Professional Articles

Silos, Bins & Bunkers

Silos for Pulverized Solid Fuels

The common method of protection against deflagration-induced damage is 2-fold: Monitoring temperature and CO gives information about stored fuel that has auto-ignited and smoulders, which provides the necessary ignition source for a deflagration and cannot be removed easily. Emergency measures like injection of CO2 or N2 aiming at a quick reduction of the O2 content of the air in the silo may then be triggered. This will eliminate one of the remaining 2 conditions (the 3 conditions are: more than 13,5% O2 – fuel suspended in air – ignition source as mentioned above) that must occur simultaneously in order to enable the ignition of a deflagration.
Even with all the right technology in place the risk of the occurrence of a deflagration cannot be fully eliminated, and so called constructional explosion protection will take care of this remaining risk. Continuous blanketing with N2 is only feasible in cases where there is an abundance of cheap N2, e.g. in steel works, and will not be discussed here.
Constructional explosion protection aims at limited or zero damage, not at avoidance. Limited or zero damage can be achieved providing pressure shock resistance (by making the equipment strong). A practicable solution is to provide a certain degree of pressure shock resistance and to equip the reinforced equipment with one or more explosion vents. The right correlation of size and effectiveness of the vents and the degree of pressure shock resistance of the equipment can be found using standards. The most common standards are EN (European Community) standard 14491 and NFPA (National American Fire Protection Association of America) standard 68.