Surrogate-assisted multi-objective optimization of hydrogen networks with light hydrocarbon recovery unit

doi:10.11949/0438-1157.20211567

Abstract

Abstract:

Global warming has become increasingly serious over the last decade. As one of the greenhouse gas (GHG) emission contributors, petroleum refineries are now encountering high GHG emissions and annual costs due to the increase of hydrogen demand. Light hydrocarbons recovery(LHR) unit can effectively reduce GHG emissions and improve resource utilization through recovering hydrogen and hydrocarbons components. Therefore, it is necessary to consider the light hydrocarbon recovery unit in the optimization of the hydrogen network. To avoid the high computational cost of rigorous process, this paper proposed surrogate models as approximations to the rigorous LHR process. Meanwhile, the environmental impact was added to the optimization goal. Finally, a hydrogen network multi-objective mathematical programming model was established. The proposed approach was applied to a case study taken from a real refinery. The results showed that the proposed method can effectively reduce the annual cost and GHG emissions of the hydrogen network, and reveal the trade-off relationship between the economic performance and the environmental impact of the hydrogen network integrated LHR unit. Hence it can provide a certain theoretical basis for further industrial application.

Key words: process system, hydrogen network, integration, mathematical programming, multi-objective, optimal design

摘要：

当前炼油企业氢气需求持续增长，导致炼厂成本及生产过程温室气体排放增加，炼油企业通过增设轻烃回收单元对氢气和轻烃组分进行回收利用，能有效缓解这一现状。因此，在氢气网络优化中有必要考虑轻烃回收单元。本研究提出了一种集成轻烃回收单元的氢气网络多目标数学规划模型，对轻烃回收单元采用代理模型建模方法，解决了直接嵌入严格机理模型可能导致的高计算成本问题，以总年度费用最小为优化目标，同时将系统的环境影响也纳入优化目标。实例计算表明，所提出的方法能够有效降低氢气网络的年度费用及温室气体排放，并揭示了集成轻烃回收单元的氢气网络经济性能与环境影响之间的权衡关系，为工业应用提供了一定的理论基础。

关键词: 过程系统, 氢气网络, 集成, 数学规划, 多目标, 优化设计

CLC Number:

TQ 021.8

Shujun ZHANG, Shihui WANG, Xin ZHANG, Xu JI, Yiyang DAI, Yagu DANG, Li ZHOU. Surrogate-assisted multi-objective optimization of hydrogen networks with light hydrocarbon recovery unit[J]. CIESC Journal, 2022, 73(4): 1658-1672.

张淑君, 王诗慧, 张欣, 吉旭, 戴一阳, 党亚固, 周利. 集成轻烃回收单元代理模型的氢气网络多目标优化[J]. 化工学报, 2022, 73(4): 1658-1672.

Figures/Tables 16

Fig.1 State space superstructure of hydrogen network

Fig.2 Flow chart of light hydrocarbon recovery unit

Fig.3 Steps for constructing the surrogate model of light hydrocarbon recovery unit

Fig.4 Input and output variables of the surrogate model

Fig.5 Schematic diagram of the current hydrogen network structure

Table 1 Detailed information of related streams in the hydrogen network

氢源供氢
单元	流量/(mol/s)	组成/%(mol)							压力/ MPa
单元	流量/(mol/s)	H₂	C1	C2	C3	C4	C5	H₂S	压力/ MPa
DHT-1	44.53	95.57	1.49	1.26	0.87	0.75	0.05	0	2
DHT-2	274.43	97.38	0.88	0.74	0.52	0.45	0.03	0	2
GHT	163.27	97.65	0.80	0.67	0.47	0.40	0.02	0	2
KHT-1	37.62	95.30	1.58	1.34	0.93	0.80	0.05	0	2
KHT-2	60.32	99.01	0.34	0.28	0.19	0.05	0.01	0	2
氢阱进口
单元	流量/(mol/s)	组成/%(mol)							压力/ MPa
单元	流量/(mol/s)	H₂	C1	C2	C3	C4	C5	H₂S	压力/ MPa
DHT-1	990.53	87.60	6.59	3.41	1.61	0.50	0.24	0.05	6.72
DHT-2	1004.5	90.00	5.21	2.75	1.34	0.47	0.19	0.04	7.00
GHT	811.8	89.32	5.62	2.94	1.41	0.46	0.21	0.04	2.70
KHT-1	60.70	92.23	3.58	2.17	1.20	0.68	0.12	0.02	3.83
KHT-2	83.43	95.75	2.14	1.18	0.60	0.25	0.07	0.01	5.45
高分气
单元	流量/(mol/s)	组成/%(mol)							压力 /MPa
单元	流量/(mol/s)	H₂	C1	C2	C3	C4	C5	H₂S	压力 /MPa
DHT-1	797.50	86.00	8.28	3.92	1.25	0	0	0.55	5.00
DHT-2	753.00	91.00	5.14	2.30	0.66	0.35	0.14	0.41	6.40
GHT	725.00	83.00	7.20	4.40	3.10	1.10	0.60	0.60	2.00
KHT-1	45.50	91.70	1.84	2.86	1.99	0.70	0.55	0.36	3.00
KHT-2	61.30	87.80	6.69	2.31	1.26	0.94	0.60	0.40	4.80
低分气
单元	流量/(mol/s)	组成/%(mol)							压力/ MPa
单元	流量/(mol/s)	H₂	C1	C2	C3	C4	C5	H₂S	压力/ MPa
DHT-1	36.00	52.30	8.08	13.52	10.80	8.22	5.98	1.10	1.1
DHT-2	43.40	50.31	16.71	11.51	8.71	7.28	3.78	1.70	1.2
GHT	19.80	42.32	20.51	15.02	9.21	8.56	2.58	1.80	1.0
KHT-1	5.20	35.21	32.36	8.64	9.73	7.90	4.66	1.50	1.0
KHT-2	5.60	67.60	10.65	8.36	5.98	4.67	0.94	1.80	1.0

Table 2 The pipe distance between the units in the case

单元	间距/m
单元	DHT-1	DHT-2	GHT	KHT-1	KHT-2
CCR	500	680	1000	1150	1280
H₂ Plant	250	430	1250	1400	1150
DHT-1	0	180	890	1000	850
DHT-2	180	0	700	820	700
GHT	890	700	0	250	400
KHT-1	1000	820	250	0	150
KHT-2	850	700	400	150	0
PSA	480	300	510	760	910

Table 3 Concentration constraint of the inlet stream of the hydrogen sink

单元	$Y H 2 M i n$ /%(mol)	$Y H 2 S M a x$ /%(mol)
DHT-1	87.60	0.15
DHT-2	90.00	0.15
GHT	86.83	0.15
KHT-1	92.23	0.15
KHT-2	89.50	0.15

Table 3 Concentration constraint of the inlet stream of the hydrogen sink

单元	$Y H 2 M i n$ /%(mol)	$Y H 2 S M a x$ /%(mol)
DHT-1	87.60	0.15
DHT-2	90.00	0.15
GHT	86.83	0.15
KHT-1	92.23	0.15
KHT-2	89.50	0.15

Table 4 Input variable range of absorption tower of light hydrocarbon recovery unit

输入变量	下限	上限
$F H 2 i n$ /(kmol/h)	157.48	236.22
$F H 2 S i n$ /(kmol/h)	0.62	0.94
$F C 1 i n$ /(kmol/h)	47.49	71.24
$F C 2 i n$ /(kmol/h)	39.68	59.52
$F C 3 i n$ /(kmol/h)	29.68	44.53
$F C 4 i n$ /(kmol/h)	24.37	36.56
$F C 5 i n$ /(kmol/h)	13.12	19.68
$F o i l i n$ /(kmol/h)	100.00	250.00

Table 4 Input variable range of absorption tower of light hydrocarbon recovery unit

输入变量	下限	上限
$F H 2 i n$ /(kmol/h)	157.48	236.22
$F H 2 S i n$ /(kmol/h)	0.62	0.94
$F C 1 i n$ /(kmol/h)	47.49	71.24
$F C 2 i n$ /(kmol/h)	39.68	59.52
$F C 3 i n$ /(kmol/h)	29.68	44.53
$F C 4 i n$ /(kmol/h)	24.37	36.56
$F C 5 i n$ /(kmol/h)	13.12	19.68
$F o i l i n$ /(kmol/h)	100.00	250.00

Table 5 Validation results of light hydrocarbon recovery unit model

装置	输出变量	RMSE	R²
吸收塔	$F H 2 o u t$ /(kmol/h)	5.40×10^-3	0.99
	$F H 2 S o u t$ /(kmol/h)	8.60×10^-3
	$F C 1 o u t$ /(kmol/h)	1.28×10^-2
	$F C 2 o u t$ /(kmol/h)	1.39×10^-1
	$F C 3 o u t$ /(kmol/h)	2.01×10^-1
脱乙烷塔	$F H 2 y o u t$ /(kmol/h)	3.07×10^-9	0.99
	$F H 2 S y o u t$ /(kmol/h)	2.66×10^-4
	$F C 1 y o u t$ /(kmol/h)	1.29×10^-6
	$F C 2 y o u t$ /(kmol/h)	3.01×10^-8
	$F C 3 y o u t$ /(kmol/h)	2.94×10^-9
	$Q c o o l y$ /kW	1.21×10^-1
	$???????? Q r e d y$ /kW	4.50×10^-1
脱丁烷塔	$F H 2 S d o u t$ /(kmol/h)	4.27×10^-8	0.99
	$F C 2 d o u t$ /(kmol/h)	1.82×10^-8
	$F C 3 d o u t$ /(kmol/h)	1.44×10^-5
	$F C 4 d o u t$ /(kmol/h)	3.32×10^-8
	$F C 5 d o u t$ /(kmol/h)	4.29×10^-9
	$??????? Q c o o l d$ /kW	1.18×10^-0
	$??????? Q r e d d$ /kW	3.31×10^-0

Table 5 Validation results of light hydrocarbon recovery unit model

装置	输出变量	RMSE	R²
吸收塔	$F H 2 o u t$ /(kmol/h)	5.40×10^-3	0.99
	$F H 2 S o u t$ /(kmol/h)	8.60×10^-3
	$F C 1 o u t$ /(kmol/h)	1.28×10^-2
	$F C 2 o u t$ /(kmol/h)	1.39×10^-1
	$F C 3 o u t$ /(kmol/h)	2.01×10^-1
脱乙烷塔	$F H 2 y o u t$ /(kmol/h)	3.07×10^-9	0.99
	$F H 2 S y o u t$ /(kmol/h)	2.66×10^-4
	$F C 1 y o u t$ /(kmol/h)	1.29×10^-6
	$F C 2 y o u t$ /(kmol/h)	3.01×10^-8
	$F C 3 y o u t$ /(kmol/h)	2.94×10^-9
	$Q c o o l y$ /kW	1.21×10^-1
	$???????? Q r e d y$ /kW	4.50×10^-1
脱丁烷塔	$F H 2 S d o u t$ /(kmol/h)	4.27×10^-8	0.99
	$F C 2 d o u t$ /(kmol/h)	1.82×10^-8
	$F C 3 d o u t$ /(kmol/h)	1.44×10^-5
	$F C 4 d o u t$ /(kmol/h)	3.32×10^-8
	$F C 5 d o u t$ /(kmol/h)	4.29×10^-9
	$??????? Q c o o l d$ /kW	1.18×10^-0
	$??????? Q r e d d$ /kW	3.31×10^-0

Fig.6 Residual plot of the surrogate model of the light hydrocarbon recovery unit

Fig.7 Pareto curve obtained by multi-objective optimization

Fig.8 Hydrogen network structure diagram with minimum total annual cost

Fig.9 Hydrogen network structure diagram with minimum total annual CO2 emissions

Fig.10 Comparison of TAC and TCE between the original hydrogen network and the two optimized hydrogen networks

Fig.11 CO2 emission composition of different Pareto optimal solutions

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