I. Oily wastewater purification process on offshore oil platforms

The design of an oily wastewater treatment scheme mainly depends on oil specific gravity and the required treated-water quality standard: oils with low specific gravity, having a large oil-water density difference, are easy to separate and require fewer treatment stages; if the injection water standard is strict, more treatment stages are needed. Based on the required treated water quality, combined with peak wastewater flow, formation water characteristics and treatment objectives, and considering offshore space constraints, economically reasonable purification equipment and processes are selected.

The oily wastewater purification steps are as follows: oily wastewater from the production separators and electrostatic dehydrators, together with the added chemicals (corrosion inhibitors, scale inhibitors, bactericides, coagulants and reverse demulsifiers), enters the inclined-plate oil separation unit, where primary separation removes free oil larger than 50 microns. The separated oil is pumped to the closed drain tank, while the oily wastewater is sent by the production water pump to a hydrocyclone for secondary treatment. The oil from the hydrocyclone enters the closed drain tank under its own pressure; at this point most oil droplets in the wastewater are smaller than 20 microns. The oily wastewater then enters the walnut shell filter unit for tertiary purification: the walnut shell filter mainly adsorbs oil from the wastewater through its filter media, effectively removing emulsified and dispersed oil. The water leaving the walnut shell filter meets the injection standard and can be delivered under its own pressure to the injection pump for injection into the formation. Regeneration of the walnut shell filter media is achieved by backwashing with water from the backwash tank; the backwash wastewater enters the post-backwash water tank and is used to clean the inclined-plate separator. This backwashing process is completed by the automatic control valves of the walnut shell filter.

II. Walnut shell filter unit

The walnut shell filter unit is an automated filtration device for oily wastewater, consisting of three filter vessels sharing one control system, with both automatic and manual operating modes. It uses walnut shell and serpentine as filter media, with fast treatment and high purification precision.

1. Structure and working principle

The walnut shell filter mainly consists of three filter vessels, a pipe manifold, an automatic control system (instrument air manifold, differential pressure lines and control circuits), a base, an operating platform, ladders, electric heat tracing and insulation.

Incoming water enters the filter layer from the filter vessel inlet through the distribution pipe and discharges from the vessel outlet. When suspended solids in the incoming water are retained by the media to a certain degree and the filtration differential pressure reaches 0.15 MPa, or the filtration time reaches 1,420 minutes, the program enters the backwash sequence, with a backwash time of 20 minutes. If the filtration time has not reached 1,420 minutes but the pressure difference between vessel inlet and outlet reaches 0.15 MPa, filtration stops and the backwash sequence begins.

2. Automatic control sequence

After connecting the power and pressing the "Power" button, the power indicator on the control cabinet panel lights up; then toggle the operation mode selector switch so the "Automatic" mode indicator lights; turn the filter vessel selector switch to choose the corresponding vessel and press the "Start" button - the selected filter vessel will then automatically cycle according to the sequence in the "process block diagram" under set time or differential-pressure control conditions; pressing the "Stop" button closes all valves and motors of that filter vessel, stopping operation automatically.

At present, oily wastewater has become the main water source for oilfield injection. For this kind of water quality, using a deep treatment process for oily wastewater can achieve ideal treatment results. The walnut shell filter shows the following advantages in this process:

(1) The walnut shell surface is rather rough with many pores, so it easily adsorbs dirty oil; walnut shell is wear-resistant and does not easily break; it is chemically stable and acid/alkali resistant; it is easy to regenerate without adding chemicals; and the raw material is widely available.

(2) In the later stage of oilfield development, the water cut of produced fluid keeps rising and the volume of oily wastewater keeps increasing, so wastewater treatment costs keep rising. How to reduce treatment costs and improve treated-water quality has attracted wide attention. Using walnut shell filters can improve oil removal efficiency, reduce later-stage wastewater treatment investment, and raise treated-water quality indicators.

(3) The effectiveness of wastewater treatment also depends on the supporting chemicals selected, so it is important to strengthen the development of low-cost supporting chemicals; at the same time, to improve treated-water quality, oilfield wastewater treatment processes should be combined with other wastewater treatment methods.

III. Polymer-containing wastewater treatment in offshore oilfields

Compared with ordinary water-flood wastewater, polymer-containing wastewater has increased viscosity due to residual polymers, and the emulsification stability of oil droplets and suspended solids is significantly enhanced, making oil-water separation and oil treatment more difficult. Conventional coagulation-settling-filtration processes can hardly meet the injection water quality specification. Because of their unique conditions, offshore oilfield platform treatment systems are equipped with various high-efficiency separation devices, so the emergence of polymer-containing wastewater directly causes failure of the platform's produced-water treatment system.

IV. Innovative CFU water treatment technology for offshore oilfields

At present, the water treatment system of the production platform adopts a process combining a hydrocyclone separator with a skim oil and degassing vessel. The hydrocyclone works on the principle of oil-water density difference, achieving oil-water separation through centrifugal force; the skim vessel is connected in series after the hydrocyclone separator, performing degassing and deep oil removal through thermal chemical settling to meet the marine discharge standard (below 18 mg/L). Given that the physical properties of produced fluids will change in the future - particularly lower crude API gravity and higher viscosity, which will significantly affect gravity and centrifugal separation performance - it is imperative to adopt new water treatment technology that seamlessly connects with the existing process.

CFU Water treatment technology

1. Working principle

The CFU water treatment process achieves oil-water separation through flotation, centrifugal force and coalescence. Its working principle: gas is introduced into the equipment inlet line (natural gas or nitrogen is commonly used in oil and gas fields), generating a large number of microbubbles in the water to form a three-phase mixture of water, gas and the substances to be removed. Under the combined action of interfacial tension, bubble buoyancy and hydrostatic pressure difference, the microbubbles adhere to tiny oil droplets, forming a mixture less dense than water, which is forced up to the wastewater surface. The stratified treated media flows out through diversion pipes set at different levels in the treatment equipment.

2. Process features

(1) No internal moving parts, small footprint, easy operation; saves operating space on offshore platforms, with a high degree of automation.

(2) The organic combination of flotation and hydrocyclone processes improves the treatment efficiency of oily wastewater.

(3) Can adapt to fairly wide flow fluctuations with stable operation.

(4) Under most operating conditions, can meet the marine discharge standard for oily wastewater without chemical dosing.

V. Shenzhen SINOKLE CDFU new technology

CDFU (Cyclonic Dissolved Air Flotation Unit) introduction:

Cyclonic dissolved air flotation integrates cyclonic centrifugal separation, ultra-fine bubble generation and dissolved air flotation technologies, achieving efficient, rapid separation of dirty oil, emulsified oil and suspended solids from wastewater through the organic combination of multiple technologies. Through a high-efficiency dissolved air pump and special microbubble generation and release devices, the microbubbles are smaller, at 5-30 um. Emulsified oil droplets are 0.5-25 um; in the same size range, microbubbles can better capture emulsified oil, achieving purely physical demulsification. Combined with cyclonic centrifugal technology, this favors the interaction between microbubbles and oil droplets and increases their collision probability; due to the difference in medium density, under cyclonic centrifugal force, bubbles and oil droplets are accelerated to coalesce toward the center of the cyclone, improving flotation performance.

Process advantages:

• High oil removal efficiency (over 90% in a single stage), small removed particle size (minimum removed particle size <= 2 um)

• Skid-mounted equipment, short residence time (only 1-5 min), small footprint (only 10%-20% of conventional dissolved air flotation), small volume and light weight.

• Strong stability. No filter screens, coalescing plates or other internals - no dependence on structures and not prone to clogging - ensuring stable treatment performance.

• Strong adaptability (robustness). Can strongly adapt to different hydraulic loads, oil viscosity and oil specific gravity changes.

• Few moving parts, high reliability, quick installation, low operation, use and maintenance costs. Automatic control, stable operation, safe and reliable.

VI. Shenzhen SINOKLE CDOF  new technology

The ozone catalytic oxidation integrated flotation technology developed by SINOKLE Technology ( CDOF ) creatively combines ozone advanced oxidation, cyclonic separation and dissolved air flotation technologies, achieving efficient oxidation, decolorization and sterilization. At present, CDOF technology has been widely applied in petroleum and petrochemical, landfill leachate and other fields. CDOF technology (Cyclonic Dissolved Ozone Flotation Unit) is an innovative device that organically integrates multi-catalytic ozone oxidation, cyclonic and dissolved air flotation technologies to achieve efficient combined oxidation and removal of various pollutants in various difficult-to-treat wastewaters. The device adopts multiple patented technologies and represents internationally advanced levels.

SINOKLE Technology's CDOF technology has the following technical advantages:

• Fast reaction rate, small footprint: ozone can dissolve quickly and be highly dispersed in the wastewater under pressurization. Compared with conventional ozone aeration oxidation, CDOF technology's ozone dispersion is at least 100 times that of conventional approaches, and the reaction rate is also greatly improved. CDOF The reaction takes only 5-10 minutes, whereas conventional technology usually requires about 60 minutes. In addition, CDOF equipment occupies only 1/10 or even less of the footprint of conventional technology.

• Multiple catalysis, high proportion of indirect ozone reaction, good oxidation performance:CDOF technology adopts supercritical catalytic oxidation, catalyst-based catalysis, hydrodynamic cavitation catalysis and other multiple catalytic oxidation technologies, converting a higher proportion of ozone into indirect reactions, with better non-selective strong oxidation performance.

• High ozone utilization, low operating cost: with the same oxidation performance, CDOF technology's ozone consumption is only 1/8-1/4 of conventional technology, saving large amounts of electricity, with low energy consumption and low cost.

• Ozone oxidation combined with flotation, good comprehensive performance:CDOF technology uses ozone for gel breaking and demulsification, reducing the amount of flocculant added during flotation; the amount of oily sludge (hazardous waste) generated is reduced by more than 90%. Meanwhile, CDOF technology enhances the flotation effect, making the effluent quality more stable and separation better.

• Fully automated closed pressurized operation, less labor, simple and reliable operation and maintenance, safe and environmentally friendly. CDOF technology enables fully automated closed pressurized operation, reducing manual operations; operation and maintenance are simple and reliable. Meanwhile, CDOF technology is also safe and environmentally friendly.

VII. SINOKLE's offshore high-polymer wastewater treatment process

Process flow

Process advantages:

• CDOF Rapidly breaks polymer chains and reduces wastewater treatment difficulty; efficient dissolved air flotation replaces large-tank gravity settling, and microbubbles achieve purely physical demulsification, reducing the generation of oily sludge;

• Short process flow, compact equipment, high treatment efficiency, short residence time, small footprint;

• Skid-mounted and intelligent equipment enabling unattended fully automatic operation; stable process operation with strong shock resistance, ensuring stable and compliant water quality;