Nutshell Filters (or Walnut Shell Filters) are typically used for the removal of fine oil droplets and suspended solids from contaminated water streams. The AIES Nutshell Filter is a down flow, deep bed media filter consisting of a blend of walnut and/orpecan graded shells. In all cases the nutshell filter serves as the tertiary treatment of choice to reduce oil and solids concentration to low levels to meet disposal requirements or have the produced water ready for well re-injection.
Principle of Operation
In the filtration mode, the Nut Shell Filter acts as a down flow filter. Contaminated water is introduced through a header that provides even flow distribution across the media bed. The influent flows down through the media bed and exits the filter through a wedge wire support screen at the base of the vessel.
Produced water enters the top of the filter, through the influent feed line. The water then flows down through the nutshell media. Suspended solids are trapped in the voidage between media grains while surface chemistry dictates the attraction of oil onto the media. As fine oil droplets and solids are removed from the influent stream, the differential pressure across the filter increases until it reaches a predetermined level causing the filter backwash cycle to commence.
During the backwash sequence, the flow direction is reversed and the media bed is fluidised. An integral recirculator located on top of the vessel is activated and circulates the media through an internal scrubber. This wedge wire screen allows contaminates to pass through and out of the vessel while retaining the nutshell media. Dirty backwash water exits out the bottom of the vessel through the backwash line.
Once cleaned, the media is allowed to gravity settle and is ready for the next filtration sequence.
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The AIES nutshell filter is designed to backwash the nutshell media once every 24 hours or when the differential pressure across the bed reaches a set point. During the backwash process, waste water is generated. This waste water will contain fine oil droplets and solid particles that could not be removed through conventional technologies and is usually sent to evaporation ponds or effluent treatment plants. As an alternative, AIES can offer further treatments by using ceramic membranes. Here, the backwash water is sent to a holding tank and then filtered through the ceramic membranes. Oil and solids are concentrated and the waste volume is reduced to less than 5% of the original volume. The AIES ceramic membranes include Cleaning In Place (CIP) and automatic backflush sequence.
Since the backwash process occurs once per day the ceramic membranes can treat the backwash water volume between cycles at a much lower flowrate than the backwash flowrate. This results in small ceramic membranes packages being required and thus reduces cost, footprint and maintenance.