Organic Rankine cycle| Turbine technology
Exergy’s HSAT increases efficiency and lowers costs
Exergy has developed a new high-speed axial turbine (HSAT) that can enhance the efficiency and competitiveness of waste heat recovery organic Rankine cycle power plants
Federico Bassi, Gabriele Marchiori Exergy
Figure 1. HSAT rotor section with multiple integrally bladed rotor (MIBR) configuration
The organic Rankine cycle (ORC) is a closed thermodynamic cycle that operates with an organic working fluid, usually refrigerants or hydrocarbons characterised by low evaporation point, able to recover heat from industrial processes (eg, cement, glass, steel production) and transform it into electricty via a turboexpander. These power generation plants, usually referred to as waste heat recovery (WHR) ORC, are characterised by a limited working fluid temperature at the expander inlet (up to 250°C) and a limited volumetric flow at the expander outlet (10-20 m3
/s).
For these operating conditions, Exergy has developed, thanks to a Ricerca e Innova grant under the Lombardy Regional Program, FESR 2021-2027, a new series of high-speed axial turbines (HSAT) optimised in terms of design and performance for modular WHR ORC plants, ranging from 0.7 MWe up to 2 MWe of electric power. The new turbine technology enables ORC systems of this size and operating in this temperature range to achieve more efficient electricity generation and thus be more economically viable.
The high-speed axial turbine The trend in the WHR ORC sector towards smaller plants with reduced flow rates strongly demanded the development of a new compact axial turbine, operating at a higher speed (12000 rpm). Compactness was a key aspect to maintain acceptable blade heights at the first stage as well as to limit the radial displacements of the rotor stages due to thermal expansion and centrifugal force. Limiting radial displacements during operation also allows the adoption of narrow labyrinth seal clearances, with a beneficial effect on leakage losses. A compact design was also required to reduce the turboexpander package manufacturing costs, compensating for
the introduction of a reduction gearbox (4:1) to accommodate the high rotational speed. With the HSAT, a cost reduction of 20% has been achieved compared to Exergy’s standard expanders (eg, employing radial outflow, see text box on next page).
Multiple integrally bladed rotors To make the axial turbine suitable for modular WHR ORC plants with a range of electrical power
outputs (0.7MWe and upwards), a multiple integrally bladed rotor (MIBR) configuration has been engineered, see Figure 1.
It consists of multiple stages and spacers held together by a single central tie rod, with torque between each stage transferred by means of interstage friction disks. This rotor section configuration can easily accommodate additional stages for ORC plants where higher expander enthalpy drops are required by the cycle. The
Figure 2. Sectional view of the high- speed axial turbine
www.modernpowersystems.com | July/August 2025 | 41
Source of images: Exergy
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
