Reduction of NOx emission
International programs have been launched to reduce the increasing harmful effects caused by nitrogen-oxide emission on the environment. In Hungary, emission limit values are currently determined by the Decree of the Ministry for Environment No. 23 of 2001 (13 Nov) up to 140 kW-50 MW performance and by the Decree of the Ministry for Environment No. 10 of 2003 (11 Aug) over 50 MW performance.
The combustion plants running with liquid fuel can meet the currently valid emission standards with difficulty only.
Methods to be applied to reduce NOx emission at power stations are not widespread in Hungary, however, emission has been reduced nationwide. The following factors have enabled the said reduction:
the use of fossil fuels has been reduced in the electric power industry (due to the involvement of the power station in Paks step-by-step)
the considerable recession of the industrial production
The legal provisions supporting the reduction of emission promoted the development and spread of operating methods or technologies enabling lower NOx emission. At power stations, a lot of solutions of this kind are applied. These solutions can be classified as primary and secondary interventions:
the aim of primary interventions is to prevent that nitrogen-oxides are generated during combustion or to promote that the nitrogen-oxides that were generated are dissociated during combustion on the spot immediately and they cannot penetrate into flue gas.
the aim of secondary interventions is that the NOx generated is separated from flue gas.
Primary interventions are cheaper as in many cases operating conditions are to be changed only.
On the other hand, they are less general and more experiments or more precise planning are required so that the features of the particular boiler are considered. The reduction of NOx emission that can be generally achieved in this way is 20-50% but in certain cases a lower percentage can also be achieved.
Secondary interventions are more expensive than primary interventions and one of their characteristics is that complete equipment required for such an intervention can be purchased. Their efficiency of separation is 80-90%.
Our company has prepared a secondary intervention that has been applied for several customers with success.