Plasma Chemistry and Plasma Processing

Supplementary material ---A mathematical modeling study for the flue gas removal of SO2 and NOxusing high energy electron beams

Plasma Chemistry and Plasma Processing

Valentina Gogulancea*, Vasile Lavric*

Chemical and Biochemical Engineering Department, University Politehnica of Bucharest, Polizu 1- 7, 011061, Bucharest Romania

,

The paper presents the modeling of the irradiation chamber from an electron beam flue gas treatment facility. A simplified schematics of such a facility is presented (Figure S1): after the pretreatment that removes particulate matter and dust, the flue gas from the boiler enters a cooling tower, in which water is sprayed in order to reduce the flue gas temperature and ensure suitable humidity for operation. Ammonia is added to the gas, before entering the irradiation facility, aiding the formation of ammonia sulfate and nitrate. Exiting the reactor, the purified flue gas is passed through an electrostatic precipitator that collects the solid by-products (high-grade fertilizers) and sent to the stack.

Figure S1 Simplified schematics of an electron beam treatment facility

The chemical reactions considered in the kinetic model for both gas and liquid phases are presented in the following tables: for the gas phase, the reaction rates are given in

cm3/(molecule∙s) for second order reactions and cm6/(molecule∙s) for third order reactions (which occur via third body mechanism). For the liquid phase, the reaction rate and equilibrium constants have the units of L/(mol∙s) and have been transformed to cm3/(molecule∙s) to ensure the sameunits are used in the system of differential algebraic equations assembled.

In the case of reactions (83,84,88 – 90), i.e. the reaction pathway for the thermo-chemical removal of SO2,the reaction rate constants were determined via regression analysis.The relationshipsgiven in Bulearca [1] and Gerasimov et al. [2] were found to over-estimate the removal efficiency of SO2 in the case of no irradiation. The rate constants were determined using the Genetic Algorithm built-in function,ga,in Matlab@ - considering a reaction system consisting only of these five chemical reactions and comparing its outcome against experimental removal efficiencies obtained in the case of zero irradiation [3]. We have not included the reverse reactions in the model as they occur with a significantly lower rate.

For the molecular reactions between ammonia and the nitrogen oxides we have only considered the forward reactions (77 and 78) as the relative humidity in the irradiation chamber is higher than the critical (deliquescence) relative humidity for both ammonium salts and thus, they are absorbed almost completely in the liquid phase.

For the reaction number 76, although the product listed in the reference is HOONO we have replaced it with its more stable isomer HNO3. As the isomerization reaction rate in gas phase is several orders of magnitude higher than the rate of reaction number 76, previous modeling efforts have shown that the amount of HOONO formed is negligible and that the HOONO can be replaced with HNO3 without significantly affecting the performance of the model [4].

1. Gas phase reactions and rate constants (here, [W] stands for the concentration number of species W and M represents the total number concentration for the gas phase)

Reaction # / Chemical Reaction / Reaction rate constant / Reference
1 / N2+ + NO → NO++ N2 / 5•10-10 / [5]
2 / N2+ + e- → 2N / 1•10-7 / [5]
3 / NO+ + e- →N + O / 4•10-7 / [5]
4 / NO+ + e- →NO / 1•10-12 / [5]
5 / NO2 + e- →NO2- / 8•10-28•[N2] / [5]
6 / NO+ + NO2- →NO + NO2 / 3•10-7 / [5]
7 / N + NO →N2 + O / 2.2•10-11 / [5]
8 / N + NO2 →2NO / 25.9•10-12 / [5]
9 / N + NO2 →N2O + O / 7.7•10-12 / [5]
10 / N + NO2 →N2 + O2 / 1.8•10-12 / [5]
11 / N + NO2 →N2 + 2O / 2.3•10-12 / [5]
12 / N + N2O →NO + N2 / 1•10-12 / [5]
13 / N + N →N2 / 3.8•10-33[N2] / [5]
14 / O + NO →NO2 / 5.4•10-32[N2] / [5]
15 / O + NO2 →NO + O2 / 7.7•10-12 / [5]
16 / O + O →O2 / 1.6•10-33[N2] / [5]
17 / N4S + NO → N2 + O3+ / 2.2∙ •10-11 / [5]
18 / N4S + NO2 → 2NO / 5.9•10-12 / [5]
19 / N4S + NO2 → N2O + O / 7.7•10-12 / [5]
20 / N4S + NO2 → N2 + O2 / 1.8•10-12 / [5]
21 / N4S + NO2 → N2 + 2O / 2.3•10-12 / [5]
22 / N4S + O2 → NO + O / 1•10-16 / [5]
23 / N4S + O3 → NO + O2 / 3.7•10-13 / [5]
24 / N4S + N4S + N2 →2N2 / 5•10-33 / [5]
25 / N2D +N2O → NO +N2 / 1.6•10-12 / [5]
26 / N2D + NO → N4S + NO / 5.9•10-11 / [5]
27 / N2D + O2 → NO + O / 5.2•10-12 / [5]
28 / O + NO →NO2 / 3.9•10-33exp(975/T)[N2] / [5]
29 / O + NO2 →NO + O2 / 3.2•10-11exp(-535/T) / [5]
30 / O + NO2 →NO3 / 1.5•10-31[N2] / [5]
31 / O + O2 → O3 / 1.1•10-34exp(510/T)[N2] / [5]
32 / O + O3 → 2O2 / 1.5•10-11exp(-2240/T) / [5]
33 / O + O → O2 / 1.6•10-33[N2] / [5]
34 / NO + O3 → NO2 + O2 / 9.5•10-13exp(-1300/T) / [5]
35 / NO + NO3 →2NO2 / 8.7•10-12 / [5]
36 / NO2 + NO3 →NO + NO2 + O2 / 4•10-16 / [5]
37 / NO2 + NO3 →N2O5 / 6.5•10-32[N2] / [5]
38 / N2O5 → NO2 + NO3 / 5•10-21[N2] / [5]
39 / CO2+ + O2 → O2+ + CO2 / 6.5•10-9T-0.78 / [5]
40 / CO2+ + H2O→H2O+ + CO2 / 1.7•10-9 / [5]
41 / O+ + CO2 →O2+ + CO / 1•10-9 / [5]
42 / CO+ + O2 → O2+ +CO / 1•10-10 / [5]
43 / CO+ + H2O → H2O+ + CO / 1.3•10-10 / [5]
44 / CO+ + CO2 →CO2+ + CO / 8.5•10-10 / [5]
45 / CO2+ + O2- →CO2 + O2 / 4•10-7(300/T)0.5+3•10-25(300/T)2.5•M / [5]
46 / CO2+ + e →CO + O / 4•10-7(300/T)0.5 / [5]
47 / CO2+ + e- →CO2 / 6•10-27(300/T)0.5•M / [5]
48 / CO+ + O2- →CO2 + O / 4•10-7(300/T)0.5+3•10-25(300/T)2.5∙M / [5]
49 / CO+ + e- →CO / 6•10-27(300/T)2.5•M / [5]
50 / N2+ + CO2 →N2 + CO2+ / 8.3•10-10 / [5]
51 / N+ + CO2 →N + CO2+ / 1.3•10-9 / [5]
52 / CO + OH →CO2 + H / 1.5•10-13 / [5]
53 / N + CO2 →NO + CO / 4•10-13 / [5]
54 / NO3 + CO →NO2 + CO2 / 1.6•10-11exp(-3250/T) / [5]
55 / SO2 + OH →HSO3 / 5•10-31(300/T)3.3•M / [5]
56 / SO2 + HO2 →SO3 + OH / 1.49•10-15 / [5]
57 / SO2 + O →SO3 / 6.64•10-14 / [5]
58 / SO3 + H2O →H2SO4 / 9.91•10-13 / [5]
59 / HSO3 + OH →H2SO4 / 8.3•10-12 / [5]
60 / HSO3 + OH →SO3 + H2O / 8.3•10-12 / [5]
61 / HSO3 + NO2 →HOSO2ONO / 8.3•10-13 / [5]
62 / HSO3 + O2 →HOSO2O2 / 6.64•10-14 / [5]
63 / HSO3 + HO2 →H2SO5 / 8.3•10-12 / [5]
64 / HSO3 + HSO3 →H2S2O6 / 5•10-13 / [5]
65 / HOSO2O2 + NO →HSO4 + NO2 / 8.3•10-12 / [5]
66 / HOSO2O2 + NO →HOSO2ONO2 / 8.3•10-14 / [5]
67 / HOSO2O2 + SO2 →HSO4 + SO3 / 1.66•10-12 / [5]
68 / HSO4 + NO →HOSO2ONO / 1.66•10-12 / [5]
69 / HOSO2O2 + N →HSO4 + NO / 5.81•10-12 / [5]
70 / SO3 + O →SO2 + O2 / 7•10-13 / [5]
71 / OH + O2 →HO2 + O / 2.95•10-11 / [5]
72 / NH +NO→N2+H / 4.75•10-11 / [6]
73 / NH2 +NO→N2O+H2 / 2.15•10-11 / [6]
74 / NO + OH →HNO2 / 7.45•10-31* (T/300)-2.4•M / [6]
75 / NO2 + OH →HNO3 / 2.65•10-30∙ (T/300)-2.7 •M / [6]
76 / NO2 + HO2→HNO3 + O / 1.85•10-31∙(T/300)-3.2 •M / [6]
77 / HNO2 + NH3→NH4NO2 / 1.05•10-8 / [5]
78 / HNO3 + NH3 →NH4NO3 / 1.05•10-8 / [5]
79 / NH3 + OH →NH2+H2O / 3.55•10-12 exp(-925/T) / [6]
80 / OH + O3 →HO2+O2 / 1.35•10-12exp(-956/T) / [6]
81 / H2SO4+NH3→NH4HSO4 / 1.9•10-16 / [2]
82 / NH4HSO4+NH3→(NH4)2SO4 / 6.6•10-15 / [2]
83* / SO2 + NH3 → NH3SO2 / 2•10-18 / [2]
84* / NH3SO2+ NH3 →(NH3)2SO2 / 6.8•10-17 / [2]
85 / NH3+ e-→NH + H2+e- / 9.35•10-11 / [7]
86 / NH3+ e-→NH2 + H+e- / 3.25•10-10 / [7]
87 / e- + O2 + N2 → O2- + N2 / 4.8•10-31 / [7]
88* / (NH3)2SO2 + 0.5 O2 →NH4SO3NH2 / 3.24168•10-18 / [2]
89* / (NH3)2SO2 + H2O → (NH4)2SO3 / 5.49221•10-23 / [2]
90* / NH4SO3NH2 + H2O→ (NH4)2SO4 / 2.5053•10-18 / [2]

1. Liquid phase reactions and rate constants

Reaction # / Chemical reaction / Rate constant / Reference
1 / OH + HO2→H2O + O2 / 7• 109 / [8]
2 / OH + O2- → OH- + O2 / 1• 1010 / [8]
3 / OH + H2O2 → H2O + HO2 / 2.7 • 107 / [8]
4 / HO2 + HO2 →H2O2 + O2 / 8.6 • 105 / [8]
5 / O2- + HO2 + H2O →H2O2 + O2 + OH- / 1 • 108 / [8]
6 / OH + O3 → HO2 + O2 / 2• 109 / [8]
7 / HO2 + O3 → OH + 2O2 / 1• 104 / [8]
8 / O2- + O3 + H2O → OH + 2O2 + OH- / 1.5• 109 / [8]
9 / SO5- + SO5- → 2SO4- + O2 / 2 • 108 / [8]
10 / HSO5- + HSO3- → 2SO42- + 2H+ / 7.5• 107 / [8]
11 / HSO5- + OH → SO5- + H2O / 1.7 • 107 / [8]
12 / HSO5- + SO4- → SO5- + SO42- + H+ / 1 • 105 / [8]
13 / SO4- + HO2 → SO42- + H+ + O2 / 5• 10 9 / [8]
14 / SO4- + O2- → SO42- + O2 / 5• 109 / [8]
15 / SO4- + OH- → SO42- + OH / 8 • 107 / [8]
16 / SO4- + H2O2 → SO42- + H+ + HO2 / 1.2 • 107 / [8]
17 / / 7.1•109 / [9]
18 / / 7.8•109 / [9]
19 / / 4.2•109 / [9]
20 / / 7.5•104 / [9]
21 / / 2.2•105 / [9]
22 / / 2.9•109 / [9]
23 / / 9.3 • 108 / [9]
24 / / 3.4•108 / [9]
25 / / 440 / [9]
26 / / 7.3•105 / [9]
27 / / 2.8•105 / [9]
28 / / 2.4•108 / [9]
29 / / 7.6•108 / [9]
30 / / 3.1•108 / [9]
31 / / 0.13 / [9]
32 / / 7.5•107 / [9]

1. Dissociation phenomena

Reaction # / Reaction / Equilibrium constant / Reference
1 / H2SO4 ↔ HSO4-+ H+ / 1000 / [8]
2 / HSO4- ↔ SO42- + H+ / 0.0266 / [8]
3 / SO2∙H2O ↔ HSO3- + H+ / 2.4554∙10-2 / [8]
4 / HSO3- ↔ SO32- + H+ / 3.8944∙10-8 / [8]
5 / HNO3 ↔ H+ + NO3- / 7.1596∙10-1 / [8]
6 / HNO2 ↔ NO2- + H+ / 7.9538∙10-4 / [8]
7 / NH3∙H2O ↔ NH4+ + OH- / 3.8502∙10-6 / [8]
8 / H2O ↔ OH- + H+ / 10-14 / [8]

The system of non-linear equations used in the mathematical model for describing the dissociation phenomena are presented in the following equations (Eq. 1- charge balance; Eq. 2-7 – mass balance; Eq 8 – general equation for the dissociation equilibrium constant of a monoprotic acid):

[H+] + [NH4+] = [HSO3-] + 2 [SO32-] + [HO-] + [HSO4-] + 2 [SO42-] + [NO3-] + [NO2-] (1)

[SO2]in = [HSO3-] + [SO2] (2)

[NH3∙H2O]in = [NH3∙H2O] + [NH4+] (3)

[H2SO4]in = [H2SO4]+ [HSO4-] (4)

[HNO3]in = [HNO3]+ [NO3-] (5)

[HNO2]in = [HNO2]+ [NO2-] (6)

[H2O]in= [H2O] + [OH-] + [H+] (7)

(8)

Where [M] denotes the molar concentration of species M, [M]in represents the concentration of the species M in the bulk liquid after the absorption and Ka is the equilibrium constant.

1. Main gas phase components concentrations

The concentration profiles of the main flue gas components are presented in the following figures: both the O2 (Fig S2) and N2 (Fig S3) are registering small decreases in their concentrations as they interact with the accelerated electrons and are decomposed to yield the radicals and ions that further react with the pollutant molecules.

The concentrations of nitrous oxide and nitrogen pentoxide are given (Fig S4), despite their low values: the concentration of N2O (generated via the reduction of NO2) is in the range of a few tens of ppm, while that of N2O5 is several orders of magnitude smaller.

In Fig S5, the concentrations of the radicals and molecular compounds involved in the radio-chemical removal pathway for SO2 are presented: the bisulfate radical’s concentration mirrors the concentration profile for SO2 for the first part of the irradiation treatment as it is generated from SO2 reaction with the hydroxyl radicals generated and consumed to yield sulfuric acid and sulfur trioxide. As SO2 is consumed in the gas phase, the profile for HSO3 becomes more linear. The sulfuric acid’s concentration in the gas phase is relatively low as it is both consumed in reaction with ammonia to yield ammonia sulfate and it nucleates with the water vapor present to form the liquid phase.

Figures S6 and S7 present the variations of the nitric and nitrous acids, which have complementary profiles and the ones of the ammonia nitrogen salts. The small number concentrations of HNO2 and HNO3 are explained by their fast reaction with ammonia yielding the fertilizer compounds.

Figure S2 Oxygen concentration profile in gas phase

Figure S3 Nitrogen concentration profile in gas phase

Figure S4 Nitrogen oxides' concentration profiles in gas phase

Figure S5 Main sulfur compounds' concentration profiles in gas phase

Figure S6 Nitrous and nitric acid concentration profiles in gas phase

Figure S7 Ammonia salts' concentrations profile in gas phase

1. Liquid phase characterization

The liquid volume fraction and the nucleation rate are presented in Figures S8 and S9. The nucleation rate registers a sharp increase in the first nanoseconds of irradiation as sulfuric acid is generated but proceeds to decrease as its gas phase concentration diminishes as a result of the chemical reactions occurring. The liquid fraction increases asymptotically; its value is close to the ones reported in the literature (10-5 – 10-6), the low value can be explained by the reduced initial concentration of the SO2 in the gas phase [10].

Figure S8 Nucleation rate vs. irradiation time

Figure S9 Liquid volume fraction vs. time

References

1. Bulearca AM (2012) Acidic pollutants removal from industrial flue gases by treating them with electron beam and microwave. PhD thesis. University Politehnica of Bucharest. Romania

2. Gerasimov GY, Gerasimova TS, Makarov VN, Fadeev SA(1996)Homogeneous and heterogeneous radiation induced NO and SO2 removal from power plants flue gases - Modeling study. Radiation Physics and Chemistry 48 763-769.

3. Basfar AA, Fageeha OI, Kunnummal N, Al-Ghamdi S, Chmielewski AG, Licki J, Pawelec A, Tymiński B, Zimek Z (2008) Electron beam flue gas treatment (EBFGT) technology for simultaneous removal of SO2 and NOx from combustion of liquid fuels. Fuel 87 (8-9):1446-1452.

4. Liu YD, Zhong R (2006) Theoretical studies on HOONO, HONOO, and HNO3 isomers and their isomerization reactions. Journal of Molecular Structure: THEOCHEM 765 (1-3):143-149.

5. Zhang J, Sun J, Gong Y, Wang D, Ma T, Liu Y (2008) A scheme for solving strongly coupled chemical reaction equations appearing in the removal of SO2 and NOx from flue gases. Vacuum 83 (1):133-137.

6. Schmitt KL, Murray DM, Dibble TS (2009) Towards a Consistent Chemical Kinetic Model of Electron Beam Irradiation of Humid Air. Plasma Chemistry and Plasma Processing 29 (5):347-362

7. Nishimura K, Suzuki N (1981) Radiation Treatment of Exhaust Gases, (XIV). Analysis of NO Oxidation and Decomposition in Dry and Moist NO-O2-N2 Mixtures by Computer Simulation. Journal of Nuclear Science and Technology 18 (11):878-886

8. Pandis SN, Seinfeld JH (1989) Sensitivity Analysis of a Chemical Mechanism for Aqueous-Phase Atmospheric Chemistry. Journal of Geophysical Research 94 (1989):1105-1126

9. Li RN, Yan KP, Miao JS, Wu XL (1998) Heterogeneous reactions in non-thermal plasma flue gas desulfurization. Chem Eng Sci 53 (8):1529-1540

10. Calinescu I, Martin D, Chmielewski A, Ighigeanu D (2013) E-Beam SO2 and NOx removal from flue gases in the presence of fine water droplets. Radiation Physics and Chemistry 85:130-138.