(530c) Dynamic Modeling, Data Reconciliation, and Simulation of Faults in a Sour Water Gas Shift Reactor

For pre-combustion CO₂ capture in an integrated gasification combined cycle (IGCC) plant, efficient operation of the water gas shift reactors (WGSRs) is necessary. The operation of the WGSRs should ensure that the desired H₂/CO ratio at the inlet of the acid gas removal (AGR) unit is achieved and most of the COS content in the syngas is hydrolyzed in the WGSR process. Due to the typical operating conditions in a WGSR process for an IGCC plant, a number of faults can occur that can cause significant deviation from the operational targets and can result in considerable down-time. For example, the residual fly ash in the syngas can deposit on the catalyst reducing the number of active sites for reaction and decreasing the porosity of the catalyst bed. As the WGS reactions are exothermic, a temperature higher than that allowed by the catalyst manufacturer can cause micro-structural changes to the catalyst. A dynamic model can help in developing a better understanding of the faulty operation of the WGSR process and therefore, can be used for monitoring and development of fault-tolerant control.

With this motivation, a first-principles dynamic model of a sour shift reactor is developed in this work. The 1-D model comprises of mass, momentum, and energy balance equations. In order to reduce the computational time, the method of Thiele modulus and effectiveness factor is used in the modeling approach. The hydrolysis of CO is assumed to be a pseudo first-order reaction and the hydrolysis of COS is assumed to follow Eley-Rideal mechanism. The model is validated with the experimental data available in the open literature for an alkali-metal-impregnated catalyst. A gross error detection and reconciliation procedure is first performed on data. The kinetic parameters are then obtained from the reconciled data. The kinetic model is integrated into the conservation equations.

The validated model is used to study the effect of changes in the operating conditions such as the inlet flow rate composition and temperature of the syngas. In addition, the detailed model is used to study the dynamics of a number of key variables in response to various faults such as changes in the catalyst activity, changes in the surface area of the catalyst, and changes in the bed porosity.  The presentation will also include a number of key observations that can be useful for process monitoring and fault diagnosis of the WGSR process.