Selective absorption process intensification of ammonia from melamine exhaust gas using a counter airflow shear-rotating packed bed

Abstract

The molar ratio of ammonia to carbon dioxide (NH3/CO2) in melamine exhaust can reach up to (2.0–2.4):1, and its direct emission will aggravate the greenhouse effect and waste of resources. Therefore, there is an urgent need to separate and recycle ammonia from the gas mixture in a more economical and efficient way. As an effective process intensification equipment, the counter airflow shear-rotating packed bed (CAS-RPB) has the advantages of high gas-liquid mass transfer efficiency, milliseconds of residence time and enhanced gas turbulence，which could enhance the absorption rate of ammonia in the gas mixture, inhibit the absorption of carbon dioxide caused by chemical absorption, and realize the selective absorption of ammonia.In this study，the CAS-RPB was adopted as an absorption device and the water was used as absorbent, the effects of the gas-liquid (G/L) ratio and high gravity factor (β) on absorption process were investigated. It was found that under suitable operating conditions, NH3/CO2 was close to 1:1 or 2:1 after absorption, which meet the requirement for the co-production of ammonium hydrogen carbonate or urea, the selectivity of ammonia was above 94 %, and the ammonia concentration in the absorption liquid were not less than 8.87 wt%. To compared with Cross-flow rotating packed bed (RPB), the absorption efficiency, selectivity, and gas volumetric mass transfer coefficient of ammonia are increased by 3.34 %, 8.83 %, and 7.02 % in CAS-RPB, respectively. The results show that the CAS-RPB can significantly enhance the selective absorption process of ammonia from melamine exhaust, therefore ammonia and carbon dioxide with potential high-added value can be obtained and utilized, and the zero-emission of ammonia and carbon dioxide can be realized.