REHOS Product Designs

trading the IP gained by the former R&D company Heat Recovery Micro Systems

Water pool power generation (REHOS Pond)

Looking closely at the RAW-Pump described before, you would notice that all the power developed by the turbine is utilized for driving the water pump. The water pump therefore carry a lot of hydraulic power, that would typically be needed for an agricultural irrigation water pump or a long distance water supply pump station. In other applications, however, some hydraulic power may need to be sacrificed to also generate some power in combination with the water pump, like in the sketch below. The percentage share of the load between hydraulic power or electrical power would, of course, only depend on the application for which it was designed for. The actual REHOS cycle providing power to a shaft stays exactly the same.  

A design used for a mine chiller underground for example, may want just enough hydraulic power to pump the cooler circulation water through the pipes and thermal radiators, but it would require a large amount of heat to be extracted from the water being pumped. In such a case a large percentage electricity may be generated, helping to remove energy from the water (chilling the water further) and providing this energy in the form of electricity for local underground lighting and ventilation fans.

 

Uses like long distance water pumping in a pump-station may need a large percentage of the power developed as hydraulic power, and a small amount of electricity to power the measurement and control equipment and maybe some lighting in the pump-station only. Such a pump-station would then be totally autarkic, with only water inlet and outlet, and no power cables, switchgear and expensive external electrical power to drive the pump-station.

In the RAW-Pump design, simplicity, with the minimum number of components as well as the minimum instrumentation provide an extremely low-cost solution to pumping applications, especially the smaller sizes, but it may be far from optimal. It would be perfect for smaller pumps of a few kW (eg. 1 - 50 kW) to for example 150 - 200 kW, but large machines, dedicated to power generation used in the utility electricity sizing of a few MW power generation would likely be designed more like the sketch below, with separated, dedicated high pressure ORC pump as well as a separate low pressure heat transformer circulation pump. Keeping these pumps separate also makes for easier control of the processes. The principles stay the same however......

Publication [22] on the download page, deal specifically with the economics of a REHOS cycle like this one sketched here, used for large utility-scale coal fired, wet cooled power stations for waste heat recovery from the cooling water. This cooling water exit the rankine cycle steam condensers at temperatures of anywhere between 35°C - 50°C and carry away more thermal energy than the actual power produced by the power station! A REHOS cycle power generator could easily produce electricity from this waste heat at an efficiency exceeding 50%, and sizing the cooling water heat recovery REHOS generators to a few MW would allow the phased (according to the annual budget) decarbonization of the power station. The phased approach represent a feasible de-carbonization process without leaving the utility with stranded assets, and guarantee the re-use of electrical infrastructure, human resources and gradual lowering of the real levelized cost of electricity (LCOE) for the power station and the utility. This option would prove extremely useful specifically for consultants and utility-scale project developers, as the global pressure for de-carbonization to mitigate global warming for utilities worldwide is escalating every day!

Obviously this type of modular add-on CW-heat-recovery-REHOS-generators may be added on to any existing large utility scale rankine cycle power block, eg. CSP, Nuclear, Coal-, oil- or gas fired power generation etc. 

A further example demonstrate the use of a 12kWe REHOS Generator coupled electrically into a micro-grid serving a home cluster of 8 - 10 residential buildings. The home cluster also have a recreational swimming pool of 60 000 liters covering a surface area of 60 m2 (6m x 10m pool). Lets assume the ambient temperature in daytime is 25°C , but the pool water temperature is slightly lower at 20°C.

Solar incidense in the area is low (for South Africa) DNI = 2000 kWh/m2.annum, implying the pool receive ~ 5.5 kWh/m2.day, totalling on average for the total pool solar receiver area 328.8 kWh/day absorbed into the water during the ~ 6 hour sunshine, each day.

The REHOS Generator circulate water through its heat exchangers continuously and deliver 12 kWe continuously to the microgrid, day and night. Energy converted to electricity is therefore 12 kW x 24 = 288 kWh per day. During the sunshine daytime, the solar heat supplement the pool heat, but during the dark 18 hours, the bulk pool thermal reservoir loose energy and cool down. The 216 kWh extracted by the REHOS Generator during the 18 dark hours and converted to electricity therefore cool the pool temperature by a calculated 3.1°C, easily made up again the next day when the sun is shining again. The swimming pool is therefore a huge thermal storage reservoir.

A very big advantage of this type of REHOS Pond thermal storage system, is that you have very little loss, as the heat reservoir temperature is below ambient, and environmental heat flow into the pool, not out!

The REHOS cycle have a large heat to power conversion efficiency, but that only influence the size of the heat exchanger (H/E) and the circulation water volume flow through it, but not the power delivered by the generator. Remember, any heat wasted by the REHOS due to inefficiency and losses, simply flow back as thermal energy  into the pool!