Sulphur removal by pyrolysis of Turkish lignites

Modes of distribution of sulphur have been determined in eleven lignite samples from major reserves in Turkey. Total sulphur contents have been found to vary 0.91%–10.32% on dry basis. The lignites contain relatively high amounts of organic sulphur. Distributions of sulphur have been determined in chars from the pyrolysis of lignites at 440 °C. Reductions in combustible sulphur contents have been found to vary 15.7%–72.0%. No correlation has been found between the extent of desulphurization by pyrolysis and the relative amounts of forms of sulphur in the parent lignites.     

Biodesulphurization of Hungarian lignite and sub-bituminous coal

The annual SO₂ emission is approx. 0.6 million tons in Hungary because of the high amount of sulphur in the power plant coals. Since Hungary has signed the European Environmental Agreement, the high sulphur emission has to be gradually reduced. To overcome the acid rain problem, the biodesulphurization of Hungarian power plant coals has also been started in Hungary. The R&D programe of biodesulphurization has been launched in 1990. According to our findings the biodesulphurization process is a suitable tool for reducing the pyritic sulphur content in lignite and sub-bituminous coal.     

Auto-desulphurization of coal

The effect of atmospheric oxidation or weathering on different forms of sulphur in coal has been studied using a coal sample ground to <63 μm and kept exposed to the atmosphere for up to 228 days. Occasionally, samples were taken from the exposed coal for analysis of total-, sulphate-, pyritic- and organic sulphur. Significant amounts of total-, pyritic- and organic sulphur were reduced up to 106 days of exposure, resulting in a total sulphur content within the permissible limits of utilization. Thus, commercial desulphurization of coal may be possible by using the simple process of atmospheric weathering.     

Comparative performance of impregnated molybdenum-sulphur catalysts in hydrogenation of Spanish lignite

Hydrogenation of a Spanish lignite of 12% sulphur content was conducted using three molybdenum-containing catalysts impregnated into the lignite: ammonium tetrathiomolybdate, a sulphided ammonium heptamolybdate, and molybdenum disulphide. The conversions to liquids and hydrodesulphurization were investigated for a series of residence times and temperatures. At 275 °C, the ammonium salts provide no greater conversion or sulphur removal than obtained in the absence of catalyst, because these salts have not decomposed to an active catalyst at this temperature. However, lignite impregnated with molybdenum disulphide does experience greater conversion and desulphurization than lignite reacted without catalyst. At 325 °C, the lignite impregnated with the ammonium salts gives conversions and desulphurization substantially superior to that achieved with molybdenum disulphide or without catalyst. This is attributed to the superior dispersion that can be achieved by impregnation using a solution of a soluble salt rather than a slurry of the insoluble disulphide. The best conversions, liquid yield, and desulphurization are achieved using impregnated sulphided ammonium heptamolybdate.     

An experimental study into pyrite transformation during pyrolysis of Australian lignite samples

Transformation of pyrite in an Australian lignite during pyrolysis was studied using a thermogravimetric analyser (TGA) and a fixed-bed reactor. Samples of a lignite with high pyrite content, a pyrite-free lignite, acid-washed lignite, a pyrite mineral, and pyrite-free lignite blended with various amounts of the pyrite minerals were employed in the experimentation. It was shown that in nitrogen the pyrite mineral (S/Fe = 2) decomposes to troilite (S/Fe = 1) at ca. 1200 K and above this temperature, some of the troilite further decomposes to form elemental iron (S/Fe < 1). However, when blended with the demineralised lignite, the pyrite mineral can be completely decomposed to troilite at 873 K as confirmed by FTIR, SEM-EDS and XRD analyses on the resulting chars. During the TGA pyrolysis of the pyrite-lignite blends, two DTG peaks were observed, indicating two major decomposition events occurring. The first DTG peak was related to the devolatilisation of the lignite, while the second peak was attributed to the pyrite decomposition. Using a mass spectroscopy coupled with the TGA, it was revealed that hydrogen sulphide and a small quantity of sulphur dioxide were released during the pyrolysis of the pyrite-lignite blends. However, only sulphur dioxide was detected during the pyrolysis of the lignite with high pyrite content. This is attributed to the reactions of the inherent pyrite with oxygenates in the lignite structure. By analysing sulphur retention in the chars, it was shown that inherent inorganic matter in the raw lignite retains part of the sulphur in the solid phase. For the pyrite-lignite blends, pyrite initially decomposes to form FeS, some of which further decomposes to elemental iron at a much slower rate.     

An experimental study of sulphate transformation during pyrolysis of an Australian lignite

The transformation of sulphate minerals during pyrolysis of an Australian lignite has been studied using pure sulphates (CaSO₄, FeSO₄ and Fe₂(SO₄)₃), a high mineral (HM) lignite sample and a low mineral (LM) lignite sample collected from different locations of the same deposit, and samples of acid-washed LM doped with sulphates (CaSO₄+ LM and FeSO₄+ LM), respectively. Thermogravimetric analysis and fixed-bed reactor techniques were used for the pyrolysis experimentation and the lignite samples and their chars were analysed using FTIR and XRD. The TGA experiments showed that CaSO₄ decomposes between 1400 and 1700 K in nitrogen and a 50/50 N₂/CO₂ mixture, while in air CaSO₄ decomposes between 1500 and 1700 K. Using a TGA-MS it was found that only a small fraction of CaSO₄ in CaSO₄+ LM decomposed at 653 K, releasing SO₂. CaSO₄ was still observed in the char recovered at 1073 K as confirmed by the FTIR and XRD analysis. FeSO₄·7H₂O released the bound water below 543 K and the remaining FeSO₄ decomposed between 813 and 953 K. FeSO₄ in FeSO₄+ LM decomposed at 500 K to release SO₂. The inherent sulphates in HM were dominated by iron sulphates which started to decompose and release SO₂ at around 500 K and all sulphate had been decomposed at 1073 K. It was observed that during the fixed-bed pyrolysis at 1073 K in nitrogen, approximately 36% of the total sulphur in the CaSO₄+ LM decomposed, 88% of the total sulphur in the FeSO₄+ LM decomposed and around 76% of the total sulphur in HM decomposed. It was also confirmed that FeSO₄+ LM produced more volatile sulphur than CaSO₄+ LM during pyrolysis.     

Comparison of sulphur in HNO3-extracted and physically cleaned coals

The sulphur contents of eight bituminous and subbituminous coals, after extraction with nitric acid, are compared with the sulphur contents of physically cleaned samples of the coals. Samples of −60 mesh (250 μm) coal were extracted with boiling 2 M HNO₃, which removes essentially all mineral sulphur. After washing and drying, the extracted samples were analysed for moisture, ash, and total sulphur. The dry, ash-free (daf) sulphur values for the eight coals obtained by this method show excellent agreement with the daf sulphur values for physically cleaned samples of the coals. The physically cleaned samples were prepared by float/sink separation of −60 mesh coal in 1.30 specific gravity media, followed by milling the float coal to particle sizes less than 10 μm and subsequent float/sink-centrifugation cleaning. The daf sulphur values determined in the HNO₃-extracted and physically cleaned samples were less than those obtained using ASTM Method D 2492 and differed by as much as 1.3%.     

Chemical reduction of sulphur dioxide to free sulphur with lignite and coal. 1. Steady-state reaction chemistry and interaction of volatile components

The chemical reduction of SO₂ with North Dakota lignite has been discovered to be a facile reaction which occurs at a relatively low temperature of 600–650 °C. Under optimum conditions, the reaction chemistry can be controlled to allow 85–90% conversion of SO₂ to free sulphur in a single-stage reaction. Major by-products of the reaction are CO₂, H₂O and a free-flowing ash. The high sulphur yield from this reaction exceeds the calculated thermodynamic gas phase equilibrium value of 66–70%. The higher experimental yield was found to be due in part to a catalysed re-equilibration of the gaseous products in the exit line. With lignite and low-rank coals, the mechanism of SO₂ reduction appears to involve reaction of hydrocarbons within the pores structure and thus allows complete conversion of the volatile matter with no tar formation. Volatilization and tar formation successfully compete with SO₂ reduction in bituminous coals under the same reaction conditions.     

Fine coal desulphurization by leaching with bromine containing hydrobromic acid

Sulphur extraction from coal by leaching with bromine-containing aqueous hydrobromic acid has been investigated in the temperature range from ambient to 120 °C. This procedure was found to be selective for the removal of high levels of sulphate and pyritic sulphur within a few minutes of leaching, while no significant reduction of the organic sulphur could be observed. Leaching led to an appreciable reduction of the ash yield and the up-take of substantial quantities of bromine. The bromine can be removed as hydrogen bromide by thermal treatment under nitrogen, without significant loss of volatile matter; for reduction of the bromine level to below 0.1 wt%, treatment for at least 1 h at ≈ 500 °C was needed.     

Evaluation of elemental sulphur in biodesulphurized low rank coals

A new procedure for elemental sulphur (S_el) determination in coal and its fractions is offered. It includes exhaustive CHCl₃ extraction and subsequent quantitative analysis of the extracts by HPLC using C₁₈ reversed phase column. Its application gives ground to achieve better sulphur balance and to specify the changes in the organic and elemental sulphur as a result of biotreatments. Two Bulgarian high sulphur containing coal samples, i.e. subbituminious (Pirin) and lignite (Maritza East), and one Turkish lignite (Cayirhan-Beypazari) are used. Prior to biotreatments, the samples are demineralized and depyritized. In the biodesulphurization processes, the applied microorganisms are: the white rot fungi “Phanerochaeta Chrysosporium” - ME446 and the thermophilic and acidophilic archae “Sulfolobus Solfataricus” - ATCC 35091.In the preliminary demineralized and depyritized coals, the highest presence of S_el is registered, which is explained by their natural weathering. As a result of the implemented biotreatments, the amount of S_el could be reduced in the range of 16.1-53.8%. The content of S_el is also assessed as part of the total sulphur and organic sulphur. The following range of S_el content is measured: 0.01-0.16 wt.% or 0.3-4.6% of total sulphur and 0.3-5.1% of organic sulphur. In this way, more precise information is obtained concerning the content of organic sulphur presence.     

Desulphurization of some low-rank Turkish lignites with crude laccase produced from Trametes versicolor ATCC 200801

In this paper, data obtained during the oxidative desulphurization of some low-rank Turkish lignites with crude laccase enzyme produced from Trametes versicolor ATCC 200801 are presented. In order to optimize desulphurization conditions, effects of incubation time, pulp density, incubation temperature, medium pH, and also lignite source on the desulphurization have been examined. The values for incubation period, pulp density, temperature and pH in optimum incubation condition were found as 30 min, 5%, 35 °C, and pH 5.0, respectively. Under optimum conditions, treatment of coal samples with crude laccase has caused nearly 29% reduction in their total sulphur content. During the study, the rate of desulphurization of coal sample provided from Tunçbilek with crude laccase was found to be relatively higher than the other examined coal samples. Results of analytical assays have indicated that the treatment of coals with crude laccase has caused no change in their calorific values but reduced their sulphur emissions. 35%, 13%, and 25% reductions of pyritic sulphur, sulphate and organic sulphur in a period of 30 min were achieved, for a particle size of 200 μm under optimal conditions with enzymatic desulphurization. Also, statistical analyses such as Tukey Multiple Comparison tests and ANOVA were performed.     

可再生胺法脱硫技术处理锡冶炼低浓度SO2烟气的应用实践

介绍了Cansolv可再生胺法脱硫技术处理锡冶炼烟气工艺流程及运行情况。与原有石灰-石膏法脱硫技术相比,脱硫效率更高,并可回收硫资源。脱硫气尾气ρ（SO₂）<400 mg/m³,脱硫效率高于98%,除酸雾效率高于50%,除尘效率高于25%,NO_x脱除率高于30%。     

Reductive pyrolysis of Miocene-aged lignite lithotypes using MS and GC/MS detection systems for analysis of organic sulphur groups

The atmospheric pressure temperature programmed reduction (AP-TPR) technique, an approach for organic sulphur speciation, was extended by mass spectral detection. The coupling gave ground for precise assignment of sulphur compounds in flue gases of lignite lithotypes pyrolyzed in H₂ atmosphere. A broad range of sulphur compounds was determined, i.e. thiols, dimethylsulphide, dimethyldisulphide, CS₂, thiophenes, benzothiophenes and their alkylated homologues. Certain peculiarities in organic sulphur distribution in lithotypes under study were noticed. Humovitrain was the lithotype with the highest organic sulphur content. A preponderance of aliphatic sulphur, thiols and dimethylsulfides were determined for both homogeneous lithotypes (xylain and humovitrain). In humovitrain, additionally thiophenes were also identified. For heterogeneous lithotypes, liptain and humoclarain, a dominance of disulphides and an almost lack of sulphides was observed. This is an indication that with coalification a gradual loss of aliphatic sulphur functions has proceeded, where more resistant disulphides sulphur bridges turned out to be present. Thiophenes are the most abundant aromatic structures, dominating in humoclarain. Some amounts of oxidised organic sulphur compounds (1% up to 4.1% of S_org) were semi-quantitative determined in lithotypes using AP-TPR-MS.     

Organic sulphur in the hard coal of the stratigraphic layers of the Upper Silesian coal basin

The paper presents the results of investigation of organic sulphur occurrence in the coal of Upper Silesian coal basin. Six hundred coal samples from 52 mines were tested. It has been found that the content of organic sulphur in the coal depends on the stratigraphic layer, coalification grade and geographic location in the Upper Silesia region. The highest mean content of organic sulphur has been found in the most recent (ca. 0.85%) and in the oldest (ca. 0.5%) strata. The lowest mean contents of organic sulphur have been found in the intermediate strata. In the case of the most recent coals, the content of organic sulphur decreases with increasing of coalification grade. When the carbon content (C^daf) exceeds 82%, the increase of coalification grade causes no further decrease of the mean content of organic sulphur. The share of organic sulphur in the total sulphur is lower in the case of more recent (<50%) and higher in the case of older coals (>50%).     

Properties and potential of formed cokes derived from two Turkish lignites by carbonization of binderless briquettes

Two high-sulphur Turkish lignites were briquetted at room temperature under pressures of 113 or 212 MPa and the briquettes were carbonized to 1158–1173 K over special heating cycles. The lower-rank lignite gave a formed coke of superior mechanical strength, lower porosity and higher sulphur content than typical blast furnace cokes. The formed coke produced from the higher-rank lignite briquettes had slightly poorer mechanical strength, lower porosity and much higher ash yield and sulphur content than conventional cokes. The products were considered attractive for use in non-ferrous metallurgy.     

Chemical cleaning of Turkish lignites by leaching with aqueous hydrogen peroxide

Two Turkish lignites (Beypazari and Tunçbilek) were leached with the solutions of hydrogen peroxide in water or in 0.1 N H₂SO₄. The effects of some process parameters, such as concentration, time and temperature, on the removal of ash and sulphur have been investigated. The rate of ash and sulphur removal are relatively high in the first 30 min, but slow after 60 min of the reaction time. Depending on the type of lignite, the maximum reductions ranged from 30 to 70% in ash, from 70 to 95% in pyritic sulphur, and from 42 to 58% in total sulphur. A relatively small reduction (a maximum of 25%) was estimated for organic sulphur. The optimum process conditions were established as a hydrogen peroxide concentration of 15 wt.%, a temperature of 30 °C and a leaching time of 60 min. High peroxide concentration or high temperature did not result in an appreciable further reduction in ash and sulphur. Due to partial dissolution or oxidation of the lignites, some organic material losses occurred but no heating value loss was estimated. An overall kinetic approach was also applied for pyritic sulphur removal, and the conversion data were analyzed by using both homogenous and heterogeneous reaction models.     

Entrained‐flow gasifier fuel blending studies at pilot scale

For the foreseeable future, coal and petroleum‐based materials, such as petroleum Coke, residuals, and high‐sulphur fuel oil, are being adopted as the feedstocks of choice for gasification projects. Of particular interest from a Canadian perspective is Coke generated from the thermal cracking of the oil sands in Western Canada. Oil sand Coke contains high sulphur (5–6%), and also typically has a low volatile content, and lower reactivity than most coals. Experimental runs have recently been conducted on the pilot‐scale entrained‐flow gasifier at CETC‐Ottawa, blending oil sand Coke with sub‐bituminous and lignite coals, to try and enhance the gasification potential of these materials. Blending Genesee sub‐bituminous coal with the delayed oil sands Coke was found to alleviate problems encountered with slag plugging the reactor when running with Genesee coal alone. Blends of Genesee sub‐bituminous and Boundary Dam lignite coals with Coke achieved higher carbon conversions and cold gas efficiencies than runs completed with the Coke by itself. While using CO₂ as the conveying gas into the gasifier was not found to significantly affect the conversion obtained, steam addition was found to have a marked effect on CO and H₂ concentrations in the syngas.     

柠檬酸盐-硫化钠法脱硫制硫磺工艺的工业应用

介绍了瑞祥化工热电厂烟气脱硫装置的工艺流程、设备选型和技术指标.该装置采用柠檬酸盐-硫化钠法对电厂烟气进行脱硫制硫磺.脱硫后排放的尾气ρ（S02）低于50 mg/m^3,且硫磺产量为4 175 t/a.该脱硫工艺副产品为易于储运的固体硫磺,吸收剂可循环使用,且无二次污染.因此,柠檬酸盐-硫化钠法脱硫制硫磺工艺是一种适合电厂烟气脱硫的方法.     

Briquetting of Afşin-Elbistan Lignite

In this study, low-quality Afşin-Elbistan lignite was mixed with a high-quality Siberian bituminous coal and optimum briquetting conditions were investigated for blends with and without binder materials. The blends of lignite and bituminous coal were prepared to contain 30, 40, and 50% bituminous coal and briquetted under pressures of 566 MPa and 708 MPa. The blends of lignite and bituminous coal were also briquetted using sunflower shell, sawdust and molasses as additives. In these experiments, the percentage of the lignite in the blends was fixed at 50%, so that the sum of the percentages of the bituminous coal and binder additive was always 50%. In this way, the low-grade lignite and high-quality bituminous coal dust are converted into a compact and stable fuel which has a higher quality.     

Ozonation/extraction coupled non-catalytic desulphurization of VGO/natural gas condensate

The desulphurization of hydrocarbon fuels with high sulphur content and a wide variety of sulphur-containing compounds brings significant challenges. In the present work, the non-catalytic desulphurization of vacuum gas oil (VGO) and natural gas condensate mixed fuel has been investigated. In this regard, ozone was employed as the oxidant in a bubble column gas–liquid contactor, and an extraction step was further incorporated. The effects of the oxidation reactor scheme, ozonation time, and extraction with different solvents, applying pre- and post-extraction strategies (i.e., ozonation/extraction/extraction and extraction/ozonation/extraction), have been studied. It was found that pre-extraction of mixed fuel increases the oxidative desulphurization (ODS) efficiency due to the removal of light sulphur-containing compounds (SCCs). N-methyl-2-pyrrolidone (NMP) has been found to be the most effective extraction agent, removing 44% of sulphur by pure extraction and 77.4% by ozonation + extraction. However, in terms of fuel loss, dimethylformamide (DMF) performs better than NMP, and it has been shown to be the most appropriate solvent for achieving a 90% desulphurization ratio. Finally, it was found that the applied procedure could effectively remove the wide range of SCCs, especially refractive components such as benzothiophene (BT) and dibenzothiophene (DBT).