Probabilistic assessment of forest biomass storage times and its effect on cost: a beech biomass case study.

Abstract

The storage time of beech forest biomass units in northern Greece were recorded through time studies in different stands, at the roadside, and at the mill yard. Probability distribution of each recorded storage time was assessed. The distribution and cost data were inserted into a simulation model. By running the model the cost for each intermediary storage time was calculated. This cost represents the interest rate cost and the loss value cost due to fiber deterioration of the beech forest biomass units (cord cubic meters) during storage. Results showed that forest site storage adds a cost of 61.12 percent of the total felling cost and 6.30 percent of the total final cost. The roadside storage adds a cost of 59.67 percent of the total cost at the roadside and 19.9 percent of the total final cost. Mill yard storage adds a cost of 61.1 percent of the at-the-mill cost and 53.81 percent of the total final cost. The introduction of a vertical integration in Greek forest biomass operational system is recommended.

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The logistical cost added, due to intermediary storage times where forest biomass units are kept idle at the forest site, forest road, and/or the mill yard contributes an additional cost to forest biomass units entering the process unit at the mill (Gallis 1997). Time of storage is a very crucial factor as this causes additional interest cost to the capital that has been invested to each forest biomass unit that remains actually idle during those storage times (Sierila and Tuominen 1991, Brown 1995, Gallis 2002).

Forest biomass storage time is a typical queuing situation where the biomass units are waiting to be picked up by a machine (Meng 1975). This queuing situation is characterized by the random waiting time of the units (Gallis 1997). Thus, the waiting time could be expressed by a probability distribution (Meng 1975, Meng 1981, Hillier and Lieberman 1995). The availability of field waiting time data and the use of statistical methods may define the probability distribution fitting the data of each intermediary storage.

The main scope of this paper is to define the probability distribution of beech biomass storage time at the stand, the roadside, and at the mill, and its effect on cost. Thus, the probability distribution of storage times were defined on the basis of field measurement. Then the probability distributions were inserted into a SLAMSYSTEM simulation language model built by Gallis (1997) to represent the forest biomass flow from forest to mill yard processing unit. Cost data were also inserted into the model. By running the simulation model, the cost for each intermediary storage was calculated. This cost represented the interest rate cost and the loss value cost due to fiber deterioration of beech forest biomass units (cord cubic meters) during storage. …