Evaluating the NOx Performance of a Steam Generator for Heavy Oil Production: Validation/Uncertainty Quantification in the Field

Paper from the AFRC 2013 conference titled Evaluating the NOx Performance of a Steam Generator for Heavy Oil Production: Validation/Uncertainty Quantification in the Field by Michal Hradisky

Chevron operates approximately 150 steam generators for heavy oil production in Californiaʼs San Joaquin Valley. To meet increasingly stringent NOx regulations, these steam generators were retrofitted with the Fives North American GLE combustion system. In an effort to better understand the combustion environment where NOx is being formed in these systems, researchers at the Institute for Clean and Secure Energy (ICSE) at the University of Utah have teamed with personnel from Chevron U.S.A. and Fives North American Combustion to perform a formal validation/uncertainty quantification (V/UQ) study using high-performance computing Large Eddy Simulation (LES) tools developed at ICSE and field data collected on a Chevron steam generator fired with the GLE system in the San Joaquin Valley. In a formal V/UQ process, the quantity of interest (QOI) is first determined. For this study, the QOI is NOx emissions. Since the NOx formation pathway is a thermal mechanism based on the local temperature and N2/O2 concentrations, these variables, if available, are also of interest. The field data used in this analysis include NOx and O2 concentrations and temperature measurements at various radial and axial locations in the GLE-equipped steam generator. To capture the dynamic motion of the flow field in the steam generator, two simulation tools have been employed. The first, Star-CCM+, is a commercial software tool that has been developed to handle complex geometries in problems involving flow, heat transfer, and stress. The second, ARCHES, couples an LES model with radiation, combustion and NOx chemistry models. This study is specifically focused on the data collected in the near burner region where temperatures are sufficiently high to produce thermal NOx. To fully resolve the turbulent length and time scales that are critical to determining local NOx formation, the computational domain is more than 100 million cells and requires close to 6000 processors for one week to run a single case. Due to the size of this problem and limited computational resources, the parameter space explored by the V/UQ analysis is very limited. This paper will focus on the results of a skeletal V/UQ analysis that utilizes the expertise of team members to reduce the parameter space explored to a couple of variables that have the greatest impact on the QOI (NOx). Particular emphasis will be paid to the difficulties arising from and solutions for performing quantified uncertainty analyses in systems that involve sparse field data and computationally-intensive simulations.