{"id":1171,"date":"2012-02-06T20:18:53","date_gmt":"2012-02-06T14:48:53","guid":{"rendered":"http:\/\/mohamediqbalp.wordpress.com\/?p=1171"},"modified":"2012-02-06T20:18:53","modified_gmt":"2012-02-06T14:48:53","slug":"cryogenic-air-separation-and-liquefier-systems","status":"publish","type":"post","link":"https:\/\/venusimportexport.com\/wordpress\/index.php\/2012\/02\/06\/cryogenic-air-separation-and-liquefier-systems\/","title":{"rendered":"Cryogenic Air Separation and Liquefier Systems"},"content":{"rendered":"


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Cryogenic air separation processes are routinely used in medium to large scale plants to produce nitrogen, oxygen, and argon as gases and\/ or liquid products.  <\/font><\/b> <\/p>\n

Cryogenic air separation is the preferred technology for producing very high purity oxygen and nitrogen. It is the most cost effective technology for high production rate plants.  All plants producing liquefied industrial gas products utilize cryogenic technology.  <\/font><\/b><\/p>\n

The complexity of the \t cryogenic air separation process, the physical sizes of equipment, and the energy required to operate the process all vary with the number of gaseous and liquid \t products, required product purities, and required delivery pressures.  <\/font><\/b> \t <\/p>\n

Nitrogen-only production \t plants are less complex and require less power to operate than an \t oxygen-only plant making the same amount of product.  Co-production \t of both products, when both are needed, increases capital and energy \t efficiency.  Making these products in liquid form requires additional \t equipment and more than doubles the amount of power required per unit of \t delivered product.  <\/font><\/b> \t <\/p>\n

Argon production is \t economical only as a co-product with oxygen.  Making it at high \t purity adds to the physical size and complexity of the plant.  <\/font><\/b> <\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table><\/div>\n

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\"Front<\/a><\/td>\n \"Nitrogen<\/td>\n \"Air<\/td>\n \"UIG<\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table><\/div>\n
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\t \t The \t Composition of Air – The Raw Material for Cryogenic Air Separation <\/span> \t <\/a><\/font><\/td>\n<\/tr>\n
General Process Description – Cryogenic Air Separation<\/font><\/a><\/font><\/b><\/td>\n<\/tr>\n
     Nitrogen Plants vs. Oxygen Plants<\/font><\/a><\/font><\/td>\n<\/tr>\n
     Argon Recovery and Purification<\/font><\/a><\/font><\/td>\n<\/tr>\n
     Product Compression and Alternatives <\/font><\/a><\/font><\/td>\n<\/tr>\n
     LIN-Assist Plants<\/font><\/a><\/font><\/td>\n<\/tr>\n
Liquefiers <\/font><\/a><\/font><\/b><\/td>\n<\/tr>\n
     Stand-alone Liquefiers<\/font><\/a><\/font><\/td>\n<\/tr>\n
     Integrated Liquefiers<\/font><\/a><\/font><\/td>\n<\/tr>\n
     Campaign mode operation<\/font><\/a><\/font><\/td>\n<\/tr>\n
Supply System Optimization<\/font><\/a><\/font><\/b><\/td>\n<\/tr>\n<\/tbody>\n<\/table><\/div>\n
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Air – The \t Raw Material<\/a> for Making Nitrogen, Oxygen and Argon:<\/b><\/font><\/p>\n<\/td>\n<\/tr>\n

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Dry air<\/a><\/b> is relatively uniform in composition<\/b>, with primary constituents as shown below. Ambient air, may have up to about 5% (by volume) water content and may contain a number of other gases (usually in trace amounts) that are removed at one or more points in the air separation and product purification system. <\/font> <\/p>\n
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Primary Components of Dry Air <\/font><\/b><\/td>\n<\/tr>\n<\/tbody>\n<\/table><\/div>\n\n\n\n\n\n\n\n
Gas<\/font><\/td>\n % by Volume<\/font><\/td>\n % by Weight <\/font><\/td>\n Parts per Million (V)<\/font><\/td>\n Chemical Symbol<\/font><\/td>\n<\/tr>\n
Nitrogen<\/font><\/td>\n 78.08<\/font><\/td>\n\n

75.47<\/span><\/font><\/p>\n<\/td>\n

 780805<\/font><\/td>\n N2<\/sub><\/font><\/td>\n<\/tr>\n
Oxygen<\/font><\/td>\n 20.95<\/font><\/td>\n 23.20<\/font><\/td>\n 209450<\/font><\/td>\n O2<\/sub><\/font><\/td>\n<\/tr>\n
Argon<\/font><\/td>\n 0.93<\/font><\/td>\n 1.28<\/font><\/td>\n 9340<\/font><\/td>\n Ar<\/font><\/td>\n<\/tr>\n
Carbon Dioxide<\/font><\/td>\n 0.039<\/font><\/td>\n 0.0606<\/font><\/td>\n 390<\/font><\/td>\n CO2<\/sub><\/font><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table><\/div>\n
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General<\/a> Process Description – Cryogenic Air Separation: <\/font><\/b><\/p>\n<\/td>\n<\/tr>\n

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There are numerous variations in air separation cycles used to make industrial gas products.<\/b>  Design variations arise from differences in user requirements.  Process cycles are somewhat different depending upon how many products are desired (either <\/i>nitrogen or oxygen; both <\/i>oxygen and nitrogen; or nitrogen, oxygen and<\/i> argon); the required product purities; the gaseous product delivery pressures desired; and whether one or more products will be produced and stored in liquid form. <\/font> <\/p>\n

All cryogenic air separation processes consist of a similar series of steps.<\/font>  <\/b>Variations in selected process configuration and pressure levels reflect the desired product mix (or mixes) and the priorities\/ evaluation criteria of the user. Some process cycles minimize capital cost, some minimize energy usage, some maximize product recovery, and some allow maximum operating flexibility.  <\/font><\/p>\n

The cryogenic air separation flow diagram shown below illustrates (in a generic fashion) many of the important steps in producing nitrogen, oxygen and argon as both gas and liquid products.  <\/b>It does not<\/u><\/i> represent any particular plant. <\/font><\/p>\n<\/td>\n<\/tr>\n

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Steps in Cryogenic Air Separation:<\/b><\/font><\/p>\n<\/td>\n<\/tr>\n

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The first process step in any air separation plant<\/font><\/a> is filtering, compressing, and cooling the incoming air.<\/font> <\/b><\/font><\/p>\n

In most cases the air is compressed to \t somewhere between 5 and 8 bar, depending upon the intended product mix and \t desired product pressures. The compressed air is cooled, and much of the water vapor in the inc
\noming \t air is condensed and removed, as the air passes through a series of \t interstage coolers plus an aftercooler following the final stage of \t compression.   <\/font><\/p>\n

Because the final temperature of the \t compressed air is limited by the temperature of the available cooling \t medium, which in almost all cases is limited by the wet or dry bulb \t temperature of the air, the temperature of the compressed air is sometimes \t well above optimum for maximizing the efficiency of downstream unit \t operations.  <\/font><\/p>\n

Consequently, the compressed air is often cooled to a somewhat lower temperature in a mechanical refrigeration system. In addition to lowering and stabilizing the inlet \t temperature to downstream compression and heat exchange systems, which \t enhances the efficiency and stability of the overall air separation \t process, reducing the compressed air temperature allows removal of \t additional water vapor by condensation, reducing the water-removal load in \t molecular sieve pre-purification equipment. with a mechanical \t refrigeration system or, In some cases, cooling may be accomplished with a \t direct contact aftercooler system (DCAC) instead of mechanical \t refrigeration.  DCAC systems utilize cool, dry waste gas to chill a a \t circulating cooling water stream in a “chill tower”, and then use the \t chilled water stream to cool the compressed air in a second tower.   <\/font><\/p>\n

<\/font> The next major step is removal of impurities, in particular, but not \t limited to, residual water vapor plus carbon dioxide<\/b>.<\/font>  <\/p>\n

These components of air must be removed to meet product quality specifications. In addition, they must be removed prior the air entering the distillation portion of the plant; because very low temperatures would cause the water and carbon dioxide to freeze and deposit on the surfaces within the process equipment. <\/font><\/p>\n

There are two basic approaches to removing the water vapor and carbon dioxide –  “molecular sieve \t units” and “reversing exchangers”. <\/b> <\/font><\/p>\n