Determination of the forms of nitrogen released in coal tar during rapid devolatilization. Semi-annual report, November 1, 1995--April 30, 1996

摘要

Control of emissions of nitrogen oxides (NO(sub x)) from coal combustion systems is becoming a major design and retrofit consideration. Most NO(sub x) in coal combustion systems comes from nitrogen in the fuel, rather than from nitrogen in the air. Practical emission control strategies include burner design strategies (e.g., low NO(sub x) burners), overfire air, reburning, selective non-catalytic reduction (SNCR) using reduction agents such as NH(sub 3) or urea, and selective catalytic reduction (SCR). The order listed also reflects the order of increasing costs for implementation. It is therefore most economically desirable to perform burner modifications to reduce NO(sub x) emissions rather than other control measures. Low-NO(sub x) burners work on the principle that devolatilized nitrogen species will form N(sub 2) rather than NO(sub x) under locally fuel-rich conditions with sufficient residence time at appropriate temperatures. The amount and form of nitrogen released during devolatilization influence the degree of NO(sub x) reduction attainable using burner design strategies for a given coal. Nitrogen in the char following devolatilization is released by heterogeneous oxidation, and may not be controlled by aerodynamic burner modifications. The objectives of this work are to perform detailed chemical measurements of the nitrogen in coal, tar, and char.