Page 189 - Materials Chemistry, Second Edition

Sustainability of (H 2 ? CH 4 ) by Anaerobic Digestion 177

installation and 2 months for the decommissioning. We adopted the GER
(Franzese et al. 2009), considering all the energy necessary to produce the
materials, including the cost for the production of energy necessary to transform
the raw material into goods (a pump for example), following the well consolidated
methodology used in LCA. The organic refuse as an energy source was considered
at its ‘‘natural state,’’ which means that it only contains the low heating value
(LHV) as the energy value, without any energy expenditure, for transport to the
plant. This means that the plant is considered to be located in proximity of the
point of generation of the refuse, as occurs in practice. As far as the direct energy
necessary to run the plant as electricity and heat were concerned as internal (to the
dashed boundaries of Fig. 4) by burning a produced quote of biogas. The indirect
energy cost to produce these quantities was computed considering two terms:
(1) the efficiency of an internal combustion engine and that of a heat exchanger,
because we considered at the end of each fermentation cycle the recovery of the
50 % of the enthalpy contained in the broth; (2) the GER of the materials to
construct the internal engine and the heat exchanger via computing their weight by
commercial catalogs. As far as the energy spent for the maintenance of the plant,
we have considered an energy cost of 15 % of the energy spent to build the plant.
This means that some of the pumps, valves, piping, sensors, etc. were substituted
during the operational time (Energy Business Report 2008). The energy amorti-
zation of the plant was evaluated as the initial GER of the materials and the energy
cost for the installation of the plant, this value was distributed over the operational
time of the facility. We have considered the consumption of sodium hydroxide and
water as chemicals. The conversion into energy unit, in this case too, was made
using GER.

2.6 Labor

The labor energy consumption deserves particular attention. It can be separated
into three components: (1) the caloric value of food for the biological support of
life; (2) both direct and indirect energy consumption necessary to produce,
transport, conserve, and prepare food; (3) all the other direct and indirect forms of
energy consumption linked to daily activities (clothing, appliances, fuel for
transportation from the house to the factory, etc.). The energy spent on labor is
intrinsically difficult to evaluate, in particular as far as the last contribution is
concerned (Brown and Herendeen 1996; Cleveland and Costanza 2010). Gener-
ally, the labor contribution is often disregarded, but it could be of utmost
importance when comparing different labor versus capital intensive technologies,
for example, gasification versus energy crop cultivation. Considering the third
term, some errors are introduced and it could be evaluated as pro-capita energy
consumption of the Nation. Using the pro-capita energy, a false energy charge is
calculated, either in the case the nation produces the plant or imports it: higher in
the first case and lower in the second one, respectively. The pro-capita energy