Sealing volatile high-pressure fluids has always been a challenge unless the temperature is cold enough to produce a true liquid state around the seal. Even handling true liquids having low boiling points can result in low life expectancy due to the flashing of the fluid as it approaches atmospheric pressure and is heated by the seal faces. As pressure levels and temperatures increase above cryogenic, there is a need for technologies other than conventional contacting seals. Fluids handled in a supercritical state are particularly difficult since they are not in a true liquid state to begin with, and lubricity of this "dense phase vapor" is extremely poor. API 682, Second Edition, (2002) recognizes the use of noncontacting dual unpressurized seals for this type of service. This paper will present the application of a dual unpressurized seal with noncontact lift-off faces to a high-pressure volatile fluid. This application required a high-energy pump at an elevated speed to create the pressure and flow required by the process. The alternative to this pump was a reciprocating compressor, which had been used on previous process units. Compared with the pump, the compressor option would have been significantly more expensive to purchase and would have resulted in increased maintenance over the life of the process unit. The pump selected was a nine-stage barrel pump rotating at 6686 rpm driven by an electric motor through a gearbox. The fluid being pumped was ethylene. Suction pressure was 950 psig. The ethylene was chilled to an operating temperature of 50℉ so that the pump could develop the head necessary to produce the required discharge pressure of 4450 psig. The seals selected have now run for over two years with no failures. This includes several issues with the pump during which the pump was disassembled to correct vibration problems. At these times, the seals were removed from the pump and were not even reconditioned but were just reinstalled. Under similar conditions, a contacting seal would have been reconditioned each time the seals were removed and would have had an ultimate life expectancy of only six months.
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机译：除非温度足够冷以在密封件周围产生真正的液态，否则密封挥发性高压流体一直是一个挑战。由于流体在接近大气压并被密封面加热时会发生闪蒸现象，因此即使处理沸点低的真液体也会导致预期寿命降低。随着压力水平和温度升高至低温以上，需要除常规接触密封件以外的技术。在超临界状态下处理的流体特别困难，因为它们开始时并不是真正的液态，并且这种“致密相蒸气”的润滑性极差。 API 682，第二版，（2002）承认此类服务使用非接触式双重非加压密封。本文将介绍具有非接触剥离面的双重非加压密封在高压挥发性流体中的应用。此应用程序需要高速运转的高能泵来产生过程所需的压力和流量。该泵的替代品是往复式压缩机，该压缩机已在以前的处理单元上使用。与泵相比，压缩机选件的购买价格会高很多，并且会增加处理单元使用寿命内的维护量。选择的泵是由电动机通过变速箱驱动的，以6866 rpm旋转的九级桶式泵。泵送的流体是乙烯。吸气压力为950 psig。将乙烯冷却至50°C的工作温度，以便泵可以形成产生4450 psig所需排出压力所需的扬程。现在选择的密封件已经运行了两年以上，没有任何故障。这包括泵的几个问题，在此期间拆卸了泵以纠正振动问题。在这些时候，从泵上拆下了密封件，甚至没有对其进行修复，而只是重新安装了。在相似的条件下，每次取下密封圈时，接触的密封圈都要进行修复，其最终预期寿命仅为六个月。
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