Page 62 - Biomass Gasification, Pyrolysis And Torrefaction Practical Design and Theory

Chapter | 2 Economic Issues of Biomass Energy Conversion 41

planned equipment. Furthermore, cost data from those projects may not be
relevant at the time when a new project is planned for. To get the projected
capital cost of a specific size at a specific future date, one needs two levels
of adjustment or scale-up: based on size and based on time of construction.

2.4.1.1 Scale-Up with Size
The specific capital cost is defined as the total capital cost per unit capacity of
the plant. In the present case of electricity generation, it is defined in terms of
electrical capacity of the plant, MWe. If the specific capital cost (in $/MWe) of
a new gasifier of capacity MW is K g , one may scale it up from an available
database cost that gives the capital cost, K g0 for a gasifier of capacity MW 0 .

c
MW 0
K g 5 K g0 (2.5)
MW
where c is an exponent whose value is known from different capital cost esti-
mation published (EPRI, 1991; Gerrard, 2000; Humphrey and Wellman,
1996). For example, for a coal-fired thermal power plant, c 5 0.15 for
500 1000 MWe range and c 5 0.3 for 300 500 MWe range.
The above equation for specific capital cost is based on per megawatt
installed cost, which generally decreases with capacity increase. To find the
total capital cost, the capacity of the plant is multiplied with the specific cap-
ital cost. For example, the total cost, C g for a gasifier of MW megawatt
capacity is obtained by multiplying the capacity with the specific capital
cost, K g :

C g 5 K g 3 MW (2.6)

To find the total capital cost instead of specific capital cost, a different
relationship is used.
n
MW
C g 5 C g0 (2.7)
MW 0
where n is the capacity index and MW is the capacity in appropriate units.
Some representative values of the index are given in Table 2.5.

2.4.1.2 Scale-Up with Time
To compute the capital cost in a certain year C gA based on a past cost data,
C gB , one can use the following linear relationship based on the cost index I.

I A
C gA 5 C gB (2.8)
I B
where I A and I B are the cost indices in year A and year B, respectively. Such
cost indices for plant and equipment are published by various organizations.