Experimental And Numerical Simulation Study On SNCR Of Different Patterns Of CFB Boiler

Circulating fluidized bed boilers have the advantages of high combustion efficiency,wide adaptibility of fuel and low emission of pollutants.However,with the advancement of ultra-low emission environmental standards(NOx<50 mg/Nm3),it's imperative to transform the denitration technologys.The selective non-catalytic reduction(SNCR)denitration technology has been widely concerned due to its advantages of small footprint,simple transformation and low costs.However,most of the experimental and theoretical studies of SNCR technology are carried out on laboratory-scale experimental facilitys.The experimental research on industrial application of this technology is limited,and the research on the denitrification characteristics of different circulating fluidized bed boilers has not been reported.In this paper,experiments and simulations on the denitrification characteristics of SNCR in two different kinds(compact cyclone separator and thermal cyclone separator)of boiler have been carried out.Which may provides some guiding significance for the operation and transformation of denitration systems for industrial boilers.Firstly,the effects of oxygen content and limestone input on the denitrification characteristics of SNCR were studied by test on the two boilers,and the denitrification conditions of the two boilers were compared.In addition,the effects of the fly ash of circulating and the amount of urea input were studied on the compact cyclone boiler.It was found that limestone had a great role in promoting the source emissions of NOx,and NOx emissions increased with the rose of limestone input.The input of the circulating fly ash and increased the dosage of urea all help to improve the denitrification efficiency.And the oxygen in flue gas of the boiler should not exceed 3%.Secondly,the two kinds of circulating fluidized bed boilers were modeled and simulated,and compared with the experimental results,the error between the experimental and simulation results was found to be within 25%,which proved that the grid and simulation settings were reasonable and could satisfy the calculation.Then compared the denitrification characteristics of the two boilers with the change of temperature and normalized stoichiomet ricratio,it was found that the optimal temperature for denitration of all the two boilers were around 900?.Under the same normalized stoichiomet ricratio,the denitration efficiency of the thermal cyclone boiler is slightly higher than that of the compact cyclone boiler,and the ammonia slip is also lower.It is considered that the mixing degree of the reducing agent and the flue gas in the boiler is the main influencing factors.Based on the comparison of the distribution of reducing agents in two boilers,it is found that in thermal cyclone boiler,the mixing degree of reducing agent and flue gas is better than that of compact cyclone boiler.For the compact cyclone boiler,the effects of temperature,the injection position of the reducing agent,initial NO concentration and O2 concentration on boiler's denitration efficiency and ammonia slip were studied.It is found that the installation of the spray gun on the wall surface of the furnace is better than that at the flue inlet of the cyclone separator,and when the n?mber of spray guns is six,the mixing effect of the reducing agent and the flue gas is better than that of the four spray guns.With the increases of temperature,the denitration efficiency first rises and then decreases,and the ammonia slip is basically 0 in the interval of temperature above 950?.With the increases of initial NO concentration,the denitration efficiency increases.With the increases of O2 concentration,the best denitrification temperature moves to the lower temperature direction,and it is considered that the O2 concentration should not exceed 3%.Finally,the insertion depth and inlet downtilt angle of the two cyclones were changed and the effects of these two factors on the SNCR denitration characteristics of the cyclone separator were studied.It was found that the performance of the two cyclones varied differently as the depth of insertion of the central cylinder increased.For compact cyclone,it has better working performance when the ratio of the center tube insertion depth s to the cyclone inlet height a is around 0.5,at the same time,the optim?m denitration efficiency can be increased by 3%.For the thermal cyclone,the optim?m denitration efficiency can be increased by 5%when s/a=0.75.It is found that the increases of the downtilt angle of the inlet of the two cyclones is beneficial to improve the denitration efficiency.Think about the influence of the structural change of the cyclone on the denitration characteristics of the SNCR and the working performance of the cyclone separator,it is considered that the downtilt angle of the compact cyclone inlet should be about 10°,and 15° for thermal cyclone.Studying the SNCR denitrification characteristics of different kins of circulating fluidized bed boilers is helpful to provides suggestions for the transformation of denitration systems for boilers,which is worthy of further research.