Key Considerations for Three-Phase Separators Testing

In the petrochemical industry, three-phase separators play a crucial role. They are mainly used to separate oil, gas, and water, and their performance directly affects production efficiency, product quality, environmental protection, and operating costs. Therefore, when selecting or evaluating a three-phase separator, it is necessary to fully consider its design, operation, and actual working conditions to ensure it can meet the complex industrial requirements.

Key Testing Points for Separation Efficiency

In the petrochemical industry, the performance of three-phase separators directly affects production efficiency, product quality, environmental protection, and operating costs. To ensure that the separator can operate efficiently, the following are some key testing points for separation efficiency.

1. Water Content in Oil (BS&W)

The water content in oil is one of the important indicators for measuring separation efficiency. Typically, the target value should be controlled below 0.5%–5%, with specific requirements depending on downstream processes. For example, refining processes have stricter requirements for water content in oil, as excessive water can affect subsequent processing, reduce product quality, and even cause equipment failures. By accurately measuring the water content in separated oil, the separator's performance in removing water can be evaluated, ensuring that the oil meets the requirements of downstream processes.

2. Oil Content in Water (OIW)

The oil content in water is equally critical, and its target value must meet environmental discharge standards or reinjection requirements. Generally, environmental standards require the oil content in water to be below 20–40 mg/L, or even lower. If the oil content in water exceeds the limit, it can not only pollute the environment but also expose the company to high fines and legal risks. Therefore, testing the oil content in water is an important step in evaluating the separator's environmental performance, ensuring it can effectively remove oil to meet discharge or reinjection standards.

3. Liquid Carryover in Natural Gas

The amount of liquid carried in the outlet natural gas (such as oil droplets or water droplets) must also be strictly controlled. The target value is usually very low, for example, below 0.1 US gal/MMscf, to meet the requirements of downstream gas processing equipment (such as compressors and desulfurization units). Excessive liquid carryover may cause instability or damage to downstream equipment, affecting the normal operation of the entire production system. By testing the liquid content in natural gas, the separator's efficiency in removing liquid impurities from gas can be evaluated, ensuring stable operation of downstream equipment.

Operational Stability Testing of the Separator

On the basis of ensuring separation efficiency, the operational stability of the separator is equally important. Only when operating stably can the separator continuously and efficiently perform the separation task, avoiding production interruptions and additional costs caused by equipment failures or performance fluctuations. The following are key points for testing operational stability.

1. Retention Time Verification

Verifying whether the actual retention time of oil and water phases in the separator reaches the design value is the basis for ensuring separation efficiency. Insufficient retention time may result in incomplete separation, affecting the separation effect. By monitoring and verifying retention time, it can be ensured that the separator can effectively separate oil, gas, and water under design conditions, achieving the expected separation efficiency.

2. Flow Handling Capability

Under specified inlet conditions (pressure, temperature, flow rate, gas-oil ratio, water content, and fluid properties), it should be tested whether the separator can stably handle the design flow while meeting the above separation efficiency requirements. Additionally, the separator's adaptability to fluctuations in flow, gas-oil ratio, and water content should be tested. For example, under complex conditions such as slug flow, whether the liquid level control remains stable and whether separation efficiency drops significantly should be evaluated. These tests can assess the separator's ability to respond to changes in operating conditions, ensuring it maintains stable operational performance under different conditions.

3. Liquid Level Control System Testing

The performance of the liquid level control system is critical to separation effectiveness. The sensitivity, stability, and accuracy of interface control systems (such as interface meters, weirs, guided-wave radar, and control valves) must be tested to ensure stable oil-water interface levels under various conditions. Additionally, the stability and response speed of oil and water phase level control must be tested, as well as the system's ability to quickly recover stability under flow, composition changes, or slug flow impact. These tests ensure that the separator can effectively control liquid levels during operation, preventing adverse effects on separation efficiency caused by liquid level fluctuations.

Safety and Reliability Testing of the Equipment

In the petrochemical industry, equipment safety and reliability are the cornerstone for ensuring smooth production and personnel safety. As a key piece of equipment, the safety and reliability of three-phase separators must undergo strict testing and verification to ensure stable operation under complex conditions and to prevent potential safety incidents. The following are key points for safety and reliability testing.

1. Pressure and Sealing Performance

Testing the separator's pressure and sealing performance under design pressure and temperature is an important step to ensure safe operation. Through pressure tests and airtightness tests, the separator's sealing performance under normal and extreme conditions can be verified, preventing safety incidents and environmental pollution caused by leaks.

2. Evaluation of Operating Parameter Effects

Verifying the impact of operating pressure and temperature on separation efficiency is also essential. Temperature affects fluid viscosity, while pressure affects gas solubility and droplet settling and coalescence. By testing the effect of these parameters on separation efficiency, operating conditions can be optimized to improve efficiency while ensuring safe operation of the equipment.

3. Safety Valve and Alarm System Testing

The reliability of safety valves and alarm systems directly affects equipment safety. The set points and discharge capacity of safety/relief valves must be verified, and the accuracy and reliability of high/low liquid level and pressure alarms and interlocks (such as emergency shutdown) must be tested. Additionally, the response speed and effectiveness of emergency shutdown systems should be tested to ensure rapid action in emergencies and prevent accidents.

Medium Adaptability and Internal Component Evaluation

Moreover, the design and performance of internal components directly affect the overall performance of the equipment. Therefore, evaluating medium adaptability and internal components is an important step to ensure long-term stable operation. Key evaluation points include:

1. Fluid Properties Testing

Assess the fluid's density, viscosity, pour point, wax content, and asphaltene content to evaluate the separator's adaptability to high-viscosity, easily solidifying, and high-wax crude oil. For such special fluids, heating or special design may be required to ensure effective operation. Additionally, the water phase system's mineralization, hardness, scaling tendency, corrosiveness (such as H₂S, CO₂, O₂, Cl⁻ content), and suspended solids content should be evaluated to assess their impact on pipelines, valves, and instruments.

2. Emulsion and Foam Handling Capability

Test the degree and stability of fluid emulsions and verify the effect of demulsifier injection systems (if used) and the separator's own handling capacity. Additionally, assess whether the fluid easily produces foam and evaluate the effectiveness of internal design (such as defoaming baffles) or defoamer injection in controlling foam. Foam can affect liquid level measurement and gas space, so the separator must be capable of handling foam effectively to avoid adverse impacts on operation.

3. Solid Settling and Discharge Capability

Evaluate the settling, accumulation, and discharge capacity of solids such as sand, scale, and sludge, and test the effectiveness of sand outlets and sludge scrapers. Accumulation of solid impurities can block the separator, reducing separation efficiency and equipment lifespan. Testing solids settling and discharge capability ensures the separator can effectively handle solids and maintain proper operation.

Maintenance and Long-Term Operation Assessment

Through regular maintenance and comprehensive long-term operation assessment, potential issues can be identified in time, equipment performance can be optimized, service life can be extended, operating costs reduced, and production efficiency improved. Key points include:

1. Material Selection and Nondestructive Testing

Evaluate material selection (such as carbon steel, stainless steel, internal coating/lining) based on the corrosiveness of the medium, and inspect wear-prone areas (such as inlet zones and sand accumulation areas). Conduct regular nondestructive testing, such as wall thickness measurement (UT) and weld inspection (RT/UT), to assess equipment integrity and service life. These measures allow potential issues to be detected in time and maintenance actions to be taken to extend equipment life.

2. Long-Term Stability Testing

Short-term tests may not expose all issues such as scaling, blockage, or instrument drift. Therefore, tests of sufficient duration should be conducted to evaluate the long-term stability of the separator. Long-term stability testing allows comprehensive assessment of performance under actual operation, ensuring consistent separation efficiency and operational status over time.

3. Compliance and Instrument Calibration

Strictly test the oil content in water at the outlet to ensure compliance with local environmental regulations for produced water discharge or reinjection. Calibrate key instruments such as pressure gauges/transmitters, thermometers/transmitters, level meters, flow meters, water content analyzers, and oil content analyzers to ensure measurement accuracy and reliability. These measures ensure separator operation meets regulations and standards, avoiding risks associated with non-compliance.

Conclusion

Selecting or testing a three-phase separator in the petrochemical industry is a complex system engineering task, requiring comprehensive evaluation from multiple dimensions including separation efficiency, handling capacity, operational stability, safety and reliability, medium adaptability, and compliance. A detailed test plan based on actual operating conditions is key to ensuring long-term efficient, safe, and compliant operation of the separator. During evaluation, special attention must be paid to oil-water interface control, emulsion/foam handling, corrosion protection, and discharge compliance, challenges unique to the petrochemical industry.