EXERGOECONOMIC ANALYSIS AND OPTIMIZATION OF NOVEL COGENERATION SYSTEMS FOR FRESHWATER PRODUCTION, POWER AND COOLING
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SATTAM MENWER LAFI ALHARBI
Global consumption of energy and freshwater is increasing continuously due to population growth and improving living standards. The world energy consumption is anticipated to increase by around 50% by 2050 according to the U.S Energy Information Administration (EIA). There is also very limited access to freshwater and cooling in many developing countries. Therefore, developing an efficient energy system, recovering the waste heat (cogeneration system or multigeneration) to produce freshwater and cooling, and using a renewable energy source are promising solutions to meet the energy demand and to reduce environment pollution associated with fossil fuels. In this study, several novel cogeneration or multigeneration systems are proposed and analyzed for the production of electricity, freshwater and cooling. The supercritical carbon dioxide (sCO2) Brayton cycle is a promising power cycle as an alternative to steam Rankine cycle due to its high efficiency, compact turbomachinery components and low capital cost. Different new configuration systems are proposed in this dissertation using solar energy, nuclear energy and waste heat of a commercial gas turbine (GT). The first proposed system is a sCO2 Brayton cycle driven by a nuclear source integrated with a multi-effect desalination (MED) system as a bottom cycle for cogeneration of power and freshwater. The second proposed system utilizes the waste heat of a commercial GT to produce freshwater, cooling and additional power. The waste heat of the GT drives a sCO2 Brayton cycle and MED with thermal vapor compression (MED-TVC), while the waste heat of the sCO2 Brayton cycle is used to power a lithium bromide-water (LiBr-H2O) absorption refrigeration cycle. The third proposed system is driven by a solar tower with two-tank energy storage and consists of an integrated sCO2 Brayton cycle and MED-TVC without reducing the power output. The waste heat of the sCO2 Brayton cycle is utilized to operate a LiBr-H2O absorption iv refrigeration cycle. In this research, comprehensive thermodynamic and exergoeconomic analyses are performed for the proposed systems. Also, a parametric analysis is conducted to investigate the influence of design parameters on the performance parameters for the configurations. Furthermore, a multi-objective optimization is performed for the proposed systems to find the optimal design using a genetic algorithm method. For the first proposed system, results indicate that integrating a MED system with a sCO2 Brayton cycle is a sound approach. The waste heat from the sCO2 Brayton cycle can be used efficiently to produce a significant amount of fresh water. For the second proposed system, results show that utilizing the waste heat of a commercial GT to produce freshwater, cooling and additional power can consume 34.2% less energy input and reduce CO2 emission by 39.3% compared to the stand-alone systems for power, cooling and freshwater production. For the third proposed system where thermal energy is supplied from a solar receiver by using a heat transfer fluid, results indicate that by extracting thermal energy to generate motive steam for MED-TVC downstream of the primary heat exchanger used to supply thermal energy to the sCO2 Brayton cycle, and by utilizing the waste heat from the sCO2 Brayton cycle to produce cooling, the proposed system is capable of producing 100 MW of power, 24.55 MW of cooling and 65,800 m3/day of freshwater production. All these proposed systems are highly recommended for implementation in countries where a significant amount of fresh water is needed such as in the Middle East.