African Fusion June 2015

Cover story: Afrox

Gas and welding solutions for the CSP industry

In response to the specific requirements and needs of establishing and operating concentrated solar power (CSP) plants, Afrox has developed a comprehensive product and energy solutions offering to specifically suit the industry. AfricanFusion talks toJohanPieterse, Afrox’s businessmanager for the manufacturing industries.

O na1100ha sitenear Pofadder in the Northern Cape, The 100MW KaXu Solar One concentrated solar power (CSP) plant has now been commissioned. It is the first CSP plant in South Africa to use parabolic trough technology. Following close on its heels are Khi Solar One, a 50 MW power tower CSP plant outside Uppington, and the 50 MW Bokpoort solar parabolic trough CSP plant, which is nearing completion. In addition, the 100MWEskomplant in Uppington has been approved for construction and three CSP plants were announced as preferred bidders by the Department of Energy in the third round of the government’s Renewable Energy Independent Power Producer Procure- ment Programme (REIPPPP): Kathu So- lar Park, Redstone Solar Thermal Power, and Xina Solar One, all of whichwill have 100 MW capacities and significant night time storage capability – Redstone is promising a full 12-hours of energy stor- age, a first in Africa. TheNorthern Cape is clearly becom- ing South Africa’s solar energy hub. Afrox has developed customised solutions in response to the specific and unique requirements of theCSP industry and, in particular, the challenges associ- ated with having operations in remote areas of the Northern Cape. “A simple visit to a CSP site takes a week, particu- larly if equipment has to be delivered,” Pieterse points out. Welding and cutting solutions At the starting point of Afrox’s CSP offer- ing are its welding and cutting products for the construction phase of projects and, later, for scheduled maintenance during shutdowns. “Our fabrication spe- cialists work closely with construction

contractors to ensure a full understand- ing of the on site needs. Once these have been established, welding consumables and gases, aswell aswelding equipment is sourced from the nearest Afrox sales outlet,” Pieterse tells African Fusion . “Parabolic trough plants such as Bokpoort require 20 000 km of pressure piping to bewelded, alongwith the sup- port structures for a solar field consist- ing of 588 600 m² of mirrors. The site is 3.0×1.5 km in area and consists or rows of piping running above the parabolic troughs, whicharepolished steelmirrors that track the suns moment across the sky to focus sunlight onto the pipes,” he explains. Inside thepipes anoil-based transfer fluid is steadily heated as it is pumped through the field towards the generation plant at its centre. “The fluid reaches temperatures of about 400 °C, which is just belowthe critical creep temperature for piping, so you don’t need to use chrome-moly materials for the piping. This is a pressurised circuit, though, so high quality welding is essential for reli- able operation,” he continues. Onsite pipe welding is done using the TIG process for root runs followed by fill and capping passes using low hydrogen MMA electrodes. “We were awarded the contract for the supply of TIG welding wires and the Argon gas for the Bokpoort CSP contract, along with the LH welding consumables,” he adds. Molten salt storage solutions A key feature of the Bokpoort CSP plant is themolten salt storage system, which will endeavour to provide more than nine hours of electrical generation ca- pacity (1 300 000 kWh thermal ) after sunset or during cloudy weather. The molten salt is contained in two

huge storage vessels. These have also been constructed onsitewith Afrox-sup- plied consumables, using a combination of MIG/MAG, flux-cored arc welding and submerged arc welding processes. Pieterse explains: “During the day, the transfer fluid heated by the para- bolic troughs is passed through heat exchangers, which heat the molten salt being stored in the tanks. At night, the hot salt is thenpumped throughanother heat exchanger where it is used to create steam for the turbine after hours.” Because of the high temperatures and corrosive nature of the molten salt, stainless steel piping is used for these circuits, which is welded using Afrox’s TIG range of wires and its Argon gas for the root passes and cappedusing Afrox’s stainless steel range of electrodes. A large part of Afrox’s contribution to the Bokpoort CSP plant arose because of its industrial gas expertise. “The salt only melts at 200 °C, and it needs to be melted before it can be used as a heat- exchange fluid. We have developed an LPG storage and supply system to melt the salt on start up of the plant and fol- lowing shut-downs,” Pieterse reveals. Afrox’s modular and portable skid- based container system consists of a series of containerised bulk LPG storage tanks along with all of the evaporators necessary to supply the fuel for the initial salt melt. The whole system is transported to site and offloaded in a designated area. Once the salt ismolten, the system is no longer needed on site, so to save space and investment costs it can be transported to and deployed at another site or returned toour stores un- til requiredagain,” he tells AfricanFusion . In addition, themolten salt requires and inert atmosphere in order to ‘blan- ket’ the thermal storagemedium, that is,

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June 2015

AFRICAN FUSION