Research On The Influences And Solutions Of Blending Lignite In Supercritical Boiler

High price and in short of high quality coal, more and more power plants using lignite blended approach to solve this problem. High moisture content and low net calorific value of lignite are the certain limit of blending combustion.To solve the high moisture content of lignite, the existing program including hot air mixed with flue gas, lignite pre-drying using flue gas or extraction steam. In this paper, the use of supercritical boiler economizer outlet water as an indirect drying medium to pre-drying lignite. By coal mill heat balance calculation, this paper analyses the influence of water content on mill output and draw a suitable lignite pre-drying moisture range while ensuring coal mill output and the adjust ability. By lignite pre-dryer heat balance, calculate the heat consumption and recover water under different pre-drying degree.Using the latest boiler thermodynamic calculate standards, to a supercritical boiler and check the thermodynamic calculation under different pre-drying degree. This paper analyses the influence of boiler under condition of blending different pre-drying lignite and different ratio, including furnace heat load, the amount of flue and flue gas volume, exhaust gas temperature and boiler efficiency, attemperation water consumption.This paper also studied boiler safety while fire blended coal, mainly the wall temperature of heating surface in varies condition. Using thermal deviation theory and pipe segment model to calculate the wall temperature. The result show that the wall temperature increased with the blending ratio increase, with a small changes of lignite pre-drying degree. Therefore, the heating surface is safety is one factor need to be consider while choose blending ratio.