Turboexpanders in Ethylene Plants

摘要

As mentioned earlier, EC units require some type of warm, dry, superheated buffer gas at adequate pressure and temperature to be used for seal gas (oil or magnetic bearing units) or for cooling gas (magnetic bearing units only). All of this seal gas is recovered and returned to the process at the compressor suction pressure. As a ballpark estimate, the minimum required supply pressure is equal to the square root of the product of the turboexpander inlet and outlet pressures. For multiple stage systems, use the first stage turboexpander inlet and outlet pressures to calculate the seal gas supply pressure. Preferably, a warm process gas source can be found at suitable pressure. If not, then expander inlet gas can be heated (using a process exchanger, electric heater, or steam sparger) to the desirable supply temperature. It is important to ensure that liquids do not form at any time in the seal gas system or in the shaft seals. Liquid hydrocarbons will contaminate the lube oil in oil bearing units, and will cause erosion in the labyrinth seals in both oil bearing and magnetic bearing units.