Question

why the dimeter of vacum distilation bigger than flash distlation?

Answer 1

Vacuum distillation diameter is bigger than flash distillation because we have to maintain vacuum inside the vacuum distillation by which maintaining lowest pressure drop and we know that if diameter is large then pressure drop reduces. In vacuum distillation , vacuum pressure is very costly affair so that we increase its diameter. In oil refining operations so much process are happened into vacuum distillation because at atmospheric pressure , separation is not possible and very high temperature it decomposed into another product. Thats why we required vacuum in this type of distillation. It is good for low vapor flow rate because when diameter increases then flow rate of vapor decreases for costant trays.

Flash distillation process is also called equilibrium distillation because here vapor and liquid are in equilibrium and we maintain constant temperature and pressure. Here heated feed is fed into the pressure reducer valve so that saturated liquid may become partially vapor and suddenly got large volume then vapor and liquid separate out by maintaining equilibrium.  Liquid settle down and vapor upward direction . Here we are using column diameter is less than vacuum distillation column. Because here no need of maintaining vacuum inside the column.