Hi, I have a concept which I would like to develop into a working technology, but since I'm not an engineer, I would appreciate any views/comments/criticisms from more knowledgeable people.
-The goal is to make a concentrating solar energy (CSE) platform that succeeds in torrefying biomass, and, in a next step, couples to a gasifier which gasifies part of the torrefied biomass to power a pelletisation plant which turns the torrefied material into pellets.
-It is important to note that the CSE platform is not used for the production of electricity; its thermal energy is only used for the torrefaction process.
Torrefaction is a process of drying which goes through several stages (see diagram of the concept). You can either use a gas to dry and roast the biomass, or you can use a pipe containing a thermal fluid (oil, water).
I would be using a combination of a pipe (as in CSP plants), and recycled hot gas from the torrefaction/gasification steps (see diagram 'recycled gas'). Alternatively torrefaction gas is used in the gasifier. Or both: torrefaction gas goes both ways. Whatever is most efficient.
I would want to tweak the system in such a way that the solar heated fluid enters 'containers' of chipped biomass at each step of the torrefaction process. Temperatures and residence times for each stage differ, so that should be taken into account in designing the plant.
After the biomass has gone through all the stages, the thermal fluid circulates back to the beginning to start the process all over again for a next batch of chips.
The torrefied biomass at the end of the process is a dry, brown powder. This powder will then be pelletised. To power the pellet plant, part of the torrefaction product will be used in a gasifier.
That's it. The end product are torrefied biomass pellets.
I would want to design the plant in as small a scale as possible (so as to use it in rural settings, close to the source of the biomass).
The advantages of this concept are, I think, manifold. First, the advantages of the end product, compared with raw biomass (pellets/briquettes/chips):
-torrefied pellets can be stored for a very long time and do not degrade, because they are hydrophobic; this is very important from a logistical point of view, because it means the pellets become independent of seasonal biomass flows (this contrasts with first generation, non-torrefied pellets which suffer under seasonal flows)
-they have a far higher energy density than ordinary biomass pellets
-therefor they can be transported over much longer distances (the literature suggests the distances can be squared), which is very important from the perspective of biomass logistics and supply chains
-torrefied biomass pellets burn much cleaner than first-generation pellets
-the pellet production is easier and more efficient than starting from raw biomass, because the torrefied biomass is hot when it enters the pelletiser
-torrefied pellets can replace *all* coal in existing power plants; first gen pellets or chips can only be co-fired at rates of up to 15 percent (in IGCCs)
-torrefied biomass pellets can be pulverised in existing coal pulverisers, without modifications; this is very important since ordinary biomass needs dedicated equipment, which drives up costs.
The benefits of using solar heat is that you do not need an outside energy source and that it is highly efficient. It should be low cost too (e.g. instead of using parabolic troughs, one could use "extra flat concentrators", which are far less costly).
Comments about feasibility/efficiency/costs welcome, and all other help would be much appreciated. Please keep in mind: I'm not an engineer.
You can always contact me at solartorrefaction@yahoo.com
Thank you.
