Experimental study on the jet characteristics of a steam plasma torch

Transcription

1 Plasma Science and Technology PAPER Experimental study on the jet characteristics of a steam plasma torch To cite this article: Fangyuan LIU et al 2018 Plasma Sci. Technol View the article online for updates and enhancements. This content was downloaded from IP address on 30/09/2018 at 03:03

2 2018 Hefei Institutes of Physical Science, Chinese Academy of Sciences and IOP Publishing Printed in China and the UK Plasma Science and Technology (9pp) Experimental study on the jet characteristics of a steam plasma torch Fangyuan LIU ( 刘方圆 ), Deping YU ( 余德平 ), Cheng LV ( 吕程 ), Yazhou DUAN ( 段亚洲 ), Yanjie ZHONG ( 钟严杰 ) and Jin YAO ( 姚进 ) School of Manufacturing Science and Engineering, Sichuan University, Chengdu , People s Republic of China williamydp@scu.edu.cn Received 23 May 2018, revised 23 July 2018 Accepted for publication 25 July 2018 Published 12 September 2018 Abstract Thermal steam plasma jet is promising for applications in environmental industries due to its distinctive characteristics of high enthalpy and high chemical reactivity. However, the performance of the steam plasma torch for its generation is limited by the problems of the large arc voltage fluctuation and serious erosion of the electrodes. In this study, a gas-stabilized steam plasma torch which can operate continuously and stably was designed. Experiments were conducted to reveal the effect of the different working parameters, including the anode diameter, the cooling water temperature, the arc current and the steam flow rate, on its Volt Ampere characteristics, arc voltage fluctuation, thermal efficiency, jet characteristics and electrodes erosion. Results showed that the use of hot water to cool the electrodes can effectively prevent the condensation of steam on the inner wall of the electrodes, thus significantly reducing the arc voltage fluctuations and electrodes erosion. This is crucial for increasing the working life of the electrodes and ensuring long-term stability of the steam plasma torch. In addition, suitable anode diameter can greatly reduce the arc voltage fluctuation of the steam plasma torch and effectively improve the stability of the steam plasma jet. Furthermore, high arc current can effectively reduce the fluctuations of the arc voltage and increase the length and the volume of the steam plasma jet. Finally, using steam as the plasma forming gas can achieve higher thermal efficiency compared to air. An ideal thermal efficiency can be achieved by properly reducing the arc current and increasing the steam flow rate. Keywords: steam plasma torch, Volt Ampere characteristics, jet characteristics, arc voltage fluctuation, electrode erosion (Some figures may appear in colour only in the online journal) 1. Introduction Thermal plasma jet is a fluid with high temperature, high enthalpy, high energy density and high chemical reactivity. It is widely used in environmental industries for the destruction of the fly ash produced in the municipal solid waste incinerator [1], organic waste pyrolysis [2], radioactive waste reduction and vitrification [3], coal gasification [4], etc. Among the various types of thermal plasma jets, the thermal steam plasma jets are particularly suitable for applications in the environmental industries due to the following distinctive advantages. (1) The specific heat content of the steam plasma jet is almost an order of magnitude higher than that of, for example, the air plasma jet at the same temperature. (2) The steam plasma jet consists of hydrogen and oxygen exclusively, both of which are active reagents that take part in oxidation-reduction reactions [5, 6]. (3) Eco-friendly method, while reaction with chlorine-containing materials, the steam plasma jet does not generate dioxin, one of the most toxic substances [7]. (4) Hydrogen delivered to the reaction space with the steam plasma jet decelerates reactions of gaseous sulfur, phosphorus and free chlorine formation, i.e. such gases, which are difficult to remove in the gas purification unit [8]. (5) The steam plasma jet can produce high quality synthesis gas (CO + H 2 ), which can be used as fuel for electric power generation or raw material for synthetic fuel /18/ $

3 Figure 1. Schematic diagram of the steam plasma generating system. production, and it makes waste processing energy-independent [9]. Due to the unique advantages of the thermal steam plasma jet in environmental applications, more and more researches have been carried out on the design, characteristics and applications of steam plasma torches in recent years. Ni et al [10] and Li et al [11] studied the characteristics of a liquid-stabilized steam plasma torch at atmospheric pressure and analyzed the unsteadiness of the steam plasma jet. This type of steam plasma torch was proved to have high thermal efficiency and high enthalpy. However, as the steam was produced by the evaporation of water from the inner surface of the vortex, the flow rate of the plasma was controlled by the balance of heat transfer in the arc column and cannot be adjusted independently like in gas-stabilized torches. Hrabovsky et al [12] investigated the properties of a hybrid gas liquid stabilized steam plasma torch and discussed the physical mechanisms that control the plasma jet properties. This type of steam plasma torch offers the possibility of control of plasma jet parameters in a wider range. But the control mechanism of the plasma flow rate is similar to that of the liquid-stabilized steam plasma torch, and the precise control of the plasma jet is difficult to be realized. Tamošiūnas et al [13, 14] designed a gas-stabilized steam plasma torch for the production of synthesis gas from waste glycerol. This type of steam plasma torch has a simple structure and can accurately control the plasma jet by controlling the flow rate of supplied steam. However, the problem of steam condensation on the cold inner wall of the electrodes has not been well solved, and it will cause severe electrodes erosion and arc voltage fluctuations, which directly affect the working life of steam plasma torches and the stability of plasma-chemical processes respectively. Anshakov et al [15, 16] designed a steam plasma torch with copper electrodes indirectly cooled by a cylindrical steel cowling to reduce the cooling rate and maintain the inner surface temperature of the electrodes higher than the saturated steam temperature. The thickness and shape of the wall of the steel cowling was calculated by simulation using ANSYS. Such structural design of the plasma torch can maintain the required high inner surface temperature of the electrodes when it works at the conditions close to that used in the simulation. However, when the working conditions changes the required high inner surface temperature may not be achieved. Surov et al [17] investigated the high power AC steam plasma torches with the output power ranging from 5 to 500 kw for gasification of organic substances. The life time of the AC plasma torches was claimed to be up to thousands of hours, but the effect of the potential steam condensation on the inner surface of the electrodes was not investigated. In this study, a gas-stabilized DC steam plasma torch with no condensation of the steam and operating continuously and stably is designed. Experiments have been conducted to reveal the effect of the different working parameters, including the anode diameter, the cooling water temperature, the arc current and the steam flow rate, on its Volt Ampere characteristics, arc voltage fluctuation, thermal efficiency, jet characteristics and electrode erosion. 2. Experiments 2.1. Experimental set-up The main experimental set-up is shown in figure 1. It consists of five parts, i.e. a steam plasma torch, a DC power supply, a gas supply system, a water cooling system, a data acquisition system. The structure of the steam plasma torch is shown in figure 2. It consists of a tungsten embedded cathode, a protecting gas distribution ring, a neutral section, a steam gas 2

4 Figure 2. Schematic diagram of the steam plasma torch: (1) cold cooling water supply, (2) cooling water exhaust, (3) hot cooling water supply, (4) cooling water exhaust, G N nitrogen gas supply, G S steam supply. distribution ring, a stepped anode, cooling water channels and gas channels. The protecting gas distribution ring is used to generate a shielding gas vortex around the tungsten embedded cathode. The steam distribution ring is placed between the neutral section and the anode to generate a steam vortex and to ensure that the area is fully preheated before the steam enters. The cooling water channels are connected in parallel. The power source is an IGBT based constant-current DC power supply with the energy conversion efficiency higher than 90% and the current fluctuation less than 1%. Nitrogen is adopted as the shielding gas with its flow rate controlled by a mass flow controller (LF400S). The steam is produced by a specialized steam generator (HSG100-M), which can accurately tune the mass flow rate and the temperature (up to 250 C) of the steam supply. In addition, the temperature of the Teflon pipe between the steam generator and the steam plasma torch is actively controlled by a resistive heating element to avoid cooling and condensation of the steam generated. The cooling system consists of two parts. The cathode is cooled by cold cooling water (about 25 C) in order to take as much heat as possible to prevent the cathode from ablating, and the cold cooling water is supplied by an industrial chiller. The neutral section and the anode are cooled by hot cooling water (about 60 C) in order to avoid excessive cooling of the electrodes, and the hot cooling water is supplied by pumping water from a water tank whose temperature is controlled by a heat exchanger between the hot water from the steam plasma torch and cool water from the industrial chiller. The data acquisition system includes a DAQ module (NI USB 6210) for recording the arc voltage and arc current and a CCD camera for capturing photos of the generated steam plasma jet Experimental methods Experimental parameters. One of the main difficulties for gas-stabilized steam plasma torch is to avoid the Table 1. The experimental parameters of the steam plasma torch. Parameters (unit) Values Arc current, I (A) Arc voltage, U (V) Arc power, P (kw) Torch efficiency, η (%) Nitrogen gas flow rate, G N (g min 1 ) 25 Steam flow rate, G S (g min 1 ) Steam temperature, T S ( C) 250 Air flow rate, G A (g min 1 ) 40 Diameter of the stepped anode (T-A1), d 1, d 2 (10 3 m) 10, 18 Diameter of the stepped anode (T-A2), d 1, d 2 (10 3 m) 20, 30 The temperature of the cooling water supply at the 25 cathode ( C) The temperature of the cooling water supply at the 60, 25 neutral section and anode ( C) condensation of the steam along the whole flow channel, especially at the inner wall of the anode. Therefore, it is necessary to [18]: (1) preheat the steam to 250 C 350 C; (2) eliminate the reasons for condensation of steam on cold surfaces of the discharge chamber and associated effects inside the arc chamber. In this paper, the effect of the temperature of the cooling water for the neutral section and anode on the characteristics of the steam plasma torch will be investigated. Preliminary experiment showed that when the cooling water temperature was set to 60 C, the wall of the discharge chamber was hot with no condensation of the steam on the inner wall of the anode. Besides the cooling water temperature, the characteristics of the steam plasma torch are also determined by the arc current, gas flow rate, diameters of the stepped anode. When investigating their effects, the cooling water temperature is set to 60 C to ensure stable operation of the steam plasma torch. Table 1 summarizes the experimental parameters for the operation of the steam plasma torch. During the experiments, 3

5 the arc voltages, arc voltage fluctuations, thermal efficiency, jet characteristics and the electrodes erosion will be investigated in detail to reveal the working characteristics of the steam plasma torch Arc ignition process. At the beginning of the experiment, an arc was ignited between the cathode and the stepped anode with only the protecting gas as the plasma forming gas. The plasma torch was kept working for a few minutes to ensure that the temperature of the inner surface of the discharge chamber is higher than the condensing temperature of the steam. Then the steam required for the experiment was gradually fed into the discharge chamber to avoid the condensation of the steam on the electrodes Measurement of the thermal efficiency. The thermal efficiency of the plasma torch is defined as the ratio of the heat absorbed by the gas from the plasma torch per unit time, to the arc power [18]. Temperature sensors were used to measure the temperature of the inlet and outlet of the cooling water, and a turbine flowmeter was used to measure the flow of the cooling water. The thermal efficiency of the plasma torch was calculated by equation (1) UIt - Cr( Q1D T1+ Q2DT2) h =, ( 1) UIt where η is the thermal efficiency, t is the working time (s), U is the arc voltage (V), I is the arc current (A), C is the specific heat capacity of the cooling water (Jkg 1 C 1 ), ρ is the density of the cooling water (kg l 1 ), Q 1 is the volume of the cooling water flowing through the cathode (l), Q 2 is the volume of the cooling water flowing through the neutral section and anode (l), ΔT 1 is the temperature difference between the inlet and outlet of the cooling water at the cathode, ΔT 2 is the temperature difference between the inlet and outlet of cooling water at the neutral section and the anode. 3. Results and discussion 3.1. Arc voltage characteristics Figure 3 shows the Volt Ampere characteristics of the T-A1 and the T-A2. The effect of the arc current, the flow rate of the working gas and the diameter of the stepped anode on the arc voltage is shown in the figure. Followings can be observed from figure 3. (1) The arc voltage slightly decreases with the increase of the arc current when the steam flow rate is constant. This is because that the arc voltage is determined by U = IR. Atafixed gas flow rate, when the arc current I increases, the arc temperature T increases due to the constriction by the plasma torch structure, which leads to the decrease of the resistance R. Under a certain steam flow rate, when the decrease rate of R is larger than the increase rate of I, the arc voltage U decreases with the increase of arc current. (2) The arc voltage increases significantly with the increase of the steam flow rate when the arc current is constant. The increase of the steam flow rate leads to enhanced aerodynamic Figure 3. The Volt Ampere characteristics of the T-A1 and the T-A2. force and stronger constriction effect on the arc column, resulting in longer average length and reduced sectional area of the arc column respectively. Both effects result in the increase of R. Therefore, with the increase of the steam flow rate, the arc voltage increases significantly. (3) The arc voltages of the T-A2 are higher than that of the T-A1 under the condition that the other experimental parameters are fixed. This is because that the larger anode diameter leads to longer length of the radial section of arc column. Under the combined action of the aerodynamic drag and the Lorentz force, the arc column tends to be extended and distorted, resulting in even longer arc length which brings about higher arc voltage. (4) The arc voltage of the T-A1 with steam as the plasma forming gas is slightly higher than that with air as the plasma forming gas at the same gas flow rate Arc voltage fluctuation characteristics The arc voltage has been demonstrated to be unsteady, which is an important physical phenomenon that influences the enthalpy of the generated plasma jet and then the performance of plasma processes [19, 20], e.g. plasma spraying and treatment of hazardous waste. The instabilities of the arc voltages can be directly reflected by the fluctuations of the arc voltage signals. Figure 4 shows the arc voltage signal of the T-A1 and the T-A2 when I = 180 A, G S or G A = 40 g min 1. To better observe the arc voltage fluctuation, a section (500 ms) of the whole arc voltage signal has been extracted and shown in figure 5(a). The frequency spectrum of the extracted section of arc voltage is shown in figure 5(b). From figure 5, it can be seen that the diameter of the stepped anode greatly affects the arc voltage fluctuation. The arc voltage fluctuation of the T-A1 is much smaller than that of T-A2. In addition, it can also be seen that the arc voltage fluctuation of the plasma torch using air as the plasma forming gas is slightly less than that using steam as the plasma forming gas when the same flow rate of steam or air was respectively injected into the T-A1. The degree of arc voltage fluctuations of the plasma torches is as follows: (T- 4

6 Figure 4. The arc voltage signal of the T-A1 and the T-A2 when I = 180 A, G S or G A = 40 g min 1. A1, air: 40 g min 1 ) < (T-A1, steam: 40 g min 1 ) < (T-A2, steam: 40 g min 1 ). The arc voltage fluctuations can be quantitatively reflected by calculating the standard deviation of arc voltage (AVSD) in a period of time (30 s for this paper). Figure 6 shows the AVSD of the T-A1 and the T-A2 at different working parameters. It is shown that arc voltage fluctuation of the plasma torch with steam as the plasma forming gas is normally larger than that with air as the plasma forming gas. However, the degree of the arc voltage fluctuation is affected by the arc current and the diameter of the stepped anode. Their effects are as follows. (1) For the plasma torch with steam as the plasma forming gas, the arc voltage fluctuation decreases with the increase of the arc current. This is due to the fact that the increase of the arc current leads to the decrease of arc resistance. Thus, the arc voltage decreases due to the reduced resistance, which ensures the stable work of the plasma torch. (2) From the figure 6, it can be seen that the arc voltage fluctuations of the T-A2 is much larger than that of the T-A1. The reason may be as follows. The forces applied on the arc column can be simplified to the forces on two junction points as shown in figure 7(a), namely the junction between the cathode and the anode column and the arc attachment of the anode column on the anode wall [21]. The imbalance of these forces, including the Lorentz force (F L ) due to the self-induced magnetic field, the reacting force (F Ra ) of the F La, the aerodynamic drag (F D ), and reacting force (F Rc ) of the F Dc, leads to the overall arc motion. Among them, the magnitude of the Lorentz force is related to the vertical distance from the axis of the anode nozzle to the anode arc attachment and decreases with the increase of the vertical distance. The aerodynamic drag is affected by the velocity of the cold gas and increases with the increase of the velocity of the gas. The reacting forces (F Ra and F Rc ), which are the net force of the magnetic body forces acting on the corresponding junctions due to the current in the anode material or the adjacent arc columns [21], are in dynamic balance with the Lorentz force F La and the aerodynamic drag F Dc. As can be seen in the figure 7(b), the T-A2 with larger anode diameter leads to longer length of the radial section of arc column, which reduces the Lorentz force F La at the arc attachment, and slower gas velocity in arc channel, which reduces the aerodynamic drag F Dc at the junction between the cathode and the anode column. Therefore, the arc column tends to move upstream, and be extended and distorted. The extension of the arc column results in even longer arc length, leading to higher arc voltage as shown in figure 3. The distortion of the arc column results in different arc shunting, i.e. small-scale shunting and large-scale shunting, leading to larger variation of the arc length and thus larger arc voltage fluctuations, as shown in figures 5 and 6. In comparison, it can be seen from the figure 7(a) that the T-A1 with smaller anode diameter leads to shorter length of the radial section of arc column and faster gas velocity in arc channel. As a result, the arc column is subjected to larger Lorentz force F La and aerodynamic drag F Dc, causing the arc column to move to downstream and to be confined at the center of the arc channel. Thus, large-scale shunting occurred in T-A2 is less likely to happen and the arc column length of the T-A1 fluctuates within a small range due to small-scale shunting as shown in figure 5. Therefore, its arc voltage is relatively stable. For example, when I = 190 A and G S = 40gmin 1, the AVSD of the T-A1 decreased to 3 V, which is close to that of the T-A1 with air as the plasma forming gas. Therefore, it can be inferred that high arc current and small anode diameter are beneficial for improving the stability of the arc voltage of the steam plasma torch Thermal efficiency Figure 8 shows the thermal efficiency of the T-A1 with steam or air as the plasma forming gas at 60 C cooling water temperature. It can be seen that the thermal efficiency varies with the arc current, the gas flow rate and the type of plasma forming gas. (1) The thermal efficiency decreases with the increase of arc current at a specific gas flow rate. This is due to the fact 5

7 Figure 5. (a) Variation of the arc voltage (a section of the arc voltage signal shown in figure 4); (b) frequency spectrum of the arc voltage. (3) By comparing steam with air at the same gas flow rate (40 g min 1 ), it can be seen that the thermal efficiency of the plasma torch working with steam is much higher than that with air, e.g. 69% for steam compared to 54% for air when I = 150 A. Therefore, it is possible to achieve a high thermal efficiency by appropriately reducing the arc current and increasing the steam flow rate. For example, the thermal efficiency of the plasma torch working with steam reaches 72% when I = 160 A and G S = 50 g min Jet characteristics Figure 6. The AVSD of the T-A1 and the T-A2 at different working parameters. that the increase of the arc current results in the increase of the diameter of the arc column, accompanied by a simultaneous decrease of the thickness of the boundary layer and thus increased heat transfer to the wall of the arc chamber by forced laminar or turbulent convection. (2) The thermal efficiency greatly increases with the increase of the steam flow rate at a fixed arc current. This is because that with the increase of the gas flow rate, the compression effect of the arc is gradually strengthened, which leads to the gradual increase of the arc voltage and thickness of the boundary layer. The increased thickness of the boundary layer reduces the heat transferred to the wall of the arc chamber, while the increase of the arc voltage increases the arc power. Under their combined effects, the thermal efficiency of the plasma torch increases with the increase of the steam flow rate. Figure 9 shows photos of the plasma jet generated with I = 190 A, G S = 50 g min 1 by the T-A2 and the T-A1. It can be seen that the morphology of the plasma jet of the T-A2 is irregular, accompanied by sharp fluctuations of the length and width of the plasma jet. It is a result of the large arc voltage fluctuation that changes the enthalpy of the plasma jet. For T-A1, it can be seen that the steam plasma jet is more concentrated and stable with a relatively regular morphology. Therefore, the proper diameter of the anode helps to suppress the generation of the large-scale arc shunting, thus obtaining a more regular and stable plasma jet. Figure 10 shows the photos of the plasma jet generated by the T-A1 with I = A, P = kw and G S = 60 g min 1. It can be seen that the length and volume of the steam plasma jets increase with the increase of the arc current or the working power. It can be interpreted that the mean temperature increased with increasing current intensity because of Joule heating of the gas, i.e. high densities of active species are being generated in the plasma with fast interspecies collisional exchanges [22]. Thus, more steam is converted into plasma at high arc currents, resulting in an increase in the column of the plasma jet. When I = 190 A, P = 40 kw, the length and diameter of the plasma jet reach the maximum values of 248 mm and 47 mm, respectively. 6

8 Figure 7. Scheme of the main forces applied on the arc columns of T-A1 and T-A2: F Dc aerodynamic drag, F Rc reacting force of the F Dc, F La Lorentz force, F Ra reacting force of the F La. Figure 9. Photos of the plasma jet generated with I = 190 A, G S = 50 g min 1 by: (1) the T-A2; (2) the T-A1. Figure 8. The thermal efficiency of the T-A1 with steam or air as the plasma forming gas at 60 C cooling water temperature. Therefore, high arc current and the resulting high working power is beneficial for the ionization of steam into plasma, leading to longer plasma plume length Effects of the cooling water temperature Figure 11 shows the Volt Ampere characteristics of the T-A1 cooled by the cooling water with different temperature (25 C or 60 C). It can be seen that the arc voltage of the T-A1 cooled by 25 C cooling water increases with the increase of the arc current. This is because that the increase of the arc current raises the temperature of the inner surface of the electrodes, which partly limits the condensation of steam on the electrodes. Therefore, the steam flow rate at high current is relatively larger than that at low current, resulting in the increase of the arc voltage. In contrast, when the T-A1 was cooled by 60 C cooling water, its voltage-ampere characteristics is different from that of the T-A1 cooled by 25 C cooling water. It is probably because that when the T-A1 was cooled by 60 C cooling water, the temperature of the inner surface of the electrodes was high enough, which avoided the condensation of the steam on the electrodes and thus the 7

9 Figure 12. The AVSD of the T-A1 cooled by the 25 C or60 C cooling water. Figure 10. Photos of the plasma jet generated by the T-A1 at different arc powers. Figure 11. Volt Ampere characteristics of the T-A1 cooled by the 25 C or 60 C cooling water. steam flow rate was almost constant when the T-A1 worked at different arc current. In addition, it can be seen that the arc voltage with 25 C cooling water is higher than that with 60 C cooling water at high arc currents (larger than A). It is probably because that the temperature of the anode inner surface for the former is lower than the latter, resulting in stronger constriction of the arc column and thus higher arc voltage. Figure 12 shows the AVSD of the T-A1 cooled by the 25 C or60 C cooling water. It can be seen that the arc voltage fluctuation of the T-A1 cooled by 25 C cooling water is much higher than that of the T-A1 cooled by 60 C cooling water. It may be explained as follows. When the T-A1 was cooled by 25 C cooling water, steam partially condensed on the cold inner surface of the electrodes, resulting in the reduction of the steam flow rate. However, when the arc struck on the condensed water on the inner surface of the electrodes, it explosively evaporated due to the high temperature of the arc, resulting abrupt increase of the steam flow rate. In addition, such explosive evaporation may bring about local high pressure and thus change the shape of the arc column, resulting in large-scale arc shunting. Therefore, the large arc voltage fluctuation was probably a result of the change of the arc length caused by both the resulted abrupt change of the steam flow rate and the large-scale arc shunting. Figures 13(a) and (b) shows photos of the plasma jet generated by the T-A1 cooled by 25 C cooling water and the inner surface of the T-A1 s anode cooled by 25 C or60 C cooling water after running for 30 min. It can be seen that during the operation of the T-A1 cooled by 25 C cooling water, a large number of sparks that are the eroded copper particles were ejected from the anode nozzle, and a large number of copper particles were stuck on the inner wall of the anode after running for 30 min. However, as can be seen from figure 13(c), when the T-A1 was cooled by 60 C cooling water, the inner surface of the TA1 s anode is still smooth after running for 30 min. These phenomena were probably a 8

10 (1) Using hot water to cool the electrodes can effectively prevent steam from condensing on the electrodes, thereby greatly reducing the arc voltage fluctuations and the electrodes erosion of the steam plasma torch. This is crucial for increasing the working life of the electrodes and ensuring long-term stability of the steam plasma torches. (2) Suitable anode diameter can greatly reduce the arc voltage fluctuation of the steam plasma torch and effectively improve the stability of the steam plasma jet. (3) High arc current can effectively reduce the fluctuations of the arc voltage. The length and volume of the steam plasma jet increases with increasing power of the steam plasma torch. (4) The use of steam as the plasma forming gas can achieve higher thermal efficiency compared to air for the designed steam plasma torch. An ideal thermal efficiency can be achieved by properly reducing the arc current and increasing the steam flow rate. Acknowledgments Figure 13. (a) Photo of the plasma jet generated by the T-A1 cooled by 25 C cooling water, (b) seriously eroded inner surface of the T-A1 s anode cooled by 25 C cooling water after running for 30 min, (c) smooth inner surface of the T-A1 s anode cooled by 60 C cooling water after running for 30 min. result of the explosive evaporation happened. When explosive evaporation happened on the inner surface of the electrode, it was usually accompanied by complex chemical physical interaction between the liquid water phase and the electrode wall and the mechanical tear of the electrode material. The tore material was then ejected from the anode nozzle with the plasma jet as sparks or stuck on the surface of the anode. In addition, the loss of material caused crater-liked depressions on the anode surface, forming preferred points of arc attack for future erosions. Therefore, the use of 60 C cooling water to limit the excessive cooling of the inner wall of the electrodes can effectively avoid the explosive evaporation of condensed water, thus greatly reducing the arc voltage fluctuations and electrode s erosion of the steam plasma torches. 4. Conclusions A gas-stabilized steam plasma torch was designed, and its Volt Ampere characteristics, arc voltage fluctuation characteristics, thermal efficiency, jet characteristics and electrodes erosion were experimentally investigated. Following conclusions can be drawn from the study: The authors appreciate the support of the Key Research Program of the Sichuan Provincial Science and Technology Department, China (No. 2017GZ0096). References [1] Zhao P et al 2010 J. Hazard. Mater [2] Huang J J, Guo W K and Xu P 2005 Plasma Sci. Technol [3] Min B Y et al 2007 J. Ind. Eng. Chem [4] He X J et al 2004 Plasma Sources Sci. Technol [5] Tendero C et al 2006 Spectrochim. Acta B 61 2 [6] Bonizzoni G and Vassallo E 2002 Vacuum [7] Kim S W, Park H S and Kim H J 2003 Vacuum [8] Murphy A B 2017 Plasma Chem. Plasma Process [9] Ansaldi M et al 2017 Environ. Sci. Pollut. Res. Int [10] Ni G H et al 2012 Plasma Sources Sci. Technol [11] Li T M, Choi S and Watanabe T 2012 Plasma Sci. Technol [12] Hrabovský M 2002 Pure Appl. Chem [13] Tamošiūnas A et al 2012 Int. J. Math. Comput. Phys. Electric. Comput. Eng [14] Tamošiūnas A et al 2016 J. Clean. Prod [15] Anshakov A S et al 2015 Thermophys. Aeromech [16] An shakov A S et al 2013 Therm. Eng [17] Surov A V et al 2017 Fuel [18] Zhukov M F and Zasypkin I M 2007 Thermal Plasma Torches: Design, Characteristics, Application (Cambridge: Cambridge International Science Publishing) [19] Coudert J F, Planche M P and Fauchais P 1995 Plasma Chem. Plasma Process. 16 S211 [20] Singh N, Razafinimanana M and Hlina J 2000 J. Phys. D: Appl. Phys [21] Collares M P and Pfender E 1997 IEEE Trans. Plasma Sci [22] Sismanoglu B N et al 2009 Spectrochim. Acta B