Distillate Flow Rate Research Articles

Pilot-scale testing of a multi-tube type falling film distillation column equipped with a biphasic thermosyphon as a new alternative for the desalination of brackish water and seawater

This paper proposes an innovative technology for desalinating brackish water and seawater using a multi-tube type falling film distillation column integrated with a biphasic thermosyphon. Based on the literature survey, this proposal has not been previously explored. In this study, the viability of the pilot-scale application of this technology for desalination was tested, and the process performance was evaluated in terms of distillate flow rate, salinity removal, and energy consumption, considering different experimental conditions. Synthetic solutions containing 10.0 and 35.0 g/L of sodium chloride were used to simulate brackish water and seawater salinities, respectively. The thermal desalination pilot plant integrating a compact falling film distillation column and a biphasic thermosyphon demonstrated high effectiveness, consistently producing desalinated water with a conductivity below 10 μS cm−1. Considering both concentrations, the optimal condition for desalinated water production was a feed temperature of 85 °C, a vapor chamber temperature of 121 °C, and an energy consumption of 16 kW. This new technological option’s energy consumption is approximately 33 % lower than that of a simulated flash distillation column operating under similar conditions. In conclusion, this study presents promising results, establishing falling film distillation technology as a viable alternative for desalinating brackish water and seawater.

РАЗРАБОТКА СИСТЕМЫ УПРАВЛЕНИЯ МНОГОКОЛОННОЙ УСТАНОВКОЙ НА ОСНОВЕ ПРОГНОЗИРУЮЩИХ МОДЕЛЕЙ

In the refining and petrochemical industries, a large percentage of all plants are distillation units, which are key to achieving the required economic indicators. Control systems for multi-column distillation units must ensure optimal and reliable operation at a given product purity. The design of a good control system for such plants is very import-ant to ensure reliable and high-quality operation of the whole process and is a challenging task due to the uncertainties associated with the complex process dynamics and the different composition of the feed stream affecting the separation behavior of the mixture. The paper summarizes the control structures developed based on predictive models to control the quality of the products produced. It is proposed to control the level in the tank of the partial condenser distillation column by (i) the distillate flow rate; (ii) the reflux flow rate, allowing the distillate flow rate to be used as a manipulated variable. The suitability of using control systems is determined based on steady-state controllability analysis and by studying the closed-loop dynamic characteristics (setpoint responses).

A novel intensified approach for treating produced water from oil extraction using a multi-tube type falling-film distillation column equipped with a biphasic thermosiphon: a promising feasibility study.

This study has the novel aim of experimentally examining the efficiency of a pilot-scale treatment plant, composed of a multi-tube type falling-film distillation column equipped with a biphasic thermosiphon, for treating a real sample of high-salinity produced water (electrical conductivity of 20,700 μS cm-1). It investigates the influence of operational parameters, including feed temperature and steam chamber temperature of the biphasic thermosiphon, on distillate flow rate and reduction of conductivity. All experimental conditions tested achieved a reduction greater than 98% in terms of electrical conductivity. The production of treated water increased with increasing feed temperature; the flow rate increased from 20.8 L h-1 to 28.2 L h-1 as the feed temperature was increased from 80 °C to 90 °C, when the steam chamber temperature was fixed at 119 °C. Within the temperature range of the steam chamber, the specific energy consumption during the treatment process, with respect to the biphasic thermosiphon, remained practically unchanged between 0.58 kWh L-1 and 0.60 kWh L-1, when the feed temperature was 90 °C. The results proved the potential of the falling-film distillation technology assisted by heat pipes to be a promising proposal for removing salinity from produced water from oil extraction operations.

Solution of the maximum distillate on a batch distillation column by a Pseudo-Newton method

This paper presents a new algorithm for the solution of the maximum distillate problem based on Pontryagin's maximum principle. Four cases of study were analyzed with the algorithm. The first case is a literature problem where the column uses twenty trays to distillate ten components, the second case is a binary mixture with no ideal behavior, the third case is a quaternary mixture, and the last case is a reactive mixture. In all cases, the desired purity was settled as a final constraint. The solution algorithm found the optimal control faster than results reported in literature concerning the CPU time.The batch distillation process is modeled by using a rigorous model with no constant volatility. The proposed algorithm uses the Hamiltonian function to reformulate the maximum distillate problem. Then, the optimal control is solved by a Broyden–Fletcher–Goldfarb–Shanno algorithm. The solution procedure of the indirect approach required the forward integration of the states, the integration of the co-state equations backward in time, and the control input is the distillate flow rate which is parameterized. The binary batch distillation column uses six stages, and the maximum recovery is 95% of the light component with a 95% mol percent on the accumulator. The multicomponent batch distillation column uses 17 stages, and the recovery of the lightest component in the product is 90% mol percent. The reactive case reached 80% conversion.

Numerical study of a novel concentrator photovoltaic-membrane distilled plate-type seawater desalination structure

Both solar energy utilization and desalination are critical needs in many parts of the world. To make more effective use of photovoltaic waste heat, a novel concentrator photovoltaic-membrane distilled plate type seawater desalination structure is proposed in this paper. To understand the performance of the photovoltaic module under natural cooling, a solar ray-tracing model is used to simulate it at different concentration ratios for the meteorological conditions of Wuhan, China. The structure is then modeled at different concentration ratios and mass flow rates, and the thermal and electrical properties of the photovoltaic module are analyzed. The performance of a hydrophobic membrane and distillation is evaluated, and the distillation performance is compared with that in the literature. The results show that the temperature of the silicon layer can exceed 150 °C at a concentration ratio of 10. When using seawater with a mass flow rate of 0.0007kg∙s-1 for cooling, the temperature of the photovoltaic module can be controlled below 150 °C, even at a concentration ratio of 100. For a higher concentration ratio, the temperature of the photovoltaic module can be controlled within a reasonable range by regulating the mass flow rate of seawater. The distillate flow rate, distillation efficiency, and specific energy consumption are evaluated at different concentration ratios and mass flow rates. When the mass flow is 0.0007kg∙s-1 and concentration ratio = 1, the distillate flow rate, distillation efficiency, and specific energy consumption are, respectively, 0.94L∙m-2∙h-1, 46.91 %, and 487.51kWh∙m-3, which shows an advantage compared with that in the literature.

Design optimization and control of dividing wall column for purification of trichlorosilane

• TA C appr . is proposed as a novel objective function for DWC parameter optimization. • Optimal energy control structure can be achieved by manipulating liquid split ratio. • MPC-PI hybrid structure balances both control performance and safety performance. • Simulated annealing algorithm is employed to optimize the weights of MPC controller. Polysilicon quality and energy consumption are directly affected by the purification process of trichlorosilane. In this work, the dividing wall column (DWC) as a promising energy-saving technology is utilized for trichlorosilane purification, with the design optimization carried out using steady-state simulation. Compared with conventional distillation process, DWC can reduce total annual cost (TAC), CO 2 emissions and exergy loss ( El ) by 35.81%, 53.56% and 54.10% on average, respectively. Established on the characteristics of superfractionator, four control structures are proposed in this work, two of which are multi-loop proportional-integral (PI) control schemes including condenser duty ( C ), distillate flow rate ( D ), bottom flow rate ( B )/reflux flow rate ( R ), side flow rate ( S ), reboiler duty ( V ) control structure and optimal energy control structure. The other two are model predictive control (MPC) schemes including standard MPC structure and MPC-PI hybrid structure. The weights of MPC controller are optimized using the simulated annealing (SA) algorithm. Dynamic simulation results demonstrate that MPC schemes achieve improved closed-loop performance in terms of minor overshoot, shorter transition time and reduced oscillation than PI control schemes. The integral absolute error (IAE) is introduced to further quantitatively evaluate MPC schemes. The simulation results demonstrate that the standard MPC structure achieves the best control performance and the MPC-PI hybrid structure enhances process safety while maintaining the desired control performance.

Dynamic Optimization Study for Cryogenic Distillation in Hydrogen Isotope Separation System

This paper presents a dynamic optimization study on a cryogenic distillation unit in hydrogen isotope separation system. A packed distillation column with an equilibrator is considered. The packed column was modeled as a theoretical equilibrium-based stage column. The equilibrator was placed to enhance separation performance. An optimal control problem was formulated to minimize the tritium holdup under two product quality constraints, in a situation where feed flowrate is periodically fluctuated. An optimal control policy was obtained for two manipulating variables, namely distillate flowrate and reboiler heat duty. The optimal control policy was analyzed by examining the operating variable profiles of the column.

Dynamic Modelling and Simulation of a Multistage Flash Desalination System

As the leading thermal desalination method, multistage flash (MSF) desalination plays an important role in obtaining freshwater. Its dynamic modeling and dynamic performance prediction are quite important for the optimal control, real-time optimal operation, maintenance, and fault diagnosis of MSF plants. In this study, a detailed mathematical model of the MSF system, based on the first principle and its treatment strategy, was established to obtain transient performance change quickly. Firstly, the whole MSF system was divided into four parts, which are brine heat exchanger, flashing stage room, mixed and split modulate, and physical parameter modulate. Secondly, based on mass, energy, and momentum conservation laws, the dynamic correlation equations were formulated and then put together for a simultaneous solution. Next, with the established model, the performance of a brine-recirculation (BR)-MSF plant with 16-stage flash chambers was simulated and compared for validation. Finally, with the validated model and the simultaneous solution method, dynamic simulation and analysis were carried out to respond to the dynamic change of feed seawater temperature, feed seawater concentration, recycle stream mass flow rate, and steam temperature. The dynamic response curves of TBT (top brine temperature), BBT (bottom brine temperature), the temperature of flashing brine at previous stages, and distillate mass flow rate at previous stages were obtained, which specifically reflect the dynamic characteristics of the system. The presented dynamic model and its treatment can provide better analysis for the real-time optimal operation and control of the MSF system to achieve lower operational cost and more stable freshwater quality.

Machine learning modeling and genetic algorithm-based optimization of a novel pilot-scale thermosyphon-assisted falling film distillation unit

Engaged in the global trend towards more energy-efficient and sustainable technologies, our research team has developed a falling film distillation apparatus with an innovative heat supply through a two-phase closed thermosyphon. In order to evaluate the performance of this energy-intensified distillation process, a supervised machine learning (ML) predictive model based on artificial neural networks is implemented for the separation of the ethanol–water binary mixture. The feed temperature, the evaporator temperature, and the feed flow rate are the three input variables of the model, whereas the ethanol mass fraction in the distillate, the distillate mass flow rate, the recovery factor, and the separation factor are the four performance indicators evaluated. The feed-forward ML has been trained, tested, and validated using a total dataset of 64 experimental runs carried out in the pilot-scale unit, covering a wide operating range of the input variables. Despite the high non-linearity, the ML approach was capable of modeling this new process accurately. The optimal topology of the ML model was achieved with a network arrangement of 10 neurons within 1 hidden layer (3:10:4), with a correlation coefficient (R) greater than 0.95 for all data. The predictive abilities of the ML model were harnessed to investigate the individual and synergistic interaction effects of the operating variables by plotting generalization graphs. Finally, the optimal operating conditions were evaluated by the genetic algorithm (GA) technique, being the feed temperature of 90.6 °C, the evaporator temperature of 109.6 °C, and the feed flow rate of 26.3 L/h, the process operating values that led the maximum of the four performance indicators, simultaneously. Under these operating conditions, a distillate mass flow rate of 4.9 kg/h, with 50.6%wt ethanol-enriched, a recovery factor of 84.9%, and a separation factor of 57.4 have been achieved, showing the high-performance feasibility of the pilot-scale unit.

Direct contact membrane distillation for liquid desiccant regeneration and fresh water production: Experimental investigation, response surface modeling and optimization

Liquid desiccant cooling (LDC) systems are being widely considered as a promising alternative for energy savings and the regeneration is one of the most significant processes of the LDC systems. This paper presents a direct contact membrane distillation (DCMD) regenerator for liquid desiccants regeneration of LDC systems and fresh water production simultaneously. The novelty of this study is to use the response surface method to establish models to predict the DCMD regeneration performance with highly concentrated lithium chloride solutions based on the experimental investigation. The interactive effects of the operating parameters, i.e. initial feed concentration, feed inlet temperature, distillate inlet temperature, and feed and distillate flow rates were studied and the optimal conditions of the DCMD regenerator to maximize the feed concentration increase and transmembrane water flux were identified. The experimental results showed that stable regeneration performance and water production with the lithium chloride salt rejection rate over 99.99% by the membrane were achieved using the DCMD regenerator. The temperature difference between the feed and distillate sides should be controlled higher than a threshold to ensure continuous liquid desiccant regeneration. Initial feed concentration and flow rate exhibited a significant interaction in improving the DCMD regeneration performance. An optimal flow rate for better regeneration performance can be observed when increasing the initial feed concentration. The optimization results showed that the feed concentration increase and transmembrane water flux can be improved by 39.7% and 41.6% respectively under the optimal conditions as compared to the best case observed in the response surface method designed experiments.

Nonequilibrium Stage Based Modeling of a Falling Film Distillation Unit

A novel nonequilibrium stage based model was developed for a falling film distillation unit. The model combines mass and energy balances in the liquid and vapor phases, without the need of separation efficiency factors. The modeled pilot scale falling film distillation unit is differentiated because the heat supply is carried out axially by means of a thermosyphon. In terms of the algorithm proposed, the central contribution is in reducing the number of variables to be determined by the method, which brings benefits such as reduction of computational time and increase of robustness in the convergence. The results obtained were compared with experimental data from the pilot scale plant, and showed good predictability, with deviations in the top temperature below 2.60%, 6.59% in the distillated ethanol fraction, 12.32% in the resistance power and only one case above 10% for distillate flow rate.

Modelling of the coupling of desalination plants with the thermal solar energy system

Abstract This work aims to develop models able to describe and predict the thermal solar collector coupled with vacuum membrane distillation (VMD) unit to determine the growth evolution of the temperature in the solar collector and the membrane module of the VMD. These models will be used to evaluate the distillate flow rates during the year. The global solar radiation data recorded on an inclined surface as well as ambient temperature data can be included in a program. First, the models were validated with some experimental data studies from appropriate literature and then they were used to predict the unit's performance under different operating conditions in the City of Bouzaréah (Algiers). The results obtained from the proposed models showed that the distillate flux water reached 10.5 kg/h·m2 in September and around 5.6 kg/h·m2 in December during midday.

Resonant energy transfer enhances solar thermal desalination

Water production from solar thermal desalination is limited by the energy consumption of phase change. Resonant heat exchange between matched saline feed and purified distillate flow rates enables optimized recovery of vaporization energy.

Seawater Desalination Using Waste Heat Recovery on Passenger Ship

This paper presents a study for sea water desalination on board of passenger ships using waste heat from the engine. Three thermal methods for water desalination were explored, namely Forward Feed Multiple Effect Evaporation, Once Through Multi-Stage Flash, and Brine Circulation Multi-Stage Flash. Computer simulation has been developed to calculate the parameters of the desalination plant; the required amount of fresh water and the corresponding total heat transfer area. The optimum plant selection is the one which achieves the required distillate flow rate with minimum heat transfer area. The effect of different variables on the plant selection has been studied, i.e. steam temperature, exhaust temperature, and intake water flow rate. An existing passenger ship has been selected to examine the proposed method where the optimum desalination method has been selected for her using the developed software. To assess the effectiveness of the proposed method, the economical, environmental, and technical gains are numerically analyzed. Using the waste heat recovery leads to reducing the unit product cost of freshwater by circa 30%. The plant reduced the emissions by about five thousand tons of CO2, 100 tons of NOx and 35 tons of SO2 per year. Applying the optimum design of the proposed salt water desalination on the case study saved 2.7 $/ m3 as a minimum comparing to the average cost of fresh water in ports. These savings can cover the plant capital cost in six years at most.

Fractionation of oleochemical fatty acid using vacuum dividing wall column: A controllability analysis

Dividing wall column (DWC) provides a good alternative for oleochemical fractionation. However, the internal configuration and multiple input multiple output (MIMO) system of DWC leads to complexity in operation and control. This work aims to analyze the controllability of fractionating oleochemical fatty acid using vacuum dividing wall column (VDWC). To achieve this, Aspen Plus and Aspen Dynamics were used to develop a rigorous steady state and dynamic model of the column. Five manipulated variables (MVs) were considered namely reflux flowrate (L), distillate flowrate (D), bottom flow rate (B), side-stream flowrate (S) and vapor boilup (V) while controlled variables (CVs) were the product compositions. Pairing of MV and CV to determine the best 3×3 control configuration was performed using relative gain array (RGA) and singular value analysis (SVA). The selected control structure was tested on PID controllers for several regulatory and servo problem. The results of RGA and SVA shows that DSV was the best control configuration. Performance analysis was found to be successful in rejecting the disturbances as well as obtaining good set point tracking. However, distillate and bottom composition shows poor controllability compare to middle composition.

Passive solar high-yield seawater desalination by modular and low-cost distillation

Although seawater is abundant, desalination is energy-intensive and expensive. Using the sun as an energy source is attractive for desalinating seawater; however, the performance of state-of-the-art passive devices is unsatisfactory when operated at less than one sun ($<$ $1$ $kW$ $m^{-2}$). Here, we present a completely passive, modular, and low-cost solar thermal distiller for seawater desalination. Each distillation stage is made of two opposed hydrophilic layers separated by a hydrophobic microporous membrane, and it does not require further mechanical ancillaries. Under realistic laboratory and outdoor conditions, we obtained a distillate flow rate of almost $3$ $L$ $m^{-2}$ $h^{-1}$ from seawater at less than one sun - twice the yield of recent passive device reported in the literature. In perspective, theoretical modelling suggests that the distiller has the potential to further doubling the peak flow rate observed in the current experiments. This layout can satisfy freshwater needs in isolated and impoverished communities, as well as realize self-sufficient floating installations or provide freshwater in emergency conditions.

Control of an Optimal Extractive Distillation Process with Mixed-Solvents as Separating Agent

In this work, process control is studied in an optimal Extractive Distillation (ED) system to dehydrate ethanol using a glycerol-ethylene glycol mixture as separating agent. ED system simulation and optimization with respect to the total annual cost (TAC) was made using the software platform Aspen Plus. The control structure of the optimized system was evaluated in Aspen Dynamics. Two control strategies were studied: a conventional control and a modified control scheme. The conventional control structure uses the distillate and bottoms flow rates to control the top and bottom levels, respectively. The second strategy uses the entrainer makeup flow rate to control the sump level in the recovery column and the recovery column bottoms flow rate to control the entrainer feed flow rate to the extractive column. Dynamic simulations show the control strategy that allows obtaining a soft-regulating control while at the same time ethanol purity is above 0.995 mole fraction. In addition, the use of solvents mixture...

ACETONE-CHLOROFORM-n-BUTANOL MIXTURE SEPARATION BY THE EXTRACTIVE DISTILLATION IN SCHEMES OF TWO-OUTLET COLUMNS

Extractive distillation of acetone-chloroform-n-butanol mixture with dimethylformamide in two-outlet column schemes is considered. Optimal parameters according to the total energy consumption criterion in the column boilers of the three extractive distillation schemes for this mixture separation are determined. Calculations were carried out in a design-verification version at 1000 kg/hr of the initial mixture with the concentrations of acetone, chloroform and n-butanol 71.3, 14.7 and 14.0% wt., respectively. Dimethylformamide concentration in the entrainer flow was set to 99.99 wt%. The main component concentration in the product stream was 99.9 wt% for chloroform and 99.5 wt%. for acetone and n-butanol. The parameters to be optimized were: the number of plates in the columns, the temperature and flow rate of dimethylformamide, reflux ratios, distillate flow rates and the position of the feed plates in the columns. The optimum location of the entrainer feed plate was found additionally in the extractive distillation column. Separation product concentrations served as the constraints of the optimization. The optimization was carried out in Aspen Plus with the use of a combination of Sensitivity Analysis and sequential quadratic programming (SQP). It is established that scheme P5 has the lowest energy consumption. In the first column of this scheme, n-butanol is separated, and then the azeotrope-forming components (acetone and chloroform) are separated by the extractive distillation subsystem. Energy consumptions for two other schemes (P1 and P2), in which dimethylformamide is used in the first column of the sequence, are significantly higher than for scheme P5 - by 69.1% and by 49.3%, respectively. The data obtained will be used: to synthesize and optimize the extractive distillation schemes including the subsystems with coupled thermal and material flows to separate the acetone-chloroform-n-butanol mixture; to estimate the energy efficiency of those schemes and to obtain the criterion for estimating the energy efficiency of systems with coupled thermal and material flows in the extractive distillation of multicomponent mixtures.

Cyclic operation as optimal control reflux policy of binary mixture batch distillation

We revisit the maximum distillate optimal control problem of batch distillation of non-ideal binary zeotropic mixtures. The direct method with full discretization is used. The problem formulation is based on full column dynamics and the distillate flow rate is used as control variable instead of the reflux. The purity constraint is handled as a new state variable, the purity deviation. Literature simulations showed that the cyclic reflux policy (bang-bang type control) performs better than variable reflux (singular type control) or constant reflux policy for small amount of light product in the load. For the first time, a cyclic reflux policy is found as the optimal control solution. The results are confirmed by rigorous simulation of the batch distillation, as the cyclic policy improves by 13% the product recovery over the variable reflux policy. Influence of the relative volatility, vapour flow rate, plate hold-up and initial load is discussed.

Control Structures Evaluation for a Salt Extractive Distillation Pilot Plant: Application to Bio-Ethanol Dehydration

This paper addresses the challenge of evaluating control structures for a salt extractive distillation column producing absolute ethanol for use as biofuel. A sensitivity analysis aided with designing a pseudo-binary distillation pilot plant and examining the conceived process and the influence of the reflux ratio on both product purity and energy consumption. We compare three control structures for inferential tracking of the distillate composition: a dual-temperature control with an RV (reflux/boilup) structure and two single-end temperature control configurations, and their performance is measured using deterministic indicators. The result is the proposal of a pilot plant design for treating 15 kg/h of a diluted mixture with mole fraction of ethanol equal to 0.2 and assuming a column efficiency of 50%. The R/F (reflux to feed ratio) configuration is the best control structure, given that its corresponding performance indicators conduct lowest steady-state errors, less oscillating responses, and reduced settling times. For this configuration, the reflux flow rate is rationed to the feed flow rate, and the temperature is controlled manipulating the distillate flow rate. Even subject to perturbations, the energy consumption of the plant remains close to the nominal value. The three evaluated control structures consistently met international quality standards for fuel ethanol and enhanced the use of salts in ethanol dehydration.