Describe TWO methods of drying compressed air for use in a pneumatic control system.(10)
Methods of drying compressed air for use in a pneumatic control system
Here are some of the common methods used to dry compressed air for use in pneumatic control systems, specifically focusing on their applicability on marine vessels:
- Aftercoolers:
- Principle: These are heat exchangers that cool the compressed air after it leaves the compressor. As the air cools, its ability to hold moisture decreases, causing water vapor to condense into liquid water, which is then collected and drained. 1. All About Compressed Air Aftercoolers | VMAC Air Compressors www.vmacair.com
- Types:
- Air-Cooled: Use ambient air to cool the compressed air. 1. The Importance of Cooling Compressed Air – Atlas Copco USA www.atlascopco.com
- Water-Cooled: Utilize seawater or a closed-loop cooling system to cool the air, often more efficient in marine environments.
- Effectiveness: Aftercoolers are effective in removing a significant portion of the moisture, but they might not achieve the low dew points required for critical control applications.
- Refrigerated Air Dryers:
- Principle: These dryers further cool the compressed air, typically to around 3-5°C (37-41°F), causing more water vapor to condense and be removed. 1. Effectively remove air moisture with a refrigerated dryer – Mark Compressors www.mark-compressors.com
- Types:
- Cycling Refrigerated Dryers: Cycle the refrigeration system on and off based on demand, saving energy during low-use periods. 1. What is a cycling refrigerated dryer? – Pneumatech www.pneumatech.com
- Non-Cycling Refrigerated Dryers: Run continuously, providing a constant supply of dry air. 1. Refrigerated Vs. Desiccant Compressed Air Dryer – Fluid-Aire Dynamics fluidairedynamics.com
- Effectiveness: Refrigerated dryers can achieve dew points in the range of 2-10°C (35-50°F), suitable for many general pneumatic control applications. 1. Cycling vs. Non-Cycling vs. VSD Refrigerated Air Dryers: Which Do You Need? fluidairedynamics.com
- Desiccant Air Dryers:
- Principle: These dryers use desiccant material (like activated alumina or silica gel) to adsorb moisture from the compressed air, achieving very low dew points. 1. Desiccant Air Dryers: Types, Applications and Working – Atlas Copco UAE www.atlascopco.com
- Types:
- Heatless Desiccant Dryers: Use two towers filled with desiccant, alternating between drying and regeneration cycles. 1. Twin tower heatless desiccant air dryers | air treatment – CompAir www.compair.com
- Heated Desiccant Dryers: Use external heat sources (like electric heaters or steam) to regenerate the desiccant, allowing for continuous operation and even lower dew points. 1. Heat regenerative desiccant dryers with up to 194.2 m³/min – kaeser www.kaeser.com
- Effectiveness: Desiccant dryers can achieve dew points as low as -40°C (-40°F) or even lower, making them ideal for critical control applications where very dry air is essential.
- Membrane Air Dryers:
- Principle: These dryers use semi-permeable membranes to selectively remove water vapor from the compressed air stream. 1. Compressed Air Drying: The 3 Most Common Methods to Use in 2023 – Atlas Copco www.atlascopco.com
- Advantages:
- Compact and lightweight 1. Air dryer types: Refrigerated, desiccant, and membrane – Pneumatic Tips www.pneumatictips.com
- No moving parts, requiring minimal maintenance 1. How Does a Desiccant Dryer work? – Van Air Systems www.vanairsystems.com
- Quiet operation
- Disadvantages:
- Limited dew point capability (typically around -5 to -10°C or 23 to 14°F)
- Sensitive to oil contamination
Choosing the Right Method:
- Dew Point Requirement: The required dew point depends on the application and operating environment.
- General pneumatic controls: Refrigerated dryers are often sufficient.
- Critical instrumentation or cold climates: Desiccant dryers are necessary.
- Space and Weight Constraints: Membrane dryers are compact and lightweight, making them suitable for installations with limited space. 1. Membrane dryers for compressed air | FST GmbH www.fstweb.de
- Energy Efficiency: Refrigerated dryers are generally more energy-efficient than desiccant dryers.
- Maintenance Requirements: Membrane dryers require minimal maintenance, while desiccant dryers need periodic regeneration.
Additional Considerations:
- Air Filtration: Proper filtration is essential before drying to remove contaminants that can damage the dryer or affect its performance.
- Drain Traps: Condensate drains should be installed after the aftercooler and dryer to remove collected water.
- Regular Maintenance: Regular maintenance of the drying system is crucial to ensure its continued effectiveness.
In conclusion, achieving clean, dry air for pneumatic control systems requires a combination of aftercooling, drying, and filtration. The specific drying method chosen depends on the dew point requirements, space constraints, energy efficiency goals, and maintenance considerations for the particular application on board the vessel.