FIELD OF THE INVENTION
The present invention effectively utilizes thermal plasma to reform carbon dioxide
(C02) and methane (CH4) gases into,syngas' (CO and H2). More specifically, it relates to an
apparatus and the method for reforming of the above said greenhouse gases. The present
invention utilizes C02 and CH4 gases as a source to produce syngas in gas phase through tricathode
DC thermal plasma torch.
'
BACKGROUND OF INVENTION
As a major contributor to greenhouse gas emissions, which leads to several
anthropogenic activities, reducing C02 and CH4 levels is imperative to mitigate climatic change
and global wanning. In this regard, on December 2015 the Paris agreement was adopted by
195 countries to limit'the rise of the average global temperature over the pre-industrial level.
The goal of this agreement was to reduce greenhouse gas emissions using the most effective,
sustainable and integrated approaches including decarbonisation, the use of renewable energy
resources and the capture, storage, and utilisation of C02 (CCS and CCU). The preceding
discussion offered considerable encouragement for greenhouse gas reform, specifically the
conversion of C02 and CH4 into syngas and other value-added products. There are four
techniques of reforming greenhouse gases that have been well explored, including dry
reforming of CH4, stream reforming of CH4, auto themal reforming of CH4 and partial
oxidation of CH4. Among these approaches, dry reforming of CH4 with C02, is receiving a lot
of scholarly attention since it uses both the primary greenhouse gases (C02 and CH4)
concurrently
c0; + CH4 —> 200 + H2; Hm = 247 kJmol" (1)
Meanwhile, attempts have been made to produce syngas through a variety of
approaches, including biological, photochemical, electrochemical, and thermal breakdown. So
far, none of the aforementioned methods have been commercialised due to distinct
shortcomings in each process. A novel, cutting-edge method is required to address all of the
issues and improve energy conversion efficiency for CH4 dry reforming.
Recent advancements in the field of plasma assisted conversion and greenhouse gas
reforming techniques have provided a partial or comprehensive solution for several problems.
Through electron impact excitation, dissociation and ionisation, a variety of species, including
excited molecules, neutral atoms and ions were generated inside the plasma. Based on thermal
equilibrium condition, plasma has been classified into thermal and non-thermal plasma. Non-thermal plasmas are considered as a non-equilibrium plasma and usually have low electron
‘density and a high electron temperature in the order of several electron volts. Many kinds of
non-thermal plasmas have been used for dry reforming of CH4 such as gliding arc discharge,
corona plasma, dielectric barrier dischaxge and spark discharge. Wu et al. designed a rotating
gliding aIc discharge reactor for efficiefit dry reforming of CH4 and explored the effects of
applied voltage and CH4/C02 mole ratios on the reforming process. The obtained results
demonsfrated that the conversion of CH4 and C02 increases with applied voltage, whereas
decreases with increasing CH4/C02 mole ratio. Wang et al. designed a coaxial dielectric barrier
dischaIge reactor to convert C02 and CH4 to syngas at ambient pressure The reactor' 5 input
power, residence period of inflow gases, discharge gap and feed gas ratios were thoroughly
investigated. The gathered data showed that the conversion rate and selectivity increased in
accordance with increase in input power. Kelly et al. fabricated microwave plasma to assess
the performance of dry reforming of CH4 and they were able to achieve maximum C02 and -
CH4 conversions of 49% and 67%, pespectively. The syngas's selectivity increased when the
CH4 mole percentage increased from 30% to 45%.
The production of syngas through the non-- thermal plasma reactor can be controlled by
many parameters such as reactor design, electrode geometry, discharge power gas flow rate,
and feed gas composition. .When compared to conventional methods, plasma assisted dry
reforming of CH4 directs the system’s energy towards molecular dissociation and exhibits a
-‘
_
higher conversion rate and selectivity with lower energy costs. The advantages of non-thermal
plasma for dry reforming of CH4 includes good chemical selectivity, low temperature and low
cost: However, lower conversion efficiency and selectivity and as well as difficulty 1n scaling
up are the disadvantages of this non-thermal plasma for dry reforming of CH4.
Thermal plasma is a more effective method for dry reforming of large amounts of CH4
in a short period of time due to its high temperature, enthalpy, electron density and as well as
its electron-induced reactions and thermochemical effects. Although thema] plasma's unique
featuresprovide a high conversion rate and good selectivity, the specific energy input for
producing one mole of syng'as is significantly higher than that of various non-thermal pla‘sma
techniques
Y
Yang Zhou et a1. developed a thermal plasma torch for the dry reforming of CH4 and it
achieved exceptional conversion rates of 92. 1% for CH4 and 81.9% for C02, respwtively. The
specific energy input and energy conversion efficiency of this system was found to be 872
kJ/mole and 28.5%, respectively. Tao et a1. explored the dry reforming of CH4 performance by
utilising thermal plasma with and without a catalyst, with the same feed flux, CH4/C02 molar ratio and inpuf power. The experimental results showed that the conversion rate and selectivity
of plasma integrated catalytic reactor were 10-20% greater 'than the thermal plasma reactor
alone. A catalyst-assified binodal thermal plasma reactor was utilized by Yu et al. to explore
the efficacy of CH4 dry reforming with Ni/A1203 catalyst. The presence of an Ni/A1203 catalyst
synergizes with thermal plasma, lowering the energy consumption rate. A catalyst-assisted
thermal plasma reactor demonstrated a maximum energy conversion efficiency of 66.4%.
Though thermal plasma surpasses non-thermal plasma-assisted reforming processes in
terms of treating large volumes in a short time, achieving high selectivity, and ensuring
conversion efficiency, it demands a relatively high specific energy input for producing one
mole of syngas. Hence, there is a need to develop a promising thennaI plasma reactor capable
of converting greenhouse gases into syngas with low specific energy values. Developing a
thermal plasma torch that can generate a sustained plasmajet utilising C02 and CH4 gases with
minimum discharge power is one of the most challenging tasks in the energy efficient dry
reforming process. Meanwhile, the efficiem use of thermal plasma energy for gas reformation
may help to reduce the specific energy required for syngas synthesis. To increase thermal
plasma energy utilisation, a unique tri;cathode thermal plasma torch capable of operating under
a constant DC power source was designed for dry reforming of CH4 at low discharge power"
levels. The electrode configuration of the tri- cathode thermal plasma torch allows for the
generation of a large volume of sustained thermal plasma 1n the form of a jet. The consistent _
distjance between the three cathodes and one anode limits the arc movement, allowing for great
plaéma stabilisation. This tri-cathode thermal plasma torch offers high temperature, enthalpy,
and electron density, which make_s it an ideal choice for effective reforming of greenhouse
gases with improved energy conversion efficiency along with low specific energy input. The
unique characteristics and electrode design of this thermal plasma torch facilitates the
establishment of a thermal plasma dry reforming process that is readily adaptable ’for industrial
applications.
OBJECTIVE OF THE INVENTION:
The main objective of the present invention is to develop a tri-cathode thermal plasma tbrch
apparatus capable of running on a DC power source for the reformation of greenhouse gases
(C02 and CH4) into syngas under atmospheric pressure circumstances.
A primebbjective of the current invention is to generate a high enthalpy and high temperature
sustainable plasma jet at a low discharge power thereby making it appropriate for efficient
greenhouse gas reforming.
Another objective of the current invention is to enhance conversion (CH4 and C02) and
selectivity (H2 and CO) with large volumes of reactant gas flow at low discharge power by
optimising the electrode configuration and processing parameters of the plasma torch.
Additionally, the present invention also intends to improve energy conversion efficiency
without forming by-products by adjusting the position of C02 gas injection into plasma.
SUMMARY:
The growing industrial sectors and social progress have resulted in the large-spills
burning 6f fossii fuels. Mammoth increase in energy consumption across all the. sectors has
significantly increased the carbon dioxide emissions and has also escalated the greenhouse
effeét thus making it imperative to reduce the negative effects of climate change and slow down
global energy consumption. Present invention details with the reforming of greenhouse gases
(CH4 and C02) into many Value-added products like syngas (CO and H2), methanol, acetic' acid
and synthetic gasoline, etc. There are several methods available for the reforming of
greenhouse gases, but dry refomfing 6f CH4 is considered as a prime approach, since it utilizes
both the greenhouse gases. However; in the current scenario, the traditional dry reforming of
CH: process has some limitations, such as high energy consumption and catalyst deactivation
at high operational temperatures.
The present invention consisting of the tri-cathode DC thermal arc plasma torch 'was
utilized for the reforming of greenhouse gases into syngas under optimum operating conditions
at 'atmospheric pressure. Arc discharge inside the thermal plasma torch produces free electrons,
excited molecules along with exited atoms and ions. The produced active species are controlled
by optimizing the opgrating parameters such as discharge power, gas flow rate, gas mixing
ratio, and configuration of electrodes, etc. The tri-cathode thermal plasma torch consists of
three rod type graphite cathodes and a single nozzle copper anode. Each graphite cathode has
a length and diameter of 25 and 65 mm, respectively. Each cathode is separated by a distance
of )7 mm and positioned at an angle of 120°. The cathodes are well insulated from the anode
by a ceramic block, which also serves as a vortex generator, passing feedsiock gases in vortex
flow inside the plasma torch. Forced cooling water flow cools both the anode of the torch-and
- the bottom of the cathodes. An IGBT-based DC power source was employed to generate a ‘continuous DC output with an OCV of 300 V to power the tri-cathode plasma torch, which
produces a sustainable plasmajet.
Herein, argon gas was used as the primary gas to ignite the plasma inside the tri-cathode
- plasma forch, followed by the addition of CH4 and C02 gases at the needed mole ratiosfiThe
presence of Ar not only ignites and stabilises the plasma jet, but it also plays an jmportant role
in infldencing the electrical and chemical properties of plasma and its constituents. The excited
and ignised A’r species (Ar* and Ar") of thermal plasma transfer energy to C02 and CH4 gas
molecules via penning excitation and dissociation reactions. -
The summary of the experimental results showed that the additionof excessive Amount
of C02 decreases the conversion of feedstock C02 and CH4 gases, without affecting the
gelectivity of H2 and CO. This is in contrast to the thermodynamic investigation results, which
show that increasing the mole concentration of C02 enhances CH4 conversion, along with
improvement in H2 and CO selectivity. The difference between thermodynamic prediction and
experimental observation is entirely due to the heterogeneous character of themlal plasma. For
example, the electric and thermal propenies of plasma near the arc column are not comparable
'to the rest of the plasma c'olumn. The obtained results demonstrated that the tri-cathode DC
plasma torch can produce syngas from C02 and CH4 gases with 55.5% energy conversion
efficiency and 144 kJ/mole of specific energy at the discharge power of 7.5 kW and the total
flow rate of 1 10 slpm (C02: 77 slpm and CH4: 22 slpm). The highest conversion and selectivity
achieVed via this reforming procedure are 62-84% and 62-84%, respectively. As confirmed,
the present invention enables the reforming of greenhouse gases with large volume of reactants
and it offers an imlovative technique for enhancing the production of syngas with excellent
energy conversion-efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 Crosé-sectional view of tri-cathode; DC thermal plasma torch.
Figure 2 FEM plot of COz-CH4 system with different moles 6f CH4 (1 to 3.5).
Figure 3 Effect of increasing C02 mole ratio on C0, H2 and H20 selectivity.
Figure 4 Effect of increasing C02 mole ratio on C02 and CH4 conversion,
Figure 5 Effect of increasing C02 mole ratio on C0 and H2 selectivity.

Figure 6 Effect of increasing C02 molg ratio on specific energy of thermal plasma dry
reforming process.
Figure 7 Effect of increasing C02 mole ratio on energy conversion efficiency of thermal .
plasma dry reforming process.
‘DETAIL DESCRIPTION OF THE INVENTION
PATENT
The present invention relates to effective utilization of thermal plasma energy by
developing tri-cathode DC thermal plasma fiorch to reform the greenhouse gases C02 and CH4
into syngas. The complete description below enlightens the apparatus and methods for
reforming of greenhbuse gases into syngas using tri-cathode DC thermal plasma torch
apparatus.
FigureJ illustrates a 3D cross-sectional view of the multi cathode thermal plasma
apparatus used for the dry reforming of CH4. The plasma torch comprises of one nozzle type
anode 1 and three rod type cathodes 2,3,4 made of copper and graphite, respectively. The rodtypé
graphite cathode has a diameter of 25 mm and a length of 65 mm. The ceramic insulator
5 was used to separate the cathode and anode and each was water cooled 6, 7 separately. For
gas injection 8, a multi— hole vortex generator was designed inside the ceramic insulator. Plasma
torch was mounted above the wa‘er- cooled stainless steel cylindrical reactor 9 (170 mm
diameter and 350 mm length) equipped with a suitable gas exhaust system and a gas sampling
per}? Initially, a pilot arc is ignited using Ar gas at a discharge current of 75 A. After that one
mole each of C02 and CH4 is added to the Ar plasma, corresponding 100 V voltage was
developed. After attaining a stable plasmajet, different mole ratios (0.5 to 2.5) of C02 gas were
externally mixed with Ar-COz-Cl-Lz plasma. The effect of C02 addition on the dry reforming
process was investigated by analysing the processed gas samples using GC-MS equipped with
thermal Conductivity detector.
In the present invention, the conversion of CH4 and C02 and the selectivity of H2 and
CO were evaluéted using the following formulas:
moles of CH4 converted (2)
10 0
moles ofinitial CH4
Conversion of CH4 = 0 A)
—moles o—fCOZ c’on—verted X 100%
(3)
Conversi n of CO =
O 2
moles ofinitial C02
moles of H2 produced 0 (4)
2 x moles ofCH4 converted
Selectivity of H2 X 100 A)

moles ofCO Pr°duced
x 100% (5)
electivi of C = S ty 0
(moles of CH4 + moles ofCOZ) converted
The specific energy (SE) and energy conversion efficiency (ECE) are calculated using the
following formulas:
_
SE
_ Input power (kW) (6)
x
I
- selectivity ofCO and H2 (mol/s)
_ selectivity of H2 x LHV H2+selectivity of CO x LHV C0 (7)
ECE
Input power +conversion of CH4 x LHV. CH4-
Where LHVi réfers to the lower heating value of substance in kJ/mol.
The thqrmal decomposition mechanism of C02-CH4 gases at high temperature is
estimated by the free energy minimization (FEM) plot of the C02-CH4 system using CSIR
Th'ermochemistry system version 5. FEM plots for different moles of C02 along with CH4 gas
compositions were constmcted over a temperature range from 500 to 2500 K in atmospheric
pressure.
Figure. 2a-f illustrates the free energy minimization (FEM) technique used to
thermodynamically anticipate the generation of syngas through the thermal decompositioh of
feedstock gasés. To accomplish this, FEM plots were generated for the C02-CH4 system using
different C02 mole ratios within a temperature range of 500 to 2500 K. The most stable
prodUcts of this themal reforming process as identified in the FEM plot are 0, C0, C02, C,
H, arid H2. During the dry reforming process, the most oxidised (C02) and reduced (CH4)
forms of carbon are mixed to produce syngas (Equation 8-11). Being a stable molecule, C02
causes the reforming reaction to occur under extremely éfidothenniqconditions. Other byproduct,
such as C2H2 and CzHa, have‘ insignificant concentrations under all conditions and axe
not shown in the FEM graphs. From the FEM plot, it was observed that the temperature more
than 1590 K results in an enormous conversion of feedstock gases and produces significant
amounts of H2 and CO. This finding shows that temperatures ranging from 1500 to 2000 K are
appropriate for producing syngas-in the thermal plasma reforming process. Increasing CQz
mole concentration enhances CO and H20 selectivity and reduces H2 selectivity (Figure 3).
CH4 + co; —» 200 + 2H2 AG"
? 171 kJ mol‘1 (8)
C02 «—> C0 + 0 AG" = 61.7 kJ mol" (9)
CH4 a c + 2H2 AG°= 50.4 kJ morl (10)
O+H2—rH20 AG°=-237 kJmol"
_
(11)

Ar gas was used to create a plasma before starting the reforming process, with a constant
discharge current of 75 A and an equivalent voltage of 35 V. It was observed that, when one
mole of molecular gases (C02 and CH4) was added, the load voltage increased from 35 V to
100 V, which leads to increase in the' plasma power to 7.5 kW. This higher concentration of
molecular gases (C02 and CH4), that dissociates before ionization and it requires m0r_e _energy
for ionization, which leads to increase in voltage. Furthermore, externally C02 was gradually
fed into the high temperature Ar-COz-CH4 plasma and reformed without significantly
impacting the resistivity of plasma medium. Through the process of thermal plasma
reformation, number of active species are produced when highly energetic electrons and ions,
as well as excited molecules and atoms, instantaneously collide with gas molecules of CH4 and
002 and convert into syngas with excellent conversion efflciéhcy and selectivity.
The conversion of C02 and CH4 as well as the selectivity of CO and Hz for external
injection of various mole ratios of C02 (0 - 2.5) are shown in Figures 4 and 5. The obtained
results showed that the conversion 6f C02 and CH4 gradually decreases with the external
injection of different mole ratios of C02 in Ar-COz-CH4 plasma. When the feed flux increased,
the internal energy of the plasma decreased and the residence time of each feedstock gas species
with the core zone decreased. Consequently, species with shorter residence time tend to acquire
less energy from ’the plasma, leading to a decrease in the conversion of C02 and CH4.
Figure 4 shows that the conversion of C02 and CH4 decreases from 84% to 62% and
85% to 75%, respectively, while the conceritration of C02 increases. Meantime, the selectivity
of H2 remains stable and the selectivity of CO reduced from 84% to 62% (Figure 5), while the
concentration of C02 increases, Herein, formation of CO is more. significant than H2 formation,
indicating that the prolonged residence time of O atoms in the plasma zone promotes oxidation
I
of C atoms, leading to the production of CO rather than the its combination with Hz to form
H20. The obtained results indicate that the external injection of C02 into Ar-COz-CH4 plasma
is the optimal choice for efficient dry reforming of CH4 in the thermal plasma process. To
activate and reform the C02 gas into syngas, the plasma temperature and the energetic electrons
and excited species present at the gas injecting (external) zone of Ar-COz-CH4 plasma are
sufficient.
C02 + (e*, Ar*) —> co + o + (e, Ar)
"
. (12)
C + 0 —» co , (13)
CH: + (6*, Ar*) —> C + 2H2 + (e, Ar) .
'
(14)

CH4 + co; + (e*, Ar*) —> 2c0 + 2H2 + (5, Ar) . (15)
In this case, Ar not only aids in the ignition and stabilisation of the plasma jet but also
plays a significant role in controlling the chemical and electrical characteristics of plasma and
its constituent species. The excited and‘ionised Ar species (Ar* and Ar+) of thermal plasma
transfer energy to C02 and CH4 gas molecules through the Penning excitation and dissociation
reactions (Equations 12, 14, and 15). Along with the electron impact and pooling, the
subsequent reactions (Equation 16 and 17) illustrate that the existence of metastable statés of
Ar attempts t6 raise the vibrational temperature of C02 and CH4 gas molecules through the
excitation transfer of C02 and CH4 from Ar“ atoms. This transferred energy can surpass the
activation energy barriers required to separate C02 and CH4, resulting in CO and H2
formation.
_
Ar. + C02 —> C02* + Ar ’ (16)
Arfg+ CH4 —> CH4" + Ar '
(17)
, For this dry reforming process, it is essential to comprehend the specific energy (SE)
inpfnt and energy conversion efficiency (ECE) value. Based on the selectivity and conversion
of the products, the SE and ECE of the dry reforming process were calculated using Equations
6 afid 7. Figure _6 and 7 show the effect of C02 mole concentration on the SE and ECE ofthis
pro’éess, respectively. It was observed that the concentration of C02 increases from 0.5 to 2.5
moklkg, the SE decreased from 288.1 kJ/mol to 144 kJ/mol and the ECE increased from 42.5%
to 55.5%.
'
The obtained fesults conclude that the dry reforming of CH4 and C02 in a tri-cathode
DC thermal plasma torch is a promising strategy for producing large amounts of syngas in a
short period of time with high selectivity and low discharge power. The current invention's
embodiment includes a revolutionary tri-cathode DC thermal plasma torch apparatus and a
method for efficient thermal plasma réforming.

CLAIMS
WE CLAIM-z
A device tri-cathode direct current themal plasrha torch to produce syngas from the
reforming of greenhouse gases.
The device of claim 1 in which the above said tri-cathodedirect current thermal plasma
torch with three graphite cathodes and one nozzle type anode.
The device of claim 1 in which the above said tri-cathode direct current thermal plasma
torch electrode design for better arc stability with large volume of plasma jet.
The device of claim 1 each graphite cathode was separated by a distance of 17mm and ,was
positioned at an angle of 120°.
The device of claim 1, facilities the electrical interface between direct current power
sources and plasma torch électrodes including three graphite cathodes and one copper
anode.
The device of claim 1, external C02 gas injection into plasma fai/ours proper mixing of
feedstock gases and efficient reformation.
The device of claim 1 in which a tri-cathodg direct current thermal plasma torch with
plasma gas (C02) which is directly introduced into the plasmajet.
A method for reforming greenhouses using tri-cathode direct current thermal plasma torch
with large volume of reactants at atmospheric pressure condition.
The method of claim 8 in which a higher conversion and selectivity were achieved using
tri-cathode direct current thermal plasma torch.
The method of claim 8 in which tri-cathode direct current thermal plasma torch produced syngas without formation of by-products.
The method of claim 8 in which tri-cathode direct current thermal plasma produced syngas with higher energy conversion efficiency.