Compressed Air Treatment

An effective compressed air treatment system lowers the dew point of the air and takes out particles that may have a negative impact the air compressor. When investing in an air compressor and compressed air system, compressed air treatment is a smart choice for protecting your system.

Contamination Overview

Air drawn in and compressed by the compressor contains a high water vapour content, and contaminants of different types such as oil aerosols, dust, bacteria, etc.

Non-filtered compressed air can destroy pneumatic pipes and tools causing unnecessary expenses on maintenance costs and production down times. This can also lead to quality losses in the production process.

Contamination may cause the following:

• Corrosion and contamination in the network
• Pressure losses resulting from contaminated pipework
• Increased wear due to reduced lubrication of pneumatic elements
• Failure or downtime of production machines
• Scrap produced in painting systems, etc

All of these troubles can prove to be very costly, most of which would be required for adequate air treatment, inline with the individual operational needs.

Procedure for Compressed Air Treatment

There are three primary ways in which contaminants are eliminated from a compressed air system.

Drying Used to eliminate residual water.
Filtration Used to eliminate unwanted particles.
Adsorption Used to eliminate oil content.

1. Drying

The physical principle of refrigeration drying involves cooling the compressed air down to a few degrees above zero, separating the condensate from the air flow and removing it into the environment.

By subsequent cooling, temperatures are obtained which retain essentially less water than vapour, the excess of water condenses and appears as liquid.

Adsorption Drying

Compressed air dryer that operate according to the sorption principle reach pressure dew points below zero degrees Celsius.

Compressed air drying systems with adsorption dryers for pressure dew points down to less than 70 degrees Celsius can be classified by their type of regeneration

  • Regeneration using heat input
  • Internally heat regenerative,  Regeneration using an auxiliary flow of dried air and an internal el heater.
  • Externally heat regenerative, Regeneration using ambient air that is taken in via a fan and heated by an el external heater.
  • With Compressor heat,   Regeneration using energy from the compression system full load partial load flow
  • Heatless, Regeneration using an auxiliary flow of dried compressed air.

Adsorption means that fluid is removed from compressed air either chemically or physically.

The principle of adsorption

Moisture that the compressed air contains is bound by adhesion, forced to the surface of a drying desiccant in granulated form. In this process, a pressure dew point of up to 70 degrees Celsius is attained. As opposed to refrigerant drying, the compressed air is not cooled.  There are two procedures available for this: Heatless and Heated regeneration.

Heatless regeneration

In heatless regeneration, a partial flow is taken form the dried main flow of compressed air, this is used as regeneration air. This partial air flow is first expanded. Thereby, it is strongly under -saturated with moisture. If it is then passed over the bed of desiccant to be regenerated air it cannot be returned to the compressed air flow again and it leaves the dryer as lost air. If you lay out a compressed air plant, you must therefore calculate the regeneration air as an additional consumer.

Heated Regeneration

In heat regeneration, hot regeneration air is used for desorption. This is generated by an external heat source. Ambient air is sucked in, heated and transported through the bed of desiccant that is to be regenerated, in this procedure, temperatures between 150 and 300 degrees Celsius are required, depending on the type of desiccant used.

Regeneration is finished when temperature at the exit of the regeneration air has reached 100 degrees Celsius. The bed of desiccant is cooled to the operating temperature with a cooling air flow. As opposed to a heatless adsorption dryer, you do not need to calculate additional compressed air consumption for a heated adsorption dryer. In a few cases only a small amount of compressed air for switching of the control valve is required, the automatic switching cycles lie at 4-8hours depending on the operating conditions.

Refrigeration Drying

Drying takes place in two phases:

First Phase: In an air heat exchanger, the warm, inflowing compressed air cools in the opposite directed current of the already cold outflowing air.

Second Phase: The compressed air flows through a refrigerant heat exchanger and cools down to the set pressure dew point, the remaining moisture cools to the pressure dew point, condenses and is automatically removed.

Storage of the Humidity

According to the mass of the drying agent of saturation, the storing capacity of the drying agent is continuously reduced during adsorption.

Membrane Drying

Membrane dryers are used as external dryers for drying compressed air and gases with low pressure dew point temperatures mainly in the performance range of up to 1000 litres per minutes.

The core of these dryers is a polymeric micro -fibre hollow membrane that is designed so that solely water vapour molecules can get through the membrane. Even oxygen and nitrogen molecules are retained.

Operating Principle

In the dryer module, thousands of highly selective hollow membranes are bundled and encapsulated in a tube with their ends open through which humid compressed air flows. Membrane dryers adapt to variable compressed air inlet temperatures and provide a pressure dew point reduction by 30 degrees Celsius.

The filtration Spectrum

Deep-bed filter (Coalescence Filter)

This filter series is also known as micro-filters or coalescence filters. The air flows from inside to outside , particles having a size of less than 0.5 micron can be filtered out.

Surface Filter

Particles are separated on the surface that is arranged transversely to the direction of flow. Particles that are greater than the pores of the filter are filtered out and retained on the surface. Poor maintenance can result in a greater pressure drop because contaminants deposit on the filter surface. The air flows always from outside to inside, in most cases, surface filters are used as pre-filters.

 Filtration Principle

Labyrinth – like openings and channels form between the fibres, the separation takes place everywhere where the aerosol makes its way through the deep filtration element, by way of

Direct contact – Particles hit the surface of the filtration medium directly, where they are retained, particles of up to 1 micron and larger can be filtered out in this way.

Inertial Impaction – If particles are unable to follow the winding channels in the filtration medium and stick to the filter matrix, this is valid for particles ranging from 0.3 to 1 micron.

Diffusion / Brownian Movement  – If very small particles can move independently in the gas flow using their own energy, they collide inevitably with the filter material and get stuck in the depth of the filtration medium, diffusion refers to particle sizes of 0.3 micron smaller.

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