(181c) A Novel Deethanizer Design at Elevated Operating Pressure without Dehydration

In order to produce high purity ethane and to prevent hydrate formation with a wet NGL feed, a novel deethanizer design has been developed.  Formations of hydrates, which are crystalline solids composed of water and light hydrocarbon molecules, can result in issues with operation and safety.  If a high purity ethane is to be produced, the deethanizer condenser and the top tray temperatures may be lower than the hydrate point.  This may cause hydrate formation at these locations if the wet NGL is not dehydrated.

Conventional methods to prevent hydrate formation include removing the content water in a glycol or a dry desiccant dehydration unit.  Either way requires a complicated dehydration system.  This paper discusses a design method to eliminate the requirement of a dehydration unit.  The deethanizer condenser temperature increases rapidly while the hydrate formation temperature increases slowly with the pressure.  Using these characteristics, a high purity ethane can be obtained by increasing the deethanizer pressure without doing dehydration.

Although the cost of a high pressure deethanizer will be higher, the savings on eliminating the dehydration system and reducing the refrigerant compression can compensate for this loss.  The CAPEX and OPEX of both methods have no significant difference.  The major benefit of the method without dehydration is its operational simplicity.  The pros and cons and the limitations of this approach will be discussed in detail in this paper.  This method has been successfully used commercially.