The Study On Corrosion And Anti-Corrosion Technique In Combustion Process Of Heavy Oil

Heavy fuel oils that come from residual oils of crude oil refining, are used as fuels of the steam boiler, furnace and gas turbine. Due to the existence of S, V, Na etc., high temperature corrosion and sulfate acid dew-point corrosion will happen during combustion of the heavy oils. In this paper, heavy fuel oils induced corrosion mechanisms and anti-corrosion methods in petrochemical industrial equipment are studied. Corrosion behaviors of the boiler pipes material 20 G, the furnace pipes material Cr5Mo and aluminized Cr5Mo, sulfate acid dew-point corrosion-resistant materials, and the methods of removing Na, V from the fuel oils are studied. The purpose of the study was to search for complex anti-corrosion methods for heavy fuel oils combustion equipments.By analyzing the metal state in heavy fuel oils, the process removing vanadium in heavy oils is put forward. V in fuel oil maybe removed by adding some substances that react with V at the high temperature and separated at the low temperature. Na also maybe removed from the heavy fuel oil by the same method. The non-corrosive organic additive and the electric fields separation technology are used to decrease the attack of heavy fuel oil to metallic materials. The experimental results show: (1) the different organic additive and parameters could be only used in the different feed oils. (2) the higher the temperature and the content of the organic additive are, the longer the reaction time is, the higher the removal rate of V is. (3) the remove rates of V, Na are obviously affected by a lots of factors, these include the separation temperature, the stay time, the mixing strength and the electric field strength. At the optimum condition, the removal rate of V and Na can be up 70%, and 90%, respectively. Hence, the high temperature corrosion induced by heavy fuel oil could becontrolled by above stated methods.Because the aluminium ferrum alloy film of 0.1~0.5mm is easy to form on the surface of aluminized steel and possesses the good properties of the oxidation-resistance, corrosion-resistance, wear-resistance, the aluminized steel have been used widely in the fields of petroleum, chemical industry, metallurgy, electricity etc.. The studies on new aluminizing technology and corrosion behavior of aluminized steel in high temperature melting ash are reported hardly on literature, but it is very important to solve the corrosion induced by heavy fuel oil. Hence, New aluminizing technology and corrosion behaviors of carbon steel, aluminized carbon steel, Cr5Mo, and aluminized Cr5Mo in high temperature melting ash are studied mainly in this paper. The good quality of aluminized layer can be gained by using optimum bath composition and aluminizing technology parameters, the steel with the layer can be used in different conditions. The optical examination indicates that the structure phase of aluminized layer is mainly FeAl alloy, and the phase is continuous, uniform, compact and no brittle area. The simulated fuel ash high temperature corrosion test at 600癈, 700癈 and 750癈shows that the oxidation corrosion-resistance and the high temperature melting ash corrosion-resistance of the aluminized materials are obviously better than that of the non-aluminized materials at the some test condition due to the excellent corrosion-resistance of FeAl alloy phase.The most of sulfur and sulfide that exist in the heavy fuel oils can be transformed into SO2, and SO2 can be oxidized to form SO3 during combustion of heavy fuel oil at certain condition. SO3 can not react with the metal without H2O, but SO3 can react with H2O(gas, 5%~ 18%) in mist incorporate to form H2SO4, the later can raise the dew point of mist. When the temperature of equipment surface touching mist is lower than the dew point, the sulfate acid drops will form and seriously erode the metal. Because the sulfate acid normally exists at the low temperature parts of the boiler air preheater, furnace air preheater and the medium entrance of convection chamber, this corrosion is called as cool-end corrosion. The study...