Design and development of DeNOx plants

Task

The reduction of pollutant emissions from combustion gases is no longer just a technical term from environmental and process engineering, but has reached the zeitgeist of politics and society. Buzzwords such as Diesel-Gate, climate conferences and driving bans confront us with this issue on a daily basis. The permissible pollutant limits for the environmentally harmful by-products of engine combustion, such as nitrogen oxides, will be further tightened in the coming years to the benefit of the environment. In addition to the automotive industry, the power plant and equipment industry in particular will have to meet these challenges. One process that has become established here is the so-called SCR or "DeNOx" plant. In an SCR (selective catalytic reduction) system, the harmful nitrogen oxides (NOx) are converted into harmless water vapor (H₂O) and nitrogen (N₂) with the addition of ammonia (NH₃).

Functionality

First, a reducing agent (urea or ammonia water) is added to the exhaust gas. The high temperatures of the exhaust gas cause the reducing agent to split into gaseous ammonia during thermolysis. This must be homogeneously distributed in the exhaust gas. The exhaust gas-ammonia mixture then flows through one or more catalyst levels, where the
"denitrification" of the exhaust gas is carried out. Uniform flow to the catalyst is essential for correct functionality.

Simulation

The uniform distribution of flow velocity, temperature and NH₃ concentration on entry into the catalyst largely determines the functionality of the SCR system. The deviations may only amount to a few percent. Such fine-tuning in a large power plant, some of which have diameters of up to 8 - 10 meters, is difficult to achieve using conventional measurement methods. Here, numerical flow simulation offers a considerable development advantage. Using a virtual model, the optimization of e.g. injector positions or internals such as mixers or baffles can be carried out effectively and quickly.
Merkle & Partner has developed a special SCR simulation kit that can be used to design and develop DeNox plants with maximum effectiveness. Successful customer projects that have already been put into operation have fully confirmed the quality of the results.