Swedish clean technology company Ripasso Energy will be presenting its PWR BLOK 400-F solution to the international ferroalloys industry at the fifteenth International Ferro-Alloys Congress (Infacon XV), which takes place at the Century City Conference Centre, in Cape Town, from February 25 to 28.
The PWR BLOK 400-F, launched in September last year, is a container-based solution in which Rispasso’s Stirling Engines are used to harness energy from the combustion of residual and and flare gas, allowing for significant electricity and cost savings.
Ripasso’s South African representative and ferroalloys industry expert, Roelof Retief, explains that the potential for this technology in the ferroalloys industry is immense. “This product could potentially be the holy grail for harnessing furnace gas for electricity generation, specifically in ferroalloys, which flares about 15% of its input energy.”
He adds that Ripasso is currently prioritising the South African ferrochrome sector. “In the local ferrochrome sector alone, the potential for cogeneration from closed furnaces is close to 250 MW. Electricity being one of the single biggest contributors to the cost of production, this technology has the potential to save ferrochrome producers millions of rands.”
Further, Retief notes that the PWR BLOK 400-F is suited to any residual or flared gas. “All industries that flare gases could be potential markets for this technology. In South Africa, about 3 000 MW gas is flared. This is equivalent to around 10% of South Africa’s generating capacity.”
He adds that, while Ripasso will definitely expand into these markets in future, “for now, we will concentrate on the ferroalloys industry.”
The PWR BLOK
Retief’s industry experience has assisted in enhancing and optimising the PWR BLOK 400-F solution for ferroalloy applications. He notes that some of his suggestions included using flared gas as a fuel source for the Stirling engine, as well as changing the configuration from a solar hybrid unit to a containerised configuration, improving unit manoeuvrability and reducing its footprint as well as the associated capital costs.
The basis of the solution is Ripasso’s Stirling engine. Since the Stirling engine is a closed cycle, it contains a fixed mass of gas, called the ‘working gas’ – most commonly, hydrogen. The engine is sealed and no gas enters or leaves the engine. Additionally, no valves are required, unlike other types of piston engines. As no contaminant enters the working part of the Stirling engine, the operating and maintenance cost is about R120/MWh. The service interval of the Stirling engine is every 6 000 hours, which contributes to high availability and low maintenance costs.
Retief explains that the Stirling engine cycle comprises four main processes: cooling, compression, heating and expansion. This is accomplished by moving the gas back and forth between hot and cold heat exchangers.
“The hot heat exchanger is in thermal contact with an external heat source, such as a fuel burner – in this case the combusting of furnace gas. The cold heat exchanger is in thermal contact with an external heat sink, such as air fins or water cooling,” he explains.
A change in gas temperature causes a corresponding change in gas pressure, while the motion of the piston causes the gas to be alternately expanded and compressed. The piston motion (mechanical energy) is converted into electrical energy by turning an electrical generator.
The PWR BLOK 400-F is equipped with 14 Stirling engines. Each of these engines is equipped with its own combustion chamber and energy recuperating system. The capacity of each engine on furnace gas is between 28 kW and 30 kW, producing about 400 kW from each PWR BLOK.
The gas from the furnace is introduced to the PWR BLOK through a gas manifold from the plant. The gas is then equally distributed to each of the 14 Stirling engines, where it is combusted to heat up the hot heat exchanger of each engine.
Retief notes that Ripasso’s management team met several of the major players in the ferrochrome industry last year. These meetings generated a “very positive response”, and culminated in the company’s first PWR BLOK 400-F sale, as well as multiple queries.
In December last year, Ripasso signed an agreement with South African ferrochrome producer Afarak Mogale for the sale of seven PWR BLOK 400-Fs. Afrarak Mogale’s order is valued at about R53-million and is expected to be delivered by the end of 2018.
Ripasso CEO Gunnar Larsson, commenting on the sale in a statement released in December, noted that the sale marked a major success for Ripasso Energy and demonstrated that the company had made the correct decision to invest resources in the development of the PWR BLOK, also providing “very concrete evidence that Stirling technology can play a very significant role in the future generation of climate-friendly energy”.
At the PWR BLOK’s current price, the payback period is estimated at about three-and-a-half years. Retief states that the technology’s service life is a minimum of about 25 years, which enables clients to reduce the volume of electricity bought from the grid by up to 15%, and produce electricity at a levelised cost of energy of $21.7/MWh
Reitief says that, should anybody require more information on this “ground-breaking” technology, Ripasso Energy representatives ca be contacted at Infacon XV.