Use Of Fluidized Bed Combustion Research Articles

Fluidized bed combustion fly ash as filler in composite polyurethane materials

Fly ash (FA) is a waste material having great potential as modifier of mechanical and thermal properties in polyurethane (PUR) technology. There are very few reporting the use of fluidized bed combustion (FBC) FA in the production of PUR foams. In this work, authors have used the as received FBC FA as an additive to PUR rigid foams. The composite materials containing 5, 10, 15, and 20 wt% of FA were obtained by hand mixing and casting method. Microscopic observations of both unmodified and composite foams showed a well formed, cellular structure of the rigid foam. The cell structure was uniform; most of the cells were closed, which was an important parameter influencing thermal insulation properties of PUR materials. FA was uniformly distributed within PUR matrix and placed between cells. When the content of FA in composite foams increased, cells’ dimensions decreased, which suggested that FA particles acted as nucleation sites during the foam formation process. The absorption bands presented in IR spectrum of PUR foam confirmed the presence of urethane bonds in the unmodified foam material. The IR spectrum of as-received FA reconfirmed the crystalline phases recognized by XRD analysis, which were anhydrite, quartz, lime, calcite and aluminosilicate. No additional bands were observed which suggested that no chemical bonding between PUR matrix and FA particles occurred in the composite foam. The incorporation of FA into the PUR matrix, up to 10 wt%, improved the mechanical performance of the composite materials, when compared to unmodified PUR foam. Such a tendency suggested the occurrence of interfacial interactions between polymer matrix and FA particles, as well as the uniform distribution of the filler within PUR material. For all the materials analyzed, the addition of FA to PUR foam reduced both carbon content and the gross calorific value. The addition of FA improved the thermal stability of the PUR foam material (barrier effect of the FA prevented the release of gases from the foam structure).

Study of Ettringite by Hydration of Yeelimite Clinker

This article describes the results of experimental works, dealing with long-term observing of ettringite stability (Ca6Al2(SO4)3(OH)12·26H2O). Thermodynamic stability of this mineral is important in terms of potential use of fluidized bed combustion (FBC) ash as an additive to Portland cement. Within the experimental work it was carried out observing of the ettringite formation by hydration of yeelimitu (Ca4Al6(SO4)·O12) in laboratory conditions. For the preparation of yeelimite it was proposed a three-component raw material mixture, consisting of a high percent limestone and gypsum and corundum. This mixture was subsequently placed in platinum crucibles and burnt in superkanthal kiln at 1200 °C. Formed clinker was mixed in chosen ratio with water and it was prepared a set of testing samples. These samples were exposed in the laboratory environment for up to 180 days. The hydration of the clinker was carried out using X-ray diffraction analysis (XRD) by determining the mineralogical composition.

Scavenging of High-Value Product from High-Ash Medium Coking Coal: A Compulsion for Less Endowed Regions

Beneficiation of a high-ash (35%) medium coking coal to obtain a low-ash (12%) clean coal product is investigated. Characterization studies indicated that this coal can be processed after reducing the size to 1.18 mm in order to achieve reasonable yield of the clean coal at such a low target-ash level. The desired ash reduction is possible only after treating different size fractions of the −1.18 mm crushed coal separately. A gravity-based processing scheme comprising of a spiral-floatex circuit along with multigravity separator for the −1.18 + 0.5 mm fraction is developed to generate clean coal at 12% ash with 10.3% overall yield. Mechanical cell flotation circuit for the −0.5 + 0.15 mm size fraction resulted in additional 5.2% yield at 12% target ash level for the clean coal. A flotation circuit for the ultrafine fraction (−0.15 mm) is also developed using Jameson cell flotation that added further 4.4% yield in the overall mass recovery of the combustibles at the desired ash level. Thus, a total of 20% yield of the clean coal with 12% ash is achieved by treating various size classes separately. Application of the clean coal is recommended for metallurgical purpose. Out of the remaining 80% material, 35% is recovered at a 27% ash level that is recommended for use in sponge iron sector. The balance 45% with an ash level of 50% is marked for use in fluidized bed combustion for power generation. A complex flowsheet such as the one described in the present article is likely to be the future requirement for processing high-ash medium coking coals to a high-value low-ash product to enhance its utilization potential for metallurgical purpose.

ASH formation mechanisms during combustion of wood in circulating fluidized beds

Fluidized-bed combustion has been increasingly applied for combustion of low-grade fuels, such as solid biomass and waste, Sometimes the use of certain fuels may be limited due to unanticipated deposition and corrosion in the boiler. Consequently, mechanistic understanding of the behavior of ash-forming compounds in Hindized-bed combustion is crucial for further increase in the use of fluidized-bed combustion for biomass and waste fuels. The mechanisms of ash formation during circulating fluidized-bed combustion of two wood-based biomass fuels, forest residue and willow were determined experimentally at a 35 MW cogeneration plant. In-duct fly ash samples were collected in two locations in the boiler. The fly ash particle mass size distributions were determined with a low-pressure impactor. In addition, samples of fly ash from electrostatic precipitator (ESP) hoppers. bottom ash, sand, and fuels were collected periodically for analysis. Flue gas composition and process parameters were monitored throughout the experiments. Approximately 25% of the ash was removed from the furnace as bottom ash The bottom ash was found to be formed by deposition of the ash particles on the surface of the quartz sand and by diffusion of the ash compounds into the sand. Fly ash consisted of two distinctly different modes. Fine fly ash particle mode was formed hynucleation of volatilized species and contained mainly KCL and K2SO4 during combustion of forest residue and willow, respectively, Coarse fly ash mode contained particles which were irregular agglomerales and they were formed from the non-volatile ash species by coalescence and agglomeration inside the char particles and on their surfaces. The agglomerate structure of the coarse ash was effective in capturing volatile species in coarse particles, and it may have a significant effect on the deposition tendency of the particles.

Coal rejects — a wasted resource?

The paper outlines potential uses for coal washery rejects. It considers in detail the use of fluidized-bed combustion as a means of lessening rejects disposal problems, as a method of recovering energy for drying, steam raising and electricity production and as a source of ash as a substitute for natural aggregate. Considerable technical information is now available on the use of fluidized beds for these purposes and the paper concludes that it is appropriate to consider a more detailed, site-specific, evaluation.

Heat Transfer in Large Particle Bubbling Fluidized Beds

The potential use of fluidized bed combustion of coal as a means of meeting air quality standards with high-sulfur fuels has motivated the development of theoretical models of heat transfer in large particle gas fluidized beds. Models of the separate contributions of emulsion and bubble phase heat transfer have been developed by Adams and Welty [1] and Adams [2, 3, 4] and have been substantiated by experimental data for a horizontal tube immersed in a two-dimensional cold bed obtained by Catipovic [5, 6]. The consolidation of these models to predict local and overall time-average heat transfer to immersed surfaces requires information regarding emulsion phase residence time and bubble phase contact fraction for the particular geometry of interest. The analytical procedure to consolidate these models is outlined in the present work, then applied to the case of a horizontal tube immersed in a two-dimensional atmospheric pressure cold bed. Measurements of emulsion phase residence time and bubble phase contact fraction obtained by Catipovic [5] are used in the calculations for particle diameters ranging from 1.3 to 6 mm. The results agree favorably with experimental data and further substantiate the fundamental assumptions of the model.

Effectiveness of SO 2 sorbents by thermogravimetry-combustion with coal

A new experimental method is described for non-isothermal thermogravimetry (TG) involving combustion of mixtures of sieved coal with sieved calcium-containing sorbents. This rapid TG method utilizes a baseline for TG combustion of coal alone, derives an equation that gives a semi-quantitative measure (±10% repeatability) of the coal's reactive sulphur retained by the sorbent, the extent of retention of S0 2 generated in situ during combustion varying with different sorbents. The method permits direct variation in separate experiments of the calcium-to-sulphur ratio during combustion and relative ranking of different sorbents by retention of reactive sulphur in combustion. Relative rankings are presented for three pre-calcined natural stones (two limestones and one dolomite); these results correlate with relative rankings from another TG method reported in the literature. It is suggested that this new method is useful for pre-screening the effectiveness of S0 2 sorbents considered for use in fluidizedbed combustion of coal.