The SCR deNOx catalyst is a high surface area, extruded catalyst. ECS has the ability to provide either a base metal or zeolite catalyst in honeycomb or pelleted form.
The process of selective catalytic reduction (SCR) of combustion flue gases reduces nitrogen oxides (NOx) into molecular nitrogen (N2) and water (H2O). NOx breaks down when it reacts with a reducing agent, usually ammonia (NH3), in the presence of a catalyst. The NH3 is mixed thoroughly with the flue gas prior to entering the catalyst. The mixing assures even distribution of the temperature and reaction components. The catalyst, by providing active reaction sites, allows the reaction to occur at temperatures between 300° – 1,050°F. The NH3 diffuses into the catalyst pore structure and is adsorbed onto an active catalyst site. The NOx then reacts with the adsorbed NH3, completing the reaction. The reaction depends primarily on available active sites (a function of geometric surface area, pore volume, and concentration of active catalyst component), flue gas temperature, and reagent concentration.
SCR Chemistry
The most significant reactions that reduce NO and NO2 with NH3 are the following:
| 4NO | + | O2 | + | 4NH3 | → | 4N2 | + | 6H2O |
| NO | + | NO2 | + | 2NH3 | → | N2 | + | 3H2O |
| + | 6NO2 | + | 8NH3 | → | 7N2 | + | 12H2O |
The first reaction is the predominant reaction. It shows that one mole of ammonia is consumed for each mole of NO removed. However, in an actual system, slightly more ammonia is injected than necessary for the desired NO removal, to account for imperfect mixing. The excess ammonia which passes through the catalyst bed non-reacted is called ammonia slip.
Some consequential reactions may also take place under certain operating conditions. Specifically:
| + | 4NH3 | + | 5O2 | → | 4NO | + | 6H2O | |
| + | SO3 | + | H2O | → | 2SO3 | |||
| 2NH3 | + | SO3 | + | 8NH3 | → | (NH4)2SO4 | + | 12H2O |
| NH3 | + | SO3 | + | H2O | → | (NH4)HSO4 | + | 12H2O |
Reaction number (4), ammonia oxidation, is not significant at normal operating temperatures below 800°F. As the flue gas temperature increases, the NH3 oxidizes more readily, increasing the concentration of NO and decreasing the available NH3 for the SCR process.
ECS’s SCR catalyst systems are manufactured for a long, trouble free life span that can operate within a wide temperature range and different NOx concentration levels.
ECS’s catalyst systems will routinely convert NOx to very low emission levels. A typical system installation will reduce NOx in excess of 98%.
Competitive Advantages
- Long Life Cycle
- Low Back Pressure
- Low Light Off Temperatures