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Cleanable Solids Processing Equipment and Systems 265
FIGURE 8 Pharmaceutical CIPable baghouse. Source: Courtesy of MikroPul, Inc.
Cartridges filter elements (Fig. 9) are more robust and cleanable than the
traditional cloth elements.
An element is spun around ametal frame and the filter surface is pleated to
increase surface area. The cartridge element has excellent strength and most are a
one-piece design. Cartridges come in avariety of material but most pharmaceutical
applications would use polytetrafluoroethylene or Teflon w (Fig. 10). The cartridge
design offers excellent powder recovery and, in some cases, is cleanable in place
with cleaning chemicals without filter removal. The cost is more than that of the
fabric elements.
Stainless steel sintered metal filter technology has been used in military and
nuclear applications for many years. The use of sintered metal filters for pharmaceutical
applications is relatively new. Stainless filters have been developed to
address issues with conventional fabric and Teflon cartridges. Conventional fabric
filters cannot be cleaned while in the baghouse. Even newer Teflon cartridge
filters, which can be cleaned in the place without removal, usually have their
problem areas. Cartridge filters are also mechanically delicate and have short
service lives.
Stainless steel filter elements by contrast have a number of advantages.
During cleaning operations, the stainless steel filters do not need to be removed
to clean. CIP cleaning chemicals are not reactive with the stainless metal of the
filters. Additional advantages include the ability to clean the baghouse and ensure
total containment for operator and product protection (Figs. 11 and 12).