Spray Dryer Explosion Protection In Food Ingredients Plant

The method of explosion protection selected involved installing pressurised cylinders to rapidly discharge explosion suppressant into the protected area in milliseconds upon activation, however the unusual combination of large spray dryer vessel size (> 400 m3), along with its low vessel strength rating meant that a high number of cylinders would normally be needed to mitigate or isolate an explosion. However, after analyzing and modelling the spray dryer operation, IEP’s design team was able to avoid using an excessive number of suppression cylinders by using a recognized methodology where a reduced explosibible volume can be used as the basis of the explosion suppression for spray drying processes of a specific design. The principle observation is that, as the top section of some spray dryers do not contain dry combustible dust, explosion suppression of the entire volume is excessive and unwarranted. This technique allows for a reduced amount of suppressant to be delivered to the upper “wet zone” to maintain its inert state, while explosion protection is concentrated in the lower zone containing dry combustible powder, resulting in a reduction in the number of suppressors needed for overall protection. In North America, NFPA codes allow for this technique based upon performance-based approvals.

Several “Piston Fire II” high-rate suppression and isolation cylinders were specified as part of the explosion protection system, offering the additional benefit of having Class II Division 1 hazardous location approval. These suppressors as well as the SMARTDS dynamic explosion detection system are electrically connected to an EX8000 Control Panel with the capability to selectively activate specific suppressors in the zone where the deflagration is occurring. The overall solution met the stated needs of the customer by providing highly targeted mitigation of explosion events at the same time as reducing the cost of equipment, installation and ongoing maintenance.