Numerical Simulation of Non-catalytic Partial Oxidation of Methane Based on Different Diluents
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摘要: 以工业装置O2/CH4体积比为0.69操作条件为基础,使用ANSYS Fluent16.1开展数值模拟,采用基于雷诺平均方程(RANS) 的 Realizable k-ε 湍流模型、涡耗散概念 (EDC) 模型与 GRI3.0 详细化学反应机理的耦合来模拟炉内的湍流燃烧与化学反应过程。考察了三种稀释剂(N2、H2O、CO2)对转化炉内的温度、自由基(OH、CH2O)分布以及炉膛火焰反应区分布的影响。结果表明:N2和H2O稀释对转化炉内温度、自由基及反应区分布的影响差别很小,CO2稀释下的影响最为显著。在CO2稀释下,炉膛内的最高火焰温度降低了约50 K;OH和CH2O自由基峰值分别降低了大约33%和24.5%。此外,CO2稀释的三种不同效应对转化炉内温度和自由基分布的影响大小依次为:稀释效应>热效应>化学效应。Abstract: The high temperature flame in the reformer of non-catalytic partial oxidation (NC-POX) of methane under pure oxygen atmosphere will affect the safe and stable operation of the actual industrial plant. Adding diluent to dilute pure oxygen in the reaction system can improve the temperature distribution and flame structure of the reformer. An O2/CH4 ratio of approximately 0.69 was typically used when NC-POX reformers were used industrially, numerical modelling was conducted using ANSYS Fluent 16.1 commercial simulation software, with a Realizable k–ε turbulence model considered for Reynolds-averaged Navier-Stokes (RANS) model, the Eddy Dissipation Concept (EDC) model coupled with GRI3.0 chemical reaction mechanism was suitable for simulating turbulent combustion and chemical reaction processes in the reformer. This study investigates the effect of three diluent (N2, CO2, H2O) on the distribution of temperature, radicals (OH、CH2O) and flame reaction zone. Results indicate that the effects of N2 and H2O dilution on the temperature, radicals and flame reaction zone distribution are basically indistinguishable, and the effect of CO2 dilution is the most significant. The increasing of CO2 content decreases the peak temperature by about 50K and peak values of OH and CH2O radicals decreased by about 33% and 24.5%, respectively. In addition, three effects of CO2 dilution on the temperature and radicals distribution in the reformer are in the order of dilution effect>thermal effect>chemical effect. Therefore, using the diluent CO2 to improve the temperature distribution of the reformer system not only realizes the effective adjustment of the H2/CO ratio of the syngas, but also provides support for the flame control in a high-temperature reducing atmosphere.
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Key words:
- non-catalytic partial oxidation /
- diluents /
- CO2 dilution /
- flame temperature /
- chemical effect
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表 1 模拟工况的设定
Table 1. Simulation conditions
Case O2
Flow/(L•s−1)$ \varphi $CO2
/%$ \varphi $N2
/%$ \varphi $H2O
/%CH4
Flow/(L•s−1)O2/CH4
Ratio1 0.177 0 0 0 0.255 0.69 1* 0.141 0 0 0 0.204 0.69 2 0.177 30 0 0 0.255 0.69 3 0.177 0 30 0 0.255 0.69 4 0.177 0 0 30 0.255 0.69 表 2 三种稀释剂条件下的出口气体组成
Table 2. Outlet gas composition under three diluent conditions
Species volume fractions H2 H2O CH4 CO CO2 N2 H2/CO N2 dilution 0.3877 0.2300 0.0297 0.1918 0.0382 0.0738 2.02 H2O dilution 0.3974 0.2914 0.0314 0.1870 0.0463 0.0008 2.13 CO2 dilution 0.3652 0.2589 0.0361 0.2390 0.0598 0.0008 1.53 No dilution 0.4460 0.2216 0.0210 0.2293 0.0359 0.0016 1.95 -
[1] SONG X, GUO Z. Technologies for direct production of flexible H2/CO synthesis gas[J]. Energy Conversion & Management, 2006, 47(5): 560-569. [2] FÖRSTER T, VOLOSHCHUK Y, RICHTER A, et al. 3D numerical study of the performance of different burner concepts for the high-pressure non-catalytic natural gas reforming based on the Freiberg semi-industrial test facility HP POX. Fuel. 2017, 203: 954-963. [3] SHI B L, HU J, ISHIZUKA S. Carbon dioxide diluted methane/oxygen combustion in a rapidly mixed tubular flame burner[J]. Combustion and Flame, 2015, 162(2): 420-430. doi: 10.1016/j.combustflame.2014.07.022 [4] 司济沧, 舒子云, 王国昌, 等. 稀释剂和氧浓度对甲烷非预混MILD富氧燃烧影响的模拟研究[J]. 中国电机工程学报, 2021, 41(11): 3692-3702. doi: 10.13334/J.0258-8013.PCSEE.201621 [5] TU Y J, LIU H, YANG W M. Flame characteristics of CH4/H2 on a jet-in-hot-coflow burner diluted by N2, CO2 and H2O[J]. Energy & Fuels, 2017, 31(3): 3270-3280. [6] 杨曹立, 高瑞, 代正华, 等. 气态烃非催化部分氧化烧嘴端面传热过程研究[J]. 华东理工大学学报(自然科学版), 2021, 47(1): 11-16. doi: 10.14135/j.cnki.1006-3080.20191024001 [7] 栾聪聪, 涂垚杰, 谢逸豪, 等. 基于WSR反应器不同稀释介质条件下MILD燃烧分区特性研究[J]. 燃烧科学与技术, 2019(6): 492-500. [8] DUAN X, LI Y, LIU Y, et al. Dilution gas and hydrogen enrichment on the laminar flame speed and flame structure of the methane/air mixture[J]. Fuel, 2020, 281: 118794. doi: 10.1016/j.fuel.2020.118794 [9] HU E J, JIANG X, HUANG Z H, et al. Numerical study on the effects of diluents on the laminar burning velocity of methane-air mixtures[J]. Energy & Fuels, 2012, 26(7): 4242-4252. [10] WANG D, JI C W, WANG S F, et al. Chemical effects of CO2 dilution on CH4 and H2 spherical flame[J]. Energy, 2019, 185: 316-326. doi: 10.1016/j.energy.2019.07.032 [11] LIU F S, GUO H S, SMALLWOOD G J, et al. The chemical effects of carbon dioxide as an additive in an ethylene diffusion flame: Implications for soot and NOx formation[J]. Combustion and Flame, 2001, 125(1): 778-787. [12] 徐月亭, 代正华, 李新宇, 等. 甲烷常压非催化部分氧化热模实验研究[J]. 化学工程, 2016, 44(5): 60-64. doi: 10.3969/j.issn.1005-9954.2016.05.012 [13] GUO W Y, WU Y Z, DONG L, et al. Simulation of non-catalytic partial oxidation and scale-up of natural gas reformer[J]. Fuel Processing Technology, 2012, 98: 45-50. doi: 10.1016/j.fuproc.2012.01.019 [14] LI X Y, DAI Z H, GUO Q H, et al. Experimental and numerical study of MILD combustion in a bench-scale natural gas partial oxidation gasifier[J]. Fuel, 2017, 193: 197-205. doi: 10.1016/j.fuel.2016.12.056 [15] GHOLIZADEH A, SHABANIAN S R, GHADIRIAN M, et al. Effect of steam addition and distance between inlet nozzles on non-catalytic POX process under MILD combustion condition[J]. International Journal of Hydrogen Energy, 2022, 47(1): 127-150. doi: 10.1016/j.ijhydene.2021.10.005 [16] 周新文, 陈彩霞, 王辅臣. 天然气非催化部分氧化反应机理模拟[J]. 华东理工大学学报(自然科学版), 2010, 36(2): 192-197. doi: 10.3969/j.issn.1006-3080.2010.02.006 [17] ERTESVÅG I S. Scrutinizing proposed extensions to the Eddy Dissipation Concept (EDC) at low turbulence Reynolds numbers and low Damköhler numbers[J]. Fuel, 2022, 309: 122032. doi: 10.1016/j.fuel.2021.122032 [18] MEDWELL P R, KALT P, DALLY B B. Simultaneous imaging of OH, formaldehyde, and temperature of turbulent nonpremixed jet flames in a heated and diluted coflow[J]. Combustion and Flame, 2007, 148(1-2): 48-61. doi: 10.1016/j.combustflame.2006.10.002 [19] SJÖHOLM J, ROSELL J, LI B, et al. Simultaneous visualization of OH, CH, CH2O and toluene PLIF in a methane jet flame with varying degrees of turbulence. Proceedings of Combustion Institute[J]. 2013, 34(1): 1475-1482. [20] ZHANG J P, DALLY B B, LI P F, et al. Moderate or intense low-oxygen dilution combustion of methane diluted by CO2 and N2[J]. Energy & Fuels, 2015, 29(7): 4576-4585. [21] 韩敏超, 艾育华, 陈 正, 等. 不同预热温度下H2/CO/O2/CO2的层流火焰传播特性[J]. 工程热物理学报, 2016, 37(1): 189-193. -