$obtained from liquid air by fractional distillation$ $obtained from liquid air by fractional distillation$

Air compression: Ambient air is compressed, using a multi-stage turbo compressor with intercoolers.

A diagram for this process can be seen in figure 2. This is the process for the production of gaseous pure oxygen and nitrogen, as well as liquid oxygen, liquid nitrogen and liquid argon, with internal compression. This method is reaching its maturity level, and industries are looking at the other air separation methods, which are continually being developed, as there is potential for high purity and lower energy consumption (Hashim, 2011).īelow are more detailed steps for a typical cryogenic air separation process (Linde Engineering, © 2017).

$obtained from liquid air by fractional distillation$

Conventionally, catalytic converters using hydrogen were needed, but modern processes only require structured packings. Some improvements to this process included using packed towers instead of traditional trayed towers, as well as introducing heat integration, and more efficient compressors in order to reduce the energy consumption. Argon can also be separated by taking a stream somewhere in the middle of the column at the point where the argon concentration is the highest and feeding this into another column where nearly pure argon is separated from the other gases. This uses the natural temperature gradient within the column to allow nitrogen to leave the top of the column as gas and oxygen as a liquid at the bottom. This liquefies the air, and this liquid stream is sent to a distillation column in order to be separated. The air is first filtered, compressed and then chilled to -185☌. This is a highly energy-intensive process due to the low temperatures that need to be achieved, as can be seen from Table 1 above. It results in a high purity product and is the most developed method currently (Hashim, 2011). Below is an early diagram of the liquefaction process.įigure 1: Von Linde’s original drawing of his air liquefaction process (Flavell-While, 2010)Ĭryogenic air separation is the most common and standard technology used for the separation of air into its constituents. Separation methods have come a long way since then. This liquefaction process took three days. It was only later that separation methods were developed. In 1895, Carl von Linde successfully liquefied air, attempting to obtain liquid carbon dioxide to be used in the brewing industry (Flavell-While, 2010). This relationship is proportional, but not linear (Linde Engineering, © 2017). This critical temperature varies depending on the pressure of the gas, in that a higher temperature is required for lower pressure. This means that air has to be cooled below this temperature in order to become a liquid and then be separated. The critical temperature of the air is -140.7☌ (132.5 K) and the critical pressure is 37.7 bar. A gas becomes a liquid when its pressure and temperature are lower than that of its critical conditions, or critical point. In order for air to be separated into its different components, the air first needs to be liquefied (liquefaction of air). Table 2: The comparisons of process alternatives for oxygen production from air separation (Adapted from Hashim, 2011). The effectiveness of these technologies is summarised in table 2. These methods also vary with the scale with which they can be used. The air separation methods mentioned above are used to separate oxygen from the air, but are also used to obtain other air products, with various by-product recoveries. The oxygen market is growing, as all future clean energy technologies will need to be fed oxygen. The production of oxygen from air separation is a large and growing industry, producing almost 100 million tons of oxygen annually (Hashim, 2011). Oxygen, which makes up 21% of air by volume, is the most widely used air product with many industrial applications.

$obtained from liquid air by fractional distillation$

Table 1: Composition of dry air (Adapted from Linde Engineering, © 2017) These three methods are explained in the sections that follow. Other methods include pressure swing adsorption (PSA) as well as membrane technology, but hybrids of these technologies also exist and new and improved methods are being researched. There are various methods or technologies that can be used to separate air into its components, the oldest and most popular being cryogenic or fractional distillation. The compositions are summarised in table 1 below.

$obtained from liquid air by fractional distillation$

The most abundant components are Nitrogen, followed by oxygen and then argon, as well as other inert gases in small amounts. 1.3 Air Separation of Cryogenic Gases: Membrane Separation Technologiesġ Air Separation of Cryogenic Gases: Current TechnologiesĪn Air Separation Unit (ASU), is a type of technology that separates air into its main constituents.1 Air Separation of Cryogenic Gases: Current Technologies.

$obtained from liquid air by fractional distillation$

Obtained from liquid air by fractional distillation