Dielectric barrier discharge plasma microbubble reactor for pretreatment of lignocellulosic biomass

Plasma Sources Sci. Technol.

Shaw

et al. 2019

Self Cite

In this study we examine both the effect of changing the applied voltage waveform shape and the modulation on-time on the amount of ozone dissolved within a liquid in a DBD bubble reactor. In this device, the discharge forms at the gas liquid interface allowing for effective transfer of the plasma effluent into the liquid. To produce different voltage waveforms, a multilevel inverter power supply capable of generating arbitrary waveforms without switching-on and switching-off transients has been used. Of the four waveforms used in the study (sinusoidal, sawtooth, square and short-pulse), the square waveform was found to be the most efficient at producing the highest ozone concentration for a fixed peak voltage and average power. To determine the effect of the modulation on-time, the number of cycles during the on-time were increased from 1 up to 1000, adjusting the off-time accordingly to maintain the same duty cycle. Shorter on-time periods were found to be more efficient. Experimental and computational results indicate that the time between subsequent discharges is critical for increased ozone generation efficacy, as this needs to be long enough for ozone produced in one discharge event to diffuse away from the discharge region before the next discharge event occurs, thereby avoiding its partial destruction in the plasma. This insight provides a valuable criterion for the optimization of DBD reactors used in novel biomedical, agricultural and environmental applications.

Section: Plasma-liquid Micro-bubble Reactormentioning

confidence: 99%

Influence of the voltage waveform’s shape and on-time duration on the dissolved ozone produced by a DBD bubble reactor

Seri

Plasma Sources Sci. Technol.

Shaw

et al. 2019

Self Cite

“…Additionally, the combined effect of ROS and RNS has been shown to be highly effective in disinfecting water born microorganisms, such as E. coli and cryptosporidium (Hayes et al, 2013;Kim et al, 2013). It is anticipated that a scalable and highly efficient APP reactor would be beneficial to many potential industrial applications such as water treatment (Loeb et al, 2012), pretreatment of lignocellulosic biomass (Wright et al, 2018), seed treatment (Sivachandiran and Khacef, 2017), food industry (Shaw et al, 2015) and chemical processing (Rumbach and Go, 2017). These emerging wide-ranging applications have led to various designs of APP reactors.…”

Section: Nomenclaturementioning

confidence: 99%

“…Microbubbles have a large surface to volume ratio which can facilitate this delivery and induce convection currents that aid mixing of dissolved species within a reactor. This can lead to high mass transfer rates (Wei et al, 2017;Wright et al, 2018).…”

Section: Nomenclaturementioning

confidence: 99%

“…Whilst this limitation can be alleviated by generating the discharge within the liquid, doing so can be challenging due to high voltage and high frequency required and the need for specialised power supplies (Pongrác et al, 2018). Here we explore the formation of the discharge in a plenum chamber under the liquid volume and disperse the plasma effluent as bubbles through the liquid (Wright et al, 2018;Zhou et al, 2016).…”

Section: Nomenclaturementioning

confidence: 99%

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Microbubble-enhanced DBD plasma reactor: Design, characterisation and modelling

Chemical Engineering Research and Design

Taglioli

Montazersadgh

et al. 2019

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The emerging field of atmospheric pressure plasmas (APPs) for treatment of various solutions and suspensions has led to a variety of plasma reactors and power sources. This article reports on the design, characterisation and modelling of a novel plasma-microbubble reactor that forms a dielectric barrier discharge (DBD) at the gas-liquid interface to facilitate the transfer of short-lived highly reactive species from the gas plasma into the liquid phase. The use of microbubbles enabled efficient dispersion of long-lived reactive species in the liquid and UVC-induced oxidation reactions are triggered by the plasma radiation at the gas-liquid interface. A numerical model was developed to understand the dynamics of the reactor, and the model was validated using experimental measurements. Fluid velocities in the riser region of the reactor were found to be an order of magnitude higher for smaller bubbles (~500 µm diameter) than for larger bubbles (~2500 µm diameter); hence provided well-mixed conditions for treatment. In addition to other reactive oxygen species (ROS) and reactive nitrogen species (RNS), �� Interfacial area m-1 Dynamic liquid velocity Pa s Volume m 3 Molecular weight g mol-1 1.0 Introduction Ozone has been established as an excellent oxidising agent and used on industrial scale for water treatment worldwide (Loeb et al., 2012). Its high oxidation potential of 2.07 V is superior to that of chlorine (1.36 V), and

“…At the centre of the reaction tank is a draft tube with a height of 50 mm and diameter of 80 mm, allowing for good mixing within the reactor when treating a liquid [28]. For the work reported in this paper, the reactor was operated without liquid; however, the reactor can be used for pre-treatment of biomass [29,30] and wastewater [31]. The gas exits the reactor through a port in the centre of the top lid.…”

Section: Introductionmentioning

confidence: 99%

Influence of the On-time on the Ozone Production in Pulsed Dielectric Barrier Discharges

Montazersadgh

Ren

et al. 2019

Plasma

Self Cite

Understanding the production mechanisms of ozone and other reactive species in atmospheric pressure dielectric barrier discharges (DBDs) has become increasingly important for the optimization and commercial success of these plasma devices in emerging applications, such as plasma medicine, plasma agriculture, and plasma catalysis. In many of these applications, input power modulation is exploited as a means to maintain a low gas temperature. Although the chemical pathways leading to ozone production/destruction and their strong temperature dependence are relatively well understood, the effect of the on-time duration on the performance of these modulated DBDs remains largely unexplored. In this study, we use electrical and optical diagnostics, as well as computational methods, to assess the performance of a modulated DBD device. The well-established Lissajous method for measuring the power delivered to the discharge is not suitable for modulated DBDs because the transients generated at the beginning of each pulse become increasingly important in short on-time modulated plasmas. It is shown that for the same input power and modulation duty-cycle, shorter on-time pulses result in significantly enhanced ozone production, despite their operation at slightly higher temperatures. The key underpinning mechanism that causes this counter-intuitive observation is the more efficient net generation rate of ozone during the plasma on-time due to the lower accumulation of NO2 in the discharge volume.