Session: 11-42-01: Heat and Mass Transfer in Heating, Cooling, and Power Systems

Paper Number: 117128

117128 - A Novel Solar Absorption Cogeneration System With an Adjustable Cooling-to-Power Ratio 

For improving the energy conversion efficiency, combined systems producing several products other than power can generally boost the energy source utilization, expand the cycle’s applicability, and may possibly enhance the cycle’s economic performance. Combining cooling production with power generation in decentralized combined cooling and power (CCP) cogeneration cycles can be considered as a suitable solution for the annually increasing demand for power and the high power consumption that is typically associated with vapor compression systems (VCS) to produce cooling. Vapor compression systems are responsible for consuming approximately 20\% of the electricity produced worldwide. For efficiently harnessing renewable energy sources, low-grade thermal power cycles need to be introduced. One reason for that need is the fact that conventional power plants employing different forms of the Rankine cycle typically require high-temperature heat sources which cannot be delivered by low-grade thermal sources such as solar energy, geothermal energy, or low-temperature waste heat. Examples of low-grade thermal power cycles include the organic Rankine cycle (ORC), the absorption power cycle (APC), the inverted Brayton Cycle, the Stirling cycle, the indirectly-heated Brayton cycle, and the trilateral cycle, along with conversion technologies employing thermionic, thermoelectric, and thermo-photovoltaic systems. However, many of the latter technologies are still in the research and development stage and some are still facing several obstacles hindering them from being commercialized. Some of the obstacles include their low thermal efficiency, their technical feasibility, or their high cost. Among the aforementioned technologies, the most potentially feasible for power generation are the ORC and the APC. Organic Rankine Cycles (ORCs) are similar to the traditional Rankine cycle except that ORCs use low-boiling-point organic fluids instead of water. Absorption power cycles, on the other hand, use low-boiling temperature binary mixtures, featuring non-isothermal heat addition and/or rejection processes as a result of concentration variation during the phase-change process. Non-isothermal heat addition and/or rejection processes allow for a better thermal match with sensible heat sources and, consequently, a better exergetic efficiency since less irreversibility will accompany the heat transfer processes involved. The most common APC is the Kalina cycle which was introduced by Kalina in 1983 as a cycle utilizing waste heat to produce power by using an ammonia-water mixture as the working fluid. The Kalina cycle consists mainly of a boiler, a separator, a turbine, two heat exchangers, a condenser, pumps, and valves. These power cycles are usually combined with thermally-driven cooling systems to build low-grade thermally-driven combined cooling and power (CCP) systems. Most of the time, the cooling effect in these cogeneration systems is achieved employing thermally-driven sorption systems. Combining stand-alone absorption chillers with ORCs or APCs at different levels of integration and complexity is the most common approach used. In this work, a novel solar double-effect absorption combined cooling and power (DECCP) system with an adjustable cooling-to-power ratio is proposed. This cogeneration system uses water-LiBr as the working fluid. The novel cycle upon which this system is based has been mathematically modeled, simulated, and parametrically analyzed to generate the system's performance characteristics for several scenarios. The performance has been compared with those of other similar combined cogeneration cycles. It was found that the proposed cycle outperforms the other cycles from the vantage point of the power produced and the cycle's ability to produce cooling. For specific operating parameters, the DECCP cycle achieves an exergetic efficiency that varies between 36.55 and 59.13% based on the refrigerant split ratio used. An effective operating strategy is proposed for the cycle when it is powered by solar energy.

Presenting Author: S.A. Sherif University of Florida

Presenting Author Biography: Abdulmajeed is a Ph.D. candidate at the University of Florida.

Authors:

Abdulmajeed M. Alghamdi University of Florida
S.A. Sherif University of Florida