(702b) Investigating Effects of High-Speed Non-Condensable Gaseous Flow on Separation of Volatile Compounds from Wastewater

The rapid expansion of hydraulic fracturing (fracking) in the United States has helped energy security but also led to production of large amounts of contaminated water. Fracking wastewater is toxic, and injecting it into disposal wells may contaminate freshwater reservoirs. Conventional and membrane-based techniques of wastewater treatment are not effective choices to treat fracking wastewater. This is because firstly, there are numerous types of contaminants in fracking wastewater. Secondly, more than half of all fracking wastewater is produced in the first few weeks of extraction. Accordingly, constructing a stationary water treatment unit is not economical. Bearing this in mind, conventional techniques have other weak points such as high energy consumption and fouling. For these reasons they are not cost-effective methods for wastewater treatment in the fracking industry.

A portable, scalable, and energy and cost-efficient wastewater treatment technology is under development at Oregon State University, which not only can treat the highly contaminated fracking wastewater, but also is applicable in a wide range of oil and gas as well as chemical industries. This technology takes advantage of a swirling nozzle in which a flow of high-speed air moving through the converging nozzle sucks in the wastewater vapor - in a process analogous to a steam ejector. As a result, a mixture of air and wastewater vapor accelerates through the converging nozzle where conversion of enthalpy to kinetic energy causes a temperature drop in the gaseous mixture. The process is carefully controlled so only water condenses while the contaminants and carrier air exit the nozzle. This technology is designed to operate at low pressure and temperatures with low-grade heat and can be integrated with solar thermal energy.

A laboratory apparatus was constructed to separate volatile contaminants from water. This setup allows to study the effects of high-speed flow of non-condensable gas on the separation. The purpose of this study is to investigate dynamic effects on phase distribution in a multi-component mixture. The phase equilibrium of a multi component mixture at stationary condition can be predicted using thermodynamic laws and suitable equations of state. However, in this study it is desired to understand how flow dynamics affect phase distribution in a multi-component system of air and wastewater. This helps to estimate the composition of mixture in presence of high-speed air at various operating conditions.

In our experimental facility, clean air at low temperature enters a mixing tube where the contaminated water is injected using a syringe pump. Then this mixture travels through an evaporator in which enough heat is supplied to the mixture via cartridge heaters to create a fully vapor mixture of air and contaminated vapor. Finally, the mixture is directed through a cooling section where the latent heat of condensation is dissipated from it, and condensed water with high quality is collected. Contaminants exit from the system along with air. This apparatus allows to control the operating conditions of the experiments including heat supply, temperature, pressure, air velocity, and contaminated water flow rate. This enables evaluations of how parameters like velocity and air-to-water mass ratio affect the condensation and separation.