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Non-cryogenic systems use principles such as diffusion and adsorption to separate components of air. Nitrogen Membrane SystemsThe general principle behind on-site non-cryogenic membrane systems is selective permeation. Each gas has a characteristic permeation rate that is a function of its ability to dissolve and diffuse through a membrane. Therefore, "fast" gases such as oxygen can be separated from "slow" gases such as nitrogen. The membrane module is the most important element in Oxair Gases’ membrane packages. These modules contain hundreds of kilometres of hollow fibre membranes that allow the oxygen, water vapour and carbon dioxide in compressed air to be selectively removed, producing in a nitrogen-rich stream. * PRISM® Membrane Systems by Air Products and Chemicals Inc.
Nitrogen PSA SystemsAdsorption and diffusion are the general principles behind nitrogen pressure swing adsorption (PSA) systems. Each gas has a characteristic adsorption rate that is a function of its ability to be adsorbed by a molecular sieve. A large surface area to absorb specific gases is created through the use of small sieve particles that contain volumes of micropores and passageways. Nitrogen molecules are able to move freely over this large surface without being held whereas gases such as oxygen are held firmly to the surface area. This is due to the ability of the sieve particle to adsorb molecules more strongly or preferentially over others. The key components of the PSA system are two adsorption vessels, each containing thousands of molecular sieve pellets. Different nitrogen purities and flow rates can be produced by altering the air flow rate through the vessels. * PRISM® Membrane Systems by Air Products and Chemicals Inc.
Oxygen PSA SystemsOxair Australia / Oxair Gases has now entered into a long term licence agreement to manufacture Oxygen Pressure Swing Adsorption (PSA) systems in Australia for the Australian and International markets. This PSA system produces oxygen gas (90 to 95% purity) from compressed air by the diffusion and adsorption of the nitrogen in the air into a Zeolite molecular sieve (ZMS). The compressed air is filtered and dried to remove entrained liquid, oil and solid particles. The cleaned air then enters one of the two adsorption towers. The nitrogen is then removed as the dried air continues upward through the ZMS. Oxygen diffuses through the ZMS pore structure and nitrogen is preferentially retained on the ZMS surface at a considerable higher rate than the oxygen. Air separation occurs in one tower for a period of time before the tower switching occurs. At the end of the period, pressure is equalised between the two towers. Then the feed air is switched to the second tower where the process begins again. The tower going off-line is depressurised down to atmospheric pressure. This depressurisation reconditions the ZMS by removing nitrogen from the ZMS, thus preparing the sieve for re-use in the next cycle. Diversion of the inlet air stream from one tower to the other is controlled by pneumatically actuated process control valves. The valves are precisely sequenced by a programmable controller (PLC), thus providing the cycle with uniformity and repeatability necessary for consistent quality product oxygen. The PLC controller allows for operator-free, reliable equipment operation. All system functions and safety interlocks are constantly monitored by the controller.
Oxygen VSA SystemsOxygen vacuum swing adsorption (VSA) systems are a reliable, energy-efficient and cost-effective alternative to cryogenic on-site systems. It is suited to production of up to 95% purity in flow ranges of 10 to 200 tons per day. The VSA system employs a specialised adsorbent which separates air at ambient temperatures. The adsorbent is an organic crystal material known as zeolite molecular sieve. It selectively adsorbs nitrogen, water vapour and carbon dioxide, leaving the oxygen molecules to pass on through the adsorbent column. High purity oxygen exits the adsorbent column. The column is evacuated using a vacuum system which desorbs the waste gases. It is then refilled with some of the product oxygen gas, allowing the cycle to be repeated.
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