ORC cycles, heat recovery and energy innovation
The ORC devices ENERBASQUE has developed are thermal machines based on the Rankine cycle. Their purpose is to convert waste and surplus heat from diverse processes into mechanical and/or electrical energy. The cycle is called Organic because it uses an organic fluid (of high molecular mass) in which the liquid/vapour phase change occurs at a lower temperature than in water.
The HRU technology operates with heat sources exceeding 80ºC, producing powers ranging from a few kW to a few hundred, depending on the machine model.
The diagram below shows the operating principle:
The pump draws the refrigerant fluid from the condenser in the liquid state at low pressure.
The fluid leaves the pump in the liquid state and at high pressure.
The fluid leaves the evaporator at high pressure, after having been heated and changed to the vapour phase thanks to the energy provided by the heat source. This means the residual energy from the process has been transferred to the refrigerant fluid, which then enters the screw expander.
Expanding the fluid at high pressure and temperature generates mechanical work on the shaft, which is coupled to the electrical generator. The refrigerant fluid pressure and temperature drop during expansion, but it remains in the vapour state, so it needs to be channelled to the condenser to transform it into a liquid and start the process again.
Machine efficiency is related to the Carnot cycle. This means the greater the difference between the hot source and cold source temperatures, the higher the machine efficiency. When the hot source temperature is set by the process, you commonly get higher efficiency in winter than in summer. This is because the cooling water or air will be at a lower temperature in winter.
