The membrane separation device has few moving parts and a high degree of automation, so the focus of inspection is not on "repair" but on "monitoring trends". The performance drift of the membrane is a slow variable, and it is already too late to take action once the recovery rate has significantly decreased; therefore, it is necessary to monitor the curves of pressure difference and vacuum degree daily, and address abnormalities at their early stages to ensure long-term stable operation of the device. This article provides a checklist that can be directly copied for inspection. In addition to the checklist, a set of judgment sequences for handling abnormalities is also provided: first check where the recovery rate has dropped, then act where the vacuum degree is low, and finally replace where the pressure difference is high. When encountering fluctuations, investigate in order, avoiding detours and unnecessary dismantling and inspection.
What indicators are the inspection centered around
The health status of membrane devices is primarily reflected in five key figures: 1. Membrane inlet pressure drop - indicating the degree of smoothness between the membrane surface and the pre-filter material; 2. Vacuum level - determining the strength of the separation driving force; 3. Permeate flow rate - linked to pressure drop, reflecting the permeate quantity; 4. Discharge outlet concentration - the ultimate indicator of recovery efficiency; 5. Membrane inlet temperature - determining whether moisture condenses on the membrane surface under high humidity conditions. By recording these five figures daily and plotting trends weekly, the information obtained is more useful than any post-analysis.
Routine inspection items
| inspection item | focus | Abnormal direction |
|---|---|---|
| Pressure difference before membrane | The trend is stable | The increase is mostly due to filter material blockage |
| degree of vacuum | Rated range | Check the pump and seal |
| Permeate flow rate | Match with pressure difference | Preprocessing before descent |
| emission concentration | Below the limit | Check the film thickness and working conditions against the standards |
| Temperature before membrane | Allowable interval | Excessive pre cooling and dehumidification |
| Vacuum pump | Oil level temperature rise | Abnormal shutdown according to procedures |
Membrane devices are mostly unattended, and the value of inspection lies not only in detecting faults but also in accumulating data for performance evaluation. Without continuous accumulation of daily data, quarterly calibration becomes a sourceless stream, and abnormal analysis can only rely on guesswork. When recording data, it's helpful to take a glance at the site: check for signs of leakage, unusual noises, and unusual smells, and verify if the instrument readings align with the recorded values. These details often provide firsthand clues beyond the data.
How to handle common abnormalities
Decreased recovery rate: First check whether the filter material and dehumidification in the pretreatment section are compromised, then inspect the vacuum system, and finally evaluate the membrane layer - most "membrane attenuation" is due to issues in the upstream section. Vacuum degree cannot be increased: Check the status of the vacuum pump, pipeline flange sealing, and permeate side back pressure item by item. Insufficient vacuum directly reduces the driving force and should be addressed as a priority. Abnormal increase in pressure difference: It is highly likely that the upstream filter material is clogged, and the issue should be determined after replacing the material. Occasional emission concentration exceeding standards: First check whether the operating conditions exceed the design concentration and gas volume, then inspect the membrane layer, and keep the data on file for comparison.
Nighttime and holidays are weak periods for inspection, relying heavily on automatic alarms: limit alarms for pressure difference, vacuum degree, and emission concentration should be confirmed one by one to be in operation, and the responsible person on duty for alarm push notifications should be assigned to a specific individual. Whenever an alarm occurs, there must be a response record. It is better to make an extra trip than to let the alarm become a habitually ignored issue.
How to use inspection records
- Record five indicators daily and draw a trend chart weekly;
- Record the dates and details of filter material replacement and vacuum pump maintenance in the ledger;
- After seasonal changes and maintenance, conduct more frequent inspections for one week;
- Record the reasons and measures for handling anomalies, and form a closed loop;
- Quarterly performance calibration, with the calibration data serving as the basis for life assessment.
Frequently Asked Questions
Is an increase in pressure difference necessarily a membrane issue?
Not necessarily. Most of the time, it's the pre-filter material that gets clogged first. First, replace the filter material and observe whether the pressure drop decreases. If it remains high after replacement, then further inspect for membrane surface contamination. Getting the order wrong can turn a minor issue into a major repair.
How is the inspection frequency determined?
For devices with high automation, visual inspection and data recording once a day are sufficient; during peak oil receiving and dispatching periods, seasonal transitions, and within one week after maintenance, inspection should be intensified; parts that have experienced abnormalities should be included in the key observation list.
What should we do if the emission concentration occasionally exceeds the standard?
First, verify the operating conditions: check if the concentration and gas volume exceed the design range; then inspect the vacuum system and membrane status. Keep the operating condition data for the period when the standards were exceeded on file. Most occasional exceedances can be traced back to the operating condition records.
This article is compiled by Luoyang Wohong Petrochemical Equipment Co., Ltd. The company provides design and manufacturing, skid-mounted customization, installation and commissioning, as well as after-sales operation and maintenance services for three-time oil and gas recovery equipment to gas stations and oil depots. If you need on-site inspection or scheme configuration, please feel free to contact us for discussion.