EPIC Distillation Systems

EPIC’s distillation, engineering and fabrication experts can take your separation needs, develop a detailed 3D model and fabricate a custom distillation system that meets your goals and your budget.

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How Extractive Distillation is like Getting Gum out of your Hair - EPIC Modular Process

Have you ever had gum stuck in your hair? It’s not fun, but there are a few techniques on how to get it out without cutting your hair. Extractive distillation is closely related to this every day situation. It is defined as: “distillation in the presence of a miscible, high-boiling, relatively non-volatile component, the solvent …

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Did you know that coffee is the second most valuable traded commodity? Second only to petroleum. Not only do coffee and petroleum share the top spots, they also use common separation technologies, specifically absorption. Industrial chemical absorption is defined as a process in which one or more soluble components (solutes) are removed from the gas …

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EPIC Sets Itself Apart with Modular Fabrication - EPIC Modular Process

One of the things that EPIC does to set itself apart from other industrial engineering firms is our in-house modular fabrication approach. What is a modular approach? Taking a modular approach to fabrication means building systems with more condensed layouts. They are built as mobile skids, that take up much less space than a traditionally …

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What is a solvent recovery or solvent reclamation system? A solvent recovery system is a process system that takes effluent and extracts useful raw materials back out of the process waste stream. They can reduce the demand for raw materials, by recovering chemicals that can be reused in production, or used to flush the system …

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Designing chemical distillation towers happens in a variety of stages. Starting with step one, the model

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Distillation Unit Highlight | EPIC Modular Process

This year, EPIC has produced multiple distillation systems that we are humbled to have been a part of. One that we can share with you is a large C02 steam stripping unit. This distillation unit consists of an absorption column, a steam stripping column, and a reboiler. This demonstration skid was installed at a at …

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90% CO2 Sequestration from Coal Fired Flue Gas Achieved with Pilot Scale Distillation System

CO2 was removed from flue gas in a two-step distillation process. A pilot-scale distillation system allowed the client to test various system parameters and prove a new CO2 removal technology

DISTILLATION SYSTEM

CLIENT: Akermin, Inc. INDUSTRY: Post-Combustion CO2 Capture for Electric Utilities

KEY ENGINEERING FEATURES:

Compact Footprint: 51 feet tall, 39,000 pound distillation pilot plant skid

Two packed distillation columns comprised of multiple pipe spools, rated for 120 psig at 266 degrees Fahrenheit with full vacuum

Re-boiler used to generate steam for CO2 stripping in the second column

Hydrotesting completed for entire system to check for leaks

FEA analysis on skid frame and load bearing members

Compression tubing and fittings from Swagelok

DeltaV DCS control system

Class 1, Division 1 system

CORE CHALLENGES:

Power plant installation location meant the industrial distillation system could not be fabricated at the power plant due to heavy restrictions on welding, metal shearing and other fabrication tasks.

Cutting edge technology requiring a pilot distillation system with large amounts of instrumentation, flexible operating parameters, and extensive data collection

Packing changes required by experimental process post installation

Compact footprint combined with a large quantity of equipment and instrumentation required careful planning

Material introduction & removal, instrumentation placement, and access points required careful placement in small gaps between packing and distributor plates

Heavy skid required careful sizing of structural members. The skid was constructed vertically and reoriented horizontally for shipment, which required careful planning of distillation skid lifting, transportation and installation

AN EPIC SOLUTION

Front-End Engineering/Design Engineering

As part of a thorough Front-End Engineering (FEE) stage, EPIC took the client provided lab-scale test data and process flow diagram (PFD) and developed the piping and instrumentation diagrams (P&ID’s). The design of the distillation pilot plant went through at least five major revisions during the front-end engineering phase, with Akermin and EPIC collaborating as a team.

Iterating through the range of desired pressures and temperature profiles within the distillation columns is an example of one of these collaborative changes. Akermin’s budget could not absorb the cost of building columns capable of the temperature ranges and pressures originally proposed. By narrowing these profiles to the critical range that could prove scalability, EPIC helped Akermin reach a pilot plant size that was suitable in budget and technical capability.

Using stainless steel tubing was suggested by EPIC’s distillation experts. Tubing is faster to install, costs less and the process systems operational parameters did not require piping. EPIC does in-house TIG welding, but it was collaboratively decided to use Swagelok tube fittings instead of TIG welded construction for cost and time advantages. Sight glasses were added so Akermin could visually verify flow within the columns.

A lifting plan was developed during FEE. Crane size & placement, shipping method and skid size were pre-planned by EPIC and approved by Akermin before fabrication moved forward. The lifting plan also thoroughly examined the path to ultimate resting place at the utility plant, ensuring the skid dimensions fit through any constrained spaces.

Distillation scale-up modeling was completed after a mutual plan was agreed upon. The finalized skid design included the following:

A modular skid design to allow safe and timely off-site construction

Two 40+ feet distillation columns

Looped CO2 sequestering system including:

Removable section of the skid to allow for packing change-out for future testing

Alternative dump height for liquid entering the second column for distillation efficiency testing

Various testing equipment including temperature sensors, flue stream flow meters, sight glasses, and sample ports between packing

Distributors between layers of packing to ensure uniform contact with column packing

Stainless steel tubing and compression fittings instead of TIG welded piping to reduce unnecessary spending.

An absorber column where CO2 is captured using potassium carbonate solution.

A stripper column where CO2 is separated from rich solution using steam

A water/steam continuous loop

Dirty solution/clean solution loop to treat flue gas

THE FINAL SOLUTION

Environmental concerns are pushing utility plants and other manufacturers to find a cost effective way to reduce CO2 emissions. This pilot plant process is testing an experimental new technology for CO2 removal from power plant flue (or exhaust) gas . Ninety percent removal of CO2 at the power plant test site is required to deem the technology a success.

Akermin’s technology integrates a special enzyme within proprietary, permeable polymer films to create a Biocatalyst Delivery System. This System can be used to accelerate CO2 absorption for a wide range of amine solvents or salt solutions. For this pilot project, Akermin elected to test the biocatalyst with potassium carbonate (K2C03) solution and apply the polymer film to structured packing. CO2 removal efficiency, biocatalyst rate enhancement, and optimal operating envelope are all parameters Akermin is testing with this pilot plant.

Lean potassium carbonate solution trickles down from the top of the absorber column and flue gas rises from the bottom. A fan helps blow the flue gas upward and the columns operate under a slight 1.5 psi pressure. Rich solution , aka CO2 infused potassium carbonate, is removed from the bottom of the first column and introduced into either the top or middle of the stripper column. Steam from a re-boiler rises from the bottom of the column and strips (or separates) the CO2 from the rich solution.

CO2 and steam rise out of the column as distillate and the lean solution is circulated back to the absorber column and picks up more CO2. CO2 laden steam is condensed and the CO2 sequestered in a holding tank. Water condensate is sent to the re-boiler and turned back into steam. Small amounts of fresh potassium carbonate are periodically added to the constantly circulating solution.

Akermin is testing the location of the rich solution dump into the second column. The higher in the column solution is introduced, the greater the temperature required to complete distillation. Energy savings may be achieved if the solution can be dumped mid-column and still realize the goal of 90% CO2 removal.

Structured packing is used in the columns. Akermin has completed baseline testing using blank (non-treated) packing. This packing has recently been removed and replaced with identical packing that has been coated with Akermin’s biocatalyst delivery system . EPIC designed the column to allow for packing change-out. Two removable steel structural sections can be detached from the distillation skid to give access to the columns and packing.

Distillation column specifications and skid layout for the distillation pilot plant required two weeks of engineering design work. The pilot plant’s footprint was designed to be small, but a lot of equipment had to fit onto the distillation skid. Material introduction and removal is achieved within tight areas between packing.

A large quantity of instrumentation was mandated by Akermin because the distillation system is a test module. Placement to prevent interference with each instrument was crucial. Probes, nozzles and valves were carefully placed between layers of packing & distribution plates and correctly oriented for operator and maintenance access.

CO2 concentration is checked through a series of sample ports at the bottom of each packing set. Liquid flow through the columns is verified through sight glasses. Temperature transmitters give live feeds for the temperature profile in each section of the columns. Distributors were placed between each layer of packaging to collect liquid moving down the walls of the column. The liquid is re-routed by the distributors to the center of the column, before passing through the next layer of packing.

A DeltaV DCS control system was programmed, installed and tested. Equipment and controls were functionally tested before the pilot plant skid was shipped.

Akermin was closely involved throughout pilot plant assembly, fabrication and testing. They completed at least a dozen walkthroughs. Akermin’s knowledge of their process technology and EPIC’s knowledge of modular distillation systems complimented each other and created a successful distillation skid. This is a typical example of the client supplying the process technology and EPIC Systems, designing and fabricating the most capital-efficient, fastest time-to-market implementation of that technology.

The “plug-and-play” skid was installed at the utility plant smoothly and plant process & utility connections made painlessly.

Modular skid design provided a major advantage to the client. Power plants have many dangerous elements and heavy restrictions in place. Welding, metal shearing, or anything else that could potentially cause a spark, is exceedingly difficult to orchestrate in a hazardous area.

Scheduling work around power plant operations would have proven difficult and costly. A modular skid allowed the distillation plant to be built in a safe and timely manner. The pilot skid was delivered fully operational, and installed with minimal down time for existing operations. Visit our Advantages to Modular page to learn more about why EPIC advocates a modular approach to most process systems.

IMPACT

Successful technology scale-up

Flexible solution for client, allowing testing of two specific dump heights and packing types

Faster and safer skid fabrication and installation due to modular design and off-site fabrication

Budget target met by trimming unnecessary costs and refining operating ranges

WHY EPIC MODULAR PROCESS?

A process design firm helps you design, fabricate and integrate an appropriate process solution that improves your manufacturing process. EPIC believes we can help you “Do It Better” by:

Utilizing Front-End Engineering to ensure that the proper steps are taken during project scope development

Designing most process systems as modular skids, which often saves time, money and creates a more efficient solution

Appointing a single point of direct contact during the entirety of the project

Applying our plant engineering experience to assist clients in identifying needs, pinpointing objectives and providing the most appropriate manufacturing equipment

Maintaining an open door client policy to promote innovation. We invite clients to visit EPIC to experiment with new processes, technologies and techniques that push the limits of traditional engineering.

Imparting a transfer of knowledge (not just a basic training) for the systems and equipment we provide

Find a better solution. Contact EPIC or learn more about industrial distillation systems, pilot plants or other modular process systems.

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What Can EPIC and Aspen Hysys do for you?

With the licensing of Aspen Technologies, EPIC has expanded process simulation capabilities available in-house for our clients. What can 3D models developed by our scale-up experts in Aspen Plus or Aspen HYSYS do for you? Improve accuracy of preliminary process design, reduce project scale-up timelines from design to installation, and lower overall job costs.

While being able to provide these benefits is good for EPIC, the outcomes from these tools are a bigger advantage to you. Why? Accuracy of process functionalities improving means you are avoiding costly change orders later down the road. We can verify through Aspen simulations whether or not your process technology is functional, long before any heavy engineering or manufacturing goes into it.

Shorter timelines from design to turnkey means spending less time on every job we do, with better design optimization. What that means for you is that we can take your process simulation from an unproven theory to a turnkey, fully engineered and designed, process system faster than ever before. In laymen’s terms, you spend money up front, to avoid problems and get a big return on investment throughout the project.

I’m sure you are wondering how this reduces costs? The accuracy of Aspen HYSYS allows us to verify your process technology before we build anything. That means instead of finding out halfway through the fabrication phase that the process isn’t going to work, we identify that very early. We can improve the design before any significant money is spent. Which also means that there are no change orders. You can have confidence that your process will meet or exceed your production requirements, before fabrication begins.

So what does that all this mean? It means that EPIC can get it done, get it done right, and get it done fast. We are the one stop shop for any and all process technologies. If you have a specific question regarding your process technology you can contact one of our process engineers here…

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Steam Distillation: When, Why, How

Steam distillation is a separation technique where heated steam is pumped through a mixture in a distillation vessel, lowering the required temperature for separation by taking advantage of water’s ability to carry other elements during evaporation. During steam distillation, steam makes contact with the solution and water molecules mix with organic elements, carrying these organics upwards as water molecules rise through the system.

Using steam distillation achieves the same purpose as vacuum distillation, lowering the temperatures required to separate elements of a mixture. While vacuum distillation is often easier to execute, steam distillation is still the method of choice in applications where compounds are especially sensitive to decay with raised temperatures. Organic compounds, such as essential oils, are a common example, though there are several other industries where steam distillation is the best separation technique, including petrochemical separation (steam stripping), fatty acids, and soaps.

A basic steam distillation system may look something like this:

Steam is heated in a boiler and then pumped into the distillation column or vessel

Steam passes through the material for separation. In this case, steam pass through plant materials in order to separate oils

Steam and organic compounds (ex. oils) rise off the top of the vessel and are pumped to a condenser, where the steam is cooled and turns into a liquid compound (oil)/water mixture

The compound (oil) and water mixture is allowed to settle, and compounds (oil) rise or fall to a concentrated layer above or below the water.

Water or the compound is then filtered off, resulting in pure compound extracts.

A more industrial example is below, where you can see petrochemicals going through a similar process. In the industrial example, several different products are separated off the distillation column by combining steam distillation with fractional distillation.

Looking for more information on distillation systems? Here are a few resources you may want to check out:

Industrial distillation systems

Basics of distillation column design

A step-wise procedure to advanced distillation column design

Distillation projects gallery

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The 5 EPIC factors of Distillation Equilibrium...

The first, and most critical, step in successful distillation system design is modeling vapor-liquid equilibrium. Understanding the factors that affect vapor-liquid equilibrium is essential for successful modeling of this key interaction. Qualified engineers should review the following five factors before moving forward to column operating objectives.

Factor #1 – Relative Volatility

Factor #2 – Activity Coefficient

Factor #3 – Solubility

Factor #4 – Maximum achievable concentration

Factor #5 – Surface area

1. Relative Volatility:

The boiling point of a pure liquid is defined as: “the temperature at which the vapor pressure of a liquid is equal to the pressure exerted on it by the atmosphere.” The basic principal behind any type of distillation is separating two or more substances based on their boiling points.

The boiling point of a mixture is a function of the vapor pressures of the various substances within the mixture. The total pressure of a solution is the sum of the partial vapor pressures of individual components. Each substance has its own dedicated boiling point at which it evaporates, leaving behind substances with higher boiling points. The boiling points and vapor pressures of each individual substance indicate the relative volatility of a chemical to the rest of the mixture. Determining the vapor pressures and, in turn, the relative volatility, will indicate how difficult it will be to separate the substances in the mixture via distillation.

During distillation, substances separate based on their boiling points. The boiling point of the mixture varies as vapor rises in a distillation column, due to changes in temperature and pressure. This process divides distillation into stages.

The liquid and vapor present at each “stage” will reach equilibrium and cannot be further separated. With each progressive stage, the ratio of substances present in the rising vapor and condensed liquid changes to more or less concentrated per the process needs. Distillate (vapor reaching the top of the column) or bottoms (liquid falling to the bottom of the column) can be further purified either through further distillation or other filtering processes, if desired.

Distillation is a little more complicated than just boiling off individual substances. When a mixture of chemicals is considered, the boiling point of the entire mixture is somewhere between the lowest and highest boiling point of the pure substances contained in the mixture, depending on the relative concentrations of the parts of the mixture. That’s when the next factor, activity coefficient, becomes important.

2. Activity Coefficient – Surface Tension Example:

The attraction of individual molecules at the surface of a solid or a liquid creates a force that is directed solely inward. This is called surface tension. It requires more energy to vaporize a liquid because individual molecules must overcome surface tension. Substances with lower surface tension vaporize with less difficulty. More vapor molecules create increased vapor pressure on a substance. If the surrounding vapor pressure is increased, the boiling point will be lowered. If the surrounding vapor pressure is decreased, the boiling point will rise. The substance with the highest vapor pressure will contribute more molecules to the vapor boiling off, because less energy is required to release molecules from the surface tension.

The lighter components (lower-boiling point) of a mixture concentrate in the vapor phase. The heavier components (higher-boiling point) remain in the liquid phase. Liquid runs down the column while vapor rises, contacting as they go. Vapor becomes richer in light components as it rises and liquid becomes richer in heavy components as it falls. Liquid reaching the bottom of the column is re-boiled and partially vaporizes back up the column. The remainder of the bottom liquid is withdrawn as bottom product (bottoms). Vapor reaching the top of the column is cooled and condensed to liquid and removed as distillate or overhead product.

Surface tension must be considered because it can cause deviations in expected behavior in a mixture of chemical substances. This is where activity coefficient comes in. An activity coefficient is a factor used in thermodynamics to account for non-ideal behaviors. Surface tension is one factor that can cause deviations. The overall separation of chemicals achieved, during distillation, depends on the following: the relative volatilities of the components, their activity coefficients, the ratio of the liquid-phase flow rate to the vapor-phase flow rate and the ratio of surface area to liquid within the distillation column.

3. Solubility:

The tendency of specific substances to dissolve in a solvent (another solid, liquid, or gaseous substance) to form a homogeneous solution affects how well a substance can be separated via distillation. The more alike two substances are, in boiling point especially, the harder they will be to separate. Solubility changes with temperature and pressure, which means it may become harder to separate two substances as distillation progresses.

What solubility usually boils down to (for distillation) is this: if you have a non-soluble, non- heterogeneous azeotrope, you will have to separate it in two different stages.

4. Maximum achievable concentration:

There is always a limit to the concentration of a certain substance that is achievable through distillation. Repeated distillation can refine a mixture only to the maximum achievable concentration, after which point distillation cannot further separate the substances. It is important to know the maximum achievable concentration of any substance through distillation so that parameters can be set for the distillation process and further refining methods, such as filtering, can be planned for, if needed.

An example of this is rubbing alcohol. If you look at a bottle of rubbing alcohol it will say that it is 91% alcohol, the remaining 9% is water. During distillation, when the mixture reaches this 91% alcohol ratio, the remaining water and alcohol form an azeotrope, in which the two components boiling points are so close together they cannot be further separated through distillation.

5. Surface Area:

Achieving the optimum amount of surface area for the liquid and vapor present in a distillation column maximizes the efficiency of a distillation column. As liquid spreads out, the amount of surface area increases, making it easier to boil the liquid and allowing more contact between liquid and vapor molecules. The more times a set of molecules cycles between the liquid-vapor state, the faster two substances can be separated. Only the molecules with the highest boiling point will reach the top of the column as vapor.

As mentioned earlier, each “stage” of a distillation column is an area in which the vapor and liquid molecules present have reached equilibrium. Equilibrium is a condition where the rate of evaporation equals the rate of condensation. At equilibrium no further vapor can be boiled off to rise higher in the column.

The number of stages required to separate the substances into the desired ratio will determine the height of the column. Reflux must also be considered in conjunction with stage requirements. Reflux is the practice of returning condensed vapors back into the column to further increase the amount of liquid and vapor running through the column. The amount of liquid refluxed backed into the column can lower the number of stages required.

The traditional way of designing a distillation column will have a tray at each stage level which collects condensed liquid and allows it to remain in constant contact with vapor in the column. Having a tray at each level allows liquid to spread out across the trays in their natural stages.

A more recent way to achieve the maximum amount of surface area is to use a packed-column design, where the distillation column is filled with packing material, in either random dumped formation or a structured formation within the column. The packing material provides large amounts of surface area for the liquids to spread out on as the mixture separates into stages.

MODULAR DISTILLATION SYSTEMS BY EPIC SYSTEMS, INC.

EPIC Modular Process is experienced in taking your distillation technology and applying our expertise in column sizing, mechanical design and process manufacturing. The process technology for each unique project is most often non-linear, and must be designed and implemented by qualified engineers. Contact EPIC to speak with an engineer, or learn more about modular distillation systems.

SOURCES:

Perry, Robert H., Don W. Green, and James O. Maloney. Perr’ys Chemical Engineers’ Handbook. 6th. New York: McGraw-Hill chemical engineering series, 1984. Print.

Nixon, Mike. “Disillation: How It Works.” JourneyToForever.Org N.p., n.d. Web. 13 Aug 2012.

“Fractionating Column.” Wikipedia. 16 08 2012: 4. Print.

“Theoretical plate.” Wikipedia. 15 04 2012: 6. Print.

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Fractional distillation is often used as a synonym with “distillation” because distillation always takes advantage of a difference in boiling points of component substances for separation. The basic steps to distillation are: …

Fractional distillation is the process of separating a substance into its parts (or fractions), taking advantage of different vapor pressure properties of those substances. Fractional distillation is often used as a synonym with “distillation” because distillation always takes advantage of a difference in boiling points of component substances for separation.

The basic steps to distillation are:

Add heat to a liquid mixture with two or more main substances; for example, a water and ethanol mixture.

As the liquid heats, components with the lower boiling points will begin to vaporize and rise through the column. In the water/ethanol example, ethanol will boil off first (BP 78° C, compared to water (BP 100° C). However, the vapor rising will still contain some molecules of the other substances. Vapor gets purer the higher it rises in the column, as heavier molecules “fall off” and turn back to liquid.

As vapor rises in the distillation column, heavier molecules will condense back into liquid and “rain” back down. At any given point in a fractionating column, vapor will be rising, liquid will be falling, and molecules will be mixing. Columns naturally have certain “stages”; a stage is an area in the column with a similar amount of molecules of each type of substance (i.e. a general certain percentage of water and ethanol). Columns are designed to be tall enough to achieve a certain percentage separation, by finding the minimum number of required stages.

Vapor reaching the top of the column (distillate) is collected into an industrial condenser (a big chiller), which cools the vapor back into a liquid, and piped to tank or storage.

Substances remaining in the column continue the process of distillation, until the desired purity is reached. Some columns are a continuous process (most common), where new base solution is added continually. Others are batch systems, where the base is removed when a desired separation is achieved. In many systems, solution is recirculated several times to make sure substances are properly separated.

What is described above is the basic process of distillation. A distillation column is sometimes referred to as a fractional distillation column in industry. Columns that only separate two columns can be called fractionating columns. A fractional distillation system usually achieves several different products at multiple points within the column. As substances rise, mixtures can be pulled at various stages, and condensed.

An easy example to think about is the distillation of crude oil, as explained by How Stuff Works. As crude oil rises in a column, heavy oils are pulled out lower in the column. Diesel and gasoline rise higher and is pulled out further up the column. Each of these substances is from the same “base solution” but contain different percentages of components found in that substance.

Do you need an industrial distillation system? Contact | [phone] for one of our distillation experts, or find out more about distillation column design today.

Related Links:

91% ethanol removal – A distillation system with an innovative design by EPIC extracted 91% of the ethanol in a water/ethanol mixture. Read the distillation system case study…

Basic Distillation Column Design – What are the basic components to consider when designing a distillation column? Check out this distillation column design infographic to learn more.

Steps to acquire a custom distillation system – Looking for a custom distillation system? Your first step is to connect with a distillation system design and build firm, and explore your distillation goals. Learn more about distillation system design...

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Distillation Column Packing | EPIC Modular Process

What the differences in Distillation Column Packaging?

When thinking of distillation columns, it is often overlooked what goes into the column itself. Distillation systems are filled with packing. Which can come in two different common varieties: structured and dump packed columns.

Structured columns, are exactly what they sound like; columns packed with a premade packing. It could be made of metal, plastic, or ceramic. Dumped packing is comprised of the same material, but like the name says, the packing is simply dumped into the column. Dumped packing generally is in individualized pieces, unlike structured packing, that comes in-preformed segments.

One column packing strategy is not better than the other. As a general guideline when it comes to packing your distillation column, if the system is four inches in diameter or smaller, dump packing is a must. There is no structured packing available that is small enough to fit.

Structured Packing

On the contrary to that, structured packing is not always the best option in larger columns. Operating conditions, vapor flow, and liquid flow must be evaluated before deciding what packing is to be implemented in your distillation system.

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Vacuum distillation is the preferred method when distillation systems face high temperature requirements or elements that decompose at atmospheric pressure...

Industrial distillation can be achieved in a variety of ways. If the elements of your solution have distinct vapor pressures and boiling points, a basic distillation system might be all you need. However, vacuum distillation is the perfect solution when you have elements that decompose when heated at atmospheric pressure – or – that have high boiling points and would have high system heating requirements.

Vacuum distillation is the process of lowering the pressure in the column above the solvent to less than the vapor pressure of the mixture, creating a vacuum, and causing the elements with lower vapor pressures to evaporate off. Lowering the pressure below atmospheric results in lower temperature requirements to achieve evaporation for elements of the distillate, lowering overall heating requirements for the system.

Of course, there are trade-offs – while you can reduce the system temperature requirements, you do have to add equipment (usually a pump) to create the vacuum inside the distillation column. This is where an experienced distillation system designer is a big help; determining which trade-offs in method and equipment will result in the biggest savings overall.

Example case of a system using a slight vacuum to lower column temperature requirements

More about distillation column design basics (infographic)

Next steps for getting a custom distillation system

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Distillation Column Design Check | EPIC Modular Process

How do you successfully design a distillation column? Generally speaking, there are five major steps that have to happen in any industrial distillation column design:

Vapor-liquid equilibrium analysis

Establish column operating objectives

Determine your operating pressure or vacuum conditions

Conduct R/Dmin, Nmin and Feed stage estimation

Determine the diameter and height of the column

How to complete each of these steps, is detailed by distillation expert, Terry Tolliver in our blog, A Stepwise Procedure for Continuous Distillation Column Design.

10 Checks for Distillation Column Design

Today, we offer some key things to check to make sure your design is on track. Below are some things to double-check when you get a preliminary model of your distillation column:

Let’s start with the basics. Have you selected the right type of distillation system for your process? Consider the number of chemicals you need to separate and how many stages this will require. A fractionating column is appropriate for separating several components in one column. A continuous distillation system maintains a steady state and is usually used to separate one chemical of interest. Other types of distillation include: steam distillation, vacuum, zone, reactive distillation, catalytic, azeotropic distillation, prevaporation, flash, freeze and extraction distillation. Have you selected the system type that is most appropriate for your separation goals?

Did you use the correct activity coefficients when determining volatility? If you are estimating this yourself, it is always a good idea to double-check with some outside sources. Calculating your coefficients correctly is critical.

Does the pressure or vacuum you selected allow an appropriate temperature difference between the distillation process and the utility processes that must occur within the distillation column? Cooling water, steam supply, hot oil systems, these will all have a bearing on your column operations. Atmospheric or pressure operation of a column is usually less expensive, but vacuum distillation can be more energy efficient.

Is your process heat sensitive? If the answer is yes, go back and verify your pressure requirements. You may have to operate at a lower pressure to avoid discoloration, fouling or decomposition.

Is your reflux ratio approximately 1.2 times the minimum reflux ratio? If yes, you have probably selected the optimal number of stages and the correct feed location. If no, consider if the trade-off between utility usage and the number of stages is optimal.

Do you have an appropriate superficial vapor velocity selected? This has a large bearing on the distillation column design for diameter and width

Are your trays spaced correctly? Did you account for flooding, weeping, and poor distribution in your distillation column design? Getting liquid to distribute correctly within the column can be difficult and will affect the purity of your distillation.

Did you select a packing size appropriate to the column diameter? Smaller diameters can use smaller packing sizes. Packing has an impact on HETP and pressure drops.

Does your column height include a sump volume that provides approximately 2-3 minutes holdup at 50% level, based on internal liquid flow from the bottom tray?

Do you have vapor space of two column diameters, or two feet (max), at each liquid/vapor distribution point and above the top tray? The last two items both affect distillation column size requirements and can contribute to less than optimal separation if done improperly.

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Distillation Column Installation: A Challenge

PROBLEM: How do you install a distillation column in the middle of manufacturing plant without interrupting operations? Alternately, how do you fabricate a process system in an environment with heavy restrictions on welding, metal shearing, or any other activity that could potentially cause a spark?

SOLUTION: You don’t. You build your distillation column off-site, in a controlled, production style environment. Recently, EPIC has built several distillation systems that saw major advantages from modular off-site construction. Below is one recent example, and some of the major ways off-site modular construction benefited the client.

A 40+ foot distillation column for a power plant

A distillation system designed to remove C02 from flue gas was built at EPIC’s facility and installed, fully tested, at the power plant. The system consisted of a forty-foot distillation column in a fifty-one foot tall skid, all of which was installed in a matter of days at the power-plant. The major advantages to off-site modular design for this project included:

Safety/risk reduced – by constructing the system off-site, fabrication in a hazardous area was never a concern. In addition, welders, pipe fitters and other fabrication personnel were able to work under controlled, accessibly conditions. This increased both the personal safety of the fabrication crew, and the quality of the work.

Minimal operational interruptions – shutting down the power plant in order to install the new system was not exactly a plausible plan. Traditional construction methods could have meant weeks of operational interruptions as new equipment arrived, new sections were welded, etc. By installing the skid all at once, normal operations were interrupted as little as possible.

Schedule compression – modular skid construction is not affected by weather or civil site upgrades. Construction of the module begins as soon as design is complete, regardless of whether civil upgrades are complete. Additionally, start-up time is minimized and system testing does not interrupt current operations.

Full testing complete before delivery – the complete system arrived in one unit, fully tested and ready to go. Process hook-ups simply had to be connected to plant utilities. The punch-list was completed and maintenance personnel trained in just a few days.

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Distillation column design begins when you provide three specifications to an experienced distillation process engineer: your process requirements, budget constraints and key properties of your chemical solution. Process Design Engineers use professional simulation software, such as Aspen HYSYS or Aspen Plus, to model the separation process inside the column. Your column designer provides experience with: field operations, separation equipment, and process capacities to provide an optimal separation solution.

Basic fractional column design concepts and considerations are presented in the presentation below. However, the process begins with a collaborative project development to ensure the model meets your required specifications.

What Distillation Column Designers Need From You

To build an accurate model, engineers must extract your process parameters, including:

Desired system parameters

The desired heating and cooling mediums

Desired operating temperature range during heating, separation and cooling

Desired operating pressure range during heating, separation and cooling

Properties of distillation feed

Composition

Feed rate and temperature

Solids?

Non-condensables?

Azeotropes?

Output specifications

Desired end product specifications

Recycle or waste stream

Chemical composition

Purity requirements

Acceptable composition?

Will further processing be required?

What you receive from your column designer

Distillation system scale-up results in the following outputs for you:

1. Complete fractionating column design, including:

Tower size and width

Optimal feed location placement

Minimum number of required trays

Tray placement and packing selection

2. Mass and energy balances for the finalized distillation column 3. Boiling point curve 4. Utility/support system requirements and basic design 5. Model of distillation column design