Periodic Control of a Reverse Osmosis Water Desalination Unit

Authors: Ali Emad

Abstract:

Enhancement of the performance of a reverse osmosis (RO) unit through periodic control is studied. The periodic control manipulates the feed pressure and flow rate of the RO unit. To ensure the periodic behavior of the inputs, the manipulated variables (MV) are transformed into the form of sinusoidal functions. In this case, the amplitude and period of the sinusoidal functions become the surrogate MV and are thus regulated via nonlinear model predictive control algorithm. The simulation results indicated that the control system can generate cyclic inputs necessary to enhance the closedloop performance in the sense of increasing the permeate production and lowering the salt concentration. The proposed control system can attain its objective with arbitrary set point for the controlled outputs. Successful results were also obtained in the presence of modeling errors.

Keywords: Reverse osmosis, water desalination, periodic control, model predictive control.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1328076

References:

[1] Madireddi K., Babcock R.B., Levine B., Kim J.H., and Stenstorm M.K., 1999. "An Unsteady-state Model to Predict Concentration Polarization in Commercial Spiral Wound membranes", Journal of Membrane Science. 157, 13-34.
[2] Finnigan S.M., and Howell J.A., 1990. "The effect of pulsed flow on ultra filtration fluxes in A Baffled Tubular Membrane System", Desalination, 79, 181-202.
[3] Vrouwenvelder J.S., Heijman S.G.J., Viallefont X.D., van der Kooij D., and Wessels L.P., 2007. "Periodic air/water cleaning for control of biofouling in spiral wound membrane elements", Journal of Membrane Science, 287, 94-101.
[4] Vrouwenvelder J.S., van Paassen J.A.M., Wessels L.P., van Dam A.F., and Bakker S.M., 2006. "The membrane fouling simulator: a practical tool for fouling prediction and control", Journal of Membrane Science, 281, 316-324.
[5] Al-Bastaki N.M., and Abbas A., 1998. "Periodic operation of A reverse osmosis water desalination unit", Separation Science and Technology, 33, 2531-2540.
[6] Al-Bastaki N.M., and Abbas A., 1990. "Improving the permeate flux by unsteady operation of a RO desalination unit", Desalination, 123, 173- 176.
[7] Abbas A., 2000. "Enhancement of productivity in reverse osmosis desalination processes, Asian Journal of Water", Environment and Pollution, 4, 23-29.
[8] Abufayad A.A., 2003. "Performance characteristics of a cyclically operated seawater, desalination plant in Tajoura, Libya", Desalination, 156, 59-65.
[9] Abbas A., and Al-Bastaki N.M., 2000. "Flux enhancement of RO desalination process", Desalination, 132, 21-27.
[10] Sarkar B., De S., and Gupta S.D., 2008. "Pulsed electric field enhanced ultra filtration of synthetic and fruit juice", Separation and Purification Technology, 63, 582-591.
[11] Al-Bastaki N.M., and Abbas A., 2001. "Use of fluid instabilities to enhance membrane performance: A Review", Desalination. 136, 255- 265.
[12] Al-haj Ali M., Ajbar A., Ali E., Alhumaizi K., 2011. "Study of cyclic operation of RO desalination process", The Canadian Journal of Chemical Engineering, 89(2), 299-303.
[13] Al-haj Ali M., Ajbar A., Ali E., Alhumaizi K., "Optimization based periodic forcing of RO desalination process for improved performance", submitted to Desalination and Water Treatment, 2011.
[14] Al-haj Ali M., Ajabr A., Ali E., and Alhumaizi K.. 2009. "Modeling the transient behavior of an experimental reverse osmosis tubular membrane", Desalination, 245, 194-204.
[15] Ali E. and Zafiriou E., 1993. "Optimization-based tuning of non-linear model predictive control with state estimation", Journal of Process Control, 3, 97-107.
[16] Qin S. J., and Badgwell T. A., 1997. "An overview of industrial model predictive technology", in Fifth International Conference on Chemical Process Control, AIChE Symposium Series 316, 93, Jeffrey C. Kantor, Carlos E. Garcia, and Brice Carnahan, eds., 232-256.
[17] Qin S. J., and Badgwell T. A., 2000. An overview of nonlinear model predictive control applications, In Nonlinear Model Predictive Control, edited by F. Allgower and A. Zheng, Birkhauser, Switzerland, 2000.