Dynamic process of steam in a super critical CFB boiler

Abstract

CFB technology has gained more attention over the past few years. Most probably due to its efficiency and ability of achieving low emissions. New strict governmental regulations regarding emissions are continuously imposed which makes CFB boilers a promising candidate for future industries. One way to facilitate the implementation of CFB boilers is by making it cheap option. Currently these boilers are equipped with expensive urgent feed water systems for boiler safety, in case of electricity loss. Since there are no accident records this equipment is still in controversy. This thesis analyses the physical process of steam in a 350 MW super critical circulating fluidized bed boiler during sudden electricity failure. By obtaining information about the dynamic process of steam properties it will be possible to estimate the necessity of the urgent water feeding system in future applications. With some simplifications a three dimensional model was created to solve energy equations. The model includes thermal processes like conduction, radiation and convection of steam, bulk material and air. The final model predicts the dynamic progress of these. The highest temperatures achieved is located in the bottom of the furnace, the conductive part, and lies around 875 K which is slowly continuing to increase. However, this temperature lies in the acceptable span for wall conditions which indicates a possibility for economic savings. Further studies need to be conducted in order to conclude whether the emergency system can be neglected.