ICCHT2010 - 5th
International Conference on Cooling and Heating Technologies. Bandung, Indonesia
9-11 December 2010
123- 1
The Development of Laboratory Scale Continuous Peat
Torrefaction Reactor System
Haryadi1, Aryadi Suwono, Toto Hardianto, Ari D. Pasek2
1Mechanical Engineering, Politeknik Negeri Bandung, Bandung, Indonesia,
2Faculty of Mechanical and Aerospace Engineering, ITB, Bandung, Indonesia,
[email protected], toto@pau pauir.itb.ac.id, [email protected]
ABSTRACT: Peat can be fourth energy resources in Indonesia, after oil coal and
natural gas. With 27 million hectares, Indonesia peat resources area is the third
largest in the world, after Canada and Russia. In the current years, peat utilization
as energy is very limited. The development of peat energy resources is expected to
support the objective of the National Energy Management Blueprint 2006-2025.
However, the environmental aspect of this matter should be emphasized
Torrefaction is a thermal process appiled to organic materials operated at medium
temperature, in absence of oxygen and at relatively long residence times, typically
10 to 60 minutes. The properties, such as heating value, fix char content, are
improved through limited devolatilisation that occurs under these conditions. Batch
torrefaction experiment showed that the heating value of the torrefied peat was at
the level of subbitminuous C to bituminuous high volatile C of ASTM D 388 coal
classification.
A development of a laboratory scale continuous peat torrefaction reactor system
will be presented. The capacity of the system is 8 kg/h of raw material. The system
consists of a dryer, a torrefaction reactor, and supporting facilities. Both the dryer
and the torrefaction reactor employed fluidized bed. The dryer worked in bubling
regime, while the torrefaction reactor worked in near minimum fluidization
condition.
The raw material of the system was natural peat with 46 % moisture content. The
dryer used hot drying air to reduce peat moisture content to 22.7%. The torrefaction
bed employed heating steam to increase peat temperature to 300°C. The peat was
held at this tempemparature for 15 - 30 minutes. The drying air was heated up with
waste steam from the torrefaction reactor. The experiment showed that the torrefied
peat heating value was 5720 kcal/kg.
Keywords: peat, continuous, torrefaction, system, development.
1. INTRODUCTION
Oil, coal, and natural gas still become primary energy resources. The world oil consumption
in year 1965 had already reach 31.25 million barrels per day, while Indonesian oil consumption
is 123,000 barrel per day. Meanwhile, in year 2004, the world oil consumption increased to
ICCHT2010 - 5th
International Conference on Cooling and Heating Technologies. Bandung, Indonesia
9-11 December 2010
123- 2
80.76 million barrel per day and for Indonesian 1.15 milion barrel per day [1]. The increase of
world population and developement of technology cause energy consumption rises rapidly.
Therefore, alternative energy resources must be developed with equivelent quality as oil, coal
and natural gas.
For Indonesia, peat could become the new source of energy after the three primary sources
mentioned above, because Indonesia is the third lagest peat area reserve in the world. The area
of peat reserve proximately 27 million hectares [2], with potential reserve equal to 200 billion
ton [3]. However, due to peat low quality as source of energy, it requires to be improved in
order to be used as new energy recources. An environmental impact analysis also should be
conducted if the usage of peat will be realized massively.
Theoretical and experimental researches on upgrading the quality of peat as solid fuel
through drying method have been conducted [4]. Further theoritical study indicates that energy
density of peat still can be improved with advanced treatment, so called torrefaction process.
Therefore this research will study the upgrading of peat quality as source of energy, especially
increasing its heating value, through torrefaction process. Based on latest research, application
of this method to wood briquette can improve its HHV up to 15% [5], while empty oil palm
bunches up to 25% [6]. Improvement of peat heating value by torrefaction process can be as
high as heating value of bituminous coal [7].
Long term research focussing on increasing the quality of peat as solid fuel should be
conducted to improve economic value of peat. To achieve this goal, several stages of research
are still required. This research is only representing the early stage, which main goal is to
examine the influence of process temperature and time reaction to thermodynamics properties
of product in peat torrefaction process.
2. PEAT TORREFACTION
Torrefaction is a method of thermochemical process to increase solid fuel heating value,
especially an organic matter. In biomass torrefaction process, the organic matters experience
treatment of heat at medium temperature in a condition without oxygen, with target to increase
its energy density by decomposition of certain fractions. The effect of decomposition process is
expected to degrade atomic ratio of oxygen to carbon, hence the heating value will increase.
Some factors that influence the product characteristic in torrefaction process are process
temperature, resident time, and particle size. The product from torrefaction process can be used
directly (such as solid fuel briquett), mixed together with other fuel (co-combustion), or as raw
material for gasification.
The main fractions of biomass are: hemicelluloses, lignin and cellulose, which all together
called lignocelluloses. Hemicelluloses decomposes at a temperature of 225 to 325 °C, cellulose
decomposes at a temperature of 305 to 375 °C, and lignin decomposed at a temperature of 250
to 500 °C [8]. Among the three compounds of lignocelluloses, hemicelluloses are the most
reactive fraction, and the most easily decomposed. Concentration of hemicelluloses in biomass
is quiet high. Biomass torrefaction process is aimed to decompose hemicelluloses. Therefore,
the process temperature of biomass torrefaction is approximately same with biomass
hemicelluloses decomposition temperature, which is between 225 to 300 °C [5, 6, 8].
Naturally, peat is partially or incomplete decomposed biomass and deposited together with
complementary minerals. Like other organic fuels, main constituent of peat are carbon (C),
oxygen (O) and hydrogen (H). If peat decomposition level is high, the content of C will
increase and the content of O will decrease. Peat contains much less hemicelluloses than
biomass. Thus, the torrefaction process of peat must be done at slightly higher temperature than
biomass torrefaction process [7].
ICCHT2010 - 5th
International Conference on Cooling and Heating Technologies. Bandung, Indonesia
9-11 December 2010
123- 3
3. PEAT TORREFACTION SYSTEM
The system consist of a dryer, a torrefaction reactor, and supporting facilities. Both the
dryer and the torrefaction reactor employ fluidized bed method for each the process. The dryer
worked in bubling regime, while the torrefaction reactor worked in near minimum fluidization
condition. The system capacity is design for 8 kg/h, which is determined based on drying bed
capacity that already exists.
The dryer uses hot drying air to reduce peat moisture content and increase peat temperature
from ambient temperature to process temperature. The torrefaction reactor uses superheated
steam to increase peat temperature to 300°C. The torrecation reactor inert atmosphere is
provided by the steam release from the peat it self, which is originated from peat moisture. The
dried peat is held at this temperature for 15 - 30 minutes.
4. THE APPARATUS
The schematic of material flow of the laboratory-scale peat continuous torrefaction system
is shown in Figure 1. A screw conveyor conveys raw material to the driying bed, then the peat
flown from driying bed to torrefaction bed. Heating steam came into internal heater of
torrefaction bed, then into external heater, and finally into drying air heater. A blower drives
fresh air to the air heater. The air heater is finned tube heater, with the heating steam is in the
tube side. The hot air came into the plenum, and than passes a distributor plate to the drying
bed. Dry peat was entrained by drying air to the freeboard. As freeboard cross sectional area
greater than that of drying bed, drying air velocity decreased into below the terminal velocity
of the dry particles, then the dry particles fall into incline plate. The plate inclination is 45°, to
ensure that the peat goes down.
Figure 1: Schematic of the developed apparatus.
A rotavalve was acting as airlock or barrier, which prevent drying air goes into torrefaction
bed and hot gas of the torrefaction reactor goes into drying bed. The rotavalve consists of: a
two side segmental cut cylindrical housing, and finned rotating shaft. The clearance between
housing and fin was about 1 mm.
ICCHT2010 - 5th
International Conference on Cooling and Heating Technologies. Bandung, Indonesia
9-11 December 2010
123- 4
Figure 2 shows schematic diagram of the torrefaction bed arrangement. The bed cross
section is rectangular. The internal heater pipe was installed in longitudinal position to reduce
disruption of material flow. Resident time of the peat was adjusted with inclination angle
adjusment of the distributor. And flow distribution of the hot gas was adjusted with regulator
plate. Another rotavalve was installed at the outlet side of the bed to separate hot torrefaction
gas from sorounding atmosphere.
All hot parts of the system apparatus were thermally insulated.
At the bigining, superheated steam was injected to the torrefaction bed to remove air and
heat up the bed. Under the operating condition, hot steam originated from peat provided inert
atmosphere in the torefaction bed.
Figure 2: Torrefaction bed arrangement.
4. RESULT AND EVALUATION
Mass flow rate of the peat raw material was 8 kg/h with 46% moisture content (AR). Drying
air flow rate was 238 kg/hr, with 83°C temperature. Heating steam flowrate, pressure and
temperature was 13 kg/hr, 2 atm, and 490°C respectively. The torrefaction temperature was
300 °C. About 20 minutes after feeding, the product started to appear. The torrefied peat
heating value increased from 2673 kcal/kg to 5720 kcal/kg. The product calorific value is
equivalent to about 30 minutes resident time in batch torrefaction experiment.
Figure 3 shows flowsheet model of AspenPlus 11TM
simulation of the experiment. The
drying bed is represented by DRY-REAC and DRY-FLASH block, and torrefaction bed is
represented by B1, TRF and GAS-SPTR block. The torrefaction gas composition was
generated from a batch torrefaction experiment.
There is very good agreement betwen the Aspen model and the experiment in drying
process. For the torrefaction process, decreasing temperature from HDRYPEAT to PRD-TGSS
strem indicated that the process was endothermic. This phenomenon needs further
investigation.
ICCHT2010 - 5th
International Conference on Cooling and Heating Technologies. Bandung, Indonesia
9-11 December 2010
123- 5
Figure 3: AspenPlus 11
TM model of the experiment.
5. CONCLUSION AND RECOMENDATION
The intial model of laboratory scale torrefaction system apparatus has beed developed. The
experiment showed that the heating value increased significantly. To reduce air leak from the
drier to the torrefaction bed, better rotavalve with smaller clearance should be developed.
Greater capacity also makes smaller leak. The mathematical model of crossflow fluidizedbed
should be developed for this porpouse.
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