Gases and welding products supplier Afrox has commissioned its liquefied petroleum gas (LPG) supply system for the $565-million Bokpoort concentrated solar power (CSP) project, in the Northern Cape.

Afrox was awarded the contract to supply high-purity nitrogen and LPG last year.

LPG will be used in the project during the start-up phase for melting salts for the thermal-energy storage system. The transfer medium is heated from a solid to a molten state.

The Bokpoort CSP project will have a 50 MWe generating capacity, with nine hours of thermal storage, following its commissioning at the end of this year.

Afrox bulk gases business manager Carte Lubbe tells Engineering News that the substantial amount of LPG is required only for the heating phase of the project.

Afrox has designed an innovative LPG modular supply system for this project that comprises skid-mounted tanks and containerised control and vapourisation. The system can be dismantled and removed from site to ensure minimal project disruption.

“After the heating period, the entire LPG supply plant will be removed from site. Fixed installations had been used for similar projects in the past, but they became redundant after the start-up phase and took up unnecessary space, while costing a fortune to maintain. Upon service completion, our unique modular plant can be removed by a fleet of dedicated and specialised vehicles in less than a week,” explains Lubbe.

Following the heating of the molten salts, a blanketing system is required to reduce the risks associated with flammable products and the carbon emissions into atmosphere, and to avoid the deterioration of process fluids.

The plant will, therefore, include a nitrogen storage and supply network that will provide an inert atmosphere for the salt storage tanks, the expansion tanks and the high-temperature fluid boiler.

The nitrogen supply system comprises liquid nitrogen storage and an on-site generating plant with pressure swing adsorption (PSA).

“However, the PSA plant will only be on site in 2016, when primary nitrogen will be generated on site, with liquid nitrogen becoming the critical backup,” he adds.

The on-site nitrogen generating facility is supplied by Afrox’s parent company, the Linde Group Engineering division, while Afrox will supply the cryogenic storage facility and custom-designed nitrogen reticulation system.

A long-term nitrogen supply agreement between Afrox and Bokpoort CSP has been concluded to ensure an uninterrupted and reliable nitrogen supply to the project.

Lubbe notes that, owing to the location of Bokpoort CSP, Afrox can deliver the backup liquid nitrogen by road from several of its regional operations across South Africa, providing even more security of supply.

In addition to using LPG and nitrogen supplied by Afrox, the Bokpoort CSP also used the company’s extended product range of welding gases, hard goods and consumables during construction.

“Afrox has provided a comprehensive and holistic solution for Bokpoort CSP, which will lead to a long-term and mutually beneficial partnership,” Lubbe concludes.