An Integrated Approach for the Assessment of Central Cooling Retrofit Using Variable Speed Drive Pump in Marine Applications

The present study describes a model-based approach for the assessment of central cooling retrofit solutions using variable speed drive (VSD) seawater (SW) pumps in marine applications. There are two main innovative features of the proposed methodology. The effect of boundary conditions (fluid stream temperatures and mass flow rates) on the performance of central SW/fresh water (FW) cooler is considered via a detailed heat exchanger simulation model. Additionally, the repercussion of the higher FW temperature on the main engine fuel consumption due to the incorporation of a VSD SW pump is examined. The proposed methodology is applied on a handy-size bulk carrier equipped with a shell and tube SW/FW central cooler and a two-stroke main diesel engine. Both the reduced power demand for the VSD pump and the increased brake specific fuel consumption (bsfc) of the main engine due to the increased low temperature (LT)/FW temperature have been considered at each operating point examined. Predictions have shown that in all part-load operating cases examined the use of a VSD SW pump has a positive effect on the reduction of total fuel consumption, whereas at full engine load, there is a SW threshold temperature under which the operation with a VSD pump leads to slightly higher total fuel consumption. This study highlights the importance of using an integrated approach for the reliable assessment of central cooling retrofit solutions, which can lead to optimized control solutions of the VSD pump operation for maximizing a ship's fuel savings.