Performance and Cost Discussion

The base case capital and operating costs [1] were updated to 1996 dollars using the Marshall and Swift Index [15]. In the year 2000, plant costs were adjusted by adding a dryer [16]. Capital and operating costs in later years were scaled from the 2000 values using a 0.7 scaling factor. Peters and Timmerhaus [17] state "It is often necessary to estimate the cost of a piece of equipment when no cost data are available for the particular size of operational capacity involved. Good results can be obtained by using the logarithmic relationship known as the 'six-tenths-factor rule,' if the new piece of equipment is similar to one of another capacity for which cost data are available. According to thi s rule, if the cost of a given unit at one capacity is known, the cost of a similar unit with X times the capacity of the first is approximately (X)06 times the cost of the initial unit." Valle-Riesta [18] states "A logical consequence of the 'sixth-tenths-factor' rule for characterizing the relationship between equipment capacity and cost is that a similar relationship should hold for the direct fixed capital of specific plants In point of fact, the capacity exponent for plants, on th e average, turns out to be closer to 0.7." The exception to this rule happens when plant capacity is increased by change in efficiency, no t change in equipment size. In this case, capital cost in dollars remains constant, and capital cost i n $/kW decreases in proportion to efficiency increase. For example, the change in capital costs between 1996 and 2000 reflects an efficiency increase, while the change between 2000 and 2005 reflects equipment scale change.

The electrical substation is part of the general plant facilities, and is not separated out in the factor analysis. Th e convention follows that used in the EPRI Technical Assessment Guide [12], as follows "It also includes the high -voltage bushing of the generation step-up transformer but not the switchyard and associated transmission lines. Th e transmission lines are generally influenced by transmission system-specific conditions and hence are not included i n the cost estimate."

Feedstock for biomass plants can be residues or dedicated crops or a mixture of the two. For purposes of this analysis, dedicated feedstock is assumed. The Overview of Biomass Technologies provides a discussion of the sustainabilit y of dedicated feedstock supplies which are assumed to be used in the systems characterized here. Fuel from dedicate d feedstock supply systems is projected to cost as little as $1/GJ and as much as $4/GJ, depending on species an d conditions [1]. For this analysis, an average cost of $2.50/GJ is used, which represents an update of the DOE goal for dedicated feedstocks.

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