Visbreaking Unit Simulation Model for the Prediction of Process Performance and Residue Stability

Sara Sousaa, Filipa Ribeiroa, Ana Rita Costab

a Departamento de Engenharia Química, Técnico Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisboa, Portugal b Galp, Rua Tomás da Fonseca - Torre C, 1600-209 Lisboa, Portugal content in bunker fuels has been reduced in order to decrease emissions of sulfur oxides into the atmosphere. In January 2020, the sulfur content in bunker fuels will be limited to 0.5%wt. The production of this fuel requires processing sweet crudes in Galp refineries. This is a challenging situation because these crudes have a higher tendency to instability. In this work, a rigorous simulation model of the visbreaking unit was developed, using the Petro- -Sim™ software, which allows a good prediction of yields, product properties, including visbreaker residue stability. This is the main component of fuel. The simulation model was solved through two methods for maximum visbreaker conversion calculation, KBC 1985 and KBC 2005. KBC method 1985 presents a good prediction of visbreaker residue stability. For KBC 2005 method, simulation model predictions are more dependent on feedstock quality and more representative of reality. A delta-base vector structure was created and allows the implementation of the data generated by the simulation model in Galp linear programming model. This structure was validated using a linear representation model. The implementation in the linear programming model of the visbreaker unit simulation model will allow an efficient and optimized selection of crudes that will maximize the refining margin, ensuring the production of low sulfur fuel oil.

KEYWORDS: Visbreaker, Petro-Sim™, Delta-Base Vectors, Thermal , Visbreaker Residue Stability, Refining

Fuel oil produced in Galp refineries can be 1 Introduction composed by atmospheric, vacuum and visbreaker residues. The visbreaker residue Fuel oil, used as a bunker fuel, causes large (RVB) is the most commonly used in the emissions of SOx (Sulfur Oxides) into the production of fuel oil, since its use brings an atmosphere, which are harmful to human health economic advantage. and to the environment. IMO (International Maritime Organization), a specialized agency of the United Nations, is the 1.1 Objectives global standard-setting authority for the safety, This work addresses the development of a security and environmental performance of simulation model of Sines visbreaking unit in international shipping. In order to reduce SOx Petro-Sim™ software. This model will predict emissions from ships, the sulfur content limit in unit performance and RVB stability depending fuel oil has been progressively reduced. As on the type of the unit feedstock. This model will from January 2020, there will be a substantial be implemented in Galp linear programming cut in the sulfur content limit, from 3.5%wt (High (LP) model in order to select the crudes that Sulfur Fuel Oil – HSFO) to 0.5%wt (Very Low maximize refining margin ensuring the Sulfur Fuel Oil – VLSFO) [1]. production of VLSFO. In order to meet the new IMO regulations, ships can limit the air pollutants installing 2 Visbreaking Unit exhaust gas cleaning systems, also known as scrubbers. 2.1 Process Description The alternative that should be adopted by The refining process starts by feeding the Galp to supply the VLSFO market consists in crude oil, or usually a mixture of crudes (crude mixing residues produced from sweet crudes mix), into an atmospheric unit. Here (sulfur content below 1%wt) with other crude are separated into several fractions components with very low sulfur content (cutter (defined by cut point – the temperature on the stocks). The production of VLSFO is a major whole crude TBP (true boiling point) curve that challenge due to the fuel high tendency for represents the upper and lower limits [2]). instability as well as sediments and coke In Sines refinery, atmospheric distillation has generation. a top gas stream, a naphtha stream, a kerosene

1 stream, two streams of gasoil (light gasoil and severity depends on the operating temperature heavy gasoil) and a bottom stream – and residence time. atmospheric residue (RAT). The RAT yield Variations in feedstock quality will have depends considerably on the crude mix fed to impact in the conversion level obtained at a the atmospheric distillation unit. The heavier the given severity [5]. Thus, the visbrekaer crude oil mixture fed, the higher the RAT yield. operations severity is generally limited by the RAT is then fed to a unit, visbroken product stability. where is produced a vacuum distillate stream, a vacuum gas oil (VGO) and a vacuum residue 3 RVB Stability (RV) stream. RV has high viscosity, which decreases its commercial value. Therefore, RV is fed to a visbreaking unit. A fuel is stable if there is no asphaltenes The main purpose of visbreaking unit (VB) is flocculation. On the other hand, instability may to convert heavy, high viscosity feedstocks, like be irreversible, i.e. precipitated asphaltenes RV, to lower viscosity products suitable for use may not be re-dissolved [6]. To ensure fuel oil in fuel oil. This reduction is obtained by stability it is necessary that RVB is also stable. decomposing heavy molecules into lighter Generally, cutter stocks are paraffinic (gasoil molecules through thermal cracking reactions. and kerosene) and, therefore, RVB stability Since VB operates at low conversions (low degree must be high enough to prevent extensions of thermal cracking reactions), its asphaltene flocculation during blending with main product is visbreaker residue (RVB), with cutter stocks. RVB stability is controlled by a yield of about 80-90%wt. Another benefit from performing a peptizing-value (p-value) test [7]. the visbreaking operation is the production of The p-value provides the peptization state of gas, naphta and gas oil (GOVB) streams that the asphaltenes in residues. A residue is then usually have higher product values than RVB considered stable for a p-value greater than [3]. 1.2. The p-value is obtained by adding cetane Sines refinery has a soaker visbreaker, (paraffinic compound, once paraffins flocculate where the bulk of the cracking reactions occurs the asphaltenes) to the sample under study not in the furnace but in a soaker drum until the asphaltenes begin to flocculate. This downstream the furnace. In the soaker drum property is determined by equation (1), where the heated feedstock is held at high Xmin is the critical dilution in cetane, i.e. the temperature for a predetermined period of time amount of cetane (ml) that can dilute 1g of the allowing cracking to occur. Then soaker effluent sample until asphaltenes flocculation begin. goes to a fractionator column where RVB is This method has a high repeatability, about separated from lighter fractions [3]. 0.07 [7].

2.2 Process Reactions Thermal cracking is the decomposition of 푉푎푙표푟 − 푝 = 1 + 푋푚푖푛 ( 3 ) at elevated temperatures, resulting in the formation of lower molecular There are methods of evaluating the stability weight products and is a first-order reaction [4]. of fuel using other solvents. However, the p-value is a widely used stability indicator and 푣 = 푘 ∙ 푐 ( 1 ) is also used in Galp refineries.

푎 3.1 Asphaltenes − ln ( ) = 푘 ∙ 푡 ( 2 ) 푎 − 푥 Asphaltenes are defined as the insoluble fraction in n-heptane and soluble in and

represent the heavier and more complex During thermal cracking, the saturated fraction of crude oil [8] [9]. Asphaltenes are high (paraffinic) compounds are transformed into polarity compounds composed by a very saturated compounds of lower molecular condensed aromatic and naphthenic structure. weight. In high severity conditions (high Asphaltenes present short paraffinic side temperature) polymerization reactions are chains and also heteroatoms, such as sulfur, favored leading to resins and asphaltenes nitrogen, oxygen and metals. The large number cracking and to coke formation. of aromatic rings gives to asphaltenes a flat

structure [10]. 2.3 Operating Conditions The extent of cracking reactions, i.e. GOVB conversion, and RV visbreaking are controlled by the severity of the unit. The visbreaker

2 4 Visbreaker Unit Simulation Model 4.4 Simulation Model Construction and Calibration In this work it was developed a rigorous The construction of VB unit simulation model simulation model of the VB unit in Petro-Sim ™ requires real unit design and operation data. software, version 7.0. The objective of calibration is to ensure that The visbreaker simulation model currently model represents the real unit performance in used by Galp is a simple planning model that terms of yields and product properties. In calculates yields and product properties calibration the model automatically calculates a according to the average reality of the unit's set of calibration factors to achieve the best operating cycle. This model does not predict the match between the predicted properties values RVB stability produced. and the real properties values. For the VB unit simulation model, In order to ensure that the simulation model Petro-Sim ™ has VIS-SIM ™ technology that mimics reality, the data used for calibration simulates the thermal cracking, based on should be representative of the visbreaking reaction kinetics. operation. The data required for model calibration are 4.1 Maximum Visbreaker Conversion real operating conditions, product yields and Maximum Visbreaker Conversion (MVC), is feed and products characterization in terms of a feedstock characterization parameter and density, viscosity, distillation curve, sulfur depends on the asphaltene content and the content, RVB p-value, wax and asphaltene nature of the feedstock (aromatic or paraffinic). content in the feed stream. These data are The MVC is defined as the conversion at which obtained through laboratory analyzes of a visbroken residue is produced at the stability samples collected directly from the unit running limit (ABN = 46, p-value = 1.15). Conversions in a steady state. above the MVC value do not guarantee a stable The days selected were November 11, 2017 RVB. Petro-Sim™ allows the calculation of this (calibration 11), March 1, 2018 (calibration 1), property using two methods: KBC method 1985 and March 8, 2018 (calibration 8). In calibration (KBC 1985) and KBC method 2005 (KBC procedure it was used the three data sets 2005). corresponding to the three different operating By the KBC 1985 method the Petro-Sim™ days. model calculates the MVC taking into account In order to choose the calibration that best RV asphaltenes content and unit feed BMCI represents the unit real performance, (Bureau of Mines Correlation Index – fuel predictions of the three days were made using aromaticity indicator [11]). each one of the three calibrations. KBC 2005 is a more accurate method that takes into account RV asphaltenes and wax 5 Linear Programming Model contents. The LP model is a fundamental tool in 4.2 Severity planning refining activity. The LP model Petro-Sim™ calculates severity using the determines monthly the refineries production, equation ( 4 ). the raw materials to be processed and the 퐺푂푉퐵 퐶표푛푣푒푟푠푖표푛 operating conditions of the process units that 푆푒푣푒푟푖푡푦 = ( 4 ) allow the optimization of the refining margin. 푀푉퐶 The LP model is also used by Galp to carry out The RVB stability is ensured if severity value economic studies and to plan annual budgets. is less than 100%. Galp’s LP model uses the software GRTPMS (Generalized Refining Transportation 4.3 P-Value Marketing Planning System). Petro-Sim ™ calculates the p-value based on the ABN (Aromatic Blending 5.1 Delta-Base Structure Number wich is a fuel aromaticity and stability The implementation of VB unit model indicator [12]) value. P-value is given through simulation data in the LP model is performed equation ( 5 ). through a delta-base structure. The delta-base structure determines the impact that linear 퐴퐵푁 푉푎푙표푟 − 푝 = ( 5 ) variations on feedstock properties have on a 40 given product property or yield. Thus, linear variations (deltas) are applied to feedstock properties and operating conditions (vectors)

3 and the effect of these variations on the 12 performance of the unit is observed. It is required to do a sensitivity analysis in 10 order to select the vectors, i.e. the feedstock 8 properties and operation conditions, that affect 6 the most the VB unit performance. In this 4 analysis, deltas are defined to ensure that they 11-11-2018 01-03-2018 08-03-2018 represent linear impacts on products yields and Yield (%wt) GOVB properties. Calib11 Calib1 Calib8 Real A case, that corresponds to a feedstock and products yields and properties is then defined. Figure 2 – Prediction of visbreaker gasoil yield This case has to be representative of the VB with each of the three calibrations using the unit operation. Deltas are applied to each vector maximum visbreaker conversion calculation method KBC 1985. of this case, which produce a linear impact on the yields and properties of the products. The case chosen will serve as the basis for the 1.04 implementation of the delta base structure. The impacts that deltas caused in each 1.02 vector on the properties and yields of the ) 1.00 products of the process unit are generated in 3 the simulation model in Petro-Sim™ using the 0.98 Linear Programming Utility (LPU) tool and are (g/cm 0.96 exported to a delta-base template file which will 11-11-2018 01-03-2018 08-03-2018 be provided to LP. Specific Gravity RVB Calib11 Calib1 Calib8 Real

5.2 MRL Predictions Figure 3 – Prediction of visbreaker residue In order to evaluate the delta-base, that will specific gravity with each of the three calibrations be implemented in LP, model a linear using the maximum visbreaker conversion representation model (MRL) is developed in calculation method KBC 1985. Excel using the data generated by LPU.

0.850

6 Results ) 3 0.840

6.1 KBC 1985 Method 0.830 6.1.1 Calibration Results 0.820

Figure 1 to Figure 7 compare the real yields GOVB Specific Specific GOVB 0.810 and properties with predicted results for each (g/cm Gravity 11-11-2018 01-03-2018 08-03-2018 model calibration corresponding to the three different days (November 11, March 1 and 8). Calib11 Calib1 Calib8 Real

Figure 4 – Prediction of visbreaker gasoil 95 specific gravity with each of the three calibrations using the maximum visbreaker conversion 90 calculation method KBC 1985.

85

80 400

C RVB Yield(%wt) RVB 11-11-2018 01-03-2018 08-03-2018 o 300

Calib11 Calib1 Calib8 Real 100 200

100 Figure 1 – Prediction of visbreaker residue yield (cSt) with each of the three calibrations using the 0 maximum visbreaker conversion calculation method 11-11-2018 01-03-2018 08-03-2018

KBC 1985. Viscosity RVB Calib11 Calib1 Calib8 Real

Figure 5 – Prediction of visbreaker residue viscosity 100 with each of the three calibrations using the maximum visbreaker conversion calculation method KBC 1985.

4 1.8 model and the rigorous simulation model 1.6 developed in this work.

Value - 1.4 92 1.2 90 RVB P RVB 88 1.0 86 11-11-2018 01-03-2018 08-03-2018 84 Calib11 Calib1 Calib8 Real 82 (%wt) Yield RVB Figure 6 – Prediction of visbreaker residue p-value with each of the three calibrations using the maximum visbreaker conversion calculation method KBC 1985. Actual Prediction Real

Figure 8 – Prediction of visbreaker residue yield for different days of operation with the actual model 30 and with the new model using the maximum 20 visbreaker conversion calculation method KBC 1985. 10

0 12 11-11-2018 01-03-2018 08-03-2018

Isoconversion(%wt) 10 Calib11 Calib1 Calib8 Real 8

Figure 7 – Prediction of isoconversion with 6 each of the three calibrations using the maximum visbreaker conversion calculation method KBC Yield (%wt) GOVB 1985.

Actual Prediction Real As can be seen from the results presented Figure 9 – Prediction of visbreaker gasoil yield above, calibration 8 presents prediction values for different days of operation with the actual model with the greatest deviation from reality. and with the new model using the maximum Calibrations 1 and 11 present good visbreaker conversion calculation method KBC predictions with similar deviations, 1985. comparatively to the reality. However, on 11-11-2017 is processed a crude mix with Isthmus crude oil, which has a high asphaltenes 1.05 content. Therefore, in order to produce a stable 1.04 RVB, the VB unit has to operate with a severity 1.03

) 1.02 lower than usual. As this is a less typical 3 situation, the calibration factors selected 1.01

correspond to calibration 1 since in this day it 1.00 (g/cm was processed a more common crude mix. 0.99

RVB Specific Gravity Specific Gravity RVB 6.1.2 Crude Mix Predictions In order to validate the model, it is important to check model performance, not only from real Actual Prediction Real RV characterized in the lab, but also when processing VB unit feed obtained through Figure 10 – Prediction of visbreaker residue simulation of the crude mix. These feedstocks specific gravity for different days of operation with the actual model and with the new model using the are obtained simulating RAT and RV streams maximum visbreaker conversion calculation method from crude assays fed to simulation models. KBC 1985. The LP model works this way. Figure 8 to Figure 14 present the real and predicted yields and product properties. All figures show the prediction using the actual

5 0.85 25 0.84 23 21 0.83

) 19 3 0.82 17

(g/cm 0.81 15

Isoconversion(%wt) GOVB Specific Gravity Gravity Specific GOVB

Actual Prediction Real Actual Prediction Real Figure 14 – Prediction of isoconversion for Figure 11 – Prediction of visbreaker gasoil different days of operation with the actual model specific gravity for different days of operation with and with the new model using the maximum the actual model and with the new model using the visbreaker conversion calculation method KBC maximum visbreaker conversion calculation method 1985. KBC 1985.

By analyzing the predictions from the crude

600 mix it is possible to verify that the new

C C o 400 simulation model built presents much more rigorous predictions than the current model, 200 mainly for the yields and isoconversion, i.e. the

(cSt) (cSt) new simulation model is sensitive to the 0 feedstock load to the unit. The new model is also able to predict the stability of RVB, which

RVB Viscosity 100 Viscosity RVB is crucial for the production of VLSFO.

Actual Prediction Real 6.1.3 MRL predictions The implementation of Petro-Sim™ Figure 12 – Prediction of visbreaker residue simulation model in LP model was validated viscosity 100C for different days of operation with using MRL. the actual model and with the new model using the Figure 15 to Figure 20 compare the MRL maximum visbreaker conversion calculation method predictions with the simulation model KBC 1985. predictions in Petro-Sim™. The figures present yields and product properties predictions and real values.

1.7 92

1.5 90 Value - 1.3 88 86 1.1

84 RVB P RVB

0.9 82 RVB Yield(%wt) RVB

Actual Prediction Real PS Prediction MRL Real

Figure 13 – Prediction of visbreaker residue p- Figure 15 – Prediction of visbreaker residue value for different days of operation with the actual yield by Petro-Sim™ model and MRL for different model and with the new model using the maximum days of operation using the maximum visbreaker visbreaker conversion calculation method KBC conversion calculation method KBC 1985. 1985.

6 12 1.7

10 1.5

Value 1.3 8 - 1.1

6 P RVB

0.9 GOVB Yield (%wt) GOVB

PS Prediction MRL Real PS Prediction MRL Real Figure 16 – Prediction of visbreaker gasoil yield by Petro-Sim™ model and MRL for different days of Figure 19 – Prediction of visbreaker residue operation using the maximum visbreaker p-value by Petro-Sim™ model and MRL for different conversion calculation method KBC 1985. days of operation using the maximum visbreaker conversion calculation method KBC 1985.

1.06 600 1.04

500 )

3 1.02 400 C C (cSt) o 300 1.00

(g/cm 200 0.98 100

0

RVB Specific Gravity Specific Gravity RVB RVB Viscosity 100 Viscosity RVB PS Prediction MRL Real PS Prediction MRL Real Figure 17 – Prediction of visbreaker residue specific gravity by Petro-Sim™ model and MRL for Figure 20 – Prediction of visbreaker residue different days of operation using the maximum viscosity 100C by Petro-Sim™ model and MRL for visbreaker conversion calculation method KBC different days of operation using the maximum 1985. visbreaker conversion calculation method KBC 1985.

0.85 The developed MRL allows to obtain results 0.84 very similar to those obtained in the simulation model built in Petro-Sim™. As can be seen 0.83 above, the predictions by the MRL and the

Petro-Sim™ model are practically coincident. (g/cm3) 0.82 These results validate the vectors, bases and deltas chosen.

GOVB Specific Gravity Specific Gravity GOVB 6.2 KBC 2005 Method PS Prediction MRL Real According to KBC, the most recent method, KBC 2005, is more accurate than KBC 1985 Figure 18 – Prediction of visbreaker gasoil method. In order to evaluate if the KBC 2005 specific gravity by Petro-Sim™ model and MRL for method leads to RVB stability with greater different days of operation using the maximum adherence to reality, a model was solved using visbreaker conversion calculation method KBC this method. 1985.

6.2.1 Real Data Predictions Figure 21 compares the real RVB p-value with RVB p-value predicted using KBC methods 1985 and 2005.

7 1.8 Regarding the RVB p-value, the model solved using the KBC 2005 method, shows 1.6 predictions with a greater amplitude of values

1.4 that better mimic the real values trend. These

Value - 1.2 predictions show a slight improvement compared to the predictions made with the KBC RVB P RVB 1.0 1985 method. 0.8 11-11-2017 01-03-2018 08-03-2018 6.2.3 MRL Predictions KBC 2005 Prediction KBC 1985 Prediction Real The implementation of the simulation model using KBC 2005 method in LP model was Figure 21 – Prediction of visbreaker residue studied using an MRL. p-value using laboratory analysis data as input Figure 23 to Figure 28 compare the MRL using the two maximum visbreaker conversion predictions with the simulation model calculation methods KBC 1985 and 2005. predictions in Petro-Sim™, when using KBC 2005 method. The figures present yields and product properties predictions and real values. This figure shows that predictions using KBC 2005 method present lower deviations from real values than predictions using KBC 1985 92 method. This shows that using KBC 2005 90 method the predictions are more accurate. 88 In what concerns to yields and other product 86 properties the VB unit simulation model results 84

with the two methods are very similar. Yield(%wt) RVB 82

6.2.2 Crude Mix Predictions In order to verify the performance of the model using the calculation method KBC 2005, predictions were made from the crude mix, PS KBC 2005 MRL KBC 2005 using crude assays, as it was done for the Real model with the KBC 1985 method. Figure 22 present the real and predicted Figure 23 – Prediction of visbreaker residue yields and product properties. The figure shows yield by Petro-Sim™ model and MRL for different the prediction using KBC 1985 and 2005 days of operation using the maximum visbreaker methods. conversion calculation method KBC 2005.

1.6 1.5 12

1.4 11 Value - 1.3 10 1.2 9

1.1 8 RVB P RVB 1.0 7

6 GOVB Yield (%wt) GOVB

KBC 2005 KBC 1985 Real PS KBC 2005 MRL KBC 2005 Figure 22 – Prediction of visbreaker residue Real p-value from crude mix using the two maximum visbreaker conversion calculation methods KBC Figure 24 – Prediction of visbreaker gasoil yield 1985 and 2005. by Petro-Sim™ model and MRL for different days of operation using the maximum visbreaker conversion calculation method KBC 2005.. Like it was observed with real data predictions, the crude mix predictions using the two MVC calculation methods are very similar too with respect to yields and properties.

8 ) )

3 1.08 1000

1.06 800 C C (cSt) 1.04 o 600 1.02 1.00 400 0.98 200

0.96 0

RVB Viscosity 100 Viscosity RVB RVB Specific Gravity (g/cm Specific Gravity RVB PS KBC 2005 MRL KBC 2005 PS KBC 2005 MRL KBC 2005 Real Real

Figure 25 – Prediction of visbreaker residue Figure 28 – Prediction of visbreaker residue specific gravity by Petro-Sim™ model and MRL for viscosity 100C by Petro-Sim™ model and MRL for different days of operation using the maximum different days of operation using the maximum visbreaker conversion calculation method KBC visbreaker conversion calculation method KBC 2005. 2005.

) ) With the simulation model built with the KBC

3 0.850 2005 calculation method, the MRL developed 0.840 can mimic the behavior of the model in Petro- -Sim™ when predicting the actual performance 0.830 of the VB unit. Therefore it is possible to state that the delta- 0.820 -base structure developed using the KBC 2005 method would present good results when implemented in the LP model, achieving a good optimization in the crudes selection for the production of VLSFO. GOVB Specific Gravity (g/cm Specific Gravity GOVB PS KBC 2005 MRL KBC 2005 Real

Figure 26 – Prediction of visbreaker gasoil 7 Conclusions specific gravity by Petro-Sim™ model and MRL for different days of operation using the maximum visbreaker conversion calculation method KBC The simulation model of the VB unit with the 2005. KBC method 1985 presents a very good prediction of the reality with respect to yields and product properties. The predicted performance is highly dependent on the 1.7 feedstock quality. Regarding the RVB stability the p-value predictions present a good

1.5 adherence to the real values meaning that the Value - 1.3 new simulation model is able to predict RVB 1.1 stability which is crucial for VLSFO production.

RVB P RVB It should be noted that the stability prediction is 0.9 not ensured by the simulation model that Galp currently use. The new simulation model corresponds to a great improvement in the Galp simulation models as a whole. The simulation model predictions using KBC PS KBC 2005 MRL KBC 2005 2005 method are very similar to those obtained Real by the simulation model using the KBC method 1985. The MVC values obtained by the Figure 27 – Prediction of visbreaker residue p- simulation model when using the KBC 2005 value by Petro-Sim™ model and MRL for different method are in a wider range than the values days of operation using the maximum visbreaker obtained by the KBC method 1985. This is also conversion calculation method KBC 2005. observed in p-value predictions of the simulation model with the KBC 2005 method. In

9 contrast to KBC 1985, the p-value predictions [6] A. Breneol, "Marine Fuel Stability with the KBC 2005 method are more dependent and Compatibility - Issues, Tests and on the feedstock quality. This method presents Management". an improvement in the p-value prediction [7] Shell Global Solutions International comparatively to the old method. B.V., "SMS 1600-01 - Determination of In this work it was carried out the State of Peptization of Asphaltenes in development of a delta-base structure, in order Heavy Oil Streams," 2001. to provide the simulation data to the LP model. The representation of the delta-base structure [8] E. Y. Sheu and D. A. Storm, in the VB unit is pioneering in Galp. Asphaltenes - Fundamentals ans To generate the delta-base representation, Applications, New York: Plenum Press, was used the Linear Programming Utility of the 1995. Petro-Sim™ software to obtain the impacts that [9] A. Pina, P. Mougin and E. Behar, variations in the feedstock properties have on "Characterisation of Asphaltenes and given products properties. This is the Modelling of Flocculation – State of the information required to implement the Art," Oil & Gas Science and simulation model in the LP model. Technology – Rev. IFP, vol. 61, no. 3, The delta-base structure was validated using pp. 319-343, 2006. the linear representation model that allows the [10] H. Groenzin and O. C. Mullins, evaluation of the new VB unit representation in "Molecular Size and Structure of the Galp LP model. Both linear representation Asphaltenes," Science nd models, constructed from the simulation model Technology, vol. 19, no. 1-2, pp. 219- with the KBC1985 method and with KBC 2005, 230, 2001. are robust and reproduce with very low [11] J. H. Gary, G. E. Handwerk and M. deviations the simulation model predictions. J. Kaiser, Petroleum Refining - The delta-base structure constructed for the Technology and Economics, CRC implementation of the simulation model in the Press, 2007. LP model is validated and is representative of reality, being sufficiently robust to be [12] KBC Andvanced Technologies Ltd, implemented in the LP model. This allows to Petro-Sim Help. perform good optimizations in the selection of crudes for the production of VLSFO. The simulation model of the VB unit with the KBC 2005 method makes good predictions of yields and product properties and its delta-base representation will be implemented in the PL model.

References

[1] IMO, "Sulphur 2020 – cutting sulphur oxide emissions," [Online]. Available: http://www.imo.org. [Accessed Fev 2019]. [2] D. S. J. Jones and P. P. Pujadó, Handbook of Petroleum Processing, Springer, 2006. [3] J. G. Speight, Handbook of Petroleum Refining, CRC Press, 2017. [4] J. Singh, S. Kumar and M. O. Garg, "Kinetic Modelling of Thermal Cracking of Petroleum Residues: A Critique," Fuel Processing Technology, vol. 94, pp. 131-144, 2012. [5] Encyclopaedia of Hydrocarbons, vol. II/Refining and Petrochemicals, Istituto della Enciclopedia Italiana, 2005.

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