Glycol Dehydration Dry Dessicant Dehydration While dehydration with glycol is the most common process used to meet the water dew- point specification for sales gas, under certain conditions solid adsorbents are also used for this purpose. Materials with a great affinity for water are silica gel, Sorbead, alumina, and molecular sieves. These solid compounds are prepared as round or slightly elliptical beads having a diameter of about 4 to 6 mm, and in the case of molecular sieves, are also manufactured in small cylindrical forms, about 2 to 3 mm in diameter and about 6 to 8 mm long. Each of these compounds has its own characteristic affinity and adsorptive capacity for water, and the designer has to chose the material best suited for the purpose. Silica gel is silicon dioxide (SiO2), manufactured as small round beads with a large pore surface area onto which the water, contained in the vapor phase in the gas, is adsorbed by the desiccant at relatively low temperatures. The affinity for water is temperature dependent, and the affinity for water is broken at high temperatures, such as 390F. It is necessary to avoid liquid water droplets from contacting the silica gel, as liquid water damages the desiccant. Thus, it is important to have effective gas/liquid separation ahead of a dry desiccant unit. Sorbead is also a silica gel product that contains about 3% aluminum oxide (Al2O3) that makes the gel more resistant to damage from water droplets. Certain manufacturers of Sorbead desiccants provide different grades of Sorbead, such as grade R for regular natural gas drying and grade WS for additional damage resistance from water droplets. A tower filled with Sorbead contains mainly Sorbead R and is topped off with a one-foot-thick layer of Sorbead WS to offer degradation protection from water droplets. Alumina is used mainly for drying air. Molecular sieves are artificial zeolites that are manufactured so that they result in solids with uniform small pore spaces. They have a great affinity for water. Molecular sieves are usually installed in applications in which very low residual water content is required, such as ahead of a low temperature hydrocarbon extraction process. Molecular sieves are suitable for drying very sour natural gas that also contains aromatic compounds. The heavier hydrocarbons might be difficult to remove from the silica gel during the regeneration step. Adsorptivities and design water contents are best obtained from the vendors of the desiccant. In general, design water adsorption is on the order of 8 to 12 lbm of water per 100 lbm of silica and Sorbead desiccants. When new, the adsorption capacity is higher than these numbers. However, when desiccant ages with a number of regeneration cycles, a good design value is about 8 to 10 lbm of water per 100 lbm of desiccant.