Abstract
The atmospheric drain condensate system of a marine steam power plant is described and evaluated from the energetic and exergetic point of view at a conventional liquefied natural gas (LNG) carrier. Energy loss and exergy destruction rate were calculated for individual stream flows joined in an atmospheric drain tank with variations of the main turbine propulsion speed rate. The energy efficiency of joining streams was noted to be above 98% at all observed points as the atmospheric drain tank was the direct heater. The exergy efficiency of the stream flows into the drain tank was in the range of 80% to 90%. The exergy stream flow to the tank was modeled and optimized by the gradient reduced gradient (GRG) method. Optimization variables comprised contaminated and clean condensate temperature of the atmospheric drain tank and distillate water inlet to the atmospheric drain tank with respect to condensate outlet temperature. The optimal temperatures improves the exergy efficiency of the tank as direct heater, to about 5% in port and 3% to 4% when the LNG carrier was at sea, which is the aim of optimizing. Proposals for improvement and recommendations are given for proper plant supervision, which may be implemented in real applications.
Highlights
There have been a number of studies on stationary steam power plant feed water regenerative groups, their exergy and energy efficiency and possible feed water heater optimization
The first group of authors studied the amount of exergy destruction for the regenerative feed water group, which is relatively low compared to the total exergy destruction of the steam power plant
According to an exergy analysis in port and at lower loads, it is clear that desuperheating water at the fresh water generator line, which comes from the main condenser feed water line, should be kept closed as fresh water generator is not in service and there is no steam for cooling down the fresh water generator
Summary
There have been a number of studies on stationary steam power plant feed water regenerative groups, their exergy and energy efficiency and possible feed water heater optimization. Adibhatla and Kaushik [10] tried to combine feed water regenerative groups to incorporate solar-aided feed water heating for a 500 MWe thermal power plant, but exergy efficiency of such a setup was lower than the classical Rankine regenerative cycle that is associated with exergy destruction in the collector–receiver system. Another study was carried out by Ahmadi et al [11], integrating a solar field instead of the feed regeneration group [11] It gained benefits by replacing high-pressure feed water preheaters with a solar farm, resulting in increased energy and exergy efficiencies of the power plant by 18.3%.
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