In many years large low speed marine diesel engines have consumed heavy fuel oils with sulfur contents in the order of 2.5−4.5 wt %. Present legislation requires that the fuel sulfur is reduced, and in the near future the limit will be 0.5 wt % globally. During combustion most of the sulfur is oxidized to SO 2 from which a fraction is further oxidized to SO 3 . SO 3 may combine with H 2 O and condense as liquid sulfuric acid that promotes corrosive wear on e.g. cylinder liners. To extend engine lifetime and reduce costs for lubrication it is pivotal to identify formation of SO 3 with respect to operational conditions and sulfur feed. This work presents a computational model of a large low speed two-stroke diesel engine where a 0D multizone approach including a detailed reaction mechanism is employed in order to investigate in cylinder formation of gaseous SO 3 where fuel burn rates are based on experimental pressure traces. In contrast to NO the SO 3 does not really form at the highest combustion temperatures, but like NO the formation of SO 3 is very sensitive to the rate that fresh air mixes with hot combustion products. Consequently a simple mixing rate is proposed and calibrated in order to meet experimental results of NO. For a large low speed diesel engine the model shows that 3−5% of the injected sulfur is oxidized to SO 3 that is formed primarily in the temperature range from 2000 to 1300 K during cylinder expansion. In addition the model is used to reduce the full reaction mechanism from 96 to 7 elementary sulfur reactions without compromising the SO 3 to SO 2 ratio.
The validation of detailed models, in terms of SO 3 formation in large marine engines operating on sulfurcontaining heavy fuel oils (HFOs), relies on experimental work. The requisite is addressed in the present work, where SO 3 is measured in the exhaust gas of an 80 kW medium-speed single-cylinder HFO-fuelled test engine. SO 3 formation is triggered by running the engine at altered operational conditions and speeds within 1050−1500 rpm. The test engine does not represent a large low-speed marine engine; however, the nature of high-temperature SO 3 formation may well be explored with the current engine and serve as reference for further modeling studies. SO 3 is measured using a continuous SO 3 monitor from PENTOL GmbH. The monitor offers online SO 3 readings and short sampling times, in contrast to other extractive methods. The measurement is based on SO 3 capture in isopropanol prior to chemical conversion and indirect detection via light absorption in a photometer. Present results show that SO 3 formation is favored by elevated pressure histories, premixed combustion, and reduced speeds. The fraction of fuel sulfur converted to SO 3 is measured to be on the order of 0.5%−2.4%, corresponding to 4− 14 ppmv. SO 3 and NO x are not comparable, according to thermodynamic considerations, yet both species involve the radical pool and are studied in parallel. Resulting emissions of SO 3 and NO x in the exhaust gas follow a comparable trend throughout the experiments.
A combined cycle power plant with inlet air heating (CCPP-IAH) system is proposed to solve the problems of ice and humidity blockages in winter climate. The performance of the CCPP-IAH system under part load conditions is analyzed via both experimental and simulation methods. The application of the inlet air heating technology significantly improves the part load efficiency and enhances the operational safety of the combined cycle power plant under complex meteorological conditions. Results show that a higher inlet air temperature will contribute a lower gas turbine thermal efficiency for proposed system. However, the heated inlet air by the recovered energy in heat recovery steam generator raises efficiencies for both the heat recovery steam generator and the overall system. The fuel consumption drops by 0.02 kg/s and 0.03 kg/s under the power load of 65 % and 80 %, respectively. The inlet air humidity decrease to 30 % under the heated inlet air temperature of 303 K. Moreover, the exergy destruction for both Brayton cycle part and Rankine cycle part decrease with the inlet air temperature increasing. The daily fossil fuel will raise up to 2.9 ton/day and to 5.1 ton/day under the power load of 65 % and 80 %, respectively. The annual economic benefit from energy saving is more than $ 5.88 10 5 and the payback period is less than 3 years.
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