Study Of The Anti-corrosion Deposits And Coatings On The New-Style Gas Condensing Exchanger

At present,to avoid the corrosion of the equipment for utilization natural gas due to the acid condensate,the temperature of flue gas was commonly over 150℃.As a result,lots of energy sources are wasted and environmental pollution is serious.For reducing the temperature of flue gas,recycling thermal energy,absorbing the bad gas,and realizing high efficiently,energy-saving and environmental-friendly,the anti-corrosion is one of the key technologies of its research and development.This paper aims at solving the corrosive problem by combining electroless deposit and coating technologies to preparation and research a multiple anticorrosive cover composed with deposit and coating,.In study of the deposits,Ni-P,Ni-Cu-P,Ni-Mo-P and Ni-W-P deposits are primarily researched and compared with each other.Their corrosion-resistance is studied by polarization curve and electrochemical impedance spectroscopy(EIS) testing methods.The results show that the corrosion rate of Ni-Cu-P deposit is the least and its self-corrosion current density is 0.03μA/cm².Therefore,it can be used as an anti-corrosion cover on cupreous condensing heat exchanger.The plating technical parameters of Ni-Cu-P deposit are optimized.As the stabilizer is sodium molybdate,the concentration of sodium hypophosphite and copper sulfate is 35g/L and 0.5g/L respectively,Ni-Cu-P deposit has the best corrosion resistance.This deposit is investigated by EPMA,XRD analytical methods.The results show that it is amorphous and the composition of it is 84.7%Ni-6.23%Cu-8.6%P(wt.%).In the condensate of different temperature,electrochemical parameters are studied.The results show that the self-corrosion potential and the self-corrosion current density of Ni-Cu-P deposit are lower than those of Cu substrate,and the electrochemical impedance is higher than that of Cu substrate.Therefore,Ni-Cu-P deposit can be used as an anti-corrosion cover and anodic sacrificial protective deposit to increase the effective life of cupreous condensing heat exchanger.The anti-corrosion mechanism of Ni-Cu-P deposits is primarily studied.In corrosive solution,Ni is dissolved selective and P is enriched on the deposit surface.Formed P enriched layer can slower the speed of Ni dissolving and Ni²⁺ diffusion.Cu accelerates Ni to dissolve and P to enrich and enhance the stability of the deposit.The chemical passivation model is established simply.For screening out a coating which is anti-corrosion,water-resistant and heat-resistant,the concocted aluminum paste coating,FEVE coatings(F400,F700,and F900) and polyurethane coating are studied by EIS,heat-resistant and temperature alternating resistant test.The results show that the electrochemical impedance of FEVE F400 coating and polyurethane coating has a less change.Their anti-corrosion,water-resistance and heat-resistance are better than others. The three others have more or less disadvantages and can't meet the operation requirement. Polyurethane coating can be made the least thin to reduce the effect on diathermancy of exchanger.Therefore,Polyurethane coating is selected as the protective coating on cupreous condensing heat exchanger.The primary sample of condensing heat exchanger is used in a boiler room in Beijing.It has a well corrosion-resistance and enhances the thermal efficiency of gas-fired boiler by 9%.