Influence of non-thermal plasma pre-treatment on the scaling characteristics of viscous oil wastewater during evaporation

• Using non-thermal plasma (NTP) pre-treatment reduced the pH, silicon content and hardness in the viscous oil wastewater.
• NTP pre-treatment inhibited scale formation.
• The scale became irregular and loose after NTP pre-treatment.

Evaporation is one of the most important measures in the recovery of viscous oil from wastewater in steam injection boilers at oil fields, whereas the formation of silicate and carbonate scales inhibits the heat transfer process. To avoid scale formation without the addition of chemicals, a non-thermal plasma (NTP) reactor was adopted to pre-treat viscous oil wastewater before evaporation. The wastewater samples from two different oil fields were first atomised and sprayed into the NTP reactor tube to mix with ions and free radicals generated from high-voltage direct current (DC) pulsed discharge, and the treated water was subsequently sent to the evaporator. The influence of the DC pulse discharge frequency was also analysed. NTP pre-treatment reduced the silicon dioxide content, hardness, metal content and salinity in the wastewater. Additionally, during the evaporation process, scale formation on the evaporator surface was inhibited, and subsequently, the heat transfer resistance of the scale was reduced. A morphological analysis determined that the scale tended to be loose and irregular in shape after NTP pre-treatment, and the silicon content in the scale decreased. Pre-treatment with NTP was demonstrated to be an effective scaling prevention technique for evaporation which could be applied to wastewater recovery from different oil fields.