Sulzer Chemtech USA, Inc.

Turbulent Mixing in DeNOx Plants

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Courtesy of Sulzer Chemtech USA, Inc.

Industrial plant designers guarantee certain efficiency. In DeNOx plants for example the mixing process has a major influence on the efficiency. Sulzer Innotec can revert to several years experience in the simulation of turbulent mixing allowing us to quantitatively predict such applications.

DeNOx plants

In the last quarter century, air pollution has become a global environmental problem. NOx emitted from thermal power plants can be decomposed into harmless N2 and H2O in DeNOx plants through the addition of ammonia and the action of the catalyst (see figure 1). In the design of the reactor, it is important to obtain uniform gas flow to improve DeNOx performance and prevent erosion and plugging of the catalyst with dust. A uniform distribution of the injected NH3 is also important for an efficient DeNOx performance. Numerical simulations can help to optimize the mixing process and, thus, to increase the efficiency of a DeNOx plant.

Turbulent mixing

Static mixers have been developed by Sulzer Chemtech for many years and cover several types such as SMI, SMV and Compact mixers. The optimization of such static mixers concerning the mixing efficiency and pressure loss is supported by Sulzer Innotec with numerical flow simulations. Measurements for most mixers and different flow conditions have been carried out by Sulzer Chemtech allowing for validations concerning grid topology and resolution as well as turbulence models, Schmidt number, etc. Extended validations of an isolated mixing device with two SMV mixing elements have been undertaken.

Numerical simulations have been performed on different grids such as three different resolution levels on a tetrahedral mesh and two different resolution levels on a hexahedral mesh. For simplicity, a tracer with identical fluid properties as the carrier gas has been injected at the upper side of the inlet. The standard deviations of the tracer in cross sections along the mean flow direction have been compared to measurements.

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