Innovative industrial plasma torch for converting biomass into high purity syngas
A. Hacala1, U. Michon
2
1EUROPLASMA, 21 rue Daugère, 33520 Bruges, FRANCE- www.europlasma.com
Abstract: In the context of climate change, reinforced legislation for industrial emissions and
the necessity to decrease CO2 emissions, biomass gasification is a relevant way to transfer
renewable energy from lignocelluloses to a liquid synthetic fuel. This paper deals with the
improvement of the mass yield of standard gasification process using a plasma torch fed with
gases that are directly recycled from the process.
Keywords: non transferred plasma torch, syngas, gas reforming, tars craking, gasification,
1. Introduction
Renewable energy production and use has become
necessary over the last decade as fossil fuel resources
keep on decreasing while the need for energy increases
every year. In the meantime, CO2 emissions have to be
reduced in order to meet the requirements of the Kyoto
protocol. Then, important technological improvements are
necessary in order to decrease energy consumption and
industrial processes CO2 emissions.
EUROPLASMA is an industrial leader in the design,
implementation and use of high power plasma torches.
EUROPLASMA plasma torches have been used for
several decades in industrial processes such as waste
treatment (asbestos vitrification, fly ashes destruction) or
steel production (heat support for cupola and blast
furnace). Typical plasma power ranges from 1 to 4 MWel.
Plasma torches provide high temperature gas streams (up
to 5000°C) with high enthalpy (in the range of 7 to 11
MJ/kg). Torch design is based on a return of experience of
more than 1 million hours operation with plasma torches
operated with air.
Since 2006, EUROPLASMA has been designing a new
generation of plasma torches that can be fed with any gas
mixture composed of CO, H2, CO2, CH4 and N2, in
particular, the torch can be fed with a gas mixture that can
be recycled from the process. Main advantages to use
process recycled gas is to prevent the introduction of
useless molecules, to choose the gas composition in order
to optimize process chemistry and to decrease CO2
emissions.
2. Presentation of the plasma torch
EUROPLASMA non-transferred plasma torches
technology is patented . Plasma torches are designed with
two metallic tubular electrodes connected by a swirling
gas injection chamber. Arc ignition is obtained through
short circuit. To increase electrodes lifetime, a time
varying magnetic field controls the upstream arc root
motion while gas injection naturally controls the
downstream one. Electrodes and injection chamber are
cooled by pressurized de-ionised water. An industrial
plasma heating system (PHS) is composed of a plasma
torch with its auxiliaries: power supply, water cooling
utility, gas injection unit, hydraulic unit (starter) and
control system. The geometry of the torch has to be
adapted case by case to the gas feed composition in order
to reach the highest efficiency with industrial electrode
lifetimes and to provide the best availability for the
process. Fig 1 represents a 300 kWel plasma torch.
Fig 1. 300 kWel plasma torch
3. Determination of the torch parameters
EUROPLASMA’s R&D Platform, located in Morcenx
(Landes, France), enables the qualification of plasma
torches from 150 kWel to 2 MWel. It is composed of the
following elements:
- gas distribution: possibility to feed the torch with
gas mixtures composed of CO2, CO, CH4, H2 and
N2. Dangerous gas storage and use is the most
challenging aspect of the installation (up to 2 tons
of CO can be stored on site) and it requires specific
security procedures.
- Air Injection: air is considered as the “reference
gas”.
- Plasma torch and its auxiliaries.
- Reactor: water-cooled vessel positioned right at the
exit of the plasma torch to handle the plasma jet,
providing variable counter–pressure on it. Capacity
of the vessel is to operate up to 5 bars.
- Flare: to respect laws on emissions, and even if test
sessions are short thus reducing the amount of
emitted gases, all process gases are burned by a
dedicated flare.
All along torch operation, all parameters such as gas and
water flows, gas composition, current, voltage, pressures
and temperatures are recorded continuously and stored in
a huge database for further treatment. These data are used
to determine the torch operating points.
3. Recycling concept for blast furnace application
In the frame of the ULCOS (Ultra Low CO2
Steelmaking) European program, EUROPLASMA
studied the use of a plasma torch to reduce the CO2
emissions of a conventional blast furnace. Fig 2 shows the
process diagram with the introduction of the plasma torch
in the blast furnace top-gases recycling loop.
Fig 2: Plasma torch on blast furnace – process diagram.
Calculations showed that the use of a plasma torch fed
with recycled top gases reduces carbon consumption of
50% compared to conventional blast furnaces (taking into
account that the plasma torch is powered with C-lean
electricity). Composition, thermodynamic and transport
properties of the ionized gas mixture produced by the
torch were calculated [1]. The result is that the gases
produced are compatible with the needs of the blast
furnace operation.
Experimental tests were performed and it was shown
that a 1 MW plasma torch can operate with any gas
mixture composed of CO/H2/CO2/N2. Table 1 gives the
compositions that were tested experimentally. These
compositions were given by Steel Making companies
Seeing how a plasma torch can improve the global
performances of a process, EUROPLASMA decided to go
further and started to work on gasification processes.
% vol
N°1 N°2 N°3
CO 60 47 52
CO2 35 14 25
N2 4 38 22
H2 1 1 1
Table 1: Gas compositions tested in a 1.5 MWel plasma torch
4. Plasma torch to improve biomass gasification
Gasification is a thermochemical process that is studied
to produce hydrogen and synthetic gas (or syngas) from
biomass. Since 2006, EUROPLASMA has been working
with CEA (French Nuclear Research Agency) on the
development of a new gasification process scheme which
aim is to reach high carbon yield, in order to maximize
the conversion of the available lignocelluloses feedstock.
Indeed, for standard biomass gasification processes, the
resulting average mass yield is about 15 % as part of the
energy contained in the biomass is consumed for the
endothermic conversion. In addition, the resulting syngas
contains lots of tars, thus limiting the production of liquid
fuel.
One way to improve lignocelluloses mass yield is to use
an external source of energy to feed the endothermic
reactions: in this case, thermal plasma is used.
EUROPLASMA and CEA have entered into a strong
collaboration agreement to develop an allothermal
gasification process called GALACSY [2] which aim is to
produce high quality syngas from the conversion of
lignocelluloses (solid or liquid) using plasma assisted
gasification [3]. The general process diagram is
represented on fig 3.
BIOMASSSOLAR
WIND
SEA
NUCLEAR
Electricity
Synthetic gas
GasShift
FisherTropsch
Syntheticdiesel
Fig 3: plasma assisted biomass gasification
EUROPLASMA is in charge of providing a plasma
torch that is compatible with the process, and also of
developing and testing the Core Process at the level of the
prototype scale on its R&D facility. It is expected that the
high temperature level and the presence of oxygenated
active species in the plasma will reduce the tar content
below 0.1 mg/Nm3 and increase the mass yield up to 30%.
In the studied process, the plasma torch is fed with gas
mixtures coming from different gas streams recycled from
the process. In particular, the plasmagene gas can be
recycled from the polishing stage, the gas shift stage and /
or from the Fischer Tropsch stage (mainly gas residues).
Facing these several potential gas streams, it is necessary
for EUROPLASMA to develop a new generation of
non-transferred arc plasma torches sufficiently reliable to
be operated with gas mixtures composed of CO, CO2,
CH4 and H2. First experiments were made on a specially
designed 300 kWel plasma torch.
5. Results and discussion
Fig 4 represents a typical Voltage – Current diagram
representing arc voltage versus arc current (for steady
state gas injection flowrate). On this graph, the
experimental values (symbols) are superimposed to a
solid line network representing constant electric power
levels. The torch is current driven. Pressure inside the
reactor is set to 1 bar (atmospheric pressure).
Fig 4: Example of voltage-current diagram obtained for the
following gas composition (%vol): H2/CO/CO2/CH4:
40/20/20/20.
Voltage-current diagrams were recorded for several
compositions of recycled gases (recycled from
gasification processes). During one year, EUROPLASMA
tried different plasma torches design to adapt the torch to
a specific gas composition. Gas compositions
correspond to gas mixtures that could be recycled directly
from the process (namely pure syngas and tail gas from
Fischer Tropsch), to gas mixtures that are evaluated to
optimize both biomass mass yield conversion and
quantity of available gas stream to be recycled.
Europlasma’s expertise lead to develop a torch model
with more 75 % energy yield whatever the gas
composition is. After optimization of the original model
85% of efficiency has been reached Let us note that
conventional industrial non-transferred arc plasma torches
operating with air have more than 80% efficiency.
The following table gives examples of gas mixtures that
were tested in 2008.
% vol
N°1 N°2 N°3 N°4 N°5 N°6
CO 50 45 30 20
CO2 100 80 10 10 20
CH4 20 20
H2 50 45 60 40
Long duration tests (over 50 hours) showed that the
electrode erosion rate is compatible with an industrial use.
It has been demonstrated that the torch can be fed with
any gas mixture composed of CO, CO2, H2 and / or CH4.
The plasma torch is ignited with CO2 and the composition
is then tuned until the final composition is reached. The
key idea of the use of thermal plasma torch operated with
process recycled gas is to prevent useless introduction of
molecules such as nitrogen and is also to choose the gas
composition in order to maximize biomass conversion
into a high quality tar free syngas.
EUROPLASMA is now moving to the next step of its
torch development : develop higher power plasma torches,
which design will be based on the non transferred torch
patented and patent pending technology to address this
technology to industrial processes. Main objective in this
new generation of plasma torches is to reach 20 MWel.
6. Acknowledgments
The authors would like to thank OSEO-Innovation, the
funding organization of SME, for its financial support.
References
[1] B. Sourd, J. Aubreton, M-F Elchinger, M. Labrot and
U. Michon, J. Phys. D:Appl. Phys. 39 (2006)
1105-1119, High temperature coefficients in
e/C/H/N/O mixtures.
[2] M. Brothier, P. Gramondi, C. Poletiko, U. Michon
and A.Hacala (2007), Biofuel and hydrogen
production from biomass gasification by use of
thermal plasma, High Temperature Material
Processes, 11, p. 231.
[3] CEA, EUROPLASMA, Device for gasifying biomass
and organic wastes at a high temperature and with an
external power supply for generating a high quality
synthesis gas, patent WO 2007/44042559, 2007.
Table2 Example of gas mixtures that were tested
with the 300 kW plasma torch.
600
800
1000
1200
1400
1600
1800
100 120 140 160 180 200 220 240 260 280 300
I arc (A)
U a
rc (
V)
Nominal flow rate
70% of nominal flow rate
100 kWélec
150 kWélec
200 kWélec 250 kWélec 300 kWélec 350 kWélec 400 kWélec
450 kWélec