(174g) Removal of Soot Particles From Diesel Exhaust Gas Using Cylindrical Plasma System

Diesel engines emissions (DE) have been the subject of increasing human health concern in recent years. DE emissions contain large quantities of fine particulate matter, which mainly consist of carbonaceous material and soluble organic fraction (SOF). Some constituents of the SOF such as polycyclic aromatic hydrocarbons and nitrated derivatives are mutagenic and/or carcinogenic [1]. Diesel Particulate emissions can be controlled either at their source or by after-treatment technologies. For eliminating of fine particles using second approach, various types of techniques have been explored to find efficient, self-consistent and less costly method [2, 3, 4].

The non-thermal plasma systems is one of the most commonly applied particulate control devices, which are used extensively since give high precipitation efficiency, negligible pressure drop and compact construction [4].

The major objective of this study was evaluating and developing reliable and efficient method using self-consistent wire-cylinder type plasma system for removing of fine particulate matter from diesel exhaust gas.

Experimental

For the purpose of this research, numerous removal efficiency measurements were performed for various geometric and electric parameter settings under laboratory and real conditions using different types of corona and collection electrodes. The carbon black particles (in range of 0.4-1.2 µm) were considered in this study to simulate soot particle behaviors in the system [5]. The average residence time in the system was about 0.28 second and was kept constant for all tests presented here.

The concentration of particles is measured at downstream of the system with a particle counter capable of measuring the number of particles in real time. The net removal efficiency was calculated then as ε = (1 -C_on/ C_off) ×100 where C_on and C_off were the concentrations at the system outlet when the voltage was turn on and off, respectively.

The experiments were carried out with a laboratory scale plasma system consist of an outer copper simple cylinder (with a length of 500 mm and an inside diameter of 22 mm) and a central discharge electrode wire. The negative voltage (up to a maximum value of 8 kV DC) was supplied to discharge electrode by a high voltage DC supply through a 2.0 MΩ resistor. To perform investigation on the effect of corona electrode geometry on removal efficiency, two kinds of electrodes consist of Ni-Cr smooth wire (with diameter of 150, 200 and 250 µm) and Ni-Cr barbed wire (with Core diameter of 700 µm) was used.

In order to develop a self-consistent system, sequential incineration of collected particles by applying electrical heating method was proposed for system regeneration and examined under real condition using two kinds of collection electrodes consist of Ni-Cr porous cylinder and Ni-Cr spiral cylinder (made of Ni-Cr narrow strip with a width of 3 mm and a thickness of 500 µm which was wound around the 10 axial supports).

Results and Discussion

The results of laboratory experiments, carried out to optimize smooth wire diameter as corona electrode, showed that under constant applied voltage, the removal efficiency will be increase by diameter decreasing. Other research were performed to select final corona electrode configuration, indicated that the barbed wire (Core Dia: 700 µm) offers better removal efficiency, higher mechanical strength and lower physical oscillations in electrical field in respect to the smooth wire (Dia: 150 µm). The data obtained also demonstrate a negligible and satisfactory variation in removal efficiency vs. Time in 28 min. Interval for the barbed wire-simple cylinder system.

In the last step, experimental results of fabricated systems consist of barbed wire-simple cylinder and barbed wire- spiral cylinder with sequential regeneration (collected soot incineration by electrical heating) under real condition, indicated that the removal efficiency about 92% and 79% was achieved respectively with Minibus Benz Model O508 exhaust gas operating in steady-state condition.

Conclusion

Presented results suggest that, the wire-cylinder type plasma system can be considered to apply for efficient elimination of fine particulate matter from diesel exhaust gas. It should be noted that investigation of fabricated system consist of barbed wire-porous cylinder under real condition is now underway.

Reference

[1]        
U.S. EPA. Health Assessment Document for Diesel Engine Exhaust,
Washington, DC, 2002a.

[2]         P. Saiyasitpanich, T.C. Keener, S.-J. Khang and M. Lu, Removal of diesel particulate matter (DPM) in a tubular wet electrostatic precipitator, Journal of Electrostatics 65 (2007) 618?624.

[3]         M. Matti Maricq, Chemical characterization of particulate emissions from diesel engines: A review, Aerosol Science 38 (2007) 1079 ? 1118

[4]         Anatol Jaworek, Andrzej Krupa and Tadeusz Czech, Modern electrostatic devices and methods for exhaust gas cleaning: A brief review, Journal of Electrostatics 65 (2007) 133?155

[5]         Michele Ambrogio, Guido Saracco, Vito Specchia, Coen van Gulijk, Michiel Makkee and J.A. Moulijn, On the generation of aerosol for diesel particulate filtration studies, Separation and Purification Technology 27 (2002) 195?209.

[6]         Ye Zhuang, Yong Jin Kim, Tai Gyu Lee and Pratim Biswas, Experimental and theoretical studies of ultra-fine particle behavior in electrostatic precipitators, Journal of Electrostatics 48 (2000) 245-260

[7]         Maria Jedrusik, Juliusz B. Gajewski and Arkadiusz J. Swierczok, Effect of the particle diameter and corona electrode geometry on the particle migration velocity in electrostatic precipitators, Journal of Electrostatics 51-52 (2001) 245-251

[8]         Takeo Takahashi, Akinori Zukeran, Yoshiyasu Ehara, Haruo Kishida, Tairo Ito and Takeshi Takamatsu, Influence of Gas Velocity and Electric Field Intensity on Particle Deposit and Re-entrainment Phenomena in an Electrostatic Precipitator, Journal of Aerosol Sci. 29 (1998) S481-S482.

[9]         J. O. Chae, Non-thermal plasma for diesel exhaust treatment, Journal of Electrostatics 57 (2003) 251-262.

[10]      Tomasz Ciach, Tomasz R. Sosnowski and Albert Podgorski, Efficient filtration methods for diesel aerosols, Journal of Aerosol Sci. 26 (1995) S723-S724.

[11]      Tomasz Ciach and Tomasz R. Sosnowski, Removal of soot particles from diesel exhaust, Journal of Aerosol Sci. 27 (1996) S705-S706.