applicationofnon-thermalplasmatechnology

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Environmental Informatics Archives, Volume 2 (2004), 628-634

EIA04-062ISEIS Publication #002

2004 ISEIS - International Society for Environmental Information Sciences

Application of Non-thermal plasma Technology for Indoor Air Pollution Control

Xiao Feng and Chen Jie-rong

Environmental & Chemical Engineering Institute of Xian Jiaotong University, Xian, 710049, Shannxi, P.R.China

Abstract. The fundamental principle of the non-thermal plasma cleaning indoor air is introduced in this paper.The discharge modes are described and the types of the reactors are discussed. A new approach, multi-function

integrated corona induced non-thermal plasma reactor, has developed to clean the air indoor. It integrates the effect

of non-thermal plasma with other effects, including chemical catalysis, ESP, etc. In a 30m3 room, using this device

to clean the indoor air, the rates of removing C6H6, NH3, H2S, SO2 are over 90% and the rates of removing NO2, CO

are 89.2% and 78.5% respectively

Keywords: indoor, non-thermal plasma, cleaning air, discharging, corona, removal efficiency

1. IntroductionWith the society entering into the information era, people spend longer and longer time in the house because of

the change of the life style. So, the indoor environmental quality becomes more and more important to humanshealth (Zhou et al, 2002, Cui, 2002, Yang et al, 1999 and Hu et al, 2002). Accumulation, durability, diversity are the

main characters of the indoor air pollution (Zhou et al, 2002).

Because more attention is paidto the air quality, many air-cleaning technologies accordingly are emerged, such as

active carbon adsorption, photocatalitic oxidation and non-thermal plasma. Non-thermal plasma technology is a

young inter-discipline related to physics, chemistry, biology and environmental science. Plasma state is the fourthnatural state, and it consists of electrons, ions and free radicals. Compared to other methods, non-thermal plasma

technology has some advantages in depredating the sulfur and nitrogen in the air. Besides, it is a technology with

high removal efficiency and low power-assumption (M.Noguchi, et al, 1997, Yan et al, 1998, Kinoshita et al, 1997).So, more and more researchers are devoted themselves to this promising field, especially the application of control

the indoor air pollution (M.Noguchi, et al, 1997, Yan, et al, 1998, Katsunhiro, et al, 1997). Our investigation

includes the principle of the non-thermal plasma, at the same time discussing some industrial applied equipment.

2. Principle of Non-thermal Plasma TechnologyAt present, the mechanism of the non-thermal plasma to cleaning the indoor air is considered as the result of the

non-elastic collision of the particles. There are a lot of electrons, ions and free radicals under non-thermal plasma

state. When the non-elastic collision takes place between high-energy electrons and gas (atoms), the producedenergy will stimulate the internal energy of the ground state elements. By stimulation, dissociation, ionization, the

gas will be an active state. On the one hand, molecular bonds are broken; on the other hand, free radicals, such as

Corresponding author: [email protected]


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OH, H2O2, and O3, are produced. During this process, high-energy electrons are the critical factors and thermal

motion plays a negative role. Under the normal pressure, the temperature of electron is far higher than atmosphere

temperature in the high non-equilibrium plasmas produced by discharging (Cui, 2002, Yang et al, 1999).

The average active energy, density of electron, , atmosphere temperature, concentration of toxic gas and other

existed gas ingredients are the decisive aspects to determine which chemical reaction will happen in this plasmacondition. According to its characters, it is maybe an ideal method to solve some contaminants of the air because

these wastes need high activation energies to degrade. Besides, it is also an effective way to deal with the industrial

gases containe the organic or sulfurated wastes with low density and high speed. There are three main methods toapply this technology: Electro-static precipitator, Catalytic purification, Negative ions generation. The discharge

type, principle and application of these three methods are showed in table 1 respectively.

Table 1. Three Different Methods Applied the Plasma Technology to Cleaning Indoor Air

Name Discharge type Principle Application

Electro-staticprecipitator

Corona discharge in a

very heterogeneous

electric field

e+M (molecules of contaminats) M ;

M SP (solid particles) (SPM) ;

+

-

(SPM) SPM.-

TSP(


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anode, the heterogeneous discharge happened. It is called corona discharge. This method is often applied to

desulfuration and denigration as well to deal with VOCs abatement in the air.

Medium barrier discharge happened between two poles. And at least, one of them is covered by a single dielectric.

It not only has the character of the glowing discharge: well-distributed discharge in a large space, but also has the

character of the corona discharge: high atmospheric pressure operation. Because the electrodes do not contact withthe discharging gas directly, the erosion problem will be avoid. Moreover, it has a potential in large-scale industrial

application because of its above characters,

3.2 Designing of Non-thermal Plasma Reactors

Non-thermal plasma reactors cleaning the indoor air are different from the high temperature plasma reactors. Its

function related with its structure, which does not have the same characters as arc discharge, determines the

degradation rate of wastes in the air. At present, many kinds of non-thermal plasma reactors are investigated, such aspoint to point, point to board, line to board, line to canister and packed bed (Hu et al, 2002).

3.2.1 Hybrid Pulsed Streamer Corona Reactor (Yan et al, 1998)

In hybrid pulsed streamer corona reactors, as illustrated in Figure.1, chemical catalyst and porous solids are

placed within corona region in order to promote heterogeneous reactions. Pulsed streamer corona are producedand/or quenched on the surface of the solids. Gas phase and heterogeneous phase chemical reaction could be

induced. In contrast with the traditional reactors, energy consumption and removal efficiencies are at least by a

factor of two for NOx and SOx removal (Yang et al, 1999). The structure of the reactor and the selection of thecatalysts will influence the efficiency very much. Fig.1.b is better than Fig.1.a because b increases the surface of the

catalyst and residence time. -Al2O3 is ordinarily chosen as porous medium. Recently, photo-catalysis oxidation is

the researchs focus. With the development of it, more and more scholars intend to choose TiO2 as the catalyst. In the

cleaning process, there is not only non-thermal plasma cleaning but also photo-catalysis oxidation cleaning. Thesetwo coupled functions improve the gas purifying efficiency.

Figure1.Schematic of hybrid pulsed streamer corona reactor

3.2.2 Integrated Corona Induced Non-thermal Plasma ReactorAccording to the same designing principle of as described in Figure.1, a kind of integrated non-thermal plasma

reactor is also studied for indoor air cleaning. Figure.2 shows the schematic. The system mainly consists of primary

filter, plasma reactor, two stage ESP, honeycomb chemical catalysis, active carbon, fan and negative ion generator. It

can be easily seen that this kind of cleaner, multiple functions for dust collection, bacteria removal, NO X, SO2

removal, VOCs abatement, odor removal could be realized.

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Regarding to the operation of plasma reactor, the removal process can be divided into three types: continuous

plasma operation, the intermitted plasma treatment under normal gas flow and plasma treatment after stopping the

gas flow for cleaning reactor itself. This system also shows similar functions as the ozone based air purifier to

control of aerosol, microbial and odor (Bernie M. Penetrante et al, 1993, S. Masuda, et al, 1995, S.S. Joshi et al,

1929).

Figure 2.Schematic of integrated corona induced non-thermal plasma reactor

4. Indoor Air CleaningOur research group developed a kind of air cleaner by utilizing the integrated corona induced non-thermal plasma

reactor as shown in Figure 2. Theoretically, plasma can be generated by pulsed corona discharge, microwavedischarge, surface discharge and so. Table 2 lists the typical result for removal of gaseous pollutants. It shows that

very high removal efficiencies can be obtained. C6H6, NH3, H2S, SO2 removal efficiencies all achieved above 90%;

NO2 and CO removal efficiencies are 89.2%, 78.5% respectively.

Table 2 Removal Tests of Various Pollutants in a 30m3 Room

Time

(min)

Initial Concentration

(mg/Nm3)

Final Concentration

(mg/Nm3)

Removal Efficiency

(%)

C6H6 9.5 6.95 0.69 90.6

NH3 20.5 0.92 0.05 93.5

H2S 20.5 0.19 0.007 96.3

SO2 20.5 1.80 0.14 92.2NO2 20.5 0.59 0.06 89.2

CO 30 14.4 3.10 78.5

In this device, excited plasma and the catalysts in the honeycomb play the most important role to clean the wastesin the air. It has a great potential to industrial fields, such as administration office, meeting room, disco bar, hotel and

hospital. So it has a wide application and a great commercial value. Smoke, dust, bacteria and virus can be collected

by the two ESP. Plasma reactor produces various kinds of active radicals. Under long time active radicals treatment,

bacteria, virus and other pollutants in the air can be killed. Chemical catalyst and active carbon placed behind theplasma reactor show longer life time and higher absorption efficiency. Figure 3 and Figure 4 are the examples of

average reduction rates of smoke and bacteria in 20 m3 and 30 m3 test rooms respectively.

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0 5 10 15 20 25

0

20

40

60

80

100

RelativeConcentration(100%)

Time (min)

B

Figure 3 Reduction of smoke in 26 m3 Room

0 5 10 15 20 25

0

20

40

60

80

100

RelativeConcentration(100%)

Time (min)

B

Figure 4 Reduction of bacteria in 30 m3 Room

5. ConclusionsAlthough it has been a very long time for studying pollutants removal by non-thermal plasmas (S.S. Joshi, 1929),

only within last fifteen years, related physical and chemical processes have been extensively investigated throughout

the world for flue gas cleaning, VOCs abatement, toxic removal and indoor air cleaning. Compared to the traditional

methods, the non-thermal plasmas do not produce the wastes such as CO2, NOX. In relation with the indoor aircleaning, the non-thermal plasmas are very close to wide industrial applications.

Because of the poor diagnostic technology, the basic theory of the non-thermal plasma is yet not understood

completely. In the future, our task is to develop our technologies to detect the respective densities of the ions,electrons, and free radicals. Then the computer model can be simulated to realize the environmental situations of the

non-thermal plasma. This is a nice way to develop this promising technology to apply to more research and

industrial fields.

Removal of gaseous pollutants with the integrated corona induced non-thermal plasma was studied. The removalefficiencies of SOx, NOx, and other pollutants are very satisfying. The excited results show that it can be widely used

under various situations. It is believed that this technology will play a lead role in the future to control the air

pollutants.

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Acknowledgments

I would like to thank Department of Environmental and Chemical Engineering in Xian Jiaotong University

(XJTU). I would also like to thank Prof. Chen Jie-rong for her suggestions, discussions and revising the

manuscript. Finally I would also like to thank many of my colleagues for their helps and discussions.

References

Zhongping Zhou, Shoutang Zhao, Li Zhu and Yihong Zhao, (2002). Monitor and Control Indoor Pollutants,

Chemical industry press and environmental and chemical engineering press centre.

Jiusi Cui, (2002). Indoor Air Pollutants Monitor, Chemical Industrial Press.

Wu Yang and Mingzhe Rong, Principle and Application of Air Purification with Low Temperature Plasma Journal of

Electrical Technology, 3(1999) 31-32.

Hui Hu, Shengli Li, Wanlin Wang and Jin Li, Study on improvement of indoor environmental by discharge plasma,

High Voltage Apparatus, 38 (2002) 48-51.

M.Noguchi, et al. Development of a New Air Cleaning System for Cigarette Smoke [A].S.S.Proc. IEJAnnu.

Meeting[C], 1997.

Keping Yan, Hexing Hui, Mi Cui, Jingsong Miao, Xiaoli Wu, Chongguang Bao, Ruinian Li Corona Induced

Non-Thermal Plasmas: Fundamental Study and Industrial Applications Journal of Electrostatics 44 (1998)

17-39.

Katsunhiro Kinoshita, Yuichi Fujiyama, Hyun-Ha Kim, Shinji Kastsura and Akira Mizuno Control of Tobacco

Smoke and Odors using Discharge Plasma Reactor Journal of Electostatics 42 (1997) 83-91.

Bernie M. Penetrante, Shirley E. Schultheis, Non-thermal plasma Techniques for Pollution Control Part A & B,

NATO ASI Series Advanced Science Institutes Series Spring-Velag, 1993.

S. Masuda, S. Hosokawa, X. Tu and Z. Wang, Novel plasma chemical technologies PPCP and SPCP for control of

gaseous pollutants and air toxic, Journal of Electrostatics, 34(1995) 415-438.

S.S. Joshi, The decomposition of nitrous oxide in the silent electric discharge, the variation of the current and the

power during the reaction, Trans of Faraday Society, 25(1929) 118-128.

Xiao Feng is presently pursuing his master degree in Xian Jiaotong University. He got his bachelor degree from the

department of the chemical engineering of Xian Jiaotong University. In his first year of the graduate period, he

investigated the application of the non-thermal plasma, such as cleaning indoor air and purifying the wastewater.

Now he is studying the dense-phase pneumatic conveying to transfer the fine coal in an iron pipe. He will simulate

the flow situation in the pipe using a two-dimension model.

Chen Jie-rong, female, born in shanghai in February, 1949. Doctor (Japan). She is the commissioner ofinstruction

committee of environmental engineering of the national ministry of education, the commissioner of degree

committee and teaching committee of school of environmental and chemical engineering of Xian Jiaotong

University, the visiting professor of macromolecule material laboratory in Sichuan University, the standing director

of environmental science institute of Shaanxi province, the commissioner of Chinese interface science and

engineering of complex material institute committee, the commissioner of plasma committee of China, the

international member of science promotion committee of America, and the commissioner of abroad environmental

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engineer and scientist committee. Now the Scientific research items which She is presiding over are National

Science Foundation of China, cooperating items of international exploitation department in Canada, national 863

programming items, specialized research Fund for the Doctoral Program of Higher Education, foundation for

visiting scholar of national emphases laboratory in university, and Scientific Research Star Fund for the Study

Abroad Returnee, and so on.

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