Abstract: The methods of computing the indirect running costs of the low NO_x staged combustion technology and the direct running costs of the reducing agent of SCR equipment are introduced. An equation for calculating the total costs of NO_x reduction with the two methods of NO_x control used in boilers is established. According to the principle of minimizing the total costs of NO_x reduction, the NO_x concentration at the inlet of SCR equipment is taken as the variable and, a viewpoint on the existence of the economic inlet NO_x concentration is put forward. The main conclusion is that the economic concentration is a critical value for equitably assigning the indirect costs of low NO_x staged combustion technology and the direct costs of SCR equipment. Only when the NO_x concentration is the economic value, are the total costs of NO_x reduction the least.

Key words: low NOx combustion, air staging technology, back-end denitration technology, SCR equipment, reducing agent, cost of NOx reduction, economic NOx concentration