Thursday, 17 February 2011

Pyrophoric Carbon, Oxygen depletion and other things

As if we didn't have enough to worry about already with Explosivity and dust generation hazards, a new and challenging issues has raised its ugly head.

Seems that torrefied biomass has this nasty little characteristic called Pyrophoricity. Essentially, it means that the product will smolder, and eventually self-ignite. Now, this can't be a good thing.

This nasty habit is a function and consequence of the thermal treatment process. While the mechanism is not well understood, the oxidation reactions seem to be integrally linked to the modification of the transverse permeability and disruption of the microstructure. We believe that this provides greater oxygen diffusion, and precipitates the reaction.

"Transverse permeability"? "Disruption of Microstructure"? What the heck is that? ;-)

Actually, in simple terms, it means that the opening of the cellular structure within the biomass (Which is a good thing - as this is the mechanism that provides for better grindability) also allows for increased diffusion of Oxygen.

Of course - Oxygen causes Oxidation, and the torrefied biomass contains large amounts of carbon to be oxidized.

Net result - the creation of CO and CO2. (and heat)

NOW - when it is stored in the fresh air - this is not a real problem - but - stick it into the hold of a ship - and what you have is a recipe for disaster.

Not too long ago, there was a tragic fatality in Sweden, where a dockworker walked down a stairway into the hold of a ship carrying wood pellets from Canada. The oxygen down there had been depleted, and replaced with CO2. The consequences were catastrophic.

Most biomass emits CO2 in storage. Switchgrass, for example, emitted about 1800 p.p.m. (Parts per million) in closed-container testing. Torrefied wood, on the other hand, emitted over 12,000 p.p.m. in the same tests. This is not a good thing.

At low concentrations, CO2 is categorized as a simple asphyxiant. A CO2 concentration of >15,000 p.p.m. will cause headaches, dizziness, heart rate increase, and induce coma. (And that can ruin your WHOLE day!)

CO, on the other hand, prevents the uptake of oxygen by the blood, and starves the brain and other parts of the body. The exposure limits are much lower ( 25-50 p.p.m.)

SO - it would appear that the two key characteristics that make Torrefied fuel so desirable (high Carbon content and good grindability) might also be their "Achilles Heel".

We're working on a solution . . . . and will let you know when we find one.


1 comment:

  1. can u explain more what does torrefied biomass means?