Experiment and mechanism investigation on advanced reburning for NOx reduction: influence of CO and temperature

Abstract

Pulverized coal reburning, ammonia injection and advanced reburning in a pilot scale drop tube furnace were investigated. Premix of petroleum gas, air and NH 3 were burned in a porous gas burner to generate the needed flue gas. Four kinds of pulverized coal were fed as reburning fuel at constant rate of 1g/min. The coal reburning process parameters including 15%~25% reburn heat input, temperature range from 1100 °C to 1400 °C and also the carbon in fly ash, coal fineness, reburn zone stoichiometric ratio, etc. were investigated. On the condition of 25% reburn heat input, maximum of 47% NO reduction with Yanzhou coal was obtained by pure coal reburning. Optimal temperature for reburning is about 1300 °C and fuel-rich stoichiometric ratio is essential; coal fineness can slightly enhance the reburning ability. The temperature window for ammonia injection is about 700 °C~1100 °C. CO can improve the NH 3 ability at lower temperature. During advanced reburning, 72.9% NO reduction was measured. To achieve more than 70% NO reduction, Selective Non-catalytic NO x Reduction (SNCR) should need NH 3 /NO stoichiometric ratio larger than 5, while advanced reburning only uses common dose of ammonia as in conventional SNCR technology. Mechanism study shows the oxidization of CO can improve the decomposition of H 2 O, which will rich the radical pools igniting the whole reactions at lower temperatures.

Aging of Premixed Metal Fiber Burners for Natural Gas Combustion Catalyzed with Pd/LaMnO3·2ZrO2

“…In the present case, NO 2 is practically absent. NO originates mainly from the Zeldowich thermal process, [23][24][25] since the CO molecule does not contain N atoms, and when the gas mixture is sufficiently lean (E a ) 20% or more), the formation of radicals CH and HCN is not significant (Fenimore mechanism). [23][24][25][26][27][28][29] Moreover, thermal NO emissions are expected to decrease with lower flame temperatures.…”

“…NO originates mainly from the Zeldowich thermal process, [23][24][25] since the CO molecule does not contain N atoms, and when the gas mixture is sufficiently lean (E a ) 20% or more), the formation of radicals CH and HCN is not significant (Fenimore mechanism). [23][24][25][26][27][28][29] Moreover, thermal NO emissions are expected to decrease with lower flame temperatures. Catalytic combustion is operated at lower temperature compared to the conventional flame combustion, thus reducing the formation of thermal NO x , which starts at about 1500 °C.…”

“…In the present case, NO 2 is practically absent. NO originates mainly from the Zeldowich thermal process, − since the CO molecule does not contain N atoms, and when the gas mixture is sufficiently lean ( E a = 20% or more), the formation of radicals CH and HCN is not significant (Fenimore mechanism). − Moreover, thermal NO emissions are expected to decrease with lower flame temperatures. Catalytic combustion is operated at lower temperature compared to the conventional flame combustion, thus reducing the formation of thermal NO x , which starts at about 1500 °C. , This is confirmed by the decreasing trend of NO emissions shown in Figure coupled with the decrease of the temperatures on the burner deck (see Figure ).…”

Syngas as a Reburning Fuel for Natural Gas Combustion

“…air flow carried out by the authors showed that calculated results of the calculations are in agreement with the model and often overlap. The perfectly stirred reactor is commonly used by researchers not only in the reburning process modelling, but also in other low-emission methods of calculating air recirculation, or air staging, which is evidenced in a large body of published studies (Adamczuk and Radomiak, 2010;Fan et al, 1998;Faravelli et al, 2001;Ljungdahl and Larfeldt, 2001;Luan et al, 2009;Szecowka et al, 2003;Wang et al, 2005;.…”