Kinetic model of SCR catalyst-based de-NOx reactions including surface oxidation by NO2 for natural gas-fired combined cycle power plants

Abstract

Natural gas-fired combined cycle power plants (NGCC) have the advantages of high efficiency and low CO2 intensity compared to coal-fired power plants. When variable renewable energy sources are introduced to the grid in large quantities, the NGCC is expected to have rapid start-ups, rapid shutdowns, and increased partialload operations to stabilize the grid. Due to these temporary operations, the ratio of NO2/NOX in the NGCC exhaust gas changes significantly. In general, when the NO2/NOX ratio is high, the efficiency of the de-NOX systems decreases. Moreover, the performance of de-NOX systems has a transient response due to changes at the catalyst surface and the adsorption of NH3. Considering the trajectory of increased variable renewable energy, it is necessary to develop an efficient NOx removal system that is effective over a wide range of NO2/NOX ratios. In the modeling of de-NOX system performance, this study extends the general Eley-Rideal reaction between adsorbed NH3 and gas-phase NOX to include the existence of O2, H2O, CO2, and transient NO2 in the exhaust gas along with changes in redox sites (i.e., V5+=O and V4+-OH). A two-dimensional transient numerical simulation code was developed and adapted using experimental results obtained from treating simulated NGCC exhaust gas using a commercial honeycomb-shaped selective catalyst. Numerical simulations incorporating the empirically determined kinetic equations accurately predict the transient and equilibrium concentrations of NOX and NH3 exiting a honeycomb catalyst even under gas conditions including high NO2.

Keywords

• eley-rideal reaction
• ammonia oxidation
• flue gas denitrification
• adsorption-desorption
• flexible operation of thermal power plant