Design of a central compressed air system: Recommended piping

The design of uA central compressed air system, supported by appropriate instrumentation and an understanding of available air compressor systems, allows the system to automatically respond to the inherent dynamic conditions of the system and provide the plant with key performance indicators to ensure optimal performance.

To achieve the proper design of a central compressed air system that meets the requirements and needs of the plant, it is advisable to consider the following factors:

1. Environmental conditions that include the cost of a production stop.
2. Guaranteed availability of electrical energy.
3. Load variations of compressors.
4. Central compressed air system costs.
5. Available space for your installation.

Why choose a central compressed air system?,In many cases, installing a centralised compressor is the chosen solution, as its operation and maintenance are less costly than many compressors distributed locally throughout the plant in different departments.

In this article, we will be visualising the Benefits of a central compressed air system and recommended piping in its design, in order to provide plant managers with timely information to make the right choice on whether to centralise or decentralise their compressed air system

6 benefits of choosing a central compressed air system for your plant

1. Compressor stations can be interconnected efficiently, resulting in lower energy consumption.
2. A central installation involves lower monitoring and maintenance costs, as well as better opportunities for energy recovery from the system.
3. Reduces the total floor area required for compressor installation.
4. The filters, coolers, other auxiliary equipment, and the common air intake can be optimally dimensioned.
5. Ease in adjusting noise measurements.
6. Greater sequential control to improve efficiency, as the central compressed air system comprises several compressors of varying sizes at a facility.

Recommended piping for the design of a centralised compressed air system

The information we will be supplying regarding pipework in a central compressed air system will likely have more pages written about it than any other subject. Consequently, we will attempt to cover the basic principles which are always applicable in system design and which, when followed, provide optimal operation.

The first thing to consider is that the piping for a central compressed air system will need to have:

1. Minimal pressure loss.
2. Minimal air loss from leaks.
3. Minimum quantity of water in the network and at the points of use.

Types of piping

The pipe materials for a central compressed air system can be divided into two types: metallic and non-metallic.

• Non-metallic piping

Commonly called «plastic» pipe, it has been offered for many years as compressed air piping, because:

• It's lighter than most metal and easier to handle.
• It can be installed without special tools, such as soldering irons or dies.
• It is not usually corrosive.
• Installation with the appropriate adhesive material is quick.
• The labour cost, which may be unskilled, is much lower than for most metals (copper, stainless steel, black iron), and the system can often be installed at a lower cost.

However, most of these materials are not compatible with compressor oils in general, and many synthetic ones in particular. In fact, fires can occur, although it is uncommon, but when there is one in a plastic pipe, the possibility of it melting and migrating around the plant increases.

If new thermoplastic materials are used, the piping system becomes quite expensive, certainly more so than a high-quality extruded aluminium alloy with compression or push-fit connections.

• Metal options

The metal tube can be black iron, stainless steel, copper, or extruded aluminium alloy, with appropriate thermal and pressure characteristics.

• Black iron or steel pipe in compressed air systems, it corrodes when exposed to condensate and therefore becomes a source of system contamination.
• Extruded aluminium alloy and stainless steel pipes they have become popular. This is because they provide a smooth, low-friction interior surface and eliminate self-contamination, whilst also offering improved flexibility to meet changing air distribution needs.

This is particularly desirable in plants such as the automotive support industry with evolving assembly and sub-assembly areas. Extruded aluminium alloy air system piping can have connections that do not require special tools or pipe threading.

The piping Extruded aluminium alloy can be installed in most areas where copper and aluminium pipe can be used. This type of piping offers certain advantages such as:

• Much lower initial price with good or better corrosion resistance, depending on site conditions.
• It can be installed, uninstalled, and reinstalled as many times as necessary without requiring specialised labour or light welding.
• It has good air handling capabilities with internal connections.

A point of consideration for the engineer responsible for the design is the type of coating to be used on the pipes of the central compressed air system, as this is the way to protect against corrosion and process contamination. For example, galvanised inlet piping resists corrosion better than standard iron piping.

However, when corrosion occurs, the zinc can peel off and produce potentially harmful solid pollutants between the filter and the compressor. This is particularly dangerous for the mechanical integrity of any compressor.

The fundamentals for material selection as a function of usage have five facets: inlet piping, discharge piping, interconnection piping, main line distribution, and header-to-process distribution. For each of these, the type of piping and coating to be used for an optimal system must be evaluated.

For this reason, regardless of the claims of the thermoplastic pipe manufacturer, no non-metallic material is recommended for pipe interconnection, and rarely for the distribution header piping. Most of these materials have precautions about not being exposed to temperatures above 200°F and avoiding any type of oil or lubricant.

Here again, extruded stainless steel or aluminium alloy is appropriate and therefore the primary recommendation for pipework interconnections between the compressor, filter and dryers, if the compressed air is oil-free.

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