Migration and transformation law of potassium in the combustion of biomass blended coal
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摘要: 通过将稻秆和褐煤混燃，研究了燃烧温度以及生物质掺混比例对于混燃过程中K的释放、灰样中K的赋存形式以及矿物质变化的影响。研究表明，燃烧温度对于混合燃料中K的释放影响显著。在600-750℃时，随着温度升高，水溶性K和醋酸铵溶性K大量释放到气相，使得K的释放速率较快；而当温度在750-850℃时，水溶性K和醋酸铵溶性K开始大量地转化为其他形式的K而被固定在灰样中，使得K的释放速率变得缓慢；当温度高于850℃时，随着温度升高，盐酸溶性K的分解导致K释放速率重新增大。通过XRD分析发现，灰样中水溶性K主要以KCl的形式存在，K2SO4的生成同时受到原料中K的含量和S/Cl比值两个因素的共同影响，原料中K的含量越高，且S/Cl比值越大，越会促进K2SO4的生成。同时也发现生物质和煤混燃时存在协同作用，煤中Al、Si等元素会和生物质中的K反应生成碱性硅铝酸盐，从而导致更多K留在灰烬中。Abstract: The effects of combustion temperature and biomass blending ratio on the release of K, the occurrence form of K in the ash and the change of mineral matter were studied. It is found that combustion temperature has a significant effect on the release of K. At 600-750℃, with an increase in temperature, water-soluble K and NH4Ac-soluble K are released to the gas phase, which makes the release ratio of K fast; while at 750-850℃, water-soluble K and NH4Ac-soluble K begin to convert into other forms of K and are fixed in the ash sample, which makes the release rate of K slow; when the temperature is higher than 850℃, as the temperature increases, the decomposition of HCl-soluble K causes the release rate of K increase again. Through XRD analysis, it is found that the water-soluble K in ash mainly exists in the form of KCl. The production of K2SO4 is affected by both the K content in the raw material and the S/Cl ratio, the higher the content of K in raw materials, and the greater the ratio of S/Cl, the more it will promote the formation of K2SO4. At the same time, it is also found that there is a synergistic effect between biomass and coal combustion. The elements such as Al, Si in coal may react with K in biomass to generate alkaline aluminosilicate, resulting in more K remaining in the ash.
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Key words:
- biomass /
- coal /
- alkali metal /
- combustion
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图 2 不同温度及生物质掺混比对成灰率的影响
Figure 2 Effect of different temperatures and biomass blending ratios on ash yield
图 3 不同温度及生物质掺混比对K释放率的影响
Figure 3 Effect of different temperatures and biomass blending ratios on release ratio of K
图 4 不同温度及生物质掺混比对灰样中不同赋存形式K含量的影响
Figure 4 Effect of different temperatures and biomass blending ratios on the K content of different occurrence forms in the ash
: water-soluble; : NH4Ac-soluble; : HCl-soluble; : insoluble
图 5 不同温度及生物质掺混比下灰样的XRD谱图
Figure 5 XRD patterns of ash at different temperatures and biomass blending ratios
(a): 25%biomass; (b): 800 ℃ A-CaSO4, B-CaCO3, C-KCl, D-SiO2, E-CaMg(CO3)2, F-KAlSi3O8, G-KAl2Si3AlO10(OH)2, H-KFe(SO4)2, I-MgSiO4, J-KAlSiO4, K-Ca2SiO4, L-CaSiO3, M-CaO, N-Fe2O3, O-MgCaSiO4, P-K2SO4
表 1 稻秆和褐煤的工业分析和元素分析
Table 1 Proximate and ultimate analyses of rice straw and lignite
Sample Ultimate analysis wad/% Proximate analysis wad/% C H O N S Cl M A V FC Straw 39.48 4.94 36.22 1.05 0.10 1.03 6.82 11.39 68.17 13.62 Lignite 46.56 3.72 17.90 1.38 1.46 0.05 13.90 15.08 39.53 31.49 
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表 2 稻秆和褐煤的灰分分析
Table 2 Ash composition of straw and lignite
Sample Content w/% K2O Na2O MgO CaO Fe2O3 SiO2 Al2O3 P2O5 Straw 29.44 2.93 2.13 2.54 0.34 43.58 4.11 1.58 Lignite 0.96 0.27 2.34 39.16 9.58 21.13 13.32 0.07
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表 3 原料中K总含量及其赋存形式
Table 3 Total K content in raw materials and its occurrence form
Sample Total/(mg·kg-1) Water-soluble /% NH4Ac-soluble /% HCl-soluble /% Insoluble /% Straw 15966.52 86.52 4.90 2.31 6.27 Lignite 370.26 5.27 21.73 67.84 5.16
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