Lars Fridh

Abstract

An increased use of forest fuels resulted in a new Timber Measurement Act, specifying the requirements for measurements of these assortments. The law has increased the demands when measuring quality parameters, e.g. moisture and ash content. This thesis aims to a) develop a robust validation method for measurement precision and accuracy; b) validate instruments using electric capacitance (CAP), magnetic resonance (MR), near infrared spectroscopy (NIR), and X-ray technologies for moisture content determination; and c) evaluate the possibility to determine other parameters using x-ray data. The tested instruments had similar measurement precision. All except for the CAP produced 95% of their measurements within less than ± 2.5 percentage points of the mean. The accuracy of moisture content measurements varied between; instruments, moisture content classes, and forest fuel materials, as well as between frozen and unfrozen materials. MR was the only instrument that was not sensitive to fuel material. MR showed the highest measuring accuracy and CAP the lowest. The X-ray instrument could determine ash content and net calorific value, but the latter needed calibration. It was possible to estimate the proportion of fines and median particle size accurately using X-ray data. The capacitance instrument is easy to transport and use in the field, but the other instruments are intended for use at a measurement station.

A calibration of the instruments would benefit from precisely defined fuel assortments, as would the customers, who could use it to optimize combustion. Automated methods to verify the delivered fuel assortment are required, e.g. by NIR or X-ray sensors. The oven-drying method and all studied instruments determine moisture content on samples, and the sampling procedure is crucial to accurately estimate the mean and sample variance. The sampling problem could be minimised if measurements could involve most of the load otherwise a sufficient number of samples must be taken. A cost-efficient measurement procedure requires a balance of sampling intensity vs measurement costs and benefits. A fast moisture measurement procedure that enables customer to optimize combustion can be more cost-effective than the oven-drying method, especially if it provides additional data.

Read the doctoral thesis here.