A method for treating liquid hydrocarbon sweetening tail gas

Abstract

The present application relates to the technical field of petroleum refining, and discloses a method for treating liquid hydrocarbon sweetening tail gas. The method is carried out in a tail gas treatment system, and comprises the following steps: introducing a sweetening solvent, a back-extraction oil and an oxidation air into a three-phase separator respectively to carry out contact mixing, so as to obtain sweetening tail gas; introducing the sweetening tail gas into a mixer to carry out mixing treatment with column top oil gas in the mixer, so as to obtain mixture I; introducing the mixture I into a crude gasoline tank to carry out gas-liquid separation, so as to obtain rich gas; introducing the rich gas into an absorption tower to carry out separation treatment, so as to obtain sulfur-containing dry gas; and introducing the sulfur-containing dry gas into a dry gas desulfurization tower to carry out desulfurization treatment, so as to obtain purified dry gas. The method provided by the present application has the advantages of less operation, low investment, precise control of the oxidation air flow in the liquid hydrocarbon sweetening process, recovery of hydrocarbons in the sweetening tail gas, and good economic and environmental benefits.

Description

Technical Field

[0001] This invention relates to the field of petroleum refining technology, and more specifically to a method for treating liquid hydrocarbon desulfurization tail gas. Background Technology

[0002] Currently, most liquid hydrocarbon desulfurization units in catalytic cracking or catalytic pyrolysis plants employ extraction-oxidation desulfurization processes, while some newly built and renovated units use liquefied gas deep desulfurization technology.

[0003] The liquid hydrocarbon extraction oxidative desulfurization process involves introducing oxidizing air (industrial air) during the desulfurization solvent regeneration process. Under the action of a catalyst, sodium thiolate in the desulfurization solvent is converted into disulfides. At the same time, low-sulfur back-extraction oil is used to absorb the sulfides in the desulfurization solvent, thus achieving solvent regeneration and reuse.

[0004] In the aforementioned technology, during the desulfurization process of liquid hydrocarbons, excess air from the oxidation process, carrying a small amount of hydrocarbons, was previously discharged directly into the atmosphere as tail gas from the three-phase separator. This tail gas amounted to approximately 1-2 Nm³ / t of liquid hydrocarbons, with nitrogen accounting for about 80% (by volume) and oxygen about 15% (by volume). Due to the inability to precisely control the oxidation air volume, the effective oxygen utilization rate was less than 40%. Furthermore, since the desulfurization tail gas contained a small amount of hydrocarbons and had an odor, direct emission into the atmosphere would cause environmental pollution.

[0005] The main treatment processes for liquid hydrocarbon desulfurization tail gas that have been industrialized include (1) condensation adsorption process, incineration and other methods.

[0006] The condensation adsorption process involves adsorbing and dehydrating the mercaptan tail gas, then condensing it in stages to approximately -70°C to recover heavy hydrocarbons, with the remaining gas being emitted into the atmosphere. This process requires a large area and involves high investment. If ethane (C2) is to be condensed and recovered, the temperature needs to be lowered to approximately -170°C, resulting in high energy consumption and poor economic efficiency.

[0007] Incineration is suitable for refineries with process heating furnaces near catalytic cracking or catalytic pyrolysis units or catalytic cracking or catalytic pyrolysis units that have their own CO incinerators. The disadvantage is that it may affect the compliance of flue gas emissions from the process heating furnaces of the relevant units.

[0008] Other methods involve mixing the desulfurization tail gas with the main air from the regenerator of a catalytic cracking or catalytic pyrolysis unit before incinerating it in the regenerator. However, if the unit experiences production abnormalities, the reaction feed is cut off, or the main air supply is interrupted, the process interlock needs to be activated simultaneously to cut off and vent the desulfurization tail gas, which poses safety risks.

[0009] Some processes involve adding an oxygen generator to a catalytic cracking or catalytic pyrolysis unit, using high-purity oxygen to replace the liquid hydrocarbon desulfurization oxidation air, and recycling the tail gas, which is the so-called zero tail gas emission. In this method, the gas phase in the three-phase separator is mostly oxygen and a small amount of hydrocarbons, raising concerns about safety and requiring high investment and significant modifications. Summary of the Invention

[0010] The purpose of this invention is to overcome the problems of high cost and poor safety in the treatment of liquid hydrocarbon desulfurization tail gas in existing catalytic cracking or catalytic pyrolysis devices.

[0011] To achieve the above objectives, the present invention provides a method for treating liquid hydrocarbon desulfurization tail gas, the method being carried out in a tail gas treatment system, the system comprising: a tail gas generation unit, a separation unit, a rich gas treatment unit, and a desulfurization unit.

[0012] The exhaust gas generation unit includes a three-phase separator and at least three online oxygen content analyzers connected in parallel.

[0013] The separation unit includes a crude gasoline tank and a fractionation tower with a mixer installed inside the oil and gas pipeline at the top of the tower;

[0014] The rich gas treatment unit includes an absorption tower;

[0015] The desulfurization unit includes a dry gas desulfurization tower;

[0016] The method includes:

[0017] (1) Desulfurization solvent, back-extraction oil and oxidation air are introduced into the three-phase separator respectively for contact mixing to generate desulfurized tail gas; the flow rate of the oxidation air entering the three-phase separator is automatically adjusted by the online oxygen content analyzer to achieve a K value of 5vol%-10vol%, where K is the oxygen content in the desulfurized tail gas;

[0018] (2) The desulfurization tail gas is introduced into the mixer to be mixed with the oil and gas at the top of the fractionation tower to obtain mixture I;

[0019] (3) The mixture I is introduced into the crude gasoline tank for gas-liquid separation to obtain rich gas;

[0020] (4) The rich gas is introduced into the absorption tower for recovery treatment to obtain sulfur-containing dry gas;

[0021] (5) The sulfur-containing dry gas is introduced into the dry gas desulfurization tower for desulfurization treatment to obtain purified dry gas;

[0022] The desulfurization solvent contains sodium hydroxide and sodium thiolate;

[0023] The back-extraction oil is the heavy gasoline fraction obtained by desulfurizing desulfurized gasoline from hydrocracking heavy naphtha and / or sulfur-containing gasoline produced by catalytic cracking or catalytic pyrolysis, after removing light fractions.

[0024] The method provided by this invention requires minimal modification, low investment, and is quick to implement. It is safe and reliable, and can not only solve the environmental emission problem of desulfurization tail gas, but also accurately control the oxidation air flow rate during the desulfurization process of liquid hydrocarbons. It can recover hydrocarbons while reducing the emission of desulfurization tail gas, and has good economic benefits. Attached Figure Description

[0025] Figure 1 This is a specific embodiment of the exhaust gas treatment system and process flow diagram provided by the present invention;

[0026] Figure 2 This is a schematic diagram of the mixer in the exhaust gas treatment system of the method provided by the present invention.

[0027] Explanation of reference numerals in the attached figures

[0028] 11. Fractionating tower; 12. Crude gasoline tank

[0029] 13. Oil-gas cooler; 110. Mixer

[0030] 21. Absorption tower; 22. Rich gas compressor

[0031] 31. Three-phase separator 32. Exhaust gas buffer tank

[0032] 33. Online oxygen content analyzer; 41. Dry gas desulfurization tower

[0033] 42. Liquid hydrocarbon desulfurization tower Detailed Implementation

[0034] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0035] As mentioned above, a first aspect of the present invention provides a method for treating liquid hydrocarbon desulfurization tail gas, the method being carried out in a tail gas treatment system, the system comprising: a tail gas generation unit, a separation unit, a rich gas treatment unit, and a desulfurization unit.

[0036] The exhaust gas generation unit includes a three-phase separator and at least three online oxygen content analyzers connected in parallel.

[0037] The separation unit includes a crude gasoline tank and a fractionation tower with a mixer installed inside the oil and gas pipeline at the top of the tower;

[0038] The rich gas treatment unit includes an absorption tower;

[0039] The desulfurization unit includes a dry gas desulfurization tower;

[0040] The method includes:

[0041] (1) Desulfurization solvent, back-extraction oil and oxidation air are introduced into the three-phase separator respectively for contact mixing to generate desulfurized tail gas; the flow rate of the oxidation air entering the three-phase separator is automatically adjusted by the online oxygen content analyzer to achieve a K value of 5vol%-10vol%, where K is the oxygen content in the desulfurized tail gas;

[0042] (2) The desulfurization tail gas is introduced into the mixer to be mixed with the oil and gas at the top of the fractionation tower to obtain mixture I;

[0043] (3) The mixture I is introduced into the crude gasoline tank for gas-liquid separation to obtain rich gas;

[0044] (4) The rich gas is introduced into the absorption tower for recovery treatment to obtain sulfur-containing dry gas;

[0045] (5) The sulfur-containing dry gas is introduced into the dry gas desulfurization tower for desulfurization treatment to obtain purified dry gas;

[0046] The desulfurization solvent contains sodium hydroxide and sodium thiolate;

[0047] The back-extraction oil is the heavy gasoline fraction obtained by desulfurizing desulfurized gasoline from hydrocracking heavy naphtha and / or sulfur-containing gasoline produced by catalytic cracking or catalytic pyrolysis, after removing light fractions.

[0048] It should be noted that, in this invention, the sodium thiolate is sodium thiolate produced by reacting a thiol with 1-3 carbon atoms with sodium hydroxide.

[0049] According to a preferred embodiment, the back-extraction oil is a heavy gasoline fraction obtained by further removing light fractions from desulfurized gasoline obtained from sulfur-containing gasoline produced by catalytic cracking or catalytic pyrolysis. The inventors of this invention have discovered that, in this preferred embodiment, the amount of hydrocarbons entrained in the desulfurization tail gas can be significantly reduced.

[0050] In this invention, when the desulfurization solvent, the back-extraction oil, and the oxidation air come into contact and mix in the three-phase separator, the sulfur content in the back-extraction oil after contact and mixing will increase over time.

[0051] In a preferred embodiment, when the sulfur content in the back-extraction oil after contact mixing is ≤0.5wt%, a portion of the back-extraction oil after contact mixing is discarded, and fresh back-extraction oil is added separately (fresh back-extraction oil is the heavy gasoline fraction obtained by desulfurizing desulfurized gasoline from hydrocracking heavy naphtha and / or sulfur-containing gasoline produced by catalytic cracking or catalytic pyrolysis after removing light fractions).

[0052] Preferably, in step (1), the desulfurization solvent, the reverse extraction oil and the oxidation air are first mixed and then introduced into the three-phase separator.

[0053] The present invention does not have special requirements for the mixing conditions, as long as the desulfurization solvent, the reverse extraction oil and the oxidation air are mixed evenly. Those skilled in the art can make the selection according to known means in the art.

[0054] Preferably, the desulfurization solvent contains sodium hydroxide at a mass fraction of 8 wt%-12 wt% and sodium thiolate at a mass fraction of 0.09 wt%-0.18 wt%.

[0055] In a preferred embodiment, in step (2), the volumetric flow ratio of the oil / gas to the desulfurization tail gas is >500:1. The inventors of this invention have discovered that, in this preferred embodiment, the increase in oxygen content in the purified dry gas is smaller, thereby improving the safety of the industrial plant.

[0056] Preferably, in step (2), the conditions are controlled such that the linear velocity of the desulfurized tail gas at the mixer outlet is 3-6 m / s.

[0057] It should be noted that, in this invention, the recovery process is used to recover C3 and higher hydrocarbons from rich gas to obtain sulfur-containing dry gas and sulfur-containing liquid hydrocarbons.

[0058] In order to successfully recover C3 and higher hydrocarbons from rich gas, the present invention may also include recovery equipment other than the absorption tower, such as reabsorption tower, desorption tower, stabilization tower, etc., which can be selected by those skilled in the art based on known technical means in the field.

[0059] In a preferred embodiment, the separation unit further includes an oil-gas cooler disposed between the fractionation tower and the mixer, the oil-gas cooler being used to condense and cool the oil and gas at the top of the fractionation tower so that the oil and gas flow to the mixer.

[0060] Preferably, the condensation cooling conditions include a temperature of 35-45°C.

[0061] In a preferred embodiment, the desulfurization unit further includes a liquid hydrocarbon desulfurization tower, which is used to remove sulfides from the sulfur-containing liquid hydrocarbons obtained through the recovery treatment to obtain the desulfurization solvent; the desulfurization solvent is introduced into the three-phase separator so that the tail gas treatment system can be circulated.

[0062] Preferably, the rich gas treatment unit further includes a rich gas compressor for pressurizing the rich gas at the outlet of the crude gasoline tank;

[0063] The conditions for pressurization include a pressure of 0.9-1.6 MPa.

[0064] In a preferred embodiment, the rich gas treatment unit further includes a rich gas cooler connected to the rich gas compressor, the rich gas cooler being used to reduce the temperature of the rich gas at the outlet of the rich gas compressor.

[0065] Preferably, the exhaust gas generating unit further includes an exhaust gas buffer tank connected to the three-phase separator. The exhaust gas buffer tank is used to deliquify the mercaptan exhaust gas from the outlet of the three-phase separator to obtain deliquified mercaptan exhaust gas.

[0066] The conditions for the dehydration treatment include: a temperature of 25-35℃ and a residence time of 15-30 min.

[0067] In a preferred embodiment, the exhaust gas generating unit includes three online oxygen content analyzers connected in parallel.

[0068] Preferably, the mixer is a ring-shaped mixer.

[0069] The present invention does not have special requirements for the material of the mixer, as long as it can effectively resist hydrogen sulfide corrosion and its strength meets the requirements for long-term operation. Those skilled in the art can make selections based on known methods in the field.

[0070] To ensure thorough mixing of the desulfurization tail gas and the oil and gas at the top of the fractionation tower, the present invention provides a preferred embodiment in which the opening of the mixer faces the flow direction of the oil and gas at the top of the fractionation tower.

[0071] Preferably, the opening of the mixer is a round hole with a diameter of 5-10 mm.

[0072] The present invention does not have any particular requirements on the number of openings in the mixer, but the openings should be uniform to ensure good mixing of the desulfurization tail gas and the oil and gas. Those skilled in the art can make selections as needed.

[0073] It should be noted that various control valves known to those skilled in the art can be installed in the circulation path of the exhaust gas treatment system used in this invention to control the flow of fluids such as oil and gas, desulfurization exhaust gas, rich gas, dry gas, desulfurization solvent, and reverse extraction oil.

[0074] It should be noted that all pressure vessels (such as crude gasoline tanks, dry gas desulfurization towers, etc.) in the exhaust gas treatment system used in this invention can be equipped with independent vent valves, and can also be equipped with pressure indicators, thermocouples, etc. to display equipment operating pressure and temperature, etc.

[0075] The following describes in detail, with reference to the accompanying drawings, a method for treating liquid hydrocarbon desulfurization tail gas provided by the present invention.

[0076] Figure 1 A specific embodiment of the exhaust gas treatment system and process flow diagram provided by the present invention:

[0077] from Figure 1 As can be seen from the above, the exhaust gas treatment system includes: an exhaust gas generation unit, a separation unit, a rich gas treatment unit, and a desulfurization unit; the method for treating liquid hydrocarbon desulfurization exhaust gas is carried out in the above system, including:

[0078] The desulfurization solvent from the liquid hydrocarbon desulfurization tower 42 is mixed with the back-extraction oil (externally supplied) and oxidation air (externally supplied) and then introduced into the three-phase separator 31. The tail gas buffer tank 32 is used to deliquify the desulfurized tail gas at the outlet of the three-phase separator 31 to obtain deliquified desulfurized tail gas. The online oxygen content analyzer 33 (three online oxygen content analyzers are connected in parallel) is used to further deliquify the tail gas. Figure 1 The diagram only shows one online oxygen content analyzer to automatically regulate the flow rate of the oxidation air entering the three-phase separator, so as to achieve a K value of 5 vol%-10 vol%, where K is the oxygen content in the desulfurization tail gas; the oil-gas cooler 13 is used to condense and cool the material generated at the top of the fractionation tower 11 (temperature 35-45℃) to obtain the oil-gas; the desulfurization tail gas after liquid removal is introduced into the mixer 110 to mix with the oil-gas at the top of the fractionation tower to obtain mixture I; mixture I is introduced into the crude gasoline tank 12 for gas-liquid separation to obtain rich gas; the rich gas compressor 22 pressurizes the rich gas in the crude gasoline tank 12 and sends it to the absorption tower 21 (other recovery equipment). Figure 1 (Not listed in the text); after the rich gas passes through the absorption tower 21 to recover C3 and above hydrocarbons, sulfur-containing dry gas and sulfur-containing liquid hydrocarbons are obtained; the sulfur-containing dry gas is introduced into the dry gas desulfurization tower 41 for desulfurization treatment to obtain purified dry gas; the sulfur-containing liquid hydrocarbons are introduced into the liquid hydrocarbon desulfurization tower 42 for purification treatment to obtain purified liquid hydrocarbons and desulfurization solvent that can be recycled to the three-phase separator.

[0079] This invention is in Figure 2 A schematic diagram of the mixer is provided as an example. Figure 2 As can be seen, the mixer is a ring-shaped mixer, which is fixedly installed in the oil and gas pipeline at the top of the fractionation tower by a support assembly. The desulfurized tail gas after liquid removal enters the mixer through the tail gas pipeline to achieve full mixing with the oil and gas.

[0080] The present invention will be described in detail below through examples.

[0081] In the following examples, unless otherwise specified, all raw materials used are either purchased or processed in-house.

[0082] Back-extraction oil: Specifically, it consists of the heavy gasoline fraction obtained by desulfurizing the sulfur-containing gasoline produced by catalytic cracking or catalytic pyrolysis, after removing the light fractions.

[0083] Desulfurization solvent: Specifically, it contains 10% sodium hydroxide by mass, 0.15 wt% sodium thiolate by mass, and the remainder is water.

[0084] Example 1

[0085] This embodiment illustrates a method for treating liquid hydrocarbon desulfurization tail gas generated from catalytic cracking and / or catalytic pyrolysis units, as detailed below:

[0086] The desulfurization solvent from the liquid hydrocarbon desulfurization tower 42 is mixed with the back-extraction oil (externally supplied) and oxidation air (externally supplied) and then introduced into the three-phase separator 31. The tail gas buffer tank 32 is used to deliquify the desulfurized tail gas at the outlet of the three-phase separator 31 to obtain deliquified desulfurized tail gas; the online oxygen content analyzer 33 (a total of 3 online oxygen content analyzers are set in parallel) is used to further deliquify the tail gas. Figure 1 The diagram only shows one online oxygen content analyzer. The analyzer automatically regulates the flow rate of the oxidation air entering the three-phase separator to achieve a K value of 5 vol%, where K is the oxygen content in the desulfurization tail gas. The oil-gas cooler 13 is used to condense and cool the oil and gas at the top of the fractionation tower 11 (temperature 40°C) so that the oil and gas flow to the mixer. The desulfurization tail gas after liquid removal is introduced into the mixer 110 to mix with the oil and gas at the top of the fractionation tower to obtain mixture I. Mixture I is introduced into the crude gasoline tank 12 for gas-liquid separation to obtain rich gas. The rich gas compressor 22 pressurizes the rich gas in the crude gasoline tank 12 (pressure 1.3 MPa) and sends it to the absorption tower 21 (other recovery equipment). Figure 1(Not listed in the text); after the rich gas passes through the absorption tower 21 to recover C3 and above hydrocarbons, sulfur-containing dry gas and sulfur-containing liquid hydrocarbons are obtained; the sulfur-containing dry gas is introduced into the dry gas desulfurization tower 41 for desulfurization treatment to obtain purified dry gas; the sulfur-containing liquid hydrocarbons are introduced into the liquid hydrocarbon desulfurization tower 42 for purification treatment to obtain purified liquid hydrocarbons and desulfurization solvent that can be recycled to the three-phase separator.

[0087] Unless otherwise specified, Example 2 and Comparative Example 1 were carried out using a similar method to Example 1, except for the process parameters, which are shown in Table 1.

[0088] The system operation results of the above embodiments and comparative examples are shown in Table 1.

[0089] Table 1

[0090]

[0091]

[0092] Note: K is the oxygen content in the desulfurization tail gas.

[0093] The results above show that the method for treating liquid hydrocarbon desulfurization tail gas provided by this invention can significantly reduce the hydrocarbons entrained in the desulfurization tail gas and keep the oxygen content in the obtained purified dry gas at a safe level, ensuring the recovery of hydrocarbons while reducing emissions from the desulfurization tail gas, thus achieving good economic and environmental benefits.

[0094] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for treating mercaptan removal tail gas from liquid hydrocarbons, characterized in that, This method is carried out in an exhaust gas treatment system, which includes an exhaust gas generation unit, a separation unit, an enrichment gas treatment unit, and a desulfurization unit. The exhaust gas generation unit includes a three-phase separator and at least three online oxygen content analyzers connected in parallel. The separation unit includes a crude gasoline tank and a fractionation tower with a mixer installed inside the oil and gas pipeline at the top of the tower; The rich gas treatment unit includes an absorption tower; The desulfurization unit includes a dry gas desulfurization tower; The method includes: (1) Desulfurization solvent, back-extraction oil and oxidation air are introduced into the three-phase separator respectively for contact mixing to generate desulfurized tail gas; the flow rate of the oxidation air entering the three-phase separator is automatically adjusted by the online oxygen content analyzer to achieve a K value of 5vol%-10vol%, where K is the oxygen content in the desulfurized tail gas; (2) The desulfurization tail gas is introduced into the mixer to be mixed with the oil and gas at the top of the fractionation tower to obtain mixture I; (3) The mixture I is introduced into the crude gasoline tank for gas-liquid separation to obtain rich gas; (4) The rich gas is introduced into the absorption tower for recovery treatment to obtain sulfur-containing dry gas; (5) The sulfur-containing dry gas is introduced into the dry gas desulfurization tower for desulfurization treatment to obtain purified dry gas; The desulfurization solvent contains sodium hydroxide and sodium thiolate; The back-extraction oil is the heavy gasoline fraction obtained by desulfurizing desulfurized gasoline from hydrocracking heavy naphtha and / or sulfur-containing gasoline produced by catalytic cracking or catalytic pyrolysis, after removing light fractions.

2. The method according to claim 1, characterized in that, The desulfurization solvent contains sodium hydroxide with a mass fraction of 8 wt%-12 wt% and sodium thiolate with a mass fraction of 0.09 wt%-0.18 wt%.

3. The method according to claim 1 or 2, characterized in that, In step (2), the volumetric flow ratio of the oil and gas to the desulfurization tail gas is >500:

1.

4. The method according to any one of claims 1-3, characterized in that, In step (2), the conditions are controlled such that the linear velocity of the desulfurized tail gas at the mixer outlet is 3-6 m / s.

5. The method according to any one of claims 1-4, characterized in that, The separation unit also includes an oil-gas cooler disposed between the fractionation tower and the mixer, the oil-gas cooler being used to condense and cool the oil and gas at the top of the fractionation tower so that the oil and gas flow to the mixer.

6. The method according to any one of claims 1-5, characterized in that, The rich gas treatment unit also includes a rich gas compressor for pressurizing the rich gas at the outlet of the crude gasoline tank. The conditions for pressurization include a pressure of 0.9-1.6 MPa.

7. The method according to any one of claims 1-6, characterized in that, The rich gas treatment unit also includes a rich gas cooler connected to the rich gas compressor, which is used to reduce the temperature of the rich gas at the outlet of the rich gas compressor.

8. The method according to any one of claims 1-7, characterized in that, The exhaust gas generating unit also includes an exhaust gas buffer tank connected to the three-phase separator. The exhaust gas buffer tank is used to deliquify the mercaptan exhaust gas from the outlet of the three-phase separator to obtain deliquified mercaptan exhaust gas. The conditions for the dehydration treatment include: a temperature of 25-35℃ and a residence time of 15-30 min.

9. The method according to any one of claims 1-8, characterized in that, The exhaust gas generation unit includes three online oxygen content analyzers connected in parallel.

10. The method according to any one of claims 1-9, characterized in that, The mixer is a ring-shaped mixer.

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