Method for chemical demulsification of solids-laden oily water in the oily water tank of a platform vessel and system

Abstract

The present invention relates to a method and system for demulsification of oil-containing water and belongs to the technical field of oil production processes, primary processing technology, oil recovery technology and effluent treatment and can be applied for treatment of solid-containing oil-containing water in slop tanks of ships, platforms, drilling and oil production facilities.

Description

Technical Field

[0001] This invention belongs to the technical fields of oil production processes, primary processing technology, oil recovery, and effluent treatment, and can be applied to the treatment of solid-containing oily water in oily water tanks of ships, platforms, drilling rigs, and oil production facilities. Specifically, this invention relates to a) a method and system for demulsifying oily water in oily water tanks. Background Technology

[0002] Oil and gas production generates substantial effluents, among which oily water is one of the major challenges facing the oil industry. In addition to rainwater and seawater, this type of effluent contains complex mixtures of hydrocarbons, heavy metals, and other elements / pollutants, such as greases, inorganic / organic solids, and shock biocides used to prevent the formation of sulfate-reducing bacteria (SRB). This makes robust treatment difficult to implement and, if not handled properly, can cause severe environmental damage.

[0003] Environmental legislation sets stringent standards for the treatment and disposal of effluents, requiring companies in the sector to invest in advanced technologies and effective separation and purification processes. However, compliance with regulations is only part of the challenge, as improper waste management can pollute water bodies, impact aquatic flora and fauna, and harm the drinking water quality of local communities.

[0004] Beyond environmental impacts, oily effluent generated during oil production also poses significant risks to human health. Exposure to hydrocarbons and heavy metals present in these effluents can cause a range of health problems, including respiratory and skin diseases, and even cancer. To mitigate these risks, the oil industry must not only implement effective treatment measures but also continuously monitor effluent quality and conduct regular audits to ensure compliance with environmental standards. Therefore, developing more efficient and sustainable technologies is crucial for reducing pollutant loads in effluents, protecting the environment, and ensuring the health and safety of populations affected by oil and gas production activities.

[0005] One of the parameters assessed when disposing of produced water / oily water into the sea is the oil and grease content (OGC), typically determined in a marine laboratory using ultraviolet / visible spectrophotometry (API-RP 45). In the case of oily water, the treated OGC must be less than or equal to 15.0 mg / L, as required by current legislation MARPOL 73 / 78. Oily water generated on platform vessels is usually directed to oil storage tanks / oil slop tanks (called sloptanks) for further treatment and to comply with current legislation.

[0006] Excess oily water exceeding specifications can be temporarily transported to oil tanks that lack suitable construction for this purpose, thus reducing the platform's operational capability for storing oil. To mitigate this problem, the oily water is typically unloaded onto other vessels that transport it to the terminal, which involves significant costs and requires compliance with OGC limits and other parameters to receive the water.

[0007] Furthermore, given that the limit for BSW (alkaline sediments and water) in oil is 0.5%, and in some places it may be even lower (e.g., about 0.2% and 0.3%), it is sometimes necessary to transport a small excess volume of non-compliant oil-containing water with the oil, so that the missing percentage of "ballast" for unloading is filled with this non-compliant oil-containing water.

[0008] Implementing solutions known in the literature, such as filtration systems, supercritical water oxidation, microelectrolysis, membrane separation, and the application of superacids, presents significant challenges. The lack of available physical space on board, the high costs associated with acquiring, installing, and implementing these technologies, and the structural integrity limitations of oily water tanks that must store water with a pH between 6 and 8 units all hinder the adoption of these solutions.

[0009] In the context of oil production, the formation of undesirable Pickering emulsions (oil / water / solids emulsions) in oily water presents an additional challenge. These emulsions are stabilized by solid particles present in the production water, such as silicates and clays, which form a physical barrier at the oil-water interface, hindering phase separation. This makes proper treatment and disposal of the effluent difficult, increasing operational costs and the environmental risks associated with oily water management.

[0010] Conventional processes, such as acidification (acetic acid and HCl), coagulation / flocculation (polyaluminum chloride, tannins and polyacrylamide, carbodiamine, acrylic polymers and mixtures of ethoxylated, propoxylated and sulfonated resins, etc.), and oxidation processes (H2O2, NaOCl, performic acid, peracetic acid, etc.), have proven inefficient in separating solid aggregates / oil from water, cannot specify TOG values, and in some cases may decrease / increase the pH of the treated water by more than 6 to 8 units.

[0011] Therefore, the effective management of oily water on the platform remains a complex challenge, requiring innovative and cost-effective solutions to meet environmental and operational requirements. Existing technology

[0012] Currently, there are no effective methods for solving the above scenarios in the market or academia. Some existing technical literature addresses the treatment of oily water.

[0013] The literature SMITH, Corinne F., “Destabilization and Separation of DrillingMud by Utilizing Chemicals and Mechanical Equipment” Dissertation (Master's) - Environmental Technology, Offshore Environmental Engineering, Faculty of Science and Technology, University of Stavanger and Norwegian-Group AS. Stavanger, p. 109. 2014 describes the evaluation of chemical mixtures for treating drilling fluid waste, optimized for different types of oil-based drilling fluids (water-in-oil emulsions, also known as inverse emulsions). This literature points to the use of chemical mixtures in oil-based drilling fluids containing solid residues, which differ from the characteristics of the fluid known as oil-water (generally characterized as a conventional emulsion (oil-in-water)) found primarily in the oily water tanks of FPSOs (Floating Production Storage and Offloading) systems. The literature describes the separation of three distinct phases—oil, water, and solids—after treating the drilling fluid with the chemical mixtures under optimized conditions. Three-phase separation means that solids settle to the bottom of the tank and are thus discharged into the sea. In benchtop testing, when solids settle to the bottom, the treated water fails to meet OGC (Total Oil Content) standards. In this way, the separation of three different phases reported by SMITH, Corinne F. differs from the phase separation indicated in this invention, where only two different phases are separated: solid aggregates / oil (floating layer) and clarified water. The aggregation of solids in the oil occurs through the action of surfactants contained in the chemical formulation, preventing the solid phase from settling to the bottom of the tank, allowing free water that meets the legal OGC parameters to be discharged into the sea without requiring additional steps to remove the solids.

[0014] Accordingly, the paper Knudsen, BL, Hjelsvold, M., Frost, TK, Svarstad, MBE, Grini, PG, Willumsen, CF, and H. Torvik. “Meeting the Zero Discharge Challenge for Produced Water.” - Paper presented at the SPE International Conference on Health, Safety, and Environment in Oil and Gas Exploration and Production, Calgary, Alberta, Canada, March 2004, doi:https: / / doi.org / 10.2118 / 86671-MS—presents technologies for the purification of oily water generated during oil exploration and production, and discusses existing technologies and methods for treating and reusing produced water to minimize environmental impact. Various methods are employed, including phase separation, chemical treatment, and advanced filtration technologies. The paper also evaluates the effectiveness of these technologies in different operational scenarios and emphasizes the importance of stringent regulations and sustainable practices for achieving zero-discharge targets. However, the literature mentions purifying produced water from oil by using C-tour technology to remove the organic phase from hydrocarbons condensed from liquefied natural gas via liquid-liquid extraction. It is important to emphasize that initially, the produced water from the oil exhibits compositional characteristics distinctly different from the oily water containing solids found in the oily water tank. Considering the use of condensate hydrocarbons, which are generally considered nonpolar covalent molecules, it can be inferred that they function in removing molecules with nonpolar properties in their chemical structure, without significant interaction with predominantly polar or inorganic molecules; therefore, there is no evidence of removal of such polar or inorganic molecules. On the other hand, the use of the chemical agents indicated in this invention demonstrates the separation of two phases: solid aggregates / oil and treated water, indicating that the presence of surfactants affects the hydrophilic properties of the solids, which would be impossible for nonpolar molecules from natural gas condensate. Furthermore, the treatment proposed by the authors involves a pressurized system, which differs from the atmospheric system proposed in this invention.

[0015] Patent document PI9714548-3 describes a method for simultaneously extracting dispersed and dissolved hydrocarbon contaminants from water. This method is based on the principle of injecting a natural hydrocarbon gas (solvent) into the water feed stream under pressure and temperature conditions that allow the gas to act as a solvent for the dissolved and dispersed hydrocarbon contaminants, thereby disrupting the oil-in-water emulsion. The dispersed particles “expand” and have a reduced density, which significantly improves the downstream separation efficiency of the liquid-liquid hydrocyclone. Unlike this invention, separation occurs in a pressurized system, which enhances the separation efficiency of the hydrocyclone. As indicated in this document, the oil-containing produced water differs from the oily water from the oily sludge tank. It is not apparent from this document that the method removes inorganic or organic solids typically present in oily water, unlike the proposal of this invention, where chemical agents facilitate the separation of two distinct phases: solid aggregates / oil and clarified water. Furthermore, it is unnecessary to transport the clarified water to the hydrocyclone equipment for final purification, as the chemical treatment is sufficient to make the water compliant with regulations for discharge into the sea.

[0016] Finally, the literature Pascoal, MSD et al., “Intensification of naphthenic acids removal by liquid-liquid extraction of synthetic offshore produced water using onboard fuel”, Process Safety and Environmental Protection, 182 (2024) 11–19. https: / / doi.org / 10.1016 / j.psep.2023.11.037 (available online November 23, 2023), describes how the high cost of produced water treatment on offshore platforms, due to the volume, flow, space constraints, and solvent availability of effluents, hinders the petrochemical industry's development of feasible alternative strategies to establish sustainable treatment of this byproduct. Therefore, this literature proposes the use of diesel fuel as onboard fuel in offshore facilities to remove naphthenic acids (model compounds of dissolved organic fractions) via liquid-liquid extraction. The method proposed in this literature involves using diesel fuel to remove naphthenic acids (water-soluble fractions) from oil-containing produced water. The produced water (synthetic water) indicated in the literature differs in characteristics from oily water from oily water tanks. The use of diesel fuel did not significantly promote the extraction of organic and inorganic solids, nor did it achieve the separation of only two distinct phases (solid aggregates / oil) as indicated in the present invention. Furthermore, in this literature, separation was more effective at pH 4, which exceeds the established pH limits (6 to 8) for water storage in oily sludge tanks.

[0017] In this way, the problem to be solved is to establish a system and method that makes it easier to handle oily water containing solids in oily water tanks on ships, platforms, drilling and oil production facilities, ensuring safer, more efficient and productive operations. Summary of the Invention

[0018] The present invention aims to improve the efficiency of oily water treatment on offshore platform vessels, minimize disposal costs, optimize the use of available physical space, and ensure compliance with environmental regulations.

[0019] In a first embodiment, the present invention relates to a chemical demulsification method for oil-water mixtures.

[0020] In a second embodiment, the present invention relates to a heated chemical demulsification system for oil-water mixtures.

[0021] According to the present invention, chemical demulsification of oily water (with or without heating) is used in the oily water tanks of platform vessels to destabilize the solids-containing oily water emulsion, facilitating the separation of oil / solid aggregates from the treated water. The total oil and grease content (OGC) is reduced to regulatory limits, and the treated water can be discharged into the sea. No excess oily water exceeding specifications accumulates from the discharge of treated water into the sea, and therefore all oil tanks can receive oil. Chemical demulsification maintains the hydrogen ion potential (pH) of the treated water within the limits set to maintain the structural integrity of the oily water tank; i.e., between 6 and 8 units, thereby preventing accelerated corrosion processes. A small portion of the oil / solid aggregates is pumped out from the "clean slop" tank and distributed to the oil tanks, where it is redissolved.

[0022] The design includes two oil sludge tanks: a "dirty slop" tank, the first-stage tank, receives various water sources and waste from the platform to form "oily water," where coarse gravity separation occurs. A "clean slop" tank, the second-stage tank, receives the "cleaner" water decanted from the "dirty slop" tank via pipes connected to the bottom of the "dirty slop" tank. After a second decantation in the "clean slop" tank, the clarified water passes through two-stage hydrocyclones in series and can be discharged into the sea or returned to the "dirty slop" tank, depending on the OGC value.

[0023] Advantageously, the present invention provides a method and system applicable to treating solid-containing oily water from oily water tanks of ships, platforms, drilling rigs and oil production facilities.

[0024] In short, due to the practicality provided by the method and system proposed in this invention, the present invention has the following advantages:

[0025] • Eliminates the high costs associated with unloading non-compliant oily water, which can amount to millions of reais.

[0026] • Stop the accumulation of non-compliant oily water in the oil tanks and preserve the original design space of these tanks.

[0027] • Protect the structural integrity of the oil tanks.

[0028] • Ensure the operational safety of oily water treatment and disposal activities from the platform.

[0029] • Reduce the risk of being fined for failing to comply with regulatory limits on oil and fat content (OGC) and prevent oil spills at sea.

[0030] These objectives and other advantages of the present invention will be better described in the following sections. Attached Figure Description

[0031] To supplement this specification and to better understand the features of the invention, a set of figures are presented in the appendix. These figures illustrate preferred embodiments in an exemplary and non-limiting manner.

[0032] Figure 1 A schematic diagram of the claimed system according to one embodiment of the present invention is presented: 1-Oil-containing water: Oily water system: - Rainwater; - Oil and grease; - Deck cleaning fluid; - Chemical waste, etc.; Others: - Seawater; - Impact biocides); 2- Chemical injection point; 3- Chemical injection point; 4- Cargo hold (oil); 5- Waste; 6- First-stage oily water tank or dirty oily water tank; 7- Second-stage oily water tank or clean oily water tank; 8- Pump; 9- Heater; 10- Offshore (at sea); 11- Online OGC analyzer; 12- Hydrocyclone; 13- Chemical injection point; 14- Pump; 15- Oily waste receiving vessel (oily water vessel) from the platform oil treatment unit. The dirty oily water tank is equivalent to the first-stage oily water tank, which receives oily water from all sources; the clean oily water tank is equivalent to the second-stage oily water tank, which receives the "cleaner" water decanted from the dirty oily water tank.

[0033] Figure 2 The results of a benchtop test using Al2O3 as a coagulant / flocculator, conducted via a conventional chemical approach, are shown.

[0034] Figure 3 The results of benchtop tests using (a) H2O2 or (b) NaOCl as oxidants via conventional chemical methods are shown.

[0035] Figure 4The results of chemical destabilization of oil-water containing solids at 25°C are shown, wherein solid / oil aggregates form an emulsion, resulting in a well-defined interface profile, and clear water is decanted out.

[0036] Figure 5 A contour plot of OGC (mg / L) versus temperature and concentration is shown in one embodiment of the invention. Detailed Implementation

[0037] According to a preferred embodiment of the present invention, a method and system for chemical demulsification of oil-water mixtures are described in detail below with reference to the accompanying drawings.

[0038] According to a preferred embodiment of the present invention, a method for chemical demulsification of oil-water mixtures includes the following steps:

[0039] a) Connect the chemical product injection system to a pre-existing point at the outlet of the "dirty oil and water tank" or "clean oil and water tank" (preferably "dirty oil and water tank");

[0040] b) Determine the known volume of oily water exceeding the specified limits in the "dirty oily water" or "clean oily water" tank;

[0041] c) Optionally, the oil-containing water is heated;

[0042] d) Calculate the amount of chemical products to be used based on the volume of oily water in the sludge tank;

[0043] e) Injecting chemical products into oily water;

[0044] f) Recycle the oil-containing water along with the product for homogenization;

[0045] g) Wait for phase separation.

[0046] After phase separation, optionally, the OGC of the treated water is measured. After bringing the OGC specifications of the treated water within the regulatory limits (less than or equal to 15 mg / L), the method optionally includes initiating the discharge of the treated water into the sea.

[0047] In one embodiment of the invention, the amount of chemical product used is 250 ppm to 3000 ppm, preferably 500 ppm to 2500 ppm, and more preferably 1000 ppm to 2000 ppm, depending on the volume of water in the sludge tank.

[0048] In one embodiment of the invention, phase separation occurs within a time frame of 10 to 240 minutes, preferably 20 to 180 minutes, and more preferably 30 to 120 minutes.

[0049] The use of commercial chemical formulations (DORF OG 4031B) ensures the instability of the emulsion, facilitates the emulsion stratification of solid / oil aggregates on the liquid surface, promotes high-quality water decanting at the bottom of the sludge tank (compliant with specified OGC), and keeps the pH within acceptable limits.

[0050] Commercial chemical formulations are based on branched aromatic hydrocarbons that exhibit phase separation at concentrations approaching 10,000 ppm, such as toluene; o-xylene; cumene; n-propylbenzene; m-ethyltoluene, p-ethyltoluene, etc.

[0051] According to a preferred embodiment of the present invention, a system for chemical demulsification of oil-water mixtures comprises:

[0052] i. At least one dirty oil and water tank;

[0053] ii. At least one cleaned oil and water tank;

[0054] iii. At least one chemical product inlet in each compartment; preferably, the chemical product inlet is located in a dirty oil and water compartment; and

[0055] iv. An additional set of hydrocyclones.

[0056] In a preferred embodiment of the invention, chemical demulsification occurs directly in the sludge tank, while the hydrocyclone, used to separate immiscible fluids (water / oil), is located after the clean sludge tank. In this way, the water reaching the hydrocyclone has already been conditioned in the clean sludge tank.

[0057] result

[0058] Figure 2 The results of a benchtop test using a conventional chemical approach with Al2O3 as a coagulant / flocculator are shown. Figure 3 (a) and Figure 3 (b) Benchtop test results are shown for conventional chemical approaches using H2O2 or NaOCl as oxidants. These results did not meet the pH limits required for OGC specifications or oily / sludge tanks.

[0059] Based on the experimental results, the conditions for applying the chemical product are: a concentration range of 1000 ppm to 2000 ppm; preferably 1500 ppm; a temperature between 25°C and 50°C; and a treatment time of 30 minutes to 120 minutes.

[0060] As shown in Table 1, at the end of the process, the OGC of the oily water decreased from approximately 200 mg / L to below 15 mg / L. The final turbidity decreased from 100 FTU to near zero FTU, and the water became clear. Furthermore, the final hydrogen ion potential (pH) of the treated water was within the limit range of 6 to 8.

[0061] Commercial chemical formulations (DORF OG 4031B) ensure the instability of the emulsion, facilitating the emulsion stratification of solid / oil aggregates on the liquid surface, resulting in high-quality water decanting at the bottom of the sludge tank (compliant with specified OGC) and pH within limits.

[0062] Table 1 Desktop test results

[0063]

[0064]

[0065] Figure 4 The results of chemical destabilization of oily water containing solids at 25°C are shown, wherein the solid / oil aggregates form an emulsion with a well-defined interface, and clear water is decanted out, demonstrating the applicability of the method according to the invention. The pH of the treated water is between 6 and 8, that is, within the limits specified in the oily water tank.

[0066] Factorial design was performed considering variables such as concentration, temperature, and OGC to better predict system behavior. Results are shown in Table 2 and... Figure 5 As shown.

[0067] Table 2 : 2 with repeated trials and triplet trials at the center point 2 Results of factor design matrix and response variable OGC (mg / L).

[0068]

[0069] Those skilled in the art will understand the knowledge presented herein and that the invention can be reproduced in the presented embodiments and in other variations covered by the appended claims.

Claims

1. A method for chemical demulsification of oil-water mixtures, characterized in that, The method includes the following steps: a) Connect the chemical product injection system to a pre-existing point at the outlet of the sludge tank (first-stage sludge tank, "dirty sludge tank", or second-stage sludge tank, "clean sludge tank"; preferably "dirty sludge tank"); b) Determine the (known) volume of oily water exceeding the specified limit in the dirty oily water tank or the clean oily water tank; c) Optionally, the oil-containing water is heated; d) Calculate the amount of chemical products to be used based on the volume of water in the sludge tank; e) Inject the chemical product into the oily water; f) The oil-containing water is recycled together with the product for homogenization; g) Wait for phase separation.

2. The method according to claim 1, characterized in that, The chemical product injection system at a pre-existing point at the outlet is preferably interconnected to the "dirty oil and water tank".

3. The method according to claim 1, characterized in that, After the phase separation, the method includes measuring the OGC of the treated water.

4. The method according to claim 3, characterized in that, When the OGC of the treated water is less than or equal to 15 mg / L, the method includes initiating the discharge of the treated water into the sea.

5. The method according to any one of claims 1 to 4, characterized in that, The amount of the chemical product used is 250 ppm to 3000 ppm, preferably 500 ppm to 2500 ppm, and more preferably 1000 ppm to 2000 ppm, depending on the volume of water in the oily waste tank.

6. The method according to any one of claims 1 to 5, characterized in that, The phase separation occurs within a time period of 10 to 240 minutes, preferably 20 to 180 minutes, more preferably 30 to 120 minutes, and at a temperature of 25°C to 50°C.

7. The method according to any one of claims 1 to 6, characterized in that, The method uses commercially available chemical agents based on branched aromatic hydrocarbons, such as toluene, o-xylene, cumene, n-propylbenzene, m-ethyltoluene, p-ethyltoluene, etc.

8. The method according to any one of claims 1 to 7, characterized in that, The commercial chemical preparation is preferably DORF OG 4031B.

9. The method according to any one of claims 1 to 8, characterized in that, The clarified oily water has an OGC concentration of less than 15 mg / L, a turbidity of zero FTU, and a pH of 6 to 8.

10. A system for chemical demulsification of oil-water mixtures, characterized in that, The system includes: i. At least one primary oily / sludge tank; ii. At least one secondary oily / sludge tank; iii. At least one chemical product inlet in each compartment; and iv. An additional set of hydrocyclones.

11. The system according to claim 10, characterized in that, The chemical demulsification occurs directly in the sludge tank, and the hydrocyclone located after the cleaned sludge tank separates the immiscible fluids (water / oil).

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