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Injector/mixer holds the key to salt content removal

21st February 2013


Desalting is a crucial step for crude oil downstream refining processes, since both the free water and emulsified water contain salt, which can cause corrosion and catalyst fouling in the crude unit.

An injector/mixer desalting technology, the ProSalt Injector/Mixer, holds the key to effective salt content removal, efficient utilisation of wash water and chemicals, and improved crude-water separability.

The salt associated with crude production is contained within the produced water, so desalting involves dehydrating (eliminating the produced water), adding ‘fresh’ water, and dehydrating again. Meeting effluent criteria often requires multiple stages; thus, the mixing of the dilution water efficiently into the crude oil is a critical step (Fig.1).

Besides significantly reduced oil reporting to effluent water, ProSalt allows for increased treatment capacity and low installation costs, and thus high returns on investment. In these days of high-priced oil, there is also potential benefit in ‘bridging’ limitations in refinery capacity until plant managers can complete ‘turnaround’ activities to expand and/or to de-bottleneck facilities.

The ProSalt System replaces the conventional static mixer and mixing valve with an inline injector/mixer assembly. The device is the same size as a typical globe valve, making it suitable for both new and retrofit applications. ProSalt requires minimum maintenance, has a high turndown ratio, and provides unobstructed flow conditions while mixing production chemicals and dilution water used in desalting. The design features of the injector/mixer have demonstrated the ability to maintain desalter performance even with an associated reduction in pressure drop of 35percent or more.

The injector/ mixer system generates a homogenous phase flow over the pipe cross-section in combination with a pressure drop that is significantly lower than conventional mixing methods, while controlling shear forces to produce a more homogeneous droplet distribution. This uniform mixing achieves an improved oil/water separation, with less emulsion. This is true of both water-in-oil and oil-in-water emulsions and results in reduced retention time for separation of water from oil and of oil from water. The more efficient injector/mixer assembly is suitable for installation in any desalting system, whether single-, two- or three-staged.

ProSalt is a key process element for improving the separability of the crude-water mixture. Clearly, generating separable droplets with relatively narrow distribution is an attractive feature, as this permits lower separator residence time – resulting in higher production rates; reduced water-oil interface levels in the separator; and smaller quantities of demulsifying chemicals.

This injector/mixer assembly has demonstrated a wide range of benefits in desalting applications: more efficient desalting; reduced dilution water requirements; greater optimisation of pressure drop; better separability of oil and water, and; lower oil-in-water discharge from the desalter.

These benefits continue to be qualified and quantified through testing and implementation in a variety of operating conditions.

John B. Sabey, VP Business Development, ProSep Technologies Inc, Houston, TX, USA. www.prosep.com

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