Raida Jirjis

The effect of seasonal storage on the chemical composition of forest residue chips

The changes in the chemical constituents of forest residue chips after seven months of storage under different conditions were determined. Two piles, one indoors and the other outdoors, were set up. Each pile comprised different sections where the chips were stored either loose or compacted. Chemical analyses showed that the Klason lignin contents were increased after storage, especially in the areas where high temperatures were measured. The extractives content declined in most of the tested samples. The uronic acid contents of all the forest residue fractions were clearly reduced after indoor storage. Storage conditions in general affected the needle and bark fractions more drastically than the twigs and wood fractions. The chemical modification of the stored material can be attributed to the microbial activity in the pile as well as to the high temperature which developed in the centre of the different sections leading to various chemical transformations.

Microbial communities in large-scale wood piles and their effects on wood quality and the environment

The demand of renewable energy sources, i.e. biomass, is steadily increasing worldwide to reduce the need of fossil energy sources. Biomass such as energy crops, woody species, forestry and agricultural residues are the most common renewable energy sources. Due to uneven demand for wood fuel, the material is mostly stored outdoors in chip piles or as logs until utilisation. Storage of biomass is accompanied by chemical, physical and biological processes which can significantly reduce the fuel quality. However, heating plants require high-quality biomass to ensure efficient operation, thereby minimising maintenance costs. Therefore, optimised storage conditions and duration times for chipped wood and tree logs have to be found. This paper aims at reviewing available knowledge on the pathways of microbial effects on stored woody biomass and on investigations of the fungal and bacterial community structure and identity. Moreover, potential functions of microorganisms present in wood chip piles and logs are discussed in terms of (1) reduction of fuel quality, (2) catalysing self-ignition processes, and (3) constituting health risk and unfriendly work environment.

Fuel quality of Norway spruce stumps – influence of harvesting technique and storage method

Abstract The interest in using stump biomass as a biofuel has recently increased in Sweden. The uneven consumption of wood fuel during the year creates a need for storage. This study examined the properties of stump biomass and how they vary at two sites in Sweden depending on harvesting technique, storage method and storage period. Norway spruce stumps, extracted using three different stump harvesting heads (Pallari, Rotary Cutter and Aalto), were stored in windrows or heaps. After 3 months, stumps stored in heaps were gathered into windrows. The fuel quality parameters moisture content (MC), ash content (AC) and calorific value (CV) were evaluated on five occasions in the period May 2008–September 2009. After 16 months of storage, the MC in all treatments had decreased to <25% (wet basis). Average AC decreased from 3.8% to around 1% (dry basis), whereas CV marginally increased. Stumps split during harvesting dried better than those harvested in one piece. The influence of storage method was minimal, although initial storage in heaps allowed better drying in the stumps harvested in one piece. In general, fuel quality improved in all treatments after storage.

Simulation-based evaluation of supply chains for stump fuel

Current concerns about climate change and fossil-fuel dependency have intensified interest in renewable energy and increased demand for suitable substrates. Softwood tree stumps could be a very interesting renewable fuel assortment, since large volumes of unutilized stump biomass are available. The stump-root system constitutes about 25% of stem volume. However, optimization of logistics issues within the supply chain of stump fuel is crucial in ensuring low procurement costs, particularly for transport and comminution operations. Bulky stumps can be transported and comminuted in different ways, and if the system is planned properly it can reduce the supply costs and help deliver a fuel at a competitive price. This study evaluated various systems for stump transport and comminution in terms of cutting unnecessary costs and making the systems more resource-efficient. A discrete-event simulation approach was applied, using the ExtendSim simulation software. Simulation results obtained using the model developed show large variations in system performance and system costs. The costs of the best and worst alternatives differed by around a factor of 2, irrespective of transport distance. The most cost-effective option proved to be crushing stumps into the ground and using a self-loading truck for wood fuel transport.

Effects of supply chain strategy on stump fuel cost: a simulation approach.

In Sweden, stump fuel extraction for energy purposes is not a well-established practice and this major resource is currently left in the forest. The stump fuel supply chain is both challenging and complex, due to distance between resource and end user, material bulkiness, and the number of subprocesses involved. This study examined the impact of different aspects such as site characteristics, fuel quality, biomass losses, and machine performance on fuel cost. Two systems, including transport of comminuted and uncomminuted fuel, were studied. Discrete-event simulation was used to model systems and to analyse the dynamics of the supply chain and its various components. For a distance of 10 km, transportation of uncomminuted fuel gave the lowest costs. For distances from 30 to 70 km, site size (odt) determined whether to comminute or not before transport. For longer distances, comminution before transport proved to be necessary. Well-planned stump storage was shown to reduce the delivery costs significantly, while high moisture content (>45%) had detrimental effects on system costs per unit energy delivered. However, the most influential parameters were productivity level and site characteristics (distance and site size).

Experimental determination of the degradation rate for some forest residue fuel components at different temperatures and oxygen concentrations

The microbial degradation of forest fuel materials of Norway spruce, including needles, outer bark and sapwood, is studied under controlled laboratory conditions. In the experiments the temperature is varied between 15–55°C and the oxygen concentration between 1–21 vol%. The experiments were run for up to 59 days. The influences of higher carbon dioxide gas concentration and initial sterilization of the material were also studied. The experiments show quantitatively the functional relations between the degradation rates for the different materials and the oxygen concentration and the temperature. The reaction rate is highest for needles, then bark and last sapwood. Maximal rates of 0.4, 0.2 and 0.05 kg/kg DM/month are obtained, respectively. A, more or less, linear dependence between degradation rate and oxygen concentration is obtained. The temperature dependence shows an optimum in the range between 25 and 40°C. At 15°C the reaction rate is low and at 55∘C it is negligible. Attempts were made to correla...

Cleaning of harvested Norway spruce stumps using a vibration-based method

With the increasing demand for renewable energy in Sweden and Finland, interest in using softwood stumps as biofuel is growing. The major drawback to using these energy-rich stumps as biofuel is the presence of contaminants, which lead to high ash content and thereby lower technical feasibility and value as fuel. To reduce contaminant levels, stumps are normally shaken during extraction, but this process is time-consuming. It is also frequently inadequate, necessitating storage for further cleaning for long periods usually exceeding one year, which can lead to high dry-matter losses. Faster and more effective cleaning methods are therefore highly desirable. A vibration-based method for cleaning, as often used in other industrial sectors, could offer a solution. The reduction in contaminants on stumps harvested from two different soil types was tested using a grid-fitted test-rig bench which could be vibrated in one or three dimensions. The vibration was performed at settings from 1.33 g to 6.15 g. Ash content was reduced by 50% of the initial value after 30 seconds, which in some cases was sufficient to achieve ash content below 4%. The cleaning process was effective regardless of vibration amplitude used or orientation. By employing vibration, clean stumps could be made available as fuel within the same harvesting season. Such rapid removal of stumps would allow prompt site regeneration processes.

Orchards Pruning to Energy – The Results of the Environmental Impact Assessment of the New Logistic Chain Developed within the Europruning Project – Part 2

Abstract To determine the environmental impact, the assessment of the Euro-Pruning project strategy has been carried out in accordance with the checking and scooping list related to Directive 97/11/EC. Additionally, some suggestions and recommendations to prevent/minimize the hazard of accidents or negative interaction on surrounding have been elaborated (according to the suggested procedure in ISO 14001 methodology: risk definition and prevention action proposal). As a consequence, the results of the inspection during the demo tests taking place in different orchards/plantations regarding the performance of the machineries operation, farmers’ habits and pruning residues harvesting procedures have been presented, in order to diagnose and determine possible risks that may occur and influence negatively the local environment. Similar activities have been carried out during the storage tests and transportation processes.