Reconcentration, glycol

Poor glycol reconcentration (exit gas dew point is 5-15°F higher than dew point in equilibrium with lean glycol concentration)... 

The most obvious indication of a glycol dehydration malfunction is a high water content or dew point of the outgoing sales gas stream. In most cases, this is caused by an inadequate glycol circulation rate or by an insufficient reconcentration of the glycol. These two factors can be caused by a variety of contributing problems listed below. 

Most glycol dehydration processes are continuous. That is, gas and glycol flow continuously through a vessel (the contactor" or absorber ) where they come in contact and the glycol absorbs the water. The glycol flows from the contactor to a reboiler (sometimes called "reconcentrator or regenerator where the water is removed or stripped from the glycol and is then pumped back to the contactor to complete the cycle. 

The gas from the glycol/condensate separator can be used for fuel gas. In many small field gas packaged units this gas is routed directly to fire tubes in the reboiler, and provides the heat for reconcentrating the glycol. This se[>.irator is sometimes referred to as a gas/glycol separator or pump gas separator. 

If a very lean glycol is required, it may be necessary to use stripping gas. A small amount of wet natural gas can be taken from the fuel stream or contactor inlet stream and injected into the reboiler. The stripping gas can be taken from the fuel stream or the contactor inlet stream and injected into the reboiler. The leaness" of the gas depends on the purity of the wet glycol and the number of stages below the reconcentrator. The stripping gas is saturated with water at the inlet temperature and pressure conditions. but adsorbs water at the reboiler conditions of atmospheric pres-... 

Diethylene glycol—High vapor pressure leads to high los.ses in contactor. Low decomposition temperature requires low reconcentrator temperature (315 F to 340°F) and thus cannot get pure enough toi most applications. 

I riethylene glycol—Most common. Reconcentrate at 340 F to 4()0°F for high purity. At contactor temperatures in excess ot 1 2(1 F tends to have high vapor Ilis.scs to gas. Dew point depressions up to 150 F are possible with stripping gas. 

Tetraethylene glycol—More expensive than triethylene but less losses at high gas contact temperatures. Reconcentrate at 400°F to 430°F. 

The degree of dehydration that can be attained with a glycol solution is primarily dependent on the extent to which water is removed from the solution in the reconcentrator. The operation of atmospheric pressure distillation units for water removal is limited by the maximum temperature that can be tolerated without excessive decomposition of the glycol (about 400°F for TEG). Concentration of TEG to 98.5 to 99.0% is attainable in a simple atmospheric pressure still. When significantly higher concentrations are needed to meet stringent gas dehydration requirements, the use of an enhanced stripping technique is necessary. 

Stahl, W., 1963, Method and System for Reconcentrating Ethylene Glycols, U.S. Patent 3,105,748, October. 

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