Massimo Rea

Industrial experiments on pulse corona simultaneous removal of NO/sub x/ and SO/sub 2/ from flue gas

The corona-induced simultaneous removal of NO/sub x/ and SO/sub 2/ from flue gas is based on the application of narrow voltage pulses to an electrode structure similar to that of an electrostatic precipitator. The free electrons of the corona discharge, having energy up to 20 eV, originate active radicals which lead to the transformation of NO/sub x/ and SO/sub 2/ into their acids which can be neutralized to salt particulate by adding to the gas a basic compound such as ammonia and calcium hydroxide. The process has been investigated with a test rig installed in the slipstream of the flue gas duct of a coal-fired thermal power plant. The experiments were performed with three reactor modules of different geometries. Further experiments are necessary to assess the effect of different electrode geometries of the reactor, the efficiency of the process attainable with an improved coupling of narrow pulse power set to the reactor, and the practical ways for integrating the DeNO/sub x/ and DeSO/sub 2/ corona process with the solid particle collection system. >

Comparison of Toluene Removal in Air at Atmospheric Conditions by Different Corona Discharges

Different types of corona discharges, produced by DC of either polarity (+/-DC) and positive pulsed (+pulsed) high voltages, were applied to the removal of toluene via oxidation in air at room temperature and atmospheric pressure. Mechanistic insight was obtained through comparison of the three different corona regimes with regard to process efficiency, products, response to the presence of humidity and, for DC coronas, current/voltage characteristics coupled with ion analysis. Process efficiency increases in the order +DC < -DC < +pulsed, with pulsed processing being remarkably efficient compared to recently reported data for related systems. With -DC, high toluene conversion and product selectivity were achieved, CO(2) and CO accounting for about 90% of all reacted carbon. Ion analysis, performed by APCI-MS (Atmospheric Pressure Chemical Ionization-Mass Spectrometry), provides a powerful rationale for interpreting current/voltage characteristics of DC coronas. All experimental findings are consistent with the proposal that in the case of +DC corona toluene oxidation is initiated by reactions with ions (O(2)(+*), H(3)O(+) and their hydrates, NO(+)) both in dry as well as in humid air. In contrast, with -DC no evidence is found for any significant reaction of toluene with negative ions. It is also concluded that in humid air OH radicals are involved in the initial stage of toluene oxidation induced both by -DC and +pulsed corona.

Evaluation of pulse voltage generators

The electrical characteristics of the positive pulsed corona in a coaxial wire-cylinder-type reactor were investigated. The energy and charge injected into the discharging volume per pulse and per unit length of corona emitting wire are used to evaluate the power source, electric circuits, and corona wire. The discharge current lasts from several hundreds nanoseconds to a few microseconds. The current, power peak values and the injected energy and charge per pulse per unit emitting wire can reach up to 60 A/m, 5 MW/m, 480 mJ/m and 8 mu C/m, respectively. The energy conversion efficiency related to the delivery of output energy from the pulse forming capacitor to the discharging volume can reach 90%. All results were obtained at room temperature and in air.<<ETX>>

Pulse power electrostatic technologies for the control of flue gas emissions

Abstract The reduction of pollutant emissions (NO x , SO 2 and solid particulate) from fossil fuel boilers has become a major objective in several industrialized countries. The removal of solid particulate from flue gas is accomplished mainly with electrostatic precipitators because of the high collection efficiency they ensure without requiring onerous operating procedures. The application of microsecond pulse voltage energization, instead of the conventional rectified a.c. voltage energization, substantially improves the collection efficiency, at a given specific collection surface; reduces the specific power consumption, from about 0.5 Wh/Nm 3 to about 0.1 Wh/Nm 3 ; and allows a flexible operation of the precipitator to attain the required efficiency values, up to 99.8%, in the presence of fly ash with different physical and chemical characteristics. Although the benefits of pulse voltage energization are more remarkable when the electrical resistivity of the fly ash is higher than 10 11 ω cm, they are still noticeable even when the electrical resistivity is lower by several orders of magnitude. Recently the nanosecond pulse voltage energization has been successfully applied for the simultaneous dry removal of NO x and SO 2 from flue gas. Experiments carried out with test reactors, having a design configuration like the conventional electrostatic precipitators, have evidenced a removal efficiency of 50% to 60% for the NO x and higher than 80% for the SO 2 with an energy input to the gas of about 15 Wh/Nm 3 . An additional benefit of the technology consist in the end products, ammonia sulphates and nitrates, which could be used as fertilizers or soil conditioners. While microsecond pulse voltage technology has already reached full industrial demonstration and reliable equipment is available, nanosecond pulse voltage technology is still at the development stage and requires further investigation of the process as well as testing of the pulse power supply on a larger industrial scale.

Removal of NOx by DC corona reactor with water

Corona plasma over water surface is effective for NOx treatment, i.e., oxidization of NO and dissolving of NO2 into water. We proposed a new type of reactor with DC corona discharge over water surface, and carried out NOx treatment tests under various concentrations with diesel exhaust gas and blended NO test gas. Removal of 90% of NOx could be achieved in the reactor with and without water for diesel exhaust gas. It showed more than 95% of NOx removal rate with water but very low removal rate without water in the treatment test for dry NO gas. Ions and conductivity in the water of the reactor after NOx removal test were measured and discussed on the effective radicals and reactions for NOx treatment processes of this reactor. It has been confirmed that the presence of water with DC corona discharge provides excellent conditions for NOx removal processes.

Treatment of NOx in exhaust gas by corona plasma over water surface

Abstract For developing NO x treatment engineering of exhaust gas in lower construction and operating cost, we propose a new type of corona reactor with some experimental results. The reactor is madeup of multi needles’ electrode placed over water and to make use of corona plasma over water surface for plasma chemical reactions. Typical corona characteristics of the reactor with positive and negative DC high voltage are alike to discharge of normal air gap, and not so much changed by different water conductivity and electrode arrangements. The result of NO x treatment test using the exhaust gas of diesel engine shows 100% of NO removal and 95% removal rate of NO x under suitable conditions.

Products and mechanisms of the oxidation of organic compounds in atmospheric air plasmas

Atmospheric plasma-based technologies are developing as a powerful means for air purification, specifically for the oxidation of organic pollutants. To achieve a better control on the emissions produced by such treatments mechanistic insight is needed in the complex reactions of volatile organic compounds (VOCs) within the plasma. An account is given here of our comparative studies of the behaviour of model VOCs in response to different corona regimes (+dc, −dc and +pulsed) implemented within the same flow reactor. Model VOCs considered include two alkanes (n-hexane and i-octane), one aromatic hydrocarbon (toluene) and two halogenated methanes, dibromomethane (CH2Br2) and dibromodifluoromethane (CF2Br2, halon 1202). Efficiency and product data are reported and discussed as well as various possible initiation reactions. A powerful diagnostic tool is ion analysis, performed by atmospheric pressure chemical ionization-mass spectrometry: it provides a map of major ions and ion–molecule reactions and a rationale for interpreting current/voltage characteristics of dc coronas. It is shown that, depending on the specific VOC and corona regime adopted, different initiation steps prevail in the VOC-oxidation process and that the presence of a VOC, albeit in small amounts (500 ppm), can greatly affect some important plasma properties (ion population, current/voltage profile, post-discharge products).

Characteristics of Pulse Corona Discharge over Water Surface

Production of ozone and OH radical is required to advance the plasma chemical reactions in the NOx removal processes for combustion gas treatment. The corona discharge to the water surface is expected to induce the good conditions for the proceeding of the NO oxidation and the NO2 dissolution removal into water. In order to get the fundamental data of the corona discharge over the water surface, the positive and negative V-I characteristics and the ozone production were measured with the multi needle and the saw-edge type of the discharge electrodes. The pulse corona characteristics were also measured with some different waveforms of the applied pulse voltage. The experiments were carried out under the atmospheric pressure and room temperature. Both the DC and the pulse corona to the water surface showed a stable and almost the same V-I characteristics as to plate electrodes though the surface of water was waved by corona wind. The positive streamer corona showed more ozone production than the negative one both in the DC and in the pulse corona.

Electrostatic precipitation tests with fuel oil ash

Online investigations and laboratory tests were conducted to determine the efficiency of electrostatic collection of fuel oil ash. The design of the experimental precipitator is described. The relationship between collection efficiency, dust concentration, and air velocity was studied. The amount of collected dust in the electrostatic precipitation process was found to be linearly dependent on the inlet dust concentration and on the test duration. Efficiency was maximized when air velocity was kept close to 1 m/sec. Removal efficiency of more than 80% was achieved when collection plate spacing was set at 30-40 cm. High fuel oil ash removal efficiencies with reduced precipitator weight were found to be attainable with accurate system design and convenient operating conditions. (3 diagrams, 5 graphs, 1 photo, 9 references, 5 tables)

Experiments with Pulsing Energization on an Industrial ESP

A single electric field of an electrostatic precipitator installed for collecting fly ash from a 320-MWb boiler burning low-sulphur coal was energized with a pulse generator of original design. The tests showed a good performance of the pulse generator, a statistically significant decrease of dust emission in comparison to the conventional energization, and a lower power consumption.