The “DualFluid” steam gasification technology was developed at the Vienna University of Technology in the 1990‘s. In the classical design (Güssing gasifier) the gasification reactor is designed as a bubbling fluidized bed. The heat transfer to the fuel particles and the main tar destruction reactions take place in contact with the bed material particles inside the bubbling fluidized bed. Above there is a freeboard region where the solids concentration approaches zero. Such a separation between bubbling bed and freeboard lead to limitations especially when inhomogeneous fuels are used. Organic fines are immediately elutriated into the freeboard where primary tars are emitted and not sufficiently converted due to lack of catalytically active solids in the freeboard. This may result in tar depositions in the product gas and may critically affect the plant availability. In the experiments performed at existing pilot plants of the Vienna University of Technology it was reflected that an increase in fluidization velocity hence an approach of turbulent fluidization regime and increases the effectiveness of gas-solids reactions. The G‑volution system (Fig. 1) enables such turbulent fluidization regimes with a bed material distribution over the whole gasifier volume. Therefore the gasification reactor is divided into a sequence of sections with flow obstacles. Gas velocities in the gasifier are chosen such, that final solids entrainment is low. 

Fig. 3 Typical qualitative pressure drop, pressure gradient and solids fraction in the countercurrent gasification reactor with zones of improved gas-solid interaction (Source J.C. Schmid TU Wien)

Partly elutriated fines at the top are recycled into the gasifier via a cyclone and a loop seal or removed from system. The combination of the dual circulating fluidized bed concept with flow obstacles leads to a completely new functionality for circulating fluidized bed reactors. The behavior of the solids loading with varying gas flow rates in the countercurrent reactor shows a similarity to random-packed gas-liquid columns with a flooding point reached at certain gas flow rates (Fig.2). Several locations of fuel input can also optimize reaction conditions with regard to a wide range of different fuels. The fluid dynamics  in the reactor are equivalent to a column of a multi-stage cascade of stirred vessels. The gasifier can also be described as a plug flow reactor for gas and a column of stirred vessels for solids with the special characteristic, that the gaseous phase and solids have contrary movements (countercurrent behavior) (Fig.3).

Project Homepage: www.g-volution.at

Industrial Partners & Financial Support

• TECON Engineering GmbH, Leobersdorf, Austria
• Österreichische Forschungsförderungsgesellschaft FFG
• Klima- und Energiefond

Weblink zusätzliche Projektinformationen:

• Science Brunch Bioenergie
• Publizierbarer Endbericht