Coal analysis using thermogravimetry

ABSTRACT Thermogravimetric analysis is being used increasingly today to obtain kinetic data related to coal decomposition. However, this method is open to criticism on the basis that the meaning of the activation energy of solid state reactions obtained from TG experiments is not clear. In this study a linear relationship between procedural activation energy and heat of reaction is developed. This is typical of elementary reactions of atoms and small radicals. The effects of alkali metal salts on the decomposition of coal under three gas atmospheres (N,. CO, and air) are investigated. Several features are reported such as the effect of the catalysts on coal conversion and CH,, CO and CO, emission. These are related to observed changes in activation energy

Experimental and theoretical performance evaluation of parabolic trough mirror as solar thermal concentrator to thermoelectric generators

This paper presents the prospects of harnessing radiative heat from the sun with a parabolic trough mirror, as a solar thermal concentrator, in comparison to the mathematical model and experimental quartz-halogen concentrator model for the electrical energy conversion utilizing thermoelectric generators (TEG). The construction and design of TEG-setup along with Parabolic trough mirrors and quartz-halogen lamps are presented. The Parabolic trough mirror used as a focal point at a distance of 19.05 cm. With eight quartz-halogen concentrated heat, the maximum performance achieved at ΔT of 11.8 K, Voc of 292 mV and Isc of 95.8 mA, recorded at the concentrated hot-side surface temperature of 317.8 K. When compared to the natural solar concentrated heat, higher temperature of 473.15 K at the hot-side surface temperature of TG was achieved. It is concluded that the heat concentration of the parabolic mirror increases with an increase in the intensity of heat using natural solar radiations. The Voc of 1.76 V and Isc of 1.1 A at a temperature difference of 110 K were measured, which are in good agreement with validated mathematical results. The parabolic through mirror utilized is smaller in size and thus collected lesser sun rays than the larger dish style mirror, and hence the heat in the focal point was very low, for better results, parabolic trough mirror with higher surface area would be important for future experiments

The autonomous city: towards a critical geography of occupation

This paper explores the recent resurgence of occupation-based practices across the globe, from the seizure of public space to the assembling of improvised protest camps. It re-examines the relationship between the figure of occupation and the affirmation of an alternative ‘right to the city’. The paper develops a critical understanding of occupation as a political process that prefigures and materializes the social order which it seeks to enact. The paper highlights the constituent role of occupation as an autonomous form of urban dwelling, as a radical politics of infrastructure and as a set of relations that produce common spaces for political action

Effect of calcium chloride and calcium acetate on the reactivity of a lignite coal at low heating rate

The effect of calcium chloride and calcium acetate on the rate of decomposition of a lignite coal and its char was investigated under both pyrolysis and combustion conditions. The experiments were undertaken in a thermogravimetric analyzer under low (20°C min-1) and intermediate (2100°C min-1) heating rates. Both calcium chloride and calcium acetate slightly reduced the amount of coal decomposed at 105 N m-2 in a nitrogen atmosphere. However, the inhibiting effect of calcium acetate was dependent on the sample size and packing density. In the presence of oxygen, addition of calcium chloride to coal produced two opposite effects: at low temperatures an inhibiting effect due to the chloride and at higher temperatures a promoting effect due to the catalytic role of the calcium. Lastly, the additives reduced the apparent activation energy and increased the heat reaction of the lignite coal. © 1988

A thermogravimetric study of the decomposition rate of chlorinated polyethylenes under ignition conditions

Decomposition and combustion of three chlorinated polyethylenes (C1PE-25%, C1PE-36% and C1PE-42%) and a high density polyethylene (HDPE) under medium heating rates (11.5-67.5°C (s-1) in an oxidant gas flow was investigated using a Du Pont 951 thermogravimetric analyzer (TGA). The decomposition rate constants prior to ignition and during combustion were obtained using an Avrami-Erofee\u27v type equation, [- In(1 - C)] 1 n= kt + A where n was chosen equal to four. The results showed that the rate constant was sensitive to the isothermal furnace temperature only if a small sample mass (about 2.40 mg) was used. Increasing O2 concentration in the gas flow greatly promoted the decomposition rate prior to ignition, but was less significant in the combustion stage. The rate of decomposition for HDPE was much higher than that of the chlorinated polyethylenes, indicating the effectiveness of substituted chlorine in suppressing the decomposition rate of the polymers. On the other hand, increasing the chlorine content from 36 to 42% did not reduce the decomposition rate further under our conditions. © 1988

Effect of operating parameters on time to decomposition of high density polyethylene and chlorinated polyethylenes

An investigation was made to determine the influence of furnace temperature (500-800 °C), concentration of oxygen in the gas flow (0-100%, v v) and sample mass (2-15 mg) on the decomposition time of several polymers. These were high density polyethylene and chlorinated polyethylenes (25, 36 and 42% by mass chlorine). Thermal oxidative degradation was undertaken in a Du Pont 951 thermogravimetric analyzer in the isothermal mode using a gas flow of 0.833 ml s-1, STP. The results indicated that the average sample heating rate influenced the decomposition time most. Operating at higher furnace temperature (≥ 700°C) and using a small sample mass (≤ 2.5 mg) reduced the variance in td. The activation energy for decomposition of the polymers was 39.3 ± 0.5 kJ mol-1. © 1987

Structural characterization of lignite coal and char with CaCl \u3c inf\u3e 2

The purpose of this investigation was to determine the effect of adding 1.4% CaCl2 (by mass) to coal on both coal and char structure. It is the fourth study in a series related to boiler application involving this salt. In this study the effect of CaCl2 on density, pore structure, and compressibility of coal were investigated. To obtain information on the state of dispersion of the calcium a number of tests were undertaken which involved x-ray diffraction analysis, x-ray microanalysis and infrared analysis. The results indicated that addition of CaCl2 to coal did not alter the coal structure to any significant extent. However, the char from treated coal showed a more disordered structure. The results also showed that calcium was highly dispersed in char which explains its higher reactivity observed in a previous study. © 1987

Coal: Kinetic analysis of thermogravimetric data

Thermogravimetry, TG, is widely used to investigate rate processes. This method involves the continuous measurement of the change in mass or rate of mass loss, DTG, of a sample with temperature (or time). Such data has been used to determine kinetic parameters, such as activation energy and order of reaction. A number of methods have been developed in the literature to permit kinetic analysis of TG data. The kinetic parameters for the decomposition of coal are frequently calculated from one TG curve obtained at a constant heating rate. Since kinetic parameters are influenced by the heating rate, methods involving one thermogram have been criticized on the basis that they may give incorrect values for the activation energy and reaction order, and that only methods involving multiple heating rates will give reliable results. In this work, comparison is made of four methods for analyzing TG data of a sub-bituminous coal. © 1983

Coal analysis using thermogravimetry

Thermogravimetric analysis is being used increasingly today to obtain kinetic data related to coal decomposition. However, this method is open to criticism on the basis that the meaning of the activation energy of solid state reactions obtained from TG experiments is not clear. In this study a linear relationship between procedural activation energy and heat of reaction is developed. This is typical of elementary reactions of atoms and small radicals. The effects of alkali metal salts on the decomposition of coal under three gas atmospheres (N2, CO2 and air) are investigated. Several features are reported such as the effect of the catalysts on coal conversion and CH4, CO and CO2 emission. These are related to observed changes in activation energy. © 1984