Modelling non-stationary precipitation systems: sources of error and theirpropagation

A laboratory well-mixed, constant supersaturation, semi-batch gibbsite prec ipitator, with clear liquor advance, was modelled using a discretized popul ation balance (DPB). This experimental configuration is inherently non-stat ionary (i.e. does not reach steady state). The model predictions of the tra nsient crystal size distribution (CSD) were found to give good agreement to the experimental CSDs initially but deviated apart with time. The cause of this deviation was identified as error propagated in the computation of th e DPB model. The source of the propagated error was investigated. The error contributions from the growth and agglomeration term discretizations were found to be small compared to the magnitude of the observed deviation. Mont e Carlo simulation demonstrated that the main contribution to the observed error is from uncertainty in the estimates of the agglomeration kernel and growth rate parameters, which are estimated from experimental data and used in the simulation. The findings highlight the need for more precise kineti cs estimation procedures and advocate care when simulating the CSD of non-s tationary precipitators over longer time scales, which may have implication s for precipitator start-up simulations. (C) 2000 Elsevier Science Ltd. All rights reserved.