Page 51 - Biomass Gasification, Pyrolysis And Torrefaction Practical Design and Theory

30 Biomass Gasification, Pyrolysis and Torrefaction

examines if a project is sustainable or unsustainable in the long run and in
the broader context, and if it would make a net positive contribution to the
health of the society. For example, ethanol production from corn is a com-
mercially viable process under the current tax and subsidy structure in some
countries like the United States. So, it would easily pass the benchmark for
conventional financial analysis, but, given the life-cycle analysis of all
energy input into the system and the associated greenhouse gas emissions,
the sustainability of this option may be questioned especially in absence of a
direct or indirect subsidy.
LCA analyzes the full range of environmental and social impact assign-
able to a specific biomass conversion project. It also examines the overall
energy impact. A broad view of all direct and indirect inputs and the outputs
of the project are taken into consideration, to help choose the least burden-
some of available technological options for an energy conversion project.
More details are available from other references like Jensen et al. (1997).

2.2 BIOMASS AVAILABILITY AND PRODUCTS

For a proper economic analysis, the input and the desired output of the bio-
mass plant have to be known. For a biomass conversion project, the input is
biomass and the output is energy, fuels, or chemicals. Unlike fossil fuel, bio-
mass is not available in one place in a concentrated form, such that it could
be collected and transported anywhere in the world where it is required.
Biomass is a considerably dispersed and low-energy density fuel. Energy
transportation through biomass is much more expensive than that through
oil, gas, or coal. As such, biomass must be collected regionally. Thus, its
local availability is critical for a biomass conversion plant.

2.2.1 Availability Assessment

Availability of biomass at acceptable prices over the lifespan of a plant is
the very foundation of a biomass project. Being a local resource, biomass
assessment and examination of availability are conducted at an early phase
of a project.
It is difficult to assess the availability of biomass from an estimate of
what is harvested or what is available in the forest. The entire body of bio-
mass produced in the forest or fields is not necessarily available for energy
production. Biomass can be collected from various steps of a biomass-based
nonenergy process flow. For example, when wood is collected from the for-
est for pulp and lumber production, much residue including the tree roots are
left on the forest floor. Further down the production stream, sawdust, barks,
and others are also available as biomass waste. It is seen that available bio-
mass for particular conversion option is only a fraction of what originally
grew in the forest.