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8/10/2019 4. Thermochemical Biomass
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Thermochemical conversion
Eko Heryadi
Biomass conversion
Thermochemical
combustion
gasification
pyrolysis Biochemical
fermentation (bioethanol)
agrochemical (biodiesel)
anaerobic digestion (biogas)
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Thermochemical
Thermochemical
Process to convert the biomass into energy by
using a thermal application
The oldest application of man has been used
Combustion, gasification, pyrolysis the
main process of thermochemical
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Combustion
The oldest energy technology used by man
Directly burnt in presence of air
Convert into : heat, mechanical power,
electricity
Combustion application
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Direct Combustion
Unprocess biomass
Process biomass
Stages of burn (combustion process)
Drying
Devolatilization
Char combustion
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3 rules of combustion
Times
Turbulence
Temperature
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Pellet application
(small scale)
Medium to large scale combustors
The major types of large scale biomass
boilers use one of the following
technologies: grate combustion systems
(stationary or travelling), stokers,pulverised fuel (PF) systems or fluidised
bed combustion (FBC) systems.
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Grate combustors Moving grate with primary air in two stages in the grate and
secondary air
With the techniques based on grates (such as inclined grate,traveling grate, chain grate and vibrating grate), the fuel isusually fed automatically onto the grate by gravity
Temperatures above the bed and in the freeboard normallyrange between 800 and 1000C. In the stationary grate design,ashes fall into a pit for collection. In contrast, a traveling gratesystem drops the ash into a hopper.
Stokers
Spreader stokers, which feed the fuel bydistributing it on the top of the bedthroughout the furnace, and retort(underfeed) stokers are successfully used insome boilers that have been converted fromcoal firing.
Understoker furnace with primary andsecondary air, mixing zone and postcombustion chamber
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Pulverised fuel (PF) systems Wood and agricultural residues powder is attractive
for larger plants, since it allows conversion to
biomass fuels with minimal investment for boiler
conversion.
Burners for wood powder are available in the range
of 1 to 30 MW. In pulverised fuel combustion, the
fuel is introduced with air in burners similar to those
used for oil or coal burners.
Fluidised bed system
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Gasification
Gasification
Convert biomass into combustible gas mixture bypartial oxidation in high temperature, heatedinsufficient air
CO + O2 CO2C + 1/2O2 CO
CO + 1/2O2 CO2CO2 + C 2CO
CO2 + 4H2 CH4 + 2H2O (methane formed)
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Technology platforms
Three categories of gasifiers can be
distinguished:
Fixed bed gasifiers.
Fluidised bed gasifiers.
Entrained flow gasifiers.
Fixed bed gasifiersFixed bed gasifiers Fluidised bed gasifiersFluidised bed gasifiers
Application
Firing in boilers or heat applications
Gas turbine operation
Co-firing with coal
Co-firing with natural gas Gasification systems for engine operation
Methanol, hydrogen and Fischer-Tropsch
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Pyrolysis
Pyrolysis
Breaking down of material by a heat
First step in combustion process
Devolatilization in absence of oxidizer
Temperature start 350-550o
C goes up 700o
C Biomass + heat charcoal, gases, bio-oil
Char or liquid yield is optimized
Types : slow pyrolysis, fast pyrolysis, flashpyrolysis, catalytic biomass pyrolysis
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The pyrolysis process and specifically the supply of heat may becarried out in three quite different ways:
The most primitive method is to treat the biomass feedstock batchwise andgenerate the heat required for pyrolysis by burning part of the biomass withadmission of air. This is the method used in charcoal kilns. This methodgives a slow pyrolysis and is mainly useful for charcoal production eventhough tar can also be obtained as a by-product
The second type of process is used for industrial production of charcoal. Thefeedstock is heated by inert combustion gases in complete absence ofoxygen. The industrial processes are continuous and the capacity is of the
order of 1 tonne of charcoal per hour or more. Modern charcoal processesare achieves efficiencies of over 30% by weight. The pyrolysis is started byburning fuel oil, but when combustible gases are released from thebiomass, these gases are burned instead of the oil. The continuous processmakes careful control of the emissions, unlike with the batchwise process.
The third type of process uses inert solid material as an energy carrier (e.g.sand in a FBC) to heat the biomass being pyrolysed. This process is suitablewhen fast heating of the biomass is desirable, i.e. when yields of gas orliquid product are the most interesting.
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Other
Fischer-Tropsch synhesis
The Fischer-Tropsch synhesis is a process
which is converted a gases form into a
liquid hydrocarbon form bases and over a
catalyst reactions
History
-1902 : French inventor Sabatier and Senderens discover :
CO could hydrogenated over Co, Fe and Ni into Methane
-1925 : Prof.Franz Fischer and Dr. Hans Tropsch :
Synthesis of hydrocarbon liquids and solid paraffins on Co-Fe
catalyst under mild conditions of 250 300oC
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Fischer Tropsch Process
1. Synthesis gas formation
CHn + O21/2n H2 + CO
2. Fischer Tropsch reaction
2nH2 + O2 -(CH2-)n- + H2O
3. Refining
- (CH2-)n- Fuels, lubricant, etc
Catalyst
Catalyst
Catalyst
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FT reactors Two classes of reactors are used :
Multi-tubular fixed bed
Fluidized bed reactor :
two-phase circulating fluidized bed reactor
two-phase fixed bed fluidized bed reactor
three-phase slurry reactor
Multi-tubular fixed bed
consist of thousands
of narrow tubes with
surrounding water
temperature is controlled
by releasing steam when
pressure is increased
FT reactors (cont.)
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Fluidized bed reactorContains immersed cooling coils and are excellent heat exchange systems
FT reactors (cont.)
circulating fluidized bed reactor fixed bed fluidized bed reactor slurry-phase bubbling bed reactor
Fischer-tropsch catalyst
4 catalyst for commercial application
Ni, very active catalyst but has a major drawbacks :
Produces much more methane than Co and Fe
Nickel forms volatile carbonyls resulting in continuous loss
of metal at operating conditions
Ru, most active catalyst but very expensive
Fe, cheaper catalyst, will result in lower heavy
hydrocarbon
Co, has a longer life and high activity
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Products The products of FT synthesis
range from C1 to high
molecular mass waxes
Important parameter :
temperature, partial
pressures of H2 and CO, feed
gas composition,reactor used
and reduction of the catalyst
General accepted reaction pathway for
the formation of higher
hydrocarbons in FT synthesis (steyberg.2004)
Technology status and operated plants
Choren, Freiburg
Figure. BIG FT pilot plants, Choren industries, Freiberg, Germany
a) -plant, fully operasional, b) -plant, currently under construction
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Carbo-V Process for manufacturing synthesis gas from solid biomass
Carbo-V
Wood as a feedstock
Circulating fluidized
bed reactor Two separate gas
streams are produced
The sensible heat of
two streams are used
for district heating
Technology status and operated plantsTechnology status and operated plants
Repotec, Gussing, Austr ia
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Process flow diagram for Gussing plant, Austria
Sekian