Otakar Trnka

Influence of temperature on the reactivity of limestone particles with sulfur dioxide

A modified version of the grain theory was used to analyse the effect of temperature on the sulfation reaction. The theory combines the influence of temperature on the grain size, its effect on the rate of transport of SO2 and the chemical reaction. An efficient numerical procedure is presented for solving the model equations which take into account the radial gradient of the effective diffusivity in a particle.

Predicting the rate of thermal decomposition of dolomite

This communication presents experimental data on the thermal decomposition of a high-grade dolomite. The objective is to determine and describe the rate of thermal dissociation of dolomite at moderate temperatures as a function of temperature and conversion

Decomposition kinetics of alkaline-earth hydroxides and surface area of their calcines

Abstract Thermal decomposition of Mg(OH) 2 and Ca(OH) 2 particles produces highly porous calcines that react rapidly with acidic gaseous pollutants at moderate temperature. Increasing- and constant-temperature gravimetric methods were employed to measure the rates of decomposition of hydroxide particles at temperatures 290–430°C. The measured data wree tested empirically by fitting to the n th-order rate equation of Arrhenius type, and the values of the kinetic parameters were estimated. Differences are explored in the course of the decompo sition of magnesium hydroxide and that of calcium hydroxide. The sintering rate of the nascent, hydroxide-derived oxides was measured in a nitrogen atmosphere at temperatures from 400 to 700°C. An empirical kinetic model has been proposed to correlate the experimental data on the specific surface area of solids. Comparison of the results indicates that particles of MgO exhibit a surface area which is half an order greater than that of CaO sintered under the same conditions.

Fluidization characteristics of dolomite and calcined dolomite particles

Abstract Experimental measurements were performed of the minimum fluidization velocities and the terminal velocities of a bed of dolomite and its calcine. Using air, experiments were conducted in an 8.5 cm i.d. column with very narrow fractions of particles in a range of 0.14– 0.72 mm . The formulas developed can be employed in engineering considerations and design of contacting coal or flue gas with dolomite sorbents.

THERMAL DEHYDRATION OF THE SODIUM CARBONATE HYDRATES

A thermal gravimetric method was employed to explore the course of dehydration of Na2CO3 · 10 H2O, and Na3CO3 · H2O particles. Experimental data were amassed both in the temperature-increasing and constant temperature mode. Very small sample masses were used in an effort to eliminate an effect of heat and mass transfer processes on the rate of reaction. Kinetic equations of Arrhenius type were proposed for two stages of the dehydration and tested against the results collected by experiment.

Behaviour of inorganic constituents of municipal sewage sludge during fluidized-bed combustion

The fate of main heavy metals in municipal sewage sludge (As, Cd, Co, Cr, Cu, Hg, Mo, Ni, Pb, and Zn) was investigated using a fluidized-bed reactor. The behaviour of metals in the incinerator was explored by comparing metal contents in the two main ash streams: bottom (in-bed) ash and ash separated by a cyclone (cyclone-catch ash). All metals showed enrichment in the cyclone ash. The ash originating from sewage sludge is thermally quite stable consisting of quartz, hematite, spar(s), mica(s), apatite, and anhydrite. It does not soften nor becomes sticky and does not tend to agglomerate at temperatures up to 950°C.

An alternative semi-implicit Euler method for the integration of highly stiff nonlinear differential equations

Abstract A relatively simple method has been developed for the integration of highly stiff sets of differential equations describing important, noncatalytic, gas-solid reaction systems. the method is based on the semi-implicit Euler scheme which makes it possible to solve the resulting algebraic equations separately with the aid of always converging procedures such as the interval halving or regula falsi. The developed, semi-implicit Euler method has been compared to some implicit and other semi-implicit techniques. Although the proposed procedure is not so effective as the conventional methods in standard stiff situations, it works reliably also under such circumstances when the conventional techniques fail.

KINETICS OF THE THERMAL DECOMPOSITION OF HYDRATED DOLOMITIC LIME AND SINTERING OF NASCENT CALCINE

A study is reported of the controlled thermal decomposition of hydrated dolomitic lime originated from a high-grade dolomite. Both increasing and constant temperature weight-loss methods have been employed to measure the rate of thermal dehydration of hydrated dolomitic lime at 305-400°C. The amassed data have been correlated with the use of an Arrhenius-type rate equation. Changes in the specific surface area of calcines due to sintering phenomena have also been studied at 400-600°C. An empirical, fractional-order kinetic relationship has been developed for surface area reduction as a function of temperature and elapsed time of sintering. Presented findings make it possible to specify the operation conditions needed for the preparation of reactive dolomite-derived sorbents.

IMPEDIMENT TO INCIPIENT FLUIDIZATION IN WET BEDS OF POROUS NONSPHERICAL PARTICLES

ABSTRACT Fluidized-bed units are efficiently and advantageously employed for drying various wet and sticky particulate materials provided that the bed of such materials can be kept under a fluidized condition. The effect was explored with the incremental addition of water to the bed of nonspherical, porous particles of ceramsite and lignite fluidized with wet air. The limiting fluidization-defluidization point was determined by experiments in a cold model fluidized bed contained in a transparent glass column using wet and dry particles. On the basis of the data amassed, an empirical correlation was developed. This relationship makes it possible to predict the dimensionless excess gas velocity that keeps the wet bed fluidized, as a function of the relative amount of moisture in the bed and the dimensionless particle size.

Performance of an afterburner chamber with a natural gas burner

The axial temperature and concentration profiles of CH4, O2, CO2 and CO in a pilot-plant refractory afterburner chamber fitted with a natural gas burner were measured as functions of the throughput and excess air ratio. The performance of the afterburner is strongly related to the overall temperature regime, concentration of oxygen and gas residence time.