THERMOCHEMICAL CONVERSION: AN INTRODUCTION TO FAST PYROLYSIS - Biomass as a Sustainable Energy Source for the Future - page 376

TABLE 11.5 Mass and energy balance of pyrolysis at
530 C. Input wood with 10 wt% moisture
Yield [kgkg -1 ] LHV [MJkg -1 ]

Wood — 16.5

Char 0.16 30

Oil 0.65 16.5

Gas 0.19 5

Data adapted from Westerhof et al. (2010).

char contact time should be minimized to
limit cracking and polymerization reactions. The holdup of biomass/char in
the reactor can be estimated by coupling a single-particle model with a bio-
mass/char population balance.
Heat transport to the reactor : Can be done directly via a heat transport medium
(e.g., sand, gas) that is cycled between the reactor and a hot utility (e.g., com-
bustor) or indirectly via the reactor wall or heating pipes. Ensyn, BTG, and
Metso circulate hot sand from a combustor (boiler) to the reactor, while
Dynamotive circulates hot gas.
Energy (heat) generation : Is generally done by combustion of the produced
char, gases, and/or light vapors. For detailed information about combustors,
see Chapter 9.
Solid (char) removal : Is usually accomplished by cyclone systems. Deep removal
of solids from the oil has to be done in the liquid phase by filtration.
Liquid recovery/collection : Typical systems used are electrostatic precipitators
(ESPs) and (countercurrent) spray columns. The recovery of the liquid does
not only involve condensation but also capturing of the aerosols. ESPs collect
the aerosols by charging them utilizing an electric field, while in spray columns
the aerosols are captured by contacting them with the spray. In spray columns,
the oil produced can be used as spraying liquid. A first separation can be
achieved by applying a series of condensers at decreasing temperature. In
Figure 11.11, it can be seen that by operating the first condenser at 80 C, an
oil can be obtained that contains only 1% of acetic acid (HAc), while the aqueous
phase recovered in the second condenser contains 8

￿ Biomass/char holdup: The vapor -

- 10 wt% HAc.

The websites of some companies give further information on pyrolysis processes
(see Internet References). Recent scientific articles dealing with fast pyrolysis processes
for further reading are Garcia-Perez and Kruger (2011), Hoekstra et al. (2012), Ouden-
hoven et al. (2013), Venderbosch and Prins (2010), and Westerhof et al. (2011).
Wet liquefaction is the pyrolysis process performed under aqueous hot, pressurized
conditions. Here, only a brief reference is made to different research works in this
specific domain; more can be read in Davis (1983), Goudriaan and Peferoen
(1990), Knezevic (2009), Naber et al. (2005), and Venderbosch (2000).