COOLISS: A MODELING TOOL FOR SCALING PREDICTION IN CONDENSER COOLING CIRCUITS WITH COOLING TOWERS

摘要

One of the main issues of condenser open recirculating cooling systems is scaling. This phenomenon can have high economic consequences due to a loss of thermal exchange, an increase of maintenance costs and potentially plant shutdown. To tackle this problem, EDF, which operates 30 condenser open cooling circuits in nuclear power plants in France, has developed a modeling computer program called CooliSS©, to help optimize chemical treatment. CooliSS is based on a chemical mass balance model and can provide predictions of cooling water chemistry evolution within the cooling circuit, as a function of operating conditions. The software was developed under the open source environment Scilab/Xcos©. Phreeqc is used for the calculation of water chemistry in each component of the circuit (chemical speciation, pH and saturation index calculation, etc.). The model is based on theoretical considerations. Currently, two states of CooliSS are available to predict scaling in condenser cooling circuits equipped with counter-flow cooling towers: one is dedicated to studies at steady state and the other one to dynamic studies, i.e. when operating conditions vary as a function of time. A case study will be presented in this paper: the dynamic version of the CooliSS model, was used to evaluate an acid injection control system before its commissioning in Cruas nuclear power plant. CooliSS is able to calculate the variations of chemical composition along the circuit according to operating conditions fluctuations with time (makeup water quality, flow rates, evaporation rate, temperature...). CooliSS allows the initial calculation of the acid flow rate as a function of operating conditions and of the makeup water quality based on the Ryznar index. Then, during operations, the program adjusts the acid flow rate as a function of the resulting quality of the circulating water according to the control parameters.