FEEDSTOCK ADAPTABILITY TO PRESSURIZED FIXED BED GASIFICATION
H. Yasuda1,*, Y. Suzuki1, Y. Oshima2 and H. Nakagome2
1 National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, JAPAN 305-8569
2 Graduate School & Faculty of Engineering, Chiba University, Chiba, JAPAN 263-8522

e-mail:yasuda-hajime@aist.go.jp; phone: +81-29-861-8040; fax: +81-29-861-8209

Abstract
In order to produce synthesis gas for BTL (biomass to liquid) process, pressurized gasification is an option. Pressurized
updraft fixed bed gasifier was chosen and an experimental setup was made. Whole apparatus including gasifier,feedstock hopper, feeder, etc. were put inside a pressure vessel. Wood chip or PKS (Palm kernel Shell) are adoptable
feedstock for updraft fixed bed gasifier. In considering the use of waste polymeric materials for gasifier, their adaptability
is a matter. Pressurized fixed bed gasification of PKS and wood pellet, which is not the same as wood chip, was carriedout. As a result, the difference between PKS and wood pellet was seen in adaptability. Gasification reaction was achieved
well in the experiment for PKS while the problem such as channeling of the gas flow was caused using wood pellet. Suchproblem for wood pellet was reduced by lowering the bed height of the materials inside the gasifier, and outlet gas
temperature increased by bed height lowering.
Keywords: biomass, gasification, pressure, BTL, DME

1. Introduction
Liquid fuels for transportation vehicles have been derived
from petroleum. It is expected to obtain a part of fuelsfrom wastes or sustainable materials in the future. BTL(biomass to liquid) process supplies fuels, especiallyused for diesel engine, from biomasses. BTL process
consists of biomass gasification and fuel synthesis. DME
is one of the most applicable fuels for diesel engine, andDME can be obtained from synthesis-gas (CO and H2).
DME is synthesized usually at around 2MPa with catalyst.

Recently, such lower pressure condition as less than
1MPa was tried to apply DME catalytic synthesis. In theBTL process, syngas has to be increased in pressure bya booster machine. Because biomass is gasified atatmospheric pressure by ordinary, syngas is usuallyobtained as in atmospheric pressure. Meanwhile, power
for syngas compressing can be reduced when biomass isgasified at pressurized condition.
Pressurized fixed bed gasifier was chosen as relative
high conversion efficiency in smaller scale. Wood chip is
adoptable feedstock for updraft fixed bed gasifier.
Considering using waste polymeric materials, adaptability
to gasifier is a matter. Powders or fibrous materials, forexample, are anticipated to cause some problems.
In this study, the experimental setup for pressurized fixed
bed gasification was used. Wood pellet, which is madefrom wood powder, was used as gasification feedstock tocompare PKS, which is as suitable feedstock as woodchip for fixed bed gasifier.

2. Materials and Methods

Fig. 1 Pressurized updraft fixed bed gasifier

2-1. Apparatus
Pressurized updraft fixed bed gasifier which is operated
at below 1MPa (gauge pressure) was used. Wholeapparatus including gasifier, feedstock hopper, feeder,etc. were put inside a pressure vessel as shown in Fig. 1.
Feedstock was supplied continuously (10-80g/min) fromthe hopper by the screw feeder. Air as the gasification
agent was supplied from the bottom of the gasifier with
10-100L/min. Temperature of 5 points inside gasifier wasmonitored by K-type thermocouples (TC) during eachexperiment. The distances from each TC to the bottom

7th International Symposium on Feedstock Recycling of Polymeric Materials (7th ISFR 2013)
New Delhi, India, 23-26 October 2013

inside gasifier are 10mm (TC1), 50mm (TC2), 115mm(TC3), 460mm (TC4), and 1008mm (TC5), respectively.
Product gas concentration was detected by GC-TCD and
GC-FID, liquid products (tar and water solution) and
residual solid products (char) were collected andweighed after experiments.
2-2. Feedstock
PKS (Palm kernel Shell), 3-25mm and wood pellet(Japanese softwood), φ6mm × 10-25mm were used.
Maximum amount was 20kg for an experiment,

3. Results and Discussion
3-1. PKS
Temperatures at the lower part inside the gasifier, TC1-3,
were raised to around 500○C at about 20min after ignition
and kept over 500○C using PKS with controlling to keep
the bed height of the materials from the bottom inside thegasifier around 300-600mm. At the same time, TC4 andTC5 which reflect the outlet gas temperature kept below
200○C. Product distribution showed mostly constant after
60min, CO: 50%, CO2: 20%, H2: 10%, CH4: 5%,approximately. Similar tendencies of changes intemperature and product distribution were shown andstable operations were kept with changing experimental
conditions such as pressure, bed height (100-600mm),
while absolute values of the temperature andconcentration were varied. There are not observed
notable heterogeneity in planar direction of the residual
solids, no such large hole as exceeding 10mm orpulverization, opening the gasifier after experiments of
PKS.
3-2. Wood pelletTemperatures change inside the gasifier during woodpellet gasification at 0.3MPa is shown in Fig. 2. The bedheight was tried to control keeping relatively low around100-150mm. TC1 reached around 600○C at 20min afterignition and kept 600-800○C. TC2 reached around 600○Cat 60min. Meanwhile, TC3 reached around 800○C at
10min and continued to rise toward 1100○C at 120min, it
tuned to drop to around 300○C after 130min, because
TC3 placed near the top of the material bed. The bedheight seemed to fluctuate depending on theconsumption rate of the feedstock. However combustion
was major reaction in the early stage of the experiment,gasification became major in the latter half leading thetop of the bed could shift under TC3. Gasification withsame rate of air supply conduce higher consumption rate
than combustion. TC4 exceeded 200○C in 30min,
continued to rise toward 400○C at 200min. The outlet gas
temperature reached higher (>400○C) when bed height islower (<150mm) comparing with the result in 3-1, which
temperature was low (<200○C) at higher bed thickness(300-600mm).
Change in major product gas distribution is shown in Fig.
3. CO2 was continued to major product with leading bycombustion until 40min. After the product gases

Fig. 2 Temperature change inside gasifier
during wood pellet gasification at 0.3MPa

Fig. 3 Change in product gas distribution
during wood pellet gasification at 0.3MPafluctuated up-and-down around 40-90min, CO exceeded
50% after 90min migrating to gasification as the major
reaction and continued until 200min.
On the other hand, with regular bed height as 300600mm for wood pellet, CO2 was inevitably continued tohigh as 40-60% and CO did not exceed 20-30%. Therewere hole inside the material bed to gas to sweep(channeling) causing accumulation of the materials,
feedstock and partial reacted char, by the observation
after the experiments. Basically, several layers, which
are combustion zone, gasification zone, pyrolysis zone,
and drying zone, are formed from bottom up in the
updraft gasifier, but their layers are hard to form witharising a hole. This is an explanation of why problem ingas stream was caused is that wood pellet waspulverized and swollen by exposing under vapors fortens of minutes at 100-300○C, the formed powdery
substance inhibited to uniform gas flow.

4. Conclusions
The difference between PKS and wood pellet was seenin adaptability for pressurized fixed bed gasification.
Gasification reaction was achieved well in the experimentfor PKS while the problem such as the channeling of thegas flow was caused using wood pellet. Such problem
was reduced by lowering the bed height of the materials
inside the gasifier, even though outlet gas temperature
increased by bed height lowering.

7th International Symposium on Feedstock Recycling of Polymeric Materials (7th ISFR 2013)
New Delhi, India, 23-26 October 2013