System Integration Study On Power/Cooling Cogeneration Systems Driven By Middle-temperature Solar Thermal Energy

Nowadays the shortage of energy supply and dramatic climate change has gradually threatened the survival of human beings. It is must to change the traditional energy stereotypy to a more efficient and environmental friendly way of energy utilization. The distributed solar energy supply system is of great potential for its free of carbon dioxide emission, high energy efficiency and tremendous solar energy reserves.Supported by the National Basic Research Program of China (973Project), the National Natural Science Foundation of China, and the National Science and Technology Support Project of China, this academic dissertation develops and analyses two distributed solar thermal energy utilization systems, including a new power/cooling cogeneration system driven by middle-temperature solar thermal energy and a new solar absorption-compression hybrid refrigeration system. Both systems are simulated by Aspen Plus software to study their thermodynamic performance deeply. It is showed that through the coupling of power cycle and refrigeration cycle, both systems have broad application prospects for their efficient utilization of middle-temperature solar thermal energy. The main research content is listed below:(1) A new power/cooling cogeneration system driven by middle-temperature solar thermal energy is proposed. A parabolic trough solar energy collection system, an ammonia/water Rankine cycle, and an ammonia/water absorption refrigeration cycle are integrated rationally. The collected solar thermal energy at350℃is utilized to generate superheated ammonia/water vapor and then the vapor expands in a turbine to generate power. The exhaust vapor of the turbine is recovered by the absorption refrigeration system to generate cooling energy at-10℃. The new system implements cascade utilization of solar thermal energy in the Rankine and refrigeration cycles. Research shows that the equivalent solar radiation energy to power efficiency reaches19.5%, the exergy efficiency is13.6%and the primary energy saving ratio is24.2%. Finally several key parameters’ effectiveness on the system’s thermodynamic performance is discussed to provide important information in system optimization.(2) A new solar absorption-compression hybrid refrigeration system is proposed to produce low-temperature cooling energy. The middle-temperature solar thermal energy generated by a parabolic trough collector is introduced to an ammonia/water Rankine cycle to generate power. The exhaust vapor of the turbine is recovered by an absorption refrigeration cycle to produce cooling energy at-10℃. An ammonia compression refrigeration cycle driven by the power output of the Rankine cycle is also integrated in the system using the same condenser and evaporator with the absorption cycle. The solar coefficient of performance (SCOP) of the proposed system, whose definition is the ratio of the cooling output to the solar radiation input, can reach0.54, greater than the separated solar absorption system by0.15. The primary energy saving ratio of the proposed system is as high as27.8%. In addition, the proposed system is very flexible to fit the frequent variation of solar radiation. When solar energy is inadequate or there is no solar energy input, the electricity can be input the system to fulfill the requirement of cooling energy. The results obtained here may provide an efficient and flexible way of producing low-temperature cooling energy using solar energy.