P.P.M. Blom

Pulsed corona for gas and water treatment

The successful introduction of pulsed corona for industrial processes very much depends on the reliability of high-voltage and pulsed power technology and on the efficiency of energy transfer. In addition, it is crucial that adequate electromagnetic compatibility (EMC) is achieved between the high-voltage pulse source and surrounding equipment. Pulsed corona (1.5 kW) is generated in a pilot unit that produces narrow 50 MW pulses at 1000 pps. The pilot unit can run continuously for use in industrial applications: cleaning of gases (100 m/sup 3//h) or fluids (e.g. waste water). Various chemical processes, such as toluene removal from an air flow are tested. To examine the processes in the reactor, the authors use current and voltage sensors and a fast CCD camera. They also developed a model to analyze the VOC conversion. Incorporated EMC techniques are based on the successful concept of constructing a low transfer impedance between common mode currents induced by pulsed power and differential mode voltages in signal lines and external mains AC.

Experimental program of the pulsed corona tar cracker

We are concentrating on the development of pulsed corona discharges to crack heavy tar components (hydrocarbons) into lighter ones. The method has the advantage that it can operate at a high temperature, and be retrofitted to existing installations. The corona discharge is energized by 100-150 ns wide voltage pulses (100 kV) at a continuous repetition rate of 600-1000 pulses per second. The power dissipated by the corona discharges is 1.5 kW average and 50 MW peak in each pulse. To be cracked by discharges, the hydrocarbons of the tar mixture need to be gaseous and therefore, the corona reactor must operate at a high temperature. In the first phase of the experiments the reactor will run at a modest temperature of 150/spl deg/C. The reactor is a 1-3 m long stainless steel cylinder, 0.25 m diameter with a corona wire along the axis. The pressure will be 1 atmosphere.

Combined optical and electrical measurements on pulsed corona discharges

To produce very intense coronas, a pulsed high voltage is applied. The peak voltage can be far above the breakdown value, if the pulse width remains below a few microseconds. Aiming at high charge production during the pulse we found that the pulse risetime is a sensitive parameter1. A DC bias voltage below the inception voltage is added to transport the charges to the wall2. The application of short pulses on top of a DC voltage instead of pure DC allows a much wider voltage range for corona operation. This wider voltage range is very advantageous in situations of serious contamination or at high operating temperatures, in the range of (400–800) °C3. Pulsing also permits a separate control of production (pulse) and transport (bias). Thus very high charge production rates can be achieved. Our work further aims at improving this charge production and at an understanding of these very high corona intensities. The absence of a full breakdown and the very interesting high corona current (we observed up to 600 A/m) are not fully understood however, a possible explanation might be connected to the ‘bright spot’ regime described later in this paper.