EARS – Monitoring Fluidised-Bed Agglomeration

Principles of EARS

The Early Agglomeration Recognition System EARS is a tool for monitoring the condition of a fluidised bed in terms of agglomeration or, more generally, particle size distribution. The tool comprises three major elements:

1) measurement system,
2) data processing system,
3) process control instructions.

In-bed pressure fluctuations are measured at a single or multiple locations using sensitive piezoelectric pressure transducers. The processing unit calculates a signal, which can be interpreted as a signature of the fluidised bed hydrodynamic behaviour. By continuous comparison of the actual signature with one obtained during a period of known stable operation, a statistically sound process signal, S, is obtained which indicates the onset of agglomeration when a threshold value is exceeded. Warning and alarm values can be set for starting manual or automated process control measures.

State of developmentEARS has proved to indicate the onset of agglomeration well before classical methods based on pressure or temperature differences, in a large number of small-scale bubbling-fluidised-bed experiments. This work included testing the reversibility of the EARS signal by means of controlled replacement of the virgin bed material.For the next level of development, several full-scale projects have been executed, shifting the R&D focus towards reliability and process control. This track record includes measurements in the heat exchanger of a 78 MWth coal/straw-fired CFB boiler and, more recently, in a 80 MWth wood-fired BFB boiler. Here, multiple measurement points are used to cover the whole 30 m2 bed surface area. Full-scale measurements in the riser of a circulating fluidised bed are currently planned for a 50 MWth coal-fired CFB utility boiler with the aim to improve control of the particle size distribution in the riser.

Partners

The fundamentals of the pressure fluctuation based detection method were developed at the Department of Chemical Engineering of Delft University of Technology (NL). In 2001, ECN Biomass and Delft University of Technology have formally teamed up to develop EARS for industrial application. IPCOS, which develops state-of-the-art process control products, is now being involved for the marketing of EARS.

More detailed information on the principles of EARS and the underlying experimental work can be found in the papers given below.

Publications

• Kiel, J.H.A., Korbee, R., Ommen, J.R. van, Bleek, C.M. van den, and Nijenhuis, J.: Early Agglomeration Recognition System (EARS). Proc. 12th European Conf. and Technol. Exhibition on Biomass for Energy, Industry and Climate Protection, Amsterdam, 17-21 June 2002, published by ETA-Florence and WIP-Munich, pp. 589-592, 2002.
• Korbee, R., Ommen, J.R. van, Lensselink, J., Nijenhuis, J., Kiel, J.H.A., and Bleek, C.M. van den: Early Agglomeration Recognition System (EARS). Paper 151, Proc. 17th Int. Conf. on Fluidized Bed Combustion, Jacksonville, Florida, USA, 16-23 May 2003.