Processed woody biomass is unloaded in different ways depending on the transportation method and capabilities of the concentration yard or facility to which it is delivered. High-volume operations, such as large combined heat and power boiler systems and elec­tric power plants, typically use hydraulic truck dumps. These systems raise conventional tractor-semi-trailers vertically and use gravity to dump the contents of their trailers into a transfer bin, pit or bunker, or onto a ground-level pad. Once dumped, the biomass can be moved from the unloading area by drag chains, conveyors, wheeled front-end bucket loaders, or similar handling equipment. Paired with large-volume chip vans, truck dumps are an extremely efficient unloading system. However, they are costly to install and main­tain, so they are generally found at facilities requiring hundreds of thousands of tons of feedstock per year. For smaller volume operations, such as distributed heating systems, self-unloading trailers are preferred. These trailers generally discharge onto a pad, where the material is moved by a rubber-tired front-end bucket loader. A variety of belly, side and end dump trailers are available for different truck and tractor configurations. However, walking floor (or live floor) self-unloading semi-trailers are a good option to maximize payload when a truck dump is not available or when the truck must unload in a covered

storage area or bunker with low overhead clearance that limits the use of side and end dump trailers.

Chipped or ground woody biomass can be stored in piles that are open to the weather (Figure 14.10). Obviously, moisture content is not a problem for conversion technologies that use wet chemical and biochemical processes, but even for thermochemical conversion processes where dry material is preferred, biomass harvested from green trees or logging residues that have received some field drying is unlikely to increase much in moisture content from precipitation when stored in piles outdoors. However, in most cases piles with high moisture content should be rotated to avoid degradation, which can change its physical and chemical properties, resulting in loss of energy content. Spontaneous combustion of green and wet chips can also occur if piles are allowed to remain outdoors without rotation for extended periods. This phenomenon is the result of microbial activity that produces heat, which can build up and cause combustion under some temperature, oxygen and moisture conditions. Regular rotation dissipates heat and changes pile conditions to make combustion unlikely.

Some woody biomass, especially residue from solid wood products manufacturing, has low moisture content as a result of kiln drying prior to final processing. In some cases, green woody biomass is dried prior to use, as in most fuel pellet manufacturing operations. Drying wood is expensive but elevates the recoverable energy content and value of the material. As a result, dry woody biomass should be kept in a dry condition using proper storage and handling procedures, which often include covered storage and short storage duration before use. Though spontaneous combustion and degradation are less of a concern with dry materials, dry biomass may require additional dust control, typically in the form of collection and exhaust systems that minimize fire, environmental and health risks. In general, the smaller the particles, the greater the need for such management systems.

For bioenergy facilities using roundwood delivered on log trucks or flatbed trailers, there are a variety of conventional options for unloading, handling, and storing wood. Log trucks can be unloaded by crane, either rotary or portal varieties, and easily stored in tall piles in a log yard. Unloading and storing wood in this fashion is an efficient option for high-volume operations and is commonly employed at conventional forest products manufacturing facilities. Grapple loaders and rubber-tired front-end log loaders can also be used effectively, although a larger land area is required due to the limited reach of the equipment. Log yards often employ both cranes and log loaders to stack and store roundwood. Low volume operations are unlikely to prefer roundwood as feedstock but can opt for grapple loading log trucks and a tractor or skidder to manage logs in the yard before processing.