Reduction of NO by Biomass Pyrolysis Products in an Experimental Drop-Tube Hai-Sam Do, †,‡ Yutthasin Bunman, †,‡ Shiqiu Gao, † and Guangwen Xu* ,† † State Key Laboratory of Multi-phase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China ‡ University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China ABSTRACT: To understand the mechanism of NO x reduction by reburning biomass pyrolysis products, the present work is devoted to investigate the capabilities of biomass char, tar, and pyrolysis gas (Py-gas) for NO reduction through experiments in a drop-tube reactor. Pyrolysis of distilled spirit lees at 500 °C produced the char and tar tested, while Py-gas was prepared from cylinder gases according to the analysis of experimental Py-gas. The realized NO reduction efficiency varied with the stoichiometric ratio (SR), reaction temperature, residence time, and initial NO and CO concentrations. At a specified mass rate of 0.15 g/min, tar enabled the best NO reduction in comparison to char and Py-gas. The presence of CO in Py-gas inhibited the homogeneous NO reduction reactions to cause lower NO reduction efficiency by this agent. For biomass char and tar, their realized NO reduction reactions were promoted by high temperature and high initial NO and CO concentrations. Moreover, the suitable SR values for obtaining the highest NO reduction efficiency by reburning pyrolysis products were found to be 0.6-0.8. 1. INTRODUCTION Distilled spirit lees (DSL), which is a biomass waste generated from the production process of distilled spirits, amounted to 20 million tons per year in China. 1 DSL can be burned to produce steam, which not only limits the pollution as a result of DSL disposal but also offers a part of energy required by distilled spirits production. 2 Considering its relatively high N content (about 3-5 wt % on a dry basis), burning DSL via the traditional way has to release high NO x emission. To reduce NO x emission in combusting this kind of high-N biomass waste, we have developed a circulating fluidized-bed decoupling combustion (CFBDC) technology that has been proven to be effective in lowering 50% NO x emission in comparison to traditional combustion. 2-4 The CFBDC system is based on a dual-bed system and is composed of a fluidized-bed pyrolysis reactor and a riser combustor, as conceptualized in Figure 1. The technology separates the combustion process into pyrolysis of biomass fuel and combustion of char and volatile products, including non- condensable pyrolysis gas (Py-gas) and tar. Volatile is sent to an intermediate position of the riser combustor to allow for its co- burning with char from the riser bottom. In this way, a reburning zone is actually formed in the riser of a CFBDC system to, thus, lower the NO x emission. The lowered NO x emission should be due to the combined actions of char, tar, and Py-gas upon reduction of NO x formed by burning char N in the riser bottom. Many researchers 5-8 have regarded reburning as an effective way for NO x removal in combustion. In CFBDC, the reduction of NO x by reburning of pyrolysis products involves both heterogeneous reactions between char and NO x and homoge- neous reactions between volatiles (tar and Py-gas) and NO x . In recent years, a lot of studies have demonstrated the significant effect of chars 9-11 and reducing gas 12-14 on NO x reduction. For CFBDC, however, it is unclear what is the dominant mechanism for NO x reduction among the reaction of NO x with char, tar, and Py-gas. Tar with non-condensable Py-gas must take part in the homogeneous NO x reduction, but it has gained little attention in the past. Luo et al. 15-18 found that tar promoted NO reduction by biogas, while the effectiveness of NO reduction by model tar compounds was also investigated. This study follows our preliminary finding about the high reactivity of DSL-derived tar compared to DSL-derived char in reducing NO in a micro-fluidized bed reactor. 19 Accordingly, DSL-derived tar was suggested as an attractive reagent for lowering NO x emission in the CFBDC process. We intend to evaluate the ability of Py-gas among three DSL pyrolysis products (char, tar, and Py-gas) in reducing NO. Thus, the characteristics of NO reduction using char, tar, and Py-gas from DSL pyrolysis as reagents were investigated in a drop-tube reactor (DTR) to further understand the low-NO x mechanism Received: January 5, 2017 Revised: March 7, 2017 Published: March 8, 2017 Figure 1. Principle conception of circulating fluidized-bed decoupling combustion (CFBDC). Article pubs.acs.org/EF © 2017 American Chemical Society 4499 DOI: 10.1021/acs.energyfuels.7b00040 Energy Fuels 2017, 31, 4499-4506