Organic Rankine cycle |
Exergy develops small- scale Smart ORC for low temperature heat recovery
A recent R&D programme undertaken by organic Rankine cycle specialist Exergy has focused on development of high-efficiency mini and micro ORC modules for exploiting low temperature waste heat. Among the key features is use of a compact high speed version of Exergy’s radial outflow turbine, with SFDs (squeeze film dampers) deployed to reduce vibration
Silvio Meletti project engineer, Exergy International srl, Italy
The challenging European objectives of decarbonising the energy sector and the growing urgency to achieve greater energy independence is driving research and development in two directions: reducing the environmental impact of fossil fuel based technologies; and replacing these technologies with carbon free power generation systems.
In the most energy-intensive industrial sectors, such as petrochemicals, but also cement, glass and steel, the use of alternative technologies, such as the recovery of waste heat otherwise exhausted to the atmosphere, can produce both economic savings and a reduction in carbon footprint. This is why, especially in highly industrialised countries, there’s growing interest in exploiting not only the noblest heat sources, thermodynamically speaking, ie, those characterised by high energy content and high temperature, but also those flows with lower temperature and lower enthalpy content, which inherently would have a lower conversion efficiency. These latter flows need technologies that can be economically sustainable with a low upfront investment.
One possible approach is the use of ORC (organic Rankine cycle) systems, which, although based on the traditional Rankine cycle, use a fluid or mixtures of organic fluids of various kinds within the cycle. Thanks to this
peculiarity, the choice of fluid used allows the exploitation of thermal resources with a range of thermodynamic characteristics.
Exergy’s ‘Smart ORC’ R&D project To meet the technical and economic requirements for ORC systems suitable for the recovery of thermal waste at low temperatures, Exergy, in collaboration with Regione Lombardia and the EU, successfully participated in the “Tech Fast Lombardia” call for proposals of the POR FESR (Programma Operativo Regionale del Fondo Europeo per lo Sviluppo Regionale 2014-2020) co-financed by the FESR.
Exergy’s project was called “Smart ORC” and involved the development of a family of “mini” (less than 1000 kW) and “micro” (less than 100 kW) modular ORC systems with very high efficiency, building on the company’s proprietary technologies.
Thanks to the involvement of the Politecnico di Milano and local manufacturing companies in the detailed design and construction of the most critical plant components, an ecosystem for the development of further high-efficiency ORC systems and turbomachinery, both turbines and compressors, has been created. The production of electricity employing ORC technology can be regarded as a form of distributed generation, and with the ability to input waste heat to the cycle as well as to meet the production site’s own consumption, ORC systems have the flexibility of being able to feed into the grid, self-consume or store the energy produced (in electrical or thermal storage systems).
In current small ORC systems, volumetric turbines, eg, screw or vane, or small centripetal radial turbines are used. Both these turbine types are characterised by lower isentropic efficiencies than those recorded for larger ORC based power plants equipped with radial outflow turbines.
If volumetric machines typically have lower
Left: Figure 2. SFD (squeeze film damper) technology designed by Exergy for the SMART ORC project
28 | July/August 2023|
www.modernpowersystems.com
peak efficiencies than turbomachinery, settling at values of around 60-75% (isentropic total to static), centripetal radial turbines are penalised by the difficulty of having to dispose of the entire enthalpy jump in a single stage and, consequently, suffer from limited efficiency. The adoption of the Exergy radial outflow turbine (ROT), Figure 1, a technology covered by several patents, has many advantages: concurrent combination of fluid expansion and increased cross-sectional area;
mechanical components designed to be easily removable, without the need to empty the system, reducing maintenance times; extended bearing life due to very low vibration; reduced rotor leakage and friction; and greater freedom of choice of both pressure levels and stage pressure gradient, limiting vortex formation and reducing fluid dynamic losses.
Overall, it is a more efficient and reliable turbine technology, with low vibration levels and less noise.
The range of sizes of standard ORC modules investigated and developed in the course of the Exergy Smart ORC project has been selected to suit a wide spectrum of possible heat sources available in the industrial world: 80 kWe;
Figure 1. Exergy radial outflow turbine
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93
