Proceedings of CUChE Alumni Symposium 2022

On “Circular Economy on Sustainable Basis: The Role of Chemical Engineers”

CUChEAA ISBN: 978-81-954649-1-3

December 2022 P a g e | 19 Volume 2, Issue 1

Air Plasma Gasification Technology in Pursuit of Clean Environment

S. Bhandari

1, *

, N. Tiwari

, Y Chakravarthy

, VC Misra

, S. Ghorui

1, *

L&PTD, Bhabha Atomic Research Centre, Mumbai-400085

Authors for correspondence, e-mail: srikumarghorui@yahoo.com, subhb@barc.gov.in

Abstract

Rapid industrialization, urbanization and modern life style make solid waste management as one of the most challenging

issues in both developed as well as developing countries. Air plasma gasification is a state-of-the-art technology for the

treatment of all types of solid wastes including municipal, industrial, medical, electronic and radioactive waste. Owing to

the presence of electrons, ions, radicals and highly concentrated thermal energy air plasma technology offers superior

thermo-chemical environment for solid waste gasification. BARC developed a coke bed-based air plasma gasifier facility

with the processing capacity of 5 TPD. The experimental observations and operational experiences of the air plasma

gasification facility involving plasma gasifier, secondary combustion chamber, venturi scrubber, packed bed scrubber have

been presented in this paper. Processing capacity as high as 99 % has been achieved for a wide range of solid waste

including MSW, RDF, PVC, cotton waste and used ion exchange resin. Good quality syn gas was produced using air

plasma gasification technology. It was successfully demonstrated that coke-based air plasma gasification is one of the most

efficient and environmentally friendly technology for management of solid waste treatment.

Keywords: Plasma gasification, Solid waste management, Decarbonization

1. Introduction

Increasing population, consumerism and fast economic

development massively enhance the quantity of solid

waste and lead to rapid depletion of natural energy

resources [1]. Consequently, it enhances the need for

sustainable, reliable, cost-effective and environmentally

compatible technology for waste management. While

several technologies are available for treatment of solid

waste including land fill method, incineration and

gasification, among all these land filling is the oldest and

most commonly used waste disposal process. However,

there are two serious drawback of landfill technology.

On one hand hazardous chemicals can leach out and

contaminate the ground water on other hand it releases

harmful gases like methane into the atmosphere.

Incineration is another widely practiced waste disposal

technology. In incineration process solid waste are

burned in presence of excess air to form carbon di-oxide

and water vapor. However, there are few severe

shortcomings of conventional incineration technology as

well. Owing to low process temperature gas emissions

from incinerator involve high level of air pollutant (NO

SOx, HCl) and carcinogenic compounds such as dioxins

and furan. Moreover, 30-40% of feed waste remains as

bottom ash which is categorized as hazardous solid

waste and necessitates further care and treatment. Public

concerns and stringent emission regulations have

resulted in enormous thrust in research and development

of new innovative waste treatment facility [2].

Gasification technology has been practiced worldwide

for more than 150 years. Before the invention of

electricity coal was used to produce town gas by coal

gasification process. Solid waste disposal by

conventional gasification has received great attention as

attractive alternative technology in past few years. The

primary prerequisite of thermal processing of solid waste

in an environmentally friendly manner is the

‘availability of high temperature’. Higher is the

temperature greater is the conversion of waste into

synthesis gas and lower is the hazardous emission. Over

the years it has been established that arc plasma jet, a

beam of highly concentrated beam of thermal energy can

meet the high temperature requirement of thermal

processing in convenient manner. Plasma gasification

has been proven to be one of the most innovative and

proficient technology for the treatment of waste in

efficient and environmentally compatible manner.

Compared with conventional gasification technology

plasma gasification offers following unique advantages.

i. Highly concentrated energy of plasma and presence of

ions, atoms and exited species provide better thermo

chemical environment for gasification compared to

conventional method. Presences of plasma greatly

enhance the kinetics and make the reaction very fast.

Large quantity of waste can be processed in smaller

reactor volume and in shorter time [3,4].

ii. Plasma gasification technology does not use any

fossils fuel and less amount air compared to

conventional process and therefore it does not release

Proceedings of CUChE Alumni Symposium 2022

On “Circular Economy on Sustainable Basis: The Role of Chemical Engineers”

CUChEAA ISBN: 978-81-954649-1-3

December 2022 P a g e | 20 Volume 2, Issue 1

excess amount toxic pollutants like NOx, SOx and

HCl. Plasma gasification process produces less

quantity of bottom ashes (<1%) compared to

conventional thermal processes (>20%). While fossil

fuel-based gasification process, does not allow easy

control of reactor temperature, plasma process allows

precise control of the temperature by adjusting

electrical power.

iii. Organic pollutants like dioxin and furan does not

form owing to higher process temperature (>1200

C). Plasma gasification produces good quality of

syn gas containing negligible amount tar compare to

conventional gasification process.

iv. Wide spectrum of waste including municipal,

hospital, sludge, industrial waste, hazardous waste

and radioactive waste can be efficiently treated by

plasma technology [5-10]. Organic components of

the waste are converted to high quality of synthesis

gas and inorganic components are converted to inert

vitrified slag. Chemically inert non leachable

vitrified slag is used in construction and building

work [11,12].

The device which produces high temperature plasma jet

is known as plasma torch. Plasma torch is the workhorse

of the plasma-based waste treatment technology. Gases

like argon, nitrogen and air is used to produce plasma

jet, however air plasma torch is most suitable as air is

freely available in nature. Most of the plasma torches

are developed by Westinghouse, Europlasma, Tetronics

and Phoenix. The key issues with these plasma torches

are [13-15] a) High capital and operating cost b)

requirement of high air flow rate high minimum

operating power c) low plasma jet length and volume d)

Low plasma jet temperature (~5000

C). These devices

do not serve the requirement of the medium to small

scale industries. Large air flow rate also dilutes the syn

gas by introducing nitrogen gas and produces low

calorific value syngas. An attempt has been made to

address all the above-mentioned limitations through

indigenous development of a medium power (30 kW)

Cu-Hf electrode-based air plasma torch in BARC

(Patent# 201721012999, Technology is transferred to

industry). Based on these torches, a unique Air Plasma

gasification technology is developed by BARC

(Technology is transferred to industry). BARC

developed air plasma torch offers unique advantages like

low operating power ( 15-30 kW), low air flow rate( 30

lpm), extremely hot (temperature > 8000

C) and long

plasma jet. More details can be found in [13,14]. The

main challenge of plasma-based waste destruction

technology is economic feasibility as plasma torch uses

electricity which is one of the costliest forms of energy

[15,16]. In this paper we report the development and

deployment of indigenously developed low-cost air

plasma gasification system for processing solid waste.

The plant can be operated both in gasification and

incineration mode.

2. Overview of the plasma gasification facility

A schematic diagram of plasma gasification/incineration

facility developed by BARC is presented in Fig. 1. The

facility consists of following sub systems, a) air plasma

torch (b) IGBT based DC power supply (c) primary

chamber (d) secondary combustion chamber (e)

quencher cum venturi scrubber (f) packed bed column

(g) ID fan (h) compressor (g) chiller (h) stack

The actual photograph of the facility is shown in Fig 2.

Two numbers of identical facility is installed at BARC.

While one facility will be used for regular operation to

process solid waste generated inside BARC campus,

another facility will be used to conduct research and

development work.

Figure 1: Air plasma gasification/incineration

facility developed by BARC

Figure 2: Air plasma gasification/incineration facility a)

for R&D b) for regular operation

2.1. Air plasma torch and power supply

Air plasma torch is the key device of plasma gasification

system. Air plasma torch developed by BARC (Fig. 3)

consists of water-cooled hafnium cathode and copper

anode. The device is designed to produce high voltage

and low arc current to avoid the requirement of thick

cables. Air plasma torch has three main sections: plasma

source, constrictor and main anode. High frequency unit

is used to generate the initial arc between cathode and

auxiliary anode. The arc is then transferred to main

anode via constrictor. Plasma thruster principle is used

to achieve longer plasma jet. 60 kW IGBT based DC

power supply is used to operate the plasma torch. The

power supply has open circuit voltage, operating voltage

operating voltage of 500 V, 200V and 150 A

respectively.

2.2 Primary chamber

Primary chamber is vertical updraft furnace made of

mild steel and internally lined with two layers of

refractory material and one layer of ceramic insulation

wool. The shape of the primary chamber is similar to

(

Proceedings of CUChE Alumni Symposium 2022

On “Circular Economy on Sustainable Basis: The Role of Chemical Engineers”

CUChEAA ISBN: 978-81-954649-1-3

December 2022 P a g e | 21 Volume 2, Issue 1

cupola furnace used in foundry industries. Solid waste is

introduced into the chamber from side port with the help

of a waste feeding system. Skip hoist system is used to

transport the waste into the feeding hoper at the top of

the primary chamber. The waste feeding system has two

flap valves and a pusher. The primary chamber has three

distinctive section namely coke bed section at the bottom

followed by waste section and free board section at the

top. In the coke bed section numbers of plasma torch at

angle of 120

apart are place as shown in Fig 4. Coke

bed section is filled with metallurgical coke and plasma

torch is discharged directly into the coke. Through inter

spacious void inside coke bed the plasma jet is dispersed

in all direction and results in uniform high temperature

zone ( >1500

C). The chamber can be operated both in

gasification as well as incineration mode by adjusting

the air supply.

2.3. Secondary chamber

The secondary chamber is a rectangular furnace made of

mild steel internally lined with refractory material. The

function of secondary chamber is to burned the residual

combustible gases like carbon monoxide, hydrogen and

hydrocarbons. High frequency igniter system is installed

which produces spark at regular (3 sec) interval. Low

power plasma torch is also installed with the secondary

chamber.

2.4. Quencher cum venturi scrubber

Quencher cum venturi scrubber is key equipment of off-

gas processing section. It serves three important roles

simultaneously. Caustic soda solution is sprayed at two

elevations. The acidic pollutants including Sox, NOx

and HCl are neutralizes by the caustic solution. The

quencher prevents the formation of carcinogenic

pollutants namely dioxin and furan by effectively

cooling the off gas from 1200

C to 80

C. The dust

particles are efficiently removed by venturi scrubber. A

demister is placed immediately after the venturi scrubber

to arrest the entrainment.

2.5. Packed bed scrubber

Packed bed scrubber is placed to remove residual

gaseous pollutants. Water is used as scrubbing solution.

Alumina pall ring is used as packing material. Mesh pad

type demister is used after the packed bed.

2.6. ID fan and stack

Entire system is kept under sub atmospheric pressure

with the help of centrifugal ID fan. The clean gas is

released to atmosphere with the help of 30 m stack. Flue

gas analyzer, dust monitoring system and thermocouple

are installed at the stack.

Figure 3: Low power air plasma torch producing long

plasma jet

Figure 4: Triple torch coke bed system

3. Results and discussion

A wide variety of solid wastes ranging from

simulated MSW, plastic waste, ion exchange resins

and cotton waste are processed using air plasma

waste management facility. The reactor is preheated

with the help of three air plasma torches discharged

into metallurgical coke bed at the bottom of the

primary chamber. Within one hour of operation

extremely hot coke bed is created having uniform

temperature (>1500

C) as depicted in Fig 5. As

soon as the waste materials are dropped into the hot

coke bed zone immediately start reacting

vigorously.

Figure 5: Extremely hot coke bed

The system can be operated in both gasification and

incineration mode. Both under gasification mode and

incineration mode extremely high solid to gas

conversion efficiency have been achieved (Table 1).

Vigorous combustion of simulated MSW is shown in

Fig. 6. The flue gas composition was measured using a

flue gas analyzer (Testo-350,Germany) as shown in Fig

7(c). As shown in Table 2, Fig 7(c) and Fig 8(a)

measured emission of the harmful gases are found within

the permissible limit by Central Pollution Control Board

(CPCB). The particulate matter was measured using a

dust monitor( Sintrol,S 305, Finland). The maesured

particulate matter is found well wuthin permissible limit

as shown in Table 1. No black smoke was visible at the

exit of the stack. No harmful gases were found at plant

operation area as presented in Fig 7(d).

Syn gas was generated using simulated MSW as feed

material. Syn gas analyzer (ETG MCA 100 Syn) was

Proceedings of CUChE Alumni Symposium 2022

On “Circular Economy on Sustainable Basis: The Role of Chemical Engineers”

CUChEAA ISBN: 978-81-954649-1-3

December 2022 P a g e | 22 Volume 2, Issue 1

used to measure the composition and calorific value of

syn gas. Good quality syn gas having calorific value

more than 6.3 MJ/m

was generated.

Figure 6: Vigorous plasma incineration of simulated

MSW

Table 1: Conversion efficiency with different types of

solid wastes

Waste type

Conversion efficiency (%)

Simulated MSW

95.8

Plastic waste

96.3

Ion exchange resin

98.9

Cotton waste

97.7

Table 2: Flue gas composition measured at stack

Pollutants

Flue gas

composition

measured

CPCB

permissible

limit

39 ppm

80 ppm

SOx

15 ppm

80 ppm

NOx

20 ppm

200 ppm

Particulate matter

11 mg/m

50 mg/m

Figure 7: Flue gas emission a) Clean flue gas emanating

from stack b) particulate matter concentration c) flue gas

composition d) hazrdous gas composition at operation

area.

Figure 8: Off gas composition at the outlet of primary

chamber a) incineration mode b) gasification mode.

4. Conclusions

A wide range of solid waste materials were processed by

using low cost indigenously developed air plasma

gasification/incineration facility in an environmentally

friendly manner. Plasma gasification technology is best

alternative to process waste like plastic and hazardous

industrial waste. This low-cost facility is highly

affordable to small and medium scale industries. This

facility can be installed at any residential colony,

university campus and smart city with a viewpoint of

mitigation of waste at source itself. Good quality syn

gas was produced using air as oxidizing agent. The

calorific value of the syn gas can be further improved by

using oxygen or mixture of oxygen and steam instead of

air.

Acknowledgments

The authors thank D. K. Baskey,T. S. Hire, Anil K. H

and V. Gosabi for their assistance in conducting

experiments. Authors also thank Head, L&PTD and GD,

BTDG for their kind support.

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Proceedings of CUChE Alumni Symposium 2022

On “Circular Economy on Sustainable Basis: The Role of Chemical Engineers”

CUChEAA ISBN: 978-81-954649-1-3

December 2022 P a g e | 23 Volume 2, Issue 1

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