烘焙生物质燃烧过程中钾的赋存形态及析出迁移特性

doi:10.11949/0438-1157.20201108

摘要/Abstract

摘要：

选取稻秆和棉秆为原料，在烘焙预处理后，通过固定床燃烧实验结合HSC Chemistry热力学平衡计算，获得了烘焙生物质燃烧过程中碱金属K的析出和迁移规律。结果表明：烘焙过程中存在着少量水溶性K的释放及其向醋酸铵溶态K的转化，而其转化和释放能力与Cl/K呈正相关。烘焙生物质的成灰率随着燃烧温度的升高而下降，而K的释放率随温度的变化则相反，其主要释放形式为K的氯化物和KOH；此外，600℃时，水溶性K和醋酸铵溶态K主要转化为char-K，700~900℃时其主要转化为K的硅酸盐，随着温度的上升，其转化量不断增加。相比于原生生物质，烘焙生物质有更高的成灰率；此外，烘焙促进了生物质燃烧过程中醋酸铵溶态K向酸溶态或残渣态K转化，同时抑制了水溶性K的释放，这些使得烘焙生物质燃烧过程中K的释放率更低，而烘焙对生物质燃烧过程中K释放的抑制与烘焙过程中Cl的释放率呈正相关。

关键词: 烘焙生物质, 燃烧, 固定床, 碱金属K, 化学分级提取, 热力学平衡计算

Abstract:

Rice straws and cotton stalks were selected as raw materials. After torrefaction pretreatment, the fixed-bed combustion experiment and HSC Chemistry thermodynamic equilibrium calculations were conducted to obtain the release and migration characteristics of alkali metal K during the combustion of torrefied biomass. The results showed that there was a small amount of water-soluble K release and its conversion to ammonium acetate dissolved K during torrefaction, and its conversion and release capacity was positively correlated with Cl/K. The ash formation rate of torrefied biomass decreased with the increase of combustion temperature, while the release rate of K changed with the temperature on the contrary; K was released in the form of water-soluble K, ammonium acetate dissolved K and acid-soluble K,and its main release form was K chloride and KOH. In addition, water-soluble K and ammonium acetate dissolved K were mainly converted to char-K at 600℃, and mainly converted to K silicate at 700—900℃. As the temperature rose, its conversion volume continued to increase. Compared with the raw biomass, torrefied biomass had a higher ash formation rate; in addition, torrefaction promoted the conversion of ammonium acetate dissolved K to acid-soluble K or potassium silicate during the combustion of biomass, and at the same time inhibited the release of water-soluble K. Therefore, the release rate of K during the combustion of torrefied biomass was lower. The inhibition of K release during the combustion of biomass by torrefaction is positively correlated with the release rate of Cl during the torrefaction.

Key words: torrefied biomass, combustion, fixed bed, alkali metal K, chemical fractionation, thermodynamic equilibrium calculations

中图分类号:

TK 6

余作伟, 刘倩, 钟文琪, 周骏. 烘焙生物质燃烧过程中钾的赋存形态及析出迁移特性[J]. 化工学报, 2021, 72(4): 2258-2266.

YU Zuowei, LIU Qian, ZHONG Wenqi, ZHOU Jun. Occurrence form and release and migration characteristics of potassium during combustion of torrefied biomass[J]. CIESC Journal, 2021, 72(4): 2258-2266.

图/表 10

图1 烘焙及燃烧管式炉

Fig.1 Torrefication and combustion tube furnace

表1 烘焙前后生物质工业分析与元素分析（收到基）

Table 1 Ultimate analysis and proximate analysis of fuels conducted (received basis)

样品	工业分析/%(mass)				元素分析/%(mass)
样品	M	FC	A	V	C	H	O	N	S
RS	7.77	12.57	12.7	66.96	39.47	5.12	33.6	1.21	0.13
CS	2.99	14.15	3.51	79.35	46.04	5.19	41	1.19	0.081
TRS	1.25	18.18	15.41	65.15	44.68	4.96	32.2	1.39	0.11
TCS	1.43	18.72	4.23	75.62	51.26	5.27	36.43	1.31	0.070

表2 烘焙前后生物质主要灰分元素分析

Table 2 Analysis of main ash elements of fuels conducted

样品	含量/%(mass)
样品	Si	Al	Fe	Mg	Ca	Na	K	P	Cl
RS	1.67	0.01	0.042	0.40	0.589	0.11	1.81	0.1	1.03
CS	0.087	0.0011	0.051	0.31	0.171	0.06	0.399	0.065	0.11
TRS	2.17	0.014	0.076	0.51	0.782	0.13	2.39	0.12	1.17
TCS	0.108	0.0015	0.088	0.38	0.216	0.073	0.494	0.08	0.055

表3 K析出转化相关元素摩尔比

Table 3 Molar ratio of elements related to K release and transformation

样品	Si/K	Ca/Si	Cl/K	Mg/K	Na/K	S/K
RS	1.276	0.246	0.611	0.214	0.105	0.087
CS	0.303	1.38	0.295	0.747	0.254	0.247
TRS	1.304	0.245	0.525	0.218	0.101	0.057
TCS	0.305	1.40	0.118	0.748	0.251	0.173

表4 烘焙过程中相关重要组分和元素的释放率

Table 4 Release rate of relevant important components and elements during torrefaction

Sample	Release rate/%
Sample	Moisture	Volatile	K	S	Cl
CS	61.74	23.76	1.04	30.86	60.00
RS	88.18	28.49	2.28	37.80	14.85

图2 烘焙对生物质不同形态K的影响

Fig.2 Effects of torrefaction on different forms of K of biomass

图3 不同原料燃烧成灰率及K释放率(a) 烘焙对生物质燃烧（800℃）成灰率及K释放率的影响; (b) 燃烧温度对烘焙生物质成灰率和K释放率的影响

Fig.3 Ash formation rate and K release rate of different fuels conducted

图4 空气条件下不同原料燃烧灰XRD谱图A—KCl; B—SiO2; C—K2SO4; D—K2SiO3;E—K2Si4O9; F—K2MgCl4;G—K0.2Na0.8Cl; H—K2Si2O5;I—CaO; J—MgO; K—CaMg(CO3)2;L—Ca2SiO4;M—K4Si8O18

Fig.4 XRD patterns of burned ash samples from different raw materials under air conditions

图5 空气气氛不同燃料燃烧灰中不同形态K的转化(a) 烘焙前后生物质800℃燃烧时不同形态K的分布; (b) 燃烧温度对TCS不同形态K的影响; (c) 燃烧温度对TRS不同形态K的影响

Fig.5 K conversion of different forms of sintered ash with different fuels in air atmosphere

图6 热力学平衡时K分布(图中仅含占总K摩尔比超过0.5%的化合物)(a) 烘焙对CS钾平衡分布的影响; (b) 烘焙对RS钾平衡分布的影响

Fig.6 K distribution under thermodynamic balance

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