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The Centre for Solar Energy and Hydrogen Research Baden-Württemberg (ZSW) in Germany is one of the leading institutes for applied research in the field of renewable energy sources and processes. There are around 300 scientists, engineers and technicians working at the ZSW sites in Stuttgart, Ulm and Widderstall. The ZSW has many years of experience of research in the field of integrated phosphorus recovery and relevant expertise in fluidised bed systems and detailed analysis.

The ZSW is showing how the phosphorus cycle can be optimised with its promising research into recycling phosphorus from phosphate-rich residues and waste materials. One innovative approach is based on fluidised bed incineration of sewage sludge combined with the incorporation of various alkali and alkaline earth additives in order to increase the plant availability of the phosphorus in the resulting ash. The ZSW is developing this new process with partners from industry and research. The aim is to optimise the properties of the ash for subsequent use in agriculture. The focus is on the plant availability of the phosphorus-rich ash with a view to closing the phosphorus cycle.

Fluidised bed pilot plant at the ZSW:

Our plant comprises a stationary fluidised bed reactor (FBR) and a FLOX® reactor (flameless oxidation - FLOX®). Both reactors use the same fluid measuring and heating unit as well as hot gas finishing treatment and gas analysis. The two reactors can also be combined by producing the gas in the fluidised bed, for example, and burning the gas in the FLOX® reactor.

ZSW reactor

The pilot plant consists of the fluid meter, fluid heater (left), stationary fluidised bed reactor with high-temperature cyclone, FLOX® reactor, high-temperature filter, gas scrubber, and gas analysis unit with volume flow measurement (right).

There are screw feeders for the separate addition of solid fuel and up to two fluidised bed additives. The facility has four solid material extraction lines with ball valve locks (fluidised bed overflow, fluidised bed sump, high-temperature cyclone and high-temperature filter) so that samples can also be taken during test operation. The fluidised bed reactor and high-temperature cyclone are designed for temperatures of up to 950 °C. The high-temperature filter can be heated to a maximum of 800 °C. The process gas leaving the high-temperature filter is treated in a two-stage gas scrubber for the product gas measurements, therefore both gasification and combustion processes can be observed in the pilot plant.

The pieces of equipment available for the process gas analysis include a drum-type gas meter for the volume flow measurement, one cold gas analyser and one hot gas analyser (FT-IR). In combination with additional measurement and analysis parameters, it is possible to take mass balance readings (e.g. with regard to phosphorus and carbon) with a high degree of accuracy.

Rheometer platform

The ash-softening action of the fluidised bed material is first analysed in order to prevent the nutrients contained in the sewage sludge from sintering and to stop deposits / agglomerations from forming which would cause disruption during the fluidised bed incineration of the sewage sludge. The ZSW carries out rheological tests on ash additive mixtures for this purpose. The rheometer / rotational viscometer is central to this process as it measures the moment of rotation during the stirring of an ash additive mixture as a function of the increasing sample temperature.

Equipment for material analysis

The ZSW has laboratory equipment which can be used for further research into associated methods and services:

  • Thermal gravimetric analysis (TGA):
    Thermogravimetry can be used to study reactions between gases and solids under defined conditions (pressure, temperature, gas atmosphere), as detected on the basis of the mass profile over time. The ZSW has a TGA unit for controlled atmospheres and a magnetic suspension balance which allows pressures of up to 40 bar and is connected to a mass spectrometer for the product gas analysis.
  • Particle size analysis by means of laser diffraction or screening
  • Mills for pulverising solids
  • Muffle furnaces

Media Contact:

Dr. Jochen Brellochs
Tel.: +49 711 78 70-211