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Electricity from 80°C hot water

Converting hot water above 80°C into electricity is now a commercial reality following the recent developments in smaller scale low temperature Organic Rankine Cycle (ORC) technology. The reduction in ORC unit and integration costs of plug and play containerised solutions from 10kWe to 100 kWe now makes additional carbon free electrical generation from Biogas, Biomass and Industrial Process Cooling a good return on investment.

For Biogas applications such as an Anaerobic Digestion plant surplus heat in the jacket water cooling the gas engine typically at 90°C can be passed through the ORC to generate electricity and reduce the electricity consumed by the radiator cooler fans.
For existing Biomass Boilers with outputs of 80°C hot water providing from 200kW to 1MW thermal power the ORC technology can be retrofitted to generate carbon free electricity converting the boiler to a combined heat and power CHP system attracting renewable generation tariffs.

Industrial processes requiring a cooling system to either cool the product or equipment reject large quantities of hot water to a cooling tower. Recovering this hot water through an ORC before it goes to a cooling tower has the double benefit of generating low carbon electricity and reducing the electrical consumption of the cooling tower fans.

In an industrial cooling process usually the cooling water is kept at a low temperature (30 to 40 Degrees Celsius), however an expert system review by a Heat Recovery Engineer can identify how splitting the cooling process into two circuits of a high temperature and a low temperature can generate and reduce cooling fan electricity. The first circuit with a higher temperature loop above 80°C is used with the ORC to generate electricity, whilst the second low temperature cooling loop below 40 Degrees Celsius cooling continues to operate at a reduced electrical load, with standby capacity when the ORC is not in operation. The diagram below illustrates how a cooling process is split.

Improved industrial cooling process with ORC technology

The role of the expert Heat Recovery Engineer once the best available ORC technology for the heat source has been matched whether it be for a Biogas, Biomass or Industrial Cooling application is to provide a full investment grade document for the cost/benefit of a turnkey Waste Heat Recovery (WHR) system. The Heat Recovery Engineers objective is to propose a WHR system that meets a simple payback investment return between 2 to 4 years, reduces carbon and mitigates against future rising energy prices.

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