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It is a common procedure to save energy in industrial distillation towers by preheating and precooling the feed with heat transfer from the bottom and top products. An example is oil sweetening by distillation. It is shown here using simulation that if, before entering the unit, the oil feed is split into two streams and only one of them is preheated, further savings of energy (up to 50%) can be achieved. The same results are achieved by splitting the feed to an ethane-ethylene distillation column and precooling only one part of it just before entering the tower. In this study, the effects of feed splitting into hot and cold towers were investigated in order to reduce the duties of the reboiler or condenser and the total annual cost (TAC). Also, consideration was given to obtaining a common design in order to achieve greater flexibility for the required operating schemes. The investigation was carried out as an optimization problem defined by effective parameters affecting the reboiler and condenser duty and product recovery. Models for finding the best feed split-fraction ratio, optimal locations for the feeds, number of trays required for a specified separation, and best operating pressure for a distillation column with feed splitting are presented. When a homotopy continuation method was used in MATLAB and it was connected to the ASPEN HYSYS simulator, the optimal values for decision variables were calculated. It is observed that the optimal feed-splitting technique leads to a 49.2% reduction in energy demand in an oil sweetening process and a 24% reduction in reboiler duty and a 22% reduction in condenser duty in an ethane-ethylene separation process in comparison with conventional processes. [ABSTRACT FROM AUTHOR]

The use of conventional reactive distillation columns for silane production has the disadvantage of large consumption of refrigerant because the silane is produced in the dome of the column and this must be condensed at about -78 °C. The incorporation of intercondensers may improve the cost and safety of the system; however, a proper study for the system is needed to determine the associated effects. Therefore, in this paper is presented an optimization approach for the silane production accounting simultaneously for economic and safety issues incorporating intercondensers. The presented approach is based on a software link between Microsoft Excel (for implementing the optimization algorithm based on differential evolution), Aspen Plus (for simulating the process), and SCRI (for quantifying the associated risk). The results show that the addition of intercondensers minimizes the total annual cost, because the amount of needed refrigerant is reduced. The safety analysis also shows that the use of intercondensers improves the risk of the system. [ABSTRACT FROM AUTHOR]

Thispaper presents a reactive distillation column for the catalyticdisproportionation of trichlorosilane to silane which includes threeconsecutive reversible reactions with a thermodynamic conversion tosilane as low as 0.2% and is of no practical significance using theconventional reactors. This reaction system is however characterizedby a large distinction in the boiling points of the components, whichmakes the reactive distillation extremely favored. Nevertheless, thenormal reactive distillation column possesses the shortage of highrefrigeration requirement as the standard boiling point of the overheadproduct silane is −112 °C. A novel reactive distillationcolumn with intercondensers placed within has been simulated usingAspen Plus package for a feasible alternative to alleviate this drawback.The calculated results show that a reduction in the refrigerationload of more than 97% can be obtained when one intermediate condenseris inserted between the rectifying and reaction zones, and that anothernormal intermediate condenser equipped within the reaction sectioncan further decrease the condensation requirement of the first intermediatecondenser by 50%. Effects of the configuration parameters and operationalconditions have also been investigated for optimal design and operationof the proposed reactor. [ABSTRACT FROM AUTHOR]

The potentialities of a membrane condenserforthe selective recovery of evaporated wastewater from industrial gaseshave been investigated in the present paper. Membrane modules havebeen prepared and their performance has been evaluated in an artificialflue gas stream. A simulation study of the process has been carriedout for predicting the membrane-based process performance. The achievedresults indicate that a 20% water recovery (the amount to make theplant self-sufficient) can be achieved with temperature reductionsless than 5 °C if flue gas is in common conditions (i.e., 50°C < T< 90 °C and 90% < RH <100%). To verify the results achieved by the simulation analysis amembrane module with microporous hydrophobic PVDF hollow fibers hasbeen built, and its performance has been evaluated by feeding an artificialflue gas stream. The experimental results showed good agreement withthe simulation ones, obtaining deviations less than 2.24%. [ABSTRACT FROM AUTHOR]

Distillation columns frequently produce both vapor andliquid distillateproduct streams from the reflux drum when the feed stream containssmall amounts of light components that would require high pressuresor low temperatures if a total condenser were used to completely condensethe overhead product. Since removing heat using cooling water in thecondenser is much less expensive than using refrigeration, many columnsare designed to operate with reflux-drum temperatures of about 120°F so that cooling water at 90 °F can be used. Fixing reflux-drumtemperature and selecting a reasonable pressure determines the splitbetween the amount of vapor product and the amount of liquid product.In the operation of these systems, we usually want to condense asmuch as possible so as to minimize compression costs of dealing withthe vapor product. Therefore the flow rate of cooling water shouldbe maximized. This paper demonstrates a realistic way to model a partial-condenserdistillation system using Aspen simulation. [ABSTRACT FROM AUTHOR]

The distillation columns of a two-column cryogenic air separation unit (ASU) are responsible for a considerable part of the total ASU inefficiencies. The efficiency of a conventional distillation column can be increased by distributing the reboiler and condenser duties over a larger part of its length. In an ASU, this can be realized by moving the low-pressure column (LPC) down along the high-pressure column (HPC), thus increasing the number of heat-integrated stages (HI stages). We present an assessment of the effect that such an intensification of the heat integration has on the performance of the ASU distillation section, using the entropy production as performance criterion. When keeping the operating pressures fixed, the entropy production in the LPC is replaced by entropy production in the HI stages, without affecting the total entropy production. Reducing the pressure ratio enables a reduction in the LPC entropy production without increasing the contribution of the HI stages. For a probable value of the heat-transfer capacity per stage, increasing the pressure in the LPC results in a decrease of 21% in the total entropy production, while decreasing the pressure in the HPC results in a decrease of 23%. Decreasing the pressure in the HPC when using an opportunistic heat-transfer capacity yields a decrease of 31%. The reductions in entropy production materialize eventually as changes in the required ASU compressor, pump, and expander duties. Compared to the addition of either an additional heat exchanger or an additional distillation column, the use of HI stages seems to be the most promising method for improving the thermodynamic performance of a cryogenic ASU. More-detailed experimental data are required to simulate heat-integrated distillation columns accurately. [ABSTRACT FROM AUTHOR]

In terms of the thermodynamic characteristics of simple distillation columns, a novel schematic of an externally heat-integrated double distillation column (EHIDDiC) is proposed and studied in this work. It consists of high-pressure and low-pressure distillation columns, with external heat integration between the whole rectifying section of the former and the whole stripping section of the latter. In comparison with conventional distillation systems (i.e., direct and indirect separation sequences), the EHIDDiC was found to require relatively small capital investment and low operating costs. It can even outperform conventional distillation systems with the condenser/reboiler type of heat integration under some favorable operating conditions. In terms of the separation of a ternary ideal mixture containing hypothetical components A, B, and C, the EHIDDiC was evaluated through intensive comparisons with its conventional counterparts. Sensitivity analysis was also conducted with respect to some relevant physical properties and design parameters, including the relative volatilities, feed composition, external heat-transfer area per stage, product specifications, and utility costs. It was confirmed that the EHIDDiC can be advantageous over conventional distillation systems with and without condenser/reboiler-type heat integration, and the results obtained reflect the salient characteristics of the EHIDDiC. [ABSTRACT FROM AUTHOR]

Industrial applications of the divided-wall column for the separation of ternary mixtures have increased in recent years with about 40 columns reported to be in service. The divided-wall column is a practical way to implement the topology of the Petlyuk column that features two columns (a prefractionator into which the feed is introduced and a main column from which a sidestream product is withdrawn) with interconnected vapor and liquid streams arising from a single reboiler and a single condenser. Many papers discuss the steady-state design issues and propose heuristic and rigorous design optimization methods. The dynamic control of the divided-wall column has been explored in a relatively small number of papers. Control is more difficult than with a conventional two-column separation sequence because there is more interaction among controlled and manipulated variables since the four sections of the column are coupled. The vapor split is fixed at the design stage and cannot be changed during operation, but the liquid split can be manipulated to achieve some control objective. A number of control structures and algorithms have been proposed, but the reported results present a somewhat confusing picture. Different authors draw conflicting and inconsistent conclusions. Most papers control the purities of the three product streams using reflux flow rate, sidestream flow rate, and vapor boilup. This paper proposes a new control structure that controls these purities and also minimizes energy consumption. This is achieved implicitly by controlling a composition of the heaviest component in the prefractionator. Disturbances in feed flow rate and feed composition are used to demonstrate the effectiveness of the proposed control structure. A comparison of the dynamic controllability of the divided-wall column with a conventional configuration is also provided. [ABSTRACT FROM AUTHOR]

We show in this article that the common method of specifying Tminfor individual heat exchangers may lead to wrong decisions and should be used with care when designing heat exchanger systems. In particular, design with constraints on Tminmay result in operation conditions that are not optimal when the resulting areas are installed. In addition, different Uvalues for the heat exchangers are not easily handled. We propose an alternative method (simplified TAC) to avoid these problems and compare it with the Tminmethod on three vapor compression (refrigeration) cycle case studies. [ABSTRACT FROM AUTHOR]

A simple adaptation of traditional "chemistry kit" condensers for the organic chemistry teaching laboratory is described. These waterless condensers have been employed safely with most solvents. They can be easily fabricated, stored, and used in the same manner as water-cooled condensers. These condensers were utilized in several different types of reactions and in an ethano-lwater distillation providing the same product yields as reactions utilizing traditional water-cooled condensers. [ABSTRACT FROM AUTHOR]