Assignment of Chemical process technologySubmitted by Shoaib Sardar SP10-BEC-047Submitted to Sir Wajih-Ur- Rehman
What is dehydration bed? Dehydration is a Process of removing water from a substance or compound. Dehydration bed works on the principal of adsorption. Desiccant is used in bed. It is a substance that absorb water and used to remove moisture. It may be calcium oxide or silica gel.
Construction It is normally a cylindrical tower filled with solid desiccant. Depth of desiccant vary from few feet to 30ft or more. Diameter vary from few inch to 10 or 15ft. Bed height to diameter ratio higher than 2.5 is desirable.
Process description Work on the principal of adsorption adsorption involves a form of adhesion b/w surface of solid desiccant and water vapour. The desiccant is a solid, granulated drying ,which have large effective surface area per unit weight because of a massive amount of microscopic pores and capillary openings. A typical desiccant might have as much as 4 million square feet of surface area per pound.
Process description Multiple desiccant bed are used to dry gas The number and arrangement may vary from two to many towers. Three separate cycles must be performed gas drying cycle, heating or regeneration cycle and cooling cycle. The essential component of dehydration bed are
Inlet gas separator, adsorption towers, A high- temperature heater, a regeneration gas cooler, a regeneration gas separator. In the drying cycle, wet inlet gas first passes through an inlet separator where free liquids, entrained mist, and solid particles are removed. In the adsorption cycle, the wet inlet gas flows downward through the tower. water molecules are adsorbed first in the top and then in the lower layers.
Advantages Producing very low dew point Which are requried for cryogenic gas plant It is adaptable for very large changes A dry bed can handel high contact temperature.disadvantage It is batch process High pressure drop Desiccant are sensitive to poisoning with liquids or impurities in the gas
usesIn natural gas dehydrationIn food industryIn oil industry used in PharmaceuticalIn production very low dew point