Truck delivery of material has a fixed cost associated with the time required to load and unload the truck, and a variable cost that is related to the time the truck is being driven and/or the distance driven. For most biomass delivery applications, truck speed is relatively constant over the route; thus, e. g., a truck picking up straw would average about 80 km/hr on rural and district roads, and a truck picking up wood chips in a forest would average about 50 km/h on logging roads. Only if the wood chips required a significant drive over highways would there be a second higher speed portion of the trip; this effect is ignored here. Figure 1 shows cost data per kilometer for truck transport of wood chips in a typical western Cana­dian setting ([3]; D. Evashiak, personal communication, 3/03); the intercept of the lines is the fixed cost of loading and unloading, and the slope is the incremental variable cost per kilometer. Table 1 provides the equations for transport costs, including straw (1). Figure 1 is adjusted to dry tonnes of biomass to make a comparison of pipeline costs easier; pipeline costs are discussed later. Typical field moisture levels for straw and wood in western Canada are 16 and 50%, respectively. The range of costs for truck transport of wood chips comes from two different types of estimate: the lower bound is from a Forest Engineering Research Institute of Canada (FERIC) study of chip transport costs from a long-term dedicated fleet, and the upper bound is based on current short-term contract hauling rates. The FERIC data are more representative of steady biomass supply to a long-term end use such as a power plant. Note that there is no change in cost with scale for any

biomass application of interest; that is, the amount of biomass moved fully utilizes multiple trucks and no savings occur with larger throughput.

Pipeline transport of wood chips was studied in the 1960. Brebner (4), Elliott (5), and Wasp et al. (6) examined solids carrying capacity and pres­sure losses, and Wasp et al. (6) did a cost analysis for a 160-km pipeline with one-way transport, i. e., no water return. These studies were focused on the supply of wood chips to pulp mills, and hence water uptake by chips did not have a downstream processing impact. More recently Hunt (7) did an extensive analysis of friction factors in wood chip slurries in water; in the present work, we utilize his formula for the friction factor.

More recently, Liu et al. (8) completed an analysis of two-phase pipelining of coal logs (compressed coal cylinders) by pipeline. In the present article, we draw on the work of Wasp et al. (6), Liu et al. (8), and discussions with a Canadian engineering contractor (D. Williams, personal communica­tion, 3/03) to develop pipeline cost estimates for transporting water slur­ries of wood chips; these costs are also shown in Fig. 1 and Table 1.

Delivery of material by slurry pipeline has a cost structure similar to that for truck transport. The fixed cost is associated with the investment in the material receiving and slurrying equipment at the pipeline inlet, and the separation and material transport equipment at the terminus. The slope of the curve comes from the operating cost of pumping, and the recovery of the incremental capital investment in the pipeline and booster pumping stations plus associated infrastructure such as power and road access, all of which increase linearly with distance. Technically, pipeline costs would have a slight "sawtooth" shape, with a slight, discrete increase in overall cost occurring when an additional pumping station is required. Practically, most of the incremental capital cost is in the pipeline rather than pumping stations, and the sawtooth effect can be ignored. (In our analysis, the pipe­line component of the total capital cost is 85% at 50 km, and 94% at 500 km.)

One key element in the pipeline scope and estimate is whether a return line for the carrying fluid is provided. This would be required in virtually

all circumstances if the carrying fluid were a hydrocarbon (e. g., oil) and would be required for water if upstream sources were not available, as might occur in a forest cut area, or if downstream discharge of separated water were prohibited. Tables 2—4 show the scope and cost estimate included in a two-way pipeline (i. e., one with return of the carrier fluid).

Key elements at the upstream end are materials receiving from trucks, dead and live storage, slurrying, and pipeline initial pumps. Key elements along the pipeline are the slurry and return pipeline and booster pumping sta­tions. Key elements at the discharge end are slurry separation and drainage of the wood chips, and material transport to the biomass processing facil­ity. As already noted, pressure drops, pumping requirements, and the overall estimate are based on water as the carrier fluid.

Note that unlike truck transport, there is an economy of scale in slurry transport of materials, since larger throughputs benefit from an economy of scale in construction of the pipeline and associated equipment, and in lower friction losses in larger pipelines.

Figure 2 compares the total transport costs of wood chips by truck and by pipeline, for an arbitrary fixed distance of 160 km. The basis of the cost estimate is a wood chip concentration of 27% by volume at the inlet end and 30% by volume at the outlet end. The close agreement between the estimat­ing formulae of Liu et al. (8) and the results of Wasp et al. (6) for a one-way pipeline is evident. The one-way pipeline cost estimates were cross-checked against a recent estimate of two short large-diameter liquid pipelines in western Canada (D. Williams, personal communication, 3/03), and showed good agreement. Figure 2 shows the impact of scale on pipeline costs, as compared with the cost of truck transport, which is independent of scale. (The formulae of Liu et al. (8) and the data from Bantrel [D. Williams, personal communication] suggest a capital cost scale factor for pipelines of

0. 59—0.62; the data of Wasp et al. (6) as not specific enough to calculate a comparable figure.) Figure 2 also shows the significantly higher cost for a two-way pipeline that returns carrier liquid to the inlet end.

From Figs. 1 and 2 it is clear that the marginal cost of transporting biomass by pipeline at a concentration of 30% is higher than truck transport at capacities <0.5 million dry t/yr (one-way pipeline) and 1.25 million dry t/yr (two-way pipeline) at a distance of 160 km. The implications of this finding are discussed in the next section.

Truck plus pipeline transport cost of woodchips with carrier return pipeline

Truck plus pipeline transport cost of woodchips

without carrier return pipeline

Truck transport of woodchips — FERIC

Э — Truck transport of woodchips — Short term contract hauling

Distance (Kms)

Fig. 3. Comparison of integrated truck/pipeline transport vs truck-only transport of wood chips at capacity of 2 million dry t/yr.