A New Approach to Evaluate and Optimize Swirl Tube Demister Efficiency

A New Approach to Evaluate and

Optimize the Swirl Tube Demister Efficiency

Authors: Kyle Anderson, Ben Reinhardt, Walead Sultani, Hannah O’ Hern, Xiang Zhang, Bahman Abbasi

Affiliation: Oregon State University          

1                 INTRODUCTION

In the United States, roughly 98% of the production water used in hydraulic fracturing operations is deposited in underground injection wells due to the economic burden of treating this highly contaminated process byproduct. With around 300-900 million cubic meters of fracking wastewater produced since 2007, and several sever human health problems linked to the unintended escape of this stored wastewater into drinking water sources, a cost-effective and more energy efficient treatment solution is highly desirable. In this regard, Dr. Bahman Abbasi conceived a novel water purification technique as FRESH-Frac project at Oregon State University’s (OSU) Water and Energy Technology (WET) lab funded by Department of Energy, USA to address aforementioned concerns. The proposed technology utilizes low-grade thermal energy to produce vapor from contaminated water in the presence of a high energy air flow. The fresh water vapor is extracted from air-water mixture using an air-water separation technique. With this simple, self-contained, and scalable water purification unit design, the operational costs of treating fracking wastewater could be reduced in the hopes of incentivizing the hydraulic fracturing industry to move towards a more sustainable future.

2                 Swirl Tube Demister Study Motivation

Swirl tube demisters have a wide range of applications in industry. Compared with reverse flow cyclones, wire mesh demisters, and vane type demisters, they have a high separation efficiency in high pressure applications. In addition, their inline nature allows them to be more easily fitted into existing piping structures.

Despite the benefits of this style of demister, there is a lack of literature on design criteria for optimization of performance. Also, most of the literature that does exist has been focused strictly on the water collection efficiency,  defined as the total mass of water collected, over the total mass of water supplied to the system in a trial period.

The goals of this experimental study are to add to the existing literature by quantifying the effect of design parameters on both the water collection efficiency and the air bypass efficiency,defined as the ratio of the air mass flowrate exiting at the desired air outlet, over the inlet air mass flowrate. This parameter is important for the overall fracking wastewater project mentioned above because the air will act as a carrier of the contaminants, necessitating that the amount of air that leaks into the purified water collection chamber to be minimized.

3                 Preliminary Results

Initial results showed there was a clear trend when comparing the air bypass efficiency to the inlet air to water ratio. As the inlet air to water ratio increased, the air bypass efficiency decreased. This trend was consistent among four different experimental apparatuses indicating that either the geometry of the swirl tube had very little effect of the air bypass efficiency, or that the ranges tested for factors affecting the swirl tube geometry were not varied enough. Future work will focus on complete experimental characterization of the swirl tube demister and develop a design guides to obtain desired separation efficiency for specific air and water mass flow rates. This work will also be used in the development of air-water separator for the aforementioned FRESH-Frec water purification project.