(b) Using the Worksheet Q3, identify ALL the components shown for a system suitable for the production of compressed air for control instrumentation.(7)
Requirements for compressed air
Compressed air used for control instrumentation on a marine vessel needs to meet specific requirements to ensure the proper functioning and longevity of sensitive pneumatic equipment. These requirements focus primarily on air quality, including:
1. Compressed Air Uses in Marine Industry – Airfilter Engineering
- Cleanliness:
- Particle Filtration: The compressed air must be free from solid particles like dust, rust, and pipe scale that can cause wear, clogging, and malfunction in control valves, actuators, and other instrumentation.
- Filtration Levels: Multi-stage filtration is typically employed, with coarser pre-filters removing larger particles and finer coalescing filters capturing smaller particles and aerosols.
- ISO 8573-1: Compliance with the relevant ISO 8573-1 standard for particulate contamination is often required, specifying the maximum allowable particle size and concentration.
- Dryness:
- Moisture Removal: Compressed air naturally contains moisture, which can condense in pipelines and equipment, leading to corrosion, freezing, and operational issues.
- Dew Point Control: The air must be dried to a specific dew point (the temperature at which water vapor condenses), typically well below the lowest operating temperature the system will encounter.
- Air Dryers: Refrigerated dryers or desiccant dryers are used to achieve the desired dew point.
- Oil Removal:
- Oil Contamination: Lubricating oil from the compressor can contaminate the compressed air, causing malfunctions in pneumatic control equipment.
- Oil Removal Filters: Coalescing filters and oil removal filters are used to remove oil aerosols and vapors from the air stream.
- ISO 8573-1: Compliance with the relevant ISO 8573-1 standard for oil content is important, specifying the maximum allowable oil concentration. 1. Air quality standards (ISO 8573-1) – Pneumatech www.pneumatech.com
- Pressure and Flow:
- Adequate Pressure: The compressed air system must deliver sufficient pressure to operate the control instrumentation reliably. This pressure typically ranges from 6 to 8 bar for most pneumatic control equipment.
- Stable Pressure: Pressure fluctuations should be minimized to ensure consistent and accurate operation of the instrumentation.
- Sufficient Flow Rate: The system must be able to provide the required flow rate to meet the demands of all connected control devices simultaneously.
- Other Considerations:
- Microbiological Contamination: In certain applications, such as those involving food processing or medical equipment, controlling microbiological contamination in the compressed air might be necessary.
- Odor and Taste: For systems that interact with potable water or food products, the compressed air should be free of any objectionable odor or taste.
- Monitoring and Maintenance: Regular monitoring of air quality parameters and routine maintenance of the air treatment equipment (dryers, filters) are crucial to ensure the compressed air meets the required standards for control instrumentation.
By adhering to these requirements, the compressed air system can provide a reliable and clean source of energy for precise and safe operation of control instrumentation, contributing to the overall efficiency and reliability of the vessel’s critical systems.
Components in a compressed air system
A system designed to produce compressed air suitable for control instrumentation on a marine vessel typically comprises several key components that work together to ensure the air is clean, dry, and at the correct pressure:
- Air Compressor:
- The primary component responsible for compressing atmospheric air to the required pressure. 1. The Basic Parts Required for the Operation of the Air Compressor – Özen Kompresör ozenkompresor.com.tr
- Common types include:
- Rotary Screw Compressors: Efficient and reliable, often used for larger systems. 1. What is a rotary screw compressor? – Ceccato www.ceccato.com
- Reciprocating Compressors: Suitable for smaller systems or as backup compressors. 1. What is a reciprocating air compressor? – Industrial Air Systems NZ www.industrialair.co.nz
- Air Receiver (Storage Tank):
- Stores compressed air to buffer fluctuations in demand and provide a continuous supply.
- Ensures adequate air is available even when the compressor is not running.
- Equipped with safety features like pressure gauges, relief valves, and drain valves. 1. Compressed Air Pressure Vessel Explained – saVRee savree.com
- Air Dryer:
- Removes moisture from the compressed air to prevent condensation and corrosion in control instrumentation. 1. Compressed air dryer – Wikipedia en.wikipedia.org
- Common types:
- Refrigerated Dryers: Use refrigeration to cool the air and condense moisture, suitable for general applications. 1. Cool compressed air with a refrigerated air dryer – Atlas Copco Greece www.atlascopco.com
- Desiccant Dryers: Use desiccant material to adsorb moisture, providing a lower dew point for critical applications. 1. Desiccant Air Dryers: Types, Applications and Working – Atlas Copco UAE www.atlascopco.com
- Filters:
- Remove particulate matter, oil, and other contaminants from the compressed air to protect sensitive control instrumentation. 1. Control Air System – Marine Insight Academy academy.marineinsight.com
- Multiple stages of filtration may be used:
- Pre-filters: Remove larger particles and debris. 1. Why Pre-filtration is Important www.commercialfiltrationsupply.com
- Coalescing Filters: Capture oil aerosols and finer particles. 1. Coalescing Filter Elements: 0.3 Micron Rating – Solberg Manufacturing www.solbergmfg.com
- Activated Carbon Filters: Remove odors and oil vapors. 1. Oil Vapor Removal – Filters, Coalescing, Adsorber & Dryers – Master Pneumatic www.masterpneumatic.com
- Pressure Regulator:
- Reduces the high pressure from the compressor/receiver to the appropriate level for control instrumentation (typically 6-8 bar).
- Maintains a stable pressure at the point of use, even with fluctuations in demand.
- Distribution Piping:
- Network of pipes to transport the compressed air from the receiver to various control devices throughout the vessel.
- Typically made of corrosion-resistant materials like stainless steel or copper.
- Valves and Fittings:
- Control and regulate the flow of compressed air within the system.
- Include isolation valves, control valves, check valves, quick-release couplings, and other fittings as needed.
- Instrumentation:
- Pressure gauges, flow meters, dew point sensors, and other instruments to monitor the system’s performance and air quality.
- Alarms and control systems may be incorporated to alert operators of abnormal conditions or automate system functions.
Additional Considerations:
- Air Quality Standards: Compliance with relevant standards like ISO 8573-1 for particulate, moisture, and oil content is crucial for control instrumentation.
- Redundancy: Critical systems may have backup compressors, dryers, and receivers to ensure continuous air supply in case of a component failure.
- Maintenance: Regular maintenance of all components, including filter replacements and dryer regeneration, is essential to maintain air quality and system reliability.
In essence, a system suitable for producing compressed air for control instrumentation needs to incorporate components that ensure the air is clean, dry, and at the correct pressure to protect sensitive pneumatic equipment and ensure its accurate and reliable operation.