Abstract
Zhundong low-rank coal is very likely to be utilized extensively in oxy-fired boilers in the near future. Its PM10 (particulate matter with an aerodynamic diameter of ≤10 μm) emission behaviors during oxy-fuel combustion need to be carefully studied before its large-scale use. The present study examines the emission behaviors of inorganic ultrafine particles (PM0.5, with an aerodynamic diameter of ≤0.5 μm), as well as PM10 during the combustion of Zhundong coal in air and oxy-fuel conditions (O2/CO2) at three characterized O2 input fractions, i.e., 21, 27 and 32 vol.%. The combustion experiments were carried out in a high-temperature drop-tube furnace (HDTF) at a combustion temperature of 1500 °C. The results show that PM0.5 is composed of Na, S, Mg and Ca, with total fractions of ~90%, while PM0.5–10 (with an aerodynamic diameter between 0.5 and 10 μm) predominantly contains Ca (~50–65%). At three characterized oxygen fractions during oxy-fuel combustion (OXY21, 27 and 32), the promoted O2 fraction was found to increase the yields of both PM0.5 and PM0.5–10. A higher particle-burning temperature and a lower CO2 fraction promote the reactions of both organically bound elements and inorganic minerals, increasing the partitioning of Mg and Ca and causing an increased yield of PM0.5. The yield of PM0.5 from air is high and similar to that from OXY32 while the yield of PM0.5–10 from air is similar to that from OXY27. The high yield of PM0.5 from air is mainly generated by the highest yields of Ca in four conditions.
Highlights
Coal is still one of the most important energy resources in China; it accounts for ~62% of the total energy demand nowadays and causes many environmental problems such as SOx, NOx, PM and heavy metals [1,2,3,4,5,6]
A typical Zhundong coal had been used in earlier research [16,32], which was crushed, ground and sieved to obtain a narrow-sized coal sample in a range of 63–100 μm
To distinguish between the occurrence forms of major inorganic elements, the coal was sequentially extracted with deionized water, 1 M ammonium acetate (CH3 COONH4, NH4 OAc), 1 M hydrochloric acid (HCl) at a temperature of 60 ◦ C for 24 h [33]
Summary
Coal is still one of the most important energy resources in China; it accounts for ~62% of the total energy demand nowadays and causes many environmental problems such as SOx, NOx, PM (particulate matter) and heavy metals [1,2,3,4,5,6]. Zhundong coal was reported to show the typical combustion characteristics of a low-rank coal [7,8], i.e., it consisted of sequential and overlapping stages of volatile release and char combustion [9,10]. To better utilize it in a power boiler, Chinese researchers have paid attention to the obvious ash deposition problems, such as slagging, fouling and corrosion, which are mainly caused. Oxy-fuel (O2 /CO2 ) combustion was proposed as a retrofit technology to allow for the capture and storage of CO2 in new or existing air-fired coal boilers [18,19,20]. The principal purpose of this study is to examine the possible difference in PM emission behaviors of Zhundong coal during oxy-fuel combustion in the three characterized O2 input fractions comparable to air combustion, i.e., 21%, 27% and 32 vol.% of O2 in a O2 /CO2 mixture
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