Experimentandmechanis_省略_nceofCOandtempe

Wang et al. / J Zhejiang Univ SCI 2005 6B(3):187-194 187

Journal of Zhejiang University SCIENCE ISSN 1009-3095

doc.guandang.net E-mail: jzus@zju.edu.cn

Experiment and mechanism investigation on advanced reburning

for NOx reduction: influence of CO and temperature

WANG Zhi-hua (王智化) , ZHOU Jun-hu (周俊虎), ZHANG Yan-wei (张彦威),

LU Zhi-min (卢志民), FAN Jian-ren (樊建人), CEN Ke-fa (岑可法)

(Clean Energy & Environment Engineering Key Laboratory of Ministry of Education, Zhejiang University, Hangzhou 310027, China)

E-mail: wangzh@sun.zju.edu.cn

Received June 1, 2004; revision accepted July 26, 2004

Abstract: Pulverized coal reburning, ammonia injection and advanced reburning in a pilot scale drop tube furnace were inves-tigated. Premix of petroleum gas, air and NH3 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 NH3 ability at lower temperature. During advanced reburning, 72.9% NO reduction was measured. To achieve more than 70% NO reduction, Selective Non-catalytic NOx Reduction (SNCR) should need NH3/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 H2O, which will rich the radical pools igniting the whole reactions at lower temperatures.

Key words: NO reduction, Advanced burning, Coal reburning, Selective Non-catalytic NOx Reduction (SNCR), CO doi:10.1631/jzus.2005.B0187 Document code: A CLC number: X511

Reduction (SCR) and Selective Non-Catalytic NOx INTRODUCTION

Reduction (SNCR) should be employed (Radojevic,

Nitrogen oxides (NOx) are one of the most toxic 1998). These techniques take advantage of an N-agent pollutions formed during the combustion process to reduce NO to N2 such as urea or ammonia. SCR especially of pulverized coal. International Energy requires noble metal catalyst, which is the most effi-Agency forecasts have indicated that some 38% of the cient but most expensive NOx emission control world’s electricity will still be generated from coal by technology, nowadays. SNCR does not require cata-2020 (Priddle, 1998). More efficient and lyst but is difficult to manipulate for the required environmental friendly and cleaner coal technologies narrow temperature window (1200~1350 K) in boiler. have therefore a major role to play in sustainable The most attractive technology proposed recently

combined reburning and SNCR process, is called development worldwide.

Nowadays, low NOx burners for stage-air com-Advanced Reburning (AR) and reportedly could bustion are widely used in power plant boilers. achieve more than 80% NOx reduction to approach Combustion modification methods can only achieve that of SCR at very low cost (Chen and Kramlich, moderate NOx emission level. Without perfect modi-1989; Tree and Clark, 2000; Hampartsoumian and fication, sludge in furnace loss of ignition (LOI) will Folayan, 2003; Nimmo et al., 2004); and so, is be-arise. With further limitation, Selective Catalytic NOx coming more attractive for detailed investigation