Hydrogenation and TMP Coupling Process: Novel Process Design

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Process Systems Engineering

Hydrogenation and TMP Coupling Process: Novel Process Design, Techno-Economic analysis, Environmental Assessment and Thermo-economic Optimization xin zhou, Hui Zhao, Xiang Feng, Xiaobo Chen, and Chaohe Yang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.9b01681 • Publication Date (Web): 15 May 2019 Downloaded from http://pubs.acs.org on May 17, 2019

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Industrial & Engineering Chemistry Research

Hydrogenation and TMP Coupling Process: Novel Process Design, Techno-Economic analysis, Environmental Assessment and Thermo-economic Optimization Xin Zhou, Hui Zhao, Xiang Feng, Xiaobo Chen, Chaohe Yang* (State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao, Shandong 266580, People’s Republic of China)

Abstract: The production of high-quality gasoline and light olefins harbors tremendous industrial and economic significance. In this paper, a novel process is proposed for converting inferior light cycle oil (LCO) into propylene and ethylene, as well as the high-octane-number gasoline with rich BTX contents. The unique feature for the novel process is the integration of LCO selective hydrogenation unit with two-stage riser catalytic cracking. For comparative techno-economic and environmental analyses, typical two-stage riser catalytic cracking for maximizing the propylene (TMP) process and conventional residue fluid catalytic cracking (RFCC) process models are developed. Based on the detailed process modeling and simulation results, techno-economic evaluation and environmental assessment have been performed. It is found that the novel process, coupled hydrogenation and TMP process, has a favorable impact on both the economic and environmental performances. The HTMP process has the highest net present value that means 2.13 times of TMP and 4.94 times of RFCC process, and reduces 15.26 t CO2 equivalents per million dollars output value compared with the TMP process. Moreover, we conduct the thermoeconomic optimization for the HTMP process based on the exergy analysis. The result shows that full scale hydrogenation and recycling of hydro-LCO and increasing of the second riser outlet temperature could significantly increase the profitability of this novel process. Key words: Catalytic cracking; LCO Hydrogenation; Techno-economic Analysis

TOC:

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1. Introduction The fluid catalytic cracking (FCC) process plays an important role in converting heavy cuts into light products.1 FCC gasoline and light cycle oil (LCO) are widely used as blending cuts of commercial gasoline and diesel in China.2 As a result, FCC units provide over 70% commercial gasoline and 30% diesel.3 However, as the feedstocks are becoming heavier and the operating conditions becoming stricter, the quality of FCC products is becoming worse, especially for LCO. One of the typical characteristics of LCO is its abundant aromatic content, especially polycyclic aromatic hydrocarbons (PAHs), which directly induces its low cetane number.4, 5 LCO is greatly deteriorated in quality and can hardly be improved even in some extreme cases.6 Accordingly, LCO is not an ideal blend composition for clean diesel, and what’s more, the direct introduction of LCO into the diesel fuel will reduce the overall quality of diesel. Moreover, the market share of diesel decreased in recent years, and the demand for high-quality vehicle gasoline, light olefins and BTX increased considerably.7-10 Therefore, how to convert these inferior LCO with abundant PAHs into high-octane-number (HON) gasoline and petrochemicals (i.e., ethylene, propylene and BTX) became a challenge problem. Previous experimental investigation indicated, as Figure 1, when treated in selective hydrogenation process, the PAHs can be partially saturated to naphthenic aromatics, which can be further cracked into single-ring aromatics constituting the HON gasoline.11-13 In general, the inferior LCO could also become potential feedstock for producing 2


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HON gasoline through the hydrogenation and FCC coupling process. Two-stage riser catalytic cracking for maximizing the propylene (TMP), which is characteristized by increasing light olefins and liquid yields,14-17 could be a preferable platform to develop further coupled hydrogenation and TMP process, namely the HTMP process. The unique feature of the HTMP process is the segmented feed strategy of hydro-LCO and heavy oil. So far, detailed experimental investigation of industrial risers and hydrotreating reactors is still a challenging task.18 However, rigorous simulation models validated with plant or pilot-scale data can identify key areas for the process development and improvement.19 And several studies executed modeling of hydrotreating and catalytic cracking units using commercial simulators such as Aspen HYSYS.20-25 The main objective of this investigation is to develop the HTMP process model for producing HON gasoline and petrochemicals, and to make comparisons with the conventional RFCC (residue fluid catalytic cracking) and TMP process to determine the most energy-efficient and cost-effective process design. Environmental assessment has been conducted to evaluate and compare the impact of environment via the RFCC, TMP and HTMP process. In addition, systematic thermos-economic optimization has been proposed for the HTMP process design to identify the optimal process parameters. It is hoped that the insights in this work are of reference importance to reducing diesel-to-gasoline consumption ratio and the support of the technologies to integrate refining chemical industry.

Figure 1. Reaction network of PAHs in the coupled hydrogenation and TMP process.

2. Overall Process Description 2.1 The RFCC Process 3



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We begin with an illustration of a typical RFCC process aimed at maximizing gasoline and diesel. As depicted in Figure 2(a), vacuum gas oil (VGO) or residue oil are injected into the RFCC unit (B101) and cracked into light fractions, then the fractionation train (B102) is employed to separate the products. Accordingly, multiple light gas and distillate products, including dry gas, propylene, mixed C4 (C4s), gasoline, LCO, HCO (heavy cycle oil) and slurry, can be separated off. The HCO separated from B102 is recycled and injected into the riser reactor.

2.2 The TMP Process A recycling strategy included in the TMP process design employs the fractionation train (B202). In the TMP process shown in Figure 2(b), VGO or residue oil are injected into the first riser of the TMP unit (B201) and cracked into light fractions, then the fractionation train is employed to separate the products. Hence, light gas and distillate products, including dry gas, propylene, C4s, light FCC gasoline (LCG), gasoline, LCO, HCO and slurry, can be separated off. The C4s separated from B202 is recycled and injected into the first riser, while LCG, LCO and HCO are recycled into the second riser where the reaction temperature is higher than the first riser and suitable for further cracking and maximizing propylene. The combination technology of light and heavy feedstock in the TMP unit is superior. For example, the riser out temperature (ROT) of the second riser is about 540℃, while the catalyst to oil ratio is over 18.

2.3 The HTMP Process On the basis of the aforementioned TMP process design, we propose a highly technology-integrated novel process design that combine the LCO selective hydrogenation unit with the TMP process, termed “HTMP process”. The unique feature of the HTMP process is the segmented feed strategy of hydro-LCO and heavy oil and aimed at maximum propylene and HON gasoline. As Figure 2(c) shows, VGO or residue oil and C4s are injected into the first riser. The effluent from the TMP unit (B301) is then sent to the fractionation train (B302), and separated into dry gas, propylene, HON gasoline and other products. The difference between the TMP process and HTMP process is that LCO from B302 is first fed into the selective hydrogenation block (B303). After being selective hydrotreated, the hydro-LCO, combined with LCG and HCO, is recycled and injected into the second riser. Notably, the ratio of the recycled LCO to the whole of feedstock (LRR) in the TMP and HTMP process, however, impacts not only the 4


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product yields and properties but the process energy consumption, so it is a significant process parameter. Details of each process design are given in the following subsections.

Figure 2. Block flow diagrams of three process designs for multiple products produced from VGO or residue oil: (a) RFCC process design, (b) TMP process design, and (c) HTMP process design.

3. Process Modeling In this study, atmospheric residue (AR) derived from Daqing crude oil (a paraffin-based crude oil) has been proposed as the feedstock for all process designs. A scaling-up design of 238 t/h processing capacity and 8400 h/yr operating time has been proposed according to the reported industrial scale commercial demonstration plant data.17, 26

The quality of the feedstock, characteristized by the density, content of sulfur and nitrogen, PNA and other

physical properties, plays an important role in process simulation and techno-economic analysis. Table S1 in the Supporting Information gives the physical properties of the feedstock in this work. To overcome the limitations of the distillation method and the missing physical properties data, Sanchez et al.27 proposed a method to fit distillation curves of different crude oils and petroleum fractions by the cumulative β 5



function involved in four parameters. Pashikanti and Liu

19

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also presented a correlation to estimate PNA by the

calculation of a series of parameters including molecular weight, density, viscosity, refractive index, etc. Then they used the PNA parameters to ensure the properties of FCC feedstock estimated in the “back-blending” of Aspen HYSYS FCC model.28 It is noteworthy that the analysis data of feedstock properties including density, PNA, content of sulfur, nitrogen and metal (shown in Table S1) is relatively complete. And what's more, we need detail material stream information of the feedstock to develop exergy analysis models.29 Therefore, an external feed information model is carried out for the purpose of calculating more accurately.23

3.1 RFCC Unit The Aspen HYSYS Petroleum Refining FCC model has been used to simulate the RFCC unit and satisfy the riser-regenerator heat balance in order to establish a complex 21-lump kinetic model.30 The FCC reactor unit module uses 21-lump kinetic lumps which derived from the Mobil ten-lump mechanism and divides the reactants and products into lumped aggregates of material classified by chemical type and boiling point range. The 21-lump kinetic model includes 40 reactions. The key advantage of this lumped kinetic model is that the composition of lumps can be measured with various experimental techniques. 31 The network of kinetic pathways is shown in Figure S1. The FCC model of Aspen HYSYS is integrated with a series of submodels which can simulate the whole operation unit and satisfy the riser reactor and regenerator heat balance at the same time.30, 31 For the RFCC and TMP unit model, our work is further in-depth development on the basis of FCC model built-in Aspen HYSYS. Single riser reactor and one-stage regenerator type are applied in the RFCC model. The structural dimension parameters and operating parameters of the RFCC unit are from an industrial RFCC unit in northeast China. The structural dimension parameters of the RFCC unit model are shown in Table S2 and the key operating parameters are listed in Table S3. A strategy of modeling steps has been proposed for better and faster convergence of the RFCC and TMP unit model, as shown in Figure 3. The routine colored green is the modeling and calibrating procedure applied in this paper. The final convergence calibration data sets are shown in Table S4. Compared with the internal estimation modeling method, the external feed information model and FCC modeling strategy, which validates their accuracy and feasibility, has better convergence, and can be applied to develop other FCC units 6


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modeling.

Figure 3. Procedure for modeling of the RFCC and TMP unit

3.2 TMP Unit Figure 4(a) illustrates the flowsheet of TMP unit and integrated fractionation train (IFT). As the reaction section shown in the figure, AR, mixed with C4s, is fed into the spray nozzle at the bottom of the first riser. LCG, LCO/hydro-LCO and HCO are recycled into the second riser for further cracking. Meanwhile, a series of measures to enhance catalytic cracking reactions such as a suitable reaction temperature (510℃-540℃) and short residence 7



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time (1.3s-1.9s) should be adopted to prevent over cracking. As for the establishment of the TMP unit model, the type of two-riser reactor and one-stage regenerator is applied. The structural dimension parameters of the TMP unit are from an industrial deep catalytic cracking unit in east China. The key operating parameters of the TMP unit are from our industrial-scale plant. The structural dimension parameters of the TMP unit model are shown in Table S5 and the key operating parameters are listed in Table S6. The final convergence calibration data sets are shown in Table S7.

3.3 Integrated Fractionation Train The integrated fractionation train (IFT) consists of three parts, fractionator, absorption and stabilization system and gas separation plant. As the IFT shown in Figure 4(a), it is applied to the TMP and HTMP process. And for the RFCC process, only the gasoline fractionator (T-110) is not included in the IFT. The effluent from R-101 is sent to the main fractionator (T-101). A part of LCO product from the stripper (T-102) is then condensed and drawn off as the sponge oil to recover gasoline components in the reabsorption column (T-105). The other part of the LCO is sent to the LCO hydrotreating unit. A portion of the stabilized gasoline product from the bottom of T-106 is split off and then pumped to T-103 as the sponge oil. The stabilized gasoline which contains a regulated amount of C4 components leaves as the feed material to T-110. The overhead liquid, LCG, is recycled back to the second riser to reduce olefins content of gasoline. Then, LPG is fed into the depropanizer (T-107), where separates most of the C3 into the overhead liquid. The bottom liquid, C4s, is then recycled back to the first riser. The bottom liquid of T-108 is heated and fed into the propylene distillation column (T-109). Ultimately, the overhead product, propylene, is sent out as the product.

8


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Figure 4. Process flowsheets of the TMP and HTMP process: (a) the TMP unit and integrated fractionation train and (b) LCO hydrotreating unit

3.4 LCO Hydrotreating Unit In the HTMP process, an Aspen HYSYS Petroleum Refining hydroprocessor bed (HBED) module which contains 97-lump reaction kinetics and 177 reactions is carried out to simulate the LCO selective hydrogenation bed.25, 32 As shown in Figure 4 (b), after heat transferred by the heat exchanger, LCO from the bottom of T-102 is preheated by the furnace (F-201). In the hydrotreating reactor, there are two treating beds where the hydrodesulfurization (HDS), hydrodenitrogenation (HDN) and the selective saturation reactions occur. Ultimately, the PAHs in the LCO which contains almost 40 wt % binuclear aromatics is selectively hydrogenated to naphthenic aromatics under the condition of 340℃. After heat transfer with a series of heat exchangers, the products are sent into a high-pressure flash separator (V-201) and removed sulfide in the DEA contactor (T-201), and then the gas is pressurized in the recycle gas compressor. The vapor product from the recycle gas compressor is recycled and mixed with the makeup H2 and LCO. The liquid from V-201 is fed into a low-pressure flash separator (V-202). The bottom liquid of V-202 is pumped into T-202. The overhead and bottom liquids are naphtha and hydro-LCO, respectively. 9



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After heat transferred by the heat exchanger, the hydro-LCO from the bottom of T-202 is recycled into the second riser reactor of TMP unit for further cracking reactions to produce HON gasoline rich with BTX. The final convergence calibration data sets of LCO hydrotreating unit (LHU) are shown in Table S8. In this section, we illustrate a novel process, the HTMP process, including with a series of process unit models for the purpose of reducing diesel-to-gasoline consumption ratio as well as maximum propylene and HON gasoline. The RFCC process and TMP process are established for comparison. We also develop the exergy calculation model and extend the application from real components to the pseudo-components through the VB code shown in the appendix of the literature 29 and integrate it in Aspen HYSYS material stream module. The procedure for calculating the exergy flows of real components as well as pseudo-components is shown as Figure S2 in the Supporting Information. The product properties of all the process designs are presented in Table S9-S13 for the purpose of verification and reference in systematic analysis. Therefore, all the process designs are modeled in detail to analyze and compare the techno-economic and exergy performance.

4. Results and Discussion 4.1 Material and Exergy Balance Three different process configuration have been proposed, including RFCC, TMP and HTMP. It is noteworthy that the TMP process (LRR=0) is the same as the HTMP process (LRR=0). Thus, we consider totally 4 cases in this work. For the specified (238 t/h AR input), the material and exergy balance for all cases are presented in Table 1 and 2, respectively. In Table 1, products including C4s, slurry, coke and fuel products are shown in mass percent (wt%). In Table 2, the overall exergy efficiency is shown in MW. In order to obtain the catalytic pyrolysis reaction performance of hydro-LCO and LCO, the conversion and selectivity of recycling hydro-LCO compared with LCO was conducted in Table S14. The simulation parameters for other separation columns are shown in Table S15. We ensure accurate mass and exergy balance on each unit operation in the 4 cases by presenting the detailed data and using a built in unit module, Aspen HYSYS spreadsheets.

10


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Table 1. Overall Material Balance for the 4 Cases The TMP process

The RFCC process

The HTMP process

LRR=0

LRR=0.171

LRR=0.171

Inputs (wt%) AR

100.00

100.00

100.00

100.00

H2 a

-

-

-

0.27

3.27

5.23

5.50

5.55

0.79

2.31

2.41

2.44

Propane

1.06

3.42

3.75

4.07

Propylene

4.56

20.16

20.35

20.70

C4s

9.65

13.49

14.58

15.27

Gasoline

49.33

29.25

31.95

37.15

LCO

23.22

17.10

10.32

5.29

2.39

4.07

2.92

Outputs (wt%) Dry gas Ethylene (included in dry gas)

Slurry

a The

Coke

8.91

8.96

9.48

9.32

Total

100.00

100.00

100.00

100.27

mass flow of H2 in all designs is based on fresh feedstock mass basis.

Exergy analysis illustrates the intrinsic thermodynamic efficiency of chemical processes, and improves the key factors of the efficiency loss, and optimize the operation costs.33 In other words, most of the efficiency loss or energy waste in a process can be distinguished by exergy analysis, and what’s more, the methods of economic analysis and optimization can be developed subsequently. We can obtain the in-depth exergy analysis of each process unit by accessing the physical and chemical exergies of process streams within the flowsheet of Aspen HYSYS.33, 34 The overall exergy balance shown in Table 2 consistently describes that for given feed exergy flow (2548.2 MW input). Apparently, in the 4 case studies, the integration level of process models has a profound effect on the exergy destruction as well as exergy efficiency. The HTMP process has a relatively low exergy efficiency rate and high exergy destruction. For example, the overall exergy efficiency of HTMP process is 1.80% and 4.0% less than that of the TMP process (LRR=0) and the TMP process (LRR=0.171), respectively. This is predominate because 11



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the HTMP process involves most chemical conversion units, such as the TMP unit and LHU. The aforementioned differences in exergy efficiency result predominately from different utility consumption including heat (coke heat of combustion), cold (cooling water), electricity, steam and water. As listed in Table 2, the RFCC processes require the least process utilities, while the HTMP and TMP process (LRR=0.171) consumes around 1.2 times of the total utilities compared to that of RFCC processes. Table 2. Overall Exergy Balance for the 4 Cases The TMP process

The HTMP process

The RFCC process LRR=0

LRR=0.171

LRR=0.171

Inputs (MW) AR

2548.2

2548.2

2548.2

2548.2

Hydrogen

-

-

-

23.7

(U1) Heat

297.8

238.7

290.2

277.4

(U2) Cold

44.6

90.4

91.1

103.4

(U3) Electricity

6.5

7.9

8.0

8.7

(U4) Steam

64.6

76.1

77.5

81.6

(U5) Water

0.22

0.71

0.76

0.85

Dry gas

67.8

80.1

81.9

87.5

Propane

31.1

110.8

120.4

122.8

Propylene

115.2

381.3

401.7

413.2

C4s

272.6

382.7

391.2

410.0

Gasoline

1366.3

915.3

1038.9

1081.4

LCO

622.3

469.1

227.4

117.3

Slurry

-

64.8

122.5

88.0

Heat

20.3

29.8

30.2

33.1

86.2

84.6

82.4

80.4

Process Utilities

Outputs (MW)

Overall exergy efficiency %

In-Depth exergy analysis of each process unit in the 4 cases is necessary to make sure the contributions to primary exergy destruction. Figure 5 (a) presents the total exergy destruction of the proposed process designs. As aforementioned before, the HTMP process leads to the highest exergy destruction, resulting in the lowest exergy efficiency in all the process models. The main contribution to exergy destruction is from the TMP unit and IFT, as 12


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shown in Figure 5 (b)−(d).

Figure 5. Results of exergy destruction: (a) overall exergy destruction of the 3 process designs and (b) the detailed exergy loss contributions of the RFCC process and (c) the TMP process and (d) the HTMP process.

In the RFCC and TMP unit, the chemical exergy degrading and the irreversibility of heat transfer between catalysts which are at high temperature and feedstock as well as the total smoke heat loss are the main resources of exergy destruction. As shown in Figure 5 (b)-(d), the exergy destruction of the IFT is between 165.77 MW and 182.93 MW, and the main fractionator column occupies an average proportion of 60.4%. That proves the exergy destruction of the main fractionator column is the biggest bottlenecks, and the exergy destruction of absorptionstabilization and gas separation system account for a less proportion because of the lower operating temperature. We also note that, however, the reason leading to this result is that the exergy destruction of heat transfer of the fractionation process and the mixing of non-isothermal material streams are universal. For the LHU, the outgoing exergy flows of hydro-LCO is not very apparent because of hydrogenation reaction. Significantly, the exergy destruction of LCO hydrogenation process is mainly due to the reaction irreversibility of selective conversion of multi-ring aromatics into single-ring aromatics and hydrodesulfurization.

4.2 Techno-economic performance 13



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It is feasible to co-produce refined oil and petrochemicals simultaneously using VGO or AR as feedstock from a technological point of view. However, whether the proposed process designs can be applied in the industry mainly depend on whether the process is economically profitable. Accordingly, techno-economic analysis and evaluation must be carried out in this section. The capital needed for manufacturing and plant facilities is termed as the total direct capital cost (TDC).35 TDC is estimated by the production capacity index approach which is defined as: m

m

i 1

i 1

TDC   CE ,i =  CBasic  (

Q  )  f (1) QBasic

Where m is the total equipment unit in each process design; corresponding to the actual capacity Q ;

CBasic

CE ,i is the capital cost of the subsystems

indicates the capital cost with the base case capacity

QBasic ;



is the cost scale factor; f is the comprehensive adjustment factor. After capital cost evaluation, the indirect plant expense (IPE) is estimated as 32% of the TDC.36 The IPE includes costs for engineering and supervision, startup, spares, construction expenses, legal, contractor fees, and contingency cost. The TDC and IPE make an estimate of the total plant capital cost (TPC) required for the project. Then, the TPC can be converted to total annualized cost (TAC), which is given by:

TAC  TPC  CRF  ARC  AOC (2)

CRF = i (i +1) N [(i  1) N  1] (3) where CRF represents the capital recovery factor, which is determined as a function of the interest rate (i) and depreciation time of the project (N); ARC represents annual raw material cost; AOC represents annual operating and maintenance cost that consists of steam (Csteam), cooling and fresh water (Cwater), main air flow capacity (CAir), and electricity (Celectricity), as defined by eq 4.

AOC =Csteam  Cwater  Celectricity  C Air (4) The project revenue (Pr) which comes from selling ethylene, propane, gasoline, and diesel at market price and the cost parameters, including TPC, discounted annual rate (Dr), tax rate (Tr), plant life span (PLS) and Pr, are

14


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taken into account for calculating the net present value (NPV) and internal rate of return (IRR), which is used as the economic measurement of the process, as given by eq 5 and 6.7, 37-38

(Pr  TAC )(1  Tr ) (5) (1  Dr )t t =0

PLS

NPV=-TPC +

(Pr  TAC )(1  Tr ) (6) (1  IRR)t t =0

PLS

0=-TPC +

All of these basic parameters and assumptions for economic analysis are listed in Table S16-S17 and the results of the techno-economic analysis of all the process designs are given in Table 3. Table 3.The results of the techno-economic analysis Items

Unit

The RFCC process

total direct cost (TDC)

M$

indirect plant expenses (IPE)

The TMP process

The HTMP process

LRR=0

LRR=0.171

LRR=0.171

210.58

227.80

227.80

243.50

M$

67.39

72.90

72.90

77.92

total plant capital cost (TPC)

M$

277.97

300.70

300.70

321.42

annualized operating cost (AOC)

M$/year

2.68

6.36

6.42

6.74

annualized raw material cost (ARC)a

M$/year

1243.59

1243.59

1243.59

1256.53

total annualized cost (TAC)

M$/year

1278.75

1285.08

1285.14

1300.82

a: The price of Daqing crude oil is based on the Brent crude oil price of 80 US dollars /barrel. The cost of hydrogen production (using coal as raw material) in the ARC of HTMP process is considered.

As can be seen from Table 3, in all the 4 case studies, the HTMP process (LRR=0.171) not only represents higher TPC but also requires more AOC. The TPC of the HTMP process (LRR=0.171) is 6.89% higher than that of the TMP process (LRR=0.171). Similarly, from the AOC aspect, compared with the TMP process (LRR=0.171), the HTMP process (LRR=0.171) is higher by 4.98%. Compared with the TMP process (LRR=0) and RFCC process, the AOR of the HTMP process (LRR=0.171) increases about 1.06 times and 2.51 times, respectively. What’s more, for the HTMP process, the total annualized cost (TAC) is 1.01-1.02% times higher than that of other process designs. In conclusion, by recycling hydro-LCO, the HTMP process is more profitable, and it is notable that the mass yield of HVPCs and HON gasoline has a significant influence on the economics because their market price is substantially higher than that of other products. On the basis of cost estimation, we can get the breakdowns of the TAC distribution, as shown in Figure 6. 15



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TAC contains raw material, equipment, annual operating cost, and indirect plant expense. The breakdown of TAC indicates that it is highly dependent on the raw material cost, which makes up 96.60-97.25% of the TAC. This strongly suggests the fact that the raw material cost is crucial to the annual total net profits. The less significant contribution is AOC followed by the IPE and TDC for equipment purchasing and installation, each accounting for 0.21-0.52%, 0.62-0.70%, and 1.92-2.19% of the TAC, respectively.

Figure 6. Breakdown of the TAC distribution

Figure 7 (a) illustrates the results of the estimated NPV for all case studies based on the techno-economics analysis results. Similarly, we can conclude that the highest NPV, the HTMP process (LRR=0.171), is 2.13-4.94 times greater than that of TMP and RFCC processes. Taking TMP and HTMP process for example, the estimated NPV increases 1.08 times from $26.60M in the TMP process (LRR=0) to $28.61M in the TMP process (LRR=0.171); finally, the NPV is increased to $58.32 M in the HTMP process (LRR=0.171). From what has been mentioned above, we can come to the conclusion that the LRR plays a more important role in project economics. In addition, as shown in Figure 7 (b), the highest IRR, 22.82%, is also the HTMP process (LRR=0.171). Although the HTMP process designs have an adverse impact on both the capital cost and overall exergy efficiency, it can obviously increase the profitability and accelerate the recovery of foundation and decrease the economic risk of the project.

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Figure 7. The results of economic performance: (a) NPV and (b) IRR.

4.3 Environment analysis The object of environment analysis is to evaluate and compare the environmental impacts of producing light fuel oil fractions and petrochemicals from Daqing AR via the proposed processing designs. The impact category to assess the environmental performance via the four cases is dedicated to greenhouse gases (GHGs) emissions, which arouse special interest in both academia and industry.39 Because the steps of RFCC, TMP and HTMP produce more than one product and the desired products of the three processes are different, the basic unit of the environmental analysis study is defined as total output value per million dollars in this paper. In addition, the corresponding mass and energy flows as well as the associated environmental burdens must be allocated to each of the products to accurately reflect their individual contributions to the environmental impacts of the studied system.40 The definition of the GHGs emissions boundary in this study is from the beginning of Daqing crude oil entering atmospheric and vacuum distillation unit to being processed into target products, as the GHGs emissions from crude oil extraction and transportation are not the main concerns of our study and the end-of-life phases of the target products could vary significantly. The system boundaries of the three processes are demonstrated in Figure 8. The corresponding mass and energy balance information on each unit is determined by HYSYS simulation. Data used to estimate the GHGs emissions during the refinery processing are collected from the corresponding mass and energy balance information on each unit in Aspen HYSYS. Data used to estimate the GHG emissions are from existing publications.40, 41

17



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Figure 8. System boundaries of manufacturing propylene and gasoline via RFCC, TMP and HTMP process from crude oil.

The inventory of GHGs emissions via three processes is depicted in Fig. 9-12. GHG emissions can be counted as the sum of direct emissions and indirect emissions. Direct emissions are generally from catalytic coke burning and process emissions, while indirect emissions are those from process energy production, such as electricity and steam. In this study, process air, steam and other process utilities are all classified as standard oil, while catalytic coke burning consumes feedstock instead of energy, and this term is not classified as standard oil. In addition, three types of GHGs emissions are accumulated with their CO2 equivalents (CO2 eq) according to their global warming potential value of a 100-year time period at last. The GHGs emissions (CO2 eq) can be calculated by Eqs 7. And all units of emission of GHGs, CO2, CH4, N2O are t.

GHG  CO2 eq   CO2  25  CH 4  298  N 2O (7)

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Figure 9. Process data of production one million dollars output value via RFCC process.

Figure 10. Process data of production one million dollars output value via TMP process (LRR=0).

Figure 11. Process data of production one million dollars output value via TMP process (LRR=0.171).

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Figure 12. Process data of production one million dollars output value via HTMP process (LRR=0.171).

Figure 13 shows the breakdowns of the equivalent GHGs emissions from the 4 case studies. As depicted in Figure 13, producing one million dollars output value, the amount of carbon dioxide produced by the TMP process (LRR=0.171) is the largest, while the amount of carbon dioxide produced by the RFCC process is least. By recycling hydro-LCO, the HTMP process (LRR=0.171) reduces 7.36 and 15.26 t CO2 eq/million dollars output value compared with the TMP process (LRR=0) and the TMP process (LRR=0.171), respectively. The catalytic reaction and separation units are the major source, which contributes over 75% of the total GHGs emissions. The other process units (including gas fractionation and LCO hydrotreating) also lead to considerable GHG emissions that occupy about 8%-17% of the total GHGs emissions. Compared with the contributors, the production of Daqing AR leads to the least GHGs emissions, taking up about 8%-9% of the total GHGs emissions. Figure 14 shows the breakdowns of the total GHGs emissions for the 4 case studies. It could be seen that CO2 represent the major emissions, and the other two emissions are less.

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Figure 13. Equivalent GHGs emissions of the 4 case studies.

Figure 14. Total GHGs emissions of the 4 case studies.

4.4 Sensitivity Analysis Economic parameters, such as feedstock prices, product prices, productivity and TDC are volatile in most circumstances, however, it is worth investigating how these parameters could affect the economic performances of the three processes. Therefore, sensitivity analyses are conducted to examine the influences of altering parameters on economic performances. Figure 15 illustrates the sensitivity analysis results for the economic parameters of propylene produced via the three processes. The price of raw materials has the greatest impact on the IRR of all the processes, followed by the product price, and the change of productivity and TDC on the processes lead to the least impact on IRR. 21



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Figure 15. △IRR sensitivity analysis results of the 4 case studies.

4.5 Thermo-economic analysis and optimization The overall exergy efficiencies are determined through exergy analysis of 4 case studies, especially exergy destruction in the degradation of chemical reaction and the irreversibility of heat transfer process. As mentioned before, increasing LRR in both the TMP process and HTMP process can significantly improve the revenue, but it also decreases exergy efficiency of the overall system and leads to higher operating cost and utilities. Notably, high exergy efficiency does not mean that the techno-economic performance is optimal. In this study, we also found that increasing ROT of the second riser (SROT) can promote pyrolysis reactions of LCO/hydro-LCO and the generation of single-ring aromatic constituting the HON gasoline. However, the severe high reaction temperature will lead to dehydrogenation reactions of PAHs and increase the mass yield of coke. Therefore, thermo-economic analysis, combined thermodynamic analysis with economic analysis, must be carried out to explore the influence of the LRR and SROT on the techno-economic performance and exergy efficiency of all the process designs and to seek the optimal model parameters. The thermo-economic analysis and optimization models for TMP and HTMP processes are built on the basis of exergy cost equation and the exergy equilibrium equation, as given by eq 8- 12. s

t

j 1

i 1

m

Object : max NPV =  C j E j   Ci Ei   Z k (8) k 1

22


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Constrain : E j  f ( LRR, SROT , Ei ) (k  1, 2,..., m) (9)

Z k  k ( Z 0 , LRR, SROT , Eik ) (k  1, 2,..., m) (10) 0.02  LRR  0.20 (11) 525  SROT  555 (12) where

Ei

and

E j denote the input and output exergy of the whole corresponding system, respectively;

f means the function between the input and output exergy of the k th subsystem; Ci and C j is the unit exergetic cost;

Zk

represents the TAC of the system;

by polynomial regression among

SROT=535℃, LRR, SROT and

 means the function relationship which can be obtained

Z 0 , which denotes the TAC of the system in the k th subsystem at LRR=0 and Eik .

Figure 16. The relationship of optimized results of the TMP process among NPV, SROT and LRR

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Figure 17. The relationship of optimized results of the HTMP process among NPV, SROT and LRR

Figure 16 provides a comprehensive thermo-economic analysis and optimization result. The optimized result of SROT=530℃, LRR=0.185 and the maximum economic benefit, $28.93M, are obtained through solving the thermos-economic optimization function of the TMP process. As Figure 16 shown, the profit of the whole model decreases when the value of LRR exceeds 0.185 and the SROT exceeds 530℃. The main reason is that the overcracking of gasoline and the selectivity of LCO converting to LPG and gasoline decrease with the increase of SROT. The optimized result of ROT= 540℃, LRR=0.201, and the maximum economic benefit, $59.39M, are obtained through solving the thermos-economic optimization function of the HTMP process. Figure 17 shows that the max profit increases with the increase of SROT, but decreases when the SROT exceeds 540℃. It is noteworthy that the max benefit increases with the increase of LRR until all the hydro-LCO is recycled. In conclusion, the refined oil produced via the RFCC process has the highest exergy efficiency and lowest production costs but the lowest profit. The HTMP process is preferably to achieve the max benefit for manufacturing high-octane-gasoline and petrochemicals.

5. Conclusions In this work, a novel process, namely the HTMP process, has been proposed for the production of highoctane-gasoline and petrochemicals. Recycling of hydro-LCO was integrated with the HTMP process for a better produce yield and better economic profit as well. For the purpose of systematic comparisons, RFCC and TMP was 24


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employed as benchmark processes. Detailed exergy analysis, techno-economic, GHGs emissions and thermoseconomic analysis further proved the advantages of HTMP process. The technoeconomic advantages of the HTMP process mainly come from the reasonable and effective conversion of PAHs, which optimize the product distribution and enhances the conversion of LCO to high value products. Moreover, as for the environmental impacts the HTMP process (LRR=0.171) reduces 7.36 and 15.26 t CO2 eq/million dollars output value compared with the TMP process (LRR=0) and the TMP process (LRR=0.171), respectively, by recycling hydro-LCO strategy. Finally, the thermoseconomic optimization model was established and the optimized process parameters, LRR and SROT, are obtained for the TMP and HTMP process. Using the optimized process parameters, the NPV for the TMP and HTMP process was $ 0.32M and $ 1.07M higher than that of un-optimized processes.

Supporting Information Input data, feedstock properties, and model parameters (Table S1-S17; Figure S1-S2) are available in the Supporting Information. Corresponding Author *Email: [email protected]. ACKNOWLEDGMENT This work was financially supported by the National Natural Science Foundation of China (21476263 and U1462205) and the Fundamental Research Funds for the Central Universities (18CX06069A). REFERENCES (1) John, Y. M.; Patel, R.; Mujtaba, I. M. Maximization of Gasoline in an Industrial Fluidized Catalytic Cracking Unit. Energy Fuels 2017, 31, 5645-5661. (2) Chen, J. W.; Xu, Y. H. Process & Engineering of Catalytic Cracking; China Petrochemical Press: Beijing, 2015. (3) Xu, Y. H. Advance in China Fluid Catalytic Cracking (FCC) Process. Zhongguo Kexue: Huaxue 2014, 44, 13-24. (4) Calemma, V.; Ferrari, M.; Rabl, S.; Weitkamp, J. Selective Ring Opening of Naphthenes: From Mechanistic Studies with a Model Feed to the Upgrading of a Hydrotreated Light Cycle Oil. Fuel 2013, 111, 763-770. 25



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Hydrogenation and TMP Coupling Process: Novel Process Design

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