Category Archives: Air compressors

Marine Compressed Air Dryer – Ensuring Efficient Operation and Reliable Maintenance

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Marine compressed air dryers are vital components used aboard ships and offshore platforms to remove moisture and contaminants from compressed air systems. These devices play a crucial role in ensuring the efficient operation of various pneumatic equipment and systems on board. In this article, we will delve into the purpose of a marine compressed air dryer, its correct operation, the significance of regular maintenance, and troubleshooting tips to keep it in optimal working condition.

Example of a control dryer

Purpose of Marine Compressed Air Dryer

The main purpose of a marine compressed air dryer is to eliminate moisture from the compressed air. In a marine environment, humidity is ever-present, and when compressed air is exposed to it, it tends to become saturated with water vapor. When moisture-laden air passes through pneumatic systems and equipment, it can lead to several detrimental consequences:

      • Corrosion of air tools and equipment – moisture in the compressed air can cause rust and corrosion in pneumatic components, pipes, and machinery, leading to premature failure and potential safety hazards.
      • Damage to electrical components – moisture can damage sensitive instruments and controls, causing malfunctions and compromising the overall safety and reliability of the vessel.
      • Reduced efficiency of air tools and equipment – water in the compressed air can hamper the performance of pneumatic tools and systems, leading to decreased productivity and higher operational costs.
      • Increased maintenance costs
      • Health and safety hazards

Correct Operation of Marine Compressed Air Dryer

Control air dryer operating principle is as follow: The humid air flows into the air inlet connection and is pre-cooled in the heat exchanger before it enters the evaporator. As the air passes through the evaporator, which is cooled by the liquid refrigerant, the air temperature drops to 10°C, which is the dew point at which the moisture in the air is condensed. The condensed water is now separated from the air and is purged out of the system through the automatic drain trap. The high pressure liquid refrigerant now passes through the expansion valve and is evaporated in the evaporator, before returning to the compressor to continue the refrigeration cycle. 

To operate a marine compressed air dryer correctly, it is important to follow the manufacturer’s instructions. To ensure the marine compressed air dryer operates efficiently and effectively, follow these guidelines:

      • Proper Installation – install the dryer in a clean, well-ventilated area away from potential sources of contamination, such as chemicals or exhaust fumes. Adequate ventilation prevents overheating and prolongs the lifespan of the dryer.
      • Filtration – prioritize the installation of filtration systems upstream of the dryer to remove larger particles, oil, and other contaminants that could clog the dryer and reduce its performance.
      • Adjust Air Pressure – normally dryer is connected to the compressed air supply line. Set the air pressure within the recommended range as per the manufacturer’s guidelines. High pressures can stress the dryer unnecessarily, while low pressures may result in insufficient drying.
      • Drain Moisture Regularly – most marine compressed air dryers are equipped with automatic drains. Ensure these drains are functional and regularly inspect and clean them to prevent blockages and ensure proper moisture removal.
      • Monitor Performance – regularly check the dryer’s output dew point and pressure levels to verify its efficiency. An increase in the dew point may indicate potential issues that need to be addressed promptly.

Maintenance of a Marine Compressed Air Dryer

To ensure the long life and reliable operation of a marine compressed air dryer, it is important to maintain it on a regular basis. Here are some maintenance practices to follow:

      • Cleaning – clean the dryer’s exterior regularly and ensure that the surrounding area is free from dust and debris that could obstruct air intake vents.
      • Filter Replacement – Follow the manufacturer’s guidelines for filter replacement intervals. Clogged or dirty filters can restrict airflow, leading to decreased performance and increased energy consumption.
      • Heat Exchanger Inspection – Regularly inspect and clean the heat exchanger to prevent a build-up of scale or debris, which can reduce the dryer’s efficiency.
      • Check Drains – Routinely inspect and test automatic drains to ensure they are functioning correctly and effectively removing moisture from the system.
      • Lubrication – If the dryer has any moving parts, ensure they are well-lubricated according to the manufacturer’s recommendations.

Troubleshooting Marine Compressed Air Dryer

Despite proper maintenance, issues may still arise. Here are some common problems associated with marine compressed air dryers and possible troubleshooting steps:

      • Insufficient Drying – if the dew point remains high despite correct settings, check for clogged filters, heat exchanger fouling, or malfunctioning drains. Clean or replace components as needed.
      • Excessive Pressure Drop – a significant pressure drop across the dryer can indicate clogged filters or obstructions in the air passages. Inspect and clean the filters and air pathways to restore normal pressure.
      • Unusual Noises or Vibrations – noises or vibrations may indicate loose components or worn-out bearings. Inspect the dryer and address any issues promptly to prevent further damage.
      • Leakage – check for air leaks around fittings, valves, and connections. Repair or replace damaged components to maintain the dryer’s efficiency.
      • If the dryer is not operating at all – it may have a problem with its electrical connections. In this case, you will need to check the dryer’s electrical connections and make sure that they are properly secured.
      • If you are still having trouble with your marine compressed air dryer, you should contact the manufacturer for assistance.

In conclusion, marine compressed air dryers are indispensable in maintaining the reliability and efficiency of pneumatic systems aboard ships and offshore installations. By understanding the purpose, correct operation, and significance of regular maintenance, operators can optimize the performance and prolong the lifespan of these essential devices. Troubleshooting skills further enable swift identification and resolution of issues, ensuring a smooth and safe marine environment with reliable compressed air systems.

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Marine Starting Air Compressors: Types, Parts, Operation, and Maintenance

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Marine starting air compressors are part of the Vessel Air System and play a crucial role in ensuring the smooth and reliable operation of large marine diesel engines. These compressors provide the necessary air pressure to start the engines, allowing vessels to set sail and maneuver efficiently. In this article, we will dive into the different types of marine starting air compressors, examine their components, and provide a comprehensive explanation of their operation and maintenance.

Types of Marine Starting Air Compressors

    • Reciprocating Air Compressors: Reciprocating air compressors are the most commonly used in marine applications. They utilize a piston and cylinder arrangement to compress air. These compressors can be further classified into single-stage and multi-stage compressors, depending on the number of compression stages involved. Multi-stage compressors provide higher pressure outputs and are often used in larger vessels.

      Example of reciprocating starting air compressor

    • Screw Air Compressors: Screw air compressors are another type used in marine settings. They employ two interlocking rotors to compress air. These compressors are known for their high efficiency, low maintenance requirements, and compact design. They are particularly suitable for applications where a constant and continuous supply of compressed air is necessary (e.g. working air compressors).

      Example of screw compressor

Components of Marine Starting Air Compressors

    • Air Intake Filter: The air intake filter prevents dust, debris, and other contaminants from entering the compressor. It ensures that the compressed air is clean and free from impurities that could potentially damage the engine.

    • Cylinder and Piston Assembly: In reciprocating compressors, the cylinder and piston assembly are the primary components responsible for compressing the air. The piston moves back and forth within the cylinder, creating a pressure differential and compressing the air.

    • Intercoolers: Intercoolers are heat exchangers used in multi-stage compressors. They cool down the compressed air between stages, reducing its temperature and increasing its density. This process enhances compressor efficiency and prevents overheating.

    • Lubrication System: Marine compressors have a lubrication system that ensures smooth operation and reduces wear and tear. The system provides lubricating oil to critical components, such as the piston rings and bearings, to minimize friction and extend the compressor’s lifespan.

Operation and Maintenance of Marine Starting Air Compressors

Marine starting air compressors are typically driven by an electric motor or engine. From an engineering point of view, the operation of marine starting air compressors involves several fundamental processes (e.g. air intake, compression, cooling, discharge and pressure regulation) that enable the compression of air to the required pressure for starting marine diesel engines.

Proper maintenance is vital to ensure the reliability and longevity of marine starting air compressors. Here are some essential maintenance tasks:

    • Regular Inspection: Inspect the compressor for any signs of leaks, loose connections, or worn-out parts. Check the intake filter for clogging and clean or replace it as necessary.

    • Lubrication: Monitor and maintain the lubricating oil levels as per the manufacturer’s guidelines. Regularly change the oil and oil filters to prevent contamination and ensure optimal lubrication.

    • Cooling System: Check the intercoolers and cooling system for any signs of fouling or blockage. Clean or repair them if required to maintain efficient cooling.

    • Valve Maintenance: Inspect the valves, such as the intake and discharge valves, for proper functioning. Clean or replace them if they show signs of wear or damage.

    • Safety Measures: Ensure that all safety devices, such as pressure relief valves and pressure gauges, are in good working condition. Regularly test and calibrate these devices to guarantee accurate readings.

Rules and regulations related to marine starting air compressors can vary depending on the jurisdiction and classification society governing the vessel. However, there are several international standards and guidelines that provide a framework for the design, installation, operation, and maintenance of marine starting air compressors. Here are some key regulations and standards commonly applicable to marine starting air compressors:

    • International Maritime Organization (IMO) Regulations: The IMO is a specialized agency of the United Nations responsible for maritime safety and environmental protection. The following regulations are relevant to marine starting air compressors:
      • SOLAS (Safety of Life at Sea) Convention: SOLAS provides comprehensive regulations for the safety of ships and seafarers. It includes requirements for the installation and maintenance of machinery and equipment, including starting air compressors.

      • MARPOL (International Convention for the Prevention of Pollution from Ships): MARPOL sets standards to prevent pollution from ships, including regulations on air emissions. Compliance with MARPOL Annex VI is essential for controlling air pollution from ships, which may involve ensuring proper operation and maintenance of starting air compressors.

    • Classification Society Rules: Classification societies, such as the American Bureau of Shipping (ABS), Lloyd’s Register (LR), and Det Norske Veritas Germanischer Lloyd (DNV GL), establish rules and standards for the design, construction, and operation of vessels. These rules often include specific requirements for starting air compressors, covering aspects such as design, materials, installation, testing, and maintenance.

    • Flag State Requirements: The flag state, under whose jurisdiction a vessel is registered, imposes additional regulations and requirements. These requirements may include periodic inspections, certifications, and surveys related to the operation and maintenance of machinery and equipment, including starting air compressors.

    • Industry Standards: There are various industry standards and guidelines that provide recommendations and best practices for marine starting air compressors. Examples include:

      • ISO 10440-1: This standard specifies requirements for the design, manufacture, and testing of reciprocating compressors, including starting air compressors.

      • ISO 10440-2: This standard covers the design, manufacture, and testing of screw compressors, which are also used in marine applications.

    • Compressor Manufacturer Guidelines: Compressor manufacturers often provide specific guidelines and recommendations for the operation, maintenance, and troubleshooting of their products. Following these guidelines ensures compliance with the manufacturer’s specifications and enhances the reliability and performance of the compressors.

In conclusion, marine starting air compressors are vital components in marine propulsion systems, providing the necessary compressed air to start large diesel engines. Understanding the different types of compressors, their components, and the proper operation and maintenance procedures is crucial for ensuring their reliable performance and longevity. Regular inspection, lubrication, cooling system maintenance, and adherence to safety measures are essential for the smooth operation of these compressors, contributing to the overall efficiency and safety of marine vessels. It is crucial for vessel owners, operators, and engineers to stay updated with the applicable rules and regulations related to marine starting air compressors. Compliance with these regulations helps ensure the safety, efficiency, and environmental responsibility of marine operations.

If you want to learn and get a “Diploma in Marine Auxiliary Machinery”, please follow THIS LINKon Alison platform. The course is free and all you need to do is just to subscribe to their platform using the link above. This will be of a great help to me as well, as I will earn small commission. You can consider this as a reward for my effort to provide guidance and advices with regard to complex, challenging and rewarding marine engineering. 

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If you have any questions regarding above, please feel free to use our existing forum Seafarer’s World, Telegram Chief Engineer’s Log Chat or Instagram and will try to answer to all your queries. You can use the feedback button as well!

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Everything about vessel air system

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The vessel air system comprises, normally, of Starting air system, Control air system and General service/working air system.
The starting air system is supplied by two or three main air compressors which provide air, usually, to two main air reservoirs and is used to start the main engine and the generator engines. The generators may also be supplied with starting air from an auxiliary air reservoir which is replenished from the main air reservoirs and on some of the vessels directly from emergency air compressor (obviously in case of an emergency).

Main starting air compressors
Emergency air compressor

Additionally, it is channeled through a pressure decreasing valve to the air typhoon, engine room alarm horns, the working/control air system, and the generator engine diesel oil emergency pump. Air is provided to the oil-fired boiler via the starting air receivers for soot blowing operations.

Starting air bottles with pressure reducing air valves

On the modern vessels and engines compressed air from the main air system is also supplied to the generators jet system and main engine top bracing cylinders. On some vessels equipped with twin 4 stroke engines the main air system is used for the engine pneumatic break.

The two starting air receivers are supplied by an oil/water separator installed in the compressor’s common receiver filling line. Normally one main air reservoir is designated as the duty air reservoir, while the other one is fully pressurized with its outlet valves closed when at sea. When the ship is maneuvering both reservoirs are used.

Each compressor is equipped with two safety valves, one following the first stage of compression and the other following the second stage. In case of water cooled type compressors, the cooling water jacket of the cylinder block is equipped with a safety plate that blows out if the cooling water system is subjected to excessive pressure.
The low temperature fresh water cooling system provides cooling water. When the lubricating oil (LO) pressure falls below a predetermined value, a pressure switch attached to the automatic control system shuts down the compressor. The bearings are lubricated using a gear pump located at the crankshaft’s end and at the compressor outlet, a high temperature sensor trips the compressor if the temperature exceeds a predetermined limit.
Each compressor is normally equipped with an automatic unloader that acts in conjunction with the compressor’s start and stop cycles. This enables the compressor to start and stop off load, hence lowering the load on the electric drive motor and compressor running gear. Where automatic drain traps are fitted to sections of starting air line or services, the isolating valve for this drain trap must remain open. If a drain does not have an automatic drain trap the drain valve should normally be closed. This type of manual drain must be opened periodically, at least once each week, in order to drain any water from the line. Manual drain valves on supply lines should be opened before services on the supply line are operated.

Automatic operation of the compressors is generally selected at the local control panel, with the selection switch set to AUTO for automatic operation or MANU for manual operation. The emergency compressor is powered from the emergency switchboard.
When selected for AUTO operation the compressors are started and stopped by pressure switches, which are fitted to the inlet line to the starting air receivers.
A three-position switch permits the duty compressor to be selected from any of the others, while the others serve as the first and second follow-on compressors. When manual control is set, each compressor must be started manually; however, stopping is automatic via the pressure switch; the compressor may also be stopped manually using a pushbutton on the compressor control panel. At all times during operation, the space heater at each compressor control panel must be turned on.

For filling the starting air receivers and supplying the main and generator engines with starting air, generally the following procedure applies:

  • The air receiver filling valve must be open to replenish a starting air receiver.
  • As the compressors operate automatically and are controlled by pressure switches the receiver valve and the line valve for the pressure switches must be open for the air receiver which is being filled.
  • Ensure that all pressure gauge and instrumentation valves are open and that gauges and instruments are reading correctly.
  • Check the oil level in the compressors and replenish if necessary.
  • Check the compressor sumps for water.
  • Ensure that the low temperature central fresh water cooling system is operating and supplying cooling water to the starting air compressors.
  • The automatic drain valves on the starting air compressors must be operational and the manual drain valves to the automatic drain traps must be open. Because the compressors are to operate automatically the drains must also operate automatically.
  • Check that the compressor unloader gear is functioning.
  • Set one air compressor to auto and the others to standby.

The first follow-up compressor will operate if the air pressure falls below a predetermined value and will function if the duty air compressor fails or is unable to maintain the receiver pressure due to excessive air demand. The second follow-up compressor will operate if the duty and first follow-up compressors fail to maintain pressure. Compressor selection for duty/follow on should be changed over weekly in order to even out the running hours on the compressors.

The control air system is supplied from the control and general service air reservoir. This reservoir is replenished by the service air compressors or the control air system may be supplied from the main starting air system via the pressure reducing unit. The pressure in the control air system is 7 to 8 bar. The air supply from the main air system is a back-up and the valves are normally closed. Control air is processed through a refrigerated control air dryer and associated filters before supplying the control air services.
Control air dryer operating principle is as follow: The humid air flows into the air inlet connection and is pre-cooled in the heat exchanger before it enters the evaporator. As the air passes through the evaporator, which is cooled by the liquid refrigerant, the air temperature drops to 10°C, which is the dew point at which the moisture in the air is condensed. The condensed water is now separated from the air and is purged out of the system through the automatic drain trap. The high pressure liquid refrigerant now passes through the expansion valve and is evaporated in the evaporator, before returning to the compressor to continue the refrigeration cycle. The control systems are supplied via grouped outlet valves for particular areas or systems.
It is important that the air is dried before entering the control system, as any moisture in the control air can cause problems at actuators or other parts leading to failure at these devices. Only in the event of failure of the control air dryer should the dryer bypass valve be opened.

Control air dryer

Air is supplied to the working air system via the control and working air reservoirs. The reservoirs for control and working air can be refilled using either the main starting air system or one or two control and working air compressors.

Working air reservoir
Working air compressors

Compressors for the control and working air supply air to the control and working air reservoirs. Compressors are controlled by reservoir pressure, loading and unloading as necessary. At the control panel, the compressors can be configured for operation; features such as starting and stopping pressures, as well as timed start and stop, are all possible. The compressors can be operated LOCALLY or REMOTELY through a selector switch on the control panel. The compressor is started and stopped in local control mode via the local panel. The compressor is started and stopped automatically in remote control mode based on the pressure in the working air reservoir. In case of two compressors, a selector switch enables master/standby air compressors to be selected as a pair, No.1/No.2 or No.2/No.1.

Normally, the duty working air compressor starts at a pressure of 7.0kg/cm2 and stops at a pressure of 8.0kg/cm2.

As mentioned at the beginning, the working air system can be supplied from the starting air system, through a reducing valve. On the modern systems, the working air supply line from the control/working air reservoir to the working air system is equipped with an automatic shut-off valve (usually operates at a pressure of 6.5kg/cm2), which will be closed automatically by low pressure in the control/working air reservoir. This saves air which is required for operation of the control systems. If the automatic shut-off valve operates it means that the control/working air compressors are unable to maintain system pressure. This may be due to excessive use of working air in which case closure of the shut-off valve will allow the compressors to restore system pressure. If the low pressure is due to failure of the control/working air compressors air must then be supplied from the starting air system via the reducing valve.

The general service air system supplies the following services: deck services; CO2 alarm horns; quick-closing air receiver and fire fan flap damper control; engine room services; accommodation service; generator engines emergency air-driven MDO pump; purifiers; emergency generator room; turbocharger cleaning unit; boiler; diesel generators; workshop; engine room air horns and ship’s main air horn; stern tube seal air control unit; ballast pumps and bilge, fire and GS pumps priming unit; local firefighting unit, etc.

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