Adsorbents for Purification in Cryogenic Air Separation Units (ASUs)
High purity industrial gases such as oxygen and nitrogen become more valued to meet the need of manufacturing development of downstream product. Cryogenic air separation units (ASUs) are built to provide nitrogen or oxygen and often co-produce argon with different boiling points. In addition to N2, O2 and Ar, ambient air contains many trace impurities including Moisture, Carbon Dioxide, nitrogen oxides, light Hydrocarbons.
Especially, impurities 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 of equipment.
ASUs plants employ a pre-purification unit (PPU) to remove impurities from the incoming air by adsorbing these molecules onto the surface of “adsorbent” at near-ambient temperature.
Fixed bed adsorption is the preferred separation technology for the removal of trace contaminants from air fluid. Molecular sieves, activated alumina adsorbents have the advantage of being able to operate in reactive environments without special processing steps. They are capable of removing detrimental impurities to extremely low levels to avoid endangering plant equipment. The adsorbent materials are typically contained in two identical vessels. One vessel is used to purify the air while the other is being regenerated. The two beds switch service at frequent intervals.
Petrotat provides the customer with the solutions to remove many contaminants and meet the high-purity requirements of air.
AA-220 activated alumina was used to remove water efficiently from feed gas at the inlet. The other impurities such as carbon dioxide, hydrocarbons and trace moisture are removed by 13X series molecular sieves.
Type 13X-APG is a spherical molecular sieve adsorbent for removing water, carbon dioxide, light hydrocarbons and sulfide. Typical molecular sieve 13X-APG is widely used for its high dynamic water and CO2 adsorption capacity above ambient conditions. In addition, adsorbent 13X-APG can adsorb molecules, such as light hydrocarbons, SOx, and NOx compounds.
13X – APG II adsorbent is the sodium form of the Type X molecular sieve and an alkali metal alumina silicate. its specifically developed for air plant feed purification. Compare with the 13X-APG, it has a 20% high capacity for dynamically carbon dioxide capacity.
13X-APG III adsorbent is specifically developed for air separation plant pre-purification units (APPU). Compare with the 13X-APG, it has a 50% high capacity for dynamically carbon dioxide capacity.
Even at the low CO2 condition, 13X-APG III still has good adsorbent capacity. For new unit designs, the use of 13X-APG III can reduce the APPU size and lower plant capital and operating costs. 13X-APG III can also be used for plant revamps to reduce energy consumption or increase plant production capability.