Optimization of High Pressure Components for LDPE Manufacturing

Coned and threaded type connection valves, fittings and tubing up to sizes of 9/16” are typical high pressure components used on the initiator injection system of a Low Density Polyethylene LDPE facility. The process pressures of up to 360 MPa (52,200 psi) on the reactor side require even higher pressures on the initiator injection lines. Based on the differential pressures and the challenging environment 414 MPa (60,000 psi) has been defined as an appropriate pressure rating for such components. Valves, fittings and tubing with this pressure rating are more or less standardized and available from multiple sources on the market. However, the technical challenges in designing and manufacturing components for this duty are sometimes under-estimated and design improvements can lead to a higher process safety and a reduced downtime. This paper covers the design requirements and has a specific focus on a filter with screwed element and a check valve with ceramic ball. The majority of high pressure in-line filters on the market have a sintered element that is press-fitted into the filter body. This design has some disadvantages in case of fast depressurizations as they occur when a safety valve or a rupture disk blows off. The sudden differential pressure may cause the element to move inside the body, and this can be accompanied by cracking of the element. Parts of the broken sintered element are a risk to the process since they would move downstream followed by a contamination of the reactor. A new generation of such filters with screw-in elements was designed and tested. The R&D work resulted in an extended element that fits into a modified filter body with standard outside dimensions. Before performing a field test at a LDPE plant three prototype samples went through intensive testing at the manufacturer’s facilities. Check valves are typical components used in order to maintain the flow in one direction. For liquids the metal to metal sealing ball type is the most common. Since the process pressure exposes the mating parts — ball and orifice — to high compression forces, imprints and marks on the ball surface are sometimes experienced. The material of these types of balls is typically bearing steel which has high mechanical strength but limited corrosion resistance. In order to improve the cycle life of high pressure ball check valves alternative materials were looked at. During the further product improvement a check valve with ceramic ball was designed and lab tested at the manufacturer’s facilities.