(244d) Prevention of Dryer Fires: Problem Analysis & Application of Results

A manufacturer of food products experienced, over a five month period, several fires in continuous product dryer systems. Ignition in each case was apparently related to the accumulation of product dust and deposits within the drying zone and exhaust ducts. Identification, analysis and remediation of the failure modes were essential to resumption of safe drying operations. This paper describes a multi-step process employed to identify dryer failure modes, product ignition sensitivity, and application of this knowledge to modify dryer operations to reduce fire risk. Discussion covers (1) the investigation of dryer operations to identify locations therein where product dust and deposits were accumulating; (2) screening of an array of products to identify the subset most susceptible to ignition when exposed to elevated temperatures; (3) determination of the Frank-Kamenetskii (FK) critical self-heating temperature, TCRT and reactivity parameters as a function of sample size; (4) analysis of the FK data to develop a parametric understanding of safe dryer operating conditions; and, finally, (5) implementation of the findings of the FK analysis to change dryer operations, primarily related to operating temperatures and cleaning cycles, to reduce the risk of future fires.