Citation

Pilkington G, Paik S. Process. Saf. Environ. Prot. 2005; 83(5): 430-436.

Copyright

(Copyright © 2005, Institution of Chemical Engineers and European Federation of Chemical Engineering, Publisher Hemisphere Publishing)

DOI

10.1205/psep.04216

PMID

unavailable

Abstract

In the fine chemical and pharmaceutical industry, batch drying processes are common-place. One type of dryer frequently used is the batch fluid bed dryer as it is efficient with respect to drying time, but is also gentle on the product being dried. Often fluid bed drying operations involve the removal of solvent from the solid in the dryer.

Since there is a flammable vapour present and as the nature of the fluid bed dryer is to produce flammable dust clouds in the drying chamber, there is a potential for explosion. Indeed, explosions in fluid bed dryers have occurred historically and because of this, it is usual to see the dryer provided with explosion protection. The exhaust system, however, is not typically protected either because it is assumed that the high air flows will render the solvent concentration below the lower flammable limit (LFL), or that the risk of ignition is low.

This paper presents an incident in a fluid bed dryer exhaust system and the work carried out as a result to understand the flammable concentration 'profiles' in the exhaust. It will discuss the inadequacies of commercially available industrial LFL measuring devices for measuring transient concentrations of vapour, resulting in the development of a custom FTIR (Fourier Transform InfraRed) measurement device. Data from this device will be presented and the implications for drying processes are discussed.