Comprehensive Investigation and Comparison of Refinery Distillation

Article pubs.acs.org/IECR

Comprehensive Investigation and Comparison of Refinery Distillation Technologies Anita Szőke-Kis,*,† Csaba I. Farkas,‡ and Péter Mizsey† †

Department of Chemical and Environmental Process Engineering, Budapest University of Technology and Economics, Mű egyetem rkp. 3-9, Budapest, 1111, Hungary ‡ MOL Plc. DS Development, Olajmunkás u. 2. Százhalombatta, 2440, Hungary S Supporting Information *

ABSTRACT: Distillation is an important and widely applied separation method. One of its major application areas is crude oil refining. We investigate and compare two different refinery technologies: (i) conventional, atmospheric and vacuum, AV-plant, and (ii) an alternative one, the so-called progressive distillation technology. For the sake of the comparison, simulation models of the two different distillation technologies are built in professional flowsheeting software environment. The investigation includes the study of crude oil fractionation on the examples of processing different types of crude oils. Both technologies are also evaluated with the tools of pinch technology. On the basis of the results of the pinch analysis, heat exchanger networks are also designed. The operating and capital costs are estimated for the energy integrated cases designed on the results of pinch technology. A comparison of the results shows that the progressive distillation plant proves to be both more energy efficient and economical than the currently applied atmospheric and vacuum distillation plants.

1. INTRODUCTION The world’s energy situation is a constant issue of technologies and also politics. The energy demands of industries and households are continuously increasing. The world’s energy supply is still significantly based on fossil fuels, the availability of which is limited. The high number of studies made by scientists and international organizations, for example, the International Energy Agency, shows the importance of a secure energy supply.1−4 The World Energy Outlook, IEA’s guideline for developing future energy policy, deals exhaustively with this problem.5−7 As a common conclusion, in the case of liquid fuels the energy demand is high since the oil demand can be connected with the economic growth of the countries. While the demand is increasing, the production yield of the currently producing crude oil fields will not increase on the long-term. Therefore, there is an urgent need to design and develop alternative technologies showing more efficient energy utilization than older/conventional technologies.8 Efficient energy consumption can be achieved by the development of alternative energy sources and technologies; and while increasing the energy efficiency, the energy intensity should be decreased.9 However, the environmental aspects of the energy industry should be taken into consideration as well. The regulations in the European Union are becoming more and more severe in the form of directives. The more efficient use of fossil energy sources can decrease the emissions of greenhouse gases and thus cooperate in achieving the aims of the environmental protection directives.10,11 When examining the possibilities of the reduction of energy consumption, it is worth starting with the most energy intensive operations, which include the distillation-based operations. In most cases the separation of liquid mixtures is carried out with © 2014 American Chemical Society

distillation or with fractionate distillation: rectification. Though the distillation is a very energy intensive process, it is a widely used separation method thanks to its advantages. Since it is a theoretically and mathematically well described and mature process, it can be designed, calculated, and operated reliably; moreover, no additional compound is needed to carry out the separation in accordance to the theories of green chemistry. There are many incentives to replace the rectification/ distillation process, but it is not always feasible because of different circumstances. In those cases it is necessary to develop and investigate alternative rectification-based technologies which have lower energy consumption, that is, higher energy efficiency. The energy efficiency of distillation has been the object of many studies. There are early researches to improve energy efficiency. Improved technologies are based on reversible rectification, with examples as thermally coupled units and dividing wall columns.12,13 The energy consumption can also be decreased by utilizing the waste heat of any process. There are several technological layouts for this aim such as the Organic Rankine Cycle or Kalina Cycle.14,15 The efficiency of different distillation processes has been studied in our research group as well.16,17 In the chemical industry the distillation technologies are used in many different cases. One of the most important sectors is crude oil refining; and one of the highest energy demand technologies is the first step of refining after the desalting, the crude oil distillation. To present the importance of this industrial activity, for instance, in the USA the energy Received: Revised: Accepted: Published: 19282

July 15, 2014 November 11, 2014 November 19, 2014 November 19, 2014 dx.doi.org/10.1021/ie502807x | Ind. Eng. Chem. Res. 2014, 53, 19282−19292

Industrial & Engineering Chemistry Research

Article

Figure 1. Schematic view of the AV unit.

consumption of petroleum refining is 3.3% of the total energy consumption of the country.18 Distillation enables the fractionation of crude oil into different fractions and this distillation-based separation cannot currently be replaced with any another operation. Though the current economic situation of the refineries in Europe is not particularly good, and a geographical rearrangement of the petroleum industry can be observed, there is a need to develop modern refinery technologies, since high quality can provide a chance also for European refineries to survive any crises.19 A high quality refinery technology can also improve the energy efficiency of this industry saving natural resources and the environment via less emission. In the petroleum industry, the conventional method for the first crude oil distillation right after desalting is the atmospheric and vacuum distillation technology, referredto as AV plant or AV unit. Despite that the AV technology perfectly processes crude oil, because of its high energy consumption there is a need to develop alternative technologies. An alternative opportunity to distillate crude oil is the socalled progressive distillation technology (PD plant/unit). In our work, the progressive crude oil distillation is examined as an alternative distillation technology. The technology was patented in 1986 in the United States20 and has not been studied by many yet.21,22 In our study, besides the progressive distillation plant a conventional technology (AV unit) is also examined. The AV unit is chosen as the base case for the comparison of the PD and AV technologies. 1.1. Description of the Atmospheric and Vacuum Distillation Technology. The flowsheet of a usual AV plant with a prefractionator selected as base case for comparison is shown in Figure 1. The preheated crude oil enters the prefractionator column, C1, in which a mixture of the light ends and light naphtha are recovered as top product. This top product is fed into the naphtha stabilizing column, C2, where

the gases are separated from the naphtha fraction. The bottom product of the column C1 is fed into the atmospheric column C10 after preheating in the atmospheric furnace. Although the separation would be feasible without a prefractionator column, it is better to use it since the application of a prefractionator decreases the energy required in the furnace.23 The atmospheric column separates the heavy naphtha, jet fuel, and gasoil fractions. The jet fuel and the gasoil fractions are withdrawn as side products and may contain compounds from adjacent fractions, which are stripped with steam in the side stripper columns. To improve the energy efficiency of the tower, pump-around streams are used: liquid flows are withdrawn from the tower and after utilizing their heat content in the heat exchanger network they are returned to the column at a higher plate generating reflux inside the column.24 The bottom product of the column C10, the atmospheric residue is processed in the vacuum tower, C12. The stream is preheated in the vacuum furnace before entering the tower. The operating pressure is 80−110 Hg mm, which enables the fractionation of the heavier fractions without thermal degradation; thus vacuum gas oil and vacuum distillate are produced as side products. The bottom product of the vacuum distillation is the vacuum residue. The columns C1, C10, and C12 are stripped with high pressure steam, while the column C2 has a reboiler. The vapor phases of the top products are condensed in the head condensers producing liquid product and the required refluxes. In the case of the vacuum tower, the vacuum is provided at the coldest point of the tower, that is at the top of the column. The energy consumption of the AV unit, the operating costs and the emissions are enormous and therefore there is a need to develop and investigate alternative crude oil processing technologies. Such technologies should be based on distillation since the alternative ones are currently not so developed to be technologically competitive. 19283

dx.doi.org/10.1021/ie502807x | Ind. Eng. Chem. Res. 2014, 53, 19282−19292


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Figure 2. Schematic view of the PD unit.

As mentioned earlier, the progressive crude oil distillation can be an alternative one. The potential of the technology is the reduced energy consumption with a more effective utilization of the recovered heat. 1.2. Description of the Progressive Distillation Technology. The flowsheet of the technology is shown in Figure 2. The technology consists of two series of distillation columns and the total number of distillation columns is more than that of the conventional AV units. The columns in the first series are connected in direct sequence, in each column the most volatile fractions are separated from the residue. The columns of the first series are the columns C1, C2, C3, and C10 that are operating at atmospheric or higher pressure. The crude oil is fed into the first column of the first series, which separates the light gases and a part of the light naphtha from the residue. The second column of the first series separates the remaining light naphtha components and a part of the heavy naphtha. At the end the third column separates the remaining heavy naphtha from the residue. The last column of the first series is the atmospheric column, C10, which operates similarly to the atmospheric column of the AV plant. The top product of the column contains the heavy naphtha and the jet fuel. One side product is withdrawn, gasoil, and the quality of the product is ensured with the operation of a stripper side column. Two atmospheric pumparounds operate to ensure reflux and improve energy efficiency. The feed of the atmospheric column must be preheated like the atmospheric column of the AV plant. The preheating is also carried out in an atmospheric furnace. The columns of the first series are heated with steam, added at the bottom of the columns below the feed plate; except column C1 which operates with a reboiler. The required

amount of reflux in the towers is ensured with operating head condensers. Since the separation in every column of the first series is not sharp and small amounts are removed as head products, the energy consumption of the columns in the first series is lower than it would be in the case of sharp separation. The top products of the columns of the first series are fed individually into a column of the second series where the sharp separation of the petroleum fractions is carried out. The columns of the second series are the columns C7, C4, and C5. The first column, column C7, processing the feed from column C1, is a naphtha stabilizing column and removes the LPG fraction. The column operates similarly to the naphtha stabilizing column of the AV plant. The bottom product of the column is then mixed with the top product of column C2, and the mixture is fed into the second column of the second series, column C4, which is a naphtha fractionating column. In this column the light naphtha is separated and withdrawn as the top product. The feed of the last column of the second series, C5, is the mixture of the top product of columns C3 and C10, and is separating the heavy naphtha from the jet fuel. The top product being mixed with the bottom product of column C4 is the heavy naphtha fraction. The bottom product is the jet fuel. Since the cuts between the fractions are sharp, the towers have a higher theoretical number of trays then the column in the first series. The columns of the second series operate with head condensers and reboilers. The last column of the unit, column C12, is a vacuum column processing the atmospheric residue. The composition of the residues are the same in both units (AV and PD) because, after the nondegradable fraction is vaporized at atmospheric pressure, the same molecules remain in the residue; thus, the vacuum column of the progressive distillation 19284



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also enables the independent operations of the towers from the feed properties. The quality of the products is monitored with their true boiling point distillation curves and that represent the results. The products of the different crude oils are shown in different figures. Figure 3 shows the curves produced both in the AV and

plant operates in the same manner as the vacuum column of the AV plant. The described PD unit can be considered as a combination of the direct and indirect separation sequences. The energy saved in the first series of columns can be utilized in the second series of columns which results in lower energy consumption of the whole technology. This implies that using progressively located columns of larger number and smaller volume results in a better heat recovery/utilization, while the produced fractions are the same quantity and quality than those of the conventional distillation technology (AV unit). The flexibility of the progressive distillation process enables the production of different products by a rearrangement of the columns.

2. CALCULATIONS Simulation models of the different technologies are built in a professional flowsheeting environment. On the basis of the data of the simulations, pinch analysis is carried out for every case and heat exchanger networks are designed. The operational and capital costs are estimated for the heat integrated units. 2.1. Simulation. The conventional AV unit is used as the base case for comparison. Simulations are built for both the AV and the PD units for the separation of three different types of crude oils. The physical properties of the crudes are shown in Table 1. The quantity of the crudes corresponds to the yearly

Figure 3. (a) Crude A, light product TBP curves. (b) Crude A, heavy product TBP curves.

PD plants processing Crude A. The light and heavy products are shown in different figures. The products of the plants processing Crude B and Crude C are represented in the same manner in Figure 4 and in Figure 5.

Table 1. Physical Properties of the Examined Crude Oils mass flow average MW mole flow density API density

Crude A

Crude B

Crude C

454 130 kg/h 172 g/mol 2645 kmol/h 817 kg/m3 42



capacity of a medium size refinery, that is, 3.633 Mt/a or 454.130 kg/h. The crudes are referred as Crude A, Crude B, and Crude C, with their densities increasing. The selected crudes are available on the stock market, and all are in largescale industrial use with existing examples of refining. The crude oils are so selected that their different physical properties allow us to check the flexibility of the two investigated refinery technologies and their comparison in a wide operational range. In the simulation step Figure 1 represents the flowsheet of the AV unit and Figure 2 represents the flowsheet of the PD unit. All the three crude oils are processed in both AV and PD units generating a case study of six cases. A professional flowsheeting software environment is used, and in every case the columns are simulated with rigorous tools. The crudes are characterized with their true boiling point curves (TBP) and 75 pseudo-components are defined.25 For the description of vapor−liquid equilibrium the Soave modified Redlich−Kwong equation of state is used.26 The amount of processed crude oil, 454 130 kg/h, is the same in all cases representing the industrial scale. During the simulation process our aim is to produce products of the same quality in every case of the different technologies and different feed stocks. The mentioned products are light petroleum gases (LPG), light and heavy naphtha, kerosene, gasoil, vacuum gas oil and vacuum distillate. To achieve the desired quality, initial and end boiling points of the product TPB curves are specified. The choice of different temperature values as specified variables

Figure 4. (a) Crude B, light product TBP curves. (b) Crude B, heavy product TBP curves.

The light products are the light and heavy naphthas and the jet. The initial and end boiling points are identical in the different cases and they fulfill the specifications. There can be differences observed between the TBP curves. The differences

Figure 5. (a) Crude C, light product TBP curves. (b) Crude C, heavy product TBP curves. 19285



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Table 2. AV Unit Mass Balance Crude A feed C2 LPG light naphtha heavy naphtha jet gasoil vacuum gas oil vacuum distillate vacuum residue total

Crude B

Crude C

kg/h

m/m %

kg/h

m/m %

kg/h

m/m %

454 130 1 766 3 772 63 372 67 044 37 891 137 444 24 442 98 159 20 360 454 251

100 0 1 14 15 8 30 5 22 4 100

454 130 73 3 560 34 996 45 928 34 881 81 692 38 985 132 034 81 430 453 580

100 0 1 8 10 8 18 9 29 18 100

454 130 808 769 19 549 44 559 35 233 103 470 34 247 130 704 84 758 454 098

100 0 0 4 10 8 23 8 29 19 100

kg/h

m/m %

kg/h

m/m %

kg/h

m/m %

454 130 1 670 2 866 66 813 66 302 29 021 14 647 29 900 95 473 20 467 454 160

100 0 1 15 15 6 31 7 21 5 100

454 130 5 263 1 667 32 347 43 717 30 194 87 752 41 777 130 172 81 151 454 042

100 1 0 7 10 7 19 9 29 18 100

454 130 1 125 852 19 890 42 817 31 823 99 950 43 653 129 608 84 307 454 026

100 0 0 4 9 7 22 10 29 19 100

Table 3. PD Unit Mass Balance Crude A feed C2 LPG light naphtha heavy naphtha jet gasoil vacuum gas oil vacuum distillate vacuum residue total

Crude B

Crude C

A study of the mass balance in the cases of the PD unit shows that the same phenomenon can be concluded. A comparison of the amounts of the same products produced in different units shows that there are only slight differences observed between the same products produced in different plants. In the case of the AV plant processing Crude B 34 996 kg/h light naphtha is produced, while in the PD plant the amount of the light naphtha obtained from Crude B is 32 347 kg/h. The reason for the differences can be due to the different installation of the distillation columns in the two technologies. The material balance is also monitored and the feed and sum values are equal as in the cases of the AV unit. 2.2. Energy Analysis. After the simulation of the units, the energy analysis of both the AV and PD units is carried out. The aim of the analysis is to determine the minimum utility consumption and the operational costs of the units with internal utilization of the heat content of the process streams via matching them the optimal way. The energy analysis is carried out with the techniques of pinch analysis.27−29 Simulation data are used as the basis for the calculations. Professional software is used to execute the energy analysis, and on the basis of the results a heat exchanger network is designed to realize the heat integration delivered by the pinch analysis. In the heat exchanger train, hot process streams are used to preheat cold process streams. In both technologies the cold streams are the crudes, the feed streams of the columns, and the reboilers. The hot streams are the products, atmospheric and vacuum circulations, and condensers of the columns. When the internal streams are integrated into the heat recovery system, their target temperatures are then determined

can be because (i) different crude oils are processed or (ii) different processing technologies (AV or PD unit is used) are applied. The mass balance of the products produced in the AV unit is shown in Table 2 and the products of the PD unit are shown in Table 3. The amounts of the same products in the cases of different crude oils differ, since the lower density crude oils contain higher amounts of light products and the higher density crude oils contain a higher amount of heavy products. Crude A proves to be significantly lighter than Crude B and Crude C, the amount of light naphtha produced in the AV unit, 63 372 kg/h is larger than in the other two cases, 34 996 kg/h in case of Crude B and 19 549 kg/h in case of Crude C. The same tendency can be observed when the heavy naphtha product is examined. According to the tendency of the density of the crudes, the amount of heavy product is higher in the case of the heavier crudes. While the vacuum residue in the AV units is 20 360 kg/h in the case of Crude A, the amount of the residue in the other two cases is four times higher, 81 430 kg/h with Crude B and 84 758 with Crude C. The results show that the difference between the densities of Crude A and Crude B represents a higher difference among the products than in the case of Crude B and Crude C. The sum of the modeled amount of the products and vacuum residue in each case equals to the amount of the feedstock within the proper limits of error giving a confidence to the modeling accuracy. The reason for a possible difference between the two values is due to the not completely decanted water added to the process as strip steam and the noncondensable components drawn as gas products. 19286



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Adding and subtracting the half of ΔTmin, which is 10 °C, there is a hot and cold pinch temperature, 248 and 228 °C. The pinch temperature divides the system into two parts, one over and one below the pinch temperature. The part that is over the pinch temperature requires heating (hot side) and the part under the pinch temperature requires cooling (cold side). According to the “pinch rules” if there is an additional cooling over the pinch temperature, to maintain the heat balance, there will be a need of additional heating as well; and the same goes to the additional heating below the pinch temperature, extra cooling will be necessary. In the case of heat transfer through the pinch temperature, both the cold and the hot side’s utility requirements will increase, generating additional cooling and heating. To sum it up, with the aim of maximal heat recovery, the following rules should be considered: (i) there is no heating at the cold side, (ii) there is no cooling at the hot side, and (iii) there is no heat transfer through the pinch temperature. The heat exchanger network is designed with a consideration of the main rules of pinch technology. Cold utilities are only applied below the pinch points and hot utilities are only applied over the pinch point. The heat exchanger networks are designed individually below and over the pinch points, and there is no heat transfer through the pinch temperatures.30 The energy analysis is performed and heat exchanger networks are built in all cases. As an example for the heat integrated technological layout, the flowsheet of the PD plant, processing Crude C, is shown in Figure 8. The graphical representation of the heat exchanger network, the Grid diagram, in the case of the PD unit processing Crude C is shown in Figure 9. It can be seen that the abovementioned rules of the pinch technology are not violated. There are three pinch temperatures, one calculated from the composite curve and the other two pinch temperatures are adjusted to the given utilities. Application of these extra pinch temperatures and following the main pinch rules exclude the possibility of a heat exchange between a process stream and a utility with a high temperature difference, and therefore an uneconomical heat exchange can be avoided. In the case of the cold streams the crude oil entering the unit has the lowest temperature, 20 °C. Thus, at the beginning of the crude oil preheating train the hot streams with lower temperatures can be applied. Such hot streams are the light fractions (naphthas, jet fuel) and the heat gained from the condensers operating at lower condenser temperature. The hot streams of higher temperature and higher heat content like the atmospheric and vacuum pumparounds, heavy products, and the vacuum residue are used to preheat the cold streams at higher temperatures. These cases are, for example, the preheating of the feed streams of the columns of the first series of a PD unit. By applying such pressure values that enable the match of two columns for the sake of heat integration, condensers can be used as reboilers of other columns and heat integration can be completed. In the example of a PD unit processing crude C, the condenser of the column C3 is matched with the reboiler of the column C7. The required duties at the operation of both the AV and the PD plants processing every crude oil are calculated for the heat integrated plants. The detailed values for every case and heat exchangers can be found in the Supporting Information. In cases of the PD units, the columns C2, C3, C10, C12 and the side stripper SS1 are supplied with high pressure steam. In the AV plant, except for the C2 naphtha stabilizing column,

from the process. That means that the temperatures of the products remain over their storage temperatures and in the case of the condensers and pumparounds the transferred duty on the heat exchanger train is equal to or lower than the duty determined by the process. The calculations are based on the simulation data at the selected operation points of the PD and AV units for the three crude oils, six cases altogether. The simulations are built so that the required data for the analysis can be exported: temperature values, flow rate, and enthalpy data. According to the pinch theory the maximal duty to be utilized in the heat recovery process can be estimated with the help of the composite curve diagram (CC). As an example the CC diagram of the progressive distillation plant, processing Crude C, is shown in Figure 6. During the calculations 20 °C is

Figure 6. CC diagram of a PD unit.

used as a minimum approach temperature (ΔTmin). The difference between the upper ends of the hot and cold composite curves gives the minimum required heating that is 196 GJ/h, and the difference between the lower ends of the hot and cold composite curves determines the minimum required cooling that is 151 GJ/h. The overlap of the two curves shows the amount of energy that can be saved, and it is 312 GJ/h. The chosen cold utilities are the air coolers and boiler feedwater preheating; the hot utilities are high pressure steam and fired fossil primary energy carrier in a furnace. The pinch temperature, the temperature where the distance of the hot and cold composite curves is exactly ΔTmin, is 238 °C. The grand composite curve (GCC) diagram, shown in Figure 7, is constructed from the shifted CC diagram, summarizing the enthalpy values for given temperatures. Thus, the pinch temperature in the GCC belongs to the enthalpy value of 0 where the GCC curve touches the axis.

Figure 7. GCC diagram of a PD unit. 19287



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Figure 8. Flowsheet of the PD unit processing Crude C.

PD plants processing the same crudes is roughly the same because of the mentioned fact that the amount of atmospheric residue is the same in the case of same crudes. The duties of the atmospheric furnaces are in the same magnitude as well. The summarized final results are shown in Table 4. The negative values represent the generated low pressure steam. These steam flows are subtracted from the total steam utility requirements. 2.3. Cost Estimation. Both the operating and the capital costs are estimated. The operating cost estimation is based on the heat requirements of the units which are based on two utilities: fuel gas burned in the furnaces and high pressure steam for heating certain heat exchangers and stripping columns. The material costs are calculated from the total mass flows per hour, multiplied with their prices in USD. The annual operating cost is calculated on the basis of 8000 h/a. The annual operating costs in million USD ($) are shown in Table 5. A comparison of the results in the case of the different units processing the same crude oils shows that the progressive crude oil distillation proves to be cheaper than the conventional atmospheric and vacuum distillation. When the result in the same units are compared, both for AV and PD, the units processing the Crude C (highest density) show the smallest costs. The capital costs are estimated based on the Douglas cost correlations.31 The correlations are updated by using a ratio of

every column (C1, C10, and C12) and the side stripper SS1 is stripped with high pressure steam. The additional heat demand derives from those heat exchangers in the heat exchanger train where the required duty could not be satisfied with process stream and there is a need for high pressure steam as a utility. The columns operating at similar parameters, the atmospheric and the vacuum towers, use approximately the same amounts of steam. The differences between the total consumed steam come from the different numbers of columns and the different heat exchanger layouts between the AV and PD units. After the heat integration is performed, there are still hot process streams left and they are used to generate low pressure steam. The generated low pressure steam can be used in both technologies, AV and PD, as a hot utility, for example, in the distillation units for stripping, or within the plant in another unit. The amounts of the generated steam are subtracted from the needed steam amounts, thus the generated steam flows decrease the amount of steam utility required at different places of the AV and PD units. A comparison of the generated steams in the two units leads to the conclusion that the PD has a higher steam generating potential. The main amount of the required heat duties in the two plants are delivered by the furnaces. The furnaces ensure the preheating of the feeds of the atmospheric and vacuum columns C10 and C12 as well as the heating of VC4. In the furnaces, fuel gas is burned to ensure the desired high temperatures. The duty of the vacuum heaters of the AV and 19288



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Figure 9. Grid diagram of the PD unit processing Crude C.

Table 4. Summary of Heat Flows GJ/h Crude A

Crude B

Crude C

PD Unit

AV Unit

PD Unit

AV Unit

PD Unit

AV Unit

64.87 −57.29 173.89 181.47

51.09 −6.22 193.73 238.60

22.58 −62.22 181.67 142.03

59.68 −34.81 173.35 198.22

16.23 −78.41 192.53 130.35

14.53 −46.26 173.98 142.25

steam use steam gen. furnace sum

Table 5. Annual Operating Costs annual operating cost. million $

AV unit Crude A

AV unit Crude B

AV unit Crude C

PD unit Crude A

PD unit Crude B

PD unit Crude C

29.41

24.06

15.80

21.58

15.54

13.50

the M&S indices.32 Its current actual value is 1512.5. The installed costs are calculated in USD. In the case of the columns, geometric values are needed at the cost estimation. These values are the heights and diameters of the columns that are obtained from simulation data. The heights of the columns are calculated from the theoretical number of plates assuming 70% tray efficiency; with a standard 0.609 m tray distance. The diameters of the columns are standard sizes. The corresponding cost estimation factors needed in the Douglas cost correlations are chosen for the appropriate pressure values and material. Additional factors are used at the cost estimation of the trays including tray type and tray spacing factors. The sum of the installed costs of the

column and tray or packing gives the total installed cost of the given columns. The results are shown in Table 6, given in million USD (M $). The installed costs of the vessels give the smaller part of the total value, the installed cost of the trays is with 1 order of magnitude higher. The total capital cost of the heat exchangers is estimated based on the heat exchangers’ areas. All of the heat exchangers including condensers, process−process heat exchangers, heaters, and coolers are shell and tube types, and the reboilers are Kettle-type heat exchangers. The factors used in the equations include the material, pressure, and design factors of the heat exchangers. The number of the heat exchangers in each unit is huge and in Table 7 the sum of the installed costs 19289



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costs of each plant are the sums of the capital costs of the columns, heat exchangers, and furnaces. The sums of the different equipment capital costs and the total capital costs for the plant are shown in Table 9. The total capital cost of the

Table 6. Column Capital Costs (M$) PD AV PD AV PD AV

unit unit unit unit unit unit

Crude Crude Crude Crude Crude Crude

installed cost, columns

installed cost, trays

total M$

5.28 5.60 4.51 4.64 4.11 4.11

28.56 40.17 21.88 28.73 25.79 19.85

33.84 45.77 26.39 33.37 29.91 23.96

A A B B C C

Table 9. Summary of the Capital Costs (M$)

column HTXR furnace total

of the different heat exchangers is shown for each unit and for each crude oil. Table 7. Heat Exchanger Capital Costs PD AV PD AV PD AV

unit unit unit unit unit unit

area m2

installed cost M$

25 875 22 167 23 075 24 406 25 129 30 952

20.73 14.59 18.84 14.34 20.73 16.08

Crude A Crude A Crude B Crude B Crude C Crude C

AV Crude A

AV Crude B

AV Crude C

PD Crude A

PD Crude B

PD Crude C

45.77 14.59 6.29 66.65

33.37 14.34 5.71 53.42

29.91 16.08 5.74 51.72

33.84 20.73 5.75 60.32

26.39 18.84 5.96 51.19

23.96 20.73 6.27 50.96

columns of the progressive distillation plants are lower than those of the AV plants considering that the same crude oil is processed. Though the number of the columns is higher in the PD plant, their sizes are lower, which allows a lower capital cost. In the case of the PD units, the number and the total area of the heat exchangers is higher than that of the AV unit, which implies a higher capital costs. However, this difference is smaller than in the case of the columns. Since the furnaces are operating under very similar conditions, their capital cost is not particularly different. Summarizing the capital costs of the different equipment items, the total capital cost of the progressive distillation plants are lower in the case of every examined crude oil. The total annual cost is calculated from the operating and capital costs assuming 10 years amortization. The annual cost values are shown in Figure 10 and are represented in million

The data needed for furnaces is the amount of heat transferred, and the furnaces are installed before the atmospheric and vacuum columns; the vacuum furnace is also preheating the C4 vacuum circulation. The furnaces are simulated as fired heaters, and their duty value is imported from the simulations. The factors include design, material, and pressure values. The installed costs of each furnace is represented in Table 8. The costs of the vacuum furnaces in Table 8. Furnace Capital Costs (M$) furnace PD unit Crude A AV unit Crude A PD unit Crude B AV unit Crude B PD unit Crude C AV unit Crude C

C10 C12 C10 C12 C10 C12 C10 C12 C10 C12 C10 C12

preheat preheat preheat preheat preheat preheat preheat preheat preheat preheat preheat preheat

Q (GJ/h)

installed cost M$

100.42 73.46 120.35 73.38 74.18 107.49 62.41 110.95 82.04 110.49 68.36 105.62

3.25 2.49 3.79 2.49 2.51 3.45 2.17 3.54 2.74 3.53 2.35 3.40

Figure 10. Annual costs diagram.

dollars (M$). The results show that the progressive distillation is not only more economic in its energy consumption but also in its annual cost. Figure 10 also displays the distribution of the operating and the capital costs in the annual cost of plants; the source of the lower annual cost in the case of the PD plant derives from the lower operating cost of the PD plants.

the PD and AV units do not differ significantly, since the quality and quantity of the atmospheric residue is the same regardless of the technology. The atmospheric furnaces have similar values as well. These consequences are true when studying the two plants processing the same crude oil. It follows from the different mass flows of atmospheric residue of the different types of oils that the duties of the vacuum furnaces are different, the lowest is the duty in the case of Crude A since it is the crude with the lowest density and the lowest amount of residue.

4. CONCLUSIONS The progressive distillation plant (PD) proves to be more energy-efficient and economical in the cases of processing three different crude oils than the conventional atmospheric and vacuum distillation plant (AV). The PD is absolutely applicable for crude oil distillation since it can produce the same products as the AV units. If the general philosophy of technology selection is followed; that is, in the case of equal operating costs that technology is

3. RESULTS The operating and the capital costs are summarized and represented in annual values and in million dollars. The annual operating costs of the progressive distillation plant is several million dollars lower than those of the AV plants. The capital 19290



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selected that has a lower capital cost, and in the case of equal capital costs that technology is selected that has lower operating cost, than it can be concluded that the PD should be selected in both cases. This means that the PD has lower energy consumption and its investment cost is also lower than that of the corresponding AV unit. The lower energy consumption means also lower greenhouse gas emission, which is favorable for environmental reasons. Our study shows that the alternative technology for crude oil distillation is as capable for the same task as the conventional AV units, and at the same time it is more economic, too. It is definitely worthwhile to develop and investigate this distillation technology since significant savings can be achieved while complying with the current strict industrial and environmental regulations.

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ASSOCIATED CONTENT

S Supporting Information *

Additional tables containing duty values. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors are grateful for the financial support from the Ph.D. program of Gedeon Richter Plc. and for the New Széchenyi Terv (KMR-12-1-2012-0066).

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ABBREVIATIONS AC = atmospheric pumparound BFW = boiler feedwater COND = condenser CR = crude oil F = feed FH = fired heater GO = gasoil GUDR = gudra (atmospheric residue) HN = heavy naphtha L = liquid LN = light naphtha LPG = light petroleum gases REB = reboiler SG = steam generation V = vapor V.D = vacuum distillate VC = vacuum pumparound VGO = vacuum gasoil

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REFERENCES

(1) U.S. Energy Information Administration. http://www.eia.gov/ totalenergy/data/annual/showtext.cfm?t=ptb0501a (accessed May 7, 2014). (2) U.S. Energy Information Administration. http://www.eia.gov/ totalenergy/data/monthly/pdf/sec1_3.pdf (accessed May 7, 2014). (3) BP Statistical Review of World Energy. bp.com/statisticalreview (accessed March 12, 2014). (4) International Energy Agency Key World Energy Statistic. www. iea.org (accessed March 12, 2014). 19291



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Comprehensive Investigation and Comparison of Refinery Distillation

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