Improving Process Operations with a Rotary Pressure Filter
By Barry Perlmutter
A plant was experiencing high solvent usage and excessive volatile organic compound (VOC) emissions in the manufacture of a specialty chemical. In addition, off-specification product quality resulted from poor cake washing because the original solvent could not be displaced efficiently. Long drying times and production bottlenecks were typical because of the extremely high final solvent content of the wet cake discharged from the conventional open-vacuum filter equipment.
Plant engineering and development personnel evaluated the feasibility of using a rotary pressure filter to improve product quality and increase production rates while adhering to environmental regulations (the filter tested at the specialty chemical plant was the FEST rotary pressure filter) . Figure 1. A rotary filter with an enclosed and pressurized control head.
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Rotary pressure filter
The rotary pressure filter discussed in this article is a continuous-pressure filter for thin-cake filtration with cake depths from 6 millimeters (mm) to 150 mm (Fig. 1). The slowly rotating drum — 6 revolutions per hour (rph) to 60 rph — is divided into segments, called cells, each with its own filter media (synthetic cloth or a single- or multilayer metal) and an outlet for filtrate or gas. The outlet is manifolded internally to a service/control head, allowing each stream to be directed to a specific plant piping scheme or a collection tank. The mother liquor can remain separate from the subsequent washing liquids.
The feed suspension enters each cell under constant pressure to form a filter cake. Internal divisions of the housing permit cake processing in separate zones. Each zone can operate under different pressures, depending upon the cake compressibility at each stage.