In a distillation column if the vapours are going up with some droplets of the liquid in the trays .. reason of this phenomenon and how to solve it ?

This called the entrainment phenomena , refers to the liquid carried by vapor up to the tray above and is again caused by high vapor flow rates. It is detrimental because tray efficiency is reduced: lower volatile material is carried to a plate holding liquid of higher volatility. It could also contaminate high purity distillate. Excessive entrainment can lead to flooding.

First of all you need to be very clear about the working of distillation column. How the binary distillation column work?. how the binary mixture is separated?

Take two components A (high volatile component) and B (low volatile component). Obviously A would have lower boiling point than the B. Therefore by basic principle A would appear as a pure Vapor at the top and B as a pure liquid at bottom (assuming ideality). But at each tray there would be heat transfer(due to temp difference) and mass transfer(due to concentration difference) between liquid from top and vapor from bottom.

Vapors coming from bottom to tray will have more temperature than the liquid coming to tray from top. Thus heat transfer. 

There will be some high volatile or some concentration of A in liquid which will get vaporized from it due to high temperature of vapor coming from bottom of tray.

Thus some liquid gets vaporized which is basically high volatile w.r.t. equilibrium temperature at that tray.

Hope u understood. If not feel free to ask again.

Due to increase in pressure drop across trays the vapour travels faster than design velocity. This cause carry over of liquid particles to trays in upper sections which eventually may cause flooding of trays. You can check pressure drop across different sections of column (there might be pressure transmitters at different elevation of the column) and also total pressure drop across the column ( top -bottom ) and compare these pressure drops with your previous operating parameters when this problem didn't exist.

 due to decreasing of pressure-  flooding

increase the quantity of reflux

Your transfer line of tower increased or reflux quantity decresed

or product specification gone changed

check the temperature contrller at the side reboilers or botom reboiler if it is working accordind to the set point of the process