the karlsruhe "bioliq" process for biomass gasification - B.A.U.M. ...

2 nd European Summer School on Renewable Motor Fuels
Warsaw, Poland, 29 – 31 August 2007
The status of the FZK concept
of biomass gasification
E. Henrich
Forschungszentrum Karlsruhe GmbH
Wednesday, 29 August 2007, 13:45 – 14:30
Paper

Summer School, University of Warsaw, 29.-31. August 2007
THE KARLSRUHE "BIOLIQ" PROCESS FOR BIOMASS GASIFICATION
E. Henrich, N. Dahmen, K. Raffelt, R. Stahl, F. Weirich
Forschungszentrum Karlsruhe, ITC – CPV, POB 3640, D-76021 Karlsruhe
ABSTRACT
Biomass is the only renewable carbon resource and expected to substitute gradually
a part of the fossil fuels. A high biomass share in our future energy mix must
comprise the agricultural by-products, mainly straw, in addition to wood. Straw and
other fast growing herbaceous biomass contains more ash, K and Cl than wood and
suitable gasification technologies are not well developed. At the Karlsruhe research
centre a two-stage process for biomass conversion into synfuel is being developed,
acronym "Bioliq". The process pays special attention to the properties of straw and
other dry, non-woody biomass feedstock. Small or thin dry biomass particles are first
liquefied by fast pyrolysis in a number of regional plants. The pulverised pyrolysis
char is suspended in the pyrolysis condensates to generate stable pastes, sludge's
or slurries for storage and economic transport by rail to a large central plant for synthesis
gas generation. Syngas cleaning followed by a selective, catalysed synthesis
of organic chemicals or synfuels e.g. to hydrogen, methane, methanol or Fischer-
Tropsch diesel are well known technologies from large - scale commercial coal and
natural gas gasification plants. The Karlsruhe biosynfuel process allows an operation
of very large and therefore more economic biosynfuel production plants with high capacities
of 1 Mt/a or more. The economy of many small-scale biosynfuel facilities is
less favourable.
1. INTRODUCTION
The combustion of finite fossil fuels supplies almost 80% of the world primary energy,
ca. 11 Gtoe (billion tonnes of oil equivalent) in year 2006; fig. 1 shows the percentage
share. Substitution of fossil fuels by renewable energy and carbon sources
is among the key challenges of this century. The capacity of biocarbon based energy
sources is not sufficient to replace all present fossil fuel applications – also in view of
the fact that applications as carbon raw material are first priority not energy; bioenergy
is a misleading aim.
Development and worldwide exploitation of renewable, environmentally compatible,
sufficient and affordable energy sources requires much time, money and innovative
ideas. Global warming and adverse climate changes as well as common sense advocate
for a substitution of fossil fuels even before the proven and economically recoverable
fossil reserves are exhausted. In the Kyoto protocol, the international
community has agreed to limit greenhouse gas emissions, especially CO2 from the
combustion of fossil fuels. With the increasing world population and corresponding
fossil energy consumption and business as usual, the proven and economically recoverable
conventional oil reserves and unconventional tar sands of ~ 170 Gtoe [FIS
04] will be exhausted in the course of this century. For the comparable reserves of
natural gas including recoverable unconvential methane hydrates, the same situation
can be expected only few decades later.

Summer School, University of Warsaw, 29.-31. August 2007
fossil fuels ~ 78 %
reserves ~ 170 Gtoe
consumption 3,4 Gtoe/a
reserves ~ 170 Gtoe
consumption 2,2 Gtoe/a
reserves ~ 800 Gtoe
consumption 2,4 Gtoe/a
21 % gas
34 % oil
23 % coal
6
6
10
nuclear power
hydropower
biomass
Doubling from ~ 10 to ~ 20 Gtoe/a in ca. 50 - 100 a from now
1 toe (tonne oil equivalent) = 42 GJ, 1 kW(th) = 0.375 kW(el)
Fig. 1: World primary energy mix 2000, total consumption 10 Gtoe
10
8
6
4
2
0
Source:BGR
in billion
world population
oil consumption
0 500 1000 1500 2000 2500
years
Fig. 2: The oil age in a timeframe of millennia
2
6,6 in 2007
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Summer School, University of Warsaw, 29.-31. August 2007
Exhaustion of the large but less convenient coal reserves of at least 600 Gtoe will
probably follow in the course of next century. Further improvements of mining and
exploration techniques are not expected to double the presently known fossil reserves.
The potential correlation between the present fossil fuel consumption bacchanal
and the world population in a time frame of millennia is illustrated in fig. 2.
To maintain our present traffic system without expensive changes of the available
infrastructure, the oil-derived hydrocarbon fuels have to be gradually substituted - at
least partly - by synthetic fuels from the more abundant coal or – finally - renewable
biomass.
Biomass is the only renewable carbon resource. The present worldwide motor
and jet fuel consumption amounts to almost 2 Gt per year and is still increasing. Fossil
motor fuel substitution by biosynfuels via biomass gasification and Fischer-
Tropsch synthesis has an energy conversion efficiency of about 50% optimistically
and would require a huge amount of at least ca. 4 Gtoe ligno-cellulosic biofeedstock
per year; this is equivalent to our present crude oil consumption or to an almost 10
billion tonne harvest of dry lignocellulosics like wood or straw. Today biomass contributes
about 10+% or ca. 1 Gtoe/y to our global primary energy consumption of ca.
11 Gtoe in 2007. The creation of such a huge biosynfuel industry with 3 to 4 times
the present biofeedstock consumption for energy is a hint to the potential supply limitations
for a sustainable biosynfuel production, also in view of other competitive or
inevitable applications of biomass as a renewable carbon source.
The technology for the conversion of syngas into synfuel and chemicals is well
known. Today, the worldwide methanol production from syngas, amounts to about 35
Mt/a - mainly from natural gas [WUR 07]. In 1944, toward the end of World War 2,
Germany produced already 0.6 Mt/a of Fischer-Tropsch synfuel via gasification of
coal – plus ca. 3 Mt/a by catalytic high pressure coal hydration. Today SASOL (South
African Synthetic Oil)-company produces 6 Mt/a of improved FT-products in Secunda
and Sasolburg, SA, from cheap hard coal, acronym CTL (coal to liquid). The photo's
of SASOL's synfuel facilities in fig. 3 give an impression of the technical maturity.
At mid 2007 crude oil prices of about 50 €/bbl, synfuel production via syngas from
very cheap natural gas, stranded gas or top gases can be already competitive with
crude oil derived motor fuels. Since 1993 two such commercial GTL (natural gas to
liquid) plants are in operation: the Shell 22,5 kbbl per day SMDS-facility in Bintulu,
Malaysia, and the 12,5 kbbl per day Mossgas-facility in South Africa. In 2007 the
34 kbbl per day Oryx I plant of Sasol/Quatar petroleum in Ras Laffan has been put
into operation [ZEN 07]. Conversion of biomass to liquid synfuel via gasification and
synthesis, acronym BTL, is not much different from the already practised CTL- and
GTL-technology. Only the first steps for the production of a clean syngas differ
somewhat because of the special adaptations required for different bio-feedstocks;
the tail end steps for catalytic syngas conversion are the same. Use of biomass as
the only renewable carbon source is the unique advantage of BTL.
2. CHARACTERISTICS OF AGRICULTURAL BY-PRODUCTS
The large arisings of agricultural by-products e.g. in form of ca. 1+ Gt/a of surplus
cereal straw correspond to ~ 5% of the world primary energy consumption. This is ca.
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Summer School, University of Warsaw, 29.-31. August 2007
Fig. 3: SASOL's 6 Mt/y synfuel production facilities from coal (CTL) in Secunda SA
Different biomass and carbon feedstock
fossil
fuel:
other
biomass:
coal ... starch, oil ...
special
chemicals
pulverised coal
coal/water slurry
synthesis products:
synfuel, chemicals, H 2
lignocellulosic biomass:
wood, straw, hay ....
biomass preparation
fast pyrolysis
bio-oil/char -slurry
rail transport from many pyrolysis plants
to large, central plant for syngas generation and use
entrained flow gasification
~ 1200 °C, ≥ 60 bar, τ 2 - 3 s
gas cleaning
with heat recovery
liquid fuel synthesis
single pass operation
electricity generation
CC turbine, engine, FC
electricity
organic waste:
paper, plastics, dung ...
low T
heat
co-generation of a marketable product mix
Fig. 4: Simplified block flow diagram of the two-step bioslurry process "Bioliq" for the
production of synfuel, chemicals and high p steam plus electricity from biomass:
1. Local biomass liquefaction by pyrolysis, 2. Bioslurry gasification and syngas conversion
in a large central plant.
4
O 2
CO 2

Summer School, University of Warsaw, 29.-31. August 2007
a billion tons of dry straw worldwide mainly from wheat, rice, maize and barley with a
share of only half of the total straw harvest of ca. 2+ Gt/a. Surplus cereal straw can
make a significant potential energy contribution of ca. 0,5 Gtoe/y and this justifies
even the development of a special gasifier suited for agricultural residues. Herbaceous
by-products from agriculture, mainly cereal straw and straw-like residues, are
among the cheapest renewables. Contrary to wood, all fast growing plants contain
more ash and heteroatoms, especially much nitrogen, potassium and chloride. These
inorganic elements are inevitable constituents of bio - catalytic systems, which are
needed for a faster metabolism and growth. Slowly growing wood contains usually
< 1% ash (without bark). Straw or hay contains 5 to 10% ash, rice straw even up to
15 - 20%; K- and Cl-contents in the 1% range are typical for non-woody feedstock.
Wood is a relatively clean fuel and traditional technologies for wood combustion as
well as gasification in fixed or fluidised beds are well developed. Technologies for the
use of herbaceous biomass are more complex and not well developed:
• Depending on feedstock composition and combustion or gasification temperatures,
the bio - ashes may become sticky or melt during thermal conversion. A
sticky ash can cause reactor slagging and agglomeration followed by breakdown
of fluidised beds. Especially a high K-content can lower the ash softening temperature
down to < 700°C; this is below a suitable combustion or gasification
temperature.
• Chlorine in the biofeedstock is liberated mainly as HCl and causes corrosion, poisoning
of catalysts and can promote the formation of toxic polychlorinated “dioxins”
and “furans” at unsuitable combustion conditions.
• K-salts like KCl, KOH etc. become volatile at > 600°C and deposition especially of
liquid eutectics in downstream gas ducts can cause serious corrosion and plugging
problems.
• Biomass residues from forestry or agriculture are distributed over large areas and
the low bulk energy density causes high direct transport costs. Large distance
transport of bulky biomass like straw becomes too expensive and has to be
avoided.
3. THE KARLSRUHE BTL - CONCEPT "BIOLIQ"
Our process concept concentrates on low-quality ligno-cellulose like residual straw
or residual wood, because ligno-cellulosics are with ~ 90% the most abundant biomass
type. There is also little competition with human and animal food production, if
only agricultural residues like straw or forest residues from the stem wood harvest
are used. Especially in densely populated regions in south-east Asia, energy plantations
compete for agricultural areas needed for food and feed production, thus impairing
food supply at the expense of a potentially more lucrative bioenergy export.
In the following, the term "straw" is used as a synonym for all thin-walled and fast
growing, non-woody biomass residues, which contain much ash and heteroatoms
(N). The technical concept is outlined in fig. 4 [HEN 03, HEN 04]. Biomass is first liquefied
by fast pyrolysis (FP) in many local plants. In rural European areas, about half
of the cereal straw harvest amounts to ca. 50 t/km 2 on the average and is not needed
to maintain soil fertility but available as an unused surplus. A large delivery radius of
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Summer School, University of Warsaw, 29.-31. August 2007
sand loop
biofuel
from char
combustor
TYPE 2 : DIRECT CONTACT HEATING WITHOUT HEAT CARRIER
see also
vortex reactor
TYPE 1: HEAT CARRIER LOOP WITH EXTERNAL HEATER
Gas fluisised beds with mixed flow
bubbling fluid bed circulating fluid bed
biofuel
sand
bed
ablative pyrolysis vacuum pyrolysis
cold
biofuel
biofuel
vapour
hot disc
hot
cyclone
char
recycle gas
•oil
•excess
gas
rotating hot
disc, cylinder, blade
biofuel
molten
salt
sand
loop
vacuum tank
char
hot
cyclone
char
twin char
combustor
recycle gas
Mechanically mixed and transported shallow beds
rotating cone twin screw (LR-) mixer
•hot cyclone
•condenser
oil, gas
sand loop
char combustion
gas heater in sand loop
condenser
hot cyclone
Fig. 5: Survey of various reactor types used for the fast pyrolysis of biomass
from straw chopper
0.5 m 3
chops
bigbag
sand-transport
∼ 500°C
sand reheater
∼ 550°C
chops sand
flow control
fast pyrolysis
reaktor
500°C, 1 bar
sand / char
separator
biofuel
char
gas, vapour
char
cyclone
•oil
•excess
gas
char
oil
gas
oil
sand heating or flare
Gas burner
⊗
gas
quench
condensor
biooil
tank
char
silo
oil
slurry
production
Fig. 6: Simplified flowsheet of the fast pyrolysis process development (PDU), grey boxes and
arrows represent the 500°C hot heat carrier (sand, SiC or steel balls) loop.
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Summer School, University of Warsaw, 29.-31. August 2007
> 200 km or more would be necessary to supply an economic, large central biosynfuel
plant with e.g. ≥ 6 Mt/y ligno-cellulosics for ≥ 1 Mt/y biosynfuel output.
For square straw bales with ~ 150 kg/m 3 bulk density, a maximum delivery distance
of 20 to 30 km is at the limits of practicability for the local farmers. Regional fast pyrolysis
facilities with ~ 30 km delivery radius are a reasonable size in central EU. About
45% of the typical straw harvest plus some forest residues from 3,14 · 30 2 ≈
3000 km 2 area correspond to a throughput of ca. 200 000 t/a of air-dry straw and
other straw-like biomass plus some woody forest residues. With a dry ligno-cellulose
feed, the output is about 134 000 t/a = 17 t/a · 8000 h/a of a pyrolysis oil/char paste,
sludge or slurry with a density of ~ 1300 kg/m 3 and a HHV of 6±1 kWh/kg. The mass
density of these pastes, sludge's or slurries is ~ 8 times higher compared to the bulk
density of square straw bales. The energy density per litre can be up to 12 times
higher and the slurry can contain up to 90% of the initial bio-energy and is easily
stored in tanks or silos. Silos for storage or transport have the big advantage of a
rather quick discharge for pastes or even solid crumbs from storage or transport vessels
into a vessel below without using a pump. Slurries from 30 – 50 or more of such
regional pyrolysis plants are transported by rail up to 300 – 500 km to a central facility
for syngas generation and use. Such a huge central BTL or biosynfuel plant is
similar to the existing GTL- and CTL-facilities and can profit from corresponding experience
with design details, if the capacities are comparable.
Central part there is a large pressurised entrained flow gasifier operated slightly
above the downstream synthesis pressure (30-100 bar) and at temperatures above
the ash melting point; thus being able to handle feedstocks with a high ash content.
After syngas cleaning and adjustment of the H2/CO ratio to ca. 2 with the water gas
shift reaction plus CO2 removal, the pure syngas can be converted with catalysts into
various products like Fischer-Tropsch (FT) diesel, methanol, dimethylether, methane,
hydrogen or other chemicals. The variants of the FT-synthesis are conducted at typical
pressures of 10 to 40 bars, those of the methanol synthesis at 50 bars or more
respectively, DME at 70 – 80 bar. The energy consuming, intermediate syngas compression
steps, with high investment and operating costs, which are necessary for
atmospheric gasification processes, are avoided for pressurised gasification.
4. EXPERIMENTAL WORK
The following sections present a brief overview of the actual development work.
Present work focuses on the head-end steps for syngas generation, because the tail
end steps for syngas conversion to synfuel via Fischer-Tropsch synthesis are well
known.
4.1 Fast Pyrolysis (FP) of ligno-cellulosics
Pyrolysis is the thermal decomposition occurring in the absence of air and generates
gases, liquids and char. The product yields depend on the operating mode. Fast
pyrolysis [PYNE] at moderate temperature of about 500°C and short vapour residence
time in the 1 second range are the optimum for producing high liquid yields
> 50 wt% from ligno-cellulose which are necessary for slurry preparation. Fig. 5
shows the various reactor types which are being investigated for biomass fast pyrolysis.
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Summer School, University of Warsaw, 29.-31. August 2007
cross-current cross-current removal removal of of gas, gas, vapours vapours and and char char powder
powder
hot hot sand
sand
straw straw chops
chops
mass ratio < 10
sand recycle
little
char recycle
flat fluidised bed at ~ 500 °C, residence time few s
fast horizontal transport with poor axial and good radial mixing
twin screws
Fig. 7: LR (Lurgi-Ruhrgas) – mixer reactor with twin screws rotating in the same
sense; length 1,5 m, diameter 0,04 m, rotation frequency few Hz.
gas
100
80
pyrolysis water
condensates
60
pyrolysis tar 40
20
char
ash 0
wood flour
spruce beech winter wheat
straw
ash
rice
ash wt % 1.0 0.8 7.4 15.7
water wt % 8.9 6.5 7.7 8.0
HHV MJ/kg 16.2 16.2 14.6 12.0
E. Henrich, E. Dinjus, R. Stahl, F. Weirich (FZK, ITC-CPV);H. Weiss, U. Zentner (Lurgi); D. Meier (BFH-Hamburg), to be published
gas
aqu.
tar
char
Fig. 8: Percentage yields of solid liquid and gaseous pyrolysis products from wood
and straw, produced in a twin screw mixer reactor.
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Summer School, University of Warsaw, 29.-31. August 2007
Most pilot facilities use bubbling or circulating fluidised beds of sand and recycle
some cooled pyrolysis gas for bed fluidisation. Gas recycle causes additional energy
loss during the typical quench condensation for the recovery of pyrolysis liquids.
Therefore we prefer mechanically fluidised beds without a fluidising gas. We have
chosen the twin screw or LR-(Lurgi-Ruhrgas) mixer reactor, because of the available
technical experience, which can simplify and accelerate the scale-up to a commercial
20 ± 10 t/h plant scale. The LR-mixer reactor has been applied since ~ 50 years first
as “flash coker” for town gas production, than as “sand cracker” for olefin production
from naphtha or later for FP of tar sands of vacuum residues [WEI 00].
A process development unit (PDU) with a LR-mixer reactor for 20 kg/h maximum
throughput of straw chops, sawdust, paper, cardboard pieces etc. has been built in
Karlsruhe. Central part is a hot heat carrier loop with a bucket elevator, operated at
~ 500°C. The simplified flow sheet in fig. 6 shows the hot heat carrier loop in grey
arrows. Heat carrier particles circulate in a closed loop and are indirectly reheated in
a special heater by hot flue gas from pyrolysis gas combustion. Then, they are mixed
with the dry bio-feed particles in the LR-mixer; biomass residence time is several
seconds. A fast stream of gaseous, vapourised and solid pyrolysis products leaves
the reactor. The pyrolysis char particles are removed first in a hot cyclone. Then the
vapours are condensed in one or two steps: first a tar fraction at ~ 100°C with little
water and than an aqueous condensate with ca. 30±10 wt% acetic acid and other
oxygenates at room temperature. Cyclone char is a fine (~ 10 – 200 µm) and brittle
powder with a high porosity. It is suspended in the tar and also in the aqueous condensate.
Various suspension types' e.g. a stable paste or pumpable sludge or slurry
can be produced in this way.
The photo in fig. 7 shows the 1.5 m long twin screw reactor in the FP-PDU; the
screws have 4 cm diameter and rotate with 1 to 4 rps. Tests have been performed
with 1 mm quartz sand or SiC as heat carrier and also with 1.5 – 2 mm steel balls.
Some attritted fine sand or SiC is carried out into the pyrolysis products and can
cause abrasion problems in downstream equipment. Such problems are avoided with
steel balls and in addition the reliability of loop and reactor operation improves significantly.
Maximum LR-reactor throughput is 10 kg/h biomass together with ca.
300 kg/h sand or up to 20 kg/h with 1 t/h steel ball circulation. Experience with short
time reactor operation showed the suitability of the twin screw reactor type for the
fast pyrolysis of biomass.
Greasy deposits of tar/char particles have been observed in cooler pipe parts of the
condensation section; this requires special attention. For the production of pumpable
slurries usually twice as much liquid than char powder is needed. Fig. 8 shows typical
product yields (dry basis) for selected biomass materials: For wood, FP liquid yields
are high (60 – 70 wt%) and char yields sufficiently low (15 – 20 wt%). This becomes
more difficult for straw due to the higher ash content, which can also catalyse vapour
decomposition to undesired pyrolysis char and gas. A typical straw pyrolysis yield
range is 50 to 60 % total condensates and 20 to 30 wt% char which contain the ash;
condensate/char-ratio's < 2 is close to the limits for slurry production.
The measured pyrolysis gas composition is given in fig. 9. For wood, the pyrolysis
gas mainly consists of carbon dioxide and carbon monoxide, small amounts of methane
and traces of small C2 - C5 alkane and alkene hydrocarbons. For straw the
amount of gas is a little bit higher when compared to wood, because more carbon
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Summer School, University of Warsaw, 29.-31. August 2007
mol/kg
6
4
2
0
CH 4
CO 2
CO
C 2 –C 5
H 2
wood straw
spruce beech winter wheat rice
ash 1.0 0.8 7.4 15.7 wt. %
water 8.9 6.5 7.7 8.0 wt. %
yields: gas 14.7 16.0 22.0 22.9 wt. %
CO 2 6.7 8.4 14.6 15.3 wt. %
m3 m /kg 3 /kg
Fig. 9: Amount and composition of pyrolysis gases from various feedstocks in the
twin screw mixer reactor at ~ 500°C.
Fig. 10: Fast pyrolysis pilot plant for 0,5 t/h biomass throughput, part of the "Bioliq"
facilities at Karlsruhe research centre.
10
0,15
0,10
0,05
0

Summer School, University of Warsaw, 29.-31. August 2007
dioxide is formed. The energy content of these pyrolysis gases corresponds to about
10% of the initial bioenergy. At unsuitable condensation conditions, e.g. higher temperatures,
several mass% of volatile, low molecular weight oxygenates like formaldehyde,
acetaldehyde, glyoxal etc. can also escape with the gas fraction. If not considered
in the gas analysis, a corresponding mass and energy balance deficit of several
percent is observed.
FP pilot plant: Operating experiences are a basis for the design of a larger FP pilot
facility with 0.5 t/h biomass throughput. With their experience from previous technical
applications of the twin screw mixer reactor, Lurgi AG company, Frankfurt, has
planned and built a fast pyrolysis pilot plant at Forschungszentrum Karlsruhe in 2006
and 2007. The plant is now almost ready for start-up; fig. 10 shows a photo of the
status mid 2007.
4.2 Bioslurry preparation and properties
For storage, transport and gasification, pyrolysis char and tar or aqueous condensates
are mixed to form either a stiff suspension paste or a free flowing slurry, that
have a much higher volumetric energy density of 18 - 26 MJ per litre than the bulky
straw bales with ca. ~ 2 MJ/l. With non-porous solid particles of regular shape,
pumpable and free flowing slurries can be obtained up to ~ 50% solids by volume.
Pyrolysis chars pose special problems due to their very high porosity of up to 80%.
The chars first soak much liquid until sufficient lubricant between the particles remains.
Production of pumpable slurries with > 30 wt% char powder therefore requires
special efforts.
A very appropriate mixing tool for the pyrolysis char powders and condensates is a
colloid mixer designed by "MAT" in Germany [MAT], a robust tool well-known for the
preparation of very homogeneous and concentrated but pumpable cement grouts.
Because of high shearing rates in the mixer, solid char agglomerations are completely
destroyed. During our gasification experiments > 20 t of slurry was prepared
in such a colloid mixer. The photo in fig. 11 shows the set-up with a colloid mixer for
continuous slurry preparation of ca. 1 t/h. At a high char content in the range around
30 wt% the slurries are stable without additives and the viscosity is like stiff honey
(several Pas). The photo in fig. 12 gives an impression of the flow characteristics of a
viscous slurry "sirup".
A stepwise preparation of the final, preheated feed for the pressurised entrained
flow gasifier has advantages. With stiff pastes of pyrolysis products, simpler preparation
procedures at the pyrolysis plant and safer storage and transport with reduced
spill risks can be achieved; silo vessels allow quick unloading into a lower vessel.
The more complex final preparation of a suitable and pumpable gasifier feed slurry in
a colloid mixer and preheating with waste heat from the synfuel process is required
only once immediately prior to gasification.
4.3 Bioslurry gasification campaigns
Our gasification experiments were carried out at FUTURE ENERGY company,
Freiberg, Saxony, (now Siemens fuel gasification technology) [SCI 02, SCI 04] in a
3 – 5 MW entrained flow pilot gasifier, at 26 bar. The pilot gasifier was part of the pilot
facilities for the Noell conversion process [CAR 94], and was put into operation in
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Summer School, University of Warsaw, 29.-31. August 2007
Fig. 11: Continuous preparation of max. 1 t/h bioslurry with a 15 kW colloid mixer.
Control of the char and bio-oil flow rates with the bioslurry density.
Fig. 12: Flow characteristics of pyrolysis
oil/char slurries
12
pilot flame
fuel oxygen
SS pressure shell
water cooled
radiation screen
~ 1300 °C ~ 50 bar
raw syngas
molten slag
Fig. 13: Design of the GSP – type
slagging entrained flow gasifier for operation
at high temperature and pressure.
The characteristic radiation
screen with SiC liner is cooled with
pressurised water and keeps the pressure
resistant steel shell at low temperature.

Summer School, University of Warsaw, 29.-31. August 2007
1996 on the site of the previous "Deutsches Brennstoff Institut" (DBI) in Freiberg,
Saxony. The design of this GSP-type (Gaskombinat Schwarze Pumpe) gasifier has
been developed for the gasification of NaCl salt-containing brown coal in central
Germany. Straw is similar as it contains comparable amounts of KCl alkali chlorides.
A 130 MW GSP-gasifier is being successfully operated since 20 years at "Schwarze
Pumpe", Saxony, in combination with CH3OH synthesis and combined cycle (CC)
electricity generation [SEI 00]. Fig. 13 outlines the design of the gasifier. Main characteristic
is a pressurised water cooled internal reaction chamber with SiC liner, covered
with a layer of down-flowing slag of honey-like viscosity which protects the wall
from corrosion and erosion. The cooled outer mild steel shell can be designed for
high-pressure up to 100 bar or even more.
Slurries are atomised pneumatically with pure O2 in a special burner at the gasifier
top and gasification proceeds in a downward flame reaction in about 1 second. The
GSP-gasifier type is specially suited for feedstocks with much ash and corrosive slag
and tolerates rapid changes of ash melting behaviour by adjusting the temperature
with the controlled O2-flow. Sudden shut down and fast start-up procedures are possible
without damaging the reactor. The GSP-gasifier type is a multipurpose "guzzler":
any feed with can be pumped and atomised pneumatically and has a heating
value above 10 MJ/kg can be digested safely. Fig. 14 and 15 show the top and bottom
part of the pilot gasifier during our tests in Freiberg, Saxony.
For our gasification campaigns we have prepared more than 40 t of different slurries
from the products of commercial beech wood pyrolysis for commercial charcoal
production, special pulverised anthracite/water slurries for kinetic studies, bio-oils
from fast pyrolysis of wood supplied by Dynamotive company, and char and bio-oil
from straw pyrolysis [HOR 05]. Purchased pyrolysis oil from Chemviron company e.g.
had a density of 1184 kg/m 3 , a room temperature viscosity of 0,16 Pas and a lower
heating value (LHV) of 19 MJ/kg. Charcoal dust had a LHV of 31 - 32 MJ/kg and has
been further pulverised in a ball mill prior to slurry preparation. To simulate a slag
layer in the gasifier which is characteristic for agricultural biomass residues, 2-3 wt%
straw ash from the 3 MW district heating plant at Schkölen, Thuringia, plus 0,3 wt%
KCl were added to raise the amount of ash.
The char slurries described in the previous 4.2 section are first pumped into a 1,2
m 3 feed storage vessel equipped with an anchor agitator and a bottom-to-top recirculation.
A constant feed stream was transferred at 26 bars with a screw pump via a
90°C heater into the gasifier burner. The feed rate was either 0.35 t/h slurry (2
MW(th)) plus 50 m 3 (STP)/h of CH4 in a pilot burner or 0,5 – 0,6 t/h slurry (3 MW(th))
without CH4 – pilot burner. Pure evaporated O2 from a LO2 - tank has been stored in
an intermediate pressurised cylinder battery at several bars above the gasification
pressure. The slurry stream was atomised with a very fast O2-jet in a special burner
nozzle at the top of the gasification chamber. To ensure proper gasification conditions,
the O2-flow was carefully controlled. Typically, O2-consumption corresponds to
about half of the slurry weight. Hot raw syngas and liquid slag flow through the concentric
exit hole at the bottom of the gasification chamber into a quench space,
where the hot raw syngas has been cooled to ~ 160°C by liquid water injection.
Gasification temperatures of 1200 - 1600°C have been generated with an O2stoichiometry
of λ = 0,4 - 0,5. In the small pilot gasifier, the heat loss via the ca. 3 m 2
13

Summer School, University of Warsaw, 29.-31. August 2007
Fig. 14: Top section of the 3-5 MW(th) 26 bar entrained flow pilot gasifier of the GSP
type in the facilities of Siemens Fuel Gasification Technology, Freiberg (previously
FUTURE ENERGY)
Fig. 15: Slag removal at the PEF pilot gasifier bottom
14

Summer School, University of Warsaw, 29.-31. August 2007
surface area of the radiation screen amounts to about 20% of the initial slurry energy.
In a much larger technical gasifier the loss will be reduced to a negligibility level < 1%
of the bioenergy. Because of the smaller surface-to-volume ratio, this results in an
O2-stoichiometry for autothermal gasification of λ between 0,3 and 0,4, λ ~ 1/3 is a
reasonable expectation value. After a change of the operating conditions, stationary
temperatures and operating data could be approached in only 1 h; stable operation
has been maintained at least for additional two hours - except ash composition due
to its long residence time.
No problems with slag removal have been observed with straw ash. Downward slag
flow at the inner cooling screen wall creates only a ≤ cm-thick layer with honey like
viscosity. Solidified slag granules have been collected in a water bath at the gasifier
bottom. Every 3 hours a wet slag batch has been removed from a pressure lock for
balance measurements. About half of the slag was SiO2; constituents like CaO, K2O
and iron oxides are in the 10 - 20% range. The melting behaviour of the straw ash
under reducing conditions is characterised by powder sintering at ~ 800°C; free flow
is obtained at ~ 1100°C.
The carbon conversion was determined from the sum of carbon removed with the
slag and the quench water. All carbon to syngas conversion percentages were found
definitely > 99% at all feed temperatures and all raw tar slurries with a char particle
size ≤ 100 µm after proper atomisation. Increasing particle size (17 < x90 (µm) < 94)
and char contents increasing from 20 to 35% show little influence upon the carbon
conversion. Gasification efficiency increases significantly to about 70% with lower
gasification temperatures of 1200°C; in a large gasifier with negligible loss to the
cooled radiation screen 80+% are possible. About 870 Nm 3 /h raw syngas have been
formed including ~ 17% of an inert purge gas for experimental reasons (O2 2%, N2
88%, CO2 15%). The composition of the quenched, dry product syngas and a brief
summary of the bioslurry gasification results are given in fig. 16. The high amount of
purge gas in the pilot gasifier can be expected to be negligible in a large technical
gasifier.
Table 1 shows the inorganic trace gases determined to be in a very low concentration
range after full water quench. Especially the amount of chlorine as HCl is not
very high as the most part is found in the process quench water. Various syngas
cleaning steps are available, which ensure the environmentally compatible gas release
via a torch. At the usual operating temperatures of 1200 – 1600°C, the very hot
syngas has a low CH4 content, usually below 0,1 vol%. The hot raw syngas is practically
tar-free because of the high gasification temperature. The measured raw syngas
composition indicates an approximate equilibration for the homogeneous shift
reaction CO + H2O � CO2 + H2, for all operating conditions tested. This allows a
simple prediction of the raw syngas composition.
Table 1: Trace gases found in the dry raw syngas after a full quench with water
HCl 1,7 mg/m 3 (STP); HCN 3,4 mg/m 3 (STP)
SO2 0,2 vol%; NH3 0,4 mg/m 3 (STP)
5 ECONOMIC ASPECTS OF BIOSYNFUEL PRODUCTION
A crude estimate of the material and energy balances for the total process train is
possible from a coherent set of stoichiometric chemical equations for the successive
15

Summer School, University of Warsaw, 29.-31. August 2007
Syngas-Composition:
for pyrolysis tar - char - slurries
H 2
CO
CO 2
N 2
(inerts)
Feed:
solids: 0 – 39 wt. %
ash: 3 % straw ash
HHV: 10 – 25 MJ/kg
density: 1250+ kg/m 3
Operating conditions:
throughput: 0.35 - 0.5 t/h
gasification pressure: 26 bar
gasfic. - temp.: 1600 – 1200 °C
feed-temperature: 40, 80 °C
no tar, < 0.1 vol % methane
equilibration:
carbon conversion ≥ 99 %
smooth operation without surprise
(CO2 • H 2) / (CO • H2O) = K(T)
straw ash m.p. < 1200 °C
Fig. 16: Summary of bioslurry gasification results
thermal loss
sum ~ 3%
~ 1,5 %
~ 0,5 %
~ 0,5 %
~ 0,5 %
lignocellulose 100 %
Schnellpyrolyse
fast pyrolysis
slightly exothermal
Kondensat/Koks condensate/char – slurry Slurry
~ 90 89 %
Flugstrom entrained -
Druckvergasung
flow gasification
Synthese-Rohgas
synthesis-raw gas
Synthese-Reingas
clean syngas
~ 76 75 %
FT - Synthese synthesis
~ 3 %
heat Reaktionswärme
of reaction
~ 13 %
FTS heat - Reaktionswärme
of reaction
synthesis Syntheseprodukte products
~ 18 %
~ 56 51 %
nicht unconverted umgesetztes syngas Syngas
~ 4 %
Trennung separation
~ 4%
pyrolysis gas
~ 6 %
C C5- 5 -P -products
rodukte
~ 5 %
~ 42 %: FTS synfuel
by- product
C 5+ products recycle ~ 5%
Fig. 17: Energy flow in the bioslurry process "Bioliq"
16
energy for
pyrolysis
~ 40 %: electricity
high- p steam

Summer School, University of Warsaw, 29.-31. August 2007
process steps. The stoichiometric reaction equations in table 2 (next side) summarise
the experimental and theoretical knowledge of the sequential process chain for cereal
straw in a condensed form. For other feedstocks like wood or other pyrolysis or
gasification conditions, another adjusted set of equations is required. All reaction
equations are coherent and relate to a formal C6H9O4 – ligno-cellulose "molecule"
(mass units 145) at start representing the empirical elemental composition of a moisture-,
ash- and heteroatom-free ligno-cellulose. These stoichiometry equations allow
a quick estimate of mass yields, in table 2 indicated as m%. The energy balance can
be derived from the higher heating value (HHV) of each reactant, which can be reliably
estimated from the elementary composition given in the lumped empirical reactant
formula using the Channiwala equation [CHA 02]; energy yields in table 2 estimated
in this way are indicated as e%.
An estimate of the energy flow in the total BTL process train including a final syngas
use via Fischer-Tropsch (FT)-synthesis in fig. 17 shows, that only about half of the
initial biomass energy can be converted into FT raw products. About 80% of the FT
raw product energy may be converted into super-clean diesel and gasoline. A synfuel
energy yield of 42% as shown in fig. 17 is an optimistic but also realistic upper value,
requiring some more development efforts. Available present-day technology is more
near 30% [SCA 04]. Synthesis pathways via other products
e.g. like methanol can be
more efficient [LIE 04].
High
long distance transport costs for the bulky biomass are prohibitive for direct
transport to a large central plant. Biomass conversion into pastes, sludges or slurries
with higher energy density solves these problems. Straw and paste/slurry transport
costs by truck and rail up to 500 km distance are compared in a simplified linearised
form in fig. 18 [LEI 07]. Costs are in € per final tonne of biosynfuel based on the following
mass yields: 7 t storable airdry straw (4 kWh/kg) → 6 t dry straw → 4,7 slurry
→ 1+ t biosynfuel (12 kWh/kg). Zero distance cost contributions are mainly for loading
and unloading; rail transport is calculated either with or without 30 km truck or
tractor pre - transport to the railway station. At delivery distances above 65 km, direct
transport of airdry straw becomes more expensive than a local supply of many regional
FP-plants by tractor followed by rail transport of the dense pastes or slurries in
silo wagons. A 65 km delivery radius corresponds to a small and less economic biosynfuel
production of only 0,2 Mt/a, equivalent to only 2% of the capacity of a modern
10 Mt/a crude oil refinery.
Not all farmers will agree with contracts for on-time delivery of their residual straw,
wood etcetera. The distribution of FP plants will therefore not cover completely all
neighbouring sites as shown at the left hand side in fig. 19, but could be more spot
like with gaps as shown on the right. This does not matter much, since slurry transport
costs by rail do not depend much on distance. Yet industrially developed "brown"
field sites with rail access are important for cost savings.
Manufacturing costs for slurries and synfuel depend on the plant size as depicted in
fig. 20 and fig. 21. The costs for straw, residual wood etc., biomass transport and
technical O2 for gasification are almost independent of plant size. This is equivalent
to a cost degression exponent of about 1. But the fixed and variable costs for the
plant and the operating personnel depend on plant capacity. Economies of scale are
represented by cost degression exponents of ~ 0.7 for the plant investment costs and
~ 0.25 for the required number of operating personnel respectively.
This means that
17

Summer
School, University of Warsaw, 29.-31. August 2007
Table
2: Stoichiometric reaction equations for the stepwise conversion of straw into biosynfuel
feedstock airdry straw:
HHV 2923 MJ/mu=186
kg
Channiwala equation: HHV
MJ/mu = 349.1 C + 1178.3 H - 103.4 O – 15. 1 N + 100.5 S – 21.1 ash, CHONS mass%
fast pyrolysis:
(straw)
(C 6H9O4 + 12 g ash + 1 g het)
6H9O4 + 12 g ash + 1 g het)
dry ligno-cellulose
m=85, e=100%
C 6 H 9 O 4 (ligno-cellulose) + 12 g ash
m=78%, e=100% m=6.5%
+ 1 g heteroatoms +
m=0.5%
28 g water
m=15%
r ∆H = -138 MJ/mu; e=5%
500 °C
. . (C2.25H2.2O0.35 + 12 g ash) + C2.75H3.2O0.75 + 1 g het. + 1.55 (H2O) l + C1H0.5O1.35 char + ash organic liquids
reaction
water gas (sum)
m=25%, e=39% m=26% , e=48%
m=0.5% m=15%,
e=0% m=18%, e=8%
slurry gasification:
(400 → 1500
K)
r∆H
= -453 MJ/mu; e=15.5%
(C5H5.4O1.1 + 12 g ash + 1 g het + 1.55 H2O) + 2.1 (O2 + 0.05 N2 )
4.3 CO
+ 3.1 H2 + 0.7 CO2 + 1.15 (H2O)
g + 0.14 N 1500 °C
2 + slag
straw slurry
m=66.6%, e=87.5%
CO-shift and
syngas cleanin
technical oxygen
m=38%, λ=0.36
(4.3 CO + 3.1 H2 + 0.7 CO2 + 0.14 N2 ) + (1.15 + 1.68) H2O g:
ca. 700 °C
catalyst
straw slurry
9.4 mole
raw syngas, 7.4 mole CO
+ H2 m=98%, e=72%
wet raw syngas
dry raw syngas,
1.68 mole H2O
recycled from FTS clean condition
ed syngas, high boilers +
m=44.6%,
e=72% m=59.8%
FT-synthe
r
(m.p.

Summer School, University of Warsaw, 29.-31. August 2007
a capacity increase by an order of magnitude reduces the specific plant investment
costs by a factor of about two.
Present 2007 crude oil prices of ~ 50 €/bbl result in a price of 0,5 € per kg
or of
0,4 € per litre of untaxed motor fuel at the crude oil refinery gate. Synfuel production
via syngas from very cheap natural gas (GTL-process) is competitive with oil-derived
motor fuels. Biosynfuel is about two times more expensive compared to untaxed
crude-oil-derived motor fuel. The main reasons for the higher bio-synfuel costs compared
to a large crude oil refinery with a throughput of ~ 10 Mt/a are related to: (1) ca.
6 times higher specific mass input, 7 t airdry straw versus 1,2 t crude oil are needed
for 1 t of motor fuel, (2) handling of solid feedstocks is more difficult technically; (3)
the more complex multi-step technology with several exothermal chemical reaction in
succession has an about two times lower energy conversion efficiency and (4) poor
economy of scale with a much smaller plant size.
In developing countries
with lower biomass and labour costs, there is still much in-
centive for further technical
simplifications. Compared with the expensive oil imports
in these countries,
synfuel production from domestic biomass will be already com-
petitive at a much lower crude oil price than
in the industrialised countries. Taking the
results of Hoogzaad [HOO 94] who analysed the situation in the Ukraine, it seems to
be possible there to produce synfuel for ~ 35 c€ per litre [RAF 04].
6. OUTLOOK
The feasibility of the Karlsruhe
BTL concept "Bioliq" has been successfully tested
and proved by experiments. Process development
is continuing in view to aspects
like scale-up, technical simplifications, reliability
and economy improvements coming
into the forefront.
The present focus is still on the steps for syngas generation. Our
next step is the operation of a fast pyrolysis
pilot facility on a scale of about 500 kg/h
air-dry fast growing biomass
with a twin screw mixer reactor. This pilot facility has
been designed
and built by Lurgi AG company, Frankfurt, in the Karlsruhe research
centre. The plant is now ready for start-up. If a reliable operation can be obtained, the
further steps for the demonstration
of our "Bioliq" process are straight-forward. Raw
syngas generation, cleaning and synthesis are well known technologies and will be
covered in future collaborations with experienced industry partners.
We appreciate financial support from the ministry for “Ernährung und Ländlichen
European Union for IP RENEW in the 6 th
ACKNOWLEDGMENTS
Raum“ (MELR), Baden-Württemberg; the
framework program, and the Fachagentur Nachwachsende Rohstoffe (FNR) of the
German ministry
of agriculture.

Summer School, University of Warsaw, 29.-31. August 2007
Rail Rail Rail Rail
Straw
Truck Truck Truck Truck
unit unit unit unit train train train train
30 30 30 30 km km km km truck, truck, truck, truck, then then then then rail rail rail rail truck
direct direct direct direct rail rail rail rail
Straw
+ Slurry
truck
Slurry
0 100 200 300 400 500
Distance Distance / / km
km
100
50
€/t
Transport costs
Fig. 18: Straw and slurry transport costs by rail and truck
integrated plant with
0.5 GW input
truck-transport 65 km
5 GW
rail
250 km
mean slurry/paste transport dis tance:
other
plants
truck
0
5 GW
x km distance
y €/t dry biomass
dry straw by truck:
y = 19 + 0,15 x
dry straw by rail:
with 30 km truck
transfer to station:
y = 46 + 0,14 x
slurry by truck:
y = 6 + 0,133 x
slurry by rail:
y = 6,5 + 0,033 x
with 30 km tractor
transfer to station:
y = 13 + 0,033 x
close pyrolysis plants scattered pyrolysis plants
transport to central syngas plant : straw by tractor, slurry by rail
rail
500 km
rail
other
plants
other
pl ants
Fig. 19: Close and scattered FP plant configurations compared to a small integrated
plant with 0,5 GW biomass input.
20

Summer School, University of Warsaw, 29.-31. August 2007
Fig.
20: Cost contributions from fast pyrolysis. At crude oil prices of ca. 50 €/bbl the
bioslurry costs are comparable at the same heating value
● industrial site:
no grass root plant
● slurry input:
4.7 Mt/a, 588 t/h
● synfuel output:
1 Mt/a, 1500 MW
8000 h · 125 t/h
● total capital investment:
500 M€, 10 a depreciation
625 M€, 20 a depreciation
comparison with GTL
● ! no energy export :
and side-products
● straw bale delivery:
3000 h/a = 2500 t/h
ca. 200 trucks per h
with 100 m 3 load ??
Extreme traffic density!
airdry straw input Mt/a
1000
100
€ / t synfuel
10
MW (th) input for 8000 h/a
reference
capacity
0.02 0.2 1.25 2 7 20
slurry
slurry gasification
O 2 without kWh(el)
40 % of 8 c€/m 3
slurry transport
personnel
sum
965
669
125
4 100 1000 10000
Production costs for 1 tonne biosynfuel: €/t
- 250 km slurry transport by rail 4,7 t · 21 €/t = 99 (69)
- oxygen 360 m 3 · 4.7 t slurry · 0.08 €/m3 = 54
(oxygen cost is without electricity)
- gasification and FT-synfuel production = 125
- personnel: 300 persons à 60 k€/a = 18
sum = 296(266)
Fig.
21: Cost contributions from bioslurry gasification and biosynfuel production
99
54
18

Summer School, University of Warsaw, 29.-31. August 2007
3
Varia
18
32
Surplus straw
residual wood
Varia1 1 €/kg
per per kg
kg
Fast Fast pyrolysis pyrolysis
personnel
5 2
22
Straw Straw transport transport
12
Slurry Slurry transport transport 10
O2 O2 without without power power
Gasification +
FT- synthesis
Fig. 22: Percentage cost breakdown for biosynfuel production with the bioslurry gasification
process "Bioliq". Plant configuration: 0,1 GW fast pyrolysis plants supply a
large plant with 1 Mt/a biosynfuel output.
13
5

Summer School, University of Warsaw, 29.-31. August 2007
REFERENCES
[CHA 02] S.A. Channiwala, P.P. Parikh; Fuel 81 (2002) 1051
[CAR 94] J. Carl, P. Fritz (eds.); “Noell Konversionverfahren zur Verwertung und
Entsorgung von Abfällen”, EF-Verlag; Berlin 1994
[FIS 04] "Der Fischer Weltalmanach" 2004, Fischer Taschenbuch Verlag, Frankfurt
2003
[HEN 03] E. Henrich, E. Dinjus; Pyrolysis and Gasification of Biomass and Waste,
Proc. of an expert meeting Strasbourg 2002, CPL-press 2003 (ed. A.V.
Bridgwater) p. 511-526
[HEN 04] E.Henrich, E.Dinjus, A.Koegel, K.Raffelt, R.Stahl, F.Weirich; A two
stage process for synfuel from biomass; Proc of the 2 nd world biomass
conf. 2004,Rome, Italy, Vol I, 729-733, ETA-Florence.
[HOO 04] J Hoogzaad, Bioenergy systems in Ukraine, doctoral thesis, University
Utrecht (2004), in press.
[HOR 05] A. Hornung et. al.; "Thermochemical conversion of straw", 14 th EU biomass
Conf. Proc. p. 913-916
[LEI 07] L. Leible et. al.; Wissenschaftliche Berichte, FZKA 7170 (2007)
[LIE 04] W. Liebner, M. Wagner; Mt-Synfuels, the Efficient and Economical Alternative
to Fischer-Tropsch Fuels, Erdöl Erdgas Kohle 120. Jg. 2004,
Heft 10, S. 323 – 326
[MAT] MAT-Mischanlagentechnik, Illerstraße 6, 87509 Immenstadt, Germany
(www.mat-oa.de).
[PYNE] http://www.pyne.co.uk
[RAF 04] K. Raffelt, E. Henrich, A. Koegel, R. Stahl, J. Steinhardt, F. Weirich;
The BTL2 process of biomass utilisation entrained flow gasification of
pyrolysed biomass slurries. 2 nd Internat. Ukrainian Conf. on Biomass for
Energy, Kiev, Ukraine, September 20 - 22, 2004
[SCI 02] M. Schingnitz; Chemie-Ingenieur Technik (74) p. 776, 7/2002
[SCI 04] M. Schingnitz, D. Volkmann; DGMK-Tagungsbericht 2004-1, p. 29
[SCA 04] G. Schaub, D. Unruh, M. Rhode; Synfuels from Biomass via Fischer-
Tropsch-Synthesis - Basic Process Principles and Perspectives, Erdöl
Erdgas Kohle 120. Jg. 2004, Heft 10, S. 327 – 331
[SEI 00] W. Seifert, B. Buttker; DGMK-Tagungsbericht 2000-1, p. 169
[WEI 00] H. Weis, V. F. Pagel; 16 th World Petroleum Congress, Calgary (CA),
2000
[WUR 07] T. Wurzel; Erdöl, Erdgas, Kohle, 123. Jahrgang, Heft 6, 2007. p. 92-96
[ZEN 07] R. Zennaro; Erdöl, Erdgas, Kohle, 123. Jahrgang, Heft 6, 2007. p. 88-91
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