Natural Gas Drying
Differences Between Glycol Treatment and Desiccant Treatment
Water removal from a natural gas stream (drying) is an important step in processing natural gas, it prevents corrosion in pipelines and also prevents plugging of pipelines by removing free water and hydrates. Natural gas drying is preceded by the removal of oil and condensate from the natural gas stream. Currently there are two common processes which see to the removal of water from gas streams: glycol treatment and desiccant treatment.
Glycol treatment primarily uses triethylene glycol , diethylene glycol, or tetraethylene glycol to adsorb and remove the water from the natural gas stream. Glycol will adsorb water from liquid gas streams in a dehydrator. As glycol adsorbs water it becomes heavier and sinks to the bottom of the dehydrator. After the glycol has adsorbed the water it is boiled out of the dehydrator leaving behind liquid natural gas.
Desiccant dehydration requires the use of adsorption towers, which contain desiccant usually molecular sieve, activated alumina, or silica gel. Wet natural gas is passed through the top of the tower which contains thousands of pounds of sieve or alumina beads and by the time it reaches the bottom of the tower the water will be removed from the gas stream. Multiple adsorption towers are used during this process to allow over saturated desiccant to be regenerated. In other words while one tower has gas running through it another tower is regenerating the previously used (and now over-saturated) desiccant.
The advantage of using dry desiccants is their ability to adsorb and reduce the water from natural gas streams to lower concentrations than glycol. Pipelines require that water content in gas streams not exceed 7lb/MMSCF (million standard cubic feet) and dry desiccants can achieve this level easily (up to 2lb/MMSCF). Glycol dehydrators can achieve this level but usually at the bare minimum and sometimes they don’t make the requirement and have to go through the treatment process again. Although glycol treatment is more popular right now, dry desiccants appear to be more effective at drying natural gas.