Tham khảo tài liệu 'arnold, k. (1999). design of gas-handling systems and facilities (2nd ed.) episode 1 part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Acid Gas Treating 161 Structure of the solids provides a very porous solid material with all the pores exactly the same size. Within the pores the crystal structure creates a large number of localized polar charges called active sites. Polar gas molecules such as H2S and water that enter the pores form weak ionic bonds at the active sites. Nonpolar molecules such as paraffin hydrocarbons will not bond to the active sites. Thus molecular sieve units will dehydrate the gas remove water vapor as well as sweeten it. Molecular sieves are available with a variety of pore sizes. A molecular sieve should be selected with a pore size that will admit H2S and water while preventing heavy hydrocarbons and aromatic compounds from entering the pores. However carbon dioxide molecules are about the same size as H2S molecules and present problems. Even though the co2 is non-polar and will not bond to the active sites the co2 will enter the pores. Small quantities of co2 will become trapped in the pores. In this way small portions of co2 are removed. More importantly co2 will obstruct the access of H2S and water to active sites and decrease the effectiveness of the pores. Beds must be sized to remove all water and to provide for interference from other molecules in order to remove all H2S. The absorption process usually occurs at moderate pressure. Ionic bonds tend to achieve an optimum performance near 450 psig but the process can be used for a wide range of pressures. The molecular sieve bed is regenerated by flowing hot sweet gas through the bed. Typical regeneration temperatures are in the range of 300-400 E Molecular sieve beds do not suffer any chemical degradation and can be regenerated indefinitely. Care should be taken to minimize mechanical damage to the solid crystals as this may decrease the bed s effectiveness. The main causes of mechanical damage are sudden pressure and or temperature changes when switching from absorption to regeneration cycles. Molecular sieves for .
