When the oil and gas recovery device is operating, the ideal state is characterized by fewer start-stop cycles and longer single operation time. If the equipment is frequently started and stopped, the lifespan of the motor and compressor will be affected, and the stability of the recovery process will also be difficult to guarantee. Frequent start-stop cycles are often caused by a combination of factors, including control settings, signal acquisition, and system capacity. When troubleshooting, it is advisable to investigate these aspects in order, starting from the top down.
What is the essence of frequent start-stop
The start and stop of the device are determined by the control system's judgment logic: the device is turned on when a certain measurement value reaches the start threshold, and turned off when it returns to the stop threshold. Frequent starts and stops indicate that the measurement value is oscillating rapidly between the two thresholds, or that the thresholds themselves are set too closely. Identifying why the value is oscillating solves most of the problem.
There are usually three sources of fluctuation: first, the signal itself fluctuates, such as when the sensor is installed in a position with unstable flow conditions, causing natural fluctuations in readings; second, the system volume is relatively small, so slight changes in the gas source immediately affect the concentration; third, the load does not match the processing capacity, meaning that when the device's processing capacity far exceeds the gas production rate, the concentration quickly drops when it is turned on, and quickly rises again when it is turned off.
How to check the control settings
{IMG}First, record the current set values of the start-stop thresholds and confirm whether they have been adjusted by referring to the design documents. It is not uncommon for the set values to be temporarily changed after several years of operation without any records being kept. The interval between two thresholds is called the return difference, and a too small return difference is a common cause of frequent start-stop operations: the thresholds for starting and stopping are almost close together, and slight fluctuations in measured values can trigger actions.
The adjustment of return difference should be carried out within the safety boundary. It is not allowed to extend the operating range beyond the process allowable limit in order to reduce the number of starts and stops. After adjustment, observe several consecutive operating cycles, record the changes in start-stop intervals, and confirm the effectiveness of the adjustment.
What should I look for in terms of sensing and signal processing
When the sensor installation location is sensitive to flow patterns, the readings will fluctuate with airflow pulsations. Check whether the sampling point is located in a straight pipe section, near a bend or a confluence point; whether there is fluid accumulation in the sampling pipeline, as fluid accumulation can cause signal delay, manifested as frequent lagging actions.
The interference from signal lines cannot be ignored: when the shielding and grounding are poor, glitches synchronized with the operation of the equipment will appear in the readings, and the response of the control system will follow these glitches. Bringing up the trend curve is the most direct way to distinguish between real fluctuations and interference.
How to determine whether the buffer volume is sufficient
| troubleshooting direction | Typical phenomenon | Processing approach |
|---|---|---|
| Return difference setting | The threshold spacing is too small | Increase the return difference appropriately within the safety boundary |
| sensor position | The readings fluctuate with the airflow pulsations | Move to the straight pipe section, away from the elbow and confluence point |
| Sampling pipeline | Signal delay, action lag | Drain the accumulated fluid and shorten the sampling pipeline |
| signal interference | Synchronous glitches appear on the curve | Check shielding and grounding |
| Buffer volume | The trigger is quickly activated after the machine stops | Install a buffer volume on the gas source side |
| Load matching | After starting up, the concentration quickly drops | Evaluate the matching between processing capacity and gas production |
If there is not enough buffer volume on the gas source side, minor changes in gas production will be directly reflected in concentration and pressure. The method of judgment is to observe the time it takes for the measured values to return to the start-up threshold after the device is shut down: if this time is only a few minutes, it indicates that the accumulation on the gas source side is slow and the system is very sensitive to fluctuations. Adding a buffer or adjusting the operation mode will significantly improve the situation.
The installation location for the buffer should be close to the air source side, as being close to the device inlet will have limited effect. After installation, continuously observe for several cycles and record the data before and after as a basis for comparison.
The order and record of investigation
- Retrieve recent start-stop records, tally the daily start-stop counts and individual operation durations, and ascertain the extent of the issue;
- Check the current settings of control thresholds and return differences, and confirm whether there are any changes compared to the design values;
- Adjust and view the trend curve of measured values to distinguish between real fluctuations and signal interference;
- Check the installation position of the sensor and the status of the sampling pipeline;
- Evaluate the buffer volume on the gas source side and the gas production pattern to determine whether additional buffering is required;
- Keep records after each adjustment, and continuously observe and compare changes in the number of starts and stops.
Frequently Asked Questions
Is frequent start-stop operation harmful to equipment?
The impact is primarily concentrated on the lifespan of motors, compressors, and valve components. The impact current from frequent starts also increases the burden on the electrical system. When the number of starts and stops is noticeably increasing, it is advisable to investigate the cause as soon as possible.
Is the larger the return difference, the better?
No. After the return difference is increased, the operating range widens, and the dwell time of the measured value within the range becomes longer. However, it is necessary to confirm that this range is still within the process allowable range, and the operating boundaries cannot be relaxed just to reduce start-stop times.
What should be considered when adding a buffer volume?
The location should be close to the gas source side, and the volume should be estimated based on the gas production pattern and the start-stop threshold interval. After installation, observe several consecutive operating cycles, compare the data before and after, and keep the records to confirm the improvement effect.
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.