2024-03-11
Importance of compressed air filtration
Correct air preparation can significantly improve the process and production reliability of the machine. Particles, water and oil in compressed air shorten the service life of components and systems and shorten their functions. They also undermine productivity and energy efficiency. In this article, various air filtration and air treatment products are summarized and discussed, as well as auxiliary equipment such as drainage devices. In addition, the purity levels of compressed air as defined by ISO 8573-1:2010 are outlined.
Why do you need compressed air filtration?What?
One cubic foot of compressed air may contain millions of dust particles, large amounts of water and oil, and even heavy metals such as lead, cadmium and mercury. If it is not filtered out, the trouble-free operation of system components (such as valves and cylinders) cannot be guaranteed for a long time. Inadequate preparation of compressed air can contaminate the control valve and cause expansion and premature wear of the sealing ring. Therefore, proper compressed air preparation is essential to reduce machine downtime, maintenance and energy costs.
Variables of compressed air preparation
There are three variables for air preparation: compressed air purity, compressed air volume (flow rate) and compressed air pressure. According to the system requirements, the coordination of these three variables can ensure a high compressed air quality and form the basis for selecting suitable maintenance unit components. The required compressed air purity improves the operating performance and efficiency of pneumatic systems and ensures compliance with legal regulations in industries such as food processing. The flow rate largely depends on the flow cross section and the design size of the machine. Generally, with the same design, larger components have higher flow rates. Optimized working pressure increases efficiency, minimizes wear and reduces power consumption. In order to coordinate the purity of the compressed air, the correct individual components must be selected for the compressed air volume and pressure of the system specifications. This includes, for example, on/off valves, booster valves, pressure regulators, water separators, filters and drying units.
Walker
Types of filters and air handling equipment
There are many types of air treatment components used to remove contaminants such as solid particles, liquid water, water vapor and oil vapors, odorants, and even bacteria and viruses. For most automation applications, the focus is on the removal of solid particles and water.
Water separatorThe condensate can be removed using a centrifugal design or the principle of coalescence.
· The centrifugal separator induces a rotational motion in the air, forcing the particles to accelerate in a radially outward motion. Once outside, it drains into a bowl. These can effectively remove water droplets and dust and dirt particles larger than 5 microns in size. This process requires no maintenance.
· The coalescing separator causes air to flow from the inside to the outside of the filter element. These filter cartridges must be replaced periodically.
FilterFor removing particles, condensate and oil.
· The pore size of the coarse/particulate filter (Figure 3) is 5 to 40 microns. The air flows through the centrifugal separator and then through the filter element. The filter element is typically a sintered material, such as polyethylene or bronze.
· Fine filters and microfilters remove particles smaller than 1 micron (down to 0.01 microns). Air flows from the inside to the outside of the filter element. The solid particles got stuck in the filter cartridge and blocked the filter cartridge. Fluid particles such as condensate or oil will coalesce or attach to larger droplets, which will float and be trapped in the filter bowl. It is important to cascade the filters to avoid premature clogging of the filter elements. For example, if 1 micron filtration is required, it is recommended to use a 5 micron filter upstream to prevent the 1 micron filter from being blocked by large particles.
· The activated carbon filter combines hydrocarbon residues, odorants and oil vapors.
· A sterile filter ensures that the air is free of bacteria.
DryerIt is used to remove water vapor, which exceeds the capacity of fine and micro-coalescing filters, and is classified according to the available pressure dew point (PDP). The pressure dew point defines the temperature to which the compressed air can be cooled without condensing. If the temperature is lower than the pressure dew point, condensed water will form. Even if the temperature is subsequently increased, this condensed water will remain and may lead to corrosion of the components.
· Refrigeration dryers are typically located downstream of the plant air compressor. The air is cooled to just freeze in the cooling unit, and the discharged condensed water is discharged. The pressure dew point reached is about 3°C(37 °F). To avoid condensation, it is recommended to set the pressure dew point to 50 °F(10°C) below ambient temperature, so for systems that never operate below 55 °F(13°C), a freeze dryer is sufficient..
· The membrane dryer suppresses the pressure dew point relative to the inlet conditions. The air flows longitudinally through a bundle of parallel hollow fibers. During this process, water vapor diffuses due to the partial pressure drop from the inside of the fiber to the outside. Purge air was used to vent the vapors. Due to the purge air, the maintenance-free membrane dryer has a certain amount of constant exhaust/air consumption.
· Adsorption dryers can be used when a pressure dew point of -40 °F(-40°C) to -94 °F(-70°C) is required. Dryers utilize molecular forces to bind gas or vapor molecules to a desiccant, such as desiccant beads. Since the desiccant is renewable, two chambers are required. When one of them is dry, the other desiccant has time for cold or hot regeneration. In equipment with cold regeneration, some dry air is used to dry the binder. When using thermal regeneration, water evaporates when heated. The desiccant must be replaced periodically (I. e. after 8,000 hours of service).
Type of filter drain
The filter unit has several different types of drainageValve：
· Manual: Drain the condensate manually by tightening the drain plug. These require a regular maintenance schedule (I. e. one per shift).
· Semi-automatic/normally open: This type of drain opens immediately after the compressed air is closed.
· Fully automatic/normally open: This type of drain pipe opens immediately when the compressed air is cut off or the bowl reaches the specified water level.
· Fully automatic/normally closed: After turning on the compressed air and reaching the specified liquid level in the filter bowl, these filters will open.
· also haveelectric drain pipe, Can be turned on/off remotely by electrical signals.
Correct maintenance of filter element
In order to maintain the effective operation of the filter, the filter element needs to be replaced periodically. How often it needs to be performed depends on variables such as the quality of the supplied air and the running time of the machine. As a method, you can determine and set up a preventive maintenance plan that replaces the filter element every 6 months. A more reliable method is to use a differential pressure sensor, which measures the pressure drop between the supply and output pressure of the filter. The pressure drop indicates when the filter is clogged. These can be electrical sensors that send signals to the PLC, which can then alert the operator, or can be visual indicators of the filter unit itself. For example, when the filter cartridge is clean, the indicator may display green, and when the filter cartridge is clogged and needs to be replaced, the indicator may display red.
Importance, filter, air, compressed air, particles, pressure, micron, need, e.g., dew point, walker
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