Slag Deposits Research Articles

Monitoring near burner slag deposition with a hybrid neural networksystem

This paper is concerned with the development of a system to detect andmonitor slag growth in the near burner region in a pulverized-fuel (pf) firedcombustion rig. These slag deposits are commonly known as ‘eyebrows’ and canmarkedly affect the stability of the burner. The study thus involved a series ofexperiments with two different coals over a range of burner conditions usinga 150 kW pf burner fitted with simulated eyebrows. These simulatedeyebrows consisted of annular refractory inserts mounted immediately in frontof the original burner quarl. Data obtained by monitoring the infra-redradiation and sound emitted by the flame were processed to yield time andfrequency-domain features, which were then used to train and test a hybrid neuralnetwork. This hybrid ‘intelligent’ system was based on self organizingmap and radial-basis-function neural networks. This system was able toclassify different sized eyebrows with a success rate of at least 99.5%.Consequently, it is possible not only to detect the presence of an eyebrowby monitoring the flame, but also the network can provide an estimateof the size of the deposit, over a reasonably large range of conditions.

Physical separation of straw stem components to reduce silica.

In this paper, we describe ongoing efforts to solve challenges to using straw for bioenergy and bioproducts. Among these, silica in straw forms a low-melting eutectic with potassium, causing slag deposits, and chlorides cause corrosion beneath the deposits. Straw consists principally of stems, leaves, sheaths, nodes, awns, and chaff. Leaves and sheaths are higher in silica, while chaff, leaves, and nodes are the primary sources of fines. Our approach to reducing silica is to selectively harvest the straw stems using an in-field physical separation, leaving the remaining components in the field to build soil organic matter and contribute soil nutrients.

Post-harvest processing methods for reduction of silica and alkali metals in wheat straw.

Silica and alkali metals in wheat straw limit its use for bioenergy and gasification. Slag deposits occur via the eutectic melting of SiO2 with K2O, trapping chlorides at surfaces and causing corrosion. A minimum melting point of 950 degrees C is desirable, corresponding to an SiO2:K2O weight ratio of about 3:1. Mild chemical treatments were used to reduce Si, K, and Cl, while varying temperature, concentration, % solids, and time. Dilute acid was more effective at removing K and Cl, while dilute alkali was more effective for Si. Reduction of minerals in this manner may prove economical for increasing utilization of the straw for combustion or gasification.

An assessment of the magnetic response of an iron‐smelting site*

The magnetic response derived from an iron‐smelting site was investigated by comparing magnetometry and magnetic susceptibility geophysical survey data and laboratory analyses of the magnetic characteristics of the furnace and slags. Magnetic analysis and microscopy (optical and SEM) of samples from the furnace lining and the slag deposits demonstrated the heterogeneity in the magnetic, morphological and mineral compositions of both materials. The comparison of the magnetic characteristics of the material with the geophysical survey data illustrated the importance of using both magnetometry and magnetic susceptibility survey techniques to maximize the information from an iron‐smelting site. The furnace was dated archaeomagnetically to the 14th century ad. The results demonstrate that the magnetic analysis of iron‐smelting sites is highly valuable, both to characterize sites and to improve the understanding of early iron‐working technology.

Red thermoluminescence of quartz and its application in dating archaeometallurgical slag.

Slag is often the only relic of early pyrometallurgical processes. In archaeological research information about the age of slag deposits is needed and diflicult to obtain with traditional methods. Thermoluminescence has a great potential in this field, because the smelting process leads to a well defined resetting of the 'Luminescence Clock'. Metallurgical slag generally consists of many components, artificial secondary minerals, e.g. fayalite and glass phases usually being the dominant parts. Primary minerals, called relics, are also components or slag. Such a complex composition leads to large difficulties in palaeodose determation if the bulk slag is used. To overcome these problems defined phases of the slag have been separated. Palaeodose determination has been carried out on separated quartz fractions by 'Single Aliquot Regeneration' procedures using the 620 nm emission. The dose rate was determined by high-resolution gamma spectrometry. Alpha autoradiography was carried out to get information about the distribution of radionuclides. The study includes first dating results.

Geophysical Investigation at the Falling Creek Ironworks, an Early Industrial Site in Virginia

AbstractA geophysical investigation was conducted at the site of the Falling Creek Ironworks (1619–1622), the first iron production facility in North America. Electrical resistance and magnetic field gradient surveys were conducted over the site of the seventeenth century ironworks. Additionally, ground‐penetrating radar was used to investigate areas under an existing roadway. Linear and rectangular anomalies that appear in the resistance data may be caused by architectural features, possibly shops or domestic structures associated with the ironworks. Several low‐amplitude magnetic anomalies that appear in the data appear to be cultural in origin, and may be caused by features associated with the ironworks. A number of high‐amplitude magnetic anomalies appear in the magnetic field gradient data that are thought to be associated with iron production, including extensive slag deposits and the possible location of the blast furnace. Ground‐penetrating radar data shows an anomalous reflection in the vicinity of the suspected blast furnace, which is partially beneath the modern roadway. Copyright © 2001 John Wiley & Sons, Ltd.

Ash deposition of a Spanish anthracite: effects of included and excluded mineral matter

This study has been undertaken to provide an insight into the effects of mineral matter distributions in coal on the nature of boiler slags formed during the combustion of a high ash Spanish anthracite. Three density fractions were prepared, and the light and heavy fractions were combined to give a sample containing mainly excluded mineral matter. The mineral matter in the medium density fraction was predominantly included. Slag deposits were prepared in the laboratory from the whole coal, the light+heavy and medium density fractions. The coal with excluded mineral matter was found to produce a slag similar in nature and chemistry to the whole coal ash deposit. The coal with included mineral matter produced a vitreous, iron-rich deposit. The deposits were compared with slags, obtained from a Spanish power station boiler, burning a blend containing the same anthracite.

Geochemical and mineralogical controls on trace element release from the Penn Mine base-metal slag dump, California

Base-metal slag deposits at the Penn Mine in Calaveras County, California, are a source of environmental contamination through leaching of potentially toxic elements. Historical Cu smelting at Penn Mine (1865–1919) generated approximately 200,000 m 3 of slag. The slag deposits, which are flooded annually by a reservoir used for drinking water and irrigation, also may be in contact with acidic ground waters (pH<4) from the adjacent mine area. Slags vary from grey to black, are glassy to crystalline, and range in size from coarse sand to large (0.6×0.7×1.5 m), tub-shaped casts. Metals are hosted by a variety of minerals and two glass phases. On the basis of mineralogy, slags are characterized by 4 main types: fayalite-rich, glassy, willemite-rich, and sulfide-rich. The ranges in metal and metalloid concentrations of 17 slag samples are: As, 0.0004–0.92; Ba, 0.13–2.9; Cd, 0.0014–1.4; Cu, 0.18–6.4; Pb, 0.02–11; and Zn, 3.2–28 wt.%. Leachates from Toxicity Characteristic Leaching Procedure tests (acetic acid buffered at pH 4.93) on two willemite-rich slags contained Cd and Pb concentrations (up to 2.5 and 30 mg/l, respectively) in excess of US Environmental Protection Agency (USEPA) regulatory limits. Analyses of filtered (0.45 μm) water, collected within the flooded slag dump during reservoir drawdown, reveal concentrations of Cd (1.7 μg/l), Cu (35 μg/l), and Zn (250 μg/l) that exceed USEPA chronic toxicity guidelines for the protection of aquatic life. Data from field and laboratory studies were used to develop geochemical models with the program EQ3/6 that simulate irreversible mass-transfer between slag deposits and reservoir waters. These models include kinetic rate laws for abiotic sulfide oxidation and surface-controlled dissolution of silicates, oxides, and glass. Calculations demonstrate that the main processes controlling dissolved metal concentrations are (1) dissolution of fayalite, willemite, and glass; (2) sulfide oxidation; and (3) secondary phase precipitation. Close agreement between model results and measured concentrations of Al, Ba, Cu, Fe, SiO 2, and SO 4 in the slag dump pore waters suggests that the dissolved concentrations of these elements are controlled by solubility equilibrium with secondary phases. Differences between predicted and measured Cd and Pb concentrations imply that field weathering rates of glass and sulfides are approximately two orders of magnitude lower than laboratory rates. Overprediction of Pb release may also reflect other attenuation processes in the natural system, such as sorption or coprecipitation.

A luminescence study for dating archaeometallurgical slagspaper

A reliable direct dating method for archaeometallurgic slag has not yet been achieved. Nevertheless, in archaeological and environmental research information about the age of slag deposits is urgently needed. Metallurgical slag consists of many components. Artificial secondary minerals, for example fayalit, olivine and glass phases are the dominant parts. In many cases primary minerals, called relicts, are also components of slag. Quartz, baryte and fluorite are examples. Such a complex composition leads to large difficulties in paleodose determination if the bulk slag substance is used. On the other hand, slag has a complicated microdosimetry caused by great differences between the individual mineral phases and the possibility of inhomogeneous radionuclide distribution. To overcome these problems in luminescence dating defined phases of the slag have been separated by special chemical and physical procedures. Quartz and glass fractions were investigated by thermoluminescence (TL) and radioluminescence (RL)-spectrometry. Alpha-autoradiography using Kodak LR-115 foil was carried out to get information about the distribution of radionuclides.

Assessment of radioecological situation of a site contaminated by technologically enhanced natural radioactivity in Croatia

The paper deals with radioactivity contamination originating from the coal fired power plant and its waste dumps located in a bay of the Adriatic which is due to geographical characteristics sensitive to any kind of pollution including radioactivity. Investigations of coal used in regular plant operation and of solid incombustible ash and slag showed increased concentrations of natural radioactivity which may cause general environmental contamination of the bay as well as contamination of the marine environment of this part of Croatian Adriatic. There are two coal slag and ash piles, one of them was closed and covered by soil and the other is a still operating pile. The location of both piles presents a considerable environmental problem: situated close to the seaside, slag and ash are accumulating in the littoral zone and, in the case of operating pile, are being filled-up directly into the sea. The aim of this study was to determine the radioactivity level at the ash and slag deposits and to assess the risk of increased radioactivity for the inhabitants of the nearby urban area, for the plant workers and general environment of the bay including the marine environment of this part of the Croatian Adriatic.

Rapid water quenching and formation of thermal fatigue cracks on the surface of a tube

In the process of combustion of low-grade solid fuels with complex composition of the mineral part, the heat exchange surfaces of boilers are covered with rapidly growing slag and ash deposits. Water cleaning is one of the most efficient methods of removal of deposits of this sort from the heated surfaces of boilers. As a result of rapid cooling of the outer surface of the metal, the protective oxide coating is destroyed and this accelerates the high-temperature corrosion of the metal and the formation thermal fatigue cracks. The criterion of appearance and the intensity of growth of thermal fatigue cracks strongly depend on the temperature field in the outer layer of the metal. We present the solution of the nonstationary heat conduction equation under the conditions of rapid cooling. The coefficient of convective heat transfer from the heated metal surface to the water jet is determined experimentally. We also study the conditions necessary for the initiation of thermal fatigue cracks and the intensity of their growth under laboratory and industrial conditions. A special formula is deduced for the evaluation of the intensity of crack growth depending on the number of cleaning cycles.

99/00666 Initiation of flame spreading on shallow sub-flash fuel layers

This is the first study in which the mechanism of burner slagging in a furnace firing pulverized coal has been investigated. The objective was to relate the in-flame transformations of the coal minerals to the nature of the slags formed on deposition probes designed to simulate a burner quarl and a superheater tube. The experiments were performed in the 2.5 MW refractory-lined IFRF furnace No. 1, using a swirl-stabilized pulverized coal burner, firing a pyrite-rich coal. In-flame samples and slag deposits were extracted and analysed for pyrite and pyrite decomposition products by electron probe microanalysis and X-ray diffraction. Immediately after injection into the flame, pyrite (FeS2) decomposed to pyrrhotite (FeS), molten droplets of which were oxidized to solid iron oxide (Fe3O4 and Fe2O3) particles in both the internal and external recirculation zones in the furnace. Owing to the complex flow pattern in the furnace, the kinetics of the pyrite conversion steps could not be directly determined but were indirectly derived from a comparison with the coal devolatilization and char oxidation steps. It is concluded that the decomposition of pyrite proceeds as fast as the coal devolatilization step and that the oxidation of pyrrhotite to iron oxide is as fast as the oxidation of the coal/char.

The geophysical evaluation of an iron-working complex: Rievaulx and environs, North Yorkshire

Geophysical techniques are often considered to have little application on iron-working sites because the responses from large quantities of iron slag can mask structural remains associated with iron production. This may result in the incomplete or erroneous interpretation of the geophysical data. Geophysical surveys, can, however, identify the strong magnetic anomaly associated with a furnace and in these circumstances have worked well. Slag can produce a wide range of responses, which may be attributed to changes in iron-content, depth of burial and thickness of the slag deposit. A more detailed examination of the data, therefore, can often lead to the identification of structures. The geophysical survey work in the Rievaulx area in North Yorkshire, England has examined iron-working activity ranging from a bloomery site to a blast furnace with a finery/chafery complex. Geophysical surveys were undertaken on eight sites to measure magnetic anomalies, magnetic susceptibility and earth resistance. One geophysically surveyed bloomery site was subsequently excavated. The geophysical interpretations can be compared with the historical evidence. Cistercian monks from Rievaulx Abbey operated several of the sites surveyed. After the dissolution of the Abbey in 1538, iron-making continued under the Duke of Rutland, who constructed a charcoal-fired furnace at Rievaulx in ca. 1570. The geophysical work has led to a reassessment of the use of water-power, which was associated with two finery/chafery complexes in the Rievaulx area. Most of the surveys have identified iron-working features that can be matched to topographic changes. The paper covers the results from some of the Rievaulx surveys and details the types of feature than can be identified, including furnace sites, buildings, leats and slag tips. Copyright © 1998 John Wiley & Sons, Ltd.

97/02755 Apparatus for coal gasification with prevention of slag deposits

97/02755 Apparatus for coal gasification with prevention of slag deposits

97/01020 Apparatus for coal gasification with fluidized bed for slag deposit

97/01020 Apparatus for coal gasification with fluidized bed for slag deposit

Rapid formation of rock varnish and other rock coatings on slag deposits near Fontana, California

AbstractManganiferous rock varnish, silica glaze and iron skins have formed on 20‐ to 40‐year‐old slag piles near Fontana, southern California. Rapid rock‐varnish formation is associated with an unidentified cocci bacterium that grows rapidly in culturing experiments, combined with the likelihood that Mn‐rich solutions flow over slag surfaces. A new model is proposed for the formation of silica glaze, involving soluble Al‐Si complexes and the nature of wetting films. Iron skins occur where runoff is concentrated, and where iron bacteria grow.Observations indicate: (i) substrate can be important in supplying Mn, as well as maintaining a stable surface and channelling runoff to microspots where varnish grows; (ii) ignorance of boundary layer pH/Eh conditions makes chemical‐physical models of varnish formation speculative; (iii) the balance between cementation of recently nucleated varnishes and erosional shear stresses is poorly understood, but is probably an important limiting factor on varnish growth rates; and (iv) there must be at least two steps in biotic varnishing‐accretion of Mn‐Fe in casts, followed by cementation of clays by either in situ cast residue or Mn‐Fe remobilized from casts. Varnish accretion may be limited by the rate at which both steps occur. Rapid development of readily distinguishable manganiferous rock varnishes at this post‐1952 site highlights the danger of speculation on the ages of landforms based solely on the appearance of rock‐varnish coatings.

Grain characteristics of crops grown on power plant ash and bottom slag deposit

Our objective was to study mature grains of crops grown on various areas of power plant ash and bottom slag deposits. It was found that good grain quality with the application of usual agricultural techniques and intensified fertilization on various parts of ash and bottom slag deposits may be achieved with: autumn rye (Secale cereale L.), alfalfa (Medicago sativa L.), barley (Hordeum sativum Jessen) and, to a lesser extent, winter raps (Brassica napus L.).

Flame transformations and burner slagging in a 2.5 MW furnace firing pulverized coal: 1. Flame transformations

This is the first study in which the mechanism of burner slagging in a furnace firing pulverized coal has been investigated. The objective was to relate the in-flame transformations of the coal minerals to the nature of the slags formed on deposition probes designed to simulate a burner quarl and a superheater tube. The experiments were performed in the 2.5 MW refractory-lined IFRF furnace No. 1, using a swirl-stabilized pulverized coal burner, firing a pyrite-rich coal. In-flame samples and slag deposits were extracted and analysed for pyrite and pyrite decomposition products by electron probe microanalysis and X-ray diffraction. Immediately after injection into the flame, pyrite (FeS 2) decomposed to pyrrhotite (FeS), molten droplets of which were oxidized to solid iron oxide (Fe 3O 4 and Fe 2O 3) particles in both the internal and external recirculation zones in the furnace. Owing to the complex flow pattern in the furnace, the kinetics of the pyrite conversion steps could not be directly determined but were indirectly derived from a comparison with the coal devolatilization and char oxidation steps. It is concluded that the decomposition of pyrite proceeds as fast as the coal devolatilization step and that the oxidation of pyrrhotite to iron oxide is as fast as the oxidation of the coal/char.

Flame transformations and burner slagging in a 2.5 MW furnace firing pulverized coal: 2. Slagging

Results are reported of a 3 day slagging trial with a 2.5 MW semi-industrial-scale furnace in which the near-burner conditions of a wall-fired boiler were simulated. The fuel was a pyrite-rich pulverized coal. Slag deposit probes were placed near the burner wall, simulating the refractory burner quarl with surrounding wall tubing. The side of the probe facing the incoming fuel stream was covered with a molten deposit similar to that on the burner quarl of the furnace and to deposits in the near-burner region of full-sized furnaces. Slag was formed on the refractory material of the probes and not on the water-cooled tubes surrounding it, suggesting that slagging in the near-burner region in real boilers may also be initiated on the refractory quarl rather than on the surrounding water-wall. The ash deposits were analysed in-depth by SEM and EPMA. The nature of the deposits was related to the changes undergone by the minerals in the flame before deposition. It was deduced that deposition of molten pyrrhotite (the first flame product of pyrite) together with silicates resulted in an iron silicate deposit with a very low melting point, accounting for the molten character of the slag. The deposit adhered less strongly to silicon carbide as the probe material than to alumina. The reverse side of the probe, facing downstream, was covered with a loose powder of discrete iron oxide and silicate particles, consistent with the presence of fully oxidized solid pyrite particles in the furnace at this position.

An investigation into the effectiveness of fireside fuel additives

A combination of laboratory prescreening tests and longer trials on a 2MW industrial chaingrate stoker have been used to investigate the effectiveness of fuel additives at alleviating alkali bonded fouling. In addition, the effect of copper oxychloride on slagging was assessed using a 150kW pilot scale pulverised fuel combustor. The studies indicated that additive performance was generally combustion regime specific. Magnesium oxide or hydroxide based additives were found to increase the level of available sodium, resulting in increased quantities and strength of fouling deposits in stokers. Kaolinite proved the most potentially beneficial antifoulant, reducing the available sodium levels and producing a corresponding reduction in deposition. Addition of copper oxychloride to an iron rich coal resulted in a change in the distribution of spinel phases in slag deposits collected.