COMPUTER EXPERIMENTAL ANALYSIS OF A TUBULAR SOFC CHP TO EVALUATE FACTORS EFFECTS ON PERFORMANCES AND S/C RATIO

The aim of this work is the description of a computer experimental session, made on a simulation model of a tubular SOFC CHP plant, whose aim has been the analysis (through a statistical methodology: 2^K factorial experiments) of the effect of the main operation variables on the electric and thermal power provided by the stack, and on a particular performance parameter, the steam-to-carbon ratio (S/C). The computer experimental analysis has the aim to supply information preliminary to the correct design of the forthcoming real experimental tests on the generator, in order to outline particular point of interest and operation variables dependence. To perform the computer experimental analysis, a mathematical model has been developed that simulates a natural gas fuelled SOFC CHP system that generates and supplies net AC power to the external grid and recovers heat from the SOFC exhaust to provide hot water. The model has been calibrated for the CHP 100 kW_e Siemens tested for 20,400 hours in Holland by EDB/ELSAM and in Germany by RWE. The statistical methodology used for the computer experimental analysis is the factorial design (Yates' Technique): using the Anova technique the effects of the main independent variables (air utilisation factor U_ox, fuel utilisation factor U_F, internal fuel and air preheating and anodic recycling flow rate) have been investigated in a rigorous manner. Each main and interaction effect of the variables is analysed referring to the generated electric power and the heat recovered, and subsequently especially for the analysis of the steam-to-carbon ratio, whose values play a very important role on both performances and degradation of a SOFC stack. The proposed methodology seems to be powerful for system analysis; moreover, it allows the design of a set of experimental tests reducing the number of experiments and focusing the main expected results.