Global Reaction Scheme for Partial Oxidation of Pure H2S and H2S +

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A Global Reaction Scheme for Partial Oxidation of Pure H2S and H2S+CH4 Mixtures in Claus Conditions Samane Zarei Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 16 May 2017 Downloaded from http://pubs.acs.org on May 17, 2017

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A Global Reaction Scheme for Partial Oxidation of Pure H2S and H2S+CH4 Mixtures in Claus Conditions Samane Zarei* Research Institute of Petroleum Industry (RIPI), West side of Azadi sport complex, Tehran, Iran

Abstract The aim of this work was to find an appropriate reaction scheme to model both pure H2S and CH4 + H2S mixture oxidation systems. The H2S decomposition rate expression constants were adjusted which the mean absolute percentage error (MAPE) of this model was 5.91%. Then three reaction schemes for pure H2S oxidation and two reaction schemes for CH4 + H2S co-oxidation system were selected and their kinetic constant were adjusted. The selected reaction schemes with optimized kinetic parameters were used to model H2S and CH4 partial oxidation which the corresponding MAPEs varied between 7.90-10.32%. Finally, a reaction schemes was chosen for complete description of the pure H2S oxidation and H2S + CH4 co-oxidation systems. The proposed kinetic reaction scheme was applied in the kinetic modeling of an industrial Claus reaction furnace (MAPEs 5.59 and 15.02 % for temperature and compositions) and provided a satisfactory representation of the experimental data. Performances of the proposed reaction scheme were validated with comparison to the detailed reaction mechanism. Keywords: Reaction Scheme; Acid Gas; Combustion; Hydrogen Sulfide; Methane; Claus Furnace.

*

E-mail Address: [email protected]

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1. Introduction Sulfur emission regulations lead to several researches and development of technologies in order to increase the sulfur recovery (H2S) and subsequently, reducing sulfur emissions from modified Claus process, the most commercial process for sulfur recovery unit. These improvements enhance the operation of the modified Claus process to satisfy the emission standards1 Conversion of hydrogen sulfide to sulfur takes place in the modified Claus process. This widely used process was made of two steps, partial combustion step and catalyst step. Partial combustion step was distinguished by a high temperature (over 1273K) which converts 60-70% of H2S in the feed stream to elemental sulfur. The catalyst stages turn the remaining H2S and SO2 made in the furnace to more sulfur. Total sulfur recoveries in the modified Claus process varied in the 99.0-99.9% range2. Contamination of inlet hydrogen sulfide with hydrocarbons create a pathway for carbonyl sulfide (COS) and carbon disulfide (CS2) productions, two undesired byproducts. The byproducts if wasn’t hydrolyzed in catalyst stages, remain unconverted and have great contributions in sulfur emission to atmosphere through oxidation in incinerator3, 4. From an emissions point of view, the partial combustion step is perhaps the most critical piece of equipments in the modified Claus process due to the fact that up to 70% of the total sulfur production in sulfur recovery plants is generated in this thermal stage. It also establishes the proper H2S/SO2 ratio for downstream catalytic stages and deals with destruction of contaminants5. Hence small improvements in this stage can yield significant benefits including lower emissions and greater sulfur production. A comprehensive understanding of all reactions occurring in this partial combustion step can ascertain these mentioned goals. Typically, CH4 exists in concentrations up to a few percent in the acid gas feed which is made mainly from H2S and CO2 compounds. For this purpose, some researchers have investigated the partial combustion of the pure H2S and the mixtures of H2S and CH4, both numerically and experimentally. Experimental studies on the oxidation of H2S in flames and shocked tubes have been reported in literatures. Frenklach et al.6 have reported an experimental study on the oxidation of H2S in the shock tube. They introduced a reaction mechanism consist of 57 reactions and 17 species, and concluded a good agreement not only between model calculations and experiments but also with


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earlier studies on H2S Oxidation. Chernysheva et al.7 acclaimed that the mechanism of H2S oxidation reported by Frenklach et al.6 does not describe the experimental data in a wide range of conditions and introduced a kinetic model containing 201 elementary reactions and 23 particles. Tsuchiya et al.8 conducted experiments on H2S oxidation in a shock tube and compared results with Frenklach et al.6 and Chernysheva et al.7 reaction mechanisms. They also constructed a new kinetic model for the H2S oxidation process. Most mentioned published studies focused on the oxidation of H2S at very high temperature (2000 ℃) or complete oxidation conditions while at the reaction furnace, we encountered with lower temperature (900-1500 ℃) and oxygen deficient conditions (partial oxidation condition). Karan3 performed partial H2S oxidation experiments in quartz reactors. Experiments on the H2S oxidation were conducted by reacting 1.65 mol % H2S and 1 mol % O2 at temperature ranges 1000-1200 ℃ and residence time 0.1-1.4 s. Karan3 declared a kinetic reaction scheme including 30 intermediate reactions and reported a deviation between model results and experimental data. Monnery et al.9also conducted H2S oxidation experiments in quartz reactors. The experiments were performed in a laboratory scale, isothermal, plug flow reactor at temperatures between 850 and 1150 ℃ and residence times between 0.05 and 1.2 s and developed a global kinetic expression. They only reported SO2 mol % in product of combustion and did not give H2 and H2S concentrations. Chin10 carried out the H2S oxidation experiments in a quartz plug flow reactor at temperatures between 1000 to 1200℃ and pressure range of 130-142 kPa. Chin10 investigated the effect of initial O2 concentration on the contribution of products. Presence of CH4 in acid gas feed leads to investigate effect of this oxygen consuming compound on product distributions. Arutyunov et al.11reported data on CH4 oxidation in the presence of low H2S concentration. In their study, experiments were carried out in a quartz reactor under static conditions at much longer residence times and at temperatures lower than 727 ℃. Karan3 conducted contemporary oxidation experiments of H2S and CH4 in the quartz tubular reactor at temperature range of 1000-1200℃ and residence time 0.1-1.4 s. Karan3 utilized a reaction scheme including 58 reactions to predict the product distributions but the simulation results were unable to predict experimental data very well. Chin10 performed experiments on partial oxidation of H2S and CH4 mixtures at temperature ranged from 1000 to 1200 ℃, pressure range of 130-


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145kPa, and residence time 0.4-0.7 s in a quartz tubular reactor. In this work, they reported experimental data but didn’t introduce a reaction scheme. As mentioned, the most of previous experimental data on the oxidation of pure H2S and the H2S+CH4 mixtures were limited to lower and higher temperature encountered in the reaction furnace and performed under complete oxidation condition. In some research, the concentrations of products for pure H2S oxidation system and in some cases for the H2S+CH4 mixtures oxidation were not reported. The experimental data reported by Chin et al.12 is solely complete data including data of the H2S decomposition, and the pure H2S and CH4+H2S mixture oxidation data at reaction furnace condition. A number of investigator including Dryer and Glassman13, Westbrook and Dryer14, and Jones and Lindstedt15introduced a global molecular reaction scheme for hydrocarbons combustion. Several Researchers focused on limiting detailed kinetic mechanism and introducing a global reaction scheme with similar performance. Selim et al.16 reduced H2S/O2 reaction mechanism including 111 elementary reaction to 24 reactions. Zhu et al.17 derived a 4-species 4-step global reaction mechanism for detonation application through thermochemical approach. Based on their claim, global reaction mechanism is deduced from elementary chemistry or experimental measurements. Hara et al.18proposed a two-step global reaction scheme for the volatile matter of coal and compared the results with the detailed reaction mechanism. A global reaction scheme that can be applied in both H2S pure oxidation and oxidation systems composed of CH4 and H2S mixtures, has not been introduced before. Previous works in this subject except Monnery et al.19, only limited to declaring a reaction scheme containing radical, intermediate and molecular species. Although detailed kinetic mechanism is required for comprehensive description of chemical system by applying elementary reactions and intermediate species, large size of mechanism reduces its applicability

20

. Large number of

conservation equations (because of number of species) prevents them from applying in CFD codes and incorporating in unsteady, two and three-dimensional calculations

20

. Different time

scales of system resulting from presence of the various chemical species increase stiffness of system20. Due to stiffness, possibly code crash and divergence, it is difficult to solve problem 16

. To enhance computational efﬁciency

21

20,

and to produce smaller size mechanism with less

stiﬀness 20, mechanism reduction methods were proposed21, 20, 16. Results obtained from reduced 4 ACS Paragon Plus Environment

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mechanisms showed its validity 16. Our literature review showed that global reaction scheme was successfully applied in kinetic modeling of Claus reaction furnace22, 23. Above reaction schemes were adjusted by utilizing industrial data. It was an incentive to perform a global kinetic scheme that adjusted by laboratory experimental data and validated with industrial data. The main object of this work is to introduce a global reaction scheme involving molecular species that completely describes the partial combustion step for feeds containing pure H2S and the H2S+CH4 mixtures. To show applicability of proposed kinetic model in laboratory and industrial situations, validations with other experimental laboratory data and industrial Claus reaction furnace were done.

2. Experimental Chin et al.12studied the oxidation reaction of CH4 and H2S in a partial oxidation environment. They looked at the partial oxidation of some simpler systems such as partial oxidation of H2S and H2S decomposition system before attempting to study the oxidation of a complicated system (H2S + CH4 mixture). They conducted the following experiments in the isothermal quartz reactors. A schematic diagram of the experimental apparatus and succinct description of its components has been given in Karan3. Chin et al.12 showed that based on hydrodynamics, this quartz reactor can be considered as a plug flow reactor with acceptable errors of less than 5 percent. Therefore in this work, this reactor was modeled with isothermal plug flow assumption. 2.1. H2S Decomposition At high temperatures of the combustion step, H2S decomposition reaction occurs significantly. It is now accepted by many researchers that this reaction occurs in the partial combustion step 24, 3. In order to model the oxidation systems, the H2S decomposition reaction should be considered. Chin10 performed some experiments for the feed containing 1mol % H2S and 99 mol % N2 at temperature range of 800-1250℃, pressure range of 120-145 kPa and residence time 0.2-0.7 s. 2.2. Pure H2S Oxidation Gathering some experimental information on H2S oxidation prior to performing experiments with more complicated systems would help to understand more complicated systems (i.e. oxidation of H2S and CH4 mixture). Chin et al.12 measured the product distribution of the H2S oxidation system for three feeds including 2.45 mol % H2S and varying oxygen content (1, 1.25 5 ACS Paragon Plus Environment

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and 1.5 mol % O2). The operating temperature and pressure of the system were 1000-1200℃ and 130-142 kPa respectively. 2.3. (H2S+CH4) Mixtures Oxidation Chin10 investigated the roles of CH4 in the acid gas feeds of the modified Claus process considering two feeds composed of 2.45%mol CH4, 2.45%mol H2S and varying O2 content (1 and 1.5%mol). The temperature, pressure and residence time of apparatus varied from 10001200 ℃, 130-145 kPa and 0.4-0.7 s respectively. H2O concentrations derived from the H atom balance and the O atom balance around the reactor agreed within 5%. Due to coke deposition in reactor, carbon balance wasn’t reported by Chin10.

3. Procedure The determination of best reaction scheme for description of the pure H2S and CH4+H2S mixture oxidation systems accomplished by developing different reaction schemes in a suitable reactor model. The parameters of each reaction scheme were regressed using the experimental data. A kinetic schemes with lower mean absolute percentage error is the best kinetic scheme. Details of procedure of developing kinetic schemes, reactor model and optimization work are presented as follows. 3.1. Kinetic Model In this work, the experimental data for partial combustion of H2S in presence and absence of methane were applied in the kinetic modeling. Therefore, a kinetic reaction scheme must be included in adjusting work. There are several researches that investigated the reactions occurring in Claus conditions, i. e. partial oxidation of hydrogen sulfide in presence and absence of methane. Paskall and Sames25 listed possible main reactions occurring in the Claus reaction furnace. Equations (1), (6) and (10) was introduced for the H2S oxidation. Karan3clarified the observed trends of H2S oxidation products along residence time and reactor temperature with considering two reactions, Equations (3) and (10). Karan3 proposed the reaction between hydrogen and sulfur dioxide (Equation (8)) as main source of hydrogen consumption. Reaction scheme was developed by Monnery et al.9 made of three main Claus reactions (Equations (4), (6) and (10)). Chin10 concluded that other reactions except Equations (6) and (10) are taken place and a simple 6 ACS Paragon Plus Environment

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pathway for the H2S oxidation introduced. The proposed reaction network was a combination of six simple reactions (Equations (1), (4), (6), (7), (10) and (11)). All of above mentioned researches only proposed the reactions and did not presented kinetic constants of the proposed reaction pathways. Determination of actual reaction scheme describing the H2S oxidation system requires further investigations. Therefore, all of proposed reactions were considered and the following reactions were offered for H2S oxidation system: H2S+0.5O2→0.5S2+H2O

(1)

2H2S+O2→S2+2H2O

(2)

H2S+O2→H2+SO2

(3)

H2S+1.5O2→SO2+H2O

(4)

2H2S+3O2→2SO2+2H2O

(5)

H2S↔H2+0.5S2

(6)

H2+0.5SO2↔H2O+0.25S2

(7)

2H2+SO2↔2H2O+0.5S2

(8)

H2S+0.5SO2↔0.75S2+H2O

(9)

2H2S+SO2↔1.5S2+2H2O

(10)

3H2+SO2↔2H2O+H2S

(11)

As seen, some reactions such as 1 and 2 have same rate expression with different stoichiometric coefficients (their stoichiometric coefficients are multiple of each other). The study of power effect on the rate expression and its impact on better estimation of product distribution are the main reasons of considering both reactions 1 and 2. In case of CH4+H2S co-oxidation and after exact review of the literatures, the following reactions based on product compositions, in addition to above equations, were offered to describe H2S+CH4 mixture oxidation: CH4+0.5O2⟶CO+2H2

(12)

CH4+1.5O2⟶CO+2H2O

(13)

CH4+2H2S↔CS2+4H2

(14)

CH4+2S2↔CS2+2H2S

(15)

CH4+S2↔CS2+2H2

(16)

CH4+SO2↔CO+H2O+H2S

(17) 7 ACS Paragon Plus Environment

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CH4+2SO2↔CO2+2H2O+S2

(18)

CH4↔0.5C2H4+H2

(19)

2CH4+S2↔C2H4+2H2S

(20)

CH4+0.5S2↔0.5C2H4+H2S

(21)

CO+0.5O2↔CO2

(22)

Paskall and Sames25considered Equations (13)-(15) and (22) for CH4 oxidation in presence of hydrogen sulfide. Karan et al.26 reported that two reactions (14) and (15) are major sources of carbon disulfide. Chin10 concluded that methane has lower tendency in reaction with oxygen in comparison to hydrogen sulfide. Therefore, it possible for methane to react with other oxygen containing compounds such as SO2 and two Equations (17) and (18) was proposed by Chin10 for considering these possibilities. Chin10 related C2H4 content of product to methane pyrolysis (Equation (19)). In all above mentioned studies, it is concluded that methane and other hydrocarbons at oxygen depletion conditions react with sulfur containing components, i. e. sulfur and hydrogen sulfide. With considering Karan3study, two reactions 20 and 21 was proposed for ethylene production by author. It must be acclaimed that above studies only limited to declaring a reaction pathway not presenting kinetic constants. Equation 12 for methane oxidation was presented by Westbrook and Dryer14. Anderson et al.27considered the Equation 16 as an alternative for reaction among methane and sulfur. Based on above studies, in present work, Equations 1-22 were introduced for complete definition of pure H2S and CH4+H2S mixtures oxidation. The rate expression of these reactions was obtained using the power law mechanism with Arrhenius temperature dependence equation. About 25 and 432 reaction schemes were considered for systems composed of the pure H2S and the CH4+H2S mixture, respectively. The procedure of selecting reaction schemes is as follows. For the pure H2S oxidation system and based on equations 1-11, two rate expressions 1 and 2 have same rate expression with different stoichiometric coefficients (H2S+0.5O2→0.5S2+H2O). Therefore we have three alternatives for this reaction including two rate expressions 1 and 2 for above reaction and a choice for absence of this reaction. With a same procedure, we have one rate expression for (H2S+O2→H2+SO2) reaction and two alternatives and so on. Therefore total number of possible reaction schemes is calculated from multiplication of all reaction alternatives. Meanwhile the presence of some reactions such as oxidation reactions are necessary, 8 ACS Paragon Plus Environment

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consequently total 25 reaction schemes were obtained for the pure H2S oxidation system. The same procedure was repeated for the CH4+H2S oxidation system and 432 reaction schemes were obtained. 3.2. Reactor Model Base on the mentioned statements in experimental section, an isothermal plug flow reactor can be applied in this modeling work. Considering isothermal plug flow assumption and negligible pressure drop, the following ordinary differential equations including mass balance equations should be solved.

dFj dz

= A∑υij ri

j = 1, ..., nc i = 1, ..., nR

(23)

i

The above ordinary differential equations were solved by Runge–Kutta order 4 and the numerical algorithm was written in MATLAB programming software. 3.3. Optimization Model Following objective function was used in optimizing the kinetic parameters of each reaction scheme: OF = ∑ w j j =1

x j ,cal − x j ,exp x j ,exp

j = 1,..., nc

(24)

Where x j ,cal is calculated gas composition at reactor outlet, x j ,exp is experimental gas composition at the effluents and w j is weight function that its values were changed for different components in proportional to their errors. Optimization work was performed by genetic algorithm in MATLAB programming software. Initial guesses of constants were chosen randomly by ga function. In next steps, Arrhenius constants of reactions were adjusted by fmin function and obtained parameters from ga function. Optimizing work were repeated several times for each reaction scheme in manner that at each stage, the weight function of compounds with higher error increased in order to attain higher accuracy in the model prediction.

4. Results and Discussions


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4.1. H2S Decomposition As mentioned before, H2S decomposition is one of the main reactions occurring in the partial oxidation condition and knowing its rate expression is useful to predict pure H2S and CH4+H2S mixture oxidation. In this part a rate expression for H2S decomposition is introduced using the experimental data. The form of this rate equation is determined according to reaction number 6 as follows: 216.86 ( kJ / mol ) 1  mol  7 −r  3 )(PH2S − PH2 PS02.5 )  = 3.1514 × 10 exp ( − RT K eq  m .sec 

(25)

Where P is the partial pressure (kPa). Figure 1 shows H2S mole fraction predicted by equation (25) and compares the model prediction with experimental H2S mole fractions as a function of reactor temperature. The mean absolute percentage error (MAPE) of this model is 5.91% compared to the experimental data. As seen, the activation energy of the rate expression 25 is 216.86 kJ/mol which is in agreement with Kaloidas and Papayannakos28and Dowling et al.29who reported the activation energy of 195.74 and 200.84 kJ/mol, respectively. However it is lower than the activation energies 241 and 286 kJ/mol which were reported by Adesina et al.30and Harvey et al.31.

4.2. H2S Oxidation The purpose of this section is to declare a reaction scheme for pure H2S oxidation system with the minimum number of reactions that can be applied to the CH4+H2S mixture oxidation and give good estimation of product distribution. Reactions 1, 3, 4, 6, 7 and 9 were considered and their kinetic expression constants were fitted for 25 reaction schemes including 3 up to 6 reactions. The adjusted kinetic constants of equation (25) were used for reaction 6. After examining several reaction schemes and fitting the kinetic parameters, three reaction schemes were chosen. The kinetic constants of these reaction schemes and their corresponding mean absolute percentage errors for H2, H2S and SO2 compounds and all other compounds including H2O and S2 have been presented in tables 1 and 2. Data of table 2 show that the reaction scheme 1 has the minimum error among three reaction schemes while differences of these three schemes are 10 ACS Paragon Plus Environment

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negligible. Parity plot for chosen reaction scheme with minimum error (reaction scheme 1) has been shown in Figure 2. Parity plot shows experimental mole percentage of reactor outlet versus model predictions. Coefficient of determination (R2) was calculated 0.96. For further comparison, experimental data of H2S oxidation system was simulated with a detailed kinetic mechanism which developed by Leeds University32, 33. The Leeds H2S/CH4 mechanism which made of 450 elementary reactions and 78 species, is widely applied in different investigations21, 16. The simulation result of detailed kinetic mechanism (MAPE) was reported in table 2. Based on table 2, the mean absolute percentage error of detailed mechanism is 31.70%, it is concluded that the developed kinetic model is more accurate. According to table 1, the activation energy of equation (4) for three reaction schemes are 47.45, 31.48 and 60.94 kJ/mol, respectively. The activation energy 46.03 kJ/mol reported by Monnery et al.9is comparable with 45.45 kJ/mol value of reaction scheme 1 while some differences between with Monnery et al.9activation energy and two other values (31.48 and 60.94 kJ/mol) in reaction schemes 2 and 3 are seen. The activation energy of equation (9) (second Claus reaction) for reaction schemes 1 and 3 (255.02 and 244.53 kJ/mol) are higher than Monnery et al.9 activation energy 208.79 kJ/mol. A comparison between the model and experimental data based on three reaction schemes has been presented in Figure 3. Based on experimental data, H2 concentration increases with temperature for the case of lowest initial O2 in the feed. As the initial O2 concentration increases gradually, the H2 concentration reaches to a maximum at 1100℃. Hence, for the case with the highest initial O2 concentration, the H2 concentration decreases when the temperature increases from 1100 to 1200 ℃10. As seen, trends of H2 production calculated from three reaction schemes as a function of feed oxygen concentration and temperature is similar to the experimental data. As previously mentioned and these three reaction schemes show, H2 concentration increases with temperature for feeds with 1 and 1.25% mole O2 but for feed with 1.5% mole O2, H2 concentration increases for temperature 1000 to 1100 ℃ and decreases from 1100 to 1200 ℃. When the initial O2 concentration increases, a sharp increase in SO2 production is observed and increasing temperature results in decreasing SO2 concentration (Figure 4). At 1000 ℃, the conversion of 11 ACS Paragon Plus Environment

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H2S increases sharply with increasing initial oxygen concentration. However, at higher temperatures, H2S conversion seemed to somewhat decrease even with increasing initial oxygen concentration (Figure 5) 10.

4.3. Simultaneous Modeling of Pure H2S and H2S+CH4 Mixture Oxidation In this section, the pure H2S and H2S+CH4 mixtures oxidation data were combined and used in the kinetic modeling. It should be noted that the adjusted kinetic constants for H2S decomposition have been used for reaction 6. Like previous section, several reaction schemes were chosen and their kinetic constants were adjusted. In the first step, reactions 19-22 which lead to CO2 and C2H4 were withdrawn in the fitting procedure because of their low concentration. The reactions 17 and 18 were considered to investigate the possibility of CH4 and SO2 reaction in O2 consuming conditions and at the same time, the effect of these two reactions were also examined. As mentioned before, in order to study the effect of power in the rate expression, some dependent reactions were also considered. Finally 432 reaction schemes were chosen and their kinetic constants were adjusted. This procedure was continued by changing CS2 and CO coefficients in the weight function and adjusting the rate expression constants for CO2 and C2H4 compounds. Finally, two reaction schemes with higher precision in both pure H2S and H2S+CH4 mixture oxidation systems were chosen. Reaction kinetic parameters of these two reaction schemes have been presented in table 3 and subsequently their mean absolute percentage errors were presented in table 4. Introduced reaction schemes is validated with H2S+CH4 oxidation experiments conducted by Karan3. MAPE 8.80 % for SO2 concentrations of the validated tests shows generality of model for different experimental conditions. In table 4, the results of global kinetic model were compared with the Leeds H2S/CH4 oxidation mechanism. It is obvious that the global kinetic model has lower mean percentage errors which implied its applicability. Because of absence of reaction in the Leeds detailed mechanism, CS2 comparison wasn’t carried out. According to this table, the reaction scheme 2 has lower error for the CH4+H2S mixtures oxidation in comparison to the reaction scheme 1 but has greater error for the H2S oxidation system. The results show that reactions 17 and 18 between CH4 and SO2 do not contribute in the CH4 and H2S co-oxidation system. The comparison between reaction schemes containing these 12 ACS Paragon Plus Environment

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reactions shows that eliminating these reactions does not have any significant effect on product distribution. Figure 6 shows parity plot of experimental data versus model calculations for reaction scheme 2. Based on figure, coefficient of determination (R2) is 0.98. According to table 3, the activation energy 58.76 and 57.83 kJ/mol of H2S oxidation rate expression (Equation (4)) for reaction schemes 1 and 2 are comparable with 46.03 kJ/mol value reported by Hawboldt24. Same result is concluded for methane oxidation activation energy of Equation (12) which are calculated 115.67 and 112.93 kJ/mol for reaction schemes 1 and 2 with 125.53 kJ/mol value reported by Jones and Lindstedt15.

Figure 7 compares the measured and calculated H2 mole percent as a function of temperature and feed composition. As the results show, these two reaction schemes can adequately predict this behavior (Table 4). According to table 4, the mean absolute percentage error of H2 for models 1 and 2, are 7.45 and 11% respectively. As seen, for the feed with higher O2 concentration and T>1050℃ some inconsistency can be observed and both models predict lower H2 concentration compared to the experimental data. Meanwhile at lower O2 concentration, both models predict the same results showing a good agreement with experimental data.

Figure 8 shows H2S mole percent for two feeds containing 2.45%mol CH4+2.45%mol H2S and variable O2 concentrations (1 and 1.5%mol O2). It is obvious that for the feed with higher O2 concentration, both models show some disparity while at lower O2 concentration, a good agreement between the models and experimental data can be seen. Determination of the best model is not possible since two models have similar accuracy in prediction of H2S mole percent. Similar to pure H2S, the influence of two reaction schemes on CH4 and H2S co-oxidation system were investigated which the results have been presented in Figures 9-14.

Figure 9 compares the measured and calculated mole percent of SO2 at reactor exit using reaction schemes 1 and 2 as a function of temperature. According to this figure, both models have similar accuracy at lower O2 feed while some deviations can be seen at higher O2 concentration. Both models over estimate experimental data at lower O2 concentration and their MAPEs are 15.21 and 18.23% respectively. Calculated CH4 concentrations for the two reaction schemes were compared with experimental data in Figure 10 which their MAPEs are 6.16 and 6.11% for the reaction schemes 1 and 2 13 ACS Paragon Plus Environment

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respectively. The results show an acceptable agreement between the calculated and experimental data though some over estimations are seen for both feeds at the entire temperature ranges. The experimental and calculated CS2 concentrations in temperature range 1000-1200℃ and two mentioned feed compositions are presented in Figure 11. The corresponding mean absolute percentage error for reaction schemes 1 and 2 are 20.49 and 16.51% respectively. According to MAPEs, reaction scheme 2 represents better estimation of product distribution but no significant difference between two models can be seen in Figure 11 and choosing the best reaction scheme according to this figure is difficult. The measured and calculated CO mole percent based on reaction schemes 1 and 2 are presented in Figure 12. The effect of temperature and initial feed composition are also declared in this Figure. The MAPE of reaction scheme 1 is 34.44% and Figure 12 shows deviation from experimental data for this reaction scheme. In other word, the reaction scheme 1 has poor performance in predicting experimental data. It is evident that reaction scheme 2 presents better estimation of CO concentration and its MAPE (14.89%) confirms this claim. The measured mole percent of CO2 and C2H4 at reactor exit and the calculated CO2 and C2H4 mole percent from reaction schemes 1 and 2 as a function of temperature for two feeds of the CH4+H2S oxidation system were shown in Figures 13 and 14. According to Figure 13, the reaction scheme 1 shows deviation with the experimental data whilst the reaction scheme 2 at higher O2 concentration matches experimental data and at lower O2 concentration overestimates CO2 concentration. Figure 14 shows that both models have the same accuracy in prediction of C2H4 concentrations. The predicted concentration of these two models coincide each other at entire temperature range and feed composition and both models have same performance in predicting C2H4 concentration. From Figures 13 and 14, it is concluded that reaction scheme 2 has better performance in prediction of CO2 and C2H4 concentrations. From all above mentioned discussion, it is concluded that reaction scheme 2 gives better estimation of product distribution in both the pure H2S oxidation and the CH4 and H2S cooxidation systems.


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High errors of hydrogen sulfide predicted from the detailed kinetic mechanism (tables 2 and 4) were investigated by performing sensitivity analysis. Figure 15 shows results of the sensitivity analysis for following rate-limiting reactions as a function of reactor length. SH+O2↔HSO+O

(26)

S+O2↔SO+O

(27)

2SH↔S2+H2

(28)

S2+H+M↔HS2+M

(29)

SO+O2↔SO2+O

(30)

SH+O2↔SO+OH

(31)

From the sensitivity analysis, it is obvious that consumption of H2S by equation (29) is controlling step in oxygen lean conditions at larger distance of the reactor. At reactor inlet, other reactions except equation (29) have contributions in hydrogen sulfide formation and consumption. Their impacts decrease by oxygen depletions along reactor length. Sensitivity analysis shows that above proposed reactions are main options for reducing observed errors.

5. Industrial Case In this section, validation of model prediction on industrial Claus reaction furnace was examined. Therefore, experimental data from industrial Claus reaction furnace is required. Data acquired by Paskall and Sames25 in outlet of Claus reaction furnace can be utilized in this validation work. Specification of the Claus reaction furnace and inlet streams in Paskall and Sames25 study are presented in Table 5. Kinetic modeling of Claus reaction furnace was performed by several authors. Pierucci et al.34(2004), Jones et al.22 and Javanmardi Nabikandi and Fatemi35modeled Claus reaction furnace with a single PFR. Manenti and co-authors

36-39

in several studies

considered a series of CSTR and PFR for describing furnace behavior. Zarei et al.23examined different reactor networks such as PFR, CSTR, a combination of CSTR and PFR, and etc. They showed that lower error can be obtained with considering a single PFR. From literature review, an isothermal plug flow reactor can be applied in this modeling work. In addition, based on previous studies on the kinetic modeling of Claus reaction furnace35, 34, 23 37, high flow rates at


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inlet and peclet number greater than 500 provide situations for Plug Flow assumption. Therefore, the Claus reaction furnace can be modelled by single adiabatic PFR reactor. Meanwhile, details of mass and energy balance equation and actual residence time equation are presented in Zarei et al.23 study. The results of kinetic modeling was compared with experimental data of reaction furnace outlet. Calculated deviation for reactor temperature is 5.59%. A good agreement between calculated and experimental mole percentages of hydrogen sulfide, sulfur dioxide, water, carbon dioxide, sulfur and hydrogen is reported. Mean absolute percentage of error for the compounds is 15.02 %. The results of the kinetic modeling show that Claus reaction furnace can be properly described by the adjusted kinetic model.

Figure 16 represent mole percentage of combustion products and reactor temperature as a function of reactor residence time. The figure show a minor deviations between calculated and experimental mole compositions and temperature. Based on figure, maximum conversion to sulfur occurs as the residence time greater than 0.5 sec and a sharp increase in temperature and sulfur composition profiles is observed. For further comparison, the industrial Claus reaction furnace was simulated with the Leeds detailed mechanism. Table 6 represents the results predicted from the Leeds detailed mechanism and the global reaction scheme in comparison to experimental data of industrial Claus reaction furnace. Based on table, H2, H2S and SO2 mole compositions obtained from the detailed mechanism exceed the experimental data. Moreover, concentrations of S2 and H2O were lower than the corresponding experimental data. In detailed mechanism, no conversion for carbon dioxide was observed. While conversion of carbon dioxide due to methane oxidation was occurred. Figure 17 shows H2S and H2 concentration profiles obtained from the global reaction scheme and the detailed mechanism in comparison to experimental data at reactor outlet. Based on figure, it is concluded that both reaction schemes have similar trend at entire reactor length. For the detailed mechanism, conversion of hydrogen sulfide to sulfur was occurred at shorter residence time (about 0.5 sec) than the global reaction scheme (about 1 sec). The global reaction scheme represents a good agreement with experiment at reactor outlet. While some deviations from experiment were observed for the Leeds university detailed mechanism.

6. Conclusions


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An appropriate rate expression with optimum kinetic parameters for H2S decomposition reaction was developed and used to model the pure H2S oxidation and CH4 + H2S co-oxidation systems. Three reaction schemes for pure H2S oxidation system were chosen and their kinetic parameters were adjusted. In second study, all possible reaction schemes were considered to describe pure H2S and CH4+H2S mixtures oxidation and finally two reaction schemes were chosen which could give good estimation of component mole percent in the effluent. These two reaction schemes could predict the temperature dependence of all compositions and also represent the effect of initial feed concentration on the product distribution. It was also concluded that the reaction between CH4 and SO2 at the oxygen consuming condition does not occur. Adjusted kinetic model was validated with industrial Claus reaction furnace operating in modified Claus Unit. The calculated MAPEs for temperature and composition are 5.59 and 15.02 %, respectively, and imply operability of the adjusted kinetic model in industrial applications. The results show that for clear understanding of reactions involved in Claus reaction furnace, further experimental investigations on partial oxidation of methane and co-oxidation of CO2-CH4-H2S mixtures in flow reactors and measuring the concentrations of all of products are required. Comparisons between the proposed reaction scheme and the detailed reaction mechanism were performed in laboratory and industrial scales. Results show good performances of the global reaction scheme compared to the detailed mechanism.

7. Nomenclatures A: Cross-sectional area (m2) C: Concentration (mol/m3) E: Activation Energy (kJ/mol) F: Molar Flow (mol/sec) k : Arrenhius constant ( mol-m-sec-kPa) Keq: Equilibrium constant nC: Number of components nR: Number of reactions OF: Objective function 17 ACS Paragon Plus Environment

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P: Pressure (kPa-Pa) r : rate (mol/ m3. s) R: Gas Constant (R=8.314 J/mol. K) tR: Actual mean residence time(sec) T: Temperature (K) x: mole percent ߭ij: Stoichiometric coefficient of component j in reaction i wj: Weight function Subscripts

cal: Calculated exp: experimental i: Reaction number j: Component number

8. References (1) Karan, K.;Mehrotra, A. K.;Behie, L. A. Industrial & Engineering Chemistry Research 1994, 33,26512655. (2) Clark, P. D.;Sui, R.;Dowling, N. I.;Huang, M.;Lo, J. M. H. Catalysis Today 2013, 207,212-219. (3) Karan, K. An experimental and modeling study of homogeneous gas phase reactions occurring in the modified claus process; Ph. D. Thesis, University of Calgary, Calgary, 1998. (4) Karan, K.;Behie, L. A. Industrial & Engineering Chemistry Research 2004, 43,3304-3313. (5) Clark, P. D.;Dowling, N. I.;Huang, M.;Svrcek, W. Y.;Monnery, W. D. Industrial & Engineering Chemistry Research 2001, 40,497-508. (6) Frenklach, M.;Lee, J. H.;White, J. N.;Gardiner, W. C. Combustion and flame 1981, 41,1-16. (7) Chernysheva, A. V.;Basevich, V. Y.;Vedeneev, V. I.;Arutyunov, V. S. Russian Chemical Bulletin 1990, 39,1775-1784. (8) Tsuchiya, K.;Kamiya, K.;Matsui, H. International Journal of Chemical Kinetics 1997, 29,57-66. (9) Monnery, W. D.;Hawboldt, K. A.;Pollock, A.;Svrcek, W. Y. Chemical Engineering Science 2000, 55,5141-5148. (10) Chin, H. S. F. The Fate of Methane in the Reaction Furnace of a Modified Claus Plant; M.Sc. Thesis, University of Calgary, Calgary, 2000. (11) Arutyunov, V.;Vedeneev, V.;Nikisha, L.;Polyak, S.;Romanovich, L.;Sokolov, O. Kinetics and catalysis 1993, 34,194-197. (12) Chin, H. S. F.;Karan, K.;Mehrotra, A. K.;Behie, L. A. The Canadian Journal of Chemical Engineering 2001, 79,482-490. 18 ACS Paragon Plus Environment

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(13) Dryer, F. L.;Glassman, I. Symposium (International) on Combustion 1973, 14,987-1003. (14) Westbrook, C. K.;Dryer, F. L. Combustion Science and Technology 1981, 27,31-43. (15) Jones, W.;Lindstedt, R. Combustion and Flame 1988, 73,233-249. (16) Selim, H.;Gupta, A. K.;Sassi, M. Applied Energy 2012, 93,116-124. (17) Zhu, Y.;Yang, J.;Sun, M. Shock Waves 2012, 22,363-379. (18) Hara, T.;Muto, M.;Kitano, T.;Kurose, R.;Komori, S. Combustion and Flame 2015, 162,4391-4407. (19) Monnery, W. D.;Svrcek, W. Y.;Behie, L. A. The Canadian Journal of Chemical Engineering 1993, 71,711-724. (20) Lu, T.;Law, C. K. Proceedings of the Combustion Institute 2005, 30,1333-1341. (21) Cerru, F. G.;Kronenburg, A.;Lindstedt, R. P. Combustion and flame 2006, 146,437-455. (22) Jones, D.;Bhattacharyya, D.;Turton, R.;Zitney, S. E. Industrial & Engineering Chemistry Research 2012, 51,2362-2375. (23) Zarei, S.;Ganji, H.;Sadi, M.;Rashidzadeh, M. Journal of natural Gas Science and Engineering 2016, 31,747-757. (24) Hawboldt, K. A. Kinetic modelling of key reactions in the modified Claus plant front end furnace; Phd, University of Calgary, Calgary, Canada, 1998. (25) Paskall, H. G.;Sames, J. A. Sulphur recovery; Western Research:Canada, 1998. (26) Karan, K.;Mehrotra, A. K.;Behie, L. A. Chem. Eng. Comm. 2005, 192,370-385. (27) Anderson, J. R.;Chang, Y. F.;Pratt, K. C.;Foger, K. Reaction Kinetics and Catalysis Letters 1993, 49,261-269. (28) Kaloidas, V. E.;Papayannakos, N. G. Industrial & Engineering Chemistry Research 1991, 30,345351. (29) Dowling, N. I.;Hyne, J. B.;Brown, D. M. Industrial & Engineering Chemistry Research 1990, 29,2327-2332. (30) Adesina, A. A.;Meeyoo, V.;Foulds, G. International Journal of Hydrogen Energy 1995, 20,777-783. (31) Harvey, W. S.;Davidson, J. H.;Fletcher, E. A. Industrial & Engineering Chemistry Research 1998, 37,2323-2332. (32) Hughes, K.;Blitz, M.;Pilling, M.;Robertson, S. Proceedings of the Combustion Institute 2002, 29,2431-2437. (33) Hughes, K. J.;Tomlin, A. S.;Dupont, V. A.;Pourkashanian, M. Faraday discussions 2002, 119,337352. (34) Pierucci, S.;Ranzi, E.;Molinari, L. Computer Aided Chemical Engineering 2004, 18,463-468. (35) Javanmardi Nabikandi, N.;Fatemi, S. Journal of Industrial and Engineering Chemistry 2015, 30,5063. (36) Manenti, F.;Papasidero, D.;Bozzano, G.;Pierucci, S.;Ranzi, E.;Buzzi-Ferraris, G. Computer Aided Chemical Engineering 2013, 32,811-816. (37) Manenti, F.;Papasidero, D.;Frassoldati, A.;Bozzano, G.;Pierucci, S.;Ranzi, E. Computers & Chemical Engineering 2013, 59,219-225. (38) Manenti, F.;Papasidero, D.;Ranzi, E. AIDIC conference series 2013, 11,221-230. (39) Manenti, G.;Papasidero, D.;Manenti, F.;Bozzano, G.;Pierucci, S. Procedia Engineering 2012, 42,414-421.


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Table 1. The Adjusted Arrhenius constants for the pure H2S Oxidation system.

Reaction 1 Reaction 3 Reaction 4 Reaction 7 Reaction 9 Reaction 1 Reaction 3 Reaction 4 Reaction 7 Reaction 1 Reaction 3

k(mol-K-m-sec-kPa) E (J/mol .K) Reaction Scheme 1 619.420 102.71 180.840 73.94 26.866 47.45 1.402×105 191.86 3.166×105 255.02 Reaction Scheme 2 2.376 34.62 10.732 39.40 6.753 31.48 6 2.852×10 208.20 Reaction Scheme 3 47.000 108.80 4.216 36.14 20 ACS Paragon Plus Environment

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Reaction 4 Reaction 9

85.356 1.592×105

60.94 244.53

Table 2. The Corresponding mean absolute percentage error (MAPEs) for H2, H2S and SO2 compounds and all compounds including H2O and S2. MAPE Reaction Scheme 1 Reaction Scheme 2 Reaction Scheme 3 Leeds University Mechanism

H2 5.64% 4.22 % 6.43 % 18.20%

H2S 6.20% 10.60% 9.90 % 21.91%

SO2 4.50% 4.93% 3.60 % 13.31%


All compounds 7.90% 10.32% 7.97 % 31.70%

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Table 3. The Adjusted Arrhenius constants for the H2S+CH4 Oxidation system.

Reaction 1 Reaction 3 Reaction 4 Reaction 8 Reaction 9 Reaction 12 Reaction 16 Reaction 19 Reaction 22 Reaction 1 Reaction 3

k(mol-m-K-sec-kPa) E (J/ mol. K) Reaction Scheme 1 1.958 37.08 53.004 57.30 19.488 58.76 6.177 59.49 9.708 95.58 621.990 115.67 37.846 73.78 3.565×107 259.65 23.527 61.15 Reaction Scheme 2 1.744 65.62 31.478 48.24 22 ACS Paragon Plus Environment

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Reaction 4 Reaction 8 Reaction 9 Reaction 12 Reaction 16 Reaction 20 Reaction 22

20.577 2.658 15.230 411.080 158.41 2.052×106 6.080

57.83 47.33 99.56 112.93 88.60 235.53 49.73

Table 4. The corresponding mean absolute percentage errors (MAPEs) of combustion products. MAPE

Reaction Scheme 1

H2 SO2 H2S

13.79% 5.38% 15.34 %

H2 SO2 H2S CH4 CO

7.45% 15.21 % 15.74% 6.16% 34.44%

Reaction Scheme 2 Leeds University Mechanism Pure H2S oxidation 13.56% 18.20% 6.29% 13.31% 18.40% 21.91% CH4+H2S mixtures Oxidation 11.00% 14.00% 18.23% 24.36% 16.36% 57.40% 6.11% 15.52% 14.89% 22.03% 23

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CS2

20.49%

Page 24 of 42

16.51%

-

Table 5. Specifications of industrial Claus reaction furnace. Streams information Molar Flow of Component (kmol/hr) Amin Acid Gas H2O 1.54 Ar 0.00 O2 0.00 N2 0.10 CH4 0.18 CO2 6.15 H2S 51.92 32.2 Temperature (℃) P (kPa) 183.8 Furnace Specification Furnace Residence time (sec) 2.1


Air 2.06 1.03 23.04 85.89 0.00 0.04 0.00 21.1 99.9

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Table 6. Product compositions for industrial Claus reaction furnace predicted from the detailed reaction mechanism and the global reaction scheme. Mole Percent (%) Global reaction scheme Leeds University Mechanism Experiment

H2

H2S

SO2

H2O

S2

3.38 8.79 2.21

3.57 13.35 3.64

3.11 8.53 1.87

25.12 9.90 26.04

11.17 3.13 11.97


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1

0.9

0.8

0.7 H2S mole fraction

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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0.6 Experiment (Residence time=0.4−0.7 s) Model (Residence time=0.4−0.7 s) Experimental (Residence time=0.2−0.3 s) Model (Residence time=0.2−0.3 s)

0.5

0.4

0.3

0.2

0.1 800

850

900

950

1000

1050

1100

1150

1200

1250

T(oC)

Figure 1.The experimental (circle for residence time= 0.2-0.3 sec and diamond for residence time=0.4-0.7 sec) and the calculated (dashed line for residence time= 0.2-0.3 sec and solid line for residence time=0.40.7 sec) H2S mole fraction for H2S decomposition as a function of temperature at different residence times


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1.6 R2=0.96 1.4

1.2 Experimental Data (mole %)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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HS 2

1

H2 SO2

0.8

0.6

0.4

0.2 0.2

0.4

0.6

0.8 Model Prediction (mole %)

1

1.2

1.4

Figure 2. Parity plot for H2S oxidation system (circle for SO2, upward triangle for H2S and square for H2)


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1.3 Experimental Data Reaction Scheme 1 Reaction Scheme 2 Reaction Scheme 3

1.2

1.1

H2 Mole Percent

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1

0.9

0.8

0.7

0.6

0.5 1000

1100

1200

1000

1100 T(oC)

1200

1000

1100

1200

Figure 3. A comparison between the experimentally measured H2 mole percent (circle marker)and the calculated H2 mole percent (solid line for reaction scheme 1, dashed line for reaction scheme 2 and dotted line for reaction scheme 3) for three feeds including 2.45 % mole H2S+(1.0-1.5) % mole O2 and balance nitrogen.


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1.1

1

Experimental Data Reaction Scheme 1 Reaction Scheme 2 Reaction Scheme 3

0.9

SO2 mole Percent

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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0.8

0.7

0.6

0.5

0.4 1000

1100

1200

1000

1100 o T( C)

1200

1000

1100

1200

Figure 4. A comparison between the experimentally (circle marker) measured SO2 mole percent and the calculated SO2 mole percent (solid line for reaction Scheme 1, dashed line for reaction scheme 2 and dotted line for reaction scheme 3) for three feeds including 2.45 % mole H2S+(1.0-1.5) % mole O2 and balance nitrogen.


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1.6 Experimental Data Reaction Scheme 1 Reaction Scheme 2 Reaction Scheme 3

1.4

1.2

H2S mole Percent

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1

0.8

0.6

0.4

0.2 1000

1100

1200

1000

1100 T(oC)

1200

1000

1100

1200

Figure 5. A comparison between the experimentally (circle marker) measured H2S mole percent and the calculated H2S mole percent (solid line for reaction scheme 1, dashed line for reaction scheme 2 and dotted line for reaction scheme 3) for three feeds including 2.45 % mole H2S+(1.0-1.5) % mole O2 and balance nitrogen.


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2.5 R2=0.98 2

Experimental Data (mole%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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HS

1.5

2

CH4 H2 SO2

1

CO CO2 C2H4 CS

0.5

0

2

0

0.5

1 1.5 Model Prediction(mole %)

2

2.5

Figure 6. Parity plot for H2S/CH4 oxidation system (square for H2S, diamond for CH4, Five-pointed star for H2, Right-pointing triangle for SO2, circle for CO, point for CO2, plus sign for C2H4 and upward triangle for CS2,).


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2.5 Reaction Scheme1 Reaction Scheme2 Experimental

2.4 2.3 2.2 2.1 2

Feed: 2.45%mol CH4+2.45%H2S +1% mol O 2

H2 Mole Percent

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1.9 Feed: 2.45%mol CH4+2.45%H2S +1.5% mol O2

1.8 1.7 1.6 1.5 1.4 1.3 1.2 1.1 1 1000

1050

1100

1150

1200

1000

1050

1100

1150

1200

T(oC)

Figure 7. The measured mole percent of H2 (circle marker) and the calculated H2 mole percent (solid line for reaction scheme 1 and dashed line for reaction scheme 2) as a function of temperature for three feeds including 2.45% mole CH4+2.45% mole H2S+ (1-1.5)%mole O2 in balance nitrogen.


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1 Reaction Scheme1 Reaction Scheme2 Experimental

0.9

0.8 Feed: 2.45%mol CH4+2.45%H2S+1.5% mol O2 H2S Mole Percent

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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0.7

0.6

0.5

Feed: 2.45%mol CH4+2.45%H2S+1% mol O2

0.4

0.3

0.2 1000

1050

1100

1150

1200

1000

1050

1100

1150

1200

T(oC)

Figure 8. The measured mole percent of H2S (circle marker) and the calculated H2S mole percent (solid line for reaction scheme 1 and dashed line for reaction scheme 2) as a function of temperature for three feeds including 2.45% mole CH4+2.45% mole H2S+ (1-1.5)%mole O2 in balance nitrogen.


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1 Reaction Scheme1 Reaction Scheme2 Experimental

0.9

0.8

SO2 Mole Percent

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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0.7

0.6

Feed: 2.45%mol CH4+2.45%H2S +1% mol O2

0.5 Feed: 2.45%mol CH +2.45%H S 4 2 +1.5% mol O2 0.4

0.3

0.2 1000

1050

1100

1150

1200

1000

1050

1100

1150

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T(oC)

Figure 9. The measured mole percent of SO2 (circle marker) and the calculated SO2 mole percent (solid line for reaction scheme 1 and dashed line for reaction scheme 2) as a function of temperature for three feeds including 2.45% mole CH4+2.45% mole H2S+ (1-1.5)%mole O2 in balance nitrogen.


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2.4 2.3

Reaction Scheme1 Reaction Scheme2 Experimental

Feed: 2.45%mol CH4+2.45%H2S+1.5% mol O 2

2.2 2.1 CH4 Mole Percent

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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2 1.9 1.8 1.7 1.6


1.5 1.4 1000

1050

1100

1150

1200

1000

1050

1100

1150

1200

T(oC)

Figure 10. The measured mole percent of CH4 (circle marker) and the calculated CH4 mole percent (solid line for reaction scheme 1 and dashed line for reaction scheme 2) as a function of temperature for three feeds including 2.45% mole CH4+2.45% mole H2S+ (1-1.5)%mole O2 in balance nitrogen.


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0.55 0.5 0.45


Feed: 2.45%mol CH4+2.45%H2S +1.5% mol O2

0.4 0.35

2

CS Mole Percent

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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0.3 0.25 0.2 0.15 0.1 1000

1050

1100

1150

1200

1000

1050

1100

1150

1200

T(oC)

Figure 11. The measured mole percent of CS2 (circle marker) and the calculated CS2 mole percent (solid line for reaction scheme 1 and dashed line for reaction scheme 2) as a function of temperature for three feeds including 2.45% mole CH4+2.45% mole H2S+ (1-1.5)%mole O2 in balance nitrogen.


Page 37 of 42


0.2 0.18

Feed: 2.45%mol CH4+2.45%H2S +1.5% mol O2

0.16 CO Mole Percent

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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0.14 0.12


0.1 0.08 0.06 0.04 0.02 1000

1050

1100

1150

1200

1000

1050

1100

1150

1200

T(oC)

Figure 12. The measured mole percent of CO (circle marker) and the calculated CO mole percent (solid line for reaction scheme 1 and dashed line for reaction scheme 2) as a function of temperature for three feeds including 2.45% mole CH4+2.45% mole H2S+ (1-1.5)%mole O2 in balance nitrogen.


Energy & Fuels


0.045 0.04 0.035

Feed: 2.45%mol CH4+2.45%H2S+1.5% mol O2

0.03 0.025


2

CO Mole Percent

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 38 of 42

0.02 0.015 0.01 0.005 0 1000

1050

1100

1150

1200

1000

1050

1100

1150

1200

T(oC)

Figure 13. The measured mole percent of CO2 (circle marker) and the calculated CO2 mole percent (solid line for reaction scheme 1 and dashed line for reaction scheme 2) as a function of temperature for three feeds including 2.45% mole CH4+2.45% mole H2S+ (1-1.5)%mole O2 in balance nitrogen.


Page 39 of 42

0.12 Reaction Scheme1 Reaction Scheme2 Experimental 0.1

0.08

Feed: 2.45%mol CH4+2.45%H2S +1% mol O 2

0.06 Feed: 2.45%mol CH4+2.45%H2S +1.5 % mol O

2 4

C H Mole Percent

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

2

0.04

0.02

0 1000

1050

1100

1150

1200

1000

1050

1100

1150

1200

T(oC)

Figure 14. The measured mole percent of C2H4 (circle marker) and the calculated C2H4 mole percent (solid line for reaction scheme 1 and dashed line for reaction scheme 2) as a function of temperature for three feeds including 2.45% mole CH4+2.45% mole H2S+ (1-1.5)%mole O2 in balance nitrogen.


Energy & Fuels

0.03 SH+O HSO+O 2

S+O SO+O 2

0.02

2SH S2+H2 S2+H+MHS2+M SO+O2SO2+O

0.01 Sensitivity Coefficient

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 40 of 42

SH+O2SO+OH 0

−0.01

−0.02

−0.03

0

50

100

150

Reactor Length (cm)

Figure 15. Sensitivity Coefficients for rate-determining reactions (Base condition: 2.45 mole % CH4+2.45 mole % H2S+1 mole %O2 in balance nitrogen, 1000℃).


Page 41 of 42

35 HS 2

30

SO Mole percent (%)

2

25

S2

20

CO2

15

H2S exp SO exp 2

10

S exp 2

5

CO exp 2

0 Reaction Furnace Temperature (K)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

0

0.5

1 1.5 Residence time (sec)

2

2.5

2000

1500 Calculated Temperature (K) Experimental Temperature (K)

1000

500

0

0.5

1 1.5 Residence Time (sec)

2

2.5

Figure 16. Product compositions (up) and temperature (down) profiles versus residence time for industrial Claus reaction furnace. The experiments were represented by markers and the model calculations by lines.


Energy & Fuels

35 H2S from the Leeds detailed mechanism H2S from the global reaction scheme 30

H S exp 2

H2 from the Leeds detailed mechanism H from the global reaction scheme 2

25

Mole Percent (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 42 of 42

H2 exp

20

15

10

5

0

0

0.5

1 Residence time (sec)

1.5

2

Figure 17. H2S and H2 compositions predicted from the Leeds detailed mechanism and the global reaction scheme versus residence time for industrial Claus reaction furnace. The experiments were represented by markers and the model calculations by lines.


Global Reaction Scheme for Partial Oxidation of Pure H2S and H2S +

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