23 JULY 2003
OPERATION AND MAINTENANCE. This paragraph summarizes typical
operation and maintenance requirements for plate and frame filter press systems. In
addition, a summary of common operational problems and associated remedial
measures or process interferences is presented.
Process Interferences. Design or operational shortcomings can create
process interferences. Although these interferences do not occur frequently, this
paragraph provides a discussion of the most common ones, resultant problems, and
potential solutions. Process interferences for filter presses can be categorized into the
following areas of concern: equipment quality problems, operational problems and
concerns, process integration, and auxiliary system selection. A summary of the most
common design and operational shortcomings and potential remedial measures is
presented in Table 2-9.
2-9.1.1 Equipment Quality Problems. Major equipment problems include plate
2-126.96.36.199 Plate Deflection. Plate deflection can be caused by several factors, including
high differential pressure across the filter plates, residual sludge buildup on plates, and
uneven sludge distribution and cake formation. To reduce the high pressure across the
filter plates, the operating pressures may be reduced to lower sludge filling pressure
(i.e., 690 kPa [100 psi]). Although some applications require higher pressures to
achieve desired dewatering results (i.e., 1550 kPa [225 psi]), most do not. For example,
a lower pressure unit (i.e., 690 kPa [100 psi]) may give the same results as a higher
pressure unit (i.e., 1550 kPa [225 psi]) for a non-compressible sludge, such as metals
hydroxide sludge. A more detailed explanation of appropriate pressure applications is
further given in Tables 2-4 and 2-5. To reduce sludge buildup on plates, they should be
washed more frequently. Remedial measures for uneven sludge distribution and cake
formation are described in Subparagraph 2-188.8.131.52.
Plate deflection problems are more common with polypropylene than cast iron
plates. For example, the life expectancy of a polypropylene plate that is larger than 48
inches square is approximately 5 to 7 years as compared with ductile iron plates, which
have been known to be in operation more than 35 years without breaking (EPA 1986).
2-184.108.40.206 Filter Cloth Wear. Wear of filter media in areas around the stay bosses and
the perimeter of the plates is a frequent problem. As described previously, stay bosses
are raised areas on the filter plate that provide additional support and reduce the
potential of deflection. As the pressure increases during the filter cycle, these stay
bosses and perimeter areas of the plate press against one another. However, during
this process, minor deflection may occur that causes a rubbing action and excessive
wear to the filter media.