Adsorption natural gas dehydration units on the base of solid adsorbent, such as silica gel, are used to reduce the moisture content of gas. During adsorption process molecules of water or other substances are condensed on the surface of adsorbent.
Method advantages:
- Low dew point of the dehydrated gas (down to -65°С).
- Simple adsorbent regeneration.
- Compact unit.
Adsorption unit has two or more adsorbents. Key difference between adsorption and absorption units is that the processes of adsorbent saturation and its regeneration are carried out cyclically and in the same unit. When adsorbent in the first adsorber reaches set moisture saturation, the flow of humid gas switches to the second adsorber, by this time adsorbent in the second adsorber is dried and cooled to the set temperature. First adsorber is under regeneration with subsequent cooling.
This is how adsorption units work in cycle.
Duration of adsorbent saturation, regeneration, and cooling is determined by the time that is required for its regeneration, it can be 4-16 hours, duration of saturation cycle 10-20 hours, cooling cycle is not always applied as adsorbent is relatively quickly cooled by the gas that enters dehydrating unit.
Humid gas goes through the separator and flows in the adsorber. While going through the silica gel, gas releases moisture and goes to the gas pipeline.
After certain period of time and depending on the load of solid adsorbent and gas flow rate, adsorber is switched to the regeneration. Gas is switched to the second adsorber that has already finished regeneration process. Silica gel is regenerated (dehydrated) by blowing hot gas through it. The process of silica gel regeneration is the following: right adsorber is switched to the regeneration of the silica gel. When adsorber starts up for regeneration, certain amount of gas, that is required to fill regeneration system, is removed from the dry gas line by the pressure control valve (with a pressure of slightly more than 1 kgf/cm2). This gas goes to the cooler and then to the separator. Under the pressure of not more than 300 mm H2O gas goes to the heater, where it is heated to the temperature of about 200°С, and then enters the adsorber, in which the silica gel is regenerated. At the exit from the adsorber heated saturated gas enters cooler and then the separator, where the moisture adsorbed in the adsorber is separated.
In the gas dehydration units silica gel with the activated carbon is used as the adsorber, which provides adsorption not only of the moisture, but also of higher hydrocarbons. Then these hydrocarbons condense and on the cooler and separate on the regeneration gas separation.
Innovative natural gas dehydration units also include forced cooling circuit with industrial cold-storage plants, which ensures the highest degree of extraction of moisture and higher hydrocarbons from the gas flow and eliminates the need to use methanol and other inhibitors. Innovative natural gas dehydration units also include adsorbers with inner insulation, which allows reducing external dimensions of the vessels and simplifying equipment operation due to the lack of need to repair external thermal insulation of the vessels.