That is particularly true for a walnut shell filter. Walnut shell filters are frequently
installed for the removal of oil and suspended solids from produced water, refinery
effluent and waste / re-circulation streams found at other industrial applications.
An optimum media cleaning system guarantees effective removal of the contaminants
collected in the filter media and consequently, consistent high flow rates. Particularly
with oil field produced water applications, where solids and heavy oil may clump
together, forming so called mud balls, effective bed clean up is essential to prevent
Effective cleaning will prevent channeling. Channeling is causing raw unfiltered
water to pass the filter bed, contaminating the filtered water stream.
And a partly blinded bed will increase the flow in the surrounding area causing excessive
high flow rates, reduced dirt holding capacity, shorter cycle lengths and increased
The internally installed scrubbersystem will effectively remove the contaminants
from the walnut shell filter media with a minimum of degradation or media loss. Raw
water is used for effective removal of the suspended solids and hydrocarbons.
During filtration, raw water does enter at the top of the filter and is evenly distributed
over the entire media bed by means of an inlet distribution system. This header system
doubles as a separator header during the backwash cycle. In general, a filter cycle
is interrupted for a back wash cleaning step after 24 hours.
In order to fluidize the filter media during backwash, the directionof flow is reversed,
and raw water is fed to the filter via the outlet header system. For removal of
the contaminants, the media circulates via the internally installed media scrubber
where high shear effectively separates the oil and solids from the filter media.
A separate centrifugal pump is installed to efficiently power the media scrubber.
All the filter media makes multiple passes through the scrubber. Simultaneously the
contaminants are removed from the filter via the separator header. A complete backwash
cycle takes less than 20 minutes.