METHOD AND APPARATUS FOR THE RAPID DETERMINATION OF THE MOISTURE CONTENT OF A SAMPLE

Abstract

The invention relates to an apparatus for the rapid and predictive determination of the moisture content of a material of the type covered by the main patent, as well as a method for implementing it, characterized in that the heating of the sample is interrupted several times, at least in the final phase of heating. The invention is particularly applicable to the analysis of metallurgical coke samples.

Description

METHOD AND APPARATUS FOR RAPID DETERMINATION OF THE MJMIDITE RATE OF A SAMPLE The present invention relates to the predictive determination of the moisture content in a material, in particular in a metallurgical coke. More specifically, the invention relates to a particular mode of operation of the device, which is the subject of main patent no. 84 / 18076 filed on November 21, 1984 in the name of the applicant, and the teaching of which is incorporated into the present description by reference. It is recalled that the main patent relates to an apparatus for the predictive determination of the moisture content of a material, in which the sample is placed in a rapid heating chamber (preferably microwave-heated) incorporating an automatic weighing device. At successive predetermined times, the weight of the sample is measured. A series i of weight measurements is used by a computing unit to determine the n parameters of the specific drying equation Y1 = f1(t) giving the loss of n is the weight of the sample during heating, and its analytical form Y = f(t) is predetermined. This curve presents a An asymptote of value A is determined by the calculation unit. When the difference between two values ​​A and A' of the asymptote, determined by two successive series of measurements, i and i + 1, is less than a setpoint value corresponding to the acceptable uncertainty in determining the moisture content of the sample, the experiment is automatically stopped and its result is returned to the operator. It is therefore not necessary to wait for the sample to dry completely to obtain a determination of its moisture content. With such a device, the time to obtain a value considered reliable for the moisture content of a metallurgical coke is on the order of 30 to 60% of the time required for the complete drying of the sample. In a preferred embodiment, the heating chamber is a microwave oven. This apparatus is particularly suited to measuring the moisture content of metallurgical coke samples. However, during the processing of such samples, the inventors observed that sometimes, towards the end of the EMI1.1 rode During heating, when the sample is almost dry, partial combustion of the coke pieces occurs. This combustion results in a loss of weight in the sample that is not due to water loss, and therefore distorts the moisture measurement. This combustion is due to the fact that the heating power used must be sufficient to cause a relatively rapid departure of most of the water trapped in the sample, so that the measurement is not excessively long. However, this heating power applied continuously to a sample that has reached the terminal phase of its drying can prove excessive to the point of initiating combustion of the sample. The purpose of the invention is precisely to propose a heating method that avoids this combustion of the sample. To this end, the invention relates to a method for determining the moisture content of a material, in particular a steelmaking coke, implementing the device according to the main claim of the main patent, characterized in that the heating of the sample is temporarily interrupted several times, at least in the final phase of drying. The invention also relates to an apparatus for determining the moisture content of a material, in particular of a steelmaking coke, according to the main claim of the initial patent, comprising means for heating the sample, characterized in that means are provided for controlling temporary interruptions of the operation of said heating means. As will be understood, the invention consists of heating the sample discontinuously, alternating periods of heating with periods during which heating is interrupted. The frequency and duration of the heating interruption periods are determined experimentally in relation to the nature of the sample and the presence of the heating element, so that, during the final drying phase, the energy imparted to the sample is never sufficient to initiate its combustion. The other operating characteristics of the device remain unchanged, in particular the times at which the sample weight measurements are taken and the predetermined general form of the equation Y = f(t). Indeed, experience shows n that the shape of the sample drying curve is not significantly altered by the new heating method. There is therefore no reason to interrupt or further space out the measurements of the sample weight during periods when heating is off. An example of a method for heating a coke sample might consist of - continuous heating for 25 minutes, followed by a 5-minute interruption of heating, - then 13 cycles each comprising a 5-minute heating period followed by a 5-minute interruption of heating. The heating of the sample is programmed to last 160 minutes. However, deducting the weight of the dry sample by extrapolation, based on weight measurements taken during drying, generally allows the operation to be stopped before this limit. Of 54 coke samples subjected to such heating, only 9 underwent combustion, and a water content of 2.5% could be determined to within 0.1% after 45 minutes of analysis. The duration of the experiment and the accuracy of the result obtained did not differ significantly from those obtained with continuous heating of the sample. Another example of a method for heating a coke sample is the following - 20 cycles, each comprising a 4-minute heating period followed by a 1-minute interruption of heating. - then 12 cycles each comprising a 2-minute heating period followed by a 3-minute interruption of heating. Thanks to this heating method, the risk of partial combustion of a coke sample containing 2% moisture can be completely eliminated, again without significantly increasing the duration of the operation and without affecting the accuracy of the moisture measurement. A water content of 2% can be determined to within 0.10% after 35 minutes of analysis. After 45 minutes, the accuracy of the result reaches 0.06%. Of course, this operating method can be applied to the measurement of the moisture content of samples of all materials other than coke, which may be subject to intense and uninterrupted heating and may cause combustion or decomposition.

Claims

DEMANDS 1) Method for determining the moisture content of a material, in particular of a steelmaking coke, implementing the device according to claim 1 of the main patent, characterized in that the heating of the sample is temporarily interrupted several times, at least in the final phase of drying. 2) Apparatus for determining the moisture content of a material, in particular of a steelmaking coke, according to claim 1 of the main patent, comprising means for heating the sample, characterized in that means are provided for controlling temporary interruptions of the operation of said heating means.