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ORGANIC RANKINE CYCLE FOR 
HEAT RECOVERY - INDUSTRIAL PROCESS


The industrial sector accounts for 1/3 of the total energy being consumed in society. Due to inefficiency around 20 to 50% of this energy eventually becomes exhaust heat that could have been usefully reused for "clean" power generation employing waste heat recovery systems.

The demand for waste heat recovery is continuously growing under the rising commitment of the industry to reduce energy consumption, operational costs and carbon emissions.

Organic Rankine Cycle (ORC) is a technology ideally suited for industrial process heat recovery. As opposed to steam heat recovery systems, ORC can give better efficiency for lower temperature applications, as well as eliminating the requirement for water treatment and make up. EXERGY use the innovative and pioneering Radial Outflow Turbine (ROT) technology in the development of heat recovery plants.

ADVANTAGES
  • No water treatment plant or make up water
  • Automated operation
  • Competitive capital costs, leading to fast payback
  • High efficiency at a variety of operating temperatures and loads
  • Fast start up and shut down
  • Flexible placement, away from the heat source if required
  • Reduces plant energy consumption, and carbon footprint
APPLICATIONS
  • Cement plants
  • Steel mills
  • Glass factories
  • Other industrial applications
VIDEO CASE STUDY ON HEAT RECOVERY FROM A STEEL MILL
 
 
WASTE HEAT RECOVERY CYCLE


A heat recovery system extracts the thermal power from the exhaust of the industrial plant to feed the ORC module via the intermediate fluid. The intermediate fluid, which is usually oil, pressurized water, or steam, transfers heat to the organic fluid in the ORC evaporator, where the organic fluid vaporizes. The vaporized fluid then passes to the turbine. Here the vapour expands causing the turbine to spin and creating electricity into the generator. The vaporized organic fluid then continues through the cycle to the condenser where it is once again becomes a liquid. It then passes through the pump before beginning the cycle again. 

The chart below reflects the most likely use of the ORC in comparison to traditional Rankine Cycle applications. Regardless of the heat source temperature, the ORC is generally the best solution for small power output. The simplicity and compactness of the system, the higher efficiency of the turbine, the optimal match with the heat release curve and the better operation at partial loads, ensure a higher system efficiency and a lower specific cost compared to conventional Rankine cycles. In certain case they become the only pratical solution. 
Conversely, at considerably high temperatures and large power output, traditional Rankine cycles using steam turbines prove to be the most suitable solution all round: in these conditions, the limited increase in perfomance for heat sources available over 350-400°C for a ORC implies lower conversion efficiency. 

Of course if water is not available, then the steam solution cannot be considered.

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