Intake filters

Figure 4-68. Typical blower intake filter-silencer. Air to blower leaves through pipe connection, which may be screwed or flanged. Courtesy of Dollinger Corp.

The air intake system should be sized to give a minimum pressure drop. Each compressor should have its own intake filter. 

Normally the filter should be placed as close as possible to the compressor. When an intake silencer is fitted, it should be fitted between the intake filter and the compressor. 

Requirements for ancillary equipment, for example, water pumps, valves, piping, anti-vibration mountings, aftercoolers, dryers, intake filters and silencers, etc.). 

In the context of industrial compressors, dust is a major consideration. Such compressors have a very high throughput of air, and even in apparently clean atmospheres, the quantity of airborne dirt is sufficient to cause trouble if the compressor is not fitted with an air-intake filter. Many of the airborne particles in an industrial atmosphere are abrasive, and they cause accelerated rates of wear in any compressor with sliding components in the compressor chamber. The dirt passes into the oil, where it may accumulate and contribute very seriously to the carbon deposits in valves and outlet pipes. Another consideration is that dirt in oil is likely to act as a catalyst, thus encouraging oxidation. 

Here is a problem that came up on a sulfur recovery facility in Punto Fijo, Venezuela. The combustion air blower, shown in Fig. 28.8, was a fixed-speed, motor-driven centrifugal machine. The air intake filters were severely fouled. They had a pressure drop of about 8 in H/). The atmospheric vent valve, used to control the discharge pressure at a constant 12 psig, was 50 percent open. The unit engineer had been asked to calculate the incentive in electrical power savings that would result from cleaning the filters. 

Dreetz CD, Lund W. 1992. Air-intake filters used for multi-element analysis of airborne particulate matter by inductively coupled plasma atomic emission spectrometry. Anal Chim Acta 262 299-305. 

Pneumatic conveying dilute phase for pressure use pressure at the outlet of the blower as prime indicator. "Ap across blower > design or 2 1 ratio restriction in downstream conveying line/check valve jammed closed/dirty intake filter/ plugged discharge silencer/increase in feed to the system/length of pipe... 

Most uses of plant air are intermittent. Design frequently provides an intake filter, a buffer tank for compressed air, and a set of pressure switches to take the compressor on and off load. The buffer tank should be large enough to prevent excessive cycling of the compressor, and the compressor should be capable of pressures high enough above the minimum header supply pressure to provide off-line periods of reasonable length. 

Vibration welding techniques have found several applications in the automobile industry including emission control canisters, fuel pumps and tanks, head and tail light assemblies, heater valves, air intake filters, water pump housings, and bumper assemblies. They have also been used for joining pressure vessels and for batteries, motor housings, and butane gas lighter tanks. 

Plugging of the air intake filters. Anything over a few inches of mercury pressure drop on these filters is excessive. 

Air intake filters plugged Pressure restriction of blower discharge Increased ambient temperature Compressor rotor fouled Blower turbine running slow Wet gas compressor problems Fractionator condensers plugged... 

Overheating Intake filter blocked Device can overheat and trip out Clean filter and move intake pipe Maintenance foreman... 

In the most simple case as shown in Fig. 4.20, an active air supply subsystem consists of an air intake filter to remove particles and possibly impurities poisoning the cathode catalysts, a compressor or blower and an air humidifier that can also include the function of an air cooler. 

Nanofibre filter fabrics are frequently in pleated constmctions for air filtration, such as pleated dust collection and engine air intake filters. They could be used to fill the... 

The degree of filtration required will depend upon the quantity of water to be treated, and the quality of treated water necessary to maintain the heat transfer surfaces as clean as possible. A strainer of some kind will be needed as the intake filter, ahead of a finer filter such as a deep bed system or a multi-bag filter. It may even be necessary to include ultrafiltration as the final step if there is much organic or colloidal matter in the intake water. 

For simple air filter duties, without silencing, the cartridge may itself form the complete filter. This sort of design would be used primarily as a crankcase breather filter, or a filter on a hydraulic reservoir breather. It may also be used as an intake filter on very small internal combustion engines, because of its simplicity, low cost and low pressure drop. The complete filter is then replaced as a unit when clogged. 

The simplest form of an effective maehine intake filter is an element of pleated impregnated paper, housed in a suitable casing. The pleats provide both rigidity for the element, so that it requires a minimum of support, and at the same time a large surfaee area for filtration. This area may be further increased by corrugating as well as pleating the paper. 

Two-stage air intake filter/silencers are usually of the panel type and are suited for centrifugal and axial compressors. 

Stationary machines installed in factories and power stations are normally located in machine honses or separate rooms taking in air throngh ducting from the ontside walls with suitable filters incorporated. Alternatively, the complete machine house is treated as a clean room, in which case a barrier system of conventional panel intake filters are usually installed in one wall. 

A typical air sample is contaminated to the extent of 140 million dust particles per cubic metre (and more in heavily industrialized areas). As many as 80% of these particles are smaller than 2 jm - 25 times smaller than the smallest particle that the human eye can see - and most of them pass straight through compressor intake filters. These are supplemented by water vapour, along with unbumed hydrocarbons from aviation, heating and vehicle fuels. When this poor quality air is compressed to 8 bar, the particle content increases to 1.1 billion particles per cubic metre. A typical analysis of the size distribution of attnospheric dust is shown in Table 6.8. 

Industrial stationary compressors are normally installed in separate rooms, drawing in air from the outside atmosphere, free of factory contaminants. When the level of dust concentration in the intake air is likely to be of the order of 10-50 mg/m, it is standard practice to fit the compressor with an intake filter (usually a panel filter or a paper cartridge type, depending on the size of the compressor), having an efficiency of 99.9% based on the dust concentration present in the ambient air. The air intake filter can, therefore, be expected to pass all particles smaller than 5 pm, as well as a proportion of larger ones, in addition to atmospheric water vapour. It will also pass all gases, vapours, odours, bacteria and viruses. 

In addition to the standard HVAC panel intake filters described in Section 6B, other types of intake filters are used (as illustrated in Figure 6.39), including ... 

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