Pass-through Distillation voted Project of the Year

POTYA sign

 

Keynote Address for PEO Gala

Good evening Ladies and Gentlemen. It is a great honour to address you tonight on behalf of Drystill, this year’s project of the year winner in the small company category. I would like to tell you our story. It is a story of how a very small Canadian company is making a big impact on world-scale problems. Removal of ethanol from watery mixtures, like fermentation broth, is an important industrial activity. Drystill has invented a device it claims can do a better job than conventional equipment. With funding assistance from NSERC, Drystill teamed up with Sheridan College to build and test a bench scale prototype under rigorous academic supervision. iphone 6 case floating The testing validated Drystill’s claims. That is the project in a nutshell. Although it may not sound remarkable, I think you will be astonished by its significance to the world in general – and to Canada in particular. The removal of ethanol from watery mixtures is only one of thousands of tasks carried out every day by the process known as distillation. Although many people associate the term mainly with whiskey and other alcoholic beverages, distillation is in fact an industrial workhorse, touching almost everything we eat, wear and use. It is also a very old technology, used by the early Egyptians to prepare fragrances and medicines. Simplicity is its main virtue: You simply boil a liquid then cool the vapours to turn them back into a liquid. dream iphone 6 case Although mankind has become a lot smarter about the science behind distillation, the same ancient process is still in extensive use all over the world. Distillation, however, it has two serious drawbacks: Its enormous use of energy is costly both in financial and environmental terms, and its hot operating temperature is troublesome in some important applications. Drystill, in contrast, champions an alternative process called Pass-through Distillation. It enables economical low temperature distillation, reducing boiling temperatures down to 30 degrees Celsius while simultaneously reducing energy use by 50%. The Pass-through distillation process is in the public domain. It is not patentable because it is an obvious combination of well-known scientific principles. But it has never been implemented industrially for want of a suitable heat and mass transfer device with which to carry it out. Drystill has met that need with its invention of the SAM: an acronym for Stripper/Absorption Module. The SAM has patents granted or pending internationally. In industrial settings, distillation is not powered by renewable sources like wind or solar energy. It is powered by steam, generated by burning fossil fuels in a steam boiler. This means that where pass-through distillation displaces conventional distillation, the same results are achieved by burning half the fuel. cat iphone 7 plus case The signing of the Paris Agreement last April marks the beginning of world-wide deliberate action against Global Warming. Each signatory country, including Canada, has pledged to cut back on the combustion of fuels to halt the progressive build-up of carbon dioxide in the atmosphere. No single measure will accomplish it. Some measures will be easy to bear – but others will be very painful. It will be painful to curtail our vacation travelling. It will be painful to have to cut back the thermostats of our domestic furnaces. But if manufacturers were to replace their conventional distillation equipment with Drystill equipment, the only pain would be its capital cost. That pain however would be offset by a fast payback due to reduced fuel costs. yellow case iphone 7 Government incentives could make that payback very rapid indeed. Once the investment has paid for itself, it will continue to save fuel costs for years to come. As countries around the world get serious about living up to their commitment to burn less fuel, this is the kind of measure that is going to be sought. It doesn’t affect anyone in a negative way. It is low hanging fruit in the quest for greenhouse gas reduction. victorias secret pink iphone 6 case But can Pass-through distillation be applied widely enough to make a significant impact on the global warming problem? Many people are surprised to learn just how much of our global energy budget is devoted to distillation. This pie chart, representing data from the US Energy Information Administration shows that 32% of all energy is used by industry. A third of that goes in to distillation! This is a whopping 9% of all energy used in the United States for any purpose. Pass-through distillation can cut that down significantly. It is applicable in many industries including food and beverage, pharmaceuticals, pulp and paper, specialty chemicals, wastewater treatment and others. It is reasonable therefore to say that Drystill’s technology is an attractive greenhouse gas control measure in the context of the current industrial environment. But industry itself is undergoing enormous changes. While coal, crude oil, and natural gas remain the dominant source of both energy and chemical feedstocks, there is a movement toward renewable sources such as agricultural crops and harvested biomass. Already in North America 10% of the fuel we burn in our cars is corn ethanol. Efforts have been underway for at least two decades to make ethanol economically from straw, wood chips, corn cobs and other waste biomass. ariana grande phone case iphone 7 plus When that effort finally succeeds, the world’s dependency on fossil fuels for transportation will be broken, and we will be well on our way to defeating the global warming menace permanently. Unfortunately there remain serious economic problems with the production of cellulosic ethanol. Many studies have shown that low temperature distillation enhances economics by keeping microorganisms alive and preventing destruction of expensive enzymes. Researchers have demonstrated this at lab scale but low temperature distillation through conventional means is not feasible at plant scale. A breakthrough technology is needed, and Drystill believes that pass-through distillation is the answer. The success of the cellulosic ethanol industry and victory over global warming may hinge on one question: Can pass-through distillation remove ethanol from a fermentation broth at a temperature of 30 degrees C? Here’s a news flash for you: Drystill and Sheridan College just tested it using a Drystill SAM. IT WORKED . For the good of our planet, this technology needs to be tested at demonstration plant scale as soon as possible. Since it is a Canadian invention, I am hopeful that a way will be found to do this testing in Canada, and that Canada will reap economic benefits by becoming the purveyor of pass-through distillation technology to biorefineries all over the world.

Akzo Nobel Announces Finalists in Imagine Chemistry Competition

 

Akzo Nobel logo

 

Developed in conjunction with KPMG, Imagine Chemistry was launched to help solve real-life chemistry-related challenges and uncover sustainable opportunities for AkzoNobel’s Specialty Chemicals businesses.

From January to March 2017, participants could submit solutions through a dedicated online challenge platform (The platform is now closed for submissions for 2017). iphone 7 case japanese Special challenge teams comprised of subject matter experts worked with participants through the platform to enrich and validate their solutions and determine if they are a good fit for AkzoNobel’s business.

An enthusiastic response resulted in more than 200 innovative ideas being submitted by chemistry start-ups, scientists, research groups and students around the world.

A jury made up of AkzoNobel business and R&D leaders and prominent international experts then selected the most promising ideas as finalists. girly iphone 6 plus case This year’s finals will take place at AkzoNobel’s RD&I Center in Deventer, the Netherlands, from June 1-3, 2017.

Drystill is one of 20 finalists that will be participating at the event. Here is an excerpt from Akzo’s website, in which they describe Drystill’s submission:

“Pass-through distillation for wastewater

Steve Furlong, Drystill, Mississauga, Ontario, Canada

Challenge area: Wastewater-free chemical sites

 

Drystill is innovating thermal evaporation technology with its Stripping Absorption Module (SAM), a pioneering heat and mass transfer device. iphone 8 plus foldable case SAM can remove water from almost any stream or water source without heating it or putting it in contact with a drying material.

 

Conventional thermal evaporation of industrial waste has a high carbon footprint and costs. iphone 6 plus rubber case SAM offers a practical, low cost, low carbon solution that leads to wastewater-free chemical sites. disney iphone 7 plus phone cases This is achieved by dewatering effluent to produce clean, reusable water and high caloric-value/low-volume liquid residue.

 

Water vapor is transported to a compartment containing hygroscopic salt solution, which is then dewatered using conventional methods. SAM consumes no external heat or power: evaporation is caused by the exothermic absorption of the effluent vapors into a flow of concentrated brine (such as LiBr).

Pass-through Distillation, Drystill Chosen by Akzo Nobel

This year Akzo Nobel launched the first global innovation challenge for startups in chemistry. bellroy iphone 8 plus case Through a competition called “Imagine Chemistry” Akzo is trying to accelerate the commercialization of important new ideas from around the world. On April 5, 2017 Program Manager Rinske van Heiningen announced that Drystill has been selected as one of ten finalists. disney iphone case 8 plus She wrote:

“We received over 200 submissions for more sustainable chemistry, which we have carefully reviewed with our team of researchers. star iphone 8 case We believe your solution ‘Drystill & Pass-through distillation: Improving the operating costs and carbon footprint of waste water concentration’ holds great potential and we are honoured to invite you to the finals, taking place in Deventer, The Netherlands from 1-3 June 2017. At the event, we will work together to further build on your idea during the workshops.

During the three-day event you will get personal feedback from our experts and AkzoNobel decision makers. running case iphone x The team will consist of senior level management, such as chief procurement officers, finance directors, operations managers, sales & marketing directors, R&D directors, etc. fall out boy iphone 6 case The composition of the team may vary depending on the phase and specifics of your startup. iphone 8 plus phone case celtic With this feedback, as well as the challenges/hurdles you perceive yourself, you will work in small teams over several rounds to further develop your concept.

Pass-through Distillation testing at Sheridan College

BRAMPTON, ONTARIO
Sheridan College and Drystill Technologies are collaborating on a project to test pass-through distillation at lab scale, assisted by funding from NSERC.

The project formally commenced on May 30, 2016 and will operate until the end of the year. Many important industrial separations will be tested using room temperature pass-through distillation, including:

*separation of ethanol from fermentation broth

*separation of essential oils from aqueous slurry

*removal of water from corn ethanol plant syrup

*separation of butanol from fermentation broth

The SAM comprises 20 heat pipes 28 cm in length by12mm  in diameter, arranged vertically in a single column. It is capable of boiling 2.3 kg/hr of water. Drystill has built other SAMs in the past, but this one breaks new ground in that it includes an external stripping column between the evaporation and absorption chambers. Another new feature is mechanical distribution devices that permit even distribution of liquids over the heat pipes at extremely low flow rates.

The video below was taken on Aug 12, 2016 when the assembly of the apparatus was nearly complete and was being tested for leak tightness.

 

Drystill explains its version of Pass-through Distillation

Pass-through Distillation (PTD) is a powerful public domain concept, 3d phone case iphone 7 plus but to date its only commercial champion is the Canadian company Drystill. tech 21 iphone 8 case Drystill’s contribution to the field is a proprietary piece of equipment called a SAM, iphone x jewl case which combines the first two process steps into a compact and efficient unit. case for the iphone 6 When PTD is carried out using a SAM, iphone 6 case pineapple the process is given a Drystill tradename, protective case iphone 7 TIEGA. iphone 6 case black and silver This video is something of a Drystill infomercial,

Definition of Pass-through Distillation

Reduced to its essentials, distillation is a two-step process, evaporation and condensation. iphone 7 case tedbaker These two steps are “coupled” because they are carried out at the same pressure.

ordinarydistillation

 

Pass-through distillation is a four step process, similar to simple distillation in that it begins by evaporating some feed liquid and ends by condensing it. iphone 8 case pink hard These steps however are decoupled by an absorption step (step 2) and a desorption step (step 3) which involve a recirculating inventory of absorbent fluid. iphone 6 case slim armor In step 2 this fluid absorbs the gases evaporated in the first step. otterbox strada iphone 7 cases In step 3 the absorbed material is boiled out of the absorbent fluid.

PTDdiag

Decoupling permits the evaporator to operate at very low pressure (and a consequent low temperature) while the condenser operates at higher pressure (with consequent low cost cooling).

The four steps lend themselves to interesting heat economies. iphone 8 plus case for men The absorption step runs at a higher temperature than the evaporator. This means that the heat released in the absorber may be used in the evaporator, permitting the first step to operate without an external energy source. iphone 6 tough case rose gold The material absorbed by the absorption fluid must be boiled out in step 3 (desorption) through externally supplied heat.

Something new under the sun?

There is much to be said regarding pas-through distillation as a separation tool. iphone 7 case full body glitter This post is going to deal with only one aspect of the topic. iphone 7 case solar system The internals of the SAM may constitute a brand new type of fractional distillation apparatus, eliminating the reboiler in favour of heated “packing”.

Let’s first of all review what we know about two simple forms of distillation which will serve as points of reference: the flash tank and the stripping column.

flash

 

FIGURE 1 Flash Distillation

As shown in Figure 1 above, a flash distillation unit heats the feed outside the vessel to a temperature above its boiling point at the pressure in the tank. When the liquid passes through the pressure reducing valve, some of the liquid vapourizes, and the liquid quickly drops to its boiling point. A stream of liquid L is removed from the bottom and a stream of vapour V from the top. These two streams are in equilibrium with each other both thermally and chemically.

stripper

FIGURE 2 Stripper Column

Figure 2 shows a stripping column with its reboiler. The column is contains trays or packing upon which descending liquid and ascending gases can exchange mass and energy. iphone 7 case running Like the flash operation, it too generates a liquid stream at the bottom and a vapour stream at the top, but this time the vapour stream will be in thermal and chemical equilibrium not with the bottoms product but rather with incoming feed at the top.

Now consider Figure 3, a SAM. The acronym stands for Stripper/Absorber Module. We are considering the left-hand compartment which I often call the evaporator section but which is, arguably, a stripper column. apple iphone 8 case pink The heat pipes serve as a coarse packing, causing mass exchange between ascending vapours and descending liquids. The feed liquid is the last thing the vapours (shown in blue) see before leaving the compartment. iphone x case floral We should expect then that the vapour stream should be in equilibrium with the feed, or at least nearly so. Most importantly, the vapour stream will be richer in the most volatile components than the bottoms. football iphone 7 case So is this a stripper? I say yes, but one you will never encounter in a chemical engineering textbook.

SAM2d

FIGURE 3 Stripper/Absorber Module

What makes it distinctive is that at every “tray” heat is added. This leads to strange flow behaviour. At the top tray both the descending liquid stream L and the rising vapour stream V are at their maximum. A portion of the feed is evaporated on this top tier of heat pipes, but the vapour flow rate is the cumulative total evaporation on this “tray” and all the trays beneath it. The flow of liquid descending from the top row of heat pipes to the second is reduced from the feed flow rate by the amount that evaporated. Similarly the amount falling from all subsequent tiers will be reduced until a minimum flow rate is reached at the bottom. bape iphone 8 plus case At that point no further evaporation takes place and the flow of vapour is zero.

McCabe-Thiele analysis will not work on this “stripper”. Its underlying assumption of constant molal overflow does not apply. Other tools will have to be used to describe its behaviour.

Zero Water Consumption

In Industry the term “water consumption” comprises three main components: water that becomes part of the Product, water which becomes contaminated in the process and is sewered, and water that is evaporated in cooling towers. Distillation, per se, involves only the latter, and it does so in a very big way. Pass-through distillation can reduce or even eliminate this loss. To understand how, it is important to first understand why it exists in the first place. Cooling towers, and the water they “consume”, are part of a distillation plant’s energy flow.

Energy cannot be created or destroyed; it flows from a high temperature source to a low temperature sink. In most distillation plants it is provided to the evaporator as steam then removed from the condenser by a stream of cooling water. From the cooling water, the heat is wasted to the environment in an evaporative cooling tower where a portion of the water changes from liquid to vapour, carrying away waste heat at low temperature in the process. iphone 8 plus case in red There are significant costs associated with the procurement and chemical treatment of the cooling water. The easiest way to mitigate these costs is to use less energy in the first place. If a conventional single effect distillation plant were retrofitted with a three-effect TIEGA process, it would produce at the same rate using half the energy input and consequently would use half the cooling water. iphone 8 rechargeable case Where there is evaporative cooling, water conservation automatically accompanies energy conservation.

A different approach to cooling is sometimes used: direct dry cooling. arctic monkeys phone case iphone 7 This operates in the same manner as a car’s radiator, and with very similar equipment. Many people know this type of equipment by the name “Fin fan”. This cooling method consumes no water at all. One of its drawbacks is higher capital cost than evaporative systems. But even when capital cost is not the most important consideration, direct dry cooling is often ruled out because it elevates operating temperatures some 20 Celsius degrees compared to evaporative cooling towers. Many distillations need to “run cool” because of the presence of temperature-sensitive materials. In some cases high temperatures cause heat exchangers to foul. iphone 8 case floral In other cases high temperatures cause delicate substances to thermally degrade, imparting objectionable odor or colour to products.

Pass-through distillation is ideal under these kinds of circumstances. The final condenser is completely decoupled from the process evaporator, so that their operating temperatures may be chosen independently. Suppose a conventional distillation operated with an evaporator temperature of 70C and a condensing temperature of 30C, furnished by evaporative cooling. personalised marble phone case iphone 6 A retrofit for pass-through distillation could be configured to operate with those same temperatures using the same cooling system. The retrofitted plant would use half the energy of its predecessor, and would reduce the load on the cooling system to the same extent.

A second benefit of the PTD retrofit might be to reduce the process evaporation temperature from 70C to, say, 40C to eliminate fouling and improve product quality. That change would leave the triple-effect absorbent regenerator unaffected. Its first effect might operate at 190C while the water cooled condenser on the third effect would operate (as always) close to the temperature of the cooling water, 30C.

The third benefit would be to replace the evaporative cooling system with a fin-fan, and turn the plant into a “Zero Water Consumption” facility. This would raise the condensing temperature in the absorbent regeneration section to 50C, and that twenty degree increase would be felt all the way back to the first effect, raising its boiling temperature from 190C to 210C. The process evaporator however would be totally unaffected, and would continue to operate at 40C.

SUMMARY

Zero water consumption is possible for any distillation process that can use direct dry cooling instead of evaporative cooling towers. Cooling towers, however, are more common partly because their capital cost is lower and partly because many processes cannot operate at the higher temperatures that direct dry cooling demands. A pass-through distillation plant overcomes these drawbacks. iphone 8 case name By virtue of using half the energy of a conventional plant, the capital cost premium of fin-fans is offset (a small fin-fan may even be cheaper than a large cooling tower).
A PDT plant can be configured to use “fin fan” cooling while reducing (rather than increasing) the temperatures seen by delicate process fluids.

PTD presented at Dutch distillation symposium

On June 17, iphone 6 case otterbox purple 2014 a technical group known as NL-GUTS (Group of Users of Technologies for Separation) met in Veenendaal, iphone 7 phone cases battery the Netherlands, case iphone 7 plus silicone for a meeting dedicated to distillation and other thermal separation processes.Click here to learn more about NL_GUTS.
Ian McGregor and Steve Furlong attended to make a presentation on Pass-through Distillation. Both men were representing two Canadian Companies: Drystill Technologies which is a patent holder on PTD hardware known as SAM (Stripper/Absorber Module), and Fielding Chemical Technologies, iphone 7 cases men a well established waste processing company that is collaborating with Drystill to test SAM technology in the processing of aqueous waste streams. iphone 8 marvel case Click here to hear the full content of the presentation,

The Temperature Map

Almost every chemical plant has a boiler and an evaporative cooling tower. The boiler sources heat at a particular temperature. A portion of that heat is wrought into the the goods the plant produces, and the remainder (usually most of it) is dissipated into the environment by the cooling tower at a lower temperature. The source and sink temperatures, sometimes referred to as the “temperature rails”, are very important. They determine the plant’s capabilities.

The lower “rail”, the plant cooling water temperature, varies with the season and the weather. Plants must be designed to operate even in the hottest summer days, so the design value of the cooling water is often a near-worst-case value. We will use 30C.

While the plant’s “upper rail” is the steam temperature, evaporators may have a much lower temperature limit. We are going to consider one with a maximum allowable heating temperature of 85C. If we were to ask why the limit was set at that value, we would likely discover that it was a compromise. People responsible for product quality, equipment maintenance and production scheduling want low temperatures where delicate molecules don’t degrade and heaters don’t foul. But low temperatures are a costly luxury. The 85C limit is probably the point where product quality is only mildly affected and the fouling of the heater is just on the edge of acceptability.

single effect2

FIGURE 1 Single Effect Temperature Map

The diagram or “Temperature Map” above represents a single effect distillation heated by 85C steam and cooled by 30C water. The pink block represents the heater and the green block the condenser. The horizontal line at the 57C mark represents the phase change from liquid to vapour in the evaporator and from vapour to liquid in the condenser (in this example boiling and condensing take place at the same temperature). The two heat exchangers here are well matched so they share the 55 Celcius degree temperature difference equally. The delta T of each is 27.5 C. This is a generous amount. For a given heat flow, the surface area required is inversely proportional to the delta T, so both heater and condenser are fairly small and inexpensive. But we want to see if we can save energy costs through the use of multiple effect distillation.

four effect2

Figure 2 MED Temperature Map

As we add effects, the delta T of each heat exchanger diminishes. If they are well matched, the five heat exchangers in the four effect unit will each have a delta T of 11 Celsius degrees. Each heat exchanger must therefore be larger and costlier than ones in a single effect plant of the same capacity, roughly by a factor of 27/11 or 2.5.

Fig 2 shows an idealized version of multiple effect distillation (MED). In real life there is always a gap between the temperature of the boiling liquid and the temperature of the condensing vapour. One cause of this is pressure drop through ducts and passages of real equipment. The other cause is boiling point elevation BPE), a difference in temperature between the boiling liquid and the vapour it produces.

Process and equipment designers work together to minimize the problem. To minimize pressure drop, huge vapour ducts are provided to convey gases from stage to stage. Boiling point elevation is a thermodynamic property of the fluid that cannot be mitigated. It dictates the kind of of process that may be considered. For example, if the fluid in the 4 effect process under discussion had a BPE of 10C, then each heat exchanger would have a delta T of only 1C. That plant would be an impractical monster, each heat exchanger having grown by a full order of magnitude. peel iphone 8 case If the boiling point elevation were 11C, four effect distillation would be utterly impossible between the temperature rails specified.

PASS-THROUGH DISTILLATION TEMPERATURE MAP

Pass-through Distillation involves two independent pieces of equipment: a SAM and a multiple effect desorber. We’re going to consider first the desorber, shown below.

Desorber four effect

FIGURE 3 Four Effect Desorber Temperature Map

The first thing to notice is that since the desorber does not see any temperature sensitive process fluid, it is not bound by the 85C process temperature limit. I set an arbitrary metallurgical limit of 230C. (Above that temperature low cost alloys suffer excessive corrosion when exposed to the absorbent fluid in this study, but with different alloys or absorbent fluids the temperature limit could be greatly extended.)

The next thing to notice is that there are white spaces between the blocks representing heat exchangers. This is because the absorbent fluid, unlike the hypothetical process liquid of the previous example, has a strong boiling point elevation.

At the top of the map is the steam temperature of 230C. The heater has a 16C delta T. The boiling temperature is 214C. But the vapours do not condense at that temperature. There is roughly a 30C gap, and the condensation occurs in the first interstage heat exchanger at 185C. The pattern of a 16C delta T across a heat exchanger alternating with a 30C gap repeats until the bottom of the chart heat is discharged into the 30C cooling water.

Although there are other absorbent fluids available, Lithium Bromide and water is the one we will consider. It is widely used in the chiller industry. Its boiling point elevation is mainly a function of concentration,as shown on the Duhring Plot below. Every point on the chart represents a system state in which the lithium bromide solution is in equilibrium with the saturated water vapour surrounding it. A common way of expressing this is to say that the liquid is at its boiling point. At any such point the addition of heat will cause some of the water in the solution to become part of the vapour (i.e. iphone 8 case hot pink boil) while removal of heat will cause some of the vapour to be absorbed into the liquid.

ashrae duhring plot

FIGURE 4 Duhring Plot

The magnified portion of the chart shown below has been marked with a red horizontal line to represent system pressure of 200 Torr (that would read 22″HG on a vacuum gauge). Since the gas in the vapour space is pure water, we know from the saturated steam tables that its temperature is 66C. The chart tells us that if that this gas is in equilibrium with a 50% lithium bromide solution, the temperature of that solution will be 93C. It will also be in equilibrium with a 60% solution if that solution temperature is 115C. The boiling point elevation (BPE) values for these two cases are 27C and 49C respectively.

Duhring detail

FIGURE 5 Duhring Plot Detail

Referring back to the desorber temperature map (Fig. 3), we now know what the white blocks represent: the boiling point elevation (BPE) of the LiBr solution. We have seen that BPE is around 30C at 50% concentration and 50C at 60%. The process designer can choose the value of BPE by specifying the working concentration of the absorbent fluid. Now we will examine what will be affected elsewhere in the pass-through distillation process.

PASS-THROUGH DISTILLATION AND BPE

Fig. 6 below shows the schematic of a pass-through distillation plant comprising a SAM and a desorber. A feed liquid enters the top of the left hand chamber, splashes over warm tubes and exits the chamber at the bottom. The absolute pressure in the SAM and the feed temperature are matched such that the liquid is at its boiling point upon entering. All the heat added to the liquid by the warm tubes causes evaporation to occur. In this example the feed liquid is an aqueous slurry for which the boiling liquid and the vapour share the same temperature (i.e. the feed liquid has no BPE) and the vapour generated is saturated water vapour.

SAMptd2

FIGURE 6 Pass-through distillation Schematic

The blue arrows indicate the path of the vapours from the left hand (evaporation) chamber to the bottom of the right hand (absorption) chamber. As the vapours rise they are absorbed into the Lithium Bromide solution as it splashes downward over relatively cool tubes. The latent heat of evaporation carried by the vapours is imparted to the liquid but immediately removed by the cool tubes. As the solution descends its LiBr concentration drops, but at all points it is in equilibrium with the vapour, and its state can therefore be found on the Duhring plot.

There pressure drop in both chambers of the SAM is negligible, so the pressure and temperature of the vapour will be the same throughout. In the evaporation chamber the temperature of the liquid and vapour are equal. In the absorption chamber the temperature of the of the liquid solution is that of the vapour plus the boiling point elevation (BPE). Thus the BPE is the delta T which drives heat from the absorption chamber into the evaporation chamber. The tubes are heat pipes, which conduct the heat with very little thermal resistance.

Figure 7 below shows a temperature map for a SAM. This map is a little different from the ones we have seen so far. While the others were merely one dimensional bar charts, this one reflects the fact that as the LiBr solution falls through the absorber, its concentration and temperature drop.

SAMtempMAP1

FIGURE 7 SAM Temperature Map

Point 1 on the map corresponds to the brine entering the SAM while point 2 is the brine leaving it. iphone 7 cases blue marble The difference in the two temperatures depends upon the ratio of the mass flow rate of the brine to the mass flow rate of the water vapour it absorbs. At infinite brine flow the concentration would be unchanged and the equilibrium temperatures would likewise be unchanged. In practical systems point 2 will always be a few degrees lower than point 1. I arbitrarily chose to show a 5 degree drop.

Points 3 and 4 are the in and out temperature of the feed liquid respectively. In this example they are assumed to be equal.

The length of the vertical line between points 1 and 3 is the BPE of the absorption brine when it is in its regenerated state. In Fig.7 it is shown larger than the 30C of our example for the sake of legibility. Even so, the temperature map of the SAM touches neither the Process Limit of 85C nor the cooling water rail of 30C. That prompts the obvious question “How does the SAM temperature map relate to the plant temperature map?” The answer may surprise you: the two are independent.

Figure 8 below shows the same SAM with the same absorbent liquid operated at two different pressures. This time the maps are to scale for 30C BPE.

SAMtempMA21

FIGURE 8 Operating Pressure Dependency

It is the vacuum train that determines the position the SAM’s temperature map. The lower the absolute pressure of operation, the lower the temperature at which the feed liquid will boil. but whatever that temperature happens to be, the absorbent fluid will absorb the vapours at a temperature higher by the amount of the BPE.

At this point in the discussion, people with plant experience are likely to protest that 17 Torr is impractical for industrial distillations. That is true when industrial distillations involve condensers cooled by normal cooling water. Below 100 Torr the condensers may do an imperfect job, and process vapours will overwhelm the vacuum pump. In some plants where low temperature distillation is needed and the business can support the added operating cost, chilled water is fed to the condenser and lower operating pressures are obtained. Generally, any technique that minimizes the flow of uncondensed gas makes inexpensive vacuum equipment capable of very low plant operating pressures. iphone 8 plus battery case 10000mah Using a version of pass-through distillation, I ran a commercial pervaporation plant for several years at pressures normally below 20 Torr and sometimes below 10 Torr.

SUMMARY

A temperature map is a useful tool in visualizing how pass-through distillation differs from conventional distillation. PTD is a two step process. One of these is a conventional multiple effect distillation applied to an absorbent fluid. It is tied to the plant “temperature rails” in the same way as any other distillation. iphone 6 cool cases for boys The other step is transfer of volatile components from the feed liquid to the absorbent fluid through evaporation and absorption.