Technical Principles

Definition of Pass-through Distillation

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

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Technical Principles

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…

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Technical Principles

PTD presented at Dutch distillation symposium

On June 17, 2014 a technical group known as NL-GUTS (Group of Users of Technologies for Separation) met in Veenendaal,  the Netherlands, 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),…

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Technical Principles

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…

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Technical Principles

That Ugly Third Term

Chemists and Chemical Engineers, you may smile inwardly as you read this, but I am addressing my Mechanical Engineering colleagues who, like myself, learned in thermodynamics class that U, the internal energy of a system, is comprised of three terms and 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)…

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Technical Principles

PTD vs. MVR

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:…

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Technical Principles

Notes on Part 4 (of PTD 101)

  Part 4 contains the surprising truth that gives pass-through distillation its real energy saving potential. In a nutshell, 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). But this heat may be at a higher temperature than the contents of the evaporator.  An appropriate heat exchange system then can supply the evaporator’s heat needs from the absorber.  If this is done, we…

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