121 Scientific Journal of Maritime Research 32 (2018) 121-131 © Faculty of Maritime Studies Rijeka, 2018 Multidisciplinary SCIENTIFIC JOURNAL OF MARITIME RESEARCH Multidisciplinarni znanstveni časopis POMORSTVO Change in Steam Generators Main and Auxiliary Energy Flow Streams During the Load Increase of LNG Carrier Steam Propulsion System Vedran Mrzljak, Jasna Prpić-Oršić, Tomislav Senčić University of Rijeka, Faculty of Engineering, Vukovarska 58, 51000 Rijeka, e-mail: vedran.mrzljak@riteh.hr; jasna.prpic-orsic@riteh.hr; tomislav.sencic@riteh.hr ARTICLE INFO Original scientific paper Received 19 March 2018 Accepted 7 June 2018 Key words: LNG carrier Steam propulsion Load variation Energy flow Steam generator ABSTRACT In this paper is presented an analysis of main and auxiliary steam energy flow streams from steam generators during the increase in steam system load at conventional LNG carrier. During the steam system load increase was presented differences in steam pressure and temperature between main and auxiliary steam flow streams. Energy power of the auxiliary flow stream is higher than energy power of the main flow stream only at the lowest steam system loads after which main flow stream takes over primacy at middle and high steam system loads. Cumulative auxiliary energy flow stream was divided on energy flow streams to each auxiliary device and energy power consumption of each auxiliary device was also investigated throughout number steam system loads. Analysis of steam production from marine steam generators presented in this paper provides insight into the operation dynamics of the entire steam propulsion system. 1 Introduction Internal combustion diesel engines in general (most- ly slow speed diesel engines) have a leading role in ship propulsion nowadays [1,2]. The wide presence of diesel engines in ship propulsion enabled the development of different numerical models for investigation of their oper- ating parameters [3,4] and for optimization of their proc- esses [5]. Steam propulsion is slightly present on ships, but is still the dominant propulsion of LNG (Liquefied Natural Gas) carriers [6] due to the specificity of their operation and the transported cargo. Any steam system as well as the steam propulsion system is very complex because it is assembled from a large number of components [7]. The marine steam propulsion system in comparison with any conventional land-based steam power system is much more dynamic in its operation. The marine steam propulsion system consists of two steam generators [8] due to safety and reliable operation and two parallel operating turbo-generators [9] to ensure NOMENCLATURE Abbreviations: Subscripts: DWT Deadweight Tonnage AD Auxiliary device AH Air heaters LNG Liquefied Natural Gas AUX Auxiliary Latin Symbols: CU Cumulative E · stream flow power, kW DEA Deaerator DES Desuperheater h specific enthalpy, kJ/kg DU Dump en energy m · mass flow rate, kg/h IN inlet (input) P power, kW MA Main Q · heat transfer, kW OUT outlet (output) SH share, % SS Splash steam