What causes pressure drop across the sieve bed to increase?

Bead dusting and breakup are common causes of pressure drop increase. This is often caused by upsets such as rapid pressure swings, liquids carryover, regeneration refluxing, and flow channeling. Rapid pressure swings can cause movement of the sieve or the entire bed in some cases. When severe enough, it can lead to flow channeling in the bed and early breakthrough in addition to increased pressure drop. Liquids carryover events in which liquids slam into the bed can cause sieve breakup, especially for repeated occurrences when it is a chronic problem. Regeneration refluxing occurs when liquids rain down on the sieve bed due to cooling and condensing at the top of the vessel early in the heating cycle while simultaneouslyliquids are being vaporized and driven from the sieve bed. It creates a rolling boil that can break down the sieve over time. In general, even under the best of circumstances, the pressure drop across the sieve bed normally goes up by 1.5-2 times over the life of the sieve due to bed settling and compaction, coke and carbon buildup on the sieve, and dust and particulate matter that collects in the bed.