Explanation of the dangers of wood chips and white pellets
Why non torrefied wood chips and white pellets are not a suitable biofuel.
Having a full understanding of the chemical makeup of all types of wood is beyond all organic chemists, it is a complex substance with infinite variation.
The variation of its moisture content, energy content and ash content are major hurdles as a process heat source, requiring modification of boilers.
The issue I am focusing on here is storage. As with all living matter once dead it tends to degrade. There is an energy slope that it wants to slide down which of course is why it burns and rots.
Some of the chemical bonds in fresh wood have a half life, when they break they produce heat (and may off-gas CO, H2, CO2 etc )
The length of the half life is controlled by heat, the higher the temperature the shorter the half life.
This auto thermal activity leads to the application of the concept of critical mass with the storage of un modified wood chips or pellets, the bigger the heap the greater the likelihood of it going up in flames.
Without forced cooling and ventilation thermal run away can occur which is seen as spontaneous combustion. However because it does not need oxygen it is not combustion but the heat generated may lead to combustion.
Such fires are hard to extinguish as the heat source is not combustion, it would be more similar to a lithium battery fire where the energy released is stored energy.
So asphyxiation (foam or N2) does not stop the heat production. Adding water to large masses of hot carbon is also dangerous with the production of toxic and explosive gasses CO and H2, old style town gas.
The injection of liquid nitrogen does work as it cools and asphyxiates the mass (and surrounding people) but is a specialized and expensive activity.
Torrefied wood has been ‘pre off gassed’ and is much easier to store.
Torrefied wood is hydrophobic, can be stored outside.