Efficiency and losses analysis of low-pressure feed water heater in steam propulsion system during ship maneuvering period

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

Energy and Exergy Efficiency Analysis of Sealing Steam Condenser in Propulsion System of LNG Carrier

In ship propulsion systems today diesel engines are dominant, but steam propulsion systems prevail in one type of ships and that are LNG carriers. Such steam propulsion systems consist of many different components. One interesting component of these systems is sealing steam condenser analysed in this paper. Measurements of all necessary operating parameters for analysed sealing steam condenser were performed during the ship exploitation and they were used for calculating the energy and exergy efficiency of this device. Except the displayed movement of both efficiencies the reasons for those changes and proposals for possible improvements were presented. Also, it was displayed all operating parameters of sealing steam condenser that has an impact on its performance and efficiency. During the ship exploitation, improvements related to the sealing steam condenser efficiency are hard to expect because improvements would cause an increase in the steam propulsion system operating costs

Analysis of Low-Power Steam Turbine With One Extraction for Marine Applications

The paper presents thermodynamic (energy and exergy) analysis of low-power steam turbine with one extraction for marine applications. Analyzed steam turbine is divided in two parts - High Pressure (HP) part before steam extraction and Low Pressure (LP) part after steam extraction. Analysis shows that HP turbine part produces the majority of cumulative turbine power and consequentially has higher mechanical, energy and exergy losses when compared to LP turbine part. Regardless of heavier operating conditions, LP turbine part has higher efficiencies and lower specific losses (in both energy and exergy analysis) when compared to HP turbine part. Whole analyzed turbine has energy and exergy efficiencies equal to 62.84% and 65.58%, while energy and exergy turbine losses are 696.74 kW and 618.50 kW. Cumulative produced power at the turbine shaft outlet is equal to 1178.40 kW. Steam extraction which divides analyzed turbine on HP and LP part can deliver a notable amount of heat to any marine heat consumer, what represents a significant advantage of observed turbine in comparison with similar low-power marine steam turbines which usually does not have steam extractions

Exergy Analysis of Supercritical CO2 System for Marine Diesel Engine Waste Heat Recovery Application

In this research is performed an exergy analysis of supercritical CO2 system which uses various waste heat flows from marine diesel engine to produce additional mechanical power. The performed exergy analysis contains whole system as well as each system component individually. The observed system produces useful mechanical power equal to 2299.47 kW which is transferred to the main propulsion propeller shaft. Additionally produced mechanical power by using waste heat only will reduce marine diesel engine fuel consumption and exhaust gas emissions. Main cooler has the highest exergy destruction of all system components and simultaneously the lowest exergy efficiency in the observed system, equal to 32.10% only. One of the possibilities how main cooler exergy efficiency can be increased is by decreasing water mass flow rate through the main cooler and simultaneously by increasing water temperature at the main cooler outlet. Observed system has five heat exchangers which are involved in the CO2 heating process, and it is interesting that the last CO2 heater (exhaust gas waste heat exchanger) increases the CO2 temperature more than all previous four heat exchangers. Whole analyzed waste heat recovery supercritical CO2 system has exergy destruction equal to 2161.68 kW and exergy efficiency of 51.54%. In comparison to a similar CO2 system which uses waste heat from marine gas turbine, system analyzed in this paper has approximately 12% lower exergy efficiency due to much lower waste heat temperature levels (from marine diesel engine) in comparison to temperature levels which occur at the marine gas turbine exhaust

Thermodynamic Analysis of Steam Cooling Process in Marine Power Plant by Using Desuperheater

Thermodynamic (energy and exergy) analysis of steam cooling process in the marine steam propulsion plant is presented in this research. Steam cooling is performed by using Desuperheater which inject water in the superheated steam to obtain wet steam. Wet steam is used in auxiliary heaters for various heating purposes inside the marine steam propulsion system. Auxiliary heaters require wet steam due to safety reasons and for easier steam condensation after heat transfer. Analysis of steam cooling process is performed for a variety of steam system loads. Mass flow rates of cooling water and superheated steam in a properly balanced cooling process should have the same trends at different system loads - deviations from this conclusion is expected only for a notable change in any fluid temperature. Reduction in steam temperature is dependable on the superheated steam temperature (at Desuperheater inlet) because the temperature of wet steam (at Desuperheater outlet) is intended to be almost constant at all steam system loads. Energy losses of steam cooling process for all observed system loads are low and in range between 10–30 kW, while exergy losses are lower in comparison to energy losses (between 5–15 kW) for all loads except three the highest ones. At the highest system loads exergy losses strongly increase and are higher than 20 kW (up to 40 kW). The energy efficiency of a steam cooling process is very high (around 99% or higher), while exergy efficiency is slightly lower than energy efficiency (around 98% or higher) for all loads except the highest ones. At the highest steam system loads, due to a notable increase in cooling water mass flow rate and high temperature reduction, steam cooling process exergy efficiency significantly decreases, but still remains acceptably high (between 95% and 97%). Observation of both energy and exergy losses and efficiencies leads to conclusion that exergy analysis consider notable increase in mass flow rate of cooling water which thermodynamic properties (especially specific exergies) strongly differs in comparison to steam. Such element cannot be seen in the energy analysis of the same system

THERMODYNAMICAL ANALYSIS OF HIGH-PRESSURE FEED WATER HEATER IN STEAM PROPULSION SYSTEM DURING EXPLOITATION

Nowadays 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 high-pressure 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

Comparison of conventional and heat balance based energy analyses of steam turbine

This paper presents a comparison of conventional and heat balance based energy analyses of steam turbine. Both analyses are compared by using measured operating parameters from low power steam turbine exploitation. The major disadvantage of conventional steam turbine energy analysis is that extracted energy flow streams are not equal in real (polytropic) and ideal (isentropic) expansion processes, while the heat balance based energy analysis successfully resolved mentioned problem. Heat balance based energy analysis require an increase of steam mass flow rates extracted from the turbine in ideal (isentropic) expansion process to ensure always the same energy flow streams to all steam consumers. Increase in steam mass flow rate extracted through each turbine extraction (heat balance based energy analysis) result with a decrease in energy power losses and with an increase in energy efficiency of whole turbine and all of its cylinders (when compared to conventional analysis). All of the obtained conclusions in this research are valid not only for the analyzed low power steam turbine, but also for any other steam turbine with steam extractions

Numerical modelling of a refrigerating system with CO2 as a refrigerant : Doctoral dissertation

Nove generacije rashladnih sustava s kompresijom pare koriste prirodne radne tvari radi očuvanja okoliša. Među njima se ističe ugljikov dioksid (CO₂ ili R744). Njegova primjena iziskuje posebne mjere zbog visokih radnih tlakova i temperatura odvođenja topline u blizini i iznad kritične točke. Razvijen je i vrednovan numerički model transkritičnog rashladnog sustava s CO₂ za simulacije u prijelaznim i ustaljenim uvjetima rada, korištenjem realnih svojstava radne tvari. Svaka komponenta rashladnog sustava opisana je svojim podmodelom. Posebno su razrađeni modeli kompresora i izmjenjivača topline. Zbog specifičnosti CO₂ kao radne tvari i rada sustava u blizini kritične točke, primjenjuju se trenutno najtočniji modeli jednadžbe stanja stvarne radne tvari i njenih termodinamičkih i transportnih svojstava. Podmodeli su korišteni za pripremu jednostavnijih i bržih modela konkretnih komponenti i integrirani su u jednostavniji model cjelokupnog rashladnog sustava za točne, pouzdane i mnogo brže numeričke simulacije. Detaljnim modelima komponenti obuhvaćeni su volumetrijski kompresori: klipni kompresori, kompresori s rotirajućim klipom i spiralni kompresori, te cjevno-lamelni izmjenjivači topline. Modeli su strukturirani prema načelima objektno orijentiranog programiranja, na način koji omogućuje fleksibilno sastavljanje različitih konfiguracija transkritičnih rashladnih sustava s CO₂, iz njegovih komponenti, bez potrebe za velikim vanjskim intervencijama u strukturi programa numeričke simulacije. Razvijeni model rashladnog sustava i njegovih komponenti vrednovan je usporedbom s eksperimentalnim mjerenjima. Postignuto je vrlo dobro slaganje rezultata numeričkih simulacija s eksperimentalnim rezultatima. Vrednovani modeli uporabljeni su za uvid u karakteristike i učinkovitost sustava u promjenjivim radnim uvjetima i za analizu nekoliko jednostavnijih poboljšanja eksperimentalno istraženog rashladnog sustava s CO₂. Razvijeni i vrednovani modeli će služiti kao alat za razvoj komponenti i cijelih sustava, kao i za nalaženje potrebnih podataka za povećanje točnosti jednostavnih i brzih približnih modela.New generations of vapor compression refrigeration systems use natural refrigerants due to ecological concerns. Carbon dioxide (CO₂ or R744) stands out among them. Its application requires special measures due to high operating pressures and heat dissipation temperatures near and above the critical point. A numerical model of a transcritical refrigeration system with CO₂ has been developed, verified and validated for simulations in transient and steady operating conditions, using real properties for the refrigerant. Each component of the refrigerating system is described by its sub-model. Models of compressors and heat exchangers have been specially developed. Due to the specificity of CO₂ as a refrigerant and the operation of the system in the vicinity of the critical point, currently the most accurate fundamental equation of state of the actual refrigerant and its thermodynamic and transport properties is applied. Submodels were used to prepare simpler and faster models of specific components and were integrated into a simpler model of the entire refrigerating system for accurate, reliable, and much faster numerical simulations. Detailed component models include volumetric compressors: reciprocating compressors, rotary piston compressors and scroll compressors, and fin-and-tube heat exchangers. The models are structured according to the principles of object-oriented programming, in a way that allows flexible assembly of different configurations of transcritical refrigerating systems with CO₂ from its components, without the necessity for extensive external interventions into the structure of numerical simulation code. The developed model of the refrigerating system and its components was validated by comparison with experimental measurements. A very good agreement between the results of numerical simulations and experimental results has been achieved. Validated models were used to gain insight into the properties and efficiency of the system during transient operating conditions and to analyze several simpler improvements of the experimentally investigated CO₂ refrigerating system. Developed and validated models will be used for development of components and entire systems, as well as to determine the necessary data to increase the accuracy of simple and fast approximate models

Numerical modelling of a refrigerating system with CO2 as a refrigerant : Doctoral dissertation

Nove generacije rashladnih sustava s kompresijom pare koriste prirodne radne tvari radi očuvanja okoliša. Među njima se ističe ugljikov dioksid (CO₂ ili R744). Njegova primjena iziskuje posebne mjere zbog visokih radnih tlakova i temperatura odvođenja topline u blizini i iznad kritične točke. Razvijen je i vrednovan numerički model transkritičnog rashladnog sustava s CO₂ za simulacije u prijelaznim i ustaljenim uvjetima rada, korištenjem realnih svojstava radne tvari. Svaka komponenta rashladnog sustava opisana je svojim podmodelom. Posebno su razrađeni modeli kompresora i izmjenjivača topline. Zbog specifičnosti CO₂ kao radne tvari i rada sustava u blizini kritične točke, primjenjuju se trenutno najtočniji modeli jednadžbe stanja stvarne radne tvari i njenih termodinamičkih i transportnih svojstava. Podmodeli su korišteni za pripremu jednostavnijih i bržih modela konkretnih komponenti i integrirani su u jednostavniji model cjelokupnog rashladnog sustava za točne, pouzdane i mnogo brže numeričke simulacije. Detaljnim modelima komponenti obuhvaćeni su volumetrijski kompresori: klipni kompresori, kompresori s rotirajućim klipom i spiralni kompresori, te cjevno-lamelni izmjenjivači topline. Modeli su strukturirani prema načelima objektno orijentiranog programiranja, na način koji omogućuje fleksibilno sastavljanje različitih konfiguracija transkritičnih rashladnih sustava s CO₂, iz njegovih komponenti, bez potrebe za velikim vanjskim intervencijama u strukturi programa numeričke simulacije. Razvijeni model rashladnog sustava i njegovih komponenti vrednovan je usporedbom s eksperimentalnim mjerenjima. Postignuto je vrlo dobro slaganje rezultata numeričkih simulacija s eksperimentalnim rezultatima. Vrednovani modeli uporabljeni su za uvid u karakteristike i učinkovitost sustava u promjenjivim radnim uvjetima i za analizu nekoliko jednostavnijih poboljšanja eksperimentalno istraženog rashladnog sustava s CO₂. Razvijeni i vrednovani modeli će služiti kao alat za razvoj komponenti i cijelih sustava, kao i za nalaženje potrebnih podataka za povećanje točnosti jednostavnih i brzih približnih modela.New generations of vapor compression refrigeration systems use natural refrigerants due to ecological concerns. Carbon dioxide (CO₂ or R744) stands out among them. Its application requires special measures due to high operating pressures and heat dissipation temperatures near and above the critical point. A numerical model of a transcritical refrigeration system with CO₂ has been developed, verified and validated for simulations in transient and steady operating conditions, using real properties for the refrigerant. Each component of the refrigerating system is described by its sub-model. Models of compressors and heat exchangers have been specially developed. Due to the specificity of CO₂ as a refrigerant and the operation of the system in the vicinity of the critical point, currently the most accurate fundamental equation of state of the actual refrigerant and its thermodynamic and transport properties is applied. Submodels were used to prepare simpler and faster models of specific components and were integrated into a simpler model of the entire refrigerating system for accurate, reliable, and much faster numerical simulations. Detailed component models include volumetric compressors: reciprocating compressors, rotary piston compressors and scroll compressors, and fin-and-tube heat exchangers. The models are structured according to the principles of object-oriented programming, in a way that allows flexible assembly of different configurations of transcritical refrigerating systems with CO₂ from its components, without the necessity for extensive external interventions into the structure of numerical simulation code. The developed model of the refrigerating system and its components was validated by comparison with experimental measurements. A very good agreement between the results of numerical simulations and experimental results has been achieved. Validated models were used to gain insight into the properties and efficiency of the system during transient operating conditions and to analyze several simpler improvements of the experimentally investigated CO₂ refrigerating system. Developed and validated models will be used for development of components and entire systems, as well as to determine the necessary data to increase the accuracy of simple and fast approximate models