Phosphorus, Yellow Phosphoric Tail Elements On The Corrosion Behavior Of Boiler Materials

The comprehensive utilization of yellow phosphoric tail gas is an important way of sustainable development in phosphoric industry. The economical way is to burn yellow phosphoric tail gas as boiler gas fuel because it contains CO 85%～95% in vol, however a difficult problem is the corrosion of boiler steels which results from yellow phosphoric tail gas. In this paper, firstly, the corrosion condition of boiler steels is studied by hanging sample corrosion tests and laboratory corrosion tests. The reasons and mechanism are studied, than some methods of avoiding corrosion and using schemes. The contents and conclusions of this paper are as follow:The corrosion properties of 316L,304 stainless steel and 20# boiler steel (20g) in a simulated corrosive atmosphere were investigated by means of accelerated corrosion test. The results show that in the simulated atmosphere the corrosion rate of 316L was significantly lower than that of 304 and 20g. At 250～300℃, the acid dew point corrosion became serious. Cavities were observed in the surface of 304 after the dew point corrosion, which means pitting corrosion was happened.The factors affecting the dew point temperature of yellow phosphoric tail gas were analyzed and discussed in respect of thermodynamics. The analysis indicated that the dewpoint temperature of the mixed system relied on the partial pressure of phosphoric acid vapor, water concentration in liquid phase and total pressure of the system and it had no direct relationwith the contents of NOx and COx in the flue gas. Their effect on the dewpoint temperature was shown by affecting the total pressure of the system.By using weight-loss method, macroscopical and microcosmic photograph of boiler steel, in this paper the author studys some factors that affect corrosion rate of boiler steel, and draws the influence law of the corrosion rate which is relate to temperature and phosph-oric acid concentration.Secondly, potentiodynamic polarization curve and EIS (Electroche-mical Impedance Spectroscopy) techniques were used to analyze the influence of different effect factors of corrosion on electrode reaction of boiler steel. EIS was applied to invest-igate the corrosion behavior of 304 stainless steel and 20g in the condition of different temperature and time. The results showed that, the corrosion resistance of the test material decreased with increasing of the temperature immersion time. Finally, this paper analyzed the corrosion step of the test material with inereasing of the soak period.