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FUELS FOREST WOOD CHIPS

CNR’s ChipCost Project state of the art on a national scale Raffaele Spinelli, C.N.R.

Italy

Working conditions in Italy for the production of woodchips are different from conditions in America or Scandinavia even though Italian companies have the same aim and face the same problems as their foreign colleagues. The National Research Centre (CNR) carried out a survey on the technical characteristics of chippers used in Italy - this survey is briefly presented in the following article.

INTRODUCTION Wood chipping is widespread in Italian forests and many forest companies produce great quantities of chips. In most cases woodchips are a by-product obtained from poor-quality wood. Chipping is the only way to make the

V. FRANCESCATO

Chipping is widespread in Italian forests and many forest companies produce considerable quantities of chips.

WOOD ENERGY N.1 / 2003 38

branches, treetops and thinnings which cannot be used for other products saleable. Obviously the quality of the chips is comparable to the quality of the original material; often the percentage of bark and leaves is too high for the paper industry, unlike the panel industry which can accept chips of

a mediocre quality and represents the main outlet for Italian chippers.

However, the growing bio-energy sector should soon offer better opportunities. Attracted by substantial incentives, many private companies plan to activate thermal and electricity plants of various sizes and capacities which will use biomass as the main fuel. Although the average plant will rarely exceed 15 MW, many projects are underway and some are up and running. The specifics of these projects indicate chips as their primary fuel.

Thus the demand for woodchips should soon undergo a changing trend, benefiting the forest companies which operate near the new plants. The chips will need to be distributed regularly and in large quantities creating considerable organisational problems. In many cases local resources are so diversi-

fied that it is impossible to think of reaching them with just one supply line. Concentrating the whole production from a few industrial operations remains a theoretical ideal which is unlikely to allow for the best exploitation of the resources offered by a territory.

Our study aims to develop a mathematical model which estimates the productivity of chipping in relation to various parameters in order to identify its cost. Such a model is obtained from the analysis of the efficiency of chipping through the study of various parameters (type and size of chipper, feeding system, working system, characteristics of the raw material and the work-station conditions).

Moreover, the model can also be used by those forest companies which decide to begin chip production and must buy the appropriate equipment. In this case the technician can use customised working hypotheses to calculate the various economic results of the given available alternatives.

Since the survey has covered a great variety of sites, the model is flexible enough to cover most situations which may arise in Italy.

THE STUDY The survey includes 102 chipping trials, each one representing a source of datation.

For each trial, we carried out a detailed study of time taken using a precision chronometer. The chipping cycle was divided into three stages: moving, chipping and other (generally the positioning of containers).

The volume of chips produced in each trial was measured with a 20m metric wheel. At least some of the volume was loaded onto a vehicle and weighed on a certified truck scale. We also counted all the pieces of wood (branches, treetops, trunks etc.) put into each load in order to obtain the size of the average chipped piece in each trial.

The work station and weather conditions, the tree type, the machine characteristics, the work system and the number of workers were all recorded on a spread

R. SPINELLI

FUELS FOREST WOOD CHIPS

sheet. In particular we recorded all the information concerning the type of chipper, the feeding method, the presentation of the wood, the container used to collect the chips, and the work system (with a fixed chipper or in the forest). Accidents, breakages, interruptions and other disturbances were separately recorded, but were excluded from the final calculation of the chipping time.

For a trial to be valid it had to last at least half a day or, in any case, long enough to produce at least one load of woodchips. This was based on the hypothesis that all the observed teams already knew their machines well, followed a consolidated procedure and had reached a stable level of productivity.

All the trials were carried out in Italy, except three located on the northern side of the Alps. Of these, two were carried out in Canton Ticino and the third in Bavaria, where the working conditions were comparable to those found in certain parts of Italy.

The 102 trials were carried out by 40 forest chipping companies working in Italy. 31 different wood-chipper models, made by 11 different constructors, were used.

70% of the trials were carried out in hardwood forests, equally split between poplar plantations and

oak, chestnut, beech and locust tree coppices found in four different geographical areas; the Arno Valley, the Po Valley, the Alpine and Apennine Regions.

THE PATTERN OF PRODUCTIVITY

The survey carried out by the CNR aimed to develop a mathematical model to estimate the productivity of chipping in relation to various parameters in order to identify its cost.

Data gathered during the tests underwent statistical analysis to produce a series of mathematical models which represented the observed phenomena as faithfully as possible.

CHIPPING TIMES On average, the time used for chipping represents 85% of the total production time. The time taken to chip a ton of wood is inversely proportional to the power of the chipper and the size of the average piece of wood. Both relationships were foreseeable – the time taken to shred an equal amount of wood drops in proportion to the increase in power of the chipper, and with equally powerful chippers, the speed of transferring wood to the feeder increases as the size of wood being fed decreases.

These relationships can be seen in the following formula:

Chip, min/t = 0.02 + 13.1 / (Price size, t* Engine power, kW) + 566. / (Engine power, kW) R2 = 0,79 n = 99

WOOD ENERGY N.1 / 2003 39

FUELS FOREST WOOD CHIPS This equation can explain almost 80% of the variability observed for chipping times.

Such high accuracy is quite rare in forest work studies, and it shows the importance of the two primary variables. We tried to add the effect of other variables to the programme.

These included the feeding system, the type of wood and its presentation, the type of chipper (disk or drum) and the size of the teams. None of these variables added anything significant to the model above.

MOVING TIMES When the chipping is carried out in the forest, the moving time per ton is inversely proportional to the size of the average piece. This can be explained in the following way; the density of the piles of wood or stacks of trees is proportional to their length and the accuracy of concentration which are generally less for lighter pieces. Thus, when chipping small-size material, the chipper must cover a larger number of piles or a greater length of stacks to obtain a ton of wood, and therefore cover a greater distance.

Contrary to towed or carried chippers, automated ones can be repositioned more quickly because the operator does not have to move two separate machines. In fact, the towed and carried chippers are fed by an independent loader - moving means the operator must first drive the loader to the new position, get off, return to the chipper and take it to the loader. The methods of unloading the chips (in a truck, container, pile etc.) and the accessibility of the terrain do not influence the moving times.

The final formula is the following:

Moving, min/t = 0.584 + 0.00744 (Terrain Var./Piece size,t) - 0.385 (Automated variable) R2 = 0,48 n = 88 Terrain variable = 1 if the chipping is carried where the wood falls, 0 if it is done in a fixed site; Automated variable = 1 if the chipper is automated, 0 if it is not.

A. BRUNORI

The mathematical model developed by the CNR is drawn from the analysis of the efficiency of chipping with a study of various parameters (type and size of chipper, feeding system, working system, characteristics of the primary material and site conditions). The chipping cycle has been divided into three stages: moving, chipping and other.

WOOD ENERGY N.1 / 2003 40

FUELS FOREST WOOD CHIPS

A group of machines – the small chipforwarders – on average requires more thanr 6 extra minutes of production time per ton produced, compared to about one minute required by other machines. This is due to the fact that the small chipforwarders observed in this study all had to cover large deforested distances. The final formula is as shown below.

CALCULATING COSTS The equations illustrated above were used to assemble an integrated model for the calculation of costs.

The model provides the cost of chipping after the user has inserted specific information about the conditions of work and hypotheses of cost. Among other things the model can be used to compare different options. The technician can select several alternative strategies and check the economic result of each one in their own working conditions.

The user has to insert a series of values into the model including the size of the average piece of wood and the power of the chipper. Other data required by the programme includes the purchase cost of the machine, the period of depreciation, labour costs and other expenses.

The machine cost is calculated using systems based on the Miyata method – as used by the United States Forestry Service. These are, however, simple financial formulas.

Several Italian forest companies carry out industrial chipping. Most started in the mid-1980s, and now have considerable experience.

Although working conditions are different from American or Scandinavian ones, Italian companies pursue the same objective and face the same problems as their foreign colleagues. The objective is to transform a residue of little value into a commercial product.

The problems are those related to the low value of the final product, which allows little margin for error. For this reason an enormous effort is being made to improve the efficiency of the worksite, reduce costs, and generally optimise the whole production chain.

Italian companies use a wide range of machines. A large number of brands and models of chippers, including American, German and Scandinavian machines, are represented. However, Italian chippers are the most widespread and dominate the market, which probably indicates that Italian technology is now mature, and enjoys a better support network.

Our investigation has covered a great variety of situations, involving over 100 cases. It has generated a model for the calculation of productivity which can be applied to most Italian sites. The model’s high statistical significance makes it a reasonably safe tool for forecasting the site’s performance in relation to the specific working conditions.

The engine power and the weight of the average piece of wood to be chipped are the most important elements for estimating the productivity of a chipper. As well as having a direct influence, these two parameters integrate the effects of other variables such as the type of operator or the feeding method. It is a fact that the most powerful machines are operated by qualified professionals and fed by a crane, while the opposite is true for the lighter ones.

Other important parameters include the working system – chipping in the forests or on a fixed

site - and the type of chipper. The automated chippers are more agile and require less time to reposition, whether they operate in the forest or in the workshop.

All this information is included in the volume “Survey on chipping in Italy”, edited by CNR-IRL in the series “Scientific-Practical Contributions”, numbered XLI. At the present time the model of costs represents a complete management tool, suitable for managers, planners and foresters. It is free and can be downloaded from either the IRL or the University of California websites www.area.fi.cnr.it/irl/irl.htm or www.engr.ucdavis.edu/~bae)

The CNR survey covered a great variety of situations.

It generated a model to calculate productivity, which can be applied to most Italian sites.

R. SPINELLI

The production time catalogued under the general term ‘other’ has also proved to be inversely proportional to the size of the average piece. The reasons are the same as those given for the moving time.

Much of the other production time regards the positioning of the woodchip container under the chipper’s discharge mechanism.

This operation must be repeated each time the machine is moved.

CONCLUSION

R. SPINELLI

OTHER PRODUCTION TIMES

Other time, min/t = 0.20 + 0.0157 / (piece size, t) + 4.72 (Small chipforwarder var.) n = 99 R2 = 0,73 Small chipforwarder variable = 1 if the machine is a small chipforwarder, 0 if it is not.

WOOD ENERGY N.1 / 2003 41