Numerical simulation research of high-alkali coal ash deposition process based on discrete element method

doi:10.11949/0438-1157.20201030

Abstract

Abstract:

Burning high-alkali coal causes ash deposition on heat transfer surface. To visualize the deposit growth process, the numerical simulation of fouling process was carried out on fluidized-bed boiler convection super heater using sticky particle collision adhesion model based on discrete element method. The influences of gas velocity, particle diameter, gas temperature and wall temperature to ash deposition characteristics were studied and compared with existing research results. The simulation results indicated that the collision efficiency increased and capture efficiency decreased with the increase of gas velocity and the decrease of particle diameter. The increase of particle surface energy caused by the increase of gas and wall temperature led to the increase of capture efficiency while the influence of wall temperature was more obvious. The maximum deposition thickness and the shape of deposition under different working conditions have little change.

Key words: high-alkali coal, fluidized-bed, discrete element method, numerical simulation, deposition

摘要：

针对锅炉燃用高碱煤产生的受热面积灰问题，以流化床锅炉对流过热器为研究对象，采用离散元方法（discrete element method）建立黏性颗粒碰撞黏附模型，对过热器对流受热面的积灰过程进行数值模拟。分别研究了烟气流速、颗粒粒径、烟气温度以及壁面温度对积灰特性的影响规律。模拟结果表明：烟气流速增大、颗粒粒径减小会导致颗粒的碰撞率上升、捕集率下降；烟气温度和壁面温度提升时，颗粒表面能上升，导致颗粒捕集率上升，且壁面温度的影响更为显著；不同工况下最大积灰厚度、沉积物形状变化较小。

关键词: 高碱煤, 流化床, 离散元方法, 数值模拟, 沉积物

CLC Number:

TK 01

JIN Mo, LIU Daoyin, CHEN Xiaoping. Numerical simulation research of high-alkali coal ash deposition process based on discrete element method[J]. CIESC Journal, 2021, 72(4): 1939-1946.

金默, 刘道银, 陈晓平. 基于离散元方法的高碱煤灰沉积过程数值模拟研究[J]. 化工学报, 2021, 72(4): 1939-1946.

Figures/Tables 13

Fig.1 Simulation domain and boundary condition

Fig.2 Calculated normal force-displacement diagram of particles

Table 1 Parameters of simulated working conditions

工况参数	数值
颗粒质量流量/(kg/s)	3.80×10^-3
颗粒粒径/μm	30/40/50/60
烟气成分（质量分数）	5%O₂/85%CO₂/10%H₂O
烟气入口速度/(m/s)	6/8/10/12
烟气温度/℃	700/750/800/850/900
积灰壁面温度/℃	500/550/600

Table 2 Particle property parameter

密度/(kg/m³)

比热容/

(W/(kg·K))

热导率/

(kg·m²/s²)

Fig.3 Comparison of impact efficiency between simulation value and calculation value under different gas velocity and diameters

Table 3 Comparison between experimental results and simulated results

文献	捕集率实验值/%	捕集率模拟值/%
[33]	4.00	3.79
[34]	6.27	6.01
[23]	0.25	0.21

Fig.4 Capture and impaction rate of particles with different diameters and gas velocity

Fig.5 Schematic diagram of deposition characteristics

Fig.6 Deposition growing process on probe surface

Table 4 Deposition characteristics of particles under different gas velocity

烟气流速/(m/s)	最大积灰厚度/mm	积灰扩展角/(°)
6	2.78	138
8	2.76	137
10	2.64	135
12	2.60	134

Fig.7 Distribution of deposition thickness on probe surface under different gas velocity

Table 5 Deposition character of particles under different wall temperature

壁面

温度/℃

碰撞率/%

捕集率/%

最大积灰

厚度/mm

Table 6 Deposition character of particles under different gas temperature

烟气温度/℃	碰撞率/%	捕集率/%	最大积灰厚度/mm	积灰扩展角/(°)	积灰平均温度/℃
700	74.19	1.89	2.74	134	553
750	74.22	1.92	2.76	135	556
800	74.26	2.01	2.77	135	557
850	74.21	2.04	2.78	136	559
900	74.25	2.09	2.79	138	560

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