Conceptual Design of Mercury Removal Systems for
Hydrocarbon Liquids in Gas Processing Facilities

Wilhelm, S. M., "Conceptual Design of Mercury Removal Systems for
Hydrocarbon Liquids", Hydrocarbon Processing, April (1999).

ABSTRACT

Mercury removal systems for hydrocarbon liquids in primary gas processing facilities are used to reduce the concentration of mercury and mercury compounds in liquid products (C3, C4, C5+) to very low levels (less than 0.1 ppb). Projects to design and install such systems represent a major capital investment and it is useful to have a thorough review and documentation of all design considerations prior to embarking on the detailed design effort. Several mercury removal systems for liquids are commercially available but performance is sometimes difficult to predict because very few commercial applications have been documented. It is essential to eliminate mercury from plant products because they are used as feeds to numerous types of chemical manufacturing plants where mercury has a pronounced negative impact on equipment and catalysts. Because of the detrimental influence of mercury and mercury compounds on downstream consumers, many gas plants are finding it necessary to retrofit existing plants with mercury removal systems for liquids in addition to those that may be present for gas.

To design a mercury removal system to a given set of criteria for mercury concentration in plant products, it is essential to understand the concentrations, distribution and mobility of mercury and organic mercury compounds in the existing process. Computer models can be used to predict mercury distribution in the plant process. The concentration of mercury in plant feeds and products must be known to a high degree of accuracy to verify model predictions. Likewise, assessment of mercury removal system performance requires extremely accurate chemical analysis capabilities for both elemental and organic mercury compounds in a liquid hydrocarbon matrix.

Several possible process locations should be critically examined for suitability for mercury removal systems. Commonly considered process locations for liquids include the main liquid feeds to the plant (or train), the existing dehydrators and treaters, the overheads of the debutanizers and depropanizers and the common product (propane, butane, condensate) lines from the plant.

The conceptual design exercise examines process locations for mercury removal systems and compares them with consideration of technical and practical limitations. Removal system chemistry is examined for its ability to work effectively for the hydrocarbon feed at candidate process locations, for its capacity (bed life) and for its ability to function in the presence of contaminants. Pilot plant data are useful, if not essential, to making sound decisions. Economic considerations include the cost of equipment, the replacement cost of the sorbent and the plant maintenance costs associated with mercury waste generated in conjunction with the removal system and sludge (containing mercury) which accumulates in equipment located upstream of the mercury removal system.



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