Janusz A. Kozinski

Thermal events occurring during the combustion of biomass residue

Abstract The purpose of this study was to identify possible events taking place during thermal treatment of biomass residue (bio-sludge) in an oxidative environment. The bio-sludge sample was collected after biological treatment of de-inking waste generated by pulp and paper mills. Combustion tests were conducted in a high-temperature Cahn TG-171 thermogravimetric furnace (TGA) coupled with Mattson Galaxy 5020 Fourier transform infrared spectrometer (FTIR). A bio-sludge sample (1.1xa0g) was heated in the TGA furnace at a rate of 40°Cxa0min −1 until a maximum temperature of 1500°C was achieved. The sample was then “soaked” at this temperature for 10xa0min and subsequently cooled or quenched at a rate of 20 or 1800°Cxa0min −1 , respectively. Temperature- and time-resolved profiles of sample weight loss were determined by the TGA while volatile release profiles were obtained from FTIR. Solid samples collected during the bio-sludge combustion process were analyzed with scanning electron microscopy, wavelength-dispersive and energy-dispersive X-ray spectrometry and electron probe microanalysis to determine morphology, particle size, composition and metals distribution in ash particles. The bio-sludge combustion process could be divided into four stages: (1) Initial Burning ( T Transition (600 T Sintering (1100 T Melting ( T >1400°C). However, it is difficult to accurately establish a clear boundary between these stages because the regimes of volatiles release, char combustion and ash transformation are overlapping. Ash formed during quenching was a condensed and packed substance while during natural cooling it revealed dendritic character with needle-like features present on the particle surface. The former structure is better from the environmental point of view because it would not allow for leaching of toxic metals if ash was disposed of in a sanitary landfill.

Numerical modeling of combustion and pyrolysis of cellulosic biomass in thermogravimetric systems

Abstract A two-dimensional axisymmetrical numerical model for pyrolysis and combustion of cellulosic biomass in a thermogravimetric system is presented. Both chemical reactions and physical phenomena are considered, using fundamental principles. This mathematical model has combined the transient mass, species and energy conservation equation, Darcy momentum equation and a global Arrhenius decomposition for a porous reacting biomass. It can predict weight loss rate, ignition temperature and gas composition. The results show that the biomass ignition is preceded by pyrolysis and subsequent release of volatiles. The secondary ignition of char occurs after pyrolysis is complete. The volatile and char ignition temperature increases with the increase in the heating rate and biomass volume, and decrease in biomass porosity. A comparison of weight loss calculations with experimental data indicates acceptable agreement at different operating conditions. The model can be used for expanding limitations of thermogravimetric furnaces. The sensitivity analysis, carried out for selected combustion parameters, was useful for setting up a pilot-scale combustor.

Effect of biomass burning on the formation of soot particles and heavy hydrocarbons. An experimental study

Abstract The effect of combustion of biomass on soot aggregates and polynuclear aromatic compounds (PACs) has been studied. Conditions similar to those in typical residential space heating systems used to burn wood have been simulated in a laboratory furnace. The biomass fuels used included (1) paper-mill residue, (2) hard pine-wood, and (3) particle board, typically used in the construction of indoor furniture. Soot formation process was most extensive during the combustion of particle board and hard pine-wood, where the highest combustion temperatures were obtained. It has been found that the effect of temperature/heat input and oxygen/local mixing conditions appear to be important within both the pre-particle chemistry, responsible for the formation of incipient soot particles, and the soot surface-mass growth. The higher combustion temperatures obtained in the wood and board experiments influenced the behavior of PACs. The overall PACs formation tendency decreased in the order: partice board > hard pinewood ⪢ paper-mill residue. The experiments have shown that the temperature-time history and C O ratio are important parameters affecting PACs formation/destruction in biomass combustion.

Biosludge incineration in FBCs: Behavior of ash particles

Abstract The evolution of ash morphology and metals behavior during incineration of a biosludge and silica sand in a 300-kW fluidized bed facility have been studied. The reactor was operated in the bubbling mode. Analyses of ash particles were performed using a computer-controlled electron probe microanalyzer equipped with four wavelength-dispersive spectrometers. The paper presents data on ash particle structure formation, size/numbers density distribution and migration/distribution of metals inside a supermicron fly ash particle. A mechanistic model of the fly ash evolution process is proposed. The major trends in the suggested mechanism are (1) the massive formation of porous particles (45–110 μm) in the splash zone, (2) their extensive fragmentatio/disintegration along the incineration pathway resulting in the particle size reduction and number density increase, (3) the presence of a phase transition in locally high-temperature regions (1650 K), and (4) the formation of smooth-surfaced compact-structured glassy fly ash submicron (

Phase behavior and combustion of hydrocarbon-contaminated sludge in supercritical water at pressures up to 822 MPa and temperatures up to 535°C

Phase behaviors of cellulose, naphthalene (NT), and benzo(a)pyrene (BaP) in subcritical and supercritical water were studied with a diamond anvil cell technique and optical microscopy at heating rates of 8–10°C/s. The homogeneous phases were obtained for cellulose at 329.5°C and 345.1 MPa, for NT at 383.2 °C and 419.7 MPa, and for BaP at 508.1°C and 770.2 MPa. Establishing the homogeneous conditions was important for the combustion study of NT- and BaP-contaminated cellulose-based sludge in supercritical water (SCW). A batch reactor (6 mL volume) was used in the SCW combustion experiments. It was found that 99.2% carbon, 99.86% BaP, and 100% NT were converted within the SCW during 300 s reaction time under 450°C, 30.6 MPa, and 17.1% excess oxygen. Thus, even residues with high ash content (∼20%) and stable polycyclic aromatic hydrocarbons (PAHs) could become almost completely oxidized to CO 2 and H 2 O in this novel type of “incineration.” The conversion rates increased at longer reaction times (up to 30 min.) and higher oxygen concentration (65.7%). During the SCW combustion, water, oxygen, sludge (mainly cellulose), and PAHs may become a single phase before their decomposition via pyrolysis or oxidation. A transformation pathway of the major components of the sludge during SCW combustion is proposed. The major trends in the suggested mechanism are (1) the rapid hydrolysis of cellulose to oligomers and glucose, (2) the dissolution of naphthalene and its oxidation to quinones, (3) the cleaving of benzo(a)pyrene and formation of acetylene and cycloalkenes with benzylic rings, and (4) the homogeneous oxidation of dissolved organic species to light hydrocarbons→acids→acetate, which is transformed to carbon dioxide and water.

Phase changes of benzo(a)pyrene in supercritical water combustion

Abstract This paper presents new data on the behavior of benzo(a)pyrene (BaP) during supercritical water (SCW) combustion. It focuses on phase changes of the BaP throughout the transition from subcritical to supercritical regions. A sequence of images illustrates BaP’s phase change for the first time. They were obtained in situ using a hydrothermal diamond anvil cell coupled with Fourier transform infrared spectrometer as well as optical and infrared microscopes. Combustion/reaction at different oxygen concentration (0–49% H2O2), and pyrolysis experiments were conducted. The results show conclusively that (1) BaP is stable at pyrolytic conditions up to 452°C; (2) It can dissolve in supercritical water at 442–452°C forming partly decomposed globule. At extended reaction times above 500°C the globule undergoes carbonization while the dissolved compounds inhibit char formation. No complete dissolution was observed. (3) BaP combustion occurs simultaneously with dissolution in a single homogenous phase. At higher oxygen content, the dissolution and complete combustion takes place even in subcritical region (353° and 145 MPa). In such a case no melting phase is present. These observations may affect the design and organization of the SCW combustion process.

Ignition behaviour of pulp and paper combustible wastes

Ignition behaviour of combustible wastes from the pulp and paper industry was studied in a modified thermogravimetric furnace. Criteria for ignition and the ignition mechanism were developed. The ignition of combustible wastes was predominantly homogeneous. The influence of different factors, such as particle size, sample type, heating rate and oxygen concentration, was studied. In general, no monotonic relationship between ignition temperature and particle size was observed. Different types of sample had different ignition temperatures (ranging from 203 to 227°C). The ignition temperature increased with heating rate but decreased with oxygen concentration. The combustible waste samples were collected and morphologically analysed at different stages of the heating process. No significant differences in morphology were observed just before and after ignition. The results obtained are useful in identifying the region for injection of combustible wastes into industrial combustors (e.g. boilers or fluidized beds).

29Si, 27Al and 23Na solid-state nuclear magnetic resonance studies of combustion-generated ash

Abstract Combustion-generated ash was synthesized, heated and analyzed by solid-state nuclear magnetic resonance spectroscopy with magic angle spinning (NMR–MAS). The structural information obtained from this study indicates that the ash contains different magnetic resonance environments for Al, Si and Na after combustion. The final ash material contains a major amorphous aluminosilicate glass phase with mullite and corundum crystals. 29 Si NMR spectra showed a single peak at −110.5xa0ppm ( δ ) for the initial powder sample due to SiO 2 . When the sample was heated to 1500°C the peak shifts to lower field ( δ =−99xa0ppm) due to the formation of aluminosilicate amorphous glass containing alkali or alkaline earth metals. The 27 Al NMR spectra of the initial sample gives a single peak at 10.1xa0ppm due to the AlO 6 (octahedral group) present in the Al 2 O 3 . When the sample is heated to 1500°C, a new peak appeared at 50xa0ppm due to the formation of AlO 4 tetrahedral represent the mullite and aluminosilicate compounds. The 23 Na NMR spectra of both the initial and the heated samples (at 1500°C) give rise to a single peak at −14.3 and −28.7xa0ppm, respectively. The sharp peak at −14.3xa0ppm is contributed from the crystalline Na 2 O and the broad peak around −28.7xa0ppm is due to the Na + present to compensate SiO − present in the amorphous aluminosilicate glass material. The presence of low amounts of heavy metals Cr (2800xa0ppm), Cd (2700xa0ppm) and Pb (2800xa0ppm) in the ash generally does not show any influence on the 27 Al, 29 Si and 23 Na solid-state NMR spectra. On the other hand, the ash sample containing higher amounts of heavy metals (Cd=14210xa0ppm, Cr=13120xa0ppm and Pb=13140xa0ppm) showed significant effect on the 27 Al NMR spectra. The replacement of Al 3+ from its octahedral sites by Cr 3+ leads to the decrease in the intensity of the AlO 6 octahedral peak. The presence of Cr 3+ , Cd 2+ and Pb 2+ in the aluminosilicate matrix exerts a deshielding effect on 29 Si resonance and thus shifts δ to low-field. The results clearly indicate an interaction between the heavy metals and the ash matrix compounds.

Numerical modeling and TGA/FTIR/GCMS investigation of fibrous residue combustion

Numerical modeling results of combustion of fibrous sludge are presented and validated in a series of experiments. Combustion experiments were conducted in a thermogravimetric coupled with Fourier transform infrared spectrometer and gas chromatograph mass spectrometer. Sludge material (open matrix of lignocellulosic fibers with inorganic fillers) was generated in pulp and a paper mill during the de-inking process. Mathematical models were developed for solid- and gas-phase combustion. The mathematical model for the decomposition of solidiphase is based on the following assumptions: (1) rate of combustion determined by oxygen mass transfer, (2) laminar gas flow, and (3) negligible radiation. The combustion of aromatic hydrocarbons formed/released during the combustion process is formulated taking the following assumptions: (1) reaction rates of methyl-naphthalene and naphthalene are relatively fast and thereby constitute the driving force for the initiation of combustion; and (2) kinetics rate data for the oxidation of methyl-naphthalene and naphthalene are equal to those of benzene. Numerical computations compare well with measurements and provide good predictions of the reactivity of the material during the combustion process. Mass fraction remaining at the end of the simulation period was predicted within 2% accuracy. Flue gas combustion simulations have shown acceptable results, however the computed overall reaction rate was over-predicted. Predictions of the behavior of major gaseous species (CO2, O2, CO and PAH) were reasonable. Simulations also revealed the mechanism of solid biomass combustion to start at the center of the sample and then propagate toward the surface. Such information could not be obtained from experimental data. It was also shown that indenyl may play an important role in the pulp and paper biomass combustion and may be considered as a catalyst for ignition.

Rearrangements in metals environment of inorganic particles during combustion and solidification

Abstract We wish to suggest a structure for ash containing high concentrations of heavy metals in which important metallic rearrangements occur during combustion and solidification. The ash consists of three main phases, namely corundum, mullite, and amorphous aluminosilicate. During ash evolution, Cr 3+ ions replace Al 3+ in its octahedral sites of corundum/mullite, whereas Pb 2+ and Cd 2+ either fill the oxygen vacancy in mullite or form stable compounds with the glass phase. These changes promote a clear pattern revealing surface predominance of alkalis and core predominance of toxic metals within the ash particle. A composite picture of the metals rearrangements in an inorganic environment was obtained by the combination of independent analytical techniques, including electron probe microanalysis, solid-state nuclear magnetic resonance spectroscopy, and x-ray diffractometry. Although we simulated ash formed during combustion of de-inking paper mill waste, its chemical composition resembled that of ash from coal. It suggests the possibility that elemental surface vs. core segregation and Cr 3+ → Al 3+ replacement may be a general phenomenon in inorganic particles derived from high temperature processes followed by solidification for which diffusion and subsequent condensation of elements are likely to occur.