Atmospheric Fluidized Bed Combustion Research Articles

Using FBC and Stoker Ashes as Roadway Fill: A Case Study

Approximately 100,000 m3 of atmospheric fluidized bed combustion (FBC) ash and stoker ash were used as structural fill in the construction of a large roadway embankment. The embankment is ∼200 m long and 10 m high, and it supports an extension of a street across a gravel quarry in West Lafayette, Ind. The use of coal combustion by-products on this project was motivated by the need to find cost-effective alternatives to the disposal of these materials in solid-waste landfills. Similar projects have been completed using the more common bottom ash and fly ash. However, little information is available related to the performance of FBC and stoker ashes in this application. An overview of the project and construction operations is described, and the results of geotechnical laboratory tests and field monitoring are presented. Instruments used in the monitoring of fill behavior include settlement plates, vertical and horizontal inclinometers, seismic cross-hole tests, and postconstruction standard penetration tests. The compacted FBC material exhibited significant swell stresses and strains and is still expanding 2 years after construction.

Experimental study on fluidized-bed start-up process with hot gas

For simulating the Pressurized Fluidized Bed Combustion (PFBC) start-up with high-temperature oil-fired gas, systematical experimental study and theoretical analyses were carried out on an Atmospheric Fluidized Bed Combustion (AFBC) test facility which has a water-cooled distributor in cross-section of 0·664 m×0·656 m. The characteristics of heat transfer of the water-cooled distributor were revealed. The effects of some operating parameters on the normal start-up process are evaluated. The findings reported in this paper are used to provide a data base for designing PFBCB start-up systems. It can also be applied to the design of AFBC boilers and the improvement of existing ones. © 1998 John Wiley & Sons, Ltd.

98/01461 Rotary regenerative heat exchanger: application to atmospheric fluidized-bed combustion boilers: Gilkey, C. H. et al. Proc. Int. Conf. Fluid. Bed Combust., 1995, 13, (1), 405–418

98/01461 Rotary regenerative heat exchanger: application to atmospheric fluidized-bed combustion boilers: Gilkey, C. H. et al. Proc. Int. Conf. Fluid. Bed Combust., 1995, 13, (1), 405–418

Peculiarities of Interactions in the CaCO3/CaO-SO2/SO3-Air System A review

Abstract The reactions occurring between CaCO3/CaO and SO2/SO3 in oxidizing atmospheres are discussed. Calcination and sulphation were carried out in a thermobalance under conditions relevant to atmospheric fluidized bed combustion. It is suggested that the quality of limestones as potential SO2 sorbents can be assessed on the basis of tests carried out in a TG apparatus adapted for use with corrosive gases. Limestone calcined under different conditions including the treatment with NaCl leads to changes in surface texture. Sulphated samples were examined in a SEM by energy dispersive X-ray and backscattered electron imaging. Two sulphur-bearing solids (CaSO4 and CaS) were identified. The sulphation rate and extent are determined by the product layer diffusion. The amount of CaS present at the end of the process depends on the particle size of the sorbent.

Physico-Chemistry of the Limestone Sulphation Process

Aspects of the mechanism of the overall reaction between CaCO3/CaO and SO2/SO3 under oxidizing conditions are discussed. The limestone and lime sulphation processes were carried out in a thermobalance under conditions relevant to atmospheric fluidized bed combustion. Sulphated samples, prepared in the form of cross-section particles, were examined in a scanning electron microscope by energy-dispersive X-ray and back-scattered electron imaging. Photomicrographs are presented. The reaction proceeded from the outer surface of the particles and along the pores. Surface textural changes during the reaction were considered. The layer of products was identified as controlling both the rate and extent of limestone/lime sulphation. In the products, two sulphur-bearing solids (CaSO4 and CaS) were identified. The presence of CaS, which may cause difficulties in practice, is attributed to CaSO3 disproportionation.

97/04849 Chlorinated organic compounds evolved during the combustion of blends of refuse-derived fuels and coals: Li, H. et al. J. Therm. Analysis, 1997, 49, (3), 1417–1422

The objective of this study was to examine the possible formation of chlorinated organic compounds during the combustion of blends of refuse derived fuels (RDF) and coal under conditions similar to those of an atmospheric fluidized bed combustion (AFBC) system. A series of experiments were conducted using a TGA interfaced to FTIR and MS systems. Additional experiments using a tube furnace preheated to AFBC operating temperatures were also conducted. The combustion products were cryogenically trapped and analyzed with a GUMS system. The chlorination of phenols and the condensation reactions of chlorophenols were investigated in this study. A possible mechanism for the formation of chlorinated organic; compounds such as dibenzodioxins and dibenzofurans, by chlorination and condensation reactions involving phenols, was proposed.

97/04867 An evaluation of the United Kingdom clean coal power generation group's air-blown gasification cycle: Wheeldon, J. M. et al. Proc. Annu. Int. Pittsburgh Coal Conf., 1996, 13, (1), 279–287

The Electric Power Research Institute (EPRI) is conducting an engineering and economic study of various pressurized fluidized-bed combustor (PFBC) designs. Studies have been completed on bubbling and circulating PFBC technologies and on an advanced PFBC power plant technology, in which the feed coal is partially gasified and the residual char burned in a PFBC. The United Kingdom Clean Coal Power Generation Group`s (CCPGG) air-blown gasification cycle (ABGC), known formerly as the British Coal Topping Cycle, also partially gasifies the feed coal, but uses a circulating atmospheric fluidized-bed combustor (AFBC) to burn the residual char. Although not a PFBC plant, the study was completed to effect a comparison with the advanced PFBC cycle.

97/04874 Improvement of coal pyrolysis yields by blending coal with lube oil wastes: Lazaro, M. et al. DGMK Tagungsber., 1997, 9703, (Proceedings ICCS '97, Volume 2), 741–744

Work on fluidized-bed combustion (FBC) began in the United States in the mid-1960s, with primary emphasis on industrial applications. With the passage of the Clean Air Act in 1970, the environmental benefits of the technology soon attracted interest. This provided the impetus for expanded effort focused on the reduced nitrogen oxides (NOx) emissions resulting from lower combustion temperature and sulfur dioxide (SO2) capture by means of chemical reaction with limestone or dolomite in the fluidized bed. The oil embargo of 1973 further stimulated interest in FBC technology. Recent interest in fuel flexibility has sustained the interest in FBC in the United States.Several U.S. manufacturers now offer atmospheric fluidized-bed combustion (AFBC) and circulating fluidized-bed combustion (CFBC) units for industrial applications. However, FBC for electric power generation remains in the development and demonstration phase. The Tennessee Valley Authority (TVA) and the Electric Power Research Institute (EPRI) are operating a 20-MW(e) AFBC utility pilot plant and are proceeding with plans for a 160-MW(e) demonstration plant with other participants. Research on pressurized fluidized-bed combustion (PFBC) has been under way at Grimethorpe in South Yorkshire, England, at the Curtiss-Wright Pilot Plant in the United States, and at other smaller test facilities. An emerging turbo-charged PFBC concept is likely to stimulate more near-term interest in PFBC technology for both industrial and utility applications.This paper describes the major U.S. programs and test facilities. The remaining technical uncertainties and the future outlook for the technology are also discussed.

97/04894 Pulse enhanced fluidized bed combustion: Mueller, B. et al. Proc. Annu. Int. Pittsburgh Coal Conf., 1996, 13, (1), 37–42

Various technologies are available for the combustion of high-sulfur, high-ash fuels, particularly coal. From performance, economic and environmental standpoints, fluidized bed combustion (FBC) is the leading candidate for utilization of high sulfur coals. ThermoChem, Inc., and the South Carolina Energy Research and Development Center (SCERDC) are installing a hybrid fluidized bed combustion system at Clemson University. This hybrid system, known as the Pulsed Atmospheric Fluidized Bed Combustor (PAFBC), will augment the University`s steam system by providing 50--60,000 lbs/hr of saturated process steam. The PAFBC, developed by Manufacturing and Technology Conversion International, Inc., (MTCI), integrates a pulse combustor with a bubbling-bed-type atmospheric fluidized bed coal combustor. The pulse combustion system imparts an acoustic effect that enhances combustion efficiency, SO{sub 2} capture, low NO{sub x} emissions, and heat transfer efficiency in the fluidized bed. These benefits of pulse combustion result in modestly sized PAFBC units with high throughput rates and lower costs when compared to conventional fluidized bed units.

5603377 Heat pipe and gas-liquid contacting apparatus capable of heat exchange using the heat pipes and heat exchanger of gas-liquid contacting plate type

Four ash samples which were deposited on four different locations in the atmospheric fluidized bed combustor, FBC, system at the TVA Shawnee Steam Plant near Paducah, KY, were employed in the present study. The SDT/MS and XRD techniques were applied to idenfity the sample composition and the mechanism that form the deposits. The major compound in the deposits from convection pass inlet, superheater and multiclone inlet was CaSO4, and the predominant minor compound was CaO in the samples. Also, CaS was found in the deposits from superheater by XRD analysis. In the case of recycle feed pipes, Ca(OH)2 and CaCO3 were the major components, and CaSO4 and CaO the predominant minor compound in the deposits. The combined SDT/MS with XRD results are useful techniques for identification of unknown ash samples.

Chlorinated organic compounds evolved during the combustion of blends of refuse-derived fuels and coals

The objective of this study was to examine the possible formation of chlorinated organic compounds during the combustion of blends of refuse derived fuels (RDF) and coal under conditions similar to those of an atmospheric fluidized bed combustion (AFBC) system. A series of experiments were conducted using a TG interfaced to FTIR. Additional experiments using a tube furnace preheated to AFBC operating temperatures were also conducted. The combustion products were cryogenically trapped and analyzed with a GC/MS system. The chlorination of phenols and the condensation reactions of chlorophenols were investigated in this study. A possible mechanism for the formation of chlorinated organic compounds such as dibenzodioxins and dibenzofurans, by chlorination and condensation reactions involving phenols, was proposed.

97/03288 Macroscopic to microscopic studies of flue gas desulfurization byproducts for acid mine drainage mitigation

The use of flue gas desulfurization (FGD) systems to reduce SO{sub 2} emissions has resulted in the generation of large quantities of byproducts. These and other byproducts are being stockpiled at the very time that alkaline materials having high neutralization potential are needed to mitigate acid mine drainage (AMD). FGD byproducts are highly alkaline materials composed primarily of unreacted sorbents (lime or limestone and sulfates and sulfites of Ca). The American Coal Ash Association estimated that approximately 20 million tons of FGD material were generated by electric power utilities equipped with wet lime-limestone PGD systems in 1993. Less than 5% of this material has been put to beneficial use for agricultural soil amendments and for the production of wallboard and cement. Four USGS projects are examining FGD byproduct use to address these concerns. These projects involve (1) calculating the volume of flue gas desulfurization (FGD) byproduct generation and their geographic locations in relation to AMD, (2) determining byproduct chemistry and mineralogy, (3) evaluating hydrology and geochemistry of atmospheric fluidized bed combustion byproduct as soil amendment in Ohio, and (4) analyzing microbial degradation of gypsum in anoxic limestone drains in West Virginia.

Petroleum Coke and Coal Start-Up Testing in Bubbling Fluidized Bed Combustors

Bench-scale and 160 MWe demonstration tests were conducted for petroleum coke and high volatile bituminous coal blends. The bench-scale apparatus was a 100-mm-dia reactor located at the Canada Centre for Mineral and Energy Technology (CANMET), Energy Research Laboratories. The demonstration tests were conducted on the Tennessee Valley Authority’s (TVA) 160 MWe Shawnee Atmospheric Fluidized Bed Combustion (AFBC) Unit located at Paducah, Kentucky. Five and ten percent nominal volatile petroleum cokes were tested in the bench-scale unit. In addition, for the five-percent petroleum coke blends of 25, 50, and 75-percent petroleum coke, with the balance coal, were also examined at the bench scale. Eight start-up tests have been conducted with 50 percent blend of green delayed petroleum coke at the Shawnee AFBC unit. The bench-scale tests revealed that the volatile content in the petroleum coke was the primary factor affecting start-up. The tests showed that the volatile content from the coke and coal ignited at similar times; the char required longer to ignite. Bench-scale tests showed adequate start-up performance with blends up to 75 percent petroleum coke. Cold start-ups were conducted at the Shawnee AFBC Unit with 7 to 10 percent volatile green delayed petroleum coke. In all the start-ups, the operating temperature of 816°C was reached within 15 min of introducing the petroleum coke blend; this is similar to when high volatile bituminous coal was used. One start-up required a longer time because limestone had to be used to generate the bed. Local hot spots (982°C) were noticed in several start-ups for short periods, but subsided when additional air was supplied. Although more difficult to control, TVA routinely starts the Shawnee AFBC Unit with 50 percent shot petroleum coke and 50 percent high volatile bituminous coal.

Chemical assessment of fluidized bed ash

Ash (FBA) from an atmospheric fluidized bed combustion (AFBC) unit similar to a western Maryland plant under construction was characterized chemically. Solid-phase samples were analysed for mineral content, elemental composition and potential toxicity. A shake test and two column experiments using different solid and liquid phases estimated leaching from solid phases under different field conditions. The FBA leachate was clean and passed currently accepted standards; elemental analyses also indicated that the FBA tested was clean. A shake test illustrated differences in analytes among FBA, overburden and an FBA-overburden mixture as well as three eluents. All Ag, As, Cd, Hg and Se levels were either below or only rarely above detection limits. In column experiments 1 and 2, tests with four solid phases and four eluents indicated that the potential for detection of Ag, As, Ba, Be, Cd, Cr, Cr 6+, Cu, Ge, Hg, Mo, Pb and Se in FBA leachate was low. FBA tested in these experiments was clean with respect to trace metal contamination and appeared to be suitable for mine disposal. The results must be viewed with caution since only a single FBA sample was tested.

97/02464 Assessment of strategic approaches to the commercialization of fuel cells

Atmospheric fluidized bed combustion (AFBC) is considered to be an environmentally favorable combustion technology where the control of emissions can be integrated into the combustion system. FBC operates at low temperatures, 800–900°C, to prevent thermal NO formation and to favor the sulfur removal by the sorbent, but it has not been taken into account that when coal is burnt, not only NOx, SOx and COx are emitted. In addition, volatile organic pollutants (VOCs) are emitted. From these VOCs, the polycyclic aromatic hydrocarbons (PAHs) constitute one of the most dangerous compounds because of the possibility of interacting with biological nucleophiles. It is expected that new legislation about the regulation on PAH emissions will be very restrictive. In this work, PAH emissions from coal AFBC as a function of the coal combustion variables (combustion temperature, gas flow and percentage of excess oxygen) are reported. In addition, the effect of bed nature on PAH emissions is also assessed.Polyaromatic hydrocarbon emissions at the standard conditions used at the AFBC power stations are assessed by the study carried out in an AFBC laboratory pilot plant. The PAHs listed by the US EPA as priority pollutants are analyzed by fluorescence spectroscopy (FS) at the synchronous mode.

Formation rates of characteristic carbon phases during fuel-water slurry injection in a hot fluidized bed

Abstract The interaction of fuel-water slurries (FWS) with a hot fluidized bed has been studied and the allocation of fixed carbon resulting after FWS dehydration and devolatilization has been investigated. An experimental technique has been purposely set up. A pneumatic injector has been used to disperse FWS into an atmospheric fluidized bed reactor, 140 mm ID. Silica sand has been used as bed material. The experiments have been carried out at typical temperatures of atmospheric fluidized bed combustion (AFBC), but under inert conditions to prevent combustion. Nitrogen as inert gas has been used for fluidization and for dispersion of FWS. Experiments provide results in terms of relative formation rates of carbon aggregates (A-phase), tiny carbon deposits on individual sand particles (S-phase) and carbon fines (F-phase). Relative formation rates are controlled by injection conditions, i.e. by the velocity of dispersing gas at the nozzle and the gas-to-slurry mass feed ration. A further operating parameter is the hydrodynamics of the bed. Finally, the nature of the parent fuel in FWS is also of great importance. The above findings are critically reviewed in the paper in order to determine the rates controlling the formation of carbon phases in an actual FWS-fired FBC unit.

Geochemistry and Mineralogy of Greek Lignites from the Ioannina Basin

Mineralogical and elemental composition of 26 lignites/lignitic shales and their ashes from the Ioannina Basin were examined using X-ray diffraction, X-ray fluorescence, and instrumental neutron activation analysis. Mineralogy consists of quartz, 2:1 interstratified layer silicates, kaolinite, and gypsum, Illite, calcite, amphi-boles, feldspars, and pyrite are the minor minerals in the samples. The major oxides SiO2, Al203, Fe2O3 TiO2, and K20 show an enrichment in the upper lignite-bearing interval within the succession, CaO shows the exact reverse trend, and Na2O and MgO do not show any trends. Arsenic in the samples ranges from 2 to 46 ppm, Br from 10 to 25 ppm, CI from 61 to 278 ppm, and Se from 2 to 14 ppm. Vertically, As content decreases from the shallower interval II to the deeper interval I. Within interval II, Cr and Br show a decrease from top to bottom. The concentration of Br and CI is higher in the samples of low mineral matter, while the opposite is true for As. Laterally, there is an increase in Br and CI from the northern to the central part of the basin, an increase of As in an eastern direction, and a decrease of Se in the same direction. Epigenetic processes related to high water table and subsurface water flow from the nearby phosphorite deposits are probably responsible for the high concentration of U, Mo, Sb, and possibly, V. The enrichment of Se is due to leaching from gypsum and/or anhydrite beds in the area. The rare earth elements follow variations in the low-temperature ash, but more specifically, the light REEs tend to mimic variations in Th and Al2O3 concentration, and the heavy REEs follow the TiO2 variation. The lignitic ash is “basic” in nature. Ash indices indicate low fouling tendency and low to high slagging potential for the lignites and interbedded lignitic shales, but these indices should be treated with caution. Volatile organic sulfur, determined between ambient and 120°C, is 0-44.3% of the total volatile sulfur, whereas sulfur lost between ambient and 930°C for all samples varies from 19.3% to 93.2%. This is of great importance because of the contribution of volatile sulfur to acid rain formation. Flue gas desulfurizotion and atmospheric fluidized-bed combustion technologies are recommended to meet the stringent sulfur emission control.

Geotechnical and Environmental Characteristics of Atmospheric Fluidized Bed Combustion Ash and Stoker Ash

Results of geotechnical and environmental laboratory tests on atmospheric fluidized bed combustion ash and stoker ash are presented. The testing program is directed toward assessing the adequacy of using these materials as structural fill in roadway embankment construction. Geotechnical tests include specific gravity, standard Proctor compaction, permeability, California bearing ratio, strength, and swell tests. Environmental tests include bulk chemical analysis of major and trace elements, toxicity characteristic leachate procedure, extraction procedure toxicity, and Indiana neutral water leachate tests. The fluidized bed combustion ash and mixtures with stoker ash exhibit significant cementitious strength increase, and swelling with time. The implications of test results relative to use as structural fill are discussed.

97/00539 Repowering with clean coal technologies

Repowering with clean coal technology can offer significant advantages, including lower heat rates and production costs, environmental compliance, incremental capacity increases, and life extension of existing facilities. Significant savings of capital costs can result by refurbishing and reusing existing sites and infrastructure relative to a greenfield siting approach. This paper summarizes some key results of a study performed by Parsons Power Group, Inc., under a contract with DOE/METC, which investigates many of the promising advanced power generation technologies in a repowering application. The purpose of this study was to evaluate the technical and economic results of applying each of a menu of Clean Coal Technologies in a repowering of a hypothetical representative fossil fueled power station. Pittsburgh No. 8 coal is used as the fuel for most of the cases evaluated herein, as well as serving as the fuel for the original unrepowered station. The steam turbine-generator, condenser, and circulating water system are refurbished and reused in this study, as is most of the existing site infrastructure such as transmission lines, railroad, coal yard and coal handling equipment, etc. The technologies evaluated in this study consisted of an atmospheric fluidized bed combustor, several varieties of pressurized fluid bed combustors, severalmore » types of gasifiers, a refueling with a process derived fuel, and, for reference, a natural gas fired combustion turbine-combined cycle.« less

Modeling of sulphur retention in atmospheric fluidized bed combustors. Sensitivity analysis and simulation

Modeling of sulphur retention in atmospheric fluidized bed combustors. Sensitivity analysis and simulation