Bed Coal Combustion Research Articles

The properties of Çan Basin coals (Çanakkale—Turkey): Spontaneous combustion and combustion by-products

The goals of this study were to investigate the susceptibility of Çan Basin (Çanakkale—Turkey) coals to spontaneous combustion and to determine the composition of the gas produced from the coal during combustion. Coal properties were determined using burned and partly burned coal samples; gas samples were analyzed for their composition. The mineralogical variations of burning coals were also investigated. Our results indicated that the pyrite content of Çan Basin coals is a significant factor for promoting combustion in addition to rank and moisture. X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses indicated that the coal samples contained pyrite, quartz, cristobalite, tridymite, kaolinite, amorphous matter, and gypsum. Fumarolic minerals (sulfur blooming and ammonium chloride) forming on the surface of coal seams were monitored. Elements including beryllium, fluorine, scandium, vanadium, cobalt, nickel, copper, zinc, arsenic, selenium, zirconium, molybdenum, tungsten, mercury, tantalum, lead, and uranium were found to be higher in Çan coal samples than the world average. The concentration of arsenic (max. 3319.7μg/g) was relatively high and is the major hazardous element in the region.Gases emitted from coal-fire vents in Çan coalfields were found to consist of a complex mixture of hydrocarbons, greenhouse gases, and toxic concentrations of carbon monoxide (CO), hydrogen sulfide (H2S), and benzene. Hydrocarbon concentrations ranged from 77 to 92%, and the dominant hydrocarbon gas was methane. Ethane (0.3 to 2.1%) and propane (0.2 to 1.4%) were also detected. Hazardous compounds such as 5-methyl-3-propyl-1,2-oxazole (C7H11NO), ethanediimidic acid, 1,2-dihydrazide (C2H8N6), and 2,3-dihydrofuran (C4H6O); high concentrations of nitrogen (N2) (max. 6.8%) and carbon dioxide (CO2) (max. 18.2%); and low concentrations of carbon monoxide were also determined. Greenhouse gases (CO2 and methane (CH4)) from burning coal beds may contribute to climate change and alter ecosystems. Gas components including furan, H2S, CO, carbon disulfide (CS2), benzene etc., can be hazardous to human health, even in trace amounts. As a result, the uncontrolled release of pollutants from burning coal beds presents potential environmental and human health hazards.

Nitrogen Oxide Formation During Fluidized Bed Combustion of Coals and Shales

Experimental data are presented on the time dependence of nitrogen oxide formation during combustion of batches of various fuels in fluidized beds. It is shown that the formation of nitrogen oxides takes place both in the stage where coke residue is burnt and in the stage where volatile substances are burnt. The nitrogen in the coke residue is oxidized by a heterogeneous mechanism similar to that by which carbon is burnt; the extent to which it is converted into oxides under oxidizing conditions depends on the ratio of the oxidation rate constants for nitrogen and carbon. The formation of nitrogen oxides during combustion of the volatiles is described adequately by the overall gaseous phase equilibrium of the reaction. Amethod for calculating the NO x yield along the height of a fluidized bed furnace is developed on the basis of the mechanisms found for nitrogen oxide formation during the different stages of combustion of the fuel particles.

Strength and water permeability of concrete containing various types of fly ashes and filler material

Abstract In this study, the strength and water permeability of concretes containing various types of fly ashes and filler material were investigated. Five types of fly ashes with two levels of fineness and ground-river sand were used to partially replace Portland cement at the dosages of 20 and 40% by weight. Results indicated that pulverized coal combustion fly ash produced concrete with good strength and low permeability. Normal fluidized bed combustion fly ashes containing very irregular particles with pores produced concrete with low strength and relatively low permeability. Fly ash from fluidized bed combustion of coal with bio-mass materials and fly ash with high amount of CaO and SO3 produced poor concretes with low strength and high permeability. The increase in fly ash fineness helped improve both strength and permeability of concrete due to the increase in the reactivity of fly ash. Filler material could also be used to replace Portland cement at low replacement level of 20% with small effects on strength and water permeability.

Effects of air distribution and refractory arch design on efficiency of coal fired travelling grate boilers

AbstractThe present paper examines the air distribution mode for a novel arch called the double herringbone arch to improve the thermal efficiency of travelling grate boilers. The influences of the three air distribution modes on coal bed combustion are first studied by measuring the gas species distributions along the grate length above the coal bed. The test result is inputted as the boundary condition of the numerical simulation, which compares the gas combustion features in the furnace of a common arch boiler with those of a double herringbone arch boiler under different air distribution modes. The results show that the cooperation of the rear enhanced air distribution mode and the double herringbone arch not only promotes the burnout of the coal bed but also reduces the combustible gas loss. Finally, industrial retrofit indicates that the thermal efficiency of a common arch boiler can be improved by about 5–10% using a double herringbone arch with the aid of the rear enhanced air distribution mode.

COAL PROPERTY EFFECTS ON N2O AND NOx FORMATION FROM CIRCULATING FLUIDIZED BED COMBUSTION OF COAL

ABSTRACT The effects of coal properties on N2O and NOx formation from circulating fluidized bed combustion of coal was examined through burning nine typical coals and a coal shale, widely used in China over a wide range of coal ranks, in a bench-scale circulating fluidized bed. It was found that N2O and NOx formation had similar dependence on coal rank. Fixed carbon content and nitrogen content were the most important coal properties to influence N2O and NOx emissions from circulating fluidized bed combustion of coal. A coal with high fixed carbon content had high conversion ratio of fuel-N into N2O and NOx. The conversion ratio of fuel-N into N2O or NOx increased with nitrogen content of coal, whereas it decreased with O/N ratio. No significant correlation between conversion ratio of fuel-N into N2O or NOx and C/N ratio was identified. To clarify the coal property effect, investigation of a wide range of coal rank, is important.

05/00855 Potential health impacts of burning coal beds and waste banks

05/00855 Potential health impacts of burning coal beds and waste banks

Potential health impacts of burning coal beds and waste banks

Uncontrolled release of pollutants from burning coal beds and waste banks presents potential environmental and human health hazards. On a global scale, the emissions of large volumes of greenhouse gases from burning coal beds may contribute to climate change that alters ecosystems and patterns of disease occurrence. On regional and local scales, the emissions from burning coal beds and waste banks of acidic gases, particulates, organic compounds, and trace elements can contribute to a range of respiratory and other human health problems. Although there are few published reports of health problems caused by these emissions, the potential for problems can be significant. In India, large numbers of people have been displaced from their homes because of health problems caused by emissions from burning coal beds. Volatile elements such as arsenic, fluorine, mercury, and selenium are commonly enriched in coal deposits. Burning coal beds can volatilize these elements, which then can be inhaled, or adsorbed on crops and foods, taken up by livestock or bioaccumulated in birds and fish. Some of these elements can condense on dust particles that can be inhaled or ingested. In addition, selenium, arsenic, lead, tin, bismuth, fluorine, and other elements condense where the hot gaseous emissions come in contact with ambient air, forming mats of concentrated efflorescent minerals on the surface of the ground. These mats can be leached by rainwater and washed into local water bodies providing other potential routes of exposure. Although there are little data linking burning coal beds and waste banks to known health problems, a possibly analogous situation exists in rural China where mineralized coal burned in a residential environment has caused widespread and severe health problems such as fluorosis and arseniasis.

Particulate emissions from fluidised bed combustion of lignite with mineral sorbents

As a part of studies on combustion processes, that include fluidised bed combustion of coal, biomass and simulated waste, we investigate particulate emissions from fluidised bed combustion of various lignites used currently for generating energy in Czech thermal power plants. The research is oriented to studies on effect of process variables on particulate emissions (Smolik et al., 1999), the control of emissions of trace elements using mineral sorbents (Smolik et al., 2000), and the influence of mode of occurrence of matrix and trace elements in coal on amount and composition of particulate emissions. The objective of this work is to continue the previous studies on the characteristic of metal capture by bed sorbents.

The combustion of coal and some other solid fuels

This paper outlines some of the key issues currently being debated regarding the combustion of coal and of some biomass materials. It attempts to summarize the present approaches toward the quantification of the fundamental processes of solid fuel combustion for use in computer models. Some aspects of the various chemical and physical processes are included, such as heating-up of particles, devolatilization, and subsequent char formation. Of particular interest is the prediction of char properties, such as composition, surface areas, and morphology, since these impact on char combustion. The available models for devolatilization, char formation, and heterogeneous, oxidation are considered for application to both coal and biomass, and a description in terms of the fundamental molecular processes of a coal particle is explored. Char combustion models, including global intrinsic reaction rates, are outlined. The latter has clear advantages, but requires inputs of char physical properties which, at present, cannot be predicted a priori . Intimately linked with the processes of devolatilization and char combustion are NO x formation and carbon burnout, and special attention is given to these important factors. Finally, the general methods for modeling coal reaction processes are outlined, and illustrative examples are given with regard to the current situation in the application of these submodels to computer modeling of pulverized and coal bed combustion.

98/00586 Sulfur capture in fluidized bed combustion of coal at oxidizing and reducing conditions

98/00586 Sulfur capture in fluidized bed combustion of coal at oxidizing and reducing conditions

Treatment of Chromic Tannery Wastes Using Coal Ashes from Fluidized Bed Combustion of Coal

A new method of treatment for chromic tannery wastes containing chrome and large amounts organic substances has been investigated. It has been found that the addition of certain types of coal ash from fluid bed combustion technologies, at a suitable temperature and pH, results in effective removal of Cr(III) compounds present in the wastes. The wastes could then be subjected to further processing in conventional biological treatment units. The method is very simple, cheap, and effective and could be used for chromic tannery wastes of different compositions.

Pressurized fluidized bed combustion and gasification of coal using flue gas recirculation and oxygen injection

A combined cycle incorporating pressurized fluidized bed combustion of coal with pure oxygen and recycled flue gas followed by pressurized combustion of the fuel gas using pure oxygen, is a process which produces electricity and heat with a high efficiency and a flue gas with a high CO2 concentration. CO2 recovery from this process can be done more easily than from conventional coal conversion processes. In this way a high efficiency coal conversion process can be realized with low CO2 emissions. The specific aim of the project is to assess the technical feasibility of this process. For this purpose a 1.6 MWth pressurized fluidized bed combustion test rig has been modified to study experimentally the gasification process and the pressurized combustion of the resulting low calorific value fuel gas. The objectives of the project, the modified test rig and the experimental results obtained from combustion experiments with coal, recirculated flue gas and pure oxygen are described. The conversion efficiencies and the emission of harmfull components measured during these experiments are analyzed and compared with values obtained during combustion and gasification using air.

97/00560 Progress on mathematical modeling of sulfur retention by limestone during finidized bed combustion of coal

97/00560 Progress on mathematical modeling of sulfur retention by limestone during finidized bed combustion of coal

96/04170 Pressurized fluidized bed combustion of coals in mixtures of recycled flue gas and oxygen

96/04170 Pressurized fluidized bed combustion of coals in mixtures of recycled flue gas and oxygen

96/00694 Formation and reduction of NOx in pressurized fluidized bed combustion of coal

96/00694 Formation and reduction of NOx in pressurized fluidized bed combustion of coal

Emission of nitrogenous species from pressurized fluidized bed combustion of coal: experimental research and modelling

Emission of nitrogenous species from pressurized fluidized bed combustion of coal: experimental research and modelling

Modelling of circulating fluidized bed combustion of coal

Modelling of circulating fluidized bed combustion of coal

Interactions between emissions of sulfur dioxide and nitrogen oxides in fluidized bed combustion of coal

Abstract NH3 is an important volatile N-containing compound and a precursor for NOx formation in fluidized bed combustion (FBC). This work focuses on the influence of the sulfation process on the oxidation of NH3 to NO catalysed by different CaO based sorbents and other bed materials (sand, Al2O3). Experiments of simultaneous sorbent sulfation and oxidation of NH3 catalysed by the sorbents were performed in a laboratory fixed bed reactor in order to study changing catalytic activity. The influence of SO2 on the oxidation of NH3 to NO for different bed materials was investigated as well. The results show that desulfurization interferes with the catalytic conversion of NH3 to NO in two ways. First, CaO based sorbents are active catalysts for the oxidation of NH3 to NO; this catalytic activity decreases with an increase in the conversion of CaO to CaSO4. For the limestones, which are subject to pore plugging, the sorbents totally lose their activity for NO formation from NH3 when the maximum conversion of CaO to CaSO4 is reached. Second, the catalytic formation rate of NO decreases in the presence of SO2 for some bed materials. This means that the presence of SO2 inhibits oxidation of NH3 to NO. Moreover, it appears that SO2 inhibits the decomposition of N2O on the surface of the catalysts as well.

Organic compounds in the flue gas from a power station with circulating fluid bed combustion of coal

Numerous organic compounds have been analyzed by coupled gas chromatography-mass spectroscopy (GC-MS) in flue gas after fluid bed combustion of four coal species from South Africa, Poland, Spitsbergen and Ruhr area (Germany). Polynuclear aromatic hydrocarbons, aliphatic hydrocarbons, chlorinated, heterocyclic and nitro compounds as well as phthalate esters are detected.

Application of FBe technology to high-ash Indian coals

AbstractVarious aspects of fluidized bed combustion of coal are reviewed and its applicability to Indian coals is considered. Such coals are high in ash and fluidized bed combustion presents a suitable method for burning middlings and rejects from coal washeries. Moreover, fluidized bed combustors have an added advantage of contributing to the abatement of atmospheric pollution due to sulphur and nitrogen oxides. Fluidized bed combustion has some disadvantages, but they can be overcome by modern innovations, as reported in this paper. This review also discusses mathematical modelling of fluidized bed combustion, with a comparison of some models for predicting the burn-out time.