Understanding the problem

NPC, which was founded in 1936 in Quezon City, generates electricity in the Philippines using hydroelectric, geothermal, natural gas, oil and coal facilities. The company owns three hydroelectric complexes with total capacity of 1,390 MW: 408 MW Angat, 255 MW Pulangi and the seven-powerhouse, 1,390 MW Agus complex.

Built in 1979, the Agus 6/7 portion of the Agus complex — located along the Maria Cristina Falls on the Agus River in Mindanao, Philippines — contains two hydroelectric power plants, 150 MW Agus 6 and 54 MW Agus 7. Agus 6 contains a total of five units, with three units currently operating — labeled Units 3, 4 and 5 — and two units undergoing rehabilitation. Agus 7 contains two units, called Units 1 and 2.

Cooling water for the seven Agus plants comes from Lake Lanao, which contains scaling minerals, zebra mussels, slime and sludge in the form of mud. Despite the strainers installed, this material eventually builds up in the generator coolers. This has been a problem since the first of the seven Agus plants was built in the 1950s. In fact, at the Agus 6 and 7 plants, sludge built up to the point where one of the seven generator coolers — five at Agus 6 and two at Agus 7 — had to be removed from the system during every planned maintenance shutdown so personnel could manually remove sludge from the copper tubing. These shutdowns occurred twice a year and lasted 15 days each.

The generator cooling systems at the Agus 6 and 7 hydro plants were experiencing significant scale buildup. Installation of the Scalewatcher computerized electronic water conditioner rectified this problem while improving efficiency.

Scale buildup reduces the efficiency of the cooling system, and just 0.25 inch of scale formation can increase costs by 40% by diminishing heat transfer from the coolers. At the Agus 6 and 7 plants, the stator temperature then would rise to 80 degrees Celsius, prompting the operators to either reduce load or shut down the unit.

Facing these negative consequences, the utility determined it needed to find a better way to deal with scale in the generator cooling systems. Plant personnel turned to the Scalewatcher technology. They understood Scalewatcher would provide an alternative to the existing practice of using acid descalers, which deteriorated the coolers and led to regular costly replacements.

The Scalewatcher technology works by producing a varying electronically applied force field, induced by a coil wrapped around the outside of the pipe work, which keeps the minerals in the cooling water in suspension and thus prevents limescale forming. The water’s increased solubility also enables it to dissolve existing scale, which is gradually flushed away.

NPC decided to install Scalewatcher computerized electronic water conditioners on all five units currently operating at these two plants.

Installing the systems

Between 2008 and 2011, five Scalewatcher conditioners were installed at the Agus 6/7 complex. In addition, one Scalewatcher system was installed at the Angat plant and one at the Pulangi plant, along with two at one of NPC’s geothermal plants.

With the Scalewatcher system installed, scale buildup has been minimal. Planned maintenance shutdowns still occur twice a year, but cleaning of the generator cooling systems required only five days after Scalewatcher technology was installed. In fact, scale, sludge and slime formation in the generator coolers had been reduced to the point where the plant maintenance team decided to discontinue the dismantling of all generator coolers for cleaning during planned maintenance shutdowns.

Another important benefit realized is increased unit capacity. For example, Unit 4 was rated at 50 MW but its capacity had deteriorated to 30 MW because of age. However, after installation of the Scalewatcher system, the unit’s capacity increased by 5 MW, which provides additional energy sales of $232,558 a month. Therefore, during the 39 months since the Scalewatcher installation, Unit 4 has earned additional revenue amounting to more than $9 million. Although it is hard to quantify the increase in capacity, as well as other benefits such as reduction in unit downtime and elimination of acid chemicals for descaling, NPC conservatively estimates that with an increase in capacity of 1%, the two plants will save 204 MW of electric capacity annually, which equates to additional revenue of PHP15,202,800 (US$350,000).

The Scalewatcher system installed at the Agus 6 and 7 plants has gained plant owner National Power Corporation $350,000 in revenue annually as a result of increased efficiency.

Currently, NPC plans to install the Scalewatcher technology on six units at its Agus 2 plant as well as one additional unit at the Angat plant.

— By Greg L. La Sangre, manager, GLS Enterprises (Scalewatcher’s representative in the Philippines), and Jose Pates, operations and maintenance manager, National Power Corporation’s Agus 6 plant