Industrial Sector

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Key Areas of Investigation

• REFRIGERATION
  AngloGold has a scheduled maintenance plan requiring refrigeration machines to be inspected and heat balanced at regular intervals. A typical finding is an insufficient heat transfer across some of the condensers and therefore efficiency losses. It is possible to cost the effects of scale build- up by a heat-balance and hence determine the optimal time to clean this equipment to minimise costs. AngloGold have already established a pilot plant testing the feasibility of automatic on line efficiency monitoring and in-line tube cleaning at their Great Noligwa mine. A further potential saving is to insulate these vessels.
• COMPRESSORS
  At AngloGold's Kopanang and Tshepong mines, hot water from compressor coolers is successfully being used for supplying hostel change houses with hot water requirements. The same could be investigated for Elandsrand. This is an effective use for waste heat. Additionally the cost of losses caused by the pressure drop across compressor inlet air filters can be calculated. This will give an indication of the best time to change the filters.
• COMPRESSOR COOLING TOWERS
  There appeared to be room for some efficiency improvement here. The cooling towers were returning water above design temperature to the compressor station. This issue was taken up with mine staff.
• ENERGY RECOVERY
  Elandsrand mine recovers energy from water supplied to the lower levels via pelton wheel turbine driven generators. AngloGold is similarly investigating alternative energy saving methods of pumping water, namely a three pipe chamber feed system, operational at Tshepong, and a water transformer being installed at Moab Khotsong.
• ENERGY MANAGEMENT
  While energy is currently accounted to macro processes, as far as the metering allows, the next level of accounting would be to individual end users, for charging direct utility costs. This is in line with current AngloGold policy to distribute energy costs as close as practicable to the end user. Elandsrand appears to be on the most cost effective tariff, currently using the Eskom Real Time Pricing option on tpo of their previous Nightsave KVA tariff.

Having highlighted the potential cost areas, the team proceeded to evaluate and categorise their benefit.

Evaluation Criteria

The following table identifies some of the key areas where energy saving could be achieved. These include: a cost estimate, the projected benefit to the company (in monetary terms), duration of the proposed project, the estimated return on investment, as well as the category of expenditure.
Type of expenditure was categorised as follows:

• IMPROVED HOUSEKEEPING (1) Covered by maintenance budget.
• LOW-COST MODIFICATION (2) Covered by maintenance budget.
• MEDIUM COST MODIFICATION (3) A one-off investment, which is expensive in relation to the value of existing equipment.
• HIGH COST MODIFICATION(4) Substantial capital outlay on new equipment.

	Costs	Return	Payback	Category
Rigorous Compressed air saving programme	R192 000 pa	R384 000 pa	6 months	(1)
Rigorous inter-stage cooling maintenance/retrofit for surface air compressors	R500 000 pa	R1 200 000 pa	5 months	(2/3)
Rigorous after-stage cooling maintenance/retrofit for surface air compressors	R500 000	See knock effects	13 months	(2/3)
Knock on effect on refrigiration from improving after-cooler performance		R308 000 pa (Value of additional heat input to mine)

*All costs indicated above are 'high cost' estimates. In most cases actual costs will be lower.( Similar low savings estimates were chosen. )

Selected Results

After having completed the more detailed analysis, new energy saving opportunities, as well as those listed in the walk through, were identified.

INVESTMENT VS ANTICIPATED PERIOD OF PAYBACK

ALL MEASURES:

• The total investment required for the execution of all the above listed projects was R 1.293m.
• The total annual energy earning for the above is: R1.99 m per annum
• The overall payback is approximately eight months

MAINTENANCE & LOW COST MEASURES:

• The total investment required for the execution of all the above listed maintenance and low-cost (category (1) & (2)) projects was R692 000
• The total annual energy earning for this is: R1 584 000 pa
• The payback for these measures (class 1 & 2) is approximately five months

ENVIRONMENTAL CONSIDERATIONS:

• GLOBAL ENVIRONMENT: Reduction in CO2 emissions: 9 700 000 tons pa
• NATIONAL ENVIRONMENT: Reduction in SO2, emissions: 70 000 tons pa

Reduced environmental emissions from coalfired power stations providing less power.

Other Areas of Activity

ETA AWARDS:

• The Eta awards, sponsored by Eskom and SABS, are awards to the year's most outstanding energy efficiency initiatives. The Energy monitoring and accounting system used on AngloGold won this award in 1997 by the developers - IST Otokon.
• This year AngloGold is one of the finalists for this year's award. Their entry involves the implementation of a comprehensive real time monitoring and control scheme to respond to real time pricing signals received daily from Eskom. The investment was 0.33 million Rand and the payback an impressive 7.2 million rand per annum.

MONITORING AND TARGETING:

• AngloGold monitors and benchmarks the energy performance of each operation. Elandsrand has formed an energy management team lead by the "utility" engineer.

RETHINKING REFRIGERATION PRACTICES:

• The current utilities' engineer at Elandsrand initiated the pre-cooling of underground hot water dams directly. This gives a better cooling thermal efficiency than conventional cooling from the hot to the cold dam.
• Another initiative included decreasing condenser water solids by changing the existing configuration of the existing plant, improving heat transfer and therefore achieving higher efficiencies and savings.

Recommendations

• PAYBACK OPPORTUNITY
  By addressing the issues identified, the exercise indicated that savings of R 2 million per year, at a capital payback of less than a year, are achievable.
• COMPRESSED AIR GENERATION
  The Elandsrand team has implemented several excellent energy efficient initiatives. They are currently improving surface compressor control. Moore Controllers will optimise compressor sequencing thus ensuring the most efficient combination of operating the five surface compressors.
• COMPRESSOR INTER-STAGE COOLING
  Ensuring that inter-stage and after-cooling for the compressors run as close to design conditions as practicably can make further savings possible. A saving of about R100 000 a month could be derived from the decreases in the input work to the compressor due to correct isothermal operation. By ensuring that compressed air is cooled before leaving the compressors would contribute to minimising the heat input to the mine. This would have further spin off in improving environmental conditions underground. In some cases savings in capital equipment could be achieved.
• COMPRESSED AIR DISTRIBUTION
  For compressed air distribution, it was recommended that a rigorous leak detection and repair program should be implemented and that the responsible staff should have more authority to enforce repair when this is feasible. This finding has confirmed previous work by AngloGold in this area. Some of the air system may be rationalised by removing or isolating dead legs and minimising pressure drops, as well as isolating certain legs during non-productive hours to prevent leakage. A saving of about R 32000 per month can be achieved by implementing an effective campaign against leaks.
• LIGHTING
  AngloGold is investigating the potential for upgrading lighting, and have produced a set of performance criteria for lighting replacements. Upgrading T12 fluorescent lighting systems to T8 (including electronic ballasts) and replacing incandescent lights with compact fluorescent lighting (CFLs) should be considered at Elandsrand. Group replacement of lights based on 70% of the lamp's rated life should also be considered.
• ENERGY MANAGEMENT TEAM
  The commitment of the engineering staff to the efficient use of energy on the mine was evident. The possible savings in any plant are directly proportional to the commitment of those who apply these principles. Elandsrand mine is to be commended in this regard.
• CHARGING USERS FOR CONSUMPTION
  AngloGold believes end-users should be held accountable for energy efficiency. This should assist in curtailing wastage.
• REWARDING INITIATIVES AND PROVIDING INCENTIVES FOR STAFF
  Energy efficiency often requires extra effort from engineers , as it is not yet a high priority issue in South Africa. Rewarding initiatives will go some way in motivating staff to encourage efficiency.