The regenerative heat of solution (REHOS) thermodynamic cycle is the culmination of ten years of intensive research and development by Johannesburg-based Heat Recovery Micro Systems, and Enslin enthuses that the benefits of the technology will become a common form of power generation globally within the next few years.
“Finding a solution that meets global demand for affordable, sustainable, baseload power generation with zero emissions has long been the ultimate goal for researchers globally,” says Enslin.
He adds that, with low-cost, emission-free, modular renewable power gaining popularity globally, there is huge demand for technology that can facilitate a rapid, but economically viable, transition from coal power generation to renewable-energy sources. “Heat Recovery Micro Systems has risen to the occasion by developing the REHOS thermodynamic cycle.”
Enslin explains that heat recovery of lower-temperature heat sources, typically below 200 ºC, such as geothermal and solar thermal sources, has led to the introduction of organic refrigerants as operating media in thermodynamic cycles. Up until now, however, waste heat at temperatures lower than 80 ºC has not been considered economically viable to convert to power on a large scale.
The REHOS cycle is a closed-loop binary cycle derived from absorption refrigeration principles. It uses existing, proven process components in a novel interconnected configuration to form a new thermodynamic cycle that is engineered to absorb ambient heat from the environment at below 70 ºC and convert it into power with high-energy conversion efficiency.
Enslin explains that, in essence, the REHOS cycle is a modified absorption refrigeration cycle, with the refrigeration effect replaced by a power turbine and external heat input achieved through using a heat pump.
The binary cycle comprises a pressure pump, heat exchangers, a vapour compressor and an organic turbo generator, all of which have been used for more than 20 years in the absorption refrigeration, geothermal and waste heat recovery power generation fields.
“The REHOS cycle is, thus, based on proven process components. The only novel aspect is the interconnected configuration of these components, which forms a new regenerative, thermodynamic cycle with many highly desirable disruptive attributes.”
Enslin stresses that the scalability of the REHOS cycle and the combination of refrigeration and power generation without the need for external cooling towers are some of the most significant features of this technology. The high heat-to-power conversion efficiency, as well as the flexibility of using different expander and compression equipment and heat exchangers in the REHOS cycle, also enhances its appeal.
This is a renewable power generation technology that uses freely available, globally abundant waste heat at temperatures well below 30 ºC, he says, adding that “the heat-to-electricity conversion efficiency is more than 80%, compared with current waste heat recovery systems for low temperatures, which struggle to maintain conversion efficiencies greater than 5%”.
In addition, Enslin highlights that the technology requires low capital investment and can deliver utility-scale power at less than half the cost of other renewable power generators such as wind and solar. The REHOS cycle is, moreover, a baseload generator, producing dispatchable power with a capacity factor of more than 80%, which compares favourably with other nonfossil baseload generators such as nuclear and hydropower generators.
The REHOS cycle may also be used for heat recovery from existing cooling water systems, effectively doubling existing power stations’ power output – or halving the primary fossil fuel energy consumption – to facilitate the gradual move from fossil combustion to renewables. Smaller REHOS generators can also be hermetically sealed for decentralised power packs for buildings, shopping centres, schools, hospitals and clusters of rural homes.
Enslin highlights that POWER-GEN & DistribuTECH Africa provides an ideal platform for networking with technology suppliers, consultants and end-users to ensure the best possible exposure of this new technology and facilitate its implementation.
“Despite its significant benefits, we expect some scepticism from the market, owing to the novelty of the concept and in lieu of a physically operational power-generation plant. However, we also expect a keen interest from consultants and power generation process suppliers, who will recognise the significant commercial value of the REHOS cycle. We believe that there will be a definite willingness from renewable power generation suppliers to participate in the project’s commercialisation.”
Enslin will present a paper, titled ‘Introducing the novel thermodynamic cycle for the economic power generation from recovered heat pumped from the huge global thermal energy storage reservoir called earth’, during the geothermal session of the Renewable Technologies and Opportunities track of the POWER-GEN & DistribuTECH Africa conference on July 18 at the Sandton Convention Centre in Johannesburg.