Replacing Filter Presses and Manual Plate Filters for Removing Trace Solids from Chemical Slurries with Thin-Cake Candle Filter Technology

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Source: BHS-Sonthofen Inc.

Abstract: The BHS technologies of Vertical Candle Filters provide improved product quality with more efficient operations compared with filter presses and manual plate filters. Fully automatic operations provide for complete containment of the solids and liquids for reduced maintenance costs and overall project savings.

Introduction
As ihe chemical industry has changed and grown since the mid-1980*s, there are increasing concerns about the safe handling of solids and slurries. To meet these requirements, with less operator interaction, the industry's need for new technologies has expanded.

One area of importance is now the efficient removal of activated carbon, metal catalysts and trace insolubles, such as dialomaceous earth, from slurries. Currently, most slurries are clarified with the use of filter presses and manual plate fillers, bag fillers, cartridge filters and other conventional filler equipment or, in some cases, a combination of equipment. All of these units require manual operations for cake discharge and cleaning between batches or campaigns as well as suffer from high labor and maintenance costs, high disposal costs and the exposure of the operators and the environment to toxic and hazardous solvents and solids as well as used and contaminated filter cloth, bag filters and filler cartridges.

This article discusses the use of thin-cake vertical candle filters as alternatives to manual and conventional filter equipment. These new technologies are described as well as the selection process. The article includes lest data and case histories.

Clarification & Recovery of Slurries
Candle Filters are installed for clarification and recovery applications from liquids with low solids content. The candle filters are vertical candles.

Description and Operation of the Candle Filter
The BHS Candle Filler provides for thin-cake pressure filtration, cake washing, drying, reslurry and automatic discharge as well as heel filtration in an enclosed, pressure vessel. Units are available up to 100m' of filler area per vessel.

Filter Candles & Media
The filler candles, as shown in figure 1, consist of three components: single-piece dip pipe for filtrates and gas, perforated core wilh ouler support lie rods and filler sock media. The filtrate pipe is ihe full length of the candle and ensures high liquid flow as well as maximum distribution of the gas during cake discharge. The perforated core can be a synthetic material, stainless steel or Hastelloy and is designed for Ihe full pressure of the vessel. The outer support rods provide for an annular space between the media and the core for a low pressure drop operation and efficient gas blowback for cake discharge. Finally, the filter media is synthetic or metallic with removal efficiency to less than 0.5 microns.

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