天然气中汞对处理系统中铝材的腐蚀研究

国内对天然气中汞的研究主要集中在通过汞的浓度判定产气地层的地质成因及特点,而忽略了汞对地面集输工艺的影响,特别是汞对天然气处理系统中大量使用的铝质材料的腐蚀破坏作用。为此,通过研究得出了汞对天然气处理系统中铝材的腐蚀机理:在铝材的内表面,汞与铝发生电化学腐蚀,使铝材锈蚀;在铝材的内部或外层,发生汞齐脆化腐蚀,使铝材变脆、易破裂。结合生产实际进行了模拟实验,发现汞对铝的腐蚀程度随着温度的升高而加剧;液态汞对铝的腐蚀作用远远大于汞蒸气。通过对某气田天然气处理系统中汞分布的模拟,总结出了汞在天然气处理系统中的聚集规律:大部分的汞都进入了脱水脱烃工艺流程的液相组分中,由于汞的比重较大,易富集在一起形成大量液态汞。并提出了相应的改进措施:①在设计含汞天然气的处理流程时,应考虑汞对生产装置的影响,尽量避免使用铝质材料;②由于汞对铝的腐蚀过程是由表及里,可以考虑研制具有抗腐蚀表面膜的铝材;③对于含汞浓度较高的天然气,可以在预处理阶段加入脱汞单元。

study on the mercury-corrosion on the aluminum-made equipment in natural gas processing plants

The present domestic studies of the mercury contained in natural gas mainly focus on the mercury concentration which helps determine the geological origin and features of gas pay zones, but unfortunately that completely ignores its effect on the equipment on the ground, especially its severe corrosion on the aluminum made materials for natural gas processing system. Therefore, its corrosion physical nature was studied: galvanic corrosion occurs at the inner sides when the element mercury meets the aluminum, and forms an amalgam on the surface or the inside layers of the metal it contacts, which will result in an embrittlement of the aluminum material. According to field practices, laboratory tests were performed to simulate how the above mentioned corrosion occurs, demonstrating that the degree of this corrosion is aggravated with the increasing temperature, and the mercury in the liquid state causes much more serious corrosion than that in the steam state. Through simulating the mercury distribution in the natural gas processing plant of the Kela-2 Gas Field, we obtained the aggregation discipline of the mercury in the plant: most mercury entered the dehydration and dealkylation process mixed with the liquid, due to its bigger specific gravity, the mercury in liquid aggregated in enormously large volume. In view of this, we present the following positive proposals for protecting the materials in natural gas processing plant from the corrosion by the mercury in the gas: a. the aluminum material facilities should be avoided to use in the gas treatment project design with the mercury corrosion being taken into account; b. since the mercury corrosion on the aluminum facilities from surface to inside, those kinds of aluminum material with anticorrosive surface film may be considered; c. the demercuration can be added into the pretreatment period for the gas with a high content of mercury. This study is of value for handling and processing natural gas containing mercury in field practices.