February 15, 2007

Focus on O&M (February 2007)

LOGISTICS

First-class maintenance in a developing country

Colombia, the third-most populous country in Latin America, gets 76% of its electricity from hydro plants. Because hydroelectricity production depends on rainfall, thermal plants fueled by coal and natural gas are used to fill shortfalls in supply during the dry season and times of drought.

Isagen S.A.E.S.P., based in Medellín, and Gensa S.A., based in Manizales, are two of Colombia's larger utilities, and they have a similar mix of hydro and thermal generating assets. For both companies, the overriding objective of plant maintenance is to ensure that gas- and coal-fired units can be started up quickly as soon as hydro plants can no longer meet demand, and that they remain on-line with minimal downtime. Often, that task is complicated by fuel transportation and maintenance support issues. Isagen's gas-fired Termocentro gas-fired combined-cycle plant in Puerto Berrío and Gensa's coal-fired Termopaipa plant in Paipa illustrate the challenges facing managers of Colombian thermal plants.

Location, location, location

Colombia has a limited number of railroad lines, and most are narrow-gauge. Their age is another problem: Only about 60% of existing track is usable. Although Colombia is blessed with many rivers (on which sit three hydro plants of more than 1,000-MW capacity), most are not navigable by barges. This is a major problem for plants such as Termopaipa, whose coal must be delivered by truck.

The availability of spare parts also is limited by transportation constraints, as well as by the reluctance of some equipment vendors to provide support services in remote areas of the country. Some of those remote areas are hotspots of the 35-year-old guerrilla war against the government by Fuerzas Armadas Revolucionarias de Colombia (FARC). As a result, extreme security measures must be taken at a number of power plants. At Termopaipa, for example, armed guards are posted at the plant entrance. At Termocentro, there are double fences with patrolling guards and guard dogs, and there is even a military detachment and barracks on the grounds of the plant.

The need for maintenance has been made more urgent by Colombia's increased attention to environmental protection. Most coal-fired plants in Colombia, like Termopaipa (Figure 1), were built in the 1960s and reflect best environmental designs and practices of that era. Since then, national air pollution standards have become much stricter. To comply with them, coal-fired plants have had to install control devices such as electrostatic precipitators and pay closer attention to efficient O&M of all equipment.

1. Colombian combined-cycle. Isagen's 2 x 1 gas-fired Termocentro power plant must start up quickly when hydroelectric power supplies dip. Courtesy: Tetra Engineering Inc.

Due to the issues mentioned, more Colombian plant managers are using predictive maintenance strategies and tactics to improve reliability and availability. A key to this approach is the baselining and condition assessment of major plant components. At Termocentro, these two steps were recently taken to determine the state of the plant's two heat-recovery steam generators (HRSGs). As part of this effort, the tubing and drums of each unit were inspected and evaluated. Armed with the results, Isagen will be able to answer important questions such as: how often to do a borescope inspection of attemperator lines, where to look for flow-accelerated corrosion damage, and what to do about it.