Achieving Total Discharge in Nutsche Filter Dryers: The Key to Optimizing Production and Maximizing Yield

A critical aspect of nutsche filter/dryer operation — often overlooked — is the importance of achieving total discharge of the product from the vessel. This blog post explores how total discharge impacts both process efficiency and economic success, as well as discussing both manual and automated methods designed to achieve discharge.

The Unseen Impact of Total Discharge

The concept of total discharge is to ensure that no residual material is left in the equipment after processing.  The ability to remove all material can significantly impact the profitability of large-scale operations with regard to:

• Optimizing Production Efficiency: Residual product in the filter can create a material recovery step after your standard unit operations, adding to vessel downtime and the amount of cleaning required between batches. Total discharge ensures that the equipment is ready for the next batch quickly, thereby enhancing overall production throughput.
• Maximizing Product Yield: In large-scale production, even minimal product losses per batch can add up to significant financial losses over time. Ensuring total discharge means that the maximum possible product yield is realized, directly impacting the bottom line.

Automated Methods for Total Discharge

The drive for efficiency and precision in large-scale production has led to the development of automated methods for total discharge in nutsche filter dryers:

• Automated Side Discharge Valve with Agitator: This preferred combination of automated valve and agitation makes automated nutsche filters a workhorse of industry. A side discharge valve can be automated to open or shut depending on process and material conditions. Once a material has reached the desired specifications, the agitator blades can then be used to push product out through the open side discharge valve, allowing for an automated discharge sequence with no operator intervention. Note, as this discharge method does not normally result in total discharge, it is often used in conjunction with other automated or manual heel removal systems.
• Auto Discharging Gas Knife: This system option utilizes a high-velocity jet of gas (often nitrogen) at the edge of the agitator blade to create a sweeping effect across the filter dryer's internal surface. The gas does not fluidize the product to be discharged, but rather relies on the mechanical effect of pressure to sweep material towards the discharge port, with the ability to adjust supply pressure based on various product characteristics. The gas knife effectively removes residual product clinging to the filter media, allowing for the agitator to discharge the product, reducing the requirement of manual intervention.  

Gas Knife System in operation

Manual Methods for Total Discharge

There are applications in which automated discharge may be cost prohibitive or ineffective, in which case manual methods for achieving total discharge are the best solution:

• Physical Scraping: In some cases, operators will use a manual tool through a side port in the nutsche to manually scrape the product heel off of the filter plate and the vessel walls. Though effective, this method is time-consuming and poses potential safety and contamination risks, highlighting the advantages of automated solutions. For reduced contamination and exposure to the product, a customer may select to install an isolator (or glovebox) through which the operator can handle sampling, scraping, and discharge of the product. Note that, because of maneuvering either through a glovebox or small opening in the side of the vessel, manual scraping can be ergonomically difficult for operators.
  
  

Glovebox installation for contained product sampling and discharge

Combining Automated and Manual Methods for Total Discharge

• Side Discharge Valve with Isolator Combination: An isolator in conjunction with a side discharge valve could be the best of both worlds for automated and manual discharge. The side discharge valve port and the isolator port can be installed 180-degrees opposite of each other, allowing for the side discharge valve and agitator to remove a bulk of the solids, as detailed earlier. From there, the operator can access the nutche via the isolator port and use a plow to push the remaining heel through to the side discharge valve port, allowing the heel to join rest of the product for further processing.

Other Considerations for Selecting a Discharge Method

Nustche filters are highly configurable, and the following nutsche and product parameters should be considered when deciding on the most effective discharge method:

• Product characterization: Understanding the physical and chemical properties of the material to be discharged can help a customer select the appropriate discharge method. Particle size distribution, density, viscosity, cohesion, electrostatic charge, moisture content, solubility, and thermal stability could all influence how readily a material can be moved by a gas knife or manual scraper.
• Filter cloth selection: The filter cloth will be supporting the material cake and therefore the heel, and the proper material selection can impact the effectiveness of the discharge method and maintenance scheduling. For example, if manual heeling is required, a sintered metal filter media could be preferred to a filter cloth, which could be damaged during the manual heeling process, resulting in further downtime and increased cost.
• Drying optimization: Drying conditions should be carefully controlled, to avoid over-drying or under-drying the product, which can affect the product’s properties and discharge performance.
• Agitator design and operation: The agitator design and controls can be optimized to enhance filter cake breakage and product scraping, as well as prevent increased product adhesion. The agitator clearance to the filter plate can also be adjusted, to avoid product trapping or blinding of the filter screen.

Achieving total discharge in nutsche filter dryers is a critical aspect of optimizing large-scale production, and as the industry continues to evolve, the focus on innovative solutions for achieving total discharge will remain a key factor in the pursuit of operational excellence and competitive advantage.