Mirjana Djurić

Portland Ash Cement Degradation in Ammonium-Sulfate Solution

Abstract This paper considers the sulphate corrosion of Portland cements (C 3 A content in clinker 6.60% and 13.31%) and the same Portland cements where the 30% of Portland cement clinker was replaced with coal ash. The test samples were prepared according to Koch-Steinegger’s method and then exposed to the influence of aggressive environment (10% (NH 4 ) 2 SO 4 solution). The measurements of several properties were carried out, the results were analyzed, and a correlation among the influencing factors was suggested through mass change, bonded SO 4 2− content, and degradation coefficient. There was a strong influence of coal ash on degradation, also.

Effect of sucrose concentration on the products of Kombucha fermentation on molasses

Fermentation of 1.5g/l of Indian black tea, sweetened with adequate quantities of molasses (containing approx. 70g/l, 50g/l and 35g/l of sucrose), was conducted using domestic Kombucha. Inoculation was performed with 10% of fermentation broth from a previous process. The fermentation in cylindrical vessels containing 2l of liquid phase, was carried out at 22±1°C for 14 days, with periodical sampling, to measure pH, content of acids (total, acetic and l-lactic), content of remaining sucrose, and the yield of biomass at the end of fermentation. A product with 70g/l sucrose from molasses corresponds to an optimal concentration of carbon source, which provided metabolites with high pH, a low content of less desired acetic acid, a high content of highly desired l-lactic acid, an acceptable content of total acids and the highest possible level of utilisation of sucrose.

Particle size range as a factor influencing compressibility of ceramic powder

The paper reports on an investigation conducted with the aim to determine whether an overall deformation stress of ceramic powder depends on the size of particles present in a system. For this purpose, six fractions (obtained by sieving of raw material, so as to contain particles with defined size range) were compacted and their compaction response diagrams were generated. For each particular fraction the parameters of the Heckel compaction model were calculated and used for estimating the deformation stress of each particular fraction. A correlation between average diameter of particles and the overall deformation stress of powder was found.

Computerized thermodynamic analysis of reactions during sintering of CaOAl2O3SiO2 system

Abstract Reactive sintering of the CaOAl 2 O 3 SiO 2 system has been investigated by many authors. Babushkin (1989) referred to the forming of ternary compounds (CaO·Al 2 O 3 ·2SiO 2 and 2CaO· Al 2 O 3 ·SiO 2 as well as the binary compounds (2CaO·SiO 2 and CaO·SiO 2 ) in the temperature interval from 1000 to 1600°K, based on Gibbs free energy calculated separately for the particular chemical reaction. The aim of this paperd was to calculate the equilibrium composition of the mentioned system as a function of both initial mixture composition and sintering temperature, taking all probable reactions into consideration. Thermodynamic analysis, performed by a specially developed computer program, shows significant influence of the initial mixture composition, but slight influence of the sintering temperature.

Process Duration and Water Consumption in a Variable Volume Diafiltration for Partial Demineralization and Concentration of Acid Whey

Process duration and fresh water consumption were determined (experimentally and statistically) for variable volume diafiltration (VVD) of cottage cheese through a flat sheet membrane (0.046 m2). The VVD process was performed at two volume decreasing ratios (α = 0.75 and α = 0.5). The VVD-0.75 process lasts much longer than the VVD-0.5 process if the same concentration degree is required. The VVD-0.5 process lasts longer than the VVD-0.75 process if it is aimed to achieve the same purification degree. At low purification degrees, both processes require similar quantities of fresh water, but better demineralization is possible after higher dilution, which is typical of the VVD-0.75 process. The mathematical model applied in estimating the duration of the process proved very accurate, which cannot be said about the fresh water consumption model.

An optimization of fly ash quantity in cement blending

Abstract The Two Goal Approach was applied to the maximization of fly ash quantity (i.e. minimization of energy consumption) in producing cement of acceptable mechanical characteristics. Mathematical model of the optimization problem consists of two objective functions; a requirement concerning ash quantity and a condition upon particular mechanical property. All data were obtained by a kind of the Mixture Design experiments, i.e. mixtures were made, by blending of various quantities of usually used components with fly ash, and their characteristics were determined by the standardized methods. The procedure was applied to a few chosen examples and optimal quantities of fly ash were suggested.

The Application of Membrane Separation Processes as Environmental Friendly Methods in the Beet Sugar Production

The sugar industry is one of the key segments of the food industry. This industry is also well known as one of the most energy-intensive in the field of food and chemical industry. In 1999, the total quantity of produced sugar was summarized. It was reported that the production reached 16 700 000 tones, while the total value of the produced sugar was 8924 million EUR. A significant quantity of thermal energy was consumed for the evaporation and beet pulp drying, as well as electrical energy needed for the pumps and for driving the centrifuges. According to CEFS, specific energy consumption was 31.49 kWh/100 kg beet in 1998 (IPPC, 2003). In a Greek study, a figure of 280 kWh/t is given for the electrical part of the energy consumption in sugar manufacturing (IPPC, 2003). While the overall water used is about 15 m3/t sugar beet processed, the consumption of fresh water is 0.25 – 0.4 m3/t sugar beet processed, or even less in modern sugar factories. Water consumption depends on the activities of each installation, e.g. more water is consumed in an installation that extracts and refines sugar beet compared to the one that does only one of these activities (IPPC, 2003). For example, the consumption of water in Austria was reported at a level of 1.5 m3/t of sugar beet processed, which is equivalent to 9 m3/t of produced sugar (IPPC, 2003). The transport water has high organic contamination due to the soil and sugar from damaged beets. Its COD is 5000 – 20000 mg/L. Waste water with high BOD levels is produced in large volumes (IPPC, 2003). Despite the fact that the sugar industry is one of the causes of the environmental pollution, not enough has been done on its improvement. The technology applied in almost all European sugar factories is based on the traditional principles and methods. The major steps in the traditional sugar beet processing are (Poel Van der et al., 1998): i) Pre treatment – Washing and slicing of the sugar-beets into cosettes are the initial operations;

Prognosis of The Mineralogical Composition of Sintered Portland Cement Clinker

The possibility of evaluating the composition of cement clinker obtained by sintering raw materials with a known composition is the basic prerequisite for synthesis of products with desired properties.