A higher temperature in the top of the still column can increase glycol losses due to excessive vaporization. The boiling point of water is 212°F and the boiling point of TEG is 546°R The recommended temperature in the top of the still column is approximately 225°F. When the temperature exceeds 250°F the glycol vaporization losses… Read More »
When the number of absorber trays and lean glycol concentration are fixed, the dew-point depression of a saturated gas is a function of the glycol circulation rate. The more glycol that comes in contact with the gas, the more water vapor is stripped out of the gas. Whereas the glycol concentration mainly affects the dew… Read More »
The lean glycol concentration leaving the reboiler can be lowered by contacting the glycol with stripping gas. Often, wet gas that is saturated with water vapor at ambient temperature and 25 to 100 psig is used. At 25 psig and 100°F this gas is saturated with 1,500 Ib/MMscf of water vapor. At atmospheric pressure and… Read More »
Pressures above atmospheric in the reboiler can significantly reduce lean glycol concentration and dehydration efficiency. The still column should be adequately vented and the packing replaced periodically to prevent excess back pressure on the reboiler. At pressures below atmospheric the boiling temperature of the rich glycol/water mixture decreases, and a greater lean glycol concentration is… Read More »
The reboiler temperature controls the concentration of the water in the lean glycol. The higher the temperature the higher the concentration, as shown in Figure 8-11. Reboiler temperatures for triethylene glycol are limited to 400°F, which limits the maximum lean glycol concentration without stripping gas. It is good practice to limit reboiler temperatures to between… Read More »
The higher the concentration of the lean glycol the greater the dewpoint depression for a given glycol circulation rate and number of trays. Figure 8-9 shows the equilibrium water dew point at different temperatures for gases in contact with various concentrations of glycol. At 100°F contact temperature there is an equilibrium water dew point of… Read More »
The temperature of the lean glycol entering the contactor has an effect on the gas dew-point depression and should be held low to minimize required circulation rate. High glycol losses to the gas exiting the contactor may occur when the lean glycol temperature gets too hot. On the other hand, the lean glycol temperature should… Read More »
The glycol and the gas do not reach equilibrium on each tray. A tray efficiency of 25% is commonly used for design. That is, if one theoretical equilibrium tray is needed, four actual trays are specified. In bubble cap towers, tray spacing is normally 24 in. The more trays the greater the dew-point depression for… Read More »
Contactor pressures have little effect on the glycol absorption process as long as the pressures remain below 3,000 psig. At a constant temperature the water content of the inlet gas decreases with increasing pressure, thus less water must be removed if the gas is dehydrated at a higher pressure. In addition, a smaller contactor can… Read More »
At constant pressure, the water content of the inlet gas increases as the inlet gas temperature increases. For example, at 1,000 psia and 80°F gas holds about 34 Ib/MMscf, while at 1,000 psia and 120°F it will hold about 104 Ib/MMscf. At the higher temperature, the glycol will have to remove over three times as… Read More »