Absorption Of Sulfur Dioxide In A Microporous Tube-In-Tube Microreactor

The emission of sulfur dioxide (SO2) and carbon dioxide (CO2) leads to a number of problems like air pollution, acid rain and global warming, which has given harmful effects on human health and the environment. The desulfurization by chemical absorption method is widely used owing to its high reaction rate with SO2 and its high SO2 removal efficiency. It has been shown that microchannel reactors with unique microstructure can greatly intensify the gas-liquid mass transfer process. In this master thesis, the microporous tube-in-tube microreactor (MTMCR) was adopted as an intensified gas-liquid mass transfer reactor for separate absorption of SO2 with deionized water (H2O), sodium hydroxide (NaOH) and ammonium sulfite ((NH4)2SO3) as absorbents; selective absorption of SO2 with low-concentration ammonia (NH3·H2O) solution as an absorbent; simultaneous absorption of SO2 and CO2 with high-concentration ammonia solution as an absorbent. The main contents were as followed:1. MTMCR was adopted to intensify the adsorption of SO2 using H2O, NaOH and (NH4)2SO3 as three absorbents. The effects of design and operating parameters such as absorbent concentration, SO2 gas concentration, gas flow rate, liquid flow rate, gas-liquid ratio, temperature, micropore size and annular channel width of microporous tube-in-tube microchannel reactor on SO2 removal efficiency were explored. The results indicated that SO2 removal efficiency increased with the increase of the absorbent concentration and liquid flow rate, as well as the decrease of SO2 gas concentration and gas flow rate. In addition, as absorption temperature rised, SO2 removal efficiency decreased; reducing the micropore size and the annular channel width would be beneficial to desulfurization. SO2 removal efficiency reached 99.1% under the optimum operating conditions (C=0.005 mol/L, G/L=50, T=293 K, dm=10?m, Rh=250?m).2. Gas-liquid mass transfer characteristics based on the overall volumetric mass transfer coefficient (Kya) in the MTMCR were investigated by using two-film theory with (NH4)2SO3 solution as an absorbent. The effects of design and operating parameters on Kya were explored. The results indicated that Kya increased with the increase of the absorbent concentration and liquid flow rate, as well as the decrease of the SO2 gas concentration. In addition, as gas flow rate rised, Kya increased firstly rapidly and then slowly decreased. Reducing temperature would lead to a higher mass transfer rate. Kya increased with the increase of the micropore size and the annular channel width.3. Selective absorption of SO2 with a low concentration of ammonia solution (0.008-0.012 wt%) as an absorbent was performed in the MTMCR. The effects of design and operating parameters on SO2 removal efficiency were explored. The results indicated that CO2 removal efficiency was less than 5% under the experimental operating conditions. SO2 removal efficiency increased with the increase of the absorbent concentration and liquid flow rate, as well as the decrease of SO2 gas concentration and gas flow rate. In addition, when absorption temperature rised, SO2 removal efficiency decreased. Reducing the micropore size and the annular channel width would be beneficial to the increase of SO2 removal efficiency.4. Simultaneous absorption of SO2 and CO2 in the MTMCR was studied with a high concentration of ammonia solution (0.5-5.5 wt%) as an absorbent. The effects of design and operating parameters on SO2 and CO2 removal efficiency were explored. The results indicated that SO2 removal efficiency reached more than 99.8% under the experimental operating conditions. CO2 removal efficiency increased with the increase of the absorbent concentration and liquid flow rate, as well as the decrease of the CO2 gas concentration and gas flow rate. In addition, with the increase of absorption temperature, CO2 removal efficiency first rapidly increased and then slowly decreased. Reducing the micropore size and the annular channel width would be beneficial to the increase of CO2 removal efficiency.