PergamonBiomass and Eioenerg~ Vol. 7, Nos. l-6, pp. 297-306. 1994

0961~9534(94)00072-7Copyright c 1995 Elsevier Science Ltd

Printed in Great Britain. All rights reserved0961-9534/94 $7.00 + 0.00

USE OF PYROLYSIS OIL IN A TEST DIESEL ENGINE TOSTUDY THE FEASIBILITY OF A DIESEL POWER PLANT

CONCEPT

YRJ~ SOLANTAUSTA,* NILS-OLOF NYLUND* and STEVEN GUST?*Technical Research Center of Finland, P.O.B. 1601, FIN-02044 Espoo, Finland

TNESTE OY, P.O.B. 310, FIN-06101 Porvoo, Finland

Abstract-The economic viability of power production in a diesel power plant utilizing flash pyrolysis oilproduced from sawmill wastes in Finland has been investigated. A combination of biomass feedstockcosts, pyrolysis oil fuel properties (ignition quality, lubricating properties, combustion speed and duration,emissions, etc.) and their effect on power plant investments and maintenance will ultimately determineelectricity busbar costs and the economic competitiveness of the concept. Pyrolysis oil is not a suitablefuel for a conventional diesel engine as such. The preliminary tests with additive treated pyrolysis oildemonstrated, however, that once ignition has taken place, pyrolysis oil bums rapidly. Pyrolysis oil maybe a suitable primary fuel for a diesel engine with a pilot injection system, which secures the ignition ofthe main fuel.

INTRODUCTION

Recent progress in the development of the py-rolysis oil production technology and the scale-up of pyrolysis oil plants to the 10 tonne oil perday level has shifted the emphasis from oilproduction to applications. Fuel applicationsare divided into those for transportation pur-poses and those for heat and power. Transpor-tation fuels or fuel components are uncertainsince the upgrading of pyrolysis oils is still at anearly stage. A number of possible heat andpower applications are being considered: fuelsfor boilers, gas turbines or stationary diesels.And while the economic prospects for pyrolysisoils for these applications look promising inthe long term, near term applications aredifficult to find due to the present low prices offossil fuels. It is therefore important to findniche markets for pyrolysis oil from whichimportant operational experience can be ob-tained and used for further oil development.These niche markets are in the waste treatmentarea where biomass can be obtained at low orno cost.

One such possible niche market could be theproduction of heat and power in a stationarydiesel engine at sawmills. The sawdust at thesemills is normally combusted to provide heatfor drying, but could also be used to produce

electricity for the plant’s own use, with theexcess sold to the grid. Diesel engines werechosen for this study mainly because of theirrelative insensitivity to the contaminant levelsfound in pyrolysis oils. They are already widelyused in power production either as a mediumspeed engine (350-900 r.p.m. with power output1-15 MW) or slow speed (90-150r.p.m.,l&50 MW). The diesel engine also has numer-ous other advantages:

??High power to heat ratio;??High efficiency also on partial load;?? Fuel flexibility (natural gas, light to heavy

oils);??Low quality fuels may be used;??Relatively low specific capital investment; and0 Low operating costs.

The medium- and slow-speed diesel enginesare known to be able to operate on quite lowgrade fuel oils. The main technical uncertaintyin this concept is concerned with the uniqueproperties of pyrolysis fuel oils: high watercontent and oxygen content which make themdifficult to ignite; possible instability which willincrease fuel viscosity; acidity which could affectmaterials and maintenance intervals and levelof emissions and need for special catalyticcleaning.

298 Y. SOLANTAUSTA et al.

In order to address these questions, the workwas broken into three tasks:

1. Pyrolysis oil analysis;2. Diesel engine tests; and3. Economic analysis.

Engine tests at the Technical Research Center ofFinland (VTT) are carried out in three steps:

??Basic tests with ignition improver enhancedpyrolysis oil in a single cylinder high-speeddiesel engine (Petter AVB) to determine basiccombustion properties;

?? Pilot-injection tests with a modified high-speed multicylinder diesel engine (Valmet 420,commercially available 40-180 kW) to studycombustion in a pilot-injection concept;

and, if these tests are promising and sufficientamounts of fuel are available:

??Tests in a medium-speed diesel engine (Wart-sila, commercially available 800-16,000 kW).

Technically, pyrolysis oil would be leastsuited for a high-speed diesel engine withoutpilot-injection. The problem of ignition can behandled by adding a cetane improver (nitratedalcohol) to the pyrolysis oil. If a small high-speed engine can run on cetane-enhancedpyrolysis oil, then certainly a medium-speedpilot-engine should be able to do it. Ignitionimprover additives are very expensive, so thiswould not be an economically viable solutionfor power generation. As costs for engine tests

will increase dramatically with engine size, itwas decided that it would be a good solution toproceed stepwise as mentioned above.

PYROLYSIS OIL ANALYSIS

The hardwood pyrolysis oil employed in thisstudy has been provided by Ensyn TechnologiesInc. (Canada). Analysis of pyrolysis oil is com-pared in Table 1 with a heavy fuel oil specifica-tion that is acceptable for the identifiedcommercial medium-speed diesel engine.’ Twoconventional fuel oils are shown also as refer-ence. The light fuel oil corresponds to No. 2 fueloil while the heavy to No. 4. It may be estimatedthat less preheating is required for pyrolysis oilthan for heavy fuel oil, because of the lowerviscosity of pyrolysis oil. This is beneficial asthe instability of pyrolysis oils when heated iswell known.’ Ash content of pyrolysis oil assuch does not seem to be excessive. However,e.g. particle size distribution of ash is oftencritical in the injection system. At this stageno data exists for particle size distribution ofash. Pyrolysis oil does not include excessiveamounts of alkali or heavy metals. It appearspossible to avoid e.g. hot corrosion, which mayoccur in combustion systems when alkali metalsand other compounds interact. Modernmedium-speed diesel engines tolerate relativelyhigh levels of impurities in fuel. Finally,it should be pointed out that no effort tooptimise fuel quality of pyrolysis oil has been

Table I. Analysis of Ensyn flash pyrolysis oil (feedstock hardwood) and fuel oils

Light Heavy DieselPyrolysis oil fuel oil fuel oil eng req.

Heating value (HHV)MJ/kg 17.5 42.4 40.0MJ/dm3 21.3 36.9 40.4

Density (kg/dm’)15°C I .22’“’ 0.87 1.01 1.01

Viscosity (cSt)20°C 128@’ 14 >lOOO50°C 13 6 175 600

Ash (wt%) 0.13”’ 0.01 0.05 0.2Water (wt%) 20S’d 0.02 0.04 1.0Condradson carbon residue (wt%) 17.8”’ 0.02 12 22Flash temperature (“C) 66”’ 30Pour point (“C) _ 2718) 0 15 30Sulfur (wt%) 0 0.18 2.3 5Metals (ppm)

Na 38’h’ 0.1 IO 100K 330’s’Ca 1 OO’h’Pb < 0.3’s’V OS’h 0.01 110 600Cl 80”’

‘“‘ASTM D 4052. @‘ASTM D 445. @‘EN 7. rd)Karl Fischer titration, a mixture of pyridine andethylenemonomethylglykolether (1:4) as solvent. ‘*‘ASTM D 189. “‘ASTM D 93. ‘g’ASTM D 97. ““AAS. “‘IC.

Use of pyrolysis oil in a test diesel engine 299

made in production. Therefore it may be poss-ible to improve its quality as diesel fuel alreadyat production stage.

Fuel oil viscosity is an important parameter inthe design of storage tanks, supply facilities andfuel atomisation. Viscosities for typical light andheavy fuel oils are shown together with twopyrolysis oil samples in Fig. 1 as a function oftemperature. Pyrolysis oils display a similarbehaviour as the mineral oils but the log vis-cosity vs temperature curve has a different slopethan for the mineral oils. The viscosity of pyrol-ysis oil increases much faster than mineral oilsas the temperature is reduced which mightrequire that storage tanks be heated. The stab-ility of pyrolysis oil is also of concern. It isknown that the properties of oil will changewhen stored, but the exact mechanism of thisprocess is not known. Based on a stabilityanalysis carried out for a wood-derived high-pressure liquefaction oil3 it may be speculatedthat some polymerisation reactions occur also inpyrolysis oils while stored. Viscosity of pyrolysisoil has been measured (@ 50°C) to increasefrom about 13 to 22 cSt in 6 months. Thisincrease is not considered critical for engineuse.

DIESEL ENGINE TESTS

Fuel parameters affecting engine performanceThe diesel combustion process involves both

physical and chemical phenomena, includingfuel injection and spray formation, fuel evapor-ation and autoignition. Fuel contaminants suchas sulphur and heavy metals interact with thelubricating oil which affects the reliability of theengine. Examples of fuel properties, that play a

major role in engine performance (includingemissions) and reliability are:

0 Ignition quality;??Chemical composition: emissions, acidity and

corrosion;??Heating value: lower energy density fuel re-

quires higher flowrate;??Density;0 Viscosity-affects pumps, flow properties;??Lubricating properties;??Deposit formation-blocking of injectors;??Sulphur content-corrosion; and??Heavy metal content--deposit build-up.

In addition, the speed and size of the dieselengine will influence the type of fuels that can becornbusted. In general, small, high-speed en-gines set more stringent requirements on fuelproperties than a large, medium- or low-speedengine. A large engine is built to withstand bothhigh mechanical and thermal stresses. Thesefactors make large engines more suitable forlow-quality fuels than small engines. One way toovercome problems caused by poor ignitionproperties of the fuel is to use a pilot-injectionsystem. In such a concept a small amount ofpilot fuel with good ignition properties is in-jected prior to the main fuel to initiate combus-tion. Once combustion has started, the fuel withpoor ignition quality can also be cornbusted.The pilot system has been applied to enginesburning natural gas, alcohol and heavy fuel oilas the main fuel.U The problem o pf oor ignitioncan also be handled by adding cetane improver(nitrated alcohol) to the fuel. Since ignitionimprover additives are very expensive, thiswould not be an economically viable solutionfor power generation for concentrations above

1,000 I

2

1 I I I I I I I-20 0 20 40 60 80 100 120 140 160

Temperature C

Fig. I. Viscosity of mineral oils and pyrolysis oils (two separate samples from Ensyn).

300 Y. S~LANTAUSTA et al.

1%. However, the concept was employed for thepreliminary engine tests.

Test engine and test procedureA small high-speed engine was used for the

tests due to fuel quantity limitations. It was a500 cc single cylinder Petter AVB diesel engine.Technical data for the engine are given inTable 2. A combustion analyzer (AVL In-diskop) was used to measure cylinder pressureand injector needle movement traces and tocalculate ignition delay, injection duration, heatrelease, etc. The engine test stand was alsoequipped with exhaust analyzers (carbonmonoxide, total hydrocarbons, nitrogen oxidesand smoke number by Bosch).

The Petter engine was run at rated speed(2000 r.p.m.) at 50% load. The 50% load con-dition (approx. 2.5 bar BMEP, Brake MeanEffective Pressure) was chosen so that all fuels(diesel, ethanol and pyrolysis oil) could be runon the same power level despite the differencesin heating value. No modifications on injectiontiming nor injector nozzle type were made. Witha fuel system designed for a higher fuel flow,pyrolysis oil would give the same power outputas diesel fuel. The viscosity of the pyrolysis oilsupplied by Ensyn was about 130 cSt (20°C)and it could be used in the engine withoutpreheating.

From previous experience at the TechnicalResearch Center it was obvious that pyrolysisoil would not ignite as such in a conventionaldiesel engine.’ Using ignition improver additivesfor methanol and ethanol in diesel engines issomewhat well established. Two different addi-tives, Diesel Improver 2 from Ethyl Corpor-ation and N-Cet from ICI were subjected tosolubility tests. The Diesel Improver 2 additivewould not mix with pyrolysis oil, whereas up to10% vol. N-Cet could be added to the pyrolysisoil. Therefore, the basic tests were carried outwith N-Cet.

Table 2. Technical data for the Petter AVB test engine6

Number of cylindersBore/stroke (mm) SO!:lODisplacement (cm’) 553Compression ratio 15.3:1Rated speed (r.p.m.) 2000Maximum power (kW) 4.8BMEP (bar at max. power) 5.2Static injection timing (“BTDC) 24Combustion system DI, naturally

aspiratedBMEP = brake mean effective pressure.

Since the amount of pyrolysis oil was limited,the engine had to be started and warmed up ona second fuel. Due to the instability of pyrolysisoil at high temperature, it might also be necess-ary in actual practice to flush the fuel system outwith a separate fuel before shutting down theengine. Initially, diesel fuel was tried for thispurpose, but since mineral fuels will not mixwith pyrolysis oils, an intermediate fuel wasrequired. Ethanol with ignition improver addi-tive as an intermediate fuel was found to beadequate for this purpose. Ethanol will mixreadily with both diesel fuel and pyrolysis oil atnormal ambient temperature. And becauseethanol is also a very effective detergent, it helpsto clean up the injector nozzle which was foundto coke very fast when pyrolysis oil was used.

The test procedure was as follows:

??Start and warming up on diesel fuel;??Switch over to ignition improved ethanol;??Switch over to ignition enhanced pyrolysis oil;0 12 min running on pyrolysis oil;??Switch over to ethanol to clean the injection

system; and??Switch over to pyrolysis oil, etc.

Although ethanol was used to clean up theengine while running the tests, engine perform-ance was not stable. Engine performancechanged as the injector nozzle got clogged, andthis took place very rapidly. This must beconsidered when evaluating the experimentaldata.

Conventional diesel fuel, one low-qualityCFR-reference fuel (cetane number 35.2) andcetane-enhanced ethanol was used as reference.Ethanol does not ignite as such, and must betreated with ignition improver for diesel oper-ation. Thus ethanol forms an interesting refer-ence to pyrolysis oil. The following notationsare used for the test fuels:

??Diesel oil: DIE??CFR reference fuel: RF35??Ethanol: ETOH,0 Pyrolysis oil: PYO,.

Here x is ignition improver concentration byvolume. For ethanol 3 and 5 and for pyrolysisoil 3, 5 and 9% ignition improver was used.

Ignition delayRESULTS

In order to achieve the same power as withdiesel fuel, injection with pyrolysis oil (with

Use of pyrolysis oil in a test diesel engine 301

lower energy density and higher viscosity) has tobe modified. Injection is started earlier (due toincreased fuel viscosity), and injection durationis increased (due to increasing amount of fuelinjected). Figure 2 shows injection timing withthe different fuels. With conventional diesel fuel,injection starts at 9”CA (degrees crank angle)BTDC (before top dead center), and the injec-tion duration is approx. 8”CA. Thus injectionends around top dead center. For ethanol,injection starts at YCA BTDC, takes around12”CA, and ends at 7”CA ATDC (after topdead center). For pyrolysis oil, injection starts at12”CA BTDC, takes 17”CA, and ends 5”CAATDC. Thus injection ends approx. 5”CA laterwith ethanol and pyrolysis oil compared todiesel oil. Injection timing and injection ratecould be changed by pump modifications. In-creased injection rate would mean increasedinjection pressure.

Ignition delay is the time delay (expressed indegrees crank angle) between start of injectionand start of combustion. For conventionaldiesel fuels, ignition delay correlates with cetanenumber.

Ignition delay with conventional diesel fuels isin this case 6”CA, and with poor ignition qualityreference fuel 8”CA. The concentration of ig-nition improver has a great influence on theignition delay with ethanol. Engine operationwith 3% additive was stable but rough, and with5% additive ignition delay could be broughtdown to normal diesel values.

The ignition improver was not as effectivewith pyrolysis oil as with ethanol. Also in thiscase, minimum concentration of additive was3%. Here, however, ignition delay was almost15”CA, and the engine operation unstable.There was only a small difference in ignition

+10

- 1 5 II I I /

DIE RF35 ETOH PYOFig. 2. Injection timing with different fuels

delay, l”CA, when improver concentration wasincreased from 5 to 9% in pyrolysis oil, andignition delay was still longer than with poorquality reference fuel (Fig. 3).

Combustion durationThe overall timing of the combustion process

depends on the timing of the injection process,ignition delay and combustion duration. Figure4 shows combustion timing (5, 10, 50 and 90%heat released) for the different fuels. Startinglocation of columns indicates start of combus-tion in “CA. Combustion starts slowly withethanol, pyrolysis oil containing 3% additiveand with poor quality reference fuel (10% heatreleased at 5-16” ATDC). Pyrolysis oil with 5and 9% improver and conventional diesel areconsiderably faster (10% heat release at 3”ATDC). Timing for 50% heat release is roughlythe same for pyrolysis oil (5 and 9% additive)and diesel. Very interesting also is the fact thatthe time needed for 90% heat release is at itsshortest with pyrolysis oil, approx. 15”CA forpyrolysis oil compared with approx. 25”CA fordiesel. The time needed between 10 and 90%heat release is roughly 22”CA for diesel and13-17”CA for pyrolysis oil.

The results show that, although pyrolysis oilis difficult to ignite, it burns readily when thecombustion has started. These results indicatethat pyrolysis oil could be a suitable main fuelfor pilot-injection engines.

Figure 5 shows the center of gravity for thecombustion heat release curve (in degrees ofcrank angle) for the different fuels. The center ofgravity of combustion has a great influence onengine performance and exhaust emissions.Though the properties of conventional diesel oiland pyrolysis oil differ considerably, pyrolysis

2o

6

n

10

-llllDIE RFJS ETOHJ ETOH5 P Y 0 3 PYO5 PYO9

Fig. 3. Ignition delay with different fuels

302 Y. SOLANTAUSTA et al.

-101 ’ I / I I I I

PYO9 PYO5 DIE ETOHS RF35 PYO3 ETOHJ

Fig. 4. Combustion timing.

oil with 5 and 9% ignition improver gave almost modern engines e.g. withthe same center of gravity of combustion as expected to be smaller.

higher BMEP are

diesel oil. The center of gravity of combustionwas delayed with ethanol, with pyrolysis oil with3% additive and with the poor ignition qualityreference fuel.

EmissionsDuring the tests, exhaust gas composition

(component concentrations) and smoke numberwere monitored. As the volumetric flow ofexhaust gases is more or less independent of fuelcomposition, a preliminary comparison can bemade by only studying component concen-trations. As to the concentration of total hydro-carbons measured by a flame ionizationinstrument, it should be noted that the chemicalcomposition of the exhaust can influence thereading. The results are presented in Table 3.

The scattering of the emission results wassomewhat high due to the poor condition of theinjector nozzle. In this engine, however, pyrol-ysis oil with 5% ignition improver gave more orless the same exhaust performance as conven-tional diesel fuel, and better emission perform-ance compared to the reference fuel with poorignition quality (see also center of gravity ofcombustion). For pyrolysis oil, best emissionresults, except for smoke number, were obtainedwith 5% ignition improver. Ethanol gave lowersmoke and nitrogen oxide emission but highertotal hydrocarbon emission than the other fuels.Detailed analyses, including unregulated emis-sions, will be measured at a later stage.

It should be noted that the engine performsfairly poorly with standard diesel fuel regardingCO and THC emissions. It is mainly due to theold design of the test engine. Emissions with

20

IITDCDIE RF35 ETOH3 ETOH5 PY03 FYO5 PYO9

Fig. 5. Center of gravity of combustion for different fuels.

The preliminary tests indicate that pyrolysisoil should do relatively well in a pilot-injectionengine. Pyrolysis oil burns readily once ignited.Normally the condition of the injection nozzleis critical for spray formation and ignition. In apilot-injection engine, however, the condition ofthe main injector should not be as critical, as themain fuel is injected in a flame that is alreadyburning. The preliminary emission results showthat there should be no major problem with

Table 3. Exhaust gas composition and smoke number withdifferent fuels (average values)

c o THC Smoke(~01%) ( p p m ) Cp%) number’“)

DIE 0.1 500 500 2.1RF35 0.2 700 600 2.9ETOH3 0.2 1000 400 0.4ETOHS 0.1 600 400 0.4PYO3 0.3 800 700 2.5PYO5 0.2 500 500 2.2PYO9 0.2 700 800 1.6

‘“‘Bosch units. CO = Carbon monoxide. THC = Totalhydrocarbons. NO, = Nitrogen oxides.

Use of pyrolysis oil in a test diesel engine 303

exhaust emissions. Still this is a part that needsfurther investigations, and more componentshave to be analyzed to get a complete picture ofthe situation. Also the possibility to use anoxidizing catalyst to reduce emissions should beinvestigated. It should also be noted that theBMEP of modern medium-speed engines isaround 20 bar compared to 2.5 bar in the testengine. The load was thus considerably less inthe tests than would be the case in commercialoperation.

PLANT PERFORMANCE AND ECONOMICS

A preliminary cost and performance study forpower production utilizing flash pyrolysis oil asfuel at a sawmill has been carried out. Theprocess concept is based on the IEA processdesign8 which in turn was largely based on theexperimental results carried out in a shallowfluidized-bed reactor by Scott and Piskorz’-” atthe University of Waterloo. In the IEA study,a circulating fluidized bed was selected asthe preferable pyrolysis reactor. The primaryvapours are condensed in an absorber tower.The drier is heated with combustion productsof char and non-condensable gases from theabsorber.

The pyrolysis process was modelled and themass and energy balances calculated with AspenPlus’” at the Technical Research Centre (VTT).The power cycle has been analysed by theFinnish engineering contractor Energy-EkonoLtd. The sawmill heat and power loads, as wellas cost for the purchased electricity are based onan existing mill in Finland.

Mass and energy balances for the proposedprocess concept are presented in Tables 4 and 5.

Table 4. Mass and energy balance for the pyrolysis oilproduction

WetDryHHV-based”)LHV-basedo

Power demand

Forest PyrolysisSawdust residue oil

(t/h) 1.3 4.9 2.5(t/h) 1.1 2.5 2.0@J/h) 22.3 51.2 44.9@J/h) 20.3 41.9 40.0(GWh/a) 45 93 89(MW) 0.5

Moisture content (%) 20 50 20 Oil yield of 70wt% (water content of 20wt%)HHV”’ (MJika) 20.7 20.7 22.6 Oil oroduction about 20.000 t/a (wet)LHV (MJ/kij 15.0 8.5 16.1Efficiency@HHV-based (%) 58LHV-based (%) 60

(‘)Higher heating value. o)Lower heating value.~“Calculated for dry matter. (“Power converted to fuel witha nominal 40% generating efficiency.

Table 5. Energy balance for the power productionPyrolysis

oil Power HeatEnergy (GWh/a) 89 36 43

Power and heat (MW) 8.1 9.5Efficiency”’ (%) 41 48Overall”’ (%) 25 31

(“From wood oil to power/heat, based on LHV values.‘*‘From wood to power/heat, based on LHV values.

The sawmill heat and power demands are about43 and 7 GWh/a, respectively. About 36 GWh/aof electricity may be produced in cogeneration(corresponding to the existing heat demand).Sawmill internal consumption substrated, about29 GWh/a of power may be sold to the grid.

The calculated energy efficiency for oil pro-duction is 61%. This value may be compared toother reported values for pyrolysis oil pro-duction from wood. Wan’* has assessed theGeorgia Tech Entrained Flow Pyrolysis System,and reports an efficiency of 52% for oil pro-duction. Char is a by-product in the concept. Anefficiency of 74% may be calculated from theassessment by BlackI for the Waterloo FastPyrolysis Process. the IEA working groups,‘4 hasanalysed two separate flash pyrolysis systems,one based on a shallow fluidized bed, and theother based on circulating fluidized-bed technol-ogy. The reported efficiencies are 57 and 65%,respectively.

Cost estimates for pyrolysis oil and powerproduction are presented below. Investmentcost estimate for the pyrolysis plant is based ondata presented by Beckman and Graham.15 In-vestment estimate for the diesel power plant isbased on data concerning actual completedprojects (employing conventional diesel fuels).Factors employed in the economic study for thebase case are presented in Table 6. Investment,

Table 6. Base factors for the economic studvTime for the assessment fall 1992Exchange rate 1 US% = 5.5 FIMContingency for pyrolysis plant investment 10%Contingency for power plant investment 0%Capital costs estimated with annuity method (rate of interest

10%. service life 20 years, corresponding to CRF 0.118)Pyrolysis plant capacity 94 ton/d dry wood corresponding

to one reactor

Wood consumption about 28,ood t d’ry matter/aDiesel engine: power 8.1 MW, heat 9.5 MWOperating time for pyrolysis plant 8000 h/aOperating time for h&i power plant 4500 h/aSawdust cost USS4.4/MWhForest residue US%8.7/MWhBy-product heat fixed @ USS22/MWh

304 Y. S~LANTAUSTA et al.

Table 7. Investment, operating and production costs corre-sponding to Table 6 factors

Pyrolysis oil Powerproduction production

(US$ million) (USS million)Plant fixed capital investment 3.5 6.3

Start-up 0.4 0.1Working capital 0.2 0.3Interest during construction 0.3 0.3

Total capital requirement 4.4 7.1USS million/a US% million/a

Feedstock/fuel cost 0.9 2.3Other operating cost 0.9 0.2Capital charges 0.5 0.8Credit for heat product -0.9Production cost 2.3 2.4

US$/MWh 26US$/kWh 6.5

operating and production costs are presented inTable 7 separately for oil and power production.

The new process concept has been assessedat an existing site in Finland in Figs 6-8. InFig. 6, the yearly income from power sale for thesawmill is presented as a function of feedstockcost. Typically for the Finnish sawmill case thesawdust price would be around US$4.4/MWh.With the existing tariff it would be possibleto sell power to the grid with US$3.l/kWh. At

Fig. 6. Power production at a sawmill in a pyrolysis oil diesel Fig. 8. Power production at a sawmill. Yearly income as apower plant. Yearly income as a function of forest residue function of price of electricity sold to the grid, a 30%cost for two electricity costs as parameter. Sawdust @ investment credit compared to a case with no credit. Saw-US$4.4/MWh. CRF for the investment 0.1175, heat @ dust @ US$4.4/MWh, forest residue @ US$8.7/MWh.

USS22/MWh, oil production (LHV) efficiency 60%. CRF for the investment 0.1175, heat @ US%22/MWh.

0.;

0.2

o 0.1

2ss”2 C._z2QI-0.1

$x--0.2

-O.!

-0.4

Cost of Forest Residues US$/MWh

Fig. 7. Power production at a sawmill. Yearly income as afunction of forest residue cost, efficiency of pyrolysis as aparameter. Sawdust @ US$4.4/MWh. CRF for the invest-ment 0.1175, investment credit 30%, heat @ US$22/MWh,

price of electricity @ 53 mills/kWh.

Pri3ce of” Sold5Pow:r c/:Wha

Use of pyrolysis oil in a test diesel engine 305

fixed sawdust cost of US%4.4/MWh, and evenwith a high selling price of produced electricity,production would be uneconomic. If a capitalinvestment subsidy of 30% is granted, as is thecase at present for plants employing new tech-nology in Finland, production would be (mar-ginally) economic with low feedstock cost(below US$6/MWh) and high selling price(US$5.3/kWh) of electricity.

The effect of uncertainty related to the per-formance of the pyrolysis unit has been studiedin Fig. 7. The thermal efficiency of oil pro-duction has been varied between 56 and 64%(based on LHV), corresponding to liquid yieldsbetween 65 and 75 wt% (wet pyrolysis liquidfrom dry feedstock). As efficiency increasesfrom 56 to 64%, production becomes economic(with the employed economic parameters) atforest residue cost below US%10 instead ofbelow US%2/MWh.

The profitability of the investment is highlydependent on the price of electricity sold to thegrid. This is shown in Fig. 8, where two case areshown: one with a 30% investment credit andone without the credit. The respective break-even points are around 5.5 and USe7/kWh.

The capital recovery factor for the capitalcost has been 0.1175 in the calculations above.With a wood cost of US%4.4/MWh the yearlyloss is about US$O.3 million. with the CRFs of0.08, the respective income would be US$O.4million.

A contingency of only 10% has been em-ployed for the pyrolysis plant investment costpresented. There are technical uncertainties re-lated to scale-up of pyrolysis technology. Theuse of pyrolysis oil in diesel engines has not beenproven in long-term tests. Therefore the resultsshould be considered preliminary. The techno-economic analysis and the models will be ver-ified as soon as more detailed data are availableconcerning pyrolysis plant and diesel engineperformance.

DISCUSSION

Preliminary tests indicate that once ignited,primary pyrolysis oils will combust readily in adiesel engine. To overcome the poor ignitionproperties of the oil, a pilot fuel engine isprojected to be employed in commercial oper-ations. Emissions from the high speed enginetest results with ignition enhancer indicate thatlevels of emissions (CO, THC NO,Y and smoke)

from medium-speed, pilot-fuel engines shouldnot be significantly greater than for referencefuels.

However, much further research is needed.Preliminary tests with a four-cylinder turbo-charged medium-speed diesel engine equippedwith pilot injection have been carried out. Moretests will be carried out with the pilot injectedengine during the spring of 1993. Performanceand emissions will be measured. Extended testswith this 60 kW engine are planned for late1993. If all these tests are successful, pyrolysisoil will be used as fuel in a larger medium-speeddiesel engine in 1994, provided enough oil isavailable.

The estimated production cost for the pyrol-ysis oil with the base value wood prices is aboutUS%26/MWh (US$7.6/MMB.t.u.). The valuemay be compared to estimated production costsfor similar systems with the same feedstock cost:from the data presented by Graham et a1.16a value of US$l9/MWh (US$5.5/MMB.t.u.)may be calculated. Production cost ofUS$l8/MWh (US%5.2/MMB.t.u.) may also bederived from correlations presented by Cottamand Bridgwater.” Earlier, Wan’* assessed aslightly different wood pyrolysis system, andreports a production cost of US%34/MWh(US%lO/MMB.t.u.).

The overall efficiency (from wood to powerbased on lower heating value of wood) for thepresented power production system is about25%. This is a relatively competitive numbertaking into account the small scale of operation.In addition more than 30% of district heating orprocess heat could be generated.

The profitability of the proposed conceptis highly dependent on the selling price ofelectricity to the grid. Even though economicswere not favourable for the proposed concept inFinland at present, it is believed that bettereconomics are available, e.g. elsewhere inEurope.”

Acknowledgements-The authors wish to acknowledgeEnergy, Mines and Resources Canada, Vapo OY, NesteOY, and the Ministry of Trade and Industry (Finland) forfinancial support of the work. We would also !ike to thankEnsyn Technologies Inc. for providing the pyrolysis oilsample. Finally we wish to acknowledge M&ten Wester-holm and Jan-Erik Sandstriim for carrying out the enginetests.

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