Abstract: With the ever-increasing requirements for steam and water quality in thermal power plants, manual dosing has been gradually replaced by automatic dosing. Currently in most automatic dosing systems single-parameter based simple PID control is utilized. However, limited by phosphate monitoring and control delay, this type of control cannot accomplish accurate and immediate regulation of phosphate concentration under peak modulation or variable load conditions. Regarding these problems, this paper proposes a multi-parameter automatic control system for boiler water phosphate dosing. The program introduces the phosphate concentration, pH value, and conductivity of boiler water together with the boiler feedwater flow as the control parameters. The calculation results of pH value and conductivity value of boiler water are corrected with the on-line monitored phosphate concentration. At the same time, in combination with the boiler feedwater flow changes, the intelligent PID control technique is used to adjust the dosage of phosphate. The program has been implemented in the dosing system innovation project in an Inner Mongolia power plant. The results show that since the commissioning of the multi-parameter automatic control system into operation, the phosphate content has been stabilized with the pH value maintained between 9.40 and 9.50 while the conductivity between 9.5 and 10.5 μS/cm in boiler water. Apparently, the boiler water quality is greatly improved, which ensures the safe and stable operation of the generation unit.

Key words: thermal power plant, boiler water treatment, pH value of boiler water, automatic dosing, multi-parameter control, intelligent PID control