Coal Bottom Research Articles

Durability and microstructure characteristics of alkali activated coal bottom ash geopolymer cement

Many studies have focused on the production of mortar and concrete without cement. This is referred to as geopolymer mortar or concrete. This paper discusses the effect of alkali oxides (Na2O = 8, 12, 16 wt.% and SiO2 = 0, 4, 8, 12 wt.%) on compressive strength, microstructure and durability of circulating fluidized bed combustion coal bottom ash (CBA) geopolymer cements (GC). Durability and morphology tests were carried out through heating and freezing tests. The highest compressive strength (25.83 MPa) was achieved at Na2O wt.% = 12, SiO2 wt.% = 8. The optimum atomic ratios for a compact microstructure were obtained for Si/Al between 3.5 and 4 and Si/Na close to 0.5. Following the sintering, the main reaction products (N-A-S-H gel) became more amorphous at 800 °C, attaining Si/Al and Si/Na atomic ratios of 4.54 and 0.98. Sodium carbonate formation was observed at 800 °C. Also, the strength loss of GC was only 6.77% after 30 freeze-thaw cycles. The results show that durable geopolymer concrete without cement can be produced by using waste bottom coal ash. Therefore, the production of geopolymer concrete has a high environmental impact, decreasing waste material in addition to global warming.

Acoustic Emission (AE) Forecasting Rock Burst Key Technology

Acoustic emission (AE) technique is a trend of non-contact technique forecasting coal and rock dynamic disaster.Coal and rock AE propagation attenuation exponent function on different AE frequencies, different quality factors and different propagation distance are acquired by theory and numerical simulation and actual experiment; the effect of AE sensor installation manners on coal and rock surface , coal and rock bottom and wave guide are studied, the results show that the effect of AE sensor installation manner on wave guide is better than on coal and rock surface ,equivalent to installation manner on coal and rock hole bottom. Based on above study results, actual rock bursts are successfully forecasted.

Geopolymer synthetized from bottom coal ash and calcined paper sludge

This study deals with the development of geopolymers synthetized from industrial waste containing aluminosilicates. Geopolymers are inorganic polymers formed by the activation of amorphous aluminosilicates (Al2O3.SiO2), which react in a strongly alkaline medium. Bottom ash (SiO2/Al2O3 = 3.3–4.5) was used as source of aluminosilicate and sodium hydroxide (NaOH = 5, 10 and 15 M) and sodium silicate (Na2SiO3, SiO2/Na2O = 1.58) were used as alkaline medium. Calcined paper sludge was used to increase the reactivity of the partially crystallized bottom ash. The solid waste was characterized by XRF and XRD and the geopolymer samples were characterized by XRF, XRD, SEM, FTIR and compressive strength tests. The best results were obtained with a solution of 15 M NaOH and sodium silicate and a mixture of 2:1 bottom ash and calcined paper sludge.

Resilient Characteristics of Bottom Ash and Bottom Ash-Soil Mixtures

Abstract Bottom ash, a byproduct of the coal combustion process to generate electricity by power plants, is generally underutilized and ends up in landfills or ponds. This paper aims at evaluating the characteristics of the coal combustion bottom ash for potential utilization in pavement construction materials. To achieve this objective, a comprehensive laboratory testing program was undertaken to evaluate the physical properties, compaction characteristics, and resilient modulus of bottom ash, subgrade soils, and bottom ash-soil mixtures. The investigated bottom ash was obtained from power plants in Wisconsin and Michigan. Test results showed that there is a wide spectrum of bottom ash properties pertaining to specific gravity and unit weight, while the investigated bottom ash samples were classified as granular material. Repeated load triaxial testing was performed to determine the resilient modulus of the bottom ash, subgrade soil, and bottom ash-soil mixtures. Specimens were tested at the maximum dry unit weight and optimum moisture content. Test results demonstrated that the resilient modulus values of bottom ash vary depending on the physical properties and unit weight of the bottom ash. For four bottom ash-soil mixtures, the resilient modulus values were low compared with the resilient modulus of subgrade soils, while for one type the resilient modulus was comparable/higher than that of subgrade soil. Therefore, mixing the bottom ash with subgrade soil showed increased resilient modulus values of the mixture for the bottom ash sample from Oak Creek Power Plan (OCPP). Mixing 50% of the bottom ash with subgrade soil, by dry weight, was considered an optimum amount to improve the resilient modulus of the bottom ash soil mixture for OCPP bottom ash.

Production of On-Specification Fuels in Coal-to-Liquid (CTL) Fischer−Tropsch Plants Based on Fixed-Bed Dry Bottom Coal Gasification

The fixed-bed dry bottom (FBDB) gasification technology is ideal for countries with no oil and gas resources but instead have low-rank coals. This technology cannot only provide a secure energy source using high-ash coals but can also in combination with Fischer−Tropsch synthesis be among those technologies able to convert carbonaceous solids to transportation fuels. The integration of refining tar products from FBDB coal gasification with products from the low-temperature Fischer−Tropsch (LTFT) process provides unique opportunities to produce final on-specification fuels.

COMPARISON OF IRRIGATION, LEACHATE AND TREE GROWTH BETWEEN SOILLESS AND COAL ASH BASED MEDIA

In nursery production, knowledge of water quality and quantity is needed to improve irrigation and fertilizer application efficiency as it relates to potential for soil and groundwater contamination. Water and fertilizer use and loss as well as tree growth were investigated for Red Sunset maple (Acer rubrum 'Franksred') trees in a pot-in-pot system with two different potting media and one coal ash based medium. The coal ash based medium (Mix #1) was mainly composed of biosolids, flue gas desulfurization gypsum, and coal combustion bottom ash. The two potting media mainly composed of aged pine bark and steamed composted nursery trimmings as well as left-over potting medium from commercial nurseries, but one with low initial amendments (Mix #2) and the other one with high initial amendments (Mix #3). Trickle irrigation was applied to each tree with an automatic control system. Watering trees started when the medium moisture was below 30%, and stopped when the moisture was 42%. During two-year tests, the amount of water including irrigation and rainfall applied to each tree with Mix #1, #2 and #3 was 741, 910 and 950 L, respectively. The amount of water loss through drainage for each tree with Mix #1, #2 and #3 was 107, 147 and 112 L, respectively. Among the tree media, Medium #3 produced the highest tree growth rate, followed by the Mix #2. The coal ash based medium had great potentials to be used for nursery production.

Electricity from Coal and Utilization of Coal Combustion By-products

Most electricity in the world is conventionally generated using coal, oil, natural gas, nuclear energy, or hydropower. Due to environmental concerns, there is a growing interest in alternative energy sources for heat and electricity production. The major by-products obtained from coal combustion are fly ash, bottom ash, boiler slag, and flue gas desulfurization (FGD) materials. The solid wastes produced in coal-fired power plants create problems for both power-generating industries and environmentalists. The coal fly ash and bottom ash samples may be used as cementitious materials.

Free Swell Characteristics of PCC Bottom Ash-Bentonite Mixtures with Curing for Use as Fill or Liner Material

Bottom ash is a coal combustion product (CCP) obtained from burning of pulverized coal to produce electricity. Most of the bottom ash from pulverized coal combustion (PCC) plants is disposed of in landfills and/or ash ponds. Over the last decade, there has been increased attention aimed toward the use of PCC bottom ash in geotechnical applications. The particle size distribution of pulverized coal combustion (PCC) bottom ash is similar to that of natural sand. Natural sand is commonly used in the construction industry in place of cohesive soils by adding admixtures to amend its properties. Several studies have been completed to determine the properties of bottom ash amended with bentonite. However, due to significant volume change characteristics of bentonite, soils or similar granular materials amended with it need to be evaluated for their swelling behavior. In addition, studies on bottom ash-bentonite mixtures have shown that strength and stiffness characteristics of these mixtures change significantly with curing. Therefore, in order to evaluate the use of bottom ash as a fill or landfill liner material, this study was initiated to investigate the effect of curing and moisture content on the swelling characteristics of pulverized coal combustion bottom ash amended with bentonite. Bottom ash specimens containing 15 and 20 percent bentonite and prepared at 14, 16 and 18 percent initial moisture content were tested in this investigation. Results presented show the swelling characteristics of bottom ash-bentonite mixtures with curing age up to 60 days.

Swell Potential of Pulverized Coal Combustion Bottom Ash Amended with Sodium Bentonite

Within the last decade several studies have been conducted to evaluate the geotechnical properties of bottom ash obtained from electric utilities burning pulverized coal amended with admixtures such as clay, bentonite, and lime. Most of these studies concentrated on evaluating strength and stiffness characteristics of the mixtures. Because of the high volume change characteristics of bentonite and clay, improper and/or excessive use of these admixtures can impart significant swelling characteristics to the mixtures. This study was conducted to evaluate the swelling properties of two bottom ash-bentonite mixtures compacted at various initial moisture contents. Results from this detailed investigation show that the swelling potential increased with the increase in bentonite content and decreased with the increase in initial moisture content. Mixtures with 20% bentonite were observed to have volume change characteristics that may not be suitable for some lightly loaded structures. Mixtures with 15% bentonite; compacted at initial moisture contents of 18% or higher; were observed to have less than 4% free swell, whereas for mixtures compacted at an initial moisture content of 16% or lower, the percent increase in free swell was observed to be greater than 7%.

Solvent de-ashing from heavy product of brown coal liquefaction using toluene 1. Solubility of heavy products and settling velocity of ash

The Brown Coal Liquefaction (BCL) process is a two-stage liquefaction (hydrogenation) process developed for Victorian brown coal in Australia. In the BCL process, the heavy product (vacuum residue) derived from the coal in the primary hydrogenation, which is named CLB (coal liquid bottom, boiling point > 420°C), is treated in a solvent (CLB/solvent ratio, 18–14, wt./wt.) under high temperature (200–290°C) and high pressure (4–5 MPa) to remove the ash and heavy preasphaltenes. This solvent de-ashing process uses toluene or coal-derived naphtha as a de-ashing solvent. After dissolving the CLB into the solvent, insoluble solid particles which consist of the ash and heavy preasphaltenes are settled in a settler by gravity and separated from the solution as an ash-concentrated slurry. The ash-concentrated slurry and the de-ashed solution are withdrawn from the settler as an underflow and overflow, respectively. The de-ashing solvent is recovered from both the overflow and underflow by distillation, and reused in the de-ashing process. The de-ashed heavy product recovered from the solution by eliminating the solvent is further hydrogenated in the secondary hydrogenation. This paper discusses the solubility of the CLB into toluene and settling velocity of the ash under the de-ashing conditions. The extraction experiments made clear that toluene dissolved ∼ 60 wt.% of preasphaltenes (benzene insoluble-pyridine solubles) in the CLB under the following conditions, temperature 100–300°C and CLB/toluene ratio (wt./wt.) of 13 or less. This solubility of CLB (ϵCLB) under the de-ashing conditions is expressed as ϵCLB = CBS + 0.6CBIorg, where CBS and CBIorg are the contents of benzene solubles and organic benzene insolubles, respectively, and organic CLB (ash-free CLB) = CBS + CBIorg. The de-ashing experiments confirmed that the insolubles including ash formed a boundary of concentration during the settling period, and the de-ashing efficiency was represented by the settling velocity of the boundary (V), V is expressed as V = ACLB(CSA/2.5)−0.91(T/573)9.5. Where, ACLB, CSAand T are parameters expressing the properties of organic CLB, ash content in the feed slurry (wt.%) and temperature (K), respectively. The ACLB is also expressed by using the analytical results of the organic insolubles in the CLB under the de-ashing conditions. The ash content of the de-ashed heavy product recovered from the upper zone of the boundary is less than 3000 ppm, which is low enough to feed as a mixture with two times of the middle distillate to the secondary hydrogenation over NiMo catalyst with fixed bed reactors.

褐炭液化重質物の性状と二次水添反応性

褐炭液化重質物の性状と二次水添反応性

COAL RANKS IN THE HARTON BOREHOLE

(Short communication) Ridd, Walker and Jones (1970) interpreted the top coals in the Harton borehole as of normally-expected rank, the middle coals as having been raised in rank by heat from three leaves of the Whin Sill, and the lowest coals to be of such a high rank that the steep rank gradient from top to bottom required a special explanation. It can be inferred that they expected no increase in rank with depth, for they stated “… instead of returning [at the bottom] to reflectivities of about 1.00 as occur at the top of the hole …”. Further, they considered that “… it seems likely that the high coal rank gradient was the result of a high heat flow from the buried granite basement”. The coals range through a depth of 1,610 metres. The carbon content of the top coal, judged by reflectivity measurements, was 82 per cent, and of the bottom coal 92 per cent. The need for a special explanation disappears if it can be shown that the increase of carbon content is within the range to be expected from the increase of depth. The carbon contents of the coals of the Pie Rough borehole in north Staffordshire (Millott et al., 1946) increase linearly from 81 to 89 per cent over a depth of 1,070 metres. Linear extrapolation of the carbon/depth gradient to 92 per cent suggests that an increase from 82 to 92 per cent carbon would be attained in 1,340 metres. Thus the depth of ...

On Two Rounded Boulders from an Anthracite Seam, South Wales

In 1942 (p. 21) the author described the occurrence, petrological characters and origin of fourteen rounded boulders found in and associated with coal seams in South Wales. Recently W. D. Ware discovered another two boulders or erratics as they are sometimes called, amongst coal on the picking belt, probably derived from the Dulais Seam, at the Cefn Coed Colliery. Three specimens have already been noted at this colliery (1942, pp. 27, 28), one found in situ in the bottom coal of the Dulais Seam and the other two in coal probably derived from this seam.

Description of the Remains of numerous Fossil Dicotyledonous Trees in an Outcrop of the Bottom Coal at Parkfield Colliery, near Bilston

At a depth varying from forty to fifty yards below the Ten-yard stratum of the South Staffordshire coal-field, there are usually found three deposits of coal, called the Top , the New Mine , and the Bottom Coal . When these beds can be readily worked, they are scarcely inferior in value to the Ten-yard coal, the Top and New Mine deposit, with the intervening shales and partings, often forming a series of strata eight yards in thickness. Below this a few beds of ironstone occur; then a bed of fire clay about three yards in thickness, and immediately under this the Bottom Coal . At Parkfield Colliery, 1 ½ miles west of Bilston, and at about the same distance south of Wolverhampton, there is a fine outcrop of this Bottom Coal , which is now being got in open work. In one part the overlying fire clay has been removed, and the surface of the coal exposed, over an area of a somewhat triangular shape, for about 2,700 square yards. This terrace of coal exhibits on its surface one of the most remarkable accumulations of the fossil remains of the vegetation of the coal period ever exposed to view. There are upwards of seventy trunks of trees, apparently dicotyledonous, broken off close to the root, and several of them are more than 8 feet in circumference; the prostrate trunks lying across each other in every direction.

On a Fossil Forest in the Parkfield Colliery near Wolverhampton

The fossils alluded to in the following notice, occur in an open work, that is, the superincumbent strata have been pared off, and we find the coal (which belongs to what is called the “bottom coal,”) well exposed to view. The bed has been bared for upwards of two years, but the fossils do not appear to have attracted attention, till Mr. William Sparrow and myself, whilst tracing the great faults of the South Staffordshire coal-field, accidentally stumbled upon them, and were struck with their number and their evident resemblance to trunks of trees. Since that time, by the kind permission of the Parkfield Company, and with the assistance of Professor Orlebar, of the Royal Bengal College in Bombay, I have carefully removed the coal attached to the roots of one of the trees. We found the stump to be perfectly bituminized, but broken off about two inches above the level of the coal measure, the inner part being somewhat hollowed to about the level of the coal itself: the surface and edges of the broken part were smoothed or probably water-worn. The tree bared was not flattened, but preserved precisely the same appearance which I have noticed with peat timber in Ireland, and was 4 feet in circumference. The principal root extended southwards 22 inches, terminating abruptly.