Effects of high steam partial pressure on desulfurization process of limestone

doi:10.11949/j.issn.0438-1157.20190067

Abstract

Abstract:

To understand the limestone desulfuration process in the water-coal-slurry fired circulating fluidized bed (CFB) boiler, in which the steam concentration in the furnace is much higher than the conventional CFB boiler, calcination and sulfuration processes of the limestone desulfuration were respectively studied at a rather wide range of steam concentration using a fixed-bed reactor. The pore structure and apparent morphology of the calcined product and the sulfurized product were analyzed by a true densitometer and a scanning electron microscope. The results show that the presence of water vapor (H₂O(g) ) promotes the sintering of calcination product. The porosity and specific surface area of calcination product are lower than those of the calcination product at H₂O(g) free condition. With the presence of H₂O(g), the macropore portion of calcination product increases, reducing the reactivity of the calcium oxide (CaO) and thereby retards sulfation reaction. With the increase of the H₂O(g) concentration, the presence of H₂O(g) promotes first and then inhibites sulfuration reaction. At an optimal H₂O(g) concentration around 10%, the conversion of calcium is the highest. The reason for the non-monotonic variation is due to that on the one hand, H₂O(g) promotes the solid-state diffusion of sulfuration product, and on the other hand, H₂O(g) promotes the sintering of unreacted CaO.

Key words: steam concentration effect, limestone, fixed-bed, sintering, calcination, sulfuration, water-coal-slurry CFB boiler

摘要：

针对水煤浆循环流化床锅炉水蒸气浓度高的特点，在较宽的水蒸气浓度内采用固定床反应器对石灰石脱硫过程的煅烧和硫化阶段分别开展机理研究，并利用低温氮吸附法、真密度计和扫描电子显微镜分析煅烧产物和硫化产物的孔结构特征、表观形貌。研究表明水蒸气促进煅烧产物的烧结，减小了煅烧产物的孔隙率和比表面积，增大了大孔份额，使产物氧化钙失去活性；水蒸气对硫化反应的作用呈非单调性，随着水蒸气浓度提高，同一时刻的钙转化率表现为先促进后抑制，在水蒸气浓度10%左右时钙转化率最高。其原因可以归结为水蒸气一方面促进硫化产物固态离子扩散，另一方面促进未反应氧化钙烧结成块。

关键词: 水蒸气作用, 石灰石, 固定床, 烧结, 煅烧, 硫化, 水煤浆循环流化床锅炉

CLC Number:

X 511

Kang WANG, Yang ZHANG, Lilin HU, Hai ZHANG, Junfu LYU, Guangxi YUE. Effects of high steam partial pressure on desulfurization process of limestone[J]. CIESC Journal, 2019, 70(8): 3188-3195.

王康, 张扬, 胡丽琳, 张海, 吕俊复, 岳光溪. 高分压水蒸气对石灰石脱硫过程的影响作用[J]. 化工学报, 2019, 70(8): 3188-3195.

Figures/Tables 13

Fig. 1 Schematic diagram of small-scaled fixed bed reactor system

Fig. 2 Calibration curve of mass spectrometer

Table 1 Compound of limestone and quartz sand/%

No.	CaO	MgO	SiO₂	Al₂O₃	Fe₂O₃	其他
1	91.70	4.21	1.60	1.01	0.64	0.84
2	0.07	0.05	99.61	0.10	0.01	0.16

Fig.3 Variation of calcium conversion with time

Table 2 Properties of calcination product

煅烧气氛

比表

面积/(m²/g)

孔体积/

(cm³/g)

真密度/

(kg/m³)

颗粒密度/

(kg/m³)

Fig.4 SEM morphology of calcination product

Fig.5 Pore size distribution of calcination product

Fig.6 Temporal variations of calcium conversion during sulfation at water free condition for calcined products at different H2O(g) concentrations

Fig.7 SEM morphology of sulfation product at different H2O(g) concentrations for calcined limestone

Table 3 Particle density of sulfation product

H₂O(g)/%	颗粒密度/(kg/m³)
0	2420
10	2790
20	2881
30	3070

Fig.8 Temporal variations of calcium conversion at different H2O(g) concentrations for calcined limestone

Fig.9 Effect of H2O(g) concentration on calcium conversion in calcination and sulfation processes

Fig. 10 Effect of H2O(g) concentration on calcium conversion between decoupled and coupled calcination and sulfation processes

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