Marine Oil Purifier’s Bowl Assembly: Causes of Failure, Maintenance, and Troubleshooting

Marine oil purifier bowl is a vital component of a centrifugal purifier that is used to separate water and solid impurities from fuel oil or lube oil on board ships. The purifier bowl is a kind of  container that rotates at a high speed and creates a centrifugal force that pushes the heavier water and solids to the periphery, while the lighter oil remains in the center. The purified oil is then discharged through a paring disc, while the water and solids are collected in the sludge space of the bowl.

The purpose of marine oil purifier bowl is to ensure the quality and efficiency of the fuel oil or lube oil used by the ship’s engines and other machinery. By removing water and solids from the oil, the purifier bowl prevents corrosion, wear, clogging, and damage to the engine components. It also reduces fuel consumption, emissions, and maintenance costs.

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Operation of marine oil purifier’s bowl

The operation of marine oil purifier bowl involves several steps:

    • The oil to be purified is heated to a suitable temperature and fed into the purifier bowl through a feed pipe.
    • The purifier bowl rotates at a high speed (up to 10,000 rpm) and creates a centrifugal force that separates the oil from the water and solids based on their density difference.
    • The purified oil flows to the center of the bowl and is discharged through a paring disc, which is a conical device that skims off the oil from the surface.
    • The water and solids accumulate in the sludge space of the bowl and are periodically discharged through an automatic or manual valve.
    • The purifier bowl is equipped with a gravity disc or a clarifier disc, depending on whether it is used as a purifier or a clarifier. A purifier separates both water and solids from the oil, while a clarifier only separates solids from the oil. A gravity disc has two holes: one for water and one for oil. A clarifier disc has only one hole for oil.

Maintenance of marine oil purifier’s bowl

The maintenance of marine oil purifier bowl is essential to ensure its proper functioning and performance. The maintenance tasks include:

    • Cleaning the purifier bowl regularly to remove any sludge or deposits that may affect its efficiency or cause imbalance.

      Example of large amount of sludge accumulated inside purifier bowl

    • Checking the condition of the bearings, seals, gaskets, springs, discs, valves, and other parts of the purifier bowl and replacing them if necessary.

      Purifier bowl cleaning and overhauling

    • Lubricating the bearings and other moving parts of the purifier bowl with suitable grease or oil.
    • Calibrating the purifier bowl according to the manufacturer’s specifications and adjusting the speed, temperature, pressure, and flow rate as required.
    • Testing the purifier bowl for leaks, vibrations, noise, or any other abnormalities and rectifying them promptly.

Marine oil purifier’s bowl failure troubleshooting

The troubleshooting of marine oil purifier bowl is important to identify and resolve any problems or faults that may occur during its operation. Some common problems and their possible causes and remedies are:

    • Low purification efficiency: This may be caused by incorrect gravity disc size, improper feed temperature or flow rate, worn or damaged discs or valves, excessive sludge accumulation, or air ingress. The remedy is to select the correct gravity disc size, adjust the feed temperature or flow rate, replace or repair the discs or valves, clean the sludge space, or vent out the air.
    • High vibration or noise: This may be caused by imbalance of the purifier bowl, loose or broken parts, misalignment of the drive shaft or motor, or faulty bearings. The remedy is to balance the purifier bowl, tighten or replace the parts, align the drive shaft or motor, or replace the bearings.
    • Oil leakage: Bowl leaking in marine oil purifiers can occur due to several reasons. Some of the main causes include:
        • Bowl Gasket Failure: The bowl of the oil purifier is sealed with a gasket to prevent leakage. If this gasket becomes worn out, damaged, or improperly installed, it can lead to oil leaking from the bowl.
        • Bowl Cracks: Over time, the bowl of the purifier may develop cracks due to wear and tear, corrosion, or improper handling. These cracks can result in oil seepage.
        • Bowl Seal Groove Damage: The seal groove in the bowl where the gasket sits can get damaged due to mishandling or prolonged use, leading to a compromised seal and eventual leakage.
        • Bowl Misalignment: Improper installation or misalignment of the bowl with the other components of the purifier can create gaps and openings that cause oil to leak.
        • High Vibration: Marine engines and machinery are subjected to high levels of vibration during operation. Excessive vibration can weaken the bowl’s integrity, leading to leaks.
        • Overpressure: If the oil purifier experiences an unexpected increase in pressure beyond its design limits, it can cause the bowl’s seals to deform or crack, resulting in oil leakage.
        • Inadequate Maintenance: Regular maintenance and inspections are essential to identify and address potential issues before they escalate into major problems. Lack of proper maintenance can lead to the development of leak-prone conditions.
        • Poor Quality or Contaminated Oil: Low-quality or contaminated oil may contain abrasive particles or corrosive substances that can cause accelerated wear and tear on the bowl’s surfaces, increasing the risk of leakage.
        • Age and Wear: As the oil purifier ages, its components may wear out, including the bowl material and gaskets, making them more susceptible to leakage.

To prevent bowl failure, it is crucial to follow the manufacturer’s maintenance guidelines, conduct regular inspections, use high-quality replacement parts, and ensure proper installation and alignment. Additionally, monitoring the purifier’s operating parameters and keeping the oil clean and free from contaminants can also help prolong the equipment’s life and reduce the risk of leaks.

Marine oil purifier bowl failure can have serious consequences for the ship’s engines and machinery. Therefore, it is essential to monitor its operation regularly and perform preventive maintenance and troubleshooting as needed. By doing so, you can ensure the quality and efficiency of your fuel oil or lube oil and extend the life span of your equipment.

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Source and credit: Video animation – Alfa Laval

Marine Oil Purifier’s Vertical Shaft Assembly: Causes of Failure, Maintenance, and Troubleshooting

In marine oil purifiers, the vertical shaft assembly plays a crucial role in ensuring efficient oil purification and engine performance. This essential component is responsible for driving the separation process, which removes impurities and water from the oil. However, like any mechanical part, the vertical shaft assembly is prone to failure and malfunction.

Purifier vertical shaft top view

In this article, we will explore the potential causes of vertical shaft failure, the necessary maintenance practices to keep it in optimal condition, and comprehensive troubleshooting techniques to address potential issues.

Causes of Vertical Shaft Failure and Malfunction

    • Lack of Lubrication: Proper lubrication is vital for reducing friction and wear between the moving parts of the vertical shaft assembly. The most straightforward cause is the absence or inadequate amount of lubricant in the system. If the lubricant level is below the recommended amount or has completely run out, it can lead to increased friction and wear on the vertical shaft.

    • Contamination and Impurities: The marine environment exposes the vertical shaft assembly to various contaminants that will affect the lubricant. Contamination of the lubricant can occur due to various factors, such as the entry of water, dirt, debris, or impurities into the system. Contaminated lubricant loses its effectiveness and can accelerate wear on the vertical shaft components. These impurities can infiltrate the assembly, causing abrasive damage to the shaft and its components.

    • Misalignment: Incorrect alignment of the vertical shaft can cause uneven stress distribution and excessive vibrations during operation. Prolonged misalignment may lead to fatigue failure of the shaft and of its bearings.

      Example of damaged bowl due shaft misalignment

    • Overloading: An overloaded vertical shaft assembly, either due to excessive flow rates, accumulated sludge or continuous operation beyond its capacity, can cause mechanical stress beyond its design limits, leading to failure.

      Example of heavy sludge accumulated into the purifier bowl

    • Corrosion: The corrosive nature of the marine environment can deteriorate the shaft’s surface, leading to pitting, cracks, and reduced structural integrity.

      Example of corroded vertical shaft

Proper Maintenance of the Purifier’s Vertical Shaft Assembly

    • Regular Inspection: Conduct routine inspections of the vertical shaft assembly to check for signs of wear, misalignment, or corrosion. Early detection of issues allows for timely maintenance and prevents major failures.

    • Lubrication Management: Follow the manufacturer’s guidelines for lubrication intervals and use recommended lubricants. Regularly check lubricant levels and ensure that the vertical shaft assembly is adequately lubricated.

    • Cleaning and Purging: Regularly clean the shaft assembly to remove accumulated dirt, impurities, and debris. Implement proper purging procedures to remove any contaminants that may have entered the system.

    • Alignment Checks: Periodically verify the alignment of the vertical shaft assembly to ensure smooth and balanced operation. If misalignment is detected, realign the components promptly.

    • Corrosion Protection: Apply appropriate anti-corrosion coatings or use materials resistant to marine environments to protect the vertical shaft from corrosive damage.

    • Load Management: Ensure the vertical shaft assembly operates within its designated load capacity. Avoid overloading the system, and if necessary, install safeguards or regulators to prevent excessive stress.

Purifier Vertical Shaft Failure Troubleshooting

    • Excessive Vibration: Vibrations can indicate misalignment or worn-out bearings. Investigate the source of vibrations and realign the shaft assembly if necessary. Check bearings for signs of wear and replace them as needed.

      Vertical shaft bearing assembly

    • Unusual Noise: Unusual noises during the purifier’s operation may suggest mechanical issues. Inspect the vertical shaft assembly for any signs of damage or misalignment and perform necessary maintenance.

    • Shaft Overheating: Overheating can result from lack of lubrication or excessive friction. Check the lubrication system, ensure proper lubricant levels, and investigate the cause of increased friction.

    • Leakage: Oil or lubricant leaks may indicate worn-out seals or damaged components. Inspect the seals and components for any signs of leakage and replace or repair as necessary.

    • Shaft Seizure: If the vertical shaft assembly seizes during operation, immediately stop the purifier to prevent further damage. Investigate the cause of the seizure, which may be due to lack of lubrication or other mechanical issues, and address it accordingly.

In conclusion, the vertical shaft assembly is a critical component of marine oil purifiers, responsible for driving the oil purification process. Proper maintenance, regular inspections, and timely troubleshooting are essential to prevent vertical shaft failure and malfunctions. By adhering to recommended maintenance practices and promptly addressing any issues, vessel engineers can ensure optimal performance, extend the lifespan of their oil purifiers, and maintain smooth and efficient marine operations.

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What are purifiers, why do we need them onboard vessels and how did they work?

Purifiers clean fuels and lubricants as well as processing bilge water and sludge, but onboard vessels they are mainly part of fuel and oil treatment system. Purifiers are usually under a junior engineer responsibility and, sometimes they proves to be real nightmares for some of them, mainly because of lack of knowledge regarding operating principle, lack of confidence and negligence.

Marine purifiers use separation technology involving a disk stack separator, known as a centrifuge.

This is used for centrifugation in which various phases of solids and liquids are isolated from one another based on difference of densities.

Simulation of centrifugal force
Liquid phases

Similar to a settling tank, disk stack separators use the force of gravity to separate liquid with a specific density from other liquids and solids. Unlike a settling tank which uses retention time as the main parameter for liquids of different densities to divide into layers of and solids to precipitate to the tank, centrifugal separators use mechanical force to separate liquids and solids with different densities from each other. In an essence a disk stack separator is a settling tank who’s base is wrapped around the center line of the bowl. Conical plates are stacked, one on top of the other, inside the bowl, to provide more separation area and to increase separation efficiency. These stacks dramatically speed up the precipitation of the solids from the liquids.

Onboard vessels usually there are two or three centrifugal self cleaning Heavy Fuel Oil purifiers fitted (depending on the Main Engine size and fuel consumption), a Diesel Oil purifier, a Main Engine Lube Oil purifier and one or two Auxiliary engines Lube Oil purifiers. One of the HFO purifiers can be used as DO purifier as well, in case of emergency or when is needed. Normally one HFO purifier is in use with the second one on stand by or under maintenance process. Each purifier is equipped with a supply pump, duplex filter and steam heater and all the equipment is located in the purifier room.

Service air is supplied to the purifiers to control the supply of oil to the bowl and the automatic discharge facility, while fresh water is supplied for sealing and flushing purposes.

Normally the HFO purifier throughput is set to match the fuel consumption in the main and auxiliary engines and in the auxiliary boiler. If the throughput is exceeding the consumption the excess delivered to the service tank will overflow back to the settling tank when the service tank become full.

Heated liquid mixtures and solid-liquid mixtures enters the purifier and the centrifugal force created by the rotating bowl causes the liquid mixture to separate into its different constituents within the disc stack. The solid particles suspended in the oil settle on the underside of the discs and slide down into the solids holding space at the periphery of the bowl. The smooth disc surface allow the solids to slide down and provide self-cleaning of the discs. A regulating ring determines the position of the interface between the oil and the collected separated water and is set according with the density of the oil to be cleaned. Greater oil density requires a smaller internal diameter of the regulating ring. Two pumps are mounted on the outlet side of the purifier and these are a sensing pump which discharges the dirty water and a centripetal pump which converts the kinetic energy in the oil to a pressure for discharging to the receiving tank. Here below you can see the working principle of Alfa Laval S and P Flex separation system:

Source and credit: Alfa Laval

Purifiers can be used and operated in a purification or clarification mode. When operating in a purifier mode a chamber cover over the centripetal pump has holes and when operating in a clarifier mode the cover has no holes. However, modern purifiers like Alfa Laval’s ALCAP™ separator technology eliminates the gravity disc to allow for automatic adjustment to fuel density.

Nowadays, purifiers being of self-cleaning type, the accumulated solids within the holding space are ejected at predetermined intervals depending on the quality of the oil. The cleaning cycle is achieved automatically, a number of air actuated control valves act to allow the oil to bypass the purifier and to open the bowl for a set period of time. The self cleaning process takes place with either partial or total discharge of the bowl. For this purpose, the bowl must be first filled with displacement water following closure of the dirty oil inlet. Depending on the discharging process the bowl will be partially or completely filled with displacement water. Control water is introduced into the opening chamber of the bowl to open it, thus the pressure exerted by the control water moves the piston valve which opens the sludge discharging ports. The content of the bowl will be discharged totally or partially depending on the process.

Bowl operation with self-cleaning process

Due high centrifugal forces and liquid velocity generated within the bowl expels almost all the sludge. Damaged seal O-rings or scratched/damaged surfaces of the sludge chamber and disks make the self-cleaning process more difficult and sometimes impossible this being signaled through a machine malfunction alarm. Control water flows out of the bowl during sludge discharge and the bowl is closed again. Here below there is an example where you can actually see the velocity generated due high centrifugal forces (this test it is done in workshop into a controlled environment):

Source and credit: D MEYERS

Usually, there is a water monitoring system which controls the discharge of water and a sludge monitoring system which controls the discharge of sludge.

Water which is separated from the oil collects in the outer part of the bowl. The separating disc in the bowl continuously directs a small flow from the outer part of the bowl to the sensing liquid pump, which discharges this flow to a conductivity sensor. if the conductivity sensor detects the presence of water it means that a reasonable amount of water is present in the bowl. The control system that opens a solenoid operated valve to discharge the water through the dirty water outlet; the separator is operating as a purifier. When the water has been discharged the valve is closed and the separator resumes operation as a clarifier.

Desludging of the bowl normally takes place at timed intervals, which are changed to suit the quality of the oil being treated. A sensor in the sludge monitoring system detects the build-up of sludge-water in the sludge space of the bowl. if the amount of sludge becomes excessive, the system will activate the automatic desludging process even though a timed desludging operation is not due. Usually if there are more than two untimed desludging operations an alarm is activated and this requires the intervention of the engineer on watch responsible with the engine room safe operation.

The alarm can be visualized on the purifier operating panel where all relevant process data and alarm condition are displayed. The components which are controlled or monitored by the control system include, but are not limited to:

  • oil inlet/bypass valve (three-way circulating valve)
  • flushing water
  • operating water
  • circuit and water discharge valve
  • water sensor
  • oil inlet temperature
  • audible alarms

Software assignment for each purifier is carried out in the factory and/or by commissioning engineer using a password function. Any alteration to the set parameters must be carried out by a qualified and authorized engineer. Changes in parameter settings are not an operational requirement of the purifiers and are not normally necessary once the system has been commissioned for the type of the oil being treated. If any change in parameter setting is required (for emergency reasons) this must only be carried out with the approval of the Chief Engineer and after consultation with control system manual. It is essential that the correct separating temperature is set for the grade of fuel or lubricating oil being centrifuged. Too low temperature can result in inefficient purification, but too high can have a cracking effect (especially on the lubrication oil).

Generally, the discharging time interval is initially set to that the bowl will open and discharge the sludge and water before the sludge space is filled. If the desludging time interval is too short there is excessive sludge and efficiency of the system can be negatively altered. Each purifier discharges sludge from the purifier to the sludge tank situated , usually underneath purifiers.

As a caution, engineers must bear in mind that purifiers operate on an automatic desludging system, but failure of the system to effectively discharge sludge can cause overload and subsequent breakdown of the bowl arrangement which rotates at high speed. After maintenance and cleaning, care is needed to ensure that the bowl is assembled correctly, as incorrect assembly can result in disintegration at high rotational speed. All operating and maintenance precaution mentioned by manufacturer in the maintenance manual must be duly observed. Moreover, hot oil and steam are present and can result in serious injuries or risk of fire if leakage occurs.

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