Mar-2006

Hydrocarbon removal from amines demonstrated experience

Bringing amine system contaminants down to low levels has reduced operational problems. Several large operating facilities are now using the latest technology from MPR Services, Inc for the removal of hydrocarbons from their amine systems.

Gary L Lawson and Arthur L Cummings MPR Services

Article Summary

These HCX units have been installed and operating from six months to over five years. The measured results show that the new technology maintains a hydrocarbon content of less than 10 ppm (the maintenance level) when the amine system is experiencing normal hydrocarbon incursion and a recovery period (return to maintenance level) of less than 30 days after a major operating system upset (large, single-event hydrocarbon incursion). Prior to installation of HCX, the amine systems had continuous hydrocarbon levels of 200 ppm to 6000 ppm (at which point foaming created a purging of the system by amine carry-over, with new amine then being introduced).

The amine removal media is fully regenerable using hot water (steam condensate) and is PLC or timer controlled for automatic switching between the absorption period, the rinse (amine displacement) step and the hot water regeneration step. The removal media life is exceeding three years before replacement is required.

The demonstrated results after several years of operating experience show that maintaining a continuously low level of hydrocarbons reduces foaming, reduces amine losses, improves amine system performance and reliability, and greatly reduces carbon filter change-outs and the associated maintenance labour and solid waste disposal.

Introduction
Hydrocarbons are second only to heat stable salts as a major contaminant in amine systems. If there is a steady incursion and accumulation of hydrocarbons in the amine-treating solution, then ultimately the amine solution will begin to foam. Foaming in turn leads to amine loss through carry- over and reduced amine system performance. The MPR HCX Hydrocarbon Removal Process has now been installed and operating in four major refineries for periods ranging from several months to several years. These units produce a continuously clean amine solution containing less than 10 ppm of hydrocarbons. The important result is that the stability and performance of these amine systems has been greatly improved with much lower loss of amine.

General operations
The performance numbers presented in Table I above are maintained by periodic regeneration of the HCX hydrocarbon removal beds. Regeneration occurs typically once per week when operating at the maintenance level and once per day during those periods when recovering from a massive instantaneous influx of hydrocarbons.

The hydrocarbons are removed from the absorption media by flushing with hot water (typically steam condensate). The oil-water mixture is routed to the oily water sewer, an API separator, or a slop tank. There is a rinse step (for amine displacement) between the amine absorption and the hot water regeneration, which reduces the amine lost to the oily water to less than 500 ppm. The rinse water is returned to the amine system, thus reducing the normal water make-up requirement.

The hydrocarbon removal capacity of the HCX absorption media is approximately 17 times the equivalent volume of charcoal. Full absorption capacity is regained upon each regeneration. The actual lifetime of the media in the operating plants has been over three years.

Slipstream operation
Full flow is not required. The above units are installed and operating on a 5% to 15% slipstream taken from the cool lean amine solution prior to it entering the amine contactor. This smaller flow reduces equipment size and cost, but will still effectively remove the contained hydrocarbons. In a typical operation mode, the slipstream flow will turnover the amine system volume approximately once per day. The daily treatment of the entire amine system volume will remove the typical daily incursion of hydrocarbons and maintain less than 10 ppm in the entire system.

But, what about the periodic incursion that occurs from an operating upset that dumps many gallons of hydrocarbons into the amine system and floods the amine flash drum? This is actually handled by the amine system carrying capacity for hydrocarbons, if the amine is routinely kept clean. Most amine systems currently operate with some contained hydrocarbon (anywhere from a hundred to several thousand ppm). If an amine system has minimal initial hydrocarbon content, it is well positioned to absorb the shock of an instantaneous influx of hydrocarbons. While there is a quantity of hydrocarbons that can overwhelm any system, there is a large potential carrying capacity in a clean system that will handle upsets that would normally destabilise an amine system already containing significant amount of hydrocarbons. For example, a 100 000-gallon amine system carrying 3000 ppm of hydrocarbon would have 440 gallons of dispersed and/or dissolved hydrocarbons. If this system contained essentially no hydrocarbons, then an upset that results in less than 440 gallons of hydrocarbons passing through the flash drum and into the amine system will be much less likely to become unstable.