Modeling and optimization of electrochemical ammonia synthesis

doi:10.11949/0438-1157.20250255

Abstract

Abstract:

Electrochemical ammonia synthesis seems potential to replace the traditional Haber-Bosch approach, owing to its more benign conditions, and quantitatively evaluating the whole process is especially desirable. Based on the lithium-mediated nitrogen reduction reaction (Li-NRR) and absorption-based ammonia separation, a complete process was modeled, simulated, and optimized with a 20-year operation cycle. The results show that the initial investment cost of the electrochemical method is much lower than that of the Haber-Bosch method, but the total cost is still higher than that of the Haber-Bosch method, of which the electricity cost of the electrochemical reaction accounts for more than 80% of the total cost. To make the electrochemical ammonia synthesis more practical, efforts should be made to increase the conversion rate and ammonia selectivity of the electrochemical reaction, and reduce the reaction voltage, in order to lower the operating cost of the process. Meanwhile, the content of precious metals in the electrochemical reactor should be reduced, or new alternative catalysts should be sought to further reduce the capital cost of the electrochemical reactor.

Key words: electrochemical ammonia synthesis, process systems, dynamic modeling, dynamic simulation, global optimization

摘要：

电化学合成氨工艺由于条件温和等优势具有取代传统Haber-Bosch法的潜力，对其全流程进行定量评估具有重要价值。基于锂介导的氮还原反应（Li-NRR）和吸收法分离合成氨，构建了整套电化学合成氨流程，并对其20年的运营周期进行了模拟与优化。结果表明，电化学法的初期投资成本远低于Haber-Bosch法，但总成本仍高于Haber-Bosch法，其中电化学反应的电费占总成本的80%以上。为提升电化学合成氨的实际应用价值，应着眼于提高电化学反应的转化率及氨选择性，降低反应的电压，以降低运维成本；同时，应降低电化学反应器中的贵金属用量，或寻找可替代的新型催化剂，以进一步降低电化学反应器的初期投资成本。

关键词: 电化学合成氨, 过程系统, 动态建模, 动态仿真, 整体优化

CLC Number:

TQ 150.8

Sanyi WANG, Wenlai HUANG. Modeling and optimization of electrochemical ammonia synthesis[J]. CIESC Journal, 2025, 76(9): 4474-4486.

王三一, 黄文来. 电化学合成氨流程建模与优化[J]. 化工学报, 2025, 76(9): 4474-4486.

Figures/Tables 18

Fig. 1 Schematic illustration of the electrochemical ammonia synthesis process

Fig. 2 Schematic illustration of the electrochemical ammonia synthesis reactor

Table 1 Li-NRR parameter values in the reference state［10-11］

参数	数值
r_c,ref/(nmol_NH₃·s^-1·cm^-2)	150
p_N₂,ref/bar	15
c_EtOH,ref/（mol·L^-1）	0.1
E_c,ref（相对于标准锂电极）/V	-0.55
η_F,ref/%	60
α	0.5

Table 2 Values of the parameters in the absorber model［14， 24-29］

参数	数值
ε_bed	0.32
ε_tot	0.728
ρ_abs/(kg·m^-3)	2507
d_p/m	2×10⁴
ĉ_p_,abs/(kJ· $k g a b s - 1$ ·K^-1)	1.21
λ_S/(W·m^-1·K^-1)	0.99
q_NH₃,max/(mol_NH₃· $k g a b s - 1$ )	4.2
k_abs/(mol_NH₃·s^-1·bar^-1· $k g a b s - 1$ )	0.4668
K_abs/bar⁶	5×10^-24
k_des/(mol_NH₃·s^-1·bar^-1· $k g a b s - 1$ )	7.002×10^-3
p_NH₃,ref/bar	1
T_ref/K	648.05
ΔH_abs,NH₃/(J·mol^-1)	-87000

Table 2 Values of the parameters in the absorber model［14， 24-29］

参数	数值
ε_bed	0.32
ε_tot	0.728
ρ_abs/(kg·m^-3)	2507
d_p/m	2×10⁴
ĉ_p_,abs/(kJ· $k g a b s - 1$ ·K^-1)	1.21
λ_S/(W·m^-1·K^-1)	0.99
q_NH₃,max/(mol_NH₃· $k g a b s - 1$ )	4.2
k_abs/(mol_NH₃·s^-1·bar^-1· $k g a b s - 1$ )	0.4668
K_abs/bar⁶	5×10^-24
k_des/(mol_NH₃·s^-1·bar^-1· $k g a b s - 1$ )	7.002×10^-3
p_NH₃,ref/bar	1
T_ref/K	648.05
ΔH_abs,NH₃/(J·mol^-1)	-87000

Table 3 Parameter values in the cooler model［14， 32］

参数	数值
T_cool,cw,in/K	298
T_cool,cw,out/K	313
ĉ_p_,cw/(kJ·kg^-1·K^-1)	4.18
κ/(kW·m^-2·K^-1)	0.03

Table 4 Capital cost parameters for other units［14， 35］

设备	基准χ	C_cap,fix/ （10⁴ CNY）	C_cap,ref/ （10⁴ CNY）	χ_ref	β
吸收器	吸收管面积/m²	64.4	1000	100	0.68
压缩机	功率/kW	7.13	7410	1000	0.90
冷却器	面积/m²	27.6	200	100	0.71
泵	功率/kW	7.13	14.5	23	0.29

Table 5 Basic working conditions of the reactor

参数	数值
p_rxn,N₂,in/bar	15
c_EtOH/（mol·L^-1）	0.1
E_c（相对于标准锂电极）/V	-0.55
E_a（相对于标准氢电极）/V	0.60
α	0.5
T_rxn/K	298
L_rxn/m	2
d_rxn/m	1
$m ˙$ _rxn,N₂,in/(kg·s^-1)	0.09
$m ˙$ _rxn,H₂,in/(kg·s^-1)	0.03
A_ele/m²	1000

Table 5 Basic working conditions of the reactor

参数	数值
p_rxn,N₂,in/bar	15
c_EtOH/（mol·L^-1）	0.1
E_c（相对于标准锂电极）/V	-0.55
E_a（相对于标准氢电极）/V	0.60
α	0.5
T_rxn/K	298
L_rxn/m	2
d_rxn/m	1
$m ˙$ _rxn,N₂,in/(kg·s^-1)	0.09
$m ˙$ _rxn,H₂,in/(kg·s^-1)	0.03
A_ele/m²	1000

Fig. 3 Evolution of the ammonia mass flow rate with time at the reactor outlet under different conditions

Table 6 Steady-state simulation results of different reactor models

反应器模型	出口氨稳态质量流率/(kg·h^-1)
稳态、轴向恒气速	86.45
稳态、轴向变气速	87.01
动态、轴向恒气速	86.41
动态、轴向变气速	86.92

Fig. 4 Dynamic results with different reactor models

Fig. 5 Evolution of qNH₃ with time during absorption and desorption

Fig. 6 Evolution of qNH₃ with time during absorption simulated with different models

Table 7 Optimal reactor electrode area under constant production with different catalyst loading and voltages

E_c（相对于标准锂电极）/V	A_ele/m²
E_c（相对于标准锂电极）/V	高负载量	低负载量
-0.50	17095	17095
-0.52	5315	5315
-0.54	1652	1652
-0.56	514	514
-0.58	160	160
-0.60	50	50

Fig. 7 Reactor capital and operating costs under constant production with different catalyst loading and voltages

Table 8 Optimal parameters for the processes of electrochemical ammonia synthesis at different scales with high loading of precious metals

规模/(kg·h^-1)	A_ele/m²	E_c（相对于标准锂电极）/V	L_abs/m	d_abs/m	n_abs	p_rxn,N₂,in/bar
100	201	-0.57	2.05	1.03	1	5
500	1078	-0.57	3.52	1.76	1	5
1000	2157	-0.57	4.43	2.22	1	5
5000	10784	-0.57	7.58	3.79	1	5
10000	21568	-0.57	9.54	4.77	1	5

Table 9 Optimal parameters for the processes of electrochemical ammonia synthesis at different scales with low loading of precious metals

规模/（kg·h^-1）	A_ele/m²	E_c/V（相对于标准锂电极）	L_abs/m	d_abs/m	n_abs	p_rxn,N₂,in/bar
100	119	-0.58	2.05	1.03	1	5
500	595	-0.58	3.52	1.76	1	5
1000	1190	-0.58	4.43	2.22	1	5
5000	5948	-0.58	7.58	3.79	1	5
10000	11895	-0.58	9.54	4.77	1	5

Fig. 8 Cost comparisons between electrochemical and Haber-Bosch ammonia synthesis processes

Table 10 Optimal parameters for the processes of electrochemical ammonia synthesis at different scales with a low electricity price

规模/(kg·h^-1)	A_ele/m²	E_c（相对于标准锂电极）/V	L_abs/m	d_abs/m	n_abs	p_rxn,N₂,in/bar
100	32	-0.60	2.06	1.03	1	5
500	162	-0.60	3.52	1.76	1	5
1000	324	-0.60	4.43	2.22	1	5
5000	1618	-0.60	5.25	2.63	3	5
10000	3235	-0.60	9.54	4.77	1	5

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