Technical Articles
Thin-Cake Filtration Theory
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In most industrial solid-liquid separation applications, the process steps of filtration, washing and
dewatering (drying) are conducted on one filter. This paper describes the thin-cake filtration
theory for these operations.
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A Treatise of Filter Cake Washing Mechanisms In Pressure and Vacuum Filtration Systems (PDF)
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Abstract:
During many chemical and pharmaceutical process operations, cake washing is required for the removal of the mother liquor, exchange of solvents, dissolution of soluble components and the displacement of insoluble contaminants. This article introduces pragmatism into cake washing theory and will help to guide engineers during their decision-making processes.
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Clarification of API Slurries and Recovery of Solids
Published in the March 2006 Issue of PharmaChem, Milano, Italy (PDF)
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Abstract:
Candle Filters and Pressure Plate Filters are installed for clarification and recovery applications from liquids with low solids content. The candle filters are vertical candles while the pressure plate filters are horizontal plates and both are designed for complete containment and automatic cake discharge. The cake structure as well as the process parameters determines the optimum thin-cake technology.
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"Reprint from "Pharmaceutical Engineering" , Jan/Feb 2007, The Official Magazine of the ISPE, International Society of Pharmaceutical Engineers.
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This article discusses how the use of thincake vertical candle filters and horizontal pressure plate filters can efficiently remove activated carbon, metal catalysts, and trace insolubles from Active Pharmaceutical Ingredient (API) slurries.
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Thin-Cake Filtration Technologies for Removing Activated Carbon, Catalysts and Other Trace Solids From Active Pharmaceutical Ingredient (API) Slurries (PDF)
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Abstract:
The BHS technologies of Vertical Candle Filters and Horizontal Pressure Plate Filters provide improved product quality with more efficient operations compared with manual pressure filters. The different technologies allow for the selection of the optimum process solution depending upon the cake characteristics and cake structure. Fully automatic operations provide for complete containment of the solids and liquids for reduced maintenance costs and overall project savings.
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A Six Sigma Approach to Evaluating Vacuum Filtration Technologies (PDF)
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Abstract:
This article compares three designs of vacuum belt filters (moving tray, rubber carrier belt and the BHS continuous-indexing technology). The evaluation had several stages from initial investigation, bench-top testing and finally pilot-scale testing. The BHS Continuous-Indexing Vacuum belt filter was the selected technology to replace a manually-operated filter press. The return-on-investment (ROI) calculation based upon the BHS process, operating and maintenance benefits allowed the project to be funded with a payback of less than 6 months.
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Clean-in-Place Operations for Thin-Cake Filtration Technologies (PDF)
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Abstract:
This article discusses the choice of thin-cake (2-25 mm) separation technologies and their benefits to optimizing the effectiveness of the production process. The paper continues with a discussion of clean-in-place operations to meet current Good Manufacturing Practices (cGMP) guidelines including riboflavin test and validations. ANSI/ISA S88 (and IEC 61512-1 in the international arena) batch process control system standards are also examined. Finally, factory and site acceptance testing is described.
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Continuous-Indexing Vacuum Filter as Replacement for Filter Presses (PDF)
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Abstract:
The BHS Continuous-Indexing Vacuum belt filter (CI-VBF) with 12 m2 of filter area replaced a 440 m2 filter press. The CI-VBF provided improved washing efficency for a higher quality product, and lower operating and lower maintenance costs with a fully automated operation.
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BHS Pharma Rotary Pressure Filter Article (PDF)
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Abstract:
The BHS Ph-RPF technology provides improved product quality with more efficient washing ratios compared with the inverting-basket centrifuges. Savings in solvent usage, energy consumption, maintenance costs and capital and installation costs result in overall project savings on the order of 4-6 to 1.
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Test it Right for Thin-Cake Filtration Operations (PDF)
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Abstract:
The appropriate BHS testing procedures can help direct the selection of pressure or vacuum filtration equipment and ensure optimum equipment operation.
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Improving Process Operations with a Rotary Pressure Filter (PDF)
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Abstract:
A rotary pressure filter can increase filtration rates, washing and drying efficiencies and eliminate organic solvent emissions.
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Evaluating thin-cake pressure filtration using the BHS Autopress technology (PDF)
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En español, Evaluación proceso de filtración por presión de tortas delgadas utilizando la tecnología Autopress de BHS.
Abstract:
Thin-cake pressure filtration technology offers an alternative to agitated nutsche filters and centrifuges for solid-liquid separation, cake washing, and drying.
Solid-liquid separation and cake washing are integral steps in the production of bulk or final pharmaceutical products. Each step must be optimized, along with the downstream dryer.
Complicating this process is the number of competing technologies and options that can be employed to accomplish these steps. For example, most pharmaceutical processes will use either an agitated nutsche filter or a centrifuge for the separation and washing step.
This article discusses the use of the thin-cake Autopress pressure filter as an alternative to agitated nutsche filters and centrifuges. The results are applicable to specialty chemical and other applications with similar process crystals and requirements.
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Comparison of Gypsum Dewatering Technologies at Flue Gas Desulfurization Plants (PDF)
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Abstract:
Recovering gypsum from flue gas desulfurization (FGD) plants is becoming more important as the technical feasibility of substituting FGD gypsum for natural gypsum in traditional applications such as wall board, cement and soil conditioners has been demonstrated. It is estimated that there are over 200 new coal-fired plants and over 1000 upgrades of existing coal-fired plants in various stages around the world. An important aspect of gypsum recovery is the solid-liquid separation technology that is used.
This paper discusses three technologies that are used by coal-fired power plants to dewater and dry gypsum. These are centrifuges, continuous vacuum belt filters (CBF) and continuous-indexing vacuum belt filters (CI-BF) and rotary vacuum filters. Each technology is examined for their ability to filter, wash and dry the gypsum to meet the moisture content for salable FGD gypsum as compared with natural gypsum. The paper continues with an analysis of the utilities required for each technology including electricity and water usage and the ability to reuse water in the process. Finally, maintenance, reliability, uptime and redundancy requirements are discussed as well as general overview of instrumentation and PLC controls and communication is covered.
The paper concludes by describing the important information that power plant engineers should review before deciding on a solid-liquid separation technology. These parameters include type of FGD process, type of coal, limestone purity, water analysis, operating data, composition of the gypsum slurry and other upstream or downstream equipment. Finally, to meet the plants overall environmental objectives, a unique approach is described that takes the wastewater treatment sludge and incorporates it with the gypsum for a cement product.
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A Review of Filter Press Basics Versus Alternative Technologies (PDF)
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Abstract:
The range of liquid/solid separation equipment is very large and without an intimate knowledge it can be confusing and even illogical, the main reason being that there are only two basic principles of liquid/solid separation. This means that equipment which an independent expert would not necessarily chose first can still be made to work, albeit with poor efficiency. This implies that you should be extra careful with suppliers who offer only one type of equipment, as it may well be that although it can be made to work, it may not be the best choice!
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PharmaChem-Alternative Batch or Continuous Technologies to Filter Presses (PDF)
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Abstract:
Filtration experts, over the years, have discussed and debated filter presses and have indicated that soon they would be a thing of the past; the last filter press would be replaced by more modern equipment. Given that filter presses were amongst the
oldest mechanical dewatering devices, this was a fairly plausible suggestion. However, now, almost half a century later, any chemical engineering exhibition shows that filter presses are alive and well and are going to be around for years to come. True, they look different from the ones in the 1950’s, but essentially they are still the same device. Their continued presence is a tribute to the filter press manufacturers who embraced new materials and upgraded the mechanics and configurations. However, the basics are still
the same and much of the issues surrounding filter presses remain valid.
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PharmaChem-Cake Washing Mechanisms for Pressure and Vacuum Filtration (PDF)
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Abstract:
During many chemical and pharmaceutical process operations, cake washing is required since no filter system can remove all of the mother liquor by pressure or vacuum dewatering only. The need for cake washing to produce a “clean cake” for further processing, drying or disposal can be for several reasons including the removal of the mother liquor, exchange of solvents, dissolution
of soluble components and the displacement of insoluble contaminants.
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Selecting Thin-Cake Candle Filter Technology for Amine Acid Gas Scrubbing Systems (PDF)
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Abstract:
The need for filtration systems in scrubbing units has been well documented. Filtration provides the benefits of reduced hot spots in the regenerator reboiler, reduced heat exchanger fouling and reduction of foaming in the absorbers. This paper discusses thin-cake candle filter technology that is used to remove trace amounts of solid contaminant fines from the recirculating fluid stream. These contaminants originate from various sources and are generally less than 3 - 5 microns in size, which makes their removal very difficult. Candle filter technology and the process of thin-cake building, is a new approach that is employed for high-efficiency and costeffective fines removal.
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Continuous Pressure and Vacuum Filtration and Washing of Organic Cellulose and Biomass Products (PDF)
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Abstract:
The processing of organic, cellulose-containing materials has been around for many years. Currently, due to high oil prices as well as the significant increase in ethanol usage nationwide from both grain based and cellulosic based sources, there is tremendous interest in developing efficient, cost-effective manufacturing processes to produce energy from cellulosic feed stocks. This article will use actual process data to highlight the choice of pressure or vacuum filtration and cake-washing techniques for these newly developed bioprocesses.
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Selection of Liquid - Solid Separating Equipment (PDF)
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Abstract:
In this three-part article, in part 1 Messrs. Pierson and Perlmutter discuss testing, selection of liquid/solid separating equipment and give practical filtration tips. In part 2 of this, Messrs. Pierson and Perlmutter discuss the finer points of filtration. Finally, in part 3 of their series, Messrs. Pierson and Perlmutter provide a summary and preliminary selection guide for various types of pressure, vacuum, batch and continuous filtration equipment.
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