Energy and exergy analysis of the turbo-generators and steam turbine for the main feed water pump drive on LNG carrier

• Published in: Energy conversion and management 2017-05, Vol.140, p.307-323
• Main Authors: Mrzljak, Vedran, Poljak, Igor, Mrakovčić, Tomislav
• Format: Article
• Language: English
• Subjects: Ambient temperature; Diesel engines; Electric power; Energy; Energy efficiency; Exergy; Exergy destruction; Exergy efficiency; Generators; Internal combustion; Internal combustion engines; Main feed water pump; Marine engines; Marine propulsion; Propulsion systems; Ships; Steam electric power generation; Steam turbines; Studies; Temperature; Temperature effects; Thermal energy; Thermodynamics; Turbines; Turbo-generator; Turbogenerators
• ISSN: 0196-8904; 1879-2227
• DOI: 10.1016/j.enconman.2017.03.007

•Two low-power steam turbines in the LNG carrier propulsion plant were investigated.•Energy and exergy efficiencies of both steam turbines vary between 46% and 62%.•The ambient temperature has a low impact on exergy efficiency of analyzed turbines.•The maximum efficiencies area of both turbines was investigated.•A method for increasing the turbo-generator efficiencies by 1–3% is presented. Nowadays, marine propulsion systems are mainly based on internal combustion diesel engines. Despite this fact, a number of LNG carriers have steam propulsion plants. In such plants, steam turbines are used not only for ship propulsion, but also for electrical power generation and main feed water pump drive. Marine turbo-generators and steam turbine for the main feed water pump drive were investigated on the analyzed LNG carrier with steam propulsion plant. The measurements of various operating parameters were performed and obtained data were used for energy and exergy analysis. All the measurements and calculations were performed during the ship acceleration. The analysis shows that the energy and exergy efficiencies of both analyzed low-power turbines vary between 46% and 62% what is significantly lower in comparison with the high-power steam turbines. The ambient temperature has a low impact on exergy efficiency of analyzed turbines (change in ambient temperature for 10°C causes less than 1% change in exergy efficiency). The highest exergy efficiencies were achieved at the lowest observed ambient temperature. Also, the highest efficiencies were achieved at 71.5% of maximum developed turbo-generator power while the highest efficiencies of steam turbine for the main feed water pump drive were achieved at maximum turbine developed power. Replacing the existing steam turbine for the main feed water pump drive with an electric motor would increase the turbo-generator energy and exergy efficiencies for at least 1–3% in all analyzed operating points.