| China is one of the most yellow phosphorus production capacity countries in the world, and the phosphorus resource in China is in the second place-all through the world. China has more than 60 years yellow phosphorus production history.Yellow phosphorus is a kind of raw materials of chemistry industry, it is very important national economy of China, and it is wildly used in many industries. For example, we use the sodium tri poly phosphate as the food additives. In 2007, the yellow phosphorus production is about 0.75 million tons. When 1 tons yellow phosphorus is produced,2500～3000 Nm3 yellow phosphoric tail gas is emitted. So, there is about 19～22 billion Nm3 yellow phosphoric tail gas has been emitted in 2007. Yellow phosphoric tail gas brings serious air pollution, so the government has established some policies to control the serious air pollution which from yellow phosphorus production, the government prescribes the plants of yellow phosphorus comprehensive utilization.The comprehensive utilization of yellow phosphoric tail gas is an important way of sustainable development, and the economical way is burning yellow phosphoric tail gas as boiler fuel gas(It contains CO85%～95% for vol.),but 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:Hanging sample corrosion tests:The chief constituents of yellow phosphoric tail gas have been analyzed, using the orsat gas analysis apparatus. Phosphorus and arsenic have been analyzed by spectrophotometry. Phosphine and Sulfid have been analyzed by chromatography. Hydrogen fluoride has been analyzed by ion selective electrode method.We used hanging sample corrosion test in hot water furnace which burning yellow phosphoric tail gas. The tests indicate that, the boiler steels are corroded seriously in the burning yellow phosphoric tail gas. Mechanical Properties after Corrosion Test of yellow phosphoric tail gas changed obviously. Analysis showed that the phosphorus and its the combustion products are the main reason of this type of corrosion.Laboratory corrosion tests:We designed and manufactured an equipment of high temperature corrosion. The equipment has excellent corrosion resistance and good running condition.Electrodynamic polarization measurements are studied using the test materials 20g,20G,16MnR. The results show that serious corrosion is found on the three test materials, they have weak corrosion resistance. The corrosion speed of 16MnR ismore than three times of 20g,20G.Dripping phosphoric acid into the equipment of high temperature corrosion follow the lab corrosion method. By X-Ray Diffraction Analysis, the tests indicate that, At 300℃,the corrosion product is ferric phosphate [FePO4];At 700℃, the corrosion product are ferric metaphosphate [Fe(PO3)3] and ferrous metaphosphate[Fe(PO3)2]. The result of SEM analysis shows that the microstructure of corrosion products are near regular hexagon tubular, but the sides of microstructure are different.Thermal decomposition of phosphoric acid is studied in this paper. The decomposition product are metaphosphoric acid [(HPO3)n] pyrophosphoric acid [H4P2O7].The phosphoric acid dew point corrosion temperature is between 250℃～300℃,so increasing temperature of heated tubes can prevent corrosion.There are some Innovation Achievements in this paper:1) An equipment of high temperature corrosion has been designed, it has excellent corrosion resistance and good running condition.2) The concept of phosphoric acid dew point corrosion temperature was put forward, the phosphoric acid dew point corrosion temperature is between 250℃～300℃.3) Painted of amorphous powders by Supersonic Spray Coating is the best material. |
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