That Ugly Third Term

Chemists and Chemical Engineers, battery case for iphone 7 plus you may smile inwardly as you read this, iphone 7 plus shockproof case but I am addressing my Mechanical Engineering colleagues who, like myself, learned in thermodynamics class that U, the internal energy of a system, iphone 8 plus case card holder is comprised of three terms uand then forgot all about one of them. It’s easy to do when the systems we work with – heat engines, steam boilers, refrigeration etc. – deal only with the interplay of thermal energy (the TS term) and mechanical work (the PV term). That ugly looking third term, chemical energy, speck iphone 6 case grip had little relevance to my world.

Some systems inhabit a realm too broad to fit that mindset, cute iphone 7 plus cases for girls and and my study of Pass-through distillation has forced me to change my point of view. I have come to appreciate the power and importance of chemical energy, and that change can be compared to leaving Flatland and entering the real three dimensional world. harry potter phone cases iphone 7 Everything interesting in the universe, spigen floral iphone 8 plus case with exception of a few coarse industrial processes, hinges on that third term.

Pass-through distillation cannot be understood without accepting the counter-intuitive truth that a warm liquid can absorb a cool gas. This phenomenon, closely linked to boiling point elevation,


I have had the privilege of explaining Pass-through distillation to many clever and accomplished engineers during the past few years. One of them said suddenly “Aha! I see what this is! It is like mechanical vapour recompression (MVR) without the compressor”. Frankly, I didn’t understand his comment at the time, but now that I have grasped what he meant I find it very apt.

Mechanical Vapor Recompression (MVR)

The diagram below illustrates the MVR process: vapour from the evaporator vessel is brought to a higher pressure by means of a mechanical compressor. At higher pressure, a fluid changes state at higher temperature. The higher pressure vapour condenses in the heating coils of the evaporator because its temperature is higher than the boiling liquid in the vessel.


Notice that no external heat is being applied to the system. The latent heat demanded by the boiling liquid is fully supplied by the latent heat of the condensing vapour; the two quantities are nearly identical. iphone 7 plus phone case tech21 Mechanical energy is being added to the system through the work of the compressor, but this amount is very small by comparison to the latent heat.The theoretical thermal efficiency of MVR can exceed that of a 100 effect evaporator. yeezy iphone 7 plus case Even with the inefficiencies inherent in real equipment, efficiencies equivalent to 30 effect evaporators are reported.

Now let’s look at a SAM in operation. The green feed stream (assume water for our present purposes) enters the left-hand chamber at its boiling point falls over metal bars at a slightly higher temperature. friends iphone x case Heat is imparted to the liquid causing evaporation. The vapour is ducted to the bottom of the right hand chamber. Induced by the pull of the vacuum train, the vapours rise counter-current to falling absorbent fluid, a brine solution, and become a part of the brine. This absorption involves a phase change; the vapour becomes liquid and its latent heat is released into the brine. iphone 8 soft leather case But that heat is immediately conveyed by the bars to the evaporator chamber. ( Note: the “bars” are actually heat pipes which have very low thermal resistance)



Like MVR, the evaporation has taken place without the application of any externally applied heat. In both cases, the heat applied to the evaporator manifests itself as the mass flow rate of the vapour times its enthalpy of evaporation. In both cases the vapour is turned back into a liquid at a higher temperature that of the evaporator, and means have been provided to move that heat back into the evaporator. iphone 8 plus grip case So my friend’s comparison has a great deal of merit.

But our first diagram shows an MVR process in its entirety while the second diagram shows only a SAM, which is half of the pass-through distillation process. The other half is the brine desorber, which restores the diluted brine from the bottom of the SAM’s right hand chamber into a stream of pure water and the stream of concentrated brine which enters the same chamber at the top. The desorption process is a multiple effect distillation (MED). A three effect desorber is likely the practical choice, perhaps a four effect.

So MVR is simpler and more efficient than PTD. But it has some serious drawbacks that PTD overcomes.

First, it involves a large piece of mechanical equipment: a fan, blower, or compressor. Aside from their high capital cost, these pieces of equipment have reliability issues.

Second, MVR is not well suited for low pressure / low temperature operation. The compressor is already large when designed for operation at 1 atm. It must be twice as large for operation at 1/2 atm, because compressors are volumetric devices. By contrast, PTD can operate at 1 atm or at 1/30 atm without much change to equipment. Yes, it has a vacuum pump which must be upsized for lower absolute pressures, but since it only handles non-condensible gases, it is not a major piece of equipment at any pressure.

Third, practical compressors for MVR have modest compression ratios and consequently the delta T across the heating coil is small – on the order of 5C. This means the surface area must be large to compensate. No problem here – the large energy savings ensure rapid payback despite the high capital cost associated with large equipment. thermal case iphone 8 The real problem is that MVR can only be applied to fluids that boil and condense at roughly the same temperature. A few degrees of boiling point elevation can make the use of MVR infeasible. Pass-through distillation does not have this limitation. Concentrated Lithium Bromide brine can absorb water vapour that was generated 40 Celsius degrees cooler than itself. ombre glitter iphone 7 case With that kind of delta T available, feed streams with high boiling point elevation are no problem, and smaller equipment can accomplish the same job.

So are the two processes, MVR and PTD, really similar? I would have to say “no”. Although both offer energy savings through the recycling of latent heat, they are quite distinct.

PTD Covered in European Journal NPT

Tony Kiss, bape iphone 6 plus case a researcher with Akzo Nobel, gudetama iphone 8 plus case learned about PTD at a technology convention and asked to collaborate on an article about the technology.
Tony is certainly well qualified to publish important technical information. iphone 7 plus case light blue See to learn more about his accomplishments. case iphone 6 black The article may be accessed in its entirety by clicking here .

Spread the Word

New Energy saving technologies in the realm of evaporators and distillation equipment should interest many people around the world. After all, evaporation and distillation are number one and two among unit processes in terms of energy consumption. If there exists a global will to address the threats of greenhouse gas and fossil fuel dependency, no stone should be left unturned in the quest for reductions in our global consumption of energy; but extra attention should be given to the Big Users: evaporation and distillation.

Should a technology arise from any quarter claiming significant reductions in Big User energy consumption, those claims should be tested and either debunked or validated. The question is “whose has the responsibility to do so?”. I have arrived at the sad conclusion that there is no such individual or group on this planet. An energy catastrophe could occur while technologies that might prevent it remain in obscurity.

But there are grounds for optimism as well. This world is populated with many intelligent people (like yourself) who care about global problems. As individuals they may little say in the affairs of technology but through their on-line associations they can have great influence in lifting an idea out of the shadows and into the light where its true merits can be determined.

I experienced the power of the internet first-hand quite accidentally. A singing group I belong to gave an impromptu performance in a coffee shop and was caught in the act by a patron with a cell-phone video recorder. He posted the clip on YouTube for the enjoyment of his friends, but the video “went viral” and was soon viewed by over a million people around the world (check out “Old Men Singing at Tim Hortons” on YouTube). No single person determined the extent of its reach. It was the “many people” who thought it worthy of the attention of friends and associates.

You know someone who might benefit from knowing about PTD. Why not send him the link to this site?

What’s “new”?

Distillation is a one of the oldest and most widely practised industrial practices known to man. Could there really be something new in such a well-worn field of study?

“Newness” has a particular meaning to patent attorneys, and in that sense pass-through distillation is not new. iphone 6 protective case lilac But there is also a subjective sense of the word, as in “That’s new to me!” For most of us, iphone 8 case comic this category includes many great inventions that failed the test of commercialization and vanished into obscurity. cases for iphone 6 silicone In this sense of the word, pass-through distillation may be new to you.

Once you have learned what it is and how it works, iphone 7 phone cases bride you will want to know if it is relevant to you. iphone 6 case french You might ask: Can it be applied to my process? What are its operating costs and capital costs as compared to conventional technology? If it enables me to reduce energy consumption, iphone 7 phone cases planets will I get carbon credits? Are there any case studies in my industry? Who is currently active in this field?

I am hoping to make this kind of multi-disciplinary information available on this site over time.

Notes on Part 4 (of PTD 101)

Part 4 contains the surprising truth that gives pass-through distillation its real energy saving potential. iphone 6 transparent gel case In a nutshell, iphone 7 mulan case gas absorption changes the state of the absorbed gas into a liquid; consequently the latent heat of evaporation must be rejected (as in a condenser). iphone case 8 plus green But this heat may be at a higher temperature than the contents of the evaporator. iphone 6 silicone case disney An appropriate heat exchange system then can supply the evaporator’s heat needs from the absorber. 360 silicone case iphone 7 plus If this is done, iphone 8 case rick and morty we get the first boil-up “for free”.

We learned in part 3 that the second boil-up can use multiple effects to reduce energy consumption by 50%. grip iphone 8 case So the combined energy use of the first and second boil-ups is 0 + 50% = 50% of conventional distillation.

I have found no instructive videos on Youtube to aid here,