Experimental Study On Low Emission Of Circulating Fluidized Bed Boiler

In China,the current situation for main energy structure of coal consumption is quite difficult to change in quite a long period in future.Air pollutants,such as dust,SO₂ and NO_x,produced by coal burning,not only destroy the environment,but also threat human health.Circulating fluidized bed boilers are widely used for the advantages of wide fuel adaptability,high combustion efficiency,high efficiency in-infurnace desulfurization,low NO_x emission,large range and high speed of load adjustment ability.As the implementation of the last edition of emission standards,circulating fluidized bed boilers are faced with air pollutant emission problems.Based on a 0.5 MW pilot plant and a 70 MW industry boiler,research on in-furnace lean-oxygen combustion with post-combustion for reducting original nitrogen oxides emission is presented in this dissertation.The results of 0.5 MW medium scale test platform show that,with the increase of air stoichiometric ratio,the primary air flow,the secondary air flow,the post-combustion air flow,and the decrease of coal consumption,the oxygen concentration and emission of NO_x increases,carbon monoxide and unburned carbon in fly decrease;The original NO_x emission concentration is 335 mg/m³;The NO_x emission decreases to 71 mg/m³,the carbon monoxide and unburmed carbon in fly ash increase obviously and combustion efficiency decreases sharply,with in-funace lean-oxygen combustion;While the NOX emission decreases to 78 mg/m³,after application of in-furnace lean-oxygen combustion with post-combustion,and the injection of post-combustion resulting the reburn of the unburned components in the back-pass gas,the combustion efficiency is 98.60%,NO_x emission decreases more than 70%.The technology of in-furnace lean-oxygen combustion with post-combustion xwas applicated to a 70 MW industry boiler,after the success on the 0.5 MW medium scale test platform.The results show that the original NO,and carbon monoxide emission concentration were 393 mg/m³ and v ppm;The NO_x and carbon monoxide emission concentration are 111 mg/m³ and 551 ppm,with just in-fumace lean-oxygen combustion;While the NOX and carbon monoxide emission are 115 mg/m³ and 4 ppm,with in-furnace lean-oxygen combustion with post-combustion.The existence of moisture,lime hydrate,carbonate,sulfate and the unburned components in fly ash and slag,influences the process of unburned carbon analysis for fly ash and slag of circulating fluidized bed boiler.Proximate analysis,ultimate analysis and thermogravimetry-mass spectrometry with equivalent characteristic spectrum analysis are used to measure the unburned carbon in fly ash and slag in this dissertation.The results show that the influence of moisture,hydrated lime,carbonate and sulfate is not completely ruled out by proximate analysis and ultimate analysis,while the influence of water,hydrated lime,carbonate and sulfate is ruled out by thermogravimetry-mass spectrometry with equivalent characteristic spectrum analysis,which can accurately measure the unburned carbon in fly ash and slag.The results on the 0.5 MW medium scale test platform and in a 70 MW industrial boiler show NO_x emission decreases significantly with high combustion efficiency with in-furnace lean-oxygen combustion and post-combustion.The thermogravimetry-mass spectrometry with equivalent characteristic spectrum analysis can realize accurate measurement of the unburned carbon in fly ash and slag.