The fly ash re-combustion system manufactured by the German company BABCOCK is used in Units 1-4 of Huaneng Beijing Thermal Power Plant and Units 5-6 of Yangliuqing Power Plant. The fly ash re-combustion system in Unit 1 of Huaneng Beijing Thermal Power Plant is the first of its kind in China. This article introduces the advantages and problems of this system, analyzes the problems encountered during commissioning, and proposes some improvement suggestions. 1. Overview of the Fly Ash Re-combustion System The entire system consists of an air preheater (hereinafter referred to as the air preheater) ash removal section, an electrostatic precipitator ash removal section, a boiler ash removal section, and a fly ash recirculation section. Before the air preheater, the ash in the flue gas is transported to the intermediate coarse ash bin using an internal ejector. The ash discharge (according to the flue gas direction) of the electrostatic precipitator ash hopper is achieved through air chute and chain conveyor. The ash is transported to the intermediate coarse ash bin by the first electric field air chute; and to the intermediate fine ash bin by the second electric field air chute and the third, fourth, and fifth electric fields. Ash from the intermediate coarse/fine ash bins is pumped to the furnace front ash collection bin and ash silo via a silo pump below. Ash in the collection bins can be pumped to the intermediate ash silo via a silo pump below, or it can be fed to the fly ash burner for fly ash re-combustion via a rotary feeder under the collection bin. The ash silo has a volume of 1000 m3. A lifting unloading machine delivers ash from the ash silo to dry ash trucks for timely removal. 1.1 Air Preheater Ash Removal Section The air preheater ash removal hopper is located at the air preheater inlet to reduce wear inside the air preheater. Each flue is equipped with one ash hopper. Ash collected in the ash hopper is transported to the intermediate ash silo using a jet-type ash conveyor. Three conveying fans are provided, one of which is a spare. 1.2 Electrostatic Precipitator Ash Removal Section This section has two electrostatic precipitators. Dust collected in the first electric field of each electrostatic precipitator is blown to the intermediate coarse ash bin by a fan located at 0 m through an air chute. Dust collected in the second electric field is blown into the intermediate fine ash silo by a fan located at 0 m via an air chute. Dust collected in the third to fifth electric fields is conveyed to a double-strand chain conveyor by a single-strand chain conveyor below, and then further conveyed to the intermediate fine ash silo. 1.3 Boiler Ash Removal Section This section includes the conveying of ash from the intermediate ash silo, the recirculation from the ash collection silo to the intermediate coarse/fine ash silo, and the conveying of ash from the ash silo to the ash cylinder. The intermediate ash silo is divided into two types: intermediate coarse ash silo and intermediate fine ash silo. The intermediate ash silo is located below the electrostatic precipitator on the original flue gas side, is straight-through, rectangular, and has a volume of 70 m3. Each ash silo has two silo pumps. The ash conveying from the intermediate ash silo is accomplished by the ash conveying function group of each silo pump, and each ash conveying function group has two ash conveying directions: ash collection silo and ash cylinder. The ash discharge system of the intermediate ash silo starts from two discharge ports. The ash falls due to gravity and falls into the silo pump under the intermediate ash silo. When the ash in the silo pump reaches its high level, the conveying fan of the intermediate ash silo starts to blow the ash out from the silo pump until it reaches the low level. The ash in the furnace front ash collection silo can be sent to the furnace for reburning through the rotary feeder at the outlet of the ash hopper below. The amount of reburning ash entering the furnace can be adjusted according to the boiler load and by adjusting the speed of the speed regulating motor. Alternatively, the ash can be recirculated to the intermediate coarse/fine ash silo through the silo pump under the ash collection silo. [b]2 Advantages of the system[/b] 2.1 Space saving Since the boiler uses gas ash removal, the ash entering the ash silo is dry ash. A 1,000 m3 ash silo can store the ash produced by the boiler at full load for one week and can be transported away in time by dry ash trucks. Therefore, a dedicated ash plant is not required, which can save a large area of ​​space. 2.2 The characteristics of the ash remain unchanged, facilitating comprehensive utilization. The boiler employs fly ash re-combustion technology, utilizing dry, hot air to transport the ash. Since the ash contains almost no moisture, its characteristics remain unchanged. Ash is divided into coarse and fine ash, each with different uses, such as as building materials, resulting in high economic benefits. 2.3 The re-combustion portion can transform ash into slag, facilitating storage and use for different purposes. Re-combusting the ash produced by the boiler transforms it into liquid slag, facilitating storage and use for various purposes, generating significant economic benefits. 2.4 Recirculation of incompletely burned ash ensures more thorough combustion. After combustion in the furnace, some unburned coal particles remain. Direct discharge of these particles not only pollutes the environment but is also uneconomical. Re-combustion (or multiple recirculations) significantly reduces the combustible content, further improving economic efficiency. 2.5 The ash hopper is less prone to scaling. High-temperature dry air is used in the gas ash removal and fly ash re-combustion processes, resulting in a higher ash temperature, facilitating ash removal. Furthermore, the high temperature of the ash in the ash hopper prevents scaling. 2.6 Saves a lot of water resources Compared with the past, the fly ash re-combustion system uses air instead of water for ash removal and conveying, which saves a lot of water resources. At present, under the condition of relatively tight water resources, this method of ash removal has high social and economic benefits. [b]3 Disadvantages of the system and suggestions for improvement[/b] (1) The fly ash re-combustion system of Huaneng Beijing Thermal Power Plant is prone to ash blockage when the amount of ash in the pipeline is large due to the small power of its conveying fan and the low temperature of the conveying air. The solution is to appropriately increase the power of the conveying fan and increase the temperature of the conveying air. (2) The ash silo unloading device can only be started after the exhaust fan is turned on, and the start of the exhaust fan must be operated in the control room, which is relatively troublesome. Therefore, the first step of starting the ash silo unloading function group should be to turn on the exhaust fan, and the start and stop function of the function group should be added on the spot to facilitate unloading. (3) The fly ash re-combustion system of Yangliuqing Power Plant operates the function group through the control panel. It is not possible to operate a single piece of equipment, such as valves and fans. The disadvantage of this method is that when a certain device malfunctions, it cannot be debugged separately, so a computer operating system should be provided for the system. (4) The start and stop of the air preheater ash removal function group is accomplished by starting and stopping the electrostatic precipitator. This will cause the pipes under the air preheater to be blocked with ash because the boiler is put into operation earlier than the electrostatic precipitator. Therefore, it should be changed to a method in which the function group can be started and stopped manually.