Tiit Kaljuvee

Thermal behaviour of urea-formaldehyde resins during curing

Urea-formaldehyde (UF) resins are the most widely used polycondensation resins today in manufacturing particleboards. The performance of UF resins in their processing is greatly influenced by curing characteristics. The cure process has been monitored by TG-DTA technique on a Setaram labsysTM instrument in dynamic heating conditions at different heating rates. Commercial UF resins from different suppliers used in Estonian particleboard factories were selected for TG-DTA measurements. Experiments were carried out without and with catalysts. Ammonium chloride and ammonium sulphate were used. Curing characteristics were evaluated both for fresh and aged resins.

TG–FTIR analysis of oxidation kinetics of some solid fuels under oxy-fuel conditions

A possible technology that can contribute reduction of carbon dioxide emission is oxy-fuel combustion of fossil fuels enabling to increase CO2 concentration in the exhaust gas by carrying out the combustion process with oxygen and replacing air nitrogen with recycling combustion products to obtain a capture-ready CO2 stream. The laboratory studies and pilot-scale experiments discussed during the last years have indicated that oxy-fuel combustion is a favorable option in retrofitting conventional coal firing. Estonian oil shale (OS) with its specific properties has never been studied as a fuel in oxy-fuel combustion, so, the aim of the present research was to compare thermo-oxidation of OS and some coal samples under air and oxy-fuel combustion conditions by means of thermal analysis methods. Experiments were carried out in Ar/O2 and CO2/O2 atmospheres with two oil shale and two coal samples under dynamic heating conditions. FTIR analysis was applied to characterize evolved gases and emission dynamics. Kinetic parameters of oxidation were calculated using a model-free kinetic analysis approach based on differential iso-conversional methods. Comparison of the oxidation characteristics of the samples was given in both atmospheres and it was shown that the oxidation process proceeds under oxy-fuel conditions by all studied fuels with lower activation energies, however, it can last longer as the same temperatures are compared.

TG-FTIR study of gaseous compounds evolved at thermooxidation of oil shale

The combined thermogravimetric (TG) Fourier transform infrared (FTIR) techniques were used for studying the gaseous compounds evolved at thermooxidation of oil shale samples from different deposits (Estonia, Jordan, Israel). In addition to H2O and CO2as the major species, the formation and emission of CO, SO2, HCl and a number of organic species as methane, ethane, ethylene, methanol, formic acid, formaldehyde, chlorobenzene, etc. was determined. Differences in the absorbance of respective bands in FTIR spectra depending on the origin of oil shale and on the heating rate used were established.

Decarbonization of natural lime-containing materials and reactivity of calcined products towards SO2 and CO2

The results obtained by studying decarbonization of different samples of Estonian limestone and dolomite and the following sulphation or carbonation of calcined products to estimate their SO2 and CO2 binding ability were presented. Experiments were carried out with thermogravimetric equipment(Q-Derivatograph, MOM and Labsys™, SETARAM) – calcination of the samples in the atmosphere of air with the heating rate 10 K per minute using multiplate crucibles, the following sulphation or carbonation of the calcined products after cooling to the fixed temperature (temperature range 400–900°C) under isothermal conditions in the flow of air-SO2 or air-CO2 mixture. Chemical, X-ray, BET nitrogen dynamic desorption, etc. methods for the characterization of the initial samples, intermediate and final products were used.In addition, the possibilities of recurrent use of oil shale ashes taken from different technological points at operating thermal power plants (Estonian and Baltic TTPs, Estonia) as sorbents for SO2 binding from gaseous phase were studied, as well as the possibilities of activation of these ashes towards SO2 binding.The results of these studies confirmed the high reactivity of Estonian limestone and dolomite towards SO2 and CO2. Dependence of SO2 binding mechanism on the SO2 concentration has been established. Modelling of SO2 capture of dolomite and limestone was carried out to establish the kinetic parameters of these processes. The possibilities of activation of oil shale ashes and their effective recurrent use for binding SO2 and CO2 from gaseous phase were confirmed.

Enrichment of carbonate-phosphate ores by calcination and air separation

Abstract The possibility of calcination-separation enrichemnt of carbonate-phosphorite ores from Karatau area has been studied. The calcination of phosphorites was recommended to be carried out in the fluidized bed kiln, the grinding of calcinated phosphorites in a centrifugal impact mill, classification of ground material in a non-rotary air separator. The phosphorite concentrate with a content P 2 O 5 more than 28% and the yield of P 2 O 5 into the concentrate not less than 85% was obtained by using carbonate-phosphorite ores containing 21–23% of P 2 O 5 and 8–10% of CO 2 .

SO2 binding into the solid phase during thermooxidation of blendsestonian oil shale semicoke

Approximately one million tons of semicoke (SC) is formed and stored in open air dumps every year in the production of shale oil by processing Estonian oil shale (OS). The content of different harmful compounds as sulphides, PAH, phenols, etc. in SC make these dumps one of the most serious sources of environmental contamination. The aim of this work was to study the behaviour of sulphur compounds in OS and its SC, formation of SO2 and possibilities of binding it into the solid phase during thermooxidation of fuel blends based on SC. Blends modified with SC ash addition were studied as well. It was determined that SO2 emission in thermooxidation of SC samples started at 280-300°C and proceeded with a steady speed up to 580-600°C and the amount of sulphur evolved was 5-10% from the total content of sulphur in the sample. The amount of SO2 emitted decreased depending on the mass ratio of the composite fuels from 49-56 to 15-35% during thermooxidation of OS samples studied or their blends with SC, respectively, from 43-80% for coal samples to 13-60% for their blends with SC and to 2-13% during thermooxidation of these blends modified with SC ash addition. In the products of thermooxidation formed at 800-900°C the only sulphur containing phase was CaSO4, at 650°C also traces of CaS and CaMg3(SO4)4 were fixed.

Thermochemical characterization of chicken litter and peat as a source for energy recovery

The shortage of raw materials and the environmental problems due to pollution require development of new green technologies utilizing some wastes and transforming them to secondary raw materials. The aim of this work is to study the properties of poultry waste to propose possibilities to minimizing the released emissions and avoiding the risk for human health and the environment. At the same time, two types of low grade peats with different origin are studied as components for the production of soil conditioners. During the studies, we applied the inductively coupled plasma (ICP) and chemical analysis, powder X-ray diffraction, thermal analysis, IR spectroscopy, and scanning electron microscopy for determining the composition, crystal phase, the shape and size of particles, and thermal stability of the investigated samples. The chemical and the phase compositions of the studied samples confirmed that the content of nutrient compounds and of the carbon substances is suitable as an effective secondary raw material for soil conditioners. It is found that the poultry wastes and peat samples have a similar phase and chemical composition and contain an organic mass in the form of carbon components with amorphous, fibrous, and skeleton-like structure, suitable to be combined with other nutrient-containing compounds. During the thermal treatment, the carbon compounds are oxidized releasing heat. Based on that the materials under study are considered as environmentally friendly fuels, releasing relatively low emissions.

Reaction pathway to Cu2ZnSnSe4 formation in CdI2

We investigated various possible chemical interactions between individual precursor compounds (ZnSe, SnSe, and CuSe) and CdI2 as a flux material used in the CZTSe monograin powder synthesis–growth process in closed vacuum ampoules. The processes occurring in these mixtures were detected by the differential thermal analysis method. The phase changes in these processes were determined using X-ray diffraction and Raman spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, thermogravimetric analysis, and mass spectrometry. The analyses showed that molten CdI2 was chemically active, forming Zn1−xCdxSe in the CdI2–ZnSe mixture by a chemical dissolution reaction; CdSe, SnI2 and SnI4 formed in the CdI2–SnSe mixtures and CdSe; and CuI formed in the CdI2–CuSe mixtures by exchange reactions.

Reaction pathway to Cu 2 ZnSnSe 4 formation in CdI 2

We investigated various possible chemical interactions between individual precursor compounds (ZnSe, SnSe, and CuSe) and CdI2 as a flux material used in the CZTSe monograin powder synthesis–growth process in closed vacuum ampoules. The processes occurring in these mixtures were detected by the differential thermal analysis method. The phase changes in these processes were determined using X-ray diffraction and Raman spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, thermogravimetric analysis, and mass spectrometry. The analyses showed that molten CdI2 was chemically active, forming Zn1−xCdxSe in the CdI2–ZnSe mixture by a chemical dissolution reaction; CdSe, SnI2 and SnI4 formed in the CdI2–SnSe mixtures and CdSe; and CuI formed in the CdI2–CuSe mixtures by exchange reactions.

Reaction pathway to CZTSe formation in CdI2: Part 2: Chemical reactions and enthalpies in mixtures of CdI2–CuSe–SnSe and CdI2–CuSe–SnSe–ZnSe

The chemical reactions between CuSe, SnSe and ZnSe and their enthalpies in molten CdI2 in closed vacuum ampoules were investigated. Differential thermal analysis (DTA) was used for the determination of the temperatures of processes occurring in the studied mixtures. X-ray diffraction and Raman spectroscopy were performed to discover the phase changes in the long-term annealed samples at higher than peak temperatures in DTA. The occurring chemical reactions and their enthalpies were derived. The recrystallization of CZTSe in CdI2 was investigated. The results confirmed the formation of Cu2SnSe3, Cu2SnSe4, CdSe, Cu2CdSnSe4, Cu2ZnSnSe4, and Zn1−xCdxSe compounds and solid solutions.