Research On Numerical Simulation Of Cathodic Protection For Coastal Power Plant Condenser

As the shortage of fresh water resources in our country, considering seawater as cooling medium of condenser which is an important auxiliary power generating set in many coastal areas. Because the sea water has strongly corrosive, so the condenser severely eroded, and even endangered the normal operation. The common corrosion protection methods of condenser have impressed current cathodic protection and sacrificial anode cathodic protection. In actual operation, the sacrificial anode consumption speedily, and the surface fouling phenomenon seriously, so as to affecting the performance of the anode, but in the traditional design of impressed current cathodic protection, mainly based on engineering experiences and the average current density. The condenser structure is complex, prone to be protected with uneven distribution of surface potential in the actual operation, even appearing to phenomenon of under protection or over protection and hydrogen evolution. In recent years, with the popularity of computer, numerical simulation technology become favorable cathodic protection design tools of coastal power plant condenser.Based on the corrosion status of coastal power plant condenser in this paper, the condenser corrosion influence factors were analyzed. This paper mainly considered the two corrosion factors: temperature and conductivity of seawater. Polarization curve measurement and analysis were done under different temperature and conductivity, corrosion electrochemical parameters were obtained by curve fitting on the measured polarization curve. According to the theory of steady flow field and ohm’s law, the condenser cathodic protection system control equations are deduced, and combined with the actual corrosion environment and electrochemical corrosion kinetics principle to determine more realistic boundary conditions for control equations of the cathodic protection. The shrink physical test model of condenser was set up according to similarity theory and dimensional analysis theory. The experiment platform structures of condenser cathodic protection system was constructed indoors, using the method of measuring surface potential of cathodic protection of condenser to verify the reliability of numerical simulation. This paper focused on the research of the influence of output voltage, location, size and quantity of auxiliary anode, cooling water conductivity and temperature on the cathodic protection potential distribution of condenser using simulation software. The quite simplified model was set up based on the actual coastal power plant condenser, and the optimal cathodic protection scheme was finally determined by using simulation software COMSOL parameterized scan function. Through the above research could get the following conclusion:(1)By comparing the potential values of numerical simulation and experimental values of the measured potential, the maximum error is 2.65%, the minimum error is 0.92%, and the average error is within 3%. From the analysis of error result, the error could be controlled within 3%, it showed that the simulation results were reliable, the correctness of the model and the reliability of the numerical calculation method were validated. It both provided theoretical basis for the condenser of cathodic protection design, and became the effective means of the evaluation of current cathodic protection system.(2)Through changing factors, which affected potential distribution of numerical simulation of cathodic protection of the condenser, potential output, position, size and number of auxiliary anode, the circulating cooling water conductivity, temperature, could determine the scope of the reasonable auxiliary anode output voltage between-1.0 V to-1.2 V, and the reasonable position between auxiliary anode and center distance was 70 mm, which could ensure water chamber to be fully protected, and reduce the hydrogen embrittlement of titanium tube.(3)when the optimization of the output voltage E =-1V, auxiliary anode diameter D = 50 mm and auxiliary anode H = 50 mm in length was applied, the surface potential of carbon steel water chamber ranged from-765.68 mV to-795.75 mV, surface potential of titanium tube range from-784.1 mV to-257.8 mV, which was in the reasonable scope of protection.The innovation points are as follows:(1)Corrosion electrochemical reaction of condenser with corresponding boundary conditions to reflect in the simulation software COMSOL in this paper, to determine the more realistic boundary conditions of the cathodic protection system of control equations.(2)The second current distribution of corrosion module in simulation software of COMSOL was applied to numerical simulation of power plant condenser cathodic protection in this paper, and ultimately determined the best auxiliary anode size and layout position using the parametric scanning function in the software, giving the theory basis of cathodic protection system design of power plant condenser.