Study on the relationship between structure, properties and size distribution of fine slag from entrained flow gasification
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摘要: 气化过程中,不同粒度颗粒的受热破裂方式、挥发分脱除行为、焦-熔渣相互作用等具有显著差异,导致所产生的不同尺寸的煤气化细渣具有不同的结构特征和反应特性,通过研究气流床煤气化细渣结构、性质与其粒度分布的关系可为溯源气化炉内细渣形成机制及入炉煤粒度优化提供重要依据。为此,本研究选用宁夏宁东典型GSP煤气化工艺细渣为原料,通过烘干、破碎、筛分处理,获取了粒度分别为<0.125、0.125–0.250、>0.250 mm的三种样品,分别称为小、中、大粒级样品,借助氮气吸附-脱附法、XRD、Raman光谱、TGA等表征分析手段对其理化结构及燃烧活性进行了研究。结果表明,不同粒级气化细渣在组成、结构及反应活性方面有显著差异,三种粒级样品在渣中所占比例分别22%、46%、32%,均含有大量的球状颗粒与不规则颗粒。其中,中粒级气化细渣气化程度最小,残炭含量最高,达19%,石墨化程度最低,仅为30%,比表面积最大,达87.8 m2/g,在不同的升温速率下综合燃烧特性指数最优,大粒级气化细渣以上性质则与其完全相反。显然,气化较充分的煤粉趋向于形成大粒级的气化细渣,气化程度较低的煤粉更易形成中粒级气化细渣,这为煤气化过程的研究提供了一定的依据。中粒级气化细渣在细渣中含量最多,且气化程度低、含碳量高,比表面积和孔隙率大,所以仍具有一定潜在的利用价值,这也为气化细渣的处理与处置提供了思路。Abstract: In the process of gasification for different size of coal particles, there are remarkable differences in the cracking mode, behavior of volatile removal and coke-slag interaction. These differences lead to the discrepancies in structural characteristics and reaction behavior for fine slag. Therefore, it is considered that the study on relationship between structure, properties and size distribution of fine slag from entrained flow gasification can provide vital guidance for analyzing the formation mechanism of fine slag and optimizing the size of coal particles for gasification. For this purpose, the fine slag from Ningdong typical GSP technology in Ningxia Province was selected as a raw material. After drying, crushing and sieving, three kinds of samples with size of <0.125, 0.125–0.250 and >0.250 mm were prepared, and called small, medium and large size samples respectively. The nitrogen adsorption, XRD, Raman spectroscopy and TGA were applied to clarify the physicochemical structure and combustion reactivity of samples. It is found that there are huge differences in the composition, structure or reactivity of the samples in different size. Precisely, three types of samples account for 22%, 46%, and 32% respectively. All the fine slag contains a large number of spherical particles and irregular particles. The sample with the middle size particles, which has the most content of residual carbon (19%) and the lowest graphitization degree (30%), shows the slightest gasification degree. It also presents the largest specific surface area (87.8 m2/g), and the optimal combustibility index regardless of the heating rate. While, the above properties of the sample with large size particles are completely opposite. Apparently, coal gasified sufficiently tends to form fine slag in large particle size, while coal gasified insufficiently is more likely to form slag in middle particle size. To some degree, all these findings can supply a certain basis to the study of gasification process. Meanwhile, the medium-sized fine slag with the most content in fine slag has low gasification degree, large content of carbon, and large specific surface area and porosity, which still has a certain potential utilization value for the treatment and disposal of the fine slag.
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Key words:
- coal gasification /
- fine slag /
- size distribution of particle /
- combustion reactivity /
- microstructure
1) #共同第一作者 -
表 1 样品的工业分析与元素分析
Table 1 Proximate and ultimate analyses of the sample
Proximate analysis wd/% Ultimate analysis wd/% V FC A C H N S O* 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 样品的灰分组成
Table 2 Ash composition of the sample
Compositions w/% SiO2 Al2O3 Fe2O3 CaO Na2O K2O MgO others 59.04 16.95 7.60 6.02 2.06 2.49 3.48 2.36 表 3 样品的烧失量
Table 3 Burn loss of samples LOI
Size fraction/mm Mass before combustion/g Mass after combustion/g LOI/% <0.125 1.00024 0.84343 15.68 0.125−0.250 1.00023 0.81071 18.95 >0.250 1.00026 0.87678 12.34 表 4 不同粒级GSPZ的比表面积及孔径分析
Table 4 BET test results of size-segmented GSPZ
Size fraction/mm BET surface area/(m2·g−1) Micropore area/(m2·g−1) Mesoporous and macroporous area/(m2·g−1) <0.125 81.085 11.046 70.039 0.125−0.250 87.871 14.080 73.792 >0.250 37.004 5.385 31.620 表 5 不同粒级GSPZ的微晶结构参数
Table 5 Microcrystalline structure parameters of size-segmented GSPZ
<0.125 mm 0.125−0.250 mm >0.250 mm d002/Å 3.411 3.414 3.395 d100/Å 2.074 2.048 2.052 θ002/(°) 26.101 26.079 26.231 θ100/(°) 43.609 44.194 44.091 β002/(°) 0.175 0.107 0.22 β100/(°) 0.107 0.394 0.232 Lc(002)/Å 14.602 23.146 14.462 La(100)/Å 28.452 7.359 12.291 g/% 33.5 30.2 52.9 表 6 不同粒级GSPZ的拉曼光谱峰面积参数
Table 6 Raman band area parameter of size-segmented GSPZ
< 0.125 mm 0.125−0.250 mm > 0.250 mm G 15736.65 14421.64 28948.20 D1 44241.26 44921.93 72385.62 D2 6319.80 11776.67 5241.44 D3 4298.84 2697.58 5448.12 D4 10792.46 15172.95 16018.01 ID1/IG 2.81 3.12 2.50 IG/IAll 0.19 0.16 0.23 表 7 不同升温速率下不同粒级GSPZ的燃烧特性参数
Table 7 Characteristic parameters of combustion of size-segmented GSPZ at different heating rate
Size fraction /mm Heating rate /(℃·min−1) ti/℃ th /℃ Wmax/(%·min−1) Wmean/(%·min−1) Ai/% Ah/% S/(%2·min −2·℃−3) <0.125 10 539.45 785.74 −0.13 −0.462 98.54 87.17 2.62×10−10 0.125−0.250 10 544.40 790.47 −0.14 −0.539 98.55 85.02 3.28×10−10 > 0.250 10 549.13 793.70 −0.10 −0.450 98.37 87.21 1.90×10−10 <0.125 15 562.47 786.38 −0.11 −0.705 98.74 88.04 3.16×10−10 0.125−0.250 15 557.41 814.79 −0.15 −0.884 98.39 82.86 5.36×10−10 >0.250 15 564.83 817.79 −0.08 −0.575 99.00 89.16 1.79×10−10 <0.125 20 559.88 794.53 −0.10 −0.810 98.08 87.60 3.55×10−10 0.125−0.250 20 561.17 855.00 −0.13 −0.901 98.02 83.81 4.71×10−10 >0.250 20 563.54 814.13 −0.07 −0.642 98.30 89.87 1.81×10−10 表 8 不同升温速率下不同粒级GSPZ的动力学参数
Table 8 Combustion kinetic parameters of size-segmented GSPZ at different heating rate
Size fraction /mm Heating rate /(℃·min−1) E/(kJ·mol−1) A/ s−1 R2 <0.125 10 39.24 5.194 0.92 0.125−0.250 10 37.91 6.767 0.92 >0.250 10 39.44 2.047 0.99 <0.125 15 40.67 4.901 0.93 0.125−0.250 15 39.23 6.805 0.93 >0.250 15 50.04 0.873 0.99 <0.125 20 39.01 9.676 0.97 0.125−0.250 20 37.52 10.917 0.94 >0.250 20 40.79 4.246 0.98 -
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