Experimental Study on the Selective Removal of SO₂ from a Ship Exhaust Gas Stream Using a Membrane Contactor

Abstract

In this study, we investigated the selective SO2 removal performance of three absorbentsdistilled water (DW), aqueous NaOH, and Na2SO3 solutionsfrom a typical ship exhaust gas stream using a hollow-fiber membrane contactor. SEM and contact angle analyses were performed to apprehend the morphological and water interaction characteristics of the membrane. A SO2/CO2/N2 gas mixture (1000 ppm of SO2, 5.50 mol % CO2, balance N2) was used and the absorbents were thoroughly evaluated in terms of SO2 gas removal efficiency over a range of operating parameters including absorbent flow rate, feed gas flow rate, absorbent concentration, and L/G ratio. The aq. NaOH absorbent had the best SO2 removal efficiency among the three absorbents under all conditions, mainly due to high alkalinity. Notably, around 100% SO2 removal efficiency can be achieved with the NaOH absorbent. The Na2SO3 solution closely followed the NaOH in SO2 removal efficiency. DW was the worst performer under all conditions. This study confirms that the use of membrane contactor is advantageous over the conventional packed towers because the membrane contactors are compact, offer high contact area, and achieve higher removal efficiencies.

Selective Sulfur Dioxide Absorption from Simulated Flue Gas Using Various Aqueous Alkali Solutions in a Polypropylene Hollow Fiber Membrane Contactor: Removal Efficiency and Use of Sulfur Dioxide

“…This is the same trend as reported in previous general research results. However, the L/G value used in this experiment is about four times lower than that in existing studies, which means that it is possible to process a larger amount of SO 2 during the same time [ 26 , 33 ].…”

“…The force applied to the membrane contactor is 1 atm, and the pressure difference is close to zero. It was confirmed that there is no difference when comparing the pressure applied to the membrane contactor through an experiment [ 33 , 50 ].…”

“…When DI water was used as an absorbent, as reported in the results for general SO 2 removal experiments, the removal rate rapidly decreased from the beginning of the experiment, and then showed a removal rate of 50% or less in less than 30 min [ 16 , 32 , 33 , 46 , 47 ]. The tendency for various types of absorbents in this study is not much different from those in the previous studies.…”

“…The removal rate was measured for one hour or until the SO 2 removal rate was less than 50% using various absorbents (simulated seawater, H 2 O, H 2 O 2 , NaOH, NaHCO 3 , Na 2 CO 3 , Na 2 SO 3 , and NH 4 OH). The chemical equation for the SO 2 removal reaction for the various absorbents used can be summarized as follows [ 26 , 33 , 42 , 43 , 44 , 45 ]: SO 2 (g) ↔ SO 2 (aq), H 2 O (aq) + SO 2 (aq) ↔ H 2 SO 3 (aq), H 2 O 2 (aq) + SO 2 (aq) ↔ H 2 SO 4 (aq), 2NaOH (aq) + SO 2 (g) → Na 2 SO 3 (aq) + H 2 O (aq), 2NaHCO 3 (aq) + SO 2 (aq) → Na 2 SO 3 (aq) + 2CO 2 (g) +H 2 O (aq), Na 2 CO 3 (s) + SO 2 (aq) → Na 2 SO 3 (aq) + CO 2 (g), Na 2 SO 3 (s) + SO 2 (aq) + H 2 O (aq) → 2NaHSO 3 (aq), 2NH 4 OH (aq) + SO 2 (aq) + H 2 O (aq) ↔ (NH 4 ) 2 SO 3 (aq) + 2H 2 O (aq), …”

“…The components of the simulated flue gas were used by mixing at concentrations of 2000 ppm for SO 2 and 15% v/v for CO 2 (N 2 balance). The SO 2 gas concentration was produced by referring to the concentration range (371–3500 ppm) used in typical FGD process studies [ 32 , 33 ]. The CO 2 gas concentration was achieved by referring to the emission components of coal-fired power plants.…”