Energy and Greenhouse Emissions
The consumption of energy, which is central to all operations, has operating cost and environmental implications for the business. Impacts of energy consumption, such as release of greenhouse gas emissions and other air pollutants, can in part be minimised through improved energy use efficiency. “Real” efficiency improvements are, however, commonly affected over time by variations in ore grade, increased haulage and process control fluctuations.
Total energy consumption and greenhouse gas emissions for OZ Minerals during 2008 are listed by operation in the table below in terms of:
- Direct energy consumption and greenhouse gas emissions – resulting from the on-site consumption of fuels and explosives or where electricity is generated; and
- Indirect energy consumption and greenhouse gas emissions – due to the import of electricity from external parties; commonly the electricity grid.
Total direct and indirect energy consumption and greenhouse gas emissions in 2008
OZ Minerals energy use during 2008 was 12.86 petajoules. Century is dominant in the group energy inventory, accounting for 7.15 petajoules (56 per cent) of energy use over the year. On a reporting period basis, total energy use was 16.50 petajoules. Purchased electricity and diesel are the dominant energy sources, contributing 43 per cent and 48 per cent, respectively, of the on-site energy use in 2008. Approximately ten per cent of electricity purchased by OZ Minerals during the year was from renewable energy sources, principally hydro-electric power.
The group’s total greenhouse gas emissions for 2008 were equivalent to 1.09 million tonnes of carbon dioxide. Approximately 780,000 tonnes of CO2-e was emitted due to our Australian-based activities, representing 72 per cent of the group inventory. Thirty-nine per cent of group emissions (424,000 tonnes of CO2-e) were produced on site largely from the use of fuel in heavy mobile equipment and vehicles (Figure 1). Forty-four per cent of emissions (480,000 tonnes of CO2-e) were associated with the purchase of electricity to run ore processing plants, ancillary equipment and other infrastructure (including offices and accommodation villages) at our mines. The remaining emission sources stem from items including processing reagents and explosives. Emissions on a reporting period basis were equivalent to 1.34 million tonnes of carbon dioxide.
OZ Minerals seeks to improve energy efficiency where clear value to the business can be demonstrated. During 2008 we met our ongoing commitments under the Energy Efficiency Opportunities and Greenhouse Challenge Plus programs, and we continued our participation in the Carbon Disclosure Project. At the same time, focus was placed on preparations to meet the requirements of the National Greenhouse and Energy Reporting Act 2007. In meeting our obligations under Greenhouse Challenge Plus, we had independent limited assurance of our Century and Rosebery energy and greenhouse data provided by Environmental Resources Management Australia Pty Limited (ERM).
As part of the Energy Efficiency Opportunities program, Century and Golden Grove operations undertook work to assess and implement cost-effective energy efficiency opportunities. An initial assessment of energy use was also conducted at Rosebery. For Century and Golden Grove, 47 opportunities were identified, with ten of these either implemented or under implementation, and a further nine opportunities planned for implementation. The range of opportunities is variable and in some case quite innovative and quick to implement:
- An opportunity was identified in the Golden Grove mill where material was passing through a bank of flotation cells, effectively acting as a transfer channel. This bank has twelve agitators to keep particles in suspension and avoid settling in the cells. This material has been diverted around a bank of flotation cells using poly piping, resulting in the agitators no longer being required to operate. The project is expected to save 4,541GJ of energy per annum (1,261MWh) resulting in a greenhouse gas emission reduction of 1,250 tonnes CO2-e.
- Century mine was recognised at the 2008 Queensland Mining Industry Health and Safety Awards for its innovative Lighting Plant Auto Start System. In order to address risks associated with people entering the mine pit on a daily basis to manually turn on lighting for night time operations, the operation introduced a system whereby automatic on/off switches were installed on all lighting plants. With 45 lighting plants in operation, the reduction in diesel use can be significant. Annual diesel use is estimated to be reduced by 65,000 litres of diesel, resulting in a reduction of 175,000 tonnes of CO2e emitted.
Our work to identify cost-effective energy use savings through the Energy Efficiency Opportunities program will remain a key component of the group’s energy and greenhouse gas management program. Opportunities will be sought to transfer value-adding ideas across the business through our group Energy Steering Committee and via our Sustainability Network forum.