Taichung Power Plant Upgrades with Switch Mode Power Supplies and RDE’s

The Taichung power plant in Taiwan is one of many coal-fired plants employing electrostatic precipitators (ESP) as a control device to collect dust from the flue gas. With an installed capacity of 5500 MW, Taichung is also regarded as one of the largest coal-fired power stations in the world.
There are a total of ten ESP units. Most have been operated for more than 20 years and the reliability of the units' internal components has decreased, leading to higher emissions being recorded. Moreover,the tightening of stack emission regulations has also motivated the plant operators to make further improvements on ESP-collecting efficiency.

In order for the plant to be more environmentally friendly and respond to more stringent emissions regulations in Taiwan, it was proposed to enhance the ESP efficiencies phase by phase, in which ESP Unit 6 was chosen as the first unit for upgrading in order to increase equipment reliability and collection efficiency. A report on this project was provided to Power Engineering by Thompson Tsai of Tai & Chyun Associates and Ken Parker who is a well-known precipitator consultant.

To increase reliability, the first and second fields in all chambers were upgraded with rigid discharge electrodes (RDEs) and the T/R set was changed to switch mode Tai & Chyun Associates power supply (SMPS) units. The ESP is comprised of four separate chambers, giving a total of eight units of T/R sets to be upgraded with SMPS units at first and second field each chamber. Mechanically, there are 16,128 pieces of serrated strip type of discharge electrode (DE), also known as “saw-band type DE,” to be upgraded with RDEs.

The project was executed within 52 days including both mechanical and electrical upgrades. The result of post-modification testing showed that the unit successfully meets the customer's expectation and environmental regulations.

The RDE electrode is more breakage-resistant and provides better durability compared with serrated type DE. Its spike and main body are integrated in a single piece of fabricated metal without any joints; therefore, after operation covering an appreciable time, the electrodes are usually found deformation-free. The aggressive spike design also generates a higher corona current with a lower onset voltage. This, together with SMPS operation, offers the advantage of producing an almost DC waveform,giving a higher field voltage, while modern electronics precisely detect and respond to any spark/arc situations more rapidly, resulting in a significant increase in the electrical operating conditions. Hence the retrofit enhanced the collection efficiency compared with the original design.