Shaft seal for a rotating SSP reactor in PET processing
Problem and challenge
PET flakes with high viscosity are needed for the manufacture of drink bottles out of PET. In the manufacture of PET and the processing of recycled R-PET, the initial viscosity figures are too low for the requirement. The PET flakes therefore undergo solid-phase condensation in a vacuum-proof rotating reactor (length 80 m (3150 “), diameter 6.2 m (244 “)). After spending between 8 and 12 hours at defined temperature and pressure, they change from an amorphous to a crystalline condition. The polycondensation starts at a set pressure/temperature level. The molecular chains lengthen while water is released, and the viscosity rises. The flow of inert gas (CO2) picks up unwanted, volatile contaminants. An easily fitted seal is needed for sealing the filling side of the reactor in order, for reasons of safety, to prevent the inert gas from escaping. It must be able to withstand the movements of the reactor shaft (100 mm (3.94 “) axially, 25 mm (0.98 “) radially).
EagleBurgmann Espey solution
For this purpose, Espey developed the Espey WD 500 A shaft seal with barrier gas connection and 4 seal rings, designed for a shaft diameter of 1190 mm (46.85 “), a temperature of 220 °C (428 °F) and a slight vacuum. Because it is very time consuming to dismantle parts of the reactor shaft and its components, Espey designed a 4-piece housing in order to meet the demand for the simplest possible assembly. In addition, the seal has to withstand huge shaft movements (up to 25 mm (0.98 “) radially), and this is achieved through a special implementation of the floating seal rings. Unlimited axial shaft movement can be absorbed by the Espey sealing system. In order for the surroundings of the reactor to be entirely safe for the operating staff, the seal of the reactor, which is filled with CO2, incorporates a nitrogen barrier.