In-bed char combustion of Australian coals in PFBC. 2. Char combustion without secondary fragmentation

Char combustion parameters that significantly affect the in-bed combustion of char in PFBC were determined experimentally using a batch-fed PFBC. The ratio of carbon to oxygen consumed on the surface of a burning char particle was determined and it was concluded that CO was the only product of char combustion in PFBC.

Model simulations revealed that, for PFBC, mass transfer controlled the combustion of large char particles ≥2 mm, whereas the combustion of small char particles below 0.9–2 mm was controlled by both mass transfer and chemical kinetics.

System pressure influenced the char combustion via the interaction between chemical kinetics and the mass transfer of oxygen to the char. Char particle temperature varied markedly with oxygen partial pressure in the particulate phase, indicating a distribution of char particle combustion rates in PFBC. In modelling char combustion in PFBC, the temperature of char particles in the bed should be calculated at different locations based on a heat balance around the burning char particle taking into account the local bed oxygen concentration.     

Reactivity study of combustion for coals and their chars in relation to volatile content

To determine the effect of volatile matter on combustion reactivity, the pyrolysis and combustion behavior of a set of four (R, C, M and K coals) coals and their chars has been investigated in a TGA (SDT Q600). The maximum reaction temperatures and maximum reaction rates of the coals and their chars with different heating rates (5–20 °C/min) were analyzed and compared as well as their weight loss rates. The volatile matter had influence on decreasing the maximum reactivity temperature of low and medium rank coals (R, C and M coals), which have relatively high volatiles (9.5–43.0%), but for high rank coal (K coal) the maximum reactivity temperature was affected by reaction surface area rather than by its volatiles (3.9%). When the maximum reaction rates of a set of four coals were compared with those of their chars, the slopes of the maximum reaction rates for the medium rank coals (C and M coals) changed largely rather than those for the high and low rank coals (R and K coals) with increasing heating rates. This means that the fluidity of C and M coals was larger than that of their chars during combustion reaction. Consequently, for C and M coals, the activation energies are lower (24.5–28.1 kcal/mol) than their chars (29.3–35.9 kcal/mol), while the activation energies of R and K coals are higher (25.0-29.4 kcal/mol) than those of their chars (24.1–28.9 kcal/mol).     

The sintering temperature of ash, agglomeration, and defluidisation in a bench scale PFBC

Five Australian black coals were studied in a bench scale pressurised fluidised bed combustor (PFBC) to investigate the agglomeration propensity. It was found that coals with higher proportions of calcium aluminosilicate showed higher propensity for agglomeration and defluidisation. The pressure-drop sintering technique can predict the agglomeration propensity for coals. Samples with a sintering temperature lower than the operating temperature of the PFBC showed agglomeration. The laboratory ash can be a good representative of the PFBC ash when studying agglomeration and defluidisation.     

Change of pyrolysis characteristics and structure of woody biomass due to steam explosion pretreatment

Steam explosion (SE) pretreatment has been implemented for the production of wood pellet. This paper investigated changes in biomass structure due to implication of steam explosion process by its pyrolysis behavior/characteristics. Salix wood chip was treated by SE at different pretreatment conditions, and then pyrolysis characteristic was examined by thermogravimetric analyzer (TGA) at heating rate of 10 K/min. Both pyrolysis characteristics and structure of biomass were altered due to SE pretreatment. Hemicellulose decomposition region shifted to low temperature range due to the depolymerization caused by SE pretreatment. The peak intensities of cellulose decreased at mild pretreatment condition while they increased at severe conditions. Lignin reactivity also increased due to SE pretreatment. However, severe pretreatment condition resulted in reduction of lignin reactivity due to condensation and re-polymerization reaction. In summary, higher pretreatment temperature provided more active biomass compared with milder pretreatment conditions.     

Gasification behaviour of Australian coals at high temperature and pressure

This paper presents gasification conversion data generated for a suite of Australian coals reacting with oxygen/nitrogen mixtures at 2.0 MPa pressure and at temperatures up to 1773 K, as part of a wider investigation into the gasification behaviour of Australian coals. The effects of O:C ratio, residence time and coal type on conversion levels and product gas composition were investigated under conditions relevant to those present in entrained-flow gasification systems. At higher temperatures, coal conversion levels are, as expected, higher, whilst product gas compositions continue to reflect the relevant gas phase equilibrium conditions. These gas phase equilibrium concentrations show strong dependence on the amount of carbon in the gas phase (i.e. coal conversion). The increased conversion achieved at high temperatures allows the contribution of coal-specific properties such as char structure and reactivity to be investigated in more detail than previously possible. Furthermore, at higher conversion levels the effects of coal type on product gas composition are more apparent than at lower conversion levels. These high temperature, high pressure gasification conversion data have been reconciled with high pressure bench-scale pyrolysis and char reactivity measurements, highlighting the significance of coal-specific effects of key gasification parameters.     

In-bed char combustion of Australian coals in PFBC. 3. Secondary fragmentation

Secondary fragmentation occurs during the char combustion stage of coal combustion in fluidised beds and was investigated at pressure in a bench-scale PFBC rig for five Australian black coals. The critical diameter of char particles above which secondary fragmentation occurred was 2 mm for all the coals studied. In contrast with previous work [1 and 2] at atmospheric pressure, secondary fragmentation was found to occur during the early stage of char combustion, explaining its influence on char burnout and in-bed char loading in PFBC.

Two normal distribution functions were found to describe the secondary fragmentation behaviour in PFBC. The first determined randomly which particle broke up, and the second predicted the size distribution of fragments. Neither char properties nor oxygen concentration significantly affected the parameters in these two statistical functions. However, the rank of the parent coal correlated with the ratio of maximum number of char fragments to initial number of char particles. This secondary fragmentation behaviour should be included in mathematical modelling of char combustion in PFBC to predict the char burnout correctly.     

Micrinite and exudatinite in some Australian coals,and their relation to the generation of petroleum

The occurrence and microscopic features of micrinite and exudatinite in some Australian coals are reported. The origin of these macerals and also the significance of their occurrence are discussed in connection with hydrocarbon genesis. In Australia, micrinite occurs in bituminous and sub-bituminous coals which are very rich in inertinite, and also in brown coal rich in inertinite. One of the possible progenitors of micrinite is oxidized porigelinite. There is little reason to conclude that micrinite was formed from resinite and other macerals at an early stage of coalification and that liquid hydrocarbons were formed during this process. Exudatinite occurs in sub-bituminous and high-volatile bituminous coals in the Gippsland Basin. There is no positive evidence of a genetic relation between liquid hydrocarbons, exudatinite, micrinite and liptinite macerals. The formation of liquid hydrocarbons from solid liptinite etc. may take place just before and during Teichmüller's so-called ‘2nd coalification jump’.     

单种煤性质对其焦炭性质的影响

通过测定11种单种煤和所炼坩埚焦的性质，得出单种煤挥发分与平均最大反射率在合适的范围内，所炼坩埚焦的反应性最小，结构强度最大。     

Prediction of unburnt carbon in tangentially fired boiler using Indian coals

Accurate prediction of percentage unburnt carbon in fly ash in the case of high ash content Indian coal, at the design stage, is generally difficult. In the present paper, a large number of laboratory test data and site data are used to understand the mechanism of unburnt carbon in fly ash as well as in bottom ash. Rigorous statistical analysis of the performance data taken from tangentially fired boilers shows that empirical correlation between a combination of coal properties and percentage unburnt carbon in fly ash exist. Equations to predict percentage unburnt carbon in fly ash and bottom ash have been proposed.     

Copolymerization behavior and properties of dimethacrylate-styrene networks

Dimethacrylate oligomers diluted with styrene (commonly known as vinyl ester resins) are important matrix resins for fiber-reinforced composites used in construction, marine craft, and transportation vehicles. These comonomers react via free radical copolymerization to yield void-free thermosets. The inter-relationships among copolymerization kinetics, physical properties of the networks, and cure temperatures for a 700 g/mol dimethacrylate oligomer with systematically varied styrene concentrations were investigated. FTIR was used to monitor the reactions of the carbon-carbon double bonds of the methacrylate (943 cm⁻¹) and styrene (910 cm⁻¹). Reactivity ratios were determined via a non-linear method at four cure temperatures. The data were analyzed using the integrated form of the copolymerization equation and assuming a terminal reactivity model to predict copolymer compositions throughout the reactions. The results indicated that at early conversion more styrene was incorporated into the networks at lower cure temperatures. The experimental vinyl ester-styrene network compositions agreed well with those predicted by the integrated copolymer equation at early and intermediate conversion. Mechanical properties of dimethacrylate-styrene networks were determined for materials cured at room temperature and at 140 °C. Materials cured at room temperature were tougher and had lower rubbery moduli than those cured at 140 °C.     

Characteristics and composition of lignites and boiler ashes and their relation to slagging: The case of Mae Moh PCC boilers

In order to examine the cause of occasional slagging problems, a dedicated 7-day sampling and data collection were carried out on two 300-MWe units of Mae Moh power plant owned by the Electricity Generating Authority of Thailand. The properties of feed lignite varied from low (∼11% in ash) to medium (∼18% in ash) CaO content during the sampling period. The elemental content was measured for collected fly ashes, bottom ashes and slags, and compared with those of the feed lignite. The analysis and operational data obtained during the 7-day sampling period were compared with those obtained from the additional laboratory-scale investigation of high Ca lignites and those obtained from one of the units during another period when slagging problem was experienced. The study found that, apart from Ca, the concentration of three other elements and their compounds - Fe, Al and Si, plays a very important role in slag formation and its control while these lignites are used in large utility units. The flue exit gas temperatures (FEGT) of the unit experiencing slagging were also found to approach the initial deformation temperatures (IT) of the lignite ash. The solution appears to be the monitoring of the concentration of four elements, i.e. oxides of Ca, Fe, Al and Si in the feed lignite, and in ensuring through proper mining or blending that concentration of CaO, Fe₂O₃ and Al₂O₃ is kept <20%, ∼15% and >15%, respectively, at all times. Also, it is important that the FEGT during operation is kept sufficiently below the IT of the ash of feed lignite at all times.     

Some aspects of changes in the macromolecular structure of coals in relation to thermoplastic properties

The development of coal thermoplasticity during the primary devolatilization region is critical in determining coke structures. The solvent swelling technique was used to study the changes in macromolecular structure of four coals of different rank (902 to 203 in the British Coal classification scheme) during carbonization to temperatures up to 600°C. The results were compared with the thermoplastic characteristics of the coals. The dilatometric and gas permeability properties are discussed in terms of changes in macromolecular structure. The study of the macromolecular structure provides new insight into the development of thermoplasticity and coke structure.     

Viscosity measurements of slags from pulverized western Canadian coals in a pilot-scale research boiler

Samples of coal-ash slags were characterized using optical and scanning electron microscopy, electron microprobe analysis and X-ray diffraction. The results show that essentially the slags contain a glassy phase with minor crystalline phases such as mullite, cristobalite and quartz. Viscosities of the slags were measured and compared with calculated viscosities. Significant differences were observed between the two sets of values.     

Reactivities of active oxygen species and their roles in the catalytic oxidation of inactive hydrocarbon

Reactivities of active oxygen species with hydrocarbons and their roles in the catalytic oxidation are discussed. The concepts and recent developments including the activation of dioxygen molecule with reducing agents are summarized with emphasis on the catalytic oxidation of inactive hydrocarbons.     

Radical polymerization and copolymerization behavior of 1-cyanoethanoyl-4-acryloylthiosemicarbzide

1-Cyanoethanoyl-4-acryloylthiosemicarbazide (CEATS) was synthesized for the first time as a new chelating monomer. Its structure was confirmed by both elemental and spectral analyses. Radical polymerization and copolymerization of CEATS was been carried out in dimethylformamide (DMF) in the presence of azobisisobutyronitrile (AIBN) as an initiator. Kinetic studies for the polymerization behavior of CEATS were performed. The complex formation of the CEATS monomer and polymer (PCEATS) with Cu II cation was investigated and its stability constant determined. The rate of copolymerization of CEATS with some conventional monomers, namely vinyl acetate, methyl methacrylate and acrylonitrile, was measured as a function of the mole fraction of the monomers. The reactivity ratios (r₁, r₂) for the various copolymer systems investigated together with the Q and e values of the CEATS monomer were determined. Moreover, the thermal gravimetric analysis of the prepared polymers and their copolymers with acrylonitrile were also studied.     

Modulus and damping of polymers in relation to their structure

For most applications of polymer products, the modulus or stiffness, i.e. resistance to deformation under load, is of prime importance. The mechanical losses or damping reveal molecular movements of small groups of atoms, which movements can be significant for the impact strength. This review illustrates the effect of crosslinking, polarity, and steric features of both side-groups and main molecular chain on both shear modulus and damping as functions of temperature. The examples are mainly taken from commercial or recently developed polymers. It is concluded that the most promising way of increasing the softening temperature of thermoplastics is to introduce rings into the main molecular chain.     

Solvent swelling behavior of Permian-aged South African vitrinite-rich and inertinite-rich coals

Two South African coals similar in rank and age, but different in maceral composition, were studied using solvent swelling. Inertinite-rich Highveld coal (dominated by semifusinite) and vitrinite-rich Waterberg coal were evaluated for swelling extent and swelling rate using N-methylpyrrolidone (NMP) and CS₂/NMP. A stop-motion videography method was developed to study individual particle swelling behavior. This method allowed observation of overshoot and climbing-type swelling, as well as swelling kinetics. Single-particle swelling experiments showed that both coals exhibited overshoot-type and climbing-type swelling. The inertinite-rich coal swelled much faster (in both solvents) than the vitrinite-rich coal. The swelling in CS₂/NMP was faster for both coals. Kinetic parameters showed that solvent swelling was governed by relaxation (super-Case II relaxation) of the coal structure. X-ray computed tomography was conducted over a 50 h swelling period in NMP for single particles of each coal. Anisotropic swelling was observed in all the particles (swelling greater perpendicular to the bedding plane than parallel to it). The subtle changes in molecular structure, fine structural and physical differences resulted in significant differences in solvent swelling behavior.     

Electrochemical behavior of uranium(VI) in 1-butyl-3-methylimidazolium chloride and thermal characterization of uranium oxide deposit

The electrochemical behavior of uranyl nitrate in 1-butyl-3-methylimidazolium chloride at glassy carbon working electrode has been investigated in the temperature range 343-373 K by transient electrochemical techniques such as cyclic voltammetry, chronopotentiometry and square wave voltammetry. Influence of bulk concentration of uranium and temperature on the electroreduction and transport properties of U(VI) in bmimCl has been examined. Diffusion coefficient (D) and the energy of activation (E_a) of U(VI) in bmimCl has been estimated and is of the order of ∼10⁻⁸ cm²/s and 54 kJ/mol, respectively. Reduction of U(VI) takes place through an irreversible single step two-electron transfer to UO₂ deposit at glassy carbon working electrode. Thermal analysis of the uranium oxide indicated the entrapment of nearly 5% of electrolyte, bmimCl, during electrodeposition, which decomposes in the range 553-653 K.