Residual heel

Starting materials (specification, nature, properties), eg. Impurities with catalytic effect Concentration increases/ decreases Residues (heels) from previous use Lowering of activator/ inhibitor concentration (e.g. due to storage beyond expiration) ... 

Note that washout of the liquid agent and residues/heels together might be possible if the treaty requirements for agent quantification can be satisfied. 

Backwashing the residual heel between each cycle rejuvenates the heel to maintain good permeability. Heel life is often extended. 

Peelers are characterized by conical baskets (Fig. 9) that are fitted with a heavy-duty plow mechanism that peels the cake away from the bowl for discharging at operating speed. This minimizes the batch cycle time and is normally used to process more rugged crystals. Peelers may provide cake rinse and may be equipped to dissolve the residual heel cake on line, promote drainage, and maintain short cycle times. 

The particle size distribution of the material and the clarity required will dictate the micron retention of the medium. Fabrics tend to have a nominal micron retention range as opposed to an absolute micron retention rating. When using precoat on a machine that leaves a residual heel of solids, a more open cloth can be used. 

Inverting the membrane and reversing air flow through the cloth while slowly rotating the system 180° back and forth releases all cake from the cloth. No operator attention is required for discharge of the solids, as no residual heel is left on the cloth. Vapors and product are contained. 

The action of the scrub is such as to leave a residual heel of fiber cake (up to 1.5 cm thick) on the sur ce of the fiber medium tire continued presence of the hed, under the washing conditions required by most processes, can lead to particle nngration, or scouring... 

Includes an allowance for the resistance due to the residual heel of cake present after knife discharge. 

The presence of the residual heel is not avoidable in either case, and it may be necessary to recondition it by suitable washes in order to restore its drainage properties. Some designs incorporate cake feeler/leveller mechanisms, which ensure that an even cake is formed. 

The dry spinning stage is completed after the wash liquor has passed through the cake and the dry solids are removed by the hydraulically activated peeling device, down to the residual cake heel. The peeled solids are removed from the basket through a chute or by a saew conveyor. The residual heel left in the basket after a batch of solids has been removed serves as the primary filter medium for the next cycle, and so on, until it becomes impermeable and needs to be removed by washing with filtrate. 

---