After filling and closing one of the reactors, pressure and temperature on the biomass will be exerted. These constant externally managed process conditions lead to defined reaction mechanisms.
In the search for the energetically most
favorable state (principle of the smallest constraint (according to Le
Chatelier)) and the first set of thermodynamics that the energy of a closed system
is always constant, the biomass first dissolves completely and goes into a suspension
with overlapping gas phases. Up to the end of the reaction, depending on the
equilibrium reactions, temperatures, pressures, masses, pH values and
intermediates change. When the energetically most favorable state and the
optimum operating point are reached, the spherical HTC coal is formed by
polymerization from the suspension phase.
For heavy metal containing biomasses, e.g.
sewage sludge, this optimum time is chosen in a way that the heavy metal
precipitation coincides with the polymerization of the HTC coal. With this
process, 95% of the heavy metals are embedded in the coal, thus removing them
from the liquid phase with its nutrients and valuable materials. The
heavy-metal-containing HTC coal obtained by separation is activated and
recycled as adsorbent into the sewage treatment plant. Here, it replaces the
4th cleaning stage for removing microparticles from peeling and nanoproducts as
well as drug and hormone residues.