KLM Technology GroupPractical Engineering Guidelines for Processing Plant Solutions Page : 1 of 62 Rev: 05 Prepared: Feb 2007 Updated : April 2008 Author: www.klmtechgroup.com KLM Technology Group #03-12 Block Aronia, Riverria Condovilla, Taman Tampoi Utama Jalan Sri Perkasa 2 81200 Johor Bahru. Distillation Column Selection and Sizing (ENGINEERING DESIGN GUIDELINES) Chew Yin Hoon & Ai L Ling Checked by: Karl Kolmetz TABLE OF CONTENTS INTRODUCTION Scope Distillation Distillation History Types of Distillation Processes Mode of Operation Column Internals General Design Consideration The Selection of Column Internals 5 6 6 8 9 10 13 16 19 21 DEFINITIONS NOMENCLATURES THEORY (A) Vapor-Liquid Equilibrium (VLE) (I) Ideal Behavior in Both Phases (II) Liquid Phase Non-Idealities 23 23 24 This design guideline are believed to be as accurate as possible, but are very general not for specific design cases. They were designed for engineers to do preliminary designs and process specification sheets. The final design must always be guaranteed for the service selected by the manufacturing vendor, but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. The guidelines are a training tool for young engineers or a resource for engineers with experience. This document is entrusted to the recipient personally, but the copyright remains with us. It must not be copied, reproduced or in any way communicated or made accessible to third parties without our written consent. KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 2 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 25 25 26 26 27 27 28 28 28 29 29 30 30 30 32 33 35 36 43 43 46 (a) Local composition equations (b) Activity coefficient estimation methods (III) High-Pressure Systems (a) Vapor fugacity coefficient, liquid activity coefficient (b) Vapor and liquid fugacity coefficients (B) Phase Distribution (I) Incompressible liquid (II) Negligible Poynting correction (III) Vapor obeying the ideal gas law (IV) Ideal liquid solution (V) Other methods to determine K-values (C) Distillation Calculations (I) Product specifications (II) Column operating pressure (III) Operating Reflux Ratio and Number of Stages (a) Minimum reflux ratio (b) Minimum stages (c) Number of actual theoretical stages (IV) Tower Diameter (a) Trayed columns (b) Packed columns This design guideline are believed to be as accurate as possible, but are very general not for specific design cases. They were designed for engineers to do preliminary designs and process specification sheets. The final design must always be guaranteed for the service selected by the manufacturing vendor, but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. The guidelines are a training tool for young engineers or a resource for engineers with experience. This document is entrusted to the recipient personally, but the copyright remains with us. It must not be copied, reproduced or in any way communicated or made accessible to third parties without our written consent. KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 3 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 APPLICATION Example 1: Determination of Theoretical Stages and Reflux Ratio Example 2: Trayed Column Diameter Determination Example 3: Packed Column Diameter Determination 51 55 56 58 REFEREENCES SPECIFICATION DATA SHEET Metric Unit British Unit 59 60 CALCULATION SPREADSHEET Tower Diameter Sizing- Trayed Column Spreadsheet.xls Tower Diameter Sizing- Packed Column Spreadsheet.xls 61 62 LIST OF TABLE Table 1: Pressure drop in difference services Table 2: Common temperature differences for difference types of medium in condenser and Reboiler. Table 3: Packing Factors (Fp) 18 32 50 This design guideline are believed to be as accurate as possible, but are very general not for specific design cases. They were designed for engineers to do preliminary designs and process specification sheets. The final design must always be guaranteed for the service selected by the manufacturing vendor, but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. The guidelines are a training tool for young engineers or a resource for engineers with experience. This document is entrusted to the recipient personally, but the copyright remains with us. It must not be copied, reproduced or in any way communicated or made accessible to third parties without our written consent. reproduced or in any way communicated or made accessible to third parties without our written consent. but are very general not for specific design cases.KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 4 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 LIST OF FIGURE Figure 1: Batch Still Distillation Process Figure 2: Still Distillation in Series Figure 3: Extractive Distillation Column Figure 4: Catalyst Distillation Column Figure 5: Schematic Diagram of Distillation Column/ Fractionator. but the copyright remains with us. but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. They were designed for engineers to do preliminary designs and process specification sheets. The guidelines are a training tool for young engineers or a resource for engineers with experience. This document is entrusted to the recipient personally. . The final design must always be guaranteed for the service selected by the manufacturing vendor. It must not be copied. Figure 6: Total Condenser Figure 7: Partial Condenser Figure 8: Relationship between Reflux Ratio and Number of Stages Figure 9: Application of McCabe-Thiele to VLE Diagram Figure 10: Constructing of Operating Line for Stripping Section Figure 11: Example of a Seven Stage Distillation Figure 12: Erbar-Maddox Correlation of Stage Vs Reflux Figure 13: Internal of Bubble-caps Trays Column Figure 14: Souders-Brown Correlation for Approximation Tower Sizing Figure 15: Valve Tray Column Diameter Figure 16: Packed Column Pressure Drop Correlation Figure 17: Internal of Packing Column 7 7 8 9 10 12 12 33 37 38 40 42 43 45 47 48 49 This design guideline are believed to be as accurate as possible. The minimum reflux ratio also depends on the VLE data of the mixture. but are very general not for specific design cases. Each design has its strengths and weaknesses. such as the Fenske-Underwood equation. An initial estimation of the tower diameter can be done based on the vapor and liquid loadings in the column. reproduced or in any way communicated or made accessible to third parties without our written consent. This could lead to a wrong choice of column internal. The selection of column internals is very critical in distillation column design. However. . The guidelines are a training tool for young engineers or a resource for engineers with experience. but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. They were designed for engineers to do preliminary designs and process specification sheets. the thermodynamics of the vapor and liquid phases must be understood.KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 5 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 INTRODUCTION Scope This design guideline covers the basic element in designing a typical distillation column. The vapor-liquid equilibrium (VLE) determines the minimum number of stages required to achieve the degree of separation needed. This document is entrusted to the recipient personally. Therefore. but the copyright remains with us. the quotations from vendors are sometimes contradictory and confusing. which includes column selection and sizing. It must not be copied. In designing a distillation column. some general considerations are depicted to aid engineers in making the right choice of column internals. The final design must always be guaranteed for the service selected by the manufacturing vendor. There is a wide variety of trays and packing in the market. Included in this guideline is an example of the data sheet used in the industry and a calculation spreadsheet for the engineering design. A few equations that are commonly used in the industry are illustrated in this guideline to estimate the minimum number of stages and the minimum reflux ratio of a column based on the VLE data. A distillation column is sized by determining the diameter of the tower. Some design heuristics are also highlighted. This design guideline are believed to be as accurate as possible. These rules are based on design experiences and take into account both the safety and economical factors. It is the separation of key components in a mixture by the difference in their relative volatility. Further advancements include placing the stills in series and interchanging the vapor and liquid from each still to improve recovery. It must not be copied. Britain and the rest of the world. On the other hand. or boiling points. The guidelines are a training tool for young engineers or a resource for engineers with experience. distillation remains the main choice in the industry. They were designed for engineers to do preliminary designs and process specification sheets. Early distillation consisted of simple batch stills to produce ethanol. Reputedly. membrane separation or adsorption process. This design guideline are believed to be as accurate as possible. with crude oil heated in batch stills. The final design must always be guaranteed for the service selected by the manufacturing vendor. and the vapor drawn from the still was condensed for consumption. This was the first type of counter-current distillation column that we have today. reproduced or in any way communicated or made accessible to third parties without our written consent. but are very general not for specific design cases. Forbes has chronicled the full history of distillation in 19481. In most cases. It is also known as fractional distillation or fractionation. but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. Crude ethanol was placed in a still and heated. Therefore. It was later introduced to India. especially in large-scale applications. it was the Chinese who discovered it during the middle of the Chou dynasty.KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 6 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 Distillation Distillation is by far the most important separation process in the petroleum and chemical industries. Distillation History The history of distillation dated back to centuries ago. these processes often have higher investment costs. The next progression in the history of distillation was to continually feed the still and recover the light product. Arabia. but the copyright remains with us. distillation is the most economical separating method for liquid mixtures. This document is entrusted to the recipient personally. it can be energy intensive. There are alternatives to distillation process such as solvent extraction. . Distillation can consume more than 50% of a plant’s operating energy cost. However. Lamp oil was later produced using the same method. but are very general not for specific design cases. It must not be copied. They were designed for engineers to do preliminary designs and process specification sheets. The guidelines are a training tool for young engineers or a resource for engineers with experience.KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 7 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 Furnace Condenser Figure 1: Batch Still Distillation Process CONDENSATE 63% PENTANE 37% HEXANE VAPORS 49% PENTANE 51% HEXANE STILL 1 STILL 2 VAPORS 35% PENTANE 65% HEXANE STILL 3 126 F o 135oF 143 F o FEED 50% PENTANE 50% HEXANE LIQUID 37% PENTANE 63% HEXANE LIQUID 25% PENTANE 75% HEXANE Heat LIQUID 15% PENTANE 85% HEXANE Figure 2: Still Distillation in Series This design guideline are believed to be as accurate as possible. reproduced or in any way communicated or made accessible to third parties without our written consent. The final design must always be guaranteed for the service selected by the manufacturing vendor. but the copyright remains with us. but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. . This document is entrusted to the recipient personally. thereby separated from the rest of the components in the mixture. In this type of process.KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 8 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 Types of Distillation Processes There are many types of distillation processes. The targeted component reacts when it is in contact with the catalyst. . forming a ternary mixture with different properties. The external solvent changes the relative volatility between two ‘close’ components by extracting one of the components. A distillation column may also have a catalyst bed and reaction occurring in it. One type of variation of the distillation processes is extractive distillation. This document is entrusted to the recipient personally. The solvent is recycled into the system after the extracted component is separated from it. The final design must always be guaranteed for the service selected by the manufacturing vendor. Each type has its own characteristics and is designed to perform specific types of separations. They were designed for engineers to do preliminary designs and process specification sheets. These variations appear due to difficulty in separation when the physical properties of the components in a mixture are very close to one another. an external solvent is added to the system to increase the separation. such as an azeotropic mixture. This type of column is called a reactive distillation column. Reflux Bed 1 Bed 2 Lean Solvent Bed 3 Bed 4 Feed Figure 3: Extractive Distillation Column This design guideline are believed to be as accurate as possible. but are very general not for specific design cases. reproduced or in any way communicated or made accessible to third parties without our written consent. but the copyright remains with us. but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. The guidelines are a training tool for young engineers or a resource for engineers with experience. It must not be copied. reproduced or in any way communicated or made accessible to third parties without our written consent. additional variations can be utilized in a continuous distillation column. the feed to the column is introduced batch-wise. The guidelines are a training tool for young engineers or a resource for engineers with experience. especially in the petroleum and chemical industries. Therefore. continuous columns are the more common of the two modes. This document is entrusted to the recipient personally. the next batch of feed is introduced. but are very general not for specific design cases. but the copyright remains with us. but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. The final design must always be guaranteed for the service selected by the manufacturing vendor. based on their mode of operation. This design guideline are believed to be as accurate as possible. When the desired task is achieved. Batch distillation is usually preferred in the pharmaceutical industries and for the production of seasonal products. No interruption occurs during the operation of a continuous distillation column unless there is a problem with the column or surrounding unit operations. On the other hand. They were designed for engineers to do preliminary designs and process specification sheets. In batch distillation. The two classes are batch distillation and continuous distillation. It must not be copied. Besides. .KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 9 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 Hydrogen Vent Hydrogen Tower Feed Reflux + Heat of Rx Catalyst Zone Net Overhead Net Bottoms Figure 4: Catalyst Distillation Column Mode of Operation Distillation towers can be classified into two main categories. such as multiple feed points and multiple product drawing points. continuous distillation handles a continuous feed stream. The column is first charged with a ‘batch’ and then the distillation process is carried out. Continuous columns are capable of handling high throughputs. This design guideline are believed to be as accurate as possible. on the other hand. Condenser Overhead Receiver Overhead Product R Feed S Reboiler Bottom Product Figure 5: Schematic Diagram of Distillation Column/ Fractionator. distributors and redistributors. This document is entrusted to the recipient personally. bubble-cap and valve trays. They were designed for engineers to do preliminary designs and process specification sheets. These include trays. They promote an intimate contact between both phases. Packing. but the copyright remains with us. In random packing. It must not be copied. baffles and etc. but are very general not for specific design cases. packings. The final design must always be guaranteed for the service selected by the manufacturing vendor. rings and saddles are dumped into the column randomly while structured packing is stacked in a regular pattern in the column. The guidelines are a training tool for young engineers or a resource for engineers with experience. The two main types of column internals discussed in this guideline are trays and packing. but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design.KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 10 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 Column Internals Column internals are being equipped into distillation columns to provide better mass and heat transfers between the liquid and vapor phases in the column. can be categorized into random and structured packing. . such as sieve. There are many types of trays or plates. reproduced or in any way communicated or made accessible to third parties without our written consent. The type of internals selected would determine the height and diameter of a column for a specified duty because different designs have various capacities and efficiencies. Some liquid is returned to the column as reflux to limit the loss of heavy components overhead. In a total condenser (Figure 6). there will be two overhead products. In most cases.KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 11 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 Figure 5 shows a schematic diagram of an example distillation column or fractionator. the condensed liquid is refluxed into the column and the overhead product drawn is in the vapor form. there are some cases where only part of the condensed liquid is refluxed. all vapors leaving the top of the column is condensed to liquid so that the reflux stream and overhead product have the same composition. On the other hand. one a liquid with the same composition as the reflux stream while the other is a vapor product that is in equilibrium with the liquid reflux. but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. only a portion of the vapor entering the condenser is condensed to liquid. At the top of the column. The vapor phase that travels up the column is in contact with the liquid phase that travels down. This design guideline are believed to be as accurate as possible. The condenser above the column can be either a total or partial condenser. This document is entrusted to the recipient personally. . Heat and mass transfer occur such that the exiting streams (bubble point liquid and dew point vapor at the same temperature and pressure) are in equilibrium with each other. The guidelines are a training tool for young engineers or a resource for engineers with experience. the vapor enters from the stage below at a higher temperature while the liquid stream enters from the stage above at a lower temperature. The final design must always be guaranteed for the service selected by the manufacturing vendor. It must not be copied. vapor enters the condenser where heat is removed. The feed enters the column as liquid. but the copyright remains with us. but are very general not for specific design cases. reproduced or in any way communicated or made accessible to third parties without our written consent. The process above the feed tray is known as rectification (where the vapor phase is continually enriched in the light components which will finally make up the overhead product) while the process below the feed tray is known as stripping (as the heavier components are being stripped off and concentrated in the liquid phase to form the bottom product). vapor or a mixture of vapor-liquid. At each separation stage (each tray or a theoretical stage in the packing). They were designed for engineers to do preliminary designs and process specification sheets. In these cases. In a partial condenser (Figure 7). but the copyright remains with us.KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 12 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 Vent Condensate Liquid Figure 6: Total Condenser Vent Vapor product Condensate Liquid Figure 7: Partial Condenser This design guideline are believed to be as accurate as possible. but are very general not for specific design cases. . The final design must always be guaranteed for the service selected by the manufacturing vendor. They were designed for engineers to do preliminary designs and process specification sheets. The guidelines are a training tool for young engineers or a resource for engineers with experience. This document is entrusted to the recipient personally. but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. reproduced or in any way communicated or made accessible to third parties without our written consent. It must not be copied. but the copyright remains with us. but are very general not for specific design cases. economics of the design and other parameters. but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. column performance. which depends on the relative volatility and concentration of each component in the feed. It must not be copied. 3) Separations where the relative volatility of two adjacent components is close to unity should be performed in the absence of other components. the steps included in distillation calculations are summarized into the following: 1) Performing a material balance for the column 2) Determining the tower operating pressure (and/or temperature) 3) Calculating the minimum number of theoretical stages using the Fenske equation 4) Calculating the minimum reflux rate using the Underwood equations This design guideline are believed to be as accurate as possible. The final design must always be guaranteed for the service selected by the manufacturing vendor. King has outlined a few design rules as follows: 1) Direct sequences that remove the components one by one in the distillate are generally favored. column diameter and tower height. In general. the mechanical design focuses on the tower internals and heat exchanger arrangements. which may constrain the work. This document is entrusted to the recipient personally. The purpose of the process design is to calculate the number of required theoretical stages. a process design followed by a mechanical design. engineering calculations follow to determine the number of theoretical stages. operating parameters and tower dimensions. . reserve such a separation until the last column in the sequence. On the other hand. Once the separation sequence is decided. The guidelines are a training tool for young engineers or a resource for engineers with experience. reproduced or in any way communicated or made accessible to third parties without our written consent. 4) Separations involving high-specified recovery fractions should be reserved until last in the sequence. 2) Sequences that result in a more equal-molar division of the feed between distillate and bottoms products should be favored. They were designed for engineers to do preliminary designs and process specification sheets. Many factors have to be considered in designing a distillation column such as the safety and environmental requirements. The first step in distillation column design is to determine the separation sequences. ie.KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 13 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 General Design Consideration A tower design is normally divided into two main steps. 4) Tower Sequencing A. relative volatility is the ratio of vapor pressures i. 5) Economically optimum reflux ratio is about 120% to 150% of the minimum reflux ratio. The guidelines are a training tool for young engineers or a resource for engineers with experience. medium temperature. It must not be copied.com) that should be considered are as follows: 1) Distillation is usually the most economical method of separating liquids. D. When the adjacent ordered components in the feed vary widely in relative volatility. 2) For Ideal mixtures (low pressure. Easiest separation first – least trays and reflux B. They were designed for engineers to do preliminary designs and process specification sheets. . When the concentration in the feed varies widely but the relative volatilities do not. Some general design rules (from Cheresources. α = P2/P1 3) Tower operating pressure is determined most often by the temperature of the available cooling medium in the condenser or by the maximum allowable reboiler temperature. 6) The economically optimum number of stages is about 200% of the minimum value. C.KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 14 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 5) Determining the operating reflux rate and number of theoretical stages 6) Selection of column internals (tray or packings) 7) Calculating the tower diameter and height The theoretical explanation and sample calculations of each step above are discussed in detail in later sections. but are very general not for specific design cases. sequence the splits in order of decreasing volatility. This design guideline are believed to be as accurate as possible. reproduced or in any way communicated or made accessible to third parties without our written consent. This document is entrusted to the recipient personally. and non-polar). The final design must always be guaranteed for the service selected by the manufacturing vendor.e. but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. remove the components in the order of decreasing concentration in the feed. remove components one by one as overhead products. When neither relative volatility nor feed concentrations vary widely. 7) A safety factor of at least 10% above the number of stages by the best method is advisable. but the copyright remains with us. KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 15 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 8) A safety factor of at least 25% about the reflux should be utilized for the reflux pumps. 10) For towers that are at least 3 ft (0. reproduced or in any way communicated or made accessible to third parties without our written consent. 4 ft (1. The guidelines are a training tool for young engineers or a resource for engineers with experience. 9) Reflux drums are almost always horizontally mounted and designed for a 5 min holdup at half of the drum's capacity.9 m) in diameter. They were designed for engineers to do preliminary designs and process specification sheets. but are very general not for specific design cases.3 D2 for atmospheric distillation Q = 0. but the copyright remains with us. This document is entrusted to the recipient personally. .8 m) should be added to the bottom to account for the liquid level and reboiler return.15 D2 for vacuum distillation Where.2 m) should be added to the top for vapor release and 6 ft (1. It must not be copied. but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. 12) The Length/Diameter ratio of a tower should be no more than 30 and preferably below 20. The final design must always be guaranteed for the service selected by the manufacturing vendor. 13) A rough estimate of reboiler duty as a function of tower diameter is given by: Q = 0. This design guideline are believed to be as accurate as possible. 11) Limit tower heights to 175 ft (53 m) due to wind load and foundation considerations. Q D : Energy in Million Btu/hr : Tower diameter in feet.5 D2 for pressure distillation Q = 0. liquid to vapor density ratio. The rules of thumb for selecting packing are: 1) 2) 3) 4) 5) 6) 7) the compounds are temperature sensitive pressure drop is important (vacuum service) liquid loads are low towers are small in diameter highly corrosive service (use plastic or carbon) the system is foaming the ratio of tower diameter to random packing is greater than 10 This design guideline are believed to be as accurate as possible. They were designed for engineers to do preliminary designs and process specification sheets. multiple downcomer trays and system limit trays.KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 16 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 The Selection of Column Internals The selection of column internals has a big impact on the column performance and the maintenance cost of a distillation tower. dual flow trays. liquid loading. Trays can be divided into many categories. reproduced or in any way communicated or made accessible to third parties without our written consent. but are very general not for specific design cases. This document is entrusted to the recipient personally. It must not be copied. conventional structured packing. packing divisions include grid packing. There are several choices of column internals and the two major categories are trays and packing. such as baffle trays. According to some rules of thumb. The final design must always be guaranteed for the service selected by the manufacturing vendor. The guidelines are a training tool for young engineers or a resource for engineers with experience. fouling potential. and most importantly the life cycle cost. random packing. high capacity trays. trays should be selected if: 1) 2) 3) 4) 5) 6) the compounds contain solids or foulants there are many internal transitions liquid loads are high there is a lack of experience in the service vessel wall needs periodic inspection there are multiple liquid phases On the other hand. conventional trays. and high capacity structured packing. but the copyright remains with us. The choice of which to utilize depends on the 1) 2) 3) 4) 5) pressure. but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. . for a tower diameter below 4 feet. use 1 in (2. but are very general not for specific design cases. Maximum efficiency is 0. a tray spacing of 18 inches is adequate as the column wall can be reached from the manway. 4) Ratio of tower diameter to packing diameter should usually be at least 15 This design guideline are believed to be as accurate as possible. .8 m/s) under vacuum conditions.) 2) Peak tray efficiencies usually occur at linear vapor velocities of 2 ft/s (0. for gas flows of 2000 ft3/min (56.25 to 0. or 6 ft/s (1. The final design must always be guaranteed for the service selected by the manufacturing vendor.5 in.2 m3/min). use 2 in (5 cm) packing. for a tower diameter of 4 feet and above. However.5 cm) packing.6 m3/min) or more. with accessibility in mind (Generally. diameter with the total hole area being about 10% of the total active tray area. 2) Packing is often retrofitted into existing tray towers to increase capacity or separation. 7) The most common weir heights are 2 and 3 in and the weir length is typically 75% of the tray diameter. but the copyright remains with us. This document is entrusted to the recipient personally. reproduced or in any way communicated or made accessible to third parties without our written consent. diameter holes each with a lifting cap. They were designed for engineers to do preliminary designs and process specification sheets. 3) A typical pressure drop per tray is 0. 12-14 caps/square foot of tray is a good benchmark. The packed tower design concepts are listed below: 1) Packed towers almost always have lower pressure drop compared to tray towers. the most common tray spacing is 24 inches to allow easy access for maintenance.007 bar) 4) Tray efficiencies for aqueous solutions are usually in the range of 60-90% while gas absorption and stripping typically have efficiencies closer to 10-20% 5) Sieve tray holes are 0.KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 17 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 Some design guidelines should be considered when designing a tray tower. 3) For gas flow rates of 500 ft3/min (14. 6) Valve trays typically have 1.5 in and 8%. It must not be copied. but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. such as follows: 1) Tray spacing should be from 18 to 24 inches.6 m/s) at moderate pressures.1 psi (0.50 in. The guidelines are a training tool for young engineers or a resource for engineers with experience. 5-3.0.76-0.15 .5 m) for other types of random packing.0.40 1.40 0. 6) Liquid distributor should be placed every 5-10 tower diameters (along the length) for pall rings and every 20 ft (6.40 0. plastic packing should be limited to an unsupported depth of 10-15 ft (3-4 m) while metal packing can withstand 20-25 ft (6-7.25 .25 . 9) Height Equivalent to Theoretical Stage (HETS) for vapor-liquid contacting is 1. The guidelines are a training tool for young engineers or a resource for engineers with experience. It must not be copied.40 . The final design must always be guaranteed for the service selected by the manufacturing vendor. They were designed for engineers to do preliminary designs and process specification sheets. but the copyright remains with us.80 0. .0 ft (0. but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design.0.31.0. but are very general not for specific design cases. They should be even more numerous in smaller towers.90 m) for 2 in pall rings. 10) Design pressure drops should be as follows: Table 1: Pressure drop in difference services Service Absorbers and Regenerators Non-Foaming Systems Moderate Foaming Systems Fume Scrubbers Water Absorbent Chemical Absorbent Atmospheric or Pressure Distillation Vacuum Distillation Maximum for Any System Pressure drop (in water/ft packing) 0.0 This design guideline are believed to be as accurate as possible. reproduced or in any way communicated or made accessible to third parties without our written consent.15 . foot of tower area for towers larger than three feet in diameter.60 0. there should be 8-12 streams per sq. This document is entrusted to the recipient personally.8 ft (0.40 .25 0.56 m) for 1 in pall rings and 2.0.4-0.KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 18 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 5) Due to the possibility of deformation.6 m). 7) For redistribution.0. 8) Packed columns should operate near 70% flooding. critical pressure and acentric factor. Equation of state – A relation between the pressure. Distillate – The vapor from the top of a distillation column is usually condensed by a total or partial condenser. Dew point – The temperature at constant pressure (or the pressure at constant temperature) at which the first liquid droplet forms when a gas (vapor) is cooled (or compressed). the constants may be generalized functions of critical temperature.Is a heat exchanger which condenses a substance from its gaseous to its liquid state. Bottoms – The stream of liquid product collected from the reboiler at the bottom of a distillation tower. Bubble point – The temperature at constant pressure (or the pressure at constant temperature) at which the first vapor bubble forms when a liquid is heated (or decompressed). but are very general not for specific design cases. The final design must always be guaranteed for the service selected by the manufacturing vendor. Heavy key is collected at the bottoms. Part of the condensed fluid is recycled into the column (reflux) while the remaining fluid collected for further separation or as final product is known as distillate or overhead product. while for a mixture. The guidelines are a training tool for young engineers or a resource for engineers with experience. For example. All non-key components heavier than the heavy key are known as the heavy components.KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 19 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 DEFINITIONS Azeotrope. but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. This design guideline are believed to be as accurate as possible. Condenser. mixing rules (which may be dependent on composition or density). from which other thermodynamic properties may be derived. This is because when an azeotrope is boiled. Heavy key – The heavier (less volatile) of the two key components. The relation employs any number of ‘constants’ specific to the system. reproduced or in any way communicated or made accessible to third parties without our written consent.Is a mixture of two or more pure compounds (chemicals) in such a ratio that its composition cannot be changed by simple distillation. This document is entrusted to the recipient personally. . They were designed for engineers to do preliminary designs and process specification sheets. for a pure component. It must not be copied. volume and temperature of a system. but the copyright remains with us. are also used. the resulting vapor has the same ratio of constituents as the original mixture of liquids. Reboiler –Is a heat exchanger typically used to provide heat to the bottom of industrial distillation columns. The volatility of the two key components must be in adjacent order when the volatilities of all the components in the feed are arranged in either ascending or descending order. The final design must always be guaranteed for the service selected by the manufacturing vendor. All non-key components lighter than the light key are known as the light components. This document is entrusted to the recipient personally. is a condition where a liquid and its vapor (gas phase) are in equilibrium with each other. This design guideline are believed to be as accurate as possible. They boil the liquid from the bottom of a distillation column to generate vapors which are returned to the column to drive the distillation separation. For moderate temperature ranges.KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 20 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 Key component – A distillation column is assigned with two key components. a condition or state where the rate of evaporation (liquid changing to vapor) equals the rate of condensation (vapor changing to liquid) on a molecular level such that there is no net (overall) vapor-liquid interconversion Vapor pressure – The pressure exerted by the vapor phase that is in equilibrium with the liquid phase in a closed system. Reflux ratio – The ratio of the reflux stream to the distillate. reproduced or in any way communicated or made accessible to third parties without our written consent.Abbreviated as VLE by some. The operating reflux ratio could affect the number of theoretical stages and the duties of reboiler and condenser. α = P2/P1 Vapor-liquid equilibrium. but the copyright remains with us. . the vapor pressure at a given temperature can be estimated using the Antoine equation. Light key is collected at the distillate. but are very general not for specific design cases. Relative volatility – Relative volatility is defined as the ratio of the concentration of one component in the vapor over the concentration of that component in the liquid divided by the ratio of the concentration of a second component in the vapor over the concentration of that second component in the liquid.e. It is used in nonideal (hydrocarbon) systems. They were designed for engineers to do preliminary designs and process specification sheets. The guidelines are a training tool for young engineers or a resource for engineers with experience. K-value – Vapor-liquid equilibrium constant or distribution coefficient. Light key – The lighter (more volatile) of the two key components. The key components in the feed are the main components to be separated in that column. but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. relative volatility is the ratio of vapor pressures i. For an ideal system. It must not be copied. ft/hr Vapor loading. Btu/hr Thermal condition of feed Vapor rate at overhead column. moles/unit time Fugacity of component i Tower height. They were designed for engineers to do preliminary designs and process specification sheets. This document is entrusted to the recipient personally. but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. .KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 21 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 NOMENCLATURES B b C CFS D DT d F fi H HBP HVF K Lo LR LS N Nm P P* Q Qc q V1 Vcalc Vcorr Vmax vmax R Rm SF T x XB xd XDi XD xf Bottom product rate. moles/unit time Bottoms product flow rate. The final design must always be guaranteed for the service selected by the manufacturing vendor. ft Distillate flow rate. but the copyright remains with us. ft3/s Distillate product rate. ft3/min Feed rate. Temperature. The guidelines are a training tool for young engineers or a resource for engineers with experience. oF Mole fraction in the liquid phase Bottom liquid rate. Btu/hr Condenser duty. ft/hr Reflux ratio Minimum reflux ratio Separation factor. ft3/min Coefficient. reproduced or in any way communicated or made accessible to third parties without our written consent. but are very general not for specific design cases. moles/unit time Tower diameter. moles/unit time Calculated vapor rate. moles/unit time Maximum volumetric flow rate. moles/unit time Mole fraction in the distillate Mole fraction of component i in the distillate Distillate liquid rate. Btu/hr Enthalpy of vaporized feed stream. ft Enthalpy of bubble point feed stream. moles/unit time Mole fraction in the feed This design guideline are believed to be as accurate as possible. moles/unit time Corrected vapor rate. ft3/hr Maximum velocity. moles/unit time Liquid molar rate in the rectification section Liquid molar rate in the stripping section Number of theoretical stages Minimum number of theoretical stages Total system pressure. It must not be copied. Btu/hr Vapor-liquid equilibrium constant Reflux liquid. psi Vapor pressure. psi Reboiler duty. Ib/ft3 Superscripts L V b liquid phase vapor phase exponent Subscripts avg bottom HHK HK i j LK LLK top average bottom section of column heavy component heavy key component i component j light key light component top section of column This design guideline are believed to be as accurate as possible. . The final design must always be guaranteed for the service selected by the manufacturing vendor. but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. The guidelines are a training tool for young engineers or a resource for engineers with experience. This document is entrusted to the recipient personally. but the copyright remains with us.KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 22 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 XFi xw y Mole fraction of component i in the feed Mole fraction in the bottoms Mole fraction in the vapor phase Greek letters α γ φ β ρ relative volatility activity coefficient vapor phase fugacity coefficient volatility factor density. They were designed for engineers to do preliminary designs and process specification sheets. but are very general not for specific design cases. It must not be copied. reproduced or in any way communicated or made accessible to third parties without our written consent. The most common methods of representation of VLE data fall into three categories: I) Ideal behavior in both phases II) Liquid phase non-idealities III) High-pressure systems (I) Ideal Behavior in Both Phases Raoult’s Law can be applied in an ideal system. as followed: fiV = yiP fiL = xiP*i where yi xi :mole fraction of i in vapor phase :mole fraction of i in liquid phase Eq (2) Eq (3) Eq (1) This design guideline are believed to be as accurate as possible. The condition for thermodynamic equilibrium is given by: fiV = fiL for every component i The purpose of a VLE model is to relate these fugacities to temperature. methods for predicting such data when measured values are not available. The guidelines are a training tool for young engineers or a resource for engineers with experience. This document is entrusted to the recipient personally.KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 23 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 THEORY (A) Vapor-Liquid Equilibrium (VLE) The design or simulation of a distillation column requires quantitative estimates of the phase equilibrium properties of the mixture. but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. pressure and mixture compositions. In a two-phase system in which a vapor mixture is in equilibrium with a liquid mixture. It must not be copied. but the copyright remains with us. It is the simplest model. The final design must always be guaranteed for the service selected by the manufacturing vendor. but are very general not for specific design cases. pressure and the composition of both phases. reproduced or in any way communicated or made accessible to third parties without our written consent. the variables of interest are the temperature. An engineer must be familiar with sources of equilibrium data. They were designed for engineers to do preliminary designs and process specification sheets. and methods for extrapolating available data. . C.KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 24 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 The only data required for this model are the vapor pressures of the pure components. the system is showing positive deviations from Raoult’s Law and vice versa. When it is greater. but are very general not for specific design cases. It must not be copied. or if it contains polar components. this model is only reliable if: a) the system only contains non-polar compounds. B. E : fitted constants. Activity coefficients can be modeled in two ways.0. T :the absolute temperature A. This document is entrusted to the recipient personally. The guidelines are a training tool for young engineers or a resource for engineers with experience. but the copyright remains with us. D. as shown in the following. ln P*i = A + Where. They were designed for engineers to do preliminary designs and process specification sheets. The final design must always be guaranteed for the service selected by the manufacturing vendor. These deviations are expressed in the form of: fiV = yiP fiL = γixiP*i where γi is the activity coefficient of component i. preferably of the same homologous series b) the pressure is low (< 5 bar) c) the relative volatility between the key components is reasonably high (α = 3) (II) Liquid Phase Non-idealities The liquid phase may show significant deviations from ideality when the components belong to different homologous series. However. reproduced or in any way communicated or made accessible to third parties without our written consent. (the same as before) Eq (5) B + DT + E ln T T +C Eq (4) Activity coefficients may be greater or less than 1. which can be estimated using an extended Antoine equation. The Raoult’s Law model is simple and useful for preliminary feasibility studies. This design guideline are believed to be as accurate as possible. for detailed design. . but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. they may be fitted by regression to the parameters of a ‘local composition’ model. such as the solubility parameter. heat of mixing data and liquid-liquid equilibrium data. but are very general not for specific design cases. ii) Group contribution methods These methods regard each molecule as an aggregate of functional groups. The Wilson and UNIQUAC equations are recommended for most applications. It must not be copied. and evaluate each activity coefficient as a sum of interactions between the groups. unless it gives a reasonable approximation to the average liquid composition on a stage (if the VLE data on either side of the immiscible region is correlated accurately). NRTL and UNIQUAC. This document is entrusted to the recipient personally. Van Laar. molecular structure (group contributions).KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 25 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 (a) Local composition equations If experimental VLE data are available. Wilson. However. infinite dilution activity coefficients. Parameters for each group and for interactions between groups can be easily found in the literature. A local composition model expresses the activity coefficient of each component in the liquid phase as a function of composition and temperature. reproduced or in any way communicated or made accessible to third parties without our written consent. but the copyright remains with us. activity coefficients can be estimated approximately from the properties of the pure components.g. These methods are only suitable for non-polar mixtures and are popular in the hydrocarbon industry. using a ‘solubility parameter’ for each component. but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. Examples of local composition models include Margules. UNIQUAC equation is recommended for rigorous simulation (if the distillation algorithm can cope with two liquid phases). The most reliable methods are: i) Solubility parameter methods These methods are based on Regular Solution Theory and employ the Hildebrand expression for activity coefficient as a function of composition and temperature. UNIFAC and ASOG) can be This design guideline are believed to be as accurate as possible. They were designed for engineers to do preliminary designs and process specification sheets. Redlich-Kister. Local composition models are usually used for moderate or strongly nonideal systems and nearly ideal mixtures with low relative volatility where high accuracy is essential. These methods (e. (b) Activity coefficient estimation methods If experimental VLE data are not available. . The final design must always be guaranteed for the service selected by the manufacturing vendor. The guidelines are a training tool for young engineers or a resource for engineers with experience. This parameter is calculated from molar liquid volume and latent heat of vaporization. the Wilson equation is algebraically not capable of representing a system showing liquid-liquid immiscibility. (III) High-Pressure Systems At high pressure. reproduced or in any way communicated or made accessible to third parties without our written consent. SRK and PR are simple and are recommended for most applications. The aqueous phase is assumed to be pure water. (a) Vapor fugacity coefficient. as in the following. φiV Eq (6) : The vapor phase fugacity coefficient of component i. This document is entrusted to the recipient personally. Some of the most popular equations of state for VLE applications are Soave-Redlich-Kwong (SRK). but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. but the copyright remains with us. but are very general not for specific design cases. The guidelines are a training tool for young engineers or a resource for engineers with experience. especially in systems where an aqueous liquid phase co-exists with a hydrocarbon process phase. When a rigorous model is used for the vapor phase. liquid activity coefficient The activity coefficient concept is retained but a rigorous expression for liquid phase fugacity is used as shown below: fiL = γixifi*L Eq (7) Eq (8) where ⎡ P vL ⎤ fi*L = P*i φi* exp ⎢ ∫ * i dP ⎥ P ⎣ RT ⎦ fi*L = fugacity of pure liquid i at T and P φi* = saturated vapor fugacity coefficient of pure i vi L = molar liquid volume of pure i R = gas constant T = absolute temperature This design guideline are believed to be as accurate as possible. They were designed for engineers to do preliminary designs and process specification sheets.KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 26 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 used for estimation of all organic systems. . including strongly non-ideal polar mixtures. It must not be copied. The final design must always be guaranteed for the service selected by the manufacturing vendor. and the solubility of water in the hydrocarbon is calculated using a derived interaction parameter. Peng-Robinson (PR) and Benedict-Webb-Rubin (BWR). The vapor fugacity may be expressed as: fiV = φiVyiP Where . Fugacity coefficients are calculated by an equation of state. the vapor phase also shows significant deviations from ideal behavior. the liquid phase should also be modeled using sophisticated methods. This approach has been applied even to polar systems at high pressure. reproduced or in any way communicated or made accessible to third parties without our written consent. Ki = yi*/xi Where. The guidelines are a training tool for young engineers or a resource for engineers with experience. equations of state are widely and successfully used in the hydrocarbon industry provided that the relative volatility is high. the liquid phase fugacity may also be represented in terms of a fugacity coefficient: fiL = φiL xi P Eq (9) φiL and φiV can be calculated using the same equation of state. This design guideline are believed to be as accurate as possible. They were designed for engineers to do preliminary designs and process specification sheets. the vapor and liquid phases show distribution volatility between pairs of components. yi* Eq (11) : Vapor mole fraction. This model is very convenient with little input information required.KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 27 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 The exponential term is called the Poynting correction. their relative volatility is defined as: α = KLK/KHK Eq (10) Each component i of the mixture has a distinct vapor-liquid equilibrium ratio or K-value. The accuracy of this method can sometimes be improved by fitting binary interaction parameters into experimental VLE data. in equilibrium with liquid mole fraction xi. A further development is to fit pure component vapor pressure data to the basic parameters of the equation of state. (B) Phase Distribution When a system is in thermodynamic equilibrium. This separation factor has its equivalent term in other methods of separation that are based on the equilibrium concept. However. It must not be copied. but the copyright remains with us. and also fit binary parameters to experimental VLE data. This model is powerful as it takes into account experimental data fitted to a semi-empirical equation within a sound thermodynamic framework. . The final design must always be guaranteed for the service selected by the manufacturing vendor. This document is entrusted to the recipient personally. but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. but cannot ultimately match the accuracy of a model based on experimental data. but are very general not for specific design cases. For light components (LK) and heavy component (HK). (b) Vapor and liquid fugacity coefficients In non-polar systems. The final design must always be guaranteed for the service selected by the manufacturing vendor. It must not be copied. It can sometimes be simplified at the following special cases: (I) Incompressible Liquid In this case. . Under such circumstances. They were designed for engineers to do preliminary designs and process specification sheets. The guidelines are a training tool for young engineers or a resource for engineers with experience. This document is entrusted to the recipient personally. Since most distillations are carried out at relatively low pressures and moderate-to-high temperatures. the vapor phase usually behaves like an ideal gas.KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 28 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 K-value can be estimated using the thermodynamic relationships as discussed earlier. reproduced or in any way communicated or made accessible to third parties without our written consent. This design guideline are believed to be as accurate as possible. Therefore. the K-values for high-pressure systems take the general form of: Ki = γiP*i φi* ⎡ P vi L ⎤ dP ⎥ / φiVP exp ⎢ ∫ * P ⎣ RT ⎦ Eq (12) Equation (12) provides a rigorous thermodynamic basis for the prediction of the vaporliquid equilibrium ratio.0. The resulting equation is: Ki = γiP*i φi* / φiVP (III) Vapor Obeying the Ideal Gas Law At pressures below 2 atm and temperatures higher than 273 K. but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. the Poynting correction (PC) is expressed as: PC = exp [ vi L (P .P*I) /RT ] (II) Negligible Poynting Correction This is usually the case at pressures less than 20 atm and temperatures greater than 273 K. Eq (14) is reduced to Ki = γiP*i /P Eq (15) Eq (14) Eq (13) The liquid-phase activity coefficient in Eq (15) is a “Raoult’s law correction factor” that takes into account liquid phase non-ideality. but are very general not for specific design cases. φi* and φiV are both set equal to 1. For example. Eq (15) is the most generally used relationship for distillation system analysis and design. but the copyright remains with us. The guidelines are a training tool for young engineers or a resource for engineers with experience. In more recent publications5. One of these correlations is presented as follows7: This design guideline are believed to be as accurate as possible. It must not be copied. In these charts. reproduced or in any way communicated or made accessible to third parties without our written consent. The final design must always be guaranteed for the service selected by the manufacturing vendor.KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 29 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 (IV) Ideal Liquid Solution In a mixture containing very similar molecules. the K-values are plotted as a function of pressure on the x-axis with temperature and Convergence Pressure as parameters. This document is entrusted to the recipient personally. later in 1958 K-value charts were curve fitted to the following equations by academic and industrial experts collaborating through the Natural Gas Association of America6. They were designed for engineers to do preliminary designs and process specification sheets.0). Therefore. Some of these are polynomial or exponential equations in which K-values are expressed in terms of pressure and temperature. as they are specific to a certain system or applicable over a limited range of conditions. Other methods have been developed to determine K-values such as the use of K-value charts. but are very general not for specific design cases. scientists and engineers have developed numerous curve fitted expressions for calculation of K-values. but the copyright remains with us. the liquid phase can be assumed to behave like an ideal solution where γi becomes unity and Eq (15) is reduced further to Ki = P*i /P (V) Other Methods to Determine K-Values Some of the methods mentioned earlier require the use of a digital computer. P is pressure in psia and the fitted values of the bij coefficients are reported in an NGAA publication6. these correlations have limited application. Convergence Pressure is the pressure where the K-values of all components in a system converge towards a common value of unity (1. but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design. However. Determination of K-values from charts can be inconvenient for computer calculations. For computer use. . ⎡ T ⎤ ∑ ai ⎢1000 ⎥ ⎣ ⎦ ln (PK) = i = 0 T ⎤ ⎡ ⎢1000 ⎥ ⎣ ⎦ i =3 i Eq (16) ⎡ ln P ⎤ where ai = ∑ bij ⎢ ⎥ ⎣ 10 ⎦ j =0 j =6 j Eq (17) In Eq (17) T is temperature in ºR. K-values for individual components are plotted as a function of temperature on the x-axis with pressure as a parameter4. (P and Pc. P is the system pressure in psi. kPa or bar. reproduced or in any way communicated or made accessible to third parties without our written consent. but are very general not for specific design cases. ωi is the acentric factor. Pci is the critical pressure in psi. They were designed for engineers to do preliminary designs and process specification sheets.5 MPa (500 psia). . but these guidelines will greatly reduce the amount of up front engineering hours that are required to develop the final design.37(1 + ω i )⎜1 − i ⎟⎥ P T ⎠⎦ ⎝ ⎣ Eq (18) where Tci is the critical temperature in ºR or K. and the K-values are assumed to be independent of composition. and T is the system temperature in ºR or K. but the copyright remains with us. This design guideline are believed to be as accurate as possible. T and Tc must be in the same units. up to about 3. kPa or bar.) This correlation is applicable to low and moderate pressure. The final design must always be guaranteed for the service selected by the manufacturing vendor. It must not be copied. This document is entrusted to the recipient personally. The guidelines are a training tool for young engineers or a resource for engineers with experience.KLM Technology Group Distillation Column Selection and Sizing Practical Engineering Guidelines for Processing Plant Solutions Page 30 of 62 Rev: 05 (ENGINEERING DESIGN GUIDELINES) Feb 2007 & April 2008 Ki = ⎡ Pc i ⎛ Tc ⎞⎤ exp⎢5.