Malgorzata Pilawska | Cracow University of Technology (original) (raw)

Papers by Malgorzata Pilawska

Some of the very damp sludge can be partly replaced by the second waste fuel, irrespective of its... more Some of the very damp sludge can be partly replaced by the second waste fuel, irrespective of its physical state (solid, liquid or gaseous). Candidate supporting fuels are, e.g., the biomass by-products of the maintenance of vegetation within the city (street trees, parks, etc.), partly segregated municipal solid waste (MSW), or even animal waste. A pilot installation, 1 Mw, was designed, with some of the heat produced employed in the gas cleaning system and for heating the premises used by the technical staff and for providing hot water. The combustor is equipped with feed systems for the sewage sludge and for the supporting fuels. An automatic process control system was developed. The effect of bed temperature and air excess on the flue gas composition and the degree of mineralisation of the sewage sludge was assessed. The flue gas concentrations monitored were: O2, CO, NO, NO2, and SO2 (using ECOM®-SG Plus instrument, with electrochemical sensors), VOCs (JUM® working on the FID principle). The mean flue gas concentrations of CO and VOC were 200 ppm and 124 mg/cu m respectively. The presence of SO2 and NOx was due to the presence of combined sulfur and nitrogen in the fuel, most likely in organic form. This is an abstract of a paper presented at the 30th International Symposium on Combustion (Chicago, IL 7/25-30/2004).

It is always better to prevent the formation of PAH than remove them from the flue gases. Burning... more 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.

The combustion of fuel-lean mixtures of methane + air in a strongly bubbling fluidized bed of qua... more 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 surface. The results obtained show that transient flames occur in the bubbles, confirming that the combustion process in fluidized bed is basically similar to that in flames, with the involvement of free radical species.

A laboratory size quartz reactor has been used to burn methane, LPG (liquid petroleum gas) and ar... more A laboratory size quartz reactor has been used to burn methane, LPG (liquid petroleum gas) and aromatic hydrocarbon vapors in a bubbling fluidized bed. Most measurements and observations were made for lean mixtures of fuel and air with quartz sand in the bed, but in some experiments NO, NO2, or CCl4 were introduced with the fuel, the stoichiometry was varied or the bed material changed. The quantities monitored were the bed temperature at two levels and the freeboard concentrations of O2, CO2, CO, NO, NO2, and in some runs, of hydrocarbons. An attempt was made to relate the measurements to the sound level and to visual observations. The results obtained suggest that with the air excess, λ, constant at 1.4 and with the bed at above ∼850 °C, the fuel can be fully oxidized and [CO] very low. [NO] is also low and does not increase even if the temperature is raised by another 150 to 200 °C. However, such a stable combustion process can be perturbed by adding a chemical inhibitor. With a suitable bed material it is possible to lower [CO] and [NO] in the freeboard to ∼1 ppm. At lower temperatures, with [CO] high, the conversion of NO to NO2 takes place. Most of the observations are consistent with the dominance of gas-phase reactions in the bubbles, but some effects can only be accounted for by the participation of heterogeneous chemical reactions.

Much less attention has been paid to bubbling fluidized bed combustion, BFBC, partly because of s... more Much less attention has been paid to bubbling fluidized bed combustion, BFBC, partly because of scaling-up problems. However, small BFBC units have many advantages for applications such as the use of biomass, wood waste, and different locally produced combustibles. Recent work focused on gaseous and liquid fuels, of various chemical characters. BFBC combustion efficiency can be high, with the flue gases cleaner than the usual with conventional burners. During flameless combustion of CH4 at over 900°C, CO, CxHy, and NO2 were produced only at the trace level of about 1 ppm. NO was under 15 ppm and did not increase when the temperature was raised to 1070°C. With the laboratory size BFBC, the flue gas concentrations of CO, CxHy, NO, and NO2 were similar as with CH4 fuel. With chlorine present as a result of CCl4 addition at below 950°C, CO emissions increased, and NO was unaffected.

In 1980s change in meat and bone meal production technology led to the spread of BSE and massive ... more In 1980s change in meat and bone meal production technology led to the spread of BSE and massive culling of beef cattle in many countries. Adding meat and bone meal to animal feed was banned, but animal carcasses still have to be disposed of. In this work the operational parameters and efficiency of a utilisation process for raw meat wastes and emissions of CO, NOx, SO2 and VOC were studied. A 5 kW thfluidised bed combustor was used and tests were repeated in a 150 kWth (KFD-s14u) boiler, with combustion of meat wastes (biomal). With combustion, the heat generated can be recovered, the meat waste is completely burned, bone pieces mineralised and fragmented and flue gas composition is similar to that with coal alone. The potential of the technology for raw meat waste utilisation has been demonstrated on a technical scale, with waste throughput of 180 kg/h*m 2 (with respect to distributor area) and factors limiting the combustion efficiency have been determined. An installation (up to 3 MW thermal) has been designed for the utilisation of 500 kg/h of raw meat waste in co-combustion with coal. The installation should fulfil the requirements with respect to waste utilisation efficiency and thermal energy production.

The combustion of hydrogen in a hot, bubbling bed of quartz sand fluidized by air has been studie... more The combustion of hydrogen in a hot, bubbling bed of quartz sand fluidized by air has been studied for the first time, by injecting hydrogen just above the distributor, via six horizontal fine tubes of Cr/Ni. Overall the fluidizing gas was oxygen-rich, with the composition varying from nearly stoichiometric to very lean mixtures. With the bed initially fluidized at room temperature, combustion (after ignition by a pilot flame) occurs in a premixed flame sitting on top of the bed. When the sand warms up, combustion becomes explosive in bubbles leaving the bed, exactly as with a hydrocarbon as fuel. However, in contrast to hydrocarbons, it is clear that when the bed reaches 500-600 °C, heat is produced both above the top of the bed (because of H2 bypassing the bed) and very low down in the bed. In fact, with hydrogen as fuel, the location of where bubbles ignite descends abruptly to low in the sand; furthermore, the descent occurs at ∼500 °C, which is ∼100 K below the ignition temperature predicted by well-established kinetic models. However, the kinetic models do reproduce the observations, if it is assumed that the Cr/Ni hypodermic tubes, through which the fuel was injected, exert a catalytic effect, producing free H atoms, which then give rise to HO2 radicals. In this situation, kinetic modeling indicates that bubbles ignite when they become sufficiently large and few enough to have a lifetime (i.e. the interval between their collisions) longer than the ignition delay for the temperature of the sand. The amounts of NO found in the off-gases were at a maximum (24 ppm), when the bed was at ∼500 °C for λ = [O2] / [O2]stoich = 1.05. The variations of [NO] with [air]/[H2] and also temperature indicate that NO is produced, at least partly, via the intermediate N2H. In addition, the air-afterglow emission of green light (from NO + O → NO2 + h ν) was observed in the freeboard, indicating the presence there of both NO and free atoms of oxygen for 1.05 < λ < 1.1.

The gas mixture was prepared by vaporization of liquids in hot air and burned in a laboratory-siz... more The gas mixture was prepared by vaporization of liquids in hot air and burned in a laboratory-sized fluidized bed reactor. The test fuels were benzene, toluene, m-xylene, methyl acetate, ethyl acetate, and ethyl formate. Fuel conversion degree was assessed in terms of CO and VOCs concentrations; [NO] and [NO2] were also measured. Pollutants were highest when used. Liquid organic substances can be effectively burned in fluidized beds and the flue gases can in most cases be cleaner than with the methane. The best results are obtained if the combustion is flameless, i.e., takes place entirely inside the bed.

Working with a small, bubbling laboratory scale fluidised bed combustor for many years, helped to... more 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 gases exploding within the bed. Much of the experience gained in running the laboratory system has been used in small scale practice, in designing and controlling small, but successful fluidised bed combustors up to about 3 MW. Several 1MW units have now been in operation for over 10 years. It has also been demonstrated that small bubbling bed combustors can be used for disposing of certain biomass and other wastes.

Much of air pollution is due to burning of fossil fuels, but some purpose-produced biofuels and b... more Much of air pollution is due to burning of fossil fuels, but some purpose-produced biofuels and biowastes can be burned very cleanly. Historic towns should maintain high standards of air purity, but deriving all heat and power from burning of biomass cannot be feasible, but using some biowastes can help locally, with savings on energy transport and flue gas cleaning systems. It can also contribute to reducing greenhouse emissions. This has been demonstrated, e.g., at NiepoŁomice where several types of waste have been effectively and cleanly burned.

Environment Protection Engineering, 2006

ABSTRACT In 1980s change in meat and bone meal production technology led to the spread of BSE and... more ABSTRACT In 1980s change in meat and bone meal production technology led to the spread of BSE and massive culling of beef cattle in many countries. Adding meat and bone meal to animal feed was banned, but animal carcasses still have to be disposed of. In this work the operational parameters and efficiency of a utilisation process for raw meat wastes and emissions of CO, NOx, SO2 and VOC were studied. A 5 kW thfluidised bed combustor was used and tests were repeated in a 150 kW th (KFD-s14u) boiler, with combustion of meat wastes (biomal). With combustion, the heat generated can be recovered, the meat waste is completely burned, bone pieces mineralised and fragmented and flue gas composition is similar to that with coal alone. The potential of the technology for raw meat waste utilisation has been demonstrated on a technical scale, with waste throughput of 180 kg/h*m2 (with respect to distributor area) and factors limiting the combustion efficiency have been determined. An installation (up to 3 MW thermal) has been designed for the utilisation of 500 kg/h of raw meat waste in co-combustion with coal. The installation should fulfil the requirements with respect to waste utilisation efficiency and thermal energy production.

Environment Protection Engineering, 2006