Letting off a Little Steam

This is a sidebar to the main story "Biofuels Thrive with Automation" which appears in the March 2008 Issue of Automation World.Geography plays a big role in how nations reduce their reliance on oil. The Corn Belt of the United States, for example, is converting some of its crop into ethanol.

The Philippines, on the other hand, is tapping into another source. “Since the country lies in the Pacific Ring of Fire, it has numerous sources of geothermal energy,” explains Pim Daza, production superintendent for the Mindanao plant at PNOC-Energy Development Corp., a governmental agency for developing and operating geothermal power plants.

“Geothermal power plants contributed 12.5 percent of the total installed generating capacity in 2006, according to statistics from the Department of Energy,” he adds. The geothermal power plant on the island of Mindanao, for example, can produce 108.5 MegaWatts of electricity.

These plants are exploiting the naturally occurring steam that is generated when molten magma close to the surface comes into contact with ground water. They extract a mixture of steam and hot brine from a series of production wells and separate the steam from the brine. The purified steam drives the turbines that generate the electricity, and the brine is returned to the ground in a series of injection wells.

The challenge to operating these plants is that the wells typically lie in a huge expanse of mountainous jungle. The injection wells returning the brine and condensed water to the ground must be far enough away from the hot production wells to avoid dousing them with the greatly cooled water and brine. So, the production wells can be more than 10 miles from the power plant, and the reinjection wells can be more than 10 miles away in the opposite direction.

Automation was necessary if PNOC-EDC was going to avoid sending people to each of these rugged, remote locations to oversee loop controllers. For this reason, it has migrated to a central control scheme based on a supervisory control and data acquisition (SCADA) system and human-machine interface (HMI) from Wonderware, a Lake Forest, Calif.-based unit of Invensys Systems Inc.

The automation allows operators at the power plant to monitor all of the remote stations. It also supervises the programmable logic controllers (PLCs) at each station, manages the alarms and collects historical information for analysis later.

When trouble arises, the automation takes charge of the emergency shutdown, ensuring that the valves going to the plant close and blow-off valves open to vent the steam. It also tracks the plant’s contribution to the grid for billing.

To view the main article, "Biofuels Thrive with Automation" go to: www.automationworld.com/view-3992

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