APPLYING RISK ASSESSMENT PRINCIPLES TO A BATCH DISTILLATION COLUMN

Some distillation columns in the chemical industry are operated in bat ch mode with a fairly short operating cycle. At the end of each cycle the columns are cooled and recharged. During the cooling cycle, air wi ll be drawn into the column by the action of a vacuum relief valve. Co nsequently, for a finite portion of the operating cycle a flammable mi xture will exist in the column. Here we evaluate the risk posed by suc h an operation to see ifa mitigation measure is justified. We develop a fault tree and estimate the frequency of ignition by all Possible ig nition sources. By comparing the risk reduction attainable by installi ng a lightning protection system with that attainable by using an iner t blanketing system the lightning protection system is found to be the preferred solution. It provides about the same risk reduction at a lo wer overall cost.