The IFPEXOL process in natural gas dehydration

I was on Encana Cutbank Ridge Project in 2015. It had  3 Sweet Gas Plants at the moment, located in Dawson Creek, BC. As of sweet gas processing, dehydration is the most essential part. Dehydration means extracting water vapor from the gas to a specified maximum limit for residual water content.

There are various processes available for dehydration, such as:

·       absorption with glycol
·       adsorption with dry desiccant
·       absorption with a deliquescent salt
·       refrigeration and hydrate suppression with a chemical

 

The greater used dehydrant is glycol. By using glycol to prevent hydrates from forming in the refrigeration process, a glycol regeneration process step must be incorporated to the overall equipment scheme. On Encana Cutbank Ridge Project, a relatively innovative process called IFPEXOL was applied. That means the additional capital and operating cost burden to the refrigeration process were saved.

 

 Schematic drawing of typical IFPEXOL dewpoint control process

From the figure we can see, in the IFPEXOL process, the prevention of hydrates in the heat exchanger and chiller is achieved by the addition of methanol to the natural gas stream being cooled.

The inlet gas stream is split into two streams. One portion of the inlet stream is contacted counter-currently with the rich methanol-water solution pumped to a small contactor from the cold separator. Because the gas stream is already saturated with water, it does not pick up any additional water. However, it contains no methanol at the inlet to this contactor. As the gas is in intimate contact with the methanol/water solution, most of the methanol leaves the water and enters the relatively warm hydrocarbon gas phase. This conserves most of the injected methanol. This gas stream joins the other stream before entering the gas/gas heat exchanger. Additional methanol is injected into this stream as required to depress the hydrate temperature of the process gas in the chiller to the boiling temperature of the propane. Because the methanol is contained in the vapor phase, the distribution of liquid methanol onto the tube sheet is not important, as is the case with glycol injection. As the gas cools inside the heat exchanger and chiller tubes, methanol condenses with the water and prevents the formation of hydrates.