NAMS 2002 Workshop - ICOM 2008

were developed to enable feed-flow reversal operation. Open-loop and closedloop
simulations demonstrated non-linear model-predictive control strategies that
transition from the high-flow to low-flow steady-states in an optimal way while
subjected to plant-model mismatch on the feed concentration, actuator
constraints, and sampled measurements. The EXSOD detection of scale is
based on direct surface imaging, whereby the appearance of surface crystals is
analyzed in real-time using novel image analysis algorithms. Upon the detection
to the onset of surface scaling, a control signal is sent to the RO plant PLC to
initiate flow reversal. The flow reversal approached was successfully
demonstrated in both laboratory bench-scale studies and in RO pilot plant
studies demonstrating the ability to maintain constant permeate flux, without the
use of antiscalants, even under conditions of supersaturation. The study has the
demonstrated that the cost of water desalination can be reduced, whenever there
is propensity for mineral scaling, by using the feed flow reversal approach, both
due to eliminating the need for antiscalants and expected reduction in the
frequency of membrane cleaning.