| Earthed atomizing corona discharge is an environmental-friendly technology to treatwaste water. This environmental management technology is notable for its high treatmentefficiency, fast reaction and freedom from secondary pollution. This paper studies thecharacteristics of earthed atomizing corona discharge when it is used alone and when it issynergized with activated carbon, as well as their effects of pre-treating of oilfield producedwater. The research contents, results and conclusions are as follows:1. Corona discharges and atomizing discharges were combined effectively, and anew-style reactor was designed. Active species of discharge plasma exist for quite a short time.Take OH as an example, it only presents for10-7S. Traditional discharge methods are not ableto synchronise the plasma zone and reaction zone completely, so the reaction time betweenactive species and pollutants is cut down. Research indicates that earthed atomizing coronadischarge forms synchronised plasma zones and atomizing liquid drops, as well as theuniform plasma zones, and active species produced by the discharge are able to interact withwaste water from oil extraction directly. Simultaneously, the water to be treated, under theaction of strong electrostatic field force and surface tension, is atomized to small liquid dropsthat pass through the discharge reaction space. The atomizing effect enlarges the reaction areabetween the water and the plasma zone. Thus, compared with other discharge treatmentpatterns, this method can transform the waste water form oil extraction to be biochemicallytreatable with relatively lower energy and realise a higher utilisation rate of energy.2. To provide a basis for the best discharge conditions, the influences of positive/negativeatomizing corona, inter-electrode distance and flux on the earthed atomizing corona dischargeare researched. According to the research finding, on the condition of the same dischargesituation, the discharge current of a negative earthed atomizing corona is greater than that of apositive earthed atomizing corona and exceeds that of a traditional corona even more. Themain reason is that a Taylor Cone formed on the surface of a line electrode during theatomizing corona discharge shortened the inter-electrode distance. Also, there is a possibilitythat the curvature radius of the Taylor Cone will facilitate the aggrandising of the dischargecurrent.3. In the research, the discharge mechanism of earthed atomizing corona discharge isanalyzed. The research suggests that: a non-uniform electric field is formed between the lineelectrode and the plate electrodes. The highest electric field intensity exists on the surface ofthe line electrode. When the voltage exceeds the onset voltage, a corona zone is formedaround the line electrode and discharges. At the same time, the water flow that covers the surface of the line electrode produces an electric fluid effect under the action of strong electrostatic field force and further acts as a liquid electrostatic spray. The atomized small liquiddrops will discharge in the discharge electrodes. Multiple cone-shaped fluxes formed whensmall electric liquid drops move will, to some extent, be quite likely to make a crossover withthose created by large liquid drops, so this discharge form would be more beneficial forcreating relatively even plasma zone to enhance its effect on waste water.4. According to I-V characteristics of earthed atomizing corona discharge, appropriateinter-electrode distance and voltage are selected to carry out advanced oxidation treatment onhigh concentration waste water from oil extraction while BOD5, COD, turbidity and pHbefore and after reaction are measured. The study indicates that when consuming little energy,earthed atomizing corona discharge to turns out to be effective on augmenting thebiodegradability of waste water from oil extraction.The initial value of biodegradability of oilfield produced water was0.079and later roseto over0.5after the treatment. And COD removal rate reached79.64%.5. The research on activated carbon’s influence on the discharge current suggests that theinvolvement of activated carbon does not cause any change in the current of earthedatomizing corona discharge. The main reason is that a good conduction formed between theactivated carbon and the plate electrodes after the activated carbon is soaked ensures thatthere is no change in the inter-electrode distance with or without activated carbon. As a result,the discharge intensity is unchanged.6. The research on the effect of pre-treating oilfield produced water with the synergy ofearthed atomizing corona discharge and activated carbon suggests that after the earthedatomizing corona discharge and the activated carbon are synergized, the turbidity of theoilfield produced water is significantly lower than the turbidity of the oilfield produced watertreated by earthed atomizing corona discharge without activated carbon. At the same time,BOD and COD of the oilfield produced water during the pre-treating are both lower thanthose without activated carbon. The reason is that the activated carbon causes ozone freeradical chain reaction which further accelerates the decomposition of ozone into hydroxylradical. The thicker the activated carbon layer, the lower BOD and COD are. This indicatesthat a thicker activated carbon layer is more helpful in removing pollutants and shows moresignificant synergy with the plasma from the earthed atomizing corona discharge.7. The research on the influences of different water flux on the treatment effect suggeststhat with or without activated carbon, the increase in water flux has a negative influence onlowering the turbidity, BOD and COD of the oilfield produced water. The reason is that theincreased flux reduces the discharge current and thus reduces the generation of active species.As a result, the reaction rate is lowered. When the voltage is13kv, the distance between the line electrode and the activated carbon is2.5cm; when the flux is50ml/min and the thicknessof the activated carbon is5mm, the treatment effect is the best. |
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