耦合溴化锂吸收式制冷与有机朗肯循环的合成气深冷分离工艺

doi:10.16085/j.issn.1000-6613.2022-0024

摘要/Abstract

摘要：

从合成气中深冷分离液化天然气（LNG）可以在调峰中发挥重要作用，并显著提升企业的经济效益。然而深冷分离的高能耗是实际工业中的一大问题。本文提出了耦合溴化锂吸收式制冷与有机朗肯循环的甲烷深冷分离工艺。新工艺可以利用原压缩制冷系统的余热从而降低制冷能耗。又因为压缩级数与能耗和可利用余热量成正相关，为使得系统的能耗最低，需同时优化压缩级数与所耦合的余热利用系统。采用自适应遗传算法对新工艺中8种不同压缩级数组合进行优化，通过对比各模型的总能耗、性能系数和单位能耗确定了能耗最低的流程。其结果表明，相比于原工艺总能耗减少了34%；性能系数增加了0.07；单位能耗减少了0.89kW/kg。经济表现为操作费用减少了33%；新增设备投资2550万元，理论上一年即可回收投资成本。

关键词: 溴化锂吸收式制冷, 有机朗肯循环, 遗传算法, 计算机模拟, 集成

Abstract:

The LNG separated from syngas by cryogenic liquefaction unit plays an important role in peak regulation, and significantly improves the economic benefits. However, the high energy consumption of cryogenic separation is a big problem in existing industries. In this paper, a cryogenic separation process coupled with lithium bromide absorption refrigeration and organic Rankine cycle was proposed. The waste heat is recovered from original compression refrigeration system, reducing the total refrigeration energy consumption. The compression stage was positively related to energy consumption and available waste heat. In order to minimize the energy consumption of the system, it was necessary to optimize the compression stages and the waste heat utilization system at the same time. The novel process of eight combination of compression stages was optimized by adaptive genetic algorithm. Then the lowest energy consumption was determined by comparing the total energy consumption, performance coefficient and unit energy consumption of each model. The results showed that the total energy consumption was reduced by 34% compared with the original process. The coefficient of performance was increased by 0.07, while the unit energy consumption was reduced by 0.89kW/kg. The economic performance showed that the novel process decreased operating cost by 33% and increased capital cost by 25.5 million. The capital cost can be recovered within one year, indicating the feasibility of novel process in economic.

Key words: lithium bromide absorption refrigeration, organic Rankine cycle, genetic algorithm, computer simulation, integration

中图分类号:

TQ03-39

李丹, 杨思宇, 钱宇. 耦合溴化锂吸收式制冷与有机朗肯循环的合成气深冷分离工艺[J]. 化工进展, 2022, 41(10): 5236-5246.

LI Dan, YANG Siyu, QIAN Yu. Syngas cryogenic separation process combined with lithium bromide absorption refrigeration and organic Rankine cycle[J]. Chemical Industry and Engineering Progress, 2022, 41(10): 5236-5246.

图/表 21

图1 传统制冷循环的合成气深冷分离工艺流程

图2 耦合LBRC-ORC的合成气深冷分离工艺流程

图3 耦合LBRC-ORC的合成气深冷分离工艺ASPEN模拟流程

表1 原料合成气与混合制冷剂的组成

参数	原料合成气	混合制冷剂
摩尔流量/kmol·h^-1	4573	3749
质量流量/t·h^-1	49.5	107.3
温度/℃	35	20
压力/MPa	3.3	0.1
摩尔分数/%
H₂	61.57
CO	27.22
CH₄	10.26	27.74
N₂+AR	0.24
C₂H₆	0.71
N₂		2.97
C₃H₈		24.27
C₂H₄		45.02

表2 模拟数据与工业数据对照

项目	合成气
项目	工业数据	模拟结果	工业数据	模拟结果
温度/°C	-173.6	-179.4	-91.5	-119.4
压力/MPa	3.1	1.1	3.1	1.2
摩尔流量/kmol·h^-1	4077	4077	496	496
质量流量/kg·h^-1	40.9	41.0	8.4	8.4
摩尔分数/%
H₂	69.75	69.06	0.00	0.00
CO	30.57	30.53	0.21	0.00
CH₄	0.01	0.15	93.20	93.31
C₂H₆	0.00	0.00	6.54	6.55
AR+N₂	0.21	0.24	0.05	0.14

表3 操作变量范围

项目	取值范围	工艺	压缩级数	压缩出口压力/MPa
项目	取值范围	工艺	压缩级数	2-1	2-2	2-3	2-4	3-1	3-2	3-3	3-4
R134A进口压力/MPa	2.0～3.7	NRC	一级	1.1~1.4	1.1~1.4	1.1~1.4	1.1~1.4	0.6~0.8	0.6~0.8	0.6~0.8	0.6~0.8
溴化锂进口质量分数/%	0.4～0.6		二级	2.4~3.0	2.4~3.0	2.4~3.0	2.4~3.0	1.2~1.6	1.2~1.6	1.2~1.6	1.2~1.6
溴化锂流量/t·h^-1	90～180		三级					2.0~3.0	2.0~3.0	2.0~3.0	2.0~3.0
溴化锂进口压力/kPa	40～80	MRC	一级	2.0~4.8	0.5~0.7	0.3~0.4	0.2~0.3	2.0~4.8	0.5~0.7	0.3~0.4	0.2~0.3
混合制冷剂流量/kmol·h^-1	2000～7000		二级		2.5~4.8	0.9~1.6	0.5~0.7		2.5~4.8	0.9~1.6	0.5~0.7
氮气流量/kmol·h^-1	2000～4000		三级			2.7~4.8	1.0~1.8			2.7~4.8	1.0~1.8
			四级				2.0~4.8				2.0~4.8

图4 AGA算法应用于合成气深冷分离的概念框图

表4 工质与公用工程单价

项目	单价
混合制冷剂/CNY·10^-3m^-3	12.5
氮气/CNY·10^-3m^-3	0.45
溴化锂/ $×$ 10⁴CNY·t^-1	2.4
R134A/ $×$ 10⁴CNY·t^-1	2.3
冷却水/CNY·t^-1	0.24
电/CNY·(kW·h)^-1	0.5

表4 工质与公用工程单价

项目	单价
混合制冷剂/CNY·10^-3m^-3	12.5
氮气/CNY·10^-3m^-3	0.45
溴化锂/ $×$ 10⁴CNY·t^-1	2.4
R134A/ $×$ 10⁴CNY·t^-1	2.3
冷却水/CNY·t^-1	0.24
电/CNY·(kW·h)^-1	0.5

图5 进料位置对再沸器冷凝器热负荷的影响

图6 节流压力与溴化锂质量分数对吸收器冷凝温度影响

图7 透平进口温度对该设备㶲损与㶲效率的影响

图8 MHX3最小传热温差对总能耗与电费的影响

表5 AGA优化结果

项目	2-1	2-2	2-3	2-4	3-1	3-2	3-3	3-4
R134A进口压力/MPa	2.4	3.4	3.3	3.1	2.7	3.1	2.5
溴化锂进口质量分数 /%	55.7	46.2	43.1	57.9	42.7	47.0	42.1
溴化锂流量/t·h^-1	96.7	99.0	117.8	88.0	111.5	96.0	126.4
溴化锂进口压力/kPa	40.14	49.36	51.36	40.16	56.87	66.04	57.71
混合制冷剂流量 /kmol·h^-1	3103	2911	2313	2452	3209	3184	2682	3973
氮气流量/kmol·h^-1	2378	2551	2261	2359	2482	2220	2293	1918
MRC出口压力/MPa
一级	3.5	0.66	0.35	0.26	3.1	0.63	0.39	0.24
二级		3.1	1.2	0.69		3.3	0.97	0.53
三级			4.2	2.5			3.5	1.2
四级				4.4				3.9
N₂压力/MPa
一级	1.1	1.4	1.3	1.1	0.75	0.74	0.62	0.73
二级	2.6	2.7	2.5	2.5	1.3	1.3	1.3	1.6
三级					2.5	2.5	2.3	2.8

图9 8种不同压缩等级的能耗对比

图10 8种不同压缩等级混合制冷剂流量对比

表6 最优流程与原流程能耗对比 (MW)

参数	原流程	最优流程
W_comp	23.3	16.8
W_pump	0	0.068
W_exp	1.4	2.5
W_net	22.0	14.4

图11 8种深冷分离过程的COP与SEC对比

表7 最优流程与原流程COP与SEC对比

参数	原流程	最优流程
m_LNG/kg·h^-1	8429	8429
h_syngas/kJ·kg^-1	-3940	-3940
h_LNG/kJ·kg^-1	-5184	-5184
W_net/MW	22.0	14.4
SEC/kW·kg^-1	2.60	1.71
COP	0.13	0.20

表8 最优流程新增设备投资

设备	投资金额
换热器/万元	1401
泵/万元	17
膨胀机/万元	1132
压缩机/万元	190
总计/万元	2550

表9 最优流程与原流程原料成本与操作成本对比 (万元)

原料	原流程	最优流程
混合制冷剂	0.105	0.065
氮气	0.002	0.002
溴化锂		283
R134A		584
电	9191	5749
冷却水	303	576
原料成本	0.107	866
操作成本	9494	6325

图12 电价波动对电费的影响

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