Experimental research on two-stage desulfurization technology in traveling grate boilers

In order to promote the desulfurization efficiency of calcium-based sorbents during coal combustion in traveling grate boilers, the influences on sulfur removal of the thermal conditions and the sorbents were discussed in this paper. It was found that the SO₂ concentration first rises, then declines along the traveling grate and reaches the peak near the midpoint of the grate. The fluctuation of the SO₂ concentration over time in the flue gas is mainly affected by the flame temperature. When the particle size of the sorbents decreases from 75 to 0.1 μm, the sulfur removal efficiency will increase slightly. A reasonable Ca/S molar ratio is about 2 when sorbents are blended with the coal on the grate and its further increase has little benefit to desulfurization. A new, so-called two-stage desulfurization process — sulfur capture firstly in the coal bed and secondly in the combustion gas — is suggested as it can greatly promote the sulfur removal efficiency up to 70∼80%. By X-ray powder diffraction analysis, some thermal stable phases were identified in the sulfur retention cinder obtained from the on-grate process.     

Ultrasonic and Microwave Desulfurization of Coal in Tetrachloroethylene

Abstract

The extractive desulfurization of four high sulfur coals from China were promoted with ultrasonic and microwave in tetrachloroethylene organic solvents. It was shown that the joint promotion with ultrasonic and microwave had an active effect on extractive desulfurization. The rate of desulfurization increased with the increase of time in ultrasonic field as well as with the power of ultrasonic, but declined with the increase of the particle size of coal. The rate of desulfurization was not identical for different coal, which was perhaps related to the existed forms of organic sulfur in coal.     

Agglomeration of Makarwal coal using soybean oil as agglomerant

The study was carried out for beneficiation of Makarwal coal using soybean oil as agglomerant. The effect of six parameters – pH, mesh size of coal particles, slurry ratio, stirring speed, soybean oil concentration, and time of agglomeration – was investigated to reduce ash and sulfur from Makarwal coal and to enhance the gross calorific value. In the cleaned product obtained after the agglomeration process, the gross calorific value was increased from 4900 to 7115 Kcal/kg. The ash of agglomerates was reduced from 30% to 7.5% and sulfur was reduced from 5.4% to 2.0% The optimum operating conditions were concentration of soybean oil 10 mL, pH 9, stirring speed 2800 rpm, mesh size 200, coal to water ratio of 15:450 (W/V), and time of agglomeration 20 min. Significant reduction in ash and sulfur showed the effectiveness for agglomeration of Makarwal coal using soybean oil as the agglomerant. The final product thus obtained may be used efficiently in various energy recovery schemes.     

Oxidative Desulfurization of Tufanbeyli Coal by Hydrogen Peroxide Solution

Abstract

It is becoming popular to use fossil fuels efficiently since the necessary energy is mostly supplied from fossil fuels. Altough there are high lignite reservoirs, high sulfur content limits the efficient use of them. In this article, we aimed to convert combustible sulfur in coal to non-combustible sulfate form in the ash by oxidizing it with a hydrogen peroxide solution. The parameters affecting the sulfur conversion were determined to be: hydrogen peroxide concentration, reaction time, mean particle size at constant room temperature and shaking rate. The maximum desulfurization efficiency reached was 74% of the original combustible sulfur with 15% (w/w) hydrogen peroxide solution, 12 hours of reaction time, and 0.25 mm mean particle size.     

Oxidative Desulfurization of Aşkale Coal by Nitric Acid Solution

Abstract

Efficient use of fossil fuels is of utmost importance in a world that depends on these for the greatest part of its energy needs. Although lignite is a widely used fossil fuel, its sulfur content limits its consumption. This study aims to capture combustible sulfur in the ash by oxidizing it with solution of nitric acid solution. Thus, the combustible sulfur in the coal was converted to sulfate form in the ash. Parameters affecting the conversion of sulfur were determined to be nitric acid concentration, reaction time and mean particle size at constant (near room) temperature and shaking rate. The maximum desulfurization efficiency reached was 38.7% of the original combustible sulfur with 0.3 M nitric acid solution, 16 h of reaction time and 0.1 mm mean particle size.     

Field measurements on the generation and emission characteristics of PM2.5 generated by industrial layer burning boilers

Particle size distributions, concentrations, morphological characteristics, and elemental compositions of PM_2.5 from 15 industrial layer-burning boilers were determined experimentally in air, before and after dust removal and after desulfurization processes. The morphological characteristics and elemental compositions were analyzed using scanning electron microscopy and X-ray fluorescence, respectively. The concentrations and particle size distributions of PM_2.5 were monitored and sampled using an electrostatic low pressure impactor. We found that before and after dust removal, the number concentration distributions of PM_2.5 displayed obvious unimodal distributions, with peaks in the range 0.07–0.38 μm. In both instances, the particle concentrations of PM_2.5 depended mainly on submicron particles (less than 1 μm in diameter), formed by gasification-condensation mechanisms. The concentration of the particles larger than 0.38 μm reflected aggregation of carbon black particles; this fraction tended to gradually decrease in concentration with increasing size. Total number and mass removal efficiencies of PM_2.5 indicate that fabric filters were superior to mechanical precipitators, although mechanical precipitators were superior to integrated dust removal and desulfurization devices. Typically, the number concentration increased after desulfurization, suggesting that better demisters need to be implemented in these systems. The PM_2.5 generated by industrial layer-burning boilers mainly comprised soot aggregates. However, the mass percentages of S, Si, K, and Al in PM_2.5 decreased after dust removal but increased after the desulfurization. In contrast, the mass percentage of Na in PM_2.5 increased after both dust removal and desulfurization processes, while the mass percentages of Ca and Fe in PM_2.5 decreased after dust removal but remained constant after desulfurization. These data clearly show that the composition of PM_2.5 changes as dust and sulfur are removed by air pollution control devices. Data generated in this study are useful for selecting the most effective strategy for reducing PM_2.5 emitted by industrial layer-burning boilers of various sizes.     

Effects of temperature and limestone on sulfur release behaviors during fluidized bed gasification

Gaseous sulfur is released during fluidized bed coal gasification, and control the yield of gaseous sulfur or the conversion between gaseous organic sulfur and inorganic sulfur at source is necessary, because it can economically satisfy the requirements of industrial production and protect the environments. In this study, sulfur release behaviors of a middle-sulfur coal called Guizhou coal were quantitatively determined through controlled experiments in a lab-scale fluidized bed during oxygen rich-steam gasification. The measured gaseous sulfur species were H₂S, SO₂, COS and CS₂. The effects of temperature (850^OC-950^OC) and limestone (Ca/S = 2) on the sulfur release behaviors were investigated. Among the above four gaseous sulfur, the yield of H₂S is the highest, followed by COS, while only less than 1.5% of sulfur in coal is released as SO₂ and CS₂. With the increase in temperature, the yield of H₂S increases while that of SO₂ decreases, and the change of COS yield and CS₂ yield is not obvious. The molar ratio of H₂S/COS increases with increasing temperature, which is qualitatively matched by thermodynamic analysis. The addition of limestone reduces the released sulfur but not change the distribution of gaseous sulfur forms. Meanwhile, the molar ratio of H₂S/COS increases after adding limestone, while the trend with temperature of H₂S/COS does not change. The removal rate of H₂S is between 23% and 28%, which increases with temperature. The distributions of sulfur in bottom char and fly ash are similar. The main sulfur species in the bottom char is organic sulfur, and thiophene dominates the organic sulfur. The increase of temperature and the addition of limestone will both promote the increase of inorganic sulfur content, and the decrease of organic sulfur content.     

Cleaning of Pakistani low-grade coal by agglomeration

This study was carried out for the beneficiation of Dukki (Pakistani) coal using agglomeration technique. The effect of six parameters, particle size, solid to liquid ratio, xylene concentration, agitation speed, agitation time, and pH, was investigated to improve the quality of coal in terms of reduced ash and sulfur content. The clean coal obtained at optimum parameters was found to have 69.25 and 26.6% reduction in ash and sulfur, respectively. The gross calorific value (GCV) increased to 6,377 kcal/kg compared with 5,300 kcal/kg in the original sample. A maximum reduction in ash and sulfur contents was achieved by the following input parameters: particle size, 100 mesh (150 µm); solid to liquid ratio, 20:80 (w/v); xylene dose, 6.8 mL; agitation time, 10 min; pH 7; and stirring speed, 2,520 rpm. Significant reduction in ash (%) and sulfur (%) showed the effectiveness for agglomeration of Dukki coal using xylene as agglomerant. The final product thus obtained may be used efficiently in various energy recovery schemes.     

Combustion behavior of KOH desulphurized coals assessed by TGA-DTG

This work presents the results obtained from the experimental study on the effects of KOH treatment and its combustion behavior of high sulfur Indian coal. Coal was treated with 5–20% KOH (v/v) concentration for 6–24 h reaction time to identify the effects of KOH treatment on coal properties. Experimental results showed that upto 36.79% of total sulfur can be removed from coal with 20% KOH concentration and 24 h contact time at atmospheric condition. However, gross calorific value of coal decreased from 6800 to 6084 kcal/kg due to removal of combustibles from coal. Combustion characteristics of treated coal were assessed by Thermo-gravimetric analysis/ Differential thermo-gravimetric (TGA/DTG analysis). Further various combustion kinetic parameters like ignition temperature, peak temperature, burnout temperature, activation energy (E), and pre-exponential factor (A) are estimated. Experimental results show that the ignition temperature of coal decreased from 321°C to 252°C, peak temperature decreased from 459°C to 409°C due to changes in the coal matrix after desulfurization. The activation energy of coal calculated decreased from 79 to 45 kJ/mol due to desulfurization using 20% KOH concentration and 24 h reaction time.     

高温燃烧两段脱硫技术的试验研究

针对链条炉内钙基添加剂燃烧脱硫率低的难题,研究了链条炉床温和烟气成分的动态变化,在研究添加剂粒径、添加量和添加方式对各种钙基添加剂脱硫率影响的基础上,提出了两段燃烧脱硫技术的解决方案,以实现煤层内和燃烧室间同时脱硫的目的,从时间和空间两个方面克服了 简单与入炉散煤预混或炉内直接喷钙脱硫方式的根本缺陷,使链条炉燃烧胶硫效率提高了70%～80%。图3表4参7     

Bacterial desulphurization of low-rank coal: A case study of Eocene Lignite of Western Rajasthan,India

High sulfur lignite samples collected from Giral mine was subjected to desulfurization using bacteria Burkholderia sp. GR 8–02 isolated from native lignite. A removal of 50.69% of total Sulfur (S_t) has been observed. The reduction in hydrogen and ash content was found up to 2.92% and 14.78%, respectively. In addition, relative carbon (up to 12.81%) and nitrogen (up to 34.52%) has also been increased. An increase in the relative concentration of volatile matter and fixed carbon (up to 19.47% & 3.29%) has been detected. In addition, the desulfurization of high sulfur lignite with Burkholderia sp. GR 8–02 increased the calorific value from 5.24% to 20.74%.     

Adsorption of Sulfur Dioxide from Coal Combustion Gases on Natural Zeolite

In this study, better efficiency of SO₂ removal in flue gas from lignite coal combustion by adding of NZ in the gas phase was achieved. Natural zeolite was exposed to flue gas containing sulfur dioxide at varying conditions of relative humidity and temperature. It was found that the amount of sulfate on the zeolite increased with increasing relative humidity and temperature. The percents of adsorbed sulfur dioxide were 86, 74, 56, and 35, while the values of relative humidity (RH) were 75, 60, 45, and 30% for 40 minutes, respectively. The percents of adsorbed sulfur dioxide sharply increased within the first 40 min for the values of RH were 75 and 60, and after 40 min, slightly increased, then reached a plateau. In general, as increasing the RH increased the amount of sulfur dioxide adsorbed by natural zeolite. The amounts of adsorbed sulfur dioxide increased with exposure time. It increased and reached 30.2 mg/g for 40 min. After 40 min, it slightly increased and then reached a plateau. The NZ adsorbs 35.1 mg SO₂ per gram adsorbent with 75% RH at 298 K from a simulated coal combustion flue gas. The amounts of adsorbed sulfur dioxide increased with increasing temperature. The NZ adsorbs 71.5 mg SO₂ per gram adsorbent with 75% RH for 100 min exposure time from the flue gas mixture.     

Retention of SO2 Emission of Coal Combustion by Using Lime in Briquetting

In this study, the effect of lime on control of SO₂ emissions was investigated by briquetting of coal particles with various lime contents. The influence of the added lime was determined not only from the view of its contribution to environmental aspects but also in terms of effects on the thermal features and reaction kinetics of coal. The extent of improvement was determined by detailed sulfur analysis. Thermal qualification and reaction kinetics of the coal briquettes with varying lime contents were performed by evolved gas analysis and its complementing kinetic model based on Arrhenius principles. At the end of experiments, utilization of lime was seen to contribute considerably to desulfurization process. However, lime addition had an adverse effect both on the effectiveness of combustion and the liability of the coal briquettes to oxidize.     

Electrochemical hydrogenation of organic sulfides

Electrochemical reduction desulfurization is a low cost, environmental friendly technology which is capable of achieving a high degree of automation. Electrochemical coupling reactions of organic sulfur hydrogenation and water electrolysis on the C/Nafion electrodes were performed. The electrochemical desulfurization was determined by cyclic voltammetry (CV), bulk electrolysis with coulometry (BEC) and electrochemical impedance spectroscopy (EIS) techniques. Thiophene and benzyl mercaptan were used as model organic sulfur compounds. The results of cyclic voltammetry showed that the electrochemical hydrogenation reduction reaction of thiophene occurred at about ?0.35 V. The process included proceeding chemical reaction and electrochemical reaction. The currents generated from thiophene hydrogenation reactions increased with the reaction temperature and the H⁺ concentration of the electrolyte acidity of anode. Under the same reaction conditions, the desulfurization efficiency of benzyl mercaptan was significantly higher than that of thiophene. From the products of electrolytic reactions, the mechanisms of electrochemical hydrogenation of thiophene were proposed, consisting of two pathways: ring opening followed by hydrogenation and directly hydrogenation followed by ring opening. The proposed reaction mechanisms were consistent with the EIS results, indicating the predominant reactions were ring opening followed by hydrogenation. The reaction products and EIS results suggested that the reaction mechanisms of electrochemical hydrogenation of benzyl mercaptan were by breaking CS bond to form H₂S and toluene.     

Comparing product distribution and desulfurization during direct pyrolysis and hydropyrolysis of Longkou oil shale kerogen using reactive MD simulations

The product distribution and organic sulfur removal during direct pyrolysis and hydropyrolysis of oil shale kerogen were investigated via reactive molecular dynamics (RMD) simulations with reactive force field (ReaxFF). Two structural models for direct pyrolysis and hydropyrolysis of kerogen were constructed about kerogen extracted from Longkou oil shale to investigate the impact of H₂ at different temperatures on the product distribution and reaction processes of oil shale. The experimental results show that hydropyrolysis could increase light shale oil (the most important product in shale oil industry), and improve the removal rate of organic sulfur simultaneously. It was found that comparing to the direct pyrolysis, hydropyrolysis can provide more H free radicals to participate in the reaction and therefore promoting the pyrolytic reaction of kerogen. In addition, hydropyrolysis greatly promoted the desulfurization due to the contribution to the production of H₂O molecules, and the transfer of sulfur to the gas products requires the participation of H₂O molecules. This work is an intensive study on hydropyrolysis mechanism at different temperatures at the atomic level. These conclusions could be helpful for the clean utilization technology of oil shale industry.     

Hydrocarbon Desulfurization to Clean Fuels by Selective Oxidation Versus Conventional Hydrotreating

Abstract

Environmental concerns have driven the need to remove sulfur-containing compounds to an extremely low level for transportation fuels. Conventional hydrodesulfurization catalysts can be used to remove a significant portion of the sulfur from petroleum distillates for the blending of refinery transportation fuels. Removing the last traces of sulfur compounds where the sulfur atom is sterically hindered, as in multi-ring aromatic sulfur compounds, is a significant challenge. One recent area of innovation to remove sulfur from upgraded crude is oxidative desulfurization, a process that can operate under mild conditions and without the need for external H₂. In this article, the mechanism, process, and the new inventions of selectively oxidative desulfurization are reviewed.     

水煤浆与煤粉燃烧脱硫比较

以煤代油是能源工业的发展方向。作为新型代油燃料,水煤浆有广阔的应用前景。从硫析出特点、脱硫影响因素（温度、Ｃａ／Ｓ比）以及烟尘排放等方面,研究了水煤浆燃烧脱硫与煤粉燃烧脱硫的异同。试验结果表明水煤浆燃烧脱硫优于煤粉,是值得推广的脱硫技术。     

Biodesulfurization of Cayirhan Lignites

In this study, the lignite was improved oxidizing sulfur compounds by Thiobacillus thiooxidans and Thiobacillus ferrooxidans bacteria. Experiments in the batch reactors have been carried out 20% aqueous suspension of coal samples. Sugar beet molasses was used as the bacterial substrate. The maximum removal of combustible sulfur was obtained as 78.2% under the following conditions; addition 5% of T. thiooxidans and 5% T. ferrooxidans into coal suspension, 0.2 g molasses/g coal change, pH value of 3, at shaking rate of 70 rpm and at 40°C for 5 days.     

440t_h CFB锅炉掺烧石油焦二氧化硫排放特性研究

在440 t/h大型循环流化床锅炉上进行了燃烧不同比例煤和石油焦混合燃料时二氧化硫排放特性的试验研究。研究了燃烧不同比例的混合燃料、炉膛温度、过量空气系数和钙硫摩尔比对二氧化硫排放特性的影响。研究结果表明,过量空气系数和钙硫摩尔比的增加可以降低二氧化硫排放浓度。存在一个最佳脱硫温度,二氧化硫排放浓度最低,对于各种混合燃料最佳脱硫温度应在830～850℃之间。     

Characteristics and Reactivities of Solid Wastes Sorbent for Medium-temperature Flue Gas Desulfurization

Abstract

In this study, sorbent for flue gas desulfurization is prepared using metallurgical dusts (MD) abundant in iron oxides as the main active component, lime as promoter, and amylum as special additive. The reactivity of the sorbent is conducted in a quartz fixed-bed reactor within the medium temperature range of 300°C–750°C under heating and isothermal conditions, while the physical and chemical properties of the sorbent are measured using ICP-AAS, SEM, XRD, and so on. The experimental results indicate that with temperature increasing from 300°C to 750°C, breakthrough sulfur capacity of the sorbent increases from 0.0257 gS/gSorbent at 300°C to 0.1391 gS/gSorbent at 650°C, then decreases to 0.0836 gS/gSorbent at 750°C, and that the removal efficiency of SO₂ and breakthrough sulfur capacity of the sorbent depend on the chemical kinetics of Fe₂O₃ and CaO in the temperature range of lower than 600°C, but on the thermodynamic equilibrium of sulfuration of Fe₂O₃, the thermal stability of the Fe₂(SO₄)₃ and content of CaO in the range of higher than 650°C. Physical and chemical analyses of the fresh and reacted sorents further verify that the effective and dominating component of the sorbent is Fe₂O₃ within the temperature range of lower than 650°C, while is CaO in higher than 650°C.