Two Phase and Three Phase Separators in CPI (Chemical Process Industry)

I would like elaborate on an important equipment in CPI, which is a SEPARATOR. This is covered in Chapter 9 of my ebook titled “The Handbook of Chemical Process Engineering” available at

 https://www.chemicalprocessengineering.in/

 Separators are used for many purposes in CPI:

a)   Remove unwanted fluids, such as water from gas or water from a gas-oil mixture.

b)   Divide a desired product (vapor or fluid) from other components.

c)   Divide phases for further processing (e.g. vapor product and liquid reflux on a fractionators overhead).

d)   Protect liquid handling equipment (e.g. pumps) from vapor entry and damage.

e)   Protect vapor handling equipment (e.g. compressors) from liquid entry and damage

 Separations are performed using following methods:

a) Momentum: Momentum separation involves changes in the direction of flow (a cyclone is an example). Often used for initial or “bulk” separation

 b) Gravity Settling: This uses velocity and time functions. The dense phase sinks through the light phase, and the light phase floats up through the dense phase. “Rise” means the lighter fluid is displaced by the falling heavier fluid.

Gravity separation is “free” of energy needs such as required by fractionation.

Therefore, it is generally the least expensive method of separation, considering installation, maintenance, and operation. Separation of small droplets will, however, require a large vessel and a long time.

 c) Coalescing: Wire mesh coalescing blankets are used to help separate light and heavy liquids by combining very small heavy liquid droplets into large droplets, which can then be separated from the light liquid by gravity. Large drops or particles settle better than smaller ones.

 Separators can be vertical or horizontal, depending on GOR (gas to oil) ratio.

Separators can be two phase or three phase type. Examples of two phase are flare KOD and reflux drums on columns. An example of three phase type is a gas plant inlet drum which will separate water, process condensate and gas.

 Three phase separators in turn can have many configurations e.g. for three phase horizontal separator having amine, oil and gas with oil quantity being very less, one could opt for a bucket and weir three phase separator. Similarly, a three phase separator having water, oil and gas with very less of water compared to oil, one could opt for horizontal vessel with a boot where the lesser water content can collect.

 Separators also have many internals. Examples are vessel inlet devices like schoepentoeter, multi-cyclones or a simple bend aimed toward dish end. Examples of gas outlet devices include demisting pad, vane pack or cyclones.

 There are also specialized separators called coalescers, where a proprietary coalescing pad is included in vessel which is very effective in separating two liquids, leading to reduced vessel size.

 The handbook contains a dedicated chapter 9 on Separators. Sizing examples are covered for each type of separator in this chapter.

Also, calculation template for bucket and weir type as well as a template for all the other types is provided in chapter 40.

Chapter 24 provides details on inlet devices.

 Please visit the website for purchase of the handbook.