2006). About 103.6 kg of sugar and 45.2 kg of molasses are
extracted from 1 tonne of sugar cane (Prasertsri 2006).
Thus, the relative contribution of sugar and molasses to the
economy has the ratio of 8.6:1. Based on this ratio, energy
use and emissions from sugar cane and sugar/molasses
production (including transportation) are allocated between
sugar and molasses at 89.6% and 10.4%, respectively. The
ratio is substantially lower than the 15.0:1 for 2005 derived
by the same allocation method. Escalating molasses price is
the main reason for the large variation in allocation ratio. A
sensitivity analysis has been conducted to see how the results
of the study are affected by changing the allocation ratio.
To enhance crop-based ethanol performance, it is
important to consider opportunities to utilize system coproducts.
With the molasses ethanol system, the three types
of utilizable residues are cane trash in sugar cane
production, bagasse in sugar production and stillage in
ethanol conversion.
In sugar cane production, burning cane trash prior to or
after harvesting is commonly practiced to favour manual
harvesting and land preparation for new growth. Worldwide,
there is increased interest in utilizing cane trash as a
fuel instead of open burning in fields. Research has shown
that up to 50% trash can be removed without leaving
behind any negative effect on soil quality (Gabra 1995).
However, such a utilization scheme needs to take into
account energy and environmental costs associated with
collecting, hauling and preparing trash for off-season use.
In sugar production, bagasse is being utilized as the
major fuel to generate both process steam and electricity.
The surplus electricity sold to the grid is counted for both
energy and environmental credits.
The distillation residue from the production of ethanol,
called stillage or spent wash, can be refined into biogas via
advanced anaerobic digestion systems, e.g. UASB reactors
(Fig. 1). This has been considered a good measure to secure