Study On Anticorrosion Mechanism And Engineering Research Of Recycled Medium - Pressure Steam By Reactive Yellow Phosphorus Reaction

China is a primary country in producing yellow phosphorus and heat processing phosphoric acid. The total production capacity and output of China had exceeded that of the70%world. Yellow phosphorus production concentrated Yunnan, Hubei, Guizhou and Sichuan province. The heat processing phosphoric acid production was mainly distributed in the consumption and transportation hub areas, such as Guangxi, Yunnan, Jiangsu, Hubei, Guizhou and Sichuan province. In21th century, energy saving and low carbon became the theme of development. China had successfully developed heat energy recovery and utilization technology which directly used natural air in the combustion of yellow phosphorus. This technology used a whole design scheme that phosphoric acid tower and the reaction heat recovery unit were combined to retrieve the reaction heat. The special phosphorus acid tower with the reaction heat recovery device had two functions simultaneously:1) it contented the demand of phosphorus chemical production and it was equivalently a reaction tower in chemical equipment;2) it contented the demand of the reaction heat recovery and it was equivalently an industrial boiler in thermal equipment. The technology was widely promoted and applied in China, which led to a new round of progress in the technology of heat processing phosphoric acid. Since2001in the industrialization, the device capability of this process and equipment technology held the47%domestic production capacity of heat processing phosphoric acid.Large scale is the basic requirement of chemical production. Apparatus enlargement is beneficial of reducing the operating personnel operates and raising labor productivity, at the same time, which is good for reducing the investment and reducing consumption. Due to the medium was yellow phosphorus combustion in the natural air, generation double molecular P4O10, P4O10combined with moisture in the air into phosphorus compounds. Those substances has strong corrosive at high temperature (=2000℃, the average local high temperature can reach2600～2800℃). The key of this study is how to prevent corrosion from high temperature. Based on the study of combustion and hydration of two steps with a heat recovery, there were three key problem solved for using nature air combustion vice during steam pressure and its large yellow phosphorus: (1) The enhancement of the vapor pressure make the inner surface temperature rising of the phosphorus furnace, which caused the water wall fin is corroded. How to acquire medium vapor pressure and solve the problem of corrosion is a core of this study.(2) The strength of the equipment requirements increase with increasing vapor pressure. How to satisfy no corrosion to equipment and the strength of the pressure vessel, stiffness requirements of equipment structure, is a core technology for long period operation in phosphorus furnace.(3) Large scale equipment is limited by the conditions of transportation, and the largest size is304,200, excluding takeover, etc. However, the actual special tower of phosphorus furnace wall shape size less than303,800. Heat transfer of original equipment was took away depend on membrane type water wall entirely. The equipment of large scale was limited, because of the relationship between combustion temperature and heat flux density that made the diameter of membrane water wall of heat exchanger is difficult to achieve high phosphorus mass flow rate of single series.Aimed at above key problems, this study carried out the following aspects of work.(1) Through the laboratory and semi-works production of studying on the production status of conjunctival matter, it initially revealed the formation mechanism of membrane, put forward corrosion control parameters of the conjunctival. Research shows that, at high temperature and low moisture conditions, P4O10reacts with H2O to form super phosphate, this substance is condensed to form a solid conjunctival conjunctival below the490℃, the corrosion rate of316L material is less than0.06mm/a, which belongs to the slight corrosion; conjunctival matter existence blocked direct contact with high temperature corrosive gas and combustion tower wall the problem of corrosion of materials, reaction tower is transformed from the high temperature corrosion of gas containing phosphoric acid and its polymer strong corrosion to the equipment for the influence of solid material conjunctival equipment material corrosion of mild, thus effectively blocking high temperature corrosive gas on combustion tower inner wall corrosion. From the studies, we obtained control condition is:H2O/(H2O+P4O10)5%-28%; regional reaction temperature is higher than1000℃, outlet temperature of burning phosphorus tower is higher than600℃; reactor wall temperature is lower than490℃. (2) Based on the research achievements of conjunctival compound, the comprehensive mathematical model which could reflect the flow, combustion and heat transfer process in the phosphorus acid tower was developed. Through taking a gradual approach, the control equations including continuity equation, momentum equation, energy equation and component transport equation was developed. Finally, the standard k-ε two equations model which described the turbulent flow, the eddy dissipation model which described the turbulent combustion and the P-1model which described the radiation heat transfer were used to limit the control equations. The tower form was circular. The diameter (D) was3600mm. The tower height (H) was11000～12000mm. The spray gun height (two spray guns) was1580～1650mm and the angle of them was41°. The excess air coefficient was1.3～1.7. The phosphorus content was2600kg/h-3000kg/h. These datas are in good agreement with the production equipment(3) The reduction of fin width could further reduce the temperature of fin center. The double ring inner and outer upper header could satisfy the demand of the strength of the medium pressure steam in the phosphorus acid tower. The connection technology of the variable diameter pipe and the lower header, and the innovative structure of small cooling water tank satisfied the demand of lower header strength and ensured the formation of conjunctival compound. Meanwhile, it ensured the safety of the natural water cycle. The local cooling water tank structure near by the spray phosphate gun effectively avoided the high temperature corrosion phenomenon, which ensured the normal operation of phosphorus acid tower. The characteristics of multiple rows of tubes and multiple head were developed. This technology (the lower header ring pipe connected with the annular internal and external connected upper header, or the radial multilayer exhaust pipe technology between upper header and lower header) achieved enough heat exchange areas with a very small equipment diameter change, which solved the large scale heating surface problem limited by the outer diameter of special phosphorus acid tower which contained the waste heat recovery device.