Development of a Robust Scrubber Level Controller

Abstract

Gas-liquid scrubbers rely on level control systems (generally consisting of a level indicator, a level controller, and a pneumatic control valve for liquid release) to maintain an appropriate liquid level within the vessel. Scrubbers are often upstream of turbomachinery and failures at the scrubber can cause liquid ingestion or downtime. In natural gas service, these control systems are subject to harsh environments due to the influx of liquid slugs, high-velocity gases, corrosive fluids, vibrations, and a chaotic gas-liquid interface. In these severe conditions, level control system failures are commonplace and lead to safety and environmental hazards, equipment damage, and lost production. A need exists to augment or replace the typical liquid level control system with an alternative solution that is cost-effective, robust, and can operate reliably in the harsh natural gas environment. A project investigated failures related to scrubber level control systems, identified improvements to these systems, developed a prototype level controller, and tested the prototype controller and a variety of commercially available controllers at various conditions that emulated certain field conditions. The results of these tests gave insight into what type of controller may be best suited to the tested conditions and what controller options should be pursued further.