UC Irvine

As awareness of greenhouse gas and harmful pollutant emissions rises, interest is also growing to curb the trend in an effort to reduce the harmful impacts that these emissions create. A large contributor to these emissions is stationary power generation sources which are typically powered by traditional heat engines. High temperature fuel cells provide an alternative solution to power generation which can have higher efficiency than heat engines, thus reducing overall harmful emissions. Fuel cells are also capable of using renewable streams of fuel so that the greenhouse gas emissions are completely negated.

Different system configurations based upon a solid oxide fuel cell power plant were modeled in bulk using Aspen Plus. The three configurations modeled were: a baseline Tri-Generation system that produces combined heating, hydrogen, and power; a Quad-Generation system that produces combined cooling, heating, hydrogen, and power; a Tri-Generation system that produces combined heating, hydrogen, and power that is supplemented with an absorption chiller within the hydrogen booster.

A parametric study was performed on the three systems in order to find any efficiency or operating gains compared to the baseline Tri-Generation system. Electricity and hydrogen generation efficiency were found to be greatest at the lowest evaluated fuel utilization of 0.6. System efficiency for the baseline Tri-Generation was the highest at 0.6 fuel utilization and decreased with increasing fuel utilization. Varying levels of power capacity had little effect on the system efficiency. Quad-Generation efficiency depended upon the coefficient of performance (COP). At a low COP of 1.1, overall system efficiency was lower than the baseline for a given fuel utilization. At a COP of 1.4, the overall efficiency was higher than the baseline and the impact of fuel utilization was reduced. The chiller supplemented Tri-Generation system also had lower system efficiency than the baseline; however, the impact of increased fuel utilization was reduced. For a given utilization, the efficiency stayed relatively unchanged. The result of unchanged efficiency as a function of fuel utilization for the Quad-Generation and the supplemented Tri-Generation systems suggests that these systems can be operated to follow dynamic loads without significant impact on system efficiency.