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A bubbling reactor is an important type of gas scrubber to reduce SO2 emissions in maritime shipping. Both experiments and simulations were conducted to study the relationship between the periodic gas bubbling process and SO2 concentration at the outlet of the reactor, and the entrainment of liquid droplets on SO2 absorption. The accuracy of the model was verified by comparing the bubble size, the depth of bubbles injected into the water, and the SO2 concentration obtained in both experiments and simulations. The gas bubbling process is accompanied by bubble formation, rise, and collapse. The gas bubbling period is affected by the disturbance of the liquid level. The period of the SO2 concentration at the outlet of the gas bubbling reactor is smaller than that at the gas jar outlet which acts as the gas buffering region. The amounts of water carried out of the bubbling reactor by the gas bubbling process increase with the gas flow rates. The droplets and liquid film in the gas jar and the connecting tube play an important role in the absorption of SO2. This study encourages more research to reduce the fluctuation of SO2 concentration and consider droplet entrainment in the design of bubbling reactors. [ABSTRACT FROM AUTHOR]

Highlights: [•] Experiments in a well-stirred reactor show three pH regions of SO2 absorption. [•] The operational pH of sodium quench units is recommended to be in region 2. [•] Operating in region 2 achieves a high absorption rate and low sodium loss. [•] The operational window narrows with the increase of sodium solution concentrations. [•] The operational window narrows at low partial pressure of SO2. [Copyright &y& Elsevier]

Abstract: Oxy-fuel combustion is an emerging technology to mitigate CO2 emissions from power plants. Compared with other CO2 capture technologies, gas impurities in oxy-fuel flue gas are highly concentrated, among which SO2 is of concern. Dynamic transient experiments have been conducted in a semi-batch well stirred reactor (WSR) relevant to the conditions of the flue gas scrubbers operating at atmospheric pressure prior to CO2 compression in oxyfuel technology for CCS. SO2 in N2 as well as in CO2 were considered. The initial pH of the solutions considered was those of NaOH (with concentrations of 0.01M and 1M), Na2CO3 (0.005M) and NaHCO3 (0.01M). Analysis of the liquid solutions showed that the concentration of bicarbonate increases with pH at a pH larger than 5.5 indicating a loss of effectiveness of the sodium reagent. A practical discharge pH of the liquid discharge from the scrubber is also greater than 4 as at a lower pH the absorption rate of SO2 reduced. This operating range is consistent with the reported operating range of the scrubber used in the Vattenfall oxyfuel pilot plant. [Copyright &y& Elsevier]

• Multiparameter optimization was proposed in modeling nitrogen oxides absorption. • Nitrogen mass balance based on measurements was achieved with a relative error±8 %. • Five pressure dependent critical parameters of the modeling were investigated. The removal of nitrogen oxides under a high pressure has been widely accepted as an effective method for the treatment of oxy-fuel combustion flue gas. The high pressure promotes the oxidation of NO to NO 2 , subsequently removed by water to form nitric acid. However, both the measurement and modeling of nitrogen oxides absorption shows uncertainties. To quantify the nitrogen mass balance, gas-phase NO/NO 2 and HNO 2 were measured online, whereas liquid-phase HNO 2 and HNO 3 were analyzed offline. Nitrogen mass balance was achieved with a relative error within ±8%. To improve modeling accuracy, a novel multiparameter optimization method was proposed. Mass transfer coefficients of NO 2 /NO, rate constant of NO oxidation, surface area, and volume of liquid were optimized. The absorption of NO 2 into a liquid was dominated by gas-phase mass transfer with the mass transfer coefficient decreasing from 1.77 × 10―4 mol m−2 s-1 Kpa-1 to 1.26 × 10―4 mol m−2 s-1 Kpa-1 with the increase of reactor pressure from 5 bar to 20 bar. The pressure dependent rate constant for NO oxidation agreed with gas-phase NO oxidation experimental measurement. It first decreased with the reactor pressure from 5 bar to 15 bar followed by an increase from 15 bar to 20 bar. The surface area of liquid decreased while the liquid volume increased with the rising reactor pressure indicating that liquid droplets were formed by gas bubbling and attached onto the inner surface of the reactor. This study resolved the uncertainties in measurement and modeling of the nitrogen oxides absorption process. [ABSTRACT FROM AUTHOR]