Jenny Nyström

Influence of Temperature in Radio Frequency Measurements of Moisture Content in Biofuel

A method that permits the determination of moisture content in biofuel in a fast and representative way is under development. The method uses radio frequency waves within the range of 310 MHz to 800 MHz and measures the reflection coefficient in samples with volume of about 0.1 m3. The influence of sample temperature in the measurements is shown in this study. Two biofuel types were used, with moisture content varying between 31% and 63% and temperature varying between 1degC and 63degC. The data was evaluated with multivariate data analysis. Results show that it is not possible to identify the sample temperature as a principal component in a principal component analysis and partial least squares regression shows no correlation between temperature and the radio frequency data. For the frequency interval and the temperature range studied, it was not possible to detect any influence of sample temperature on moisture content prediction with the radio frequency method

Moisture Content Measurements on Sawdust With Radio Frequency Spectroscopy

An increasing number of power plants in Scandinavia are beginning to use biofuel instead of coal or oil. The material in the new fuel is a mixture of woodchips, mostly Pine, Spruce and Salix, bark, GROT (tops and branches from felling waste) and sawdust from sawmills. It is heterogeneous, having a moisture content varying from 15% up to 65%. The moisture content affects the combustion of the fuel and therefore its commercial value. The industry is now interested in obtaining a method for measuring the moisture content of biofuel, quickly and reliably; preferably on delivery at the power plant. The measuring technique presented in this thesis is the first reported in the literature capable of measuring the moisture content of a large sample of such an heterogeneous material as biofuel. The equipment is today calibrated for a sample volume of 0.1 m3. A radio frequent signal is supplied from an antenna and penetrates the biofuel. Its reflection is modeled using partial least squares. As part of the work presented in this thesis, a new type of measuring rig and an analysis method for measurement of the moisture content of large samples of heterogeneous material have been developed. A statistical model for moisture content measurements of five different biofuel materials using radio waves has been built, having a root mean square error of prediction of 2.7. The interactions between biofuels and radio frequent signals have been demonstrated, indicating a variation of the reflection with varying types of biofuel material and variation in the reflection and delay of the signal with varying moisture content.

Radio Frequency System for Measuring Characteristics of Biofuels

In this paper, a measurement system for making rapid measurements of moisture content, fuel mixture, volume and the bulk density of bio fuels is presented. The method uses radio frequency spectroscopy, and is a small scale version of what is intended to be used directly in the fuel containers arriving to the power plants. The advantages with the method are that it is fast and reliable, and it can be used for measuring mean value characteristics of large amounts of biofuel. Reflection characteristics for frequencies from 310 to 1300 MHz are simulated and measured for sawdust. The attenuation is evaluated in frequency and time domain. It is concluded that a calibration of the whole system is needed to compensate for disturbances in the test system. Both the surface and the bottom reflection are possible to detect in time domain. The simulated and measured attenuation in frequency domain have a similar periodic behavior up to around 800 MHz. Above 800 MHz the system is disturbed by the higher order modes