Yokogawa is improving plant efficiency by reducing pump horsepower while maintaining needed SO2 removal. The optimization system typically consists of three functions: enhanced regulatory control, model-based prediction, and process value prediction. The system uses these three functions to continuously determine the minimum required number of recirculation pumps in operation, and to calculate the setpoint for the limestone slurry flow PID (proportional-integral-derivative) control loop……………... Enhanced regulatory control governs the number of recirculation pumps in operation and calculates the slurry flow setpoint. It also calculates the optimal pH setpoint, using feed-forward control for some abnormal cases. Enhanced regulatory control also keeps track of the run time of each recirculation pump, and uses this data to equalize the operating times of the pumps.……………... This optimization system automatically adjusts to different coal types because it uses the inlet SO2 value as an input to the system. This value varies significantly based on the coal type and is an important parameter for optimizing control. The system also automatically adjusts for spray nozzle plugging and pump performance deterioration. Varying plant load is not a problem as the optimization system works well in the range from low to full load.……………... A 700-MW coal-fired power plant in Japan implemented the optimization system described above. This plant runs about 300 days per year at baseload, and is not in operation for the other 65 days of the year. The energy savings realized by running only the required number of recirculation pumps was 12.4% of the unit’s total house load, equating to about $900,000 in energy savings per year based on market conditions in Japan. Another benefit was reduced pump run times, which resulted in lower pump maintenance costs and extended pump life. A third benefit was less limestone usage.………………

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