In a very good summary of the research in UK they discuss the issues surrounding torrefaction. To summarize here are some key questions:
1) which crops/trees are best for torrefaction. Grasses vs wood (softwood or hardwood?
2) whether torrefied biomass causes spontaneous combustion and potential explosiveness?
3) what are the environmental impacts - for example how much energy is used in making torrefied biomass?
All these lead to the big question. Is torrefaction economical? According the article and the researchers interviewed : we still a number of years off from answering this question.
In our region Terra Green Energy is a leader of torrefaction technology. Check them out.