Development Of A100MWe Reheat Biomass-fired Circulating Fluidized Bed Boiler

With the continuous development of economy and society, there is a growingdemand for coal, oil and other traditional fossil fuels, however, which brings prominentenvironmental issues. Therefore, it is the only way that seeking to develop the newenergy to solve the current energy dilemma. Among all currently available new energysources, biomass has got much attention worldwide due to its various superiorities suchas renewable, fewer atmospheric emissions and promotion on the economic and socialdevelopment in rural areas. Currently, among those utilization technologies of biomassresources, including pyrolysis, gasification, liquefaction and direct combustion, thecombustion technology, which possesses advantages of reducing CO2emissions, wideuse of combustion products, low cost and scale utilization, is considered to be the mostfeasible technology in large-scale development and utilization of biomass resources.Compared with the layer burning technology, pulverized combustion technology andbubbling-bed combustion technology, the circulating fluidized-bed combustiontechnology, which has high combustion efficiency, wide fuel adaptation and convenientload regulation, is considered to be the most promising utilization technology ofbiomass resource in future.In this paper, based on the analysis of components, combustion characteristics andash properties of biomass, it is found that due to the high volatile content in biomass,the pyrolysis coke is rich in pore structures, which results in high combustion activityand combustion efficiency with rational operation. Usually, there are relatively highcontent of K, Na and other alkali metals in biomass, which brings rather low ashmelting point and causes coking, fouling as well as corrosion and other problems inbiomass combustion processes. According to the fouling-corrosion mechanism of thebiomass-fired circulating fluidized bed boiler, inhibiting fouling is considered thefundamental way to reduce corrosion, which provides designing criteria for a100MWereheat biomass-fired circulating fluidized bed boiler while the performances of theboiler is also predicted. In B-MCR condition, the thermal efficiency is up to89.93%based on the mixture of the biomass and limestone, while89.86%based on theconverted content of the fuel. Moreover, under condition of maintaining a constantexcess air ratio and moral ratio of S and Ca, the desulfurization efficiency is no less than 80%, and the concentration of NOxand CO in flue gas is not more than200mg/Nm3and100mg/Nm3respectively.In addition, the influencing factors of the acid dew point of flue gas is analyzed inthis paper, and given that sulfur content in the biomass is typically lower compared tocoal, and the flue gas acid dew point of the biomass-fired circulating fluidized bedboiler should be lower than the coal-fired circulating fluidized bed boilercorrespondingly. Therefore, in order to further improve the efficiency of biomass-firedcirculating fluidized bed boiler, there is an urgent need for accurate prediction of theflue gas acid dew point. In this paper, based on the principles of conductive dew pointmeter, the flue gas acid dew point and its influencing factors is experimentally studiedby cooling the heated mixture gases of dilute sulphuric acid vapor, water vapor, carbondioxide, oxygen and nitrogen. A correlation formula of flue gas acid dew point on thevapor pressure of H2SO4as well as H2O is proposed while the simulation on the gascondensation by means of Aspen Plus is performed with simulated data compared withthe experimental data. Moreover, a self-designed flue gas acid dew point measuringdevice is made according to the principles of conductive dew point meter. A newmeasuring method for SO3concentration in the flue gas is put forward based on the factthat the SOxcan be selectively absorbed by the saturated NaHSO3solution. Field test onthe flue gas acid dew point in the backpass of a150MWe coal-fired circulatingfluidized bed boiler is performed and the obtained data serves as validation reference forlaboratory data.