The debate gets hot and heavy at times, and veers into biochemical debates difficult for a layperson to follow. Yet, the evidence in support of thermal depolymerization seems to be encouraging. It's not a new technology, just one that was not efficient enough to be practical before. In fact, to this layperson, it seems that thermal depolymerization, or "thermochemical conversion of biomass", is essentially the same geological process used by the earth for millions of years to do exactly the same thing, except with TDP it is run by humans at a much faster rate of conversion.
Up until recently, TDP was impractical because of high processing costs, low yield, impurity of yield, high energy input requirements or other problems, depending on the particular methods and equipment used. The excitement now is because Appel claims to have developed an efficient TDP process that is self-fueling and has a high-quality, high-volume yield, according to feedstock.
This report (Thermochemical Conversion Of Swine Manure To Produce Fuel And Reduce Waste by Zhang, Riskowski, and Funk), while lacking in grace and in want of an editor, has a fairly lay-accessible description of the process as undertaken by the authors as well as information regarding the need for such a process and the results of other experiments.
Appell and colleagues (1980) focused on converting organic wastes to oil in batch and continuous mode. The results show that bovine (dairy) manure was not readily to be converted to oil at 250°C or lower, but with the treatment of CO and steam at 380°C and 40 MPa (6,000 psi) resulted in high conversions of dairy manure to oil. The conversion rate was 99% and the oil yield was 47%…
Another important finding in Appell's research is the function of water in the thermal conversion process as a solvent and a reactant. This is even more important in the conversion of livestock manure slurry where a large quantity of water exists and dewatering is infeasible costly. Taking advantage of water content in raw manure will greatly value the conversion process, not only producing energy but also lightening the wastewater intense from livestock farm…
Through thermochemical conversion technology, the conversion rate of organic matter in the raw manure can be as high as 90% or more (Appell et al., 1980; White and Taiganides, 1971). The solids and the wastewater are separated and COD in the wastewater is greatly reduced. The successful TCC processor shall be an on-site unit that directly processes fresh manure from the barn. Thus, much less storage is required. TCC processor will be compact and much less space occupying than those of biological treatment processes such as lagoons and digesters do. Another benefit of such a short period of manure storage time is the odor reduction – less storage time means less odor emission.
As a successful TCC unit for a large confinement hog farm, the energy needed for running the processor is most likely self-sustainable, i.e., the liquid fuel produced from the TCC processor could be used as the energy input for the processor needs. With the major portion of the organic solids removed from the swine manure, the post-processes waste is most possibly suitable for municipal treatment with a simple pre-treatment. The solid residues are greatly minimized and convenient for disposal.
[Lots of useful info for clarification on this issue presented through embedded links.]