Seven loops of pH control for wastewater treatment plant at Oji Paperboard Saga Mill, which used to be taken control of with conventional PID algorithm, did not totally satisfy with its control response.
Generally, pH controls for neutralization process have non-linear characteristics. In addition, dead time would be long at the wastewater treatment plant because of limited installation location of pH meter and would vary depending upon discharge volume. Accordingly, time consuming fine tuning procedure for PID parameters just covers some specific conditions, but never represents satisfactorily entire status of the plant.
In this article, introduction of fuzzy control system in two out of seven pH control loops which had worse performance and had been strongly claimed for modification, significant improvement in control response and reduction of neutralizing agent cost after installation as well as principle of two loops with fuzzy system are summarized.
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