Improving the efficiency of fluidized bed comminution of limestone samples

Purpose: The aim of the research was to describe the properties and methods of using limestone for desulfurization of flue gases and to analyse the process of fluidized bed comminution and the influence of selected parameters and stand modification on quality of product of fluidized bed comminution. Design/methodology/approach: Tests of the grinding process on the fluidized bed were carried out using a modified fluid bed mill for operational variable parameters and their results were compared with the results received before modification. The modification of the test stand consisted of increasing the height of the grinding chamber, which ensured an increase in the volume of the fluidized layer where the grinding process takes place. Findings: Main parameters that determined the effects of comminution in the analyzed case were: overpressure of working air and the rotor speed of the classifier. The introduction of the modifications of the test stand ensured an increase in the volume of the fluidized layer in which the grinding process takes place. As well as a greater gravitational classification, which caused larger grains to be stopped in the grinding chamber and shift of characteristics of grain compositions towards finer grains. Research limitations/implications: It is assumed that the diameter of sorbent grains used in the fluidized bed can not exceed 6 mm. The granularity of the offered sorbents ranges from 0.1 mm to 1.2 mm. The quality of the desulfurization process depends on the overall granulation of used sorbent grains. Practical implications: Appropriately selected sorbent grains used in wet and dry flue gas desulphurisation plants ensure improved efficiency of the desulphurisation process and lower operating costs of the installation. Originality/value: Thanks to the comminution method used, a sorbent is obtained without impurities and with an increased specific surface, which can be used in fluidized bed boilers.

MATHEMATICAL MODELING OF PROCESSES OF SEPARATION OF COMPONENTS OF GRAIN MATERIAL IN THE COMBINED VIBRATION-AIR SEPARATOR

Development of a mathematical model and calculated analytical dependencies for determining the trajectories and parameters of grain movement in a vibro-fluidized layer of grain material components under the action of a pulsating air flow. They are based on the methods of deterministic mathematical modeling and theoretical mechanics based on the equations of motion of a material point at a variable air flow speed and the action of a pulsating air flow. Theoretical studies were carried out using the methods of mathematical analysis and modeling. The research results were processed using elements of the theory of probability and mathematical statistics using software packages; to determine the rational parameters of the process, the method of statistical experiment planning was used. A mathematical description of the motion of the grain material particles in a combined vibration-air separator under the action of a pulsating air flow of variable speed is given. The trajectories of motion of particles with different sizes are obtained. The obtained equation of motion of a particle under the influence of a pulsating air flow makes it possible to determine the dependence of the speed of movement of the material in a vibro-fluidized layer of grain material on a number of factors: the geometric parameters of the sieve-free sieve, the feed angle of the material, the initial kinematic mode of the material, the index of the kinematic mode of the sieve-free sieve, as well as the coefficient of windage of the grain. On the basis of theoretical studies, the possibility of separating particles of grain material into fractions according to aerodynamic properties with vibropneumatic loading of grain into the channel has been determined. The use of a pulsating air flow as a separating carrier, and taking into account the deflecting forces, made it possible to significantly increase the splitting of the trajectories and the criterion for dividing the grain into fractions.

INTENSIFICATION OF HEAT TRANSFER IN TUBES WITH FLUIDIZED LAYER

It is shown that one of the promising methods of heat exchange intensification in the air-cooling unit is the organization of a fluidized layer.

Inferences on Mixed Snow Avalanches from Field Observations

Observations of the deposits, flow marks, and damages of three mixed-snow avalanches of widely different size were analyzed with regard to flow regimes, velocities, pressures, densities, flow depths, erosion modes, and mass balance. Three deposit types of different density and granulometry could be clearly discerned in these avalanches. They are attributed to dense, fluidized, and suspension flow regimes, respectively. Combining observations, we estimated the density in the fluidized layer as 35–100 kg m − 3 , in good agreement with inferences from pressure measurements. Upper bounds for the suspension layer density, arising from the run-up height, velocity, and damage pattern, are about 5 kg m − 3 at the valley bottom. An approximate momentum balance of the dense layer suggests that the snow cover was eroded to considerable depth, but only partly entrained into the flow proper. The suspension layer had largely lost its erosive power at the point where it separated from the denser parts of the avalanche. Our estimates shed doubt on collisions between snow particles and aerodynamic forces at the head of the avalanche as sole mechanisms for creating and upholding the fluidized layer. We conjecture that the drag from air escaping from the snow cover as it is being compressed by the overriding avalanche could supply the missing lift force.

Preparation of syngas from the semi-coke of Borodino coal for solid oxide fuel cells

Syngas for the battery of solid oxide fuel cells is produced in a gas generator with a fluidized layer consisting of a mixture of electrocorundum and semi-coke of the Borodino coal at the temperature of 850 °C, fluidizable by steam in a retort heated from the outside. The concentration of semi-coke is 627 kg per 1m3 of mixture of electrocorundum and semi-coke. The heat of combustion of the obtained syngas is 13359 kJ/kg. Syngas is purified in a cyclone – dust collector and gas purification from SO2 and H2O.

Mathematical Modeling and Optimization of Fluidized Layer Carbonitriding Process for 1C 25 Steel

This paper presents the experiment-based mathematical modelling of fluidized bed carbonitriding process for 1C 25 steel meant to optimize this type of thermochemical processing.Based on experimental results, the mathematical model was developed, which is a second order equation with three unknown terms (parameters): temperature, depth of carbonitrided layer, the percentage of ammonia.The mathematical model allowed the simulation of the fluidized layer carbonitriding process according to its parameters and the thermal energy optimization for obtaining HV hardness values in the range 300-400 MPa.Using the software package Matlab a graphical interface was done, through which all the combinations of technological parameters of the carbonitriding process are determined, leading to obtaining values of microhardness between 300 and 400 MPa, as well as the amount of energy consumed for each variant. The variant consuming the lowest energy is considered optimal.