Abstract

Induced Gas Flotation (IGF) technology is well known in the oil industry for its effective treatment of produced water to meet environmental oil-in-water discharge requirements.

This paper presents technical considerations for development of a new generation of IGF units, a discussion of the process kinetics, and actual operating data and performance analysis of a full size four-cell WEMCO® cylindrical depurator.

A pilot test program was developed and executed in collaboration with ChevronTexaco Overseas Petroleum on platform Gathering Station Mike, located offshore in Cabinda Province, Angola. Pilot data indicates the flotation kinetic rate for the oil removal from a four-cell cylindrical depurator is comparable with a conventional depurator.

Introduction

Industrial application of the flotation process can be traced back to the 1930s. Flotation machines were originally developed as devices for removing suspended solids in the mining and mineral industries. By the 1960s, economic considerations triggered modifications to flotation methods which resulted in the development of large multi cell units with dissolved gas capacities of up to 3000 cu. ft. capacity per cell1.

Success of flotation machines in the mining and paper industries paved the way for utilization of this equipment in oil field water treatment applications. Very little has changed in the design of this equipment since the first application of the flotation machine in the oil industry.

IGF technology utilizes a motor-driven vaned rotor or impeller for inducing and mechanically mixing gas with produced water. Gas is drawn from the vapor space in the vessel and mixes with the produced water resulting in small bubbles which rise to the surface. Negatively charged oil-droplets will adhere to the bubbles which are positively charged and quickly rise to the surface forming an oil froth layer to be removed mechanically or hydraulically through the oil trough. Cationic polymer is typically added up stream of the IGF unit to enhance the oil removal efficiency. Produced water flows through each of four cells in series resulting in overall oil-in-water removal efficiency of about 95 %.

The WEMCO® cylindrical depurator, a mechanically-induced gas flotation (IGF) unit, is specially designed to incorporate many new features which enhance equipment performance, reduce capital, operating, and maintenance costs, and allow other applications including higher operating pressure and off-gas containment.

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