science

Low-temperature distillation

Low-temperature distillation is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Low-temperature distillation rather than just read about it. In short: The low-temperature distillation (LTD) technology is the first implementation of the direct spray distillation (DSD) process. The first large-scale units are now in operation for desalination.

Key takeaways

Low-temperature distillation belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Low-temperature distillation to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Low-temperature distillation from memory before moving on to harder problems.

Reference excerpt

The low-temperature distillation (LTD) technology is the first implementation of the direct spray distillation (DSD) process. The first large-scale units are now in operation for desalination. The process was first developed by scientists at the University of Applied Sciences in Switzerland, focusing on low-temperature distillation in vacuum conditions, from 2000 to 2005. Direct spray distillation is a water treatment process applied in seawater desalination and industrial wastewater treatment, brine and concentrate treatment as well as zero liquid discharge systems. It is a physical water separation process driven by thermal energy. Direct spray distillation involves evaporation and condensation on water droplets that are sprayed into a chamber that is evacuated of non-condensable permanent gases like air and carbon dioxide. Compared to other vaporization systems, no phase change happens on solid surfaces such as shell and tube heat exchangers.

Applications Currently, the only implementation of DSD technology is low-temperature distillation (LTD). The LTD process runs under partial pressure in the evaporator and condenser chambers, and with process temperatures of below 100 °C. The first large-scale LTD systems for industrial water treatment are now in operation.

History The DSD process was invented in the late 1990 by Mark Lehmann with the first successful demonstration of the process in a factory hall of the Obrecht AG, Doettingen, Switzerland. The results of the experiments were evaluated and double-checked by Prof. Dr. Kurt Heiniger (University of applied Sciences and Arts, Northwestern Switzerland) and Dr. Franco Blanggetti (Alstom, Co-author of the VDI Wärmeatlas). During the next years, the process has been further researched in the framework of many thesis supervised by Heiniger and Lehmann. The objective has been the examination of the influence of non-condensable gases in lowered pressure environments on the heat transfer during the condensation process on cooled droplets. It has been found that the droplet size and distribution as well as the geometry of the condensation reactor has the most significant influence on the heat transfer. Due to the absence of common tube bundle heat exchangers, the achievable efficiency gains result from the minimized heat resistance during the condensation process.

Technology description

Low temperature distillation (LTD) is a thermal distillation process in several stages, powered by temperature differences between heat and cooling sources of at least 5 K per stage. Two separate volume flows, a hot evaporator flow and a cool condenser flow, with different temperatures and vapor pressures, are sprayed in a combined pressure chamber, where non-condensable gases are continuously removed. As the vapor moves to a partial pressure equilibrium, part of the water from the hot stream evaporates. Several serial arranged chambers in counter flow of the hot evaporator and cold condenser stream allow a high internal heat recovery by the application of multiple stages. The process excels in a high specific heat conversion rate caused by the reduction of heat transfer losses, which results in a high thermal efficiency and low heat transfer resistance. The LTD process is tolerant to high salinity, other impurities, and fluctuating feed water qualities. The precipitation of solids is technically intended to allow for zero-liquid-discharge operation (complete ZLD). It is possible to combine the low-temperature distillation process with existing desalination technologies serving as downstream process to increase the water output and reduce the brine generation.

Physical principle The following figures show and explain the thermodynamic principle on which the LTD technology is built. Considering Fig. 1, there are two cylinders given with open buttons and filled with water in two basins with two different temperatures (assumption: hot at 50°C and cold at 20°C). The temperature related vapor pressure of the water is 123 mbar for 50°C and 23 mbar for 20°C. It is assumed that the two cylinders are 10 meters long and allow to be pulled out the same distance.

The pulled-out cylinders in Fig. 2 show now a different situation regarding the level of the water column. Due to the higher vapor pressure at 50°C, in the hot water column the Atmospheric pressure is capable to elevate the hot water column about 877 cm. In the remaining space, the water starts to evaporate at a pressure of 123 mbar. The cold water column at 20°C, the atmospheric pressure (1000 mbar) is 977 cm high in equilibrium with the according vapor pressure of 23 mbar. If no heat exchange takes place, this situation remains unchanged and is thermodynamically in equilibrium. Now, the two tops of both columns are connected with a vapor channel in Fig. 3. If they are connected, the two vapor chambers (123 mbar and 23 mbar) spontaneously equalize their pressure to an average pressure. As a result, the two water columns tend to have the same level on both sides. However, this connection causes an energetical imbalance of the physical conditions of the water surface on top of the columns. On the 50°C hot column, the vapor pressure of the media is higher than the average pressure. On the 20°C cold side, the average pressure is higher than the vapor pressure of the water. This situation leads to a spontaneous boiling on the hot side and a vapor condensation on the cooler side on the water surface. This process continuous until the temperature on both sides has been balanced out in both columns. After the temperature adaption, both pressures and levels in the chambers are equal.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Low-temperature distillation

Start with the simplest possible case. Write down what Low-temperature distillation claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Low-temperature distillation before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Low-temperature distillation ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Low-temperature distillation

In research: Low-temperature distillation appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Low-temperature distillation in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Low-temperature distillation is common in secondary-school and first-year university syllabi. It links to neighbouring topics Water desalination, Water treatment, so understanding it makes those chapters shorter.
In everyday life: Look for Low-temperature distillation outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Low-temperature distillation in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Low-temperature distillation means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Low-temperature distillation out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Low-temperature distillation in simple terms?

The low-temperature distillation (LTD) technology is the first implementation of the direct spray distillation (DSD) process. The first large-scale units are now in operation for desalination.

Why does Low-temperature distillation matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Low-temperature distillation?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Low-temperature distillation.