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

Thermodynamic Analysis and Comparison of Two Marine Steam Propulsion Turbines

This paper presents thermodynamic (energy and exergy) analysis and comparison of two different marine propulsion steam turbines based on their operating parameters from exploitation. The first turbine did not possess steam reheating and had only two cylinders (high-pressure and low-pressure cylinders), while the second turbine possesses steam reheating and has one additional cylinder (intermediate-pressure cylinder). In the literature at the moment, there cannot be found a direct and exact comparison of these two marine steam turbines and their cylinders based on real exploitation conditions. Along with energy and exergy analyses, the research it is investigated the sensitivity of exergy parameters to the ambient temperature change for both turbines and each cylinder. It is also presented the influence of the steam reheating process on the energy and exergy efficiency of the entire power plant. For both observed turbines and their cylinders it is valid that relative losses and efficiencies (both energy and exergy) are reverse proportional. The operation of an intermediate pressure cylinder from a steam turbine with reheating is the closest to optimal. Due to the different origins of losses considered in energy and exergy analyses, each analysis detects different turbine cylinders as the most problematic ones. The steam reheating process decreases losses and increases efficiencies (both energy of each turbine cylinder and the whole turbine. The whole turbine with reheating has an energy efficiency equal to 81.46% and an exergy efficiency equal to 86.48%, while the whole turbine without reheating has energy and exergy efficiencies equal to 76.47% and 80.94%, respectively. Exergy parameters of a steam turbine without reheating as well as its cylinders are much more influenced by the ambient temperature change in comparison to the steam turbine with reheating and its cylinders. The steam reheating process will increase the efficiency of the whole power plant in real exploitation conditions between 10% and 12%

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

Fuel mass flow variation in direct injection diesel engine – influence on the change of the main engine operating parameters

A change in the main operating parameters of a high speed turbocharged direct injection diesel engine MAN D0826 LOH15 during the fuel mass flow variation has been analyzed. On the basis of two measurement sets, on two different engine rotational speeds, performed with standard diesel fuel, several operating parameters have been calculated: engine torque, effective power, excess air ratio, specific effective fuel consumption and heat released per engine process. The calculated parameters are presented for a wide engine operating range. In addition to measurement sets, several important parameters have been measured. Additional measured parameters have been lubrication oil temperature and exhaust gas temperature before and after the turbocharger turbine. The presented engine operating parameters allow deep insight into the analyzed diesel engine process

Analysis and Comparison of Ship Propulsion Systems

One of the highest cost of building the ship refers to the ship’s propulsion system. It is therefore very important to know all the types and specificities of propulsion systems for the optimal selection. This paper presents the conventional and the combined propulsion systems, where are briefly given their characteristics and specificities. Special attention is given to the combined propulsion systems, whose extensive use is still under expectation. At the end, the paper discusses the cost calculation of a marine propulsion system of selected passenger cruiser and comparison to the possible alternative system

Exergy Analysis of Steam Pressure Reduction Valve in Marine Propulsion Plant on Conventional LNG Carrier

Paper has presented an exergy analysis of steam pressure reduction valve, unavoidable element in the steam propulsion plant on LNG carrier. The steam pressure reduction valve was analyzed in a wide range of steam system loads. Along with pressure decrease, through the valve also occur decrease in steam temperature and increase in steam specific entropy. The pressure decrease of the analyzed valve ranges from 4.846 MPa up to 5.027 MPa while the average steam temperature decrease for the whole observed operating range amounts 74.8 °C. At the ambient temperature of 25 °C, valve exergy destruction ranges from 121.72 kW up to 180.64 kW, while exergy efficiency amounts from 80.28 % up to 80.54 %. Variation in the ambient temperature, for the expected engine room temperature range, showed that the exergy destruction of pressure reduction valve increases and exergy efficiency decreases during the increase in the ambient temperature. The lowest average value of pressure reduction valve exergy destruction was obtained at the ambient temperature of 10 °C and amounts 152.03 kW, while at the same ambient temperature was obtained the highest average exergy efficiency of 82.77 %. The highest valve exergy destruction and the lowest exergy efficiency were obtained at the highest observed ambient temperature of 40 °C

EXERGY ANALYSIS OF THE MAIN PROPULSION STEAM TURBINE FROM MARINE PROPULSION PLANT

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