Sometimes, people just need to make the best with what they have got to work with. This is what paper mills are trying to do by burning the "black liquor" waste which is a leftover remnant of chemicals and the lignin. As part of the Kraft process (.pdf link), the leftovers are burned to create steam which turns large generators, which in turn provide electricity for the plant. In fact, enough electricity is generated that they can feed some back into the grid. This Kraft process is used for about 80% of all paper made. But what if there was a better way to generate power than by burning the black liquor for steam generators?
According to Andre Boehman, professor of fuel science at Penn State, "Black liquor is routinely burned in a recovery boiler, but it has more energy value as a synthesis gas which is then used to create other fuels." The researchers are suggesting that the black liquor instead be turned into a syngas and then into DME or dimethyl ether.
Diesel engines can be configured to run on DME, and Penn State actually has a staff shuttle which runs on the fuel. The researchers found that by adding a coal slurry to the black liquor and processing it into the DME, as opposed to using the Fischer Tropsch method, is the right way to use the waste. The researchers further say that DME is close to gasoline in efficiency, but not quite there. But, the black liquor/coal slurry process that they are suggesting would reduce greenhouse gas emissions much more than if only coal were used to make DME. Since the U.S. has so much coal available, until the country is truly weaned off our current power sources, we should clean them up as much as possible. As much as we would all love to see that coal stay in the ground, realistically we know how unlikely that is to happen. For now, let's use it as cleanly as possible.
[Source: Penn State]