Coal-fired Flames Research Articles

Alkali sulfation during combustion of coal in a pilot scale facility using additives to alter the global sulfur to potassium and chlorine to potassium ratios

Due to the urgent needs to reduce anthropogenic carbon dioxide emissions there is an increasing interest in the use of alternative fuels. For this reason, there is a need for new knowledge on how to design and adapt existing heat and power plants to biogenic and waste-derived fuels. This work relates to co-firing of biomass and coal and the sulfation of alkali chlorides in coal-fired flames doped with chemical additives. We aim to examine the global time scales of alkali sulfation and chlorination based on combustion experiments that were conducted in a 30-kW coal flame. Temperature, gas and particle composition measurements were conducted. Both experiments and modelling support that the apparent alkali sulfation kinetics are fast in a coal-fired flame and that it is dominated entirely by the presence of SO2. The availability of oxygen and carbon monoxide, or hydrocarbons, is also critical to sustain the sulfation reaction cycle; low concentrations are sufficient. For industrial boilers this implies that sulfur addition, in combination with reburning, should constitute an efficient strategy to mitigate alkali-chlorination and the related high temperature corrosion.

3D Instantaneous Reconstruction of Turbulent Industrial Flames Using Computed Tomography of Chemiluminescence (CTC)

Computed Tomography of Chemiluminescence (CTC) was used to reconstruct the instantaneous three-dimensional (3D) chemiluminescence field of a high-power industrial flame, which was made optically accessible, for the first time. The reconstruction used 24 projections that were measured simultaneously, in one plane and equiangularly spaced within a total fan angle of 172.5°. The 3D results were examined by plotting both vertical and horizontal slices, revealing highly wrinkled structures with good clarity. The results presented are one of a series of experimental demonstrations of CTC applications to turbulent gaseous flames. The work reveals the potential to use any kind of luminescence measurement, such as emission from heated particles in coal-fired flames, for analysis of the flame shape directly in 3D.

Pulverized Coal-Fired Flame Temperature and Emissivity Measurement Based on Spectral Analysis and the Two-Color Method

A method for judging the gray property of flames based on spectral analysis and the two-color method for determining the temperature and emissivity of flame has been demonstrated. A calibrated spectrometer system was used for the data acquisition of the radiation intensity profile of a flame over a range of wavelengths (200 – 1100 nm). The wavelength range that meets the gray body assumption, in which the emissivity can be assumed as a constant, can be determined from the emissivity profile obtained by spectral analysis and the two-color method. Then the temperature and emissivity of the flame and their relative mean square deviations were calculated within that range. Experiments were conducted on pulverized coal-fired flames in a commercial 300MW boiler furnace. The results show that the coal-fired flame can be assumed as gray body between 500 nm and 1000 nm, and the temperature and emissivity calculation results of coal-fired flames are found to be in reasonable agreement with results using other methods from the literature.

A simple judgment method of gray property of flames based on spectral analysis and the two-color method for measurements of temperatures and emissivity

A method for judging the gray property of flames based on spectral analysis and the two-color method for determining the temperature and emissivity of a flame has been demonstrated. A calibrated spectrometer system was used for the data acquisition of the radiation intensity profile of a flame over a range of wavelengths (200–1100nm). The wavelength range that meets the gray body assumption, in which the emissivity can be assumed to be constant, can be determined from the emissivity profile obtained by spectral analysis and the two-color method. Then the temperature and emissivity of the flame and their relative mean square deviations were calculated within that range. Experiments were conducted on solidified gasoline and red phosphorus flames, and pulverized coal-fired flames in a commercial 420ton/h boiler furnace. The results show that the gasoline flame can be assumed to be a gray body in the range between 550 and 900nm, for the coal-fired flame the range is between 500 and 1000nm; while the red phosphorus flame cannot be assumed to be a gray body within the measurement wavelength range. The temperature and emissivity calculation results of coal-fired flames are found to be in reasonable agreement with results using other methods described in the literature. The wavelength interval in the two-color method to calculate temperature is also discussed.

A simple measurement method of temperature and emissivity of coal-fired flames from visible radiation image and its application in a CFB boiler furnace

The two-color method is widely used in non-contact temperature measurement of combustion flames from radiation images, traditionally based on the spectroscopic characteristics of the image sensor, and/or the representative wavelengths for the red, green and blue filters of the image-forming devices, for example, Charge Coupled Device (CCD) cameras. In this paper, a new method to derive the temperature and emissivity images from a color CCD image is presented for coal-fired combustion processes, which is independent of the spectroscopic characteristics and the representative wavelengths of the CCD and the image processing system. In this method, it is only necessary to capture image information by the image processing system from a blackbody furnace at different temperatures which cover the possible temperature range of the combustion processes to be measured. In a 480 ton/h coal-fired circulating fluidized bed (CFB) boiler experiments are conducted. The temperature measured by this method is validated by that obtained by thermocouple, and it varies obviously with the load the boiler. The flame emissivity provided by this system is worthy for further study.

Three-Dimensional Tomographic Reconstruction of the Luminosity Distribution of a Combustion Flame

This paper presents the design, implementation, and evaluation of a 3-D imaging system for the reconstruction of the luminosity distribution of a combustion flame. Three identical red-green-blue charge-coupled device cameras together with appropriate optical transmission units are used to capture concurrently six equiangular 2-D images of a flame. A new tomographic approach that combines the logical filtered back-projection and the algebraic reconstruction technique is proposed to reconstruct flame sections from the images. A direct comparison between the proposed approach and other tomographic algorithms is performed through computer simulation for different test templates and number of projections. Experimental tests were undertaken using both gas- and coal-fired flames in order to evaluate the effectiveness of the system. This research has led to the establishment of an effective tool for the reconstruction of the luminosity distribution of flame sections and, ultimately, the quantitative characterization of the interstructures of a combustion flame.

Temperature Profiling of Pulverized Coal Flames Using Multicolor Pyrometric and Digital Imaging Techniques

This paper presents an imaging-based multicolor pyrometric system for the monitoring of temperature and its distribution in a coal-fired flame. A novel optical splitting/filtering device is designed and used to split the light of flame into three beams at three selected wavelengths as required in the multicolor principle. A high-resolution charge-coupled device camera is employed to collect the three beams of the light of flame. The three resulting images provide the basis for the determination of temperature and its distribution in the flame field. The system is evaluated on a 0.5-MW/sub th/ coal-fired combustion test facility under various combustion conditions. Results obtained demonstrate that the system is capable of measuring the temperature and its distribution concurrently in the flame field. Quantitative relationships between the measured results and the main combustion process data are also discussed.

Transient Performance of a TPP-210A Boiler Performed with the Use of a System of RCA-2000 Analyzers

Results of a study of transient performance of a TPP-210-A boiler with natural-gas division of the coal-fired flame are presented. The parameters of the transient process are determined with the use of a system for continuous measurement of the content of combustibles in the fly ash based on RCA-2000 analyzers (Denmark).

Concurrent measurement of temperature and soot concentration of pulverized coal flames

This paper presents a novel instrumentation system for the concurrent measurement of temperature and soot concentration of pulverized coal flames. The system operates on the two-color principle, combining CCD camera optical sensing and digital image processing techniques. The temperature and its distribution in a flame are calculated from the ratio between the grey-levels of corresponding pixels within two images captured at two carefully selected wavelengths. The soot concentration distribution of the flame is represented and estimated using the KL factor that is derived from intermediate information obtained during the temperature measurement. The system is calibrated using a tungsten lamp as a standard temperature source. The maximum relative error in the temperature measurement is 1.83%. Experimental results obtained on a 0.5 MW/sub th/ combustion test facility show that the temperature distribution of a coal-fired flame ranged from 1380 to 1700/spl deg/C, while the KL factor ranged from 0.18 to 0.33.

Vision-based measurement of temperature distribution in a 500-kW model furnace using the two-colour method

This paper describes the design and evaluation of a novel optical instrumentation system that has been developed for the on-line continuous measurement of temperature distribution in a furnace. The system comprises optical filters, a CCD camera, a frame-grabber and associated software. Based on the two-colour method, the average temperature of the flame field is calculated from the ratio of averaged grey levels of the two images alternatively captured at two different wavelengths. Accordingly, a pseudo-instantaneous temperature distribution is obtained from a single-wavelength image and presented by pseudo-colour. Experimental results obtained from a 500-kW model furnace show that the temperature distribution ranged from 1331 to 1606°C for coal-fired flames and from 1156 to 1358°C for gas-fired flames. A continuous monitoring of the temperature distribution in the furnace has also been performed over a period of 100 min. A comparison between the results measured by the system and those from a conventional pyrometer demonstrates that the system is capable of measuring the temperature distribution with a reasonable accuracy.

Sulphate capture in ash and boiler deposits in relation to SO 2 emission

The paper reviews the chemical reactions and physical changes of mineral impurities in pulverized coal-fired flames which result in the formation, deposition and retention of sulphates in boiler deposits and in the ash captured in the electrical precipitators. The review is based mainly on the author's own work and it includes the results of laboratory research and boiler plant investigations. British coals when consumed in pulverized fuel-fired boilers result in a retention of sulphates in the ash and boiler deposits which accounts for between 12 and 18% of the total sulphur in coal. The residual alkalinity of pulverized fuel ash derived from bituminous coals is equivalent to a further 4–6% of SO 2 in the flue gas.