Development and assessment of integrated energy systems with ammonia synthesis and fuel cells

Abstract

Hydrogen and ammonia comprise two important clean fuels, which are expected to play a vital role in the development of clean energy production and utilization. Currently, their production relies heavily on fossil fuel-based resources that entail considerable environmental detriments. The utilization of renewable energy such as solar and wind energy resources for the production of these important commodities can address the current challenges associated with conventional production methods. However, their intermittent nature have hindered their usage in such applications. Nevertheless, ammonia entails several favorable properties that make it a promising candidate to be utilized as an energy storage medium. In this thesis, integrated solar and wind energy-based energy systems are developed for clean production of electricity, hydrogen and ammonia. Three new integrated energy systems are developed utilizing ammonia as a medium to store energy. Direct ammonia fuel cells are utilized for clean power generation via electrochemical ammonia oxidation through the utilization of alkaline electrolytes. A new multi-bed catalyst reactor was developed and investigated experimentally for ammonia synthesis. Performance improvement in comparison with a conventional catalyst-based reactor is determined. Comprehensive thermodynamic, electrochemical, exergoeconomic and multi-objective optimization studies are also performed on the developed systems to assess their performances. The peak daily ammonia and hydrogen production amounts are found to reach 98045.8 kg and 19887.6 kg, respectively. The peak overall energy and exergy efficiencies of 57.8% and 60.5% are attained. Multi-objective optimization results provided optimal operational points entailing overall exergy efficiencies of 51% and 44.6% at total cost rates of $4503.3 per hour and $6007.2 per hour, respectively. These correspond to different combinations of solar intensity and wind speed levels. The direct ammonia fuel cell stack is found to have an open circuit voltage of 1399 mV and a peak power density of 13.4 W/m2 that entailed an increasing trend with rising humidification temperatures. Various sensitivity analyses are also performed to determine system performances under varying operating conditions and system parameters.