Development of Simulation Techniques for Thermal Storage Coupled to Cogeneration/Trigeneration Systems
thesisposted on 27.11.2018 by Luca Romano
In order to distinguish essays and pre-prints from academic theses, we have a separate category. These are often much longer text based documents than a paper.
The objective of this thesis is to study and compare different plant layouts for the fulfilment of the energy needs of an hospital facility located in Chicago, IL. A cogeneration and a trigeneration plant, driven by a gas turbine, were modeled and analyzed using a simulation software called eQuest® (QUick Energy Simulation Tool). In particular, the benefits of the introduction of a hot thermal storage system was evaluated and discussed. Partial improvements to the ASHRAE Standard 90.1-2004 prototype hospital model were introduced in order to guarantee the achievement of the required design conditions, enabling every section of the structure to reach the intended temperature. An upgrade of the eQuest® model describing the gas turbine was introduced. In particular, the new model brought an improvement in the e ciency of the equipment at partial load conditions. Various turbine sizes were studied (from 600 kW to 1,300 kW) in terms of energy output and wasted products. Among various performance parameters, the percentage reduction in source energy consumption (PRSEC) was considered for the optimal sizing of the plant, since it was the one better describing the overall performance of the system. In the cogeneration system, the highest value of PRSEC reached 19.0%, resulted from the operation of a 700 kW turbine. This system enabled a better utilization of the source energy compared to a traditional separated generation system, in particular, it permitted a reduction in the boiler’s fuel consumption due to the exploitation of the heat coming from the exhaust gasses of the turbine. Moreover a trigeneration plant was analyzed. In this second case, like in the previous, the heating needs of the hospital were satisfied by the recovery of the heat coming from the prime mover, in addition the cooling loads were partially fulfilled by an absorption chiller driven by the exhaust gasses of the turbine. To guarantee the best accuracy of the results, an improvement in the absorption chiller model was implemented starting from the technical sheet of the Millennium YIA TM, manufactured by YORK ®. The same turbine sizes considered in the cogeneration plant were investigated. It emerged that a 800 kW gas turbine was able to reach the highest value of PRSEC of 22.7%. Major improvements in the performance resulted in a lower electricity consumption and electricity peak demand. Furthermore, especially during warmer months, the introduction of the absorption chiller guaranteed a better usage of the waste heat deriving from the turbine. To conclude the analysis, the effects of the introduction of a hot thermal storage were evaluated in both types of plant’s layouts. A fully mixed water tank model was created and implemented in eQuest® starting from the information provided by Advance Tank, Co. Various capacities were studied ranging from 11,800 gal to 53,000 gal. For both types of plant a feasibility study and an optimal sizing procedure was elaborated. In the cogeneration system, a 14,000 gal tank paired to a 700 kW turbine enabled to reach a value of PRSEC of 20.3%, resulting in an improvement of 1.3% compared to the case of a cogeneration plant without storage. The major benefit introduced by the use of the tank resulted in lower boiler’s fuel consumption due to an increment of the recovered heat used for heating purposes. Much more evident were the benefits brought by the thermal storage in the case of a trigeneration layout. In fact, it resulted in an increase of the size of the prime mover compared to the original layout (from 800 kW to 900 kW). In particular, a reduction in overall electricity consumption and total fuel consumption was observed. These benefits must be attributed to a higher availability of recovered heat, which also resulted in a more extensive use of the absorption chiller. A 39,500 gal tank coupled to a 900 kW turbine allowed to have a 25.1% PRSEC, 2.4% higher than a 800 kW trigeneration plant.