BAKER HUGHES - Drilling Fluids Reference Manual

FLUIDS ENVIRONMENTAL SERVICES
A typical 1000 sq ft filter press uses approximately 85 kg of D.E. to produce a 3mm pre-coat on the
internal screens. To ensure that the pre-coat solids form a uniform cake on the plate screens, the filter
press is circulated with diluted pre-coat slurry before introducing the balance of the diatomaceous
earth pre-coat solids. The slurry mix tank will circulate to “clear” at the end of the pre-coat cycle
indicating that all of the diatomaceous earth pre-coat solids have been captured on the filter plate
screens.
Body Feed
The filtration of slurries which contain gelatinous, slimy, and/or compressible solids typically results
in poor filter performance; e.g. low flow rates, short cycle times, high operating pressures and low
filter efficiency. The addition of non-compressible solids (Diatomaceous Earth) to the inlet slurry
being filtered can cancel or significantly reduce these undesirable effects and improve the
performance level of the filtration operation. A body-feed therefore can be defined as the solids
which are added to process slurry for the purpose of enhancing the filterability of the slurry. The
addition of body-feed will change the physical characteristics of the cake solids by increasing its
permeability (reducing the resistance). The amount of body-feed required cannot be accurately
predicted due to the many variables involved. A good starting point is to use a 1:1 ratio of body feed
solids to suspended solids in the feed and then adjust the injection rate of the body feed so as to obtain
the optimum performance which:
• Minimizes the initial filter differential pressure.
• Prevents a rapid increase in the rate of differential pressure.
• Prevents terminal differential pressure until the filter press plate recesses are fully utilized.
• Slimy, gelatinous and highly compressible solids (barite and clay) typically require higher
body-feed addition rates to effect cake permeability.
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 14-56