INCREASED ENERGY SAVINGS THROUGH A COMPRESSED AIR
LEAKAGE DOCUMENTATION SYSTEM
JH Marais, M Kleingeld, R Pelzer
Contracted to North West University and consultants to HVAC International and TEMM International
The compressed air systems used on the mines can
easily span a distance of 40 kilometres on the surface
alone which makes the presence of leaks very possible.
It is estimated that at least 10% of the compressed air is
lost through leaks in the compressed air piping
An efficient system is required to reduce air leaks on
compressed air systems. The Compressed Air Leakage
Documentation System (CALDS) has been designed to
replace the existing manual process for pipe leakage
detection and data logging. A saving of 7 kW can be Figure 2: Cost components in a typical compressed air
achieved on a typical mine compressed air system by system 
repairing a single 5 mm diameter leak.
The compressed air pipelines found on the mines can
1. INTRODUCTION often cover a distance of 40 kilometres on the surface
alone. The occurrence of leaks in these pipes is therefore
Compressed air systems account for approximately 9% of not unexpected. In practice a large number of leaks do
South Africa’s maximum electricity demand in the exist on mine compressed air systems. It is estimated that
industrial sector . The various contributors to the total a typical industrial compressed air system will waste
electrical demand can be seen in Figure 1. It is evident between 10% and 30% of the compressed air generated
from this graph that compressed air is one of the major by the compressors .
energy consumers in the South Africa’s industrial sector.
In a normal mining environment, repairing of equipment
used for production, usually takes preference over repairs
that are not essential for production. Compressed air leaks
are generally not accepted as essential for production,
unless they cause a significant drop in air delivery
pressure that will adversely effect mining operations.
However, some mines do employ people specifically to
detect and repair leaks on the compressed air system.
This practice is not implemented on all the mines which
results in many air leaks remaining undetected. One of the
major reasons for missed load reduction opportunities on
compressed air systems is precisely because of
compressed air leakage.
Figure 1: Maximum Demand in the industrial sector 
The compressed air consumed for different orifice
The segments of the various component expenditures diameters at a constant pressure of 550kPa is shown in
incurred over the first five years of a typical compressed Figure 3. It can be seen from this figure that the air flow
air system can be seen in Figure 2. This five year life increases exponentially with the increase in leak size.
cycle shows that energy costs are responsible for 80% of
the total expenses of the compressed air system .
Reducing the energy consumption of a compressor will
greatly reduce the overall costs of a compressor system.
Flow rate at 550 kPa for different orifice appropriate management system is required to ensure that
diameters compressed air leaks are kept to a minimum and that
400 repairs are carried out promptly after being identified and
reported. CALDS is a computerised system that can assist
200 in the management of compressed air leakage
100 documentation. This system is described in more detail in
0 the following section.
1 2 3 4 5 6 7 8 9 10
Orifice diameter (mm)
3. AUTOMATION OF AIR LEAKAGE
Figure 3: Air flow rate vs. orifice size DETECTION AND MONITORING
A single 5mm diameter leak will consume approximately One of the most essential characteristics of an efficient
88m3/h of compressed air at a pressure of 550kPa . A compressed air leakage management system is effective
compressor consumes approximately an extra 7kW to administration and documentation. All the leaks that are
compensate for the compressed air lost due to such a leak. detected must be correctly documented in terms of
The financial loss as a result of this single leak amounts to location, size of leak, and pipe diameter. This information
R 17 200 per year. The introduction of an efficient must then be passed on to the responsible person who
compressed air leak and repair maintenance unit on the must ensure that the leaks are fixed by a specified date.
mines will result in major cost savings throughout the
industry. All the information concerning the leaks must be stored
on a central database including the date of repair. A
The Compressed Air Leakage Documentation System properly qualified person must be able to use this system
(CALDS) is a computerised system that replaces the to manage the detection and repairing of each leak.
existing manual process for pipe leakage data logging. CALDS is a system that meets all these requirements and
CALDS detects, reports and manages compressed air can also be used for other purposes.
CALDS can be used to log various parameters of other
2. MINE COMPRESSED AIR SYSTEMS compressed air systems. Essential compressor information
such as the electrical current drawn by the compressor,
Most deep mines in South Africa make use of a vibration levels, temperature, oil pressure, etc. can also be
combination of different compressors situated on the logged and stored on this handheld computer.
surface to supply both surface and underground
compressed air demands. Centrifugal compressors with CALDS consists of two main parts, namely the handheld
installed capacities of up to 12 300kW are normally palm computer, and a desktop computer. The handheld
installed in centrally located compressor houses . palm computer is used by various workers to log
compressed air leakage information during routine
A simplified layout of a mine’ s surface compressed air inspections, checks and maintenance on equipment.
system can be seen in Figure 4. Pipelines of compressed air
systems can extend over more than 40km on the surface The CALDS interface was developed to be user friendly.
alone. The total compressed air network pipe system used Information can easily be entered by making use of the
to supply underground air demand is normally very menus and functions on the handheld computer. Examples
complex and much longer in total length. of the user interface can be seen in Figure 5 and Figure 6.
Figure 4: Simplified compressed air system layout Figure 5: Entering of data in a predetermined field
The possibility of developing air leaks in such an extensive
compressed air network is therefore very real. As opposed
to a 5mm leak and an 88 m3/h leak rate, Figure 3 also
shows that a 10mm orifice in the same compressed air
system would result in a leakage rate of 350m3/h .
An efficient compressed air leakage detection and repair
system could therefore result in substantial savings. An
At one of the mines, 24 leaks were detected in one month
alone. Eight of these leaks were repaired within two weeks
of detection and reporting. It is however difficult to
quantify the exact amount of energy saved as a result of
such leak repairs. This is because other system
improvements were implemented simultaneously.
The consequence of compressed air leaks is reduced system
performance whenever compressors are in operation. The
Figure 6: Entering the date of the entry effect of leak repairs will therefore occur throughout the
day. Other system improvements will only be evident
The information on the handheld computer can be during non peak production periods. These improvements
downloaded to a desktop computer as soon as the operator include techniques such as system pressure reduction
returns to the office. The database of equipment during non peak production periods.
information, leak detection and repairs can then be used to
improve system maintenance and availability. This The amount of energy efficiency as a result of leak repairs
information will be available on the desktop computer for can therefore be quantified by determining its contribution
further management as shown in Table 1. to the electricity saving during peak production periods.
The peak production period varies from mine to mine.
Table 1: Example of data on the CALDS desktop However, in general peak periods occur from 10:00 to
computer 12:00. The DSM compressor projects implemented by
HVAC International realised an average energy efficiency
saving of 18.4% during this peak production period. The
energy saving during peak production periods is indicated
Properly used, CALDS can do more than just manage and by the green area in Figure 8.
report on compressed air leakage detection and repair. It
can also improve on system availability by monitoring
and managing other components of the compressed air
The combined baseline and savings profile on 11 DSM
projects on mine compressed air systems implemented by
HVAC International can be seen in Figure 7. This graph
shows that an average electricity savings of 52.4 MW was
realised over a 24 hour period. Compressor automation and
optimised control systems are the primary contributors to
Figure 8: Energy efficiency component during peak
HVACI’s total compressor project performance
The 18.4% energy efficiency measured during the peak
Combined project baseline Combined project performance
production period will be evident throughout the day. This
250000 energy efficiency component was applied to the total 24
200000 hour electricity profile. The effect of this energy efficiency
is shown in Figure 9.
P ower (kW)
Combined DSM project performance
Baseline Current profile EE component
Figure 7: HVACI’ s combined baseline and project 180000
Per unit power
CALDS was implemented during DSM project 80000
implementation to ensure sustainable electricity savings. 40000
Most of these mines did not employ dedicated leak 20000
detection and repair teams before the commencement of
these projects. This situation changed dramatically as leaks Time
were being detected and logged by the implementation of Figure 9: Energy efficiency component applied throughout
CALDS. The obvious benefits from using this new system the day
were immediately apparent.
It has already been stated that between 10% and 30% of the 5. CONCLUSION
electricity consumed by a typical industrial compressor
system can be attributed to leaks . An estimated average Approximately 9% of South Africa’ s maximum electricity
saving of 5% in energy consumption as a result of repairing demand in the industrial sector is as a result of
leaks in the compressed air lines is therefore very realistic. compressed air systems . The electricity costs of the
There are other factors that can also influence compressor mines can be reduced by 1.25% by repairing compressed
power consumption. air leaks. However, until recently, compressed air leaks
were not always repaired on a regular basis. An effective
The said saving as a result of the leak repairs will only be system must be put into place to limit compressed air leaks
valid if these factors remained unchanged. Certain on mines. CALDS is an automated system that can assist
assumptions were made to quantify the savings. It is workers in their ability to reduce air leaks.
assumed that the system pressure during peak production
periods before project implementation is the same as that CALDS has been implemented at various South African
after project implementation. A further assumption is that mines to ensure DSM project sustainability. A total saving
the mine’ s production levels are the same as that prior to of 9.7 MW was achieved as part of 11 different compressor
project implementation and that equipment used during DSM projects implemented by HVAC International. It is
peak production periods remained unchanged. estimated that a further 405 GWh can be saved in South
Africa by promptly repairing all the leaks on mine
A saving of 5% from the original total project baseline for compressed air systems . This will result in a reduction
the compressor projects implemented by HVAC of 405 000 tons of CO2 emissions .
International is shown in Figure 10. This saving implies
that approximately 19% of the energy efficiency achieved 6. REFERENCES
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Compressed air savings  Berkeley, L, et al.: Improving compressed air
Combined project baseline Combined project performance system performance: a sourcebook for industry, 2nd
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Profile after EE Profile after leakage repair
 Lodewyckx, J.W.: “Investigating the effects of
150000 ‘ different DSM strategies on a compressed air ring”,
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Figure 10: Effect of leakage repair on compressor systems Johannesburg, 2008, pp 219-220.
Investigations at South African Platinum mines have 7. AUTHORS
shown that compressors are responsible for approximately
25% of the total electricity costs. A saving of only 5% on Principal Author: Mr Johan Marais is contracted to
the compressed air system would result in a saving of North West University and consultant
1.25% on the total electricity costs of the mine. to HVAC International and TEMM
Eskom sold a total of 32,373 GWh of electricity to the
mining sector in 2008 . This means that the mines were
responsible for more than 14% of the all the electricity sold
by Eskom . A saving of 405 GWh can therefore be
realised if all of the leaks on the compressed air systems in
South Africa mines are repaired. This will have the added
benefit of reducing CO2 emissions by 405 000 tons in South Co-author: Dr Marius Kleingeld is contracted to North
Africa . West University and consultant to HVAC International
and TEMM International.
Co-author: Dr Ruaan Pelzer is contracted to North West
University and consultant to HVAC International and
Presenter: The paper is presented by Johan Marais .