Flow pattern dependent model for airlift pumps performance: Analytical simulation and experimental verification

Abstract

Airlift pumps are widely applied in different industries largely for flow recirculation purposes such as in petroleum exploration, deep-sea mining, wastewater and sewage treatment, and chemical processing industries. Their performance is significantly dependent on the two-phase flow patterns within their riser pipe and difficult to be accurately predicted. Most previous studies have developed mathematical models to predict lifted liquid flow rate and pumping efficiency of these pumps assuming one flow pattern in the pump riser. However, several flow patterns such as bubbly, slug, churn, and annular flow patterns can exist in the pump riser. Furthermore, most of the current models are developed and validated for use with small-diameter riser pipes, mainly tested in laboratory settings, while industrial applications usually utilize larger pump sizes. To address these limitations, the present study aims at developing a mechanistic model that is applicable for use across a wide range of airlift pump sizes. To verify the proposed model, a series of experiments was conducted under a wide range of operating and geometrical conditions. An airlift pump with a riser diameter of 3.175 cm (small pump) was tested in the lab for an adjustable submergence ratio (0.5, 0.7, and 0.9) at inlet air flow rates up to 20 kg/hr. High-speed imaging was carried out to visualize flow pattern within the riser pipe and instantaneous void fraction data was collected using a capacitance sensor to identify flow patterns and transitions. Four large airlift pumps, featuring riser pipe diameters of 5.08, 10.16, 15.24, and 20.32 cm—dimensions commonly encountered in industrial settings—were tested on-site at an industrial facility, with inlet air flow rates of up to 100 kg/hr. The model showed ∓20% agreement with experimental results of both small and large size pumps. The proposed model was also used to analytically simulate the impact of riser pipe diameter and length as well as submergence ratio on an airlift pump’s performance.