Harshad Katre:
You are a student and therefore you are missing some practical details in what you are presenting. An adsorption dryer removes water from compressed air by attracting the water molecules to the surface of an adsorbent (in your case, activated alumina).
Additionally, before introducing the humid compressed air into the adsorbent bed(s), the compressed air is cooled using the compressor's intercoolers (in the case of a multi-staged compressor) and after-cooler. As abubakarce19 points out, as the air is compressed and cooled, liquid water is formed in the product air because it is in excess to the amount of water vapor required for 100% saturation. This liquid water is separated and drained in vapor liquid separators after the inter- and aftercooler of the compressor, prior to entering the adsorption unit. In your supplied sketch, you show a so-called "HOC" (Heat of Compression) adsorption scheme. This is a simplification of the entire process and only shows that the heat of the compressed air exiting the compressor is apparently used to regenerate the spent adsorption bed (there is a minimum of two beds used in an adsorption dryer). After using some of the compression heat to pre-heat the spent bed, the exiting humid air is further cooled and the resulting liquid water condensed is drained out. The remaining, cooled, saturated air is sent to the drying adsorption bed being used. Your sketch is faulty. There is no "moisture separator" used after the adsorption dryer unit, simply because there is no practical liquid moisture left in the dried air product. So you have supplied a sketch of something that doesn't apply or simply doesn't make sense - or doesn't have appropriate identification of the vessels being used and the process employed.
You simply want (or need) to make a heat and material balance around the compressed air process - even though you don't state it as such. Therefore, make a material balance first: find the amount of water in your compressor suction inlet, in your compressor intercooler traps (both liquid and vapor), in your compressor aftercooler (both liquid and vapor), in your adsorber inlet (vapor), and in your adsorber outlet (vapor). The water amount difference between the working adsorber inlet and outlet is the amount left in the adsorbent bed to be regenerated later. You find the amounts of water vapor existing in the compressed air by referring to water content tables or charts. Today, you may even use a simulation program to calculate the amounts.
Refer to the attached workbook for examples of how to find water content in air.
Air Moisture Content Conversion.xlsx 497.26KB
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