Three‐stage well‐mixed reactor model for a pressurized coal gasifier

Three Canadian coals of different rank were gasified with air‐steam mixtures in a 0.1 m diameter spouted bed reactor at pressures to 292 kPa, average bed temperatures varying between 840 and 960°C, and steam‐to‐coal feed ratios between 0.0 and 2.88. In order to analyze gasifier performance and correlate data, a three‐stage model has been developed incorporating instantaneous devolatilization of coal, instantaneous combustion of carbon at the bottom of the bed, and steam/carbon gasification and water gas shift reaction in a single well mixed isothermal stage. The capture of H₂S by limestone sorbent injection is also treated. The effects of various assumptions and model parameters on the predictions were investigated. The present model indicates that gasifier performance is mainly controlled by the fast coal devolatilization and char combustion reactions, and the contribution to carbon conversion of the slow char gasification reactions is comparatively small. The incorporation of tar decomposition into the model provides significantly closer predictions of experimental gas composition than is obtained otherwise.     

Model for coal oxidation kinetics. 2. An effectiveness factor interpretation

Rate expressions are developed to describe the oxidation of coal in a fixed-bed reactor under conditions of significant diffusional effects. The model defines individual effectiveness factors for carbonic gas formation, oxygen deposition, and water production, to modify a chemical model derived previously. Experiments carried out on seven coals ranging in rank from lignite to bituminous to anthracite. All the coals exhibited particle size effects and the results fit the model in most cases to within ±10% both in the rate of overall oxidation and with respect to the individual reaction rates for several products. Activation energies and effectiveness factors were obtained for each coal and for each reaction. The effluent gas $\text{CO}{}_2\text{CO}$ ratio was found to be virtually constant for all five bituminous coals, being independent of reaction temperature, coal particle size, and oxygen partial pressure.     

Influence of coal preoxidation and the relation between char structure and gasification potential

A study was carried out to ascertain the effects of coal preoxidation and carbonization conditions on the structure and relative gasification potential of a series of bituminous coal chars. Chars were prepared from two freshly mined bituminous coals and preoxidized samples derived from them. Carbonization conditions included a wide range of heating rate (0.2–10000K s^?1), temperature (1073–1273 K) and time (0.25–3600 s). Char properties were characterized in terms of analysis of char morphology, surface area, elemental composition, and gasification reactivity in air. Over the range of conditions used, preoxidation substantially reduced coal fluid behaviour and influenced macroscopic char properties (char morphology). Following slow heating (0.2 K s^?1), preoxidized coals yielded chars having higher total surface areas and higher reactivities toward gasification in air than did similar chars prepared from fresh coal. Following rapid heating (10000 K s^?1) and short residence times (0.25 s), chars prepared from preoxidized and fresh coals exhibited similar microstructural and chemical properties (surface area, $\text{C}\text{H}$ ratios, gasification rates). Carbonization time and temperature were found to be the critical parameters influencing char structure and gasification potential.     

Heavy media separation of SRC-II feedstocks: 1. Effect on coal properties

The objectives of this investigation were to determine the effects of coal preparation on the properties of Run-of-Mine (ROM) and washed Powhatan and Ireland Mine coals and to assess the potential effects on SRC-II liquefaction yields. The effect of washing on the two coals was found to be quite similar. For both coals, the properties were altered more significantly by changes in separation media gravity than by changes in the coal size. The elemental composition of the Powhatan and Ireland washed coals was correlated with carbon content. It was shown that both the hydrogen and oxygen levels increased linearly with the carbon content of the coal samples. However, the $\text{H}\text{C}$ and $\text{O}\text{C}$ ratios were not changed significantly by coal cleaning. Only small variations in the nitrogen and organic sulphur levels were observed while the sulphate sulphur and chlorine levels were not affected by coal cleaning. The major impact of the coal cleaning was to reduce the pyritic sulphur (and hence the total sulphur) content of the coals. Most of the pyritic sulphur was shifted into the middling coal and refuse fractions while the clean coals had much lower contents and the pyritic sulphur level decreased with increasing carbon content. Coal cleaning did not significantly alter the maceral contents of vitrinite, exinite, total reactive macerals (TRM), or the reflectance of vitrinite; all these parameters varied over a very narrow range, probably within the precision of the measurement technique.     

Ash-agglomerating gasification of coal in a spouted bed reactor

Australian bituminous coal (Hoskisson) was gasified with oxygen and steam in a 0.4m diameter spouted bed reactor at atmospheric pressure and temperatures of 1050–1170 °C to produce medium calorific value gas. High-ash agglomerates fell through the throat of the spouted bed under restricted gasification conditions, with no simultaneous loss of coal. The effects of temperature, steam-oxygen ratio, coal feed rate and coal size on carbon conversion, production of ash agglomerates, gas composition and decompsition of steam were established.     

Oxygen-steam gasification of coals in a spouted bed

A bituminous and a sub-bituminous coal from Western Canada have been gasified in oxygen-steam and air-steam mixtures in a 0.30-m diameter, 50 kg coal/h continuous spouted bed reactor. Results are presented to show the effects of the blast composition and reactor temperature on gas heating value and carbon conversion. Operation in the ash agglomeration mode is illustrated, and the role of K₂CO₃ as catalyst explored. Results from a wide range of experimental gasification conditions are compared with predictions of an equilibrium model.     

Flash pyrolysis of coals. Devolatilization of bituminous coals in a small fluidized-bed reactor

The devolatilization behaviour of ten bituminous coals was investigated under rapid heating conditions using a small-scale fluidized-bed pyrolyser. The pyrolyser operated continuously, coal particles being injected at a rate of 1–3 g h^?1 directly into a heated bed of sand fluidized by nitrogen. Yields of tar, C₁–C₃ hydrocarbon gases, and total volatile-matter and an agglomeration index are reported for all coals. Maximum tar yields were obtained at about 600 °C and were always substantially higher than those from the Gray-King assay. Total volatile-matter yields were also substantially higher than the proximate analysis values. The maximum tar yields appear to be directly proportional to the coal atomic $\text{H}\text{C}$ ratio. The elemental analysis of the tar is strongly dependent on pyrolysis temperature. The tar atomic $\text{H}\text{C}$ ratio is proportional to that of the parent coal. The effect on the devolatilization behaviour of two coals produced by changes in the pyrolyser atmosphere and the nature of the fluidized-bed material were also investigated. Substituting an atmosphere of hydrogen, helium, carbon dioxide or steam for nitrogen, has no effect on tar yield and, with one exception, little effect on the hydrocarbon gas yields. In the presence of hydrogen the yield of methane was increased at temperatures above 600 °C. Tar yields were significantly reduced on substituting petroleum coke for sand as the fluid-bed material. A fluidized bed of active char virtually eliminated the tar yield.     

Macerals in bituminous coals and the coking process: 2. Coal mass properties and coke mechanical properties

Bituminous coals produced in the Ostrava-Karviná coal basin show considerable variation in their maceral composition, vitrinite reflectance and fluidity. There is a close association of the latter with the $\text{H}\text{O}$ atomic ratio expressing the different chemico-structural properties of vitrinites of lower coalification. These properties of the coal mass all influence the coke mechanical properties; moreover the $\text{H}\text{O}{}_{\mathrm{at}}$ parameter is of principal importance to the course of the coking process. Laboratory, pilot-plant and full-scale experiments show that coals rich in inertinite may give cokes of suitable mechanical properties, providing the $\text{H}\text{O}{}_{\mathrm{at}}$, ratio and the bulk density are high enough. It should be noted, however, that these coals contain finely dispersed inertinite in the vitrinite mass and this may have a positive effect on the coke mechanical properties.     

Relation of the chemical structure of coal to its hydropyrolysis

The hydropyrolysis of Illinois No. 6 coal has been studied in a batch reactor, in which the reactions were initiated by explosion of $\text{H}{}_2\text{O}{}_2$ mixtures. The ratio of H₂ to O₂ was kept at 8, while the total pressure of the gas mixture was changed to vary the reaction temperature. The heating rate was ≈ 50 000 °C s^?1, and the reaction time was < 50 ms. The conversion of the feed coal increased from 19% at 620 °C to 81%at ? 1500 °C. At conversions < 50%, the gaseous product consisted of mainly CH₄ and CO in almost equal proportions, and at conversions ? 60% the concentration of CO increased. Comparison with results from a large flow reactor revealed that comparable conversions were obtained in the present batch reactor, although product distributions were markedly different from each other. The dissimilar product distribution is attributed to different reacting media: preburning of H₂ and O₂ in the flow reactor versus in situ burning of the mixture in the batch reactor. The H/C ratios of solid residues after the hydropyrolysis decreased linearly as the conversion increased, revealing that the portions of coal having high H/C ratios were preferentially gasified. This observation was substantiated by a high H/C ratio, 1.74 of the first portion of coal gasified, and by a sharp decrease in H/C ratio in subsequent gasified portions. These data indicated that aliphatic side chains (or linkages) and single-ring aromatic clusters in the feed coal were gasified first, followed by larger aromatic clusters. Semi-quantitative determination of the distribution of different aromatic clusters showed good agreement with current structural information on coal. Thus, the effects of reaction variables were explained in terms of the structural features of coal, and the ratelimiting steps in the hydropyrolysis process were identified.     

Gasification of lignite and hard coal with air and oxygen enriched air in a pilot scale ex situ reactor for underground gasification

The main goal of the study presented in the paper was an experimental comparison of the underground lignite and hard coal seams air gasification simulated in the ex situ reactor. In the study lignite and hard coal were gasified with oxygen, air and oxygen enriched air as gasification agents in the 50- and 30-h experiments, respectively, with an intrinsic coal and strata moisture content as a steam source. Application of air as a sole gasification agent was problematic for a resulting rapid decrease in temperatures, deterioration of gas quality and, finally, cessation of gasification reactions. Use of oxygen/air mixture of an optimum ratio led to valuable gas production. In lignite seam gasification with oxygen/air (of 4:2 volume ratio) the average H₂ and CO contents in product gas were 23.1 vol.% and 6.3 vol.%, respectively, and the calorific value was 4.18 MJ/m³, whereas in hard coal gasification with the oxygen/air ratio (of 2:3 volume ratio) the average H₂ and CO contents in produced gas were 18.7 vol.% and 17.3 vol.%, respectively, and product gas calorific value equaled 5.74 MJ/m³.     

Photoacoustic microscopy of coal macerals

Photoacoustic microscopy, in which laser-light energy absorbed by coal macerals is converted into thermal energy, has recently emerged as an in-situ technique for coal maceral characterization. By employing two possible detection modes, different thermal properties can be measured and correlated with the material properties of the coal macerals. For the piezoelectric detection method, the photoacoustic signal is proportional to $\text{aB}\text{pc}$, where a is the coefficient of thermal expansion, B is the bulk modulus, p is the mass density, and c is the specific heat capacity of the maceral. The second method employs a gas microphone where the photoacoustic signal is proportional to $\text{l}\text{√Kpc}$, where K is the thermal conductivity. Photoacoustic data gathered by both methods on vitrinite and pseudovitrinite macerals from Appalachian basin coals agree with values predicted from known values of a, B, p and c. Data indicate that the thermal-elastic and thermal-conductance properties vary in a systematic manner from low- to high-rank coals. Throughout the entire rank range up to 92% carbon, vitrinite exhibits a significantly different photoacoustic response than pseudovitrinite. The photoacoustic measurements reflect the chemical composition and molecular structure of the individual coal macerals.     

Flash pyrolysis of coals: comparison of results from 1 g h−1 and 20 kg h−1 reactors

The performances of 1 g h^?1 and 20 kg h^?1 flash pyrolysers are compared for three Australian coals: Loy Yang brown coal (Victoria), Liddell bituminous coal (New South Wales), and Millmerran sub-bituminous coal (Queensland). The two reactors gave comparable yields of tar, char and C₁–C₃ hydrocarbon gases over a range of operating conditions for each particular coal. The yield of total volatile matter from Millmerran coal was similar from both reactors, as were the compositions of chars from Loy Yang coal and tars from the Liddell and Millmerran coals. For Millmerran coal, the yields of tar, C₁–C₃ gases and volatiles from the large reactor below 650 °C, were slightly lower than for the small reactor, possibly owing to a shorter retention time of Millmerran coal particles in the large-scale reactor. At a temperature near 600 °C tar yields were independent of tar concentration in the effluent gas, over a range 0.0025–0.1 kg m^?3 for Liddell coal, 0.005–0.26 kg m^?3 for Millmerran coal and 0.0045–0.09 kg m^?3 for Loy Yang coal. The tar yields from Millmerran and Liddell coals at 600 °C in the large reactor, correlate directly with the atomic $\text{H}\text{C}$ ratio of the parent coal, in the same manner as that found for a wider range of bituminous coals in the small-scale reactor.     

串行流化床煤气化试验

针对串行流化床煤气化技术特点,以水蒸气为气化剂,在串行流化床试验装置上进行煤气化特性的试验研究,考察了气化反应器温度、蒸汽煤比对煤气组成、热值、冷煤气效率和碳转化率的影响。结果表明,燃烧反应器内燃烧烟气不会串混至气化反应器,该煤气化技术能够稳定连续地从气化反应器获得不含N₂的高品质合成气。随着气化反应器温度的升高、蒸汽煤比的增加,煤气热值和冷煤气效率均会提高,但对碳转化率影响有所不同。在试验阶段获得的最高煤气热值为6.9 MJ&#8226;m^-3,冷煤气效率为68％,碳转化率为92％。     

Mössbauer study of the thermal decomposition of FeS2 in coal

The Mössbauer effect has been used to study the transformations of FeS₂ in four different coals: IL No. 6, Ky $\text{9}\text{14}$, Blacksville No. 2, and Powhatan No. 5. The transformations of FeS₂ in the coals were studied in an inert atmosphere. It was observed that the pyrrhotites formed from FeS₂ have a considerable reduction in the isomer shift at 440 °C as compared to the values obtained in the absence of coal. This effect is associated with the interaction of the pyrrhotites with the coal constituents at high temperatures. There is also a significant line-broadening at 440 °C. This broadening is due either to vacancy motion in the iron sulphides and/or to motional broadening due to particle motion in the coal-derived liquids. The percentage conversion of pyrite to pyrrhotite depends markedly on time as well as type of coal. The weathering of the coal has a detrimental effect on the rate of conversion of pyrite to pyrrhotite. The ferrous sulphate layers covering the pyrite particles hinder the removal of sulphur from that surface. The major factor affecting the $\text{Fe}\text{S}$ ratio is the total amount of sulphur available for H₂S formation. Partial H₂S pressure is the crucial quantity controlling the stoichiometry of the pyrrhotites. Hence, a high percentage of H₂S in the reactor at high temperature will assure the formation of pyrrhotites with a high number of metal vacancies.     

Storage of bituminous coals under argon

Two bituminous coals, crushed to < 0.32 cm ($\text{1}\text{8}$ in), have been stored for 455 days under argon at room temperature and examined for indications of oxidation. The only changes noted over this time were a 20–30% reduction in maximum fluidity from the Gieseler plastometer test for both coals, and conversion of 5% of the pyrite to iron oxyhydroxide in one coal. Although minor, these changes do indicate that more stringent conditions are necessary to minimize oxidation during long-term storage (>2 years).     

Flash pyrolysis of coals: influence of cations on the devolatilization behaviour of brown coals

The influence of cations on the pyrolysis behaviour of brown coals under flash heating conditions was investigated by means of a small fluidized-bed pyrolyser. A stream of coal particles in nitrogen was injected at rates of 1–3 g coal/h directly into a heated bed of sand fluidized by nitrogen. Yields of tar, C₁–C₃ hydrocarbons and total volatile matter from four Gelliondale brown coals and a Montana lignite were determined as a function of pyrolysis temperature. With all coals the maximum tar yield was obtained at 600 °C. Removal of cations present in the coals markedly increased the yields of tar and total volatile matter, with little effect on the yields of hydrocarbon gases. The converse was also observed in that the addition of Ca²⁺ to a cation-free coal decreased the yields of tar and total volatile matter. The extent of the reduction in tar yield at 600 °C in the presence of cations was found to be similar for all coals. After acid washing, tar yields appear to correlate with the atomic $\text{H}\text{C}$ ratios of the coals in a manner similar to that observed previously with bituminous coals.     

Electron paramagnetic resonance studies of South Wales coal

Nine South Wales coals of different rank and composition and seven structurally disturbed outburst prone coal samples were studied using electron paramagnetic resonance. An increase in baseline spin concentration with fixed carbon content was observed across the South Wales coalfield. Enhanced spin concentrations were observed for the structurally disturbed outburst prone coal samples. The $\text{g}$ value remained more or less constant with varying structural condition, fixed carbon, and volatile matter content of the coal.     

Fluidized bed gasification of Kingston coal and marine microalgae in a spouted bed reactor

Steam gasification experiments were performed using a low-rank coal from South Australia, a marine microalga, and a blend of leached microalgal biomass and coal, in a spouted, fluidized bed reactor. The effect of different operating conditions – air-to-fuel ratio (A/F), steam-to-fuel ratio (S/F) and bed temperature (T_b) – on the producer gas composition was investigated. Producer gas compositions were analyzed and samples of bed material were also examined to identify ash components formed during each experiment. The optimum operating conditions for coal gasification, in this system, were identified to occur with A/F = 1.82, S/F = 0.75 and T_b = 850 °C. These conditions resulted in a producer gas with the highest heating value (per mass of fuel fed), the highest extent of carbon conversion and the optimum H₂:CO ratio for Fischer–Tropsch synthesis. In addition, preliminary attempts to gasify a sun-dried marine microalga are reported. The dried biomass, sieved to 1.0–3.35 mm, was gasified with air and steam. Preliminary experiments, utilizing the as-received biomass, proved unsuccessful due to rapid bed sintering. Leaching of the algal biomass to remove the extra-cellular salt and co-gasification of the resultant biomass (10 wt%) with low-rank coal also proved unsuccessful due primarily to blockages of the downstream product lines most likely due to attrition of the algae feed in the screw feeder and elutriation from the bed.     

CO2 gasification kinetics of two alberta coal chars

CO₂ gasification kinetics of chars from two Alberta coals (Obed Mountain, high volatile bituminous and Highvale, subbituminous) have been studied using a thermogravimetric analyzer (TGA) and a fixed bed reactor. Charification and gasification reactions were performed sequentially in both the TGA instrument and in the fixed bed reactor to simulate real gasifier operating conditions. TGA and fixed bed data were processed numerically to evaluate the kinetic rate of CO₂ gasification of the chars. Calculated gasification kinetics could be correlated using both the volume reaction and the grain models. Activation energies of the kinetic rate constants were near 200 kJ/mol for both Highvale and Obed Mountain coal chars using the TGA data. The activation energies calculated for the Obed Mountain coal char using the fixed bed reactor were about 250 kJ/mol. For all the cases studied the calculated activation energies were nearly the same for both the volume and grain reaction models.     

煤气化工艺过程模拟研究

应用Aspen Plus过程模拟软件,对3种高灰熔点煤进行shell气化炉和GSP气化炉气化过程模拟研究。结果表明:对同一矿区煤样,与精煤相比,加入助熔剂后,产气率有所下降,但有效气体中的CO H2并没有减少。另外,由于加入助熔剂,使得入炉煤灰熔点降低,操作温度降低,从而氧耗降低,有利于节约能源。配煤使产气率大大降低,合成气的有效成分含量减少。