Automated Nutsche Filter Dryers (ANFD) have a vertically translating agitation system. The agitation system is designed for processing and manipulation of solids.
This includes the functions of smoothing the filter cake, re-slurry of the filter cake, agitation of solids during drying, and discharge of solids. The agitation systems are designed with tight tolerances to minimize product hold up within the vessel and provide for more efficient agitation and drying. The tightness of the agitator to vessel tolerance is a function of the unit size and filter media selection. Based on this tolerance, the unit will leave residual solids within the filter. The residual material is known as product “heel”. The amount of material will be a function of filter size and the setup of the unit. Based on a maximum solids loading and lowest agitator to filter plate clearance, the residual material will range from 1.5% to 3.5%. If the product has characteristics that negatively impact discharge, such as tendencies to dust, stick, or agglomerate, the percentage of heel can increase. In addition, if the unit is not fully utilized to capacity, the percentage of residual material will increase accordingly.