Ultrafine Particle Capture for High-temperature Processes Using Active and Passive Thermally-induced Potential Fields

Project Number 311

Ceramic candle filters currently set the standard in the field of high-temperature ultrafine particle capture. These filter elements can be used at temperatures of up to 800 to 900 °C. At temperatures above this limit candle filters do not exhibit a sufficient service life, as the dust cake becomes soft and tacky. This affects the regeneration performance and there is an accompanying increase in pressure loss. Ultrafine particle capture for high-temperature processes has still not been developed on an industrial scale.

For this reason, high-temperature processes usually cool the gas to such a level that the filtration process can take place at temperatures below 900 °C, which allows ceramic candle filters to be used. In power station processes this reduction in temperature leads to a decrease in electrical efficiency.

Pioneering work on an almost isothermal flue-gas cleaning process for the high-temperature range has been carried out in recent years as part of a research programme designed to develop combined-cycle power station technology with pressurised pulverised coal combustion (PPCC). These investigations succeeded in demonstrating that the waste gases from coal combustion can be cleaned at temperatures of about 1,400 °C in an electrostatically supported packed bed until compatible with the gas turbine system (particle content < 3 mg/m³ and particle diameter < 3 µm, alkali < 1 ppm).

The operating mechanisms that underlie the empirically developed waste-gas cleaning process for ultrafine particles were investigated in an extensive programme of experimental and theoretical tests carried out as part of AiF Project 149 Z (VGB No. 265 ). These investigations showed that the operating principle was essentially based on the use of electron emissions from ceramic system components in conjunction with active and passive, thermally-induced potential fields at temperatures above 800 °C.

The research projects, which were carried out at the pilot plant in Dorsten, indicated that there was a considerable potential for applying high-temperature ultrafine particle separation to other areas too, including coal gasification (IGCC processes), coal combustion in oxygen/flue-gas mixtures using the OXYCOAL-AC process and biomass gasification processes with hot-gas cleaning.

AiF project no. 275 Z set out to investigate the fundamental principles underlying the PPCC process under the constraints of coal and biomass gasification. This was aimed at presenting the basic criteria for an isothermal (if applicable) ultrafine particle capture system for high-temperature processes in the temperature range above 800 °C, with the investigations focussing specifically on the effect of different material pairings on the electrical charging of model (TiO₂ and metal) and slag particles in the electrical field.

The project, which was sponsored by the AiF (German Federation of Industrial Research Associations) from funds provided by the German Federal Ministry of Economics and Technology, is to run from 2008 to 2011 and will be carried out jointly by the Institute for Energy and Environmental Technology (IUTA) in Duisburg under the leadership of Prof. Dr. D. Bathen, by the Institute for Mechanical Process Technology and Mechanics (MVM) of Karlsruhe University under the leadership of Prof. Dr. G. Kasper and by the Institute for Energy Research (IEF-2) of the Jülich Research Centre under the leadership of Prof. Dr. L. Singheiser. The investigations are supported by the Working Panel Flue Gas Cleaning Technology .