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The paper presents exergy analysis of main propulsion steam turbine from LNG carrier steam propulsion plant. Measurement data required for turbine exergy analysis were obtained during the LNG carrier exploitation at three different turbine loads. Turbine cumulative exergy destruction and exergy efficiency are directly proportional-they increase during the increase in propulsion propeller speed (steam turbine load). Cumulative exergy destruction and exergy efficiency amounts 2041 kW and 66.01 % at the lowest (41.78 rpm), up to the 5923 kW and 80.72 % at the highest (83.00 rpm) propulsion propeller speed. Increase in propulsion propeller speed resulted with an increase in analyzed turbine developed power from 3964 kW at 41.78 rpm to 24805 kW at 83.00 rpm. Analyzed turbine lost power at the highest propulsion propeller speed is the highest and amounts 3339 kW. Steam content at the main propulsion turbine outlet decreases during the increase in propulsion propeller speed. Exergy flow streams can vary considerably, even for a small difference in propulsion propeller speed. Steam turbine in land-based power plant (high power steam turbine) or in marine steam plant (low power steam turbine) is not the component which exergy destruction or exergy efficiency is significantly influenced by the ambient temperature change. A detail analysis of main propulsion steam turbine from the marine steam power plant at several loads is hard to find in the scientific and professional literature.

SummaryNowadays diesel engines prevail as ship propulsion. However, steam propulsion is still primary drive for LNG carriers. In the presented paper high-pressure feed water heater was analyzed, as one of the essential components in LNG carrier steam propulsion system. Measurements of all operating parameters (fluid streams) at the analyzed heat exchanger inlets and outlets were performed. Change of the operating parameters was measured at different steam system loads, not at full load as usual. Through these measurements was enabled the insight into the behaviour of the heat exchanger operating parameters during the whole exploitation. The numerical analysis was performed, based on the measured data. The changes in energy and exergy efficiency of the heat exchanger were analyzed. Energetic and exergetic power inputs and outputs were also calculated, which enabled an insight into the change of energetic and exergetic power losses of the heat exchanger at different steam system loads. Change in energetic and exergetic power losses and operating parameters, which have the strongest influence on the highpressure feed water heater losses, were described. Analyzed heat exchanger was compared with similar heat exchangers in the base loaded conventional steam power plants. From the conducted analysis, it is concluded that the adjustment and control modes of these high-pressure heat exchangers are equal, regardless of whether they were mounted in the base loaded conventional steam power plants or marine steam systems, while their operating parameters and behaviour patterns differ greatly.

This paper presents energy analysis of entire marine main propulsion steam turbine and both of its cylinders at three different loads. Marine steam propulsion plant in which main turbine operates is described in detail. Measured data from real exploitation at each required turbine operating point enables calculation of energy losses and efficiencies. Real developed power distribution between both turbine cylinders is not the same at all observed loads. Energy losses and efficiencies of main turbine cylinders and entire main steam turbine increases during the increase in turbine load. An increase in turbine load resulted with in a sharp increase in energy efficiency of HPC (High Pressure Cylinder) from 51.01 % to 74.13 %, while the increase in energy efficiency of LPC (Low Pressure Cylinder) is not as sharp (from 73.88 % to 78.50 %). The change in energy efficiency of the entire main steam turbine during the load increase (from 65.54 % to 79.45 %) is mostly influenced by a change in energy efficiency of HPC. Energy loss and real developed power ratio is reversely proportional to energy efficiencies and losses of both steam turbine cylinders and the entire turbine. Sažetak Ovaj članak prikazuje energijsku analizu čitave glavne propulzijske parne turbine i oba njezina kućišta pri trima različitim opterećenjima. Opisuje se podrobno, brodsko parno propulzijsko postrojenje u kojemu radi glavna turbina. Izmjereni podatci stvarne eksploatacije za svaku zahtijevanu radnu točka turbine omogućavaju izračun energijskih gubitaka i učinkovitosti. Stvaran raspored distribucije snage između oba kućišta turbine nije isti na svim promatranim opterećenjima. Energijski gubici i učinkovitosti turbinskih kućišta i cijele glavne turbine, povećavaju se za vrijeme porasta opterećenja turbine. Povećanje opterećenja turbine rezultira naglim rastom energijske učinkovitosti HPC (High Pressure Cylinder = kućište visokoga tlaka) od 51.01 % do 74.13 % dok povećanje energijske učinkovitosti LPC (Low Pressure Cylinder = kućište niskoga tlaka) nije tako naglo (od 73.88 % do 78.50 %). Promjena energijske učinkovitosti cijele glavne parne turbine, za vrijeme povećanja opterećenja (od 65.54 % do 79.45 %), najviše je pod utjecajem promjene energijske učinkovitosti HPC. Gubitak energije i stvarni omjer razvijene snage obrnuto je proporcionalan energijskim učinkovitostima i gubicima za oba kućišta i cijelu parnu turbinu. KEY WORDS main marine steam turbine marine propulsion plant energy analysis change in load conditions KLJUČNE RIJEČI glavna brodska parna turbina brodsko propulzijsko postrojenje energijska analiza promjena opterećenja

Dominant propulsion systems of today’s LNG carriers are steam propulsion systems. Although a number of alternatives are developed, only steam propulsion systems in LNG carriers can fulfill a double function: the function of propulsion and on the other side the combustion of large amounts of BOG (Boil Off Gas) in one or more steam generators. In this paper was provided an analysis of the low-pressure feed water heater, as one of the important components of LNG carrier steam propulsion system. Based on the measured data for all flowing substances throughout the low-pressure feed water heater, it was performed numerical analysis of his energy and exergy efficiency, as well as calculation of energetic and exergetic power losses. The measurements were performed during LNG carrier maneuvering period, what enables insight into the operating parameters of heat exchanger during partial loads of steam propulsion system. From the energetic point of view the low-pressure feed water heater is a nearly perfect balanced device. Analyzed heat exchanger noticeable problems can be seen in exergy efficiency and exergy losses. Exergy represent the maximum available energy potential of any observed component in relation to the environment state. Impact of ambient temperature on the size of the exergy losses has been investigated at the end of conducted analysis. The low-pressure feed water heater is an example of a device which is very well balanced on the one side, even in the conditions of the steam system partial loads, and on the other side his available exergy potential is very poorly exploited.

Air heaters are commonly used devices in steam power plants. In base-loaded conventional power plants, air heaters usually use flue gases for air heating. In this paper, the air heater from a marine steam propulsion plant is analyzed, using superheated steam as a heating medium. In a marine propulsion plant, flue gases from steam generator are not hot enough for the air heating process. In a wide range of steam system loads, the analyzed steam air heater has low energy power losses and high energy efficiencies, ranging from 98.41% to 99.90%. Exergy analysis of the steam air heater showed that exergy destruction is quite high, whereas exergy efficiency ranged between 46.34% and 67.14%. Air heater exergy destruction was the highest, whereas exergy efficiency was the lowest at the highest steam system loads, which was an unexpected occurrence because the highest loads can be expected in the majority of marine steam plant operations. The change in the ambient temperature significantly influences steam air heater exergy efficiency. An increase in the ambient temperature of 10 °C reduces analyzed air heater exergy efficiency by 4.5%, or more, on average.

The paper presents an analysis of marine Turbo-Generator Steam Turbine (TGST) energy losses at turbine gland seals. The analyzed TGST is one of two identical Turbo-Generator Steam Turbines mounted in the steam propulsion plant of a commercial LNG carrier. Research is based on the TGST measurement data obtained during exploitation at three different loads. The turbine front gland seal is the most important element which defines TGST operating parameters, energy losses and energy efficiencies. The front gland seal should have as many chambers as possible in order to minimize the leaked steam mass flow rate, which will result in a turbine energy losses' decrease and in an increase in energy efficiency. The steam mass flow rate leakage through the TGST rear gland seal has a low or negligible influence on turbine operating parameters, energy losses and energy efficiencies. The highest turbine energy efficiencies are noted at a high load -on which TGST operation is preferable.