SAMPLING PROCESSES FOR USE IN THE CONTROLLED ADDITION OF CONDITIONING MATERIAL TO SUSPENSIONS, SLUDGES AND THE LIKE AND APPARATUS THEREFOR

摘要

The invention provides a sampling process and apparatus therefore for the control of the addition of expensive conditioning material, referred to as polymers, to suspensions, sludges and the like, particularly sewage sludge, to facilitate its dewatering. The process employs a viscometer able to measure rapidly the shear stress of the sludge and obtain a typical peak value characteristic of optimum conditioning of the sludge. The process and apparatus also operate in a new mode involving charging a sample vessel with unconditioned sludge, taking a measurement to obtain an "unconditioned" signal, and then filling with conditioned sludge and obtaining a "conditioned" signal, the unconditioned signal indicating the solids content of the sludge and being used to modify the signal controlling the polymer flow and therefore the dosage to compensate for this change. The viscometer rotor and the vessel interior are rinsed to remove the conditioned sludge before a fresh batch of unconditioned sludge is introduced. The system employs a minimum-seeking algorithm to minimise polymer usage. Changes are made to the polymer flow rate when the conditioned signal change is greater than a dead-band straddling the optimum value, the minimum-seeking also taking place within the dead-band. It is sometimes found that the peak value/polymer flow rate characteristic includes a secondary peak, whereby the peak value reduces with increase of polymer flow, and this potentially unstable condition is detected and corrected.