Process system and process method for treating low-concentration hydrogen sulfide acid gas containing organic sulfur

Abstract

The invention provides a process system and a process method for treating low-concentration hydrogen sulfide acid gas containing organic sulfur. The process system comprises a sulfur recovery unit, a tail gas treatment unit with an acid gas concentration function, and a flue gas alkali washing unit, sulfur-containing tail gas is subjected to concentration treatment through an absorption tower of the tail gas treatment unit and then enters the sulfur recovery unit to be subjected to a Claus reaction, sulfur and sulfur recovery tail gas are obtained through separation, the sulfur recovery tail gas enters the tail gas treatment unit and is subjected to combustion and hydrotreatment in sequence, and obtained gas enters the absorption tower of the tail gas treatment unit; in the tail gas treatment unit, the gas absorbed by the absorption tower enters the flue gas alkali washing unit and is sequentially subjected to incineration and alkali washing, and desulfurized gas is discharged. The SO2 content in the tail gas treated by the process system is less than or equal to 50mg / Nm < 3 >, and the requirement that the tail gas sulfur dioxide emission reaches the standard in the whole time period during the start-stop and normal operation can be met.

Description

Technical Field

[0001] The present invention belongs to the field of tail gas treatment, and relates to an acid gas concentration, sulfur recovery and tail gas treatment system suitable for low-concentration hydrogen sulfide acid gas containing organic sulfur, and specifically to a process system and process method for treating low-concentration hydrogen sulfide acid gas containing organic sulfur. Background Art

[0002] Natural gas has been used more and more widely in modern industrial production and life, but most of the natural gas extracted from gas fields contains acidic components such as hydrogen sulfide, organic sulfur, and carbon dioxide. These acidic components can cause problems such as corrosion of transportation and downstream processing equipment and pipelines and environmental pollution. Therefore, natural gas is generally treated with amine desulfurization and decarbonization. The acid gas generated by amine solution regeneration must be treated to meet environmental protection requirements before it can be discharged.

[0003] If the concentration of hydrogen sulfide in the acid gas is high (>50 mol%), the acid gas treatment process of Claus + tail gas treatment can often be directly adopted. The acid gas can directly enter the sulfur recovery device, add air in a specific proportion, burn in the combustion furnace and react in the downstream reactor. The hydrogen sulfide and organic sulfur are converted into elemental sulfur through the Claus reaction. In combination with the tail gas treatment device, the sulfur recovery rate can reach more than 99.5%, and the generated tail gas can also meet environmental protection requirements.

[0004] When the concentration of hydrogen sulfide in the acid gas is low (15 mol% to 50 mol%), if all the acid gas enters the combustion furnace, it will be difficult for the combustion furnace to maintain a stable combustion temperature. At this time, the Claus diversion process is used. This process is based on the Claus reaction principle and only introduces 1 / 3 of the acid gas into the combustion furnace for combustion. After being converted into sulfur dioxide, it is mixed with the remaining acid gas for Claus reaction. This process can ensure the combustion furnace temperature, but when the acid gas contains heavy hydrocarbons, it may cause problems such as catalyst contamination.

[0005] When the concentration of hydrogen sulfide in the acid gas is lower, an acid gas concentration system can be added before the Claus unit. The main principle of this system is to use the selective absorption characteristics of amine liquid for hydrogen sulfide to first concentrate the acid gas and then enter the sulfur recovery unit for treatment. However, this process requires the addition of equipment such as a concentration tower and a regeneration tower on the basis of the Claus + tail gas treatment unit, and the process flow is complicated. When the acid gas also contains organic sulfur, the amine liquid cannot absorb it, and the organic sulfur can only be discharged into the atmosphere with the tail gas, causing the tail gas emission to exceed the standard and pollute the environment. At this time, the process technology route of direct incineration of acid gas and then alkali washing can also be adopted. The alkali washing absorption process uses chemical reactions to absorb the acid gas converted into sulfur dioxide by incineration with alkali liquid. The reaction is fast, and the tail gas produced can meet high environmental protection requirements, but there is a problem of excessive alkali consumption, which is only suitable for treating acid gas with extremely low sulfur content.

[0006] In response to the above technical problems, increasing the concentration of hydrogen sulfide in the acid gas and treating the organic sulfur in the acid gas while achieving ultra-low exhaust gas emissions has become a current direction for improving the process. Summary of the invention

[0007] In order to solve the above problems, the present invention provides a process system and process method for treating low-concentration hydrogen sulfide acid gas containing organic sulfur. The SO2 content in the tail gas treated by the process system is ≤50mg / Nm 3 , meet the special emission limit requirements in the "Petroleum Refining Industry Pollutant Emission Standard" (GB13570-2015), and can meet the requirements for exhaust sulfur dioxide emissions to meet the standards at all times during start-up, shutdown and normal operation.

[0008] In order to achieve the above object, the present invention provides a process system for treating low-concentration hydrogen sulfide acid gas containing organic sulfur, which includes a sulfur recovery unit, a tail gas treatment unit with an acid gas concentration function, and a flue gas alkali washing unit;

[0009] The sulfur recovery unit is provided with a main combustion furnace 15 and a Claus treatment device. The upper outlet of the regeneration tower 6 is connected to the inlet of the main combustion furnace 15 through the regeneration tower reflux tank 9. The outlet of the main combustion furnace 15 is connected to the Claus treatment device. The gas outlet of the Claus treatment device is connected to the inlet of the online combustion furnace 24 of the tail gas treatment unit. The Claus treatment device is provided with a sulfur condenser, a reheat furnace, and a Claus reactor.

[0010] The tail gas treatment unit is provided with an online combustion furnace 24, a hydrogenation reactor 25, an absorption tower 1, a lean-rich liquid heat exchanger 5, a regeneration tower 6, and a regeneration tower reflux tank 9. The gas outlet of the Claus treatment device is connected to the inlet of the online combustion furnace 24, the outlet of the online combustion furnace 24 is connected to the inlet of the hydrogenation reactor 25, the outlet of the hydrogenation reactor 25 is connected to the middle and lower inlet of the absorption tower 1, the sulfur-containing tail gas enters the tail gas treatment unit through the bottom inlet of the absorption tower 1, the bottom outlet of the absorption tower 1 is connected to the upper inlet of the regeneration tower 6 through the lean-rich liquid heat exchanger 5, the upper outlet of the regeneration tower 6 is respectively connected to the upper inlet of the regeneration tower 6 and the inlet of the main combustion furnace 15 of the sulfur recovery unit through the regeneration tower reflux tank 9, the bottom outlet of the regeneration tower 6 is connected to the upper inlet of the absorption tower 1 through the lean-rich liquid heat exchanger 5, and the upper outlet of the absorption tower 1 is connected to the inlet of the tail gas incinerator 2 of the flue gas alkali washing unit;

[0011] The flue gas alkali washing unit is provided with a tail gas incinerator 2, a flue gas heat exchanger 28, an alkali washing tower 29, and a purified flue gas liquid separator 31. The upper outlet of the absorption tower 1 is connected to the inlet of the tail gas incinerator 2, the outlet of the tail gas incinerator 2 is connected to the inlet of the alkali washing tower 29 through the flue gas heat exchanger 28, the upper outlet of the alkali washing tower 29 is connected to the flue gas heat exchanger 28 through the purified flue gas liquid separator 31, the flue gas heat exchanger 28 leads to the atmosphere, and the liquid outlet of the purified flue gas liquid separator 31 is connected to the alkali washing tower 29.

[0012] According to a specific embodiment of the present invention, preferably, in the tail gas treatment unit, a rich liquid pump 4 is provided between the bottom outlet of the absorption tower 1 and the lean-rich liquid heat exchanger 5, an acid gas air cooler 7 and an acid gas aftercooler 8 are provided between the upper outlet of the regeneration tower 6 and the regeneration tower reflux tank 9, a lean liquid pump 11, a lean liquid air cooler 12, and a lean liquid aftercooler 13 are provided between the lean-rich liquid heat exchanger 5 and the upper inlet of the absorption tower 1, a regeneration tower reflux pump 10 is provided between the regeneration tower reflux tank 9 and the upper inlet of the regeneration tower 6; and a regeneration tower reboiler 14 is provided at the lower part of the regeneration tower 6.

[0013] According to a specific embodiment of the present invention, preferably, in the sulfur recovery unit, a waste heat boiler 16 is provided between the outlet of the main combustion furnace 15 and the Claus treatment device, and the Claus treatment device comprises a primary sulfur condenser 17, a primary reheat furnace 18, a primary Claus reactor 19, a secondary sulfur condenser 20, a secondary reheat furnace 21, a secondary Claus reactor 22, and a tertiary sulfur condenser 23, and a gas outlet of the tertiary sulfur condenser 23 is connected to the inlet of the online combustion furnace 24 of the tail gas treatment unit.

[0014] According to a specific embodiment of the present invention, preferably, a waste heat boiler 26 and a quenching tower 27 are provided between the outlet of the hydrogenation reactor 25 and the lower inlet of the absorption tower 1 .

[0015] According to a specific embodiment of the present invention, preferably, a flue gas waste heat boiler 3 is provided between the outlet of the tail gas incinerator 2 and the flue gas heat exchanger 28, the flue gas heat exchanger 28 is connected to a chimney 32, and the bottom outlet of the alkali washing tower 29 is connected to the upper inlet of the alkali washing tower 29 through a desulfurization liquid circulation pump 30.

[0016] According to a specific embodiment of the present invention, preferably, in the tail gas treatment unit, the acid gas is discharged from the top of the regeneration tower reflux tank 9, part of the acid gas enters the bottom of the absorption tower 1 through the super concentration line, and the remaining acid gas enters the main combustion furnace 15 of the sulfur recovery unit.

[0017] According to a specific embodiment of the present invention, preferably, the alkali washing tower 29 is provided with a spray section, and a packing section is provided on the upper part of the spray section.

[0018] The present invention also provides a process for desulfurizing sulfur-containing tail gas by using the above process system for treating low-concentration hydrogen sulfide acid gas containing organic sulfur.

[0019] According to a specific embodiment of the present invention, preferably, the sulfur-containing tail gas is concentrated by the absorption tower of the tail gas treatment unit and then enters the sulfur recovery unit, where a Claus reaction occurs to separate sulfur and sulfur recovery tail gas. The sulfur recovery tail gas enters the online combustion furnace of the tail gas treatment unit, where combustion and hydrogenation treatment are performed in sequence, and the resulting gas enters the absorption tower; in the tail gas treatment unit, the gas absorbed by the absorption tower enters the flue gas alkali washing unit, where incineration and alkali washing are performed in sequence to discharge desulfurized gas.

[0020] According to a specific embodiment of the present invention, preferably, in the tail gas treatment unit, sulfur-containing tail gas is introduced from the bottom of the absorption tower 1, and rich liquid is obtained after being absorbed by the countercurrent absorption liquid. The rich liquid enters the regeneration tower 6 from the bottom of the absorption tower 1 through the rich liquid pump 4 and the lean-rich liquid heat exchanger 5 in sequence. The lean liquid obtained after the regeneration treatment enters the top of the absorption tower 1 from the bottom of the regeneration tower 6 through the lean-rich liquid heat exchanger 5, the lean liquid pump 11, the lean liquid air cooler 12, and the lean liquid aftercooler 13 in sequence; the acid gas obtained after the regeneration treatment enters the regeneration tower reflux tank 9 from the top of the regeneration tower 6 through the acid gas air cooler 7 and the acid gas aftercooler 8 in sequence, the separated condensed water enters the regeneration tower 6 from the bottom of the regeneration tower reflux tank 9 after being pressurized by the regeneration tower reflux pump 10, and the acid gas is discharged from the top of the regeneration tower reflux tank 9 and enters the sulfur recovery unit.

[0021] In the above-mentioned tail gas treatment unit, low-concentration hydrogen sulfide acid gas containing organic sulfur first enters the absorption tower from the bottom of the absorption tower, and contacts with a highly selective composite formula amine liquid in the absorption tower. Since the amine liquid has a higher selectivity for hydrogen sulfide, most of the hydrogen sulfide and part of the carbon dioxide in the acid gas can be absorbed, and the unabsorbed carbon dioxide and organic sulfur and other components in the acid gas are discharged from the top of the absorption tower and sent to the tail gas incinerator; the rich liquid flowing out from the bottom of the absorption tower is heated by the lean-rich liquid heat exchanger and enters the regeneration tower, and is countercurrently contacted with the amine liquid steam from bottom to top in the tower for regeneration, and hydrogen sulfide and carbon dioxide gas are resolved; the regeneration heat is provided by the reboiler at the bottom of the tower; the hot lean liquid is drawn out from the bottom of the regeneration tower at a temperature of about 125°C, and is cooled by heat exchange with the rich liquid in the lean-rich amine liquid heat exchanger, and then cooled to about 35°C by the lean amine liquid air cooler and the lean amine liquid aftercooler, and then pumped into the filtration system by the lean liquid pump to remove mechanical impurities and degradation products in the solution, and finally enters the absorption tower to complete the circulation of the entire solution system. The acid gas at about 110°C coming out of the top of the regeneration tower is cooled to about 35°C by the acid gas air cooler and the acid gas aftercooler, and then enters the regeneration tower reflux tank. The separated acid gas with high hydrogen sulfide concentration is sent to the sulfur recovery unit device, and the separated acid condensed water is sent to the top of the regeneration tower by the regeneration tower reflux pump for reflux. The present invention sets a "super concentration line" on the pipeline for the acid gas to the sulfur recovery unit. When the acid gas concentration needs to be further increased, part of the high-concentration acid gas can be introduced into the absorption tower as concentrated gas to increase the concentration of hydrogen sulfide in the acid gas in the absorption tower, further improve the selectivity of the amine liquid, and thus further increase the concentration of the acid gas sent to the sulfur recovery unit.

[0022] According to a specific embodiment of the present invention, preferably, in the sulfur recovery unit, the acid gas discharged from the tail gas treatment unit enters the main combustion furnace 15 for Claus reaction to generate process gas containing elemental sulfur, the process gas containing elemental sulfur is discharged from the main combustion furnace 15, passes through the waste heat boiler 16 and the primary sulfur condenser 17, is cooled to obtain liquid sulfur and is discharged from the bottom of the primary sulfur condenser 17, and the remaining process gas is discharged from the upper part of the primary sulfur condenser 17 and then enters the primary reheat furnace 18 and the primary Claus reactor 19 in sequence to generate process gas containing elemental sulfur. The process gas is discharged from the lower part of the primary Claus reactor 19 and enters the secondary sulfur condenser 20. Liquid sulfur is obtained by cooling and discharged from the bottom of the secondary sulfur condenser 20. The remaining process gas enters the secondary reheat furnace 21 and the secondary Claus reactor 22 from the upper part of the secondary sulfur condenser 20 to generate a process gas containing elemental sulfur. The process gas containing elemental sulfur is discharged from the lower part of the secondary Claus reactor 22 and enters the tertiary sulfur condenser 23. Liquid sulfur is obtained by cooling and discharged from the bottom of the tertiary sulfur condenser 23. The remaining tail gas is discharged from the upper part of the tertiary sulfur condenser 23 and enters the tail gas treatment unit.

[0023] In the above-mentioned sulfur recovery unit, acid gas with high hydrogen sulfide concentration enters the main combustion furnace of the sulfur recovery unit. By adjusting the air ratio, the Claus reaction begins to occur in the combustion furnace, and part of the hydrogen sulfide begins to be converted into elemental sulfur. The process gas coming out of the combustion furnace enters the waste heat boiler and the first-stage sulfur cooler for cooling. After the generated sulfur is separated, the process gas enters the first-stage reheat furnace. The process gas heated by the first-stage reheat furnace enters the first-stage Claus reactor and further undergoes the Claus reaction under the action of the catalyst. The process gas after the reaction enters the second-stage condenser for condensation and separation of sulfur. The separated process gas enters the second-stage Claus reactor for further reaction, and then enters the third-stage condenser to separate the sulfur. The tail gas generated by the third-stage condensation enters the tail gas treatment unit.

[0024] According to a specific embodiment of the present invention, preferably, in the tail gas treatment unit, the tail gas discharged from the sulfur recovery unit enters the online combustion furnace 24 for combustion, then enters the hydrogenation reactor 25 for hydrogenation reaction, and then passes through the waste heat boiler 26 and the quenching tower 27, and finally is discharged from the top of the quenching tower 27, and then enters the middle and lower part of the absorption tower 1.

[0025] In the above tail gas treatment unit, the tail gas from the sulfur recovery unit is mixed with the combustion gas in the online combustion furnace and heated to 280°C. The mixed process gas enters the hydrogenation reactor for reaction, and most of the sulfides in the process gas are reduced to hydrogen sulfide. In the waste heat boiler, the process gas is cooled to 170°C, and then enters the quenching tower, where it is countercurrently contacted with cooling water and further cooled to 35°C. The cooled gas enters the absorption tower from the lower part of the absorption tower, mixes with the low-concentration acid gas entering from the bottom of the tower, and contacts with the amine liquid together to absorb the hydrogen sulfide in the process gas.

[0026] According to a specific embodiment of the present invention, preferably, in the flue gas alkali washing unit, the gas absorbed by the absorption tower enters the tail gas incinerator 2 from the top of the absorption tower 1 to generate flue gas, and the flue gas enters the flue gas waste heat boiler 3, the flue gas heat exchanger 28, and the alkali washing tower 29 in sequence. The flue gas after alkali washing is discharged from the top of the alkali washing tower 29, and enters the purified flue gas separator 31 and the flue gas heat exchanger 28 in sequence, and is finally discharged through the chimney 32. The desulfurization liquid is discharged from the bottom of the alkali washing tower 29 and enters the alkali washing tower 29 through the desulfurization liquid circulation pump 30 or is discharged as waste liquid.

[0027] In order to solve the technical problem that the organic sulfur in the acid gas cannot be absorbed by the amine liquid, resulting in excessive emissions, a flue gas alkali washing unit is set up. The tail gas containing organic sulfur and trace hydrogen sulfide generated by the tail gas treatment unit absorption tower enters the tail gas incinerator and is incinerated at 760°C. The flue gas containing sulfur dioxide generated by the incineration is cooled by the flue gas waste heat boiler and the flue gas heat exchanger and enters the bottom of the alkali washing tower. It is countercurrently contacted with the atomized desulfurization liquid sprayed from the solid cone nozzle, and absorbs sulfur dioxide while the flue gas is cooled. The cooled flue gas then enters the packing section of the alkali washing tower, and further countercurrently contacts with the desulfurization liquid in the packing section to further remove sulfur dioxide. After the purified flue gas is separated from most of the carried mist by the demister at the top of the alkali washing tower, it enters the purified flue gas liquid separation tank, and finally after being heated by the flue gas heat exchanger, it is discharged into the atmosphere through the chimney. The pH of the desulfurization liquid is controlled by injecting a certain concentration of NaOH solution at the bottom of the alkali washing tower. An oxidation section is also set at the bottom of the alkali washing tower to introduce a certain amount of air to reduce the COD value of the sewage to meet the discharge requirements. Most of the liquid at the bottom outlet of the alkali washing tower is sent back to the alkali washing tower as circulating liquid through the desulfurization liquid circulation pump, and a small part enters the water treatment system through the sewage discharge device.

[0028] According to a specific embodiment of the present invention, preferably, the pH of the bottom circulating liquid at the bottom of the alkali washing tower 29 is 6.2-8.2.

[0029] According to a specific embodiment of the present invention, preferably, the hydrogen sulfide content in the sulfur-containing tail gas is ≤15 mol%.

[0030] According to a specific embodiment of the present invention, preferably, the H2S concentration of the acid gas entering the sulfur recovery unit can be increased to above 50 mol%.

[0031] According to a specific embodiment of the present invention, preferably, the sulfur dioxide content in the flue gas finally discharged by the desulfurization method of sulfur-containing tail gas is ≤50mg / Nm 3 .

[0032] According to a specific embodiment of the present invention, preferably, the amine liquid used in the absorption tower in the tail gas treatment unit comprises, by weight, 97 parts of MDEA, 1-2 parts of phosphoric acid, 0.5-1 parts of corrosion inhibitor, 0.5-1 parts of defoaming agent, and water.

[0033] According to a specific embodiment of the present invention, preferably, the mass concentration of the amine solution is 40-45%.

[0034] According to a specific embodiment of the present invention, preferably, the corrosion inhibitor includes one or a combination of two or more of imidazolyl dithiourea, 2-amino-imidazolidinone, di(propynyloxymethyl)isopropylbenzyl ammonium chloride, and di(propynyloxymethyl)butylbenzyl ammonium chloride.

[0035] According to a specific embodiment of the present invention, preferably, the defoaming agent includes polyether-modified silicone oil.

[0036] The process system for treating low-concentration hydrogen sulfide acid gas containing organic sulfur of the present invention can be applied to the treatment of hydrogen sulfide acid gas in the processes of petroleum refining, chemical industry, natural gas processing, etc. It can not only treat acid gas with a hydrogen sulfide concentration lower than 15 mol% which is difficult to be treated by the traditional sulfur recovery + tail gas treatment process, but also treat acid gas with a hydrogen sulfide concentration higher than 15 mol%, especially the treatment of acid gas with a hydrogen sulfide concentration of ≤15 mol% containing organic sulfur, and the SO2 content in the tail gas after treatment is ≤50 mg / Nm 3 , meeting the special emission limit requirements in the "Petroleum Refining Industry Pollutant Emission Standard" (GB13570-2015), and meeting the requirements for the full-time compliance of exhaust sulfur dioxide emissions during start-up, shutdown and normal operation. Compared with the prior art, the present invention has the following positive effects:

[0037] (1) The present invention introduces low-concentration acid gas and tail gas generated by the sulfur recovery unit into the same absorption tower, so that the absorption tower has two functions of acid gas concentration and tail gas treatment, avoiding the need for a separate concentration tower, which is beneficial to reducing the footprint of the device and the number of equipment;

[0038] The acid gas and sulfur recovery tail gas enter the absorption tower from different positions (acid gas enters from the bottom of the tower, tail gas enters from the middle and lower part of the tower), which helps to reduce the absorption of carbon dioxide by amine liquid and enhance the concentration effect;

[0039] (2) The present invention is provided with a "super concentration line". When the acid gas concentration needs to be further increased, part of the high-concentration acid gas can be introduced into the absorption tower as the concentration gas, thereby increasing the concentration of hydrogen sulfide in the acid gas in the absorption tower, further improving the selectivity of the amine liquid, and thus further increasing the concentration of the acid gas sent to the sulfur recovery unit;

[0040] (3) The present invention adds an alkaline washing system on the basis of the process of sulfur recovery + reduction absorption tail gas treatment, adopts NaOH solution as absorbent for chemical absorption, and the alkaline washing tower adopts a combination of one-stage spraying + two-stage fillers. The desulfurization liquid with desulfurization function is divided into two streams, which enter the alkaline washing tower from the spraying section and the lower filler. The sulfur-containing flue gas enters from the lower part of the spraying section and contacts with the desulfurization liquid. The temperature drops rapidly, and most of the sulfur dioxide in the flue gas is rapidly absorbed. Then the low-temperature flue gas enters the lower filler and further contacts with the desulfurization liquid. The remaining sulfur dioxide in the flue gas is further absorbed. Finally, the flue gas enters the uppermost filler and contacts with the water flowing into the top of the tower. The water replenishment at this place can maintain the liquid level of the alkaline washing tower and the concentration of the desulfurization liquid while washing away the desulfurization liquid entrained in the flue gas. The present invention also arranges a flue gas liquid separator downstream of the alkaline washing tower to further separate the entrained liquid in the flue gas, thereby avoiding the waste of alkaline liquid and the corrosion of the downstream heat exchanger to a great extent. The process method reacts quickly and thoroughly, and can achieve the requirement of ultra-low emission of sulfur dioxide in tail gas by adjusting the injection amount of alkali solution. It solves the technical problem that the low hydrogen sulfide concentration acid gas also contains organic sulfur, which cannot be absorbed by the amine solution used for concentration, resulting in substandard tail gas, and avoids the waste of alkali solution.

[0041] (4) During the desulfurization process of the start-up and shutdown equipment, because the sulfur recovery device and the tail gas treatment device are not put into operation or are not running smoothly, the traditional sulfur recovery + tail gas treatment process can only send the sulfur-containing acid gas into the incinerator for direct incineration and conversion into sulfur dioxide before discharge. The tail gas cannot meet the emission standards during the start-up and shutdown process, causing environmental pollution. The present invention can put into operation an alkali washing system. The acid gas generated during the desulfurization process of the device is incinerated in the incinerator and then enters the alkali washing system. By adjusting the injection amount of the alkali solution, the absorption capacity is improved. After the sulfur dioxide is absorbed, the tail gas is discharged through the chimney, so that the tail gas sulfur dioxide meets the standard at all times. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The process flow chart for treating low-concentration hydrogen sulfide acid gas containing organic sulfur. DETAILED DESCRIPTION

[0043] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be construed as limiting the applicable scope of the present invention.

[0044] The present invention provides a process system for treating low-concentration hydrogen sulfide acid gas containing organic sulfur, such as Figure 1As shown, the system comprises: an absorption tower 1, an exhaust gas incinerator 2, a flue gas waste heat boiler 3, a rich liquid pump 4, a lean and rich liquid heat exchanger 5, a regeneration tower 6, an acid gas air cooler 7, an acid gas aftercooler 8, a regeneration tower reflux tank 9, a regeneration tower reflux pump 10, a lean liquid pump 11, a lean liquid air cooler 12, a lean liquid aftercooler 13, a regeneration tower reboiler 14, a main combustion furnace 15, a waste heat boiler 16, a primary sulfur condenser 17, a primary reheat furnace 18, a primary Claus reactor 19, a secondary sulfur condenser 20, a secondary reheat furnace 21, a secondary Claus reactor 22, a tertiary sulfur condenser 23, an online combustion furnace 24, a hydrogenation reactor 25, a waste heat boiler 26, a quenching tower 27, a flue gas heat exchanger 28, an alkali washing tower 29, a desulfurization liquid circulation pump 30, a purified flue gas liquid separator 31, a chimney 32, etc. The specific process flow of desulfurization using the system is as follows:

[0045] (1) Acid gas with low hydrogen sulfide concentration (35°C, 60 kPag, hydrogen sulfide content of 11 mol%) containing organic sulfur enters absorption tower 1 from the bottom of absorption tower 1, and countercurrently contacts with lean liquid entering from the top of absorption tower 1. Most of the hydrogen sulfide and part of the carbon dioxide in the acid gas are absorbed by the lean liquid. The tail gas after absorption is discharged from the top of absorption tower 1, and the rich liquid that absorbs the acid gas is discharged from the bottom of absorption tower 1;

[0046] The amine solution used is prepared by the following steps: 97% MDEA, 1% phosphoric acid, 1% 2-amino-imidazolidinone and 1% polyether modified silicone oil are mixed according to mass fraction; after mixing, the mixture is diluted with water to prepare an aqueous solution with a mass concentration of 45%.

[0047] (2) The rich liquid described in step (1) is pressurized by the rich liquid pump 4, and then heated to 95° C. by the lean-rich liquid heat exchanger 5 before entering the regeneration tower 6, the acid gas is discharged from the top of the regeneration tower 6, and the regenerated lean liquid is discharged from the bottom of the regeneration tower 6;

[0048] (3) The lean liquid described in step (2) is cooled by the lean-rich liquid heat exchanger 5, pressurized by the lean liquid pump 11, and further cooled to 35° C. by the lean liquid air cooler 12 and the lean liquid aftercooler 13, and then returns to the absorption tower 1 to continue absorbing hydrogen sulfide in the raw acid gas;

[0049] (4) After the acid gas in step (2) is cooled to 35° C. by an acid gas air cooler 7 and an acid gas aftercooler 8, the concentrated acid gas with a high hydrogen sulfide concentration and condensed water enter a regeneration tower reflux tank 9. After separation, the acid gas is discharged from the top of the regeneration tower reflux tank 9, and the condensed water is pressurized by a regeneration tower reflux pump 10 from the bottom of the regeneration tower reflux tank 9 and then returned to the regeneration tower 6 as a reflux liquid;

[0050] (5) When the super-concentration line is not turned on, the acid gas (hydrogen sulfide concentration ≥ 50 mol%) discharged in step (4) all enters the main combustion furnace 15 of the sulfur recovery unit; when the super-concentration line is turned on, most of the acid gas (hydrogen sulfide concentration ≥ 60 mol%) discharged in step (4) enters the main combustion furnace 15 of the sulfur recovery unit, and at the same time, a small part of the acid gas (10 mol%-20 mol%) is used as concentrated gas and returns to the absorption tower 1 through the super-concentration line;

[0051] (6) The acid gas entering the sulfur recovery unit in step (5) is mixed with a specific proportion of air and burned in the main combustion furnace 15, and a Claus reaction occurs, whereby most of the hydrogen sulfide is converted into elemental sulfur and discharged from the rear of the main combustion furnace 15 along with the process gas;

[0052] (7) After the process gas in step (6) is cooled by the waste heat boiler 16 and the primary sulfur condenser 17, the condensed liquid sulfur is discharged from the bottom of the primary sulfur condenser 17, and the process gas is discharged from the top of the primary sulfur condenser 17;

[0053] (8) The process gas discharged from the upper part of the primary sulfur condenser 17 in step (7) is heated in the primary reheat furnace 18 and then enters the primary Claus reactor 19 to continue the reaction. The remaining hydrogen sulfide and sulfur dioxide in the process gas are further converted into elemental sulfur under the action of the catalyst. The formed process gas containing elemental sulfur is discharged from the lower part of the primary Claus reactor 19.

[0054] (9) In step (8), the process gas discharged from the lower part of the primary Claus reactor 19 is cooled by the secondary sulfur condenser 20, and the condensed liquid sulfur is discharged from the bottom of the secondary sulfur condenser 20, and the process gas is discharged from the upper part of the secondary sulfur condenser 20;

[0055] (10) The process gas discharged from the upper part of the secondary sulfur condenser 20 in step (9) is heated in the secondary reheat furnace 21 and then enters the secondary Claus reactor 22 to continue the reaction. The remaining hydrogen sulfide and sulfur dioxide in the process gas are further converted into elemental sulfur under the action of the catalyst. The formed process gas containing elemental sulfur is discharged from the lower part of the secondary Claus reactor 22.

[0056] (11) In step (10), the process gas discharged from the lower part of the secondary Claus reactor 22 is cooled by the tertiary sulfur condenser 23, and the condensed liquid sulfur is discharged from the bottom of the tertiary sulfur condenser 23, and the tail gas containing a small amount of sulfur dioxide and hydrogen sulfide is discharged from the upper part of the tertiary sulfur condenser 23 and enters the tail gas treatment unit;

[0057] (12) The tail gas from step (11) enters the online combustion furnace 24, is mixed with the combustion gas containing reducing gas generated by the sub-equivalent combustion of the fuel gas, and is heated to 280° C. The generated process gas is discharged from the rear of the online combustion furnace 24;

[0058] (13) The process gas discharged from the rear of the online combustion furnace 24 in step (12) enters from the top of the hydrogenation reactor 25. Under the action of the catalyst, the sulfur dioxide in the process gas is completely converted into hydrogen sulfide and discharged from the bottom of the hydrogenation reactor 25.

[0059] (14) In step (13), the process gas discharged from the bottom of the hydrogenation reactor 25 is cooled to 35° C. by the waste heat boiler 26 and the quenching tower 27, and the process gas after condensed water is separated is discharged from the top of the quenching tower 27;

[0060] (15) The process gas discharged from the top of the quench tower 27 in step (14) enters the lower middle part of the absorption tower 1, mixes with the raw acid gas entering from the bottom of the absorption tower 1 in step (1), and contacts with the lean liquid in countercurrent to absorb hydrogen sulfide, and finally the tail gas after absorption is discharged from the top of the absorption tower 1;

[0061] (16) The tail gas containing organic sulfur and trace amounts of hydrogen sulfide after absorption in step (1) and step (15) enters the tail gas incinerator 2, where the temperature is raised to 760° C., and at the same time, all the organic sulfur and hydrogen sulfide are converted into sulfur dioxide. The generated flue gas enters the flue gas waste heat boiler 3 connected to the rear of the tail gas incinerator 2, and after cooling to 300° C., the flue gas enters the alkali washing unit;

[0062] (17) The flue gas cooled to 300°C in step (16) enters the flue gas heat exchanger 28 and is cooled to 175°C, then enters the alkali scrubber 29, and is countercurrently contacted with the desulfurization liquid entering from the spray section and the upper part of the packing section of the alkali scrubber. The sulfur dioxide in the flue gas is rapidly absorbed by the desulfurization liquid to generate a sodium sulfite solution. The purified flue gas generated is discharged from the top of the alkali scrubber 29, enters the purified flue gas separator 31 to separate the carried liquid, and after being heated to 180°C by the flue gas heat exchanger 28, the flue gas is discharged into the atmosphere through the chimney 32. At this time, the sulfur dioxide content in the flue gas can be reduced to 50 mg / Nm 3 The following can meet the current stringent environmental protection standards. The generated desulfurization liquid is discharged from the bottom of the alkali washing tower 29;

[0063] (18) The desulfurized liquid discharged from the bottom of the alkali washing tower 29 in step (17) passes through the desulfurized liquid circulation pump 30, with a portion discharged as saline wastewater, a portion entering from the packing section of the alkali washing tower 29 as circulating liquid, and a portion entering from the spray section of the alkali washing tower 29 as circulating liquid.

[0064] The present invention needs to inject a certain concentration of sodium hydroxide solution from the bottom of the alkali washing tower 29, control the pH of the circulating liquid at the bottom of the tower to be between 6.2 and 8.2, ensure the reaction efficiency of the desulfurization liquid and sulfur dioxide, and thus ensure the absorption effect of the desulfurization liquid. The present invention needs to continuously inject a certain amount of water into the top of the alkali washing tower to ensure the liquid level of the tower and maintain the salt concentration in the desulfurization liquid. The present invention also needs to inject air into the bottom of the alkali washing tower 29 to oxidize the sodium sulfite solution generated by the reaction of sulfur dioxide and sodium hydroxide into sodium sulfate to ensure that the COD value of the sewage is not too high.

[0065] In a traditional Claus sulfur recovery unit, the air distribution in the main combustion furnace is often controlled to burn 1 / 3 of the hydrogen sulfide in the raw acid gas, thereby achieving the optimal chemical ratio of Claus reactants (i.e., hydrogen sulfide / sulfur dioxide = 2 / 1). However, when treating low-concentration hydrogen sulfide acid gas, this cannot maintain the temperature for stable combustion of the acid gas flame, resulting in the unit not being able to operate normally and smoothly. The principle of the present invention is to utilize the selective absorption characteristics of amine liquid for hydrogen sulfide, first introduce the acid gas into the amine liquid absorption tower, increase the concentration of hydrogen sulfide in the acid gas, thereby ensuring the smooth operation of the sulfur recovery unit. At the same time, after the acid gas is concentrated, the total amount of acid gas is greatly reduced compared to before concentration, which helps to optimize and reduce the equipment and pipeline size of the sulfur recovery unit. In addition, the present invention combines the two functions of acid gas concentration and sulfur recovery tail gas treatment in the same absorption tower, further simplifying the process flow.

[0066] For low hydrogen sulfide concentration acid gas containing organic sulfur, if only the above-mentioned process of first concentrating and then recovering is used, the organic sulfur in the acid gas cannot be absorbed by the amine liquid, and can only be converted into sulfur dioxide with the tail gas incineration and discharged into the atmosphere, resulting in problems such as substandard tail gas emissions and environmental pollution. The present invention organically combines the reduction-absorption tail gas treatment process and the alkali washing tail gas treatment process into an integral process, and absorbs sulfur dioxide by the reaction of sodium hydroxide solution and sulfur dioxide. The reaction formula involved is as follows:

[0067] 2NaOH+SO2→Na2SO3+H2O;

[0068] 2NaOH+CO2→Na2CO3+H2O;

[0069] Na2CO3+SO2→Na2SO3+CO2↑;

[0070] Na2SO3+SO2+H2O→2NaHSO3;

[0071] 2NaHSO3+NaOH→Na2SO3+H2O;

[0072] Na2SO3+1 / 2O2→Na2SO4.

[0073] The alkali washing method reacts quickly and thoroughly, and the flue gas treated by the present invention can meet the special emission limit requirements in the "Petroleum Refining Industry Pollutant Emission Standard" (GB13570-2015). First, the recyclable amine liquid is used to absorb hydrogen sulfide as a raw material for sulfur recovery, and the organic sulfur in the acid gas is burned into sulfur dioxide and then treated by the alkali washing method, which not only meets the environmental protection requirements, but also reduces the consumption of alkali liquid.

[0074] In the process of starting and shutting down, the traditional reduction absorption process often fails to meet the tail gas emission standards due to unavoidable conditions such as unstable operation of the device and non-operation of some equipment. However, since the present invention organically combines the alkali washing unit, the load of the alkali washing unit can be temporarily increased during the start-up and shutdown process, and the alkali solution consumption can be increased, so that the tail gas discharged into the atmosphere can meet the standards at all times, and has good operability and environmental friendliness.

Claims

1. A process system for treating low-concentration hydrogen sulfide acid gas containing organic sulfur, which comprises a sulfur recovery unit, a tail gas treatment unit with acid gas concentration function, and a flue gas alkali washing unit; The sulfur recovery unit is provided with a main combustion furnace (15) and a Claus treatment device, the upper outlet of the regeneration tower (6) is connected to the inlet of the main combustion furnace (15) through the regeneration tower reflux tank (9), the outlet of the main combustion furnace (15) is connected to the Claus treatment device, the gas outlet of the Claus treatment device is connected to the inlet of the online combustion furnace (24) of the tail gas treatment unit, and the Claus treatment device is provided with a sulfur condenser, a reheat furnace, and a Claus reactor; The tail gas treatment unit is provided with an online combustion furnace (24), a hydrogenation reactor (25), an absorption tower (1), a lean-rich liquid heat exchanger (5), a regeneration tower (6), and a regeneration tower reflux tank (9); the gas outlet of the Claus treatment device is connected to the inlet of the online combustion furnace (24); the outlet of the online combustion furnace (24) is connected to the inlet of the hydrogenation reactor (25); the outlet of the hydrogenation reactor (25) is connected to the middle and lower inlet of the absorption tower (1); the sulfur-containing tail gas enters the tail gas through the bottom inlet of the absorption tower (1); The gas treatment unit comprises a bottom outlet of an absorption tower (1) connected to an upper inlet of a regeneration tower (6) through a lean-rich liquid heat exchanger (5), an upper outlet of the regeneration tower (6) connected to an upper inlet of the regeneration tower (6) and an inlet of a main combustion furnace (15) of a sulfur recovery unit through a regeneration tower reflux tank (9), a bottom outlet of the regeneration tower (6) connected to an upper inlet of the absorption tower (1) through a lean-rich liquid heat exchanger (5), and an upper outlet of the absorption tower (1) connected to an inlet of a tail gas incinerator (2) of a flue gas alkali washing unit; The flue gas alkali washing unit is provided with a tail gas incinerator (2), a flue gas heat exchanger (28), an alkali washing tower (29), and a purified flue gas liquid separation tank (31); the upper outlet of the absorption tower (1) is connected to the inlet of the tail gas incinerator (2); the outlet of the tail gas incinerator (2) is connected to the inlet of the alkali washing tower (29) through the flue gas heat exchanger (28); the upper outlet of the alkali washing tower (29) is connected to the flue gas heat exchanger (28) through the purified flue gas liquid separation tank (31); the flue gas heat exchanger (28) leads to the atmosphere; and the liquid outlet of the purified flue gas liquid separation tank (31) is connected to the alkali washing tower (29).

2. The process system for treating low-concentration hydrogen sulfide acid gas containing organic sulfur according to claim 1, wherein: In the tail gas treatment unit, a rich liquid pump (4) is provided between the bottom outlet of the absorption tower (1) and the lean-rich liquid heat exchanger (5), an acid gas air cooler (7) and an acid gas aftercooler (8) are provided between the upper outlet of the regeneration tower (6) and the regeneration tower reflux tank (9), a lean liquid pump (11), a lean liquid air cooler (12), and a lean liquid aftercooler (13) are provided between the lean-rich liquid heat exchanger (5) and the upper inlet of the absorption tower (1), a regeneration tower reflux pump (10) is provided between the regeneration tower reflux tank (9) and the upper inlet of the regeneration tower (6); and a regeneration tower reboiler (14) is provided at the lower part of the regeneration tower (6); Preferably, in the sulfur recovery unit, a waste heat boiler (16) is provided between the outlet of the main combustion furnace (15) and the Claus treatment device, and the Claus treatment device comprises a primary sulfur condenser (17), a primary reheat furnace (18), a primary Claus reactor (19), a secondary sulfur condenser (20), a secondary reheat furnace (21), a secondary Claus reactor (22), and a tertiary sulfur condenser (23), and the gas outlet of the tertiary sulfur condenser (23) is connected to the inlet of the online combustion furnace (24) of the tail gas treatment unit; Preferably, a waste heat boiler (26) and a quenching tower (27) are provided between the outlet of the hydrogenation reactor (25) and the lower inlet of the absorption tower (1); Preferably, a flue gas waste heat boiler (3) is provided between the outlet of the tail gas incinerator (2) and the flue gas heat exchanger (28), the flue gas heat exchanger (28) is connected to a chimney (32), and the bottom outlet of the alkali washing tower (29) is connected to the upper inlet of the alkali washing tower (29) through a desulfurization liquid circulation pump (30).

3. The process system for treating low-concentration hydrogen sulfide acid gas containing organic sulfur according to claim 1 or 2, wherein: In the tail gas treatment unit, the acid gas is discharged from the top of the regeneration tower reflux tank (9), part of the acid gas enters the bottom of the absorption tower (1) through the super concentration line, and the remaining acid gas enters the main combustion furnace (15) of the sulfur recovery unit.

4. The process system for treating low-concentration hydrogen sulfide acid gas containing organic sulfur according to claim 1 or 2, wherein: The alkali washing tower (29) is provided with a spray section, and a packing section is provided on the upper part of the spray section.

5. A process for desulfurizing sulfur-containing tail gas using the process system for treating low-concentration hydrogen sulfide acid gas containing organic sulfur as described in any one of claims 1 to 4; Preferably, the sulfur-containing tail gas is concentrated by the tail gas treatment unit and then enters the sulfur recovery unit to undergo Claus reaction to separate sulfur and sulfur recovery tail gas. The sulfur recovery tail gas enters the tail gas treatment unit to undergo combustion and hydrogenation treatment in sequence, and the resulting gas enters the absorption tower of the tail gas treatment unit. In the tail gas treatment unit, the gas absorbed by the absorption tower enters the flue gas alkali washing unit, is incinerated and alkali washed in sequence, and the desulfurized gas is discharged.

6. The sulfur-containing tail gas desulfurization process according to claim 5, wherein: In the tail gas treatment unit, sulfur-containing tail gas is introduced from the bottom of the absorption tower (1), and is absorbed by the countercurrent absorption liquid to obtain rich liquid. The rich liquid passes through the rich liquid pump (4) and the lean-rich liquid heat exchanger (5) from the bottom of the absorption tower (1) in sequence and enters the regeneration tower (6). The lean liquid obtained after the regeneration treatment passes through the lean-rich liquid heat exchanger (5), the lean liquid pump (11), the lean liquid air cooler (12), and the lean liquid aftercooler (13) from the bottom of the regeneration tower (6) in sequence and enters the top of the absorption tower (1). The acid gas obtained after the regeneration treatment passes through the acid gas air cooler (7) and the acid gas aftercooler (8) from the top of the regeneration tower (6) in sequence and enters the regeneration tower reflux tank (9). The separated condensed water passes through the regeneration tower reflux pump (10) from the bottom of the regeneration tower reflux tank (9) and is pressurized before entering the regeneration tower (6). The acid gas is discharged from the top of the regeneration tower reflux tank (9) and enters the sulfur recovery unit.

7. The sulfur-containing tail gas desulfurization process according to claim 5, wherein: In the sulfur recovery unit, the acid gas discharged from the tail gas treatment unit enters the main combustion furnace (15) to undergo Claus reaction to generate process gas containing elemental sulfur. The process gas containing elemental sulfur is discharged from the main combustion furnace (15), passes through a waste heat boiler (16) and a primary sulfur condenser (17), is cooled to obtain liquid sulfur, and is discharged from the bottom of the primary sulfur condenser (17). The remaining process gas is discharged from the upper part of the primary sulfur condenser (17) and then enters a primary reheat furnace (18) and a primary Claus reactor (19) in sequence to generate process gas containing elemental sulfur. The process gas containing elemental sulfur is discharged from the primary Claus reactor. The sulfur is discharged from the lower part of the reactor (19) and enters the secondary sulfur condenser (20). Liquid sulfur is discharged from the bottom of the secondary sulfur condenser (20) after being cooled. The remaining process gas enters the secondary reheat furnace (21) and the secondary Claus reactor (22) from the upper part of the secondary sulfur condenser (20) to generate a process gas containing elemental sulfur. The process gas containing elemental sulfur is discharged from the lower part of the secondary Claus reactor (22) and enters the tertiary sulfur condenser (23). Liquid sulfur is discharged from the bottom of the tertiary sulfur condenser (23) after being cooled. The remaining tail gas is discharged from the upper part of the tertiary sulfur condenser (23) and enters the tail gas treatment unit.

8. The sulfur-containing tail gas desulfurization process according to claim 5, wherein: In the tail gas treatment unit, the tail gas discharged from the sulfur recovery unit enters the online combustion furnace (24) for combustion, enters the hydrogenation reactor (25) for hydrogenation reaction, passes through the waste heat boiler (26) and the quenching tower (27), and is finally discharged from the top of the quenching tower (27) and enters the middle and lower part of the absorption tower (1).

9. The sulfur-containing tail gas desulfurization process according to claim 5, wherein: In the flue gas alkali washing unit, the gas absorbed by the absorption tower enters the tail gas incinerator (2) from the top of the absorption tower (1) to generate flue gas, and the flue gas enters the flue gas waste heat boiler (3), the flue gas heat exchanger (28), and the alkali washing tower (29) in sequence. The flue gas after alkali washing is discharged from the top of the alkali washing tower (29), enters the purified flue gas liquid separator (31) and the flue gas heat exchanger (28) in sequence, and is finally discharged through the chimney (32). The desulfurization liquid is discharged from the bottom of the alkali washing tower (29) and enters the alkali washing tower (29) through the desulfurization liquid circulation pump (30) or is discharged as waste liquid. Preferably, the pH of the bottom circulating liquid at the bottom of the alkali washing tower (29) is 6.2-8.

2.

10. The desulfurization process of sulfur-containing tail gas according to claim 5, wherein: The hydrogen sulfide content in the sulfur-containing tail gas is ≤15 mol%; Preferably, the hydrogen sulfide concentration of the acid gas entering the sulfur recovery unit is ≥50 mol%; Preferably, the sulfur dioxide content in the flue gas finally discharged by the desulfurization method of sulfur-containing tail gas is ≤50mg / Nm 3 ; Preferably, the amine liquid used in the absorption tower in the tail gas treatment unit comprises, by weight, 97 parts of MDEA, 1-2 parts of phosphoric acid, 0.5-1 parts of corrosion inhibitor, 0.5-1 parts of defoaming agent, and water; Preferably, the mass concentration of the amine solution is 40-45%; Preferably, the corrosion inhibitor includes one or a combination of two or more of imidazolyl dithiourea, 2-amino-imidazolidinone, di(propynyloxymethyl)isopropylbenzyl ammonium chloride, and di(propynyloxymethyl)butylbenzyl ammonium chloride; Preferably, the defoaming agent comprises polyether-modified silicone oil.

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