Application of a new pilot-scale distillation system for monoethylene glycol recovery using an energy saving falling film distillation column

Journal Pre-proof Application of a New Pilot-Scale Distillation System for Monoethylene Glycol Recovery Using an Energy Saving Falling Film Distillation Column Ana Paula Braga Pires, Valdemar Francisco da Silva Filho, Jose´ Luiz Francisco Alves, Cintia Marangoni, Ariovaldo Bolzan, Ricardo ˆ Antonio Francisco Machado

PII:

S0263-8762(19)30503-9

DOI:

https://doi.org/10.1016/j.cherd.2019.10.033

Reference:

CHERD 3868

To appear in:

Chemical Engineering Research and Design

Received Date:

28 November 2018

Revised Date:

6 August 2019

Accepted Date:

18 October 2019

Please cite this article as: Braga Pires AP, da Silva Filho VF, Francisco Alves JL, Marangoni C, Bolzan A, Francisco Machado RA, Application of a New Pilot-Scale Distillation System for Monoethylene Glycol Recovery Using an Energy Saving Falling Film Distillation Column, Chemical Engineering Research and Design (2019), doi: https://doi.org/10.1016/j.cherd.2019.10.033

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Application of a New Pilot-Scale Distillation System for Monoethylene Glycol Recovery Using an Energy Saving Falling Film Distillation Column

Ana Paula Braga Piresa,†, Valdemar Francisco da Silva Filhoa,

†,*

, José Luiz Francisco

Laboratory of Control and Polymerization Processes, Chemical Engineering Graduate

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Alvesa,†, *, Cintia Marangonia, Ariovaldo Bolzana, Ricardo Antônio Francisco Machadoa

Program (PósENQ), Department of Chemical and Food Engineering (EQA), Federal

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University of Santa Catarina (UFSC), Reitor João David Ferreira Lima University Campus,

E-mail

addresses:

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Florianópolis, 88040-900, SC, Brazil

[email protected];

[email protected];

[email protected];

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[email protected];

[email protected];

[email protected]

These authors are co-first authors because they contributed equally to this work.

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†

*Corresponding authors: V. F. Da S. Filho ([email protected]) and J. L. F. Alves ([email protected])

Graphical abstract

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Highlights

Falling film distillation integrated is offered for recovering MEG

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Effects of various inputs conditions on separation performance are studied

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Intensified falling film distillation was compared with the conventional process

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Energy consumption was by 47% in comparison to the conventional distillation

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

Abstract

Monoethylene glycol (MEG) is a desiccant widely used in the Oil and Gas and Sugar Cane

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Alcohol industries and generates a large volume of MEG-water mixture effluent. This original study explores the use of a new pilot-scale distillation system for separating MEG from a MEG-water mixture. The distillation tests were performed with a single-tube falling film distillation column assisted by a thermosyphon system operating at atmospheric pressure (Destubcal Technology). The results attained high MEG contents, with a MEG loading of 66.00% (m/m), yielding a MEG separation of 88.61%. Additionally, a distillation

arrangement with two single-tube falling film distillation columns in series was able to reach values of separation similar to those used by companies in the Oil and Gas sector, while operating at atmospheric pressure. It was also found that Destubcal Technology leads to a 46.93% reduction of the energy required and is more compact than a conventional-industrial

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distillation column.

% BMEG

Mass fractions of water in the bottom stream (%)

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Nomenclature % BH2O

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Energy Savings; Atmospheric Pressure; Pilot Scale.

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Keywords: Monoethylene Glycol; Falling Film Distillation; Experimental Evaluation;

% DMEG

Mass fractions of monoethylene glycol in the distillate stream (%)

% BMEG1

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% BMEG2

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% DH 2O

Mass fractions of monoethylene glycol in the bottom stream (%) Mass fractions of monoethylene glycol in the bottom stream of the first column (%) Mass fractions of monoethylene glycol in the bottom stream of the second column (%) Mass fractions of water in the distillate stream (%)

% FMEG1

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Mass fractions of monoethylene glycol in the feed of the first column (%) Mass fractions of monoethylene glycol in the feed of the second column % FMEG2 (%) CDS Conventional Distillation System (−) CENPES/Petrobras Petrobras Research and Development Center (−) DWC Dividing Wall Column (−) Separation factor FS hDT Height of the distillation tube (m) HIDiC Internal Heat Distillation Column (−) LABTUCAL Heat Pipes Laboratory (−) LCP Laboratory of Control and Polymerization Processes (−) mb Bottom mass flow rate (kg h-1) MEG Monoethylene glycol (−)

Feed mass flow rate (kg h-1)

𝑚̇𝑡 NRTL p P PDC

Distillate (Top) mass flow rate (kg h-1) Non-Random Two-Liquid (−) Pressure of steam chamber Power (kJ h-1) Working pressure in the distillation column (kPa)

Pmass

Mass power (kJ h-1 kg-1)

T1

Temperature of the under extremity of the steam chamber (ºC)

T10

Temperature of the upper extremity of the steam chamber (ºC)

Tb

Bottom temperature (ºC)

Te

Evaporator temperature (ºC)

Tf

Feed temperature (ºC)

Tt

Distillate Top temperature (ºC) Recovery of monoethylene glycol (%)

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Z

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1. Introduction

Monoethylene glycol (MEG) is a desiccant widely used in the oil-and-gas and sugarcane

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alcohol industries. In the former, it is used as a hydrate inhibitor, and in the latter is used in extractive distillation to obtain anhydrous ethanol. The regeneration (removal of water) of

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this glycol is necessary for economic and environmental reasons so that it can be reused to avoid its disposal in and contamination of natural environments. Different processes can be used to regenerate MEG; for example, pervaporation, absorption and adsorption. However, the most common process is separation by distillation.

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Although this method is thermodynamically inefficient, usually reaching between 5.00 and 20.00% (de Koeijer and Kjelstrup, 2000; Jana, 2015), it is the most frequently used procedure after salt removal, because the components are easy to separate, and can be operated in a continuous process with large volumes. A conventional distillation system (CDS) is a traditional unitary operation responsible for high energy consumption that may account for

more than 50.00% of the operating cost of an industrial plant (Kiss and Bildea, 2011). It is estimated that distillation processes account for approximately 3.00% of world energy consumption (Premkumar and Rangaiah, 2009). To support sustainable global development, focused on reducing, reusing and recycling, and because of the energy inefficiency of conventional distillation columns, several advanced

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techniques of this separation process have been studied. With improved energy efficiency, many of these units tend to be small in size, which can be very attractive to the oil and gas

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industry, especially in offshore environments. Distillation processes that incorporate the

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concept of energy integration (energy-saving column configurations) have been implemented by making structural modifications to conventional distillation systems to reduce energy

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consumption.

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Dividing Wall Columns (DWC) and Internal Heat Distillation Columns (HIDiC) are the main configurations used to reduce energy consumption whose designs are based on structural modifications to the CDS. The DWC configuration combines two conventional

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units into a single piece of equipment. This thermally coupled configuration has advantages in the distillation processes in comparison to CDS, namely, energy saving, smaller size, and lower maintenance, capital and investment costs (Kaibel, 2014; Staak et al., 2014). Several

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studies are found in the literature involving the use of HIDiC that found reduced energy consumption compared to the CDS (Abushwireb et al., 2007; Iwakabe et al., 2006a, 2006b). However, these configurations of energy-saving columns have not gained significant attention in the industrial environment because they involve complex operations and there is a lack of basic data about pilot-scale systems in the field of intensified separation technology.

In addition, most studies on the configuration of these energy-saving columns were performed at theoretical, modeling and simulation levels. In the context of unconventional distillation methods, technologies based on film distillation have been developed such as Linas technology, Short Path Distillation and Destubcal Technology. These technologies present a high mass and heat rate transfer and are

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notable for their small size, lower energy consumption, simple construction and good separation capacity. Linas Technology involves the use of compact columns for processing

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multicomponent mixtures; however, it is not readily applicable in large-scale industrial

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distillation because the vapor stream velocity would have to be on the order of 1.50 to 2.00 m · s-1 to form a stable film (Saifutdinov et al., 2014, 2009, 2002). Short-path distillation,

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with the use of a high vacuum, is usually expensive and only small volumes are processed, hence it is generally indicated for purification of compounds with high added value

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(Blahušiak et al., 2012; Hu et al., 2013; Teleken et al., 2012). Therefore, a technology is needed that combines falling film distillation with energy savings.

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The new energy-saving column configuration known as “Destubcal Technology”, i.e, a falling film distillation technology equipped with a heat pipe, proposes uniform temperature distribution along the distillation tube (by using a thermosyphon system), unlike the CDS, in

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which energy is only supplied at the lower end (via a reboiler system). The concept of integral energy supply along the distillation tube was extracted from the Linas Technology. The Destubcal Technology involves distillation by a descending liquid film assisted by a biphasic thermosyphon, using a compact distillation column that operates under atmospheric pressure and with a lower energy requirement. This promising technology has been used recently in the separation of aromatic compounds. The innovation proposed by the Destubcal

Technology using a single-tube type falling film distillation column reduced energy consumption by 45.14% in comparison to a simulated CDS, (da Silva Filho et al., 2018). The use of Destubcal Technology with low energy consumption as an optional process for recovering MEG from aqueous streams has not yet been reported on. For this reason, the objective of this study was to experimentally investigate the influence of input conditions: -

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evaporator temperature ( Te ), feed temperature ( T f ) and feed mass flow rate ( m f ) - on the separation of a MEG-water mixture under two different experimental approaches: an

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isothermal approach and under conditions in which a temperature profile is imposed along

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the axial direction of the distillation column (a non-isothermal approach). An additional assessment was conducted of the performance of a distillation arrangement with two single-

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tube falling film distillation columns in series, used to increase MEG recovery in the bottom stream and thus to compare the Destubcal Technology with a conventional distillation

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process. It is expected that this experimental study can provide information useful to the

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future implementation of Destubcal Technology in industrial environments. 2. Materials and methods

Initially, heat-supply variables, which include the evaporator and feed temperatures, were defined based on simulations of conventional industrial distillation at atmospheric pressure

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and on possible conditions that could be used in the single-tube falling film distillation column. Based on the simulation results, pilot-scale distillation experiments were conducted to evaluate the feasibility of the recovery of the MEG from a MEG-water mixture using a single-tube falling film distillation column equipped with a biphasic thermosyphon. Firstly, the experimental behavior of this new distillation system was evaluated under an isothermal power supply mode (constant temperature along the entire length of the distillation tube) for

separation of the MEG-water mixture. Subsequently, an evaluation was also performed of the non-isothermal or profile condition (with a temperature gradient of approximately 10.00°C along the distillation tube) for separation of the MEG-water mixture. After this step, the isothermal approach and non-isothermal approach were compared to provide useful indications about the suitability of each mode of power supply.

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In addition, a distillation arrangement with two single-tube falling film distillation columns arranged in series was applied to ensure MEG recovery similar to that currently

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attained in conventional industrial distillation columns. The second single-tube falling film

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distillation column was fed with the higher mass fraction ( %BMEG,1  %FMEG,2 ) previously obtained from the first single-tube film falling column, as illustrated in Figure 1. Finally, the

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energy consumption of the Destubcal Technology was compared with that of a conventional

2.1 Materials

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industrial distillation system.

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The compounds used in the experiments were monoethylene glycol with 99.00% mass purity provided by QUIMISA (Brusque - SC, Brazil) and distilled water. 2.2 Single-tube falling film distillation column

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The single-tube (one distillation tube) experimental column was developed by equipping falling film distallation technology with a heat pipe (Destubcal Technology). The project of this technology was conducted under a partnership between the Laboratory of Control and Polymerization Processes (LCP) and the Heat Pipes Laboratory (LABTUCAL), both at the Federal University at Santa Catarina (UFSC), and sponsored by the Petrobras Research and Development Center (CENPES/Petrobras). The pilot scale system consists of a single-tube

falling film distillation column, a feed tank, mixture tank, accumulator tank, condenser and evaporator (biphasic thermosyphon). These components are made of 304 stainless steel. In the biphasic thermosyphon used in the pilot unit, the thermal fluid is heated and vaporizes; it then reaches the vapor chamber, where it loses heat in the distillation tube, condenses and returns to the evaporator by gravity. The evaporator temperature is controlled by manipulating the dissipated power in the biphasic thermosyphon (formed by two electrical

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resistances totalling 34560.00 kJ h-1). By using the biphasic thermosyphon, energy

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consumption can be reduced because only latent heat is supplied rather than sensible heat.

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Figure 2 shows a side and front view of the single-tube falling film column.

Figure 3 shows a longitudinal view of the pilot scale system, and illustrates the distillation

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tube and steam chamber apparatus. The distillation column is composed of two concentric cylinders, a vapor chamber (external cylinder) and a distillation tube (internal cylinder). Ten

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thermocouples were attached along the steam chamber (labeled T1 to T10 from the bottom to the top of the distillation column). As in a conventional industrial distillation column, the

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distillate stream is enriched with a lighter component (water), while the bottom stream is enriched with a heavier component (MEG). Heat and mass transfer occurs radially by a diffusion process from the direction of the column wall to the liquid film, and at the threshold

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of the liquid film where the phase change occurs. The liquid falling film flows on the inner surface of the vertical tube for heat and mass transfer, while the steam is generated in a counter current. The wall temperature of the distillation tube is continuously heated (radially) through the steam chamber. The single-tube falling film distillation column has exceptional characteristics, such as its ability to operate in a continuous regime at atmospheric pressure; a steam chamber (for

energy minimization); and its small size (the internal vertical distillation tube is 1.00 m tall, 26.40 mm in diameter and 3.00 mm thick). The steam chamber is where the phenomena of heat and mass transfer occur. Gas distribution is performed from the lower extremity of the distillation tube where the steam chamber is filled with the steam produced by the evaporator. As mentioned previously, the experimental tests were conducted under two different experimental approaches, depending on the mode of power supply: an isothermal operating

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approach and a non-isothermal operating approach. This difference in the power supply mode

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is due to the presence of non-condensable gas in the steam chamber (was imposed a pressure value of 0.34 bar in the vapor chamber). For the isothermal condition, a vacuum condition

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was created in the steam chamber by using a vacuum pump (model 830, Fisatom, São Paulo,

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Brazil) to remove non-condensable gas (atmospheric air).

The feed stream was heated by a plate heat exchanger, Figure 2(l), and fed to the top of

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the distillation tube through a distribution system that used a hollow steel cone (Teleken et al., 2012) 5.00 cm long made from 304 stainless steel. It is used at the top of the distillation

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tube to ensure film formation throughout the distillation tube. The feed is transported through the outer wall of the hollow steel cone until it reaches the distillation tube, and the liquidsteam separation occurs through the formation of the film, in which the steam generated rises through the inner part of the hollow steel cone, while the liquid film descends through the

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bottom of the distillation column. The feed temperature was controlled with a thermostatic bath (model USH 400, Lauda, Lauda-Königshofen, Germany), which is presented in Figure 2(b). The single-tube falling film distillation column is insulated with rock wool. Previous studies (da Silva Filho et al., 2018; Querino et al., 2018) provide more details of the singletube falling film column.

2.3 Definition of operational conditions in Aspen Hysys Based on typical industrial data from a MEG regeneration column used in natural gas extraction, simulations were performed using the software Aspen Hysys® version 8.6 to determine the operating conditions to be used in the single-tube falling film distillation column. The software allows simulating a conventional distillation column operating in

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steady state. This methodology successfully defined the operating conditions for Destubcal Technology in previous studies (da Silva Filho et al., 2018). For simulations, the Non-

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Random Two-Liquid (NRTL) model was used as a thermodynamic package. Previous studies

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have shown that the NRTL model was satisfactorily used to describe the phase equilibria between glycols and water (Garcia-Chavez et al., 2013, 2012). For the simulation of the

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conventional distillation column, the binary interaction parameters for the MEG and water are available in the Aspen Properties database. The simulation was performed at atmospheric

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pressure with a mixture of MEG and water of 66.00% and 34.00% (m m-1), respectively. Importantly, the conventional industrial recovery column used as a reference operates

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under a vacuum condition, and the single-tube falling film distillation column employed in this study operates at atmospheric pressure. The simulation results allowed defining the heat supply variables ( Te and T f ). To evaluate the MEG regeneration using Destubcal

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Technology, three operating conditions were defined: evaporator temperature ( Te ), feed temperature ( T f ) and feed mass flow rate ( m f ). The m f values used in the isothermal experiments were 12.00 kg h-1 and 23.00 kg h-1. In the non-isothermal experiments, the values used were 23.00 kg h-1 and 43.00 kg h-1, because in the non-isothermal condition, lower m f values can cause the liquid falling film formed

inside the distillation tube to break up, thus higher values were employed. The results of the simulations indicated the temperature of the reboiler in a conventional industrial column to be 150.00 °C. Thus, the value of Te was defined as 148.00 °C and 158.00 °C, the first temperature was a condition similar to the one defined by the simulation corresponding to the separation of MEG in a conventional industrial column, and the second temperature was

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a hotter condition. The values of the feed temperature changed from 90.00 °C to 100.00 °C; the latter value

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(100.00 °C) was determined by the temperature limit of the more volatile component (water).

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Since the bubble point of the MEG and water mixture ( % FMEG ,1 = 66.00%) at atmospheric pressure is 112.80 °C, the feed mixture was supplied under a sub-cooled liquid condition to

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increase the temperature gradient between the bottom and top of the distillation tube (feed is carried out at the top, and the evaporator of the steam chamber promotes the highest

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temperature at the bottom). When T f is lower than the bubble temperature, there is an increase of mass fraction, according to previous experiments with the single-tube falling film

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distillation column. The experimental conditions used in this experimental step were summarized in Table S1 (supplementary material). The composition employed in the simulation stage was similar to the one used in the

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experimental stage. Each experiment was carried out at least three times to ensure the reproducibility of the experimental results. 2.4 Karl-Fischer analysis After reaching the steady state for each experimental condition, samples of the distillate and bottom stream were collected; the mass fraction of water was determined by the Karl

Fischer method using a Karl Fischer moisture titrator (model Q349-2, Quimis, Diadema-SP, Brazil). % BMEG was calculated by difference. The Karl-Fischer titration method has been used successfully for measurement of water concentration (Pal, 1994). Each sample was analyzed at least thrice to ensure the reproducibility of the Karl Fischer analysis. 2.5 Statistical analysis

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An experimental plan was used to identify significant effects and the interaction between

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them. Statistical analysis of the experimental data was evaluated using the software Statistica® version 10.0; the level of confidence intervals was 95.00% in each study. To

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visualize the effects of each response, Pareto diagrams for each response surface were designed and analyzed. The experiments followed a factorial design 23 and the variables were

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dependent on the values of m f , Te and T f , and on two levels. Table S1 (supplementary

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material) shows a complete factorial plan for isothermal operating conditions and nonisothermal operating conditions, respectively. The analyzed response was expressed as

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% BMEG .

2.6 Recovery calculation

The recovery of monoethylene glycol ( Z ) was calculated according to Equation 1.

mb  % BMEG 100 m f  % FMEG

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Z  % 

Equation 1

where mb is the bottom mass flow rate (kg h-1), % BMEG is the mass fractions of monoethylene glycol in the bottom stream (%), m f is the feed mass flow rate (kg h-1) and % FMEG is the mass fractions of monoethylene glycol in the feed stream (%).

Another parameter used to analyze the distillation process was the separation factor ( FS ), obtained by Equation 2. FS is the ratio of the mass fractions of the light (water) and heavy (monoethylene glycol) compounds in the top and bottom chains (Skogestad, 1997), hence FS in a process is a measure that indicates the effectiveness of separation of a mixture of the feed.

% BH 2O

% DMEG

Equation 2

% BMEG

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FS 

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% DH 2O

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where % DH 2O is the mass fractions of water in the distillate stream (%) , % DMEG is the mass fractions of monoethylene glycol in the distillate stream (%), % BH2O is the mass fractions of

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water in the bottom stream (%), and % BMEG is the mass fractions of monoethylene glycol in

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the bottom stream (%). 3. Results and discussion

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3.1. Isothermal operating conditions

Figure S1 (supplementary material) shows the variation in temperature inside the chamber; it can be seen that the temperature variation is within the measurement error (1.00

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°C), considering that the entire steam chamber operated at the same temperature. 3.1.1 Effects of input conditions Table 1 shows the results found by the study for MEG separation in the pilot scale single-

tube falling film distillation column with isothermal operating conditions. The highest value obtained for % BMEG was 88.61%, in the VI condition, under the mildest conditions studied,

i.e., m f of 11.90 kg h-1, T f of 90.00 °C and Te of 148.35 °C. A temperature difference was noticed between the bottom and top of the single-tube falling film distillation column “ T  Tb  Tt ”, this temperature difference is attributed to the condensation and evaporation

of the components present in the liquid film, thus creating a section enriched in the most volatile (with the lower boiling point) component, on the top of the distillation column (which

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characterizes a distillation process), hence the lowest temperature is assigned at this point. It should be emphasized that there is interaction at the top of the distillation column with the

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feed temperature (the feed mixture is fed from the top of the distillation column).

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The difference between the highest value obtained for % BMEG (condition VI, % BMEG =

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88.61%) and the lowest value (condition IV, % BMEG = 81.83%) was 6.78%, which cannot be considered very relevant. Based on this result, it can be inferred that there are no relevant

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differences in the operating conditions (in terms of separation performance) for MEG separation with the vapor chamber providing heat under an isothermal operating approach.

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However, in condition IV, the lowest power consumption was achieved by the biphasic thermosyphon, and there was also higher energy consumption by the feed bath, since the feed temperature used in this condition was around 100.00 °C. Condition II ( % BMEG = 86.52%) indicates a tendency of a lower m f to favor MEG recovery. Figure 4 (a) and (b) shows the

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behavior of % BMEG and % DMEG for all the conditions tested, respectively. Figure 5 (a) shows the behavior of Pmass for all the studied conditions, in addition to

% BMEG and T  Tb  Tt , which relates the bottom temperature and top temperature. As can

be seen, conditions with lower values of m f required a higher mass power ( Pmass ). It is

believed that in this condition of lower flow in the distillation column, a higher rate of heat and mass exchange occurs between the vapor chamber and the distillation tube because of the formation of a resulting thinner liquid film, which consequently requires more power. In summary, an increase in the evaporator temperature causes an increase in the ratio of power consumption to the feed mass flow rate ( Pmass ). According to Marangoni et al. (2019), there

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is a relationship between the feed temperature and evaporator temperature. The feed temperature has a direct effect on the evaporator temperature. Thus, if the feed temperature

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is higher, the power consumption must be lower to compensate for the expected effect that is related to the increase in the evaporator temperature. As a consequence, the ratio of the

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power consumption and feed mass flow rate is also reduced.

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The condition that required the highest Pmass was applied in condition I, which has a lower

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value of m f ,and higher values for T f and Te – in other words, it was the hottest condition used in the single-tube falling film distillation column. The second highest value required for

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Pmass was found in condition VI, where the lowest values of m f , T f and Te were imposed; this was the condition with the lowest heat imposed in the single-tube falling film distillation column. In this way, it can be stated that the amount of power required under each condition

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was a function of m f .

Table 1 shows that higher amounts of power were required at higher % BMEG values. As

discussed previously, this behavior can be explained by the application of lower m f . In condition VI, the % BMEG value obtained was 88.61%, hence requiring a lower Pmass value than in condition I, where the value of 84.40% was found. In condition VI, the lowest values

of T f and Te were used, while for condition I, the highest values of T f and Te were used. This result indicates that the milder experimental conditions may be the most suitable for the separation process. 3.1.2 Statistical analysis of interactions between variables Figure S2 (supplementary material) shows the Pareto diagram, which represents the

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relationship between % BMEG and the variables studied when the vapor chamber was operated

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under isothermal mode, and considering a confidence level of 95.00%. The results show that for the levels studied, the individual effect of the variables studied as well as the interaction

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between them were statistically significant. Although no variables had a significant influence

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on the % BMEG value, it can be seen that, among the variables studied, m f and Te (and the interaction between them) were able to produce the greatest effect on the % BMEG value.

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Figures 6 (a), (b) and (c) show the response surface and contour plots as well as the influence

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of the study variables on % BMEG and confirm the analysis based on the Pareto diagram. 3.2.Non-isothermal operating conditions Figure S3 (supplementary material) shows the behavior of the temperatures along the

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nozzle in the non-isothermal condition. 3.2.1 Effects of input conditions The results found for the MEG separation in the pilot-scale single-tube falling film

distillation column are shown in Table 2. The feed mass flow rate was studied with experiments at 23.00 kg h-1 and 43.00 kg h-1, given that the single-tube falling film distillation column operating under a non-isothermal condition had a film break at 12.00 kg h-1. An

analysis of the results shown in Table 2 indicate that the most satisfactory condition allowed the separation of % BMEG = 83.44%; this is called condition IX - T f = 100.17 °C, Te = 158.50 °C, and m f = 22.48 kg h-1, under these conditions the greatest difference occurred between bottom and top temperatures ( T  Tb  Tt = 16.10 °C). Figure 4 (c) and (d) shows the variation of % BMEG and % DMEG for the tested conditions, respectively.

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For Te and T f , there was no trend that related these variables with the required Pmass. The

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condition that required the highest value of Pmass (515.41 kJ kg-1 h-1) was condition IX, which

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had the lowest level of m f , and the highest level of Te and T f (the hottest condition in the single-tube column). It was found that for the tests operating in a non-isothermal condition,

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the power required in the experiments performed was a function of m f .

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An analysis of the influence of m f showed that, regardless of Te and T f , % BMEG decreased when m f was increased. Similarly to the behavior observed under the isothermal

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operating conditions, this behavior was attributed to the fact that an increase of m f led to an increase in the thickness and velocity of the liquid film, which made MEG separation difficult. Figure 5 (b) shows that an increase in m f leads to a decrease in the bottom and top

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temperatures in all cases, and clearly shows the cooling effect caused by the increase in m f . Thus, the increase of m f in the distillation unit in non-isothermal operating conditions has a similar behavior to the isothermal condition in falling film distillation and to a conventional column. An increase in values of m f causes a reduction in the difference between the bottom and top temperatures ( T  Tb  Tt ) of all conditions. At higher values of % BMEG , a high

temperature difference was achieved between the bottom and the top temperatures of the distillation tube. After the increase in m f , there was an increase in the flow of the bottom product, but with less separation of % BMEG . This behavior was expected in distillation processes, because the increase in the values of m f causes cooling in the column, generating greater bottom m f and a decrease of the contact time inside the distillation tube, and thus

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less thermal exchange. This effect was also found in the tests conducted with the chamber

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operating under an isothermal condition.

An analysis of the influence of Te showed that the increase of this variable favors the

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% BMEG value when the steam chamber is operating under a non-isothermal condition,

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different from what occurs when the chamber is operating under isothermal conditions. Similarly, an analysis of the vapor chamber operating under isothermal conditions showed

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that the influence of Te on the bottom mass flow rate was not relevant and the increase of Te

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induces the increase of the bottom temperature in all the conditions. Evaluation of the influence of T f found that a variation in T f did not interfere under the warmer conditions ( Te = 158.00 ° C). But in the milder conditions ( Te = 148.00 ° C) this increase in T f favored the separation of the MEG along the distillation tube, according to

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Figure 5 (b).

3.2.2 Interaction analysis between variables by statistical analysis Figure S4 (supplementary material) shows the Pareto diagram, which illustrates the

relationship between % BMEG and the examined variables, with the steam chamber operating under an non-isothermal mode, and considering a level of significance of 95.00%. The

statistical analysis shows that, for the levels studied, the individual effect of the variables studied as well as the interaction between them were statistically significant. Although no variables had a significant influence for the value of % BMEG , it can be seen that, among the variables studied, T f and the interaction between Te and T f had the greatest effect on the response ( % BMEG ). Unlike the isothermal experiments, variables m f and Te were more

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be considered significant for non-isothermal operating conditions.

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relevant under the non-isothermal condition. Moreover, m f had a very similar effect that can

Figures 7 (a), (b) and (c) show the response surface and contour plots for the non-

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isothermal mode, which indicate the influence of the variables studied on the % BMEG value.

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An analysis of the response surfaces and contour lines shows that the highest values were found for low values of m f , and high values of Te and T f . This last variable was not

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influential when the value of m f was low.

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3.3. Comparison between recovery of MEG under isothermal and non-isothermal conditions

Among all the experiments conducted, the highest % BMEG (88.6%) was found in isothermal operating conditions (condition VI). Figs. 5 (c) and (d) show the average results

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of % BMEG , FS and Z in this experiment, for isothermal and non-isothermal operating conditions, respectively. Fig. 5 (c) (isothermal condition) shows that the conditions III and VII had the highest Z value (>98.00%). In Fig. 5 (d) (non-isothermal condition), condition XVI had the highest Z value (99.36%). Over all, non-isothermal operating conditions had a higher Z value than isothermal operating conditions. In distillation processes, FS is a

measure that can indicate effectiveness in separating a feed mixture. The conditions that presented the lowest FS levels were Conditions III and VII (isothermal condition) and conditions XIII and XV (non-isothermal condition) because of the higher value of % DMEG . A comparison between the tests with the chamber in isothermal and non-isothermal conditions is important since this is how energy is supplied for distillation. Table S2

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(supplementary material) shows the experimental data of the two operating conditions for the

1

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tests, where variations of T f and Te were used, and m f was maintained constant at 23 kg h. The condition of the vapor chamber in the isothermal condition resulted in higher values

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of %BMEG for low T f and Te (condition VIII). For the non-isothermal condition, the variables must be as high as possible (condition IX). Comparing the higher results in the two operating

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conditions of the pilot unit, the imposition of a temperature profile in the vapor chamber

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favored MEG separation. However, when comparing similar conditions, in the case of the lowest Te condition, the isothermal mode of energy supply allows higher % BMEG . Table S2

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(supplementary material) also shows the test in which the highest % BMEG value for the nonisothermal operating condition (83.44%, condition IX) had a similar recovery percentage (97.86%) and separation factor (75.39) as those of the highest % BMEG for the isothermal

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operating condition (82.45%, condition VIII), which were 97.96% and 70.56%, respectively. Considering energy consumption, the isothermal operating conditions with the highest

separation factor (75.80, condition VII) consumed aa Pmass of 612.61 kJ h-1 kg-1, while the non-isothermal operating conditions with the greater separation factor (76.80, condition XVI) consumed a Pmass of 290.86 kJ kg-1 h-1. This indicates that the non-isothermal operating condition achieved the same separation factor with less energy consumption.

3.4.Comparative performance of a distillation system with two single-tube falling film distillation columns in relation to a conventional industrial distillation column A complementary investigation was performed using a distillation system comprised of two single-tube falling film distillation columns arranged in series to achieve the same separation obtained by a conventional-industrial distillation column ( % BMEG = 93.50%), as

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can be seen in Fig. 8. Data provided by a Brazilian Oil & Gas company indicate that a

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conventional distillation column for recovery of MEG from a MEG-water mixture ( % FMEG = 66.00%) has a total height of 17.69 m and a diameter of 1.70 m. This conventional

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distillation column is capable of processing 12104.37 kg h-1 ( mF ), operating under a vacuum

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condition, and achieved a % BMEG value of around 93.50%, with average energy consumption of 6448.00 kW.

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In the first step of this study, a % BMEG value of around 88.61% was achieved using a single-tube falling film distillation column with the steam chamber under an isothermal

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operating approach (Condition VI - better recovery condition). In the second single-tube falling film distillation column, the following experimental conditions were applied: m f ~ 12 kg h-1; T f ~ 90 °C; Te ~ 148 °C (steam chamber under an isothermal operating approach).

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These experimental conditions were based on the best separation in the first column. As shown in Fig. 8, the bottom stream obtained from the first column was used to feed the second column.

Table 3 shows the results found for the second single-tube falling film distillation column in the proposed distillation system. The distillation system comprised of two single-tube

falling film distillation columns arranged in series resulted in a % BMEG value of 93.60% (starting from 66.00%), thus confirming that the use of the Destubcal Technology for MEG separation was very promising. In the distillation system proposed here, each single-tube falling film distillation column has a distillation tube that is 1.00 m tall with a diameter of 26.40 mm, and was fed with about 12.00 kg h-1, operating at atmospheric pressure; and

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reached a value of MEG recovery similar to that achieved by conventional-industrial distillation column.

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Table 4 compares the experimental performance and design parameters of an

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experimental system with two single-tube falling film distillation columns arranged in series with a conventional-industrial distillation column (referred to as “design data”). The

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operating power of the conventional industrial column can be 6448.00 kW under certain conditions (referred to as “operating data”). Thus, it is possible that the relationship between

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power consumption and feed mass flow rate ( Pmass ) can be enhanced from 363.92 W kg-1 (design data) to 532.70 W kg-1 (operating data). It has been demonstrated that a distillation

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arrangement using two single-tube falling film distillation columns arranged consecutively was able to obtain separation similar to the recovery of MEG achieved in a conventional distillation process.

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In accordance with the experimental conditions described in Table 4, for conventionalindustrial distillation, the liquid mass is supplied continuously in an overheated condition, while in the intensified falling film distillation, the liquid mass is supplied continuously in a subcooled condition. Consequently, feed enthalpy is higher in the conventional distillation. The use of this falling film distillation arrangement operating at atmospheric pressure resulted in a 22.56% reduction in energy consumption per kilogram of MEG-water mixture

processed in relation to design data, and a 46.93% reduction in power consumption per kilogram of MEG-water mixture processed in relation to operating data. This reduction in energy demand can be explained by a few reasons, including the uniform distribution of thermal heat along the distillation tube, and the optimum utilization of the heat condensation of the mixture (both incorporated from the Linas Technology) (Marangoni et al., 2019). Thanks to the use of the biphasic thermosyphon in the distillation process, only the latent

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heat is supplied (da Silva Filho et al., 2018) and thermal resistance to heat transfer is reduced

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(Michels et al., 2012). The use of thermosyphons to minimize energy requirements in the operation of different processes has been reported in the scientific literature (Mantelli et al.,

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2010; Oliveira et al., 2016). In addition, distillation columns designed from Destubcal

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Technology are smaller (miniaturization concept), operate at atmospheric pressure, and do not require the use of external reflux (zero external reflux condition), thus operating costs

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and energy demand are minimized.

The occurrence of the low processing capacity in the single-tube falling film distillation

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column is a reason for further studies to explore falling film distillation columns with high production capacity to operate at processing capacity similar to those used in conventional commercial columns. The results found in our previous work demonstrated that the use of a multi-tube falling film distillation column can improve processing capacity while

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maintaining a good separation efficiency (da Silva Filho et al., 2018). Thus, the multi-tube falling film distillation column appears to be a promising option for increasing the processing capacity, since it contains nine distillation tubes and was thus designed to operate at a processing capacity at least nine times greater than a single-tube falling film distillation column.

4. Conclusions The influence of the three input conditions, namely, m f , Te and T f , allowed understanding the experimental behavior of a single-tube falling film distillation column processing a MEG-water mixture on a pilot scale. The analysis of the influence of the three input conditions showed that under both isothermal and non-isothermal operating conditions,

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m f has the greatest influence among all of the variables studied. Low m f values were

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identified as recommended for both the isothermal operating condition and the nonisothermal operating condition. However, it should be noted that a limit is established by the

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point where the film breaks and non-film formation occurs. As for the influence of the other

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input conditions, the isothermal operating condition should be used with lower Te and T f conditions. In the non-isothermal operating condition, Te and T f should be higher.

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The mass fractions of MEG in the bottom stream using a single-tube falling film distillation column with thermosyphon assistance were considered to have satisfactory results

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under both the isothermal operating condition and the non-isothermal operating condition. The higher mass fraction occurred in the isothermal test; however, the non-isothermal condition showed higher separation efficiency of the MEG mass in the bottom stream and,

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when comparing the same operating parameters, the energy consumed by the distillation was practically the same. The study also found that two pilot falling film distillation columns can be used in

sequence in sequence to obtain the same mass fraction separation as that of conventional industrial systems. Based on the comparison between falling film distillation and conventional industrial distillation, it has been concluded that the use of Destubcal

Technology for MEG separation is promising. It has energy advantages (savings of 22.56% in project cost, reaching 46.93% in operational cost) and in size because it is compact; it operates at atmospheric pressure, and can be optimized for use in offshore environments. Acknowledgments The authors are grateful for the financial support provided to this research by Brazil’s

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National Council for Scientific and Technological Development (CNPq), the Coordination for the Improvement of Higher Education Personnel (CAPES), and the Ministry of Science

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Petroleum,

Natural

Gas

and

Biofuels

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Agency

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and Technology (MCT) through the Human Resources Program from the Brazilian National (PRH/ANP-34)

and

CENPES/PETROBRAS. We are thankful to LCP/UFSC and LABTUCAL/UFSC for

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Leandro da Silva for their constant help.

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permission to use their facilities. Special thanks to engineer Luiz Domingos and technician

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Saifutdinov, A.F., Beketov, O.Y., Ladoshkin, V.S., Nesterov, G.A., 2014. Rectification tower with internal heat and mass exchange and method for separation of multicomponent mixtures into fractions using a rectification tower with an internal heat and mass exchange (WO2014009762). Saifutdinov, A.F., Beketov, O.Y., Ladoshkin, V.S., Nesterov, G.A., Tlousty, A.S., Ivanov, G.I., 2009. Compact rectifying unit for separation of mixed fluids and rectifying process

for separation of such mixed fluids (US7588666B2). Skogestad, S., 1997. Dynamics and Control of Distillation Columns: A tutorial introduction. Chem. Eng. Res. Des. 75, 539–562. doi:10.1205/026387697524092 Staak, D., Grützner, T., Schwegler, B., Roederer, D., 2014. Dividing wall column for industrial multi purpose use. Chem. Eng. Process. Process Intensif. 75, 48–57. doi:10.1016/j.cep.2013.10.007

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845–849. doi:10.1016/B978-0-444-59507-2.50161-X

Figure Caption Figure 1 Illustration of the distillation system comprised of two energy saving single-tube

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falling film distillation columns arranged in series.

Figure 2 Pilot unit - front and side view: (a) condensator; (b) feed heating bath; (c) feed tank; (d) feed input into the distillation tube; (e) thermosiphon system; (f) bottom product collector;

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(g) mixing tank (distillate collector and bottom product); (h) non-condensable gas reservatory; (i) single-tube distillation surrounded by the steam chamber (with insulation); (j) distillate product collector; (k) accumulator tank (distillate collector); (l) heat exchanger

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(plate type); (m) evaporator (energy capacity 34560 kj h-1 ) and (n) pumps.

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Figure 3 Illustration of a single-tube longitudinal section, presetting the distillation tube and

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the steam chamber.

Figure 4 Results found for mass fraction of MEG and water in the bottom (a) and distillate product (b) when the steam chamber was operated in the isothermal condition; and results found for mass fraction of MEG and water in the bottom (c) and distillate product (d) when

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the steam chamber was operated in the non-isothermal condition.

Figure 5 Representation of the influence of the gradient temperature T (difference between

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Tb and Tt) and of Pmass in the value of % BMEG for the single-tube falling film distillation column under isothermal conditions (a) and under non-isothermal conditions (b); and representation of the mean values of % BMEG , FS and Z for the single-tube falling film

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distillation column under isothermal conditions (c) and under non-isothermal conditions (d).

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Figure 6 Response surface for the influence of m f with Te (a), with T f (b) and the influence

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of T f and Te (c) for % BMEG when the steam chamber was operated in the isothermal

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condition;

Figure 7 Response surface for the influence of m f with Te (a), with T f (b) and the influence of T f and Te (c) for % BMEG when the steam chamber was operated in the non-isothermal

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condition.

Figure 8 General flow diagram of the distillation system comprised of two energy saving

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single-tube falling film distillation columns arranged in series.

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Table Caption Table 1 Mean results and respective standard deviations found for the experimental tests for the isothermal condition in the single-tube. Table 1 - Mean results and respective standard deviations obtained for the experimental tests for isothermal condition. Conditions I

II

III

IV

V

VI

± 100.24 0.11

± 99.00 0.00

± 90.65 0.00

147.67 0.12

± 158.44 0.11

± 148.10 0.00

± 158.42 ± 148.35 ± 158.06 ± 149.55 0.01 0.07 0.2 0.07

±

11.92 0.11

± 22.75 0.15

± 22.89 0.11

± 12.34 0.21

± 11.90 0.16

± 23.13 0.04

± 22.70 0.14

±

8.64 0.42

± 17.85 0.21

± 8.83 0.12

± 8.46 0.21

± 18.30 0.29

± 17.80 0.07

±

3.28 0.01

±

3.51 0.09

± 3.44 0.17

± 4.83 0.20

±

135.33 0.07

± 144.72 0.11

± 134.00 0.16

± 144.89 ± 134.08 ± 145.34 ± 132.50 0.13 0.70 0.08 0.10

±

122.00 0.29

± 127.51 0.09

± 119.00 0.22

± 129.87 ± 122.75 ± 123.61 ± 119.64 0.08 0.11 0.08 0.10

±

149.50 0.10

± 158.87 0.01

± 150.00 0.03

± 159.71 ± 149.00 ± 158.35 ± 150.33 0.05 0.16 0.04 0.23

±

150.14 0.10

± 158.59 0.01

± 150.00 0.03

± 159.80 ± 149.00 ± 158.05 ± 150.35 0.05 0.16 0.04 0.23

±

500.00 0.15

± 645.00 0.11

± 511.00 0.15

± 657.00 ± 500.00 ± 636.00± 0.21 0.22 0.10

±

mb d (kg h- 7.38

± ) 0.08 4.73 𝑚̇𝑡 e (kg h-1) ± 0.22 145.6 Tb f (°C) 1 ± 0.21 122.9 Tt g (°C) 7 ± 0.11 159.0 T1 h (°C) 9 ± 0.03 158.9 T10 i (°C) 6 ± 0.03 646.0 p j (kPa) 0 ± 0.10 1110 P k (kJ h-1) 7.12

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± 17.82 0.07

4.90 ± 0.11 5.07 ± 0.21

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1

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Results

± 90.00 0.02

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100.00 0.03

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100.1 5 ± 0.01 158.0 Te b (°C) 3 ± 0.01 m f c (kg h- 12.11 ± 1 ) 0.23

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Mass fraction of MEG in feed = 66.00%

T f a (°C)

VIII

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Inputs conditions

VII

± 90.40 0.02

± 90.00 0.02

8725.46 ± 13630.39 ± 11640.60 ± 9182.88 ± 8987.29 ± 14169.56 0.00 0.00 0.00 0.00 0.00 ± 0.00

±

4.90 ± 0.25

514.00 0.15

12869.17 ± 0.00

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ro

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± 0.00 Pmass l (kJ 917.1 732.00 ± 599.14 ± 508.55 ± 744.16 755.23 ± 612.61 ± 566.92 ± 9 ± 9.74 4.65 3.86 ±9.43 7.00 2.98 1.58 h-1 kg-1) 5.00 % BMEG m 84.40 86.52 ± 82.44 ± 81.83 ± 82.58 ± 88.61 ± 81.93 ± 82.45 ± ± 0.43 0.64 0.59 1.10 0.14 0.55 0.46 (%) 0.22 a Tf - feed temperature; b Te - evaporator temperature; c 𝑚̇𝑓 - feed mass flow rate; d 𝑚̇𝑡 - top (distillated) mass flow rate; e 𝑚̇𝑏 - bottom mass flow rate; f Tb - bottom temperature; g Tt – top temperature; h T1 - temperature of the under extremity of the steam chamber; i T10 - temperature of the upper extremity of the steam chamber; j p -maximum pressure of steam chamber; k P - power; l Pmass - power in relation to the mass flow of the feed; m %BMEG – mass fractions of monoethylene glycol in the bottom stream.

Table 2 Mean results and respective standard deviations for the experimental tests for the non-isothermal condition in the single-tube. Table 2 - Mean results and respective standard deviations obtained for the experimental tests for non-isothermal condition. Conditions IX

X

XI

XII

XIII

XIV

± 90.52 0.03

± 90.48 0.11

XV

XVI

± 90.16 0.01

± 90.54 0.02

151.29 0.01

± 157.73 0.05

± 150.39 ± 148.57 0.03 0.07

22.75 0.11

± 22.58 0.25

± 22.89 0.30

± 18.00 0.20

± 18.70 0.10

± 0.09 5.08 e -1 𝑚̇𝑡 (kg h ) ± 0.11 135.1 Tb f (°C) 3 ± 0.17 119.0 Tt g (°C) 3 ± 0.16 158.3 T1 h (°C) 7 ± 0.11 146.2 T10 i (°C) 7 ± 0.10 642.0 p j (kPa) 0 ± 0.10 1158 6.46 P k (kJ h-1) ± 0.00 )

0.08

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± 38.48 0.14

±

43.00 0.19

± 42.79 0.11

± 43.12 0.18

±

± 38.12 0.11

± 38.36 0.20

± 38.10 0.10

±

±

128.14 0.21

± 130.23 0.12

± 129.00 ± 115.18 0.20 0.15

± 124.33 0.20

± 115.52 ± 125.83 0.22 0.02

±

122.02 0.19

± 118.37 0.10

± 120.34 ± 114.08 0.20 0.08

± 119.14 0.11

± 114.47 ± 118.69 0.10 0.17

±

150.85 0.19

± 157.23 0.23

± 150.15 ± 148.66 0.11 0.09

± 158.32 0.20

± 148.71 ± 158.42 0.23 0.21

±

140.71 0.11

± 144.74 0.22

± 139.02 ± 137.94 0.15 0.06

± 149.74 0.14

± 137.84 ± 149.90 0.22 0.12

±

531.00 0.20

± 627.00 0.20

± 518.00 ± 495.00 0.15 0.20

± 633.00 0.22

± 494.00 ± 634.00 0.05 0.10

±

4.58 ± 0.14

6128.28 ± 11080.48 0.00 ± 0.00

4.19 0.16

±

±

3.25 0.11

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1

± 100.74 ± 100.69 0.09 0.03 ± 148.62 ± 157.23 0.02 0.08

± 42.50± 0.21

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Results

mb d (kg h- 17.40 19.50

± 157.78 0.00

-p

99.83 0.01

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100.1 7 ± 0.02 158.5 Te b (°C) 0 ± 0.05 m f c (kg h- 22.48 ± 1 ) 0.11

T f a (°C)

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Mass fraction of MEG in feed = 66.00%

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Inputs conditions

4.02 ± 0.15 4.88 ± 0.18

7602.55 ± 10010.09 0.00 ± 0.00

12919.50 ± 0.00

4.43 0.10

±

10015.06 ± 0.00

5.02 ± 0.21

12541.82 ± 0.00

Pmass l (kJ 515.4 269.37 ± 490.72 ± 332.13 ± 235.53 ± 300.45 ± 234.05 ± 290.86 ±

1 ± 4.23 3.56 4.00 5.60 6.21 5.00 4.02 5.48 % BMEG m 83.44 75.74 ± 81.34 ± 79.49 ± 68.62 ± 72.62 ± 67.35 ± 74.22 ± ± 0.09 0.26 0.72 0.53 0.03 0.06 0.45 (%) 1.22 a Tf - feed temperature; b Te - evaporator temperature; c 𝑚̇𝑓 - feed mass flow rate; d 𝑚̇𝑡 - top (distillated) mass flow rate; e 𝑚̇𝑏 - bottom mass flow rate; f Tb - bottom temperature; g Tt - top temperature; h T1 - temperature of the under extremity of the steam chamber; i T10 - temperature of the upper extremity of the steam chamber; j p -maximum pressure of steam chamber; k P - power; l Pmass - power in relation to the mass flow of the feed; m %BMEG – mass fractions of monoethylene glycol in the bottom stream.

Jo

ur na

lP

re

-p

ro

of

h-1 kg-1)

Table 3 Mean results and respective standard deviations found for the experimental tests for the isothermal condition in the second column. Table 3 - Mean results and respective standard deviations found for the experimental tests for the isothermal condition in the second column. Conditions

VI (Second Column) Inputs conditions

90.84 ± 0.10

Te b (°C) m f c (kg h-1)

148.16 ± 0.07

ro

T f a (°C)

of

Mass fraction of MEG in feed = 88.61%

12.45 ± 0.15

𝑚̇𝑡 (kg h )

3.75 ± 0.19

Tb f (°C)

137.15 ± 0.01

Tt g (°C)

110.83 ± 0.03

T1 (°C)

148.64 ± 0.05

T10 (°C)

-1

h

i

-p

8.70 ± 0.20

e

re

mb d (kg h-1)

lP

Results

148.64 ± 0.05

ur na

3095.50 ± 0.00 P j (kJ h-1) k -1 -1 Pmass (kJ h kg ) 248.65 ± 4.23 % BMEG l (%)

93.60 ± 0.63

Tf - feed temperature; b Te - evaporator temperature; c 𝑚̇𝑓 - feed mass flow rate; d 𝑚̇𝑡 - top (distillated) mass flow rate; e 𝑚̇𝑏 - bottom mass flow rate; f Tb - bottom temperature; g Tt - top (distillated) temperature; h T1 temperature of the under extremity of the steam chamber; i T10 - temperature of the upper extremity of the steam chamber; j P - power; k Pmass - power in relation to the mass flow of the feed; l %BMEG - fractions of monoethylene glycol in the bottom stream.

Jo

a

Table 4 Comparison of the experimental performance between the two single-tube falling film distillation columns in series (Destubcal Technology) with a conventional-industrial distillation column. Table 4 - Comparison of the experimental performance between the two single-tube falling film distillation columns in series (Destubcal Technology) with a conventional-industrial

Conventional industrial column

Destubcal Technology

hDT a (m)

16.62

1.00*

PDC b (kPa)

23.00

101.00

P e (W)

4.41·106

a

ur na

lP

Pmass f (W 363.92 kg-1) % BMEG g 93.50 (%)

-p

~ 90.00

~ 12.00

re

T f c (°C) 127.00 m f d (kg h1.21·104 1 )

ro

Conditions

of

distillation column.

3.36·103 281.81** 93.60

hDT - height of the distillation tube; b PDC - working pressure in the distillation column; c T - feed temperature; d m f - feed mass flow rate; e P - power; f P - power in relation to f

g

mass

Jo

the mass flow of the feed; % BMEG - fractions of monoethylene glycol in the bottom stream. * An experimental system with two single-tube falling film distillation columns was requested to ensure a similar MEG recovery achieved by conventional industrial column, these columns were arranged consecutively and horizontally. ** Sum of power consumption in the two single-tube falling film distillation columns.