| Phosphorus off-gas is a high calorific value industrial off-gas containing complex impurities. The existence of phosphors and sulfur cause serious corrosion to the facilities, as a result, the facilities will lose their efficiency in a short time. Meanwhile, the off-gas application efficiency is less than 50%, the other part of the off-gas will be burned into the atmosphere. As a result, the valuable CO resource was wasted and the environment is being polluted. This kind problem restricts the development of the phosphor industry. So, efficient application of the phosphors off-gas becomes the hot point of investigation over the world. The impurities and their concentration, the types of the burning products and their changing in the burning process, the corrosion type and the combustion characteristic are the essential problem determining the effective application of phosphorus tail-gas.In this dissertation, qualitative and quantitative determinations were carried for the raw phosphorus and the burning gas as well as the tail-gas compositions. As a result, a lot of authentic and effective data were obtained. In the meantime, the site corrosion and imitation investigation were carried. Also, the corrosion products and their structure organization pattern of phosphorus itself and the co-corrosion of phosphorus-sulfur to different materials were determined and analyzed. Finally, their corrosion mechanisms were revealed. The concept of phosphorus corrosion dew point was put forwarded. The corrosion dew point of mixed COx-POx-NOx-H2O-PH3 in the phosphorus tail-gas accelerating the corrosion of the facilities was tested and verified. Based on traditional burning gas combustion theory, the combustion characteristics of this tail-gas were investigated, the indexes of mean mass of mixed phosphorus tail-gas system, the mean dynamic viscosity, the theoretical combustion temperature were put forwarded. Conclusions are as the follows.1.Theoretical corrosion mechanism investigation with traditional methodBy means electrochemical methods together with identification of actual corroded components the corrosion behavior of the facilities were investigated, where a series of patented units owned by our group were used, with which the formation process of corrosion products were able to be revealed for different materials in phosphoric acid environment and phosphoric acid-sulfuric acid environment. The corrosion products and their tissue morphology and structure were identified by XRD,XPS, SEM etc. it revealed that the phosphorus off-gas corrosion belong to a combination corrosion of electrochemical corrosion, inter-granular corrosion, dew point corrosion high temperature corrosion, sulfide stress cracking (SSC) and sulfuric acid inter-crystal corrosion. Corrosion kinetic studies shows.(1) In the phosphoric acid environment of COx-POx-NOx-H2O, corrosion rate of materials are Q245R> 16MnR>>304> 316L; low-temperature corrosion resistant ability to phosphoric acid are 16MnR>>Q245R; high-temperature corrosion-resistant phosphate are 316L>304> 16MnR>>Q245R.(2). In the phosphoric acid environment of COx-POx-SOx-NOx-H2O, corrosion rate are 16MnR> Q245R>> 304> 316L> alloy; high temperature resistant to phosphoric acid-sulfuric acid corrosion are Alloy> 316L stainless steel> 304>>16MnR> Q245R.2. Corrosion kinetics and thermodynamics investigationsBy means of new theoretical calculation method, phosphorus dew point corrosion concept is put forwarded through the determination of low temperature corrosion polarization curves, Tafel curves, AC impedance corroded and related analysis. The COx-POx-NOx-H2O system phosphoric acid corrosion dew point calculation formula was deduced with the help of Gibbs phase rule. Finally, the low temperature and high temperature corrosion dew point of phosphorus were obtained. Also, the assume of PH3 accelerating off-gas corrosion to the facilities was tested and verified.(1)In the phosphoric acid environment of POx-NOx-COx-H2O, the high temperature phosphoric acid dew point temperatures are 300℃-350℃ for Q245R,304,316L, alloys. Meanwhile, for 16MnR dew point temperature corrosion is 700℃.(2) In the phosphorus-sulfur coexistence environment of POX-SOX-NOX-COx-H2O, the corrosion dew point temperature is 300℃～350℃ for Q245R,304,316L, alloy.In phosphorus tail-gas of CO-H2-CH4-H2S-PH3-COS-SC2-P4 system, the determined corrosion dew point temperature is consistent with theoretical calculation value 358.25℃, validating the concept that PH3 accelerates corrosion to the devices.3.Combustion characteristics investigation of yellow phosphorus off gasThe combustion characteristics of yellow phosphorus off gas were investigated combining theoretical calculations and actual testing. In the patented devices invented by our group, the theory of Tanford diffusion, ESCIMO turbulence combustion and so on were carried to determine the combustion temperature of phosphorus off-gas.Also, the combustion temperature distribution field in different excess air coefficient were measured. The temperature field and flow field distribution of yellow phosphorus off gas were obtained by studying the radiation characteristics of the flame. The CO-H2-CH4-H2S-PH3-COS-SC2-P4 system’s entropy, enthalpy, Gibbs free energy and equilibrium constant under different temperature were calculated by the thermodynamic software Factsage 6.1. The estimated average mass of phosphorus off-gas mixture of CO-H2-CH4-H2S-PH3-COS-SC2-P4 is 28.48806667g/mol, the average dynamic viscosity is 1.68232E-05 (Pa. s), the ignition point is 100℃, the average theoretical combustion temperature is 2017.267℃, the average combustion characteristic coefficient β is 0.283646933.For the optimum air excess coefficient a of phosphorus off-gas mixture system:before purification, α= 1.2-1.4, after purification,α=1.3,while the theoretical calculation of α=1.02, etc. These are theoretical basis for phosphorus off-gas recycle.Combining all the above study results, a series of yellow phosphorus tail gas boiler were successfully developed. As a result, phosphorus enterprises are able to bring about phosphorus exhaust gas boiler in the industrial applications, which has been expected for decades.
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