One of the problems facing the utilization of biomass as a power source is the waste associated with moving it around. Fossil fuels are really convenient in this respect because tons of the stuff come out of a single hole in the ground. It’s already in one, high energy density package just waiting to be refined and distributed. Half a million tons of oil, crude or refined, can be put on a tanker and shipped anywhere in the world. There is no equivalent source of renewable biomass that can be produced in such high quantities at one location or with such high energy content.
The problem is one of densities. Crude oil has an energy density of about 45 GJ/tonne, black coal has between 23 and 29 GJ/tonne, and ethanol has about 30 GJ/tonne; where as your average plant mass has only 18 GJ/tonne. On top of that, oil and coal are pumped or mined at individual locations, while plants must be grown over a very large area. With all the raw materials for energy from plant mass spread out over such an expansive area, how best can the available energy be utilized without losing most of it in transportation to a refining center?
To deal with the transportation issue, I think the best solution would be focusing on the development of compact refining technologies. So, instead of collecting and transporting plant material from every farm, the refineries could be distributed once or driven from farm to farm during harvest time. I imagine a tractor trailer sized box that could be dropped off at a farm and all of the corn husks, wheat chafing, and cotton leftovers could be dropped into one side of the machine. Fuel would come out of the other side. The important part is that the low energy density plants would be turned into something with much higher energy density that could then be trucked or piped away more efficiently than raw biomass.
Some may question whether this technology is feasible. I think it is. As a graduate student in chemical engineering, I am currently working on some of the technology that could be applied to this. By using a substance called an ionic liquid, it is possible to dissolve plant material and break down the cellulose and sugars into usable hydrocarbons. My research focuses on the processing of the lignin (lignin is the glue that holds together the cellulose and comprises about a third of the dry weight of a plant). There are many other promising technologies in this field as well (microbial breakdown or gasification come to mind).
If biofuels are to become a major source of energy in this country, I think that we will soon see this kind of distribution in the near future. This is not a novel idea and I’m sure an entrepreneur will capitalize on it when the time and technology is right.
Angew.Chem.Int.Ed. 2008, 47,8047–8050
Science. 2007, vol. 316, 1597-1600