Turning Summer Heat into Savings - Maximizing Energy Recovery from Combustion Turbine Exhaust

摘要

Large water resource recovery facilities (WRRFs) with anaerobic digestion have several alternatives for capitalizing on the energy in the digester gas. A combined heat and power (CHP) system with combustion turbines is commonly considered as an option initially. However, the combustion turbine CHP system is not often selected for installation because combustion turbines have lower electrical efficiency and higher capital cost than other types of CHP system technologies. Combustion turbine CHP systems offer benefits such as consistent, low maintenance operation and a significant amount of recoverable heat. The combustion turbine system becomes a more favorable CHP alternative if WRRFs can recoup the capital cost more rapidly. One way to facilitate this is to capture and use all of the energy within the hot combustion turbine exhaust gas, even in the warmer months of the year, rather than releasing the excess heat to the atmosphere. This paper presents an assessment of three unique enhancements to a WRRF combustion turbine CHP system that were selected to maximize cost savings from the capture and use of the heat produced by the combustion turbines. The enhancements for a CHP system analyzed for this project include: 1 Heat recovery steam generators (HRSGs) and steam turbine to produce additional power and plant steam 2 Organic Rankine Cycle (ORC) units to capture wasted exhaust heat in warmer months to produce additional power 3 Absorption chillers to convert excess exhaust heat to chilling capacity for cooling plant facilities. A comparative analysis of the CHP enhancements and a financial analysis resulted in the following observations: 4 All of the alternatives, including the base case, provide an annual benefit above the annualized cost of the CHP system and the enhancement. 5 HRSGs and a steam turbine added the most financial benefit to the combustion turbine system despite requiring supplemental building heat in the winter months. 6 ORCs added little financial benefit to the combustion turbine system. 7 Absorption chillers added a modest financial benefit to the combustion turbine system but required a complex system of chilled water, cooling water and hot water piping.