Temperature swing adsorption (TSA) is another technique use for regenerating a bed of adsorbent that is loaded with the targeted impurity gas. Whereas pressure swing adsorption (PSA) uses changes in pressure to release adsorbed gas, TSA modulates or swings temperature to drive off the adsorbed gas.
TSA technology began commercially in the 1960's and continues today for drying compressed air and natural gas as well as other purification applications such as carbon dioxide stripping from air. TSA exploits the capacity of certain adsorbent materials, such as activated alumina, silica gel and zeolites, to adsorb gases at moderate temperatures (40°C, 100°F) and later release them when the temperature rises above 120°C (250°F). TSA can separate a single gas from a mixture of gases. A typical TSA system employs a cyclic process where a number of connected vessels containing adsorbent undergo successive loading with the target gas followed by heating and cooling steps to produce a continuous stream of dried or purified product gas.
There are a few reasons for selecting TSA over PSA:
- At pressures below 4 bar (60 psig)
- When PSA operating costs are too high, TSA is often less expensive to operate, despite initially costing more to buy
- When high product purities are not achievable with PSA, TSA may be suitable
The operation of a simplified TSA process to dry compressed air is illustrated in following diagram:
TSA Technology Schematic
- The wet feedstock gas is pumped into a cylinder at pressure. The cylinder contains beads of adsorbent material.
- The moisture in the feedstock gas is adsorbed onto the internal surfaces of the adsorbent beads, leaving dry gas in the vessel.
- Heated purge gas raises the temperature of the loaded bed. Thehigh temperature drives off the adsorbed moisture.
- Before returning online, the desorbed bed must cool down so that it can adsorb again in the next cycle.