Overview

Over the past 20 years, the hydrocyclone has become the primary treatment mechanism for free oil removal from oilfield produced water. Rising levels of environmental concern however have led to the need to meet increasingly arduous discharge limits, such that new complementary technologies must be used to supplement the hydrocyclone's performance and reduce not only the free oil levels in discharge waters but also engage the problem of dissolved hydrocarbon content. Some of these secondary systems are introduced and described here, the objective being to provide a whole system approach to meet the needs of both the oilfield operator and the environment.

In all of these systems, Alderley's objective is to provide comprehensive process and mechanical support, coupled with extensive project management capability and experience, to deliver a fully integrated package on time and on budget that exceeds client expectations - an approach which has repeatedly satisfied clients the world over for 40 years.

Technologies Available

For most production facilities and where water is to be reinjected, a secondary polishing stage provides final cleaning of the naturally dispersed oil in a residence time based process, whereas single cell Compact Flotation Units and Induced Gas Flotation units provide a more efficient flotation of the oil by gas injection for skimming at the water surface.

Degassers
Two or Four Cell IGF's - for use where enhanced performance is required e.g. for re-injection or in order to meet tight environmental restrictions.
Compact Flotation Units (CFU)

Photos

Degassers

The degasser uses the gas breakout from the reduction is pressure of the produced water entering the vessel to float oil to the surface of the liquid. Liquid enters the vessel through the bottom entry nozzel. The liquid slowly passes from one end of the vessel to the other and is removed through a low level outlet nozzel. As it passes through, sufficient residence time must be given to allow all the gas to be released from the water (typically around 120 seconds).

Oil droplets are attracted to the gas bubbles and agglomerate at the water/gas interface, floating to the surface of the water to form a very thin layer, which is removed by overflowing through a weir at the opposite end of the vessel. The oily water removal rate is controlled with the use of V-notch weirs which overflow a nominal 5% of inflowing water to the oil collection compartment.

Induced Gas Flotation (IGF) Systems

The IGF vessels operate using a flotation process whereby fine gas bubbles are introduced in the stream of oily water. These bubbles will lift the oil globules, together, with any suspended particles towards the liquid surface forming a 'froth' on the water surface which is removed on a continuous basis, overflowing the weir into the oil water reject compartment. This process combined with a controlled residence time system in each cell of the vessel creates a very efficient secondary polishing stage in the produced water treatment system.

The operation and efficiency of the IGF can be further improved with the addition of chemicals to encourage flocculation and to break emulsions. The necessity for these chemicals can only be determined during the detailed design stage.

Compact Flotation Units (CFU)

Where maximum polishing performance is required together with a compact footprint, compact flotation technology can be used. Please contact us for more information.

For more information on our degasser or flotation technologies, or if you have specific system requirements not listed, please contact us. We have other technologies/processes/systems available under confidentiality agreements which cannot be openly promoted at this time.