Design of Hydrogen Network Integrated with the Shared Purifier in

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Design of Hydrogen Network Integrated with the Shared Purifier in Hydrogen Production Plant Chun Deng, Jian Liu, Yuhang Zhou, and Xiao Feng Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.9b01590 • Publication Date (Web): 28 May 2019 Downloaded from http://pubs.acs.org on June 2, 2019

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Industrial & Engineering Chemistry Research

Design of Hydrogen Network Integrated with the Shared Purifier in Hydrogen Production Plant Chun Deng1*, Jian Liu†1, Yuhang Zhou†1, Xiao Feng2 1State

Key Laboratory of Heavy Oil Processing, College of Chemical Engineering and Environment, China University of Petroleum, Beijing, 102249, China

2School

of Chemical Engineering & Technology, Xi’an Jiaotong University, Xi’an, 710049, China

*Corresponding author. E-mail address: [email protected] (Chun Deng); Jian Liu†1 and Yuhang Zhou†2 contributed equally to this work. Current address of Yuhang Zhou: Sinochem Xingzhong Oil Staging, CO, LTD., Zhoushan, 316000, China

Abstract: The shared purifier (i.e. pressure swing adsorption (PSA)) embedded in the hydrogen production plant would avoid the investment of additional purifier and save the resource consumption (i.e. natural gas). Few work has been conducted on the design of purification reuse/recycle hydrogen network integrated with the purifier in hydrogen production plant. In this paper, the generalized improved problem table is used to determine the targets of hydrogen network with purification reuse/recycle. The material balance analysis in different cases of hydrogen network with purification reuse/recycle is conducted. The first case is conventional hydrogen network with additional purifier, and three scenarios are analyzed to illustrate the impact of hydrogen composition in hydrogen utility and PSA product gas on the design of hydrogen network. The other case considers the integration of PSA in hydrogen production plant and two scenarios are proposed. Results show that the direct utilization of the converted gas and the overall optimization of the hydrogen network integrated with the PSA in the hydrogen production plant can reduce the 1

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Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

flowrates of hydrogen utility and raw resource consumption for hydrogen production. Keywords: Hydrogen system; hydrogen production; purification reuse/recycle; problem table; sharing

1. Introduction The purchase and processing amount of inferior crude oil has been increasing yearly in modern refineries. Both the European Standard1 and Chinese standard2 regulate the sulfur content of gasoline less than 10 ppm. To meet this condition, the proportion of hydrotreating and hydrocracking processes continues to increase, which consume a large amount of hydrogen. The dramatic increase in hydrogen consumption in refineries has made the problem of hydrogen deficiency even more prominent. Therefore, it is desirable to optimize the hydrogen network system and increase the utilization of hydrogen in refinery. The purification techniques, i.e. pressure swing adsorption (PSA), membrane, H2S and CO2 absorption tower, are widely used in the industries to upgrade hydrogen-rich gas for reuse in hydrogen sinks. Synthesis of refinery hydrogen networks is extensively used to improve the efficiency of hydrogen system. The methods for the synthesis of refinery hydrogen network can be classified into pinch analysis and mathematical programming approaches. Pinch techniques include two sequential steps: flowrate determining and network design. Alves and Towler3 firstly introduced the Hydrogen Surplus Diagram (HSD) to determine the minimum flowrate of hydrogen utility prior to detailed network design. Later, the extensions of Hydrogen Surplus Diagram were developed by Liu and her co-workers, i.e. determining the minimum flowrate of hydrogen utility considering multiple impurities4, optimal5 and maximum6 purification feed

2


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flowrate of hydrogen network. Many other insight-based Pinch techniques have been developed to locate the minimum flowrate targets for hydrogen network, e.g. Gas Cascade Analysis7, Composite Algorithm Table8, Material Recovery Pinch Diagram9 and its extension which consider purification process10, Source Composite Curve11 and Material Surplus Composite Curve12. Hallale et al.13 pointed out that the best placement of purifier is across the pinch. Foo et al.7 determined the flowrate targets for the hydrogen network with purification reuse via Gas Cascade Analysis7. The Pinched process hydrogen source is divided into two parts: one part is allocated to the region above the Pinch and the other is sent to the region below the Pinch. Agrawal and Shenoy8 located the optimal flowrate targets via CTA and the Pinch concentration is assumed to be the optimal purification concentration. The purifier (i.e. PSA) which separates a feed steam into two outlet streams with different qualities is referred as partitioning regeneration system14. The automated targeting model was introduced to locate the optimal targets of resources conservation network (i.e. hydrogen network and water network)14. Liao et al.15, 16 deduced the optimal conditions for locating the targets for hydrogen networks without16 and with one purifier15 and developed a rigorous systematic targeting approach based on mathematical deduction. Based on Composite Algorithm Table8, Deng et al.17 proposed the generalized Improved Problem Table (IPT) to address two scenarios (with and without purification) about the flowrate targets of in-plant and inter-plant hydrogen network. In addition, the approaches of design hydrogen network that satisfies the flowrate requirements have also been presented. Nearest Neighbors Algorithm (NNA)18 is one of the widely accepted method to design hydrogen network. The preliminary hydrogen network that has been design can be simplified by the evolution strategies19. Other design method of hydrogen network with multiple impurities have been developed, including evolutionary method20, ternary diagram21, and improved 3



ternary diagram approach22. Recently, the Nearest Neighbors Algorithm is extended to design hydrogen network with mixing potential23 and the pressure constraint24. The purpose of hydrogen system optimization with purification reuse/recycle is to reduce the flowrate of hydrogen utility. Almost none of the previous researches on hydrogen system optimization have considered the source of hydrogen utility, i.e. the hydrogen production plant. A typical steam-methane reforming (SMR) process in refinery is taken as an example. It consists of three steps: reforming, shift conversion, and purification. Normally, the pressure swing adsorption (PSA) is used to purify the converted gas stream to produce hydrogen utility. Hydrogen utility in the current literature generally refers to product gas stream rich in hydrogen purified by PSA, and the composition of hydrogen is generally greater than 95%. In those papers, additional purification units (such as PSA, membrane separation, etc., as shown in Figure 1(a)) are used to purify the process hydrogen source and the product hydrogen rich stream can be reused via the hydrogen sink, thereby reducing the flowrate of hydrogen utility. The composition of the product hydrogen rich stream of the additional purifier may be higher than, equal to, less than the hydrogen composition of the hydrogen utility. How to determine and optimize the flowrate of hydrogen utility and the flowrate of purified product gas is worthy of investigation. However, the hydrogen production plant in the actual refinery includes a purifier (such as PSA), and an additional purification unit may be not necessary. To avoid the investment of additional purifier, it would use the purifier of the hydrogen production plant to simultaneously purify the converted gas stream and the process hydrogen sources (shown in Figure 1(b)). Shariati et al.25 developed a modified automated targeting approach to determine the flowrate targets of hydrogen network considering the usage of PSA of hydrogen plant. 4


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In this paper, the detail material balance analysis of hydrogen system with purification reuse/recycle was conducted. The material balance equations were integrated in the improved problem table. It can be used to determine the optimal target value, including optimal flowrates of hydrogen utility, the raw material of hydrogen production plant and purified product gas stream. When the hydrogen composition of the product gas stream of the additional purifier is higher than, equal to, or lower than that of hydrogen utility, we can utilize the improved problem table to determine the optimal target value. In addition, we also considered the sharing of purifier embed in the hydrogen production plant, which can be used to upgrade the converted gas and the process hydrogen sources. Two scenarios of purification reuse and direct reuse of the converted gas are investigated. Literature cases are analyzed to validate the proposed approach.

2. Problem Statement Given a set of process hydrogen sources ( i  NSR ) and hydrogen sinks ( j  NSK ) in a refinery or petrochemical industrial park. Each source has a specified flowrate and hydrogen composition ( yHSRi2 ). Each sink has inlet flowrate ( F

SKj

) and a minimum requirement hydrogen composition

( yHSKj2 ). A hydrogen production plant may provide the hydrogen utility to supplement the use of process hydrogen sources. To reduce the usage of hydrogen utility and the raw material of hydrogen production, the process hydrogen sources and converted gas should be reused/recycled as much as possible. The additional purifier (Figure 1(a)) or PSA in the hydrogen plant (Figure 1(b)) can be used to upgrade the process hydrogen sources and converted gas (hydrogen rich gas stream from shift conversion of hydrogen production plant) for further reuse/recycle. We aim to develop a unified approach to determine the optimal usage of raw material of hydrogen production hydrogen

5



network with purification reuse/recycle. Several assumptions are made as listed: (1) Compared with membrane technique, PSA is more widely used for upgrading the hydrogen-rich stream. In the paper, PSA is used as the purifier. (2) H2S compositions contained in the hydrogen sources are treated to acceptable level via H2S absorption tower. (3) Typically, the continuous catalyst reforming unit in the refinery plant includes the PSA to upgrade hydrogen stream. Its product stream is taken as process hydrogen source. (4) Hydrogen rich gas streams from ethylene plant and fertilizer plant can be considered as process hydrogen sources. (5) The influence of fluctuation of feed impurity on the performance of PSA (i.e. hydrogen recovery ratio) is neglected.

(a) Hydrogen network with additional PSA

6


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(b) Integration of PSA in Hydrogen Production Plant Figure 1. Schematic diagram for mass flows of hydrogen network with purification reuse/recycle

3. Mass Balance Analysis and Procedure of Generalized Improved Problem Table The mass balance for hydrogen network with purification reuse/recycle is addressed prior to the flowrate targeting procedure via generalized improved problem table (IPT). Figure 1(a) shows schematic diagram for the mass flows of hydrogen network with additional PSA. As shown, the converted gas stream is fed to PSA in the hydrogen production plant to increase the hydrogen composition. The additional PSA is used to upgrade process hydrogen sources and its product stream can be further reused by hydrogen sinks. Figure 1(b) shows schematic diagram for the mass flows of hydrogen network integrated with the PSA in the hydrogen production plant. The PSA can receive the converted gas streams and process hydrogen sources. The mass balance analysis for

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Figure 1(a) and (b) will be discussed separately. The mass balance equations will be embedded in the improved problem table to check the feasibility of mass balance.

3.1 Hydrogen Network with Additional PSA The mass balance formulations for additional purifier (i.e. PSA shown in Figure 1(a)) are given by Equations (1) and (2). The hydrogen recovery ratio (R) is defined by Equation (3). F in  F prod  F resd

(1)

F in yHin2  F prod yHprod  F resd yHresd 2 2

(2)

R

F prod yHprod 2

(3)

F in yHin2

where F in , F prod and F resd represent the feed, product and residual flowrates of PSA and their hydrogen compositions are specified as yHin , yHprod and yHresd . The optimal F prod can be determined 2

2

2

via improved problem table with the specified yHprod . There would be two options for the residual 2

flowrate of PSA: reuse/recycled by hydrogen sinks in the direct reuse/recycle system ( Fsysresd ) or resd discharged to the fuel system ( Ffuel ) and it is given by Equation (4).

resd resd F resd  Fsys  Ffuel

(4)

The overall mass balance is given by Equation (5). sys sys resd F HU  Floss  Ffuel  Ffuel

(5)

sys resd where Ffuel and Ffuel denote the flowrates that discharged from direct reuse/recycle system and

sys residual of purifier to fuel system. Floss denotes the total flowrate loss for direct reuse/recycle

system and it can be determined via Equation (6). It is identical with the net flowrate in the last sys impurity interval calculated by Step 2 of improved problem table in Section 4.1. Note that, Floss is

specified the direct reuse/recycle system and it keeps unchanged if the system is selected. To

8


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sys resd minimize the flowrate of hydrogen utility, Ffuel and Ffuel should be minimized as well. NSK

NSR

j

i

sys Floss =  F SKj   F SRi

(6)

The overall mass balance for the direct reuse/recycle system is given by Equation (7). resd sys sys F HU  F prod  Fsys  Floss  Ffuel  F in

(7)

3.2 Integration of PSA in Hydrogen Production Plant As shown in Figure 1(b), the converted gas stream F cg from shift conversion process can be divided into two streams. A stream of F cg1 is sent to PSA, and its product gas F prod is commonly called as hydrogen utility for hydrogen network. Another stream F cg2 is hydrogen-rich gas that can be considered as a hydrogen source. The PSA can receive converted gas stream and process hydrogen sources. The mass balance formulations and hydrogen recovery ratio for the PSA are identical with Equations (1) (2) and (3). Its feed can be calculated via Equations (8) and (9).

F in  F wh +F cg1  F prod  F resd

(8)

F in yHin2  F wh yHwh2  F cg1 yHcg12  F prod yHprod  F resd yHresd 2 2

(9)

where F prod , F resd F wh and F cg1 represent product, residual flowrate of purifier, the flowrate of waste hydrogen streams and converted gas allocated to purification. Their hydrogen compositions are specified as yHprod , yHresd 2

specified

yHprod 2

2

yHwh2 and yHcg12 . The optimal F prod can be determined via IPT with the

and hydrogen recovery ratio R. The residual flowrate of purifier can be

reuse/recycled by hydrogen sinks in the direct reuse/recycle system ( Fsysresd ) or discharged to the fuel resd system ( Ffuel ) and it is given by Equation (10).

resd resd F resd  Fsys  Ffuel

(10)

sys The overall mass balance is given by Equation (11) and Floss also can be determined via

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Equation (6). sys sys resd F cg  Floss  Ffuel  Ffuel

(11)

The overall mass balance around the direct reuse/recycle system is given by Equation (12). resd sys sys F cg2  F prod  Fsys  Floss  Ffuel  F wh

(12)

3.3 Procedure of Generalized Improved Problem Table The procedure of generalized Improved Problem Table for the determination of the optimal flowrates of hydrogen system with purification reuse/recycle can be summarized as shown in Figure 2. The literature cases are used to illustrate its applicability in detail.

Figure 2. Systematic procedure of generalized improved problem table

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4. Case Studies 4.1 Hydrogen Network with Additional PSA

When the hydrogen composition of the product stream of additional purifier is higher than, equal to, or lower than that of hydrogen utility, the conventional pinch techniques may not be directly used to determine the optimal flowrate targets for hydrogen network. Then, we introduce the detailed steps (shown in Figure 2) to set the flowrate targets using the improved problem table method by case studies. The material balance equations derived in Section 3.1 is integrated into the improved problem table to verify the feasibility of material balance.

 yHHU2 ） Scenario 1 ( yHprod 2

It is assumed that hydrogen composition of PSA product stream is lower than that of hydrogen utility in this scenario. The system must be supplied by hydrogen utility when the required inlet hydrogen composition of hydrogen sink is higher than that of PSA product stream. The improved problem table is utilized firstly to determine the initial minimum flowrate of hydrogen utility and PSA product stream. Next, waste hydrogen streams will be identified and introduced to PSA to satisfy its inlet demand. Note that, there will be two cases, one of which is that the flowrate of waste gas streams cannot satisfy the flowrate demand of PSA. Another case is that the flowrate of purge gas streams is sufficient to meet the inlet demand of PSA. The limiting data extracted from the literature 3 for hydrogen sources and sinks in Example 1 is shown in Table 1. The hydrogen composition for the PSA product gas stream is given as 0.9 and hydrogen recovery ratio is defined as 0.95. The PSA product gas stream can be treated as an external

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hydrogen source. Table 1 Limiting data for example 1 Hydrogen source

Hydrogen composition (mole fraction)

Flowrate

Hydrogen

(mol·s-1)

source


Flowrate (mol·s-1)

SRU

0.93

623.8

HCU

0.8061

2495

CRU

0.8

415.8

NHT

0.7885

180.2

HCU

0.75

1801.9

DHT

0.7757

554.4

NHT

0.75

138.6

CNHT

0.7514

720.7

DHT

0.73

346.5

CNHT

0.7

457.4

Hydrogen utility

0.95

To be determined

Step 1: Hydrogen compositions and impurities arrangement: The first step of IPT is arranging all the hydrogen compositions (of hydrogen sources and sinks together) in descending order in the first column (Table 2). Do not repeat the same value if the composition occurs more than once. Add one more arbitrary hydrogen composition at the bottom of the column such that it is the smallest value, i.e. 0.25 in the first column. The arbitrary hydrogen composition serves to provide an only endpoint and facilitates to plot the last segment of the Limiting Composite Curve (LCC, graphical representation of the IPT). The plotting procedure of LCC will be presented in Step 4. The impurities composition ( y ) calculated by 1  yHv are listed in the second column. The impurities composition 2

in the second column satisfy the relationship shown as Equation (13). y1  y 2  L  y  L  y arbitrary

(13)

Step 2: Net flowrate deficits calculation: Calculate the net flowrates Fnetv in the third column (Table 2). The total flowrate of the hydrogen sources is subtracted from the total flowrates of hydrogen sinks present in each impurity interval. Once the impurities composition of hydrogen sources and sinks are less than y , these hydrogen sources and sinks will appear in the impurity interval

y



v , y 1  , and the net flowrate Fnet of this impurity interval can be calculated by Equation

(14). v   F SKj   F SRi y SRi , y SKj  y Fnet j

i

12


(14)

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For a given hydrogen network, the total flowrate deficit is a constant. Positive values indicate a deficit, and negative values represent a surplus. The value shown in the last entry of the third column of Table 2 is 166.3 mol/s and it indicates that at least such a flowrate of external hydrogen source (i.e. hydrogen utility) is needed for the network. Step 3: Net mass loads calculation: Tabulate the net mass loads in the fourth column (Table 2) using Equation (15). The net mass loads for each impurity interval can be obtained by multiplying the net flowrate and the impurity difference of the related interval. v M net  Fnet  y  y 1 

(15)

Step 4: Cumulative mass loads calculation: Calculate the cumulative mass loads in the fifth column (Table 2) using Equation (16). The value of the first row for this column is zero because of no cumulative mass load. The cumulative mass load of other rows is the mass loads summation of previous rows. v M cum 0

 

t 

 t M cum   M net   t 1

(a) Limiting composite curve

13


(16)


(b) Supply lines for hydrogen utility & product of PSA

(c) Optimal composite hydrogen supply line Figure 3. Limiting composite curve and optimal hydrogen supply line for example 1: (a) Limiting composite curve; (b) Supply lines for hydrogen utility & product of PSA; (c) Optimal composite hydrogen supply line; 14


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The drawing procedures of Figure 3 will be presented step by step: (1) Drawing limiting composite curve: The Limiting Composite Curve (LCC) (i.e. the bold line shown in Figure 3a) can be obtained by plotting the impurity column (i.e. the second column in Table 2) against the cumulative mass load column (i.e. the fifth column in Table 2). Its represents the net hydrogen demand of the system. Note that, the shaded part in Figure 3(a) indicates a hydrogen pocket, where the hydrogen source can satisfy the hydrogen demand and no external hydrogen source is needed in the hydrogen impurity interval. (2) Drawing hydrogen supply line: In the impurity concentration intervals of 0.05 and 0.1, the system can only be satisfied by hydrogen utility. The hydrogen supply line OA can be determined and its inverse of slope is related to the flowrate of hydrogen utility (197.71 mol·s-1, finally determined in Step 7). Next, the line OA is extended and the extension cord intersects with the horizontal line of the PSA feed impurity composition (yin=0.3) at point B. In Figure 3(b), the arrow line from PSA feed impurity composition (0.3) to purified product impurity composition (0.1) represents the purification process. Let us draw the vertical line cross point B. Then line intersects with the horizontal line of purified product impurity composition (yprod=0.1) at point C. Next, the purified product supply hydrogen line can be drawn from the point C. Its slope is the reciprocal of the purified product flowrate (i.e. 88.89 mol/s, determined in Step 7), and collides with Limit Composite Curve to form a pinch point, which is so-called the pinch point for purification reuse/recycle. (3) Draw composite hydrogen supply line: In the interval of purified product gas impurity composition (0.1) and feed impurity composition (0.3), extension line of hydrogen utility (AB) and purified product gas hydrogen supply line (CD) are combined. The Composite Hydrogen Supply Line can be formed by directly connecting with AD and its slope is reciprocal of the total flowrate of hydrogen utility and purified product gas. It indicates that the system is satisfied via the hydrogen utility and the purified product gas in the hydrogen impurity composition interval. Note that, the slope of the hydrogen supply line above the purified feed impurity composition (yin=0.3) is consistent with the slope of the first segment of hydrogen supply line (OA), that is, the flowrate is equal to that of hydrogen utility. It is in agreement with reported in the literature8. 15



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Step 5: Flowrate targeting for external hydrogen sources: For cases where only one external hydrogen source is considered, tabulate all the possible hydrogen supply flowrates in the sixth column via solving Equation (17) and the maximum value in this column of Table 2 (i.e. 268.82 mol·s-1) indicates the minimum flowrate of hydrogen utility for the network. Worthy to mention, the hydrogen composition (i.e. 0.7) in the first column of Table 2 in the same raw of maximum value (i.e. 268.82 mol·s-1) represents the pinch hydrogen composition for direct reuse/recycle, which is identical with those reported in the literature3. F ex   where M cum and

y

M cum

(17)

y  y ex

denote the cumulative mass load and impurity composition for νth

hydrogen composition level. The composition y ex represents the impurity composition of external hydrogen source. For hydrogen networks with multiple external hydrogen sources (different impurity levels), to reduce the overall cost, the external hydrogen source with higher impurities composition (usually less costly) will be given priority over the external impurities with lower impurities source. The PSA product gas stream is considered as an external hydrogen source and the hydrogen composition of the PSA product is given as 0.9 and hydrogen recovery is defined as 0.95. The product impurity pinch composition ( y prod =0.1 ) fulfills the condition ( y prod  yHU ) and thus the flowrate of hydrogen utility

can be further reduced with the use of the PSA product gas stream. All the possible flowrates of the the PSA product gas stream can be calculated using Equation (18). The maximum value (803.88 mol·s-1) in the seventh column of Table 2 can be determined as the optimal flowrate of the PSA product gas stream and its feasibility should be checked in Step 7.

F prod 

 M cum  F HU  y prod  y HU 

y  y prod

 F HU

16


(18)

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To calculate all the possible flowrates for rth external hydrogen sources, Equation (18) can be generalized to Equation (19). r 1

F HUr 



 M cum   F HUn y HUr  y HUn n 1



y y

HU r



r 1

  F HUn

(19)

n 1

Step 6: Waste hydrogen streams identification: The part of the hydrogen sources and sinks above the pinch can be considered as a sub-system of hydrogen network. The hydrogen stream with the pinch impurity can be considered as an external hydrogen source for the sub-system above the pinch. For each impurity interval above the pinch, the required flowrate that can be calculated via Equation (20). The flowrates above impurity pinch can be listed in the eighth column of Table 2 and the maximum value of this column is essentially the minimum flowrate for the sub-system above the pinch ) max of hydrogen pinch. But this column is not reflected in IPT. Thus, only the flowrate ( Fabove

source at the pinch impurity is distributed to the sub-system. The residual flowrate which is identified as the waste hydrogen stream can be fed to PSA or discharged into the fuel system. The waste hydrogen streams can be calculated by solving Equation (21) and they are shown in the last column of Table 2. pinch  Fabove

 pinch M cum  M cum y  y pinch y  y pinch

ex pinch F wh  Fpinch  ( Fabove ) max

(20) (21)

Step 7: Flowrate targets re-calculation and checking: The mass balance for the system with purification reuse/recycle shall be performed to verify the feasibility. The results determined via IPT (Table 2) show that F HU =-374.28 mol·s-1 and F prod =803.88 mol·s-1. It indicates that there is no need of hydrogen utility and the flowrate of purification product is targeted as 803.88 mol·s-1. Hence, F prod yHprod in Equation (3) can be calculated as 729.49 mol·s-1 2

by multiplying the value F prod (803.88 mol·s-1) by yHprod (0.9). Then, the required flowrate of PSA 2

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F in yHin2 is determined as 761.57 mol·s-1 via solving Equation (3). In addition, the total flowrate of

all the identified waste hydrogen streams (  F wh ) is calculated as 637.58 mol·s-1. However, the maximum flowrate supplied by identified wasted hydrogen F wh yHwh is 446.31 mol·s-1, which is 2

lower than the targeted PSA feed flowrate. The difference between two feed streams ( F in ) is determined as 315.26 mol·s-1. It indicates that it is infeasible. Therefore, hydrogen utility is required to increase to satisfy the demand of PSA. The calculation results of F HU , F prod , F prod yHprod , F in yHin , 2

2

F wh y wh and F in are listed in Table 2, respectively.

Table 2 Improved problem table for example 1 with preliminary solution Hydrogen

Impurity

Net

composition

composition

flowrate

(mole fraction)

(mole fraction)

(mol·s-1)

0.95

0.05 0

0.93

0

0

0

0

0 -18.71 -18.71

-374.28

0

-77.29

-537.10

-249.52

-65.87

-439.16

-97.32

-49.14

-304.26

101.42

-28.2

-161.80

297.95

25.02

125.96

668.56

29.09

145.45

692.98

48.49

220.43

769.62

67.21

268.82

803.88

75.52

251.73

751.22

-58.57 11.41 16.74 20.94 53.22 4.07 19.4 18.71

0.3 166.3

0.65

(mol·s-1)

0.27 623.7

0.7

(mol·s-1)

0.25 970.2

0.73

(mol·s-1)

0.2486 2910.7

0.75

(mol·s-1)

0.2243 2190

0.7514

(mol·s-1)

0.2115 1635.6

0.7757

F wh

0.2 1455.4

0.7885

F prod

0.1939 1871.2

0.8

F HU

0.1 -623.8

0.8061

Cumulative load

0.07 -623.8

0.9

Net load

8.31

0.35

18


637.58

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R (mole fraction) 0.95

yHprod 2 (mole fraction) 0.9

F HU

F prod

(mol·s-1)

(mol·s-1)

0

803.88

F prod yHprod 2

F in yHin2

(mol·s-1)

(mol·s-1)

723.49

761.57

F wh y wh

F in

(mol·s-1)

(mol·s-1)

446.31

315.26

Note that F in is 315.26 mol·s-1 and it indicates the result is infeasible. The optimal and feasible target for F in should be zero. The Excel Goal Seek feature is utilized to find the optimal target F in by changing the value of F HU . The value of F in achieves zero and the values of all other variables are changed to be new results as shown in Table 3. The optimal flowrate of the PSA product gas stream is determined as 88.89 mol·s-1 with the minimum flowrate of hydrogen utility. The optimal inlet flowrate of the purification is 120.3 mol·s-1 with the optimal feed hydrogen composition of 0.7 (i.e. the impurity composition is 0.3). Table 3 Improved problem table for example 1 with optimal solution Hydrogen

Impurity

Net

composition

composition

flowrate

(mole fraction)

(mole fraction)

(mol·s-1)

0.95

0.05

(mol·s-1)

0 -18.71

-77.29

-1126.1

-65.87

-955.31

-49.14

-727.07

-28.2

-504.13

25.02

-95.9

29.09

-69.68

48.49

29.4

11.41 16.74 20.94 53.22

0.2486 4.07

0.25 19.4

0.27 623.7

197.71

-58.57

0.2243

970.2 0.73

(mol·s-1)

0.2115

2910.7 0.75

(mol·s-1)

0.2

2190 0.7514

(mol·s-1)

0.1939

1635.6 0.7757

(mol·s-1)

-18.71

1455.4 0.7885

F wh

0.1

1871.2 0.8

F prod

0

-623.8 0.8061

F HU

0.07 -623.8

0.9

Cumulative load

0 0

0.93

Net load

18.71 19



0.7

0.3 166.3

0.65

0.35

R

yHprod 2

(mole fraction)

(mole fraction)

F HU

F prod

(mol·s-1)

(mol·s-1)

0.9

197.71

88.89

yHin2

yHresd 2

F in

F resd

(mol·s-1)

(mol·s-1)

120.3

31.41

(mole fraction)

0.7

0.13

67.21

88.89

75.52

64.83

120.3

8.31

0.95

(mole fraction)

Page 20 of 51

F prod yHprod (mol·s-1) 2

F in (mol·s-1)

80

0

F in yHin2 (mol·s-1)

F wh yHwh2 (mol·s-1)

84.21

84.21

Base on the results calculated in Table 3, one possible hydrogen network can be designed by Nearest Neighbors Algorithm (NNA) 18 shown in Figure 4.

Figure 4. One optimal hydrogen network for example 1 (flowrate unit is mol·s-1, hydrogen composition is in brackets) 20


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Once the identified wasted hydrogen gas streams can satisfy the feed flowrate requirement of PSA, the example adopted from Liu et al.5 is analyzed. The limiting hydrogen data for example 2 is shown in Table 4. The hydrogen composition of PSA product is specified as 0.73 and the hydrogen recovery ratio R is set as 0.75. Table 4 Limiting hydrogen data for example 2 Hydrogen source


Flowrate

Hydrogen

(mol·s-1)

source


Flowrate (mol·s-1)

SR1

0.86

80

SK1

0.9

130

SR2

0.82

50

SK2

0.78

125

SR3

0.73

100

SK3

0.71

150

SR4

0.69

135

SK4

0.67

123

SR5

0.65

190

SK5

0.63

145

SR6

0.6

100

SK6

0.54

185

SR7

0.57

90

SK7

0.4

110

SR8

0.45

136

SK8

0.28

130

SR9

0.33

51

SR10

0.3

180

Hydrogen utility

0.98

To be determined

Step 1- Step 4: They are similar with those presented in the example 1 in Scenario 1 and the data are listed in Table S1. Step 5: The flowrates for external hydrogen sources are calculated by Equation (17) and listed in the sixth column of Table S1. The maximum value in the sixth column is 65.18 mol·s-1. Since the hydrogen composition of PSA product (0.73) is lower than that of hydrogen utility (0.75), the subsystem with the hydrogen composition intervals above 0.73 are satisfied by hydrogen utility. The sub-system with the hydrogen composition intervals below 0.73 will be satisfied by both hydrogen utility and PSA product. Considering PSA product as second hydrogen utility, the flowrates of PSA product and hydrogen utility are determined as 46.95 mol·s-1 and 53.8 mol·s-1, respectively. The results show that the flowrate of hydrogen utility is reduced by 8.6% compared with the literature5 21



(58.86 mol·s-1). Step 6: Solving Equations (20) and (21), we can calculate the waste hydrogen streams as F wh1 =40.75 mol·s-1 (at 0.35 mole fraction of impurity composition), F wh2 = 3 mol·s-1 (at 0.4 mole fraction of impurity composition), F wh3 = 15.83 mol·s-1 (at 0.55 mole fraction of impurity composition), F wh4 = 5.17 mol·s-1 (at 0.67 mole fraction of impurity composition) and F wh5 = 50 mol·s-1 (at 0.7 mole fraction of impurity composition). These waste hydrogen streams will be sent to PSA or fuel system. Step 7: Using Equation (3), the value of F in yHin can be calculated as 45.693 mol·s-1. To reduce the 2

feed flowrate of PSA, the waste hydrogen stream with lower impurity composition is chosen in priority to send to PSA. Thus, waste hydrogen streams 1 to 5 are sent to PSA in sequence. As the total flowrate ( F wh1 yHwh1 +F wh2 yHwh2 +F wh3 yHwh3 +F wh4 yHwh4 =37.12 mol·s-1) of waste hydrogen stream 1 to 4 2

2

2

2

is lower than the inlet flowrate ( F in yHin =45.698 mol·s-1) of PSA, an extra flowrate is needed and 2

residue flowrates of waste hydrogen stream 5 are calculated as 28.6 mol·s-1 and 21.4 mol·s-1 via solving material balance calculations. Finally, solving Equations (1) and (2) yields F resd =46.4 mol·s-1 and

yHresd =0.2462. The results show that the total flowrate of hydrogen streams that 2

discharged to fuel system (67.8 mol·s-1) is reduced by 7.2% compared with the result (73.06 mol·s-1) in the literature5. Table S1 Improved problem table for example 2 The Nearest Neighbors Algorithm (NNA)

18

is applied to design the hydrogen network (i.e.

Figure 5).

22


Page 22 of 51

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Figure 5. One optimal hydrogen network for example 2 (flowrate unit is mol·s-1, hydrogen composition is in brackets)

Scenario 2 ( yHprod =yHHU ） 2

2

Since the hydrogen composition of hydrogen utility and PSA product are equal, the PSA product can be considered as another hydrogen utility. The IPT is utilized to determine the minimum flowrates of external hydrogen source (hydrogen utility and PSA product). The targeted flowrate of PSA product is the reduced flowrate of hydrogen utility. Table 5 shows the hydrogen sources and sinks data for Scenario 2. The limiting hydrogen data taken from Foo7 is used to analyze this case. The hydrogen composition of PSA product and purification recovery are assumed to be 0.999 and 0.9, respectively. 23



Page 24 of 51

Table 5 Limiting hydrogen data for Scenario 2 Hydrogen Source


Flowrate

Hydrogen

(mol·s-1)

Sink


Flowrate (mol·s-1)

SR1

0.983

80

SK1

0.999

120

SR2

0.85

75

SK2

0.986

27.8

SR3

0.96

28.55

SK3

0.975

80

SR4

0.95

80

SK4

0.975

60

SR5

0.9

120

SK5

0.97

100

SR6

0.983

40

SK6

0.9

150

SR7

0.975

80

Hydrogen utility

0.999

To be determined

Step 1- Step 4: They are similar with those in the example 1 in Scenario 1 and the data are listed in Table S2. Step 5: The flowrates for hydrogen sources are calculated by solving Equation (17) and shown in the sixth column of Table S2. The flowrate of fresh hydrogen source needed for Scenario 2 is 125.21 mol·s-1via IPT. Step 6: Solving Equations (20) and (21), the waste hydrogen streams can be determined as F wh1 =30.96 mol·s-1 (at 0.05 mole fraction of impurity composition) and F wh2 =60 mol·s-1 (at 0.15 mole fraction of impurity composition), respectively. Step 7: The results determined via IPT (Table S1) show that F HU =0 mol·s-1 and F prod =125.21 mol·s-1. It indicates that there is no need of hydrogen utility and the flowrate of PSA product is targeted as 125.21 mol·s-1. The inlet flowrate of PSA F in yHin can be calculated as 138.98 mol·s-1 2

by solving Equation (3). However, the total flowrates of identical waste hydrogen streams

F

wh

yHwh2

is 84.41 mol·s-1, which means waste hydrogen streams are insufficient to satisfy the

demand of PSA. It indicates that it is infeasible. The results of F HU , F prod , F prod yHprod , F in yHin , 2

F

wh

yHwh2 and F in are listed in Table S2.

Table S2 Improved problem table for Scenario 2 with preliminary solution 24


2

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Note that the feasible target of F in should be zero. Same to example 1, the Excel’s Goal Seek feature is applied to determine the optimal solutions by changing the value of F HU . New results solved by Goal Seek are shown in Table S3. The optimal flowrates of hydrogen utility and PSA product gas stream are calculated as 52.77 mol·s-1 and 72.45 mol·s-1, respectively. The optimal inlet flowrate of PSA is equal to total flowrates of waste hydrogen streams. Then, the flowrate F resd and hydrogen composition yHresd of residual stream can be obtained by Equations (1) and (2). 2

Compared with the flowrate of hydrogen utility (54.23 mol·s-1) and residual flowrate of PSA (22.70 mol·s-1) reported in literature 7,the results ( F HU =52.77 mol·s-1， F resd =18.52 mol·s-1) obtained via generalized IPT in this paper are better. Table S3 Improved problem table for Scenario 2 with optimal solution The NNA17 is used to design a hydrogen network, as shown in Figure 6.

Figure 6. One optimal hydrogen network for Scenario 2 (flowrate unit is mol·s-1, hydrogen composition is in brackets) 25



Page 26 of 51

Scenario 3 ( yHprod  yHHU ） 2

2

The limiting hydrogen data extracted from Alves & Towler

3

are shown in Table 1. The

hydrogen composition of PSA product and hydrogen recovery ratio are assumed to be 0.98 and 0.95, respectively. The PSA product gas is considered to utilize firstly because the cost of purifying hydrogen by PSA is lower than that of hydrogen production. Step 1- Step 4: They are similar with those in the example 1 in Scenario 1 and the data are listed in Table S4. Step 5: Because of the priority to use PSA product gas, the flowrate of hydrogen utility is assumed to be zero and F prod can be determined as 240.02 mol·s-1. Step 6: The flowrate of identified waste hydrogen stream is 73.72 mol·s-1 (at 0.3 mole fraction of impurity composition) via Equations (20) and (21). Step 7: The results determined by IPT (Table S4) show that F prod =240.02 mol·s-1 and =73.72 mol·s-1. The value of F in yHin

2

F

wh

can be calculated as 247.6 mol·s-1 by solving Equation (3).

But the maximum flowrate of waste hydrogen stream ( F wh yHwh ) is 51.6 mol·s-1 and the difference 2

between inlet flowrate of PSA and waste hydrogen stream ( F in =F in yHin  F wh yHwh ) is 196 mol·s-1. 2

2

Thus, the hydrogen network needs external hydrogen. The calculation results of F HU , F prod , , F in yHin ,  F wh yHwh and F in are shown in Table S4. F prod yHprod 2 2

2

Table S4 Improved problem table for Scenario 3 with preliminary solution in Note that, the feasible target of F should be zero. Same to example 1, the Excel’s Goal

Seek feature is applied to determine the optimal solutions by changing F HU . The results are shown in Table S5. The optimal flowrates of hydrogen utility and PSA product gas stream are calculated as 196.77 mol·s-1 and 64.33 mol·s-1, respectively. The optimal inlet flowrate of PSA is 94.8 mol·s-1 26


Page 27 of 51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


at hydrogen composition of 0.7. The optimal results are equal to those reported in the literature14. Then, the flowrate F resd and hydrogen composition yHresd of residual stream can be calculated via 2

solving Equations (1) and (2). Table S5 Improved problem table for Scenario 3 with optimal solution The NNA 18 is applied to design the hydrogen network shown in Figure 7.

Figure 7. One optimal hydrogen network for Scenario 3 (flowrate unit is mol·s-1, hydrogen composition is in brackets) The optimal results for different scenarios determined by IPT are summarized in Table 6, which are compared with those reported in the literatures. In example 2, the flowrate of hydrogen utility 27



Page 28 of 51

(i.e. 53.8 mol·s-1) is reduced compared with that (i.e. 58.86 mol·s-1) in the literature5 by the increment of the flowrate of product hydrogen from PSA. In Scenario 2, because the flowrate of hydrogen reuse/recycle is increased, both flowrates of hydrogen utility and product gas of PSA are reduced compared with the results in the literature7. In scenario 3, the determined values are consistent with the results in the literature25. In addition, the determined flowrate targets are validated by mathematical models. Table 6 Results for different scenarios of hydrogen network with purification reuse/recycle Scenario 1 ( yHprod  yHHU ) 2

Example 1

2

Example 2

Scenario 2

Scenario 3

( yHprod  yHHU )

( yHprod  yHHU )

2

2

2

2

This work

This work

Literature5

This work

Literature7

This work

Literature25

FHU (mol·s-1)

197.71

53.8

58.86

52.77

54.23

196.77

196.77

Fprod(mol·s-1)

88.89

46.95

26.10

72.45

97.30

64.33

64.33

Fin (mol·s-1)

120.3

93.35

44.56

90.96

-

94.8

94.8

yHin2

0.7

0.489

0.43

0.884

-

0.7

0.7

4.2 Integration of PSA in Hydrogen Production Plant The limiting hydrogen data taken from Shariati et al25 is given in Table 7. The hydrogen composition of PSA product and hydrogen recovery ratio are assumed to be 0.999 and 0.9. There are two different scenarios for the usage of the converted gas from the steam methane reforming in the hydrogen production process. We illustrate the detailed steps to set the flowrate targets using the improved problem table method by case studies. The material balance equation

28


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derived in Section 3.2 is integrated into the improved problem table to validate the feasibility of ng

material balance.The flowrate of natural gas ( F ) for hydrogen production can be converted by the flowrate of converted gas ( F cg ), and the conversion factor is defined as λ. F ng    F cg

(22)

where λ is determined as 0.2282 and the data is taken from the case of a petrochemical enterprise in Northeast China. Table 7 Limiting data for Scenario A and B Hydrogen source


Flowrate

Hydrogen

(mol·s-1)

sink


Flowrate (mol·s-1)

RG

0.999

50

RG

0.999

53

HT

0.9242

369.7

HT

0.9233

406.2

HG

0.8504

157.5

AF

0.9145

40

DP

0.7966

1399.4

RG

0.9145

28

TA

0.67

1626.9

HG

0.8663

209.1

AF

0.6

50

DP

0.8

1421

IS

0.5031

4266.7

TA

0.7

1709.8

IS

0.506

4308.5

Scenario A

The converted gas from the methane steam reformer is completely purified by the PSA to obtain the product gas stream with higher hydrogen composition ( F cg  F cg1 ). Step 1: The hydrogen and impurity composition of hydrogen sources and sinks are listed in the first and second columns of Table S6. Add one more arbitrary hydrogen composition (i.e. 0.45) at the last entry in the first column. Step 2: The net flowrates for each impurity interval are calculated by Equation (14) and listed in the third column of Table S6. Note that, the last entry of the third column is 255.4 mol·s-1 which 29



Page 30 of 51

indicates the flowrate deficit of this hydrogen network. Step 3: The net mass loads are calculated in the fourth column (Table S6) via solving Equation (15). Step 4: The cumulative mass loads are calculated in the fifth column (Table S6) via solving Equation (16). Step 5: All the converted gas enters the PSA for purification, so the required hydrogen in the hydrogen system is provided by the hydrogen utility. And the minimum flowrate of hydrogen utility can be calculated. Step 6: The results determined via Equations (20) and (21) show that F wh =46.4 mol·s-1 (at 0.3 mole fraction of impurity composition). Step 7: It is assumed that all identified waste hydrogen streams are sent to the purification for reuse wh

sys ( Ffuel =0) in this scenario. Next, the flowrate of waste hydrogen stream ( F ) and hydrogen

composition ( yHwh2 ) can be obtained. The required inlet flowrate of PSA ( F in yHin ) can be determined 2

via Equation (3) and F resd yHresd can be calculated using Equation (9). Thus yHresd can be determined. 2

2

The difference between F in yHin and ( F wh yHwh  F cg yHcg ) is F in and the value should be zero. Then, 2

2

2

in the Excel’s Goal Seek feature is applied to determine the optimal solutions. The target value F

cg is set to be zero while F is set to be altered. The optimal results are shown in Table S6. The

optimal flowrate of converted gas (Fcg1) and PSA product gas F prod are 340.79 mol·s-1 and 301.8 mol·s-1, respectively. The flowrate of natural gas F ng can be calculated as 77.77 mol·s-1 via Equation (22). Table S6 Improved problem table for Scenario A with optimal solution A hydrogen network as shown in Figure 8 can be designed via NNA17.

30


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Figure 8. Hydrogen network for integrated hydrogen production and purification unit (Scenario A) (flowrate unit is mol·s-1, hydrogen composition is in brackets)

Scenario B

The converted gas from the steam-methane reforming can not only be purified by the purification unit, but also can be used as a hydrogen source to supply hydrogen to the hydrogen network system. The converted gas is considered as a hydrogen source when the required hydrogen cg cg2 composition of hydrogen sinks is equal or lower than that of converted gas. In this case, F  F .

The limiting hydrogen data, the hydrogen composition of PSA product and hydrogen recovery ratio are same with those in Scenario A. Step 1- Step 4: They are identical with those in Scenario A and the data is listed in Table S7. Step 5: The converted gas is considered to directly utilized in this scenario. The converted gas will be priory to use when the required hydrogen composition is lower than or equal to the hydrogen 31



composition of converted gas. The minimum flowrates of converted gas and PSA product gas can be determined. Step 6: Solving Equations (20) and (21), the flowrate of identified waste hydrogen streams can be obtained as Fwh1=68.67 mol·s-1 with impurity composition of 0.33 (mole fraction) and Fwh2=54.03 mol·s-1 with impurity composition of 0.4969 (mole fraction). Step 7: Based on material balance calculations, the Excel’s Goal Seek feature is applied to cg determine the optimal solutions. F in is set to be the target value of zero while the value of F is

set to be altered. The optimal results are calculated and listed in Table S7. The optimal flowrates of converted gas ( F

cg1

) and PSA product gas ( F prod ) are 312.16 mol·s-1 and 65.94 mol·s-1, respectively.

Next, the flowrate of natural gas F ng can be determined as 71.24 mol·s-1 via solving Equations (22). Table S7 Improved problem table for Scenario B with optimal solution The NNA 18 is applied to design the hydrogen network shown in Figure 9.

32


Page 32 of 51

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Figure 9. Hydrogen network for integrated hydrogen production and purification unit (Scenario B) (flowrate unit is mol·s-1, hydrogen composition is in brackets) To perform the comparative analysis, the flowrate of natural gas in the original literature25 was calculated using Equation (22). The mathematical programming models are also used to solve the problems and the results are identical with those determined via IPT. The results for those reported in the literature and Scenarios A and B in the paper are compared as shown in Figure 10.

33



Page 34 of 51

mol/s 466.25

500 450 400

340.79

350

301.8

312.16

300 250 200

195.45

150 100

106.4 65.94

77.77 71.24

50 0

Hydrogen utility

Converted gas

Literature25

Scenario A

Natural gas Scenario B

Figure 10. Results comparison for different Scenarios As shown in Figure10, compared with the results in the literature25, the flowrate of hydrogen utility in Scenario A is increased by 54.4%, while the flowrates of converted gas and natural gas are reduced by 26.9%. The converted gas is directly reused in Scenario B, and the flowrate of hydrogen utility is reduced by 66.3%, and that of natural gas is reduced by 33.0%. As the direct utilization of converted gas and overall optimization of hydrogen network integrated with purification unit of hydrogen plant are not considered in the literature25, the resource consumption or the flowrate of natural gas for hydrogen production is the biggest one. In Scenario A, there is no direct use of converted gas and all the hydrogen are provided by hydrogen utility, and it leads to the highest flowrate of hydrogen utility. In Scenario B, because of direct use of converted gas and optimization of hydrogen network integrated with purification in hydrogen plant, both the flowrates of hydrogen utility and resource consumption for hydrogen production are the lowest ones.

5. Conclusion This paper presents the generalized improved problem table for the targeting of hydrogen 34


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network with purification reuse/recycle. We performed the material balance analysis in two different cases of hydrogen system. The first case is conventional hydrogen network with additional purification unit (i.e. PSA). When the hydrogen composition of PSA product stream is higher than, equal to, or lower than that of hydrogen utility, the generalized IPT can be utilized to determine the optimal targets, such as flowrates of hydrogen utility, feed and product streams of PSA, hydrogen composition of PSA feed stream. Another case is the hydrogen system integrated with purifier (i.e. PSA) in hydrogen production plant, in which the sharing of PSA is considered. Two scenarios are proposed, one is that all the converted gas is purified by PSA for further usage, and the other is the directly utilization of converted gas. Optimal flowrates of hydrogen utility, converted gas and natural gas were determined by using the generalized improved problem table. Results show that the flowrates of hydrogen utility and resource consumption for hydrogen production can be reduced via the direct utilization of the converted gas and the overall optimization of the hydrogen network integrated with purifier in the hydrogen production plant. It shows the benefits of the sharing of purifier in hydrogen production plant.

Notation Sets and indices i = index for sources j = index for sinks ν = index for impurity level NSR = NSK

set of process hydrogen sources

= set of process hydrogen sinks

Parameters 35



F SKj = flowrate of each process hydrogen sink, mol/s F SRi = flowrate of each process hydrogen source, mol/s yHHU2 = hydrogen composition of hydrogen utility, mole fraction

yHarbitrary = arbitrary hydrogen composition, mole fraction 2 yHSKj2 = lower limit of inlet hydrogen composition for hydrogen sinks, mole fraction yHSRi2 = outlet hydrogen composition for hydrogen sources, mole fraction yHprod = hydrogen composition of PSA product, mole fraction 2 sys Floss = total flowrate loss for direct reuse/recycle system, mol/s

R = hydrogen recovery of PSA

 = conversion factor

Variables F ex = flowrate of external hydrogen source, mol/s pinch Fabove = flowrate needed above pinch point, mol/s

 Fnet = net flowrate in νth impurity level, mol/s

M cum = cumulative mass load of the νth impurity level, mol/s

F in = inlet flowrate of purifier, mol/s F HU = flowrate of hydrogen utility, mol/s F prod = product flowrate of purifier, mol/s F resd = residual flowrate of purifier, mol/s yHin2 = inlet hydrogen composition of purifier, mole fraction

yHcg2 = hydrogen composition of converted gas, mole fraction yHresd = residual hydrogen composition of purifier, mole fraction 2 resd Ffuel = residual flowrate of purifier discharged to the fuel system, mol/s sys Ffuel = residual flowrate of purifier allocated to the direct reuse/recycle system, mol/s

36


Page 36 of 51

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F wh = flowrate of waste hydrogen stream, mol/s F cg = flowrate of converted gas, mol/s F cg1 = flowrate of converted gas to PSA, mol/s F cg2 = flowrate of converted gas to the direct reuse/recycle system, mol/s y = impurity composition for νth hydrogen composition level, mole fraction y ex = impurity composition of external hydrogen source, mole fraction

Subscripts/Superscripts cum = cumulative ex = external in = feed of purifier max = maximum min = minimum net = net flowrate or load pinch = pinch point prod = product of purifier resd = residual of purifier ng = natural gas cg = converted gas wh = waste hydrogen stream SRi = ith process hydrogen source SKj = jth process hydrogen sink HU = hydrogen utility or external hydrogen source Abbreviations LCC = Limiting Composite Curve CNHT = Cracked Naphtha Hydrotreater CRU = Catalytic Reforming Unit DHT = Diesel Hydrotreater HCU = Hydrocracker Unit 37



IPT = Improved Problem Table NHT = Naphtha Hydrotreater NNA = Nearest Neighbors Algorithm PSA = Pressure Swing Adsorption SRU = Steam Reforming Unit HT =Hydrotreating HG = Hydrogenation AF = Arofining IS = Isomerization RG = Regeneration TA = Transalkylation DP = Disproportionation

Acknowledgements The authors thank National Natural Science Foundation of China (No. 21878328) for supporting. The research is also supported by Science Foundation of China University of Petroleum, Beijing (No. 2462018BJC003).

Supporting Information

The improved problem tables (Tables S1-S7) are presented in the supplementary file. This information is available free of charge via the Internet at http://pubs.acs.org/.

Author Information

Corresponding Author Tel.: +86-10-8973 9113. E-mail: [email protected].

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Notes The authors declare no competing financial interest.

Reference 1.

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4328. 10. Zhang, Q.; Feng, X.; Liu, G.; Chu, K. H., A novel graphical method for the integration of hydrogen distribution systems with purification reuse. Chemical Engineering Science 2011, 66, (4), 797-809. 11. Bandyopadhyay, S., Source composite curve for waste reduction. Chemical Engineering Journal 2006, 125, (2), 99-110. 12. Saw, S. Y.; Lee, L.; Lim, M. H.; Foo, D. C. Y.; Chew, I. M. L.; Tan, R. R.; Klemeš, J. J., An extended graphical targeting technique for direct reuse/recycle in concentration and property-based resource conservation networks. Clean Technologies and Environmental Policy 2011, 13, (2), 347-357. 13. Hallale, N.; Moore, I.; Vauk, D., Hydrogen: Liability or asset? Chemical Engineering Progress 2002, 98, (9), 66-75. 14. Ng, D. K. S.; Foo, D. C. Y.; Tan, R. R., Automated Targeting Technique for Single-Impurity Resource Conservation Networks. Part 2: Single-Pass and Partitioning Waste-Interception Systems. Industrial & Engineering Chemistry Research 2009, 48, (16), 7647-7661. 15. Liao, Z. W.; Rong, G.; Wang, J. D.; Yang, Y. R., Rigorous algorithmic targeting methods for hydrogen networks--Part II: Systems with one hydrogen purification unit. Chemical Engineering Science 2011, 66, (5), 821-833. 16. Liao, Z. W.; Rong, G.; Wang, J. D.; Yang, Y. R., Rigorous algorithmic targeting methods for hydrogen networks--Part I: Systems with no hydrogen purification. Chemical Engineering Science 2011, 66, (5), 813-820. 17. Deng, C.; Zhou, Y.; Chen, C.-L.; Feng, X., Systematic approach for targeting interplant hydrogen networks. Energy 2015, 90, Part 1, 68-88. 18. Prakash, R.; Shenoy, U. V., Targeting and design of water networks for fixed flowrate and fixed 40


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Graphical abstract

42


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(a) Hydrogen network with additional PSA

(b) Integration of PSA in Hydrogen Production Plant Figure 1. Schematic diagram for mass flows of hydrogen network with purification reuse/recycle



Figure 2. Systematic procedure of generalized improved problem table

(a) Limiting composite curve


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(b) Supply lines for hydrogen utility & product of PSA

(c) Optimal composite hydrogen supply line Figure 3. Limiting composite curve and optimal hydrogen supply line for example 1: (a) Limiting composite curve; (b) Supply lines for hydrogen utility & product of PSA; (c) Optimal composite hydrogen supply line;





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Figure 6. One optimal hydrogen network for Scenario 2 (flowrate unit is mol·s-1, hydrogen composition is in brackets)


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Figure 7. One optimal hydrogen network for Scenario 3 (flowrate unit is mol·s-1, hydrogen composition is in brackets)



Figure 8. Hydrogen network for integrated hydrogen production and purification unit (Scenario A) (flowrate unit is mol·s-1, hydrogen composition is in brackets)

Figure 9. Hydrogen network for integrated hydrogen production and purification unit (Scenario B) (flowrate unit is mol·s-1, hydrogen composition is in brackets)


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mol/s 500

466.25

450 400

340.79

350

301.8

312.16

300 250 200

195.45

150 100

106.4 65.94

77.77 71.24

50 0

Hydrogen utility

Converted gas

Literature25

Scenario A

Natural gas Scenario B

Figure 10. Results comparison for different Scenarios

Graphical abstract


Design of Hydrogen Network Integrated with the Shared Purifier in

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