Determination of Salt Component Concentrations in Boiler Water using Conductivity and pH Measurements

Abstract

Implementation of automatic water chemistry control at power units of thermal power stations (TPS) is hindered by the unavailability of analyzers required for monitoring certain standardized characteristics of the coolant. Important characteristics include salt content and ammonia concentration in the feedwater and salt content and phosphate concentration in the boiler water. If automatic analyzers are not available, phosphate concentration in the boiler water of drum boilers with an operating pressure above 10 MPa can be determined using conductivity measurements. In this case, the concentration of phosphates is calculated using the regression equation correlating phosphate concentration with electric conductivity of a cooled boiler water sample from the salt compartment or the equation derived by transformation of the system of equations describing the ionic equilibrium in the feedwater and the boiler water. The procedure was developed based on the results of a full-scale experiment performed at the TETs-26 cogeneration power station of PAO Mosenergo. It has been demonstrated that the correlation coefficient is 1.0 and the phosphate concentration is a function of the specific electric conductivity of a direct sample and an H-cation-treated cooled sample of water taken in the salt compartment of a drum boiler. However, for practice, the results of measurement of the specific electrical conductivity of an H-cation-treated sample are the only correct ones that enables the effect of a change in the quality of the working solution of sodium phosphate or feed water to be eliminated. Additional measurements of boiler water pH make it possible to calculate the concentration of salt components and improve the reliability of chemical control if fast upsets of the water chemistry occur. The developed calculation method for determining phosphate concentrations in boiler water using conductivity measurements was verified in a TP-87 boiler with a drum pressure of 13.8 MPa at the Ivanovo TETs-3.