1, The main mechanism and slag discharge principle of the oil separator
The spiral gear on the horizontal axis is connected to the vertical shaft, which drives the vertical shaft to rotate, thereby driving the separation cylinder on the upper part of the vertical shaft to rotate and separate the fuel (lubricating oil) inside the separation cylinder.
The separation cylinder is the core component of the oil separator, and the separation cylinder and the cylinder cover are fastened together by threaded connection;
There is a separation disk group inside the separation cylinder, which is placed on the oil distributor in the factory order;
Under the action of water pressure, the sliding chassis and separation cylinder cover below the oil distributor form a sealed space for the separation cylinder.
The fuel (lubricating oil) to be separated enters the separation chamber through the oil distributor. Under the centrifugal force of the high-speed rotation of the separation cylinder and the elastic force of the separation disc, the oil to be separated floats up through the small holes on the separation disc and begins to separate due to the difference in density. Impurities and water with higher density move outward, while oil with lower density moves upward and inward through the gaps between the separation discs.
Under high-speed rotation, impurities and fuel are separated due to their different densities. Impurities with higher density move towards the edge of the separation cylinder, while those with lower density are in the middle.
The separated oil enters the oil collection chamber and is discharged from the oil outlet pipe through the centripetal impeller.
The separated water enters the collection chamber through the gap between the top cover of the separation cylinder and the top cover of the separation disk, and is discharged from the drainage pipe through the centripetal impeller.
The water collection chamber and the oil collection chamber are separated by a specific gravity ring, and the oil-water contact point is a water interface. The specific gravity ring is an important component for controlling the oil-water interface.
The separated impurities accumulate at the edge of the separation chamber, and during slag discharge, the water pressure of the sliding chassis rapidly decreases, the sliding chassis moves downward, and the oil residue is quickly discharged.
There is a sealed water outlet on the outside of the separation cylinder, which is sealed by a pilot valve.
When separating oil, the pilot valve is seated on the valve seat under the action of centrifugal force, and the working water accumulates under the sliding chassis. Through water pressure, the sliding chassis is lifted up, and the sealing ring at the lower edge of the separation cylinder is squeezed to achieve sealing.
2. Working principle of slag discharge
When the separation reaches the set slag discharge time or the moisture sensor is triggered, the oil separator begins to discharge slag:
Open the water channel through the oil separator to reach between the pilot valve core and the valve seat, and use water pressure to overcome the centrifugal force caused by the high-speed rotation of the valve core; The sealing water quickly leaks out through the pilot valve hole, and the sliding chassis moves down rapidly under the action of the water pressure in the separation chamber. The slag discharge port opens, and the oil impurities are discharged under the action of centrifugal force.
After the slag discharge is completed, the oil separator separates the oil again according to the set program.
2, Analysis of the causes of oil leakage at the slag discharge outlet of the oil separator
1. Fault phenomenon
There are three heavy oil separators on a certain ship of Dongfang Overseas Container Shipping Company. One day, the No. 3 separator was in operation, and the engine room was unmanned. At around 2:00 am, the engine room alarm was triggered. The large tube wheel (on duty) immediately went to the separator room to check after responding in the room. The assistant engineer then arrived and found that the red "leak" indicator light on the separator control panel was on, and the separator motor had been powered off and was slowing down.
After eliminating the alarm and restarting, it was found that the oil separator could be used. After observing for 10 minutes, no abnormal situations occurred, and the engine room was set to an unmanned engine room again.
At around 8:00 on the same day, the No. 3 heavy oil separator issued the same alarm again.
2. Common Fault Analysis
(1) Fault in the working water system
The opening and sealing of the separation cylinder of the oil separator are completed by working water. Insufficient or no water pressure in the sealing water can cause the sliding chassis and separation cylinder cover to completely close, resulting in oil leakage.
The working water of this oil separator comes from the pressure water tank, and faults in the working water system usually require troubleshooting three items:
① Check the water volume in the pressure water tank and the water pressure in the pipeline. The water pressure is low and the sealing water is insufficient to move the sliding chassis to the appropriate position, resulting in poor sealing;
② Check if the Y-shaped filter in the working water pipeline is dirty or blocked, as low water flow, low pressure, and insufficient sealing water can cause poor sealing;
③ Disassemble and inspect the condition of the water distribution plate and whether the sealing ring is aging.
(2) Sealing system malfunction
The storage of working water in the water chamber and the separation of fuel in the separation cylinder are both achieved through the sealing effect of the sealing ring. Any failure of the sealing ring will lead to the failure of the oil separator.
1) The sliding chassis and separation cylinder cover are sealed with a main sealing ring. Once the main sealing ring is severely worn or damaged, it will cause oil leakage from the slag discharge port.
The factors that affect the service life of the sealing ring include:
The oil separator operates for a long time; The slag discharge outlet has been opened multiple times, causing multiple squeezes on the main sealing ring; Friction of impurities on the sealing ring during slag discharge; During the fuel separation process, the oil temperature can reach up to 98 ℃, and high temperatures can also affect the service life of the sealing ring.
2) The opening and closing of the pilot valve controls the sealing and discharge of the sealing water under the sliding chassis. Any damage to the sealing ring of the pilot valve will cause leakage of the sealing water under the sliding chassis, and the sliding of the sliding chassis will lead to oil leakage from the slag discharge port.
3) Damage to the sealing ring under the sliding chassis and leakage of bottom sealing water can also lead to poor sealing of the slag discharge port and oil leakage.
(3) Control system malfunction
1) The working water solenoid valve is damaged or the valve core is stuck or the solenoid valve has poor contact, resulting in insufficient sealing water pressure or continuous water supply, causing poor sealing of the separation cylinder.
2) The pressure sensor at the oil outlet of the oil separator is faulty, and the oil leakage alarm at the slag discharge outlet is checked through the pressure sensor at the oil outlet.
During normal slag discharge, there will be fluctuations in the pressure at the oil outlet. If the alarm value exceeds the fluctuation time during slag discharge, an alarm will be triggered and the slag discharge will be stopped.
Of course, it cannot be ruled out that the failure of the pressure sensor without an alarm may cause the oil separator to shut down.
3, Fault handling
1. Manual slag discharge treatment
The general sequence for manual slag discharge is:
1) Check that the oil temperature of the fuel heater is normal; Check that the fuel pressure is normal; Check the control water system and ensure that the water pressure is normal.
2) Turn off the power to the control panel, start the oil separator motor, and accelerate the oil separator to normal speed (due to the oil separator control panel not being turned on, the fuel is in a circulating state).
At this time, the oil separator is in an idle state.
3) Check the slag discharge of the oil separator and the sealing function of the separation cylinder.
First, open the sealing water valve for 21 seconds, then close the sealing water valve and open the replacement water valve for 34 seconds.
Close the replacement water valve, open and open the water valve for 5 seconds, and immediately close it (listen carefully to whether the slag discharge sound is normal).
Open the sealing water valve again for 21 seconds, then close it and open the replacement water valve for 34 seconds before closing it.
4) Upon opening the slag discharge outlet, it was discovered that water droplets were intermittently thrown out. Therefore, the No. 3 oil separator was shut down and the No. 2 oil separator was activated.
Through the above investigation, it was found that there was indeed a leakage at the slag discharge outlet of the oil separator, and the possibility of false alarm was ruled out.
At the same time, if the sound of slag discharge is normal, it can be ruled out that there is no serious blockage in the working water pipeline.
After the control panel is turned off and powered on again, the alarm is eliminated, which basically eliminates the possibility of control system failure.
2. Disassembly processing
When disassembling, refer to the instructions for disassembly steps. Handle the internal moving parts gently and slowly, and lay wooden boards on the workbench to reduce unnecessary collisions.
After disassembly, clean each component.
Then, according to the fault analysis, investigate the fault points one by one, with a focus on identifying the prone fault points.
When disassembling and repairing, it is necessary to first turn off the heater and fuel supply pump of the oil separator, turn off the power supply of the control panel, hang a warning sign, close the inlet and outlet valves of the oil separator, close the inlet valve of the working water, and then disassemble in the following order.
(1) Check the main sealing ring.
The main sealing ring is located in a harsh environment and is most susceptible to wear and tear. It is also the last component for controlling slag discharge.
Check the contact surface for any obvious radial scratches or pressure marks.
Upon disassembly, it was found that the contact surface of the main sealing ring had a flat indentation, no radial scratches or pressure damage, and no obvious aging, discoloration, or brittleness.
(2) Remove the control water pipeline, manually drain, and ensure normal water flow.
Measure the water volume with a graduated cylinder for 1 minute, and the result is within the range specified in the manual, indicating that the working water pipeline system is normal.
(3) Disassemble the separation cylinder and check for a faint yellow mark (which should be a water stain) in the sealed water chamber. A small amount of water stain has little effect on the oil separator; Check each sealing ring and find that it has good elasticity without obvious wear, cracks, or gaps.
(4) Disassemble the water distribution tray.
The sealing ring of the water distribution tray is in good condition. Wipe the water distribution tray with a hairless paper towel. There are many yellow water stains and a slight earthy smell.
The water distribution plate is divided into sealed water channel and open water channel. The water channel is tortuous, and the flow velocity changes when the water passes through here, causing significant erosion of the water distribution plate. At the same time, impurities in the water settle, which has little impact on the oil leakage of the slag discharge outlet.
There are no obvious issues with the other parts.
(5) Loosen the sealing screw from the side of the separation cylinder, use a special tool to pull out the pilot valve, clean the pilot valve and valve hole, and disassemble the pilot valve.
Upon inspection of the valve seat and valve core, it was found that there were varying degrees of pitting, which is speculated to be caused by cavitation.
Under the high-speed rotation of the separation cylinder, due to the high kinetic energy of the sealing water, it is quickly discharged when the water rushes out, causing cavitation due to changes in water pressure.
(6) Remove the sealing ring and inspect it, and it was found that the two sealing rings on the inner side of the valve seat were twisted.
After replacing the sealing ring and cleaning and assembling the oil separator, manual slag discharge operation was carried out again, and no oil leakage was found at the slag discharge port.
3. Post fault analysis
Based on the analysis of the disassembly situation above, the oil leakage at the slag discharge outlet is caused by poor sealing of the pilot valve.
During the last disassembly and cleaning of the oil separator, the pilot valve was not thoroughly cleaned. When installing the sealing ring, necessary lubricants such as Vaseline were not used to lubricate the valve body and sealing ring, resulting in distortion of the sealing ring. However, the sealing ring has good elasticity, so it can achieve good sealing effect in previous work.
With multiple opening and closing operations of the pilot valve and flushing of the working water, the elasticity and sealing performance of the sealing ring decrease, and the slag discharge port of the oil separator begins to leak oil.
4, Daily management of oil separator
Suggestions for regular disassembly and cleaning
(1) Daily management, conduct at least two inspections per day, listen to the sound of the oil separator rotating with a stethoscope, check the condition of the oil separator bearings, and stop immediately if there is obvious noise;
Check the pressure and temperature parameters of the oil separator to ensure that the operating pressure and temperature of the oil separator are within the normal range;
Measure the oil level in the oil residue tank daily, and promptly identify the cause if there is an abnormal increase;
The lubricating oil level of the gearbox of the oil separator should be checked daily.
(2) Try not to adjust the parameters set on the oil separator control panel during normal operation.
When changing oil on a ship, it is necessary to minimize the oil level in the settling tank to avoid mixing.
There are many impurities in the oil at the low position of the sedimentation tank, and the slag discharge time of the oil separator can be appropriately shortened to reduce false alarms.
(3) The oil separator should be cleaned and overhauled regularly according to the instructions.
The oil separator is a high-speed operating equipment that requires regular replacement of bearings.
In addition, when separating heavy oil, the oil temperature is set to 98 ℃ (92 ℃ for lubricating oil). High temperature and high pressure conditions can easily cause aging of the sealing ring, so the sealing ring should also be replaced regularly.
(4) When installing the sealing ring, it is best to lubricate the sealing ring or installation groove, which can ensure easy installation and reduce surface wear of the sealing ring during installation.
Also, be sure to choose the original sealing ring from the factory.
(5) A plan should be made in advance for the disassembly and assembly of the oil separator, including testing of the spare oil separator, preparation of spare parts, preparation of tools, preparation of personnel, and risk assessment. It is essential to copy the disassembly and assembly instructions.
In the process of disassembly and assembly, it is important to understand the uncertain steps and follow the principle of "slow rather than chaotic" during construction.
Additionally, the instruction manual is the most reliable 'helper'