SNCR: Operating in the right temperature window
The SNCR (Selective non-catalytic reduction) is the method of choice for the denitrification in waste incineration plants today. Also for power plants the method becomes increasingly important.
The temperature window in which the reaction takes place is crucial for the effectiveness of the SNCR. Temperature fluctuations and imbalances must be detected early in time in order to inject the reacting agents into the right areas of the boiler.
Only the gas temperature counts
The true gas temperature is the crucial parameter for the process of the chemical reaction during denitrification. Thermal radiation is, however, irrelevant for the reaction. Here our acoustic gas temperature measurement AGAM shows its advantages: Fast, precisely, two-dimensionally and free from radiation effects, it determines the gas temperature and thus provides the main control parameters for the accurate injection of the reacting agents.
More complex SNCR due to change of fuels used
The quantity and quality of the fuels vary substantially, particularly at waste incineration and coal-fired power plants. This usually leads to strong local temperature variations – 200-400 °C deviation are not uncommon when the effects from combustion performance and temperature distribution overlap.
In modern plants high-performance SNCR systems are used which inject in various individually controlled zones at several levels. Basis for the optimization are the local gas temperatures which are determined with AGAM in more than 100 paths at different levels.
Lower limits – more optimization
Due to an increasing push from national regulatory authorities towards lower limits for nitrogen oxides, the demands on SNCR systems increase permanently, thus guaranteeing that furnaces can still be operated in the future. In modern SNCR systems AGAM makes a significant contribution to the flue gas denitrification, thus ensuring that even stricter limits can be achieved in the future.
Switchover from SCR to SNCR
The first waste incineration plants have switched from SCR to SNCR. This leads to considerable savings of gas for reheating in front of the catalysts and to a better efficiency due to lower pressure losses. The NOx emissions are at the level of the previously installed catalytic denitrification systems. The Wijster plant, e.g., reaches NOx clean gas concentrations below 100 mg continuously.