Compressed air pipes

Approach to compressed air systems according to best practices

The hardest part of starting the journey to efficient and cleaner production (RECP) is taking that first step. The National Cleaner Production Center of South Africa (NCPC-SA) has made the journey to achieve significant resource savings with little investment and sustain them by creating the tools for industrial efficiency.

These tools promote the continued application of RECP – the implementation of preventative environmental strategies to processes, products and services to increase efficiency and reduce risk to communities and the environment.

Tools vary from case studies, guides and reports to videos, which have been created in line with the Centre’s mandate to promote the implementation of RECP methodologies to help industry reduce costs through reduced use energy, water and materials, and waste management. To see more guides, visit: www.ncpc.co.za.

This particular feature focuses on the compressed air system best practice guide developed by NCPC-SA Quality Manager, Tanya Van Zyl. It is important to focus on compressed air because it is the most commonly used process utility, but it is also the most overlooked consumer of energy. There are many applications ranging from process control to driving hand tools in industry. There are also many misapplications of compressed air such as personal cooling, sweeping, and liquid mixing.

Below is a list of opportunities for companies to reduce energy costs, CO2 emissions and the environmental footprint of facilities by ensuring optimal use of compressed air systems.

Systematic approach

• Accurately obtain compressed air demand considering pressure and volume for the entire system. Match compressor and accumulator power to demand, taking into account not only peak demand, but also intermittency.

• Consider implementing an energy management system (EnMS) such as the one used for ISO 50001. The CUSUM calculation would be particularly useful to easily see when performance drops.

Condition of pipes, fittings, seals, filters and moisture eliminators

• Walk through each branch of the distribution system, including applications and air consuming devices.

• Note leaks (see section below on leaks) and establish a schedule of regular checks.

• Eliminate or insulate unused sections of pipe.

air pressure

• Use pressure appropriate for system equipment. The need for a higher pressure than specified for the tool or equipment could suggest another problem. Often it can be too small pipes and/or insufficient air volume.

Pipe sizing

• Pipe sizing relates to the pressure and volume required at the point of use (see previous point).

• Undersized lines can result in higher pressure requirements and greater leakage losses.

• Oversized pipes can reduce friction losses and increase investment costs.

• Life cycle cost is likely to be lower for a system with larger diameter pipes as operating costs could dominate the life of the system.

Compressor(s)

• Make sure the compressor air intake is in the coolest place possible. This would often be outside the compressor room, i.e. in a shaded area.

• Generate air at the lowest possible pressure to meet demand.

• Make sure the compressor is running in the most economical way. Idle compressors (when there is no demand for air) still consume a lot of energy without any productive output.

• Switch them off when not in use.

• Multiple compressors serving a manifold should be staged so that successive compressors are not started until the previous one has reached full capacity.

• Preferably, the last compressor in a sequence should be equipped with a variable speed drive so that it follows demand as closely as possible. Compressed air system best practice guide can be found in most industrial plants. Although compressed air is the most commonly used process utility, it is the most overlooked consumer of energy. They have many applications ranging from process control to driving hand tools. There are also many erroneous applications such as personal cooling, sweeping and liquid mixing.

heat recovery

• Much of the energy supplied to an air compressor is released as heat. This is generally ventilated, but there are two alternatives to capture this heat. Recently, models of air compressors have the option of installing recovery devices in the cooling air stream so that the waste heat is converted into hot water for use elsewhere. Another option is to position an air-to-water heat pump in the outlet hot air stream.

Water drainage

• Water and scale buildup in the system can cause pressure drops.

• Slope the pipes to the drain points which are equipped with siphons which open to expel the water when they are full.

Leaks

• Air leaks are a direct energy and financial loss.

• Most leaks can be detected easily by walking the route of the pipe. Leaks in hard-to-reach places can be detected using a special leak detector.

• During maintenance, leaks are usually easy to fix.

Air receivers

There may be a part of the system that experiences short-term spikes in demand. This does not mean that larger compressors are necessarily needed, or even that a dedicated compressor is necessary. It may be possible to meet this intermittent demand by installing an appropriately sized air receiver near the demand. The receiver empties to satisfy the short-term demand, then gradually fills up while the compressor operates normally.

Air receivers generally allow more stable operation of systems because they act as shock absorbers to reduce short cycling.

Air treatment

• Compressing air condenses water vapor in the air. This moisture-laden air can be supplied to loads that may not be up to par.

• Compressor lube oil mist can also enter the distribution system without positive results.

• The air can also contain dirt and germs.

• These contaminants can be removed by different types of filters, dryers or refrigerated coolers.

• Do not overtreat air beyond end use requirements.

Maintenance

• A regular maintenance plan will capture the deficiencies mentioned above.

• Repairing leaks and cleaning the filter is particularly important.