S.A. Nair

Tar removal from biomass-derived fuel gas by pulsed corona discharges

Tar removal from fuel gas obtained from biomass gasification offers a significant challenge in its deployment for power generation as well as for other applications such as production of chemicals by processes such as Fischer–Tropsch. The present investigation focuses on pulsed corona discharges for the mentioned objective. The paper is meant to give an overview of our developments in the area of pulsed power development for large-scale plasma processing. In addition, lab-scale results as well as pilot-scale results for tar removal on an actual gasifier are presented.

An Industrial Streamer Corona Plasma System for Gas Cleaning

For pulsed corona plasma applications, it becomes important to develop pilot systems with large average power and high-energy conversion efficiency. Since the beginning of 2000, we have been working on an industrial corona plasma system with tasks of 10-30 kW in average power and higher than 90% of total energy conversion efficiency. The pulsed-power source should have the following specifications: rise time of 10-25 ns, pulsewidth of 50-150 ns, pulse repetition rate of up to 1000 pulses per second, peak voltage pulse of 70 kV, peak current of 3.5 kA, dc bias voltage of 10-35 kV, and energy per pulse of up to 30 J. Sixteen parallel wire cylinder reactors are used to match the source. Gas and reactor temperatures can be controlled individually with water flow around the outside of those cylinders. The system is designed for gaseous oxidation and electrostatic dust precipitation. The system has been used for up to 17 kW in average power. This paper reports the system in detail, discusses issues related to the matching between the source and the reactor, and presents an example of industrial demonstrations on odor abatement at 1000 m3/h. Finally, this paper also gives a general guideline for design of corona plasma systems

Chemical Processes in Tar Removal from Biomass Derived Fuel Gas by Pulsed Corona Discharges

Cleaning or conditioning of fuel gas from biomass gasification is perhaps one of the main obstacles for utilization of biomass as a source of power generation. Various methods exist, but, so far, none of them have been reported to be reliable for long-term operation. In our present research, we try to couple our advancements in pulsed power technology for industrial applications to the application mentioned. Here we focus on the chemical processes that occur during pulsed corona fuel gas cleaning. Experimental results at 200°C show that the main process for tar (heavy aromatic hydrocarbons) removal is mainly via oxidation.

A novel circuit topology for pulsed power generation

This paper presents novel circuit topologies based on multiple switches and transmission line transformers (TLTs). The proposed pulsed power circuit topologies produce high levels of pulsed power either at higher voltages or at higher currents. The TLTs are used for impedance matching and synchronization of multiple switches. This paper also presents our first experimental results to verify the circuit topologies.

Pulsed Corona Discharges for Tar Removal from Biomass Derived Fuel Gas

To supply combustion engines or gasturbines with fuel gas obtained from biomass gasification, it is necessary to clean the fuel gas. Also the production of chemicals by processes such as Fisher-Tropsch requires a high gas quality. Especially heavy aromatic hydrocarbons (“tars”) must be removed. In this work, we give an overview of our investigations on tar removal by pulsed corona discharges as an alternative approach to catalytic or thermal tar cracking. Experimental results (at a gas temperature of 200°C) are reported for the removal of various model tar components in synthetic fuel gas. In order to identify the major reaction pathways, experiments were also done on tars in individual fuel gas components. The results show that tar removal by pulsed corona processing is possible. The process for tar removal is mainly via oxidation. Also termination reactions by CO play an important role.

Transmission line transformers for up to 100 kW pulsed power generation

Transmission line transformers (TLTs) are usually used for impedance match. In this paper, we present a novel circuit topology based on multiple switches and TLTs for both the impedance match and synchronization of multiple switches. In contrast to the Marx pulse generator, our proposed pulsed power systems produce high levels of pulsed power not only at higher voltages but also at higher currents.

Evaluation of Pulsed Power Sources for Plasma Generation

Abstract This paper reports repetitive pulsed power sources for generation of pulsed streamer corona and electrohydraulic spark discharge plasmas, respectively. Single- and multiple-switch circuit topologies are used for scaling the average power up. For positive streamer corona plasma, ultra-short (~ 50 ns) hybrid pulsedpower technologies have been under investigations with an industrial pilot system. For electrohydraulic spark discharge plasma, an all solid-switch pulsed power technology has been developed and introduced into the market since 2002. This paper also discusses critical circuit elements, such as heavy-duty thyristor, transmission line transformer, and triggered spark-gap switch, and their industrial applications.

Repetitive pulsed power to serve nanotechnology, sustainability and hydrogen production

Repetitive pulsed-power has enormous enabling potential for a wide range of unconventional processes, such as nanotechnology, hydrogen production, gas and water processing and direct pulse interactions. The technology focuses on multiple switch concepts, a multiple pulsed plasma torch for thermal and nonthermal plasma and the combination of a near zero-erosion spark gap or an opening switch with a transmission line transformer.

High temperature pulsed corona processing of biogas

Abstract To utilize fuel gas obtained from biomass gasification for the production of energy or chemicals, it is necessary to clean the fuel gas. Especially heavy aromatic hydrocarbons (“tars”) must be removed. This paper gives an overview of our work on tar removal from fuel gas by means of pulsed corona discharges. A setup for pulsed corona processing at fuel gas temperatures up to 850 °C will be described. Experiments were done at gas temperatures up to 400 °C. Effects of the gas temperature on the energization of a corona reactor and on tar removal will be discussed.

Recent advances of power conditions for streamer corona plasma applications

Publisher Summary This chapter reviews the state-of-the-art of power conditions for streamer–corona plasma applications. It also discusses some critical issues when developing industrial systems. Based on streamer generation and interaction between power sources and reactors, the power conditions can be divided into two groups—namely, hybrid pulsed-power system (HPPS) and DC/AC. Today, single- and multiple-switch circuit topologies have become available to scaleup the HPPS system. DC/AC sources are being introduced into the market. Over the past 20 years, pulsed corona plasma system was expected to be integrated together with electrostatic precipitator for a simultaneous removal of dusts, SO 2 , NO x , and heavy metals from exhaust gases. The data available would be sufficient enough for commercial-scale design for either odor-emission control or exhaust-gas cleaning. By retrofitting available electrostatic precipitation (ESP), a plasma-based gas cleaning system to simultaneously remove polluting gases, heavy metals, and particles will be applied in the near future.