technologies of wood combustion

Ecological Engineering 16 (2000) S25S40

Technologies of wood combustion

A. Strehler *Bayerische Landesanstalt fur Landtechnik, Abt. Technik in Pflanzenbau und Landschaftspflege, Vottinger Strae 36,

85354 Freising, Germany

Accepted 14 December 1999

Abstract

Wood is the oldest but even today the most important carrier of solar energy. The actual potential of wood energydepends on waste- or by product quantities, which have no better use in the non energy sector and of energyplantations via short rotation forestry. The economical sensitive potential depends additional on the energy-price-level. The fuel characteristics with low ash and low sulfur content allow the comparison with straw (high ash-c.) coal,oil, and gas. The most important aspect of wood as renewable energy carrier is its nearly closed C-circle. Wood isprocessed to wood logs (discontinuous charging) and wood chip and:or pellets (automatic charging). Wood logfurnaces have to be combined with heatstores (100 l:kW) to avoid emission problems with a heating performancebelow 50%. Wood chip and pellet furnaces allow similar handling comfort as oil fired boilers. The costs of energyfrom wood are in the range of 0.060.15 DM:kWh. Heating oil leads to total cost of 0.070.11 DM:kWh with a oilprice of 0.40 DM:l. 2000 Elsevier Science B.V. All rights reserved.

Keywords: Wood; Energy; Oil

www.elsevier.com:locate:ecoleng

1. Introduction

The critical greenhouse effect caused by green-house gases, mainly CO2, and the limitedavailability of fossil energy sources call for in-creased efforts in energy saving and utilization ofrenewable energy systems. Due to this large po-tential and many positive side effects, biomass hasa high priority in replacing fossil energy. Biomass

resources, caused from solar radiation, have atheoretical potential that is ten times higher thanthe total world consumption of primary energy,with around 7 billion tonnes of oil equivalent(OE) per year. If we evaluate all growing biomasson land worldwide we obtain an energy equivalentof 70 billion tonnes of OE. The limitation ofavailability of fossil energy is in the range of5070 years for crude oil and natural gas, andabout 200 years for coal (BMWI, 1997:1998).Climate experts tell us that we are not allowed touse fossil energy over such a long period. We willface a climatical catastrophe if we continue usingfossil energy at this high rate. There is a need tosave energy, our largest potential, and to replace

Presentation for Expo 2000World Forum Forests andenergy.

* Tel.: 49-81-61713303; fax: 49-81-61713527.E-mail address: [email protected] (A. Streh-

ler).

0925-8574:00:$ - see front matter 2000 Elsevier Science B.V. All rights reserved.

PII: S0925 -8574 (00 )00049 -5

A. Strehler : Ecological Engineering 16 (2000) S25S40S26

fossil fuels soon by using renewable systems likebiomass.

2. Potential of renewable energy systems

Fig. 1 shows in column 1 the total energyconsumption, in column 2 the consumption offossil energy. Column 3 offers the total energy inbiomass fixed on land per year. The next columnsare ideas of how much land would be necessary tocover a part of the demand of energy via energyplantations. As there is a very high need to fightagainst growing deserts, energy plantations wouldbe an appropriate procedure. Many people dis-cuss the competition between energy plantationand nutriation of mankind. Regionally there is nodoubt some competition, but not in a global pointof view. As figures from FAO Rome show, by theyear 2000 about 50% of the arable land will nolonger be in use for crop production. This area

alone would cover the energy demand shown incolumn 6 in Fig. 1.

It seems very sensible to utilize land for energycrop production, because otherwise it would beendangered by water and wind erosion as a resultof the greenhouse effect.

In Germany we have a relatively high energydemand. The primary energy consumption is inthe range of 340 million tonnes of OE, coveredmainly by fossil resources. They have to be re-placed. In case of an ecological tax reform, asavings of 50% seems possible. The rest has to bereplaced mainly by renewable energy systems.There are the cheap resources such as byproducts(straw, woodwaste) and more expensive energycrops. When grown on 5 million ha of so-calledsurplus areas in agriculture, the potential couldreach 2036 million tonnes of OE. The low valueis for a high share of oil crops, the high valuereflects a high share of high yielding energy cropsas solid fuel, as shown in Fig. 2 (Strehler, 1994).

Fig. 1. Energy consumption worldwide energy potential from biomass.

A. Strehler : Ecological Engineering 16 (2000) S25S40 S27

Fig. 2. Substitution of fossil energy in Germany via saving and use of regenerative energy.

Table 1Fuel characteristics

Calorific value (MJ:kg) Ash (%) C (%) O (%)Fuel H (%)Volatiles (%) N (%) S (%)

Straw 14.280.3 4.3 44.0 35.0 5.0 0.5 0.115.3 0.5 43.0 37.085.0 5.0Wood 0.1

23.0Charcoal 30.1 0.7 71.0 11.0 3.0 0.1 13.5 1.8 47.0Peat 32.070.0 5.0 0.8 0.313.6 115 58.0 18.057.0 5.0Brown coal 1.4 2.0

26.0Mineral coal 29.5 115 73.0 5.0 4.0 1.4 1.025.9 917 80.0 2.0 2.0 0.5 0.8Coke 4.0

3. The fuel

3.1. Energetical 6alue of biomass fuels

Different types of biomass fuels have a calorificvalue in the range of 15 50016 500 kJ:kg, with15% water content. Apart from the calorific value,the ash content is very important. Pure wood hasonly 0.5%, wheat straw up to 6% ash content. Thedifference in ash content leads to differentcalorific values. The most important chemical ele-

ments delivering the energy are carbon, hydrogen,sulphur, and phosphorus. Table 1 shows theseimportant values characterizing biomass fuel in-cluding a comparison to coal and fuel oil.

Just some figures for practise: 10 tonnes ofstraw harvested from 2.5 ha arable land or 30 m3

of wood (stacked rolls or logs) deliver as muchheat as necessary to supply a medium-sized housein Central Europe for 34 months during winter-time. The fuel demand of a middle-sized farmcould be covered by straw from 5 to 10 ha or by


using 60120 m3 fuel wood. Special energy-savingdwellings have a much lower demand in the rangeof 68 m3:year.

3.2. Biomass fuel properties

The combustion characteristics of straw, wood,and other biomass sources depend basically ontheir moisture content and chemical characteris-tics. Table 2 shows the specific weight andcalorific value in relation to its moisture content.Fuel should be air dried in order to have a storagewithout losses. Especially in small furnaces, a lowmoisture content is the basis of a high combustionquality. Wood and straw should be stored rain-protected and with aeration systems (forced ornatural draft).

The high content of volatiles causes problems instraw and wood combustion. Therefore, it is nec-essary to control the power when using discontin-uous charging. Burning systems with a separatechamber for gasification and a secondary combus-tion chamber to burn the gas perfectly are neces-sary. Wood furnaces do not work properly in therange below 50% of performance. To cover alower heat demand, a heat store is necessary. This

can be a big water tank, whose size should reach100 l per 1 kW heating performance. This combi-nation allows the furnace to run in the optimalrange with low emission and to utilize as muchheat as necessary without influencing on the boilerefficiency. Surplus heat will be stored in the watertank. As soon as the water tank is heated up,charging of the furnace has to be stopped. Whenthe heat store starts to reduce its temperature evenin the upper layer, charging of furnace has to bestarted again. There is also a possibility of burn-ing vegetable oil to gain energy from biomass. Butthis possibility will not be discussed in this paper.

4. Harvesting, storing and processing of wood forcombustion

The combustion behavior of the biomass fuelsdepends on the one hand on their chemical prop-erties and on the other hand on the physicalstructure of the organic materials. The physicalstructure can be influenced by different processingtechniques, like milling, cutting, compaction, bal-ing, or pelleting.

Table 2Specific weight and calorific value of wood and selected biomass fuels

Bulk density (kg:m3)Moisture content (%)Biomass Fuels Calorific value

kcal:kg kJ:kg Spruce Beech

31018 56044200Meter logs (Spruce and Beech) 400391010 42033016 400

20 3400 14 280 350 45030 2900 12 180 370 480

51039010 1002410405301920 810050 410

Wood chips (Spruce) 18016016 40039101014 2803400 18020 200

2202900 12 18030 20040 2410 10 100 215 235

Plant residues High density bales15 500370010Cereal straw 120

10 3440Corn stalk 14 400 10010Flax stive 4040 16 900 140


Fig. 3. Technical characteristics of wood for combustion.

4.1. Wood har6esting and storage

Wood is available in different forms of process-ing, from sawdust to big, voluminous woodpieces. The different types of processing areshown in Fig. 3. Sawdust is mainly available inwood processing industries and sawmills. It canbe utilized in special small stoves with discontinu-ous charging, in units with automatic fuel charg-ing or in large injection units. Wood chips areproduced from soft wood, mainly in the forestwhere wood should be predried naturally to di-minish the technical drying costs (Hartmann andStrehler, 1995). To prevent moulding, the mois-ture content of the predried wood chips should bebelow 20%. Drying of wood chips increases itscalorific value and makes handling easier (Streh-ler, 1984).

The most conventional means of wood process-ing for small voluminous hand-charged stoves isthe preparation of short rolls or logs and split logs

with lengths up to 1 m for large-sized combustionunits. Briquettes and pellets are mainly producedfrom sawdust and bark. Briquetting and pelletingis the basis of utilizing this fuel in small combus-tion units outside the agricultural and forestrysectors. The energy demand of compaction rangesfrom 40 to 80 kWh:t.

4.2. Technical routes of wood processing, storage,and charging for different types of combustionunits

Many forms of biofuels are available. Depend-ing on its origin, wood is processed and stored indifferent ways. Sawmill and sawdust from woodprocessing and the saw industry can be utilizeddirectly in special injection furnaces or it can becalibrated to different sized pieces via pelletingand briquetting. Pellets can be utilized in smallunits with automatic charging. Briquettes mainlyreplace wood logs. The briquettes with up to 60


mm diameter can also be charged automaticallyto big boilers. Wood waste from thinning in theforest and from sawmill residues is most oftenchipped to pieces from 5 to 50 mm diameter. Forall these forms of fuel, special furnaces have beendeveloped. The possible routes from processing tocharging in furnaces are shown in Fig. 4. Themost important are wood log and wood chipcombustion (Strehler, 1996).

5. Technical characteristics of wood stoves andwood boilers

5.1. Furnaces with discontinuous fuel charging

5.1.1. Sto6es and boilers for short logs, briquettes,and coarse wood chips

Many manufacturers produce stoves and boil-ers for short wood logs and most of them are alsoappropriate for briquettes and coarse wood chips.Fig. 5 shows a common single stove working witha through-burning system.

Simple through-burning stoves require shortcharging intervals for good combustion quality.When buying a single stove, people should payattention to the possibilities in heat control, mov-able grate, and large-sized ash-box. Regarding thecombustion system, most of the warm air-tiltedstoves are similar to this construction. In order toreach higher efficiency, the primary combustionchamber is connected to a heat exchanger thatleads the heat to the surrounding air. The heatedair leaves the tiled stove through openings thatcan be adjusted to the heat demand required. Thecold air enters the tiled stove at the bottom, isheated inside, and leaves the unit at the top usingthe thermic effect. The stoves used only for woodshould have a large combustion chamber.

Recently, tiled stoves have also been producedwith an underburning system. This type of com-bustion unit has the advantage of longer intervalsin charging while maintaining a high combustionquality. More common are systems with top burn-ing in connection with a secondary combustionchamber. This type is shown in Fig. 6.

Fig. 4. Storing and processing lines of wood for combustion.


Fig. 5. Through-burning stove for short wood logs, briquettes,and coarse wood chips.

chimneys are delivered with parts of boilers to beable to circulate the heat of the chimney in thecentral heating system. So-called chimney stoveshave a glass charging door in front of the com-bustion chamber. They are very popular as addi-tional heater.

Heat-herd : another variety is the so called heat-herd-system. This furnace is used mainly in smallor medium-size agricultural dwellings in forestryregions. New types include a movable grate(with adjustable height) for optimal adaptation tothe type of fuel and to summer and winterconditions. The power regulation is satis-factory. The high frequency charging is less fa-vourable. To save labour, as a result of the workload with ash removal and charging, it is increas-ingly common to install a central boiler in aspecial room.

Central boiler : in contrast to the single stoves,central boiler systems deliver the heat in a radia-tor grid all over the dwelling. Heat circulationpumps distribute the hot water to the radiatorsand thermostats regulate the heating power in therooms to be heated. A boiler thermostat switchesthe circulating pump on as soon as the boilertemperature reaches 7080C, in order to avoidcorrosion in the boiler.

The boilers are sold mainly with under-burningsystems, in order to save labour. Fig. 7 shows thesystem of a boiler for short wood pieces. Allmanufacturers deliver bottom-burning systems forshort wood pieces, coarse wood chips, and bri-quettes from bark, straw, and sawdust. About fivemanufactures produce furnaces for 1 m woodlogs. The most important and points are theproper connection to a secondary combustionchamber of high temperatures and the satisfactoryretention time for the flue gases for oxidation. Thesecondary combustion air must be adjustable, andit should be preheated. Modern furnaces adjustthe secondary combustion air additionaly via fluegas quality using O2- or CH-sensors.

Many manufacturers produce highly efficientwood boilers with low emissions (BMWI, 1997:1998). In the last 10 years, CO-emissions havebeen reduced at least ten times from 2000 mg COto 150 mg CO:m3 flue gas.

The so-called tiled ground stoves having avery good heat storage property are sold mostlyfor wood combustion. These stoves are producedby local specialists and are usually very expensive,especially when using high value parts requiring aspecific work of art.

This basic stove delivers the energy mainlythrough radiation. Here the main disadvantage isthe long delay (at least 2 h) from ignition to thedelivery of heat. However, the advantage of thistype of stove is providing heat for up to 10 h afterthe combustion has stopped.

Combined furnaces : there are many varieties ofwood stoves, from open chimney to tiled stoves.There are chimneys with the possibility of closingthe combustion chamber. They are manufacturedeither from glass or metal. This type is a compro-mise between fun and heat efficiency. Even open


5.1.2. Boilers for long wood-logs and small strawbales

In order to save labour for charging of biomassboilers, large-volume furnaces for whole baleburning and wood-logs are often used in agricul-ture. In this case there are through-burning and

under-burning systems in practice.Through-burning systems : the first small-bale

boilers came from Denmark and originally theywere relatively simple in construction to keepcosts low. The combustion chambers were cylin-drical, in a horizontal position with a length of 1.2

Fig. 6. Warm-air tiled stove with heatbox.

Fig. 7. Bottom burning boiler with flue gas fan and top charging.


Fig. 8. A heat store system.

m and a diameter of 0.81.2 m. In front was a bigcharging door and inside of this door a smallcharging door to prevent flue gas from enteringthe heating room during charging operations. Thecombustion air entered the boiler through twoflaps controlled by a thermostat. With too lowsuction of the chimney, it was difficult to runthese boilers, because critical flue gases left duringcharging and even up to 20 min after charging viachimney with high pollution. The low combustionquality, especially with straw and wet wood, ledto improvements of this boiler by many manufac-turers. For utilization of hot air, additional heatexchangers and gas cleaning units were applied.

Wood ash has to be removed every 2 monthsand straw ash every 13 weeks. To avoid lowcombustion quality when the furnace is not oper-ated at full power, the boiler has to be combinedwith heat stores. The minimum size of the store isa water tank of 100 l for each kW heating power.In this case, the stored heat is sufficient to coverthe night heat demand even in the cold season.During the day, when the furnace runs at fullpower, it covers both the day heat demand and

the heat necessary for the night. In summer, it isenough to heat up the store once a week or lessoften, depending on the hot water requirement.Many manufacturers of boilers deliver their ownheat store system.

One example of a well-proven heat store systemis shown in Fig. 8. The specific prices of handcharged biomass boilers are between 300500DM:kW in Germany. Including costs of heatstore, the total investment cost becomes 400600DM:kW (thermal). Including the installation andheat distribution devices, the specific investmentcost of straw and wood heating systems are in therange of 7001000 DM:kW.

Meanwhile, there are bottom-burning boilersfor meterlogs predominate on the market. A wa-tercooled fuel chamber of at least 1.10 m length,0.5 m broad, and 0.82 m high can store fuel for310 h. The charging door can be placed on thesidewall (good for wood log feeding) or on thetop (for wood and straw bales). All modern fur-naces for wood and straw are equipped with a fluegas fan to ensure proper function and lowemission.


5.2. Furnaces with automatic fuel charging forwood chips and pellets

Soft wood produced in the forest or woodresidues from forests and sawmills have to bechopped to make them suitable for efficient com-bustion with low labour demand.

5.2.1. Pre-furnace systemThe main advantage of the so-called pre-fur-

naces is that the old oilboiler can be used as aheat exchanger. Replacing the oil-burner, the pre-furnace can be directly adapted to the system.Pre-furnaces are usually fed through automati-cally controlled augers or hydraulic cylinders. Thefeeding rate of biomass fuel follows the actualheat demand automatically. The combustion air isprovided by a fan. Some furnaces are divided intoprimary and secondary combustion chambers.The combustion air flows through different sec-tions. The newest pre-furnaces are equipped withan automatic electrical ignition system.

The flames produced in the pre-furnaces reachthe boiler together with the hot gases, which arenot completely burned in the pre-furnace. The

boiler is used as a secondary combustion chamberand heat exchanger. The fuel is charged automat-ically from a feeding box that contains the fuel forhalf a day up to 2 months. Between the feedingbox and combustion unit, there is security equip-ment to protect the unit against return burning.The feeding box can be charged automaticallyfrom a large pre-container (long-time fuel store)or it has a big sice directly.

Some pre-furnaces are relatively cheap; there-fore, they can already be proposed for wide-scalepractical applications. A simple pre-furnace in-cluding fuel supply, 1-day fuel container and feed-ing box costs about 20 000 DM, having a poweroutput of 50 kW, which means approximately 400DM:kW. One example is shown in Fig. 9. If thereis a higher heat demand of 150 kW the price ofthe low-tech pre-furnaces is only 30 000 DM,which is equal to a specific price of 200 DM:kW.Daily function control is necessary with thesepure units. There are many high-tech prefurnaceson the market, but the price is higher. Under-charging and movable grate systems are engaged.The performance is in the range of 12 kW up tosome megawatts.

Fig. 9. Arrangement of a pre-furnace system.


Fig. 10. Pre-furnace with movable grate.

In the case of a higher demand in combustionquality (urban area) more expensive pre-furnaceshave to be applied. If fuel is to be fed directly intothe combustion chamber, and ash removal has tobe performed automatically, then movable gratesor ash bars should be applied.

The pre-furnace with sloping grate can also becharged by auger conveyors. A level control sys-tem protects the furnace from overcharging. Theprimary and secondary combustion air supplyresults in a higher combustion quality. The WVTmanufacturer produces this type of pre-furnaceswith fixed and movable grates (Fig. 10).

The undercharging combustion systems havebeen applied with great success in big and evensmall furnaces as well as in pre-furnaces anddirectly in boilers. In these furnaces, the reliableremoval of ash from the combustion area is liable.Many manufacturers install too small ash con-tainers, which leads to an additional workload.

If an almost fully automatic biomass combus-tion system is requested with wood chip burning,a furnace with mo6able grate should be applied;however, these combustion units are much moreexpensive than the simple pre-furnaces withstepped movable grates. The pre-furnace can also

be operated efficiently with chopped straw, saw-dust, cereals processing waste, and other biofuel.

Stoker systems : if a large-sized boiler is avail-able which can be used as a heat exchanger, theoil-burner can be replaced by a so-called stoker-system instead of a pre-furnace. In this case, thecombustion takes place in the boiler (Fig. 11),which probably leads to a lower combustion qual-ity; on the other hand, the heat losses and costsare much lower. In the case of a low powerdemand (below 50 kW) the stoker-system is rela-tively economic. Electrical ignition is also avail-able for stokers. The cost of this type of furnace is13 00015 000 DM for 2040 kW units.

5.2.2. Boiler integrated wood chips furnacesIn the case of a new investment, boiler-inte-

grated furnaces are more reasonable than pre-fur-nace types. They need less space. The combustionsystems are the same. Very common are under-charging types with low performance, shown inFig. 12 and with high performance in Fig. 13, thelast one with the possibility of vapour productionand power generation.

Wood chip district heating plants : In the begin-ning, the district heating plants installed furnace


systems that were similar to the ones used longbefore in the wood processing industries. Nowthey have been modified to meet the requirements

of whole-tree chips, especially as regards the con-veyor systems and combustion chamber. The fur-nace system for fuel chips must cope with a

Fig. 11. Stoker as undercharging system.

Fig. 12. Undercharging system in a small boiler (Froling).


Fig. 13. Undercharging system for high performance with a steam boiler.

relatively high moisture content, i.e. in the rangeof 5560% moisture of the total weight. Specialheat exchangers allow recondensation of water inthe flue gas in order to improve the heatefficiency.

Fig. 14 shows the layout of a chip-fuelled dis-trict heating plant. Todays operational experi-ences with such plants show that greatinterruptions in operations belong to the past.Smaller disturbances do occur, but greater break-downs are rare for the latest plants. When prob-lems occur, the reason is often the feeding system,where oversized wood fragments cause interrup-tions. All in all, the operational stability of mostmodern chip-fuelled heating plants is close to theoperation stability of coal-fired heating of thesame size. Also, critical flue gas emitants could bereduced drastically in the last decade. The heatdistribution costs nearly as much as the boilerincluding the charging system at 8001000 DM:kW.

6. Economic aspects of wood combustion

The market prices of different heat generatorscan be compared if their so-called specific pricesmeasured, e.g. in DM:kW, are calculated. Thesespecific prices are shown in Fig. 15 for variousenergy sources and different types of heat genera-tors on the left side. The specific price ranges forsome types of biomass heating plants from 200 to1000 DM:kW, having automatic charging facili-ties and high efficient burning systems. The an-nual cost results from interest and depreciationwith 15% from investment.

Furnaces with low heating performance have,in general, a higher specific price, especially whenexpensive technology is adapted for automaticcharging. Hence furnaces with high power outputshow a comparatively low specific price.

The economy of biomass combustion dependsbasically on fuel prices, while the net usable heat,which can be generated from the different fuels,


has to be evaluated in relation to the costs of thecombustion unit. Fuel prices for wood lead toheat costs from 0.03 to 0.06 DM:kWh, as shownin Fig. 15 on the right side. Labour costs are inthe range of 0.010.04 DM:kWh heat. The capi-tal cost results from annual costs divided by heat-ing hours per year (2000).

The capital costs (basic line Fig. 15) plus labourcosts fuel costs are the main components fortotal costs, ranging from 0.05 DM:kWh up to0.20 DM:kWh under less favourable conditions.Fig. 15 shows the total costs for oil combustionwith 0.080.11 DM:kWh when fuel oil costs only0.40 DM:l. All 0.10 DM:l price lift leads to a costincrease from 0.01 DM:kWh. Fuel oil prices from1.10 DM:l, as given in Sweden and Denmark,would improve wood combustion in Germany toa high level of competition (Strehler).

7. Environmental aspects

The environmental aspects of using biomass forheat generation can be summarized as follows: when using biomass as energy carrier, there is

always a closed CO2 circle. That means that inthe case of energy generation from biomass,there is no growing CO2 content in the atmo-sphere, when crops are planted continuously;

the heavy metal content in biomass raw materialis close to zero, therefore there is no or very lowheavy metal emission during combustion;

the sulphur content in biomass is extremely low.Even in the case of straw, the sulphur contentof flue gas is much smaller than that of the lightheating oil combustion;

the nitrogen content in biomass is also low,except for some crops of high protein content.In this case there should be a NOx-control whenburning the material.Unfortunately there are also negative environ-

mental effects of biomass combustion that shouldalways be kept at low level: particularly in straw combustion there is a high

dust emission; therefore the filters have to beused for partification of the flue gas. Hydrocar-bons will also be emitted when wet fuel is used;

smell and carbon-monoxide (CO) are also devel-oped in a higher degree when the solid biomass

Fig. 14. District heating plant for wood chips combustion.


Fig. 15. Cost calculation.

fuel has too high a moisture content or thecombustion chamber is not constructed andadjusted properly. In general, the hot secondarycombustion area should be applied, the gasretention time should be at least 0.5 s, and thecombustion temperature should be kept around1000C;

slag problems occur with straw combustion andwith wood and high bark content when theprimary combustion area in the region of the fluehas too high a temperature, i.e. greater than1000C in the ash;

it is very important to avoid the smell of biomasscombustion, which is caused by CH at lowtemperature levels. This is possible when thesecondary combustion area is well-designed.Temperature has to be more than 1000C, andgas retention time should be at least 0.5 s.Two-step combustion should be standard whena discontinuous charging is applied.

The following parameters are usually measuredand evaluated when the environmental effects ofbiomass are analysed:

Parameters ComputerizedInstrumentsanalysis

Brigon indica-CO2 xtors with liquidsBrigon indica-CO xtors with liquidsSpecial gas indi-CH xcator devices

xO2 Liquid indicatorxFuel gas analysisNox

Pump, filters, Dustcompactinstrument

New results of the Weihenstephan test unit showthat the combustion of non-polluted wood leads


to unimportant low emission of dioxin, polycyclicaromates, and other poisonous gases when fur-naces are of adequate design and well-used (Laun-hardt, 1998).

References

BMWI: Energiedaten, 1997:1998. Nationale und interna-tionale Entwicklung, Bundesministerium fur Wirtschaft, S:pp. 6569.

Hartmann, H., Strehler, A., 1995. Die Stellung der Biomasseim Vergleich zu anderen erneuerbaren Energietragern ausokologischer, okonomischer und technischer Sicht, Land-wirtschaftsverlag GmbH Munster, 428 Seiten, ISBN 3-7843-2717-6.

Launhardt, T., 1998. Dioxin- und PAK-Konzentrationen imAbgas und Aschen von Stuckholzfeue-rungen, Forschungs-bericht, Materialien, Bayerisches Staatsministerium furLandesentwicklung und Umweltfragen, Nr. 142.

Strehler, A., 1984. Moglichkeiten der Trocknung vonHolzhackschnitzeln, Sonderdruck der Landtechnik Wei-henstephan, 17 Seiten.

Strehler, A., 1994. Warmegewinnung aus Biomasse, Potentialein der Bundesrepublik Deutschland und Stand der Tech-nik, im Tagungsband 3. Symposium Biobrennstoffe undumweltfreundliche Heizanlagen Regensburg, 27 bis 28 Sep-tember 1994, Herausgeber: Ostbayerisches TechnologieTransferinstitut, S.2335.

Strehler, A., 1996. Warme aus Stroh und Holz, Arbeitsunterla-gen DLG Fachbereich Landtechnik, Marz, DLG Verlag.

Strehler, A., Moglichkeiten der energetischen Nutzung vonHolz, Landtechnik Berichte 2:5, SchriftenvertriebLandtechnik Weihenstephan.

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