Samenvatting

OOS International is a Netherlands-based international offshore service provider for accommodation, ship management and heavy lifting. OOS provides highly qualified construction services within the oil and gas industry. The OOS Tiradentes is a Semi-Submersible Accommodation Vessel (SSAV), which can accommodate 580 people. A 3D-compensated 'gangway' is installed to transfer people between the OOS Tiradentes and the client's platform. Dynamic Positioning (DP) is used to maintain position next to the platforms.
The vessel is currently in operation near the Brazilian coast. This area is labelled as a temperate climate which means the rainfall and temperature differences between seasons is not significant. The regulations for safe operation in "Dynamic Positioning" mode on the OOS Tiradentes describe that at least three of the six main engines must be running. As not all engines are running all the time and not at full load the cooling water pumps have more cooling capacity than needed. By installing variable frequency drives on the six cooling water pumps the RPM of the electric motor can be reduced, this leads to lower energy consumption. This can save fuel and prolong the life of mechanical parts in the pump due to lower mechanical stresses.
This study is a recommendation to OOS International on optimizing the cooling water system using variable frequency drives, and answers the question, " What is the expected return on investment of the opted installation of variable frequency drives on the seawater cooling pumps?”.
Desk-research and quantitative research were combined for this study. VFD calculations on the OOS Tiradentes show that usually only 30 percent or less of the pumped cooling capacity is effectively used. Fuel savings after installing the variable frequency drives are estimated between €64,747.54 and €77,462,26 per pump configuration per year.
For the six pumps that will be equipped with VFDs, the upgrade was calculated on material costs, installation, and man-hours. The cost for this conversion is estimated at €509,734.19. The Return on Investment is calculated based on four models and in the worst-case scenario it takes around 15 months.