Waste heat recovery method for the air pre-purification system of an air separation unit

Highlights: • The three-bed temperature swing adsorption air pre-purification unit was proposed. • The partition theory was proposed, and the 13× molecular sieve was divided into four zones. • The waste heat recovery from the heat-blowing stage was verified via experiment. • The maximum saving energy of the three-bed TSA recovery strategy was up to 51.1%. • The regenerative heat mass transfers of the three- and two-bed were distinguished. A novel three-bed temperature swing adsorber was built to recover low-temperature waste heat from heat- and cold-blowing stages in a double molecular sieve of an air pre-purification system. The regenerative mass transfer in the adsorption bed was divided, and the temperature and concentration breakthrough curves of the adsorber regenerator were obtained via an experiment. Experimental results show that the relationship between the starting point and the energy of waste heat recovery is parabolic. However, energy saving reached the peak at 52.5% when the starting point of heat recovery was 23 min; this result would yield additional H₂O and CO₂ into the bed, thereby affecting the purification effect of the absorbers. The starting time of exhaust gas recycling for limit waste heat recovery strategy was 26 min, which resulted in 51.1% energy savings by recycling different stages of regeneration exhaust. The starting time of exhaust gas recycling for the optimal heat recovery strategy was 29 min, in which energy saving reached 46.5%. The starting time of exhaust gas recycling for the best regeneration strategy was 35 min, which generated energy saving of 29.8%.