The ORegen™ Waste Heat Recovery Cycle: Reducing the CO2 Footprint by Means of Overall Cycle Efficiency Improvement

Abstract

The growing concern for the role of man-made CO2 emissions with respect to global warming combined with the large increase in energy demand spurred by developing nations and a growing global population that is foreseen over the next 15 years have recently turned attention to potential CO2-neutral energy supply solutions. Waste heat recovery cycles applied to fossil fueled plants offer a local zero-emission solution to producing additional electric energy, thereby increasing the overall plant efficiency with a considerable reduction in the emission of CO2 per unit of energy produced. GE Oil & Gas with GE Global Research Europe has developed a new and attractive solution for recovering waste heat energy from a variety of thermal sources ranging from reciprocating combustion engines to gas turbines. This new recovery cycle is called ORegen™. The ORegen™ recovery cycle is a rankine cycle, with superheating, that recovers waste heat and converts it into electric energy by means of a double closed loop system. The ORegen™ system represents one of the very few viable solutions for recovering heat from sources (such as mechanical drive gas turbines) whose load may vary dramatically over time or where the equipment is located at a site where water is not readily available. For the temperature range of interest, a thorough comparison between many working fluids was performed, leading to the conclusion that the substance that delivers the highest efficiency is Cyclopentane. A high-efficiency Rankine cycle based on such a working fluid places a particularly high demand on the expansion ratio, which influences some of the basic architectural choices of the expander machine. This article introduces the ORegen™ recovery cycle and describes the process used in GE Oil & Gas to design the family of double supersonic stage turboexpanders, covering the power range of 2–17MW. Examples of the application of the ORegen™ cycle to gas turbine are also provided to demonstrate attractive opportunities to increase the overall plant efficiency.

Organic Rankine Cycle Power Systems: From the Concept to Current Technology, Applications, and an Outlook to the Future

“…This is testified either by the starting of R&D work devoted to new applications, see, e.g., Refs. [83,163], or by the acquisition of companies that developed ORC technology [176].…”

“…Few ORC modules are installed as bottoming cycles of mechanical drive gas turbines [83], though the number of installations is increasing [119]. In the case of pipeline compressor stations, 19 units of 5-6 MW e are in operation in North America and Europe, the first one since 1999 [120].…”

Off-Design Performances of an Organic Rankine Cycle for Waste Heat Recovery from Gas Turbines

“…When a working fluid for ORC application is chosen, several criteria need to be considered: environmental sustainability, safety, thermal stability and critical temperature. The employed fluids meet most of the criteria listed, indeed ORC cycles based on such fluids are widely analysed in the literature [17,18]. The three fluids are dry and belong to the hydrocarbons family: the first two are aromatic and the third is a cycloalkane.…”

“…Several papers have focused on combined cycles employing gas turbine as topper cycle and alternative solutions to the traditional steam-water Rankine cycle for the bottoming one. Chacartegui [17] proposed ORC as an alternative bottoming cycle for a combined cycle power plant, while Del Turco [18] proposed the so-called ORegen cycle. Carcasci [19] studied the ORC bottoming cycle at design conditions for different working fluids (benzene, toluene and cyclopentane), showing the best efficiency settings by varying fluid evaporation pressure and oil temperature, with a GE10 gas turbine [20].…”

“…The condenser air mass flow rate cannot exceed a lower and upper limit (generally referred to the design value and depending on fan size, increasing this value raises the fan cost [18]): m con,air /m con,air,des ≤ α air,up ; •…”