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Kalvis Kons
Department of Forest Biomaterials and Technology, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden

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Journal article
Published: 26 March 2020 in Forests
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The rising throughput of log-yards imposes new constraints on existing equipment and increases the complexity of delivering an optimal and uninterrupted supply of pulpwood to pulp mills. To find ways of addressing these problems by reducing log cycle times, this work uses a discrete-event mathematics model to simulate operations at a log-yard and study the impact of three different log-yard inventory strategies and two alternative machine systems for log transportation between main log-yard and buffer storage. The yard’s existing inventory strategy of last load in and first out limits access to older logs at the main storage site. By allocating space for 89,000 m3 and 99,000 m3 of pulpwood at the buffer storage it is possible to keep the log cycle time at the main storage to a maximum of 12 and 6 months. Additionally, the use of an alternative log transportation machine system comprising a material handler with a trailer increased the work time capacity utilization relative to the yard’s current machine system of two shuttle trucks and a material handler for transporting logs between the main and buffer storage areas. Compared to the currently-used last in first out inventory strategy and purposely emptying the main storage area once or twice per year did reduce the total work time of both machine systems by 14% and 30%. Consequently, the volume delivered from the buffer to the log-yard decreased on average by 17% and 37% when emptying the main storage area once and twice per year. Even with reduced work time when emptying the main storage area, both machine systems could fulfil given work load for transporting logs from the buffer storage to the main log-yard without interrupting operations of the log-yard.

ACS Style

Kalvis Kons; Pedro La Hera; Dan Bergström. Comparison of Alternative Pulpwood Inventory Strategies and Machine Systems at a Log-Yard Using Simulations. Forests 2020, 11, 373 .

AMA Style

Kalvis Kons, Pedro La Hera, Dan Bergström. Comparison of Alternative Pulpwood Inventory Strategies and Machine Systems at a Log-Yard Using Simulations. Forests. 2020; 11 (4):373.

Chicago/Turabian Style

Kalvis Kons; Pedro La Hera; Dan Bergström. 2020. "Comparison of Alternative Pulpwood Inventory Strategies and Machine Systems at a Log-Yard Using Simulations." Forests 11, no. 4: 373.

Journal article
Published: 30 January 2020 in Forests
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This article deals with the topic of modelling the log-yard of one of our industry partners. To this end, our framework is based on discrete-events modelling (DEM), as consequence that many stages of the process run as a sequence of events. The sequence starts when trucks, trains or ships arrive loaded with logs to the log-yard. A machine unloads these logs and accumulates them in different storage areas. Consequently, a machine transports logs from these areas to the pulp mill, thus finishing the process. As using probability density functions is the core concept of DEM, the necessary process data to build these PDFs have been partly provided by the company. Other necessary data have been acquired through time studies, and by defining operational requirements. The company data tell when trucks, trains, or ships arrive to the log-yard, and the amount of volume they carry. The objective is to develop the necessary formulations, model calibration techniques, and software, such that computer simulations reproduce the quantities observed in these data. To this end, this work suggests two alternatives to analyse the data itself. These two alternatives lead to two different models: (1) The first being a hybrid model, in the sense that it involves the events in the process, and the logic decisions taken by machine operators for handling the incoming load, and (2) the second containing only the main mathematical essence of the process. After running 100 simulations, both mathematical models show that the simulated values for input and output, in terms of transport units and their volume, differ only by less than 3% compared to company data. The first model has also shown the ability to replicate the decision making that a machine operator undergoes for driving the logs to the storage areas, and from there to the mill. Therefore, the framework adopted provides the necessary mathematical tools and data analysis to model the log-yard and obtain highly reliable results via simulations.

ACS Style

Kalvis Kons; Pedro La Hera; Dan Bergström. Modelling Dynamics of a Log-Yard through Discrete-Event Mathematics. Forests 2020, 11, 155 .

AMA Style

Kalvis Kons, Pedro La Hera, Dan Bergström. Modelling Dynamics of a Log-Yard through Discrete-Event Mathematics. Forests. 2020; 11 (2):155.

Chicago/Turabian Style

Kalvis Kons; Pedro La Hera; Dan Bergström. 2020. "Modelling Dynamics of a Log-Yard through Discrete-Event Mathematics." Forests 11, no. 2: 155.

Original articles
Published: 04 May 2015 in International Journal of Forest Engineering
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Primary residual forest biomass is an important source of energy in Sweden. The fuel quality of this biomass depends on several factors including its moisture content, ash content, and particle size distribution. For optimal combustion, the fuel should have a low content of fine particles. The objective of this study was to compare these quality metrics for five common fuel assortments produced with a drum chipper operated using two different sieve sizes (standard & large). Sieve size had no significant effect on any of the studied fuel quality metrics. On average, 37–63% of the fuel’s dry mass was distributed in particles of 16–31.5 mm. Because logging residues (tops and branches) contain relatively little stem wood, the average fine particle (˂3.15 mm) content of the fuel produced by their chipping was around 10% greater than that of the other studied assortments. Moreover, the ash content of these fines was 2–3 times greater than that of the fines from other assortments. For all assortments, the ash content decreased rapidly with increasing particle size, levelling out at 1.14% for particles of 16–31.5 mm. The average ash contents of the five assortments ranged from 0.84–2.98%. For all assortments, and logging residues in particular, the fuel quality could be significantly increased by screening out fine particles. However, the economic value of such screening depends heavily on the costs of the refining process and the value/utility of the separated fine particles, which should therefore be investigated further.

ACS Style

Kalvis Kons; Dan Bergström; Fulvio Di Fulvio. Effects of sieve size and assortment on wood fuel quality during chipping operations. International Journal of Forest Engineering 2015, 26, 114 -123.

AMA Style

Kalvis Kons, Dan Bergström, Fulvio Di Fulvio. Effects of sieve size and assortment on wood fuel quality during chipping operations. International Journal of Forest Engineering. 2015; 26 (2):114-123.

Chicago/Turabian Style

Kalvis Kons; Dan Bergström; Fulvio Di Fulvio. 2015. "Effects of sieve size and assortment on wood fuel quality during chipping operations." International Journal of Forest Engineering 26, no. 2: 114-123.

Journal article
Published: 02 September 2014 in International Journal of Forest Engineering
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ACS Style

Kalvis Kons; Dan Bergström; Ulf Eriksson; Dimitris Athanassiadis; Tomas Nordfjell. Characteristics of Swedish forest biomass terminals for energy. International Journal of Forest Engineering 2014, 25, 238 -246.

AMA Style

Kalvis Kons, Dan Bergström, Ulf Eriksson, Dimitris Athanassiadis, Tomas Nordfjell. Characteristics of Swedish forest biomass terminals for energy. International Journal of Forest Engineering. 2014; 25 (3):238-246.

Chicago/Turabian Style

Kalvis Kons; Dan Bergström; Ulf Eriksson; Dimitris Athanassiadis; Tomas Nordfjell. 2014. "Characteristics of Swedish forest biomass terminals for energy." International Journal of Forest Engineering 25, no. 3: 238-246.