The purpose of this project is the development of a compact steam
turbine as a central and robust component for a new type of micro-CHP
and solar thermal power plant in regions with high impact of sunlight.

The idea:
At the heart of this innovative project is a compact heat engine. Thermal energy will be converted into electrical energy, with the remaining energy being used for heating purposes.
The concept was developed by the University of Darmstadt. The main advantages of the compact steam turbine are the close integration of steam and power generation, its small size and the simplicity of its construction, which is characterized by the absence of valves, controls, or pumps.
The use of this robust technology has significant advantages over existing solutions in the field of combined heat and power generation (CHP). Low maintenance costs as well as a simple and robust construction provide significant advantages over piston engines. Therefore you should familiarize yourself with this compact steam turbine for consumer-effective solutions because combined heat and power generation can be easier and better achieved than with existing technologies. The thermal performance range of the turbine lies in the region between 10 kW – 20 kW. The calculated mechanical efficiency turns out to be approximately 10% for working fluids such as toluene or benzene at temperature differences of approximately 200C. Still, significant development work is required. There are first experiments with a rotating container at 1000 – 6100 rpm. Design studies even suggest 10000 rpm. Due to its small size the turbine operates at low flow rates.

Thermodynamically, the ORC (Organic Rankine Cycle) is of interest here, since pentane as working fluid can be used because it has a low heat of vaporization. Here, the residual heat is larger than when using water as working fluid. Thermodynamic studies indicate, depending on the temperature difference, high efficiencies of around 20% – up to 28% in xylene, toluene, pentane, benzene  and siloxanes.
Pentane at low temperatures has pretty decent thermal efficiencies. Geothermal power plants that run at relatively low temperatures, are often operated with pentane as working fluid. Although pentane is highly inflammable, this risk is taken into account for environmental reasons and the use of CFC’s is preferred.

Our vision:
Mass production of a compact steam turbine with a volume of more than 100,000 units/year from 2016 on at favorable unit prices that are comparable to the typical prices for turbochargers for cars – that is less than 1000 €.
Reduction of net carbon dioxide emissions by 8.5 million tons per year in Germany by about 1 million micro-CHP (baseline of the estimation for the benefit of a micro-CHP is a comparision of natural gas compared to coal power plant – For the operation with biogas or biodiesel the carbon footprint is even lower).

As of 2021 approximately 500,000 heaters are equipped with this new technology.
2025 first compact steam turbines will produce heat and electricity with hydrogen – no emission of carbon dioxide – decentralized power generation.
Low cost systems based on the compact steam turbine, with energy intake from a parabolic mirror, which can provide transhipment sites in southern off-grid locations with electricity and heat for cooking purposes.
Building an alternative to conventional combined heat and power systems and thus improving the energy efficiency.
2126,(2009)] that small-scale CHP systems need to be simplified in order to be competitive with medium or large-scale systems. The Kompakte Dampf Turbine (KDT, meaning compact steam turbine), originally invented at the Hochschule Darmstadt [Heddrich et al., Patent DE10315746, 16.9. 2004, Deutsches Patent- und Markenamt,] addresses this demand. The KDT consists of a rotating cylinder (200mm in diameter and 300mm in height) and a static axis, therefore reversing the traditional arrangement in a turbine. The cylinder is divided by a plate into evaporation- and condensation chamber. The plate is fixed to the cylinder and therefore rotates with it. Between the rim of the dividing plate and the cylinder exists a small gap, allowing the working fluid to pass through it. Laval-nozzles are fixed to the dividing plate. The working cycle is similar to that of a traditional turbine. The thrust from Laval-nozzles of the vaporized and accelerated working fluid is used as the first stage in the power transfer. Further power is generated by a suitable arrangement of blades similar to a traditional turbine, only the roles of blade and guide wheel are interchanged.

After expansion the condensed working fluid is caught by the rotating cylinder wall and fed back through the gap between the plate and cylinder into the evaporation chamber. By choosing the right amount of working fluid in combination with the right rotational speed the gap will always be covered. The working fluid serves as a seal between evaporation and condensation chamber.  If the KDT is enclosed in a sealed static housing then the vapors of the working fluid are well insulated from the environment. Such a setup also reduces the friction of the rotating cylinder.
The goal is to achieve an overall electrical efficiency of 10%. For a typical residential home heating this would yield 1.5-2 kW of electrical output. In order to achieve the necessary thermal efficiency for the temperatures and pressures under consideration one has to use some kind of ORC fluid [ Ngoc Anh Lai, Martin Wendland, Johann Fischer, Energy 36 (2011), 199-211]. So far experiments have been carried out with air and water, simulating the pressure difference between evaporation and condensation chamber and testing the sealing behavior of the working fluid. In the next step an organic fluid will be used together with an appropriate heat source. On the theoretical side we have done calculations relating to the fluid seals the heat transfer and the Ljungström like blade assembly for a 2-stage turbine with rotating nozzles.
The KDT is essentially a fully integrated power plant with numerous advantages: Very few parts, no valves, and no seals, allowing for a competitive realization and low maintenance costs. The goal is to build a robust integrated CHP heat-power transfer for € 1.000,-.

A more technical  description of KDT can be found at:


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