The application of strong electric fields in water and organic liquids has been studied for several years, because of its importance in electrical transmission processes and its practical applications in biology, chemistry, and electrochemistry. More recently, liquid-phase electrical discharge reactors have been investigated, and are being developed, for many environmental applications, including drinking water and wastewater treatment, as well as, potentially, for environmentally benign chemical processes. This paper reviews the current status of research on the application of high-voltage electrical discharges for promoting chemical reactions in the aqueous phase, with particular emphasis on applications to water cleaning.

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Electrohydraulic Discharge and Nonthermal Plasma for Water Treatment

As transformers age, their internal condition degrades, which increases the risk of failure. To prevent these failures and to maintain transformers in good operating condition is a very important issue for utilities. Traditionally, routine preventative maintenance programs combined with regular testing were used. The change to condition-based maintenance has resulted in the reduction, or even elimination, of routine time-based maintenance. Instead of doing maintenance at a regular interval, maintenance is only carried out if the condition of the equipment requires it. Hence, there is an increasing need for better nonintrusive diagnostic and monitoring tools to assess the internal condition of the transformers. If there is a problem, the transformer can then be repaired or replaced before it fails. An extensive review is given of diagnostic and monitoring tests, and equipment available that assess the condition of power transformers and provide an early warning of potential failure.

Review of condition assessment of power transformers in service

Production and utilization of biochar: A review

Biomass is an important primary energy source as well as renewable energy source. As the most promising biomass utilization method, gasification/pyrolysis produces not only useful fuel gases, char and chemicals, but also some byproducts like fly ash, NOx, SO2 and tar. Tar in the product gases will condense at low temperature, and lead to clogged or blockage in fuel lines, filters and engines. Moreover, too much tar in product gases will reduce the utilization efficiency of biomass. Therefore, the reduction or decomposition of tar in biomass derived fuel gases is one of the biggest obstacles in its utilization for power generation. In this paper, we review the literatures pertaining to tar reduction or destruction methods during biomass gasification/pyrolysis. On the basis of their characteristics, the current tar reduction or destruction methods can be broadly divided into five main groups: mechanism methods, self-modification, thermal cracking, catalyst cracking and plasma methods.

The reduction and control technology of tar during biomass gasification/pyrolysis: An overview

Biomass gasification presents highly interesting possibilities for expanding the utilization of biomass as power generation using internal combustion engines or turbines. However, the need to reduce the tar in the producer gas is very important. The successful application of producer gas depends not only on the quantity of tar, but also on its properties and compositions, which is associated with the dew-point of tar components. Class 5, 4, and 2 tar become a major cause of condensation which can foul the engines and turbines. Hence, the selectivity of tar treatment method to remove or convert class 5, 4, and 2 tar is a challenge in producer gas utilization. This review was conducted to present the recent studies in tar treatment from biomass gasification. The new technologies with their strengths and the weaknesses in term of tar reduction are discussed.

Tar reduction in biomass producer gas via mechanical, catalytic and thermal methods: A review

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.

Chemical kinetic modeling of tar removal from biomass derived fuel gas by pulsed corona discharges

Two pilot pulsed power sources were developed for fundamental investigations and industrial demonstrations of treatment of conducting liquids. The developed heavy-duty power sources have an output voltage of 100 kV (rise time 10 ns, pulse duration 150 ns, pulse repetition rate maximum 1000 pps). A pulse energy of 0.5-3 J/pulse and an average pulse power of 1.5 kW have been achieved with an efficiency of about 80%. In addition, adequate electromagnetic compatibility is achieved between the high-voltage pulse sources and the surrounding equipment. Various applications, such as the use of pulsed electric fields (PEFs) or pulsed corona discharges for inactivation of microorganisms in liquids or air, have been tested in the laboratory. For PEF treatment, homogeneous electric fields in the liquid of up to 70 kV/cm at a pulse repetition rate of 10-400 pps could be achieved. The inactivation is found to be 85 kJ/L per log reduction for Pseudomonas fluorescens and 500 kJ/L per log reduction for spores of Bacillus cereus. Corona directly applied to the liquid is found to be more efficient than PEF. With direct corona we achieve 25 kJ/L per log reduction for both Gram positive and Gram negative bacteria. For air disinfection using our corona pulse source, the measured efficiencies are excellent: 2 J/L per log reduction.

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A fast pulsed power source applied to treatment of conducting liquids and air

The European energy transition is leading to a transformed electricity system, where Distributed Energy Resources (DERs) will play a substantial role. Renewable Energy Sources (RES) will challenge the key operational obligation of real-time balancing and the need for flexibility will consequently increase. The introduction of a local flexibility market (LFM) would allow the trading of flexibility supplied by both producing and consuming units at the distribution level, providing market access to DERs, a support tool for Distribution System Operators (DSOs) and a value stream for energy suppliers. Aggregators and DSOs for different reasons can enhance the valuation of flexible DERs. Several research papers have assumed aggregators fully interacting with the electricity markets and DSOs contracting services with power system actors. These interactions are still not allowed in many European countries. This article aims to analyze the European regulation to identify the most important enablers and pave the way towards the full exploitation of DER flexibility, culminating in the establishment of an LFM. Therefore, three main stages, emerging from the progressive withdrawal of the current regulatory and market barriers, are identified: (1) enabling the aggregator’s trading, (2) evolution of the DSO’s role, and (3) key-design challenges of an LFM.

Local Markets for Flexibility Trading: Key Stages and Enablers

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 35 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

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An Industrial Streamer Corona Plasma System for Gas Cleaning

In this paper, we present a large-bandwidth, high-current, and high-voltage measuring system for pulse measurements in pulsed power systems. The developed sensors can be easily calibrated, require no extensive (3-D) modeling, are very compact, are inexpensive, and have a bandwidth of up to several gigahertz. Moreover, they can be used in any pulsed power system, where a pulse source is connected to its load by a coaxial cable (without disturbing the coaxial geometry). We developed this sensor system for the use with our nanosecond pulse source system. The type of sensors we used is D-dot and B-dot sensors, which are compactly mounted on the coaxial cable that connects our nanosecond pulse source to its load. This enables us to measure the characteristics of each sensor very precisely with a vector network analyzer. With these characteristics—combined with the characteristics of the measuring cable assembly—we can numerically reconstruct the voltage and current waveforms that passed the sensor positions. Our calibration approach, the mounting on the coaxial cable and the postprocessing of the results makes these sensors very flexible. While we use the sensors for energy measurements, camera triggering, and the general measurement of the pulses, other researchers can use these types of sensors as well in any system, where a (coaxial) cable connects a pulse source to its load.

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A.J.M. Pemen

Papers

Chemical kinetic modeling of tar removal from biomass derived fuel gas by pulsed corona discharges

A fast pulsed power source applied to treatment of conducting liquids and air

Local Markets for Flexibility Trading: Key Stages and Enablers

An Industrial Streamer Corona Plasma System for Gas Cleaning

B-Dot and D-Dot Sensors for (Sub)Nanosecond High-Voltage and High-Current Pulse Measurements