(180ag) Dynamic Modeling of the Modifed Claus Process

The purpose of the current study is to investigate the transient behavior of the Claus process used for sulfur removal from coal-fired IGCC plants. To accomplish this, chemical kinetics for reactions taking place within the reaction furnace and the waste heat boiler were identified and used as the model basis rather than the more commonly used methods of restricted equilibrium or correlations. To model the system, a dynamic, pressure driven simulation of the process was carried out within the Aspen Plus Dynamics® process simulator. It was desired to determine the effects of feed composition, temperature and pressure on the performance of the Claus process and how effects of variation in feed conditions will propagate in the system. Verification of the developed steady state model was accomplished using available published plant data for the output of the reaction furnace and waste heat boiler as well as a comparison of the results of this model with predicted products from TSWEET®. In determining the dimensions of the reaction furnace, typical configurations and sizes were found within the literature. To determine heat transfer coefficients of the waste heat boiler along the length of the waste heat boiler, Aspen HTFS+® was used and the variations in the heat transfer coefficient were modeled across the length of the waste heat boiler, typically beginning near 80 W m-2 K-1 and dropping to 20 W m-2 K-1 towards the end.

The configuration of interest for this study was a split flow furnace with a 95% oxygen feed, two catalytic reactors and sulfur condensers. The feed to the process is high concentration NH3 and CO2 stream from a sour water stripper and a high concentration CO2 and H2O acid gas, with furnace residence times of 0.5 to 2.0 seconds. Waste heat boiler configurations were made to ensure a mass flux of 6 – 7 kg m-2 s-1 through the tubes.

Results of the steady state and dynamic simulations will be discussed and the implications of changes in IGCC feeds and operating variables on the composition of the tail gas from the Claus unit will be discussed.