Posted by Jennifer Mayo Nov 6, PM Filtration and drying are critical operations in a variety of industrial processes that require the separation of solid matter from a liquid. Filtration can be broken down into two types of processes — continuous and discontinuous or batch operations. Some benefits of using this technology include product isolation, minimal operator exposure, reduced product handling, and environmental protection against solvent vaporization. Additionally, the level of containment supplied can comply with GMP and other health and safety requirements that companies often face. So what exactly goes on in this closed vessel from start to finish?
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Posted by Jennifer Mayo Nov 6, PM Filtration and drying are critical operations in a variety of industrial processes that require the separation of solid matter from a liquid.
Filtration can be broken down into two types of processes — continuous and discontinuous or batch operations. Some benefits of using this technology include product isolation, minimal operator exposure, reduced product handling, and environmental protection against solvent vaporization. Additionally, the level of containment supplied can comply with GMP and other health and safety requirements that companies often face.
So what exactly goes on in this closed vessel from start to finish? The filter should be sized appropriately to handle the solids volume that is being charged. A general rule of thumb to follow is that the maximum solids height should be equal or less than the agitator stroke, typically 12 - 20 inches. The process is stopped when solids are visible, or can be continued until all the liquid is pushed out.
There are various types of filter media available in nutsche filters — cloth, single layer metal screen, or multi-layer sintered metal. The media should be determined based on the characteristics of the slurry including particle size and shape, cake porosity, and compressibility which are all factors that, when taken into account with the filter media selected, will determine filtration rate.
Displacement Washing Here, fresh wash liquid is sprayed on top of the solid cake taking care not to disturb the surface of the cake. The liquid is forced through with pressure or vacuum. Displacement washing serves several purposes — it removes the liquid and its impurities while keeping the cake intact and it replaces the previous liquid with fresh liquid. There is also the opportunity prior to this step to try and close cracks if the cake has any via smoothing.
Reslurry Washing As an additional washing option, a re-slurry washing can be performed if additional extraction or dissolving of impurities is necessary. This is executed by the addition of fresh wash liquid that is mixed with the solids. The agitator is stopped and raised before filtering the wash liquid.
The re-slurry process is also used when a long contact time is needed between the wash fluid and the solids or the displacement wash does not provide the required wash quality. Smoothing This next step may be used after any filtration or wash, especially after the final wash, when gas is blown through the cake. The agitator is used to close cracks and compress the cake to reduce residual moisture level.
This function will help to achieve uniform flow of liquid or gas through the filter cake, while helping to eliminate liquid and gas channelling that reduces the efficiency of displacement washing and gas blow through. To accomplish this, the vessel surfaces including the wall, base, and agitator are heated.
There are two types of drying that can be conducted — vacuum drying and convection drying. The method used depends on the product behavior. Vacuum drying, the most common method, involves a vacuum source, agitation, and dust filter.
This type of drying utilizes vacuum to reduce the temperature at which the solvent evaporates, reducing the average drying temperature. During convection drying, hot, pressurized gas usually nitrogen is blown down through solids and out of filtrate lines and even recirculated as necessary ; this will eventually dry the solids.
Unlike vacuum drying, it does not require agitation. At this point the vessel and product may need to be cooled to an ambient temperature prior to discharge. The agitator is slowly lowered as it rotates, effectively moving product to the side discharge valve. There are certain applications where the desired product to be discharged is not a dry solid.
Understanding the steps that make up the nutsche filtration and drying process help to differentiate this equipment from other types of separation technology. From an environmental and personal health perspective, safety is maintained throughout the process. Stay in the know! Subscribe today and receive weekly or monthly notifications when new blog posts are published: Recent Posts.
FILTRATION & DRYING
The bottom bed is trolley mounted for easy movement. Variants 1. Additionally, these can be combined with automatic packing systems further downline. Special Heel removal discharge valve A specially designed quick openable discharge valve which allows much closer access to interior of machine for heel removal is also available 4.
AGITATED NUTSCHE FILTER OPERATION PDF
Goltiramar The ends must be cut in an angle to ensure a perfect seal. The filter is charged with slurry and pressure is applied to displace the filtrate leaving the cake retained over the filter medium. Hydraulic Cylinder for Reslurry Arms. In addition two auger arms smoothen the cake by rotating in one direction and convey the cake towards the center for discharge by rotating in the opposite direction. To take advantage of the drying ability of the Nutsche Filter it is worth considering the option of heating components such as the vessel, filter floor and paddles to enhance drying. As such these are very sophisticated machines with tight process control on parameters such as pressure, temperature and pH.
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Filter features[ edit ] A typical unit consists of a dished vessel with a perforated plate. The entire vessel can be kept at the desired temperature by using a limpet jacket, jacketed bottom dish and stirrer blade and shaft through which heat transfer media can flow. The vessel can be made completely leak-proof for vacuum or pressure service. Agitator[ edit ] A multipurpose agitator is the unique feature of this system. The agitator performs a number of operations through movement in axes both parallel and perpendicular to the shaft. When filtration is complete, the cake develops cracks causing upsets in the vacuum operation.
Agitated pressure filter and vacuum dryer for solid-liquid separation