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The use of biomass pellets is increasing. As a consequence, large indoor storage facilities are needed along the transportation chain. A number of fire incidents due to spontaneous ignition in wood pellets have been reported. The aim of the present work is to provide methods for estimating risks for self-heating from pellets stored in bulk quantities. The experimental work ranges from small-scale characterizations to medium-scale storage tests and includes different types of pellets. One aim has been to develop small scale screening methods to assess the propensity for self-heating, thereby trying to define the specific type of “activity” occurring in the pellets as well as characterising it. Isothermal calorimetry (micro calorimeter) has been used as small scale screening test method and the results has then been validated with crossing point tests and in medium scale tests (1 m3). Thirteen samples from different types of pellets have been ranked relative to each other in micro calorimeter tests and two pellet types; one “reactive” and one “less reactive” were also tested for validation in crossing point and medium scale. The results clearly reveal that different activity levels of the pellets can be measured using small scale screening methods.

The use of biomass pellets is increasing. As a consequence, large indoor storage facilities are needed along the transportation chain. The increased production volumes, transportation, handling and storage of pellets result in increased risks. A number of fire incidents due to spontaneous ignition in wood pellets have been reported. Increased efforts concerning safety and quality assurance are, therefore, important. The aim of the present work is to provide methods for estimating risks for self-heating from pellets stored in bulk quantities. The experimental work ranges from small-scale characterizations to medium-scale storage tests and includes several different types of pellets. One aim has been to develop small scale screening methods to assess the propensity for self-heating, thereby trying to define the specific type of “activity” occurring in the pellets as well as characterising it. Isothermal calorimetry (micro calorimeter) has been used as small scale screening test method and the results has then been validated with crossing point tests and in medium scale tests (1 m3). Thirteen samples from different types of pellets have been ranked relative to each other in micro calorimeter tests and two pellet types; one “reactive” and one “less reactive” were also tested for validation in crossing point and medium scale. The results clearly reveal that different activity levels of the pellets can be measured using small scale screening methods.

The use of biomass pellets is increasing. As a consequence,large indoor storage facilities are needed along the transportation line. Theincreased production volumes, transportation, handling and storage of pellets resultin increased risks. A number of fire incidents due to spontaneous ignition inwood pellets storages and accidents due to CO intoxication have been reported.Increased efforts concerning safety and quality assurance are, therefore,important. The aim of the present work is to provide methods for estimatingrisks for self-heating of and off-gassing from pellets stored in bulk. Theexperimental work ranges from small-scale characterizations to large-scalestorage tests and includes several different types of pellets. One aim has been to develop smallscale screening methods to assess the propensity for self-heating andoff-gassing, thereby trying to define the specific type of “activity” occurringin the pellets as well as characterising it. In addition to using said methods,isothermal calorimetry (micro calorimeter) and Oxipres (oxygen depletion), theformation of different gases (e.g. aldehydes) was analyzed. Thirteen samples from different types of pellets havebeen ranked relative to each other. Effects of processes like aging can also beseen in the results. The results clearly reveal that different activity levelsof the pellets can be measured using small scale screening methods and thatthere are certain correlations between off-gassing and heat development, althoughthese are not yet fully understood.

One major concern when it comes to storage of wood pellets is the risk for self-heating. The propensity for self-heating varies between different types of pellets. It also depends on how the pellets have been handled and on the storage conditions, e.g. the temperature and humidity. Within the framework of the research project “Large scale Utilization of Biopellets for Energy Applications –LUBA” different laboratory-scale methods have been used to study different thermal properties and the propensity for self-heating for different types of pellets. The different methods used include micro calorimetry also called isothermal calorimetry, basket-heating tests and transient plane source (TPS). In total 21 different pellets samples were tested in the micro calorimeter, three in the basket-heating test and three in the TPS. The samples showed significant differences in propensity for self-heating. Differences could be seen both between different types of pellets and depending on the age of the pellets. Comparing the reactivity rates from the basket-heating tests and those from the isothermal calorimetry tests with the same type of pellets, both methods gave the same ranking of reactivity. It was shown that the TPS-method is applicable for the determination of thermal properties both for measurements on single pellets and for measurement on bulk pellet material.

The probable magnitude of a shortfall of Navy physicians below programmed strength is analyzed. Alternative methods of providing medical care under shortfall conditions are examined for feasibility. Cost analysis is performed on feasible alternatives. (Author)