基于CO2循环的低碳高效白云石煅烧新工艺

doi:10.11949/0438-1157.20191466

摘要/Abstract

摘要：

白云石是一种广泛应用的冶金、建材和化工原料。针对白云石煅烧过程中CO₂排放严重等问题，构建了基于CO₂循环载热与资源化回收的白云石低碳煅烧竖窑新工艺。通过白云石（CaCO₃·MgCO₃）煅烧过程的Gibbs自由能变计算，发现提高煅烧温度（50~100 K）可有效克服CO₂对反应的抑制作用；通过纯CO₂环境中CaCO₃分解过程的热重实验分析，验证了CO₂循环煅烧白云石煅烧的可行性；通过化学反应动力学计算，解析了全CO₂组分环境下CO₂压力对CaCO₃·MgCO₃高温分解过程的影响，并发现提高CO₂压力可促进气固传热，从而提升分解速率和改善矿料分解均匀性；对CO₂循环煅烧工艺系统能-质平衡计算表明：该工艺理论能耗仅为140 kg/(t 煅白)，且煅烧过程的CO₂排放降低70%以上，环境效益显著。

关键词: 二氧化碳, 循环, 白云石, 煅烧, 热解, 反应动力学

Abstract:

Dolomite (CaCO₃·MgCO₃) is a widely-used raw material in metallurgy, building materials and chemical industry. Aiming at the problem of serious CO₂ emission during dolomite calcination, a new process of low-carbon calcined shaft kiln based on CO₂ cycle heat carrying and resource recovery was constructed. According to thermochemistry, Gibbs free energy change of CaCO₃·MgCO₃ decomposition in pure CO₂ environment is analyzed which shows that increase of temperature (50—100 K) is an efficient way to overcome the reaction depression by high CO₂ concentration. Thermogravimetric analysis of CaCO₃ decomposition in pure CO₂ atmosphere is conducted, which confirms the feasibility of dolomite calcining in high CO₂ concentration. The effect of CO₂ pressure ( $P C O 2$ ) on CaCO₃·MgCO₃ decomposition is investigated. The heat transfer between gas and solid can be enhanced attributed to the high $P C O 2$ , which therefore improve the dolomite calcination efficiency. Afterwards, thermal analysis of the dolomite calcination system with CO₂ loop is conducted, which turns out that the theoretical energy consumption is 140 kg/(t MgO), and more than 70% CO₂ emission would be reduced from the calcination process.

Key words: carbon dioxide, looping, dolomite, calcination, pyrolysis, reaction kinetics

中图分类号:

TQ 021.8

蒋滨繁, 夏德宏, 安苛苛, 张培昆, 敖雯青. 基于CO₂循环的低碳高效白云石煅烧新工艺[J]. 化工学报, 2020, 71(8): 3699-3709.

Binfan JIANG, Dehong XIA, Keke AN, Peikun ZHANG, Wenqing AO. Efficient low-carbon dolomite calcination process based on CO₂ looping and recovering[J]. CIESC Journal, 2020, 71(8): 3699-3709.

图/表 11

图1 产物气循环煅烧白云石与CO2资源化回收新工艺

Fig.1 Dolomite calcination process based on CO2 looping and recovering

图2 CO2环境中碳酸盐分解模型

Fig.2 Kinetic model for carbonate decomposition with CO2 surrounding (from outside to inside: product layer, reacting layer and unreacted layer)

表1 CaCO3·MgCO3分解热力学计算参数

Table 1 Calculation parameters for thermochemical analysis of CaCO3·MgCO3 decomposition

Chemical	ΔG^? (298 K) / (kJ/mol)	ΔH^? (298 K) /(kJ/mol)	ΔS^? (298 K) / (J/(mol K))
CaCO₃	-1128.8	-1206.9	92.9
CaO	-604.2	-635.1	39.7
MgCO₃	-1012	-1096	65.7
MgO	-569.4	-601.7	26.9
CO₂	-394.4	-393.5	213.6

表2 CaCO3·MgCO3传热与分解动力学计算参数

Table 2 Calculation parameters for kinetic analysis of CaCO3·MgCO3 decomposition

参数	数值
$ρ C a C O 3 / M g C O 3$ /(kg/m³)	2700
ρ_CaO/MgO/(kg/m³)	3000
$ρ C O 2$ /(kg/m³)	2
$λ C a C O 3 / M g C O 3$ /(W/(m·K) )	1.16
λ_CaO/MgO /(W/(m·K) )	1.2
$λ C O 2$ /(W/(m·K) )	0.014
$c C a C O 3 / M g C O 3$ /(kJ/(kg·K) )	0.8~1.3
$c C O 2$ /(kJ/(kg·K))	1.0~1.2
$μ C O 2$ /(Pa·s)	5×10^-5
T_s / K	300
T_g / K	1600
v_g /(m/s)	2
r/m	0.03
Pr	0.724

表2 CaCO3·MgCO3传热与分解动力学计算参数

Table 2 Calculation parameters for kinetic analysis of CaCO3·MgCO3 decomposition

参数	数值
$ρ C a C O 3 / M g C O 3$ /(kg/m³)	2700
ρ_CaO/MgO/(kg/m³)	3000
$ρ C O 2$ /(kg/m³)	2
$λ C a C O 3 / M g C O 3$ /(W/(m·K) )	1.16
λ_CaO/MgO /(W/(m·K) )	1.2
$λ C O 2$ /(W/(m·K) )	0.014
$c C a C O 3 / M g C O 3$ /(kJ/(kg·K) )	0.8~1.3
$c C O 2$ /(kJ/(kg·K))	1.0~1.2
$μ C O 2$ /(Pa·s)	5×10^-5
T_s / K	300
T_g / K	1600
v_g /(m/s)	2
r/m	0.03
Pr	0.724

图3 CaCO3和MgCO3分解反应ΔG随CO2分压PCO2的变化

Fig.3 ΔG of CaCO3 and MgCO3 as a function of PCO2

图4 MgCO3和CaCO3理论起始分解温度T随CO2分压PCO2的变化

Fig.4 Decomposition temperature T of MgCO3 and CaCO3 as a function of PCO2

图5 纯CO2环境下CaCO3分解热重分析（PCO2=1 atm）

Fig.5 Thermogravimetric analysis of CaCO3 decomposition in pure CO2 atmosphere (PCO2=1 atm)

图6 PCO2为 0.2 atm和1 atm时碳酸盐矿分解反应层厚度Dr随时间t的变化（橘色为产物层，高亮黄色为反应层，蓝色为未反应核）

Fig.6 Reaction layer thickness in carbonate ore at PCO2 = 0.2 atm and 1 atm (orange: product layer; yellow: reacting layer; blue: unreacted layer)

图7 不同CO2分压下CaCO3和MgCO3转化率γ随时间t的变化

Fig.7 Decomposition ratio γ of CaCO3 and MgCO3 as a function of time t under various PCO2

图8 预热段和冷却段内气固温度随高度的变化（预热段和冷却段均以CO2的入口为h = 0）

Fig.8 Temperature variations of gas and solid in preheating and cooling zone (h =0 is CO2 inlet of each zone)

表3 稳定运行后CO2载热循环煅烧白云石（CaCO3·MgCO3）系统热平衡分析

Table 3 Thermal analysis of dolomite calcination system with CO2 looping and recovering (steady state)

区域	收入项		支出项
区域	参数	值	参数	值
预热段	白云石质量流量 q_b /(kg/h)	5000	白云石质量流量 q_b/(kg/h)	5000
	CO₂质量流量 q_c,3/(kg/h)	18400	CO₂质量流量 q_c,3/(kg/h)	18400
	入口白云石温度 T_b,yⁱⁿ/K	300	出口白云石温度 T_b,y^out/K	900~1000
	入口CO₂温度 T_c,yⁱⁿ/K	900~1000	出口CO₂温度 T_c,y^out /K	500
	白云石显热上升 Q_b/(kJ/s)	750
煅烧段	白云石质量流量 q_b /(kg/h)	5000	煅白质量流量 q_db/(kg/h)	2600
	CO₂质量流量 q_c,1 /(kg/h)	16000	CO₂质量流量 q_c,3/(kg/h)	18400
	入口白云石温度 T_b,dⁱⁿ /K	900	出口煅白温度 T_b,d^out /K	900~1000
	入口CO₂温度 T_c,dⁱⁿ/K	1400~1600	出口CO₂温度 T_c,d^out /K	900~1000
	白云石反应热 Q_b,r/(kJ/s)	2050	白云石分解产生CO₂q_c,2 /(kg/h)	2400
冷却段	煅白质量流量 q_db/(kg/h)	2600	煅白质量流量 q_db/(kg/h)	2600
	CO₂质量流量 q_c,1/(kg/h)	16000	CO₂质量流量 q_c,2 /(kg/h)	16000
	入口煅白温度 T_b,lⁱⁿ /K	900~1000	出口煅白温度 T_b,l^out /K	500
	入口CO₂温度 T_c,lⁱⁿ /K	400	出口CO₂温度 T_c,l^out /K	600
蓄热式加热炉	CO₂质量流量 q_c,1 /(kg/h)	16000	CO₂质量流量 q_c,1/(kg/h)	16000
	入口CO₂温度 T_c,xⁱⁿ /K	600	出口CO₂温度 T_c,x^out /K	1400~1600
	燃料消耗/(kg ce/(t 煅白))	140	燃烧产生和排放的CO₂ /(kg/h)	980

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基于CO₂循环的低碳高效白云石煅烧新工艺

Efficient low-carbon dolomite calcination process based on CO₂ looping and recovering

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