Photo by Forest Concepts
Loggers Unlimited cutting and gathering material to drop into piles along the roadside.

PG&E Pilot Evaluates Chipped Versus Baled Debris

May 18, 2022
PG&E trials baling equipment as an alternative to chipping to lower noise pollution, produce biomass products

Vegetation management along T&D lines results in untold amounts of woody biomass that must be gathered and dealt with by tree-trimming crews. Today, most of that material is chipped using tow-behind chippers to reduce the bulk and first-mile hauling costs. A 10-yd (9.1-m) chipper truck box might hold a few tons of chips. If that same volume of loose debris was put in a dump truck or hook-lift bin, it would only amount to maybe a half-ton of brushy debris. Baling allows decoupling of biomass gathering and transportation. In these established gathering schemes, when the truck is full, the crew must stop work and travel to and from a designated place to unload the truck. The lost on-site work time is considerable for the thousands of crews working to maintain electric grids every day.

Outlets for chipped biomass include mulch, biomass power and compost bulking materials. Most vegetation management contractors have well-developed relationships and logistics systems to minimize disposal costs through traditional outlets.

Current initiatives to improve energy sustainability, reduce carbon intensity and enable a circular bioeconomy are casting VM debris in a new light as an opportunity rather than a problem. Properly processed woody biomass is emerging as valuable feedstock for use in gasifiers, pyrolysis systems and other advanced thermal systems to produce heat, electricity and renewable chemicals. Methanation of syngas can produce pipeline quality renewable natural gas. High-moisture biomass can be blended with other wet organic wastes, such as food waste, green waste or manure in anaerobic digesters, to directly produce methane for upgrading to renewable natural gas. These new outlets and markets for VM debris are likely to be more centralized and distant for daily power line maintenance work sites.

New and improved methods are needed for gathering, transporting and processing VM debris to deliver fuels and feedstocks economically to these new outlets. To stimulate and evaluate potential innovations, Pacific Gas and Electric Co. (PG&E) partnered with ADL Ventures to conduct a broad search for innovative approaches to reduce biomass gathering, transportation and processing costs (see T&D World articles from Jan. 11, 2021, and April 26, 2021). They selected a woody biomass baling technology for its potential to improve safety; reduce noise issues, dust and biomass gathering labor; and enable lower-cost transportation of VM biomass to users more than 50 miles (81 km) from a work site. PG&E recently completed a pilot trial of the baling equipment in Lake County, California, as an alternative to chipping in areas where alternative biomass markets exist or are being developed.

Baling Pilot

The woody biomass baling method PG&E is using was developed by Forest Concepts LLC. The technology has proven effective in other locales to increase the transportation density of woody biomass from VM, wildfire protection projects and forest management activities. Additionally, the company has developed woody biomass size reduction, screening and drying technologies that enable increased value-added usage of chipped and baled PG&E VM trimmings.

The current full-scale engineering prototype baler is mounted on a flatbed trailer and has completed field trials across Washington, Oregon and Northern California. Earlier applications and field work focused on reducing the cost of gathering and transporting forest trimmings, logging slash and wildfire protection vegetation debris. This pilot was the first evaluation of baler technology for use with power line VM crews as a direct alternative to tow-behind chippers. Field experience was needed to develop the final design and optimize the baler models for this important and growing equipment market. For firms who were aware of the technology, a lack of application-specific pilot tests and data limited their willingness to purchase and add baling equipment to their fleets.

The PG&E pilot project site was in Lake County, California, along rural roads where Loggers Unlimited was conducting routine power line trimming under contract to PG&E. For the pilot, Loggers Unlimited assigned two bucket truck crews to work as a team directly ahead of Forest Concepts’ baling crew. The trimming crews dropped and piled materials that were mostly oak and walnut alongside the road using the same methods as for chipping. The baling crew picked up the material with an onboard grapple loader to feed the baler.

The two-person baling crew included an operator and one ground person. During the pilot field trial — because of the high frequency and short distance for most moves, for example, 2 minutes to bale a pile followed by 1-minute moves of 100 ft (30 m) or less — the ground person did the driving within a work area and the baler operator/crew lead did longer-distance driving between work sites. Traffic control was provided by a combination of the Forest Concepts ground person and nearby Loggers Unlimited trimming truck ground personnel. The main observation about crew size from those who participated in the pilot was the physical effort for the baler ground person was minimal compared to a chipper ground crew. The person easily had time to clean up the site and assist with traffic control.

As with chipping, the production rate of baling was directly tied to the rate trimming crews dropped biomass. During the pilot, most stops of the baler only lasted one minute to three minutes, then moved to the next pile along the road. In one area of high-trimming intensity, an entire 800-lb (363-kg) bale was produced in 20 minutes. In other areas, it took more than 90 minutes to make a bale, and biomass was gathered from nearly a mile of power line.

Sound Level

Noise complaints from neighbors often are associated with roadside chipping of woody vegetation debris. Among the proposed benefits of baling vs. chipping is the much quieter environmental noise levels.
An engineer from Forest Concepts collected sound-level measurements around the baling, chipping and bucket truck equipment. Measurements were taken 5 ft and 30 ft (1.5 m and 9.1 m) from each piece of equipment while it was actively working. Noise production by the trimming crew’s bucket truck and the baler were associated with their engines and hydraulic systems. Chipper noise levels were associated directly with the amount and diameter of biomass being processed. The baler system had similar loudness to that of the bucket truck trimming crew. As expected, the chipper was much louder.

“The noise level was good,” said Aaron Stanger, safety manger with Loggers Unlimited. “You could actually hold a conversation next to the baler and even a couple of customers commented on how quiet it was.”

Biomass Transport

The most dramatic operational difference between baling and chipping is how materials are handled and transported. Most chipping crews use trucks that have a fixed chip box. It is rare a power line VM crew produces less than one truckload per day. This means when the box is full, the crew must drive away from the work site to wherever the box can be unloaded. VM companies advertise widely and maintain call centers to identify private landowners close to each day’s work sites to minimize the off-site time and distance. Lacking close private dump sites, the load must be hauled to a central yard, compost facility or other location. In any event, the lost gathering/chipping work time can range from 30 minutes to one hour or more per day.

The pilot project demonstrated a decoupled approach to bale gathering and delivery. As bales were completed, they were either set off to the side of the road or stacked in groups at turnouts within the work site. A traffic cone was set next to each bale to provide some safety notice.

Loggers Unlimited then used its existing flatbed grapple trailer to pick up all the completed bales. The crew followed the same practices traditionally used for picking up oversized and merchantable logs. Although this site did not have oversized logs that could not be baled, it is plausible logs and bales could be gathered as a mix during a pickup route.

In the pilot, the bales were found to be a bit bigger and heavier than for what the grapple trailer was designed. This mismatch will be addressed as the bale size and baler specifications are finalized for manufacturing of commercial models.

Biomass Processing

While most VM chips today are delivered at no cost to private landowners or compost mulch facilities, the bioeconomy and bioenergy markets are creating new outlets. High-moisture biomass can be incorporated with other wet wastes in anaerobic digesters to produce methane for energy or upgrading into renewable natural gas. The biomass power industry is seeing a resurgence with traditional combustion power plants and more advanced gasifier systems. Solid biofuels, such as wood pellets and solid biocarbon in the form of biochar, also are looking at VM debris for feedstocks.

Most of these value-added uses for power line VM debris have feedstock specifications that do not align well with arborist chips as their feedstocks. Where chips are available, they must be further processed to remove twigs and shards, milled to specified particle sizes and sometimes upgraded by removing leaves. These emerging markets are leading to the creation or expansion of biomass utilization centers and centralized processing operations that can mill, sort, dry, and otherwise convert low-value VM debris into products that reliably and profitably meet the requirements of a range of biomass users.

Bales are more desirable for at least some biomass yards because the vegetation is largely intact when it enters their processes. For example, one biomass power plant in Northern California wants its fuel to be “larger than a golf ball and smaller than a soda can.” Arborist chips are mostly too small for this potential user. However, baled material can be milled to the specification with reasonably high yields.

Omni BioEnergy LLC was recruited to the pilot to provide its expertise and evaluate alternative feedstocks derived from power line VM biomass for use in its gasifiers. In general, its specifications called for the feedstock to be smaller than 0.25 inch (6 mm), highly flowable, not shardy and reasonably dry. This spec could be met with both processed wood chips and ground/chipped bales.

Bales and chips from the PG&E VM sites in upper Lake County were ground by Donahoo Inc. using a horizontal grinder. Subsequently, the grinder output was screened for size and length by Forest Concepts to achieve the size and flowability characteristics needed by Omni BioEnergy. In this evaluation, feedstocks from all sources were able to be processed into high-yielding feedstocks that met Omni BioEnergy’s requirements.

Lessons Learned

The PG&E pilot project provided an end-to-end comparative evaluation of the current chipped debris pathway vs. the proposed baled debris pathway. The potential value of the technology is threefold:
1. Increased transportation density for reduced transportation costs
2. Reduced noise and air pollution
3. Final processing and milling of biomass into conversion-ready feedstocks (for example, to renewable natural gas), which happens at or near the point of use. Baled biomass enables gasifiers and other plants with strict feedstock requirements to process the biomass once to meet their required specification on-site, thus reducing overall processing costs.

Engineer Kevin Pease, a member of the PG&E Gas R&D and Innovation team, participated in the field trials. His main takeaways were the decreased labor requirement, less manual nature of the labor for baling and reduced environmental impact through less noise pollution and criteria pollutants. The environmental benefits make baling an option in some locations where chipping may be a nuisance to neighbors.

ADL Ventures organized and facilitated a ProblemSpace competition sponsored by PG&E that led to the selection of Forest Concepts among two other winners. Chris Richardson, a partner in ADL Ventures, noted successful pilots such as the one executed by Forest Concepts and PG&E are key desired outcomes of any open innovation challenge. PG&E posed a vexing technical challenge, with cost and safety issues: It was difficult for the utility to remove biomass from high-threat fire districts. Forest Concepts submitted and later proved through this pilot how those challenges could be overcome.

Mike Perry, Forest Concepts’ CEO, was on-site and talked with cooperators and several landowners along the worksite who came out to observe the removal of tree trimmings along their fence line. Perry heard firsthand comments about low noise levels for balers vs. chippers and enthusiasm when learning that biomass from their property was going to a renewable energy application. “The general consensus of all who observed the project, including the VM team, was that baling definitely has a place in their fleets and operations just based on the improved safety and public acceptance,” Perry said.

This pilot project was sponsored and managed by PG&E’s Gas R&D and Innovation team. Within that team, Senior Engineer Danielle Mark led the pilot project from start to completion. The value Mark initially saw in the technology was “woody biomass densification to reduce transportation costs and open access to the use of woody biomass downstream for processing into valuable products, including renewable natural gas for injection into the PG&E gas grid.” Following the pilot and reviewing the results, Mark still believes that “wood baling has the potential to reduce costs, reduce noise and air pollution, improve crew safety and productivity, and is of continued interest.”

After seeing the pilot and reviewing the results, Mark concluded that baling has sufficient potential to reduce costs, improve crew productivity and reduce community noise issues, among other benefits, to be of continuing interest to PG&E.

Technical lessons learned from the pilot are being incorporated already into specifications and designs for biomass baler models that will be optimized for use by roadside power line VM crews. Jim Dooley, Forest Concepts’ chief technology officer, has proposed changes to the bale dimensions to make them easier to gather using existing grapple trucks and trailers. Although the prototype received high safety marks, additional safety features such as an operator seat dead-man switch tied to the hydraulic system wer recommended by the experienced Loggers Unlimited VM team.

Danielle Mark and Kevin Pease are engineers in PG&E Gas Operations’ R&D and Innovation group. They both focus on decarbonizing the gas system by supporting technology advancement and deployment. One focus area for Danielle and Kevin is enabling renewable natural gas, which can originate from woody biomass, and can be a direct substitute for fossil natural gas.

Jim Dooley is co-founder and Chief Technology Officer of Forest Concepts, LLC in Auburn, Washington. He received engineering degrees from Cal Poly, UC Davis, and the University of Washington. Dr. Dooley combines a deep understanding of plant biology with disciplined engineering design and business development to create innovative products, processes, and equipment. He has been involved in the use of biomass for biopower and biofuels since 1975.

For More Information

Forest Concepts LLC | https://forestconcepts.com/

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