Article pubs.acs.org/EF
Scale Effect of Ceramic Foam Burner on the Combustion Characteristics of Low-Concentration Coal Mine Methane Huaming Dai*,†,‡ and Baiquan Lin†,‡ †
School of Safety Engineering and ‡State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, Xuzhou 221116, China ABSTRACT: The apparatus of low-concentration coal mine methane (LCM) combustion, from experimental scale to industrial scale, is necessary for the large volume of LCM. In this paper, an experimental system has been set up for the LCM combustion to validate the corresponding numerical model. Following this, the revised burner, with increased inlet diameter and burner length, was used to study the combustion characteristics numerically based on the reliable model. Results indicated that the temperature distribution exhibits a one-dimensional nature evidently and the temperature discrepancy among different inlet diameters is negligible with the adiabatic wall. However, the temperature discrepancy is apparent when the heat loss of the wall is considered, which shows the importance of heat preservation outside the burner wall. As the burner diameter increases, the total temperature increases and appears to be more homogeneous with the heat loss wall. In addition, NO emissions decrease gradually and CO emissions increase rapidly with the increasing of the diameter. When the inlet diameter triples, the NO emissions decrease by 31.4% and the CO emissions increase by a factor of 11. With the increasing of the burner length, the temperature, NO emissions, and CO emissions at the burner outlet decrease when the heat loss of the wall was not ignored. In addition, the NO emissions and CO emissions decrease by 18.6% and 22.7-fold, respectively, when the length triples. The velocity limit of different equivalence ratios, together with the temperature distribution and pollutant emission at different scales, should be considered systematically when the large-scale burners are designed.
1. INTRODUCTION Coal, which is an important resource in China, represents ∼70% of China’s primary energy resources.1 In the process of coal mining, coal mine methane (CMM) is the main factor affecting safety in the coal mine.2 Thus, CMM extraction has been the dominant measure to improve the safety.3 With the development of mining technology, the CMM extraction volume increases year by year. For instance, the CMM extraction volume reached 15.6 billion m3 and the utilization volume increased to 6.6 billion m3 in 2013, which represented increases of 10.6% and 13.8%, respectively, over the previous year in China. However, low-concentration coal mine methane (LCM) accounts for more than 70% of the total CMM extraction volume. Because the concentration of LCM is too low and fluctuating, its utilization is very difficult and often discharged directly. Nevertheless, the environmental pressure is increased for the greenhouse effect of methane (included in the LCM) is 21 times stronger than carbon dioxide. Consequently, a new effective method is necessary for the utilization of LCM. Premixed combustion technology in porous media has been considered as an effective method for the utilization of low calorific gas (including LCM). Compared with traditional combustion method, this technology combines several outstanding features, such as good performance of flame stability, high combustion efficiency, extensional flammable limits, and lower pollutant emissions, which is useful for energy savings and environment protection.4−7 Even though catalytic combustion (CC) has similar features,8 the deactivation of the catalyst can easily involve sintering or poisoning,9 which is unsuitable for industrial applications. In addition, the higher volatility and poor economics of some catalysts greatly prevent the development of CC technology.10 Many researchers have © XXXX American Chemical Society
verified the merits of porous media combustion technology. Xu11 found that the minimum limit of the equivalence ratio can reach 0.4 at a mass velocity of 0.163 g/s. Meanwhile, the nitrogen oxide (NOx) emissions are
