Material of yellow phosphorus metering tank

Industrial phosphoric acid produced from yellow phosphorus does not cause significant corrosion to 316L (or 304 and 18-8) at temperatures below 100 degrees； The cause of corrosion may be impure phosphoric acid; even a small amount of sulfuric acid or hydrofluoric acid can cause corrosion in 316L (although it can still be used, and it can last for about half a year in the production of wet phosphoric acid). The main type of corrosion is intergranular corrosion.

The comprehensive utilization of yellow phosphorus off-gases is an important approach for the sustainable development of the yellow phosphorus industry. The most direct and economical method for utilizing these off-gases is to use them as fuel (containing 82%–95% v/v CO). However, corrosion and damage to boiler materials caused by yellow phosphorus off-gases represent a significant challenge at present. This paper begins with an analysis of the corrosion of boiler materials in the combustion atmosphere of yellow phosphorus off-gases, and conducts laboratory-scale tests for high-temperature corrosion and dew point corrosion. The causes and mechanisms of phosphorus corrosion in the mixed atmosphere of yellow phosphorus exhaust gases were initially studied, and corresponding material selection plans were proposed, providing experimental and theoretical basis for the development and design of gas boilers using yellow phosphorus exhaust gases. The main research contents and conclusions are as follows: First, by comparing laboratory simulations of the combustion corrosion experiment of yellow phosphorus exhaust gases, the corrosion resistance of 316L and 304 stainless steels as well as 20G was studied under simulated corrosion conditions caused by yellow phosphorus exhaust gases. The results show that the corrosion resistance of 316L stainless steel is superior to that of 304 stainless steel and 20G. At temperatures between 250 and 300°C, both 304 and 316L stainless steels suffered from dew point corrosion caused by phosphoric acid vapor, with 304 stainless steel exhibiting more severe pitting corrosion. Through thermodynamic analysis of the mixed atmosphere of yellow phosphorus off-gases, it was determined that the dew point temperature of these off-gases is related to the concentrations of the components present in them. The effect of nitrogen oxides and carbon oxides on the dew point temperature of yellow phosphorus off-gases manifests itself through their influence on the total pressure of the mixture. In addition, the acid leaching weight loss method was used to simulate acid dew point corrosion, and macroscopic and microscopic photographs were employed to study the various factors affecting the corrosion of boiler steel; as a result, the influence patterns of factors such as phosphoric acid concentration and temperature on the corrosion rate of boiler steel were determined. Secondly, potentiodynamic sweep polarization curves and electrochemical AC impedance spectroscopy were employed to study the effects of various influencing factors on the corrosion electrode reaction process of boiler steel, as well as the corrosion mechanism of dew point acid. The results show that the corrosion rate at 20 g is 5–6 orders of magnitude higher than that of 304. The corrosion behavior of the test materials in phosphoric acid at different temperatures and immersion times was studied using AC impedance spectroscopy. The results show that as the temperature rises and the immersion time increases, the resistance of 304 stainless steel decreases, indicating a decline in its corrosion resistance.