It is critical to minimize the amount of free hydrocarbon entrained in the aqueous phase (i.e., Produced Water or Rich Monoethylene Glycol (MEG) streams) in order to mitigate impact on the operational performance of the Effluent Water Treatment and MEG Recovery Unit facilities. Hydrocarbon entrainment in Produced Water or Rich MEG is often the result of process conditions that favour emulsion formation and/or hinder emulsion separation. Consequently there is a need to look at the process and equipment design employed, along the flow path that the hydrocarbon/aqueous phase travels through, prior to entering the separation equipment used for hydrocarbon removal from the aqueous phase, as well as the separation equipment itself.
The paper will present a roadmap of the overall route that the aqueous stream can take to offer insight into the process units affected by improper hydrocarbon removal. Operational situations arising from the impact of excessive hydrocarbon entrainment will be given as well as a summary of wellhead operating parameters that need to be considered in terms of their impact on equipment selection/design.
The flow path, to be focused on, starts at the reservoir/wellhead and ends where the aqueous stream leaves the final hydrocarbon removal equipment, just upstream of either the Effluent Water Treatment or MEG Recovery Unit facilities.
Factors concerning emulsion formation and separation are introduced as required to describe how process fluid properties and flow conditions influence the formation of emulsions and the separation of hydrocarbons from the aqueous phase.
How to improve on existing methods for the selection/design of liquid-liquid separators by considering and trying to estimate the entire droplet size distribution (DSD) of the dispersed phase in the stream entering the separation equipment, along with estimating the amount of coalescence, will be elaborated on. This is paramount to ensure the correct equipment is selected, especially when the low end of the distribution, particularly drops below 20 μm, can be quite difficult to remove.
Design considerations to minimize hydrocarbon content in the aqueous phase will be discussed and involve looking at key areas of energy dissipation (e.g., choke and control valves) regarding the range of fluid properties and process conditions, and the estimation/influence of drop size distribution/fractional interface coalescence efficiency (fICE) on the selection/sizing of fluid-fluid separator technology.
Examples of dealing with emulsion issues occurring in industry, as per vendor experience, will be presented as well as available vendor equipment technology. General recommendations concerning lab bench testing, modelling, and equipment/chemical vendor testing will also be discussed.