About project

The Optimised expanders for small-scale distributed energy systems (Dexpand) project benefits from a € 1 430 000 grant from Iceland, Liechtenstein and Norway through the EEA Grants and the Technology Agency of the Czech Republic within the KAPPA Programme. The aim of the project is to design, test and analyze potentials and feasibility of prospective expanders for organic Rankine cycles (ORC) based on impulse turbomachines and rotary vane expanders in power range of 1-50 kW.

The project is a joint research project between CTU in Prague, NTNU Trondheim, SINTEF Energi AS and company GT-Progress s.r.o. with duration between 10/2020 and 04/2024.

Working together for a green and competitive Europe

Objectives of project

Efficient, reliable and cost-effective expanders are the key enabling components for many distributed energy systems, such as, organic Rankine cycles (ORC) and other thermodynamic cycles for waste heat recovery (WHR), biomass-fired power generation, or low-temperature geothermal resources based on deep energy wells. Current expanders for small systems (1–50 kW electrical power output) are either not in the market, are too expensive, or don’t provide satisfactory performance [1]. Therefore, most of the possible energy sources are not utilized. Cost-effective expanders could enable a significant market for these type of distributed energy systems and offer large potential for overall CO2 savings. This project focuses on development and testing of cost-effective expanders for power generation in distributed energy systems, reporting expanders data and on mapping of the technologies over the power range 1–50 kW based on cost, application feasibility, and performance

A key element of the project will be to make the experimental and expander geometry data available to the industry and research community since there is currently a big lack of expander data openly available. This is especially the case for off-design performance data, which will be published as well.

Three target applications, all backed up by attached market analyses, will be explored:

  1. Waste heat recovery from industry.
  2. Micro-cogeneration based on biomass fuel.
  3. Low-temperature geothermal ORC systems using deep energy wells.

The project will be based on mathematical modelling, expander design optimisation, and experimental testing for expanders development. For the considered applications, an important activity will be a comprehensive mapping of several interesting technologies, while learning from the specific expertise from all research partners. This project will not be alone among projects on modelling, design and experimental testing of expanders, but it is unique by focusing and combining several prospective technologies and approaches. These are:

  • Rotary vane expander as a volumetric expander for the smallest applications.
  • Impulse or reaction single stage axial or radial turbines with possible partial admission as a method for acceptable rotational speed. Variable speed for off-design operation will be implemented.
  • Novel impulse turbine concepts — single-wheel radial Curtis-type historically known as Elektra turbine and radial outflow multistage impulse turbine — both with prospective of very high-pressure ratio, low rotational speed and low cost.
  • Exploration of the potential of additive manufacturing technologies for the expanders.
  • Mapping of the expanders in terms of cost, application feasibility and performance. The mapping will also include other expander technologies, like radial inflow turbines, based on results from previous projects.
  • Methodology to translate process performances into expander design parameters through system modelling, simulation and optimisation. This will allow bridging the gap between technology development and process design so to identify expander designs able to maximise system efficiency and flexibility for a given application.

Specifically, three expanders with nominal power output range of 1–50 kW will be built and tested: one rotary vane expander, one turboexpander for hexamethyldisiloxane (MM) as working fluid, and one turboexpander for the natural working fluid isobutane (R600a). At least one of the expanders will utilise additive manufacturing methods.

The obtained data sets and expander designs, that should be made available to the public via open access publications and an open data repository, will allow for researchers and companies to validate their expander models and mathematical codes.

The essence and the timetable of the project proposal

The progress of works will be structured into several work packages. Timetable, in brief, follows the order of the work packages and it can be seen in the Gantt chart and a graphic showing WPs/tasks and their connections in the chapter below. These are:

  • WP 1 System modelling and simulation
  • WP 2 Expander modelling, design and optimisation
  • WP 3 Mechanical design, manufacturing of expanders
  • WP 4 Experimental verification
  • WP 5 Assessment and recommendation


Applicability outputs/results in practice, the benefits of the project

Efficient, reliable and cost-effective expanders are the key enabling component for many distributed energy systems such as organic Rankine cycles (ORC) and other thermodynamic cycles for waste heat recovery, biomass-fired power production or low-temperature geothermal resources. Current expanders for small systems (1–50 kW) are either not at all on the market, or too expensive and don’t provide satisfactory performance. Therefore, most of the possible energy sources are not utilised. Effective expander could enable a significant market for these systems and offer a large potential for CO2 emissions savings.

Through the combination of young as well senior supervising researchers from top universities in respective countries and research institute with experience in the investigated field, as well as by combining with the highly applied industrial company with much of energy engineering experience, the level and quality of results will be on a high level to ensure applicability.

The applicability is supported by market research and more detailed analysis as well as letters of intent (see the attachments Market research and Letters of Intent).

The research results will serve to generally increase TRL of micro expanders for distributed applications, including guidance on suitability for various applications (through the feasibility mapping). The data set and expander design should be made available to the public via open access publications and an open data repository. Published data and findings will also help other researchers and companies to validate their models and codes and boost their development. Expander functional samples may serve as a basis for further commercial products.

The expected benefit is also on closer cooperation and academic exchange, leading mainly to the improvement of R&D level in the Czech Republic and closer cooperation in future on research and applied projects.