INCREASED ENERGY SAVINGS THROUGH A COMPRESSED AIR LEAKAGE

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					       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


ABSTRACT

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
network.

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 [2]
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 [1]. 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 [3].
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 [2]
                                                               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 [2].
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
                   350
                                                                                        reported. CALDS is a computerised system that can assist
            3/h)




                   300
 Flowrate (m




                   250
                   200                                                                  in the management of compressed air leakage
                   150
                   100                                                                  documentation. This system is described in more detail in
                    50
                     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 [2]. 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.
leakages.
                                                                                        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 [4].                                   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 [2].

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
system.

4.                          RESULTS

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
this saving.
                                                                                                                                                                                                                         production
                                                                    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.
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                                                                                                                                                                                                                                                                       Baseline                       Current profile                                EE component
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Figure 7: HVACI’ s combined baseline and project                                                                                                                                                                                           180000
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CALDS was implemented during DSM project                                                                                                                                                                                                    80000
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implementation to ensure sustainable electricity savings.                                                                                                                                                                                   40000

Most of these mines did not employ dedicated leak                                                                                                                                                                                           20000
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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 [1]. 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 [1]. 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 [1]. This will result in a reduction
the compressor projects implemented by HVAC                                                                                                                                                                            of 405 000 tons of CO2 emissions [1].
International is shown in Figure 10. This saving implies
that approximately 19% of the energy efficiency achieved                                                                                                                                                               6.     REFERENCES
by these projects is a result of leak repairs. A saving of
approximately 9.7 MW was realised by repairing leaks in                                                                                                                                                                [1]    “Energy Efficiency and Demand Side Management
the compressed air systems.                                                                                                                                                                                                   in South Africa”, 2007, Eskom, p8.

A saving of 9.7 MW will result from repairing 344 leaks                                                                                                                                                                [2]    “Electrical Energy Equipment: Compressors and
each with a diameter of 10mm. Only 31 leaks must                                                                                                                                                                              compressed air systems”, Energy Efficiency Guide for
therefore have been repaired at each of the 11 projects to                                                                                                                                                                    Industry in Asia, Greenhouse Gas Emission Reduction
realise such a saving. It is very likely that even more leaks                                                                                                                                                                 from Industry in Asia and the Pacific (GERIAP),
were repaired resulting in a bigger saving.                                                                                                                                                                                   2006, p2.

                                                                               Compressed air savings                                                                                                                  [3]    Berkeley, L, et al.: Improving compressed air
                                                                Combined project baseline                                      Combined project performance                                                                   system performance: a sourcebook for industry, 2nd
                                                                                                                                                                                                                              edition US department of Energy, Washington, p27.
                                                                Profile after EE                                               Profile after leakage repair

              250000


              200000
                                                                                                                                                                                                                       [4]    Lodewyckx, J.W.: “Investigating the effects of
 Power (kW)




              150000                                                                                           ‘                                                                                                              different DSM strategies on a compressed air ring”,
              100000                                                                                                                                                                                                          Dissertation submitted in partial fulfilment of the
               50000
                                                                                                                                                                                                                              degree Master of Mechanical Engineering, NWU,
                   0
                                                                                                                                                                                                                              November 2007, pp96-97.
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                                                                                                                   Time                                                                                                [5]    “Eskom - Annual report 2008”,               Eskom,
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
                                                                                                                                                                                                                                           International.
Eskom sold a total of 32,373 GWh of electricity to the
mining sector in 2008 [5]. This means that the mines were
responsible for more than 14% of the all the electricity sold
by Eskom [5]. 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 [5].                                                                                                                                                                                                            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
TEMM International.

Presenter: The paper is presented by Johan Marais .