CONTACTOR COLUMN (Absorption Column)


Contactor Column

The function of the contactor column, also called absorber, is to remove water vapor from natural gas by physically bringing together. The up flowing natural gas with the down flowing glycol solution. The glycol absorbs the water vapor from the natural gas.
                                                                 Design Specifications
Contactor column are design to accommodate certain gas volume and pressure, if these design specification are exceeded, then glycol losses and outlet gas dew point will increase.


Contactor column usually contain either
  • Trays
  • Random packing
  • Structural packing
Contactor at Nandpur field contain structure packing. Structure packing is group of core gadded metal sheets welded into a specific pattern and place on edge in the contactor. Glycol coats these sheets and the gas flow between them. This type of packing is more efficient than bubble caps or random packing. Structure is used in columns 6 inch to 10 feet in diameter. 
The up flowing gas is force through the structural packing of specific pattern evenly through the flowing glycol. The glycol gives up water and becomes dryer as its passes upward through packing. The glycol becomes more saturated with water as its flow downward.

Nandpur Contactor Column Design Specifications
Size
1000 MM I.D. × 1158 MM S/S
Design
1500 PSIG @ 150oF
Capacity
50 MMSCFD

Comparison With Trays and Random Packing Systems
Trays
·         Usually a tray column consisting of 4 to 12 trays.
·         This is more expensive than random and structural packing.
Random Packing
·         Random packing is metallic, plastic and ceramic.
·         These structures provided the larger surface area for the glycol solution to spread out and make better contact with the gas.
·         4 feet of packing is usually standard and sufficient to achieve the dew point depression up to 13oC to 18oC (55oF to 65oF).
·         Channeling is disadvantage of random packing.
·         Channeling limits the surface area with the glycol and the gas coming poor contact.

Before the lean glycol enters the contactor two things are happen.
  • The glycol is pumped up to the contactor pressure and
  • The glycol temperature is lower to within 10 to 15oC of inlet gas temperature.
 Now remember it’s best to have glycol enter the contactor 10 to 15oC warmer than the inlet gas to eliminate condensation of hydrocarbon vapor.

Mist Eliminator and Glycol Scrubber
Above the column a mist eliminator in the top of contactor for remove any entering glycol
particles in the gas stream that not settle out. 
Glycol scrubber is a separate column from the contactor column and it work like mist eliminator. It has two mist eliminators inside.
Advantage of Mist Eliminator
Following are the advantages.
  • This prevents liquid glycol for being carried out of the contactor and into the gas discharge line commonly referred to carryover.
Carryover Causes
  • Carryover occurs when glycol contamination causes foam buildup. 
  • Carryover also happens when gas rate is high enough to agitate the liquid on the top tray, so that a foam forms that is too thick for the eliminator to handle.
The gas rate must be reduced to eliminate carryover. 

Glycol Level Control
Glycol level control on the contactor is important and stabilizing unit operation.

The level controller should be adjusted to hold the uniform flow rate of glycol out of contactor. It is more important to hold the constant flow of a glycol out and let the glycol level in the contactor and let the glycol level in the contactor vary of few inches, and then hold the constant level in the contactor and let the flow out of fluctuate.
Causes of Flow Rate
Flow rate surges leaving the contactor will cause the re-boiler to operate inefficient and may overload.

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