The dynamics of SO2 emission during thermooxidation of Estonian oil shale, its semicoke, different samples of coal and their mixtures, as well
as the influence of Estonian oil shale ash addition (for modelling the CFBC process) on the dynamics were studied. The experiments
were carried out with thermogravimetric equipment under dynamic heating conditions (5 K min-1) in the atmosphere of dried air, with simultaneous gastitrimetric EGA.
It was established that SO2 emission from the fuels started at 200-320C. Depending on the form of sulphur (organic, pyritic, sulphate), the emission
took place in two or three steps, and continued up to 580-650C, during which 35-75% of the total sulphur was emitted into
the gaseous phase. Regulating the mole ratio of free CaO/S in the mixtures of fuels with oil shale ash addition the emission
of SO2 ceased abruptly at 460-540C and it was limited to the level of 7-30%.
Ammonium nitrate (AN) is one of the main nitrogen fertilizers used in fertilization programs. However, AN has some serious
disadvantages — being well soluble in water hardly 50% of the N-species contained are assimilated by plants. The second disadvantage
of AN is associated with its explosive properties. The aim of this paper was to clarify the influence of different lime-containing
substances — mainly Estonian limestone and dolomite — as internal additives on thermal behaviour of AN.
Commercial fertilizer grade AN was under investigation. The amount of additives used was 5, 10 or 20 mass%, or calculated
on the mole ratio of AN/(CaO, MgO)=2:1 in the blends. Experiments were carried out under dynamic heating condition up to 900°C
(10°C min−1) in a stream of dry air or N2 by using Setaram Labsys 2000 equipment coupled to Fourier transform infrared spectrometer (FTIR).
The results of analyses of the gaseous compounds evolved at thermal treatment of neat AN indicated some differences in the
decomposition of AN in air or in N2. At the thermal treatment of AN’s blends with CaCO3, MgCO3, limestone and dolomite samples the decomposition of AN proceeds through a completely different mechanism — depending on
the origin and the content of additives, partially or completely, through the formation of Mg(NO3)2 and Ca(NO3)2.
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 400–900C) 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.
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 280-300C and proceeded with a steady speed up to 580-600C 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 800-900C
the only sulphur containing phase was CaSO4, at 650C also traces of CaS and CaMg3(SO4)4 were fixed.
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.
Authors:K. Siimer, T. Kaljuvee, P. Christjanson, T. Pehk, and I. Saks
Thermal behaviour of cure-accelerated phenol-formaldehyde (PF) resins was studied using the addition of commercial mixture
of water soluble oil shale alkylresorcinols (AR) to PF resin, 5-MR being as model compound. The acceleration effect of AR
is based on the promotion of condensation of resin methylol groups and subsequent reaction of released formaldehyde with AR.
Commercial PF resins SFŽ-3013VL and SFŽ-3014 from the Estonian factory VKG Resins have been used. The chemical structure of
resins was characterised by 13C NMR spectroscopy. TG-DTA analysis was carried out using labsysTM instrument Setaram. By TG-DTA measurements, the shift of exothermic and endothermic peaks and the changes of mass loss rate
in the ranges of 1.5–10 g AR/100 g PF resin were studied. The effect of AR on the curing behaviour of PF resins was also followed
by gel time.
Testing of the plywood when using PF resin with 5 mass% of AR shows that the press time could be reduced by about 15%.
Authors:K. Siimer, P. Christjanson, T. Kaljuvee, T. Pehk, and I. Saks
Urea–formaldehyde (UF) and phenol–formaldehyde (PF) resins are the most widely used wood adhesives. The first stage in resin
manufacturing is the formation of methylol derivatives which polycondensation leads to building the tridimensional network.
Understanding the behaviour of methylol compounds in curing provides useful information for developing appropriate resin structures.
Thermal behaviour of N,N′-dihydroxymethylurea, 2- and 4-hydroxymethylphenols, urea and phenol as model compounds for UF, PF and phenol–urea–formaldehyde
(PUF) resins was followed by TG-DTA method. The measurements were carried out by the labsys instrument Setaram at 30–450 °C in nitrogen flow. The characteristic signals for model compounds and for some reaction mixtures
were measured by high resolution 13C NMR spectroscopy.
Authors:K. Siimer, T. Kaljuvee, P. Christjanson, and T. Pehk
Summary The curing behaviour of commercial UF and MUF resins, stored at room temperature nearly up to gelation, is studied by simultaneous TG-DTA technique and structural changes of resins are also followed during aging. On the basis of 13C NMR spectra, the main chemical reaction during UF resin storage is the formation of methylenes and dimethylene ethers linked to secondary amino groups. Aging of resins results in a decrease of cure rate which is related to lower concentration of active functional groups and decrease in molecular mobility. On DTA curve, the resin with higher content of methylol groups reveals the curing exotherm earlier. With decreasing methylol content during storage, the peak maximum of exotherm is shifted to higher temperature value. Advanced polycondensation and sedimentation processes during storage produce partly locked in macromolecule structure water, and the water evaporation endotherm on DTA curve shifts to considerably higher temperature. The aged MUF resins are chemically less changed than UF resins and the aging process mainly involves noncovalent network formation due to complex molecular structure.