Hydrogen Sulfide Combustion Research Articles

Effect of carbon dioxide on oxy-fuel combustion of hydrogen sulfide: An experimental and kinetic modeling

CO2 is an important component in the acid gas and it is necessary to study the effect of CO2 presence on the oxy-fuel combustion of H2S with particular focus on the formation of carbonyl sulfide (COS). The oxy-fuel combustion of acid gas was conducted in a coaxial jet double channel burner. The distribution of flame temperature and products under stoichiometric condition along axial (R = 0.0) and radial at about 3.0 mm (R = 0.75) were analyzed, respectively. The Chemkin-Pro software was used to analyze the rate of production (ROP) for gas products and the reaction pathway of acid gas combustion. Both experimental and simulation results showed that acid gas combustion experienced the H2S chemical decomposition, H2S oxidation and accompanied by H2 oxidation. The CO2 presence reduced the peak flame temperature and triggered the formation of COS in the flame area. COS formation at R = 0.0 was mainly through the reaction of CO2 and CO with sulfur species, whereas at R = 0.75 it was through the reaction of CO with sulfur species. The ROP results indicated that H2 was mainly from H2O decomposition in the H2S oxidation stage, and COS was formed by the reaction of CO2 with H2S. ROP and other detailed analysis further revealed the role of H, OH and SH radicals in each stage of H2S conversion. This study revealed the COS formation mechanisms with CO2 presence in the oxy-fuel combustion of H2S and could offer important insights for pollutant control.

СІРКООРГАНІЧНІ СПОЛУКИ КОКСОВОГО ГАЗУ ТА ЇХ ВКЛАД У ВИКИДИ ДІОКСИДУ СІРКИ З ДИМОВИХ ТРУБ КОКСОВИХ БАТАРЕЙ

The article touches upon the problem of cleaning of the coke oven gas from sulfur compounds, which is relevant in connection with the requirements for reducing of the sulfur dioxide emissions into the atmosphere and ensuring of the environmental safety of production in general. At present, the sulfur dioxide emissions from coke-chemical plants account for about 20 % of the total emissions of pollutants from coke ovens and are calculated from the concentration of hydrogen sulfide in coke oven gas after its purification before feeding to coke oven batteries heating systems. However, in addition to hydrogen sulfide, coke oven gas also contains organosulfur compounds such as carbon disulfide (CS2), carbon oxysulfide (COS), thiophene (C4H4S), mercaptans, etc. The authors of the article carried out a study to determine the content of organic sulfur compounds in the original and purified coke oven gas, as well as the contribution of these substances to sulfur dioxide emissions from the smokestacs of coke oven batteries. The calculation has been performed of the additional volume of sulfur dioxide, which is formed due to the combustion of organosulfur compounds of coke oven gas during its combustion in the heating system of coke ovens. It has been found that under the condition of complete conversion of organic sulfur compounds into sulfur dioxide during the combustion of coke oven gas in the heating system of coke ovens, the concentration of sulfur dioxide in flue gases can be approximately 25.0-35.0 mg/m3 (in recount on 5 % oxygen content in flue gases). It has been also shown that the share of emissions of the sulfur dioxide formed as a result of the combustion of hydrogen sulfide in coke oven gas is 90-95 %, and that formed as a result of combustion of the organic sulfur compounds is 5-10 %, even if they are completely transformed into the sulfur dioxide. It has been concluded that it is legitimate to calculate the volume of sulfur dioxide emissions based on the concentration of hydrogen sulfide in purified coke oven gas, supplied as an energy carrier to the heating system of coke ovens.

Shock-tube water time-histories and ignition delay time measurements for H2S near atmospheric pressure

Hydrogen sulfide combustion has been of interest in recent years due to its presence in coal-derived syngas and in sour gas. However, there are limited data available for the calibration of chemical kinetics models of high-temperature H2S oxidation. Ignition delay times and laser-absorption water time histories were therefore measured in two different shock tubes around atmospheric pressure over a range of temperatures from 1445 to 2210K for H2S-O2 mixtures diluted in 98% Ar. While modern H2S models from the literature predicted the ignition delay times with fair accuracy, the water profiles were initially very poorly predicted with the same kinetic mechanisms. A model analysis showed that the reaction R62, SH+HO2 ⇆ H2S+O2 (in reverse), was chiefly responsible for these poor predictions. It was possible to obtain better water predictions when the rate for R62 was divided by 10. A tentative model is proposed herein, based on this assumption for R62, and good predictions were obtained for both the ignition delay times and water profiles, as well as for former high-pressure shock-tube data with H2-H2S mixtures. The present study shows that more accurate rates for the reactions R62 (SH+HO2 ⇆ H2S+O2), R75 (SH+O2 ⇆ HSO+O), and R46 (SH+SH (+M) ⇆ HSSH (+M)) would be needed to better predict H2S combustion chemistry.

Experimental Study of Gas Explosions in Hydrogen Sulfide-Natural Gas-Air Mixtures

An experimental study of turbulent combustion of hydrogen sulfide (H2S) and natural gas was performed to provide reference data for verification of CFD codes and direct comparison. Hydrogen sulfide is present in most crude oil sources, and the explosion behaviour of pure H2S and mixtures with natural gas is important to address. The explosion behaviour was studied in a four-meter-long square pipe. The first two meters of the pipe had obstacles while the rest was smooth. Pressure transducers were used to measure the combustion in the pipe. The pure H2S gave slightly lower explosion pressure than pure natural gas for lean-to-stoichiometric mixtures. The rich H2S gave higher pressure than natural gas. Mixtures of H2S and natural gas were also studied and pressure spikes were observed when 5% and 10% H2S were added to natural gas and also when 5% and 10% natural gas were added to H2S. The addition of 5% H2S to natural gas resulted in higher pressure than pure H2S and pure natural gas. The 5% mixture gave much faster combustion than pure natural gas under fuel rich conditions.

Investigation of sulfur chemistry with acid gas addition in hydrogen/air flames

Investigations on the effect of acid gas (H2S and CO2) addition in hydrogen/air flame are presented. The specific equivalence ratios examined include Claus conditions (Φ=3.0) as well as stoichiometric conditions (Φ=1.0) and fuel-lean conditions (Φ=0.5). Two different acid gas compositions of 100% H2S, and 50% H2S/50% CO2 are reported. Addition of pure hydrogen sulfide acid gas deteriorated the rate of hydrogen oxidation in the hydrogen/air flame. Combustion of hydrogen sulfide alone formed sulfur dioxide rather than more favorable elemental sulfur. In contrast combustion of 50% H2S/50% CO2 acid gas stream produced faster decomposition/production of H2S, SO2, and H2. Presence of carbon monoxide was a distinct mark on the release of oxygen from CO2 into the reaction pool. The presence of carbon monoxide triggered the formation of other sulfurous–carbonaceous compounds, such as COS and CS2.

Role of toluene in hydrogen sulfide combustion under Claus condition

Experimental investigations on the effect of different amounts of toluene addition to H2S combustion in oxygen under Claus condition (Φ=3) are presented. Three toluene concentrations of 0.5%, 1% and 5% in H2S are presented and compared with the baseline case of 100% H2S oxygen combustion. Temperature data showed that addition of toluene to H2S gas stream increases the flame temperature because of large heating value associated with toluene. Addition of toluene resulted in the production of H2, which increased with increase in the amounts of toluene addition. Furthermore, increased addition of toluene concentration increased the asymptotic minimum value of hydrogen sulfide due to oxidation competition between the formed H2 and H2S. The results also showed that the presence of CO triggers the formation of COS with toluene addition due to reaction of CO with SO2. The results showed that SO2 mole fraction increased to a maximum value then decayed with distance along the reactor. Addition of toluene increased the rate of SO2 decay. These results have direct impact on sulfur capture in the Claus reactor and its performance.

Effect of reaction parameters on the quality of captured sulfur in Claus process

Quality of sulfur deposits collected from hydrogen sulfide combustion has been examined. Experimental conditions representing selected practical systems have been investigated. Combustion of hydrogen sulfide was allowed to occur under the different conditions with sulfur deposits collected for analysis. Experimental conditions represented effect of equivalence ratio of rich (Claus) conditions and stoichiometric conditions; effect of contaminants, other than H2S, in the acid gas stream; combustion of H2S with hydrocarbon fuels (methane and propane). Sulfur deposits from H2S combustion under various conditions were captured and analyzed using X-ray powder diffraction and laser induced breakdown spectroscopy (LIBS) diagnostics. X-ray powder diffraction was used to determine the type of deposited sulfur allotrope, while LIBS was used to identify the elemental analysis of deposited sulfur.

Hydrogen Sulfide Combustion: Relevant Issues under Claus Furnace Conditions

The major chemical paths for the combustion of hydrogen sulfide under conditions typical of the Claus furnace (i.e., fuel-rich conditions) are presented. The manuscript begins with a brief survey of recently published research that involves sulfur chemistry in high-temperature environments, including the results of sensitivity analysis for some of the systems involved. Recommended values for the heats of formation of sulfur species are included. The reaction mechanism that is presented consists of more than 150 reactions. Issues such as the formation and destruction of COS and CS2 are presented: new chemical paths for the formation of COS and CS2 (not involving elementary carbon) are illustrated, on the basis of sound thermochemical and kinetic considerations. The formation of COS and CS2 is of great importance in the design of sulfur plants in industry. Possible reactions of COS and CS2 with SO2, and CO2 with H2S and sulfur species, also are discussed, prompted by experimental observations in flow reactors. The mechanism can explain the formation of hydrogen, which also is an important issue in sulfur plant design and associated tail gas units. Species such as H2S2 seem to have an important role during the combustion of hydrogen sulfide. Higher-molecular-weight linear H2Sx species are also considered, and it is concluded that their role is possibly minor. The chemical steps leading to the formation of Sx species by molecular growth are presented. The ring structure of some of the Sx species is discussed, as well as intramolecular ring conversions for S8, S7, S6, and S5. The possibility of H,OH radical recombination catalyzed by oxygenated sulfur species may explain the delayed oxidation of hydrocarbon species in the Claus furnace that has been observed in previous experiments by other authors. This could be an important design consideration for Claus plants to minimize the coking of catalyst beds in the process. The most likely chemical paths for the radical quench are presented and based on past observations. Controversy persists in regard to the actual mechanism and the rate constants of the reactions involved in the radical recombination, as well as the thermochemistry of some of the oxygenated sulfur species involved. More studies are needed to resolve the issues. The study also reveals the lack of high-temperature data for the kinetic coefficients of some of the reactions. Much rate data are based on atmospheric studies, rather than high-temperature oxidation. Similarly, better thermodynamic data are lacking for some important oxygenated sulfur species in the mechanism. This is most important for temperature- and pressure-dependent reactions, such as unimolecular reactions and chemically activated reactions. Studies that involve hydrogen sulfide flames under fuel-rich conditions are lacking. Most of the studies have been limited to the impact of sulfur species on the formation of other species, such as CO and NOx, in flames or reactors.

Hydrogen production in ultra-rich filtration combustion of methane and hydrogen sulfide

Filtration combustion waves formed in an inert porous media were analyzed comparatively for methane (CH 4)/air and diluted hydrogen sulfide (20% H 2 S+80% N 2)/ air mixtures. Temperature, velocity, and chemical products of the combustion waves were studied experimentally in the range of equivalence ratios ( ϕ) from 1 to 2.5 for methane and from 1 to 5.5 for hydrogen sulfide, at a filtration velocity of 12 cm/ s . The practical goal of the study in the rich and ultra-rich region was to explore the extent of conversion of these reactants into commercially viable products such as hydrogen (H 2), syngas (H 2+CO), and sulfur (S 2). For both methane and hydrogen sulfide combustion, upstream (underadiabatic) propagation corresponds to the range of equivalence ratios from stoichiometry to 1.7, and downstream (superadiabatic) wave propagation was observed for ultrarich ( ϕ⩾1.7) mixtures. The products of methane partial oxidation, dominant for ultra-rich waves, were: H 2, CO, and C 2 hydrocarbons where up to 60% of the methane was converted to CO and H 2. Similar observation for H 2S partial oxidation products reveals a maximum conversion rate of 20% to H 2 and 50% for S 2.

Investigation of low-pressure flames of a number of compounds containing sulfur by the ESR method

Low-pressure flames of H 2 S, CS 2 , sulfur and COS vapors have been studied by the ESR method. High concentrations of atomic hydrogen, oxygen, and SO and OH radicals were discovered in the hydrogen sulfide flame. It has been established that the combustion of hydrogen sulfide proceeds in two steps. Initially hydrogen sulfide is, oxidized to the intermediate compounds SO and H 2 . After the consumption of H 2 S and SO, which are inhibitors for the hydrogen oxidation, combustion of H 2 starts, accompanied by the formation of OH radicals and H and O atoms. High concentrations of atomic oxygen and SO radicals were discovered in the rarefied flames of CS 2 mixtures with O 2 rich in oxygen, α=(O 2 )/(CS 2 ) ⋍2.5 It has been shown that, near the point α-2.5, the concentration of atoms is the greatest, while that of SO radicals is the least. It has been established that such a behavior of O atoms and SO radicals is connected with the reaction O+COS=CO+SO. SO radicals and very high concentrations of O atoms were found in the low-pressure flames of sulfur vapor amounting to 30% of the initial O 2 . A considerable amount of O atoms and SO radicals were detected in the flame of COS mixtures with O 2 .

Detection of free hydrogen and oxygen atoms in a rarefied flame of hydrogen sulfide with oxygen by the method of electron paramagnetic resonance

1. The cold flame of H2S + O2 was investigated by the EPR method for the first time. 2. At temperatures of 350–450° and pressures of 5–15 mm Hg, substantial concentrations (1014–1015 particles per cm3) of atomic oxygen (at a relative H2S content from 10 to 15%) and atomic hydrogen (H2S from 15 to 40%) were obtained. 3. The results obtained indicate the important role of O and H atoms in the mechanism of the combustion of hydrogen sulfide with oxygen.