A Process Intensification Methodology Including Economic

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Process Systems Engineering

A process intensification methodology including economic, sustainability and safety considerations Arick Castillo-Landero, Andrea Paulina Ortiz-Espinoza, and Arturo Jimenez-Gutierrez Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b04146 • Publication Date (Web): 13 Nov 2018 Downloaded from http://pubs.acs.org on November 22, 2018

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Industrial & Engineering Chemistry Research

A process intensification methodology including economic, sustainability and safety considerations Arick Castillo-Landero, Andrea P. Ortiz-Espinoza, Arturo Jiménez-Gutiérrez* Chemical Engineering Department, Instituto Tecnológico de Celaya, Celaya, Gto., 38010 México

Abstract A methodology for the design of intensified processes that includes economic, sustainability and inherent safety factors is presented. Given an original synthesis problem to produce a desired chemical from a set of feedstocks, a base design is first generated, from which a gradual intensification procedure is carried out until a fully-intensified design with a minimum number of pieces of equipment is achieved. A novel approach in this work is that in addition to economic and sustainability factors, inherent safety metrics are evaluated at each step of the intensification methodology. In particular, the evaluation of inherent safety poses an important challenge because of the hybrid types of equipment units that inevitably appear as part of the intensification task. An adjusted FEDI index is included for such an evaluation as part of the methodology. Two case studies, one dealing with the production of isoamyl acetate and another one with the production of dioxolane products are taken to show the applicability of the intensification methodology. It is shown that a fully-intensified structure does not necessarily represent the best option when the three metrics are taken into account.

*Corresponding author. Tel. +52-461-611-7575 Ext 5577. Email: [email protected]

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

1. Introduction Process intensification has gained significant attention as a tool to design new processes that meet additional objectives to the sole consideration of economic performance. As a consequence, the typical process synthesis problem has been expanded to consider synergistic effects in the process equipment, which has given rise to the implementation of hybrid equipment in a chemical plant.1 Applications of intensified processes have been increasingly observed. Thus, the design of intensified process that require hybrid equipment has been the topic of particular interest in recent publications, for example, to name a few, the development of gas membrane separation processes and its application to purify ethanol solutions,2 the design of a mixerseparator reactor to carry out a transesterification reaction involved in the production of biodiesel,3 the design of reactive distillation systems for the production of silane products,4 and the use of dividing-wall columns as part of intensified processes and their applications for aromatics separations.5,6 It should be noted that most of the works related to process intensification, as those noted above, take an integrated or intensified process as a basis to develop the design of the unit and carry out relevant economic, energetic and/or sustainability analysis, without the application of a formal methodology that takes the conceptual design from its idea to the final intensified process. On these lines, the pioneering work by the group of Gani and co-workers deserves special consideration.7,8,9 They have proposed the task of process intensification as the integration of the phenomena involved in different pieces of equipment in a chemical process, and developed a methodology to carry out the intensification task. The intensification methodology is based on a three-stage algorithm. The first stage consists in the generation of a base case design. In the second stage, rigorous simulations and an analysis of possible improvements of the process are carried out. Finally, the phenomena involved in each individual equipment are analyzed so that possible integration options that provide alternative flowsheets to improve the performance of the process are identified. The problem has been formulated as an MINLP optimization model, whose solution provides an intensified process that meets an established objective function, such as the minimization of total annual cost. Applications from this methodology have been shown to design intensified processes for the production of isopropyl acetate with significant savings in energy


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requirements with respect to both a conventional production system and another one based on reactive distillation,7 for the production of di-methyl carbonate using propylene carbonate and methanol as raw materials, in which several flowsheets with advantages in economic and sustainability metrics, as well as LCA factors were obtained,8 and for the design of a more energy-efficient process for ethylene glycol production with respect to a conventional flowsheet.9 In all these cases, the inclusion of hybrid/intensified separation units has played a significant role to achieve the improvement of conventional base designs. Kuhlman and Skiborowski10 applied a similar methodology for the design of an intensified ethanol dehydration process by formulating a process superstructure and solving it via an optimization approach. Castillo-Landero et al.11 took the work by Babi et al.8 as a basis and developed a procedure to intensify a given flowsheet aiming to minimize the number of pieces of equipment. As opposed to the work by Babi et al.,8 in which a solution is obtained from the application of an optimization model, a gradual intensification was developed such that several intermediate structures were identified and rated according to the economic and sustainability parameters of interest. The application to the design of an intensified process for the production of dioxolane products showed that each gradual intensification step provided incremental benefits in terms of economic and sustainability factors. The aforementioned intensification methodologies are based on the concept of phenomena building blocks (PBBs), which quantitatively describe the phenomena involved in each equipment unit in the process, namely mixing, heating, cooling, chemical reaction, mass or heat transfer, separation or division of streams. The basic assumption of the method is that PBBs of multiple units can be combined into fewer pieces of equipment. Then, the combination of one or more PBBs, which describes the task performed in a piece of equipment, usually results in novel units, such as multifunctional reactors, hybrid separation units, or reactive distillation columns One item still not considered in the intensification methodology described above is that related to inherent safety. The inclusion of inherent safety principles during the conceptual design of a process is a major topic that is gaining significant attention in process systems engineering.12 Typically, the assessment of safety in a chemical process plant is carried out



once the final design has been completed and all the operating conditions have been specified. As a natural consequence, addressing safety properties of a process after the design has been done reduces the opportunities to modify key parameters in the design in order avoid sources of risk instead of controlling them.13 A typical method to evaluate safety with wide industrial use is the hazard and operability (HAZOP) analysis. The main characteristic of the HAZOP analysis is that it requires detailed information of the process that is only available once the design of the plant has been finished, thus making it not suitable for application at the conceptual stage of the process design. Another option for safety assessment is the application of a quantitative risk analysis (QRA) technique. The QRA estimates failures and consequences in a piece of equipment with a probabilistic approach. The works by Medina-Herrera et al. have shown how QRA can be applied for the design of inherently safer distillation systems,14 for the design of optimal plant layouts,15 and for the selection of solvents for extractive distillation processes.16 Even when the QRA technique represents a convenient tool for individual pieces or systems with a few units, its application for more complicated systems, for instance full process flowsheets, does not provide a convenient option because of the complexity with which the analysis grows with the number of process units. The assessment of inherent safety during the design stage of a process, therefore, requires metrics that allow more direct calculations and that can be applied with the limited information available at that stage. The first safety index found in the literature that could be considered for inherent safety evaluation is the Dow fire and explosion index (F&EI), which is based on material and process factors.17 Given that in the Dow F&EI the material factor is independent from the process operating conditions, other indices have been proposed to overcome this limitation. One of such indices is the fire and explosion damage index (FEDI) proposed by Khan and Abbasi18 as part of their hazard identification and ranking (HIRA) methodology. The FEDI estimation process includes the classification of units according to their purpose, the evaluation of energy factors through chemical properties and operating conditions, the assignment of penalties, and the estimation of potential damage. The outcome of the index is a score for each unit in the process that can be characterized in terms of its hazardous characteristics according to the HIRA methodology. Table 1 gives the rating of hazard levels for processes according to such a methodology taking FEDI values as a basis.


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Other indices suitable for inherent safety evaluation that allow their implementation with simulation and optimization tools have been developed. Examples of these types of indices are the prototype index for inherent safety (PIIS), the inherent safety index (ISI), and the iSafe index.19 The process route index (PRI)20 and the process stream index (PSI)21 also belong to this category and are used to rank chemical process and streams according to the level of explosiveness. A review of safety indices suitable for application in process design is available in Roy et al.12 Even though some efforts have been made to include safety in process design, e.g. choosing the best option among some process alternatives,22,23,24,25 only few of them deal with the inclusion of safety aspects in intensified processes or hybrid units.16,26 In general, the main focus of these projects has been the evaluation of safety in the final intensified process, without considering a methodology to transform a base design into the intensified structure, or the analysis of some “less-intensified” alternatives that could represent safer processing options. In this work, an intensification methodology in which economic and sustainability factors are complemented with the evaluation of inherent safety properties for alternative flowsheets is carried out. Gradual intensification structures are developed until a design with a minimum number of processing units is obtained. Each structure is rated with the three metrics to provide a more complete assessment of the intensified alternatives generated with this methodology.

2. Approach Given a process that has the potential to be intensified, a methodology to reduce the number of pieces of equipment is carried out. This methodology gives as a result different process alternative that gradually reduce the number of units until the minimum number of pieces of equipment is reached. The effect of the gradual intensification is assessed from the evaluation of economic, sustainability and safety parameters. The procedure allows the identification of the best design from each of these metrics, so that possible trade-offs can be identified. The intensification algorithm and the safety assessment methodology are described next.



2.1 Process intensification methodology The basis for the intensification method used in this work is taken from Castillo-Landero et al.11 The approach considers the decomposition of the process in different levels, i.e. process, equipment, task and phenomena levels. The method consists of a three-stage algorithm. A detailed description of each stage, which includes the set of data needed as part of the intensification problem, is given in Babi et al.8 so we give here only a conceptual description of each one. In the first stage, a base case flowsheet is synthesized, for which information about raw materials, products and catalysts, physical properties, operating conditions and performance of the reaction and separation systems is recollected. Once the base case design has been completed (or if a base design is already available as part of the initial information) and all the relevant information has been gathered, a rigorous simulation is carried out in the second stage to validate the base case flowsheet and to obtain information such as mass and energy balances and key parameters from the streams and operation units. The design is then analyzed to assess its economic and sustainability metrics. For this purpose, new tasks suitable for intensification must be established, for which the flowsheet is transformed into a block diagram, and then each block is changed into its equivalent PBB. Finally, in the last stage the parts of the process that could improve its performance are identified. In particular, a list of guidelines for enhancing economic and sustainability considerations is provided in Castillo-Landero et al.11 Then, through the combination of different PBBs new design alternatives can be generated. The combination of PBBs to describe a given operation within a process is known as simultaneous phenomena building blocks (SPBs). Once the SPBs have been generated, one can identify which ones have the potential to improve the performance of the process, and by merging SPBs from different pieces of equipment new units are generated to develop intensified options. These new configurations must then be validated through rigorous simulations and analyzed to compare their performance metrics with respect to the original design. The procedure is applied until a structure with a minimum number of process units is achieved. The novelty of this work is that inherent safety is considered as part of the intensification methodology. In addition to economic and sustainability factors, inherent safety is evaluated at each step of the intensification procedure, such that its possible conflict with the other metrics can be assessed at this stage of the process design.


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2.2 Safety evaluation The assessment of inherent safety is included as part of the intensification methodology. After an analysis of the different indexes that could be used for this task, the FEDI was selected because of its suitability for application at the conceptual stage of design and for the more detailed evaluation it provides with respect to other indexes. The outcome of the FEDI is a score for each of the process units that can be characterized according to the HIRA methodology. Base designs subject to intensification are commonly based on conventional units, for which the evaluation of the FEDI index is quite straightforward. Intensified options, however, give rise to hybrid units, for which a modification to the original FEDI estimation proposed by Khan and Abbasi18 has to be made in order to provide a proper inherent safety assessment for such new units. The estimation of the FEDI consists of five steps. First, each unit is classified according to the task it performs. The classification includes storage, physical operations, chemical reactions, transportation and other units. In the second step different energy factors are considered. The first energy factor (F1) accounts for chemical energy, for which the main influence is given by the amount of chemical handled by the process unit. Energy factors F2 and F3 account for physical energy. A fourth factor (F4) is used for units that perform chemical reactions. Equations 1 to 4 show how to calculate each energy factor.

𝐹2 =

(1)

6 (𝑃𝑃)(𝑉𝑜𝑙) 𝐾

(2)

)

(3)

𝐾

()

(

𝐹3 = (1𝑥10 ―3)

𝐻𝑐

( )

𝐹1 = (0.1)(𝑀)

1 (𝑃𝑃 ― 𝑉𝑃)2(𝑉𝑜𝑙) 𝑇 + 273

𝐹4 = (𝑀)

𝐻𝑟𝑥𝑛

( ) 𝐾


(4)


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In these equations, M is the mass of chemical (kg/s), Hc is the heat of combustion (J/mol), PP and VP are the processing and vapor pressure (kPa), Vol is the vessel volume (m3), T is the temperature (°C), Hrxn is the heat of reaction (kJ/kg) and K is a constant equal to 3.148. In the third step, penalty values are assigned to account for the severity of some process parameters such as temperature, pressure, capacity, and the characteristics of the chemicals. In the fourth step energy factors and penalties are put together and the damage potential is estimated (the details for the estimation of damage potential as a function of the penalty factors are given in the appendix). Finally, the damage potential is transformed into the FEDI as shown in Equation 5. 1

𝐹𝐸𝐷𝐼 = 4.76 (𝑑𝑎𝑚𝑎𝑔𝑒 𝑝𝑜𝑡𝑒𝑛𝑡𝑖𝑎𝑙)3

(5)

The modifications proposed in this work to the FEDI calculations are related to the estimation of the energy factors, specifically for its application to different types of distillation columns. Three types of distillation columns can be considered with special interest, the conventional, the reactive distillation (RDC) and the divided wall column (DWC). The procedure to calculate the energy factors for each distillation system is shown next. (a) Conventional distillation columns A representation of a conventional distillation column is shown in Figure 1. The mass handled by the equipment unit (M) is taken as the sum of the feed, the reflux and the boilup streams, as shown in equation 6. The volume (Vol) term for this case is the volume of the column. 𝑀 = 𝐹𝑒𝑒𝑑 + 𝐿 + 𝑉′

(6)

Once M and Vol are defined, equations 1 to 3 are used to estimate the energy factors. (b) Reactive distillation column For the safety assessment of complex distillation systems such as the reactive distillation columns, the system is divided into three zones, namely the reaction zone, the rectification


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section and the stripping section. Assuming the distribution shown in Figure 2, one can evaluate the term M from equations 7 to 9. 𝑀𝑧𝑜𝑛𝑒1 = 𝐿 + 𝑉2 ― 1

(7)

𝑀𝑧𝑜𝑛𝑒2 = 𝐹𝑒𝑒𝑑 + 𝐿1 ― 2 + 𝑉3 ― 2

(8)

𝑀𝑧𝑜𝑛𝑒3 = 𝑉′ + 𝐿2 ― 3

(9)

The term Vol corresponds to the volume of each of the sections. With the mass and volume terms defined, three energy factors are computed for each zone. Additionally, factor F4 is estimated for the reaction zone. (c) Divided-wall distillation column For the safety analysis of the DWC, the unit is divided into four zones as shown in Figure 3. Equations 10 to 13 show the calculation of the mass term for each zone, and the volume term will correspond to the volume of each section. Then, energy factors are estimated for each zone with equations 1 to 3. In the case of an existing reactive zone in the DWC, the factor F4 is also estimated. 𝑀𝑧𝑜𝑛𝑒1 = 𝐹𝑒𝑒𝑑 + 𝐿2 ― 1 + 𝑉4 ― 1

(10)

𝑀𝑧𝑜𝑛𝑒2 = 𝐿 + 𝑉1 ― 2 + 𝑉3 ― 2

(11)

𝑀𝑧𝑜𝑛𝑒3 = 𝐿2 ― 3 + 𝑉4 ― 3

(12)

𝑀𝑧𝑜𝑛𝑒4 = 𝐿1 ― 4 + 𝐿3 ― 4 + 𝑉′

(13)

In summary the intensification algorithm is sequentially applied until the minimum number of pieces of equipment has been achieved, thus generating a series of intensified process alternatives with the assessment of the three metrics of interest for each alternative, namely economic, sustainability and inherent safety. The methodology allows the identification of a superior design based on all of them, or possible trade-offs among the metrics, in which case the selection will depend on the relative weight given to each one as part of the decisionmaking process. 3. Case studies



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To illustrate the intensification approach together with the evaluation of the inherent safety index, two cases of study are presented. The first case deals with a design to produce isoamyl acetate, while the second case considers the production of dioxolane products 3.1 Case study 1. Isoamyl acetate production The first case study is a process for isoamyl acetate production via esterification of isoamyl alcohol with acetic acid. The data for this process is taken from the work by Osorio-Viana et al.27 The esterification reaction is as follows, 𝐶𝐻3𝐶𝑂𝑂𝐻 + 𝐶5𝐻11𝑂𝐻⇄𝐶5𝐻11𝐶𝑂𝑂𝐶𝐻3 + 𝐻2𝑂

The kinetic model is,28 𝐸𝑎

( )

𝑟 = 𝑘0 ∗ exp ―

𝑅𝑇

( )

𝑎𝐴𝑎𝐵 ― 𝑘′0 ∗ exp ―

𝐸′𝑎

𝑅𝑇

𝑎𝐶𝑎𝐷

(14)

Where ai refers to the activity of component i in the mixture. The constants are given by, 𝑘𝑚𝑜𝑙𝑖 𝑘0 = 8.88 𝑥 105 𝑘𝑚𝑜𝑙𝑚𝑖𝑥 ― 𝑠 𝐽 𝐸𝑎 = 6.20 𝑥 104 𝑚𝑜𝑙 𝑘𝑚𝑜𝑙𝑖 𝑘′0 = 8.78 𝑥 103 𝑘𝑚𝑜𝑙𝑚𝑖𝑥 ― 𝑠 𝐽 𝐸′𝑎 = 6.07 𝑥 104 𝑚𝑜𝑙 The first part of the intensification algorithm used by Babi et al.8 and Castillo-Lanero et al.11 calls for the synthesis part of the problem, that is the development of a flowsheet that transforms the given feedstocks into specified products to provide a base design. In this case, a design was developed in the work of Osorio-Viana et al.27 and we take it as the base case design for the application of the methodology. The flowsheet of the base design is shown in Figure 4. It consists of a reactor followed by two distillation columns. The first distillation


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column yields isoamyl alcohol as a bottom product, and the second column is used to separate water from unreacted raw materials that are sent back to the reactor. An initial analysis of the process is carried out. Open and closed loops of the process flowsheet are analyzed to identify critical paths (or “hot spots”) to detect inefficiencies that may lead to potential improvements as part of the intensification procedure. Several loops are identified, and Table 2 shows the most critical closed and open paths detected for the flowsheet. The open path S1-S2-S3-S4-S5-S6-S8-S9 (streams refer to Figure 4) shows losses of the raw material isoamyl alcohol, which does not react and represent an economic loss of $768,240/y. As for the closed paths, the loop S2-S3-S4-S5-S6-S7-S12 involves 121 kg per hour of isoamyl acetate that is not obtained as a bottom product in column 1, and represents losses of $12,880 per year due the energy needed to recycle it. The flowsheet is then translated into tasks and phenomena diagrams. Figure 5 shows the corresponding block flow diagram and the phenomena flow diagram for each unit. One reaction task and two separation tasks are carried out in the original process. From here, one can generate the superstructure shown in Figure 6 that serves to analyze the potential for integration of one or more units as part of the sequential intensification methodology. The two separation tasks are first considered for intensification. This implies that the two distillation columns can be integrated into a single unit, from which water is obtained as a top product and isoamyl alcohol as a bottom product, as shown in Figure 7. For this design, the utility cost is 11.8% lower than in the base case and the carbon footprint is reduced by 84.7%. We can then consider the combination of the reaction and separation tasks of the two units of the previous alternative into one piece of equipment, which corresponds to a reactive distillation column, from which the products isoamyl acetate and water are obtained as bottoms and top product, respectively (see Figure 8). The economic and environmental analysis of this alternative shows that utility costs are further reduced to reach savings of 20.9%, along with a reduction of carbon footprint by 85.3% with respect to the original design.



The result of the application of the intensification methodology in terms of the hot spots detected for the base design shows that the open path inefficiency dealing with losses of isoamyl alcohol was reducted by 59%, while the examination of the closed loop showed that the losses of isoamyl acetate observed in the original design were corrected. An interpretation of the intensification task based on the SPBs can be viewed in Table 3, where one can observe how SPBs change with each intensified option. This analysis is complemented by the block representation of each alternative given in Figure 9, which shows how the three tasks of the original flowsheet were merged into a single one that combines reaction plus separation. Table 4 gives a summary of the economic and sustainability analysis carried out for each alternative. The software ECON8 was used for the economic analysis, while LCSoft8 was used for the sustainability analysis through the estimation of carbon footprint. One can observe how the intensified processes provide more energy-efficient options and higher profit, along with more environmentally-friendly metrics. Inherent safety evaluation The safety assessment was carried out considering the following assumptions. 1. For a hybrid unit, such as RDC and RDWC, a FEDI score was computed for each of the zones of the equipment unit. Then, the most critical number was selected as the representative score for that piece of equipment. 2. FEDI was computed using the operating conditions of each equipment zone. As far as the parameters related to the characteristics of the chemical, the component with lowest flash point was taken as the basis for calculation. 3. For conventional distillation columns, FEDI was estimated using top and bottom conditions, and the most critical value was used for safety assessment. The results of the safety evaluation per equipment unit per zone of the design alternatives to produce isoamyl acetate are reported in Table 5. Different equipment units show different FEDI values, and distillation and reactive distillation columns show values that depend on the section that has been defined for each unit.


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Figure 10 shows the individual FEDI values that arise from the analysis of the results from Table 5; the highest value from all the sections represents the index for each piece of equipment. Then, the highest value for all of the equipment units is taken as the inherent safety index for each of the flowsheets that result after the application of the intensification methodology (see Figure 9). In this case, the safest alternative from the three flowsheets is the Alternative 1 from the intensified options, that is, a partially intensified process with a reactor and an intensified distillation system. Additionally, if the HIRA methodology is considered, both pieces of equipment of such an alternative lie in the category of moderately hazardous, while the riskiest equipment units in the base case and the fully intensified alternative lie in the hazardous category. Such a distinction calls for a special consideration of the flowsheet from Alternative 1. Therefore, even when the fully intensified design shows the best economic and sustainability parameters, the first intensified alternative (i.e. a process with partial intensification) might be considered as a more suitable options, since it improves the base design in all of the three factors, and provides the safest choice. 3.2 Case study 2. Dioxolanes production The production of 2-methyl-1,3-dioxolane (2MD) and 4-ethyl-2-methyl-1,3-dioxolane (4EMD) can be achieved via aldolization of ethylene glycol (EG) and 1,2-butanediol (1,2But) with acetaldehyde. The reaction mechanism is as follows. 𝐸𝐺 + 𝐶𝐻3𝐶𝐻𝑂→𝐻2𝑂 + 2𝑀𝐷 1,2 ― 𝐵𝑢𝑡 + 𝐶𝐻3𝐶𝐻𝑂→𝐻2𝑂 + 4𝐸𝑀𝐷 Castillo-Landero et al.11 applied the intensification methodology used in this work without safety evaluations to minimize the number of equipment units for the aldolization process proposed by Li et al.29 Since the methodology is the same one used in this work, we just summarize the major findings in such work and complement them with the inherent safety assessment for each alternative. The base case flowsheet (Figure 11a) consists of a reactor followed by a train of three distillation columns. The first column separates the acetaldehyde in excess, the second column is used to purify the 2MD product, and the third column is used to produce the 4EMD stream. The first partially intensified design (Alternative 1, Figure 11b) incorporates the integration of the reactor and the first column in a RDC. In this flowsheet, 2MD is recovered ACS Paragon Plus Environment


in column 2 and 4EMD is produced in column 3. This alternative leads to a reduction of 8.6% of the utility cost and 6.1% in carbon footprint. In the second intensified option (Alternative 2, Figure 11c), the integration of the last two columns of the base case design was performed; the resulting design consists of a reactive distillation column and a conventional distillation column, where 2MD is produced at the top and 4EMD at the bottom. The utility costs for this alternative are reduced by 30.5% compared to the base case, and the carbon footprint shows a reduction of 32.7%. The third alternative (Figure 11d) represents the fully integrated option, with one piece of equipment. This design considered the integration of the two columns used in the second intensified alternative (Figure 11c) that resulted in a reactive divided-wall distillation column (RDWC). This integration showed reductions to the original design that amounted to 69.9% in utility costs and 65.3% in carbon footprint. The safety assessment was carried out to complement the economic and sustainability parameters. Table 6 details the results for the safety evaluation of the four design alternatives of Figure 11 per piece of equipment per zone. It can be observed that for the conventional distillation columns values of the FEDI evaluated at both top and bottom conditions are fairly equivalent if the HIRA methodology is considered. For the hybrid units, however, some discrepancies are observed between the bottom and the top sections; this is mainly due to the mass of chemical handled in each zone. Figure 12 shows the resulting FEDI values for each piece of equipment of the alternatives presented in Figure 11. As can be seen, in the base case process and in the first intensified alternative, the equipment that represents the highest risk is the distillation column 2. In the second intensified alternative, column 2 keeps the same score, even when it has been integrated with the third column of the first alternative. Interestingly, for the fully intensified alternative, once all the pieces of equipment have been merged into a single RDWC, the FEDI score lowers from the previous intensified alternative, which means that the fully intensified option is at least as inherently safe as the previous one, if not slightly better. As a result, given the significant reduction for utility costs and carbon footprint, and the beneficial inherent safety level provided by the FEDI index, the last alternative, a fully intensified structure, offers the best design for this case taking economic, sustainability and safety factors into account.


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4. Conclusions A methodology for process intensification that includes inherent safety assessment in addition to economic and sustainability metrics has been presented. The process alternatives were generated using an intensification methodology aiming to minimize the number of pieces of equipment. Each step of the methodology provides a gradual intensification from an initial base design, which leads to the use of hybrid pieces of equipment in the flowsheet options; therefore, a reported index for safety assessment was modified to include such types of equipment units. Two case studies, one dealing with the production of isoamyl acetate and the other one with the production of two types of dioxolane products have been used to show the application of the methodology. The results indicated that the best metrics for the dioxolane process were all achieved with the process with the minimum number of pieces of equipment. For the production of isoamyl acetate, however, conflicts were observed between the economic/sustainability factors and the inherent safety metric. This result indicates that, depending on the priority given to each factor, the best design might not correspond to a fully intensified structure. The results from this work provide the incentive for the development of multiobjective optimization techniques to generate Pareto fronts for designs with different levels of intensification that offer optimal trade-offs. It should be noticed that the methodology is flexible to accommodate any safety index preferred by the user, such as the Dow’s Fire and Explosion Index,17 the Process Route Index,20 or the Inherent Safety Index,30 for instance, or new metrics that combine the three factors considered in this work, such as the one developed recently by Guillén Cuevas et al.31 Also, since the methodology is based on a sequential procedure, larger processes can be easily analyzed, with the main computational work provided by the use of process simulators, which would then be followed by the quantification of the economic, sustainability and safety metrics selected to rate the performance of the process. Supporting information The procedure for the evaluation of FEDI indexes in given in the supporting information. This information is available free of charge via the Internet at http://pubs.acs.org/. Acknowledgements



Authors wish to thank Prof. Rafiqul Gani from PSE for SPEED Co. for allowing access to ECON and LCSoft software, and for the inspiration he has provided to carry out this work. Financial support from the Mexican Council for Science and Technology (CONACYT) through grant CB-255164 is also gratefully acknowledged. References 1. Stankiewicz, A. I.; Moulijn, J. A. Process intensification: Transforming chemical engineering. Chem. Eng. Progress. 2000, 96, 22. 2. Shukla, S.; Méricq, J. P.; Belleville, M. P.; Hengl, N.; Benes, N. E.; Vankelecom, I.; Sanchez-Marcano, J. Process intensification by coupling the Joule effect with pervaporation and sweeping gas membrane distillation. J. Membrane Sci. 2018, 545, 150. 3. Fayyazi, E.; Ghobadian, B.; Mousavi, S. M.; Najafi, G. Intensification of continuous biodiesel production process using a simultaneous mixerseparator reactor. Energy sources. 2018, 40, 1125. 4. Medina-Herrera, N.; Tututi-Avila, S.; Jiménez-Gutiérrez, A.; Segovia-Hernández, J.G. Optimal design of a multi-product reactive distillation system for silanes production. Comp. Chem. Eng. 2017, 105, 132. 5. Tututi-Avila, S.; Domínguez-Díaz, L.A.; Medina-Herrera, N.; Jiménez-Gutiérrez, A.; Hahn, J. Dividing-wall columns: Design and control of a Kaibel and a Satellite distillation column for BTX separation. Chem. Eng. Proc. 2017, 114, 1. 6. Kiss, A. A.; Ignat, R. M.; Flores-Landaeta, S. J.; Haan, A. B. Intensified process for aromatics separation powered by Kaibel and dividing-wall columns. Chem. Eng. Process. 2013, 67, 39. 7. Lutze, P.; Babi, D. K.; Woodley, J. M.; Gani, R. Phenomena based methodology for process synthesis incorporating process intensification. Ind. Eng. Chem. Res. 2013, 52, 7127. 8. Babi, D.; Holtbruegge, J.; Lutze, P.; Gorak, A.; Woodley, J.; Gani, R. Sustainable process synthesis-intensification. Comput. Chem. Eng. 2015, 81, 218.


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9. Wisutwattana, A.; Frauzem, R.; Suriyapraphadilok, U.; Gani, R. Intensification of ethylene glycol production process. Comp. Aided Chem. Eng. 2017, 40, 1135. 10. Kuhlmann, H.; Skiborowski, M. Optimization-based approach to process synthesis for process intensiﬁcation: General approach and application to ethanol dehydration. Ind. Eng. Chem. Res. 2017, 56, 13461. 11. Castillo-Landero, A.; Jiménez-Gutiérrez, A.; Gani, R. Intensification methodology to minimize the number of pieces of equipment and its application to a process to produce dioxolane products, Ind. Eng. Chem. Res. 2018, 57(30), 9810. 12. Roy, N.; Eljack, F.; Jiménez-Gutiérrez, A.; Zhang, B.; Thiruvenkataswamy, P.; ElHalwagi, M.; Mannan, M. S. A review of safety indices for process design. Curr. Op. Chem. Eng. 2016, 14, 42. 13. Kidam, K.; Sahak, H. A.; Hassim, M. H.; Shahlan, S. S.; Hurme, M. Inherently safer design review and their timing during chemical process development and design. J. Loss Prev. Process Ind. 2016, 42, 47. 14. Medina-Herrera, N.; Jiménez-Gutiérrez, A.; Mannan, M.S. Development of inherently safer distillation systems. J. Loss Prev. Process Ind. 2014, 29, 225. 15. Medina-Herrera, N.; Jiménez-Gutiérrez, A.; Grossmann, I.E. A mathematical programming model for optimal layout considering quantitative risk analysis. Comp. Chem. Eng. 2014, 68, 165. 16. Medina-Herrera, N.; Grossmann, I. E.; Mannan, M. S.; Jiménez-Gutiérrez, A. An approach for solvent selection in extractive distillation systems including safety considerations. Ind. Eng. Chem. Res. 2014, 53, 12023. 17. Dow’s Fire and Explosion Index Hazard Classification Guide, 7th Ed.; AIChE: New York, 1998. 18. Khan, F. I.; Abbasi, S. A. Multivariate hazard identification and ranking system. Process Safety Progress. 1998, 17, 157.



19. Rahman, M.; Heikkilä, A. M.; Hurme, M. Comparison of inherent safety indices in process concept evaluation. J. Loss Prev. Process Ind. 2005, 18, 327. 20. Leong, C. T.; Shariff, A. M. Process route index (PRI) to assess level of explosiveness for inherent safety quantification. J. Loss Prev. Process Ind. 2009, 22, 216. 21. Shariff, A. M.; Leong, C. T.; Zaini, D. Using process stream index (PSI) to assess inherent safety level during preliminary design stage. Safety Sci. 2012, 50, 1098. 22. Martínez-Gómez, J.; Nápoles-Rivera, F.; Ponce-Ortega, J. M.; El-Halwagi, M. M. Optimization of the production of syngas from shale gas with economic and safety considerations. Appl. Therm. Eng. 2017, 110, 678. 23. Ortiz-Espinoza, A. P.; Jiménez-Gutiérrez, A.; El-Halwagi, M. M. Including inherent safety in the design of chemical processes. Ind. Eng. Chem. Res. 2017, 56, 49, 14507. 24. Ruiz-Femenia, R.; Fernández-Torres, M. J.; Salcedo-Díaz, R.; Gómez-Rico, M. F.; Caballero, J. A. Systematic tools for the conceptual design of inherently safer chemical processes. Ind. Eng. Chem. Res. 2017, 56, 7301. 25. Thiruvenkataswamy, P.; Eljack, F. T.; Roy, N.; Mannan, M. S.; El-Halwagi, M. M. Safety and techno-economic analysis of ethylene technologies. J. Loss Prev. Process Ind. 2016, 39, 74. 26. Tian, Y.; Mannan, M. S.; Pistikopoulos, E. N. Towards a systematic framework for the synthesis of operable process intensification systems. In: Eden, M. R.; Ierapetritou, M.; Towler, G. P. Proceedings of the 13th International Symposium on Process Systems Engineering – PSE 2018. 2018, USA, Elsevier, 2383. 27. Osorio-Viana, W.; Ibarra-Taquez, H. N.; Dobrosz-Gómez, I.; Gómez-García, M. A. Hybrid membrane and conventional processes comparison for isoamyl acetate production. 2014, 76, 70. 28. González, D. R.; Bastidas, P.; Rodríguez, G.; Gil, I. Design alternatives and control performance in the pilot scale production of isoamyl acetate via reactive distillation. Chem. Eng. Res. Des. 2017, 123, 347.


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29. Li, H.; Huang, W.; Li, X.; Gao, X. Application of the aldolization reaction in separating the mixture of ethylene glycol and 1,2-butanediol: Thermodynamics and new separation process. Ind. Eng. Chem. Res. 2016, 55, 9994. 30. Heikkilä, A.M.; Hurme, M.; Järveläinen, M. Safety considerations in process synthesis. Comput. Chem. Eng. 1996, 20, S115. 31. Guillen-Cuevas, K.; Ortiz-Espinoza, A.P; Ozinan, E.; Jiménez-Gutiérrez, A.; Kazantzis, N. K.; El-Halwagi, M. M. Incorporation of safety and sustainability in conceptual design via a return on investment metric. ACS Sustain. Chem. Eng. 2018, 6(1), 1411.



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Table 1. Hazard ranking according to FEDI values from the HIRA methodology Fire and explosion damage index Hazard characterization (FEDI) FEDI > 500 Extremely hazardous 500 > FEDI > 400 Highly hazardous 400 > FEDI > 200 Hazardous 200 > FEDI > 100 Moderately hazardous 100 > FEDI > 20 Less hazard else No hazard

Table 2. Open and closed paths for the isoamyl acetate process.

Path Open S1 to S9 Closed S2 to S12

1

Mass Value Added (103 $/y) -768.24

Energy Waste Cost, 103 $/y 0.15

121

-

12.88

Flow-rate (kg/h)

Component Isoamyl alcohol Isoamyl acetate


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Table 3. SPBs generated of the base case and alternatives SPBs

Task Base case

M(L)=R(L)=C M=C=2phM=PC(VL)=PT(VL)=PS(VL) M=2phM=PC(VL)=PT(VL)=PS(VL) … M=2phM=PC(VL)=PT(VL)=PS(VL) M=H=2phM=PC(VL)=PT(VL)=PS(VL) M=C=2phM=PC(VLL)=PT(VLL)=PS(VLL) M=2phM=PC(VLL)=PT(VLL)=PS(VLL) … M=2phM=PC(VLL)=PT(VLL)=PS(VLL) M=H=2phM=PC(VLL)=PT(VLL)=PS(VLL)

Intensified Alternative 1 M(L)=R(L)=C M=C=2phM=PC(VLL)=PT(VLL)=PS(VLL) M=2phM=PC(VLL)=PT(VLL)=PS(VLL) … M=2phM=PC(VL)=PT(VL)=PS(VL) M=H=2phM=PC(VL)=PT(VL)=PS(VL)

Intensified Alternative 2 M=C=2phM=PC(VLL)=PT(VLL)=PS(VLL) M=2phM=PC(VLL)=PT(VLL)=PS(VLL) M=R=2phM=PC(VLL)=PT(VLL)=PS(VLL) … M=R=2phM=PC(VL)=PT(VL)=PS(VL) M=2phM=PC(VL)=PT(VL)=PS(VL) M=H=2phM=PC(VL)=PT(VL)=PS(VL)



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Table 4. Sumary of parameters calculated of the base case and alternatives of the production of isoamyl acetate Parameter (units)

Base case

Alternat1

Alternat2

Isoamyl acetate product (kg h-1)

122.02

123.47

122.72

Water subproduct (kg h-1)

18.78

17.34

18.08

Product purity (Isoamyl acetate)

0.99

0.99

0.99

Subproduct purity (water)

0.89

0.97

0.93

Energy usage (GJ h-1)

0.71

0.24

0.21

Utility cost (M$ y-1)

14.55

12.84

11.51

Purchase cost (M$ y-1)

1.62

0.58

0.43

Operating cost (M$ y-1)

84.44

83.54

83.41

Profit (M$ product-1)

0.03

0.05

0.06

Total carbon footprint (kg CO2 eq.)

0.47

0.07

0.06


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Table 5. Safety evaluation for the three flowsheets to produce isoamyl acetate. Unit Reactor Base case design

Column 1 Column 2 Reactor

Alternative 1

Alternative 2

Column 1 RDC

Zone Top Bottom Top Bottom Top Bottom Zone 1 Zone 2 (reaction) Zone 3


FEDI 171 205 292 109 169 110 168 178 98 222 287


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Table 6. Safety evaluation for the four flowsheets to produce dioxolanes. Unit Reactor Column 1 Base case design

Column 2 Column 3 RDC

Alternative 1

Column 2 Column 3 RDC

Alternative 2 Column 2

Alternative 3

RDWC

Zone Top Bottom Top Bottom Top Bottom Zone 1 Zone 2 (reaction) Zone 3 Top Bottom Top Bottom Zone 1 Zone 2 (reaction) Zone 3 Top Bottom Zone 1 Zone 2 Zone 3 Zone 4


FEDI 241 249 266 364 379 212 244 147 231 235 335 356 215 245 146 228 231 321 355 222 277 259 300

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CAPTIONS FOR FIGURES Figure 1. Conventional distillation column. Figure 2. Reactive distillation column. Figure 3. Divided-wall distillation column. Figure 4. Base case design for the isoamyl acetate process. Figure 5. Analysis of the base design. (a) Diagram of block flow. (b) Interpretation as a phenomena flow diagram Figure 6. Superstructure generated to for the intensification of the isoamyl alcohol process. Figure 7. First intensification of the isoamyl acetate process. Figure 8. Intensified reactive distillation column for the isoamyl acetate process. Figure 9. Base case design and best alternatives selected in the production of isoamyl acetate Figure 10. FEDI score for each equipment piece in the process alternatives for isoamyl acetate production. Figure 11. Flowsheet alternatives from the integration study for dioxolane production. (a) Base case. (b) First intensification. (c) Second intensification. (d) Full intensification. Figure 12. FEDI score for each equipment piece in the process alternatives for dioxolanes production.



Figure 1. Conventional distillation column.


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Figure 2. Reactive distillation column.



Figure 3. Divided-wall distillation column.


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Figure 4. Base case design for the isoamyl acetate process.



(a)

(b) Figure 5. Analysis of the base design. (a) Diagram of block flow. (b) Interpretation as a phenomena flow diagram


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Figure 6. Superstructure generated to for the intensification of the isoamyl alcohol process.



Figure 7. First intensification of the isoamyl acetate process.


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Figure 8. Intensified reactive distillation column for the isoamyl acetate process.



Figure 9. Base case design and best alternatives selected in the production of isoamyl acetate


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Figure 10. FEDI score for each equipment piece in the process alternatives for isoamyl acetate production.


d ) c)

a)

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

b )


Figure 11. Flowsheet alternatives from the integration study for dioxolane production. (a) Base case. (b) First intensification. (c) Second intensification. (d) Full intensification.


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Figure 12. FEDI score for each equipment piece in the process alternatives for dioxolanes production.



Table of Contents graphic


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A Process Intensification Methodology Including Economic

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