Carbon neutrality has quickly become a world-shared mission in the past years. In September 2020, Chinese government announced its target of achieving carbon emission peak before 2030 and carbon neutrality before 2060. Under this background, wind and solar power are soaring in both installed capacity and power generation. While for coal-fired power units, flexibility especially deep power reduction capacity became extremely important and necessary because it can make room for more wind and solar power and ensure the safety of power grid meanwhile. However, ultra-low load condition is very challenging for coal-fired power units especially the boilers. The main challenges can be summarized as 6 aspects: the stability of boiler combustion; the hydrodynamic characteristics of one-through boiler; the safe operation of the Selective Catalytic Reduction (SCR) denitration system; the sulfuric acid condensation and resultant blockage at the air preheater’s cold end; the sharp unit efficiency drop; the decoupling of heat and power loads for combined heat and power units. Many attempts to solve the above problems have a common shortcoming that the improvement of one aspect is at the cost of other performances, like unit efficiency, safety or investment. Due to the complexity and difficulty of the deep power reduction, most of the coal-fired power units can hardly achieve a load rate lower than 40%. Our team, however, has developed innovative deep power reduction technologies that based on the whole thermal system of the unit, rather than the individual equipment like the boiler itself. The core of these technologies is a series of the Generalized Regeneration technologies that can greatly improve the operating condition of the boiler. These technologies have been successfully applied on several units. One representative project is a 320MW subcritical unit that its lowest operating load achieves as lower as 20% of rated load, certificated by the authoritative third party with a formal test. Another project is a national demonstration project. Despite its highest design net efficiency (48.9% LHV under rated condition) in the world, this 1350MW double reheat USC unit also achieves lowest load as 20% of rated load during commissioning, with its waterwall separator still being overheated and the unit efficiency drops only about 40% of other units can achieve. These state-of-the-art innovative technologies can help the power generation industry to reduce remarkable carbon emission and ensure the safety of power grid meanwhile.

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