The drum deck, equipped with replaceable filter grids, supports the filter medium (cloth made from fabric or metal). A vacuum pump provides the necessary gas stream to accomplish dewatering. The vacuum sucks the liquor through the filter medium and forms a filter cake out. Several stations have specially designed rotary vacuum filters capable of producing wallboard grade gypsum with a filter cake moisture content of less than 10%. The K-S High-Rate FGD Drum Filters operating at CWL&P Dallman, TECO Big Bend, and NB Power Coleson Cove 1. The rotary vacuum filters (also called drum filters) enable an efficient filtering in a continuous cycle with perfect results. Compare this product Remove from comparison tool. Belt vacuum rotary drum. Sefar produces belts and drum filter covers for different filter.

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K-S Rotary Drum Vacuum Filters

Komline-Sanderson continuous rotary drum vacuum filters for the separation of liquids from solids offer great flexibility in meeting the needs of many industries.

Our experience ranges from simple separations to complex multi-stage applications involving filtration, clarification, extraction, cake washing, and drying.

The rotary drum vacuum filter offers:

• Continuous Operation
• Application Versatility
• Wide Range of Sizes

For horizontal vacuum filtration, please see our Horizontal Vacuum Filter

For information on our filtration media please visit Fabrics

The Komline-Sanderson Rotary Drum Vacuum Filter is applied to process and waste slurries for filtering, clarifying, cake washing and extraction, and dewatering. Industries served by K-S include inorganic and organic chemicals, pharmaceuticals and biotech, plastics, food products, minerals, electric power and other utilities. Specific process applications are referenced in the Design Section.

How does it work?

The process of the RDVF is continuous. Each revolution of the drum consists of cake formation, cake washing (if needed), dewatering or drying, and cake discharge.

1. As the drum rotates, it is partially submerged in the feed slurry.
2. Vacuum draws liquid through the filter medium (cloth) on the drum surface which retains the solids. Vacuum is applied using a liquid ring vacuum pump or other means.
3. The vacuum pulls air (or gas) through the cake and continues to remove moisture as the drum rotates.
4. Finally, the cake is discharged from the drum to a conveyor or chute to the next process step.
5. The filtrate and air pulled through the medium flow through internal filtrate pipes and pass though the rotary valve and into the filtrate receiver.
6. The liquid stream is separated from the vapor stream in the receiver.
7. Liquid filtrate is then pumped to the next step in the process.

If required, the cake can be washed to remove impurities or to extract more product. Additional drying of the cake follows washing.

How do I know if an RDVF is right for my process?

If your process involves any of the following, then the Komline-Sanderson Rotary Drum Vacuum Filter may fit your needs.

• Continuous separation of solid and liquid
• Solid or Liquid Product recovery
• Clarification of liquid product
• Cake washing for cake purity or liquid product extraction
• Clarification of a wastewater stream

Our equipment requires minimal operator attention as well as low maintenance time and expense, and is designed and built for long equipment life.

If you can relate to these objectives, then follow these steps:

• Establish process inlet and outlet conditions as accurately as possible
• Complete the K-S Applications Questionnaire
• Contact us to assist in making a preliminary selection
• Perform lab and/or pilot scale testing if necessary
• Make final selection

Other important considerations:

• What is immediately upstream and downstream of the filter?
• What is most important: cake solids, filtrate clarity, capital or operating cost, etc.?
• What have you tried before? Why did/didn’t it work?
• What materials of construction are acceptable? What are not?
• Do you need auxiliary equipment?
• Do you need any instrumentation or controls?
• Do you have any standard specifications?

There are many factors affecting the operation of a filtration process. Among these are the need for chemical pretreatment; the need for precoat or filter aid; power, water, air, or other utilities; operator attention; cleaning requirements; and maintenance needs. All of these should be considered when selecting a filter.

K-S RDVF offers

• Continuous operation
• Application versatility
• Ease of operation, requiring minimal attention
• Simple, durable design for low maintenance and long life
• Wide Range of Sizes

How can we help you?

Komline-Sanderson has been a leader in liquid/solid separation equipment design and manufacturing for over 60 years, meeting the needs of both industrial and municipal clients. Our filters operate worldwide in an ever-growing range of process and wastewater applications. Expert process insight, outstanding customer service and high quality equipment make K-S a valuable partner throughout the project cycle.

Lab and pilot testing service is available to assist in equipment selection and sizing. Testing is also used to determine cake washing needs or other operating aspects.

RDVF Cake Discharge Types

The rotary vacuum filter discharges its filter cake using one of several arrangements. A discharge mechanism is selected based on the process material characteristics and on how readily it releases from the filter media.

K-S Flexibelt® discharge features a filter belt that passes over a variable speed discharge roll with raised helix for positive cake removal. It is typically applied:

• Where filter medium washing is required to prevent blinding.
• For the discharge of thin cakes.
• For dry cake discharge or sluice (wet) cake discharge.

Typical Flexibelt® Discharge Applications

• Corn Gluten
• Starch
• Pharmaceuticals
• Fermentation Broths
• Pigments
• Organic/Inorganic Chemicals
• Water Softening Sludge
• Steel Mill Waste
• Hydroxide Sludge
• Industrial Wastewater

The Precoat discharge is used when direct filtration against a cloth medium is not possible because the cake cannot be removed from the cloth or when blinding is indicated. It is typically used:

• For slimy, sticky, oily and blinding solids.
• For clear filtrates.
• For filtering dilute slurries with varying feed concentrations.
• For the discharge of very thin filter cakes.

Typical Precoat Discharge Applications

• Corn Syrup Clarification
• Fruit Juices and Wines
• Pharmaceuticals
• Fermentation Broths
• Food Processing Wastes
• Hydroxide Sludge
• Slop Oil
• Flexographic Ink Wastes
• Industrial Wastewater

Scraper Discharge

Scraper discharge is usually used along with air blowback to release the filter cake from the cloth just above the scraper. It is used:

• For fast filtering materials.
• For filtering/dewatering granular or crystalline solids.
• For discharging cakes in excess of 1/4″ thick.
• For non-blinding cakes where cloth washing is not required.

Typical Scraper Discharge Applications

• Flue Gas Desulfurization (FGD) Scrubber Sludge
• FGD Gypsum Dewatering and Cake Washing for Wallboard
• Inorganic Chemicals and Minerals
• Pigment Processing
• Plastics Resins (Polymers)
• Calcium Compounds
• Titanium Dioxide
• Edible Oil Dewaxing

Roll Discharge

Roll discharge filter is usually fitted with a very tight filter medium to retain very small particles and is used:

• For discharging very thin, sticky (tacky) cakes.
• For discharging dilatent and thixotropic materials.
• For applications with very small particle sizes.

Typical Roll Discharge Applications

• Kaolin Clay
• Titanium Dioxide
• Pigments
• Ceramic Materials
• Magnesium Hydroxide

String Discharge

String discharge filters utilize closely spaced parallel strings to lift the cake from the cloth. The strings then pass over a discharge roll and the cake is released. Since no mechanical wear occurs to the filter medium, long life is assured. It is used:

• For discharging cohesive cakes.
• For discharging gelatinous cakes.

Typical String Discharge Applications

• Starch
• Fruit Juice
• Fermentation Broths
• Mineral Processing

K-S process and project engineers provide assistance at all phases of the project. Depending on your specific requirements, K-S can provide you with a Rotary Drum Filter or a complete system.

A successful plant depends on the integration of the key process units with properly selected ancillary equipment and the right facility design. Reliability, ease of operation, rugged construction, performance, and superior customer service are all trademarks of a K-S installation.

A typical system includes a vacuum pump, filtrate pump, and vacuum/filtrate receiver. Also required in some cases are feed or drain pumps and precoat or chemical prep tanks with mixers. Often these items are mounted, wired and piped on a common base for ease of installation. Depending on customer needs, cake-handling equipment can also be provided. Controls and instrumentation are available to complete the system.

When necessary, our vapor tight design allows for the processing of material containing organic solvents and hazardous materials in an enclosed safe manner. Inerting of the process with nitrogen can also be accomplished with a minimal purge rate.

Why use an RDVF?
The rotary drum vacuum filter is a very versatile liquid/solid separation device. It is used where a continuous separation of a solid from a liquid stream is desired. It can be used in process applications where the solid is the product or where the liquid is the product (and sometimes when both phases are the product). In wastewater applications it can be used to dewater a variety of sludges or to clarify wastewater.

Is there an easy test to tell if an RDVF is right for an application?
A simple Buchner funnel test will generally determine if the use of an RDVF is feasible. Further testing using a test leaf can be done to simulate the operation of the RDVF under specific operating conditions.

Can an RDVF be used in a batch process?
Yes, although the filter operates as a continuous separation device, it can be used in batch processes. In these cases, the filter would be operated intermittently as needed to filter a batch of feed slurry.

When is cake washing used?
Cake washing is used when a given cake purity is required. It is also used to improve extraction of liquid products or dissolved materials from the filter cake. Lab or pilot testing can be used to determine the effectiveness and efficiency of cake washing on an RDVF.

How is the correct size and style of cake discharge determined?
Lab testing is often the best way to determine the correct filtration characteristics of a given material. In many cases, an RDVF has been previously installed or tested for the same or a similar application. This provides a good starting point in selecting equipment.

What designs are available?
The design of the RDVF can be changed to suit specific needs for a given application. Various types of cake discharge mechanisms are used depending on the characteristics of the filter cake. Our equipment can be constructed of a variety of materials including carbon steel, stainless steel, plastic, Hastelloy, or titanium. Special material finishes for food or pharmaceutical applications can also be specified.

What if my process produces hazardous vapors?

Designs are available for applications requiring vapor containment. Vapor-retaining hoods can be used much like the hood in a lab. Completely sealed, vapor-tight designs are used where absolutely no leakage is permitted.

Generally items required are: vacuum pump(s), filtrate pump(s), and vacuum/filtrate receiver. Also required in some cases are feed or drain pumps and precoat or chemical prep tanks with mixers. Depending on customer needs, cake handling equipment can also be provided. Auxiliary equipment can be provided by K-Sfor a complete system including controls and instrumentation.

What utilities are required?
Electric power is required to run the filter drives as well as the vacuum pump and the filtrate pump. Water is needed as seal liquid for the vacuum pump and also for cloth wash and sometimes cake wash depending on the application.

How much operator attention and maintenance are required?
The RDVF is essentially a hands-off machine that requires very little operator attention. Also, it runs at a very slow speed (typically between 0.25 to 1.0 rpm). This means that it will generally operate trouble free with very little maintenance. Maintenance usually involves lubrication of drives and bearings and occasional changing of filter cloth and replacement of wear items.

How much do spare parts cost?
It is difficult to give a specific cost since there are many sizes and designs of RDVFs, however, spare parts costs are generally low on a yearly basis. Replacement filter cloth is the most common spare part. Other items requiring yearly maintenance include certain wear items on the filter valve and the cake discharge assembly.

What technical service is available?
Technical service is available for installation and start-up of new equipment. Existing units can also benefit from a service visit to assist in optimizing performance. Contact us for a service proposal.

Are pilot filters available?
RDVF pilot units are available for rental. The filters have 316SS wetted parts and can be fitted with a cake discharge assembly suited to the application.

The cylinder is divided into compartments like pieces of a pie (see Fig 2), and drainage pipes carry fluid from the cylinder surface to an internal manifold.

Filter diameters range from three to twelve feet, with face lengths of one to twenty-four feet, and up to 1000 ft2 of filtration area.[5 J Filtration rates range from 5 GPH per square foot to 150 GPH per square foot. Moisture levels are, of course, dependent upon particle size distribution and tend to range from 25% to 75% by weight and cake thickness tends to be in the 1/8-1/2 inch range, as most applications are for slow-filtering materials.

With the exception of the precoat applications, RVF's do not usually yield absolutely clear filtrate. Although still widely used, rotary vacuum filters are, in some cases, being replaced by membrane separation technology as the method of choice for clarification of fermentation broths and concentrating cell mass. Membranes can yield more complete filtration clarification, but often a wetter cell paste.

The drum is positioned in a trough containing the agitated slurry, whose submergence level can be controlled. As the drum rotates, a panel is submerged in the slurry. The applied vacuum draws the suspension to the cloth, retaining solids as the filtrate passes through the cloth to the inner piping and, subsequently, exiting the system to a vapor-liquid separator with high/low level control by a pump. Cake formation occurs during submergence. Once formed, the cake dewaters above the submergence level and is then washed, dewatered and discharged.

Discharge mechanisms will vary depending upon cake characteristics. Friable, dry materials can use a 'doctor' blade as in Fig. 3. Difficult filiations requiring thinner cakes incorporate a string discharge mechanism. This is the primary method for starch and mycelia applications. A series of 1/2 inch spaced strings rest on the filter medium at the two o'clock position. The cake is lifted from the drum as shown in Fig. 4. Fermentation broths containing grains, soybean hulls, etc., are applications for this type of discharge mechanism. The solids may be used for animal feed stock, or incinerated. String or belt discharge mechanisms facilitate cake removal and, therefore, can eliminate the need for filter aid.

Continuous belt discharge (Fig. 5) is employed for products that have a propensity for blinding the filter medium. A series of rollers facilitate cake removal in this case.

Precoated rotary vacuum drum filters (Fig. 6) are used by filtering a slurry of filter aid and water first, then subsequent product filtration. Difficult filtering materials, which have a tendency to blind, are removed with a doctor blade. Precoat is removed along with the slurry to expose a new filtration surface each cycle.

Figure 2. Rotary vacuum filter schematic.

Figure 3. Cake discharge mechanism.

Figure 4. String discharge.

Figure 6. Precoat rotary vacuum filter.

The progressively advancing blade moves 0.05 to 0.2 mm perrevolution. Vacuum is maintained throughout the cycle, instead of just during submergence, so that the precoat is retained. Once the precoat is expended, the RVF must be thoroughly cleaned, and a fresh coat reapplied.

10.2 Optimization

Pressure leaf tests are used to model the operating cycle of a RVF. The cycle, consisting of cake formation, dewatering, washing, dewatering and discharge, is simulated by the apparatus shown in Fig 7.

The test leaf is immersed in the agitated slurry for cake formation, then removed for drying. If washing is required, the leaf is placed in the wash liquor and then dried again. Discharge from the leaf will indicate type of discharge mechanism required. By varying the time of the portions of the cycle, rotational speeds can be simulated.

It is recommended that optimization be carried out by developing three different cake thicknesses. From this, a capacity versus cake thickness curve can be developed. Additional parameters that have to be evaluated are vacuum level, wash requirements, slurry concentration, and slurry temperature. If cake cracking occurs, the wash should be introduced earlier to avoid channeling.

Several leaf tests should be performed for repeatability. Data collected will permit scaleup to plant scale operations. Significant data will be pounds of dry cake per square foot per hour, gallons of filtrate per square foot per hour, filtrate clarity, wash ratios, (pounds of solids/gallon of wash), residual moistures, filtermedia selection, knife advance time, precoat thickness, solids penetration into precoat, and submergence level should also be evaluated. For the optimization equation, refer to Peters and Timmerhaus, and Tiller and Crump.

11.0 NUTSCHES

Rotary Vacuum Filter

11.1 Applications

The nutsche filter is increasingly prevalent in postcrystallization filtrations. It would not be used directly from the fermenter. Relatively fast filtrations with predictable crystal structures, often found in the intermediate and final step purifications of antibiotic drugs, work well on this batch filter. Batch sizes range from 100 to 7500 gallons.

Figure 7. Pressure leaf test.

s

260 Fermentation and Biochemical Engineering Handbook 11.2 Operation

The term nutsche is derived from the German word for sucking. Vacuum is applied at the bottom of a vessel that contains a perforated plate. A filter cloth, screen, perforated plate, or porous ceramic plate may be the direct filtration medium (see Fig. 8). Subsequently, products should have lower cake resistances and well-defined crystal structures to facilitate separation. The driving force for the separation is vacuum and/or pressure.

With an agitated vessel, the blade can be used to smooth or squeeze the cake, eliminating cracks, when rotated in one direction or for reslurrying and/ or discharging the cake when rotated in the opposite direction. The rotation of the agitator can be by electric motor with variable speed drive; however, the translational movement is achieved by a separate hydraulic system. The agitator requires a stuffing box or mechanical seal for pressure or vacuum operation of the unit. Filling is accomplished by gravity feed or pump. Large cakes, in the 10-12 inch range, are developed. When plug flow displacement washing is not effective, and as diffusion of impurities through the cake becomes difficult, reslurrying is the required method. Displacement washing is more efficient and minimizes wash quantities, however, may not always be possible. Filtering, reslurrying and refiltering can all be accomplished in the same unit, thus achieving total containment. See Fig. 9.

Rotary Vacuum Filter Drum

The vessel can also be jacketed for heating and/or cooling and the agitator blade heated. This design can now be a reactor in combination with a filter-dryer or alone as a filter-dryer (Fig. 10) (see also Chapter 17). This is particularly advantageous for dedicated production of toxic materials requiring an enclosed system. Operator exposure and product handling are minimized.

The nutsche can have limitations for difficult filtrations, as the thick filter cakes can impede filtration. A two-stage system for filtration and drying can offer greater flexibility in plant operations, especially if either the filtration or drying step is rate-limited. Predictable crystals that filter and dry well are the best applications for this all-encompassing system.

Mechanical discharge incorporating the agitator facilitates solids removal centrally or a side discharge is possible. A residual heel of product will be left as the agitator is limited on how close to the screen or filter medium it can go. Residual heels can be reworked by reslurrying or remain until the campaign changes. For frequent product changes, the nutsche can be provided with a split-vessel design. Upon lowering the bottom portion, free access to the inside of the vessel and the filter bottom itself for cleaning purposes is possible. Some manufacturers have air-knife designs that remove the residual heel. Heels as low as one-quarter inch can be obtained.

Figure 8. Agitated nutsche type pressure filter. (Courtesy of COGEIM SpA),

Movable Bottom Side Discharge Permanent Agitator 100* Jacketed

Drive - Bon-Heated

Spray Hozzles

Spray Hozzles

Single Or Multi-Layer Filter Cloth

Figure 9. Agitated nutsche type pressure filter. (Courtesy of C0GE1M SpA).

Single Or Multi-Layer Filter Cloth

Figure 9. Agitated nutsche type pressure filter. (Courtesy of C0GE1M SpA).

Figure 10. Agitated nutsche type filter/dryer. (Courtesy of COGEIMSpA).

Materials of construction can vary widely depending upon the application. Typically, 304 or 316 stainless steel, and Hastelloy are supplied, although many other types of material of construction are available. Metal finishes, in keeping with good manufacturing practices (GMP), particularly for areas in contact with final products, require welds to be ground smooth. Finishes can be specified in microns, Ra, or grit. The unit, Ra, is the arithmetical average of the surface roughness in microinches. The rms is the root mean square of the surface roughness in microinches; rms =1.1 Ra.

A mechanical finish of400 grit is an acceptable pharmaceutical finish, however, mechanical polishing folds the surface material over itself. When viewed under a microscope, jagged peaks and crevices are visible. Product on the micron level can be accumulated in these areas. Electropolishing of the surface is often used to eliminate these peaks and valleys to provide a more cleanable surface. A layer of the surface material is removed in this case. A mechanical finish of400 grit is achieved by progressively increasing the grit spec from 60 up to 400. If a 400 grit surface was to be electropolished, the amount of material removed would result in an equivalent 180-220 grit surface roughness. Therefore, a mechanical finish of approximately 180— 220 grit need only be specified when electropolishing. A considerable cost savings is realized. It is always advisable to specify the Ra value of the surface whether electropolishing is specified or not. (See Table 4.)

Filter areas will range from 0.5 to 16 m2. For large-scale processing, significant floor area is occupied perunit area offiltration.'11 Thoseproducts that tend to blind filter media, i.e., colloidal slurries, gelatinous and protein compounds, will require alternate equipment, filtration or centrifugation.

11.3 Maintenance

When used for dedicated production, maintenance is minimal. The agitator sealing system (usually a stuffing box or mechanical seal), however, must be maintained.

Filter cloth change and O-ring changes would be the primary maintenance required. This depends on the filter design. The split vessel design allows for easy access. A removable bottom which can be fixed to the vessel through a bayonet closure system is completely hydraulically controlled and can be lowered in 1-2 minutes. By first using the spray nozzles and flushing the system with a solvent that the product is soluble in, operator exposure will be minimized. Cleaning between final products for 99% validation, can take 1-2 twelve-hour shifts.

Screen lifetime will depend upon the type of screen used. Various types of filter cloths or monolayer metal screens can be used. A multilayer sinterized filter screen is also available. Installation of filter cloths and screens is usually by the use of clamping rings and hold-down bars screwed on the bottom.

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