The Pros and Cons of Dry Gas Seals Installation in an Existing Synthesis Gas Compressor

摘要

Six years ago, in 2000, the Petrobras' Ammonia and Urea plants located in the Petrochemical Complex of Camacari, Brazil, were revamped in order to increase the capacities to 1500 metric ton/day, in both plants. Several technological upgrades were carried out, as an effort to modernize the process and the equipments. One of these upgrades was the replacement of the synthesis gas compressor shaft seals, from floating ring oil seals to dry gas seals. The synthesis gas train has two compressor cases, driven by two steam turbines with a total output of 30,400 HP (22,670 kW). The low pressure compressor case suction pressure is 370 psia (25.5 kgf/cm~2a) and the discharge pressure is 927 psia (65.2 kgf/cm~2a). The high pressure compressor case suction and discharge pressure are 884 psia (62.2 kgf/cm~2a) and 2,218 psia (156 kgf/cm2a) respectively. The seals chambers had to be machined to fit the new dry gas seals and the sealing gas panels connections ports. In the low pressure case the seals modification has been a success, we are operating for six years with the seals installed in 2000, without failures. But, unfortunately, it has not been the case with high pressure compressor. In five years of operation, from 2000 to 2005, the HP case seals have failed seven times, presenting an unacceptable failure rate (1.4 failures per year). The purpose of this paper is to describe the problem and the solution adopted, as well as to discuss the reliability aspects involved in a major change in the shaft sealing system of an existing compressor.