"INCREASED ENERGY SAVINGS THROUGH A COMPRESSED AIR LEAKAGE"
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  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 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 . 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 . 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 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. P ower (kW) 150000 ‘ 100000 50000 Combined DSM project performance 0 00:00 01:00 02:00 03:00 04:00 05:00 06:00 07:00 08:00 09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 Baseline Current profile EE component Time Figure 7: HVACI’ s combined baseline and project 180000 160000 performance 140000 Per unit power 120000 100000 CALDS was implemented during DSM project 80000 60000 implementation to ensure sustainable electricity savings. 40000 Most of these mines did not employ dedicated leak 20000 0 detection and repair teams before the commencement of 00:00 01:00 02:00 03:00 04:00 05:00 06:00 07:00 08:00 09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 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 by these projects is a result of leak repairs. A saving of approximately 9.7 MW was realised by repairing leaks in  “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  “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  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  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. 00:00 01:00 02:00 03:00 04:00 05:00 06:00 07:00 08:00 09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 Time  “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 . 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 TEMM International. Presenter: The paper is presented by Johan Marais .