Action of nickel catalyst during steam gasification of bituminous and brown coals

Steam gasification of a bituminous coal and a brown coal has been carried out in the presence of a nickel catalyst. The action of catalyst particles during gasification was investigated by comparing a series of scanning electron microscope (SEM) photographs taken at stages throughout the experiment. Finely dispersed catalysts with an average diameter of <10 nm were observed upon devolatilization. During the steam gasification of bituminous coal, the carbon substrate around the catalyst was gasified. At higher catalyst loadings considerable catalyst agglomeration occurred and was associated with a decrease in effectiveness of the catalyst. On the other hand, catalyst particles remaining well-dispersed in brown coal after 80 wt% char conversion maintained an extraordinarily high activity.     

Calcium catalysed steam gasification of Yallourn brown coal

Steam gasification of calcium-loaded Yallourn coal has been carried out with a thermobalance. Calcium catalyst showed a high activity at ≈950K. Calcium hydroxide, carbonate, acetate, nitrate and chloride exhibited similar catalyst effectiveness. The gasification rate increased with increasing the calcium loading, and at a loading of 5 wt%, complete gasification was attained within 25 min at 973 K. Comparison of the uncatalysed and catalysed rates showed that calcium catalyst can lower the reaction temperature by 150K. The impregnation of calcium salt on devolatilized char in place of raw coal resulted in the formation of rather large catalyst particles, and their activity was low. High temperature X-ray diffraction analysis revealed that the interconversion between calcium carbonate and oxide takes place readily in the gasification temperature region. Calcium carbonate was the predominant species during the gasification at 923 K. Catalysis of calcium was discussed in terms of a carbonate-oxide cycle mechanism.     

Fluidized-bed gasification of some Western Canadian coals

Three Western Canadian coals were gasified with air and steam in a fluidized bed of 0.73 mm sand and coal, at atmospheric pressure and temperatures of 1023–1175K to produce a low-calorific-value gas. One non-caking and two caking coals were tested. The effects of temperature, coal feed rate, $\text{air}\text{coal}$ ratio, $\text{steam}\text{coal}$ ratio, coal quality, coal particle size and bed depth on gas composition, gas calorific value and operating stability of the gasifier were established. Results are compared with those previously obtained for the same three coals when gasified in essentially the same equipment, but operated as a spouted bed.     

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.     

Laboratory gasification of five Canadian coals

Results of a gasification study of five Canadian coals in a 100g laboratory fixed-bed gasifier are reported. The coals were three bituminous coals (Byron Creek, Prince and Devco) and two lignites (Coronach and Bienfait). When gasified in an equal mixture of nitrogen and oxygen at 850 °C, the lignites reacted more rapidly and produced more liquid and gaseous products than the bituminous coals, whereas the bituminous coals produced more methane but less carbon monoxide. Overall rates for both the gasification and combustion processes were 3.20, 2.80, 1.84, 1.70 and 1.25 wt% carbon conversion per min for Coronach, Bienfait, Prince, Byron Creek and Devco coals, respectively.     

Catalytic activity of physically-mixed nickel compounds on the CO2 gasification of phenol-formaldehyde resin char

In order to account for the various activities of different nickel compounds in low temperature catalytic gasification of carbon the reducibility of individual nickel compounds in carbon dioxide to metallic was studied by thermogravimetry and the behaviour of mixture of nickel salts with a phenol-nickel formaldehyde resin char was investigated by temperature-programmed X-ray diffraction analysis. A correlation was found between the order of reducibility of the nickel salts and their order of activity in catalytic gasification. Low temperature gasification up to 98 wt% was demonstrated for char mixed with nickel acetate (up to 9/10 wt% Ni), which suggests that there may be good prospects for finding a method of complete gasification with nickel.     

Nickel-catalysed gasification of brown coal in a fluidized bed reactor at atmospheric pressure

Pyrolysis and steam gasification of nickel-loaded Yallourn coal were carried out in a fluidized bed reactor at ambient pressure. The pyrolysis mode was influenced by the addition of nickel catalyst. The yield of total volatile matter decreased whereas the gas yield markedly increased, when compared with uncatalysed pyrolysis. This is considered to result from tar decomposing on the catalyst and being converted to gases and deposited carbon. For the catalysed steam gasification, ≈ 80 wt% of coal conversion was achieved at 873 K and the gas yield was twelve times as much as that for the uncatalysed reaction. The homogeneous equilibrium in the gas phase controlled the composition of the product gas. The product gas contained little tarry material and a negligible amount of hydrogen sulphide. Nickel was efficiently recovered from the residue by an ammonia-leaching method.     

Reactivities of 34 coals under steam gasification

The reactivities of 34 coal chars of varying rank with H₂O have been determined to examine the effect of coal rank on the gasification rate of coal char. The reactivities of chars derived from caking coals and anthracites (carbon content > 78 wt%, daf) were very small compared with those from non-caking (lower-rank) coals. The reactivities of low-rank chars do not correlate with the carbon content of the parent coals. To clarify which factor is more important in determining the reactivity, the evolution of CO and CO₂ from char, the moisture content of char and the amount of exchangeable cations were determined for these low-rank coals or their chars. These values were considered to represent the amount of active carbon sties, the porosity and the catalysis by inherent mineral matters, respectively. It was concluded that the amount of surface active sites and/or the amount of exchangeable Ca and Na control the reactivity of low-rank chars in H₂O.     

Supercritical gas extraction of Polish brown coals

Properties of nine selected samples of Polish brown coals from both strip mines and perspective deposits varying in lithotype have been determined. This involved technical analysis of the elementary, group and petrographie compositions. The coals were extracted with supercritical toluene at 410 °C and 13 M Pa. The humic acid content and humodetrinite content were found to be well correlated with the yield of coal extract. The optimal conditions of gas extraction for a selected coal sample were determined.     

Low-temperature gasification of a woody biomass under a nickel-loaded brown coal char

Catalytic gasification of a woody biomass, Japanese cypress, was investigated under a prepared nickel-loaded brown coal (LY-Ni) char in a two-stage fixed-bed reactor. The nickel-loaded brown coal was prepared by ion-exchange method with a nickel loading rate of 8.3 wt.%. Nickel species dispersed well in the brown coal, and the LY-Ni char via devolatilization at 600 °C showed a great porous property with a specific surface area of 382 m² g^− 1.The LY-Ni char was confirmed to be quite active for the Japanese cypress volatiles gasification at a relatively low-temperature range from 450 to 650 °C. For example, at 550 °C, 16.6 times hydrogen gas and 6.3 times total gases were yielded from the catalytic steam gasification of Japanese cypress volatiles under the LY-Ni char, compared with the case of non-catalyst. The biomass tar decomposition showed a dependence on catalyst temperatures. When the catalyst temperature was higher than 500 °C, Japanese cypress tar converted much efficiently, high gas yields and high carbon balances were obtained.     

Integrated instrumental analysis of soft brown coals

A method for the simultaneous determination of calorific value Q^r, ash yieldA^r and total water content W^r_t of soft brown coals is described. The method involves instrumental analysis of brown coal samples using neutron thermalization and gamma back-scattering techniques. Over 80 coal samples (1.1 kg) were analysed, having Q^rvalues up to 15.5 MJ kg^?1,A^r ranging from 3.6 to 76.1 wt% and W^r_t ranging from 11.4 to 61.7 wt%. A comparison of the results from the instrumental method with those of standard laboratory analyses is given, followed by a discussion of the accuracy of the method and of possible ways for improving it.     

H2O/O2气氛下胜利褐煤气化半焦的孔隙特性

采用实验室气流床反应器, 在H₂O、O₂及其混合气氛, 900℃条件下进行了胜利褐煤气化实验, 研究了气化半焦的孔隙结构特征。结果表明, 在所有气氛下, 半焦的吸附等温线均属于第II类型, 吸附回线为H3型, 褐煤气化半焦具有连续的较完整的孔体系, 孔隙结构类似。反应气氛影响气化半焦的孔径分布, 半焦中的大孔在3种气氛下均较少, 中孔从多到少的顺序是:H₂O > O₂ > H₂O+1%O₂, 微孔与之相反。在水蒸气气氛下, 随水蒸气浓度增加, 半焦的比表面积先增大后趋于稳定。添加1%O₂后, 比表面积提升30多倍。低浓度O₂气氛下, 随O₂浓度的增加, 比表面积呈线性增长。褐煤转化率与微孔容积和总孔容积的比值以及比表面积的关系式为X=0.196(V_m/V)+45.651, X=0.037S+48.066。     

Nature of insoluble residues accumulated during hydrogenation of Victorian brown coals

The carbonaceous material and mineral matter in hydrogenation residues from two Victorian brown coals have been characterized. Preliminary data indicate that the mineral and inorganic content of the coal may be related to the formation of different types of carbonaceous solids. The minerals such as quartz, kaolinite and halite appear to be essentially unchanged by hydrogenation, whereas pyrite is reduced to pyrrhotite. Some iron carboxylate also reacts under hydrogenation conditions to form pyrrhotite. The type of carbonate species formed during hydrogenation depends on the distribution of exchangeable cations present in the coal and when high levels of Mg are present in addition to Ca, dolomite is the predominant carbonate phase.     

不同沉积环境下煤的热解与气化特性

采用煤热解.气化连续方法,在TG-DTA/DSC热分析仪器上对煤化程度接近但沉积环境不同的5种煤的热解与气化特性进行研究,运用Coats-Redfem积分法求解煤热解动力学参数.研究结果表明:5种煤的热解机制是相似的,反应级数n=3;还原程度较弱的SH与SF煤,热解表观活化能在43-54 kJ/mol,而还原程度较强的...     

Extraction of brown coals with supercritical fluid mixtures: Implications for coal structure

Supercritical fluid extractions of brown coals with mixtures of hydrocarbon and polar solvents showed that aliphatic alcohols and amines are beneficial in the extraction of these coals. Conversions of > 90% were obtained for extraction with benzene-amine mixtures (80:20 w/w) at 300 °C. The results are consistent with the view that ester bond cleavage is an important step in dissolution of low-rank coals.     

Significant parameters in the catalysed CO2 gasification of coal chars

Alkali and alkaline earth carbonates have been used to catalyse the C0₂ gasification of coal chars prepared by pyrolysis of Illinois No.6 coal. This study found that alkaline earth carbonates are fair gasification catalysts, though throughputs are insensitive to loadings in the range of 5–20 wt%. The order of efficacy is Ba > Sr > Ca. Alkali carbonates are excellent catalysts, with throughputs showing a dependence on loadings and atomic number. In particular, at high loadings (20 wt%) the order is Cs > K > Na > Li. As kinetic parameters for the alkali carbonate catalysed Boudouard reaction with coal chars differ significantly from those for graphites, an alternative redox cycle mechanism has been proposed involving an alkali hydride intermediate.     

Distribution of volatile sulphur containing products during fixed bed pyrolysis and gasification of coals

Three sub-bituminous and two bituminous coals from Western Canada were used to study the evolution of H₂S, COS and SO₂ during the pyrolysis and gasification processes in a fixed bed reactor. For all types of coals, most of H₂S and SO₂ were released during the devolatilization stage. COS was formed only during the gasification stage in the presence of CO₂. The mineral matter of coal may have played a role during the gasification stage. Some observations made during this latter stage in CO₂ and/or steam were interpreted in terms of the equilibrium effects.     

The influence of geometrical factors and feedstock on gasification in a high temperature fluidised bed

Results are presented for gasification of coal and char by means of air or air-steam mixtures in fluidised bed reactors of three different volumes. Two sizes of coal feedstock particles, 0.5-1.0 mm and 1.0-1.5 mm, and one size of char particles, 0.5-1.5 mm, were used. The calorific value of generated gas and the carbon conversion are presented as a function of particle residence time. For coal gasification higher carbon conversion has been obtained at the same particle residence time than for char gasification. For the steam gasification, a lower gas heating value of about 4 MJ/m³ (S.T.P.) was obtained.     

煤催化气化过程中钾催化剂回收的实验研究

对内蒙平庄煤-蒸汽催化气化过程残渣中KOH催化剂的回收进行了实验研究,考察了时间、温度、水渣比和洗涤次数等条件对钾催化剂回收率的影响。实验结果表明,水蒸气催化气化过程中,催化剂的流失可忽略不计。水洗法回收可溶钾占总钾量的80%,回收所得催化剂的有效成分为K2CO3和KOH,占总回收钾量的90%以上。钾收率随时间的增长而快速提高,一般洗涤4 h即可达到预期的收率;升高温度和增大水渣比能明显提高催化剂的收率;水洗洗涤3次,能回收90%左右的可溶钾。