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The most volatile polycyclic aromatic hydrocarbons remaining in the flue gas leaving cyclones placed at the exit of a fluidized bed coal combustor and classified by the US EPA as priority pollutants were trapped on filters and adsorbents, dissolved in dimethylformamide and analysed by synchronous fluorescence spectroscopy. The results are discussed.
Mean and fluctuating velocity components and turbulence characteristics of the flow in the outlet of a cavity bluff-body burner were measured using three-dimensional laser particle dynamics anemometry (3D PDA). Results are also given on the choice of model particles, particle diameter distribution in and out of the recirculation zone, particle number density and volume flux distribution, and the...
Mean and fluctuating velocity components and turbulence characteristics of the flow in the outlet of a cavity bluff-body burner were measured using three-dimensional laser particle dynamics anemometry (3D PDA). Results are also given on the choice of model particles, particle diameter distribution in and out of the recirculation zone, particle number density and volume flux distribution, and the combustion...
The most volatile polycyclic aromatic hydrocarbons remaining in the flue gas leaving cyclones placed at the exit of a fluidized bed coal combustor and classified by the US EPA as priority pollutants were trapped on filters and adsorbents, dissolved in dimethylformamide and analysed by synchronous fluorescence spectroscopy. The results are discussed.
Changes in the combustion reactivity of sets of chars from five coals have been determined as a function of increasing devolatilisation temperature, heating rate and pressure. Chars were prepared in wire-mesh pyrolysis reactors, where evolving volatiles are rapidly removed from the vicinity of the heating coal. Samples were heated at rates between 1 and 5000 Ks -1 to temperatures up...
The P-1 model for thermal radiation transfer is re-examined in view of its potential applications to industrial problems as part of a computational fluid dynamics (CFD) analysis. The concept of radiation temperature adopted is shown to be particularly useful when this model is used in a general curvilinear coordinate system. An explanation is given as to why the P-1 model gives reliable predictions...
A thermogravimetric method was used to study the behaviour of seven pulverized commercial coals during the first instants of their combustion and devolatilization and combustion of the corresponding chars. Their weight variations are related to the evolution of the surface characteristics of the carbonaceous materials. In particular, BET surface areas of the chars appear to be strictly related to...
Combustion reactivity plays a significant role in the development of optimal strategies for the efficient utilization of coal. A promising technique for characterization of combustion reactivity involves measurement of the gas temperatures which lead to the ignition of coal particles of different sizes, and the use of classical ignition theory to extract the relevant reaction rate parameters. This...
The results of extensive predictive studies using a mathematical model of pulverised coal combustion are presented. Predictions for two swirl burner types are compared with data collected in a large scale combustor expressly for validation purposes. One of the burner types is reasonably well simulated, while the performance of the other is less well reproduced. A wide ranging study to explore the...
One method of improving the overall efficiency of a power plant or increasing the power output is to re-power the existing boilers, using gas turbines in a combined cycle system. For the case of coal-fired plants, this option known as gas turbine topping is limited by the difficulties in coal burnout due to the low oxygen content (12 vol%) in the exhaust gas of modern gas turbines. A possible option...
Using a shock tube facility the combustion characteristics of pulverised char (<10μm) were measured. A prediction was made for the burnout behaviour of a commercial sized char particle (75-90μm) in different ambient conditions using a `pseudo kinetic' approach. In this approach the kinetic rate of a surface containing micro pores is determined and these `pseudo kinetics' are then applied to the...
Coal reactivity is an important parameter related to efficiency of boilers, and learning how to predict it can reduce costs when screening for new fuels. We have measured the reactivity of Spanish coals in a high pressure thermogravimetric analyzer, under operational conditions similar to those found in Pressurized-Fluidized-Bed-Combustion (PFBC). The results obtained from non-isothermal tests were...
A laboratory scale spouted bed combustor was used to study the effectiveness of various control methodologies in alleviating ash-related problems such as particle agglomeration and bed defluidisation during fluid bed combustion of low-rank coals. The three control techniques investigated are: (i) the use of mineral additives; (ii) alternative bed materials; and (iii) pretreatment of coal. Mineral...
A laboratory investigation into the effect of inorganic matter on spontaneous combustion behaviour of a Victorian brown coal. Fourteen samples were prepared, namely, the raw coal, water-washed coal, acid-washed coal, and acid-washed coal doped with 11 additives. Each of the samples was then tested in an isothermal reactor to obtain its critical ambient temperature, above which spontaneous combustion...
The solid combustion residues generated during fluidized bed coal combustion and pulverized coal differ as a result of different operating conditions. This paper summarizes a study carried out on the combustion residues arising from two types of fluidized bed combustors, both pressurized bubbling and atmospheric circulating (Escatron power plant and Ciemat pilot plant, respectively), and a pulverized...
Laboratory tests have been undertaken on a suite of 12 mineral samples to ascertain their effectiveness as fouling alleviating additives to coal during combustion. Two samples of Victorian coal from the Loy Yang and Yallourn coal mines were used in the investigation. The laboratory tests include measuring the total chemisorption capacity of the minerals for different Na compounds (NaCl, NaOH and Na...
Coal combustion computational fluid dynamic (CFD) models are a powerful predictive tool in combustion research. In existing coal combustion CFD models, the process is described by three kinetic rates: coal devolatilisation, volatile combustion and char combustion. A general, representative devolatilisation rate for coal is a matter of some contention, and measured rates depend upon the type of experimental...
In this study, the use of an artificial neural network for predicting the reactivity of coal/char combustion was investigated. A database containing the combustion rate reactivity of 55 chars derived from 26 coals covering a wide range of rank and geographic origin was established to train and test the neural networks. The heat treatment temperature of the chars ranged from 1000 to 1500 o ...
The behaviours of ten minor coal elements (Al, Ca, Fe, K, Mg, Mn, Na, P, Si and Ti) during coal combustion in the temperature range 400-2000K, under both oxidising and reducing conditions, have been studied in detail by a thermodynamic equilibrium analysis.The partitioning of these elements is calculated both in single minor element-coal-chlorine systems and in minor elements co-existing systems....
This paper reports the control methods for mitigating fouling and slagging in brown coal-fired power utilities. Two control methods were investigated, i.e. wet pretreatment of coal and the use of mineral additives. By the first technique, samples of brown coal were treated with aluminium solutions to adjust the levels of Na, Al and Cl. The effect of cleaning was tested under closely controlled conditions...
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