Centrifugal Turbines for Mini-Organic Rankine Cycle Power Systems

2014 ◽  
Vol 136 (12) ◽  
Author(s):  
Emiliano Casati ◽  
Salvatore Vitale ◽  
Matteo Pini ◽  
Giacomo Persico ◽  
Piero Colonna
Keyword(s):  
High Temperature ◽  
Power Systems ◽  
Heat Recovery ◽  
Fluid Dynamic ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Expansion Ratio ◽  
Preliminary Design ◽  
Dynamic Design ◽  
Radial Outflow

Organic Rankine cycle (ORC) power systems are rapidly diffusing as a technology for the conversion of thermal energy sources in the small-to-medium power range, e.g., from 150 kWe up to several MWe. The most critical component is arguably the expander, especially if the power capacity is small or very small, as it is the case for innovative high-potential applications such as waste heat recovery from truck engines, or distributed conversion of concentrated solar radiation. In these so-called high-temperature applications, the expansion ratio is very high; therefore, turbines are the expanders of choice. Recently, multistage radial-outflow turbines (ROT), a nonconventional turbine configuration, have been studied, and first commercial implementations in the MWe power range have been successful. The objective of this work is the evaluation of the radial-outflow arrangement for the turbine of high-temperature mini-ORC power systems, with power output of the order of 10 kWe. To this end, a method for the preliminary fluid-dynamic design is presented. It consists of an automated optimization procedure based on an in-house mean-line code for the one-dimensional preliminary design and efficiency estimation of turbines. It is first shown that usually adopted simplified design procedures, such as that of the so-called repeating-stage, cannot be extended to minicentrifugal turbines. The novel methodology is applied to the exemplary case of the 10 kWe turbine of an ORC power system for truck engine heat recovery documented in the literature. The expansion ratio is 45. The preliminary fluid-dynamic design of two miniturbines is presented, namely, a five-stage transonic and a three-stage slightly supersonic turbine. The outcome of the preliminary design leads to two turbine configurations whose fluid-dynamic efficiency exceeds 79% and 77%, respectively. The speed of revolution is around 12,400 and 15,400 RPM for the five-stage and the three-stage machine, respectively. These results show that the ROT configuration may allow for compact and efficient expanders for low power output applications.

Preliminary Design of the ORCHID: A Facility for Studying Non-Ideal Compressible Fluid Dynamics and Testing ORC Expanders

2016 ◽  
Author(s):  
Adam Joseph Head ◽  
Carlo De Servi ◽  
Emiliano Casati ◽  
Matteo Pini ◽  
Piero Colonna
Keyword(s):  
Power Systems ◽  
Power Output ◽  
Fluid Dynamic ◽  
Supersonic Nozzle ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Operating Conditions ◽  
Performance Estimation ◽  
Preliminary Design ◽  
Integrated Device

Organic Rankine Cycle (ORC) power systems are receiving increased recognition for the conversion of thermal energy when the source potential and/or its temperature are comparatively low. Mini-ORC units in the power output range of 3–50 kWe are actively studied for applications involving heat recovery from automotive engines and the exploitation of solar energy. Efficient expanders are the enabling components of such systems, and all the related developments are at the early research stage. Notably, no experimental gasdynamic data are available in the open literature concerning the fluids and flow conditions of interest for mini-ORC expanders. Therefore, all the performance estimation and the fluid dynamic design methodologies adopted in the field rely on non-validated tools. In order to bridge this gap, a new experimental facility capable of continuous operation is being designed and built at Delft University of Technology, the Netherlands. The Organic Rankine Cycle Hybrid Integrated Device (ORCHID) is a research facility resembling a state-of-the-art high-temperature ORC system. It is flexible enough to treat different working fluids and operating conditions with the added benefit of two interchangeable Test Sections (TS’s). The first TS is a supersonic nozzle with optical access whose purpose is to perform gas dynamic experiments on dense organic flows in order to validate numerical codes. The second TS is a test-bench for mini-ORC expanders of any configuration up to a power output of 100 kWe. This paper presents the preliminary design of the ORCHID setup, discussing how the required operational flexibility was attained. The envisaged experiments of the two TS’s are also described.

Aerodynamics of Centrifugal Turbine Cascades

2015 ◽  
Vol 137 (11) ◽  
Author(s):  
Giacomo Persico ◽  
Matteo Pini ◽  
Vincenzo Dossena ◽  
Paolo Gaetani
Keyword(s):  
Power Systems ◽  
Coriolis Force ◽  
Gas Turbines ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Secondary Flows ◽  
Preliminary Design ◽  
Axial Turbines

The centrifugal turbine architecture is a promising solution for small-to-medium organic Rankine cycle (ORC) power systems. The inherent compactness of the multistage arrangement makes this configuration very attractive for dealing with the high volumetric flow ratios typical of ORC turbines. In absence of experimental evidence, a thorough assessment of the technology can be uniquely based on sufficiently accurate computational fluid dynamic (CFD) simulations. In the present work, the aerodynamic performance of a fixed and a rotating cascade of centrifugal turbine are investigated by applying a three-dimensional CFD model. Precisely, the study is focused on the sixth stage of the transonic centrifugal turbine proposed in Pini et al. (2013, “Preliminary Design of a Centrifugal Turbine for ORC Applications,” ASME J. Eng. Gas Turbines Power, 135(4), p. 042312). After recalling the blade design methodology, the blade-to-blade and secondary flow patterns are carefully studied for both stator and rotor. Results show that the centrifugal configuration exhibits distinctive features if compared to axial turbine layouts. The diverging shape of the bladed channel and the centrifugal force alter significantly the pressure distribution on the profile. Moreover, the Coriolis force induces a slip effect that should be properly included in the preliminary design phase. Provided that the flaring angle is limited, the almost uniform spanwise blade loading greatly augments the three-dimensional performance of the cascades compared to axial rows. In the rotor, the low inlet endwall vorticity and the Coriolis force further weaken the secondary flows, resulting in even lower secondary losses with respect to those predicted by loss models developed for axial turbines. Ultimately, the efficiency of the stage is found to be two points higher than that estimated at preliminary design level, demonstrating the high potential of the centrifugal turbine for ORC applications.

Method for the Preliminary Fluid Dynamic Design of High-Temperature Mini-Organic Rankine Cycle Turbines

2017 ◽  
Vol 139 (8) ◽  
Author(s):  
Sebastian Bahamonde ◽  
Matteo Pini ◽  
Carlo De Servi ◽  
Antonio Rubino ◽  
Piero Colonna
Keyword(s):  
Power Plants ◽  
Design Space ◽  
Organic Rankine Cycle ◽  
Thermodynamic Cycle ◽  
Rankine Cycle ◽  
Inlet Temperature ◽  
Preliminary Design ◽  
Design Calculations ◽  
Radial Outflow ◽  
Turbine Design

Widespread adoption of renewable energy technologies will arguably benefit from the availability of economically viable distributed thermal power conversion systems. For this reason, considerable efforts have been dedicated in recent years to R&D over mini-organic Rankine cycle (ORC) power plants, thus with a power capacity approximately in the 3–50 kW range. The application of these systems for waste heat recovery from diesel engines of long-haul trucks stands out because of the possibility of achieving economy of production. Many technical challenges need to be solved, as the system must be sufficiently efficient, light, and compact. The design paradigm is therefore completely different from that of conventional stationary ORC power plants of much larger capacity. A high speed turbine is arguably the expander of choice, if high conversion efficiency is targeted, thus high maximum cycle temperature. Given the lack of knowledge on the design of these turbines, which depends on a large number of constraints, a novel optimal design method integrating the preliminary design of the thermodynamic cycle and that of the turbine has been developed. The method is applicable to radial inflow, axial and radial outflow turbines, and to superheated and supercritical cycle configurations. After a limited number of working fluids are selected, the feasible design space is explored by means of thermodynamic cycle design calculations integrated with a simplified turbine design procedure, whereby the isentropic expansion efficiency is prescribed. Starting from the resulting design space, optimal preliminary designs are obtained by combining cycle calculations with a 1D mean-line code, subject to constraints. The application of the procedure is illustrated for a test case: the design of turbines to be tested in a new experimental setup named organic rankine cycle hybrid integrated device (ORCHID) which is being constructed at the Delft University of Technology, Delft, The Netherlands. The first turbine selected for further design and construction employs siloxane MM (hexamethyldisiloxane, C6H18OSi2), supercritical cycle, and the radial inflow configuration. The main preliminary design specifications are power output equal to 11.6 kW, turbine inlet temperature equal to 300 °C, maximum cycle pressure equal to 19.9 bar, expansion ratio equal to 72, rotational speed equal to 90 krpm, inlet diameter equal to 75 mm, minimum blade height equal to 2 mm, degree of reaction equal to 0.44, and estimated total-to-static efficiency equal to 77.3%. Results of the design calculations are affected by considerable uncertainty related to the loss correlations employed for the preliminary turbine design, as they have not been validated yet for this highly unconventional supersonic and transonic mini turbine. Future work will be dedicated to the extension of the method to encompass the preliminary design of heat exchangers and the off-design operation of the system.

Sign in / Sign up

Export Citation Format

Share Document