Coal combustors

Hot Corrosion. Hot corrosion is an accelerated form of oxidation that arises from the presence not only of an oxidizing gas, but also of a molten salt on the component surface. The molten salt interacts with the protective oxide so as to render the oxide nonprotective. Most commonly, hot corrosion is associated with the condensation of a thin molten film of sodium sulfate [7757-82-6], Na2S04, on superaHoys commonly used in components for gas turbines, particularly first-stage turbine blades and vanes. Other examples of hot corrosion have been identified in energy conversion systems, particularly coal gasifiers and direct coal combustors. In these cases the salt originates from alkali impurities in the coal which condense on the internal... 

Desulfurization with Dry Lime Limestone or lime or dolomite (CaCO,3-MgCO,3) in a fluidized bed coal combustor reacts with SO9 in... 

A semi-industrial pilot plant has been developed in which air-borne ultrasound has been applied to the reduction of particle emissions in coal combustion fumes [62]. The installation basically consists of an acoustic agglomeration chamber with a rectangular cross-section, driven by four high-power and highly directional acoustic transducers operating at 10 and/or 20 kHz, and an electrostatic precipitator (ESP). In the experiments, a fluidised bed coal combustor was used as fume generator with fume flow rates up to about 2000 m /h, gas temperatures of about 150 °C. and mass concentrations in the range 1-5 gm. The acoustic filter reduced fine particle emissions by about 40 %. 

Flagen, R. C. Taylor, D. D. "Aerosols from a Laboratory Pulverized Coal Combustor", This Symposium. 

Aerosols from a Laboratory Pulverized Coal Combustor... 

Particle size distributions of smaller particles have been made using electrical mobility analyzers and diffusion batteries, (9-11) instruments which are not suited to chemical characterization of the aerosol. Nonetheless, these data have made major contributions to our understanding of particle formation mechanisms (1, 1 ). At least two distinct mechanisms make major contributions to the aerosols produced by pulverized coal combustors. The vast majority of the aerosol mass consists of the ash residue which is left after the coal is burned. At the high temperatures in these furnaces, the ash melts and coalesces to form large spherical particles. Their mean diameter is typically in the range 10-20 pm. The smallest particles produced by this process are expected to be the size of the mineral inclusions in the parent coal. Thus, we expect few residual ash particles smaller than a few tenths of a micrometer in diameter (12). 

TAYLOR AND FLAGAN Pulverized Coal Combustor Aerosols... 

The composition distribution of the particles produced in a laboratory pulverized coal combustor will be explored in this paper using aerosol classification techniques capable of resolving the composition distribution to 0.03 ym diameter. Unlike previous attempts to measure the composition distribution, the particles were classfied directly, without having to resort to resuspension, using calibrated instruments. Experiments were conducted in a laboratory combustor in which operating parameters can be varied over a wide range. Data are presented which demonstrate that the composition of fine particles varies substantially with combustion conditions and does, under some conditions, differ considerably from that of the bulk ash. 

Figure 1. Schematic of the laboratory pulverized coal combustor...

The aerosol produced by a laboratory pulverized coal combustor was size classified in the range 0.03 to 4 ym Stokes equivalent diameter using a low-pressure cascade impactor. The samples thus collected were analyzed using a focussed beam particle induced X-ray emission technique. This combination of techniques was shown to be capable of resolving much of the structure of the submicron coal ash aerosol. Two distinct modes in the mass distribution were observed. The break between these modes was at a particle size of about 0.1... 

Li Y, Suriyawong A, Daukoru M, Zhuang Y, Biswas P (2009) Measurement and capture of fine and ultrafine particles from a pilot-scale pulverized coal combustor with an electrostatic precipitator. J Air Waste Manag Assoc 59 553-559... 

Helble, J.J. (2000) Model for the air emissions of trace metallic elements from coal combustors equipped with electrostatic precipitators. Fuel Processing Technology, 63(2), 125-47. 

A fly ash sample from a fluidized bed coal combustor is analyzed to obtain particle size data. Table PI. 1 shows the distributions of the projected area equivalent diameter of the particle dA obtained by the image analysis and the volume diameter of the particle d obtained by the electrozone technique [Ghadiri et al., 1991]. 

N0X emissions have been reduced in pulverized coal combustors by injecting ammonia gas (NH3) downstream of the flame zone (46,47). The process is controlled by complex free radical reaction chains (48), but the overall reaction is described by ... 

The control of nitric oxide emission from a fluidized bed coal combustor has been extensively investigated and it was found that the level of nitric oxide emission was determined by the relative contribution of nitric oxide formation and reduction processes. (l.,2) There is a great need for quantitative information concerning the rate of these processes.(2)... 

In coal combustion in China, both fundamental research and industrial experience have resulted in improved understanding of CFB combustion. It is reported that more than 100 commercial CFB coal combustors have been... 

Spacil, H. S. and Luthra, K. L. "Thermochemistry of a Pressurized Fluidized Bed Coal Combustor/Gas Turbine Combined Cycle". 1980. GE Report 80CRD238. See also, CFCC Development Program 1978. 

Horio, M Mori, S. Muchi, I. "A Model Study for the Development of Low NOx Fluidized-Bed Coal Combustors" Proc. 5th Intern. Conf. on Fluidized-Bed Combustion, Vol. II, 1977, 605-624. 

Gibbs, B. M. A Mechanistic Model for Predicting the Performance of a Fluidized Bed Coal Combustor Inst, of Fuel Sym. Series No. 1, Proc. Fluidized Combustion Conference Paper No. A5, 1975, A5-1-A5-10. 

Van der Honing, G. Volatile and Char Combustion in Large Scale Fluidized Bed Coal Combustors", Ph.D dissertation, Twente University, Netherlands, 1991. Konnov A. A., Detailed Reacrion Mechanism for Small Hydrocarbons Combustion, Release 0.4, http //homepages.vub.ac.be/ akonnov/, 1998. 

Rizeq, R.G Shadman, F 1989, Alkali-induced agglomeration of solid particles in coal combustors and gasifiers, Chem. Eng, Conun. Vol.81, 83-96. 

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