Conversion Of Nitrogen During Pyrolysis And Combustion Of Solid Fuels And Control Of NO_x Emissions

NO_x and N₂ O are the main gaseous pollutants during combustion of solid fuels.To research the conversion of fuel-N during pyrolysis and combustion of solid fuels is conductive to reduce the emissions of NO_x and N₂ O.In this study,the conversion routes of fuel-N during pyrolysis of biomass and petroleum coke were investigated with the help of XPS technology and the experimental results of N-containing model compounds pyrolysis.Then,research of the influence of limestone addition on the emission of NO_x during petroleum coke combustion was proceeded from the abnormal phenomena of NO_x emission caused by the absence of limestone.This research was conducted by means of experimental methods,including laboratorial and industrial experiments,as well as phase analysis.After that,the influence of limestone on NO_x emission during biomass combustion was also researched in the same way.This study provides valuable informations for the control of NO_x during biomass combustion.First,the formation of catalyzed thermal NO_x and non-fuel NO_x(including catalyzed thermal NO_x and prompt NO_x)during combustion of solid fuels was researched.Results showed that N₂ molecule in the air could converted into NO with the catalysis of ashes and common inorganic components.However,the convert ratio was less than 1%.Besides,prompt NO_x might be also produced during the combustion of solid fuels in N₂+O₂ atmosphere.Secondly,pyrrole,pyridine,glycine and phenylalanine were selected to research the release of nitrogen during pyrolysis of N-containing model compounds at temperature 500⁹00 ?.Pyrrole and pyridine were decomposed at temperature higher than 700 ? and were largely decomposed at 900 ?.HCN was the only N-containing products during pyrolysis of pyrrole and pyridine.NH₃,HCN,HNCO and NO were all detected during amino acid pyrolysis.However,the formation routes of these products were quite different for glycine and phenylalanine.Deamination and dihydrogen reactions were simultaneously occurred during glycine pyrolysis,while deamination was unimportant for phenylalanine.The conversion of fuel-N during pyrolysis of biomass and petroleum coke was then studied based the results of N-containing model compounds pyrolysis and XPS technology.The nitrogen in petroleum coke was existed as pyrrolic and pyridinic functional groups.During pyrolysis,onle 3.04% of the fuel-N was released as HCN and NO,while 81.97% was remained in the char.Most of nitrogen in biomass was identified as amino nitrogen,the percentage of which was more than 75%.However,the pyrolysis characteristic of biomass was relevant to the nitrogen content rather than the Nfuctionalities.The conversion of fuel-N to gaseous products decreased with the increasd of nitrogen content.Deamination of amino nitrogen was the only path for NH₃ formation.However,a very small fraction of amino nitrogen was converted to NH₃ and most of it was converted to HCN,HNCO,NO as well as pyrrolic and pyridinic functionalities that remained in the char.pyrrolic and pyridinic functionalities were the main nitrogen functionalities in the biomass chars and a small qutantity of them was converted into quaternary nitrogen and nitrogen oxides.Besides,the formation of NO_x and N₂ O during combustion of petroleum coke and the effect of limestone addition were investigated in horizontal tube furnace,bubbling bed and CFB reactors.NO and N₂ O were produced during petroleum coke combustion,while NO₂ was not detected.NO emission was facilitated with the addition of limestone in the horizontal tube furnace and bubbling bed reactor,while it was suppressed in CFB reactor.Ca SO₄ was idetenfied to be responsible for the decrease of NO emission after limestone added.The decrease of NO emission was deduced to be caused by the catalysis of Ca SO₄ on the reduction reaction of NO and CO.Finally,the formation of of NO_x and N₂ O during combustion of biomass and the effect of limestone addition were also investigated.NO and N₂ O were produced during petroleum coke combustion,while NO₂ was not detected.NO emission was almost not affected with the addition of limestone in the horizontal tube furnace and bubbling bed reactor,while it was suppressed in CFB reactor.Thus,the influence of limestone addition on NO emission was also mainly reflected in the dilute phase zone at up part of the CFB reactor.Meanwhile,Ca O,Ca SO₄ and CO₂ also suppressed the emission of NO_x.Therefore,more researches should be carried out to find the real substance that suppressed NO emission.