A method for cascade desulfurization of refinery rich gas

Abstract

The present invention belongs to the field of petrochemical industry, and specifically relates to a method for cascade desulfurization of refinery rich gas. The method adopts a process of first mixing and desulfurizing the refinery rich gas and then separating and utilizing it, thereby improving the shortcomings of the existing process of first separating the rich gas and then desulfurizing it, making full use of the composition characteristics of the raw materials, improving the desulfurization rate, and producing ultra-low sulfur rich gas products. The total sulfur content of the refined dry gas is less than 0.5ppm, and there is no mercaptan sulfur; the total sulfur content of the refined liquefied gas is less than 1ppm, and the mercaptan sulfur content is less than 0.2ppm; and at the same time, equipment investment is reduced.

Description

Technical Field

[0001] The invention belongs to the field of petrochemical industry, and in particular relates to a method for cascade desulfurization of rich gas in a refinery. Background Art

[0002] In existing catalytic cracking / pyrolysis and delayed coking processes, the reaction products undergo fractional distillation to yield components such as rich gas, crude gasoline, diesel, and heavy oil. Rich gas contains hydrogen, methane, ethane, ethylene, propane, propylene, C4 hydrocarbons, and a small amount of C5 hydrocarbons. After separation and purification, it can be used as a feedstock for aromatic alkylation, olefin polymerization, etherification, and alkylation reactions. Rich gas also contains sulfide impurities such as hydrogen sulfide, carbonyl sulfide, methyl mercaptan, ethyl mercaptan, and dimethyl sulfide. These sulfides are not only highly corrosive to metals, plastics, and rubber materials, but also have a foul odor and are highly toxic. These sulfides require refined desulfurization to meet product quality requirements or meet downstream equipment requirements.

[0003] In traditional refinery processing, rich gas passes through an absorption stabilization system to obtain dry gas and liquefied gas products; dry gas can be used as ethylbenzene feed gas, hydrogen production feed gas or fuel gas after desulfurization of hydrogen by alcohol amine method, alkaline liquid desulfurization of mercaptans and MTBE desulfurization to separate propane, propylene, MTBE, ether-containing C4 and sulfur-containing heavy components. The sulfur-containing heavy components need to be further desulfurized by hydrogenation.

[0004] Traditional desulfurization processes are performed after the rich gas separation process. Therefore, active sulfur compounds such as COS, hydrogen sulfide, and mercaptans contained in the rich gas can cause corrosion in the absorption and stabilization system. Furthermore, the high pressure of the entire absorption and stabilization system poses safety concerns due to H2S leakage. Furthermore, the desulfurization process for dry gas and liquefied gas produces a large amount of waste liquid and waste residue. Current liquefied gas desulfurization processes also suffer from insufficient desulfurization depth, with the total sulfur content in the desulfurized liquefied gas below 5ppm. This results in an excessively high sulfur content in the product, necessitating further desulfurization before further use.

[0005] In the rich gas desulfurization process, the dry gas and liquefied gas desulfurization processes are performed separately. Alkanolamine desulfurization is generally used for crude dry gas, while a two-step process is typically used for crude liquefied gas: alcoholamine desulfurization in the first step, followed by alkaline desulfurization in the second step. Refined liquefied gas is then washed with water. The main drawbacks of alcoholamine desulfurization for dry and liquefied gas are the separate construction of alcoholamine desulfurization units, resulting in high equipment investment and large footprint. Furthermore, the high sulfur content of the desulfurized products, particularly carbonyl sulfide, prevents direct use of the dry gas and liquefied gas, requiring further carbonyl sulfide removal, such as dry gas adsorption conversion desulfurization and propylene adsorption conversion desulfurization. Multiple repetitions are required to remove a single sulfide compound, resulting in a large desulfurization system with low efficiency and high investment.

[0006] The most widely used technology for mercaptans removal in liquefied petroleum gas is the Merox extraction-oxidation deodorization technology. The basic principle of this technology is to thoroughly mix a NaOH solution containing sulfonated cobalt phthalocyanine with the liquefied gas in a tower, causing the oxygenated mercaptans to react with the NaOH to form sodium mercaptide, which is then transferred to an alkaline solution. The alkaline solution containing sodium mercaptide then enters a regeneration tower. Under the action of the sulfonated cobalt phthalocyanine catalyst, air oxidizes the sodium mercaptide into disulfide, allowing the alkaline solution to be regenerated and recycled. The main challenges of this process include: due to the large amount of caustic soda and catalyst used, the alkaline solution needs to be frequently replaced when the mercaptan content in the liquefied petroleum gas is high, resulting in large amounts of alkaline residue discharge and making it difficult to separate the disulfide from the oxidizing regeneration agent alkaline solution. Furthermore, when the total sulfur content in the feed gas is high, the desulfurization effect cannot meet the design requirements. Merichem Co. has developed a fiber-membrane contactor alkali treatment demercaptan technology, disclosed in patents US 4675100, US 4746494, and US 4753722. Its technical principles are similar to those of the Merox technology. Traditional static mixers and packed towers are gradually being replaced by fiber-membrane reactors. Because the alkali liquid membrane is smaller than the alkali droplet diameter, the mass transfer efficiency is increased by approximately 50 times, significantly improving the removal efficiency of mercaptans. Its advantages include increasing the contact area between the alkali and liquefied gas, reducing caustic soda consumption to a certain extent, and achieving higher extraction efficiency. However, both technologies consume alkali and result in large amounts of alkali residue discharge, placing significant pressure on the environment. Furthermore, fiber-membrane reactors are prone to clogging and increased pressure drop, which are particularly serious when processing coking liquefied gas, making the systems unable to operate for long periods of time.

[0007] CN1418937A discloses an industrial liquefied petroleum gas (LPG) refining method. This method uses a mercaptan removal catalyst placed in a fixed-bed reactor to convert mercaptans into LPG after hydrogen sulfide removal. Mercaptans react with trace amounts of oxygen remaining in the LPG (or an appropriate amount of oxygen artificially added) under the action of the catalyst to form disulfides. The disulfide-containing LPG is then rectified to obtain a refined LPG product at the top of the distillation tower and a disulfide-enriched mixture at the bottom of the distillation tower.

[0008] CN1702157A discloses a method for refining liquefied petroleum gas. The method involves adding a liquid oxygenating agent containing tert-butyl hydroperoxide as its active ingredient to the liquefied petroleum gas, which is then passed through a double-acting catalyst bed for mercaptan conversion. Under the action of the double-acting catalyst, the tert-butyl hydroperoxide decomposes to release active oxygen, which oxidizes the mercaptans into disulfides. The active ingredient of the double-acting catalyst is a manganese compound. Finally, the liquefied petroleum gas after the mercaptan conversion is subjected to gas fractionation and rectification, yielding refined liquefied petroleum gas and a heavy fraction enriched in disulfides.

[0009] To address the issue of alkali discharge, the methods disclosed in the aforementioned two patent applications both utilize a fixed-bed catalyst to convert mercaptans. While these methods avoid the use of caustic soda, they both require additional reactive oxygen species for mercaptan conversion. While introducing an appropriate amount of oxygen or an oxygenating agent can achieve relatively complete conversion of mercaptans in LPG by controlling the amount of oxygenating agent added, this requires direct contact between the oxygen and the LPG, posing significant safety concerns.

[0010] CN 103965984 discloses a method for catalytically removing mercaptans from liquefied petroleum gas. This method involves mixing liquefied petroleum gas with hydrogen before entering a fixed-bed reactor, where it contacts a catalyst loaded therein for a thioetherification reaction. Under the action of the catalyst, the mercaptans in the liquefied petroleum gas react with the active unsaturated hydrocarbons in the liquefied petroleum gas to form high-boiling-point sulfide compounds. This method suffers from the incomplete conversion of mercaptans, resulting in 1-20 ppm by weight of mercaptans in the refined liquefied gas. Further separation of the liquefied gas further increases the mercaptan content, which does not meet final product quality requirements, such as failing the doctoral test and copper sheet corrosion tests. Furthermore, fresh hydrogen needs to be supplied during the reaction, increasing the equipment footprint and investment.

[0011] CN 104194833 discloses a process for deep desulfurization of liquefied gas. The liquefied gas is mixed with hydrogen and then fed into a sulfur transfer reactor. The reactor has a hydrogen partial pressure of 0.2 to 2.0 MPa, a reaction temperature of 100 to 280°C, a liquid hourly space velocity of 1 to 20 h, and a hydrogen-to-oil ratio of 2 to 300 v / v. Sulfides in the liquefied gas are converted to high-boiling-point sulfides under the action of a sulfur transfer catalyst. However, this method requires fresh hydrogen during the reaction, increasing the equipment footprint and investment.

[0012] To address the alkali liquor discharge issue, the methods disclosed in the aforementioned three patent applications all utilize a fixed bed to convert mercaptans in the presence of hydrogen and a catalyst. However, the refined liquefied gas still contains 0.5-20 ppm by weight of mercaptans. As the liquefied gas is further separated, the mercaptan content is further enriched and increases. Furthermore, all methods require the addition of fresh hydrogen, increasing the plant footprint and investment. Summary of the Invention

[0013] The present invention addresses the deficiencies in the prior art and provides a method for cascaded desulfurization of refinery rich gas. The method adopts a process in which the refinery rich gas is first mixed and desulfurized and then separated and utilized, thereby improving the deficiencies of the prior process in which the rich gas is first separated and then desulfurized. The method fully utilizes the composition characteristics of the raw materials, improves the desulfurization rate, and produces ultra-low sulfur rich gas products. The total sulfur content of the refined dry gas is less than 0.5 ppm and is free of mercaptan sulfur; the total sulfur content of the refined liquefied gas is less than 1 ppm and the mercaptan sulfur content is less than 0.2 ppm. At the same time, the equipment investment is reduced.

[0014] The specific technical solution adopted in the present invention is:

[0015] A method for cascade desulfurization of rich gas, specifically, the refinery rich gas is pressurized by a first rich gas compressor, and then sequentially passes through a carbonyl sulfide hydrolysis tower, a hydrogen sulfide absorption tower, a second rich gas compressor, and a mercaptan conversion reactor for step-by-step sulfide conversion or removal; the rich gas is then separated into refined dry gas and sulfur-containing liquefied gas by an absorption distillation system, and the sulfur-containing liquefied gas is distilled into refined liquefied gas and sulfur-containing heavy components;

[0016] The absorption and distillation system consists of a condenser, an absorption tower and a distillation tower.

[0017] The more specific process flow is:

[0018] The rich gas separated by the catalytic cracking / cracking and coking unit fractionation tower is first pressurized by a first rich gas compressor, which can be a centrifugal compressor or a reciprocating compressor; the pressure of the pressurized rich gas is 0.3-1.0 MPa and the temperature is 30℃-120℃;

[0019] The pressurized rich gas enters the carbonyl sulfide hydrolysis tower, where the carbonyl sulfide contained in the rich gas is hydrolyzed into CO2 and H2S under the action of the catalyst. Carbon dioxide and hydrogen sulfide are adsorbed and removed in the subsequent absorption tower. The specific reaction equation is as follows:

[0020] COS+H2O→CO2+H2S;

[0021] According to the reaction principle, water participates in the reaction process, so the water content in the rich gas is controlled to be greater than 20ppm and n(H2O):n(COS) ≥3:1; the catalyst is composed of a carrier and an active component, the carrier is composed of one or more of SiO2, Al2O3, X-type molecular sieve, Y-type molecular sieve, A-type molecular sieve, and granular activated carbon, and the carrier content is 80-95wt%; the active component is one or more of sodium hydroxide, calcium hydroxide, potassium hydroxide, barium hydroxide, ammonia water, sodium nitrate, and potassium carbonate, and the active component content is 5-20wt%;

[0022] The operating temperature of the carbonyl sulfide hydrolysis tower is 35℃-100℃, the operating pressure is 0.3-1.0Mpa, and the gas volume space velocity is 1000-8000h -1 ; Can be designed as single tower or multiple towers, can be designed in series or parallel.

[0023] The rich gas after removal of carbonyl sulfide enters the hydrogen sulfide absorption tower, where carbon dioxide and hydrogen sulfide in the rich gas are removed through countercurrent contact with the alcoholamine liquid. The alcoholamine rich liquid after adsorption saturation enters the alcoholamine liquid regeneration system to separate hydrogen sulfide and carbon dioxide. The regenerated alcoholamine liquid can be recycled.

[0024] The operating conditions of the hydrogen sulfide absorption tower are as follows: reaction temperature of 40-60°C, reaction pressure of 0.3-1.0 MPa, and mass ratio of alcoholamine liquid to rich gas of 2-7:1; the alcoholamine liquid is composed of water and active components, wherein the active components are composed of a desulfurizer and a defoamer, wherein the desulfurizer is selected from any one of diethanolamine, diisopropanolamine, N-methyldiethanolamine, and N,N-dimethylacetamide; the defoamer is tributyl phosphate or dimethyl silicone oil; the weight ratio of the desulfurizer to the defoamer is (95-99.5):(0.5-15), and the content of the active component is 15-40% of the mass of the alcoholamine liquid.

[0025] The rich gas after the hydrogen sulfide absorption tower is pressurized by the second rich gas compressor and then enters the mercaptan conversion reactor. Under the action of the conversion catalyst, low molecular weight mercaptans such as methyl mercaptan and ethyl mercaptan are converted into sulfides and disulfides with higher boiling points.

[0026] The reaction temperature of the above reactor is 80-200°C, the reaction pressure is 1.40-2.60 MPa, and the volume space velocity is 500-4000 h -1 The conversion catalyst consists of a carrier and an active component; the carrier is composed of one or more of SiO2, Al2O3, TiO2, β-type molecular sieve, and Y-type molecular sieve granular activated carbon, and the active component is composed of one or more of CoS, NiS, MoS3, and WS3, and the content of the active component accounts for 10-30% of the mass of the conversion catalyst.

[0027] The rich gas from the conversion reactor enters the absorption distillation system, which separates the rich gas into refined dry gas and refined liquefied gas. The specific process is as follows:

[0028] The rich gas coming out of the conversion reactor has a pressure of 1.40-2.60 MPa and a temperature of 100-200°C. The rich gas is first sent to the condenser to cool down to 40-45°C. The cooled rich gas is separated into lean gas (mainly C1-C2, a small amount of C3-C4) and crude liquefied gas (mainly C3-C4, a small amount of C1-C2 and C5). + );

[0029] The lean gas and wash oil enter the dry gas absorption tower in reverse, and the heavy components in the lean gas are absorbed and separated in the dry gas absorption tower. Refined dry gas is obtained after separation in the dry gas absorption tower. The operating pressure of the dry gas absorption tower is 1.20-1.60Mpa, and the operating temperature is 40℃-45℃;

[0030] The wash oil is one or more of petroleum ether, hydrogenated naphtha, reformed raffinate, reformed tops, and catalytic gasoline; the mass ratio of lean gas to wash oil is 1:1-3;

[0031] Through the action of washing oil, a small amount of C3-C4 in the lean gas is absorbed to obtain refined dry gas;

[0032] The crude liquefied gas enters the distillation tower for refining to remove a small amount of C1-C2 and C5 + Components, to obtain refined liquefied gas, the distillation tower operating pressure 1.30-2.00Mpa, operating temperature 100 ℃ -180 ℃;

[0033] A small amount of C1-C2 is discharged from the top of the distillation tower and can be mixed with the above-mentioned refined dry gas; C3-C4 components are discharged from the middle of the distillation tower as refined liquefied gas, and C5 + The components are discharged from the bottom of the distillation tower, and the high boiling point sulfides, disulfides, etc. in the crude liquefied gas are discharged along with C5 + The components are discharged from the bottom of the distillation tower, thereby achieving the removal of sulfur-containing components.

[0034] The wash oil produced in the process of refining dry gas can be separated from the C3-C4 components by passing through a wash oil refining tower. The refined wash oil can be recycled. The operating pressure of the wash oil refining tower is 0.2-0.6Mpa and the operating temperature is 50℃-90℃.

[0035] After the above-mentioned treatment process, the refined dry gas has a total sulfur content of less than 0.5ppm and is mercaptan-free, making it suitable as a feedstock for benzene alkylation and hydrogen production. The refined liquefied gas has a total sulfur content of less than 1ppm and a mercaptan-sulfur content of less than 0.2ppm, allowing it to be directly separated into propane and propylene products. The C4 component serves as a high-quality feedstock for etherification and alkylation. Subsequent processing of these components eliminates the need for additional desulfurization steps, such as desulfurization of MTBE heavy components or post-etherification C4 refining and desulfurization.

[0036] Compared with the prior art, the advantages of the present invention are:

[0037] 1. Traditional rich gas processing involves separation followed by separate desulfurization. Active sulfides such as COS, hydrogen sulfide, and mercaptans contained in rich gas can cause corrosion in the rich gas separation system. Multiple units are required to completely remove a single sulfide species, resulting in a large and inefficient desulfurization system. This fundamentally addresses the issue of H2S leakage in absorption and stabilization systems. This invention, however, employs a mixed desulfurization followed by separation approach. This allows for the complete removal of each sulfide species in a single step, reducing corrosion and clogging in the separation system while also reducing the number of desulfurization units and investment.

[0038] 2. Traditional dry gas and liquefied gas desulfurization processes generate large amounts of waste liquid and waste residue. Current liquefied gas desulfurization processes also suffer from insufficient desulfurization depth, resulting in excessively high sulfur content in the product (typically mercaptan sulfur <5 ppm, total sulfur <25 ppm), requiring further desulfurization before further use. The refined dry gas produced by this technical solution has a total sulfur content of <0.5 ppm and is mercaptan-free; the refined liquefied gas has a total sulfur content of <1 ppm and a mercaptan sulfur content of <0.2 ppm. No additional desulfurization process is required for subsequent processing of the components.

[0039] 3. Although the mercaptan conversion technologies disclosed in CN 103965984 and CN 104194833 avoid the use of caustic soda, they both require additional reactive oxygen species or hydrogen, posing significant safety concerns. The present invention fully utilizes the hydrogen component contained in the rich gas feedstock, eliminating the need for additional hydrogen and reducing equipment footprint and investment. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a process flow chart of the rich gas cascade desulfurization method of the present invention;

[0041] In the figure: 1 is the first rich gas compressor; 2 is the carbonyl sulfide hydrolysis tower; 3 is the hydrogen sulfide absorption tower; 4 is the second rich gas compressor; 5 is the mercaptan conversion reactor; 6 is the condenser; 7 is the dry gas absorption tower; 8 is the distillation tower; 9 is the wash oil refining tower. DETAILED DESCRIPTION

[0042] The following is a further detailed description of the present invention through specific embodiments in conjunction with the accompanying drawings. However, this should not be construed as limiting the scope of the present invention to the following examples. All technologies implemented based on the above-mentioned contents of the present invention fall within the scope of the present invention. Unless otherwise specified, the raw materials used in the following examples are commercially available products.

[0043] The rich gas to be treated in the following examples is the rich gas obtained by coarse separation in the fractionation tower of a catalytic cracking unit of a local refinery in Shandong Province. The specific composition is shown in Table 1:

[0044] Serial number Material Name Rich Rich Two Rich Three 1 hydrogen 12.87% (v / v) 15.65% (v / v) 8.40% (v / v) 2 <![CDATA[C 1-4 Hydrocarbons]]> margin margin margin 3 <![CDATA[C5 + Hydrocarbons]]> 6.37% (v / v) 10.22% (v / v) 4.91% (v / v) 4 oxygen 0.22% (v / v) 0.11% (v / v) 0.00% (v / v) 5 Nitrogen 2.52% (v / v) 1.43% (v / v) 1.15% (v / v) 6 CO 0.01% (v / v) 0.00% (v / v) 0.00% (v / v) 7 <![CDATA[CO2]]> 1.73% (v / v) 1.67% (v / v) 0.19% (v / v) 8 hydrogen sulfide 5.26% (v / v) 1.87% (v / v) 4.92% (v / v) 9 carbonyl sulfide <![CDATA[53mg / m 3 ]]> <![CDATA[26mg / m 3 ]]> <![CDATA[155mg / m 3 ]]> 10 Methyl mercaptan <![CDATA[768mg / m 3 ]]> <![CDATA[347mg / m 3 ]]> <![CDATA[1568mg / m 3 ]]> 11 Ethyl mercaptan <![CDATA[94mg / m 3 ]]> <![CDATA[13mg / m 3 ]]> <![CDATA[203mg / m 3 ]]> 12 Other organic sulfur <![CDATA[25mg / m 3 ]]> <![CDATA[14mg / m 3 ]]> <![CDATA[74mg / m 3 ]]> 13 water <![CDATA[70mg / m 3 ]]> <![CDATA[55mg / m 3 ]]> <![CDATA[170mg / m 3 ]]>

[0045] Processing device uses Figure 1 The specific processes used in the device shown are the following embodiments 1-3, corresponding to enriched gases one to three respectively.

[0046] Example 1

[0047] A method for cascade desulfurization of rich gas, the specific steps are as follows:

[0048] The raw material rich gas is pressurized to 0.60-0.75Mpa by a single-stage reciprocating compressor, and the temperature after pressurization is 80℃-90℃; the pressurized rich gas enters the carbonyl sulfide hydrolysis tower, and the carbonyl sulfide contained in the rich gas is hydrolyzed into CO2 and H2S under the action of the catalyst. Carbon dioxide and hydrogen sulfide are adsorbed and removed in the subsequent absorption tower. According to the reaction principle, water participates in the reaction process, and the water content in the rich gas is controlled to 80-95ppmv, ensuring that n(H2O):n(COS) ≥3:1. The operating temperature of the carbonyl sulfide hydrolysis tower is 70℃-80℃, the operating pressure is 0.60-0.70Mpa, and the gas volume space velocity is 2000h -1;Adopt single tower design.

[0049] The carbonyl sulfide hydrolyzer consists of a carrier and an active component, wherein the carrier content is 90.5% by mass; the carrier is composed of Al2O3 and X-type molecular sieve, wherein the mass fraction of Al2O3 is 85%; and the active component is sodium nitrate.

[0050] The rich gas after removal of carbonyl sulfide enters the hydrogen sulfide absorption tower, where carbon dioxide and hydrogen sulfide in the rich gas are removed through countercurrent contact with the alcoholamine liquid. The alcoholamine rich liquid after adsorption saturation enters the alcoholamine liquid regeneration system to separate hydrogen sulfide and carbon dioxide. The regenerated alcoholamine liquid can be recycled.

[0051] The hydrogen sulfide adsorption tower operates at a reaction temperature of 45°C-55°C and a pressure of 0.50-0.60 MPa. The ammonia-rich liquid after hydrogen sulfide adsorption is regenerated, dehydrogenated, and recycled. The mass ratio of alcoholamine liquid to rich gas is 4.5:1. The alcoholamine liquid consists of water and an active component, consisting of 29.8% by mass of N-methyldiethanolamine and 0.3% dimethyl silicone oil, with the remainder being water.

[0052] The rich gas after the hydrogen sulfide absorption tower enters the mercaptan conversion reactor. Under the action of the conversion catalyst, low molecular weight mercaptans such as methyl mercaptan and ethyl mercaptan are converted into sulfides and disulfides with higher boiling points.

[0053] The reaction temperature of the reactor is 120℃-140℃, the reaction pressure is 1.7-1.8Mpa, and the volume space velocity is 2000h -1 The conversion catalyst consists of a support and active components. The active component content is 22.6% by mass. The active components are composed of CoS, NiS, and MoS3, accounting for 6.2%, 55.8%, and 38% of the active components, respectively. The support is composed of Al2O3 and TiO2, of which Al2O3 accounts for 85% of the support by mass.

[0054] The rich gas after treatment in the mercaptan conversion reactor has the following specific composition as shown in Table 2:

[0055] Serial number Material Name Rich Rich Two Rich Three 1 hydrogen 12.86% (v / v) 15.63% (v / v) 8.30% (v / v) 2 <![CDATA[C 1-4 Hydrocarbons]]> margin margin margin 3 <![CDATA[C5 + Hydrocarbons]]> 6.37% (v / v) 10.22% (v / v) 4.91% (v / v) 4 oxygen 0.22% (v / v) 0.11% (v / v) 0.00% (v / v) 5 Nitrogen 2.52% (v / v) 1.43% (v / v) 1.15% (v / v) 6 CO 0.00% (v / v) 0.00% (v / v) 0.00% (v / v) 7 <![CDATA[CO2]]> 8ppmv 5ppmv 3ppmv 8 hydrogen sulfide 0.13ppmv 0.15ppmv 0.1ppmv 9 carbonyl sulfide 0.1ppmv 0.15ppmv 0.1ppmv 10 Methyl mercaptan 0ppmv 0.1ppmv 0.1ppmv 11 Ethyl mercaptan 0.1ppmv 0ppmv 0.15ppmv 12 dimethyl sulfide <![CDATA[538mg / m 3 ]]> <![CDATA[279mg / m 3 ]]> <![CDATA[1007mg / m 3 ]]> 13 dimethyl disulfide <![CDATA[342mg / m 3 ]]> <![CDATA[127mg / m 3 ]]> <![CDATA[535mg / m 3 ]]> 14 Other organic sulfur <![CDATA[27mg / m 3 ]]> <![CDATA[54mg / m 3 ]]> <![CDATA[39mg / m 3 ]]>

[0056] The rich gas coming out of the conversion reactor has a pressure of 1.70-1.80 MPa and a temperature of 120-140°C. The rich gas is first sent to the condenser to cool down to 40-45°C. The cooled rich gas is separated into lean gas (mainly C1-C2, a small amount of C3-C4) and crude liquefied gas (mainly C3-C4, a small amount of C1-C2 and C5 + );

[0057] The lean gas and the wash oil enter the dry gas absorption tower in reverse flow and are absorbed and separated in the dry gas absorption tower to obtain refined dry gas;

[0058] The washing oil used is reforming raffinate oil, the operating pressure of the absorption tower is 1.20-1.60Mpa, the operating temperature is 40℃-45℃, and the mass ratio of lean gas to washing oil is 1:2.5; through the action of washing oil, a small amount of C3-C4 in the lean gas is absorbed to obtain refined dry gas.

[0059] The crude liquefied gas enters the distillation tower for refining to remove a small amount of C1-C2 and C5 + The components are used to obtain refined liquefied gas. The operating pressure of the distillation tower is 1.30-1.80 MPa and the operating temperature is 100℃-180℃. A small amount of C1-C2 is discharged from the top of the distillation tower and can be mixed with the above-mentioned refined dry gas. The C3-C4 components are discharged from the middle of the distillation tower as refined liquefied gas, and C5 + The components are discharged from the bottom of the distillation tower, and the high boiling point sulfides, disulfides, etc. in the crude liquefied gas are discharged along with C5 + The components are discharged from the bottom of the distillation tower, thereby achieving the removal of sulfur-containing components.

[0060] The wash oil produced in the process of refining dry gas can be separated from the C3-C4 components by passing through a wash oil refining tower. The refined wash oil can be recycled. The operating pressure of the wash oil refining tower is 0.2-0.3Mpa and the operating temperature is 85℃-90℃.

[0061] The refined dry gas has a total sulfur content of 0.3 ppm and is mercaptan-free, making it suitable for use as a feedstock for dry gas production of ethylbenzene. The refined liquefied petroleum gas has a total sulfur content of 0.7 ppm and a mercaptan-free content of 0.11 ppm. The refined liquefied petroleum gas can be further separated into propane and propylene products, with the C4 component serving as a high-quality feedstock for etherification and alkylation. The subsequent processing of these components eliminates the need for additional desulfurization.

[0062] Example 2

[0063] A method for cascade desulfurization of rich gas, the specific steps are as follows:

[0064] The raw material rich gas 2 is pressurized to 0.40-0.55Mpa by a single-stage reciprocating compressor, and the temperature after pressurization is 50℃-60℃; the pressurized rich gas 1 enters the carbonyl sulfide hydrolysis tower, and the carbonyl sulfide contained in the rich gas 1 is hydrolyzed into CO2 and H2S under the action of the catalyst. Carbon dioxide and hydrogen sulfide are adsorbed and removed in the subsequent absorption tower. According to the reaction principle, water participates in the reaction process, and the water content in the rich gas is controlled to 50-65ppmv, ensuring that n(H2O):n(COS) ≥3:1. The operating temperature of the carbonyl sulfide hydrolysis tower is 50℃-60℃, the operating pressure is 0.40-0.55Mpa, and the gas volume space velocity is 6000h -1The single-tower design is used. The carbonyl sulfide hydrolyzer consists of a carrier and an active component, with the carrier comprising 92% by mass. The carrier is composed of Al2O3 and SiO2, with Al2O3 comprising 70% by mass. The active components are calcium hydroxide and sodium hydroxide, with calcium hydroxide comprising 20% ​​by mass.

[0065] After carbonyl sulfide removal, the rich gas enters the hydrogen sulfide absorption tower, where it undergoes countercurrent contact with an alcoholamine solution to remove carbon dioxide and hydrogen sulfide. The saturated alcoholamine-rich solution then enters the alcoholamine regeneration system, where hydrogen sulfide and carbon dioxide are separated. The regenerated alcoholamine solution can be recycled. The hydrogen sulfide absorption tower operates at a reaction temperature of 40°C-50°C and a pressure of 0.35-0.50 MPa. The ammonia-rich solution, which has absorbed hydrogen sulfide, is regenerated and dehydrogenated before being recycled. The mass ratio of alcoholamine solution to rich gas is 3:1. The alcoholamine solution consists of water and an active ingredient, consisting of 25.2% N-methyldiethanolamine and 1.0% N,N-dimethylacetamide (by mass), with the remainder being water.

[0066] The rich gas after the hydrogen sulfide absorption tower enters the mercaptan conversion reactor. Under the action of the conversion catalyst, low molecular weight mercaptans such as methyl mercaptan and ethyl mercaptan are converted into sulfides and disulfides with higher boiling points. The reaction temperature of the reactor is 100℃-120℃, the reaction pressure is 1.40-1.60Mpa, and the volume space velocity is 4000h -1 The conversion catalyst consists of a support and an active component, with the active component content being 19.8% by mass. The active component is composed of NiS and MoS3, accounting for 65% and 35% of the active component, respectively. The support is Al2O3 and β-zeolite, with Al2O3 accounting for 88% of the support by mass.

[0067] The specific composition of the rich gas after treatment in the mercaptan conversion reactor is shown in Table 2 in Example 1.

[0068] The rich gas coming out of the conversion reactor has a pressure of 1.40-1.60 MPa and a temperature of 100-120°C. The rich gas is first sent to the condenser to cool down to 40-45°C. The cooled rich gas is separated into lean gas (mainly C1-C2, a small amount of C3-C4) and crude liquefied gas (mainly C3-C4, a small amount of C1-C2 and C5). + );

[0069] The lean gas and the wash oil enter the dry gas absorption tower in reverse flow and are absorbed and separated in the dry gas absorption tower to obtain refined dry gas;

[0070] The washing oil used is petroleum ether, the operating pressure of the absorption tower is 1.20-1.60Mpa, the operating temperature is 40℃-45℃, and the mass ratio of lean gas to washing oil is 1:3; through the action of the washing oil, a small amount of C3-C4 in the lean gas is absorbed to obtain refined dry gas.

[0071] The crude liquefied gas enters the distillation tower for refining to remove a small amount of C1-C2 and C5 + Components are obtained to obtain refined liquefied gas. The operating pressure of the distillation tower is 1.30-1.60Mpa and the operating temperature is 150℃-160℃. A small amount of C1-C2 is discharged from the top of the distillation tower and can be mixed with the above-mentioned refined dry gas; C3-C4 components are discharged from the middle of the distillation tower as refined liquefied gas, and C5 + The components are discharged from the bottom of the distillation tower, and the high boiling point sulfides, disulfides, etc. in the crude liquefied gas are discharged along with C5 + The components are discharged from the bottom of the distillation tower, thereby achieving the removal of sulfur-containing components.

[0072] The wash oil produced during the dry gas refining process can be separated from the C3-C4 components by passing it through a wash oil refining tower. The refined wash oil is then recycled. The wash oil refining tower operates at a pressure of 0.25-0.30 MPa and a temperature of 75°C-85°C. The refined dry gas has a total sulfur content of 0.3 ppm and is mercaptan-free, suitable for use as industrial fuel. The refined liquefied petroleum gas has a total sulfur content of 0.5 ppm, including 0.07 ppm mercaptan, with no detectable levels of hydrogen sulfide or carbonyl sulfide. The refined liquefied petroleum gas can be further separated into propane and propylene products, with the C4 component serving as a high-quality feedstock for etherification and alkylation. The subsequent processing of these components eliminates the need for an additional desulfurization stage.

[0073] Example 3

[0074] A method for cascade desulfurization of rich gas, the specific steps are as follows:

[0075] The raw material rich gas 3 is pressurized to 0.80-0.95Mpa by a single-stage reciprocating compressor, and the temperature after pressurization is 95℃-110℃; the pressurized rich gas 3 enters the carbonyl sulfide hydrolysis tower, and the carbonyl sulfide contained in the rich gas 1 is hydrolyzed into CO2 and H2S under the action of the catalyst. Carbon dioxide and hydrogen sulfide are adsorbed and removed in the subsequent absorption tower. According to the reaction principle, water participates in the reaction process, and the water content in the rich gas is controlled to 200-230ppmv, ensuring that n(H2O):n(COS) ≥3:1. The operating temperature of the carbonyl sulfide hydrolysis tower is 80℃-95℃, the operating pressure is 0.70-0.85Mpa, and the gas volume space velocity is 2000h -1The reactor uses a dual-tower series design. The carbonyl sulfide hydrolyzer consists of a carrier and an active component, with the carrier comprising 85.0% by mass. The carrier is composed of Al2O3 and Y-type molecular sieve, with Al2O3 comprising 80% by mass. The active components are potassium hydroxide and potassium carbonate, with potassium hydroxide comprising 30%.

[0076] After carbonyl sulfide removal, the rich gas enters the hydrogen sulfide absorption tower, where it undergoes countercurrent contact with an alcoholamine solution to remove carbon dioxide and hydrogen sulfide. The saturated alcoholamine-rich solution then enters the alcoholamine regeneration system, where hydrogen sulfide and carbon dioxide are separated. The regenerated alcoholamine solution can be recycled. The hydrogen sulfide absorption tower operates at a reaction temperature of 55°C-60°C and a pressure of 0.65-0.70 MPa. The ammonia-rich solution, which has absorbed hydrogen sulfide, is regenerated and dehydrogenated before being recycled. The mass ratio of alcoholamine solution to rich gas is 6:1. The alcoholamine solution consists of water and an active ingredient, consisting of 33.5% N-methyldiethanolamine and 1.0% N,N-dimethylacetamide (by mass), with the remainder being water.

[0077] The rich gas after the hydrogen sulfide absorption tower enters the mercaptan conversion reactor. Under the action of the conversion catalyst, low molecular weight mercaptans such as methyl mercaptan and ethyl mercaptan are converted into sulfides and disulfides with higher boiling points. The reaction temperature of the reactor is 140℃-160℃, the reaction pressure is 2.2-2.4Mpa, and the volume space velocity is 2500h -1 The conversion catalyst consists of a carrier and active components, with the active component content being 22.3% by mass and the rest being an Al2O3 carrier; the active components are composed of NiS, MoS3 and WS3, with mass proportions of 55%, 24% and 21% of the active components respectively.

[0078] The specific composition of the rich gas after treatment in the mercaptan conversion reactor is shown in Table 2 in Example 1.

[0079] The rich gas coming out of the conversion reactor has a pressure of 2.20-2.40 MPa and a temperature of 140-160°C. The rich gas is first sent to the condenser to cool down to 40-45°C. The cooled rich gas is separated into lean gas (mainly C1-C2, a small amount of C3-C4) and crude liquefied gas (mainly C3-C4, a small amount of C1-C2 and C5 + );

[0080] The lean gas and the wash oil enter the dry gas absorption tower in reverse flow and are absorbed and separated in the dry gas absorption tower to obtain refined dry gas;

[0081] The washing oil used is catalytic gasoline, the operating pressure of the dry gas absorption tower is 1.20-1.60Mpa, the operating temperature is 40℃-45℃, and the mass ratio of lean gas to washing oil is 1:2; through the action of the washing oil, a small amount of C3-C4 in the lean gas is absorbed to obtain refined dry gas.

[0082] Through the action of washing oil, a small amount of C3-C4 in the lean gas is absorbed to obtain refined dry gas;

[0083] The crude liquefied gas enters the distillation tower for refining to remove a small amount of C1-C2 and C5 + Components are obtained to obtain refined liquefied gas. The operating pressure of the distillation tower is 1.60-2.00Mpa and the operating temperature is 170℃-180℃. A small amount of C1-C2 is discharged from the top of the distillation tower and can be mixed with the above-mentioned refined dry gas; C3-C4 components are discharged from the middle of the distillation tower as refined liquefied gas, and C5 + The components are discharged from the bottom of the distillation tower, and the high boiling point sulfides, disulfides, etc. in the crude liquefied gas are discharged along with C5 + The components are discharged from the bottom of the distillation tower, thereby achieving the removal of sulfur-containing components.

[0084] The wash oil produced in the process of refining dry gas can be separated from the C3-C4 components by passing through a wash oil refining tower. The refined wash oil can be recycled. The operating pressure of the wash oil refining tower is 0.3-0.4Mpa and the operating temperature is 80℃-90℃.

[0085] The refined dry gas has a total sulfur content of 0.48 ppm and is used as a feedstock for hydrogen production from dry gas. The refined liquefied petroleum gas has a total sulfur content of 0.9 ppm, including 0.15 ppm of mercaptan sulfur. Neither hydrogen sulfide nor carbonyl sulfide is detected. The refined liquefied petroleum gas can be further separated into propane and propylene products, with the C4 component serving as a high-quality feedstock for etherification and alkylation. The subsequent processing of these components eliminates the need for additional desulfurization.

[0086] Comparative Example 1

[0087] In traditional refinery processing, the enriched gas first passes through a complex absorption and stabilization system to produce crude dry gas and crude liquefied gas products. The crude dry gas undergoes alcohol amine desulfurization, while the crude liquefied gas undergoes alcohol amine desulfurization and alkaline desulfurization. Using enriched gas 1 as the raw material, the refined dry gas after traditional processing has a sulfur content of 3.1 ppm, including 0.8 ppm hydrogen sulfide and 2.3 ppm carbonyl sulfide. The refined liquefied gas contains 8.5 ppm sulfur, including 1.2 ppm mercaptan sulfur, 0.8 ppm carbonyl sulfide, and 6.5 ppm unknown sulfides.

[0088] By comparison, it can be seen that the product finally obtained by treating the rich gas with the existing technology has a high sulfur content, which is difficult to meet the requirements of subsequent use and requires further refining.

[0089] For ordinary technicians in this field, the specific embodiments are only illustrative descriptions of the present invention. It is obvious that the specific implementation of the present invention is not limited to the above-mentioned methods. As long as various non-substantial improvements are made using the method concepts and technical solutions of the present invention, or the concepts and technical solutions of the present invention are directly applied to other occasions without improvement, they are all within the scope of protection of the present invention.

Claims

1. A method for cascade desulfurization of refinery rich gas, characterized by: The specific steps are as follows: After being pressurized by the first rich gas compressor, the refinery's rich gas is sequentially passed through a carbonyl sulfide hydrolysis tower, a hydrogen sulfide absorption tower, a second rich gas compressor, and a mercaptan conversion reactor for sulfide conversion or removal. The rich gas is then separated into refined dry gas and sulfur-containing crude liquefied gas through an absorption distillation system. The sulfur-containing crude liquefied gas is then distilled into refined liquefied gas and sulfur-containing heavy components. The absorption and distillation system consists of a condenser, a dry gas absorption tower and a distillation tower; The rich gas is the rich gas obtained by separation in a fractionating tower of a catalytic cracking / cracking or coking unit; The rich gas after removal of carbonyl sulfide enters the hydrogen sulfide absorption tower, where carbon dioxide and hydrogen sulfide in the rich gas are removed by countercurrent contact with alcohol amine liquid; The rich gas after the hydrogen sulfide absorption tower is pressurized by the second rich gas compressor and then enters the mercaptan conversion reactor. Under the action of the conversion catalyst, low molecular weight mercaptans are converted into sulfides and disulfides with higher boiling points. The rich gas from the mercaptan conversion reactor is sent to a condenser to be cooled to 40°C-45°C; the cooled rich gas is separated into lean gas and crude liquefied gas through gas-liquid separation; the lean gas and wash oil are reversely fed into a dry gas absorption tower, where they are absorbed and separated, and refined dry gas is obtained through separation in the dry gas absorption tower; the crude liquefied gas is fed into a distillation tower for refining to remove a small amount of C1-C2 and C5+ components contained therein, thereby obtaining refined liquefied gas.

2. The method for cascade desulfurization of refinery rich gas according to claim 1, characterized in that: The specific process is: The rich gas is first pressurized by the first rich gas compressor, which can be a centrifugal compressor or a reciprocating compressor; the pressure of the rich gas after pressurization is 0.3-1.0Mpa, and the temperature is 30℃-120℃; The pressurized rich gas enters the carbonyl sulfide hydrolysis tower, where the carbonyl sulfide contained in the rich gas is hydrolyzed into CO2 and H2S under the action of the catalyst. The carbon dioxide and hydrogen sulfide are absorbed and removed in the subsequent hydrogen sulfide absorption tower. The saturated alcoholamine rich liquid enters the alcoholamine liquid regeneration system to separate hydrogen sulfide and carbon dioxide. The regenerated alcoholamine liquid can be recycled; The rich gas coming out of the mercaptan conversion reactor enters the absorption distillation system, which separates the rich gas into refined dry gas and refined liquefied gas.

3. The method for cascade desulfurization of refinery rich gas according to claim 2, characterized in that: When the pressurized rich gas enters the carbonyl sulfide hydrolysis tower, the water content in the rich gas must be controlled to be greater than 20ppm and the ratio of n(H2O):n(COS) must be ≥3:

1. The catalyst is composed of a carrier and an active component. The carrier is one or more of SiO2, Al2O3, X-type molecular sieve, Y-type molecular sieve, A-type molecular sieve, and granular activated carbon, and the carrier content is 80-95wt%. The active component is one or more of sodium hydroxide, calcium hydroxide, potassium hydroxide, barium hydroxide, ammonia water, sodium nitrate, and potassium carbonate, and the active component content is 5-20wt%.

4. The method for cascade desulfurization of refinery rich gas according to claim 2, characterized in that: The operating temperature of the carbonyl sulfide hydrolysis tower is 35℃-100℃, the operating pressure is 0.3-1.0Mpa, and the gas volume space velocity is 1000-8000h -1 .

5. The method for cascade desulfurization of refinery rich gas according to claim 1, characterized in that: The operating conditions of the hydrogen sulfide absorption tower are: reaction temperature of 40°C-60°C, reaction pressure of 0.3-1.0 MPa, and a mass ratio of alcoholamine liquid to rich gas of 2-7:1; the alcoholamine liquid is composed of water and an active component, wherein the active component is composed of a desulfurizer and a defoamer, wherein the desulfurizer is selected from any one of diethanolamine, diisopropanolamine, N-methyldiethanolamine, and N,N-dimethylacetamide; the defoamer is tributyl phosphate or dimethyl silicone oil; the weight ratio of the desulfurizer to the defoamer is (95-99.5): (0.5-15), and the content of the active component is 15-40% of the mass of the alcoholamine liquid.

6. The method for cascade desulfurization of refinery rich gas according to claim 1, characterized in that: The reaction temperature of the mercaptan conversion reactor is 80-200°C, the reaction pressure is 1.40-2.60 MPa, and the volume space velocity is 500-4000 h -1 The conversion catalyst consists of a carrier and an active component; the carrier is one or more of SiO2, Al2O3, TiO2, β-type molecular sieve, and Y-type molecular sieve granular activated carbon, and the active component is one or more of CoS, NiS, MoS3, and WS3, and the content of the active component accounts for 10-30% of the mass of the conversion catalyst.

7. The method for cascade desulfurization of refinery rich gas according to claim 1, characterized in that: The absorption distillation system separates the rich gas into refined dry gas and refined liquefied gas. The specific process is as follows: The rich gas coming out of the mercaptan conversion reactor has a pressure of 1.40-2.60 MPa and a temperature of 100-200°C; The dry gas absorption tower operates at a pressure of 1.20-1.60 MPa and a temperature of 40°C-45°C. Through the action of wash oil, a small amount of C3-C4 in the lean gas is absorbed to obtain refined dry gas. The operating pressure of the distillation tower is 1.30-2.00Mpa, and the operating temperature is 100℃-180℃.

8. The method for cascade desulfurization of refinery rich gas according to claim 7, characterized in that: The wash oil is one or more of petroleum ether, hydrogenated naphtha, reformed raffinate, reformed topped oil, and catalytic gasoline; and the mass ratio of lean gas to wash oil is 1:1-3.

9. The method for cascade desulfurization of refinery rich gas according to claim 1 or 2, characterized in that: The total sulfur content of the finally obtained refined dry gas is less than 0.5ppm; the total sulfur content of the refined liquefied gas is less than 1ppm, and the mercaptan sulfur content is less than 0.2ppm.

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