Saud H. Al-Mudaibegh
Saudi Aramco
Dhahran
| Based on a presentation to 19th Annual Technical Conference of the GCC Chapter of the Gas Processors Association, May 4, 2011, Kuwait. |
Testing of an amine-regeneration technology at two natural gas processing plants owned and operated by Saudi Aramco revealed an improvement in amine performance and quality.
Performance of an amine solution in gas plants is reduced mainly by accumulation of such contaminants as suspended solids, hydrocarbon liquids, and degradation products.
Results of tests of the Amine Shield slipstream unit in the Aramco plants showed that suspended solids-removal rate across the unit reached up to 90%. In addition, the total amine system solids content dropped by more than 80% at one plant. Such treatment will reduce contaminants and hence decrease problems related to foaming and fouling in the system.
The Amine Shield slipstream technology, developed by MPR Services Inc., Dickinson, Tex., employs a multifunctional unit that removes solids, hydrocarbons, and heat-stable salts from an amine system.
Several amine-treating units at Saudi Aramco's gas plants experience amine losses, poor quality amine, and foaming. Antifoam is injected continuously at many units, and the current conventional solution filtration systems (precoat filter) are inefficient.
The test was implemented in the Hawiyah and Uthmaniyah gas plants
Amine losses
Gas treating units that use amine and glycol solvents encounter a variety of operational problems. Most are caused or aggravated by the presence of such contaminants as degradation products, solids, and hydrocarbon that accumulate in the system.
These contaminants are produced within the system by corrosion or erosion or introduced into the system with the feed gas. Contaminated amine or glycol solutions degrade solvent performance and lead to foaming, solvent losses, and equipment fouling.
Overcoming these operational issues requires several measures. These include antifoam injection, fresh solvent addition, and installation of conventional mechanical solution filters on a slipstream for continuous cleaning. In many systems, these methods are ineffective and do not represent the optimum solution and the solvent remains contaminated.
Amine losses are generally categorized by the following:
• Entrainment. This is physical carryover that is largely related to column hydraulics, foaming, and contaminants in amine solvent.
• Mechanical. These losses result from equipment and piping leaks, filter changeout, and drainage.
• Vaporization. These losses result from the equilibrium vapor pressure of the amine in the solution varying with operating conditions. Normally the actual losses due to vaporization are less than equilibrium losses because amine treating units operate lower than full equilibrium.
• Degradation. Some amines, specifically diglycol amine (DGA) go through different reactions with different components in a sour-gas stream, such as CO2 and COS, and as a result produce degraded products.
• Solubility in hydrocarbon liquid (in liquid-treating units). Such losses resemble vaporization in which amines establish equilibrium with the liquid hydrocarbon.
Typical losses in amine treating units range 0.5-3.0 lb/MMscf of treated gas. Saudi Aramco's gas plants consume more than 900,000 gal/year of DGA as solution make-up to compensate for losses.
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