heat exchange can be carried out through an air cooler to ensure the normal use of the co-produced soft water. The insufficient heat recovery refers to the failure of the temperature to drop below 90°C when using the hot water heat exchanger to condense the low-temperature flue gas.

[0034] Preferably, the hot water heat exchanger condenses and cools the low-temperature flue gas. The heating medium enters from the bottom inlet pipe of the hot water heat exchanger and exits from the top outlet pipe, exchanging heat with the flue gas. The heated medium after heat exchange is then fed into the pipeline heat tracing system of the crude benzene hydrogenation unit for pipeline heat tracing.

[0035] Preferably, when the pipeline heating system of the crude benzene hydrogenation unit is shut down during non-winter periods, the hot water heat exchanger does not exchange heat. After passing through the hot water heat exchanger, the low-temperature flue gas enters the air cooler. The air is forced to condense and cool the flue gas by a forced ventilation fan. After the air cools the flue gas, it forms hot air, which is introduced into the inlet of the gas boiler blower for distribution air to the gas boiler. After the hot air is distributed, the problem of insufficient heat exchange in the air preheater can be solved, the distribution air temperature of the gas boiler can be increased, thereby reducing the consumption of coke oven gas, reducing energy waste, and the excess air is discharged to a safe location.

[0036] More preferably, during winter, if the heat recovery of the hot water heat exchanger is insufficient, the flue gas temperature can be controlled by the frequency conversion regulation of the air cooler fan to further stabilize the temperature of the cooled and condensed flue gas, so that the water vapor can be fully liquefied and the flue gas temperature can be around 90°C; if the heat recovery of the hot water heat exchanger is sufficient, the air cooler will not perform condensation.

[0037] Preferably, the dehydration and desulfurization process via the gas-liquid separator involves the flue gas entering the separator through the bottom flue gas inlet pipe. The flue gas first undergoes a 2-5 cm high liquid layer wash, dissolving most of the SO2. Simultaneously, most of the water is atomized and condensed by a demister at the top of the front chamber, remaining in the front chamber to further enhance the SO2 dissolution capacity. After passing through the demister, the flue gas enters the rear chamber from the top. At this point, the atomized water not captured by the demister settles at the bottom of the container under physical sedimentation, forming a liquid layer. After being fully demisted by the second demister, the flue gas is discharged from the middle of the rear chamber. Soft water remains at the bottom of the gas-liquid separator and is then pumped into a soft water tank.

[0038] To ensure the water seal function of the front chamber, a connecting port is provided at the bottom of the rear chamber and the front chamber to connect the front and rear of the partition. The water level in the front chamber is controlled by the level gauge and the connecting pipe valve to ensure that the water level in the front chamber is between 2-5cm. The water level in the rear chamber is controlled by the level gauge and the variable frequency water pump. The drain outlet of the rear chamber is >5cm higher than the bottom of the container to ensure the water replenishment function of the front chamber.

[0039] Preferably, the desulfurized flue gas first enters the induced draft fan, which uses frequency conversion control and has a larger air volume than the blower of the gas boiler. Under the suction of the induced draft fan, the flue gas enters the chimney for normal discharge.

[0040] Preferably, the desulfurized soft water is introduced into a soft water tank via a water pump. The soft water tank is also equipped with an external soft water pipeline. The soft water tank enables the combined supply of the desulfurized soft water and the external soft water to meet the normal needs of the hydrogenation unit.

[0041] In a further preferred embodiment, after the co-produced soft water and external soft water are used in the crude benzene hydrogenation unit, sulfur-containing wastewater is generated. The sulfur-containing wastewater is purified by a sulfur wastewater purification device and then sent to the subsequent biological water treatment system for further treatment.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] (1) This invention uses a hot water heat exchanger and an air cooler for cooling and condensation, liquefying, recovering, and reusing the water vapor in the flue gas. Utilizing the water solubility of SO2, a harmful component in the flue gas, the gaseous SO2 is efficiently liquefied during the water vapor liquefaction process, achieving flue gas desulfurization and meeting the requirements for efficient and low-consumption environmental protection facility operation, ensuring that the flue gas meets emission standards. Considering the special process characteristics of the crude benzene hydrogenation unit with a gas-fired boiler, and taking advantage of the fact that the flue gas-recovered soft water and the sulfur-containing wastewater after crude benzene hydrogenation have the same chemical properties, the flue gas-recovered soft water is used to replace the externally supplied soft water, saving production costs.

[0044] (2) This invention uses a hot water heat exchanger and an air cooler to fully recover waste heat from the flue gas of a gas-fired boiler, liquefying water vapor and co-producing hot water and soft water. The hot water heat exchanger uses large-diameter finned tubes to improve heat exchange efficiency, reduce equipment resistance, prevent flue gas side blockage, facilitate disassembly and maintenance, and recover waste heat from the flue gas to form hot water for winter heating of the hydrogenation unit's pipeline equipment. When seasonal temperature changes, the air cooler is adjusted to cool and condense the flue gas, ensuring the normal use of the co-produced soft water. This invention completely eliminates the inherent limitations of existing process equipment, replaces inefficient and ineffective traditional desulfurization and environmental protection equipment, significantly improves the efficiency of flue gas waste heat utilization, and simultaneously realizes the reuse of beneficial resources in the flue gas.

[0045] (3) In the process of flue gas water vapor liquefaction, the present invention adopts a self-designed gas-liquid separator: it is a two-chamber structure, and the liquid level connection control between the front and rear chambers is added. The flue gas enters from the bottom of the water layer in the first chamber, is washed by water, and enters the second chamber for separation, which increases the dissolution power of SO2 in the flue gas, fully dissolves SO2 in the flue gas, and realizes the function of flue gas desulfurization.

[0046] (4) This invention utilizes the characteristic that the soft water recovered from the waste heat of flue gas does not conflict with or cause harmful reactions to the hydrogenation reaction products, and uses the soft water produced in the desulfurization process for the hydrogenation process to achieve the process objective of washing ammonium salts and sulfides. At the same time, it does not have any adverse effects on the subsequent wastewater treatment process.

[0047] (5) This invention replaces traditional chemical desulfurization environmental protection facilities with a physical dehydration and desulfurization method for flue gas, solving the problems of poor operating effect and low operating efficiency of traditional desulfurization environmental protection facilities. It also solves the problem of high investment costs for special environmental protection facilities and the problem of severely limited processing benefits due to the operating costs of environmental protection facilities. By co-producing hot water, the waste heat utilization capacity is improved, the wasted heat is recovered, and the effect of pipeline heating in winter is guaranteed. According to the process characteristics, the operating cost of external soft water supply is greatly reduced, and it does not have any negative impact on wastewater treatment equipment and other processes, nor does it increase any additional operating costs for production equipment.

[0048] (6) This invention combines the process and equipment characteristics and material properties of the crude benzene hydrogenation unit, and through a novel process flow and method of recovering waste heat from flue gas to co-produce soft water and accompanying hot water, it achieves the environmental protection goal of efficient desulfurization of the gas-fired boiler in the crude benzene hydrogenation unit, and the energy-saving goal of recovering waste heat from flue gas to co-produce accompanying hot water and soft water. It is a brand-new solution for the energy-saving and environmentally friendly operation of the gas-fired boiler in the crude benzene hydrogenation unit. Utilizing the direct proportional relationship between the processing load and heat load of the crude benzene hydrogenation unit, and the direct proportional relationship between the soft water co-produced by the matching gas-fired boiler and the processing load of the crude benzene hydrogenation unit, and combining the physical and chemical similarity between the co-produced soft water and the sulfur-containing wastewater from hydrogenation, the soft water co-produced from the flue gas is used for the flushing of ammonium salts and sulfides in the hydrogenation process, achieving the goal of energy saving and pollution-free operation. Attached Figure Description

[0049] Figure 1 This is a process flow diagram of the physical desulfurization method for flue gas from a crude benzene hydrogenation gas-fired boiler.

[0050] Figure 2 This is a schematic diagram of a gas-liquid separator;

[0051] Figure label:

[0052] Figure 1 The components are as follows: 1. Air duct; 2. Blower; 3. Coke oven gas duct; 4. Thermal oil heater; 5. Thermal oil duct; 6. Hot water heat exchanger; 7. Thermal tracing system for crude benzene hydrogenation unit; 8. Air cooler; 9. Gas-liquid separator; 10. Exhaust fan; 11. Chimney; 12. Water pump; 13. Soft water tank; 14. External soft water duct; 15. Soft water injection pump for hydrogenation process; 16. Hydrogenation reactor; 17. Cold separator; 18. Sulfur-containing wastewater purification device.

[0053] Figure 2 In the middle section, 19. Gas-liquid separator body; 20. First chamber water level gauge; 21. Flue gas inlet pipe; 22. First chamber demister; 23. Connecting pipe regulating valve; 24. Second chamber demister; 25. Flue gas outlet pipe; 26. Second chamber water level gauge; 27. Soft water outlet regulating valve; 28. Soft water priming pump. Detailed Implementation

[0054] Example 1

[0055] A physical desulfurization device for flue gas from a crude benzene hydrogenation gas-fired boiler, such as Figure 1 and Figure 2As shown, the device includes a heating unit, a heat exchange unit, a desulfurization and soft water collection unit, and a crude benzene hydrogenation unit connected in sequence by pipelines. The heating unit is a gas-fired boiler. The heat exchange unit includes a hot water heat exchanger 6 and an air cooler 8 connected by pipelines. The desulfurization and soft water collection unit includes a gas-liquid separator 9 and a chimney 11 connected by pipelines, as well as a water pump 12 connected to the gas-liquid separator 9 via a soft water pipeline, and a soft water tank 13 connected to the water pump 12 via a pipeline. The crude benzene hydrogenation unit includes a hydrogenation reactor 16 and a cold water separator 17 connected by pipelines.

[0056] The gas-liquid separator 9 includes a gas-liquid separator body 19. The inner cavity of the gas-liquid separator body 19 is divided into a front chamber and a rear chamber by a vertical partition. The tops of the front chamber and the rear chamber are connected, and the volume of the rear chamber is larger than that of the front chamber. The gas-liquid separator 9 is also provided with a flue gas inlet and a flue gas outlet. The flue gas inlet is located in the middle of the lower wall of the front chamber and is connected to the flue gas outlet of the air cooler 8 through a flue gas inlet pipe 21. The flue gas outlet is located in the middle of the side wall of the rear chamber and is connected to the chimney 11 through a flue gas outlet pipe 25. The gas-liquid separator 9 is also provided with a first-chamber demister 22 and a second-chamber demister 24. The first-chamber demister 22 is located at the top of the front chamber, and its height is lower than the height of the vertical partition. The second-chamber demister 24 is located in the middle of the side wall of the rear chamber and is connected to the flue gas outlet of the gas-liquid separator.

[0057] Specifically, the gas-fired boiler includes an air duct 1, a coke oven gas duct 3, a thermal oil furnace 4, and a thermal oil duct 5. The air inlet of the thermal oil furnace 4 is connected to the air duct 1, and a blower 2 is installed on the air duct 1. The coke oven gas duct 3 is connected to the gas inlet of the thermal oil furnace 4. The thermal oil outlet of the thermal oil duct 5 is connected to the crude benzene hydrogenation unit through a pipeline to form a circulation loop. The thermal oil is used as a heat carrier to provide a heat source for the crude benzene hydrogenation unit. The gas-fired boiler also has a flue gas outlet, which is connected to the flue gas inlet of the hot water heat exchanger 6 of the heat exchange unit through a pipeline. The generated flue gas is transported to the heat exchange unit through the pipeline.

[0058] Specifically, in the heat exchange unit, the flue gas inlet of the hot water heat exchanger 6 is connected to the flue gas outlet of the gas-fired boiler via a pipe, the flue gas outlet of the hot water heat exchanger 6 is connected to the flue gas inlet of the air cooler 8 via a pipe, and the flue gas outlet of the air cooler 8 is connected to the flue gas inlet of the gas-liquid separator 9 via a flue gas inlet pipe 21; the hot water heat exchanger 6 has a water inlet at the bottom and a water outlet at the top, and the tube bundle of the hot water heat exchanger 6 adopts large-diameter finned tubes; the heat exchange unit also includes a crude benzene hydrogenation unit pipeline heat tracing system 7, and the top water outlet of the hot water heat exchanger 6 is connected to the crude benzene hydrogenation unit pipeline heat tracing system 7 via an outlet pipe for pipeline heat tracing.

[0059] Specifically, the gas-liquid separator 9 is also equipped with a soft water outlet, which is located at the bottom of the rear chamber side wall and is 5cm higher than the lower wall. The soft water outlet is connected to the water pump 12 through a soft water pipe.

[0060] Specifically, the gas-liquid separator 9 is also equipped with a first-chamber water level gauge 20 and a second-chamber water level gauge 26 for monitoring water level. The first-chamber water level gauge 20 is located at the lower part of the front chamber side wall, and the second-chamber water level gauge 26 is located at the lower part of the rear chamber side wall.

[0061] Specifically, the gas-liquid separator body 19 has connecting ports on the lower walls of both the front and rear chambers, which are connected by pipes, and the pipes are equipped with connecting pipe regulating valves 23.

[0062] Specifically, the soft water pipeline connecting the soft water outlet and the water pump 12 is equipped with a soft water priming pump 28 and a soft water outlet regulating valve 27. The inlet of the soft water priming pump 28 is connected to the soft water outlet via a pipeline, the outlet of the soft water priming pump 28 is connected to the inlet of the soft water outlet regulating valve 27 via a pipeline, and the outlet of the soft water outlet regulating valve 27 is connected to the inlet of the water pump 12 via a pipeline. The water pump 12 is used to inject the co-produced soft water into the soft water tank 13.

[0063] Specifically, the bottom of both the anterior and posterior chambers is a liquid layer. The liquid layer in the anterior chamber is controlled between 2-5 cm by a level gauge 20 in the first chamber and a regulating valve 23 in the connecting pipe. The liquid layer in the posterior chamber is controlled by a level gauge 26 in the second chamber and a soft water pump 28. The soft water outlet is 5 cm higher than the bottom to ensure water replenishment to the anterior chamber.

[0064] Specifically, in the desulfurization and soft water collection unit, the flue gas inlet of the gas-liquid separator 9 is connected to the flue gas outlet of the air cooler 8 through the flue gas inlet pipe 21, and the flue gas outlet of the gas-liquid separator 9 is connected to the chimney 11 through the flue gas outlet pipe 25. A frequency-controlled induced draft fan 10 is installed on the flue gas outlet pipe 25. The soft water outlet regulating valve 27 of the gas-liquid separator 9 is connected to the inlet of the water pump 12 through a pipe. The outlet of the water pump 12 is connected to the inlet of the side wall of the soft water tank 13 through a pipe. The outlet at the bottom of the soft water tank 13 is connected to the crude benzene hydrogenation unit through a pipe. An external soft water pipe 14 is also connected to the side wall of the soft water tank 13.

[0065] Specifically, the crude benzene hydrogenation unit also includes a hydrogenation process soft water injection pump 15. The inlet of the hydrogenation process soft water injection pump 15 is connected to the outlet at the bottom of the soft water tank 13 through a pipe, and the outlet of the hydrogenation process soft water injection pump 15 is connected to the pipe connecting the hydrogenation reactor 16 and the cold separator 17 through a pipe.

[0066] Specifically, the device also includes a sulfur-containing wastewater purification device 18, which is connected to the liquid outlet of the cold low-temperature separator 17 of the crude benzene hydrogenation unit via a pipeline.

[0067] Example 2

[0068] A physical desulfurization method for flue gas from a crude benzene hydrogenation gas-fired boiler, specifically as follows:

[0069] The high-temperature flue gas generated by the combustion of the gas-fired boiler that provides heat for the crude benzene hydrogenation process is cooled to low-temperature flue gas by an air preheater. The low-temperature flue gas is condensed by a hot water heat exchanger 6 and an air cooler 8, and its temperature drops to below 90°C. Then it is dehydrated and desulfurized by a gas-liquid separator 9. The desulfurized flue gas is discharged, and the soft water produced by desulfurization is used in the crude benzene hydrogenation unit.

[0070] Specifically, in winter, hot water heat exchanger 6 is used to condense and cool the low-temperature flue gas, and the latent heat generated is used for pipeline heat tracing system 7 of crude benzene hydrogenation unit; in non-winter periods, pipeline heat tracing system 7 of crude benzene hydrogenation unit is shut down, hot water heat exchanger 6 does not perform heat exchange, and air cooler 8 is used to force condense and cool the low-temperature flue gas, and the latent heat generated is used as air distribution for gas boiler.

[0071] Specifically, after heat exchange between the combustion flame and the heat transfer oil in the gas-fired boiler, high-temperature flue gas of 250-350℃ is formed. After passing through an air preheater, the high-temperature flue gas becomes low-temperature flue gas with a temperature of 150-200℃ and a moisture content of more than 10%. At this point, the flue gas is in a fully gasified state. The latent heat of vaporization of the 150-200℃ low-temperature flue gas containing more than 10% water vapor is much higher than the sensible heat of the flue gas. Although the latent heat of vaporization of the flue gas is high, the temperature potential difference is insufficient, making recovery and liquefaction difficult.

[0072] To solve this problem, the present invention uses large-diameter finned tubes for the tube bundle of the hot water heat exchanger 6 to realize the waste heat recovery of flue gas.

[0073] Specifically, the hot water heat exchanger 6 includes a tube side and a shell side. To reduce equipment resistance, the tube side diameter is DN50 and the length is <5 meters. Because the flue gas is acidic, the internal tube side of the heat exchanger uses 316L material. To prevent blockage on the flue gas side, fins are used on the heating medium side. The flue gas flows through the tube side, and the heating medium flows through the shell side. The floating head design facilitates disassembly and maintenance. To improve heat exchange efficiency, the fins are made of copper.

[0074] During the cooling process, the condensate in the flue gas flows downwards gradually along the temperature gradient, preventing liquid resistance and thus avoiding pressure increases in the furnace of the gas-fired boiler. Hot water enters from the bottom of the shell side and exits from the top, flowing in the opposite direction to the flue gas flow. The hot water is in direct contact with the fins, which are spirally coiled around the outer wall of the tube side, maximizing the heat exchange area within a limited space.

[0075] Specifically, in winter, the low-temperature flue gas is condensed and cooled by the hot water heat exchanger 6. The heating medium enters from the bottom inlet pipe of the hot water heat exchanger and exits from the top outlet pipe, exchanging heat with the flue gas. The heated medium after heat exchange is discharged from the top outlet pipe of the hot water heat exchanger and fed into the pipeline heat tracing system 7 of the crude benzene hydrogenation unit for pipeline heat tracing.

[0076] Specifically, when the heating system 7 of the crude benzene hydrogenation unit pipeline is shut down during non-winter periods, the hot water heat exchanger does not exchange heat. After passing through the hot water heat exchanger, the low-temperature flue gas enters the air cooler. Through the air cooler 8, air is forced to condense and cool the flue gas by a forced ventilation fan. After the air cools the flue gas, it forms hot air, which is then introduced into the inlet of the gas boiler blower 2 for use as air distribution for the gas boiler.

[0077] Specifically, after passing through the hot water heat exchanger, the flue gas temperature can be reduced to below 90℃. However, in other seasons besides winter, the heat tracing is stopped, so the heat of the flue gas cannot be recovered. Therefore, the hot water heat exchanger does not perform heat exchange. After passing through the hot water heat exchanger, the low-temperature flue gas enters the air cooler 8, where air is forced to condense and cool the flue gas through forced ventilation by a fan.

[0078] Specifically, the air cooler 8 has a tube diameter of DN50 and a length of <10 meters. Because the flue gas is acidic, the internal tubes of the air cooler are made of 316L stainless steel. A fan is also installed at the cooling end of the air cooler 8; the fan is frequency-controlled and can be adjusted according to the flue gas temperature. To prevent blockage on the flue gas side, fins are used on the shell side, while the flue gas flows through the tube side. A fan with a flow rate greater than twice the flue gas volume is used outside the tube side, exchanging heat with the flue gas through the fins.

[0079] After the flue gas is cooled by air, its temperature rises and it becomes drier. This hot air is then introduced into the inlet of the gas-fired boiler fan 2 and used as the distribution air for the fuel gas boiler. The distribution of hot air solves the problem of insufficient heat exchange in the air preheater, increases the distribution air temperature of the gas-fired boiler, thereby reducing coke oven gas consumption, minimizing energy waste, and allowing excess air to be safely discharged.

[0080] The flue gas passes through the air cooler 8, which controls the flue gas temperature to be reduced to below 90°C. At this point, most of the water vapor in the flue gas has been liquefied, and the latent heat of vaporization of the flue gas is fully recovered.

[0081] During winter, if the heat recovery of the hot water heat exchanger 6 is insufficient due to a small amount of hot water or other reasons, the temperature of the flue gas can be controlled by adjusting the fan of the air cooler 8 to further stabilize the temperature of the cooled and condensed flue gas, so that the water vapor can be fully liquefied and the flue gas temperature can be around 90°C. If the heat recovery of the hot water heat exchanger 6 is sufficient, the air cooler 8 will not perform condensation.

[0082] After passing through a hot water heat exchanger and an air cooler, the flue gas temperature drops to around 90℃, at which point most of the water vapor can be liquefied to produce soft water. At this point, due to its highly polar chemical properties, SO2 in the flue gas dissolves into the soft water during the water vapor liquefaction process. However, because the SO2 content in the flue gas is between 100-200 mg / Nm³,... 3 The dissolution kinetics cannot guarantee sufficient dissolution. The flue gas passes through a gas-liquid separator 9 to increase the solubility of SO2. A vertical baffle is installed in the middle of the gas-liquid separator, allowing the flue gas to flow first from bottom to top and then from top to bottom. A demister is installed at the top of the front chamber, and a water seal (liquid layer) is installed at the bottom of the front chamber. A water jacket (liquid layer) is installed at the bottom of the rear chamber. The drain outlet is located in the upper part of the water jacket to ensure water level and maintain dissolution efficiency, achieving physical dehydration and desulfurization.

[0083] like Figure 2 As shown, after multi-stage cooling and condensation, the flue gas enters the gas-liquid separator from the bottom. The flue gas first passes through a 2-5 cm high liquid layer, where it is washed with water, dissolving most of the SO2. However, due to the large volume of flue gas and the immiscibility of flue gas and water, most of the water will atomize. This water mist is condensed by a demister 22 located at the top of the front chamber, remaining in the front chamber to further increase the SO2 dissolution capacity. After passing through the demister 22, the flue gas enters the rear chamber from the top. The rear chamber is wide and high, increasing the physical settling space for the flue gas. The atomized water not captured by the demister settles at the bottom of the container under physical settling, forming a liquid layer. After being fully demisted by the second-chamber demister 24, the flue gas exits from the middle of the rear chamber, while the water remains at the bottom of the container. To ensure the water seal function of the front chamber, a connecting opening is provided at the bottom of the rear and front chambers to connect the partitions. The water level in the front chamber is controlled by a level gauge 20 and a regulating valve 23 in the connecting pipe to ensure that the water level in the front chamber is between 2-5 cm. The water level in the rear chamber is controlled by a level gauge 26 in the second chamber and a soft water outlet regulating valve 27. The drain outlet of the rear chamber is more than 5 cm higher than the bottom of the container to ensure water replenishment to the front chamber.

[0084] Because the flue gas undergoes multi-stage cooling and condensation as well as a gas-liquid separator, the flue gas resistance increases. To ensure safe operation under negative pressure inside the gas-fired boiler, an induced draft fan 10 is installed after the gas-liquid separator. The induced draft fan is frequency-controlled and has a larger air volume than the gas-fired boiler's forced draft fan.

[0085] Specifically, after passing through the gas-liquid separator, the flue gas enters the induced draft fan, which uses frequency conversion control to regulate the suction force via the motor frequency. The induced draft frequency is adjusted by monitoring the furnace pressure to maintain a slightly negative pressure in the furnace, ensuring the safe operation of the gas-fired boiler. After the induced draft fan, the flue gas enters chimney 11 for normal emission. At this point, after multi-stage cooling and condensation of the flue gas, thorough condensation of water vapor, and complete dissolution by the gas-liquid separator, the SO2 content has been significantly reduced, fully meeting the emission standards. The SO2 content can vary depending on the cooling and condensation process and the dissolution effect of the gas-liquid separator; with proper adjustment, it can even be far below the ultra-low emission requirements.

[0086] Because the processing load of the crude benzene hydrogenation unit is directly proportional to its heat load, the soft water co-produced by its associated gas-fired boiler is also directly proportional to the processing load of the crude benzene hydrogenation unit. The heat load of the crude benzene hydrogenation unit is generally 5-6 GJ / t of feedstock, and the water vapor content in the flue gas is about 10%. Therefore, the maximum amount of soft water co-produced through flue gas waste heat recovery is 0.1 t / t of feedstock, and the required soft water injection volume for the hydrogenation process is 0.1-0.15 t / t of feedstock. The co-production efficiency of soft water is generally 70-80%, so excessive discharge of co-produced soft water will not occur. In special circumstances where excessive discharge occurs, the co-production water volume can be controlled through the hot water heat exchanger 6 and the air cooler 8.

[0087] After flue gas waste heat recovery, the main impurities in the soft water are trace amounts of SO2, naphthalene, and organic tar, as well as ammonium salts produced during denitrification and trace amounts of oxygen. In the crude benzene hydrogenation unit, the reaction products contain large amounts of NH3 and H2S. As the materials cool, a large amount of ammonium salts are generated, requiring the use of soft water to dissolve them and prevent pipeline crystallization and blockage. The impurities in the soft water after flue gas waste heat recovery are consistent with the hydrogenation products and will not cause product contamination. Furthermore, trace impurities such as SO2, naphthalene, and tar will not produce secondary harmful reactions with the hydrogenation materials. Even if SO2 reacts preferentially with H2S, it will dissolve and produce ammonium salts due to the action of water and NH3, posing no safety risk to the hydrogenation equipment pipelines.

[0088] After waste heat recovery from the flue gas, the co-produced soft water is introduced into the soft water tank 13 of the desulfurization and soft water collection unit via water pump 12. The start-stop status of the hydrogenation unit is consistent with that of the gas-fired boiler, so under normal circumstances, there will be no interruption or disconnection in the process. To avoid process disconnection or insufficient water supply under special circumstances, the soft water tank is still equipped with an external soft water supply pipeline. The soft water tank achieves a combined supply of co-produced soft water and external soft water to meet the normal needs of the hydrogenation process.

[0089] After soft water is injected into the crude benzene hydrogenation unit, sulfur-containing wastewater is formed. Following the normal process flow, this wastewater enters the sulfur-containing wastewater purification unit 18, where it undergoes desulfurization and deammoniation before being sent to the biological water treatment system. Since no additional water volume or other harmful substances are added, it will not have any additional impact on subsequent processes.

Claims

1. A physical desulfurization device for flue gas from a crude benzene hydrogenation gas-fired boiler, characterized in that, The device includes a heating unit, a heat exchange unit, a desulfurization and soft water collection unit, and a crude benzene hydrogenation unit connected in sequence by pipelines. The heating unit is a gas-fired boiler. The heat exchange unit includes a hot water heat exchanger (6) and an air cooler (8) connected by pipelines. The desulfurization and soft water collection unit includes a gas-liquid separator (9) and a chimney (11) connected by pipelines, as well as a water pump (12) connected to the gas-liquid separator (9) through a soft water pipeline, and a soft water tank (13) connected to the water pump (12) through a pipeline. The crude benzene hydrogenation unit includes a hydrogenation reactor (16) and a cold air separator (17) connected by pipelines. The gas-liquid separator (9) includes a gas-liquid separator body (19), the inner cavity of which is divided into a front chamber and a rear chamber by a vertical partition, the tops of which are connected, and the volume of the rear chamber is larger than that of the front chamber; the gas-liquid separator (9) is also provided with a flue gas inlet and a flue gas outlet, the flue gas inlet is located in the middle of the lower wall of the front chamber, and the flue gas inlet is connected to the flue gas outlet of the air cooler (8) through a flue gas inlet pipe (21); the flue gas outlet is located in the middle of the side wall of the rear chamber, and the flue gas outlet is connected to the chimney (11) through a flue gas outlet pipe (25); the gas-liquid separator (9) is also provided with a one-chamber demister (22) and a two-chamber demister (24), the one-chamber demister (22) is located at the top of the front chamber, and its height is lower than that of the vertical partition; the two-chamber demister (24) is located in the middle of the side wall of the rear chamber and is connected to the flue gas outlet of the gas-liquid separator; The heat exchange unit also includes a crude benzene hydrogenation unit pipeline heat tracing system (7), and the top outlet of the hot water heat exchanger (6) is connected to the crude benzene hydrogenation unit pipeline heat tracing system (7) through an outlet pipe; The flue gas outlet pipe (25) is equipped with a frequency-controlled induced draft fan (10); The device is also equipped with a sulfur-containing wastewater purification device (18), which is connected to the liquid outlet of the cold low-temperature separator (17) of the crude benzene hydrogenation unit through a pipeline.

2. The physical desulfurization device for crude benzene hydrogenation gas boiler flue gas according to claim 1, characterized in that, The gas-fired boiler includes an air duct (1), a coke oven gas duct (3), a thermal oil furnace (4), and a thermal oil duct (5). The air inlet of the thermal oil furnace (4) is connected to the air duct (1), and a blower (2) is installed on the air duct (1). The coke oven gas duct (3) is connected to the gas inlet of the thermal oil furnace (4), and the thermal oil outlet of the thermal oil duct (5) is connected to the crude benzene hydrogenation unit through a pipe. The gas-fired boiler also has a flue gas outlet, which is connected to the flue gas inlet of the hot water heat exchanger (6) of the heat exchange unit through a pipe.

3. The physical desulfurization device for crude benzene hydrogenation gas boiler flue gas according to claim 1, characterized in that, The heat exchange unit has a flue gas inlet of the hot water heat exchanger (6) connected to the flue gas outlet of the gas boiler via a pipe, a flue gas outlet of the hot water heat exchanger (6) connected to the flue gas inlet of the air cooler (8) via a pipe, and a flue gas outlet of the air cooler (8) connected to the flue gas inlet of the gas-liquid separator (9) via a flue gas inlet pipe (21).

4. The physical desulfurization device for crude benzene hydrogenation gas boiler flue gas according to claim 3, characterized in that, The hot water heat exchanger (6) has an inlet at the bottom and an outlet at the top. The tube bundle of the hot water heat exchanger (6) is made of large-diameter finned tubes.

5. The physical desulfurization device for crude benzene hydrogenation gas boiler flue gas according to claim 1, characterized in that, The gas-liquid separator body (19) is also provided with a soft water outlet, which is located at the bottom of the rear chamber side wall and is 5cm higher than the lower wall. The soft water outlet is connected to a water pump (12) through a soft water pipe. The gas-liquid separator (9) is also provided with a first-chamber water level gauge (20) and a second-chamber water level gauge (26) for monitoring the water level. The first-chamber water level gauge (20) is located at the lower part of the front chamber side wall, and the second-chamber water level gauge (26) is located at the lower part of the rear chamber side wall.

6. The physical desulfurization device for crude benzene hydrogenation gas boiler flue gas according to claim 5, characterized in that, The lower walls of the front and rear chambers of the gas-liquid separator body (19) are provided with connecting ports, which are connected by pipes. A connecting pipe regulating valve (23) is provided on the pipes. A soft water inlet pump (28) and a soft water outlet regulating valve (27) are connected in sequence on the soft water pipe connecting the soft water outlet and the water pump (12).

7. The physical desulfurization device for crude benzene hydrogenation gas boiler flue gas according to claim 5, characterized in that, The desulfurization and soft water collection unit has a flue gas inlet of the gas-liquid separator (9) connected to the flue gas outlet of the air cooler (8) via a flue gas inlet pipe (21), and a flue gas outlet of the gas-liquid separator (9) connected to the chimney (11) via a flue gas outlet pipe (25); the soft water outlet regulating valve (27) of the gas-liquid separator (9) is connected to the inlet of the water pump (12) via a pipe, the outlet of the water pump (12) is connected to the inlet of the soft water tank (13) via a pipe, and the outlet at the bottom of the soft water tank (13) is connected to the crude benzene hydrogenation unit via a pipe; the soft water tank (13) is also connected to an external soft water pipe (14) on its side wall.

8. The physical desulfurization device for crude benzene hydrogenation gas boiler flue gas according to claim 1, characterized in that, The crude benzene hydrogenation unit also includes a hydrogenation process soft water injection pump (15). The inlet of the hydrogenation process soft water injection pump (15) is connected to the outlet at the bottom of the soft water tank (13) through a pipe. The outlet of the hydrogenation process soft water injection pump (15) is connected to the pipe connecting the hydrogenation reactor (16) and the cold low-temperature separator (17) through a pipe.

9. A desulfurization method using the physical desulfurization device for crude benzene hydrogenation gas-fired boiler flue gas according to any one of claims 1 to 8, characterized in that, Includes the following steps: After the high-temperature flue gas generated by the gas boiler that provides heat for the crude benzene hydrogenation unit is cooled to low-temperature flue gas, it is condensed by hot water heat exchanger (6) and air cooler (8) until the temperature drops to below 90°C. Then it is dehydrated and desulfurized by gas-liquid separator (9) and the desulfurized flue gas is discharged. The desulfurized soft water is used in the crude benzene hydrogenation unit.

10. The method according to claim 9, characterized in that, The condensation process via the hot water heat exchanger (6) and air cooler (8) can be condensed in the following three ways: a. The hot water heat exchanger (6) is activated separately for condensation, while the air cooler (8) is in a shutdown state. b. The hot water heat exchanger (6) stops operating and is forced to condense by the air cooler (8); c. The hot water heat exchanger (6) and the air cooler (8) start up simultaneously to perform two-stage condensation.

11. The method according to claim 10, characterized in that, When the low-temperature flue gas is cooled by condensation using the above method a, the latent heat generated is used for pipeline heating in the crude benzene hydrogenation unit pipeline heating system (7); when the low-temperature flue gas is cooled by condensation using the above method b, the latent heat generated is used as air distribution for the gas boiler.

12. The method according to claim 11, characterized in that, When using method a to condense and cool the low-temperature flue gas, if the heat recovery of the hot water heat exchanger (6) is insufficient, then method c is used, in which the hot water heat exchanger (6) and the air cooler (8) condense simultaneously to ensure the normal use of the co-produced soft water.

13. The method according to claim 9, characterized in that, The dehydration and desulfurization method of the gas-liquid separator (9) is as follows: flue gas enters the front chamber of the gas-liquid separator (9) from the lower wall flue gas inlet through the flue gas inlet pipe (21). The flue gas first passes through a liquid layer of water with a height of 2-5cm to dissolve most of the SO2. At the same time, a large amount of water is atomized and passes through the first chamber demister (22) at the top of the front chamber to condense the water mist and keep it in the front chamber to further increase the ability to dissolve SO2. After the flue gas passes through the first chamber demister (22), it enters the rear chamber from the top. At this time, the atomized water that is not captured by the demister is deposited at the bottom of the container under the action of physical sedimentation to form a liquid layer. After the flue gas is fully demisted by the second chamber demister (24), it is discharged from the rear chamber. The soft water stays at the bottom of the gas-liquid separator (9) and is introduced into the soft water tank (13) by the water pump (12).

14. The method according to claim 9, characterized in that, The flue gas desulfurized by the gas-liquid separator (9) is drawn into the chimney (11) and discharged normally under the suction of the frequency-controlled induced draft fan (10); the co-produced soft water desulfurized by the gas-liquid separator (9) is introduced into the soft water tank (13) by the water pump (12). In the soft water tank, the co-produced soft water and the external soft water are supplied together to meet the needs of the hydrogenation unit.

15. The method according to claim 14, characterized in that, After the co-produced soft water and external soft water are used in the crude benzene hydrogenation unit, sulfur-containing wastewater is generated. The sulfur-containing wastewater is purified by the sulfur-containing wastewater purification device (18) and sent to the subsequent biochemical water treatment system for further treatment.

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