Large energy consumers are looking to find alternative, sustainable power generation methods. Renewable energies may be the solution, but finding local cost competitive technologies is the challenge. Or is it?It is no secret that Eskom is energy constrained, so much so that its integrated demand management (IDM) programme continues to provide financial incentive for mining houses looking to invest in energy alternative solutions. Eskom recently approved proposals to construct three concentrated solar power (CSP) heated plants (of 600, 1 200, and 2 400 kW thermal) at Gold Fields and AngloGold Ashanti mines through its IDM budget. Once operational, these systems will likely be the only CSP heated plants of their kind in the world. All three of the gold mine plants are for elution heating systems, with two mines using steam and one using thermal oil in the CSP collector to provide heat. The CSP plants have been designed by BBEnergy, an independent business unit within the BBE Group, specialising in power and energy management in mine ventilation, refrigeration, compressed air and renewable energy systems. BBEnergy is also a registered ESCo (Energy Services Company) with Eskom. Last year, BBEnergy became the first South African company to design, develop and implement its own CSP heated plant, and manager Chris Nell describes the latest data as “positive and exciting”. Based on the performance of its prototypes at the company’s Bryanston premises, Eskom awarded the company a contract to construct the 150 kW pilot linear Fresnel CSP heated plant at Eskom’s research and innovation centre in Rosherville, Johannesburg. The plant was completed towards the end of 2012 and is now in the final stages of testing.
To date, the test data generated from the pilot plant indicates that the system is performing above its design objectives. It is the biggest plant of its kind in South Africa. Investigations at the pilot plant include practical operational issues, such as stowing during storms, maintenance effects, start-up and shut-down, remote monitoring and control. The thermodynamic test programme included a closed system test, which demonstrated that in less than one hour the system exceeded 40 bar and 250°C when relief valves blow off. A daily cycle variable temperature test with a range of flow rates from 1 to 4 kg/s achieved a maximum of 162.3 kW, while fixed temperature duty tests indicated an 11.2% variation in heat duty, as the operating temperature varied from 230 to 250°C.“This third-generation plant has exceeded our design expectations and, based on all the development to date, we’ve recognised its immense potential for power station augmentation,” says Nell. “This is a local design, built by a local company, with more than 95% local content,” BBE CEO Steven Bluhm adds. “It’s poised to bring meaningful energy savings to the national grid and has potential for significant job creation. “The Linear Fresnel process has been used extensively around the world to generate electricity, but this is the first time that it is being harnessed in South Africa to assist BBEnergy clients in the mining industry to save on energy costs in a predictable and meaningful way. CSP systems are able to produce energy more cost-effectively than existing electrical and fossil-fuelled boilers, thereby easing the burden on the already over-loaded national grid, particularly during the high-demand daytime periods.” The design strikes a balance between cost, reliability and efficiency, resulting in a commercially viable, modular, solar steam generator that provides industrial companies with a strategic source of energy. The system generates heat using mirrors and tracking systems to focus a large area of sunlight into a fluid-carrying, thermal, receiver-tube. Concentrated energy from the sun heats the fluid flowing through the tube and the resulting thermal energy can then be used for various industrial processes such as absorption refrigeration. CSP technology is also inherently environment-friendly and has the potential to attract funding from carbon reduction mechanisms.