Productivity Estimates for Chippers and Grinders on Operational Southern Timber Harvests

Transcription

1 Productivity Estimates for Chippers and Grinders on Operational Southern Timber Harvests Addison Aman, Graduate Research Assistant Shawn Baker, Research Professional Dale Greene, Professor Center for Forest Business, Warnell School of Forestry & Natural Resources University of Georgia, Athens, GA ABSTRACT Growth in bioenergy interests in the southeastern United States has created a need for costeffective woody biomass harvesting systems. Three operational systems were evaluated for their potential production and cost: horizontal grinders fed with residue from roundwood harvests, horizontal grinders fed with residue from clean chipping harvests, and whole tree chippers fed entire stems. We evaluated three contractors operating each of the three system types over the course of one week each. Hourly production did not differ significantly between the three systems, but per ton costs were lower for the grinding operations than for the chipping operation. Hauling capacity and per acre volume removal were highly influential on costs. INTRODUCTION Renewable energy sources are receiving increased attention as more is understood about worldwide petroleum reserves, the threat of global warming from rising CO 2 levels, and energy security issues (Turner 1999). Renewable energy sources will no doubt play a vital role in shaping the economy of the future as fossil fuel prices rise. Biomass is one source of renewable energy that is being closely examined nationwide and particularly in the Southeast. In this context, biomass is defined as plant material that can be used to fuel other processes. The southeastern United States, with over 30 million acres of land dedicated to managed pine plantations, is the largest producer of forest products in the country. These forests have the potential to play a major role in producing biomass feedstocks for various industries. The goal of this study was to study harvesting systems that can produce biomass feedstock in an efficient and economic manner. We examined systems that grind logging residues left behind after roundwood timber harvests (GRW) and after in-woods chipping systems that produce high quality chips for pulp and paper (GCC), as well as whole tree chipping systems that produce dirty chips (WTC). METHODS Site and Crew Characteristics All of the crews visited in this study were operating in either Alabama or Georgia on loblolly pine (Pinus taeda) stands. Three different operations of each 1

2 system type were observed for three to four days. Two of the WTC harvests were first thinnings while the third was a clearcut of a low-quality pine stand. Five of the grinder operations were following first thinnings, with the sixth, a GCC crew, following a clearcut. Pre-harvest inventories of stands to determine trees/acre and ton/acre estimates were not performed due to time and budget constraints. Crew sizes varied by operation type, with grinding crews using one or two employees and WTC crews employing a larger crew to handle the harvesting functions (Table 1). One GCC crew used four employees during the study period to fell residual hardwood stems and feed them to the grinder. This was not a typical operation for that crew. Available trucking capacity varied between two and five trucks. Table 1. Characteristics of forest biomass grinding and chipping systems in Georgia and Alabama studied during Crew Type Crew Size No. of Trucks Chipper/Grinder WTC 4 5 Morbark 50/48 WTC Precision Husky WTC 2366 WTC 4 4 Morbark 30/36 GRW 1 4 Peterson 4710B GRW 1 5 Vermeer HG 6000 GRW 2 3 Morbark 4600 XL GCC 4 4 Peterson 4700C GCC Peterson 4700B GCC 1 2 Morbark 3800 Time Study Techniques Elemental time studies were performed at each of the sites that were visited. The studies typically lasted three to four days, or until approximately 30 truckloads were observed and recorded. Work sampling was conducted by recording the activity of each piece of equipment every two minutes throughout the day. These data were combined by harvest system type to calculate utilization rates and identify causes of delays. We grouped the delay categories into trucking related delays and non-trucking delays to assess the impact of available trucking on production. Work categories that were grouped under non-trucking delays include: waiting on trees/chipper/loader, mechanical delays, miscellaneous delays, and operational delays. The time required to load each truck was recorded along with the length of any delays that prolonged the loading process. Total number of bites or swings of wood required to feed the chipper or grinder were also recorded. Mill scale tickets were used to record the weight of each load. This information was used to calculate average tons/scheduled machine hour (SMH) and tons/productive machine hour (PMH) for each of the three system types observed. Cost Analysis Two modified versions of the Auburn Harvest Analyzer were used to create cost estimates for grinder and whole tree chipping systems (Tufts et al. 1985) on a green ton 2

3 basis. The assumptions that were used in the cost analysis of the grinding and chipping systems are available from the author. RESULTS Machine Utilization Analysis Chipper/grinder utilization was the highest for WTC systems with a utilization rate of 44% (Figure 1). Both grinder systems had a slightly lower utilization rate of 38%. The utilization of the chipper/grinder could have been greatly increased if trucking related delays could have been avoided. These delays were the highest for the GRW and GCC systems with a rate of 49%. 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% WTC GRW GCC Other Delays Trucking Related Delays Chipping/Grinding Figure 1. Utilization rates for chippers or grinders for each of the systems studied. Delays are categorized by trucking related and other delays. While trucking related delays were not as significant for WTC systems, in this study chippers had more mechanical delays than grinder systems with a rate of 11%, compared to 4% for GRW crews and 9% for GCC crews (Figure 2). Overall, mechanical delays did not greatly reduce production for any of the systems studied. Knuckleboom loaders were used by every system that was observed except for one GRW crew. On grinding crews they were typically teamed with front-end loaders that piled material within reach of the knuckleboom and loaded the chipper/grinder when possible. Knuckleboom loader utilization rates 42%, 32%, and 33% on the WTC, GRW, and GCC crews, respectively. Combined loading and piling utilization rates for front-end loaders on the GRW and GCC crews were 38% and 51% respectively. Feller-bunchers and skidders were used by the WTC systems because harvests occurred concurrently with the chipping operation. Feller-buncher utilization was excellent with an 3

4 average rate of 76% for the systems observed. Skidder utilization was a bit lower than the felling machine with a rate of 57%. Part of the reason for this is that most operations used more than one skidder, but we were only able to observe one of them given our manpower in the field. Therefore wood may have still been skidded to the deck even though the machine we were observing was idle/off. 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% WTC GRW GCC Non mechanical Delays Mechanical Delays Chipping/Grinding Figure 2. Utilization rates for chippers or grinders for each of the three systems studied. Delays are categorized by mechanical and non-mechanical delays. Production Rate Analysis We summarized the production rates for the three system types on both a potential production (tons/pmh) and observed production (tons/smh) basis (Figure 3). Neither average production per SMH nor per PMH differed siginificantly between the three systems (p > 0.05). 4

5 Tons/SMH Tons/PMH 20 0 WTC GRW GCC Figure 3. Comparison of tons/smh and tons/pmh for the three forest biomass harvesting systems observed. System Cost Analysis - Whole tree chipping systems had the highest calculated cost per green ton of delivered material with $ The larger crew sizes needed to fell and extract trees for the chipper added substantial cost, particularly given the small diameter of felled stands (less than 8 inches DBH). Grinder systems had lower delivered costs per green ton with $21.18 for GCC operations and $20.25 for GRW operations. GCC operations required more effort on the part of both the knuckleboom and the front-end loader to accomplish the same production rate as the GRW operations, driving costs slightly higher. Sensitivity analyses were performed on a variety of key inputs for each of the system models that were created. Ton per acre removals were examined for grinding and whole tree chipping systems separately because they differ drastically from one another. Removals between 3 to 15 tons/acre of residual material represent a typical range for the grinder operations that were observed. The delivered price per ton falls by $2.55 as the per acre removals increase to 15 tons (Figure 4). The same trend occurs for WTC systems over a typical removal range of 20 to 100 tons per acre (Figure 5). The delivered price decreases $1.65 as the removals increase to the maximum of 100 tons/acre. 5

6 $/ Green Ton $22.00 $21.50 $21.00 $20.50 $20.00 $19.50 $19.00 $18.50 GRW GCC $ Tons/Acre Figure 4. Delivered material cost estimates for increasing ton/acre removals for biomass harvesting systems using grinders and chippers. $23.00 $/ Green Ton $22.50 $22.00 $21.50 WTC $ Tons/Acre Figure 5. Delivered material cost estimates for increasing ton/acre removals for whole tree chipping systems The limited availability of trucking caused increases in haul distances to have a very large effect on the delivered cost of material for each system type (Figure 6). As haul distance increases from 50 to 120 miles the delivered cost of material rises by $18.13 for WTC systems and $17.01 for grinder systems. Additionally, payload maximization is important to maximize trucking efficiency (Figure 7). Decreases in total payload cause substantial increases in delivered costs. 6

7 $40.00 $/ Green Ton $35.00 $30.00 $25.00 $20.00 WTC GRW GCC $ Haul Distance (miles) Figure 6. Delivered material cost for increasing haul distances (miles) for all 3 system types. $28.00 $26.00 $/ Green Ton $24.00 $22.00 $20.00 WTC GRW GCC $ Load Size (tons) Figure 7. Delivered material cost for increasing truck load weights (tons) for all 3 system types. CONCLUSIONS All three systems showed relatively low chipping or grinding machine utilization during our study period. The availability of trucks was a major contributing factor in the grinding operations. While trucking was also a factor in the chipping operations, feller-buncher utilization averaged over 75%, suggesting that felling capacity is very close to limiting when 7

8 using one feller-buncher to feed a full-sized chipper in the smaller stands typically being used for biomass-only harvests. Productivity was statistically equal between the three systems, but the additional machinery and personnel needed to produce whole-tree chips drove the cost per green ton higher for the WTC crews. All three systems were sensitive to changes in trucking availability, payloads, and per acre tonnage removals. ACKNOWLEDGEMENTS This research was funded by a grant from the Georgia Traditional Industries program. The authors also wish to acknowledge the cooperation of all harvesting contractors in this project as well as Plum Creek Timber Company for their assistance. LITERATURE CITED Tufts, R.A., B.L. Lanford, W.D. Greene, and J.O. Burrows Auburn harvesting analyzer. The COMPILER Forest Resources Systems Institute, Florence, AL. 3(2): Turner, J. A. (1999). "A Realizable Renewable Energy Future." Science 285(5428):