Regeneration of Triethylene Glycol

SOLUTION The contact time is the time required for a bubble to rise one diameter. 

The low flux mass transfer coefficient may now be calculated from Eq. 9.2.11 as k = lyjD/rrtg 

The molar flux at the interface follows from the bootstrap solution (Eqs. 7.2.18) 

The mass transfer rate factor is obtained from Eq. 9.2.14 as 

The molar fluxes are calculated as before with the results 

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Figure 9.5. Schematic diagram of the froth on a distillation tray used for regeneration of triethylene glycol. Inset shows composition profiles in the liquid phase.

Estimate the composition of the vapor above the froth on a tray in a column for the regeneration of triethylene glycol(2) (TEG) from a mixture with water(l) under the following conditions ... 

Example 13.2.2 Point Efficiency for the Regeneration of Triethylene Glycol... 

In addition to close cycle absorption cooling, open cycles are of potential interest. Desiccants can be used to absorb water vapor from room air, which then can be evaporatively cooled. The desiccant is regenerated and recycled, LOf has suggested the use of triethylene glycol as a desiccant, with solar-hcatcd air for regeneration. Lithium chloride also has been proposed as a desiccant. 

If the gas is to be compressed andiransported by sub-sea pipe line, then it may be necessary to remove carbon dioxide. If only a few per cent is present it is cheaper to transport the unwanted gas and remove it on-shore than to remove it off-shore. If, as with one North Sea field, the amount is 20 per cent, then removal off-shore is undertaken. The absorption process uses monoethanolamine and is basically the same as that on an ammonia plant. Absorption can also be used to remove water, and the re-usable absorbent which is cycled between absorption tower and regenerator is triethylene glycol. Water removal limits corrosion damage and prevents the formation of solid hydrocarbon hydrates which can plug gas lines. 

A typical triethylene glycol (TEG) dehydration unit is made up of two main components. The absorber, often known in the industry as the glycol "contactor" and the regenerator, is normally based on direct fired reboiling. The feed gas enters the bottom of the contactor and travels upward. The glycol enters the top of the tower and travels down. Thus dry gas leaves the top of the contactor and rich glycol (containing more water) leaves the bottom. 

In gas dehydration service, triethylene glycol (TEG) will absorb limited quantities of BTEX from the gas. Based on literature data, predicted absorption levels for BTEX components vary from 5-10% for benzene to 20-30% for ethylbenzene and xylene [2]. Absorption is fa vored at lower temperatures, increasing TEG concentration and circulation rate. The bulk of absorbed BTEX is separated from the glycol in the regeneration unit and leaves the system in the regenerator overhead stream. 

Figures 11-18 and 11-19 are useful for the design of regenerators. The vertical lines drawn at 340 F for diethylene glycol and 375 F for triethylene glycol represent approximate...

For the case shown in Figure 11-32, it is assumed that a natural gas stream is saturated with water at SOO psia and 90°F and that it is desired to dehydrate this gas to a water content of 10 Ib/MMscf (dew point 28°F). With triethylene glycol a concentration of 98.5% can readily be attained with simple atmospheric pressure regeneration. The dew-point chart. Figure 11-15, shows an equilibrium dew point of about I5°F for this glycol concentration, equivalent to a 13°F approach at the top of the column. 

In general, where a simple triethylene glycol unit (atmospheric-pressure regeneration) is applicable, it is more economical from both an initial and operating-cost standpoint than a typical di7-desiccani. system. A comparison of approximate equipment costs for natural-gas dehy-... 

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