A. Site Selection
The site location of a biomass CHP plant is critical
since the cost of transportation of the biomass increases
as the distance from the harvest site to the CHP plant
increases. To this end, many studies have tried to
optimize the location of biomass plants [12-13].
Furthermore, the CHP plant must be located such that its
residual heat be utilized efficiently, normally in the
vicinity of the CHP plant. It was shown in a similar
study [14], that the spatial distribution of heat demands
has a significant impact on CHP production and costs.
The study concluded that the heat demand is more
important than the distance to biomass supply and
resulting biomass transportation costs, such that the heat
demand makes the CHP plant more efficient and more
economical, rather than the cost of transportation of the
biomass.
In such, the selection of potential CHP sites should
take into account the location of cities, towns and
villages, along with industries with important heat loads,
in the study area because of their potential heat demands.
For its part, the heat demand can be in the form of
residential, commercial, or institutional space heating, or
in the form of industrial process heating, etc.
Another specific criteria useful for the site selection of
potential CHP sites is the connection to the electricity
grid. Sites closest to high voltage electrical transmission
lines have lower plant integration and connection costs,
which ultimately improve the project’s economics and
viability.
B. Procurement Areas
The next step in the methodology is to establish the
procurement areas for each potential CHP site identified
in the study area. Since biomass is assumed to be
transported by trucks from its point of loading to the CHP
sites, Geographical Information System (GIS)-based tools
are used along with the road network of the study area to
delimit the procurement areas around each CHP site
location. Since the transportation costs increase as the
distance from the biomass point of loading to the CHP
plants, other studies have showed that CHP plants can be
economical when their biomass supplies originate from
procurement areas of approximately 4,000 to 5,000 km
2
[15-16].
C. Biomass Assessment
Before evaluating the power potential of forest
biomass in a study area for the cogeneration of heat and
power, a biomass procurement assessment must first be
performed. Depending on the biomass data available,
several methods can be used to achieve the biomass
assessment.
Biomass inventory data, if available, is generally used
because of its level of details and accuracy [15, 17]. For
example, in the case of forest biomass, Annual Allowable
Cut (AAC) data derived from management plans can be
used to undertake a biomass assessment [18]. In
traditional forest management practices, the AAC
represents the amount of wood that can be harvested
within a one year period and is used as the basis for
regulating harvest levels in order to ensure a sustainable
supply of timber, without compromising the ability of the
biomass to regenerate itself.
Other methods that can be used to estimate the
amount of biomass in a study area include the use of
remote sensing data [12, 16] and analytical models such
as biomass expansion factors (BEF) [19] and biomass
allometric equations [15].
Once the amount of biomass has been determined over
the study area, the next step, if needed, is to allocate an
amount of available biomass to each procurement area.
In order to achieve this, GIS-based tools can be used if
the biomass data is available in a GIS-based format,
while simpler methods, such as rules of three can be used
[18].
D. Conversion of Biomass to Energy (CHP)
Once the quantities of biomass have been determined
and allocated to the corresponding procurement areas, the
next step in the large scale biomass assessment consists
in finding the amount of energy that this biomass could
produce in the form of heat and power if used as input
fuel in a dedicated biomass combined heat and power
plant.
To this end, several steps are performed. In the first
instance, effective heating values are determined for all
corresponding biomass components considered [20].
Secondly, the total energy content of each biomass
component for all procurement areas is estimated from:
E = m ( EHV
)
(1)
where
E
is the energy content of the biomass (MJ),
m
is
the quantity of biomass (kg) and
EHV
is the effective
heating value of biomass (MJ/kg).
From the energy content of the biomass, the electrical
power output of a biomass-fired CHP plant can be
determined:
P
e
= ( E / t ) η
e
(2)
where
P
e
is the electrical power (MW),
E
is the energy
content of the biomass (MJ) as per Eq.(1),
t
is the time
period (seconds) and
η
e
is the electrical efficiency of the
CHP plant.
For its part, the thermal power output of the same CHP
plant is given by:
P
th
= ( E / t ) η
th
(3)
where
P
th
is the thermal power (MW),
E
is the energy
content of the biomass (MJ) as per Eq.(1),
t
is the time
period (seconds) and
η
th
is the thermal efficiency of the
CHP plant.
The CHP plant electrical and thermal efficiencies refer
to the proportion of energy contained in the fuel that is
converted to electricity and heat, respectively [20].
Ultimately, the efficiency of a given CHP plant is a
function of the fuel properties, the type of boiler and the
plant’s load factor.
2013 International Conference on Alternative Energy in Developing Countries and Emerging Economies
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