Effect of longwall face advance rate on spontaneous heating process in the gob area - CFD modelling

A commercial CFD software programme, FLUENT, was used to study the oxidation process of coal in the mined-out longwall (gob) area. A three-dimensional, single-phase model with a continuously advancing longwall face has been developed. For the model, the gob longwall area was designed on the basis of the actual longwall panel operating in the Ostrava-Karviná Coal Mines (OKD, Czech Republic). The behaviour of the coal to oxygen was modelled using the results arising mainly from the former laboratory-scale experiments with Czech bituminous coals. Basically, the technique of pulse flow calorimetry and measurements at a continuous airflow reactor were applied during the laboratory investigations. In the contribution, the main focus was to understand the effect of the longwall face advancing speed on the oxidation heat production as well as evolution of the gases in the gob area. Simultaneously, the effect of coal crushing in the mined-out area on the spontaneous heating process was examined.Numerical simulations confirmed the existence of a “favourable” zone for the onset and development of the spontaneous heating process in the gob area. The location and the maximal temperature reached in the “favourable” zone were found to be significantly affected by the advancing rate of the coalface. The slower the advancing rate is, the higher the maximal temperature and smaller the depth of the “favourable” zone in the gob area are. When the rate drops to a certain “critical” value, spontaneous heating turns to flammable combustion of the coal. The value of the “critical” advancing rate was confirmed to increase if the grain size of the coal left in the gob decreases. Numerical examinations of carbon monoxide concentrations then proved that small incidents of spontaneous heating could occur in the gob area that need not be detected in the airflow of the longwall tail gate.     

Subaquatic oxidation of coal by water-dissolved oxygen

Subaquatic oxidation of two bituminous coals by water-dissolved oxygen was investigated using batch reactor equipped with membrane oxygen sensor. Effects of time, temperature and coal grain size were studied as basic parameters influencing the oxidation process. Obtained results showed the subaquatic coal oxidation can be considered as interaction of the first reaction order with respect to oxygen. From temperature dependence of oxidation rate, activation energies E = 72 ± 4 kJ mol⁻¹ and/or 50 ± 4 kJ mol⁻¹ were calculated. For the samples, oxygen consumption R_O2 was found to be in the range of 2 × 10⁻⁷ mol O₂ kg⁻¹ s⁻¹ to 6 × 10⁻⁷ mol O₂ kg⁻¹ s⁻¹, such values being quite comparable with R_O2 for aerial oxidation of bituminous coals.     

Patients' information needs and decision-making processes: What can be learned from genetic counselees?

This field study investigated the information needs and decision-making strategies of 161 genetic counselees interviewed just prior to counseling. Patients were interested mostly in information about the outcomes and consequences of the alternative options at their disposal and about measures to defuse the risks. They wanted mainly information stated with certainty and were less interested in probability information. There was no difference in the search for information between the alternative eventually chosen and the one not chosen. There was a difference, however, among types of decisions and the interest in the various categories of information. These findings were interpreted within the theoretical model of decision making in natural risky situations (O. Huber, 1997). Practical implications for shared medical decision making are presented. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Optimization of genetic algorithm for reconstruction of cross‐phase modulation frequency‐resolved optical gating data

We implemented a frequency‐resolved optical gating (FROG) measurement method using cross‐phase modulation in a highly birefringent microstructure optical fiber. The standard FROG data reconstruction algorithm of generalized projection failed for this setup and we successfully used the genetic algorithm (GA) instead which is less prone to get stuck to local minima. GA has several parameters that must be set up to suitable values. We describe the experimental setup and the algorithm and present our findings on what GA parameters are crucial and what are their optimal values. A single run of the algorithm takes 7 min on contemporary CPUs, making the algorithm suitable for routine laboratory work. Copyright © 2010 John Wiley & Sons, Ltd.     

SOLVENT EXTRACTION OF COBALT(II) WITH TRI-n-BUTYL PHOSPHATE FROM AQUEOUS-ORGANIC SOLUTIONS

Cobalt(II) has been extracted by 50% (v/v) TBP solution in benzene from HC1, HBr, and LiC1 solutions containing water miscible alcohols and nonbesic and basic aprotic solvents. All solvents used caused the distribution ratio of Co(II) to increase due to diminished water activity and shifts in equilibria of cobalt(II) complexes in solutions. Hexamethylphosphor-triamide (HMPTA) has been found to behave exceptionally in that it extracted Co(II) from LiC1 solutions into neat benzene and in the presence of TBP induced a weak synergism caused by extraction of at least two mixed solvates.     

Calorimetric investigation of chemical additives affecting oxidation of coal at low temperatures

Interactions in the system “coal-chemical additive-oxygen” were studied at the temperature 30 °C with the aim of recognising inhibitors of the coal oxidation process that are able to modify the coal surface in a chemical way. Three coals of different ranks were tested. As possible inhibitors, 14 aqueous solutions (10 wt.%) of both inorganic (chlorides, sulphates, nitrates, phosphates, and sulphites) and organic (formates, acetates, urea, and thiourea) substances were examined. The action of additives on coal was evaluated from the heat effect during immersion of the coal in the additive solution. It was found that most of the studied substances proved immersing heats quite comparable with that of pure water. However, rather a chemical action was ascertained for sodium sulphite, phenol, urea and/or thiourea with heat effects several times exceeding heats for pure water. To quantify oxyreactivity of original coals as well as additive-treated ones, oxidation heats were measured by the pulse flow calorimetric method. Urea was found to be the chemically acting additive with the most significant inhibiting efficiency (up to 70%) of coal oxidation at low temperatures.