The efficacy of carbon molecular sieve and solid amine for CO2 separation from a simulated wet flue gas by an internally heated/cooled temperature swing adsorption process

Abstract

Considering that most sources of carbon dioxide (CO2) emissions are also waste heat sources, CO2 recovery using self–generated low–temperature waste heat is desirable. This study examines CO2 enrichment and recovery via a temperature swing adsorption (TSA) process. The low–temperature heating–driven TSA process requires an alternative regeneration method to conventional air heating to avoid dilution of the desorbed CO2, and to apply it to actual gas, using an adsorbent that does not lose its CO2 adsorption capacity because of coexisting water vapor is necessary. Zeolites tested in our previous study lose their CO2 adsorption ability under a humid feed gas and a low–temperature regeneration condition. For the former, efficacy of an internally heated and cooled adsorbent–packed fin–coil heat exchanger has been confirmed. This study thus attempts to overcome the latter issue by employing carbon molecular sieve (CMS) and solid–supported polyethyleneimine (PEI) as CO2 adsorbents. The effects of moisture in the inlet gas on the separation performance of adsorbents were investigated. The study reveals that PEI required moisture to extend for CO2 adsorption, and CO2 separation performance increased with higher humidity. PEI can produce the desorbed gas with a CO2 concentration of ∼ 45 % and a recovery ratio of ∼ 70 % from feed gas (CO2 concentration of ∼ 10 %) at a dew point temperature of 15 °C. Conversely, the CMS separation performance is almost independent of humidity. The desorbed gas of CMS indicates a CO2 concentration of only ∼ 30 % and a recovery of ∼ 30 %. The flow of the volumetric desorbed gases and the CO2 concentration rate indicates that CMS has the potential for reducing heat consumption by shortening the regeneration time because most of the CO2 desorbs during the early regeneration step. For increasing the concentration of recovered CO2, a severe control valve is required to eliminate the desorbed nitrogen (N2) accompanied by CO2. In contrast, CO2 desorption from PEI is slower than that in CMS, and PEI needs a relatively longer regeneration time.