Author: Yuan, Tianpei
Title: Utilization of tri-generation technology in a Hong Kong sewage treatment plant for increasing energy efficiency
Advisors: Yang, Hongxing (BSE)
Degree: M.Eng.
Year: 2018
Subject: Hong Kong Polytechnic University -- Dissertations
Cogeneration of electric power and heat
Cooling systems
Electric power production
Department: Department of Building Services Engineering
Pages: x, 76 pages : color illustrations
Language: English
Abstract: As one of the major renewable energy resources in Hong Kong, biogas is widely produced in the sludge anaerobic digestion process of sewage treatment plants. 50% - 80% of the biogas is CH4, which is an ideal clean gas fuel. Sewage treatment plants in most areas in the world usually use biogas for power and heat production from combined heat and power generation systems (CHP system), but this method is not suitable for Hong Kong as Hong Kong is located at the subtropical region where no space heating is needed in winter. Compared with a CHP system, tri-generation might be more suitable in Hong Kong as space cooling is needed throughout a year for commercial buildings. To improve the energy efficiency of the CHP system used in a local Wastewater Treatment Plant, this project proposes two different tri-generation system designs to use flue gas from the CHP unit to run an absorption chiller to produce chilled water for space cooling of a building and heating the digesters in the system. A general introduction on the tri-generation systems and its development were briefly presented first in the paper. Second, according to the situation of the CHP system, two designs of tri-generation systems have been designed: the single effect absorption chiller tri-generation system and double effect absorption chiller tri-generation system. Next, the heat load, heat balance, cooling capacity and other energy consumption are simulated and calculated for these two systems. Finally, through the analysis of thermal efficiency, cooling capacity, economy, stability and other aspects, an optimized tri-generation system is obtained. The average thermal efficiency of the CHP system for a year is 20.6%, but the tri-generation system 1 can improve its thermal efficiency to 22.3% and the tri-generation system 2 can improve its thermal efficiency to 38.9%. Compared with a boiler auxiliary heating system of 76,935 kWh per year of the CHP system and tri-generation system 1, the system 2 only needs boiler auxiliary heating of 45,590 kWh per year. Its energy consumption is reduced by 40%. Overall, the double effect absorption chiller tri-generation has high thermal efficiency, good stability, and a controllable system with a 2-4 years payback period. The double effect absorption chiller tri-generation system is the optimal solution.
Rights: All rights reserved
Access: restricted access

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