Newly Patented Process Cleans Up Produced Water without Chemicals

December 5, 2007 // Published as a news service by IHS

The chemical-free electroflotation method promises additional oil recovery from a process stream with fewer manpower demands, said the Society of Petroleum Engineers (SPE).

Flotation as a separation and purification process is well known and has been used widely in various industries, from municipal water treatment to mineral-ore processing.

While conventional flotation methods employ a separate gas source to pump gas bubbles into the liquid, electroflotation generates the gas in situ.

According to Trionetics, electroflotation is the process by which gas bubbles of hydrogen and oxygen, which are generated by the electrolysis of the produced water, remove dispersed particles (in this case, oil) from the water.

An anode and a cathode are typically arranged in the flotation cell holding the water to be treated, and a power source applies a low, direct current through them.

This current causes electrolysis of the produced water, producing hydrogen and oxygen gas bubbles which rise to the surface of the electroflotation cell.

As they rise, the bubbles collide with oil droplets dispersed in the water, adhere to them and then carry them to water surface. As with other flotation systems, a skimmer is used to remove the concentrated oil-laden foam from the cell, leaving the produced water behind.

Electroflotation reportedly offers several benefits over conventional flotation processes. There are no chemical additives necessary to control foam formation at the top of the cell, which makes water treatment easier and more efficient.

In addition, an adjustable transformer allows more precise control of both the size and quantity of gas bubbles formed. This allows fluctuations in oil-in-water content to be compensated for automatically and provides for an optimized treatment, said SPE.

While electroflotation has been used for years in wastewater treatment for both municipalities and process industries such as the electroplating and paper industries, it has not found widespread use in the oil and gas industry.

ONGC was awarded the patent for this application by the patent office of the government of India, after the technology was configured for the oil field by Keshavdev Malviya Institute of Petroleum Exploration (KDMIPE) and the Institute of Oil and Gas Production Technology (IOGPT).

These institutes partner with ONGC on various research projects aimed at improving economics of operations and boosting indigenous hydrocarbon exploration and hydrocarbon production.

ONGC holds the patent for a period of 20 years and is looking for interested customers, both onshore and offshore, on a global basis as per company business policy.

"The clue in developing this product for the oil field came from observing basic operational trends in the pharmaceutical industry, sewage treatment plants, and pulp and paper mills, to name a few," said Surendra Kapoor, project team leader.

"We envisage using this product for maximum benefit after integration with existing separation processing hardware, like heater-treaters. Any number of electroflotation cells can be installed, and initial field trials show that up to 250 m3/day of water can be treated."

Kapoor also stated that in many cases the oil can be recovered easily for additional production gains.

Source: Society of Petroleum Engineers (SPE).