Sulfur recovery method and system suitable for low-concentration acid gas

Abstract

The invention provides a sulfur recovery method and system suitable for low-concentration acid gas, the sulfur recovery system comprises an oxidation reaction sulfur recovery unit, a tail gas trapping unit, a sulfur interception treatment unit and a tail gas desulfurization unit which are connected in sequence, and the sulfur interception treatment unit comprises at least one pair of sulfur interceptors, the sulfur interceptors alternately receive the process gas output from the tail gas trapping unit, coil pipes are arranged in the sulfur interceptors, and cooling media / steam are communicated in the coil pipes for alternate switching, so that the sulfur interceptors alternately cool the process gas, intercept liquid sulfur and melted and condensed sulfur, and the process gas is discharged from the tail gas trapping unit. And the tail gas desulfurization unit is used for carrying out desulfurization treatment on the process gas output by the sulfur interceptor and then discharging the process gas. Therefore, the operation load and the energy consumption of the desulfurization system are reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of sulfur recovery, and in particular, to a sulfur recovery method and system suitable for low-concentration sour gas. Background Art

[0002] In industries such as natural gas, coal chemical industry, and bio-based aviation kerosene production, sour gas containing low-concentration H2S is generally by-produced (for example, the H2S concentration in the sour gas is generally below 25 mol% during actual operation). Therefore, it is not suitable to directly adopt the traditional Claus sulfur recovery process. Currently, when treating sour gas in this concentration range, the direct oxidation process is usually adopted.

[0003] For example, in the conventional direct oxidation process, two-stage reactions and two-stage condensations are usually adopted, namely, one-stage isothermal reaction and one-stage adiabatic reaction. The process gas after the reaction enters the sulfur condenser respectively to condense the by-produced sulfur, and the process gas will pass through one-stage tail gas trapping before entering the subsequent tail gas treatment to trap the sulfur contained in the process gas. Then, the tail gas enters the tail gas incineration unit to convert all the sulfur-containing substances in the process gas into SO2 and then enters the desulfurization unit.

[0004] However, although the existing direct oxidation process has a short process flow, its actual sulfur recovery rate is relatively low, only about 90-95%. And as the service life of the catalyst extends, the sulfur recovery rate will gradually decrease, which will bring great pressure to the subsequent tail gas treatment, and make the tail gas incinerator need to operate for a long time, consuming a large amount of fuel, and at the same time increasing the operation load and energy consumption of the desulfurization system, thereby affecting the long-term stable and reliable operation of the desulfurization system. Summary of the Invention

[0005] Therefore, the main object of the present invention is to provide a sulfur recovery method and system suitable for low-concentration sour gas to reduce the operation load and energy consumption of the desulfurization system.

[0006] To achieve the above object, according to one aspect of the present invention, there is provided a sulfur recovery system suitable for low-concentration sour gas, which includes: an oxidation reaction sulfur recovery unit, a tail gas trapping unit, a sulfur interception and treatment unit, and a tail gas desulfurization unit connected in sequence. The sulfur interception and treatment unit includes: at least a pair of sulfur interceptors, which alternately receive the process gas output from the tail gas trapping unit. Coils are arranged in each of the sulfur interceptors, and the cooling medium / steam is respectively communicated inside the pipes to alternately switch, so as to alternately cool the process gas between the sulfur interceptors, intercept the liquid sulfur and the melted and condensed sulfur, and the tail gas desulfurization unit performs desulfurization treatment on the process gas output from the sulfur interceptors and then discharges it.

[0007] In a possible preferred embodiment, the oxidation reaction sulfur recovery unit includes: a primary heater, a primary oxidation reactor, a primary sulfur condenser, a secondary heater, a secondary oxidation reactor, and a secondary sulfur condenser, which are connected in sequence.

[0008] In a possible preferred embodiment, the sulfur recovery system suitable for low-concentration acid gas further includes: a steam drum unit, which is connected to the primary oxidation reactor, exchanges the reaction heat in the primary oxidation reactor, maintains the temperature in the reactor relatively stable, and by-produces saturated steam for supply to the steam pipe network.

[0009] In a possible preferred embodiment, an H2S / SO2 analyzer is provided on the process gas outlet pipeline of the primary sulfur condenser to dynamically regulate the amount of oxidation air entering the primary oxidation reactor; an oxygen content analyzer is provided on the process gas outlet pipeline of the secondary sulfur condenser to dynamically regulate the amount of air entering the secondary oxidation reactor.

[0010] In a possible preferred embodiment, the sulfur interceptor is arranged vertically. In the interception chamber of the sulfur interceptor, several coiled pipes are arranged at intervals in a vertical array. The head and tail ends of each coiled pipe are respectively connected to the input / output pipes of steam / cooling medium. A tail gas outlet is provided at the top of the interception chamber. A tail gas input pipe is provided near the lower part of the coiled pipes in the interception chamber, and the nozzle of the tail gas input pipe is arranged downward. A liquid sulfur outlet is provided at the bottom of the interception chamber, and a condensate outlet is provided near the bottom side wall. The lower part of the interception chamber is of a jacket structure to access the tracing steam and prevent sulfur from solidifying and blocking.

[0011] In a possible preferred embodiment, the tail gas desulfurization unit includes: a desulfurization tower, a circulation pump, a cooler, and a fresh caustic solution pump. The circulation pump extracts the desulfurization liquid at the bottom of the desulfurization tower, sends it to the cooler for cooling, and then sprays it into the desulfurization tower to contact the process gas output from the sulfur interceptor reversely for desulfurization. The fresh caustic solution pump is connected to the desulfurization liquid pipelines at the bottom of the desulfurization tower and the outlet of the cooler to transport fresh caustic solution to be added to the circulation.

[0012] In a possible preferred embodiment, the sulfur recovery system suitable for low-concentration acid gas further includes: a circulation fan unit, which is connected to the exhaust port of the tail gas desulfurization unit, extracts at least part of the tail gas and transports it to the oxidation reaction sulfur recovery unit to ensure the catalyst space velocity in the primary oxidation reactor, prevent local temperature runaway and the occurrence of temperature hot spots, and affect the reaction effect.

[0013] To achieve the above object, corresponding to the above sulfur recovery system, according to another aspect of the present invention, a sulfur recovery method suitable for low-concentration acid gas is further provided, and its steps include:

[0014] Mix the acid gas with a certain amount of oxidation air, heat it, and then input it into the first-stage oxidation reactor for oxidation reaction to obtain sulfur; at the same time, start the heat exchange between the steam drum unit and the first-stage oxidation reactor, extract the reaction heat, and by-product saturated steam to supply the steam network.

[0015] Transport the process gas generated by the first-stage oxidation reactor to the first-stage sulfur condenser to produce liquid sulfur, heat the output process gas and transport it to the second-stage oxidation reactor, conduct oxidation reaction to obtain sulfur, and then transport the output process gas to the second-stage sulfur condenser to produce liquid sulfur.

[0016] After the tail gas capture unit performs sulfur capture treatment on the process gas output from the second-stage sulfur condenser, the output process gas is sent to the sulfur interception treatment unit for sulfur interception treatment. After removing liquid sulfur particles and cooling, the output process gas is sent to the tail gas desulfurization unit for desulfurization treatment and then discharged.

[0017] In a possible preferred embodiment, the steps of the sulfur interception treatment unit for sulfur interception treatment include:

[0018] Set up main / backup sulfur interceptors to alternately receive the process gas output from the tail gas capture unit.

[0019] The sulfur interceptor receiving the process gas starts the condensation mode, switches the internal coil circulation cooling medium, condenses the process gas until a preset amount of sulfur is intercepted, then closes the process gas input, starts the desulfurization mode, switches the internal coil circulation steam, and melts the sulfur condensed in the sulfur interceptor for desulfurization treatment.

[0020] The sulfur interceptors alternately receiving the process gas repeat the opening of the condensation / desulfurization mode, so that the main / backup sulfur interceptors are alternately connected in a cycle to process the process gas.

[0021] In a possible preferred embodiment, the sulfur recovery method suitable for low-concentration acid gas, the steps further include:

[0022] Extract at least part of the tail gas after desulfurization treatment by the tail gas desulfurization unit and transport it to the first-stage oxidation reactor to be mixed with the raw material acid gas.

[0023] Through the sulfur recovery method and system suitable for low-concentration acid gas provided by the present invention, a sulfur interception treatment unit is ingeniously designed to replace the traditional tail gas incinerator. Thus, not only can the amount of process gas entering the tail gas desulfurization unit be reduced to reduce the consumption of alkali liquor, but also the sulfur in the process gas output from the tail gas capture unit can be efficiently intercepted, reducing the sulfur content brought into the subsequent desulfurization system, avoiding system blockage, and improving the sulfur recovery rate. In addition, since the tail gas incinerator is no longer set up, the fuel consumption can also be reduced, and the wet desulfurization technology can be directly adopted to remove the sulfur-containing substances in the tail gas, thereby overall reducing and stabilizing the operation load and energy consumption of the desulfurization system to support the long-term stable and reliable operation of the desulfurization system. Brief Description of the Drawings

[0024] The drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0025] Figures 1 to 2 is a schematic diagram of the pipeline connection structure of the sulfur recovery system suitable for low-concentration acid gas of the present invention;

[0026] Figure 3 is a schematic diagram of the structure of the sulfur interceptor in the sulfur recovery system suitable for low-concentration acid gas of the present invention;

[0027] Figure 4 is a top view schematic diagram of the coil structure of the sulfur interceptor in the sulfur recovery system suitable for low-concentration acid gas of the present invention;

[0028] Figure 5 is a schematic diagram of the steps of the sulfur recovery method suitable for low-concentration acid gas of the present invention.

[0029] Description of the Reference Numerals

[0030] Primary heater 1, primary oxidation reactor 2, steam drum unit 3, primary sulfur condenser 4, secondary heater 5, secondary oxidation reactor 6, secondary sulfur condenser 7, tail gas capture unit 8, sulfur interceptor 9, desulfurization tower 10, circulation pump 11, cooler 12, fresh caustic solution pump 13, circulation fan unit 14, interception chamber 91, coil 92, tail gas outlet 93, tail gas inlet pipe 94, liquid sulfur outlet 95, condensate outlet 96, input / output pipe 97. Detailed Description of the Embodiments

[0031] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the following will clearly and completely describe the specific technical solutions of the present invention in combination with the embodiments to help those skilled in the art further understand the present invention. Obviously, the embodiments described in this case are only a part of the embodiments of the present invention, rather than all of the embodiments. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention and without conflict with each other, the embodiments and features in the embodiments of this application can be combined with each other. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the scope of disclosure and protection of the present invention.

[0032] In addition, in the description, claims and drawings of the present invention, terms such as "first", "second", "S100", "S200", etc. are used to distinguish similar objects and do not necessarily describe a specific order or sequence. It should be understood that the features used in this way can be interchanged under appropriate circumstances so that the embodiments of the present invention described herein can be implemented in an order other than those described herein. At the same time, the stages recorded in each step are not necessarily implemented in the same step. It should be understood that the implementation order of the content in each step stage can be adjusted and interchanged without violating the inventive concept so that the step embodiments of the present invention described herein can be implemented in an order other than those described herein. In addition, the terms "comprising" and "having" in the present invention and any variations thereof are intended to cover non-exclusive inclusion. Unless otherwise clearly defined and limited, the terms "arranged", "deployed", "installed", "connected", "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. At the same time, the "tail gas" and "process gas" in this article can be understood as equivalent to each other according to the input / output relationship between the devices where they are located. For those of ordinary skill in the art, the specific meanings of the above terms in this case can be understood according to specific circumstances in combination with the prior art.

[0033] The inventors believe that the main reason for the large process energy consumption and system load of the existing direct oxidation process is that in the traditional process, for the process gas output from the tail gas collector, before desulfurization treatment, a tail gas incinerator is usually used to convert all the sulfur-containing S substances in the process gas into SO2. However, in actual operation, due to the limited capture effect of the existing tail gas collector on the residual sulfur S in the process gas, it is necessary to use a tail gas incinerator to convert the S-containing substances into SO2, so that the tail gas incinerator must operate for a long time to complete the conversion. On the one hand, this will increase fuel consumption, and on the other hand, it will also bring a large amount of tail gas, thus increasing the burden of subsequent desulfurization treatment.

[0034] Therefore, in order to improve the existing direct oxidation process, reduce the operation load and energy consumption of the desulfurization system, and improve the sulfur recovery rate, as Figures 1 to 4 shown, the present invention provides a sulfur recovery system suitable for low-concentration acid gas, and its example includes: an oxidation reaction sulfur recovery unit, a tail gas capture unit 8, a sulfur interception and treatment unit, and a tail gas desulfurization unit connected in sequence.

[0035] Specifically, as Figures 1 to 2As shown in the figure, in this embodiment, the oxidation reaction sulfur recovery unit includes, for example: a primary heater 1, a primary oxidation reactor 2, a primary sulfur condenser 4, a secondary heater 5, a secondary oxidation reactor 6, and a secondary sulfur condenser 7 connected in sequence.

[0036] Among them, as Figure 1 shown, the acidic gas containing hydrogen sulfide coming from the upstream device is buffered and separated by the acidic gas buffer tank, and then mixed with a quantitative amount of oxidation air. After that, it enters the primary heater 1 and is heated to ~200 °C, and then enters the primary oxidation reactor 2 for a direct oxidation reaction to produce sulfur.

[0037] Among them, the primary oxidation reactor 2 in this example preferably uses an isothermal reactor, and a titanium-based catalyst is selected and filled. TiO2 is greater than 85%, with strong anti-volatility, which can extend the service life. The catalyst space velocity in the reactor is 200 h-1, and the catalyst is installed outside the tubes, with a large filling coefficient. It adopts a shell-and-tube structure, has a large specific cold surface, and has good heat transfer performance, which can avoid overheating inside the reactor. The boiler water flows through the heat exchange tubes, and the water vaporizes and absorbs heat inside the tubes, removing the reaction heat from the catalyst bed layer and generating saturated steam at the same time.

[0038] At the same time, in an alternative embodiment, in order to improve the total sulfur conversion rate, a steam drum unit 3 can also be set up, which is connected to the primary oxidation reactor 2 to exchange the reaction heat in the primary oxidation reactor 2, so as to maintain the reaction temperature rise and ensure that the temperature inside the reactor is relatively constant, and by-product saturated steam is supplied to the steam pipe network. For example, when starting the water / steam circulation system of the steam drum unit 3, deaerated water is supplied into the heat exchange tubes of the heat exchanger built in the primary oxidation reactor 2 to remove the reaction heat, and by-product 2.5 Mpag saturated steam (which can be incorporated into the 1.0 MPaG steam pipe network after pressure reduction) is produced to maintain the reaction temperature rise not exceeding 270 °C and avoid generating SO2, which affects the total sulfur conversion rate.

[0039] In addition, at the inlet of the primary oxidation reactor 2, a nitrogen pipeline can also be optionally set up. When the temperature inside the reactor is too high, nitrogen can be used to dilute the acidic gas to ensure that the reactor temperature is within a constant range.

[0040] After that, the process gas exiting the primary oxidation reactor 2 enters the primary sulfur condenser 4 and is cooled to 160 °C and demisted. The liquid sulfur enters the liquid sulfur tank from the bottom of the condenser through a sulfur seal tank. The process gas is heated to ~200 °C by the secondary heater 5 and enters the secondary oxidation reactor 6. Among them, the secondary oxidation reactor 6 in this example preferably uses an adiabatic reactor, and a selective oxidation catalyst is selected and filled, with the main components being SiO2 + Al2O3 + Fe2O3 + Cr2O3. The catalyst space velocity in the reactor is 200 h-1. The process gas exiting the secondary oxidation reactor 6 enters the secondary sulfur condenser 7 and is cooled to 155 °C and demisted. The liquid sulfur enters the liquid sulfur tank from the bottom of the secondary sulfur condenser 7 through a sulfur seal tank.

[0041] Among them, in order to ensure that the conversion rate of the primary oxidation reactor 2 can reach the highest, in an alternative embodiment, an on-line H2S concentration analyzer may be provided on the acid gas pipeline at the outlet of the acid gas buffer tank to analyze the H2S content in the acid gas in real time and accurately adjust the amount of oxidation air entering the primary oxidation reactor 2, so that the reactor is in a slightly under-oxygen state to avoid the generation of SO2, ensure that the conversion rate of the reactor reaches the highest, such as O2 / H2S = 0.5 - 0.8 at the process gas inlet, and ensure that the total sulfur recovery rate is between 91% and 92% under rated conditions (at the initial stage of the catalyst) to improve the sulfur recovery rate and reduce sulfur loss.

[0042] Meanwhile, an oxygen content analyzer may also be provided on the pipeline at the outlet of the process gas of the secondary sulfur condenser 7 to quantitatively analyze the oxygen content in the process gas and accurately adjust the amount of air entering the secondary oxidation reactor 6.

[0043] After that, the process gas output from the secondary sulfur condenser 7 is further used to capture sulfur mist by the tail gas capture unit 8 (such as a tail gas catcher). The liquid sulfur produced by the reaction is sent to a liquid sulfur tank, and the liquid sulfur is cooled and formed on-site. The tail gas then enters the sulfur interception and treatment unit for removing sulfur particles and cooling treatment to intercept sulfur in the tail gas as much as possible to avoid blockage of the desulfurization system due to sulfur deposition, and then enters the tail gas desulfurization unit.

[0044] Specifically, as Figure 2 shown, in this example, the sulfur interception and treatment unit example includes: a pair of main / backup sulfur interceptors 9 arranged alternately to receive the process gas output from the tail gas capture unit 8 alternately, facilitating online switching and cleaning to ensure the long-term operation of the device. Each of the sulfur interceptors 9 is provided with coiled pipes 92 inside, and the inside of the pipes is respectively connected to the cooling medium / steam for alternate switching, so as to alternately cool the process gas between the sulfur interceptors 9, intercept the liquid sulfur and the melted and condensed sulfur.

[0045] Among them, as Figure 3 shown, the structure of a sulfur interceptor 9 is exemplified. The sulfur interceptor 9 is arranged vertically. Inside the interception chamber 91 of the sulfur interceptor 9, as Figure 4 shown, a number of coiled pipes 92 are arranged vertically and at intervals in an array. The head and tail ends of each of the coiled pipes 92 are respectively connected to the input / output pipes 97 of the steam / cooling medium. A tail gas outlet 93 is provided at the top of the interception chamber 91. A tail gas inlet pipe 94 is provided near the lower part of the coiled pipes 92 in the interception chamber 91, and the nozzle of the tail gas inlet pipe 94 is arranged downward. A liquid sulfur outlet 95 is provided at the bottom of the interception chamber 91, and a condensate outlet 96 is provided near the bottom side wall. The lower part of the interception chamber 91 is of a jacket structure to access the tracing steam.

[0046] With this arrangement, the vertically arranged sulfur interceptor 9 can reduce the volume of this equipment in the horizontal direction, save floor space. At the same time, the tail gas outlet 93 is at a high position, which is convenient for pipeline layout. There is no low point or U-shaped bend, and the condensed water in the tail gas will not accumulate, which can avoid the corrosion of the pipeline. In addition, the downward bending design of the nozzle of the tail gas input pipe 94 can increase the residence time of the tail gas in the sulfur interceptor 9, ensuring that the tail gas realizes a primary gas-liquid separation before contacting the coiled pipe 92, and improving the sulfur diversion efficiency.

[0047] When the sulfur interceptor 9 that receives the process gas is switched to intercept sulfur, cooling water (such as demineralized water) can enter from the lower end of the tail of the coiled pipe 92 and exit from the upper part. When switching sulfur removal, steam can enter from the upper head end of the coiled pipe 92, and the steam condensate exits from the lower part. The flow direction of the steam / condensate is opposite to that of the cooling water. In addition, the coiled pipe 92 can be coated with PFA. In this way, during use, there will be no phenomenon that a large amount of sulfur or dust adheres to the coiled pipe 92, and it has strong corrosion resistance and high temperature resistance, ensuring the long-term use of the equipment.

[0048] During the interception process, when cooling water flows through the coiled pipe 92 of the sulfur interceptor 9 to cool the process gas, sulfur will drip to the bottom of the interceptor or condense on the outer wall of the coiled pipe 92. At this time, the amount of intercepted sulfur can be judged according to the differential pressure of the tail gas at the inlet and outlet of the sulfur interceptor 9, and it can be determined whether sulfur removal needs to be started. When starting sulfur removal, switch the sulfur interceptor 9 to a standby one, and switch the cooling water in the coiled pipe 92 of the sulfur interceptor 9 that needs sulfur removal to 0.4 Mpag steam to melt the sulfur and deposit it at the bottom of the sulfur interceptor 9. The jacket structure at the bottom of the interception chamber 91 is internally connected with 0.4 Mpag steam during sulfur removal, so that the sulfur at the bottom can be melted and will not be blocked, for output from the liquid sulfur outlet 95.

[0049] By alternately receiving the process gas through the main / standby sulfur interceptor 9 and repeatedly starting the condensation / sulfur removal mode, the main / standby sulfur interceptor 9 can alternately connect and cycle to process the process gas, ensuring that the sulfur interception efficiency is about 95%. At the same time, since the steam for the sulfur removal mode of the sulfur interceptor 9 comes from the steam pipe network, and the energy consumption of the cooling water circulation required for condensation is also very low, the overall energy consumption is greatly reduced compared with the tail gas incinerator, and no more process gas will be generated due to incineration, thus further reducing the load pressure of the subsequent tail gas desulfurization unit. In addition, after being intercepted by the sulfur interceptor 9, the temperature of the output tail gas can be directly reduced to 60 - 70 °C, and there is no need to use a heat exchanger to cool down before entering the tail gas desulfurization unit for caustic washing, reducing the consumption of process water for cooling.

[0050] After that, the tail gas desulfurization unit desulfurizes the process gas output by the sulfur interceptor 9 and then discharges it. Among them, as Figure 2As shown, in this example, the tail gas desulfurization unit includes: a desulfurization tower 10, a circulation pump 11, a cooler 12, and a fresh caustic solution pump 13. The circulation pump 11 extracts the desulfurized liquid at the bottom of the desulfurization tower 10, sends it to the cooler 12 for cooling, and then sprays it into the desulfurization tower 10 for reverse contact with the process gas output from the sulfur interceptor 9 for desulfurization. The fresh caustic solution pump 13 is connected to the desulfurized liquid pipelines at the bottom of the desulfurization tower 10 and the outlet of the cooler 12 to transport fresh caustic solution to be added to the circulation.

[0051] Specifically, sodium hydroxide is used as the desulfurizer in the tail gas desulfurization unit. The desulfurization tower 10 is preferably provided with two layers of spray nozzles. The desulfurized liquid coming out from the bottom of the tower is pressurized by the circulation pump 11, sent to the cooler 12 for cooling to 50 - 60 °C, and then enters the desulfurization tower 10 for spraying, making reverse contact with the tail gas to absorb H2S / SO2, etc. in the tail gas. The desulfurized tail gas is sent to be treated outside the battery limit. In the upper part of the desulfurization tower 10, an entrainment separator layer is preferably provided and backflushed regularly with demineralized water to avoid blockage.

[0052] During operation, according to the pH value of the desulfurization circulating liquid at the inlet of the circulation pump 11, the pH of the desulfurization circulating liquid is controlled between 7 and 8. At the same time, in this example, a caustic soda dissolving tank is preferably set up to dissolve solid caustic soda into a 20 - 30 wt% solution as the fresh desulfurized liquid, and the fresh caustic solution pump 13 is used to supplement the fresh sodium hydroxide solution to the inside of the desulfurization tower 10 and the outlet of the desulfurization liquid circulation pump 11. Then, the salt-containing waste water is discharged according to the desulfurized liquid density value and the liquid level of the desulfurization tower 10.

[0053] With this setting, since the amount of the process gas output from the sulfur interceptor 9 is small, and a large amount of sulfur S in it has been intercepted and the process gas has been cooled down, this tail gas desulfurization unit is sufficient to directly handle it. And compared with the traditional scheme adapted to the tail gas incinerator, since there is no longer a large amount of incineration flue gas containing SO2, the consumption of the caustic solution used in the caustic washing process is less.

[0054] In addition, in an alternative embodiment, in order to improve the stability of the entire sulfur recovery system, a circulation fan unit 14 can be provided at the exhaust port of the desulfurization tower 10 to extract at least part of the tail gas and transport it to the oxidation reaction sulfur recovery unit, so that under low sulfur conditions (corresponding to normal operating load), part of the tail gas is circulated through the circulation fan unit 14 and mixed with the raw material acid gas to meet the space velocity of the first-stage oxidation reactor 2, ensuring uniform reaction in the reactor and avoiding the occurrence of temperature hot spots.

[0055] On the other hand, corresponding to the above sulfur recovery system, as Figure 5 shown, the present invention also provides a sulfur recovery method suitable for low-concentration acid gas, and its steps include:

[0056] Mix the acid gas with a certain amount of oxidizing air, heat it, and then input it into the first-stage oxidation reactor 2 for oxidation reaction to obtain sulfur. At the same time, start the heat exchange between the steam drum unit 3 and the first-stage oxidation reactor 2 to control the reaction heat and by-product saturated steam to supply the steam pipe network.

[0057] Transport the process gas generated by the first-stage oxidation reactor 2 to the first-stage sulfur condenser 4 to produce liquid sulfur, and heat and transport the output process gas to the second-stage oxidation reactor 6 for oxidation reaction to obtain sulfur, and then transport the output process gas to the second-stage sulfur condenser 7 to produce liquid sulfur.

[0058] After the tail gas capture unit 8 performs sulfur capture treatment on the process gas output from the second-stage sulfur condenser 7, the output process gas is sent to the sulfur interception treatment unit for sulfur interception treatment to remove liquid sulfur particles and cool down, and then the output process gas is sent to the tail gas desulfurization unit for desulfurization treatment and then discharged.

[0059] Among them, the steps of the sulfur interception treatment unit for sulfur interception treatment include:

[0060] Set the main / backup sulfur interceptor 9 to alternately receive the process gas output from the tail gas capture unit 8;

[0061] The sulfur interceptor 9 receiving the process gas turns on the condensation mode, switches the internal coil 92 to circulate the cooling medium, condenses the process gas until a preset amount of sulfur is intercepted, then closes the input of the process gas, turns on the desulfurization mode, switches the internal coil 92 to circulate steam, and melts the sulfur condensed in the sulfur interceptor 9 for desulfurization treatment;

[0062] The sulfur interceptor 9 that alternately receives the process gas repeats the opening of the condensation / desulfurization mode, so that the main / backup sulfur interceptors 9 are alternately connected in a cycle to process the process gas.

[0063] Furthermore, in an alternative embodiment, the sulfur recovery method suitable for low-concentration acid gas, the steps further include: extracting at least part of the tail gas after desulfurization treatment by the tail gas desulfurization unit, transporting it to the first-stage oxidation reactor 2 and mixing it with the raw material acid gas to ensure uniform reaction in the reactor and avoid the occurrence of temperature hot spots.

[0064] Experimental example

[0065] Taking the sulfur recovery system using the conventional direct oxidation method as an example (using an ordinary tail gas catcher to capture the liquid sulfur in the tail gas, and then entering the tail gas incinerator for incineration, and the flue gas after incineration is subjected to desulfurization treatment after heat recovery). Taking the treatment of 13660.74 kg / h of tail gas as an example, the tail gas temperature is 130 °C, the sulfur content in the tail gas is 5.8 kg / h, using the conventional process, the sulfur content in the tail gas entering the incinerator is 3.48 kg / h, the incineration temperature of the tail gas incinerator is controlled at 700 °C, the required supplementary fuel gas volume is 240.6 kg / h, and the electricity consumption of the tail gas combustion air blower is 110 KW·h.

[0066] While adopting the sulfur recovery system solution of the above example of the present invention, after setting the sulfur interceptor 9 to replace the tail gas incinerator, the sulfur content in the tail gas entering the tail gas desulfurization unit is 0.29 kg / h, and it directly enters the tail gas desulfurization unit without fuel gas consumption and the power consumption of the combustion-supporting fan. The amount of lye required for the operation of the desulfurization system is reduced by 26.58 kg / h, greatly reducing the operation cost of the whole system, and the overall sulfur recovery rate can reach about 99%. The tail gas after alkali washing can also meet the environmental protection emission requirements and can be directly discharged through the chimney.

[0067] In summary, through the sulfur recovery method and system suitable for low-concentration acid gas provided by the present invention, the sulfur interception treatment unit is ingeniously designed to replace the traditional tail gas incinerator, so that not only the process gas volume entering the tail gas desulfurization unit can be reduced to reduce the consumption of lye, but also the sulfur in the process gas output by the tail gas capture unit 8 can be efficiently intercepted, reducing the sulfur content brought into the subsequent desulfurization system, avoiding system blockage, and improving the sulfur recovery rate. In addition, since the tail gas incinerator is no longer set, fuel consumption can be reduced, and the wet desulfurization technology can be directly adopted to remove the sulfur-containing substances in the tail gas, thereby reducing and stabilizing the operation load and energy consumption of the desulfurization system as a whole to support the long-term stable and reliable operation of the desulfurization system.

[0068] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor limit the invention to the specific embodiments described. Obviously, many modifications and changes can be made according to the content of this specification. These embodiments are selected and specifically described in this specification to better explain the principle and practical application of the present invention, so that those skilled in the art can understand and utilize the present invention well. The present invention is only limited by the claims and their full scope and equivalents. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

[0069] Those skilled in the art can understand that in addition to implementing the systems, devices, units and their respective modules provided by the present invention in the form of pure computer-readable program codes, the method steps can be logically programmed to make the systems, devices, units and their respective modules provided by the present invention be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, embedded microcontrollers, etc. to achieve the same program. Therefore, the systems, devices and their respective modules provided by the present invention can be regarded as a kind of hardware components, and the modules included therein for implementing various programs can also be regarded as the structures within the hardware components; the modules for implementing various functions can also be regarded as either software programs for implementing the methods or the structures within the hardware components.

[0070] In addition, all or part of the steps in the methods of the above embodiments can be completed by instructing relevant hardware through a program. The program is stored in a storage medium, including several instructions for causing a single-chip microcomputer, a chip, or a processor to execute all or part of the steps of the methods described in various embodiments of the present application. The aforementioned storage medium includes: various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disc.

[0071] In addition, any combination can be made among various different implementation manners of the embodiments of the present invention, as long as it does not violate the idea of the embodiments of the present invention, and it should also be regarded as the content disclosed in the embodiments of the present invention.

Claims

1. A sulfur recovery system suitable for low-concentration acid gas, comprising: An oxidation reaction sulfur recovery unit, a tail gas capture unit, a sulfur interception and treatment unit, and a tail gas desulfurization unit connected in sequence, wherein the sulfur interception and treatment unit includes: at least a pair of sulfur interceptors that alternately receive the process gas output from the tail gas capture unit, and a coil is arranged in each of the sulfur interceptors, and the cooling medium / steam is respectively communicated in the pipes to alternately switch, so as to alternately cool the process gas between the sulfur interceptors, intercept the liquid sulfur and the melted and condensed sulfur, and the tail gas desulfurization unit performs desulfurization treatment on the process gas output from the sulfur interceptors and then discharges it.

2. The sulfur recovery system suitable for low-concentration acid gas according to claim 1, wherein the sulfur recovery unit for oxidation reaction comprises: A primary heater, a primary oxidation reactor, a primary sulfur condenser, a secondary heater, a secondary oxidation reactor, and a secondary sulfur condenser connected in sequence.

3. The sulfur recovery system suitable for low-concentration sour gas according to claim 2, further comprising: A steam drum unit, which is connected to the primary oxidation reactor, exchanges the reaction heat in the primary oxidation reactor, maintains the temperature in the reactor relatively constant, and by-produces saturated steam to supply the steam network.

4. The sulfur recovery system suitable for low-concentration acid gas according to claim 2, wherein an H2S / SO2 analyzer is provided on the process gas outlet pipeline of the primary sulfur condenser to dynamically regulate the amount of oxidation air entering the primary oxidation reactor in association; an oxygen content analyzer is provided on the process gas outlet pipeline of the secondary sulfur condenser to dynamically regulate the amount of air entering the secondary oxidation reactor in association.

5. The sulfur recovery system suitable for low-concentration acid gas according to claim 1, wherein the sulfur interceptors are arranged vertically, and a number of coils are arranged at intervals in a vertical array in the interception cavity of the sulfur interceptors. The head and tail ends of each coil are respectively connected to the input / output pipes of the steam / cooling medium. A tail gas outlet is provided at the top of the interception cavity, and a tail gas input pipe is provided near the lower part of the coils in the interception cavity, and the pipe orifice of the tail gas input pipe is arranged downward. A liquid sulfur outlet is provided at the bottom of the interception cavity, and a condensate outlet is provided near the bottom side wall. The lower part of the interception cavity is of a jacket structure to access the tracing steam.

6. The sulfur recovery system suitable for low-concentration acid gas according to claim 1, wherein the tail gas desulfurization unit comprises: A desulfurization tower, a circulation pump, a cooler, and a fresh caustic solution pump. The circulation pump extracts the desulfurization liquid at the bottom of the desulfurization tower, sends it to the cooler for cooling, and then sends it into the desulfurization tower for spraying, and contacts the process gas output from the sulfur interceptors reversely for desulfurization. The fresh caustic solution pump is connected to the bottom of the desulfurization tower and the desulfurization liquid pipeline at the outlet of the cooler to transport fresh caustic solution to be added to the circulation.

7. The sulfur recovery system suitable for low-concentration acid gas according to claim 1, further comprising: A circulation fan unit, which is connected to the exhaust port of the tail gas desulfurization unit and extracts at least part of the tail gas and transports it to the oxidation reaction sulfur recovery unit.

8. A sulfur recovery method suitable for low-concentration acid gas, the steps of which include: Mix the acid gas with a quantitative amount of oxidation air, heat it, and then input it into the primary oxidation reactor for oxidation reaction to obtain sulfur; at the same time, start the heat exchange between the steam drum unit and the primary oxidation reactor, take out the reaction heat, and by-produce saturated steam to supply the steam network; Transport the process gas generated by the primary oxidation reactor to the primary sulfur condenser to produce liquid sulfur, heat the output process gas and transport it to the secondary oxidation reactor, perform oxidation reaction to obtain sulfur, and then transport the output process gas to the secondary sulfur condenser to produce liquid sulfur; After the tail gas capture unit performs sulfur capture treatment on the process gas output from the secondary sulfur condenser, the process gas is output to the sulfur interception treatment unit for sulfur interception treatment. After removing sulfur liquid particles and cooling down, the process gas is output to the tail gas desulfurization unit for desulfurization treatment and then discharged.

9. The sulfur recovery method suitable for low-concentration acid gas according to claim 8, wherein the steps of the sulfur interception treatment unit performing sulfur interception treatment include: Set up main / backup sulfur interceptors to alternately receive the process gas output from the tail gas capture unit; The sulfur interceptor receiving the process gas turns on the condensation mode, switches the circulating cooling medium of the internal coil, condenses the process gas until a preset amount of sulfur is intercepted, then closes the input of the process gas, turns on the desulfurization mode, switches the circulating steam of the internal coil, and melts the sulfur condensed in the sulfur interceptor for desulfurization treatment; The sulfur interceptors alternately receiving the process gas repeat the condensation / desulfurization mode, so that the main / backup sulfur interceptors are alternately connected in a cycle to process the process gas.

10. The sulfur recovery method suitable for low-concentration acid gas according to claim 8, wherein the steps further include: Extract at least part of the tail gas after desulfurization treatment by the tail gas desulfurization unit and transport it to the primary oxidation reactor to be mixed with the raw material acid gas.

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