Fuel Processing Technology (v.76, #3)

A new approach is proposed for the simulation of electrical conditions in a DC energized wire-duct electrostatic precipitator under dust free conditions. Voltage–current characteristics under clean air conditions are considered as a reference in analyzing the performance of a precipitator. This paper gives the simultaneous solution for the governing Poisson's and current continuity equations using a combined Boundary Element and Finite Difference Method over a one-quarter section of the precipitator. The solution of the domain integral, which represents the effect of space charges in the Poisson's equation, is also simplified using a numerical technique.The significant features of this paper are, reduced problem domain and hence less memory space and cost, less number of iterations and closer agreement of voltage–current characteristics with published experimental data when compared to other methods. The results are validated against the data obtained from experiments conducted by authors on a laboratory scale precipitator at Bharat Heavy Electricals, Ranipet, India. The distribution of electric field and current density along the plate have also been presented and discussed in this paper.
Keywords: Voltage–current characteristics; Precipitator; Boundary element method; Poisson's equation;

Domestic low rank lignites are widely used for power production in the Far East of Russia and in Northern Thailand. The quality of lignites fired in boilers of the power plants in both regions is somewhat variable because of significant fluctuations in the moisture and ash content as well as in the ultimate analysis of fuel. The effect of the fuel quality on airborne emissions (NO x , SO x , CO2 and PM) from the power plant boilers is the focus of this work. The emission concentrations of NO x (as NO2) in flue gas leaving the boiler are predicted based on the fuel analysis, as well as the boiler furnace geometry and operating conditions. The rates of SO x (as SO2) emitted into the atmosphere are estimated taking into account the sulfur content in fuel together with the effect of absorption of sulfur dioxide by fly ash and also efficiency of the FGD units. The emission concentration and rate, as well as the specific emission (per kW h) for the pollutants of interest, were quantified for the selected 55- and 100-MW units (Russian case study) and for the 150- and 300-MW units (Thai case study) fired with lignite of different qualities.
Keywords: Lignite-fired power plants; Steam boilers; Emission concentrations and rates; Specific emission;

A flotation study of refuse pond coal slurry by D. Tao; B. Li; S. Johnson; B.K. Parekh (201-210).
The flotation behavior of a refuse pond fine coal slurry sample was studied using mechanical and column flotation techniques. Flotation parameters investigated included type and dosage of frother and collector, agitation speed, scrubbing time, slurry pH, etc. for the mechanical flotation cell, and air flow rate, feed flow rate, and wash water flow rate for the column flotation. Flotation kinetics was also studied in the mechanical flotation cell. The results showed that the coal sample was very difficult to clean by flotation. Low yield (5–15%) and low combustible recovery (6–23%) and high product ash (about 22%) were obtained when methyl-isobutyl-carbinol (MIBC) was used as frother and #2 fuel oil as collector. Adjustment of operating parameters such as agitation intensity showed limited effects. However, flotation yield was significantly improved when MIBC and #2 fuel oil were replaced with frother P948 and collector SPP. Mechanical scrubbing was unable to restore the floatability of the coal sample. ‘Ken-Flote’ column flotation was inferior to mechanical flotation for oxidized coal and possible reasons were given.
Keywords: Column flotation; Kinetics; Mechanical flotation; Oxidized coal; Refuse pond slurry;

Use of asphalts for formcoke briquettes by Steven A Paul; Ashley S Hull; Henry Plancher; Pradeep K Agarwal (211-230).
Increasing demand for coke is coupled with diminishing supplies of cokeable coals. Formcoke technology, which involves briquetting of char, coke and/or raw coals with a binder material (usually coal tar), permits the use of a much wider range of coals as feedstock. The major objective of this study was to explore the use of petroleum residues as binders. The effects of properties of feedstock, char and binders, and operating conditions were investigated. The interaction of oxygen with the binder can be beneficial in increasing the mechanical strength of formcoke briquettes. The outcome depends on competing carboxyl-forming and depolymerization reactions. This interaction of oxygen with the binder can be effected through air-blowing and curing in air. The strength is also enhanced by the addition of asphaltenes and increased coking temperature. A new measure, the cokeable fraction of the binder, provided the best correlation with briquette strength.
Keywords: Asphalts; Formcoke; Binders;

In this study, the interpretation of float–sink test data by simple equations on coals of different origins with respect to sulfur content has been investigated. Primarily, the cumulative weight and sulfur content of the floating fraction have been determined for each coal in all relative densities tested. For deriving of the equations, the recoveries of both non-sulfur and sulfur compounds in cumulative floating part have been calculated. Then, the relationship between the recoveries and relative densities has been stated as simple equations and the calculated values from equations have been compared with the experimental results. Furthermore, it has been found that these types of equations are suitable for the interpolation of sink–float data. The results reveal that the float–sink test results can be stated by simple equations relating to the sulfur content.
Keywords: Float–sink data; Coal; Sulfur; Washability; Interpolation;

Generating a representative signal of coal moisture content to anticipate combustion control in thermal power stations by Ismael Prieto-Fernández; J.Carlos Luengo-Garcı́a; Manuela Alonso-Hidalgo; Daniel Ponte-Gutiérrez (241-255).
This article describes the possibilities of continuously measuring coal moisture in the boiler feeding circuit of a thermal power station so that the measurement can be used as a signal for the boiler combustion control system. To do so, in the first place, the point through which coal would be fed into the boiler was chosen. After studying the different parts of the circuit, the feeder was selected. Then, an installation was designed, at semi-industrial scale, faithfully reproducing the operation of a belt conveyor. In order to measure the moisture content, a microwave system was installed, and a large number of coal samples with different ranks and grain sizes was tested showing eventually the likelihood of the objective.
Keywords: Signal; Coal moisture; Thermal power station;

Calendar (257-258).

Author Index (259).

Subject Index (261).