Abstract
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.
Highlights
Awareness of energy efficiency in the maritime sector has become of vital importance over the last decade [1], supported by strict international environmental legislation adopted by the International Marine Organization (IMO) and the continuous effort of the shipping industry to reduce its exposure to fuel price fluctuations and maximize the economic profits [2]
The proposed methodology was applied on a handy-size bulk carrier and a parametric study was conducted to estimate the real effect of substituting the conventional constant speed SW cooling pump with a variable speed drive (VSD) one, under the whole range of engine loads and for sea-water temperatures ranging from 13 ◦C up to 32 ◦C
With the exception of full engine load, in all other cases examined the usage of a VSD SW pump has a positive effect on the total fuel consumption, while at full engine load, there is a threshold temperature of the seawater, under which the operation with a VSD pump leads to higher total fuel consumption
Summary
Awareness of energy efficiency in the maritime sector has become of vital importance over the last decade [1], supported by strict international environmental legislation adopted by the International Marine Organization (IMO) and the continuous effort of the shipping industry to reduce its exposure to fuel price fluctuations and maximize the economic profits [2]. The effect of the increased LT/FT temperatures on the main engine bsfc due to the reduced SW mass flow rate is captured using a software application which is publicly available from the engine manufacturer [21] Based on this integrated approach and beyond existing aforementioned literature, taking into account the reduced power demand of the SW pump and the consequent effect on main engine fuel consumption, it becomes feasible to reliably estimate the overall impact of incorporating the VSD technique, on a vessel’s total fuel consumption depending on the actual operating conditions (seawater temperature, cooling load and engine load)
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