Gross calorific value of leaves, bark, and branches of selected deciduous trees

Transactions of the VŠB - Technical university of Ostrava Safety Engineering Series Vol. VII, No. 1, 2012 32 GROSS CALORIFIC VALUE OF LEAVES, BARK, AND BRANCHES OF SELECTED DECIDUOUS TREES Emília ORÉMUSOVÁ1, Linda MAKOVICKÁ OSVALDOVÁ2, Anton OSVALD3 1 Technical univesity in Zvolen, Department of Fire protection, Faculty of wood and science technology, Zvolen, Slovak Republic, [email protected] 2 University of Žilina, Department of Fire engineering, Faculty of special engineering, Žilina, Slovak republic, [email protected] 3 University of Žilina, Department of Fire engineering, Faculty of special engineering, Žilina, Slovak republic, [email protected] Abstract: If we want to reduce the fl ammability of wood and wood materials we must be based on deep knowledge of the composition of these materials, their structure and their elementary building and other factors infl uencing many aspects of their fl ammability. The most important aspects of the fl ammability characteristics are important indicators as to the dynamics of fi re development, determination of fi re load and fi re risk and smoke production and its subsequent toxic gases. The paper deals with characteristics such as fl ammability and gross calorifi c value. Measurements were conducted on six selected species of deciduous trees, particularly in their leaves, twigs, bark and wood. Gross calorifi c value was determined in oven-dry sample. Key words: Gross calorifi c value, forest fi re, deciduous trees. Introduction Forests are an integral part of nature and have paramount importance for man. They are a rare source of material, which is always renewed; their fruits in many cases provide food and vitamins. The extensive forest complexes and also forests in the vicinity of human settlements are an important component of air regeneration and direct the production of oxygen, but also minimize the harmful effects of various air pollutants and dust. In addition, the diversity form and variety of colours during active season is aesthetic and relaxing (Pagan and Randuška, 1987). Forest ecosystems except the positive properties, currently represent a danger of forest fi res in our area. The cases of the past year confi rm the previous sentence. Changes in climatic conditions, methods and systems in forestry and climatic and geographic conditions create an environment in which forest fi re may occur. The terms "recorded" not only fi re but also its development and that way we record forest fi res with large scale, high damages to forests and costly work of a fi re-works (Černý and Šenovský, 2010). Most studies of forest fi res have focused on forests with dominant of conifers wood. However, the mentioned fi res (Old Mountains and Bošáca) occurred in mixed environment with greater representation of deciduous trees. There was a new phenomenon, new fuel - leaves that complicate the work of fi remen and threatened affecting components. For this reason we deal with gross calorifi c value of selected deciduous species in this article. Of these species, we selected those parts (leaves, branch and bark), which contribute mostly to the development of a forest fi re (Tureková, 2009). Materials and methods Selective deciduous wood Red oak, Quercus rubra Linnaeus Red Oak is 30 to 50 m tall, fast growing deciduous tree, its crown is conical at fi rst, in the elderly age large and spherical. Leaves: alternate, stem is 2 - 5 cm long, the blade in the outline is elliptical, 10 - 25 cm long and 5 - 15 cm broad, at base cuneate to rounded, lobed to slit on each side with 4 - 6 indented irregularly spiny lobes. The lobes are rounded wedge-shaped cores and cuttings mostly do not extend deeper than ¼ the width of the blade. The obverse is red oak leaves matt dark green colour, lighter on the reverse. Autumn colour is orange-red to scarlet. Bark: gray, long smooth dark gray bark, scaly thin (Aas and Riedmiller, 1997). Research article p. 32 - 36 Transactions of the VŠB - Technical university of Ostrava Safety Engineering Series Vol. VII, No. 1, 2012 33 Beech, Fagus sylvatica L. Beech is one of our most common species. Root system early passes into the heart shape. The bark is greyish brown in young age, later constantly grey-white and remains smooth. Branches are from mature green to brown twigs. The buds are long spindle, alternate, pointed, built-row. Leaves are alternate, ovate, shortly pointed and short stem, with a bright upside. Physical age of beech is 200 to 500 years. Beech is a timber, which increases the importance of developing chemical treatment of wood. Soil protects shading and litter enriched with nitrogen and lime and a good rooting contributes to its aeration. We anticipate that beech litter supplies 80 kg of lime for 1 h. Beech is very sensitive to smoke, so it is not a suitable tree species for cities. Wood is a multiple porous, glossy, hard and heavy, not a different colour core. However, it often creates a false heart. (Aas and Riedmiller, 1997; Mračková, 2005). White birch, Betula pubescens Ehrh White Birch is a medium-high (up to 20 m), deciduous tree with ellipsoidal crown, its branches rigid stand out at an acute angle to equilibrium. The tops are usually not overhag twig. Leaves: alternate, rather rigid, stem 1 to 2.5 cm long, hairy at least initially, to egg-shaped diamond blade, rounded at the corners, usually shorter than the pointed and upturned white birch, 3 - 5 cm long, just to double saw blade on the cheek more or less bare, the reverse have down look and later (except veined leaves) bald. Bark: Initially mat-white, annular peels off in thin lateral strips, bark is hilarious, blackish, hard, and is made later (Aas and Riedmiller, 1997). Maple, Acer saccharum Linnaeus Maple is 25 (35) m tall deciduous tree with a dense spherical crown with large branches. Leaves: opposite, very variable size, the stem is 17 cm long, blade 8 - 17 cm long, 10 - 20 cm wide, with 5 - 7 lobes, lobes of the front teeth, teeth sharply pointed and upturned, rounded cores, on the obverse and reverse slightly glossy, pale green. Fall colour yellow to yellow - red. Bark: light gray, smooth bark dark gray to blackish, densely longitudinally hilarious, does not peel off in scales (Aas and Riedmiller, 1997). Aspen poplar (aspen), Populus tremula Linnaeus Aspen poplar is rapidly growing to 30 m tall deciduous tree with large sparse crown. Leaves: alternate, stem side compressed, about as long as 3 - 8 cm large, round to egg-shaped blade on the edge of thick blunt teeth, hairy only at fi rst, early glabrous, on the face shine-green, lighter on the reverse. Leaves of long shoots are more powerful (up to 15 cm), ovate to triangular, rather short-petiolate. Bark: Initially gray-green, long, smooth, black-gray, longitudinal bark hilarious. (Aas and Riedmiller, 1997) Purple Willow, Salix purpurea Linnaeus Purple Willow is a shrub, sometimes occurs as a 10 m tall deciduous tree. It has thin branches, rod, and tension upright. Leaves: alternate, but opposite, lanceolate, short pointed and upturned, the widest in the upper third, 4 - 12 cm long and 1.5 cm wide, the top of the fi nely serrated on both sides of the bare, blue-green on the back to grey-green, always without add leaves. Bark: Willow has abundant, watery bark, its sap is heavily charged with salicylic acid. (Aas and Riedmiller, 1997, Požgaj et al., 1997, Durenda et al., 2010). Of these trees, was prepared samples of leaves, branches and bark for further search. Removed samples were homogenized to the same size, and dried at 0 % moisture (oven-dry sample). Determination of gross calorifi c value with the bomb calorimetric method The essence of determining gross calorifi c value is complete combustion of mass or volume of fl ammable substances in pure oxygen at a given pressure. Water, which burned, contained fl ammable substance, is excreted in the liquid state. Fig. 1 Calorimetric equipment IKA C5003 control The calorimetric determination of gross calorifi c value was performed according to the standard ISO 1928. Calorifi c value was determined for all these broad-leaved trees, especially the leaves, branch and bark. p. 32 - 36 Transactions of the VŠB - Technical university of Ostrava Safety Engineering Series Vol. VII, No. 1, 2012 34 For experimental determination of gross calorifi c value, calorimeter IKA C5003 control device is used (Fig. 1). Used equipment meets the requirements of standard EN ISO 1928 and ČSN EN 14918 (Kalorimetrický systém IKA C 5000, 1999). Calorimetric measurement is based on the fact that in the calorimeter, the combustion process occurs under precisely defi ned conditions. For this purpose, to the decomposition is given a weighing of sample containers of fuel, it ignites and measures the temperature rise in the calorimetric system. Specifi c gross calorifi c value of the sample is calculated from the following: • sample weight of fuel, • heat capacity (C) calorimetric system, • increase the water temperature in the inner container, a measuring device. To optimize the burning process, the decomposition vessel meets with pure oxygen (99.95 %). Pressure of oxygen in the atmosphere decomposition vessel was 3.0 MPa. Accurate detection of gross calorifi c value is based on the requirement that the burning took place under precisely defi ned conditions. The applicable conditions are based on the following assumptions: • temperature of the substance to be burned, temperature before burning is 22 °C, • water fi lled in the substance and the water formed during combustion of compounds containing hydrogen are present in the liquid state after burning, • there is no oxidation of atmospheric nitrogen, • gaseous decomposition products are oxygen, nitrogen, carbon monoxide and sulphur dioxide, • the reminder is a solid ash. To ensure exactly reproducible measurement results, the calorimetric system is calibrated after launch, after maintenance, the replacement of parts and the transfer of the calorimeter to a different location in periodic intervals (once every two months). Last calibration of the used calorimeter was made on January 10, 2011, when the calorimeter was set for heat capacity of 10 736 J.°C-1. At the calibration, the heat capacity (C value) of calorimetric system (amount of heat required to heat the calorimetric system by 1 °C) is repeatedly determined. The essence lies in the determination of thermo chemical burning normal (certifi ed benzoic acid) of known calorifi c value, under the same conditions, the same equipment and the same pressure vessel as determined by the gross calorifi c value samples. Regular calibration is absolutely necessary to maintain the accuracy of measurements (STN ISO 1928, 2003). Calorifi c value was determined for samples tested at 0 % moisture (oven-dry samples). The gross calorifi c value is calculated for each test according to the relation: (1) where HOan calorifi c density in the reference state analysis of moisture [J.g-1], C heat capacity of the calorimeter [J.°C-1], ΔT increase of the temperature in calorimetric system during the combustion experiment [°C], Qz excess energy from the ignition, ignition of cotton fi bres, the auxiliary combustion substance, energy produced at HNO3 [J], m mass of burnt substance [g]. Calorimetric system makes it possible to set the mode without titration. In that case, the energy produced at HNO3 production is calculated according to the formula (Kalorimetrický systém 1999): (2) where QN energy produced at HNO3 production [J], N the percentage of nitrogen in sample [%], m mass of burnt substance [g]. The measured gross calorifi c value in an oven-dry sample state is recalculated to w % moisture. The formula for calculation of gross calorifi c value at constant volume for water: (3) where qv·gr·d gross calorifi c value at w % moisture [J.g-1], qv·gr gross calorifi c value at 0 % moisture [J.g-1], MT the water content in the fuel, which was found in trial [%]. Results The fuel at forest fi res comes from all part of the tree. The fi rst contact is the bark, branches, and we must not forget the leaves, which is the leaf litter. Each part of the tree has some representation, and the parts are evaluated separately. First, we evaluated the leaves that have a different composition, size, shape, thickness and as confi rmed by (Fig. 2), the value of gross calorifi c value. The beech has the largest representation percentage between selected trees and it reached the second highest gross calorifi c value. It is interesting that the leaves of birch reached the highest gross calorifi c value among other selected species. For specifi c fi re, which we mentioned in the introduction, there were just the leaves which burnt or smouldered, creating different formations to move on steep terrain and lit another part of the forest. If so far only coniferous trees were p. 32 - 36 z Oan CTQ Hm    43 N QNm  1 – 0,01 vgrd vgr T qq M    Transactions of the VŠB - Technical university of Ostrava Safety Engineering Series Vol. VII, No. 1, 2012 35 considered the fi re risk, after this experiment can be seen that also deciduous trees leaves with their high calorifi c value can cause some problems. The birch is in gross calorifi c value followed by beech and maple has the lowest calorifi c value. Fig. 2 Gross calorifi c value - Leaves Gross calorifi c value of branches does not exhibit signifi cant difference between the trees, see (Fig. 3). Birch and willow reached the highest value, while poplar had the lowest. For branches, we chose ridges 0.5 to 0.8 mm cross section and in the creation of samples to maintain the overall structure of branches, bark, fi bber and woody parts of the branches. The difference in the branches is likely to determine the structure of wood holding relatively high density of wood, making the results somewhat homogenized. The difference between the trees is minimal. Fig. 3 Gross calorifi c value - Branches Bark has a signifi cant impact particularly on the development of fi re and the transition from ground fi re on treetop. Results of the experiment confi rm what is known in scouting, that a circle of birch bark is the best for the ignition of fi re. Calorifi c birch bark has reached the highest value among all testing materials thus the leaves and branches (Fig. 4). Results which can be seen on (Fig. 5) show the tested components of diversity, leaves, branches and bark of the selected wood species. When we plan the experiment, we might even foresee that these differences will be great. Wood such as oak, birch, maple and poplar (not absolute values) have the lowest gross calorifi c value in the leaves, followed by branches and eventually peel which has all testing trees at the highest value. The gross calorifi c value of the thermal birch bark has already been mentioned, surprising results have been achieved mainly by beech trees where leaf has the largest gross calorifi c value among selected parts, followed by branches, and the lowest gross calorifi c value has bark of beech, which is thin, smooth, and shiny. The willow reaches the highest gross calorifi c value at branches. It's their tax structure and tree character. In particular, we evaluated the wood because it is only a secondary source of fi re and a secondary fuel. Fig. 4 Gross calorifi c value - Bark Conclusion The aim of the experiment was to evaluate the gross calorifi c value, at zero moisture, of leaves, branches, bark at wood (oak, beech, birch, maple, poplar and willow). Already on the basis of previous experiments, which have been carried out on conifer wood, we found differences in weight loss and the rate of burning of branches, stem and roots of conifer wood. Description and experiment confi rmed the signifi cant differences that were found also in this case. This fact is important to know in order to characterize fuel which is present in this section and which constitutes a potential risk for the emergence of a particular course of forest fi res. Based on these values, forest management plans, environmental relief and other parameters can be made more accurately to determine potential development site with fi re and the direction of stronger fi re development by the presence of the type of fuel. Acknowledgments Paper was within the projects VEGA (GD 1/0446/12 - Utilization of laboratory method for combustibility quantifi cation of wood, wooden composites and upholstery materials). p. 32 - 36 10 000 12 000 14 000 16 000 18 000 20 000 22 000 24 000 Calorific value (J/g) (w=0%) Oak Beech Birch Maple Poplar Willow Wood 10 000 12 000 14 000 16 000 18 000 20 000 22 000 24 000 Calorific value (J/g) (w=0%) Oak Beech Birch Maple Poplar Willow Wood 10000 12000 14000 16000 18000 20000 22000 Grosscalorificvalue (J/g)(w=0%) Transactions of the VŠB - Technical university of Ostrava Safety Engineering Series Vol. VII, No. 1, 2012 36 References AAS, G., RIEDMILLER, A. (1997). Vreckový atlas STROMY (Praktická príručka na určovanie európskych listnatých a ihličnatých stromov). Bratislava: Slovart, 1997. 3 (in Slovak). ČERNÝ, O., ŠENOVSKÝ, P. (2010). Nekonvenční metódy modelování rozvoje požáru. 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