Heel

Heel is the residual solids and liquid that remain in a filter after filtrate drainage and cake discharge. In candle, leaf and press filters, heel forms in low‑drainage zones, at internals and around nozzles; in belt systems, heel may persist at the discharge edge or in return runs. While a small heel can protect media at start‑up by acting as a precoat, excessive heel reduces yield, dilutes the next batch and complicates cleaning. Engineering measures aim to minimise and control heel: optimised manifold and tray design, slope‑to‑drain geometries, air or gas blow to evacuate hold‑up, and discharge devices that leave clean surfaces. Operating strategies—controlled ramp‑down, short air holds, or a brief heel‑removal step—recover valuable product without re‑entrainment. For audited processes, heel is quantified by mass balance (solids/liquid), by conductivity or density profiles during drain, and by visual or sensor inspection. Clear SOPs define acceptable residuals and document how heel is handled at changeover so that quality and yield remain predictable.