Labour Daily: SEP Employees Win Technology Innovation Awards, SEP Ushers in Wide-load De-NOx Technology

Aimed at pollutants produced by coal-fired power plants, SEP staff conducted bold innovation for various types of boiler, and finally ushered in the wide-load de-NOx technology for coal-fired power plants.
SEP has already installed SCR de-NOx facilities in all of its owned and affiliated units. However, there exist temperature range limits between 315℃~420℃ in catalytic reaction for SCR de-NOx facilities. Along with the unit load reduction, the flue gas temperature will drop accordingly; when the temperature is below 315℃, the ammonia injection system will automatically drop out, and then the NOx emission will exceed the standard. Therefore, in order to ensure the coal-fired boiler reach the NOx emission standard at full load and all times, it is particularly necessary to carry out research on wide-load de-NOx technology.
After the R&D team was established, they developed a brand new rehabilitation scheme, that is, transform the current boiler water system, convey part of high-temperature saturated water to the water inlet header of economizer and let it mix with and warm up the feed water, then increase the temperature of flue gas at the economizer outlet to reach the applicable temperature for SCR de-NOx. This rehabilitation system is called Gas Temperature Rising System (GRS), which was first introduced in the renovation project at the boiler of Waigaoqiao Power Plant Unit 3 in 2013. However, subject to the lift of boiler water pump, they could not deliver more boiler water to the economizer inlet, thus unable to further increase the water temperature at economizer inlet. Although the rehabilitation could reach the applicable temperature for units with capacity above 140MW, the maximum temperature increase of flue gas was only 10℃, which means the system was still unable to meet the de-NOx operation requirement for units below 140MW. Hence, based on the original GRS, the R&D team put forward another new idea of conveying part of feed water to the downcomer through bypass when mixing part of boiler water with feed water, in order to raise the water temperature at the economizer inlet to a larger extent without increasing the flow of economizer, and thus acquire a better effect on flue gas temperature increase. Such upgraded Super Gas Temperature Raising System (SGRS) is able to satisfy the need for a bigger rise in boiler gas temperature, also providing approaches for raising flue gas temperature in DC and supercritical boiler. SGRS has advantages of small changes to the system, low rehabilitation costs and wide range of temperature rise.

After commissioning, SGRS can satisfy flue gas temperature conditions for de-NOx operation with units at minimum load of 125MW, and the gas temperature could rise by 23℃ at the most. The system scheme has effectively solved the problem that the low temperature at the inlet may lead to the suspension of SCR de-NOx system. SGRS also has the characteristics of simple system, low rehabilitation costs and small impact on other working conditions, etc.

The two technologies developed by the system, i.e. Natural Circulating Drum Boiler with GRS and Forced Circulating Drum Boiler with GRS, acquired utility model patent, while De-NOx Temperature Rising System at Low Load won the first prize of SEP Technology Advancement Award in 2013, the third prize of National Electricity Employee Technology Achievement Award and the first prize of the first SPIC Outstanding Employee Technology Innovation Award in 2014.

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