As eco-friendly energy demand globally increases, the weight of coal and nuclear energy in global energy production keeps decreasing. Since the same energy trend occurred in Korea, the Korean government has started to put more importance on new and renewable energy. However, the operation of the coal-fired power plant will last at least 10~20 years in that every made from the coal occupies 40% of the whole energy production in Korea.
Major issues of the coal-fired power plant in Korea can be defined as two words, environment and safety. Especially, it is essential to control and eventually decrease CO₂, NOx, SOx and fine dust in order to deal with the global greenhouse gas reduction plan immediately. But most of the environmental issues can be simply resolved by investing in expensive technical equipment and facilities. However, when it comes to a safety issue, a strict safety system for operators such as prohibiting a working plan on dangerous sites, or increasing the replacement period of the consumable parts in dangerous areas is highly required because most safety accidents occur while dangerous maintenance or cleaning job is commencing.
In this thesis, two different methods to increase the service life of the consumable parts and to minimize maintenance service, which are extremely significant in the eyes of the operator who has worked about 40 years at the coal-fired power plant, are described except the investment method. One is to increase the service life of the PA(Primary Air) nozzles in the CFBC(Circulating Fluidized Bed Combustion) boiler by improvement of its shape and material properties. The other is to detach coal from the inner surface of the coal conveyor chute.
In Chapter 2, a method to improve the service life of the PA nozzles in CFBC boiler is stated. The velocity of the fluid sand could be controlled by adding different shapes of the vanes at the top of the fluid cavity of the PA nozzle. It was obvious that V-type vane is more effective than U-type vane to reduce abrasion of the PA nozzle in an aspect of uniform fluid and backflow prevention of the fluid sand.
Next, an additional method to improve material properties for service life expansion of the PA nozzles in the CFBC boiler is elaborated. The material selection parameter was calculated using the following equation based on the expensive Ni content and mechanical specifications:
S.I. = (Strength Room Temperature x Strength High Temperature)/(Wear Amount x Ni Content)
From the parameter, a Ni alloy(Ni 26%-Cr 22%-Si 1%) was manufactured through the investment casting process. It resulted in approximately 59% of reduction in the wear amount of the PA nozzle with V-type vane compared to the existing PA nozzle. But it was not merely a unilateral effect of material improvement, but a combined effect of the material and fluid dynamical improvements.
Chapter 4 mainly focuses on a study to desorb coal, which adhered and got accumulated over time, from the inner surface of the coal conveyor chute using vibration by the resonance frequency of the coal while the coal free-fell along the chute. The study was done at coal chute #5 and #6 in Dangjin Power Station of EWP(Korea East-West Power Co., LTD). The first and second natural frequencies of the field facility were specified as 15.8Hz and 24.55Hz through 3D modeling and modal analysis. The natural frequencies of the coal were 65~67Hz for 1st natural frequency and 25~27Hz for 2nd natural frequency. The desorption experiment was done on the test module, which was manufactured at scale 1:1 to have a similar natural frequency to the field facility. After the coal was artificially attached to the inner plate of the coal chute, the experiment showed 70% of the coal desorption at 30~32Hz, and 70% at 30~32Hz which was the most effective. The main reason why the most desorption had occurred at 30~32Hz that are not the natural frequency of the facility and the coal was a shift of the natural frequency by the attached coal and the moisture contained in the coal. As a result, the experiment proved the possibility of coal desorption avoiding resonance of the coal facilities.
In the last chapter, the overall conclusion from the results was described.