Performance Evaluation of Induced Gas Flotation Machine Through Mathematical Modeling
Authors: Leech C.A. , Radhakrishnan S. , Hillyer M.J. , Degner V.R. 
Published: December 2007

Oil removal from produced water was studied in an induced gas flotation machine to (1) determine influential parameters in oil removal efficiency, (2) develop efficiency models, and (3) predict machine settings for optimal performance. Chemical concentration and flow rate were found to be the performance. Chemical concentration and flow rate were found to be the most important variables affecting oil removal efficiency.

Introduction

Standards have been promulgated recently by the U.S. Environmental Protection Agency for oil and grease content of offshore produced-water discharges. Other instances where water quality requirements must be met are (1) steam generator feedwater in thermal recovery operations, (2) flood water for low-permeability oil reservoirs, and (3) underground disposal of waste waters containing viscous oils and/or excessive suspended solids.Dissolved gas flotation cells have been used extensively as the final step in oil removal from produced water. Shell Oil Co. has used induced produced water. Shell Oil Co. has used induced gas flotation (IGF) machines in produced-water service since 1970. Degner reviewed the application of induced air flotation technology to industrial wastewater contaminant removal. He discussed the operational parameters and flotation cell design and their relation to removal efficiency. These cells now are used principally in minerals beneficiation. However, no published information was available on full-scale IGF machine processing of actual produced water. As such, it was felt that a systematic study could lead to improved design for oil/water separation. Optimal design and operation of these machines could help meet offshore discharge regulations and would result in lower operating costs for treating produced water. A program was initiated to study a full-scale four-cell experimental IGF machine. This machine was purchased from WEMCO Div. of Envirotech Corp. It was installed in Shell's Coalings, CA, oil field to (1) determine the parameters that influence oil removal efficiency in parameters that influence oil removal efficiency in IGF machines, (2) develop performance models and curves based on these parameters, (3) predict machine parameter settings for optimal performance, (4) develop a mathematical model for performance, (4) develop a mathematical model for power usage, and (5) develop economical methods of power usage, and (5) develop economical methods of operation.The study was conducted in two phases. The initial-phase test results determined parameters that significantly influence oil removal efficiency. These parameters were studied in more detail in the final parameters were studied in more detail in the final phase. This allowed regression models to be built for phase. This allowed regression models to be built for predicting oil removal percentage at each stage. predicting oil removal percentage at each stage. These models were used to generate several plots of oil removal efficiency as a function of important parameters. Optimization runs at various flow rates parameters. Optimization runs at various flow rates indicated machine settings for maximum oil removal efficiency. A total cost expression was developed by combining the total rotor horsepower model with chemical costs derived from the oil removal efficiency model for the overall machine.

JPT

P. 48