THERMAL REACTIVITIES OF SOME TURKISH LIGNITES

Abstract

A DTA study has been made to investigate the thermal reactivities of five Turkish lignites (Elbistan, Ilgin, Karliova, Xangal, Yatagan) in an air atmosphere. The coal samples exhibited thermal reactivity at temperatures starting from 20 °C and continuing up to 671 °C. Endothermic peaks were observed at the lower end of the temperature range, the highest endothermic peak temperature being 146°C for Elbistan lignite. Exothermic peaks appeared at around 260, 360 and 600 °C. These temperatures are considered to signify the release and combustion of single benzene ring structures and combustion of condensed aromatic rings respectively. Corresponding stages are observed in the TGA traces. After correcting for differences in methodology, the overall heat effects measured by DTA are within greater than 90% of the calorific values of the coal samples determined by bomb calorimetry.     

SOLID STATE 13C NMR STUDY OF THERMALLY UPGRADED LOW RANK COALS

The results of solid-state ¹³C NMR study aimed at evaluating the chemical changes and extent of upgrading achieved in the thermal treatment of two western Canadian low rank coals are discussed. The coals were thermally treated at varying temperatures (200 - 500°C) using different process media (nitrogen, steam and products of combustion)

Apparent aromaticity of the two coals was increased after the thermal treatment and increased with treatment temperature. Significant chemical changes, such as loss of the protonated aromatic carbons, quaternary carbons in alkylated rings and aliphatic ethers, were observed at 400°C and above. Condensation and polymerization of the chemical components were also evident. The effect of process medium was found to depend on the coal feed and the treatment temperature.     

PYROLYSIS OF SOME TURKISH LIGNITES BETWEEN 200 - 600°C

This study was undertaken to examine the effect of pyrolysis between 200-600°C on sulphur content, proximate and ultimate analyses of four (Seyitomer, Tuncbilck, Elbistan and Kangal) lignite samples. A decrease in semi-coke yield and an increase in tar and gas yields with increasing temperature were observed for all samples. Percent reduction of volatile matter was the same up to 400°C for the lignites. It has been observed that total sulphur contents were reduced significantly during carbonization. The highest sulphur reduction, 45%, was obtained with Elbistan lignite. By increasing temperature, hydrogen, carbon dioxide, methane and hydrogen sulphur yields increased notably but ethane and propane yields increased only slightly for all samples. In order to study effect of C, H and O contents of the original lignites on the yield and the distribution of the products, a linear regression analysis has been carried out and the model relations have been obtained. Experimental data and the model values from the relations have been compared. Yield values appear to be in good agreement with the model values for all samples.     

THERMAL ANALYSIS OF DIFFERENT FOSSIL FUELS

In this study DTA and TGA were applied to some fossil fuels. Peat, lignite, bituminous coal, anthracite, oil shale and asphaltite were heated at a constant 15 °C/min up to 1000 °C under nitrogen atmosphere. The DTG curves of the samples were derived using the TG curves. The results are compared and discussed.     

PROGRESSIVE HYDROTREATMENT OF HOKKAIDO COALS (JAPAN)

Hokkaido coals were subjected to benzene extraction and non-catalytic hydrotreatment, alternatively, under progressive increase of temperature from 200 to 400 °C. For Taiheiyo coal the aliphatic materials in the hydrogen-rich part of the coal were converted to benzene soluble products at lower temperatures. With the increasing reaction temperature, aromaticity of the benzene solubles increased gradually. On the other hand, for Ohyubari coal, the structure of the benzene solubles were essentially the same for products obtained under all temperatures. Also, in the case of Taiheiyo coal (C : 76.9 %) the plastic state was not observed up to 400 °C, but for Ohyubari coal (C : 85.6 %) the onset of the plastic state was evident. It was assumed that there was an intimate relationship between the occurrence of plastic state and the structural uniformity of coal.     

SUPERCRITICAL EXTRACTION AND DESULPHURIZATION OF BEYPAZARI LIGNITE BY ETHYL ALCOHOL/NaOH TREATMENT 2. KINETICS

The reaction of Beypazari lignite with ethyl alcohol/NaOH was carried out using a microreactor of 15 ml capacity. The microreactors were developed to examine the reaction kinetics of coal extraction and desulphurization under supercritical conditions. The experimental temperature in the microreactor was adjusted to 245°C, 275°C and 295°C. The duration of the experiments was changed between 0 to 90 minutes.

The solubilization of Beypazari lignite increased sharply from 15% to 50% within 30 minutes after the temperature reached to 245°C and gradually decreased from 50% to 48% in 90 minutes. The total sulphur (pyritic and organic) content of the acid washed lignite decreased from 3.78% to 2.50% in the first 10 minutes and insignificant changes were observed at longer durations. The percentage of the pyritic sulphur remained constant at about 0.25% throughout the experiments. As the temperature was increased from 245°C to 295°C the time for steady state decreased from 32 minutes to 21 minutes. Solubilities obtained in the steady state for experiments at 245°C, 275°C and 295°C were 50%, 52% and 60%, respectively. The order of the reaction changed between 0.85-0.89 for experiments run at 245°C, 275°C and 295°C. The activation energy of the solubilization reaction for the interaction of Beypazari lignite with ethyl alcohol/NaOH system was calculated as 28.8 kcal/mole. As the reaction time is increased from 18 minutes up to 90 minutes the infrared spectra became more complex and both the number of the peaks due to sulphur groups and the intensity of these peaks increased. When the temperature was increased from 245°C to 295°C the average molecular weight of the liquid products increased from 465 to 550.     

STEAM GASIFICATION OF BALMER COAL IN THE PRESENCE OF LIGNITE ASH

Steam gasification of blends prepared from Balraer coal and the ash from combustion of Onakawana lignite was performed in a fixed bed reactor. The blends were prepared by co-slurrying followed by drying. In the presence of 20 wt % ash the gasification rate doubled at 830° and 930°C. Direct blending of coal and lignite resulted In an overall increase in carbon conversion at 830°C but had no effect at 930°C.     

LIQUEFACTION OF BEYPAZARI LIGNITE USING NiCl2-KCl-LiCl CATALYSTS. 1. DIFFERENCE IN SOLID AND MOLTEN SALT CATALYSIS

Liquefaction of Beypazan lignite in tetralin using NiCl₂-KCl-LiCl (14:36:50 molar percentages) as catalyst was investigated. Effects of the catalyst/lignite ratio and temperature were determined in experiments done at 275°C, 300°C and 360°C. Liquid products were separated into oils, asphaltenes and asphaltols by a solvent extraction method. Yield of liquefaction increased with temperature in all experiments, the highest yield was observed in experiments performed at the eutectic temperature of the catalyst mixture. The highest yields of oils were 20% and 30% with a catalyst/coal ratio of 0.5 at 275°C and 300°C, respectively. The activity of the catalyst increased in experiments in which the catalyst was molten. The yield of asphaltenes were not affected with increases in the catalyst/coal ratio in the experiments done at 275°C or 300°C in which the catalyst mixtures were in solid state. Asphaltene yields decreased from 25% to less than 5% with increasing values of catalyst/coal ratio and the asphaltol yields remained constant at 10% between catalyst/coal ratios of 0.25 and 1.00 and suddenly increased to 30% and 40% for catalyst/coal ratios of 1.50 and 2.00, respectively, at 360°C. The molecular weights of the oils decreased from 340 to a minimum value of 245 as the catalyst/coal ratio was increased from 0 to 1.00 in experiments done at 360°C where the catalyst was molten. As the catalyst/coal ratio was further increased from 1.00 to 2.00 the molecular weight increased to 310.It seemed that the N1Cl₂-KCl-LiCl catalyst mixture in all catalyst/coal ratios was more efficient in molten phase than it was used as a solid mixture.     

THE EFFECT ON THE THERMAL EFFICIENCY OF LIME ADDED TO THE COMBUSTION CHAMBER FOR RETENTION ON SULPHUR

In order to prevent the emission of SO_x, with the flue gas, certain amount of the sulphur of the coal can be retained by adding an adequate amount of lime in the combustion chamber. In this study, two series of experiments were conducted by adding lime at the molar ratios of CaO/S = 0·5 to 2·0 using Ankara-Beypazan lignites, which have around 5 % sulphur content as received form. In one of the series lime was added directly in to the lump coal, and in the other, coal was briquetted together with lime using molasses as binder. It was observed from the experimental results that the increase in the lime ratio leads to an increase in the retained sulphur percentage while it leads to a considerable decrease in thermal efficiency. In order to retain 50 % of sulphur, it was necessary to add lime into lump coal at a CaO/S molar ratio of at least 1,1. This minimum ratio was 0·70 for briquetted coal. When lime was added at these ratios, the thermal efficiencies in the first case dropped to as low as 82 % and to 92 % in the second.     

DESULPHURIZATION OF A TURKISH LIGNITE BY PYROLYSIS COMPARISION OF SLOW AND FLASH PYROLYSIS

To observe the effect of the heating rate on the desulphurization. Bolu- Mengen lignite was desulphurized in the temperature range of 450-750 °C using flash and slow pyrolysis methods. A reduction of 57.6 % and 34.2 % In the total sulphur was obtained for the slow and flash pyrolysis at a pyrolysis temperature of 750 °C. respectively. It was observed that the flash pyrolysis is shifted toward higher temperatures with respect to the slow pyrolysis. The flash pyrolysis having high thermal efficiency has a potential as a desulphurization process.     

Characterization of Thermally Degraded Asphaltene Fractions Using Gel Permeation Chromatography

Petroleum asphaltene goes through three stages of mass reduction under thermogravimetric analysis from 25°C to 1,000°C at a heating rate of 1°C/min. The products from thermal degradation of asphaltene at three different temperature intervals are collected. Two residual fractions left in the sample cup are also obtained at two specific temperatures. The collected fractions and the residual fractions are characterized using gel permeation chromatography. The fraction collected between 25°C and 350°C demonstrates similar molecular weight distribution to that collected between 350°C and 450°C, with both fractions showing a typical molecular weight distribution for polymeric material. The fraction collected between 450°C and 650°C illustrates three different molecular weight distributions. The chromatogram of the residual fraction obtained at 350°C resembles that of the undegraded asphaltene. The residual fraction obtained at 450°C also demonstrates three different molecular weight distributions. The experimental data indicate that the mass reduction of asphaltene heated from 25°C to 350°C is mainly due to the evaporation of low boiling point and/or low molecular weight substances in asphaltene. Thermal decomposition and coke production occur significantly in the 350°C-450°C temperature interval. Thermal degradation continues to finish until 650°C.     

LIQUEFACTION OF ELB�STAN AND YATAĞAN LIGNITES I N CARBON MONOXIDE/HYDROGEN GAS MIXTURES

Thc effects of experimental parameters on the liquefaction yields of Elbistan and Yatagan lignites vcre investigated by using different solvents, guses and catalysts.

In hydroliquefaction of Elbistan lignite with anthracene and creosote oils, higher oil yields were obtained with anthracene oil. Based on this result, anthracene oil was chosen as solvent for further work done with Elbistan lignite. First the effect of moisture in lignite samples vas observed with synthesis gas as medium gas: then, the effect of carbon monoxide/ hydrogen ratio in liquefaction gas mixture was determined using moist lignite samples. The highest oil yield was obtained with moist lignite sample in 3CO/IH₂gas mixture and it was 57.3 % (daf).

The hydroliquefaction oil yields of Yatagan lignite obtained with creosote oil were higher than those obtained in anthracene ail. On Further work done with Yatagan lignite, creosote oil was chosen as solvent. First, the effects of CoMo and red mud catalysts, then in catalyzed medium, the effects of moisture in lignite samples and at last, using moist lignite samples and red mud catalyst. the effects o f carbon monaxide/hydrogen in synthesis gas medium and also, the increase in the oil yield a s an effect of catalyst presence, increased further: the 3CO/lH, ratio in gas medium was suitable for obtaining higher oil yields; and also for obtaining high oil yields, 440°c could be taken a s the most suitable temperature value and the pressure should be increased a s much as technical and economical conditions permit.     

ELEMENTAL COMPOSITION OF ASPHALTENES FROM COAL LIQUEFACTION

The elemental composition (C, H, N, S, O) of asphaltenes isolated from coal liquefaction experiments carried out at different temperatures and tetralin/coal ratios has been determined. The liquefaction experiments were conducted in a 250 ml autoclave, with 10 g of a Spanish subbituminous A coal, for 1 hour, and at 17 ± 1 MPa operating pressure and 400 rpm stirring speed. The liquefaction products were fractionated into oils, asphaltenes and preasphaltenes using pentane, toluene and THF as extractive solvents. The % S and % O are lower in asphaltenes than in coal, while the % C and % N are higher and % H depends on the temperature and tetralin/coal ratio used. On the other hand asphaltenes % C decreases, and % H and % O increase as the tetralin/coal ratio is raised at every temperature except 475 °C, while % S and % N do not have a clear variation.     

PYROLYSIS OF SUNNYSIDE (UTAH) TAR SAND: CHARACTERIZATION OF VOLATILE COMPOUND EVOLUTION

Sunnyside (Utah) tar sand was subjected to programmed temperature pyrolysis and the volatile products were detected by tandem on-line mass spectrometry (MS/MS) in real time analyses. A heating rate of 4°C/min from room temperature to 900°C was employed.

Evolution of hydrogen, light hydrocarbons, nitrogen-, sulfur-, and oxygen-containing compounds was monitored by MS or MS/MS detection. Evolution of volatile organic compounds occurred in two regimes: 1) low temperature (maximum evolution at 150 to 175°C), corresponding to entrained organics, and 2) high temperature (maximum evolution at 440 to 460°C), corresponding to cracking of large organic components. Alkanes and alkenes of two carbons and higher had temperatures of maximum evolution at approximately 440°C, and methane at approximately 474°C. Aromatic hydrocarbons had temperatures of maximum evolution slightly higher, at approximately 450° C. Some nitrogen-, sulfur-, and oxygen-'ccntaining compounds were also detected in the volatile products.

Comparing the Sunnyside pyrolysis to the pyrolysis of other domestic tar sands indicated the following for hydrocarbon evolution: 1) the evolution of entrained organics relative to the total evolution was much less for Sunnyside tar sand, 2) the temperatures of maximum evolution of hydrocarbons due t o cracking reactions were slightly lower, and 3) the temperatures of maximum evolution for benzene and toluene are slightly higher than observed for other tar sands.

In general, the noncondensible gases, H₂, CO, and CO₂, exhibited evolution associated with hydrocarbon cracking reactions, and high temperature evolution associated with mineral decomposition, the water-gas shift reaction, and gasification reactions. Pyrolysis yields were dominated by the evolution of carbon oxides and water. The CO₂ primarily appeared t o cane from the decomposition of carbonate minerals. Compared t o other domestic tar sands, the gas evolution reflected more mineral decomposition character for Sunnyside tar sand.     

CHARACTERIZATION OF ASPHALTENE PARTICLES BY LIGHT SCATTERING AND ELECTROPHORESIS

The solubility of asphaltenes in heptane/toluene mixtures was studied at several temperatures. A significant increment in asphaltene solubility was observed when the temperature increases from 0°C to 20°C and a moderate increase when the temperature rose from 20°C to 50°C. These results indicate that asphaltenes behave as a higher consulate temperature system, similar to nonpolar waxes. Examined by photon correlation spectroscopy, diameters from the particles formed a range between 125 and 400 nm, depending on the amount of non-solvent (n-heptane) used for the precipitation process and the initial concentration of asphaltenes. The particles presented a small positive surface potential that was not altered by the addition of resins.     

Characteristic Properties of a Locally Produced Paraffinic Oil and Its Suitability as a Heat-Transfer Fluid

The thermo-physical properties of a paraffinic mineral oil produced in a local refinery were experimentally determined over a wide temperature range of 30-360°C to determine its suitability for use as a heat-transfer fluid. The effect of temperature on the physical characteristics of the oil and two synthetic organic heat transfer fluids was evaluated at high temperatures (180-360°C). Comparison of the main properties of the mineral oil with other heating fluids revealed its compatibility with synthetic organic fluids, some other paraffinic and mineral oils employed as heat-transfer fluids. The study further confirmed that the investigated mineral oil which was produced locally can be used to replace the imported synthetic oils in heat transfer systems operating at a maximum application temperature of 310°C, as indicated by the thermal stability test.     

FEASIBILITY OF IN-SITU COMBUSTION OF TAR FROM A TARMAT RESERVOIR

Combustion-tube tests were conducted on a tar of physical and chemical characteristics similar to a natural reservoir tar. Ottawa sand of 20-30 mesh size was used to prepare tar-sand mixtures of about 37% porosity, 19 to 25% water saturation and 21 to 32% tar saturation. In runs with distilled water, a combustion front was successfully initiated and moved into the sand pack. Later, however, the front's temperature dropped below 500°C causing the front to stagnate and become extinguished a short distance away from the tube's inlet. When ferric nitrate was added to the water, sustained combustion was achieved with front temperatures maintained above 500°C and high oxygen utilization. It appears that a minimum iron concentration in the water of about 2700 ppm is required for stable combustion. Concentrations above 4200 ppm did not enhance combustion performance.     

SOLID STATE 13C NMR STUDY OF THERMALLY UPGRADED LOW RANK COALS

ABSTRACT

The results of solid-state ¹³C NMR study aimed at evaluating the chemical changes and extent of upgrading achieved in the thermal treatment of two western Canadian low rank coals are discussed. The coals were thermally treated at varying temperatures (200 - 500°C) using different process media (nitrogen, steam and products of combustion)

Apparent aromaticity of the two coals was increased after the thermal treatment and increased with treatment temperature. Significant chemical changes, such as loss of the protonated aromatic carbons, quaternary carbons in alkylated rings and aliphatic ethers, were observed at 400°C and above. Condensation and polymerization of the chemical components were also evident. The effect of process medium was found to depend on the coal feed and the treatment temperature.     

High Temperature Thermal Stability Investigation of Paraffinic Oil

The physical and thermal properties of paraffinic oil were investigated at 250-360°C to determine its suitability for use as a heat-transfer fluid. Thermal stability test was conducted at 360°C for a period of 480 hr in a stainless steel high-pressure autoclave. The paraffinic oil offered sufficient thermal stability for a period of about 300 hr and then became unstable resulting in thermal break down or cracking of the oil. Degradation of the oil led to the formation of gases, liquid components, and solid coke of about 5 wt.% of the starting material. The distillation test performed on the liquid components showed that the composition varied from light naphtha to heavy bituminous material.

The paraffinic oil compared favorably with synthetic organic fluids and the typical properties revealed its suitability as a heating fluid in a system with maximum usage temperature of 310°C as indicated by the thermal stability test. Comparative evaluation of the general properties of the tested paraffinic oil with other paraffinic and mineral oils of different product formulations showed excellent agreement. From these results, it is concluded that the paraffin oil sample produced by the local refinery is suitable for use as a potential thermal fluid at temperatures below 315°C, which is quite adequate for many industrial applications.     

THE EFFECT OF VISBREAKING CONDITIONS ON THE STABILITY OF SOME IRAQI LONG RESIDUES

A study has been done to investigate the change in the stability of residue during thermal process (visbreaking) at different cracking severity using flocculation ratio method. For this purpose, three long residues (350°C+) of different crude oils were used. The obtained results were discussed as a function of reaction temperature and residence time. Moreover, the stability was correlated with the nature and chemical composition of the feedstock.We observed that the intermediate paraffinic base feedstock (type A) was more stable than the other two asphaltenic base (Types B & C) when visbreaking temperature was 460°C. At higher temperatures, a sudden and large decrease in the stability of type A visbroken products was observed while only a gradual decrease in the stability of the other two products was noticed when visbreaking process was carried out at the same operating conditions.