Column internals are only devices which dominates in the distillation process. They are nothing but the catalysts of mass transfer operation.
Most used column internals are packing and trays (Plates). Various industrial sectors like energy, petrochemicals, biofuel, water treatment, refining, gas processing etc. has exposed to importance of these column internals. Types of internals has been described below,
Packing are divided in further 2 types,
1. Structured Packing –
Structured packing is type of internals in which materials are arranged in unique way to enhance the efficiency of the mass transfer operation. Corrugated sheets or wire mesh materials are being used in structured packing which allows to fluid and vapour streams to get interacted with each other for better output. Structured packing has textured design which helps to increase the spreading of the liquid.
Various types of structured packing like gauge/wire mesh, knitted type, sheet metal type and grid type of packing. Each of the type has separate specifications and contribution to the process.
Without vapour liquid contact it’s impossible to have mass transfer of fluids. Bettermass transfer will be followed if we use the packing which can create thin filmedliquid distribution which enhances the performance. Some packing types hastextured designing on plates which increase spreading of the liquid. Such packing is more effective in case of low pressure applications.
It’ll be the best choice if the process requires the high flow rate and lower pressure drop. Lower pressure drop leads to higher volatility which turn to be an advantage in operation. Structured packing also helps to reduce foaming and increase energy efficiency. Higher capacity of packing tends to increased operating rates.
2. Random Packing-
These are the type of internals which directly get dumped into the column to carry out the process. Required surface area for operation is being provided by whole random packing. It’s used in various operations like distillation, stripping, scrubbing and Liquid-liquid extraction Etc.
Random packing is used to allow contact between 2 fluids such as liquidwith gas or with liquid-liquid contact. Random packing offers higher pressure drop comparatively to structured packing. The packing selected should offer large surfacearea to achieve optimum surface area and effective mass transfer.
Various types of random packing which is being used in process like Raschig Ring, Pall Ring, IMTP Saddle Ring etc. which will be preferred as per the process recommendation. These packing are used in cases of small diameters towers, processes with low pressure drop, corrosive applications and in case of increased capacity as well.
Binary, tertiary or mixtures containing more components can be separated using trays. Trays are nothing but the perforated plates which are the one of the popular way of mixture separation. Trays separation process is the time proven, economical process for the mixture. More advanced processes can be only handled using high performance trays.
In the separation process using trays, liquid flows across the trays and down to the column in crossflow or counter-flow manner. The energy required to separation is supplied by the steam at the reboiler placed below the column which allows the vapour form of liquid to flow throughout the plates and to occur separation process.
Trays consists of various segments like down comers, weir, active tray area, hole area etc. Liquid falls down from one tray to another through this down comer area by gravity force. Weir ensures the specific holdup level on the trays or plates of the column so that the trays shouldn’t run in dry state and it maintains the flowrate of vapour and liquid to avoid flooding and weeping.