Feasibility Evaluation of A Novel Middle Vapor Recompression

Subscriber access provided by UNIV OF DURHAM

Process Systems Engineering

Feasibility evaluation of a novel middle vapor recompression distillation column Haifeng Cong, Jaden Patrick Murphy, Xingang Li, Hong Li, and Xin Gao Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b00038 • Publication Date (Web): 13 Apr 2018 Downloaded from http://pubs.acs.org on April 19, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 43 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

Industrial & Engineering Chemistry Research

Feasibility Evaluation of A Novel Middle Vapor Recompression Distillation Column Haifeng Conga, Jaden Patrick Murphya, b, Xingang Lia, Hong Lia, Xin Gaoa ∗

a

School of Chemical Engineering and technology, National Engineering Research Center of

Distillation Technology, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin University, Tianjin 300072, China b

Department of Chemical and Biological Engineering, University of Ottawa, Ottawa, Ontario, K1N 6N5, Canada

Abstract: Internal heat integrated technology was developed to improve the thermodynamic efficiency of distillation columns to save energy and increase profit. A novel internal heat integrated distillation column, middle vapor recompression distillation column (MVRC) was proposed, and simultaneously investigated in comparison to the vapor recompression distillation column (VRC) and the heat integrated distillation column (HIDiC). Temperature difference from top to bottom (∆T ), operating pressure (P ) and feed state in the conventional distillation columns (CDiC) were considered when studied the feasibility and flexibility of these three columns. Moreover, the economic evaluation was completed by calculating the total annual cost (TAC) for the selected economic model. The results show that the MVRC is a formidable internal heat integrated distillation column configuration with

∗

Corresponding author. Tel: +86-022-27404701(X.G.); Fax: +86-022-27404705(X.G.). E-mail: [email protected] (Xin Gao). 1

ACS Paragon Plus Environment

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

Page 2 of 43

a wide range of applications due to its operational flexibility. Keyword: distillation column; internal heat integration; energy saving; economic evaluation

1. Introduction The chemical industries consume vast amounts of energy by burning coal, natural gas and crude oil.1 The energy-intensive chemical industry also faces particular challenges of the increasing energy demand and declining natural resources.2, 3 To increase sustainability, the chemical industries should use thermal intensification approach to improve the energy efficiency. Widely used in the chemical industries, distillation is an energy-intensive separation technology,4, 5 which energy consumption accounts for 40–60% of whole chemical engineering processes.6 However, the distillation columns just provide a thermodynamic efficiency of about 5–10%.7 Especially for separating close boiling mixtures, too much lost work should be provided to create the gas-liquid counter-current flow.8 Large energy consumption and low thermodynamic efficiency make the distillation a potential candidate for reducing its utility demand.9 In a conventional distillation column (CDiC), high-temperature heat is injected to the reboiler and the rejection of low-temperature heat happens at the condenser. Except further optimization of operation parameters and internal structures,10,

11

the heat

recovery of distillation columns can be realized by the technology of internal heat integration which making use of heat sources and heat sinks available within the distillation process, so to reduce the consumption of utilities.12 Upgrading heat from a 2


Page 3 of 43 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


lower temperature level to a higher one, considerable attention to the heat pump-assisted distillation processes has been paid by the academic and industrial communities.9,

11, 12

There are many schemes have been proposed for the heat

integration within a distillation column. Known as mechanical vapor recompression heat pump, the most preferred scheme is to directly compress the column vapor stream needed for cooling and uses it as a source for heat injection.13 This kind of scheme, also called the internal heat integrated technology, has attracted more attention from the chemical researchers. Vapor recompression distillation column (VRC)14 and overall heat integrated distillation column (HIDiC)15, have been developed and reckoned as two most practical models for industrial applications.16 Through sharply reducing the lost work, the thermodynamic efficiency of distillation process can be efficiently improved by applying these two models.8, 17, 18

Figure 1. Schematic diagram of two internal heat integrated distillation columns

A working principle diagram of a VRC is presented in Figure 1a. By applying the compressor, the overhead vapor is compressed to a higher pressure, which causes 3



the temperature to increase as well. By transferring heat to the reboiler, the high quality overhead vapor could be used as the heat source to provide upward steam needed for distillation, and also be condensed into liquid as well. The column’s condenser and reboiler can be integrated into one single heat exchanger when the condenser duty and reboiler duty are comparable. If applicable, this concept could cause considerable reduction in the column’s energy requirements.19 There are a few industrial sized VRCs that have been built across the world; these industrial VRCs are used to separate close-boiling liquid mixtures such as propylene and propane.20 These VRCs have been exemplary in reducing energy waste and they provide several economic benefits.21 Unfortunately, a VRC cannot be used within a wide range.11 The compressor duty strongly depends on the compression ratio needed to be applied to improve the temperature level of top product to ensure the heat transferring to the bottom liquid. Thus, the thermodynamic efficiency of VRC will be higher for the close boiling systems which requiring lower increase in the energy quality.22 There will be no economic advantage when transforming the conventional distillation column (CDiC) which the temperature difference between the top and bottom is large.23 Moreover, the outlet temperature will also limit the operation of compressors. Based on these concepts, it is concluded that high economic efficiency of VRCs is limited to a portion of distillation systems. A HIDiC (Figure 1b) is another internal heat integrated distillation scheme originally developed to reduce the compression ratio and outlet temperature of compressors. It was thought to be a competitive technology to extend the 4


Page 4 of 43

Page 5 of 43 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


thermodynamic efficiency and application of the internal heat integrated distillation column. Under the traditional HIDiC configuration, the column is divided into two parts at the feed stage, and then housing the stripping column and rectifying column respectively. The stripping column is equipped with a reboiler, and the rectifying column is with a condenser. A compressor is used to elevate the pressure of rectifying column by compressing the vapor from the top of the stripping column. Moreover, the liquid leaving the bottom of rectifying column is depressurized by a throttling valve before returning it to the stripping column. Consequently, the rectifying column will be operated with a properly higher temperature than the stripping section. The hot and cold utility consumption can be both lowered when integrating the heat rejection of the rectifier with the heat injection of the stripper. As an advanced distillation scheme, exhaustive researches on heat exchange distribution,24 simplified mathematical methods,25, 26 and process optimization16, 27 for HIDiCs has been conducted. However, developed for about 40 years, the HIDiC is not yet industrialized except some lab-scale and pilot-scale experimental setups.28 It is because the varied HIDiC configurations are quite complicated to operate and control. To transfer heat from the rectifying column to stripping column needs intermediate heat exchangers for the tray-to-tray heat transfer process. This results in the modification of column internals, and a very complex controlling system. Moreover, some researchers still disagree on the performance of HIDiCs regarding energy savings.29

5



Figure 2. Schematic diagram of the middle vapor compression column (MVRC)

In this paper, we have proposed a novel new middle vapor compression distillation scheme (MVRC), to reduce the compression ratio and outlet temperature as the HIDiC and simplify the heat exchange structure as the VRC. Figure 2 presents the simplified working diagram of a MVRC. Like a HIDiC, the column has been separated into two parts at the feed stage. The vapor from the top of the stripping section will flow into the compressor to be compressed to the prescribed pressure and temperature. Then the high temperature vapor will act as the heat source for the reboiler at the bottom of the stripping section, and then be transported into the bottom of the rectifying section after heat exchange. Meanwhile, the reflux liquid leaving from the bottom of the rectifying section will be depressurized by the throttle valve and naturally cooled. The low temperature liquid will be used to condense the vapor 6


Page 6 of 43

Page 7 of 43 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


from the top of the rectifying section, and then flow into the top of the stripping section. As a result, the internal heat integration is accomplished by two independent heat exchange processes. Till date, no such thermal integration scheme is reported in literature. A simulative investigation into the performance of the MVRC was carried out with comparison to the VRC and HIDiC. The practical configurations of these three columns were determined first for the convenience of process simulation and economic evaluation. By the method of process simulation, the energy saving performance of these three columns compared with CDiCs was estimated for various miscible liquid mixture separations. These mixtures were selected carefully to represent different systems with distinct characteristics. Consequently, in combination with an economic evaluation, the feasibility and adaptability of each of the columns can be determined by investigating different conditions; the conditions investigated include the temperature difference between the top and bottom of the column, the operating pressure, and the feed state. As a result, this paper will clarify the direction in which further development of internal heat integrated distillation columns should proceed.

7


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

Page 8 of 43

Table 1. Operating information of CDiCs to separate the selected mixtures P-xylene O-xylene

N-butane N-pentane N-hexane

N-butene N-butane

Vapor = 0.5

Bubble point

Bubble point

Bubble point

12500 0.5/0.5

12500 0.5/0.5

12500 0.242/0.400/0.358

12500 0.5/0.5

Benzene Toluene

Mixture

Feed state

Bubble point

Flow of feed (kg/hr) feed purity (mass) Top production purity (mass) Bottom production purity (mass) Flow of top production (kg/hr) Operating pressure (Kpa) Pressure drop per stage (Kpa) Reflux ratio (mass) Top temperature (K) Bottom temperature (K) Stages in rectifying section Stages in stripping section Condenser duty (kW) Reboiler duty (kW)

12500 0.5/0.5

333.15 K (supercooled) 12500 0.5/0.5

0.99/0.01

0.99/0.01

0.99/0.01

0.99/0.01

0.99/0.01/0

0.99/0.01

0.01/0.99

0.01/0.99

0.01/0.99

0.01/0.99

0.005/0.523/0.472

0.01/0.99

6250

6250

6250

6250

3000

6250

100

100

100

100

400

400

0.06

0.06

0.06

0.06

0.06

0.06

1.355 353.0 384.2 13 13 1595.0 1625.3

1.277 353.0 384.2 13 13 1541.6 1762.7

1.749 353.0 384.2 13 13 1861.7 1227.5

13.89 411.2 417.0 68 64 8810.1 8811.3

1.997 315.5 368.8 13 13 866.2 960.2

12.066 308.5 315.2 58 55 8014.3 8016.7

8


Page 9 of 43 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


2. Representative miscible liquid mixtures For comprehensive evaluation of the performance of the internal heat integrated distillation columns, the miscible liquid mixtures being tested should be chosen to be abundant and representative. Table 1 presents the properties of the selected mixtures and the operating conditions required to separate them using a CDiC. The operating parameters were obtained via process simulation and optimization in the simulating software Aspen Plus v7.2, while also considering industrial experience. When studying the influence of the temperature difference between the top and bottom of the CDiC on energy use of the three columns, several mixtures were used, such as: p-xylene/o-xylene, benzene/toluene, and n-butane/n-pentane/n-hexane. These three mixtures have a 5.8 K, 31.2 K and 53.3 K top to bottom temperature differences respectively, and are all nonpolar systems. Liquid mixtures of p-xylene/o-xylene and n-butene/n-butane were used to analyze the performance of the three columns when applied in atmospheric and relative high-pressure conditions. Finally, the internal heat integrated distillation columns for separating benzene & toluene were estimated under different feed states. It is necessary that the selected testing system pair should be single-variable as far as possible when evaluating every impact factor.

3. Process Flow Diagram and Simulation Through process simulation, operating investment was the only economic benefit that could be predicted for the three columns. An overall economic evaluation should also consider the capital cost. For both process simulation and economic evaluation, the process flow diagram (PFD) of these three columns are detailed presented in 9



Figure 3. The PFDs contain not only the feed flow direction but also the kinds and number of industrial equipment. It is obvious that the configurations of these three columns are different from each other. In Figure 3a, fed above the feed stage, the column tower of VRC is the same as the CDiC. The overhead vapor can be directly transported to the condenser or compressed by a compressor, while the bottom liquid will be pumped to the reboiler or the heat exchanger. In steady operation, the compressed overhead vapor and bottom liquid respectively pass through the shell and tube of the heat exchanger to complete the heat transfer process. Then, the condensate liquid of top product depressurized by the throttle valve will be partially distillated out, and the rest will be returned at the top of column as the reflux liquid. Meanwhile, the vaporized bottom product will flow back to the column bottom. The dividing wall heat transfer type shows promise as the most suitable configuration of the HIDiC for industrialization. In Figure 3b, the HIDiC configuration used here is the multi-tube type one, where a vertical multi-tube type heat exchanger is adopted as the heat transfer column. The configuration of the multi-tube type HIDiC has been detailed described in our previous research.30 The tube and shell pass are designed as the rectifying and stripping section respectively to ensure that the heat from the rectifying section is delivered into the stripping section but not environment. by a specific design distributor, the feed is distributed at the top of the shell pass. The vapor taken out from the top of the shell will be compressed and returned to the bottom of the tube, while the reflux liquid from the tube bottom will be 10


Page 10 of 43

Page 11 of 43 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


depressurized and then distributed at the top of the shell pass along with the feed. In Figure 3c, the rectifying column and stripping column are respectively housed in the configuration of MVRC. Similar to VRC, the overhead vapor of stripping column will be first get through the compressor to elevate the pressure and temperature. Then high-temperature vapor in the shell will transfer enough heat to the bottom liquid in the tubes at the heat exchangerⅠ, to ensure boil up in the bottom of the stripping column and as less hot utilities as possible. The non-condensate vapor will flow to the bottom of the rectifying column, while the condensate liquid will be mixed with the bottom liquid of the rectifying column and together depressurized by the throttle valve. The depressurized liquid can be divided into two parts: one part will be transported to the top of the stripping column, the other part will flow into the tube pass of the heat exchangerⅡto cool the high-temperature vapor from the top of the rectifying column and be vaporized itself. Then, the vapor will be returned to the top of the stripping column, while the liquid will flow to the top of the rectifying column. In all three configurations, the placement of the reboiler and condenser is for the startup of the distillation processes, and also making up the shortage of the reboiler duty or condenser duty after heat integration. Otherwise, the product outlets of three configurations are arranged similar to CDiC. Based on these three PFDs, the process simulating models were established in Aspen Plus v.7.2. For VRC and MVRC, the operating unit models, such as distillation column, heat exchanger and pump, are ready-made in Aspen Plus and convenient to develop the flowsheet by the mass and heat stream. But for HIDiC, there is no existing model for such a multi-tube type 11



distillation column. However, it is feasible to adopt the exsiting distillation model and tray-to-tray heat duty stream to realize the function of the multi-tube type HIDiC. The simulating method has been detailed describe in our previous research about the multi-tube type HIDiC.30 To be emphasized, the RADFRAC model was selected for simulating the distillation columns, and the isentropic efficiency was averagely set as 72% for all the compressors.

12


Page 12 of 43

Page 13 of 43 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


(a)

(b)

(c)

Figure 3. Process flow diagram (PFD) of three internal heat integrated distillation columns: a. VRC, b. HIDiC, c. MVRC 13



4 Economic Evaluation Method Based on the PFDs, equipment selection and economic evaluation of the capital cost can be finalized. In many papers, the economic evaluation method given by Douglas31 were adopted to estimate the cost of operating units in the chemical engineering process.24, 27, 32, 33 Although not very accurate, the Douglas’ method is sufficient for this study and provides a convenient comparison for the three columns being investigated. Total annual cost (TAC) is popular in the field of payback period evaluation. Generally, the TAC consists of the annual capital cost (ACC) and the annual operating cost (AOC). For evaluating these three distillation columns, the ACC mainly consists of the average cost of the column shell, the tower internals, the reboiler, the condenser, the external heat exchanger and the compressor during its service cycle. Whereas the AOC includes the annual cost of electricity, steam and condensate water. The costs of these utilities can be together calculated if inputting their unit price into the process simulating models in Aspen Plus. The results can be found in the project of “Utilities” after finishing the process simulation. Additionally, the ACC was summarized using the following cost correlations given by Douglas.31 Annual cost of column shell (ACSC, $/year): &

= 3919.32 . . 1 Annual cost of structured packings (ATC, $/year):

= ! 2 Annual cost of heat exchanger (AHEC, $/year): 14


Page 14 of 43

Page 15 of 43 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


&

" = # .$ 3 The value of # depends on the form of the exchanger. When these equations are applied to the reboiler and the condenser, # is equal to 1775.26 and 1609.13 respectively. Annual cost of compressor (ACPC, $/year): &

. % = 2047.24 )*+, 22 < )*+,- /0 < 7457 4

These correlations were created for all distillation columns. Therefore, for calculating Eq. (1)~(4), the diameter of column was estimated when set the operating velocity of gas phase as 70% of the flooding velocity. The internal structure of the multi-tube type distillation column is more complex than traditional ones, which design method has been detailed described in our previous research.30 The height of column was decided by the number of theoretical trays and the height equivalent to a theoretical plate of the selected packings (HETP). The area of the exchangers should be determined according to local conditions, including heat transfer temperature difference, rate of heat transfer and heat transfer coefficient. By referring the work of Ž. Olujić et al,34 the heat transfer coefficients of reboiler, condenser, heat exchanger and stage to stage in HIDiC are different and have been detailed presented in Table 2. The 2& represents the Marshall & Swift economic factor, while 3 is the service cycle of the equipment. The 4 represents the price of the structured packings used in the column. Moreover, other economic considerations such as cost index and utility costs are almost the same as those applied by Ž. Olujić et al.34 as shown in Table 2. 15



Page 16 of 43

Table 2. Economic Basis for Process Design and Optimization Parameter Value Equipment life time (years) 10 M&S (2013) 1432.5 Heat transfer coefficients 5 (W·m-2·K-1) Reboiler Condenser Heat exchanger Stage to stage in HIDiC Utility costs Electricity ($/kW·h) Low pressure steam ($/t) Cooling water ($/t)

1000 800 500 500 0.1 13 0.03 1920 0.4

Packings costs 4 ($/m3) (in China) HETP (m)

5. Results and Discussion 5.1 Top to bottom temperature difference in CDiCs The top to bottom temperature difference in the CDiC (∆6786 ) is always considered as the main factor to decide the compression ratio of the internal heat integrated columns. The larger the ∆6786 the more power that will be spent by the compressor to achieve the reversion of the temperature difference in the internal heat integrated columns. A larger ∆6786 may affect the energy saving performance of these internal heat integration columns. The energy saving percentage (9 ) were calculated by Eq. (5) 35. Where ): and ): is the reboiler duty of the CDiC and the internal heat integrated column respectively. Additionally, )*+,- represents the electric duty of the compressor. Because the efficiency of the turbine is about 35% when converting heat to electric energy, the coefficient is three when converting the

)*+,- to the equivalent ): . 9=

): − 5 ): 16


Page 17 of 43 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


(a)

(b)

(c)

Figure 4. Energy saving performance of three internal heat integrated distillation columns for separating different mixtures: a. p-xylene/o-xylene; b. benzene/toluene; c. n-butane/n-pentane/n-hexane ( represents the state operated with a 10 K heat exchange temperature difference) 17



The energy saving results of each system tested are summarized in Figure 4. The ranges of the compression ratio were established to guarantee the temperature difference of heat exchange varied from 5 K to 20 K. For the same testing system, the operating range of the compression ratio is different among these three columns, and the distinction becomes more obvious as ∆6786 increases. As expected, the heat integrated configuration of the MVRC and the HIDiC can reduce the operating compression ratio in comparison with the VRC. However, the lower compression ratio has no means to improve the energy saving percentage of the MVRC and the HIDiC to the desired level. For separating the mixture of p-xylene/o-xylene (Figure 4a), which have close boiling points, the VRC exhibits the best performance for saving energy. When a 10 K heat exchange temperature difference is set, the VRC could save 79.9% power used in the CDiC, compared to 72.9% and 75.5% respectively for the MVRC and the HIDiC. Each of these columns exhibit commendable energy saving performances when separating mixtures with close boiling points. Furthermore, a peculiar phenomenon arises as a result of the VRC performance: why is it that the MVRC and the HIDiC, which operate with lower compression ratios, do not save more energy than the VRC. By increasing ∆6786 , the energy saving performance of these three columns will be reduced. As shown in Fig. 4 (b), the separation of the benzene/toluene mixture yields energy savings of 49.8%, 44.6%, and 22.0% for the VRC, the HIDiC, and the MVRC, respectively. As for the n-butane/n-pentane/n-hexane mixture, the energy savings are 2.8%, 7.8%, and -21.4%, respectively. Obviously, the effect of the ∆6786 on the 18


Page 18 of 43

Page 19 of 43 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


energy saving performance is distinguishing among the three columns. The HIDiC is the most sensitive to variation in the ∆6786 , making it just suitable for separating mixtures with close boiling points. By comparison, the application scope of the VRC is larger, and the MVRC has the widest application range. Unfortunately, this finding contradicts the original purpose of the HIDiC, which was to be adopted to extend the application range of internal heat integrated distillation columns.

Figure 5. Comparison of compressor and reboiler duty of three internal heat integrated distillation columns for separating p-xylene/o-xylene, benzene/toluene, n-butane/n-pentane/n-hexane: (a)/(c)/(e) are the compressor duty; (b)/(d)/(f) are the reboiler duty ( represents the state 19



operated with a 10 K heat exchange temperature difference)

According to Eq. (5), the energy saving performance is determined by )*+,and ): which could not be integrated in these three columns. In Figure 5, )*+,and ): are presented to provide a detailed analysis on the energy saving performance of these three columns. First, we have noticed that not all of ): could be totally omitted in these three columns. The MVRC is the only column that could totally integrate ): within itself no matter what the compression ratio is or what system is being separated. The two separate heat integrated systems in the MVRC make it possible to change the operating conditions of the stripping and the rectifying section. When allocating the heat duty of the two heat exchangers, the stripping section is a priority and is set with total heat integration ( ): = 0 ). Although the two heat integrated systems are structurally independent, there is heat and mass balance in the whole distillation system. Consequently, once the integrated heat duty in the stripping section is decided, the integrated heat duty in the rectifying section can be determined. However, the integrated heat duty in the rectifying section cannot meet the total condenser duty requirements, therefore an extra utility to supply cooling is required to compensate for the condenser duty shortage. In comparison, the ): of the VRC and the HIDiC is not equal to zero under most conditions. For the VRC, there is only one heat exchanger to complete the heat integrated process. Therefore, the ): of the VRC can be omitted if the required condenser duty (reflux with bubble point) is larger than the required reboiler duty. Nevertheless, with the bubble point feed, the required condenser duty is always less than the required reboiler duty, so there is always a fraction of the reboiler 20


Page 20 of 43

Page 21 of 43 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


duty that cannot be integrated. However, with an increased compression ratio, the reflux liquid can be supercooled to establish a suitable heat transfer temperature difference. This reflux cooling is a covert way to raise the condenser duty to the required value, and consequently, integrate more reboiler duty in the VRC. For the multi-tube type HIDiC, with the dividing wall heat transfer configuration, the heat rejection of the top product condensation cannot be integrated. As a result, the reboiler duty of the HIDiC cannot be eliminated in most situations.30 Additionally, since the price of hot steam is more expensive than cold water, it is more advantageous to reduce the reboiler duty as much as possible. In this regard, the MVRC exhibits the best performance of flexibility. On a different note, when comparing the )*+,- of the three columns, several unexpected results were obtained. For all testing systems, the )*+,- of these three columns has a positive linear relationship with the compression ratio. There is an obvious difference among the slopes of the three increasing curves for the same testing system. The )*+,- of the MVRC has a steep increasing curve, while the VRC curve is the least steep of all three columns. Furthermore, when separating the same mixture, we have noticed that the )*+,- of the MVRC is always the largest while that of the VRC is the least when operated with the same compression ratio. Moreover, when the heat exchange temperature difference was set to 10 K, even though operated with a lower compression ratio, the )*+,- of the MVRC and the HIDiC is still larger than the VRC. Additionally, as the ∆6786 is raised, the difference of )*+,- become more obvious, an observation that is averse to the 21



original intention of MVRC and HIDiC development.

Figure 6. Compressor input of three internal heat integrated distillation columns for separating different mixtures: a. p-xylene/o-xylene; b. benzene/toluene; c. n-butane/n-pentane/n-hexane ( represents the state operated with a 10 K heat exchange temperature difference)

22


Page 22 of 43

Page 23 of 43 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


Actually, the compression ratio is not the only factor to determine the value of )*+,- , while the input of compressor is also a significant component. To calculate )*+,- , Eq. (6) can be applied as a mathematical expression, where ? represents the compressor input and @∆%, BC is the compressor duty per unit of mass which is relative to the compression ratio and the components of the input gas. )*+,- = ?@∆%, BC 6 In Figure 6, it is shown that there exists a large difference among the compressor inputs of the three columns. The VRC has a minimum amount of gas flowing through the compressor, comparable with the quantity of gas in the top of the CDiC. Additionally, the compressor input of the VRC remains constant despite an increasing compression ratio. As demonstrated in previous papers,24, 32, 34 there will be more gas running through the compressor of the HIDiC than the VRC, a difference which will increase when ∆6786 increases. What’s more, the compressor input of the MVRC is almost twice as much of the VRCs for all systems tested. The distinction between compressor inputs can be attributed to the different heat integrated configurations used in the three columns. Transferring the heat from the top of the VRC to the bottom does not alter the original operating state in a CDiC; variables such as vapor liquid ratio and minimum reflux ratio remain the same. However, in the HIDiC, the heat injection and rejection are respectively distributed along the stripping and rectifying sections. The HIDiC has a varied vapor flow rate in the column; this varied flow rate has a maximum above the feed stage but reaches a minimum value at the top and bottom of the column. After compression, the maximum vapor flow in HIDiC 23



will be more than that in CDiC, so that the average vapor flow can satisfy the requirements for separating the mixture. The compressor input in the MVRC can be divided into two parts: one part is the upward vapor which supports mass transfer, like that in a CDiC. The second part is the vapor in the Rankine cycle which continuously transfers heat from the top to the bottom. When operated with a bubble point feed, these two vapor flows are almost equal due to the similar enthalpy of phase change. Consequently, the compressor input of the MVRC is nearly twice as much as that in a VRC. Moreover, the compressor input is increased in tandem with the compression ratio in the HIDiC and the MVRC. This is a result of the pressure lifting in the rectifying section reducing the relative volatility of the mixture leads to a larger reflux ratio. This larger reflux ratio leads to more production of vapor, which aids in the separation process.

5.2 Operating pressure in CDiC ( EFGHF ) Besides most CDiCs operated at atmospheric pressure, some columns should adjust their operating pressure to fit the applied range of utilities. Additional interest in how the operating pressure impacts the energy saving performance of these three columns has been expressed. Figure 7 represents the energy saving performance of these three columns when applied to transform the atmospheric column for separating p-xylene/o-xylene ( ∆6786 =4.8 K) and the relative high-pressure column for separating n-butene/n-butane ( ∆6786 =6.7 K). Due to a similar ∆6786 , there is no obvious change in the operating compression ratio of these columns when the %6786 is varied. 24


Page 24 of 43

Page 25 of 43 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


Figure 7. Energy saving performance of three internal heat integrated distillation columns for transforming CDiCs with different operating pressure: a. p-xylene/o-xylene; b. n-butene/n-butane ( represents the state operated with a 10 K heat exchange temperature difference)

Additionally, the energy saving percentage of the columns in separating the n-butene/n-butane mixture is slightly smaller than the percentage observed for the p-xylene/o-xylene mixture. This reduction in energy savings is caused by the larger ∆6786 for the n-butene/n-butane mixture. It is possible that the increase in temperature and compression duty per unit mass of vapor is determined solely by the compression ratio, and not by the increase of absolute pressure. Calculated by Aspen 25



Plus, the compression duty per unit mass of vapor under different compression ratios is plotted in Figure 8. Regardless of whether the vapor is compressed from 100 kPa or 400 kPa, the slope curves of the compression duty are mostly the same. This demonstrates that the initial vapor pressure has no influence on the compression duty per unit mass.

Figure 8. Compression duty comparison of p-xylene/o-xylene and n-butene/n-butane (mass fraction of light component is 0.5) with different initial vapor pressure

However, except for the VRC, there is an obvious difference between the rate of decrease of the energy saving percentage curves versus increasing compression ratio shown in Figure 7. This difference is visible when comparing the same heat integrated column to separate p-xylene/o-xylene and n-butene/n-butane. This difference is still evident when the two mixtures share the same compression ratio while increasing the absolute pressure of the n-butene/n-butane vapor to four times that of the 26


Page 26 of 43

Page 27 of 43 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


p-xylene/o-xylene vapor. The tower of the VRC will always be operated with the same pressure as the CDiC, and consequently the mass transfer process will not be impacted by increasing the absolute pressure of the vapor. But for the MVRC and the HIDiC, their rectifying sections will be operated with the compressed vapor which reduces the relative volatility of the mixtures and has a negative effect on the separation process. As a result, the MVRC and the HIDiC should be operated with a larger reflux ratio to overcome this disadvantage. The larger the absolute pressure is, the more vapor that will be compressed, and the faster the energy saving percentage will decrease. Consequently, because the flexibility of the MVRC and the HIDiC has a relationship with %6786 , the VRC is the best internal heat integrated column to transform the CDiC when operated at relative high-pressure. 5.3 Feed state

Figure 9. Energy saving performance of three internal heat integrated distillation columns under different feed states (at a 10 K heat exchange temperature difference)

The feed state is an important parameter which has a great influence on the 27



operation of the CDiC. As shown in Table 1, with different feed states, the benzene/toluene column will be operated with varied reflux ratios, as well as a varied reboiler and condenser duty. It is demonstrated in Figure 9 that the energy saving percentage of these three columns will also be varied as the feed state changes. In comparison, these three columns have the worst energy saving performance when operated with a gas-liquid feed. The internal heat integrated columns seem to be suited to work solely with super cooled or bubble point feeds. Actually, the reboiler duty of the CDiCs are different due to the feed state, and the energy supplied to attain the fixed feed state will not be considered in the energy saving evaluation process. Assessing the feasibility and flexibility of these three columns just by the energy saving percentage, which directly reflects the conditions of the compressor and reboiler duty, would not provide a comprehensive result in these columns. The operating parameters in Table 3 are summarized to comprehensively present the variation of operating condition caused by changing feed stage. Although with the varied feed state, the compression ratio of all three columns is unchanged to maintain the 10 K heat transfer temperature difference. However, in the VRC and the HIDiC, the compressor duty will be increased as the feed temperature increases. Operated with the same compression ratio, the input of the compressor is the most important factor that affects the compressor duty. With the supercooled feed, the rate of the vapor flow will be reduced in the stripping section, while the gas-liquid feed will sharply increase the vapor above the feed stage. Consequently, the compressor input of the VRC and the HIDiC will be decreased and increased, 28


Page 28 of 43

Page 29 of 43 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


respectively, in comparison with the bubble point feed. The compressor input of the HIDiC is 35% more than the VRC when operated with supercooled feed, while this exceeding will reach to 50% when vapor fraction is 0.5 in the feed. Moreover, the feed state could significantly change the vapor-liquid conditions as well as the condenser and reboiler duty in the CDiC. The supercooled feed will turn some gas into liquid on the feed stage. Increasing the heat injection into the reboiler is to guarantee that there will be enough vapor flowing into the rectifying section. Similarly, for the overheated feed, more heat rejection from the condenser is required to allow for more liquid refluxing into the stripping section. As a result, shifting from supercool to overheating, the reboiler duty will decrease, while the condenser duty will increase gradually. After the heat integration in the VRC and the HIDiC, it is expected that the extra reboiler duty will decrease to zero, while by contrast, extra cold utility must be adopted to eliminate the extra condenser duty. It is optimal to operate the system with no extra reboiler duty since the price of steam is more expensive than cold water. However, the subsequent increase in compressor duty counteracts this advantage.

29



Page 30 of 43

Table 3. Parameters of three internal heat integrated columns under different feed states Project Average heat exchange temperature difference (K) Compression ratio Compressor input (×104 kg/hr) Compressor duty (kW) Reboiler duty (kW) Condenser duty (kW)

333.15 K

VRC Bubble point

333.15 K

MVRC Bubble point

333.15 K

HIDiC Bubble point

Vapor = 0.5

Vapor = 0.5

Vapor = 0.5

10

10

10

10

10

10

10

10

10

3.25

3.25

3.25

2.1

2.1

2.1

2.37

2.37

2.37

1.416

1.472

1.712

2.891

2.890

2.898

1.912

2.003

2.563

241.4

247.0

283.3

300.2

300.0

300.4

215.8

243.6

333.3

254.0

63.0

0

0

0

0

751.7

536.3

0

263.3

280.3

898.7

0

218.1

750.5

649.9

649.9

860.7

30


Page 31 of 43 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


Compared to the VRC and the HIDiC, it is peculiar that the operating parameters, besides the condenser duty, do not significantly change during variation of the feed stage. The supercooled and gas-liquid feeds have no influence on the input of the compressor in the MVRC. Consequently, the power supply of the compressor is very stable. The MVRC can achieve the ideal heat integrated configuration with the supercooled feed (333.15 K), which does not require additional hot or cold utility. For separating the benzene/toluene mixture, the feed with the temperature of 333.15 K seems to be the “perfect state” for the MVRC. As shown in Table 3, the condenser duty is increased when the temperature of the feed increases, and the amount of duty increase is equal to the enthalpy change of the feed. It can be concluded that the vapor-liquid ratio in the stripping and rectifying section of the MVRC will maintain at a fixed value and not be affected by the change of the feed state. The change of the feed enthalpy will be buttered off by the “Rankin cycle”, where the decreased enthalpy will be replenished by the reboiler and the increased enthalpy will be removed from the condenser. Although the energy saving percentage of the MVRC is 5% ~ 10% less than the VRC, the MVRC exhibits more operational flexibility, specifically when the feed state changes, which is very important for industrialization.

6. Economic evaluation In Figure 10a, 10c, 10e and 10g, the TACs under different compression ratios were plotted to find the optimal conditions for each of the three columns, and to compare their economic performance. Usually, the increased compression ratio will raise the operating cost and the capital cost of the compressor, but reduce that of the 31



external heat exchanger. In view of this, there often exists the optimal compression ratio to achieve the least TAC for the column. However, for most of the cases in this study, the TAC always increases along with the increasing compression ratio, do not meet this regulation like other researches.24, 32 Considering the design principle of the heat exchanger, 10 K was selected as the desired heat transfer temperature difference as a compromise, and as the standard for comparison among these columns. For separating the close boiling point mixtures of p-xylene/o-xylene and n-butene/n-butane, the VRC could save about 45% of the TAC in comparison with the CDiC, while HIDiC and MVRC could save 41% and 35% of the TAC, respectively. As reported by other papers,36, 37 VRC and HIDiC,as well as the novel MVRC are very suitable to transform the CDiC to allow for separation of mixtures with close boiling points. Nevertheless, the TAC saving percentage is much lower than the energy saving percentage. In Figure 10b and 10d, it is shown that the addition of the compressor and the external heat exchanger has significantly increased the capital cost. The capital cost of the VRC and the HIDiC are almost the same and both are approximately 41% more expensive than the CDiC. A detailed breakdown of costs of each of these three columns is provided in Table 4. The exceeding capital cost of the VRC is mainly contributed to the compressor and the external heat exchanger. These two pieces of equipment occupy 31% of the capital cost of the VRC, while that is 38% for the HIDiC. However, the integration of the tower and the heat exchanger in the HIDiC has reduced the height of tower and thus its capital investment.

32


Page 32 of 43

Page 33 of 43 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


Figure 10. Economic evaluation of three internal heat integrated distillation columns: a, c, e, g are the TACs under different compression ratio ( presents the state operated with a 10 K heat exchange temperature difference); b, d, f, h are the AOCs and ACCs at the 10 K heat exchange temperature difference 33



Page 34 of 43

Table 4. Cost summarization of three internal heat integrated columns (at a 10 K heat exchange temperature difference)

CDiC

VRC

MVRC

HIDiC

CDiC

VRC

MVRC

HIDiC

CDiC

VRC

MVRC

HIDiC

CDiC

N-butane N-pentane N-hexane VRC MVRC

—— 1.812 14.995 16.808

3.243 0.133 0 3.375

4.004 0.202 0 4.206

3.992 0.151 0 4.143

—— 1.649 13.643 15.292

3.468 0.141 0 3.609

4.201 0.161 0 4.363

4.629 0.165 0.000 4.794

—— 0.328 2.766 3.094

1.265 0.058 0.107 1.430

1.512 0.036 0 1.548

1.228 0.134 0.913 2.274

—— 0.178 1.634 1.812

1.065 0.085 0.503 1.653

1.442 0.018 0 1.460

1.819 0.047 0.140 2.007

2.446 3.568 0.280 0.268 ——

2.446 3.568 0.051 0.267 2.149

1.727 3.568 0.280 0.268 2.548

1.775 2.115 0.264 0.252 ——

1.775 2.115 0.053 0.251 2.271

0.253 0.115 0.092 0.089 ——

0.253 0.115 0.030 0.089 0.993

0.177 0.059 0.062 0.063 ——

0.177 0.059 0.038 0.063 0.863

——

0.813

1.075

——

0.271

0.241

——

0.160

6.563

9.309

9.385

4.407

7.279

7.859

0.550 1.752

1.691

0.362 1.360

0.177 0.059 0.062 0.063 1.106 0.152 0.256 1.876

0.129 0.059 0.062 0.063 1.338

0.993

0.253 0.115 0.098 0.089 1.150 0.244 0.262 2.211

0.184 0.115 0.092 0.089 0.969

0.828

1.788 2.134 0.286 0.252 2.658 0.981 0.910 9.009

1.258 2.134 0.264 0.252 2.877

——

2.446 3.568 0.301 0.268 2.555 0.883 0.837 10.858

13.528 19.698 10.889

13.371

12.653 3.644 3.182

3.759

3.966

2.174 3.014

3.336

3.882

P-xylene O-xylene

Project

Operating cost (× 10$ $/yr) Electricity Water Steam Total (AOC) Capital cost (× 10$ $/yr) Shell of tower Packings Condenser Robiler Compressor Extra heat exchanger Total (ACC) Total annual cost (× 10$ $/yr)

23.371 12.685 15.064

N-butene N-butane

Benzene Toluene

34


HIDiC

0.224 1.875

Page 35 of 43 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


The capital cost of the MVRC is the largest among these columns, which is nearly 65% higher than the capital cost of the CDiC. It is manly contributed to the fact that there are two external exchangers in the MVRC, which will double the investment in the external heat exchanger. Regardless, the cost of the compressor is significantly the highest. To separate the mixture of benzene & toluene, the TAC saving percentage of the VRC rapidly decreases to 13%, while there is no economic advantage in the MVRC and the HIDiC. The increased compressor duty not only decreases the energy saving percentage, but also greatly increases the cost of the compressor. The capital cost of both the VRC and the HIDiC is nearly three times as that of the CDiC, while 60% of the capital cost will be spent on the compressor. The capital cost of the MVRC is still the largest, at four times the capital cost of the CDiC. Although the compressor occupies just half of the capital costs of the MVRC, it is still the most expensive among the three columns. In Figure 10g and 10h, it is shown that the TAC of these three

columns

are

much

more

than

the

CDiC

when

separating

n-butane/n-pentane/n-hexane mixture. The investment in the compressor is more than 70% of the total capital costs. It is demonstrated that the internal heat integrated columns are not suitable to be applied to separate mixtures with a large difference in boiling point, even though there still exists a potential for energy savings with these columns. In conclusion, high capital costs, due mainly to the compressor, will negate all economic advantages created by saving energy through the internal heat integration 35



process. With the selected economic evaluation method, the VRC seems to be the best configuration to achieve the maximal economic saving performance. However, the TAC calculation relies heavily on the selected economic model. It could provide some useful information for comparison among the different columns, but not completely represent veritably the industrialized value of these columns. Certainly, reducing the cost of the compressor and the external heat exchanger is the major way to extend the application range of these internal heat integrated columns. Finally, the controllability in response to typical disturbances, mainly change of feed flow rate and component, is also important for the application of internal heat integrated columns. It is necessary to investigate and compare the effect of disturbances on the controllability of these three columns. However, limited by our weakness in the control theory of distillation process, the related work will be done in the further research with the assistance of the experts majored in control theory.

7. Conclusion The novel internal heat integrated technology was developed to improve the thermodynamic efficiency of the distillation column to save energy and increase profits. Besides the VRC and the HIDiC, the MVRC was proposed here as a novel internal heat integrated configuration. The process simulating models of these three columns were developed in Aspen Plus to investigate their feasibility and flexibility under different conditions. Firstly, the temperature difference from top to bottom in the CDiC (∆6786 ) has a great influence on the energy saving performance of these columns. The MVRC has the widest application range in terms of ∆6786 , followed 36


Page 36 of 43

Page 37 of 43 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


by the VRC, while the HIDiC could only be applied to separate mixtures with close boiling points. Secondly, the operating pressure in the CDiC (%6786 ) will not affect the energy saving performance of the VRC, but the performance will decrease for the MVRC and the HIDiC due to a reduction of the relative mixture volatility in the rectifying section. Finally, the change of the feed state has a strong impact on the operating conditions of the VRC and the HIDiC, such as compressor input, the reboiler duty, and the condenser duty. However, the operating conditions of the MVRC are very stable despite changing the feed state. It has been proven that the separated heat integrated process gives the MVRC the largest operational flexibility. Moreover, by calculating the TAC, it is demonstrated that the internal heat integrated columns in this study are more suitable to separate mixtures with close boiling points. The high cost of these columns, due to the compressor and external heat exchanger, is the main factor limiting the application of these columns. In conclusion, compared to the HIDiC, the MVRC and the VRC have better energy saving performance and have a larger operational flexibility. Furthermore, the MVRC and VRC are more suited for industrialization compared to the HIDiC.

Acknowledgement The authors acknowledge financial support from National Nature Science Foundation of China (Nos. 21336007, 21776202), and Key Technology R&D Program of Tianjin (No. 15ZCZDGX00330).

Nomenclature

area of exchanger, m2 37



diameter of column, m

height of column, m

NO

local heat transfer coefficient, W/m2K

2&

Marshall & Swift economic factor

%6786

The operating pressure in CDiC, kPa

)6

condenser duty, kW

)*+,-

compressor duty, kW

):

reboiler duty, kW

):

reboiler duty of conventional column, kW

5

heat transfer coefficient, W/m2K

?

compressor input, kg/s

BC

components in the input gas

∆%

compression ratio

∆6786

the temperature difference from top to bottom in CDiC, K

Greek Letters 4

price of structured packings, $/m3

3

service cycle of the equipment, year

9

fractional energy saving, %

References (1) Nigam, P. S.; Singh, A., Production of liquid biofuels from renewable resources.

Prog. Energy Combust. Sci. 2011, 37, 52-68. (2) Holtbruegge, J.; Wierschem, M.; Lutze, P., Synthesis of dimethyl carbonate and propylene glycol in a membrane-assisted reactive distillation process: pilot-scale 38


Page 38 of 43

Page 39 of 43 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


experiments, modeling and process analysis. Chem. Eng. Process. 2014, 84, 54-70. (3) Suárez, F.; Ruskowitz, J. A.; Tyler, S. W.; Childress, A. E., Renewable water: direct contact membrane distillation coupled with solar ponds. Appl. Energy 2015, 158, 532-539. (4) Górak, A.; Sorensen, E., Distillation: fundamentals and principles. Academic Press: 2014. (5) Sarbatly, R.; Chiam, C.-K., Evaluation of geothermal energy in desalination by vacuum membrane distillation. Appl. Energy 2013, 112, 737-746. (6) Waheed, M.; Oni, A.; Adejuyigbe, S.; Adewumi, B.; Fadare, D., Performance enhancement of vapor recompression heat pump. Appl. Energy 2014, 114, 69-79. (7) Jana, A. K., Heat integrated distillation operation. Appl. Energy 2010, 87, 1477-1494. (8) Seider, W. D.; Seader, J. D.; Lewin, D. R., Process design principles: synthesis,

analysis, and evaluation. John Wiley & Sons: 1999. (9) Jana, A. K., Advances in heat pump assisted distillation column: A review. Energy

Convers. Manage. 2014, 77, 287-297. (10) Babu, B.; Uday, G.; Jana, A. K., Reducing total annualized cost and CO2 emissions in batch distillation: dynamics and control. AIChE J. 2013, 59, 2821-2832. (11) Kiss, A. A.; Landaeta, S. J. F.; Ferreira, C. A. I., Towards energy efficient distillation technologies–Making the right choice. Energy 2012, 47, 531-542. (12) Chua, K. J.; Chou, S. K.; Yang, W., Advances in heat pump systems: A review.

Appl. energy 2010, 87, 3611-3624. (13) Palenzuela, P.; Roca, L.; Zaragoza, G.; Alarcón-Padilla, D. C.; García-Rodríguez, L.; de la Calle, A., Operational improvements to increase the efficiency of an absorption heat pump connected to a multi-effect distillation unit. Appl. Therm. Eng.

2014, 63, 84-96. 39



(14) Null, H. R., Heat pumps in distillation. Chem. Eng. Prog.;(United States) 1976, 72, 58-64. (15) Shimizu, K.; Mah, R. S. H., Dynamic characteristic of binary srv distillation systems. Comput. Chem. Eng. 1983, 7, 105-122. (16) Kiran, B.; Jana, A. K., Introducing vapor recompression mechanism in heat‐ integrated distillation column: Impact of internal energy driven intermediate and bottom reboiler. AIChE J. 2015, 61, 118-131. (17) Mostafa, H. A., Thermodynamic availability analysis of fractional distillation with vapour compression. Can. J. Chem. Eng. 1981, 59, 487-491. (18) Takamatsu, T.; Nakaiwa, M.; Nakanishi, T.; Aso, K., Possibility of energy saving in the ideal heat integrated distillation column (HIDiC). Kagaku Kogaku Ronbun.

1997, 23, 28-36. (19) Shahandeh, H.; Ivakpour, J.; Kasiri, N., Internal and external HIDiCs (heat-integrated distillation columns) optimization by genetic algorithm. Energy 2014, 64, 875-886. (20) Papastathopoulou, H. S.; Luyben, W. L., Control of a binary sidestream distillation column. Ind. Eng. Chem. Res. 1991, 30, 705-713. (21) Díez, E.; Langston, P.; Ovejero, G.; Romero, M. D., Economic feasibility of heat pumps in distillation to reduce energy use. Appl. Therm. Eng. 2009, 29, 1216-1223. (22) Brousse, E.; Claudel, B.; Jallut, C., Modelling and optimization of the steady state operation of a vapour recompression distillation column. Chem. Eng. Sci. 1985, 40, 2073-2078. (23) Harwardt, A.; Marquardt, W., Heat‐integrated distillation columns: Vapor recompression or internal heat integration? AIChE J. 2012, 58, 3740-3750. (24) Suphanit, B., Optimal heat distribution in the internally heat-integrated distillation column (HIDiC). Energy 2011, 36, 4171-4181. 40


Page 40 of 43

Page 41 of 43 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


(25) Gadalla, M.; Jiménez, L.; Olujic, Z.; Jansens, P., A thermo-hydraulic approach to conceptual design of an internally heat-integrated distillation column (i-HIDiC).

Comput. Chem. Eng. 2007, 31, 1346-1354. (26) Ho, T.-J.; Huang, C.-T.; Lee, L.-S.; Chen, C.-T., Extended Ponchon− Savarit Method for Graphically Analyzing and Designing Internally Heat-Integrated Distillation Columns. Ind. Eng. Chem. Res. 2009, 49, 350-358. (27) Kiran, B.; Jana, A. K.; Samanta, A. N., A novel intensified heat integration in multicomponent distillation. Energy 2012, 41, 443-453. (28) Matsuda, K.; Iwakabe, K.; Nakaiwa, M., Recent advances in internally heat-integrated distillation columns (HIDiC) for sustainable development. J. Chem.

Eng. Jpn. 2012, 45, 363-372. (29) Bisgaard, T.; Huusom, J. K.; Abildskov, J., Modeling and analysis of conventional and heat‐integrated distillation columns. AIChE J. 2015, 61, 4251-4263. (30) Cong, H.; Li, X.; Li, H.; Murphy, J. P.; Gao, X., Performance analysis and structural optimization of multi-tube type heat integrated distillation column (HIDiC).

Sep. Purif. Technol. 2017, 188, 303-315. (31) Douglas, J. M., Conceptual design of chemical processes. McGraw-Hill New York: 1988; Vol. 1110. (32) Chen, H.; Huang, K.; Wang, S., A novel simplified configuration for an ideal heat-integrated distillation column (ideal HIDiC). Sep. Purif. Technol. 2010, 73, 230-242. (33) Li, H.; Cong, H.; Li, X.; Li, X.; Gao, X., Systematic design of the integrating heat pump into heat integrated distillation column for recovering energy. Appl. Therm. Eng.

2016, 105, 93-104. (34) Olujić, Ž.; Sun, L.; De Rijke, A.; Jansens, P., Conceptual design of an internally heat integrated propylene-propane splitter. Energy 2006, 31 (15), 3083-3096. 41



(35) Iwakabe, K.; Nakaiwa, M.; Huang, K.; Nakanishi, T.; Røsjorde, A.; Ohmori, T.; Endo, A.; Yamamoto, T., Energy saving in multicomponent separation using an internally heat-integrated distillation column (HIDiC). Appl. Therm. Eng. 2006, 26 (13), 1362-1368. (36) Jana, A. K., A new divided-wall heat integrated distillation column (HIDiC) for batch processing: Feasibility and analysis. Appl. Energy 2016, 172, 199-206. (37) Kiran, B.; Jana, A. K., A hybrid heat integration scheme for bioethanol separation through pressure-swing distillation route. Sep. Purif. Technol. 2015, 142, 307-315.

42


Page 42 of 43

Page 43 of 43 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


Graphic abstract

43


Feasibility Evaluation of A Novel Middle Vapor Recompression

Recommend Documents