Structural features and combustion reactivity of residual carbon in fine slag from entrained-flow gasification
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摘要: 气流床气化过程中产生的细渣含碳量很高,目前多以填埋的方式进行处理,将细渣用于循环流化床锅炉掺烧有望为细渣处理提供有利的技术。本研究选用宁东能源化工基地典型气化工艺GE、OMB及GSP产生的气化细渣为研究对象,利用物理吸附仪、激光拉曼及热重分析仪等仪器,系统研究了气化细渣中残炭的结构特征与燃烧特性。结果表明,原始气化细渣中的物质可分为黏结球形颗粒、多孔不规则颗粒与孤立的大球形颗粒,而酸洗后的气化细渣多以疏松细小的颗粒和多孔不规则块状颗粒存在;细渣中残炭的孔径尺寸主要分布在4−8 nm,且比表面积与残炭的活性位点大小顺序均为:GE > OMB > GSP;GE渣中残炭结构有序度最低,无定形炭结构最多,GSP则相反;GE渣中残炭燃烧速率最快,主要是由于GE渣中残炭有较大的比表面积、较多的无定形炭结构及较高的的活性位点,且GE渣中残炭的综合燃烧指数为5.26 × 10−7%2/(min2·℃3)。Abstract: The carbon content in fine slag during entrained-flow gasification is very high, at present, most of the fine slag was disposed by landfill. It is expected to provide a favorable technology by adding the fine slag to the circulating fluidized bed boilers to participate in combustion reaction. In this study, the gasification fine slags generated from GE, OMB and GSP gasifier, which are typical gasification processes in Ningdong energy and chemical base, was selected for investigation. The structural features and combustion reactivity of the residual carbon in the gasification fine slag were systematically studied by physical adsorption apparatus, laser Raman spectrum and thermogravimetric analyzer. The results showed that the materials in the original gasification fine slag could be divided into cohesive spherical particles, porous irregular particles and isolated large spherical particles, while the acid-washed gasification fine slag was mostly composed of loose fine particles and porous irregular massive particles. Additionally, the particle size of the residual carbon was clustered to 4–8 nm, and the specific surface area and active sites of that decreased orderly as follows: GE>OMB>GSP. The order degree of the residual carbon structure in GE slag was the lowest, and the amorphous carbon structure in it was the highest, while the case in GSP was the opposite. The combustion rate of the residual carbon in GE slag was the fastest, mainly due to its large specific surface area, more amorphous carbon structure and active site, and the comprehensive combustion index of residual carbon in GE slag was 5.26×10−7 %2/(min2·oC 3).
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表 1 细渣的工业分析与元素分析
Table 1 Proximate and ultimate analyses of fine slags
Sample Proximate analysis wd/% Ultimate analysis wd/% V FC A C H N S O* FSGE 10.12 25.21 64.67 20.25 1.03 0.18 2.07 11.80 FSOMB 3.88 14.26 81.86 16.40 0.53 0.10 0.45 0.60 FSGSP 6.96 12.43 80.61 16.33 0.71 0.08 1.51 0.76 note: V:volatile matter; FC:fixed carbon; d:dry basis; *:calculated by difference 表 2 细渣的灰分组成
Table 2 Ash composition of fine slags
Sample Compositions w/% SiO2 Al2O3 Fe2O3 CaO Na2O K2O MgO others FSGE 44.86 19.63 9.03 9.82 5.22 2.31 6.23 2.90 FSOMB 43.72 20.06 10.63 9.74 5.08 1.98 5.51 3.28 FSGSP 59.04 16.95 7.60 6.02 2.06 2.49 3.48 2.36 表 3 脱灰前后细渣的孔隙特征参数
Table 3 Pore characteristic parameters of fine slag before and after demineralization
Sample BET surface
area/(m2·g−1)Pore volume/
(× 103 cm3·g−1)Average
pore diameter/nmFSGE 160.39 0.232 2.892 DFSGE 737.31 3.026 16.419 FSOMB 82.50 0.151 3.659 DFSOMB 716.79 2.861 15.968 FSGSP 102.61 0.133 2.591 DFSGSP 429.28 3.089 28.786 表 4 拉曼光谱峰面积比
Table 4 Raman band area ratio
Parameter DFSGE DFSOMB DFSGSP ID1/IG 5.430 4.928 4.383 IG/IAll 0.107 0.124 0.141 ID3/IG + D2 + D3 0.164 0.134 0.131 ID3/IAll 0.057 0.044 0.045 ID4/IAll 0.067 0.064 0.038 ID3 + D4/IAll 0.124 0.108 0.083 表 5 燃烧曲线的特征参数
Table 5 Characteristic parameters of combustion curve
Fuel t1/℃ th/℃ tpeak/℃ Wmax/(%·min−1) Wmean/(%·min−1) S/(%2·min−2·℃−3) DFSGE 503.7 630.2 584.1 20.71 4.06 5.26×10−7 DFSOMB 502.7 634.7 554.2 18.55 4.27 4.94×10−7 DFSGSP 502.8 745.0 543.2 12.64 1.78 1.19×10−7 -
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