Method for removing elemental mercury deposited in equipment

Abstract

The invention discloses a method for removing elemental mercury attached to the inner wall of equipment. The method comprises the following steps: 1) soaking treated equipment with a low-concentration strong oxidant and draining a strong oxidant solution; (2) soaking the treated equipment by using a low-concentration dialkyl dithiophosphonate solution, and discharging the dialkyl dithiophosphonate solution until the dialkyl dithiophosphonate solution is dry; and (3) repeating the steps (1) and (2) for multiple times until the elemental mercury on the inner wall of the equipment is completely oxidized and removed. The method can be used for removing the elemental mercury attached to the inner wall of the natural gas treatment equipment.

Description

Technical Field

[0001] This application belongs to the field of natural gas equipment processing, and in particular relates to a method for removing elemental mercury adhering to the inner wall of natural gas processing equipment. Background Technology

[0002] Natural gas is a mixture of hydrocarbon and non-hydrocarbon gases naturally occurring in underground strata. When burned, it produces less carbon dioxide than other fossil fuels, resulting in a lower greenhouse effect. With increasing global concern about air pollution, natural gas, as a clean energy source, has gradually become one of the main energy sources for industrial and residential use, leading to huge market demand and extensive development of global natural gas resources. However, most natural gas contains trace amounts of harmful mercury, primarily in the form of elemental mercury, with a small amount existing in the form of alkylmercury.

[0003] Trace amounts of elemental mercury in natural gas can condense and adhere to the inner walls of natural gas processing equipment, gradually increasing over time. This adhering mercury is permeable to metal equipment, and some can even penetrate into the equipment materials, causing corrosion. Therefore, after a period of operation, natural gas processing equipment needs to be inspected to remove the mercury deposits on the inner walls and reduce mercury penetration and corrosion. Furthermore, due to the volatility and toxicity of mercury, maintenance work can cause mercury levels inside the equipment and in the surrounding air to exceed safe limits, potentially leading to mercury poisoning for operators and posing a health risk. Therefore, removing adhering mercury from the inner walls of the processing equipment and reducing mercury volatilization during maintenance is essential. However, mercury adhering to metal surfaces has a strong interaction with the metal substrate, and natural gas processing equipment lacks agitation devices to provide shear force. Therefore, removing adsorbed mercury from the inner walls using physical methods is challenging, and incomplete removal can lead to excessive mercury levels inside the equipment, making manual maintenance and repair impossible.

[0004] The current method involves using high-temperature steam to boil the equipment for an extended period during maintenance shutdowns. This causes the adhering mercury to evaporate and detach from the metal substrate. The mercury condenses into the liquid phase and is then removed from the equipment as mercury beads, thus reducing the concentration of gaseous mercury inside the equipment. However, because mercury evaporates slowly, this boiling method requires a long time, typically 7-10 days, and the mercury concentration remains above 100 ug / m³. 3 The above-mentioned issues indicate that the cleaning process is incomplete, requiring maintenance personnel to wear heavy protective gear to enter the equipment and limiting their work time to short periods, thus reducing maintenance efficiency. Therefore, steaming is not an efficient method, and it is necessary to develop new methods.

[0005] In recent years, chemical methods for mercury removal have been proposed. A common approach is to use strong oxidants, such as potassium permanganate, to oxidize mercury into mercury oxides. Mercury oxides are non-volatile and can reduce the mercury content in the gas phase. However, when strong oxidants oxidize elemental mercury, the resulting metal oxides are relatively dense, preventing the oxidant from penetrating the interior. Furthermore, due to the unique physical properties of mercury, it usually exists in the form of mercury beads. Without a stirring device in natural gas processing equipment, large mercury beads cannot be dispersed into smaller ones. In this situation, oxidation typically occurs on the surface, while internal oxidation is difficult to occur. Therefore, conventional methods using strong oxidants cannot completely remove elemental mercury. Moreover, this structure, where liquid mercury is encased in metal oxides, is easily destroyed by external forces, allowing mercury to still volatilize into the gas phase, making it difficult to reduce the mercury content in the gas phase within the equipment. This still does not solve the problems faced during maintenance. Furthermore, publicly available literature reports high concentrations of strong oxidants, which can corrode equipment while oxidizing mercury, making their application in practical applications difficult.

[0006] In summary, existing mercury cleaning processes, whether physical methods using high-temperature steam or chemical methods using strong oxidants, have two main problems: first, the cleaning efficiency is low, making it difficult to quickly remove attached mercury; second, the cleaning is not thorough, and the mercury content inside the equipment still exceeds the standard, making it impossible to perform manual inspection and maintenance on the equipment. Summary of the Invention

[0007] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0008] In existing technologies for treating mercury with strong oxidants, using high concentrations of strong oxidants will form a denser mercury oxide layer, making it more difficult for the oxidant to penetrate. Without stirring, it is difficult to destroy the mercury oxide layer, so the mercury inside the oxide layer still exists. When maintenance personnel enter the equipment, they will destroy this oxide layer, and the harm of mercury will still exist. Moreover, high concentrations of strong oxidants can also cause equipment corrosion.

[0009] This application proposes a novel method for the complete removal of elemental mercury, based on the treatment of mercury with strong oxidants. Its main objective is to provide a method for removing elemental mercury deposits on the inner walls of equipment, particularly natural gas processing equipment, using multiple oxidation processes. This addresses the problems of long cleaning times, incomplete removal, and equipment corrosion associated with existing mercury cleaning methods. The method described in this application is characterized by high mercury removal efficiency and thorough removal.

[0010] This application provides a method for removing elemental mercury deposits inside a device, comprising: oxidizing elemental mercury into volatile mercury oxides through the oxidation of a strong oxidant, then rapidly destroying the metal oxide layer, and repeating this process of destruction followed by oxidation with a strong oxidant and destruction, and repeating this process multiple times, thereby achieving complete conversion of mercury and achieving the purpose of removal.

[0011] In one exemplary embodiment, the method includes the following steps:

[0012] 1) Immerse the equipment to be treated in a solution of low concentration of strong oxidant until the elemental mercury on the inner wall of the equipment is oxidized to form a mercury oxide layer, and then drain the solution of strong oxidant.

[0013] 2) Immerse the equipment to be treated in a low-concentration solution of organic-based thiophosphoric alkali metal precipitant to quickly destroy the mercury oxide layer, and then drain the solution of organic-based thiophosphoric alkali metal precipitant.

[0014] 3) Repeat steps 1) and 2) multiple times until the elemental mercury on the inner wall of the equipment is completely oxidized and removed.

[0015] In one exemplary embodiment, the strong oxidant may be an inorganic water-soluble strong oxidant or a water-soluble organic strong oxidant. Preferably, the strong oxidant is an inorganic water-soluble strong oxidant. More preferably, the strong oxidant is selected from potassium permanganate, persulfate, potassium ferrate, etc. Most preferably, the strong oxidant is potassium permanganate.

[0016] In one exemplary embodiment, the mass concentration of the strong oxidant is 0.001%-1%, preferably 0.1% or 0.5%.

[0017] In one exemplary embodiment, in step 1), the soaking time is greater than or equal to 0.1 hours, preferably 1-4 hours; the soaking temperature is room temperature (25°C) to 100°C.

[0018] In one exemplary embodiment, in step 1), the soaking time is 2 hours or 3 hours.

[0019] In one exemplary embodiment, in step 1), the immersion temperature is room temperature.

[0020] In one exemplary embodiment, the organic-based thiophosphoric alkali metal precipitant is a dialkyl dithiophosphonate. Preferably, the dialkyl dithiophosphonate can be a water-soluble salt such as a sodium or potassium salt. More preferably, the dialkyl dithiophosphonate can be a sodium salt solution.

[0021] In one exemplary embodiment, the alkyl group in the dialkyl dithiophosphonate is a straight-chain or branched alkyl group having 1-6 carbon atoms, preferably an isobutyl group.

[0022] In one exemplary embodiment, the dialkyl dithiophosphonate is sodium diisobutyl dithiophosphonate.

[0023] In one exemplary embodiment, the mass concentration of the dialkyl dithiophosphonate is not less than 0.1%; preferably, the mass concentration of the dialkyl dithiophosphonate is 0.2% or 0.5%.

[0024] In one exemplary embodiment, in step 2), the soaking time is greater than or equal to 0.1 hours, preferably 0.5-4 hours; more preferably, the soaking time is 1 hour.

[0025] In one exemplary embodiment, in step 3), steps 1) and 2) are repeated more than or equal to 2 times; preferably, 2, 4 or 6 times.

[0026] In one exemplary embodiment, in order to reduce corrosion of the equipment, steps 1) and 2) are performed under alkaline conditions; alternatively, a pH adjuster may be added to make the pH of the system greater than 7.

[0027] In one exemplary embodiment, in steps 1) and 2), the soaking is either flood irrigation or high-pressure spray soaking; preferably, the soaking is flood irrigation in order to treat mercury in dead corners.

[0028] Compared with existing methods, this application has the following technical advantages:

[0029] 1) This application provides a method for removing elemental mercury deposited on the inner wall of equipment, especially natural gas processing equipment, by multiple oxidation processes. This method solves the problems of long mercury removal time, incomplete mercury removal, and equipment corrosion in existing mercury cleaning methods. The method of this application has the characteristics of high mercury removal efficiency and thorough removal.

[0030] 2) This application uses oxidation-destruction of the oxide layer followed by oxidation with a strong oxidizing agent, and then destruction, alternating in this way multiple times, to achieve complete conversion of mercury and achieve the purpose of removal.

[0031] 3) In this application, although mercury is an inert metal, it can still be oxidized by strong oxidizing agents such as potassium permanganate. Furthermore, the oxidizing power of strong oxidizing agents is concentration-dependent; excessively high concentrations result in excessively strong oxidizing properties, which, while oxidizing mercury, will also oxidize the metal components of the equipment, thus damaging the equipment. Therefore, this application uses a low-concentration potassium permanganate solution to oxidize mercury into a metal oxide layer without corroding the equipment's metal components. However, the concentration cannot be too low, otherwise, the processing time will be excessively long.

[0032] 4) This application employs dialkyl dithiophosphonic acid salts for immersion after oxidation, which can rapidly destroy the mercury oxide layer without reducing the mercury oxide to elemental mercury. Furthermore, dialkyl dithiophosphonic acid salts are water-soluble, allowing for rapid destruction of the mercury oxide layer even at very low concentrations, and are non-corrosive. Additionally, since dialkyl dithiophosphonic acid salts can react with strong oxidants, they must be used separately and alternately. First, the strong oxidant is used to oxidize the mercury, forming mercury oxide on the surface. After draining the strong oxidant solution, dialkyl dithiophosphonic acid salts are used to destroy the metal oxide layer, allowing it to enter the solution and exposing the elemental mercury. This process can be repeated with the addition of a strong oxidant for further oxidation and destruction, alternating multiple times to completely convert the mercury into non-volatile mercury oxide, thus achieving mercury removal.

[0033] 5) The process of oxidizing mercury and destroying the metal oxide layer on the surface of mercury described in this application is repeated at least twice, which can not only oxidize mercury more completely into divalent mercury, but also reduce the mercury content in the gas phase space inside the equipment, thus meeting safety requirements.

[0034] 6) The method described in this application demonstrates excellent cleaning results and also shortens the cleaning time, typically requiring only 8-10 hours. This reduces the mercury content inside the equipment to a safe range, enabling manual maintenance and repair. After cleaning away the adhering mercury, the mercury content inside the equipment meets the standard: less than 28 ug / m³. 3 .

[0035] Other features and advantages of this application will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the application. Other advantages of this application may be realized and obtained by means of the methods described in the description. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to embodiments, but this is not intended to limit the present invention. Any equivalent substitutions made in accordance with the disclosure of the present invention shall fall within the protection scope of the present invention.

[0037] The raw material information used in the embodiments and comparative examples of this application is as follows:

[0038] (1) Potassium permanganate, purchased from Sinopharm Chemical Reagent Co., Ltd.

[0039] (2) Sodium diisobutyl dithiophosphonate, purchased from Solvay.

[0040] Unless otherwise stated, all raw materials used are commercially available.

[0041] In the examples and comparative examples:

[0042] 1) The steps for testing the mercury oxidation rate are as follows: Weigh the mercury before oxidation treatment (G1) and the mercury after oxidation treatment (G2). The formula for calculating the mercury oxidation rate (OR) is: OR = (G1 - G2) / G1 × 100%.

[0043] 2) The mercury content in the container gas was measured using a gas phase mercury analyzer (maximum range 2000 ug / m³). 3 ).

[0044] Example 1.

[0045] Follow these steps to process:

[0046] (1) Weigh a small amount of mercury G1 and put it into a 50ml glass bottle;

[0047] (2) Add a 0.1% potassium permanganate solution to immerse the mercury beads, keep at room temperature for 2 hours, and drain the liquid for later use;

[0048] (3) Add a 0.2% sodium diisobutyl dithiophosphonate solution to immerse the mercury beads, keep at room temperature for 1 hour, and drain the liquid for later use; wherein, the operating environment in steps (1) and (2) is: room temperature, pH value is 7;

[0049] (4) Repeat steps (2) and (3) twice in sequence, drain the liquid, and weigh the remaining mercury G2;

[0050] The oxidation rate (OR) of mercury was calculated, and the results are shown in Table 1.

[0051] Example 2

[0052] The steps are the same as in Example 1, except that steps (2) and (3) are repeated 4 times.

[0053] The oxidation rate of mercury was calculated, and the results are shown in Table 1.

[0054] Example 3

[0055] The steps are the same as in Example 1, except that steps (2) and (3) are repeated 6 times.

[0056] The oxidation rate of mercury was calculated, and the results are shown in Table 1.

[0057] Example 4

[0058] The steps are the same as in Example 1, except that the concentration of the potassium permanganate solution used is 0.5%.

[0059] The oxidation rate of mercury was calculated, and the results are shown in Table 1.

[0060] Example 5

[0061] The steps are the same as in Example 1, except that the concentration of the sodium diisobutyl dithiophosphonate solution used is 0.5%.

[0062] The oxidation rate of mercury was calculated, and the results are shown in Table 1.

[0063] Example 6

[0064] The steps are the same as in Example 1, except that the processing time in step (2) is 3 hours.

[0065] The oxidation rate of mercury was calculated, and the results are shown in Table 1.

[0066] Example 7

[0067] 10g of liquid elemental mercury was added to a 1-liter pressure-resistant metal container of the heating system. The container was sealed and heated at 200℃ for 8 hours to allow all the elemental mercury to evaporate and adhere to the inner wall of the container. After being left at room temperature for 7 days, a gaseous sample was taken from the container to test the mercury content. The test result showed that the mercury content was greater than 2000ug / m³. 3 .

[0068] After the container was subjected to the flooding treatment described in Example 1, the content of gaseous mercury in the gas inside the container was measured, and the mercury content was found to be 18 ug / m³. 3 .

[0069] Table 1: Results of Mercury Oxidation

[0070] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Before treatment (g) 0.2026 0.2314 0.1938 0.2234 0.2105 0.2097 After processing (g) 0.050 0.0241 0 0.0474 0.0516 0.0461 Oxidation rate (%) 75.3 89.6 100 78.8 75.5 78.0

[0071] Comparative Example 1

[0072] The steps are the same as in Example 1, except that step (4) is not included.

[0073] The oxidation rate of mercury was calculated, and the results are shown in Table 2.

[0074] Comparative Example 2

[0075] The steps are the same as in Example 1, except that the concentration of potassium permanganate in step (2) is 2%.

[0076] The oxidation rate of mercury was calculated, and the results are shown in Table 2.

[0077] Comparative Example 3

[0078] The steps are the same as in Example 1, except that the processing time in step (2) is 3 minutes.

[0079] The oxidation rate of mercury was calculated, and the results are shown in Table 2.

[0080] Comparative Example 4

[0081] The steps are the same as in Example 1, except that the processing time in step (3) is 3 minutes.

[0082] The oxidation rate of mercury was calculated, and the results are shown in Table 2.

[0083] Comparative Example 5

[0084] 10g of liquid elemental mercury was added to a 1-liter pressure-resistant metal container of the system to be heated. The container was sealed and heated at 200℃ for 8 hours to allow all the elemental mercury to evaporate and adhere to the inner wall of the container. After being left at room temperature for 7 days, a sample of the gas inside the container was taken and the mercury content in the gas was tested. The result showed that the mercury content in the gas was greater than 2000ug / m³. 3 .

[0085] The containers described above were subjected to the same flooding treatment as in Comparative Example 1. After 8 hours, the mercury content in the gas inside the containers was measured, and the mercury content was found to be greater than 2000 ug / m³. 3 .

[0086] Table 2: Mercury Oxidation Results

[0087] Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Before treatment (g) 0.2178 0.2069 0.2209 0.2257 After processing (g) 0.1492 0.1072 0.1409 0.1483 Oxidation rate (%) 31.5 48.2 36.2 34.3

[0088] Comparative Example 6

[0089] 10g of liquid elemental mercury was added to a 1-liter pressure-resistant metal container of the system to be heated. The container was sealed and heated at 200℃ for 8 hours to allow all the elemental mercury to evaporate and adhere to the inner wall of the container. After being left at room temperature for 7 days, a sample of the gas inside the container was taken and the mercury content in the gas was tested. The result showed that the mercury content in the gas was greater than 2000ug / m³. 3 .

[0090] The container was treated with 120°C high-temperature steam for 240 hours, and the mercury content in the gas inside the container was measured. The mercury content in the gas was found to be greater than 150 μg / m³. 3 .

[0091] Corrosion assessment

[0092] The effects of potassium permanganate solution and sodium diethyldithiophosphonate solution concentrations on the corrosion of the equipment were tested. The procedures and results are as follows:

[0093] 1) Add 1 ml of 0.1% potassium permanganate solution to an R345 steel plate, leave it at room temperature for 4 hours, clean the surface of the steel plate, and observe the corrosion. No corrosion was found.

[0094] 2) Add 1 ml of 5% potassium permanganate solution to an R345 steel plate, leave it at room temperature for 4 hours, clean the surface of the steel plate, observe the corrosion, and find corrosion.

[0095] 3) Add 1 ml of 10% sodium diethyldithiophosphonate solution to an R345 steel plate, leave it at room temperature for 4 hours, clean the surface of the steel plate, and observe the corrosion. No corrosion was found.

[0096] 4) A solution of 0.1% potassium permanganate and 10% sodium diethyldithiophosphonate was dropped onto the steel plate and left at room temperature for 4 hours. The surface of the steel plate was cleaned and the corrosion was observed. No corrosion was found.

[0097] in conclusion:

[0098] The method described in this application can improve the oxidation rate of elemental mercury inside the equipment and reduce the content of mercury vapor, effectively solving the problems of long mercury cleaning time, incomplete mercury cleaning, and equipment corrosion in existing mercury cleaning methods.

[0099] This application describes several embodiments, but these descriptions are exemplary and not restrictive, and it will be apparent to those skilled in the art that there are many more embodiments and implementations within the scope of the embodiments described herein.

Claims

1. A method for removing elemental mercury adhering to the inner wall of equipment, comprising the following steps: 1) Immerse the equipment to be treated in a solution of a low concentration of strong oxidant, and then drain the solution of the strong oxidant; 2) Immerse the equipment to be treated in a low-concentration solution of organic-based thiophosphoric alkali metal precipitant, and then drain the solution of the organic-based thiophosphoric alkali metal precipitant. 3) Repeat steps 1) and 2) multiple times until the elemental mercury on the inner wall of the equipment is completely oxidized and removed.

2. The method according to claim 1, wherein, The strong oxidant is an inorganic water-soluble strong oxidant or a water-soluble organic strong oxidant. Preferably, the strong oxidant is an inorganic water-soluble strong oxidant. More preferably, the strong oxidant is potassium permanganate, persulfate, or potassium ferrate. Most preferably, the strong oxidant is potassium permanganate.

3. The method according to claim 1, wherein, The mass concentration of the strong oxidant is 0.001%-1%, preferably 0.1% or 0.5%.

4. The method according to claim 1, wherein, In step 1), the soaking time is greater than or equal to 0.1 hours; and / or The soaking temperature is from room temperature to 100°C.

5. The method according to claim 4, wherein, In step 1), the soaking time is 1-4 hours; preferably, the soaking time is 2 hours or 3 hours; and / or The soaking temperature is room temperature.

6. The method according to claim 1, wherein, The organic-based thiophosphoric alkali metal precipitant is a dialkyl dithiophosphonate. Optionally, the dialkyl dithiophosphonate may be a sodium salt or a potassium salt; Optionally, in the dialkyl dithiophosphonate, the alkyl group is a straight-chain or branched alkyl group having 1-6 carbon atoms; preferably, the alkyl group is isobutyl.

7. The method according to claim 6, wherein, The dialkyl dithiophosphonate is sodium diisobutyl dithiophosphonate.

8. The method according to claim 6, wherein, The mass concentration of the dialkyl dithiophosphonate is not less than 0.1%; preferably, the mass concentration of the dialkyl dithiophosphonate is 0.2% or 0.5%.

9. The method according to claim 1, wherein, In step 2), the soaking time is greater than or equal to 0.1 hours, preferably 0.5-4 hours, and more preferably 1 hour; and / or In step 3), steps 1) and 2) are repeated at least twice; preferably, twice, four times or six times.

10. The method according to any one of claims 1 to 9, wherein, The operations in steps 1) and 2) are carried out under alkaline conditions; optionally, a pH adjuster is added to make the pH of the system greater than 7; and / or In steps 1) and 2), the soaking is either flood irrigation or high-pressure spray soaking; preferably, the soaking is flood irrigation.