Optimization of a Scroll Expander Applied to an Ammonia/Water Combined Cycle System for Hydrogen Production – Paper No. 1645
power production and refrigeration capacity. It must also be constructed out of steel, aluminum, or another material compatible in an ammonia environment. Various expander designs using unique expansion methods exist throughout industry. These designs can be organized into two categories, positive-displacement and turbo-machinery, based on the method of fluid displacement. This paper provides a comparison of these expander designs with emphasis on the scroll compressor.
Current energy consumption and forecasted demand with regard to limited fossil fuel reserves is driving the necessity for the conversion to a renewable resources- based global energy market. Economical, environmental, and political factors are further motivations. Hydrogen is becoming more significant as a potential energy carrier for this renewable energy market.
Approximately 85.7% of the world’s energy is currently supplied by fossil fuels, with crude oil making up 38.8% of that total. Global energy consumption is projected to increase 54% over the next 25 years (Energy Information Administration, 2004).
This increased demand is being fed primarily from countries with rapidly industrializing and emerging economies such as India and China. Proven oil reserves are sufficient to satisfy this demand over the next 20 years, after which there is debate as to whether oil production will peak before 2030 or that continued technological progress and new oil discoveries will satisfy the demand well into this century (Ramsay, 2003).
The economic effects of increasing energy demand on a limited supply are apparent today with peak 2004 oil
Herbert A. Ingley, PhD,PE University of Florida
P. O. Box 116300 Gainesville, FL 32611 firstname.lastname@example.org
Robert Reed University of Florida PO Box 116300 Gainesville, FL 32611
D. Yogi Goswami, PhD,PE University of Florida P.O. Box 116300 Gainesville, FL 32611 email@example.com
The ammonia-water combined power/cooling cycle proposed by Goswami (1995) utilizes a binary ammonia/water working fluid to produce both power and refrigeration. The cycle is a combination of an ammonia- water refrigeration system and an ammonia-based Rankine cycle.
The unique ability of this cycle to produce both power and refrigeration gives rise to two advantages for use in a hydrogen economy. First, the cycle can utilize low- grade renewable heat sources such as that available from inexpensive flat plate solar collectors to produce the power needed to drive an electrolyzer and liquefier. Second, the cooling produced by the cycle can be used to pre-cool hydrogen prior to liquefaction, thereby reducing the power requirement of the liquefaction compressor equipment. In this manner renewable energy source utilization is improved compared to technologies such as wind or photovoltaic electrolysis.
The power output and cooling capacity of the cycle under given operating parameters is highly dependent on the expander efficiency. Irreversibilties due to friction and leakage decrease the amount of work extracted from the fluid. Because less work is extracted, the expander exhaust temperature is higher and the cooling capacity is reduced.
The main criteria for expander selection are operating pressures and temperatures, flow rate of ammonia vapor and material compatibility with ammonia. Ammonia is a corrosive substance that reacts with metals such as copper, brass, and bronze, all of which are commonly used as bearing or bushing material.