Fly ash slurry

Naik, T.R., Ramme, B.W., and Kolbeck, H.J., Filling abandoned underground facilities with CLSM fly ash slurry, Concrete International, 12 (7), 19-25, July 1990. 

J. Moreda-Pineiro, P. Fopez-Mahia, S. Muniategui-Forenzo, E. Fernandez-Fernandez and D. Prada-Rodriguez, Direct As, Bi, Ge, Hg and Se(IV) cold vapor/hydride generation from coal fly ash slurry samples and determination by electrothermal atomic absorption spectrometry, Spectrochim. Acta, Part B, 57(5), 2002, 883-895. 

Maia SM, Pozebon D, Curtius AJ. Determination of Cd, Hg, Pb and T1 in coal and coal fly ash slurries using electrothermal vaporization inductively coupled plasma mass spectrometry and isotopic dilution. J Anal At Spectrom... 

Fluosilicic acid fumes - 688, 779 Fluosulfonic acid - 194, 504 Fluothane - 63 Flux - 505 Fly ash 618 Fly ash slurry -194 Food brine - 505 Food processing - 433, 729 Foods and food products - 618, 737, 743, 884 Accent - 848 Bacon - 14 Bacon fat 227 Bakery products - 382 Barbeque sauce 839, 858 Beans - 613 Beef - 142, 228 Beef, extract 839, 858 Beef, gravy - 227... 

The gypsum slurry is dewatered in a solid bowl decanter centrifuge. The byproduct gypsum, which is essentially dry, is taken to storage, and the centrate is recycled. A bleed stream of the precooler water is continuously circulated through a thickener to concentrate captured fly ash. The fly ash slurry is mixed with a bleed stream of centrate, neutralized with limestone slurry, and filtered. The resulting solids are discarded. A portion of the filtrate is also discarded to maintain the water balance and dispose of soluble salts while the main stream is recycled to the absorption circuit. 

Gmtzeckand Siemer [45] have investigated the synthesis of zeolites from a mixture of class-F fly ash and slurry of sodium aluminate prepared in proportion of 3 1 (i.e., Na Al). They have reported that a class-F fly ash reacts with the slurry to synthesize zeolites from a highly alkaline waste stream. The reaction has been studied as a function of mixture (i.e., fly ash slurry) composition (3 2, 1 1, and 1 2), time (1, 3, and 7 days), and temperature (80, 130, and 180 °C). The X-ray diffraction analysis of the products has indicated that the reaction between fly ash and sodium aluminate can result final yield as zeolite A, Na-Pl, and Hydroxy-sodalite at 80, 130 and 180 °C, respectively. It has been clarified that the bulk of the sodium has been incorporated into the zeolitic phases. 

Pozzolan. Diatomaceous earth is a type of pozzolan. Pozzolan refers to a finely ground pumice or fly ash that is marketed as a cement additive under that name. The specific gravity of pozzolans is slightly less than the specific gravity of cement. The water requirements for this additive are about the same as for cements. Only a slight reduction in specific weight of a slurry can be realized by using these additives. The cost of pozzolans is very low. 

Foamed cement slurries have been used to provide a low density cement slurry to reduce permeability damage to highly sensitive formations through reduced fluid loss (29). Glass microspheres have also been used to substantially reduce cement slurry density (30, 31). Other additives which reduce cement slurry density to a lesser extent include bentonite, fly ash, silicates, perlite, gilsonite, diatomaceous earth, and oil emulsions (see citations in reference 29). 

The throw-away processes with aqueous slurries of lime or limestone as the scrubbing media are the most extensively installed processes. These processes create a waste sludge containing calcium sulfite, calcium sulfate, fly ash, unreacted alkali, and other minor dissolved species in the free water contained in the sludge. Since flue gas contains oxygen, some of the dissolved sulfur dioxide is oxidized, and calcium sulfate is formed. 

Improved control devices now frequently installed on conventional coal-utility boilers drastically affect the quantity, chemical composition, and physical characteristics of fine-particles emitted to the atmosphere from these sources. We recently sampled fly-ash aerosols upstream and downstream from a modern lime-slurry, spray-tower system installed on a 430-Mw(e) coal utility boiler. Particulate samples were collected in situ on membrane filters and in University of Washington MKIII and MKV cascade impactors. The MKV impactor, operated at reduced pressure and with a cyclone preseparator, provided 13 discrete particle-size fractions with median diameters ranging from 0,07 to 20 pm with up to 6 of the fractions in the highly respirable submicron particle range. The concentrations of up to 35 elements and estimates of the size distributions of particles in each of the fly-ash fractions were determined by instrumental neutron activation analysis and by electron microscopy, respectively. Mechanisms of fine-particle formation and chemical enrichment in the flue-gas desulfurization system are discussed. 

As in the case of the slag tank, there was no way to measure quantitatively the precipitator residue flow rate. These residues are slurried with water and flushed continuously into the ash pond. However, for all of the elements except selenium, the precipitator was extremely efficient (>95%) as calculated from the inlet and outlet fly ash concentrations using Equation 6. The reason that selenium fails to be scavenged effectively is not known and certainly warrants investigation. One possibility is that part of the selenium is in a volatile state but is readily adsorbed on particulates trapped by the alundum thimbles. 

Figure 15.7. Roofing tiles, extruded from an 80 vol. % fly ash, 20 vol. % Portland cement slurry and treated with supercritical COz...

Land releases of radium are related to atmospheric fallout of coal fly ash (see Section 5.2.1). For example, elevated radium-226 concentrations in snow have been detected near a coal-fired power plant in Poland (Jaworowski et al. 1971). Other land releases may include the disposal of coal fly ash, lime slurry derived from water softening processes, and uranium mine tailings and associated wind-blown dusts. However, no information was located on the total amount of land-released radium... 

Figure 1. Sampling points for fuels (1 and 2), ESP fly ash (5), ash slurries (6 and 8), sluice water (7), sediment and water (9), organic vapors (3 and 4), and suspended particulate matter (4).

Spray drying has become increasingly important in recent years as an alternative to wet scrubbing for sulfur dioxide control. In the spray dryer the sulfur-containing flue gas is contacted with a fine mist of an aqueous solution or a slurry of an alkali (typically Ca(0H)2 or soda ash). The sulfur dioxide is then absorbed in the water droplets and neutralized by the alkali. Simultaneously, the thermal energy of the gas evaporates the water in the droplets to produce a dry powdered product. After leaving the spray dryer the dry products, including the fly ash, are removed with collection equipment such as fabric filters or electrostatic precipitators. 

Particulates of fly ash are very fine. Some of the silica in the ash is found in the form of small silica spheres, called cenospheres or extendospheres, which make ash a very flowable material. This property not only makes ash miscible in a CBPC slurry, but it reduces the viscosity of the slurry and makes the slurry smooth, easily pumpable, and pourable. This property is a great advantage with CBPC-based drilling cements (Chapter 15). 

The earliest use of a small ultrasonic probe to prepare slurries from coal fly ash directly in the autosampler cups was reported by van Loenen and Weers [13]. They found ultrasonic stirring not to ensure slurry homogeneity during the time required for the autosampler to withdraw each sample aliquot unless the analyte was completely leached. 

The hot gas contains soot, formed because of insufficient mixing of the reactants, and fly ash. A waste-heat boiler, a proprietary item of the Shell process, raises 100 bar steam and cools the gas to 340 °C. Soot is removed from the raw gas in a two-stage water wash. Older installation used an elaborate technique to remove the soot from the water by extraction with naphtha and light oil to form soot pellets which could be burnt or recycled to the feed oil. In newer installations the carbon-water slurry is filtered off in automatic filters, and the moist filter cake is subjected to a controlled oxidation in a multiple-hearth furnace. 

Information on the velocity of the particle is found by measuring the transit time of the particle through the sample volume [104]. The instrument has been used in large scale pulverized coal boilers [105-108] char fragmentation and fly ash formation during pulverized coal combustion [109] and for coal slurries [110,111]. 

The solid-liquid limestone slurry enters the scrubber at 50 C the liquid portion of the slurry flows at a rate of 15.2 kg liquid/kg inlet gas and the solid-to-liquid ratio in the slurry is 1 9 by weight. The liquid is saturated with CaCOs and CaS03. The cleaned flue gas meets the EPA standard on SO2 emissions it leaves the scrubber saturated with water at 53X, containing the CO2 generated in the scrubbing but none of the entering fly ash. Sulfur dioxide is the only constituent of the flue gas that is absorbed in the scrubber. The cleaned flue gas is then reheated to 80°C, blended with the cleaned flue-gas stream from the other train, and sent to the stack where it is released to the atmosphere. 

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