A Resourceful Solution for Na Duong

In an effort to make the most of Vietnam ’s coal resources, the Vietnam National Coal Corporation (Vinacoal) is helping to construct a series of power plants. As part of this effort, CCI will be supplying turbine bypass and auxiliary steam valves for the coal-fired thermal power plant Na Duong, located in the Loc Binh district in the northern mountainous province of Lang Son.

The valves include a VLB and a VST-SE for the turbine bypass system. The VLB design features an integrated cooling system with steam flow throttled through a cage type plug with multiple drilled holes. This provides optimum characteristics for control of the steam pressure. The spray water is injected through spring-loaded variable nozzles after final pressure reduction of the steam, providing an excellent spray pattern during the whole load range. This means no erosion problems with valve internals.

The VST-SE is a multistage steam conditioning valve that combines the benefits of low noise and vibration levels with high rangeability, typically at least 50:1. VST-SE was designed to provide this improved rangeability even when a multistage pressure reduction arrangement is required to minimize noise and vibration. All spray water injection takes place after the final steam pressure reduction stage, avoiding risk for erosion and cracking of valve body and internals.

For the auxiliary steam application, CCI is providing its 840G cage-guided valve which is specially designed to control a wide variety of relatively clean liquids and gases at high pressure differentials.

The design is very flexible in that it allows a variety of trim types to be installed in the body. Additionally, the cage-guided construction reduces plug vibration and provides stable performance throughout travel. The valve also has a quick change design so it guarantees convenient repair and easy replacement of trim.

The design flows for the turbine bypass valves are 125 t/h for 60% BMCR, and 160 t/h for the auxiliary. Design pressures are 143 (kg/cm 2) at 1018 F (548 C) for turbine bypass, and (142 kg/cm 2) at 1018 F (548 C) for auxiliary. Operating temperatures for the turbine bypass valves range between 920 F to 1000 F (495 to 540 C), and between 930 F to 1000 F (500 to 540 C) for the auxiliary valves.

When completed, Na Duong will use 535,000 tones of high sulphurous coal and 187,000 tones of limestone a year when it becomes operational. By the end of the decade, the corporation is hoping that these plants will be responsible for 8 percent of energy sectors’ total capacity, which will be an increase compared to the year 2000.

Published in SOLUTIONS Spring 2003