IMPACT OF SEA COOLING WATER (SCW) MANAGEMENT AND HEAT EXCHANGER DESIGN ON TUBE FAILURE IN ONCETHROUGH SEA COOLING WATER SYSTEM L'IMPACT DE LA GESTION DE L'EAU DE REFROIDISSEMENT DE MER (SCW) ET LE DESSEIN DE L'ECHANGEUR DE CHALEUR SUR UNE PANNE DE TU

摘要

The Petronas LNG Complex in Bintulu, Malaysia comprises the MLNG, MLNG Dua and MLNG Tiga plants. MLNG (1/2/3) has a once-through sea cooling water (SCW) system that uses about 160,000 m~3/hr of seawater and all the exchangers are fed from the bottom. MLNG Dua (4/5/6) is a partly seawater cooled. The seawater cooling system for train 4,5 and 6 were connected to the existing sea water system of train 1,2 and 3 respectively. Due to head limitations of the sea cooling water system, all the MLNG Dua exchangers are designed to be fed from the top with the total sea cooling water consumption of about 50,000 m~3/hr. MLNG Tiga (7/8) is fully air-cooled plant. Since start up of MLNG Dua in 1996, the propane condensers and sub-coolers (aluminum brass low finned tubes) has experienced a number of tubes failures in these condensers. Tube leaks was considered to be due to air ingress through the sea cooling water standpipes on the 112" Sea cooling water supply lines and in combination with insufficient water pressure levels in the system and varying internal tube diameters. Combination of these factors leads to erosion-corrosion damage as observed in particular at tube inlet and at the internal diameter transitions at the unfinned sections of the tubes under the tube support plate. Severe fouling leading to under-deposit corrosion was also experienced in some of the tubes. Measures taken to improve the SCW system includes, throttling the main outlet valves of the condensers to prevent air ingress into the SCW standpipe, installation of 36" crossover line between the three 112" SCW line and improvement in chlorination of the sea cooling water to prevent biofouling. Other measures taken to improve the reliability of the condensers are, re-tubing with equal diameter tubes, installation of mesh screen at the tube sheet, passivation of aluminum brass tubes and installation of soft anode. A detail Computational Fluid Dynamic (CFD) study was also carried out to see the impact of the hydraulics due to SCW fed from the top of the exchanger. This paper discusses the impact of sea cooling water management and heat exchanger design on tube failure in the once-through sea cooling water system.