Malgorzata Pilawska

The paper presents the results from studies on co-combustion of dry, “high” calorific value wastes with/without supplementary fuels. Two fluidisation techniques were employed, circulating and bubbling, in facilities of three sizes; a bench scale circulating fluidized bed combustor (CFBC) designed to burn coal and two were bubbling fluidised bed reactors (BFBC): ~100 kWth with a ceramic-lined combustion chamber and outer insulation of the freeboard and 1MWth insulated reactor burning wastes. Tests have been carried out in the CFBC reactor using coal or pelletised Refuse Derived Fuels (RDF) separately or mixed together. Municipal Segregated Wastes (MSW) alone and mixed with Wood Waste (WW) were burned in the BFBC reactors. In the BFBC experiments, continuous records were obtained of temperature and flue gas concentrations of O2, CO, SO2, NO, NO2 and VOC. With the CFBC unit, continuous measurements of temperature, bed pressure at different heights and concentrations of O2, CO, SO2, NO,...

It is always better to prevent the formation of PAH than remove them from the flue gases. Burning polymer waste in a fluidized bed, with plenty of oxygen and efficient mixing could be promising. Polymer pellets were burned in a bed of glass making sand, fluidized with a mixture of air and propane. The pellets were dropped into the reactor operating under steady conditions and the effect on O2 consumption, CO2 and CO production, total hydrocarbon, and NOx emissions was monitored. The combustion of a pellet depends on the thermal decomposition of the polymer and burning of the volatile decomposition products. The pyrolysis was fast and a local streak of fuel-rich gases appeared. The efficient oxidation of these depends on the local availability of O2 and the efficiency of mixing. With larger pellets, the importance of the initial "background" increased. At higher temperatures the rate of the oxidation of the intermediates increases, but their rate of production also increases which outweighs the benefit of higher reaction rates. Original is an abstract.

Working with a small, bubbling laboratory scale fluidised bed combustor for many years, helped to gain some insights into the fundamental physicochemical processes taking place in fluidised bed combustors in general, irrespective of size. For example, it has been demonstrated that during coal combustion as a rule the gases leaving the bed cannot be assumed to be at full thermal equilibrium and that when gases are burned the associated acoustic and visual phenomena can be explained in terms of bubbles of the combustible ...

ABSTRACT Fluidised bed combustion (FBC) is a technology which can use waste materials and low quality fuels along with coal. Mixed with wastes, coal can burn more efficiently. The present study aimed at the co-combustion of refuse derived fuels (RDF) with coal in a bench scale circulating fluidised bed combustor (CFBC). Tests were carried out at different ratios of RDF/coal at temperatures from 830 to 960 degrees C. Compared with coal alone, RDF - coal mixtures gave a more uniform temperature distribution in the combustor and the emissions were lower when burning. Improved efficiency and stability of co-combustion were attributed to the higher volatile matter content in RDF. However, the advantages could be lessened if a too high secondary air ratio was used. NOx and SO2 emissions were due to the presence of S ( mainly in the coal) and fuel N ( more than S) in both fuels. The SO2 concentration decreased with increasing RDF rich in Ca in the fuel. It was shown that CFBC units could burn RDF efficiently and cleanly.

ABSTRACT The process of selective non-catalytic reduction of NO, SNCR, is important for limiting emissions of nitrogen oxides from coal-fired power plants. Such a process has been studied for many years, both in the laboratory and under practical conditions. This work was an attempt at elucidating some of the problems associated with the method when used under circulating fluidized bed (CFB) conditions and in particular, the formation of the N2O by-product. The NO + NH3 reaction has been studied in the laboratory, over quartz sand in a heated fixed bed flow reactor. In comparison with a combustion environment, the composition of the gas phase was drastically simplified and limited to NO and NH3, in nitrogen as the carrier gas, with O2 added in some experiments. The product gases were analyzed for NO, N2O and NH3. The effects the following parameters were studied: temperature inside the reactor between 850 and 1250 K, height of the sand bed, NH3/NO molar ratio over the range 0.54–2.0 and the addition of 1 or 2% of O2 in volume. Baseline tests with an empty reactor were also made. With no sand in the reactor, the results were both qualitatively and quantitatively different. The sand helped to increase the efficiency of NO reduction, particularly at lower temperatures, but N2O formation also appeared to be strongly enhanced, except at the highest temperatures. Higher molar NH3/NO ratios favored NO reduction and N2O production, both with and without sand. The reduction of NO did not appear to require the presence of O2, but the introduction of 1% or 2% of O2 gave some benefit. The results confirmed that under practical conditions more attention should be paid to the role of the bed solids in the SNCR process.

The combustion of fuel-lean mixtures of methane+ air in a strongly bubbling fluidized bed of quartz sand has been studied in the laboratory. Video color images of the burning bed, at 25 frames/s, were examined and used to obtain images in three color bands, red, green, and blue. A mathematical procedure was then employed to analyze the color images further, to discriminate between continuous radiation from the hot sand and discrete emission, mostly in the blue wavelength region, from bubbles exploding inside the bubbling bed or at its ...