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Recovering of forest biomass from Spanish hybrid poplar plantations
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Recovering of forest biomass from Spanish hybrid poplar plantations Eduardo Tolosana a,*, Rube´n Laina a, Rocı´o Martı´nez-Ferrari a, Yolanda Ambrosio b a b
E.T.S.I. Montes, Technic University of Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain E.U.I.T. Forestal, Technic University of Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain
article info
abstract
Article history:
Residues recovering from traditional poplar plantations for timber production are
Received 12 May 2009
a potential relevant biomass source in Spain and other temperate countries. Three
Received in revised form
different residual biomass harvesting systems have been work-studied in order to char-
7 February 2011
acterize the work methods and analyze their productivity and cost. Two were oriented to
Accepted 10 February 2011
branches, top and/or energy wood collection, chipping and transport using different work
Available online 22 April 2011
methods, while the other one consisted of after-logging stumps removal and shredding. Different sized and powered chippers worked in the two first cases, besides different farm
Keywords:
tractors with trailers for off-road chips transport. Also the trucks and the loading machines
Populus
were different. In the third site, a backhoe excavator removed the stumps, and a bucket
Residual forest biomass
loader collected them to be grinded by a shredding machine. Productivity and cost have
Harvesting techniques
been analyzed using IUFRO standards, providing average figures and, when possible,
Work study
predictive productivity equations. Most capital-intensive equipment option has shown to
Logistics
be most productive, but less investment requiring system is cheaper and may be most
Spain
interesting for some enterprise and plantation sizes. In addition, logistics of biomass and timber supply has been analyzed, and some indications about equipment sizing, machine annual production and relocation costs related to supply area and average plantation size are provided. ª 2011 Elsevier Ltd. All rights reserved.
1.
Introduction
According to the RES National Action Plan 2011e2020 [1], Renewable Energies contributed in Spain to a 9.4% of primary energy consumption in 2009, being the goal for 2020 a share of 20.1%. Regarding electricity production, RES had a contribution in 2009 of 24%, being the objective for 2020 to reach a 36%. Focusing in biomass and biogas, they are supposed to grow up at a yearly rate between 7 and 12.6% during the period 2009e2020. The measures fostering the energy use of forest and agricultural products or residues, besides woody crops, are
supposed to have as result an additional consumption of 5.5$106 tonnes$year1. This aim would require huge efforts to mobilize every biomass sources, particularly woody biomass [1]. Hybrid poplar (Populus x euroamericana ¼ P. x canadensis) plantations are one of the main timber resources in central Spain. Located along the basins of the most plentiful rivers, they provide roughly 700 000 to 800 000 timber o.b. m3 yearly, around 5% of the annual felling. Cutting system usually combines chainsaw for felling and processing with a wheeled grapple front loader to support oriented felling, move and pile logs off the terrain and pile tops and branches. The same
Abbreviations: RES, renewables energies; IUFRO, International Union of Forest Research Organizations; dbh, diameter at breast height; ob, over bark; odt, oven dried tonne. * Corresponding author. Tel.: þ34 678 459466; fax: þ34 91 5439557. E-mail address: [email protected] (E. Tolosana). 0961-9534/$ e see front matter ª 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biombioe.2011.02.007
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machine loads the timber on trucks that get into the felling plot. Piled branches and tops are usually burnt after some months during which these residuals get dry. A backhoe excavator extracts the stumps in order to avoid sprouting and facilitate plantation, often simultaneously with residuals burning and immediately before the new plantation. These stands have gentle terrain conditions and good accessibility from roads. This should ease the recovery of poplar residuals, which have become the first forest biomass systematically collected in Spanish forests. The goals of this work have been to time study and analyze the productivity, cost and some logistic aspects of three commercial harvesting operations in hybrid poplar Spanish plantations that share the common fact of integrating the biomass recovery of what used to be residuals within the traditional logging operations. As long as the studied sites are very different stands and harvesting systems, the aim has not been to make a comparative study but to provide the detailed results of their time and productivity studies, in order to serve as a reference about representative Spanish poplar logging sites. Another objective has been to provide some logistic considerations and operational recommendations to improve the future planning of biomass recovery from hybrid poplar plantations under similar conditions.
2.
Materials and methods
2.1.
Analyzed work systems
System 1 consisted of the collection of branches and tops e until 8 cm of diameter e using a Helca JCB 528 tele-handler with a purpose-designed raking implement (Fig. 1), after motor-manual felling and mechanized processing of poplar timber whose main destination was a local sawmill. Machines used for felling and processing were a Stihl MS441 chainsaw
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and a Keto harvesting head mounted in a Komatsu wheeled backhoe excavator. After timber hauling off, terrain chipping with a Pezzolato 480/660 chipper attached to a 210 HP Fendt 916 farm tractor followed on site biomass piling (Fig. 2). A Valmet tractor with trailer extracted and dumped the chips on a landing chip pile. Finally, a Caterpillar wheeled bucket loader deposited the chips on 70 loose m3 trailer trucks. This site was near Santa Fe, in Granada province, southern Spain. The operations took place during May, July and October 2007, affecting a 1.8 hectares plantation, with a density of 714 trees ha1 and an average diameter of 25 cm. Timber accounted for 453 o.b. m3 ha1. A sawmilling company called Maderas Calero Tejera S.L., which owned the machinery, used the timber and sold the chips to a particleboard factory, performed the operations. Biomass production was 65.8 tonnes ha1 at 43% of moisture measured in fresh biomass samples, equivalent to 37.5 odt or 219 chips loose m3 ha1. That is, for a top diameter of 8 cm, 0.484 chip m3 (loose volume) or 82.8 dry kg timber o.b. m3. System 2 followed a motor-manual felling of 401 larger poplars$ha1 whose main destination was plywood. It consisted of bunching similar branches and energy wood e up to a 14 cm top diameter e, now using a grapple front loader with another attached raking implement, also specifically designed to pile branches and tops without carrying together stones or sand. An Erjo Oswald chipper with its own 550 HP engine, integrated in a John Deere 1410 D forwarder, chipped the biomass, loading a Spanish Santamarı´a Fliegl Gigant trailer attached to a John Deere 8400 farm tractor. The trailer was equipped with a scraper hydraulic conveyor which permits a quick backwards unloading operation to a large chip heap, at the landing (Fig. 3). Afterward, a light Manitou telescopic loader deposited the chips on a 90 m3 bulk volume truck e an aluminum trailer with mobile platform -.This site belongs to Santa Cristina de la Polvorosa municipality, Zamora province, central north-western Spain. Garnica Plywood, the main
Fig. 1 e Tele e handler piling biomass from poplar branches and tops (System 1).
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Fig. 2 e Pezzolato chipper attached to farm tractor blowing chips to the trailer of the forwarding vehicle (System 1).
poplar plywood manufacturer in Spain, performed the operations. Operations were studied in September and November 2007.Poplar plantation surface was 1.5 hectares where 601 trees were felled, with an average d.b.h. of 35 cm, yielding 621.5 timber o.b. m3. Biomass production was 99.4 tonnes$ha1 at 53% of moisture measured in fresh biomass samples, equivalent to 46.7 odt or 280 chips loose m3 ha1, so for the 14 cm top diameter, 112.24 dry kg or 0.675 chips loose m3 timber o.b. m3 were produced. System 3 consisted of the stumps removal, piling and shredding in a poplar plantation, following a motor-manual
timber harvesting for plywood as main product. A Daewoo OLC-V backhoe loader extracted the stumps, that were collected and piled on a big heap using a Hanomag 66 D wheeled bucket loader and, after a month period, were grinded by a Hammel 750 DK shredder with counter-rotating shafts, fed by means of a light Manitou telescopic loader, that was followed by a Komptech Multistar M3 screen in part of the trials (Fig. 4). The site was close to Carrio´n de los Condes village, Palencia province, central northern Spain. The plantation covered 18.4 ha, with a density of 278 trees$ha1 and an average dbh of 32.1 cm. The enterprise in charge,
Fig. 3 e Special trailer unloading chips (system 2).
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Aprovechamientos Ecolo´gicos (AECO) S.A., is specialized in comminuting forest and other residues. Total biomass production over a 9300 m2 surface was estimated in 35.3 odt ha1e47.0 tonnes ha1 at 25% of moisture over humid weight -, coming from 278 stumps ha1.
2.2.
Forest inventory and biomass estimation
In all the cases, the Forest Services provided a detailed inventory in which every dbh was measured. Regarding biomass estimation, in the plantations corresponding to the systems 1 and 2, a couple of trees belonging to each diameter class were felled and measured. Weight tables were fitted and the results regarding biomass e not including timber e are shown in Fig. 5, where “Weight” refers to a moisture percentage of 46 and 53% over humid basis, respectively for the systems 1 and 2. These figures were obtained by oven drying 3 samples from different sizes of branches and leaves from each sample tree, at 105 C until constant weight. In the case of System 3, felling was over when the time study crew got to the site, so it was not possible to weigh tree samples. Besides, biomass was not been transported, so it was not possible to get weight data of shredded material from a certain stumps number. The estimation of stumps weight is based upon the Spanish most recent set of root biomass equations [2]. As long as they refer to dry weight, the green weight estimations have considered a moisture percentage of 25% over humid basis, close to the observed figures in similar materials.
2.3.
Time studies
As long as logging was integrated to the residuals recovery in the case of systems 1 and 2, the productivities and costs of felling, processing and residues piling were affected by the
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intend to most efficiently collect the biomass afterward. Because of that, the time studies of every logging operations were carried out. The time study methods were different depending on the task type: if it were a cyclical one, performed by a single actor e for example, a chainsaw operator felling and processing trees or a single tractor hauling the timber off e the continuous control method was the procedure adopted, using a Psion Workabout hand-held computer with the purposedesigned software Kronos 3.0 [3]. In case the operation were not cyclical or were performed by more than an actor e for example, chipping at landing or motor-manual processing by several operators, the “stopwatching” method was chosen: the controller registered, when a chronometer beeped, the work phase performed by each worker observed following a pre-fixed sequence. Time studies are always combined with productivity control, in different ways depending on the operation: if it dealt with trees, they were counted; if it had to do with tractor loads, their number was registered, or even the bulk volume of each load was measured. In any case, the time dedicated to a certain work piece was put in relation to the timber volume or biomass weight produced. When the estimation was indirect e through the number of trees and a weight table, for example -, it was obliged to measure the biomass percentage left on the terrain, by weighing the biomass left in several 10 m radius circular plots in each site.
2.4.
Time and productivity analysis
Time has been classified using the IUFRO standards [4], with the table formats developed by the European Concerted Action AIR3-CT94-2097 [5]. Coefficients relating work time with productive or worksite time have been calculated. Where the continuous method for time studying was chosen,
Fig. 4 e On the right side, the telescopic loader feeds the shredder with poplar stumps. On the left side, the screen and on the back, the backhoe excavator (System 3).
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Fig. 5 e Biomass weight curves from sites corresponding to systems 1 and 2.
predictive equations have been fitted by means of standard statistics software (Statgraphics, SPSS).
3.
Results
2.5.
3.1.
Productivity
Cost estimation
3.1.1. System 1: terrain chipping with Pezzolato 480/660 attached to farm tractor
Machines and operators hourly costs were estimated using classical methods [6]. Once work time is defined as the common basis for calculations, hourly cost and productivity have been expressed regarding to work time. It allows estimating the direct unit cost on a production basis (timber o.b. m3, biomass odt and/or loose m3). Relocation costs have been derived from the number and kind of machines to be transported and the transportation distance or cost among biomass harvesting sites for plantation sizes between 0.5 and 10 hectares.
Felling & processing Productivity according to IUFRO standards was, for the harvester, 17.4 timber o.b. m3$productive hour1e10.9 m3$work hour1 or 9.9 m3$worksite hour1. Controlled timber was 217 m3, with a 760 kg m3 density. Time study lasted 22 h. There was some lack of coordination between chainsaw operator and harvester, leading to low percentages of productive time related to worksite time (57% for harvester, 45% for chainsaw operator). Additionally, a 150 HP farm tractor
Table 1 e Time and productivity table for chipping (System 2). ERJO CHIPPER MOUNTED ON JOHN DEERE FORWARDER
Productive Time (direct)
Work Time
Productivity, chips (m3 loose volume·work hour-1)
TIME %
Machine movement
86
5.42
Crane approaching to a load
219
13.70
Feeding
218
13.60
Waiting for a load to be chipped
58
3.58
Unloading
83
5.21
Breakdowns / repairs
127
12.68
Waiting for other system elements
8
0.51
Refueling
32
3.27
Knives change
273
27.91
Other tasks
28
2.86
Meals
110
11.26
11.26
11.26
TOTAL
1242
100.0
100.0
100.0
47.23
Productivity (tonnes·work hour-1)
Productive Time 16.96
Productive Time 72.20
41.51
88.74
Indirect Work Time
Not Work Time
TIME (min)
Work Time 33.77
Worksite Time 29.97
Work Time 7.93
Worksite Time 7.04
Table 2 e Hourly costs, productivities and unit costs. Hourly costs and Productivities Work System
System 1
Operation
Timber felling & processing
Chip forwarding TOTAL COST System 2
Timber felling & processing Timber hauling off, branches piling and help to felling Branches and energy wood Chipping Chip forwarding TOTAL COST
Hourly costs (V$work hour1)
Chainsaw operator Harvester Winch tractor Tractor w/trailer Raking tele-charger
15.22 55.63 34.4 36.45 35.41
Chipper Tractor w/trailer
74.69 36.45
Productivity (timber m3$ work hour1)
Productivity (chip green tones work hour1/odt $ work hour1)
Productivity (chips loose m3 work hour1)
V$timber o.b. m3
Chipper Tractor w/trailer
22.3 59.97 149.31 50.32
Stump extraction Stumps hauling off and piling Stumps shredding
Backhoe loader Wheeled bucket loader Grinder Hammel machine þ Manitou loader TOTAL COST (Not including stump removal, only shredding)
74.00 48.00 130.00
V$chips loose m3
e
e
9.65
e
e
e
18.58 41.95 equivalent timber m3 e e
e 3.44/3.05
e 17.82
1.96 0.68
e 23.77
e 26.80
e 4.59
10.73/9.52
56.16
3.83 30.63
0.65 5.24
e 3.88
e 0.53
16.54 16.54
e 2.62/1.55 (eqiv.)
e 11.16 (equiv.)
1.36 3.26
3.40 27.17 (11.3% moisture) e 2.29
e
7.93/4.68
33.77
e
19.6
33.22
4.42
7.93/4.68
33.77 4.62
6.35 28.24 (41.0% moisture)
10.76 47.86
1.49 6.44
V$shredded V$shredded V$stump1 biomass biomass odt1 green tonne1
Productivity Productivity (shredded Hourly costs (V$work hour1) biomass tonnes$work (stump number$ work hour1) hour1, 25% moisture/ 1 odt$$work hour ) System 3
V$chips odt1
10.91
12.29 Chainsaw operator Wheeled Front Loader
V$chips green tonne1
11.3/8.48 20.1/15.1 6.11/4.58
65.9 119.0 36.16
e
6.55 2.38 21.28
8.73 3.17 28.37
1.12 0.40 3.60
e
21.28 (25.0% moisture)
28.37
3.60
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Timber hauling off Branches and topspiling and Chipping
Machinery
Unit direct costs
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equipped with winch was present during this task, being utilized to support felling operation when felling direction was dangerous or complicated. Its productivity has been considered the same as the felling team, but its percentage of productive time was very low e less than 25%. Timber hauling off A productivity equation was fitted using the continuous time-study data.
A productivity over work time equation (3) was fitted for both machine and operator involved in felling and processing tasks. Main explanatory variables were d.b.h.(cm) and branch abundance e codified as 1 for large branched or bifurcated trees, and as 0 in other casese 1 268 þ 0:026$DBH2 ¼ 6000$Vu m3 $tree1 Prod m3 $wh þ 2:59$DBH þ 17:5$BRANCHCODEð0=1Þ
TWS ðcmin=cycleÞ ¼1681:05 þ 10:83$NL þ 5:29$HD;
R2 ¼ 98:3%
(3) ð1Þ
where TWS is worksite time, NL is the number of logs forwarded per load as an average, 77- and HD is the hauling distance (one way, m, 50e200 m, 95 m as an average). Average log volume was 0.13 m3, so the correspondent productivity equation is 1 ¼ 0:13$NL$6000=ð1681 þ 10:83$NL Prod m3 $worksite hour þ 5:29$HDÞ
(2)
Piling biomass and mobile chipping Chipping productivity was 17.8 loose m3$work hour1, 3.05 odt$work hour1 or 3.43 tonnes at 11.3% moisture - with 193 kg$loose m3 density e. Chips were so dry because of the delay between felling and chipping more than a month during Spanish summer. Although the chipping task was efficient - the chipper was blowing chips 69% of the productive time -, figures drop when referred to work time, because of the waiting times due to the lasting trailer change when it got full (29% of worksite time). This was the main system bottleneck. There is an additional non-registered time, due to blades maintenance out of the worksite. Control time was 9.4 h. A farm tractor equipped with a tele-handler with a specifically designed raking implement piled the biomass. Its productivity was also low, because it worked simultaneously with the chipper, not only making branches piles or stripes, but also pushing biomass toward the chipper crane to facilitate feeding operation, avoiding sand or stones. Global productivity was, then, the same as the chipper one. Efficiency of biomass collection was high, measured branches left on the terrain were only 7.5% of their estimated total amount. Chip forwarding Chips were transported to a landing where 70 m3 covered trailers could access. The terrain transport distance was 4.8 km and the average work time per cycle was 31 min. As the average load size was 29 m3 bulk volume, the productivity figures were 56.16 loose m3 work hour1 (10.84 tonnes at 11.3% moisture or 9.64 odt).
3.1.2. System 2: terrain chipping with Erjo Oswald integrated to a John Deere 1420D forwarder Felling & processing Productivity following IUFRO standards was 30.4 o.b. timber m3 productive hour1 (21.7 m3 work hour1 or 16.5 m3$worksite hour1). Controlled timber was 1046 m3 or 571 tonnes, for a 546 kg m3 density. Time study lasted 63 h. Productivity figures are much higher than for the system 1, due to the bigger tree dimensions. Anyway, there was some lack of coordination between implied actors, leading to low percentages of productive time related to worksite time (53.4 for chainsaw operator, 58% for wheeled front loader).
The branch code may also be used as an estimation of the ratio of heavy branched or bifurcated stems. As the ratio was 25%, Branch code ¼ 0.25. Cycle time is much more sensitive to diameter than to the branch code. Productivity for wheeled front loader was 28.6 o.b. timber m3$productive hour1, 22.3 per work hour and 16.5 per worksite hour. Besides piling the timber, the front loader hauled the timber off and loaded the logs on the trucks. Additionally, it piled the biomass, so 10% of its operational cost was charged to it. Branches left on terrain were sampled, accounting for a 12.0% of the estimated yield. Mobile chipping & chip forwarding Productivities following IUFRO standards are shown in Table 1. Studied time was 21 h. Chip green density was 235 kg loose m3, not so low as in Granada because less time spent between piling and chipping (sampled chips moisture was 41.0%). Chipping cycle time (to load a complete chipper container) was 15 min. The full load of the chipper container was 22 loose m3 volume, while the trailer bulk capacity was 34 m3, so two uncomplete unloading operations filled a full trailer. The tractor was supposed to have the same productivity as the chipper, but having a lot of waiting time. That is acceptable because the tractor is much cheaper than the chipper. The most expensive machine would only have to stop if hauling distance reached 1.5 km, when an additional tractor would have been needed.
3.1.3.
System 3: stumps removal and shredding
Time study lasted 53 h during October and November 2007. Analyzed phases were stump extraction and shredding. Stumps extraction Productivity following IUFRO standards was 66 stumps$work hour1, corresponding, at 25% moisture, to 11.1 tonnes (8.3 odt). Controlled worksite time was 4 h. After stumps extraction, several machines were tried to transport the stumps to a big heap where the grinder would comminute them. The most productive one was a wheeled bucket loader, that reached 119 stumps$work hour1 (equivalent to 20.1 tonnes at 25% moisture or 15.5 odt). It had the disadvantage of carrying much sand and stones, which in some occasions may not be an important constraint, but frequently is. A reasonable alternative is a dumper truck equipped with a crane, although in the present case the dumper was loaded by the bucket loader with an estimated productivity of 66 stumps$work hour1 (11.1 tonnes at 25% moisture or 8.3 odt) for a 200e400 m distance e 3 trips per work hour, 22 stumps per cycle. Fixed shredding The productivity according to IUFRO standards was 46.7 stumps$productive hour1 (7.9 biomass tonnes at 25% of moisture, 5.9 odt), 36.2 stumps$work hour1 (6.1 green tonnes, 4.6 odt) or 34.0 stumps$worksite hour1 (5.7 green tones, 4.3 odt). Shredding productivity using only the
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Table 3 e Relocation and (Direct D relocation) unit costs depending of harvesting site surface. System Surface
SYSTEM 1 Biomass harvested (odt), 92.5% efficiency
Biomass harvested (chips loose m3)
Unit relocation cost (V$chip loose m3)
Unit relocation cost (V$chip odt1)
Unit Direct þ relocation cost (V$chip odt1)
Biomass harvested (odt), 88% efficiency
17.3 34.7 52.0 69.5 173 347
102 203 304 405 1013 2026
0.54 0.27 0.18 0.14 0.05 0.03
3.18 1.59 1.06 0.79 0.32 0.16
33.8 32.2 31.7 31.4 31.0 30.8
20.5 41.0 61.6 82.1 205.0 410.1
0.5 ha 1 ha 1.5 ha 2 ha 5 ha 10 ha
Hammel grinding machine was compared to that from the additional use of a screen that removed the stones from the biomass. In the last case, productivity dropped to slightly more than 75%.
3.2.
Harvesting direct costs and logistics aspects
In each of the studied systems, the direct costs have been estimated from market data and local figures about consumptions. Table 2 shows the estimated hourly costs for every machines, besides the direct costs per timber m3 as well as for chips - or shredded biomass e loose m3, green tonne (at the measured moisture of the sampled chips) and dry tonne (odt) for the different tasks and for the whole work. These values do not include either stumpage price e for the timber; in the case of biomass there is not such a price in these Spanish recovering operations, at the moment, transport, structural and indirect cost or benefits. Average productivities for every studied system, besides their estimated hourly and unit direct costs, are reflected in Table 2.
3.2.1.
SYSTEM 2
System 1
The cost of piling the branches and energy wood, as long as this operation is necessary for plantation management but must be performed more carefully, has been attributed 80% to timber and 20% to chips. Regarding the relocation costs, the described system operates within a maximum radius of 40 km from the sawmill. Moreover, there is a good rural road network, so machines are transported by driving from one site to another. Average transport time is 30 min, so relocation cost was half the work hourly cost for each machine. Depending on the plantation size, the quantity to add to the biomass direct costs is shown in Table 3. Relocation cost for the transports of raking tele-charger and tractor with trailer has also been assigned to biomass in a 20%. Thus, relocation unit costs range from 0,16 to 3.18 V$chips odt1 if plantation size varies from 0.5 to 10 ha and direct unit plus relocation costs would then range from 30.79 to 33.81 depending on plantation size (when it varied from 10 to 0.5 ha). Global productivity of the “harvester e chainsaw operator e winch tractor” team (10.9 timber m3$work hour1) corresponds to 5.3 chips m3 (loose volume). The productivity of the “raking tele e charger e chipper e tractor with trailer” team was 20.6 chips m3, so that the biomass team theoretically
corresponds to almost 4 harvesters, that is, four felling teams would be necessary to supply biomass enough to maintain the chipper fully operative. Following the enterprise estimations, chipper yearly work time is 1200 h. This low figure comes partially from deficient logistics, as long as, according to the moving time from one plantation to another, for an average plantation size of 2 ha (405 chips loose m3), moving and settling times should not be more than 1.5 h. If chipping work time per site were 23 h, moving time per year would be 76.6 h. Remaining yearly time for major repairs or other idle times would be more than 400 h, which seems to be much. Besides, the theoretical production in 1200 work hours would be 21 384 loose m3 or some 305 covered 70 m3 trucks. This is still far from the actual figures, so logistics could probably be strongly improved in several ways.
3.2.2.
System 2
The cost of branches piling has been attributed 90% to timber and 10% to chips, because of the ancillary timber related tasks e help to felling, loading logs e balanced the cost to the timber side if compared to the system 1. Regarding logistics, system 2 covers a much wider area than system 1 and average poplar size is greater. These facts lead to e or allow e higher relocation costs; chipper is big enough to need a big special truck, whose average cost was 450 V per trip. Tractor with trailer was transported by another specialized truck, while telescopic loader was moved together with it, with an average cost of 300 V per trip. Depending on plantation size, the relocation unit additional cost is shown in Table 3, ranging from 36.6 to 1.8 V$chip odt1 when plantation size varies from 0.5 to 10 ha. Final direct unit cost is higher than in Granada e from 80.1 to 49.5 V$odt1 at landing when plantation size varies from 0.5 to 10 ha -, but productivity is as high as needed to maintain a “hot chain” production system and supply a much larger biomass amount e in fact, Garnyca Plywood is operating 2 forwarder -mounted chippers. Regarding teams sizing to supply biomass to both chippers, equivalent biomass productivity of chainsaw operator plus front loader is 11.16 chips loose m3 worksite hour1, while chipper and tractor with trailer produce 33.77 loose m3. The two chippers need 6 felling teams. Therefore, the company should maintain six harvesting sites e adequate for biomass collection e at a time, as an average, to have its chippers
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SYSTEM 2
SYSTEM 3
Unit Unit Biomass Unit Direct þ Biomass Unit Biomass Unit relocation Direct þ produced relocation harvested relocation produced relocation cost relocation (odt), cost (chip loose m3) cost (V$chip cost (V$chip (stump units) (V$shredded odt1) cost (V$chip odt1) unknown (V$shredded loose m3) biomass odt1) efficiency biomass odt1) 123 246 370 493 1230 2460
6.10 3.05 2.03 1.52 0.61 0.30
36.6 18.3 12.0 9.2 3.7 1.8
80.1 64.0 58.6 55.9 51.1 49.5
operative. Yearly production, if both machines reached the supposed 1800 work hours, would be 120,000 chips m3 loose volume, that is, 1350 mobile platform 90 m3 trucks. In fact, the company does not obtain so much, but present yearly production is closer to the theoretical capabilities than in system 1, due to the bigger enterprise and plantation sizes, that allow a better planning.
3.2.3.
System 3
In this case, stump extraction/piling costs are not charged on biomass, because they are needed for plantation management anyway. The system is not a “hot chain” one: stumps collection occurs later than timber harvesting e time is needed to let stumps get dry. There are high relocation costs, because four machines are moved. Besides, worksites are spotted throughout a large area, so transport distances are longer than in the former cases. Neither backhoe nor bucket loader transport cost must be assigned to biomass production, so only shredder and Manitou transport is considered (420 V). An advantage of the truck-mounted shredder is that it does not need a special transport. Unit relocation costs referred to green and oven dried weight and to stump units are shown in Table 3. They range from 23.9 to 1.2 V$odt1 when plantation size varies from 0.5 to 10 ha, and direct plus relocation costs at landing range from 52.3 to 29.6 V$odt1, indicating that stumps extraction in small plantations must be avoided. These costs may only be competitive in large plantations, even considering that biomass must be transported, screened and refined e chipped e because the obtained product is coarse and stony. Some coordination with plantation owner is needed because possibly he/she will ask the biomass company to share stumps removal and piling costs. These facts must increase the cost and make logistics difficult.
4.
Discussion
Two out of the three Poplar biomass recovering cases studied dealt with branches and tops collection. In both sites, harvesting method was terrain chipping, that has been progressively less used in Nordic Countries [7], but it is well adapted to the Spanish Poplar plantations clearcuts prevalent conditions
17.6 35.3 52.9 70.5 176.2 352.5
139 278 417 556 1390 2780
23.9 11.9 8.0 6.0 2.4 1.2
52.3 40.3 36.4 34.4 30.8 29.6
e plain terrain, densely piled biomass before residues burning. Anyway, certain changes in the conventional timber and residues harvesting operations were needed, in order to get a denser biomass accumulation in strips, trying to avoid stones and much sand. The appropriate biomass piling is essential for an optimized chipper feeding, which is the basis factor to improve the efficiency of residual biomass chipping [8,9]. In both sites, the different involved companies used tractors with trailer as “shuttles” for hauling the chips off, to avoid the chipper to be involved in expensive hauling tasks. The System 1 corresponds to medium-sized poplars (dbh ¼ 25 cm) whose destination was sawmilling within a small supply radius. In this case, the harvested biomass was estimated in 34.7 odt ha1, equivalent to 159.5 MWh ha1 [10]. The chipper was coupled to a moderate power farm tractor (210 HP), fitting to the strength requirement but with a productivity of 3.05 odt$work hour1, well behind the figures corresponding to this power in fixed chipping [11]. The System 2 corresponds to larger poplar clearcuts (dbh ¼ 35 cm), whose main destination was plywood. Branches, tops and energy wood up to a diameter of 14 cm, produced a harvested estimated amount of 41.0 odt ha1, equivalent to 188.6 MWh ha1 [10]. In this case, the chipper was integrated in a forest forwarder, with its own 550 HP engine. Productivity is higher than in system 1, as productivity grows with engine power, reaching 4.68 odt$work hour1, also well behind the productivity attributed to this power range for chipping at landing [11]. The higher productivity corresponded to a larger company which worked within a bigger supply radius and required more biomass per day. Nevertheless, the direct and fixed (relocation) unit costs of chips at landings were higher for the System 2 (49.5e80.1 V$odt1 in front of 30.8e33.8 V$odt1 for system 1, which is equivalent to 10.76 to 17.4 V$MWh1 for system 2 e very sensitive to plantation size e in front of 6.7e7.3 V$MWh1 for system 1). In the last case, the moderate cost is associated with a productive system confined to a smaller supply radius, using less productive but cheaper machines with more reduced relocation costs. The System 1 costs are similar to the referenced ones for biomass harvesting in Nordic conifer plantations clearcuts without transport, while system 2 cost are clearly greater [10,12]. Given the gentle conditions and easy access of poplar clearcuts, and the need of residuals management inside the conventional logging systems, it should be easily possible to reduce these
b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 5 7 0 e2 5 8 0
observed costs. Some possibilities lies in improving the present harvesting systems e several bottlenecks have been identified e or in trying different logistics alternatives, such as those based on chipping at landing. The third studied biomass harvesting system consisted of the stump extraction, collection and shredding after a clearcut in a poplar plantation similar to the last one (dbh ¼ 32.1 cm). Estimated biomass production reached 35.3 odt ha1, equivalent to 178.6 MWh ha1 [2,10]. Poplar root biomass production is much higher than references from Italy [13], probably because poplars were larger, but also to the fact that the weight estimation has been based on weight tables [2]. Stumps were extracted using backhoe excavators with conventional implements, as in more than 50% of the cases in Finish stumps recovery operations [7]. Nevertheless, the energy destination of the stumps, besides the particular morphology of poplar roots, could make interesting to try dedicated implements, such as the Pallari-type lifting device equipped with splitting knife used in conifer stands in Scandinavia, or the auger-type extractors attached to general-purpose prime movers used in Italy, Hungary and the Balkans in poplar plantations [13]. In the studied case, direct plus fixed (relocation) unit cost of shredded biomass at landing range, depending on plantation size, between 29.6 and 52.3 V$odt1, equivalent to 5.8 to 10.3 V$MWh1. Costs are also quite sensitive to plantation size, and they are indeed high, having into account that they only refer to in situ shredding direct costs plus machines transport costs. Productivity and cost of stumps extraction are worse than referenced [10,13], so the harvesting system could be strongly improved. In Finland or Sweden, logistic chains based on chipping at terminals are much more common than chipping or shredding at landings [7,10]. This can be an interesting alternative method to be tried for poplar stumps biomass recovery operations in Spain. The possible combination of branches and tops collection with the stumps recovery would also constitute an interesting option, very convenient also in terms of CO2 emissions [10].
5.
Conclusions
Three residual forest biomass harvesting methods have been analyzed in Spanish hybrid poplar plantations. System 1 consists of a medium-sized chipper attached to a farm tractor for biomass chipping in small-sized plantations with small unit volume and limited to moderate transport distance. Another tractor with trailer hauled the chips off. System 2 is based on two powerful chippers mounted on forest forwarders and complemented with high capacity farm tractors with specialized trailers and large mobile platform trucks. System 3 is based on after-logging stumps extraction and shredding, and the studied machine covers a large area where poplar stumps are not the only alternative for its grinding work, but also non-forest residues. Biomass growing stocks have been estimated. Medium-sized (25 cm d b h) and higher density (714 trees$ha1) plantation e System 1, for a reduced top diameter - 8 cm, yielded 0.48 chips loose m3 timber o.b. m3 (37.5 odt ha1). In the System 2 case, with bigger poplars (35 cm d b h), smaller density (400 trees$ha1)
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and a larger top diameter e 14 cm, produce 0.68 m3 loose volume of chips per timber o.b. m3 (46.7 odt ha1). For System 3, the dry estimated weight for a 32.1 cm dbh poplar stump was 127 kg, so the 278 trees$ha1 plantation produced 35.3 odt ha1. Operations productivity and cost have been analyzed, including timber harvesting operations; averages figures, some tables and predictive equations for some tasks are provided. System 2 has shown to be the most productive, but high relocation costs make it interesting only for large enterprises and plantations. System 1 is less efficient, but its competitiveness lies in the reduced relocation cost and small investment needs. Nevertheless, logistic troubles increase the theoretical costs, because it is hard to get the chipper fully operative in this case. System 3 is cost-competitive in larger plantations but produces a worse biomass quality and has logistic difficulties. It is convenient to have other alternatives to shred; if not, it should be implemented by a company controlling many poplar plantations. Logistic aspects have also been analyzed: for system 1, four felling teams are needed to feed the chipper and for system 2, six felling teams are needed for both chippers -; potential annual production has been estimated too (21 000 and 60 000 chips m3 per chipper for systems 1 and 2). Some comments about each system operative bottlenecks and opportunities have also been provided. Trials covering chipping at landing for branches and tops, as well as terminal chipping in the stumps case are recommended, while the integration of stumps, branches and tops recovery is considered as an advantageous alternative.
Acknowledgments We are indebted to the CESEFOR Foundation for the Promotion of Forestry and Forest Industry in Castilla y Leo´n Region (Spain), that funded that applied research and coordinated the field experiences. Also the Forest Regional Service from Castilla y Leo´n Region supported the research. We would like to thank the participant enterprises, Garnica Plywood, Maderas Calero Tejera S.L. and AECO S.A. and to give our best wishes for their professional and personal future to the young Forest Engineers that collaborated in the field work: Luis Garoz, Javier Guinea, Laura Gonza´lez and Tania Garcı´a. Finally, we must thank Mrs. Diane Aird very much because of her kind and efficient help to revise the grammar of our English manuscript, as well as to the Biomass & Bioenergy peer e reviewers, that contributed to improved the original manuscript through their wise suggestions.
references
[1] IDAE (Spanish Institute for Diversification and Saving of Energy). Plan de Accio´n Nacional de Energı´as Renovables de Espan˜a (PANER) 2011e2020. Spanish Domestic Action Plan for Renewable Energies 2010e2010 (in Spanish). Available at: http://www.idae.es/index.php/mod.documentos/mem. descarga?file¼/documentos_20100630_PANER_Espana_ version_final_%255B1%25255D_cdb842de.pdf; June 2010.
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[2] Montero G, Ruiz-Peinado R, Mun˜oz M. Produccio´n de biomasa y fijacio´n de CO2 por los bosques espan˜oles. Monografı´as INIA, Serie Forestal, n. 13th ed. Madrid: Instituto Nacional de Investigacio´n y Tecnologı´a Agraria y Alimentaria; 2005. In Spanish (English summary). [3] Ambrosio Y, Tolosana E. El control de tiempos y rendimientos en los trabajos forestales. El programa Kronos, Montes 87 (2007) 14e20, In Spanish, Madrid; 2007. [4] Bjorheden R, Thompson MA. An international nomenclature for forest work study. In: Field DB, editors. In: Proceedings of IUFRO 1995 S3.04 Subject area: 20th World Congress; Tampere, Finland: University of Maine: 190e215. Orono, Maine; 2000. [5] De Menthiere N. Harmonization of ongoing european research in the field of harvesting operations. In: Proceedings of IUFRO XX World congress. 6e12 August 1995. Tampere, Finland. Caring for the forest: research in a changing World. Tampere; 1995. [6] Miyata ES. Logging system cost analysis. Comparison of methods used operating costs of logging equipment. St. Paul, Minnesota: U.S.D.A. Forest Service. North Central Forest
[7]
[8] [9]
[10]
[11] [12]
[13]
Experimentation Station; 1981. U.S.D.A. Forest Service, General Technical Report NC-55. Ka¨rha¨ K. Industrial supply chains and production machinery of forest chips in Finland. Biomass Bioenergy; 2010:1e10. doi: 10.1016/j.biombioe.2010.11.016. Suadicani K. Production of fuel chips in a 50-years old Norway spruce stand. Biomass Bioenergy 2003;25:35e43. Tolosana E. Manual Te´cnico para el aprovechamiento y elaboracio´n de biomasa forestal. Madrid: MundiPrensa e FUCOVASA; 2009. 348 pages [in Spanish]. Eriksson LN, Gustavsson L. Biofuels from stumps and small roundwooddcosts and CO2 benefits. Biomass Bioenergy 2008;32(10):897e902. Spinelli R, Hartsough B. A survey of Italian chipping operations. Biomass Bioenergy 2001;21(6):433e44. Kallio M, Leinonen A. Production technology of forest chips in Finland. Project Report PROP2/P2032/05. 103 pages. VTT Processes; 2005. Spinelli R, Nati C, Magagnoti N. Harvesting and transport of root biomass from fast-growing poplar plantations. Silva Fennica 2005;39:539e48.
Available at www.sciencedirect.com
http://www.elsevier.com/locate/biombioe
Recovering of forest biomass from Spanish hybrid poplar plantations Eduardo Tolosana a,*, Rube´n Laina a, Rocı´o Martı´nez-Ferrari a, Yolanda Ambrosio b a b
E.T.S.I. Montes, Technic University of Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain E.U.I.T. Forestal, Technic University of Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain
article info
abstract
Article history:
Residues recovering from traditional poplar plantations for timber production are
Received 12 May 2009
a potential relevant biomass source in Spain and other temperate countries. Three
Received in revised form
different residual biomass harvesting systems have been work-studied in order to char-
7 February 2011
acterize the work methods and analyze their productivity and cost. Two were oriented to
Accepted 10 February 2011
branches, top and/or energy wood collection, chipping and transport using different work
Available online 22 April 2011
methods, while the other one consisted of after-logging stumps removal and shredding. Different sized and powered chippers worked in the two first cases, besides different farm
Keywords:
tractors with trailers for off-road chips transport. Also the trucks and the loading machines
Populus
were different. In the third site, a backhoe excavator removed the stumps, and a bucket
Residual forest biomass
loader collected them to be grinded by a shredding machine. Productivity and cost have
Harvesting techniques
been analyzed using IUFRO standards, providing average figures and, when possible,
Work study
predictive productivity equations. Most capital-intensive equipment option has shown to
Logistics
be most productive, but less investment requiring system is cheaper and may be most
Spain
interesting for some enterprise and plantation sizes. In addition, logistics of biomass and timber supply has been analyzed, and some indications about equipment sizing, machine annual production and relocation costs related to supply area and average plantation size are provided. ª 2011 Elsevier Ltd. All rights reserved.
1.
Introduction
According to the RES National Action Plan 2011e2020 [1], Renewable Energies contributed in Spain to a 9.4% of primary energy consumption in 2009, being the goal for 2020 a share of 20.1%. Regarding electricity production, RES had a contribution in 2009 of 24%, being the objective for 2020 to reach a 36%. Focusing in biomass and biogas, they are supposed to grow up at a yearly rate between 7 and 12.6% during the period 2009e2020. The measures fostering the energy use of forest and agricultural products or residues, besides woody crops, are
supposed to have as result an additional consumption of 5.5$106 tonnes$year1. This aim would require huge efforts to mobilize every biomass sources, particularly woody biomass [1]. Hybrid poplar (Populus x euroamericana ¼ P. x canadensis) plantations are one of the main timber resources in central Spain. Located along the basins of the most plentiful rivers, they provide roughly 700 000 to 800 000 timber o.b. m3 yearly, around 5% of the annual felling. Cutting system usually combines chainsaw for felling and processing with a wheeled grapple front loader to support oriented felling, move and pile logs off the terrain and pile tops and branches. The same
Abbreviations: RES, renewables energies; IUFRO, International Union of Forest Research Organizations; dbh, diameter at breast height; ob, over bark; odt, oven dried tonne. * Corresponding author. Tel.: þ34 678 459466; fax: þ34 91 5439557. E-mail address: [email protected] (E. Tolosana). 0961-9534/$ e see front matter ª 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biombioe.2011.02.007
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machine loads the timber on trucks that get into the felling plot. Piled branches and tops are usually burnt after some months during which these residuals get dry. A backhoe excavator extracts the stumps in order to avoid sprouting and facilitate plantation, often simultaneously with residuals burning and immediately before the new plantation. These stands have gentle terrain conditions and good accessibility from roads. This should ease the recovery of poplar residuals, which have become the first forest biomass systematically collected in Spanish forests. The goals of this work have been to time study and analyze the productivity, cost and some logistic aspects of three commercial harvesting operations in hybrid poplar Spanish plantations that share the common fact of integrating the biomass recovery of what used to be residuals within the traditional logging operations. As long as the studied sites are very different stands and harvesting systems, the aim has not been to make a comparative study but to provide the detailed results of their time and productivity studies, in order to serve as a reference about representative Spanish poplar logging sites. Another objective has been to provide some logistic considerations and operational recommendations to improve the future planning of biomass recovery from hybrid poplar plantations under similar conditions.
2.
Materials and methods
2.1.
Analyzed work systems
System 1 consisted of the collection of branches and tops e until 8 cm of diameter e using a Helca JCB 528 tele-handler with a purpose-designed raking implement (Fig. 1), after motor-manual felling and mechanized processing of poplar timber whose main destination was a local sawmill. Machines used for felling and processing were a Stihl MS441 chainsaw
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and a Keto harvesting head mounted in a Komatsu wheeled backhoe excavator. After timber hauling off, terrain chipping with a Pezzolato 480/660 chipper attached to a 210 HP Fendt 916 farm tractor followed on site biomass piling (Fig. 2). A Valmet tractor with trailer extracted and dumped the chips on a landing chip pile. Finally, a Caterpillar wheeled bucket loader deposited the chips on 70 loose m3 trailer trucks. This site was near Santa Fe, in Granada province, southern Spain. The operations took place during May, July and October 2007, affecting a 1.8 hectares plantation, with a density of 714 trees ha1 and an average diameter of 25 cm. Timber accounted for 453 o.b. m3 ha1. A sawmilling company called Maderas Calero Tejera S.L., which owned the machinery, used the timber and sold the chips to a particleboard factory, performed the operations. Biomass production was 65.8 tonnes ha1 at 43% of moisture measured in fresh biomass samples, equivalent to 37.5 odt or 219 chips loose m3 ha1. That is, for a top diameter of 8 cm, 0.484 chip m3 (loose volume) or 82.8 dry kg timber o.b. m3. System 2 followed a motor-manual felling of 401 larger poplars$ha1 whose main destination was plywood. It consisted of bunching similar branches and energy wood e up to a 14 cm top diameter e, now using a grapple front loader with another attached raking implement, also specifically designed to pile branches and tops without carrying together stones or sand. An Erjo Oswald chipper with its own 550 HP engine, integrated in a John Deere 1410 D forwarder, chipped the biomass, loading a Spanish Santamarı´a Fliegl Gigant trailer attached to a John Deere 8400 farm tractor. The trailer was equipped with a scraper hydraulic conveyor which permits a quick backwards unloading operation to a large chip heap, at the landing (Fig. 3). Afterward, a light Manitou telescopic loader deposited the chips on a 90 m3 bulk volume truck e an aluminum trailer with mobile platform -.This site belongs to Santa Cristina de la Polvorosa municipality, Zamora province, central north-western Spain. Garnica Plywood, the main
Fig. 1 e Tele e handler piling biomass from poplar branches and tops (System 1).
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Fig. 2 e Pezzolato chipper attached to farm tractor blowing chips to the trailer of the forwarding vehicle (System 1).
poplar plywood manufacturer in Spain, performed the operations. Operations were studied in September and November 2007.Poplar plantation surface was 1.5 hectares where 601 trees were felled, with an average d.b.h. of 35 cm, yielding 621.5 timber o.b. m3. Biomass production was 99.4 tonnes$ha1 at 53% of moisture measured in fresh biomass samples, equivalent to 46.7 odt or 280 chips loose m3 ha1, so for the 14 cm top diameter, 112.24 dry kg or 0.675 chips loose m3 timber o.b. m3 were produced. System 3 consisted of the stumps removal, piling and shredding in a poplar plantation, following a motor-manual
timber harvesting for plywood as main product. A Daewoo OLC-V backhoe loader extracted the stumps, that were collected and piled on a big heap using a Hanomag 66 D wheeled bucket loader and, after a month period, were grinded by a Hammel 750 DK shredder with counter-rotating shafts, fed by means of a light Manitou telescopic loader, that was followed by a Komptech Multistar M3 screen in part of the trials (Fig. 4). The site was close to Carrio´n de los Condes village, Palencia province, central northern Spain. The plantation covered 18.4 ha, with a density of 278 trees$ha1 and an average dbh of 32.1 cm. The enterprise in charge,
Fig. 3 e Special trailer unloading chips (system 2).
b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 5 7 0 e2 5 8 0
Aprovechamientos Ecolo´gicos (AECO) S.A., is specialized in comminuting forest and other residues. Total biomass production over a 9300 m2 surface was estimated in 35.3 odt ha1e47.0 tonnes ha1 at 25% of moisture over humid weight -, coming from 278 stumps ha1.
2.2.
Forest inventory and biomass estimation
In all the cases, the Forest Services provided a detailed inventory in which every dbh was measured. Regarding biomass estimation, in the plantations corresponding to the systems 1 and 2, a couple of trees belonging to each diameter class were felled and measured. Weight tables were fitted and the results regarding biomass e not including timber e are shown in Fig. 5, where “Weight” refers to a moisture percentage of 46 and 53% over humid basis, respectively for the systems 1 and 2. These figures were obtained by oven drying 3 samples from different sizes of branches and leaves from each sample tree, at 105 C until constant weight. In the case of System 3, felling was over when the time study crew got to the site, so it was not possible to weigh tree samples. Besides, biomass was not been transported, so it was not possible to get weight data of shredded material from a certain stumps number. The estimation of stumps weight is based upon the Spanish most recent set of root biomass equations [2]. As long as they refer to dry weight, the green weight estimations have considered a moisture percentage of 25% over humid basis, close to the observed figures in similar materials.
2.3.
Time studies
As long as logging was integrated to the residuals recovery in the case of systems 1 and 2, the productivities and costs of felling, processing and residues piling were affected by the
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intend to most efficiently collect the biomass afterward. Because of that, the time studies of every logging operations were carried out. The time study methods were different depending on the task type: if it were a cyclical one, performed by a single actor e for example, a chainsaw operator felling and processing trees or a single tractor hauling the timber off e the continuous control method was the procedure adopted, using a Psion Workabout hand-held computer with the purposedesigned software Kronos 3.0 [3]. In case the operation were not cyclical or were performed by more than an actor e for example, chipping at landing or motor-manual processing by several operators, the “stopwatching” method was chosen: the controller registered, when a chronometer beeped, the work phase performed by each worker observed following a pre-fixed sequence. Time studies are always combined with productivity control, in different ways depending on the operation: if it dealt with trees, they were counted; if it had to do with tractor loads, their number was registered, or even the bulk volume of each load was measured. In any case, the time dedicated to a certain work piece was put in relation to the timber volume or biomass weight produced. When the estimation was indirect e through the number of trees and a weight table, for example -, it was obliged to measure the biomass percentage left on the terrain, by weighing the biomass left in several 10 m radius circular plots in each site.
2.4.
Time and productivity analysis
Time has been classified using the IUFRO standards [4], with the table formats developed by the European Concerted Action AIR3-CT94-2097 [5]. Coefficients relating work time with productive or worksite time have been calculated. Where the continuous method for time studying was chosen,
Fig. 4 e On the right side, the telescopic loader feeds the shredder with poplar stumps. On the left side, the screen and on the back, the backhoe excavator (System 3).
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Fig. 5 e Biomass weight curves from sites corresponding to systems 1 and 2.
predictive equations have been fitted by means of standard statistics software (Statgraphics, SPSS).
3.
Results
2.5.
3.1.
Productivity
Cost estimation
3.1.1. System 1: terrain chipping with Pezzolato 480/660 attached to farm tractor
Machines and operators hourly costs were estimated using classical methods [6]. Once work time is defined as the common basis for calculations, hourly cost and productivity have been expressed regarding to work time. It allows estimating the direct unit cost on a production basis (timber o.b. m3, biomass odt and/or loose m3). Relocation costs have been derived from the number and kind of machines to be transported and the transportation distance or cost among biomass harvesting sites for plantation sizes between 0.5 and 10 hectares.
Felling & processing Productivity according to IUFRO standards was, for the harvester, 17.4 timber o.b. m3$productive hour1e10.9 m3$work hour1 or 9.9 m3$worksite hour1. Controlled timber was 217 m3, with a 760 kg m3 density. Time study lasted 22 h. There was some lack of coordination between chainsaw operator and harvester, leading to low percentages of productive time related to worksite time (57% for harvester, 45% for chainsaw operator). Additionally, a 150 HP farm tractor
Table 1 e Time and productivity table for chipping (System 2). ERJO CHIPPER MOUNTED ON JOHN DEERE FORWARDER
Productive Time (direct)
Work Time
Productivity, chips (m3 loose volume·work hour-1)
TIME %
Machine movement
86
5.42
Crane approaching to a load
219
13.70
Feeding
218
13.60
Waiting for a load to be chipped
58
3.58
Unloading
83
5.21
Breakdowns / repairs
127
12.68
Waiting for other system elements
8
0.51
Refueling
32
3.27
Knives change
273
27.91
Other tasks
28
2.86
Meals
110
11.26
11.26
11.26
TOTAL
1242
100.0
100.0
100.0
47.23
Productivity (tonnes·work hour-1)
Productive Time 16.96
Productive Time 72.20
41.51
88.74
Indirect Work Time
Not Work Time
TIME (min)
Work Time 33.77
Worksite Time 29.97
Work Time 7.93
Worksite Time 7.04
Table 2 e Hourly costs, productivities and unit costs. Hourly costs and Productivities Work System
System 1
Operation
Timber felling & processing
Chip forwarding TOTAL COST System 2
Timber felling & processing Timber hauling off, branches piling and help to felling Branches and energy wood Chipping Chip forwarding TOTAL COST
Hourly costs (V$work hour1)
Chainsaw operator Harvester Winch tractor Tractor w/trailer Raking tele-charger
15.22 55.63 34.4 36.45 35.41
Chipper Tractor w/trailer
74.69 36.45
Productivity (timber m3$ work hour1)
Productivity (chip green tones work hour1/odt $ work hour1)
Productivity (chips loose m3 work hour1)
V$timber o.b. m3
Chipper Tractor w/trailer
22.3 59.97 149.31 50.32
Stump extraction Stumps hauling off and piling Stumps shredding
Backhoe loader Wheeled bucket loader Grinder Hammel machine þ Manitou loader TOTAL COST (Not including stump removal, only shredding)
74.00 48.00 130.00
V$chips loose m3
e
e
9.65
e
e
e
18.58 41.95 equivalent timber m3 e e
e 3.44/3.05
e 17.82
1.96 0.68
e 23.77
e 26.80
e 4.59
10.73/9.52
56.16
3.83 30.63
0.65 5.24
e 3.88
e 0.53
16.54 16.54
e 2.62/1.55 (eqiv.)
e 11.16 (equiv.)
1.36 3.26
3.40 27.17 (11.3% moisture) e 2.29
e
7.93/4.68
33.77
e
19.6
33.22
4.42
7.93/4.68
33.77 4.62
6.35 28.24 (41.0% moisture)
10.76 47.86
1.49 6.44
V$shredded V$shredded V$stump1 biomass biomass odt1 green tonne1
Productivity Productivity (shredded Hourly costs (V$work hour1) biomass tonnes$work (stump number$ work hour1) hour1, 25% moisture/ 1 odt$$work hour ) System 3
V$chips odt1
10.91
12.29 Chainsaw operator Wheeled Front Loader
V$chips green tonne1
11.3/8.48 20.1/15.1 6.11/4.58
65.9 119.0 36.16
e
6.55 2.38 21.28
8.73 3.17 28.37
1.12 0.40 3.60
e
21.28 (25.0% moisture)
28.37
3.60
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Timber hauling off Branches and topspiling and Chipping
Machinery
Unit direct costs
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equipped with winch was present during this task, being utilized to support felling operation when felling direction was dangerous or complicated. Its productivity has been considered the same as the felling team, but its percentage of productive time was very low e less than 25%. Timber hauling off A productivity equation was fitted using the continuous time-study data.
A productivity over work time equation (3) was fitted for both machine and operator involved in felling and processing tasks. Main explanatory variables were d.b.h.(cm) and branch abundance e codified as 1 for large branched or bifurcated trees, and as 0 in other casese 1 268 þ 0:026$DBH2 ¼ 6000$Vu m3 $tree1 Prod m3 $wh þ 2:59$DBH þ 17:5$BRANCHCODEð0=1Þ
TWS ðcmin=cycleÞ ¼1681:05 þ 10:83$NL þ 5:29$HD;
R2 ¼ 98:3%
(3) ð1Þ
where TWS is worksite time, NL is the number of logs forwarded per load as an average, 77- and HD is the hauling distance (one way, m, 50e200 m, 95 m as an average). Average log volume was 0.13 m3, so the correspondent productivity equation is 1 ¼ 0:13$NL$6000=ð1681 þ 10:83$NL Prod m3 $worksite hour þ 5:29$HDÞ
(2)
Piling biomass and mobile chipping Chipping productivity was 17.8 loose m3$work hour1, 3.05 odt$work hour1 or 3.43 tonnes at 11.3% moisture - with 193 kg$loose m3 density e. Chips were so dry because of the delay between felling and chipping more than a month during Spanish summer. Although the chipping task was efficient - the chipper was blowing chips 69% of the productive time -, figures drop when referred to work time, because of the waiting times due to the lasting trailer change when it got full (29% of worksite time). This was the main system bottleneck. There is an additional non-registered time, due to blades maintenance out of the worksite. Control time was 9.4 h. A farm tractor equipped with a tele-handler with a specifically designed raking implement piled the biomass. Its productivity was also low, because it worked simultaneously with the chipper, not only making branches piles or stripes, but also pushing biomass toward the chipper crane to facilitate feeding operation, avoiding sand or stones. Global productivity was, then, the same as the chipper one. Efficiency of biomass collection was high, measured branches left on the terrain were only 7.5% of their estimated total amount. Chip forwarding Chips were transported to a landing where 70 m3 covered trailers could access. The terrain transport distance was 4.8 km and the average work time per cycle was 31 min. As the average load size was 29 m3 bulk volume, the productivity figures were 56.16 loose m3 work hour1 (10.84 tonnes at 11.3% moisture or 9.64 odt).
3.1.2. System 2: terrain chipping with Erjo Oswald integrated to a John Deere 1420D forwarder Felling & processing Productivity following IUFRO standards was 30.4 o.b. timber m3 productive hour1 (21.7 m3 work hour1 or 16.5 m3$worksite hour1). Controlled timber was 1046 m3 or 571 tonnes, for a 546 kg m3 density. Time study lasted 63 h. Productivity figures are much higher than for the system 1, due to the bigger tree dimensions. Anyway, there was some lack of coordination between implied actors, leading to low percentages of productive time related to worksite time (53.4 for chainsaw operator, 58% for wheeled front loader).
The branch code may also be used as an estimation of the ratio of heavy branched or bifurcated stems. As the ratio was 25%, Branch code ¼ 0.25. Cycle time is much more sensitive to diameter than to the branch code. Productivity for wheeled front loader was 28.6 o.b. timber m3$productive hour1, 22.3 per work hour and 16.5 per worksite hour. Besides piling the timber, the front loader hauled the timber off and loaded the logs on the trucks. Additionally, it piled the biomass, so 10% of its operational cost was charged to it. Branches left on terrain were sampled, accounting for a 12.0% of the estimated yield. Mobile chipping & chip forwarding Productivities following IUFRO standards are shown in Table 1. Studied time was 21 h. Chip green density was 235 kg loose m3, not so low as in Granada because less time spent between piling and chipping (sampled chips moisture was 41.0%). Chipping cycle time (to load a complete chipper container) was 15 min. The full load of the chipper container was 22 loose m3 volume, while the trailer bulk capacity was 34 m3, so two uncomplete unloading operations filled a full trailer. The tractor was supposed to have the same productivity as the chipper, but having a lot of waiting time. That is acceptable because the tractor is much cheaper than the chipper. The most expensive machine would only have to stop if hauling distance reached 1.5 km, when an additional tractor would have been needed.
3.1.3.
System 3: stumps removal and shredding
Time study lasted 53 h during October and November 2007. Analyzed phases were stump extraction and shredding. Stumps extraction Productivity following IUFRO standards was 66 stumps$work hour1, corresponding, at 25% moisture, to 11.1 tonnes (8.3 odt). Controlled worksite time was 4 h. After stumps extraction, several machines were tried to transport the stumps to a big heap where the grinder would comminute them. The most productive one was a wheeled bucket loader, that reached 119 stumps$work hour1 (equivalent to 20.1 tonnes at 25% moisture or 15.5 odt). It had the disadvantage of carrying much sand and stones, which in some occasions may not be an important constraint, but frequently is. A reasonable alternative is a dumper truck equipped with a crane, although in the present case the dumper was loaded by the bucket loader with an estimated productivity of 66 stumps$work hour1 (11.1 tonnes at 25% moisture or 8.3 odt) for a 200e400 m distance e 3 trips per work hour, 22 stumps per cycle. Fixed shredding The productivity according to IUFRO standards was 46.7 stumps$productive hour1 (7.9 biomass tonnes at 25% of moisture, 5.9 odt), 36.2 stumps$work hour1 (6.1 green tonnes, 4.6 odt) or 34.0 stumps$worksite hour1 (5.7 green tones, 4.3 odt). Shredding productivity using only the
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Table 3 e Relocation and (Direct D relocation) unit costs depending of harvesting site surface. System Surface
SYSTEM 1 Biomass harvested (odt), 92.5% efficiency
Biomass harvested (chips loose m3)
Unit relocation cost (V$chip loose m3)
Unit relocation cost (V$chip odt1)
Unit Direct þ relocation cost (V$chip odt1)
Biomass harvested (odt), 88% efficiency
17.3 34.7 52.0 69.5 173 347
102 203 304 405 1013 2026
0.54 0.27 0.18 0.14 0.05 0.03
3.18 1.59 1.06 0.79 0.32 0.16
33.8 32.2 31.7 31.4 31.0 30.8
20.5 41.0 61.6 82.1 205.0 410.1
0.5 ha 1 ha 1.5 ha 2 ha 5 ha 10 ha
Hammel grinding machine was compared to that from the additional use of a screen that removed the stones from the biomass. In the last case, productivity dropped to slightly more than 75%.
3.2.
Harvesting direct costs and logistics aspects
In each of the studied systems, the direct costs have been estimated from market data and local figures about consumptions. Table 2 shows the estimated hourly costs for every machines, besides the direct costs per timber m3 as well as for chips - or shredded biomass e loose m3, green tonne (at the measured moisture of the sampled chips) and dry tonne (odt) for the different tasks and for the whole work. These values do not include either stumpage price e for the timber; in the case of biomass there is not such a price in these Spanish recovering operations, at the moment, transport, structural and indirect cost or benefits. Average productivities for every studied system, besides their estimated hourly and unit direct costs, are reflected in Table 2.
3.2.1.
SYSTEM 2
System 1
The cost of piling the branches and energy wood, as long as this operation is necessary for plantation management but must be performed more carefully, has been attributed 80% to timber and 20% to chips. Regarding the relocation costs, the described system operates within a maximum radius of 40 km from the sawmill. Moreover, there is a good rural road network, so machines are transported by driving from one site to another. Average transport time is 30 min, so relocation cost was half the work hourly cost for each machine. Depending on the plantation size, the quantity to add to the biomass direct costs is shown in Table 3. Relocation cost for the transports of raking tele-charger and tractor with trailer has also been assigned to biomass in a 20%. Thus, relocation unit costs range from 0,16 to 3.18 V$chips odt1 if plantation size varies from 0.5 to 10 ha and direct unit plus relocation costs would then range from 30.79 to 33.81 depending on plantation size (when it varied from 10 to 0.5 ha). Global productivity of the “harvester e chainsaw operator e winch tractor” team (10.9 timber m3$work hour1) corresponds to 5.3 chips m3 (loose volume). The productivity of the “raking tele e charger e chipper e tractor with trailer” team was 20.6 chips m3, so that the biomass team theoretically
corresponds to almost 4 harvesters, that is, four felling teams would be necessary to supply biomass enough to maintain the chipper fully operative. Following the enterprise estimations, chipper yearly work time is 1200 h. This low figure comes partially from deficient logistics, as long as, according to the moving time from one plantation to another, for an average plantation size of 2 ha (405 chips loose m3), moving and settling times should not be more than 1.5 h. If chipping work time per site were 23 h, moving time per year would be 76.6 h. Remaining yearly time for major repairs or other idle times would be more than 400 h, which seems to be much. Besides, the theoretical production in 1200 work hours would be 21 384 loose m3 or some 305 covered 70 m3 trucks. This is still far from the actual figures, so logistics could probably be strongly improved in several ways.
3.2.2.
System 2
The cost of branches piling has been attributed 90% to timber and 10% to chips, because of the ancillary timber related tasks e help to felling, loading logs e balanced the cost to the timber side if compared to the system 1. Regarding logistics, system 2 covers a much wider area than system 1 and average poplar size is greater. These facts lead to e or allow e higher relocation costs; chipper is big enough to need a big special truck, whose average cost was 450 V per trip. Tractor with trailer was transported by another specialized truck, while telescopic loader was moved together with it, with an average cost of 300 V per trip. Depending on plantation size, the relocation unit additional cost is shown in Table 3, ranging from 36.6 to 1.8 V$chip odt1 when plantation size varies from 0.5 to 10 ha. Final direct unit cost is higher than in Granada e from 80.1 to 49.5 V$odt1 at landing when plantation size varies from 0.5 to 10 ha -, but productivity is as high as needed to maintain a “hot chain” production system and supply a much larger biomass amount e in fact, Garnyca Plywood is operating 2 forwarder -mounted chippers. Regarding teams sizing to supply biomass to both chippers, equivalent biomass productivity of chainsaw operator plus front loader is 11.16 chips loose m3 worksite hour1, while chipper and tractor with trailer produce 33.77 loose m3. The two chippers need 6 felling teams. Therefore, the company should maintain six harvesting sites e adequate for biomass collection e at a time, as an average, to have its chippers
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SYSTEM 2
SYSTEM 3
Unit Unit Biomass Unit Direct þ Biomass Unit Biomass Unit relocation Direct þ produced relocation harvested relocation produced relocation cost relocation (odt), cost (chip loose m3) cost (V$chip cost (V$chip (stump units) (V$shredded odt1) cost (V$chip odt1) unknown (V$shredded loose m3) biomass odt1) efficiency biomass odt1) 123 246 370 493 1230 2460
6.10 3.05 2.03 1.52 0.61 0.30
36.6 18.3 12.0 9.2 3.7 1.8
80.1 64.0 58.6 55.9 51.1 49.5
operative. Yearly production, if both machines reached the supposed 1800 work hours, would be 120,000 chips m3 loose volume, that is, 1350 mobile platform 90 m3 trucks. In fact, the company does not obtain so much, but present yearly production is closer to the theoretical capabilities than in system 1, due to the bigger enterprise and plantation sizes, that allow a better planning.
3.2.3.
System 3
In this case, stump extraction/piling costs are not charged on biomass, because they are needed for plantation management anyway. The system is not a “hot chain” one: stumps collection occurs later than timber harvesting e time is needed to let stumps get dry. There are high relocation costs, because four machines are moved. Besides, worksites are spotted throughout a large area, so transport distances are longer than in the former cases. Neither backhoe nor bucket loader transport cost must be assigned to biomass production, so only shredder and Manitou transport is considered (420 V). An advantage of the truck-mounted shredder is that it does not need a special transport. Unit relocation costs referred to green and oven dried weight and to stump units are shown in Table 3. They range from 23.9 to 1.2 V$odt1 when plantation size varies from 0.5 to 10 ha, and direct plus relocation costs at landing range from 52.3 to 29.6 V$odt1, indicating that stumps extraction in small plantations must be avoided. These costs may only be competitive in large plantations, even considering that biomass must be transported, screened and refined e chipped e because the obtained product is coarse and stony. Some coordination with plantation owner is needed because possibly he/she will ask the biomass company to share stumps removal and piling costs. These facts must increase the cost and make logistics difficult.
4.
Discussion
Two out of the three Poplar biomass recovering cases studied dealt with branches and tops collection. In both sites, harvesting method was terrain chipping, that has been progressively less used in Nordic Countries [7], but it is well adapted to the Spanish Poplar plantations clearcuts prevalent conditions
17.6 35.3 52.9 70.5 176.2 352.5
139 278 417 556 1390 2780
23.9 11.9 8.0 6.0 2.4 1.2
52.3 40.3 36.4 34.4 30.8 29.6
e plain terrain, densely piled biomass before residues burning. Anyway, certain changes in the conventional timber and residues harvesting operations were needed, in order to get a denser biomass accumulation in strips, trying to avoid stones and much sand. The appropriate biomass piling is essential for an optimized chipper feeding, which is the basis factor to improve the efficiency of residual biomass chipping [8,9]. In both sites, the different involved companies used tractors with trailer as “shuttles” for hauling the chips off, to avoid the chipper to be involved in expensive hauling tasks. The System 1 corresponds to medium-sized poplars (dbh ¼ 25 cm) whose destination was sawmilling within a small supply radius. In this case, the harvested biomass was estimated in 34.7 odt ha1, equivalent to 159.5 MWh ha1 [10]. The chipper was coupled to a moderate power farm tractor (210 HP), fitting to the strength requirement but with a productivity of 3.05 odt$work hour1, well behind the figures corresponding to this power in fixed chipping [11]. The System 2 corresponds to larger poplar clearcuts (dbh ¼ 35 cm), whose main destination was plywood. Branches, tops and energy wood up to a diameter of 14 cm, produced a harvested estimated amount of 41.0 odt ha1, equivalent to 188.6 MWh ha1 [10]. In this case, the chipper was integrated in a forest forwarder, with its own 550 HP engine. Productivity is higher than in system 1, as productivity grows with engine power, reaching 4.68 odt$work hour1, also well behind the productivity attributed to this power range for chipping at landing [11]. The higher productivity corresponded to a larger company which worked within a bigger supply radius and required more biomass per day. Nevertheless, the direct and fixed (relocation) unit costs of chips at landings were higher for the System 2 (49.5e80.1 V$odt1 in front of 30.8e33.8 V$odt1 for system 1, which is equivalent to 10.76 to 17.4 V$MWh1 for system 2 e very sensitive to plantation size e in front of 6.7e7.3 V$MWh1 for system 1). In the last case, the moderate cost is associated with a productive system confined to a smaller supply radius, using less productive but cheaper machines with more reduced relocation costs. The System 1 costs are similar to the referenced ones for biomass harvesting in Nordic conifer plantations clearcuts without transport, while system 2 cost are clearly greater [10,12]. Given the gentle conditions and easy access of poplar clearcuts, and the need of residuals management inside the conventional logging systems, it should be easily possible to reduce these
b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 5 7 0 e2 5 8 0
observed costs. Some possibilities lies in improving the present harvesting systems e several bottlenecks have been identified e or in trying different logistics alternatives, such as those based on chipping at landing. The third studied biomass harvesting system consisted of the stump extraction, collection and shredding after a clearcut in a poplar plantation similar to the last one (dbh ¼ 32.1 cm). Estimated biomass production reached 35.3 odt ha1, equivalent to 178.6 MWh ha1 [2,10]. Poplar root biomass production is much higher than references from Italy [13], probably because poplars were larger, but also to the fact that the weight estimation has been based on weight tables [2]. Stumps were extracted using backhoe excavators with conventional implements, as in more than 50% of the cases in Finish stumps recovery operations [7]. Nevertheless, the energy destination of the stumps, besides the particular morphology of poplar roots, could make interesting to try dedicated implements, such as the Pallari-type lifting device equipped with splitting knife used in conifer stands in Scandinavia, or the auger-type extractors attached to general-purpose prime movers used in Italy, Hungary and the Balkans in poplar plantations [13]. In the studied case, direct plus fixed (relocation) unit cost of shredded biomass at landing range, depending on plantation size, between 29.6 and 52.3 V$odt1, equivalent to 5.8 to 10.3 V$MWh1. Costs are also quite sensitive to plantation size, and they are indeed high, having into account that they only refer to in situ shredding direct costs plus machines transport costs. Productivity and cost of stumps extraction are worse than referenced [10,13], so the harvesting system could be strongly improved. In Finland or Sweden, logistic chains based on chipping at terminals are much more common than chipping or shredding at landings [7,10]. This can be an interesting alternative method to be tried for poplar stumps biomass recovery operations in Spain. The possible combination of branches and tops collection with the stumps recovery would also constitute an interesting option, very convenient also in terms of CO2 emissions [10].
5.
Conclusions
Three residual forest biomass harvesting methods have been analyzed in Spanish hybrid poplar plantations. System 1 consists of a medium-sized chipper attached to a farm tractor for biomass chipping in small-sized plantations with small unit volume and limited to moderate transport distance. Another tractor with trailer hauled the chips off. System 2 is based on two powerful chippers mounted on forest forwarders and complemented with high capacity farm tractors with specialized trailers and large mobile platform trucks. System 3 is based on after-logging stumps extraction and shredding, and the studied machine covers a large area where poplar stumps are not the only alternative for its grinding work, but also non-forest residues. Biomass growing stocks have been estimated. Medium-sized (25 cm d b h) and higher density (714 trees$ha1) plantation e System 1, for a reduced top diameter - 8 cm, yielded 0.48 chips loose m3 timber o.b. m3 (37.5 odt ha1). In the System 2 case, with bigger poplars (35 cm d b h), smaller density (400 trees$ha1)
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and a larger top diameter e 14 cm, produce 0.68 m3 loose volume of chips per timber o.b. m3 (46.7 odt ha1). For System 3, the dry estimated weight for a 32.1 cm dbh poplar stump was 127 kg, so the 278 trees$ha1 plantation produced 35.3 odt ha1. Operations productivity and cost have been analyzed, including timber harvesting operations; averages figures, some tables and predictive equations for some tasks are provided. System 2 has shown to be the most productive, but high relocation costs make it interesting only for large enterprises and plantations. System 1 is less efficient, but its competitiveness lies in the reduced relocation cost and small investment needs. Nevertheless, logistic troubles increase the theoretical costs, because it is hard to get the chipper fully operative in this case. System 3 is cost-competitive in larger plantations but produces a worse biomass quality and has logistic difficulties. It is convenient to have other alternatives to shred; if not, it should be implemented by a company controlling many poplar plantations. Logistic aspects have also been analyzed: for system 1, four felling teams are needed to feed the chipper and for system 2, six felling teams are needed for both chippers -; potential annual production has been estimated too (21 000 and 60 000 chips m3 per chipper for systems 1 and 2). Some comments about each system operative bottlenecks and opportunities have also been provided. Trials covering chipping at landing for branches and tops, as well as terminal chipping in the stumps case are recommended, while the integration of stumps, branches and tops recovery is considered as an advantageous alternative.
Acknowledgments We are indebted to the CESEFOR Foundation for the Promotion of Forestry and Forest Industry in Castilla y Leo´n Region (Spain), that funded that applied research and coordinated the field experiences. Also the Forest Regional Service from Castilla y Leo´n Region supported the research. We would like to thank the participant enterprises, Garnica Plywood, Maderas Calero Tejera S.L. and AECO S.A. and to give our best wishes for their professional and personal future to the young Forest Engineers that collaborated in the field work: Luis Garoz, Javier Guinea, Laura Gonza´lez and Tania Garcı´a. Finally, we must thank Mrs. Diane Aird very much because of her kind and efficient help to revise the grammar of our English manuscript, as well as to the Biomass & Bioenergy peer e reviewers, that contributed to improved the original manuscript through their wise suggestions.
references
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