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