Page 142 - Advances in bioenergy (2016)

the laboratory into scaled-up process demonstration systems.

BIOMASS FAST PYROLYSIS

Pyrolysis is the thermal decomposition and devolatilization by heating in the absence of
oxygen. Biomass pyrolysis is an ancient technology, as old as fire itself. The terra preta soils
of the Amazon basin have been attributed to charcoal production by pyrolysis and burial of the
3
charcoal by prehistoric inhabitants. Wood tar was produced from pyrolysis by the ancient
4
Egyptians. The biostructures in biomass begin to thermally decompose at temperatures as low
as 200°C. By processing biomass in an oxygen-deficient atmosphere, a range of products is
derived as a function of temperature and amount of oxygen. A second operating axis to
consider is the time at temperature, which at extended times leads to the formation of
secondary products from the primary pyrolysis products. In the case of biomass pyrolysis,

low-temperature processing releases primary decomposition products mostly water vapor and
carbon dioxide with a residual solid condensation product. With increasing temperature, the
decomposition of the biopolymers increases and volatile products tend toward a higher
molecular weight, which, if cooled and condensed quickly, can be recovered as liquid with
minimal amounts of gas or solid products. At higher temperature, the decomposition products
continue to be broken down to lower molecular weight gaseous products. The old, simple
technology of pyrolysis as practiced at relatively lower temperatures and long heating and
cooling times, maximizes the solid product yield. More recent interest has moved the process
research to focus on liquid organic products, and, as a result, fast pyrolysis has been
developed with moderately higher temperatures but very short residence times.

Table 6.1 Composition of Oil Products

Characteristic Fast Pyrolysis Bio-oil Hydroprocessed Bio-oil Heavy Petroleum Fuel

Water content, wt% 25 0.1 0.1
Insoluble solids, wt% 0.5 0.00 0.01

Carbon, wt% 45 87.5 85.2

Hydrogen, wt% 7.5 12 11.1
Oxygen, wt% 47 0.5 1.0

Nitrogen, wt% 0.15 <0.05 0.3

Sulfur, wt% 0.02 <0.005 2.3

Ash, wt% 0.3 0.00 <0.1
HHV, MJ/kg 17 45 43

Density, g/ml 1.2 0.84 0.94

Viscosity, cp 50 at 40°C 1 at 40°C 180 at 50°C

Biomass resources are broadly distributed and their solid nature makes their collection and