www.forestconsult.ch Christof Hugentobler dipl. Forstingenieur ETH / SIA

Sound Use of Wood, 24 - 27 March 2003, Romania UNECE / FAO

Energy Wood and Wood Energy

Forests are solar energy collectors – besides all their other public and property functions. Harvesting fuel wood means an intervention into the ecosystem as well as into the landscape shaping function of the forests. The latter is one of the effects of their huge dimensions. Other effects are the difficulty of management, including property discription and the large distances.In forests grows wood – besides very many other products. Wood increment fixes CO2 in large quantities using solar energy and stores it over the life time cycle of the wood. Eventually CO2 and energy are set free – regardless weather the energy is used or not. Therefore wood energy is CO2 neutral. Its CO2-circle is recent contrary to the fossile CO2 cycle.The growing wood can be harvested and used in the most various ways. We recommend sustainable management of forests and the adequate (sound) use of wood– to win the highest possible value and should – eventually, in the correct phase of life cycle - be used for efficient energy reclaim.

Cold chips can be loaded and moved with a snow blower. Cold, because the machine is built under the assumption, that gears etc. will be cooled by the handeled snow. Chips do this only when cold. Otherwise temperatures have to be watched and cooling allowed by interruptions. Chips dumped into a bunker move away from the truck. So it is not possible to fill the volume near the truck. The necessary consequences have to be taken into account when planning the building. A medium duty frontloader is always advantageous to have on hand when handling wood chips.Chippers became very handy in the last years: even small machines will handle diameters up to 30 cm. It may be sensible to have a restricted chipper diameter and leave some oversize stems behind: moving the smaller chipper is a tremendous advantage – and the leftover wood serves to other people or to insects, bacteria and birds. Please note: poorly cutting knives bring lots of loss and difficulties. A chipper is not complete without a second set of knives! Built in chipppers in sawmills receive their material directly from the saw – if the wood is not treated directly by chipper heads.

Wood processing operations often produce more fuel wood than they need themselves. Their product (fuel wood) is often predefined by the machinary: to use them in the furnace system needs compatibility of the qualities. As they usually supply dry restwood it can be interesting to mix it with green wood from the forest. Here we come to an interesting solution in several parts of Switzerland (www/vhe.ch): in several regions all the supplyers of fuel wood have created a fuel wood supply company which collects the wood from the supplyers and dispaches it to the consumers. Please note: it is not important that all the fuel wood goes through the company’s storage – on the contrary: basically there are bilateral connections. The corporation comes only in function in unusual situations: to level peaks. Such corporations are highly sophisticated on paper – while the practical day to day business runs very easy. An unsafe legal basis though brings very difficult situations into day to day operations.“Debris wood” from liquidated constructions is a complex field because of exhaust problems. As the exhaust is most probably poisenous it is not recommended to mix this wood qualitiy with untreated wood. In beween are the residues of particalboards (and similar), which in Switzerland must be burnt in special waste furnaces because of poisenous exhaust. Please note: we cannot propagate wood as an ecological fuel, yet burn wood derivates which produce poisenous exhaust gases – or only burn them with high particle exhaust.

Fuel wood is won after each step of wood processing. Fresh wood can be used in adequate installations or dryed to 25-20 % moisture content before or after chipping. At this point begin the complex logistical questions around fuel wood. Easy logistics for green fuel wood demand furnaces able to win efficiently energy from green wood. This decision is made by ordering the system. Dry wood can be used in a moist wood system – but there is a surplus investment. The contrary does not apply!Chip piles of fresh wood go through a fermentation process. Anaerobic bacteria consume parts of the wood and produce heat. There is no danger of fire because the bacteria die much before. The wood loss is minimal, the drying effect quite efficient (25-20% moisture are reached within 1-2 months). On the surface of the pile vapour condenses and leaves a soaking wet layer of approx. 20 cm. It can dry up during a dry period if uncovered. The best drying effect is reached in well areated open shelters.Several logistic chains are possible: storing and hauling round wood to a mobile or fix chipper with or without another storage and transport phase before bunkering near the installation. Please note: the Installation is calibrated to a certain chip size. It makes very much difficulties if the chipper doesn’t fit the installation’s necessities. Energy consumption for chipping (2-5% of the energy contents) reduces exponentially with growing chip size.Wood chip logistics include several transportation, loading and unloading steps. Moist chips stored outdoors in frost in a container cannot be dumped without thawing up. Even under normal conditions chips need a steep angle to slide: storage rooms have to be high enough that trucks can lift theyr dumper completely.

Effective – efficient: It’s evident: we want to work in an efficient way – reach our aim (energy) with a minimum of resources. Effective means: we work efficiently towards the right aim (contrary: to work efficiently towards the wrong aim). When planning a wood energy system, effectivity needs first a discussion of the aims – mainly short term or mainly long term aims? It is always cheaper to install an earthgas or fuel furnace. To invest into the more expensive wood energy system means to take the responsibility to amortize the investment over a period of time. In safe surroundings over years, in riskier surroundings over months or very few years. If the risks lay in the global or state policy, than it is high – if it lays in local conditions, than it is smaller, better to be overlooked. Therefore local autonomy is helpful for the development of wood energy applications.In some countries huge networks for energy transport in water and steam have been installed. If really the necessary amount of wood on a sustainable basis (incl. transportation) is availble, it should be considered to use them. In Switzerland constructing the networks is the most difficult point in using wood energy at a large scale.

There are also small and very small automatic (chips) or hand fed applications available. For owners of small woodlots with enough time and strength, a samll central heating can be an intresting alternative. Please note: wood gases have to burn at high temperatures. They condense to very difficult substaces on cool surfaces. It is therefore important to have an installation which allows a furnace water circuit with steady 60-70°C and a house circuit with reduced temperature. The necessary mixer valve (manual instead of electric) may be difficult to come by.

The type of energy production installation should be defined by the type of  Energy conversion installation. The simplest case - straight forward heating - may be an application of steam. It is helpful to have one or more “industrial” consumers (also Hospital or Hotel) in the network which consume an important minimum of energy also in summer. Building up a network may recommend to expand in phases. Any larger installation should comprise an earthgas or oil unit for summer and for extremly cold temperatures. It can be practical to use this buffer capacity while expanding into a new phase – until an additional wood furnace or a larger one can be amortized. There is a possibility to finance energy production installation through Energy Contracting: the provider of the furnace invests into the installation and gets payd with current heating payments. His risk premium for missing payments depends on his “feeling” for the real risk, which he knows exactly only “afterwards”.More complex, but also with more potential are Cogenerating Installations. Here the furnace produces steam for a steam turbine (or wood gas for a gas turbine) which in turn runs an electric generater. All the heat ocurring in this process is used for heating and similar applications. So the low degree of effectivity of electricity production is compensated by the heating application. If the electric power runs a heat engine there may occur degrees of effectivity >100%.

www.chiptrac.ch

www.baumgartner.ch

www.holzfeuerung.ch

Energy/HeatExhaust GasAshes

heating – expulsion and burning –of Wood Gas

Energy ProductionInstallations

Energy Conversion Installationselectrical / mechanical

Energy Reclaim Process• small/large• Heating/Process Heat• Mechanical Energy• dry/moist wood 

Dry/Humid WoodTransports StorageProcessing

Logistics

Solar Energy Collector: Forest

LandscapeEnvironment Property

Provision

manual mechanical

high valuemedium valuelow value

Life Cycle:Recycled Wood

Percentage industrial/fuel Usage

direct individualConsumption

Fuel Wood

Efficient & effectiveEnergy reclaim

Discussion of AimsLocal Autonomyexisting Steam Networks vs wood hauling distance

Soil SpaceDistances

Wood Increment – CO2 Absorbtion

Silviculture Wood YieldEnterprise