Residues to Riches: Piling for Dollars

Moisture content is the enemy of direct uses for forest biomass such as heat or combined heat and power (CHP) and is undesirable for most other uses of biomass, whether as feedstock for pellets or other bioconversion pathways. If we recognize the true value of biomass and reward for it, we can start to invest in managing it properly.

The delimber operator piles residues and conventional products on opposite sides of the road during processing.	The residue pile is angled to facilitate loading the chipper and to accommodate the exit direction of the van. Photos: Feric

There are various ways of reducing moisture content, both in the field and at the mill. The choice of techniques will depend on the final use for the biomass. For heat or CHP, expending energy to dry the material at the mill is not the general practice. To produce a feedstock for pellets, however, the moisture content needs to be very low, say below 15%, before pressing. This level is almost impossible to achieve in the field, so additional drying energy is needed at the mill. Drying methods may employ steam dryers, belt dryers, rotary drum dryers, or other methods, with the more efficient ones using waste heat streams from the conversion process. Whatever method used at the mill, a good head start and more efficient system overall can be achieved by proper residue management in the field. Residues may not be the feedstocks for some applications, but may be used to furnish the drying heat.

Residue management is a matter of common sense and integration with the conventional harvest. Piles should be made in exposed, sunny and windy locations. A log or tree length should be put under the large end of residues to reduce their contact with wet soil. Aligned piles, as opposed to haystacks, allow for air circulation. They also facilitate feeding the grinder or chipper, as the material is not tangled like a bird’s nest and the operator can easily identify the pieces to grab with less boom manipulation. Properly constructed piles also reduce costs by maximizing grinder productivity.

On full-tree operations with stroke delimbers or roadside processors, the operation is problematic because the creation of residue piles can interfere with delimbing or processing, and skidding may be occurring at the same time in a hot-logging operation. A post-harvest, pre-comminution piling operation may be the simplest way to go, considering that residues are still not viewed as a coproduct on many operations across Canada, and the contractor recovering the residues is usually separate from the logging contractor. However, residue piles can be built during the conventional harvest on a well-integrated operation.

The photos show an excellent example of an integrated operation with biomass recovery. On Boyd B. Harding’s operation in northern New Brunswick, the top of the tree is placed on the residue pile during delimbing. The delimber then swings across the road with the tree length and makes a pile of conventional products on the other side. The residue pile is angled to facilitate loading the chipper, with the butt of the tops pointing in the direction where the van will exit the block. The contractor also controls the harvesting operation, so any small trees pushed over with soil in the roots are left in the cutover. He also builds the road to a standard for the chipping operation. Despite lower delimber productivity, the company sees the financial benefit of managing the operation for both biomass and conventional roundwood products.

In pre-comminution piling operations, an excavator should be used, rather than a bulldozer. Dozers are faster and readily available but put excessive amounts of snow and dirt into the pile. An excavator or purpose-built piling machine with a boom and open-tined grapple or rake is much better at building a proper pile in terms of shape and orientation, proximity to the road, and cleanliness. Ideally, the pre-piling operation should take place a few months ahead of the comminution operation to facilitate drying; some of the contaminants may fall or wash off the debris.

The pre-piling machine can also be used as the loader for the grinder.

Based on our studies to date, the cost of pre-piling residues after full-tree harvesting is easily recuperated by higher productivity and uptime of the grinder and through a better quality product, i.e., lower moisture content and less contamination.

Mark Ryans is with FPInnovations–Feric Division and can be reached at mark.ryans@fpinnovations.ca.