Metal substrate reduction catalysts are often used to reduce NOx from large-scale biomass combustion processes.
The substrate is made from very thin (typically 0.05mm) foil consisting of Fecralloy, an alloy of iron, chromium and aluminium. This is held together by vacuum brazing and often support bars too in the case of very large diameters.
There are several advantages of metal substrates for this type of catalytic converter, as follows:
- They can be made up to 1200mm diameter in one piece
- The pressure drop for a given size is lower than for a ceramic substrate
- Due to the high thermal conductivity of Fecralloy, local overheating can be avoided
The catalytic coating is usually either a combination of vanadium pentoxide, titania and tungsten, or zeolite.
Cell densities typically range from 25 cells per square inch (cpsi) up to 200 cpsi. The size of the cells is selected based on the size of any solid particles in the flue gas, so that they do not easily become blocked.