This paper explains the complexity in marine tanker loading of highly waxy RJ Crude via Single Point Mooring System at Bhogat Terminal. It mainly presents the key challenges in temperature sustenance of Rajasthan Crude in the marine pipelines during the tanker loading operation. It also presents how the pump logic and valve closure timings are configured to prevent high pressure surge in the system.
Due to the waxy crude characteristics of Mangala Crude, it is required to always maintain the Crude temperature above its Wax Appearance Temperature of 65 Deg C. As the marine system partly consists of non-heated section like the under buoy and the floating hoses, it was required to simulate the temperature losses in the system and provide a pipeline flushing sequence at the end of the operation. Various flow and operational scenarios are modelled in OLGA and recommendations are implemented for the system. Similarly, Surge analysis was performed in PIPENET to determine acceptable valve closure timing for the tanker valves, breakaway couplings (BAC), SPM and PLEM valves to prevent overpressure in the marine system.
Based on the transient simulations, temperature loss during RJ crude export (at 4,636m3/hr) from terminal to the tanker in 24 hours is negligible (less than 10 Deg C). This indicates that the insulations in the pipelines are adequately designed for preventing heat loss. Whereas, the temperature in the hoses falls below 42 Deg C within 12 hours of shutdown which may lead to wax formation and may block the hoses. Therefore, RJ crude is to be flushed out of the system using flushing oil before it can cool to below its wax appearance temperature of 65 Deg C. It is recommended to insulate the bare pipe-works such as the PLEM, SPM and tanker if possible to facilitate a reasonable response time for setting up flushing oil displacement. It is also recommended that the pipelines are heated to 50 Deg C prior in advance of commencing flushing oil displacement operations to terminal and in preparation for RJ crude export.
Based on the hydraulic surge analysis, a closure time of 30 seconds is acceptable for PLEM valve closure. It is recommended to trip the export pumps at loading arm pressure High High of 7 bara. However, closure of both the breakaway couplings (BAC) cause pressure surges which exceed the MASP of the hoses for BAC closure times of 10 to 60 seconds.