Water, electricity and gas are purchased forms of power and are clean metered and paid for from the local municipality. Compressed air and steam are produced on site and are vital forms of energy for many plants. They also happen to be expensive, so what can an ultrasonic leak detection survey and a compressed air energy audit and optimisation do to help.
Leak detection on its own will definitely reduce energy wastage; however, it is only one part of the broader optimisation process.
What do the various components of an air energy audit reveal?
From experience we know that on average 30% of all compressed air produced is either wasted via leaks to atmosphere or miss-used on the wrong application. At Artic Driers we also know that spot leak detection without a long-term plan is almost pointless.
Leak detection
A methodical system is essential when tackling a leak detection survey. Speed of data capture is important as this auditing process is time consuming. The leaks must be tagged, photographed and commented on in a clear and concise manner. The report should contain a page per leak, the tag number, a picture, a GPS location, the description within the plant of its location as well as a description of the leak type and severity.
Where possible, the total loss should be verified by a separate leak rate check via a calibrated flowmeter. The two methods of leak detection are then compared. In the event of discrepancies, further investigation may be required. Be aware of underground airlines that may have developed leaks that will not have been captured by a simple leak detection audit. The total leak loss should be expressed as a volume, as the kWs used to generate this volume as well as the cost to produce the lost air.
The worst leaks should be repaired first. After rectification, the same auditor should return and verify that the leak is properly repaired, and only then, remove the numbered tag.
This leak detection system should be implemented three or four times a year. In this way the repair of air leaks becomes ingrained in the maintenance system of a company and thousands of Rand worth of energy is saved every year.
Compressed air system optimisation
To obtain the best return on investment, an optimal design for the compressor system is vital. The optimisation process should consider and review the following:
Compressor station position: the position of the station will influence the pipeline length. Longer lines can easily lead to airline pressure losses, so compressor stations should be centrally located in the factory. On larger systems, it may be advantageous to have multiple compressor stations to reduce long pipe runs and the pressure drops associated with them.
Pipeline sizing and design: undersized air lines will create pressure losses that waste energy. High velocities created by undersized pipe lines are an indication of this and are easily identified by a specialist air audit company using the right equipment. Undersized air lines in the compressor room are one of the biggest culprits of energy wastage. Undersized lines choke the air flow from the compressor room to the plant and the resulting back pressure is often enough to create a false signal for the compressor to offload, when in reality the plant is suffering from a lack of line pressure. Do not assume that the discharge flange on the compressor is the line size to use, invariably it is too small.
A pipe line design that allows for minimal pressure drops as well as future plant expansion is a vital part of the optimisation process for any factory. Part of this design must allow for drainage of condensates, even if low dew point dryers are in place. It must also allow for the removal of any oily waste condensates for proper disposal. It is illegal to allow oils into a storm water drain.
Compressor selection: prior to installing a new compressor station, a qualified air energy auditor should be appointed to ensure that compressed air is going to be used effectively and at the correct pressure. If using an existing plant as a baseline, air flow auditing should be used to establish a compressed air consumption base line. This assumes that an air leak audit has been undertaken and the leaks repaired. Air flow audits should last for at least a week to provide solid trend lines.
Once this process is completed, base load compressors can be confidently selected and variable speed units can be used to balance the final top-end air load. Remember to allow degree of excess for future expansion. Review the need for oil free or lubricated compressors, oil free compressors can carry a heavy price tag if the air quality requirement is not needed for the majority of the plant.
Compressed air treatment: the correct selection for inline filters and dryers is essential to ensure pressure losses are minimised or even eliminated and that air treatment is not under or over specified.
Over specification will lead to increased capital and operating costs, while compressed air that is not fit for purpose will lead to failure of pneumatic equipment. If only one or two applications demand ultra-clean air, then treat these applications at point of use, higher specifications for air quality come at a higher price. Consult a specialist air treatment company before making a decision. We at Artic Driers consider that the air treatment sector is a different industry to the typical compressor supply chain and requires different skill sets.
Air auditing: to achieve consistency the air lines should be monitored for air quality, flow and pressure. Permanent air monitoring instruments are assets that will provide a fast ROI, as with these in place, engineers can keep abreast of changes in the plant.
On many sites compressors are not operated at full capacity. By logging the flow and the power from the compressors, engineers will be able to determine a base load for the plant, with perhaps a variable speed drive compressor to top up the flow when required. This type of decision will use power more effectively and reduce energy wastage.
Air velocity: velocity often identifies a problem in a facility. High line velocities will carry over solids and condensate into the air line from the quiet zones within a dryer. High velocities also carry airline contamination straight to the point of use.
Pressure: along with velocity, pressure is an indicator of what is going on in the plant. On occasions we have found that the compressors discharge pressures have been increased to overcome a poorly designed distribution system, which increases maintenance costs and wastes electricity.
Dew point: a blocked condensate drain, an open bypass valve, or a fractured heat exchanger, are all sources causes of air pollution. A dew point probe identifies contamination problems faster than any machine minder. Many dryers are on line showing a dew point of 3°C, but are busy passing thousands of litres of water per week into the plant due to a simple fault such as a stuck auto drain.
Air dryers are not usually fitted with dew point probes as these are expensive; the dryer’s fascia merely monitors the air temperature in the main heat exchanger or the suction gas line to the Freon compressor. A fault can be present and the dryer will still indicate a 3° or 4°C dew point. A dew point meter will identify the problem in minutes and can sound an audible and/or visual alarm, or even be connected to a factory’s scada system.
A good air audit will show the flow, pressure and relative humidity and dew point in one concise graph.
Is air auditing a science?
We at Artic Driers believe so. Auditing is no longer just a ‘look’ at the compressor system, it requires the auditing company to invest substantial amounts of money to provide clients with a large data capture capacity as well as having the ability, experience and knowledge to analyse and interpret the data to provide a meaningful report at the end.
Many companies can capture data, but few can provide the insight into the status of the compressed air system showing the potential for optimisation and possible power savings. Engineers are on a constant search for perfection. Auditing is the first step to an optimised compressed air system
For more information contact Allen Cockfield, Artic Driers International, +27 (0)11 420 0274, allen@articdriers.co.za, www.articdriers.co.za
| Tel: | +27 11 420 0274 |
| Email: | paul@articdriers.co.za |
| www: | www.articdriers.co.za |
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