(145e) Method of Measurement of Carbon Permittivity
AIChE Spring Meeting and Global Congress on Process Safety
2012 Spring Meeting & 8th Global Congress on Process Safety
Process Development Division
Modeling, Measurement, and Optimization
Wednesday, April 4, 2012 - 3:30pm to 4:00pm
Coal is the most abundant fuel, versatile and available in the earth, global stocks are expected to continue until 250 years, so it becomes the most important energy source as it has been throughout its since history began to be implemented on locomotives and other transportation that worked with coal, promoted for the industrial revolution.
The use of coal as raw material requires a prior analysis of their composition that allows knowing the best process that should be used. Moreover, the complexity of coal in general, is such that there may be a wide variation of certain properties, even in coals that have the same origin or treatment, so it is essential to keep a detailed analysis of their composition and properties. Between these analysis are the dielectric properties, as is the permittivity, which is a physical constant that describes how an electric field affects and is affected by a medium, the permittivity is determined by the capacity of a material to polarize to the application of an electric field and thus partially cancel the internal field of the material, this property set to the behavior that will have the coals when exposed to an electromagnetic signal, marked as it spreads the energy in the material, as transforms the energy supplied by the microwave to heat the inside of it and, finally, indicates whether a material can be treated by means of microwave, providing valuable information for process heating and drying by microwave, which is the most viable way of warming and greater projection into the future because it provides even heating and fast, as it interacts with the material directly heats from the inside causing an agitation of the molecules which facilitates and speeds up the warming process.
Previous studies have identified several methods for the characterization of dielectric properties among which are the techniques of time domain reflectometry (TDR), the method of the guide shorted, perturbation method and some as the resonant cavity, S parameter method or the reflected wave method. These measurement methods have yielded data, processes and information that form the basis for further studies and designs, although still not enough for having performed for a frequency range or a specific frequency but difficult to achieve or is not handled.
The method of measuring the absorbed power, is proposed in this study, which is to apply to the test material a power known as a power which is provided to measure the amount of power absorbed by the material and then through a mathematical model to calculate the value of the permittivity.
In a first step to achieve this, it is necessary to use a device of waveguide tube has a rectangular cross section that is responsible for directing the microwaves from the generator to the sample. The device has the necessary instruments for measuring temperature and power consumption as well as a regulator of these two properties. This equipment is calibrated to identify what should be the power and heating time of the operation. This calibration is performed with distilled water and varying the power supplied to develop calibration curves to determine the most suitable operating power for the measurement of coal samples. These curves show the profile of heating and cooling. After an analysis of these is determined, in addition, the heating time, which is the time during which the coal samples are exposed to the action of microwaves.
It implements also an antenna inside the waveguide for measuring the intensity of the magnetic field generated by the device, because this value is of vital importance for the calculation of the permittivity.
With all this, the equipment can be standardized, which works with microwaves at a fixed frequency of 2.45 GHz.
The samples characterized in this study are of different types of coals are subjected to a pretreatment of grinding and sieving to obtain a homogeneous sample and is handled the same particle size for all types of coals analyzed. Also, for the analysis to be as accurate as possible all samples have the same mass and to the extent possible the same initial temperature.
The sample is introduced into an assay tube at the same time is introduced into the device and is subjected to a heating power and time. Parallel to the main sample is being heated by microwaves, another sample of equal mass and size of particle is heated by a resistance system that is placed within the respective assay tube and connected to a source of energy electrical and within this circuit are connected to each amperage and voltage meters and heated in the same proportion of the sample temperature main analysis, so we can determine the amount of power absorbed by the sample parallel would equal the main sample.
The temperature of both samples is measured by an infrared thermometer strategically located to capture directly the heat of the respective sample.
After obtaining the data of power consumption, temperature, power supplied, magnetic field strength and some physical properties of the material under study, can proceed to calculate the permittivity through a mathematical model to relate these data and properties. This procedure is repeated several times to compare with each other so that they can be correlated and get a more accurate value of permittivity.
Keep in mind that these values of the permittivity have a frequency of 2.45 GHz for very few substances. The scope of this paper is precisely that, to be able to provide data that are not known and knowing that at that frequency is working commercial microwave generators and this is the best way of warming, these data become a even greater importance and can help large industries to reduce costs, reduce processing times, have a more controlled process or implement new technologies in them.
Another advantage of this method of measuring the permittivity is that it is carried out at low cost, while the existing and currently being used have a very high cost of operation or equipment used in these processes are very expensive.
In this paper we also hope that later you can implement this process for calculating the permittivity of solid substances, and why not? Adjust the equipment to find the property to liquid substances, data are not yet known.