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Environ Eng Res > Volume 29(4); 2024 > Article
Jeong, Cho, and Lee: Effect of organic additives on NO2 removal in the simultaneous absorption of SO2 and NO2 into limestone slurry

Abstract

When SO2 and NO2 are simultaneously absorbed into limestone slurry, the SO32− (including HSO3) ions formed by the hydrolysis of SO2 enhance the absorption rate of NO2. However, NO2 absorption decreases due to the oxidation of SO32− in the presence of O2. To address this issue, simultaneous absorption was performed by adding organic additives: formic, acetic, propionic acid, monoethanolamine (MEA), diethanolamine (DEA), and triethanolamine (TEA). These limestone slurries were denoted FS, AS, PS, MS, DS, and TS, respectively. As the acidity of the organic acid increases, SO32− oxidation inhibition also increases. Accordingly, the denitrification rate of the slurries with added organic acid was in the order of PS < AS < FS. SO32− oxidation inhibition by the ethanolamine additives increased with the number of 2-hydroxyethyl. The denitrification rate within 50 min of reaction was in the order of MS < TS < DS, which is attributed to the basicity and SO32− oxidation inhibition by ethanolamine. The denitrification rate after 50 min of the reaction was in the order of MS < DS < TS, which is presumed to be the result of SO32− oxidation inhibition and degradation due to the CO2 absorption rate.

1. Introduction

SO2 and NOX emitted during the combustion of fossil fuels used in power plants are considered important substances in air pollution control, as they react with water vapor to form acid rain or generate particulate matter through photochemical reactions [1]. Processes such as wet flue gas desulfurization (WFGD), nonthermal plasma, membrane separation processes, and catalytic absorption have been proposed to simultaneous absorb SO2 and NOX [23]. Among these, the WFGD process is the most economical technique as it can be easily integrated with desulfurization and denitrification technologies, reducing the total system investment cost and usage area [34]. However, in the wet limestone FGD process, while SO2 is easily removed due to its high solubility, NOX is difficult to remove as more than 95% exists in an insoluble NO form [45]. Therefore, in WFGD, to effectively remove SO2 and NOx simultaneously, NO must be oxidized to a higher valency NOx (such as NO, NO2, N2O5, NO3) with higher solubility [67]. Ozone oxidation is often used owing to its strong oxidizing power and high selectivity for NO [89]. However, a disadvantage is that it requires excessive ozone injection or long residence time for oxidation to N2O5 and NO3 [68]. Therefore, focusing on the denitrification of NO2 for practical application in WFGD is essential. At the gas-liquid interface, NO2 possesses a large diffusion resistance which results in a low removal efficiency of 15–30% in scrubbing systems [5,9]. To enhance the NO2 absorption, researchers have used absorbents such as Na2SO3 and (NH4)2SO3, including SO32−, and confirmed that sulfite enhances the NO2 absorption [1011]. Since sulfite is produced from the SO2 absorption, the presence of SO2 can be effective in the absorption of NO2. Therefore, simultaneously injecting SO2 and NO2 into WFGD can achieve both denitrification and desulfurization, even without the addition of sulfite-containing additives. However, the NO2 absorption enhancement reaction by sulfite is inhibited due to the oxidation of SO32− to SO42− by oxygen, which is typically present in industrial gases [12]. To achieve high NO2 absorption, inhibiting sulfite oxidation using O2 is essential, various oxidation inhibitors have been proposed. When using thiosulfate, sulfite oxidation was inhibited and the absorption efficiency of NO2 improved [1314]. When Mn2+ was added to a sulfite absorbent, the sulfite radical oxidation chain reaction was blocked [8], and triethanolamine (TEA) acted as a radical scavenger to inhibit sulfite ions oxidation [15]. Researchers have confirmed that, in FGD, the capacity to inhibit sulfite ion oxidation increases with increasing organic acid additive acidity [16].
Previous studies [1011, 1314, 1722] applied novel absorbents or Ca-based slurries with additional additives for the simultaneous absorption of SO2 and NO2 and reported the effect of sulfur species on NO2 absorption (Table S1). However, these studies were performed under conditions different from those of the FGD process based on South Korea limestone slurry, and the NO2 absorption effect of organic additives was not reported. In this study, we investigated the oxidation inhibition effect of sulfite ions produced from the absorption of SO2 by using organic acid and ethanolamine additives for NO2 absorption enhancement in the limestone slurry in a bubbling reactor. Formic acid, acetic acid, and propionic acid were selected as organic acid additives while monoethanolamine, diethanolamine, and triethanolamine were ethanolamine additives. The simultaneous absorption efficiency of SO2 and NO2, slurry pH, and anion concentration was measured, and the denitrification enhancement effects of the additive types were compared.

2. Experiments

2.1 Materials

Limestone (97% CaCO3) obtained from Yeongheung Power Station (Incheon, Republic of Korea) was ground and sieved to prepare samples of 325 mesh or less for use in this study. The organic acids used included formic acid (AR, ≥ 85.0%), acetic acid (AR, ≥ 99.5%), and propionic acid (AR, ≥ 99.0%) purchased from Daejung Chemicals (Siheung, Republic of Korea), and the limestone slurries to which these organic acids were added were denoted FS, AS, and PS, respectively. The ethanolamines used included monoethanolamine (MEA; AR, ≥ 99.0%), diethanolamine (DEA; AR, ≥ 99.0%), and triethanolamine (TEA; AR, ≥ 99.0%) purchased from Samchun Chemicals (Seoul, Republic of Korea), and the limestone slurries to which ethanolamines were added were denoted MS, DS, and TS, respectively. Limestone slurry without adding these additives or distilled water was denoted NS and DW, respectively.

2.2 Experimental Procedure

A schematic diagram of the absorption experimental equipment is shown in Fig. S1 (as shown in supplementary data). The equipment consisted of a bubbling reactor, gas supplier, a slurry sample collection section, and analytical apparatus. The reactor had a double-jacket structure made of glass with a diameter of 13 cm, a height of 20 cm, and an internal volume of 1 L. The quantity of limestone slurry (1 wt%) within the reactor was 600 mL. When adding the additives to the limestone slurry, the respective additives were injected into the reactor at a concentration of 10 mmol/L and stirred for 20 minutes before starting the experiment. The SO2/N2 NO2/N2, O2/N2, and N2 gases used in the experiment were each flow-controlled using MFC (5850E; Brook-MFC, Hatfield, PA, USA). Gas was injected through two bubble sprayers which were inserted into the limestone slurry in the reactor. The total flow rate of the gas injected into the reactor was 3 L/min. The concentrations of SO2 and NO2 were set at 500 and 200 ppm, respectively, based on the concentrations typically generated by coal-fired power plants in South Korea [17]. The oxygen concentration of the actual exhaust gas was less than 6% [2324]. The O2 concentration varied at 0, 3, and 6%, and was fixed at 3% in all experiments, excluding those investigating variations in O2 concentration. The stirring speed was consistently maintained at 300 rpm to smoothly mix and diffuse the gas injected into the limestone slurry within the reactor.

2.3 Analysis

The gas discharged from the reactor was injected into an analysis device after removing moisture using a cooling trap. SO2 was measured using a Horiba gas analyzer (VS-3000; Horiba, Germany), and the NO2 was measured using an Ecom gas analyzer (MK 3000; Ecom, Germany). The absorption experiment ended after 180 min for all samples. The removal rates of SO2 and NO2 in the reaction gas were calculated as follows.
(1)
Removal rate (%)=Cin-CoutCin×100
where Cin refers to the gas concentration injected into the reactor, and Cout refers to the gas concentration discharged from the reactor.
During the reaction process, a predetermined amount of slurry was collected and vacuum-filtered to analyze four types of anions in the limestone slurry, SO32− (including HSO3), SO42−, NO2, and NO3. During the filtration process, the oxidation of HSO3 and SO32− to SO42− was prevented by conducting the process within a nitrogen box. The anion analysis of the filtrate was performed using an ion chromatograph (Eco IC; Metrohm, Switzerland). The pH of the limestone slurry was continuously measured in the reactor using a pH meter (pH 340i; WTW, Germany).

3. Results and Discussion

3.1 Simultaneous Absorption of SO2 and NO2 in Limestone Slurry

The individual absorptions of SO2 and NO2, as well as their simultaneous absorption in NS and DW, were conducted in a bubbling reactor. After the absorptions, the desulfurization and denitrification rates, and slurry pH changes were presented in Fig. 1. The main reactions during SO2 absorption in limestone slurry were the SO2 hydrolysis in Eq. (23), and the CaCO3 dissolution in Eq. (4), while for NO2 absorption, the NO2 hydrolysis in Eq. (57) was the main reaction [25]. When SO2 was absorbed into the NS sample, the desulfurization rate increased considerably compared with that following absorption into the DW sample owing to the pH buffering effect of the limestone; the desulfurization rate of reached 99.6% at the end of the 180 min absorption period (Fig. 1). When NO2 was absorbed into the NS sample, slurry pH increased considerably compared with that following absorption into the DW sample; however, the denitrification rate only increased by approximately 3%, reaching approximately 22%. When simultaneously absorbing SO2 and NO2 into the NS sample, the slurry pH was slightly higher, and the desulfurization rate was slightly lower at approximately 98% compared with that for the absorption of SO2 only. In contrast, while the slurry pH was lower compared with that of NO2 absorption alone, the denitrification rate increased by approximately 12%, reaching approximately 35%. Fig. 2 presents the concentration of SO32− (including HSO3), SO42−, NO2, and NO3, measured at 30 min intervals during the absorption of SO2 and the simultaneous absorption of SO2 and NO2 in the NS shown in Fig. 1. When only SO2 was absorbed in the NS sample, SO42− and SO32− (including HSO3) were detected. In contrast, when SO2 and NO2 were simultaneously absorbed, only SO42− was detected along with NO2 and NO3, whereas SO32− (including HSO3) was not detected. When SO2 and NO2 were simultaneously absorbed, the concentration of SO42− did not substantially differ from the combined concentrations of SO42− and SO32− (including HSO3) when only SO2 was absorbed. These results were attributed to the conversion of HSO32− and SO32−, which were the products of the hydrolysis of SO2 in limestone slurry, into SO42− ions by reacting with NO2(aq) as shown in Eq. (89) [26].
(2)
SO2+H2OSO2(aq)+H2OH2SO3
(3)
H2SO3HSO3-+H+SO32-+2H+
(4)
CaCO3+2H+Ca2++HCO3-+H+Ca2++CO2(aq)+H2O
(5)
2NO2+H2O2NO2(aq)+H2OHNO2+HNO3
(6)
HNO2NO2-+H+
(7)
HNO3NO3-+H+
(8)
2NO2(aq)+HSO3-+H2O2NO2-+SO42-+3H+
(9)
2NO2(aq)+SO32-+H2O2NO2-+SO42-+2H+
To examine the impact of O2 concentration on the desulfurization and denitrification rates when SO2 and NO2 are simultaneously absorbed in the NS samples, the changes in the desulfurization and denitrification rates, and slurry pH with respect to O2 concentration were presented in Fig. 3. As the O2 concentration increased, slurry pH increased, however the desulfurization rate remained consistent between 96.3–97.9% regardless of the O2 concentration at the end of the experiment. This result was attributed to the high concentration of limestone in the slurry compared with the SO2 input concentration and the limitation of the absorption time to 180 min for the end of the experiment. In contrast, the denitrification rate decreased considerably with increasing O2 concentration. In addition, at the end of the experiment, the denitrification rates were approximately 58, 33, and 26% for samples with O2 concentrations of 0, 3, and 6%, respectively. The concentrations of the four types of anions comprising SO32− (including HSO3), SO42, NO2, and NO3 were measured at 30 min intervals in experiment of Fig. 3, and the SO42− and NO3 fractions according to O2 concentration are presented in Fig. 4. The SO42− fraction in the 0% O2 sample was approximately 0.5–0.7. However, the SO42− fraction in the 3 and 6% O2 samples was 1. The NO3 fraction in the slurry increased as the O2 concentration increased. The ion chromatography analysis results suggest that the increase in O2 concentration led to an increase in the oxidation of SO32− (including HSO3) and NO2 by O2, as shown in Eq. (1012) [2527]. Therefore, the increased HSO3 and SO32− oxidation in the slurry resulted in a decrease in the reactions of Eq. (89), leading to a decrease in denitrification and an increase in slurry pH, as shown in Fig. 3.
(10)
HSO3-+1/2O2(aq)SO42-+H+
(11)
SO32-+1/2         O2(aq)SO42-
(12)
NO2-+1/2O2(aq)NO3-

3.2 Simultaneous Absorption of SO2 and NO2 in Limestone Slurry with Added Organic Acid

Fig. 5 presents the desulfurization and denitrification rates, denitrification amount, and slurry pH when SO2 and NO2 are simultaneously absorbed in the limestone slurry with added formic, acetic, and propionic (FS, AS, and PS, respectively). In addition, these were compared with the NS sample. As shown in Fig. 5A, the desulfurization rates of the slurry samples were similar, ranging from 96.3 to 97.9%. The denitrification rate of each sample increased in the order of NS (33.5%) < PS (35.9%) < AS (38.7%) < FS (42.9%) by the end of the experiment. As shown in Fig. 5B, the denitrification amounts of each sample, increased in the order of NS (1.50 mmol) ≈ FS (1.51 mmol) < AS (1.59 mmol) < PS (1.85 mmol). Comparison with the NS, the denitrification amount increased by 6% for the AS and 23% for the FS. As shown in Fig. 5C, the slurry pH of each sample was in the order of FS < AS < PS < NS. In the simultaneous absorption of SO2 and NO2 in limestone slurry with organic acids, an additional reaction was the pH buffering of organic acids as shown in Eq. (1315) [26,28]. In these equations, HA represents the organic acids. Since HSO3 is produced by the reaction shown in Eq. (14), the reactions shown in Eq. (89) could increase. In Fig. 5C, the slurry pH of the NS sample shows a trend of rapidly decreasing at the start of absorption and then gradually slowing down. In contrast, the slurry pH of the samples with organic acids displayed a gradual decrease from the start of absorption due to the organic acids being mixed in the limestone slurry before the absorption experiment. According to our previous research [16], in the absorption of SO2 in limestone slurry, the more acidic the added organic acid, the more likely it is to inhibit the oxidation of SO32− (including HSO3). As shown in Table S2, the slurry added formic acid, with low pKa, had a high SO32− (including HSO3) oxidation inhibitory capacity. In contrast, the slurry with added acetic acid and propionic acid, both with high pKa, had a low SO32− (including HSO3) oxidation inhibitory capacity, similar to the slurry without additives. Thus, as the acidity of the organic acid added to the limestone slurry increased, the denitrification amount of the sample increased, and the slurry pH decreased.
(13)
HA(aq)A-+H+
(14)
SO2(aq)+A-+H2OHSO3-+HA(aq)
(15)
NO2(aq)+A-+H2OH++NO3-+HA(aq)
Fig. 6 presents the concentrations of four types of anions, SO32− (including HSO3), SO42−, NO2, and NO3 and the SO42− and NO3 fractions measured at 30 min intervals for the slurry samples shown in Fig. 5. As shown in Fig. 6A, SO32− (including HSO3) was not detected in all FS, AS, and PS samples, but only SO42− was detected, whereas NO2 and NO3 were detected in all three samples. The X-ray diffraction analysis confirmed the formation of gypsum in all samples. In Fig. 6B, the fraction of SO42− in the NS, FS, AS, and PS samples, was 1, and the fraction of NO3 was in the order of NS < FS < AS < PS. These results imply an increase in the oxidation of NO2 to NO3 in the same order. It is consistent with PS < AS < FS in the order of the inhibitory capacity for the SO32− (including HSO3) oxidation of each sample that contributed to the denitrification amounts of the samples shown in Fig. 5B. However, the reason for the higher NO3 fraction in the FS sample, which had the highest oxidation inhibitory capacity, than in the NS sample could be explained by the reaction shown in Eq. (15), wherein the NO3 fraction increased, aside from the reactions shown in Eq. (89). Therefore, combining the denitrification amounts of NS ≈ PS < AS < FS in Fig. 5B and the NO3 fraction order of NS < FS < AS < PS in Fig. 6B, it was presumed that the ratio of the Eq. (15) reaction in the NO2 absorption reactions of Eq. (89), and (15) also gradually increased as the acidity of the organic acid and the denitrification of the samples increased.

3.3 Simultaneous Absorption of SO2 and NO2 in Limestone Slurry with Added Ethanolamine

Fig. 7 presents the desulfurization and denitrification rates, denitrification amount, and slurry pH when SO2 and NO2 were simultaneously absorbed in limestone slurry with added MEA, DEA, and TEA (MS, DS, and TS, respectively). As shown in Fig. 7A, the desulfurization rates of the samples were similar, ranging from 97.2% to 98.2%. The denitrification rates of the samples increased in the order of MS (30.7%) < DS (31.1%) < NS (33.5%) < TS (40.1%) by the end of the experiment. In contrast, the denitrification rates showed a different order of NS < MS < TS < DS until approximately 50 min into the absorption reaction. As shown in Fig. 7B1, the denitrification amounts of the samples were in the order of NS (1.50 mmol) < MS (1.53 mmol) < DS (1.86 mmol) < TS (1.94 mmol) by the end of the experiment. Compared with the NS, the DS and TS increased by 24% and 29%, respectively. As shown in Fig. 7C, the slurry pH of the samples, displayed an order of NS < TS < DS < MS within 50 min of absorption, subsequently exhibiting an order of TS < NS < DS ≈ MS afterwards. The reaction between SO2 and ethanolamine was an acid-base reaction due to the basicity of ethanolamine, as shown in Eq. (1618) [29]. Since HSO3 and SO32− were produced by the reactions shown in Eq. (1617), the reactions shown in Eq. (89) could increase. As shown in Fig. 7C, the slurry pH of each sample followed the order MS < TS < DS within 50 min of absorption, corresponding to the order of ethanolamine basicity as shown in Table S2. Nevertheless, the order of the denitrification rate of the samples differed, being in the order of MS < TS < DS (Fig. 7A).
(16)
SO2(aq)+EA+H2OEAH++HSO3-
(17)
SO2(aq)+2EA+H2O2EAH++SO3-
(18)
CaCO3+EAH+Ca2++HCO3-+EA(aq)
(19)
·SO3++CH3CH2OHCH3CH2OSO2-+·OH
(20)
·SO3-+·OHSO42-+H+
(21)
·SO3-+NH2CH2CH2OHNH2CH2CH2OSO2-+·OH
Fig. 8 presents the concentrations of the four types of anions, SO32− (including HSO3), SO42−, NO2, and NO3 and the SO42− and NO3 fractions measured at 30 min intervals for the slurry samples shown in Fig. 7. As shown in Fig. 8A, the SO32− (including HSO3) concentration was the highest in the order of MS < DS < TS during the absorption experiment. This indicates that the inhibitory capacity for SO32− (including HSO3) oxidation was higher in the same order of samples. The X-ray diffraction analysis confirmed the formation of gypsum in all samples. In Fig. 8B, the SO42− and NO3 fractions were lower in the order of NS > MS > DS > TS. Wang et al. [30] reported that in Wet FGD, the calcium sulfite oxidation, in the presence of ethanol in limestone slurry, is controlled by the reactions shown in Eq. (1920). In these equations, ·SO3 acts as a radical, with HSO3 becoming an intermediate in the oxidation process to SO42−. Eq. (21) is the application of MEA with a 2-hydroxyethyl group to Eq. (19). If the reaction shown in Eq. (21) is assumed to be reversible, the inhibitory capacity of the HSO3 oxidation of ethanolamines depends on the number of 2-hydroxyethyl groups in the ethanolamine, and it could be inferred that it increases in the order of MEA < DEA < TEA. Therefore, the results in Fig. 7A, which show the order of denitrification rate by sample as MS < TS < DS, can be attributed to the complex effects of the basicity differences in ethanolamine and the inhibitory capacity for the SO32− (including HSO3) oxidation of ethanolamines.
(22)
RNH2+HNO2RHN-NO+H2O
(23)
R2NH+HNO2R2N-NO+H2O
(24)
R3N+HNO2R2N(CH2CH2ONO)+H2O
(25)
R3N+HNO3R2N(CH2CH2ONO2)+H2O
(26)
R3N+NO2(aq)+2OH-R3NO-+NO2-+H2O
Fig. 7B2 presents the denitrification amount of each sample from 60 to 180 min, excluding the denitrification amount under 60 min. The denitrification amount of slurry with added ethanolamine presented a linear increase over time, similar to that of slurry without the addition of ethanolamine. This indicates a considerable reduction in the acid-base reaction due to the basicity of the ethanolamine. As shown in Fig. 7B2, the denitrification amounts of the samples were in the order of MS < NS ≈ DS < TS. It could be presumed that for the MS and DS samples, the added ethanolamines were consumed, and the inhibitory capacity for SO32− (including HSO3) oxidation had mostly disappeared. Choi et al. [31] reported that among the amines used in CO2 absorption liquids, primary and secondary amines have a fast CO2 absorption rate but a low absorption amount, while tertiary amines have a slow absorption rate but a high absorption amount. Also, some researchers have reported that the CO2 absorption capacity of ethanolamine is in the order of MEA > DEA > TEA [3233]. In Fig. 7A, the denitrification rate of the slurry with added ethanolamine decreased after approximately 10 min of absorption. The denitrification rates of the MS with added primary amine, MEA, and the DS with added secondary amine, DEA, were lower than that of the NS from approximately 50 and 100 min of absorption, respectively. In contrast, the TS with added tertiary amine, TEA, maintained a higher denitrification rate than that of the NS until the end of the experiment at 180 min. These results are attributed to the decrease in the reactions shown in Eq. (1617) due to the increased degradation of MEA and DEA in the slurry, which rapidly reacted with the CO2(aq) generated from the reactions shown in Eq. (4) and (18). As shown in Fig. 8A, the total concentrations of NO2 and NO3 in the TS and DS samples, which had high denitrification amounts, were lower than those of NO2 and NO3 in the FS sample, which had a low denitrification amount as shown in Fig. 6A. The total concentrations of NO2 and NO3 in the MS sample were also lower than those of the NS and PS samples, which had a similar denitrification amount. The reaction of ethanolamine and the hydrolysis product of NO2 are represented in Eq. (2226), where R represents the 2-hydroxyethyl group. In the case of MEA and DEA, n-nitrosoethanolamine and n-nitrosodiethanolamine are generated in the reactions shown in Eq. (22) and (23) respectively, through which MEA and DEA are degraded [34]. For TEA, triethanolamine nitrite and nitrate are formed as shown in Eq. (2425), and degradation of TEA can also occur through Eq. (26) [15,35]. Although nitrosamine can be formed in the reaction between TEA and NO2, this reportedly occurs when TEA is not sufficiently hydrated [36]. Therefore, the lower total concentrations of NO2 and NO3 in the slurries with added ethanolamines than those in slurries with added organic acids in Fig. 8A are attributed to ethanolamine degradation during the absorption process of NO2. Moreover, the total concentrations of NO2 and NO3 in the DS and TS samples appear similar. It is presumed that if the ethanolamine degradation by NO2 does not greatly differ, ethanolamine is degraded more in the DS with added DEA, which has a faster CO2 absorption rate than that of TEA.

4. Conclusions

When SO2 and NO2 were simultaneously absorbed in limestone slurry, the SO32− (including HSO3) generated through the hydrolysis of SO2 reacted with NO2, enhancing the NO2 absorption rate. However, as the concentration of O2 increased during the simultaneous absorption, the desulfurization rate remained almost constant while the denitrification rate decreased, in addition the SO42− and NO3 fractions in the slurry increased. This indicated that the enhancement of NO2 absorption by SO32− (including HSO3) was inhibited due to the oxidation of SO32−. Generally, since exhaust gas contains O2, the absorption rate of NO2 inevitably decreases. Therefore, to reduce the decrease in NO2 absorption, three types of organic acids and three types of ethanolamines were added to the limestone slurry for simultaneous absorption. In the limestone slurries with added organic acids, the denitrification rate was in the order of NS ≈ PS < AS < FS, which corresponded to the acidity of the organic acids. These results indicate that the stronger the acidity of the organic acid, the inhibition of SO32− oxidation is improved, which subsequently enhances the NO2 absorption reaction. In the limestone slurries with added ethanolamines, the denitrification rates varied with the reaction time. The reaction of SO2 and ethanolamine is an acid-base reaction, leading to the generation of SO32−, which subsequently improves the NO2 absorption rate. However, the denitrification rate within 50 min of reaction was in the order of MS < TS < DS, which varied from the order ethanolamine basicity. Here, the SO42− and NO3 fraction in the slurry was lowest in the sample order of NS > MS > DS > TS. These results suggest that the SO32− (including HSO3) inhibitory capacity of ethanolamines depends on the number of 2-hydroxyethyl groups in the ethanolamine and increases in the order of MEA < DEA < TEA. Thus, the denitrification rate within 50 min of the reaction could be attributed to the complex effects of the basicity differences in ethanolamine and the SO32− oxidation inhibitory capacity of ethanolamines. In contrast, at the end of the experiment, the denitrification rate was in the order of MS < DS < NS < TS owing to MES and DES reacting quickly with the CO2 and being consumed. Therefore, it was presumed that most of the capacity to inhibit SO32− oxidation disappeared. Meanwhile, the total NO2 and NO3 concentrations in the slurries with added ethanolamines were lower than those with added organic acids, indicating the degradation of ethanolamines by NO2.

Acknowledgements

This work was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korean government (MOTLE) (20213400000020, Development of Simultaneous Reduction technology of SOx and NOx in wet flue gas desulfurization system).

Notes

Conflict of Interest Statement

The authors declare no conflict of interest.

Author Contribution

J. E. J. (Ph D student) co-wrote and revised the manuscript. I. A. C. (Master) performed the experiments and collected related literature. C.Y. L. (Professor) supervised the research and co-wrote the manuscript. All authors read and approved the manuscript.

Supplementary Information

References

1. Xiang J, Zhang Z, Tian L, et al. Enhanced wet flue gas desulfurization properties by additives of organic acids, organic salts, inorganic salts, and organic amines. Energy Fuels. 2020;34:14429–14438. https://doi.org/10.1021/acs.energyfuels.0c02658
crossref

2. Wang Z, Zhang X, Zhou Z, Chen WY, Zhou J, Cen K. Effect of additive agents on the simultaneous absorption of NO2 and SO2 in the calcium sulfite slurry. Energy Fuels. 2012;26:5583–5589. https://doi.org/10.1021/ef3007504
crossref

3. Shi F, Li K, Li J, et al. Simultaneous wet absorption of SO2 and NOx with mixed Na2SO3 and (NH4)2SO3: Effects of mass concentration ratio and pH. Chem. Eng. J. 2021;421:129945. https://doi.org/10.1016/j.cej.2021.129945
crossref

4. Li Y, Yang C, Yao M, et al. Research and engineering practice of catalytic absorption of NO2 by tetrabutylammonium hydrogen sulfate for simultaneous removal of SO2/NOx. Fuel. 2021;283:118858. https://doi.org/10.1016/j.fuel.2020.118858
crossref

5. Yang L, Cai Y, Lu L. Experimental study on simultaneous desulfurization and denitrification by DBD combined with wet scrubbing. Appl. Sci. 2021;11:8092. https://doi.org/10.3390/app11188592
crossref

6. Lian Z, Liu S, Li G, Zhang S, Ma W, Zhong Q. Using polyethylene glycol to facilitate the absorption of NO2 in sulfite solutions: Kinetics and mechanism. J. Hazard. Mater. 2022;422:126825. https://doi.org/10.1016/j.jhazmat.2021.126825
crossref pmid

7. Li Y, Che D, Zhao H, et al. Tributyl phosphate additive enhancing catalytic absorption of NO2 for simultaneous removal of SO2/NOx in wet desulfurization system. J. Energy Inst. 2020;93:474–481. https://doi.org/10.1016/j.joei.2019.07.004
crossref

8. Liu S, Lian Z, Zhang S, Zhang M, Zhong Q. Using Mn2+ to inhibit the adverse oxidation of sulfite solutions during the NO2 absorption: Mechanism and kinetic model. Fuel Process Technol. 2022;238:107529. https://doi.org/10.1016/j.fuproc.2022.107529
crossref

9. Mok YS. Absorption–reduction technique assisted by ozone injection and sodium sulfide for NOx removal from exhaust gas. Chem. Eng. J. 2006;118:63–67. https://doi.org/10.1016/j.cej.2006.01.011
crossref

10. Guo RT, Pan WG, Zhang XB, Ren JX, Jin Q, Xu HJ. Absorption of NO2 into aqueous (NH4)2SO3 solution in a stirred tank reactor. Environ. Prog. Sustain Energy. 2013;32:465–469. https://doi.org/10.1002/ep.11645
crossref

11. Hao R, Yang S, Zhao Y, Zhang Y, Yuan B, Mao X. Follow-up research of ultraviolet catalyzing vaporized H2O2 for simultaneous removal of SO2 and NO: Absorption of NO2 and NO by Na-based WFGD byproduct (Na2SO3). Fuel Process. Technol. 2017;160:64–69. https://doi.org/10.1016/j.fuproc.2017.02.021
crossref

12. Shao J, Ma Q, Wang Z, et al. A superior liquid phase catalyst for enhanced absorption of NO2 together with SO2 after low temperature ozone oxidation for flue gas treatment. Fuel. 2019;247:1–9. https://doi.org/10.1016/j.fuel.2019.02.120
crossref

13. Schmid D, Hupa M, Paavola M, Vuorinen I, Lehikoinen A, Karlström O. Role of thiosulfate in NO2 absorption in aqueous sulfite solutions. Ind. Eng. Chem. Res. 2023;62:105–110. https://doi.org/10.1021/acs.iecr.2c04299
crossref

14. Schmid D, Karlström O, Kuvaja V, Vuorinen I, Paavola M, Hupa M. Role of sulfite oxidation in NO2 absorption in a pH-Neutral scrubber solution. Energy Fuels. 2022;36:2666–2672. https://doi.org/10.1021/acs.energyfuels.1c03914
crossref

15. Wu Q, Sun C, Wang H, Wang T, Wang Y, Wu Z. The role and mechanism of triethanolamine in simultaneous absorption of NOx and SO2 by magnesia slurry combined with ozone gas-phase oxidation. Chem. Eng. J. 2018;341:157–163. https://doi.org/10.1016/j.cej.2018.01.150
crossref

16. Jeong JE, Cho IA, Lee CY. Desulfurization characteristics of limestone slurry with added organic acid. Fuel. 2023;336:126859. https://doi.org/10.1016/j.fuel.2022.126859
crossref

17. Kang MS, Hwang J. Effect of SO2 concentration on NOx removal efficiency in NaOH-based wet scrubbing. J. Korean Soc. Atmos Environ. 2018;34:659–667. https://doi.org/10.5572/KOSAE.2018.34.5.659
crossref

18. Hu G, Sun Z, Gao H. Novel process of simultaneous removal of SO2 and NO2 by sodium humate solution. Environ. Sci Technol. 2010;44:6712–6717. https://doi.org/10.1021/es101892r
crossref pmid

19. Chen G, Gao J, Gao J, et al. Simultaneous removal of SO2 and NOx by calcium hydroxide at low temperature: effect of SO2 absorption on NO2 removal. Ind. Eng. Chem. Res. 2010;49:12140–12147. https://doi.org/10.1021/ie101594x
crossref

20. Wang Z, Zhang X, Zhou Z, Chen WY, Zhou J, Cen K. Effect of additive agents on the simultaneous absorption of NO2 and SO2 in the calcium sulfite slurry. Energy Fuels. 2012;26:5583–5589. https://doi.org/10.1021/ef3007504
crossref

21. Tang N, Liu Y, Wang H, Xiao L, Wu Z. Enhanced absorption process of NO2 in CaSO3 slurry by the addition of MgSO4 . Chem. Eng. J. 2010;160:145–149. https://doi.org/10.1016/j.cej.2010.03.022
crossref

22. Gao J, Chen G, Fu X, Yin Y, Wu S, Qin Y. Enhancement mechanism of SO2 removal with calcium hydroxide in the presence of NO2 . Korean J. Chem. Eng. 2012;29:263–269. https://doi.org/10.1007/s11814-011-0157-7
crossref

23. Shin D, Woo CG, Hong KJ, et al. Development of a new dilution system for continuous measurement of particle concentration in the exhaust from a coal-fired power plant. Fuel. 2019;257:116045. https://doi.org/10.1016/j.fuel.2019.116045
crossref

24. Pudasainee D, Kim JH, Seo YC. Mercury emission trend influenced by stringent air pollutants regulation for coal-fired power plants in Korea. Atoms. Environ. 2009;43:6254–6259. https://doi.org/10.1016/j.atmosenv.2009.06.007
crossref

25. Córdoba P. Status of flue gas desulphurisation (FGD) systems from coal-fired power plants: Overview of the physic-chemical control processes of wet limestone FGDs. Fuel. 2015;144:274–286. https://doi.org/10.1016/j.fuel.2014.12.065
crossref

26. Zheng C, Xu C, Zhang Y, et al. Nitrogen oxide absorption and nitrite/nitrate formation in limestone slurry for WFGD system. Appl. Energy. 2014;129:187–194. https://doi.org/10.1016/j.apenergy.2014.05.006
crossref

27. Ma Y, Yuan D, Zhang X, Qu Z, Huang W. Inhibiting oxidation and enhancing absorption characteristics of sodium sulfite for SO2 removal from the non-ferrous smelting flue gas. Environ Eng. Res. 2021;26:200043. https://doi.org/10.4491/eer.2020.043
crossref

28. Jeong JE, Lee CY. The simultaneous removal of sulfur dioxide and nitrogen dioxide by the limestone slurry with addition of organic acid additives. Korean J. Chem. Eng. 2021;38:2064–2071. https://doi.org/10.1007/s11814-021-0850-0
crossref

29. Yang J, Yu X, An L, Tu ST, Yan J. CO2 capture with the absorbent of a mixed ionic liquid and amine solution considering the effects of SO2 and O2 . Appl. Energy. 2017;194:9–18. https://doi.org/10.1016/j.apenergy.2017.02.071
crossref

30. Wang LD, Ma YL, Hao JM, Zhao Y. Mechanism and kinetics of sulfite oxidation in the presence of ethanol. Ind. Eng. Chem Res. 2009;48:4307–4311. https://doi.org/10.1021/ie801731h
crossref

31. Choi SH, You JK, Park KT, et al. Carbon dioxide absorption characteristics according to amine mixtures with different order. J. Korea Acad. Ind. Coop. Soc. 2013;14:4635–4642. http://dx.doi.org/10.5762/KAIS.2013.14.9.4635
crossref

32. Rinprasertmeechai S, Chavadej S, Rangsunvigit P, Kulprathipanja S. Carbon dioxide removal from flue gas using amine-based hybrid solvent absorption. Int. J. Chem. Biol. Eng. 2012;6:296–300. https://doi.org/10.5281/zenodo.1332827
crossref

33. Choi JH, OHSG , Kim YE, Yoon YI, Nam SC. Carbon dioxide absorption characteristics of aqueous alkanolamine using nuclear magnetic resonance spectroscopy. Environ. Eng. Sci. 2012;29:328–334. https://doi.org/10.1089/ees.2010.0484
crossref

34. Fostås B, Gangstad A, Nenseter B, Pedersen S, Sjøvoll M, Sørensen AL. Effects of NOx in the flue gas degradation of MEA. Energy Procedia. 2011;4:1566–1573. https://doi.org/10.1016/j.egypro.2011.02.026
crossref

35. Aoyama T, Yashiro T. Analytical study of low-concentration gases : IV. Investigation of the reaction by trapping nitrogen dioxide in air using the triethanolamine method. J. Chromatogr A. 1983;265:69–78. https://doi.org/10.1016/S0021-9673(01)96699-3
crossref

36. Heal MR, Laxen DPH, Marner BB. Biases in the measurement of ambient nitrogen dioxide (NO2) by palmes passive diffusion tube: A review of current understanding. Atmosphere. 2019;10:357. https://doi.org/10.3390/atmos10070357
crossref

Fig. 1
Comparison of SO2 and NO2 removal rates and slurry pH in limestone slurry (NS) or distilled water (DW). Inlet concentration of O2 = 3%.
/upload/thumbnails/eer-2023-513f1.gif
Fig. 2
Ion concentration of sulfur and nitrogen species in limestone slurry. Inlet concentration of O2 = 3%.
/upload/thumbnails/eer-2023-513f2.gif
Fig. 3
Effect of inlet oxygen concentration on removal rate of SO2 and NO2 (A) and slurry pH (B) of limestone slurry.
/upload/thumbnails/eer-2023-513f3.gif
Fig. 4
Effect of inlet oxygen concentration on the fraction of sulfate and nitrate ions in limestone slurry.
/upload/thumbnails/eer-2023-513f4.gif
Fig. 5
Comparison of SO2 and NO2 removal rates (A), absorption amount of NO2 (B), and slurry pH (C) of limestone slurries with the addition and non-addition of organic acids. Inlet concentration of O2 = 3%.
/upload/thumbnails/eer-2023-513f5.gif
Fig. 6
Ion concentration of sulfur species and nitrogen species of limestone slurries with the addition of organic acids (A) and the fraction of sulfate ions and nitrate ions (B). Inlet concentration of O2 = 3%.
/upload/thumbnails/eer-2023-513f6.gif
Fig. 7
Comparison of SO2 and NO2 removal rates (A), absorption amount of NO2 (B), and the pH (C) of limestone slurries with and without the addition of ethanolamine. Inlet concentration of O2 = 3%.
/upload/thumbnails/eer-2023-513f7.gif
Fig. 8
Ion concentration of sulfur and nitrogen species of limestone slurries with the addition of ethanolamine (A) and the fraction of sulfate and nitrate ions (B). Inlet concentration of O2 = 3%.
/upload/thumbnails/eer-2023-513f8.gif
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