Study On The Transformation Of Nitrogen During Hydropyrolysis Of Shengli Brown Coal And Gasification Of Char

Hydropyrolysis is one of the technologies for efficient utilization of brown coal resources.However,the nitrogen present in brown coal will migrate to the gas phases,the tars,and remain in the chars during hydropyrolysis of brown coal.Char is a high-yield solid product after coal pyrolysis.Char gasification can be used to produce high-energy gas or chemical synthesis gas,while,the nitrogen remaining in the char will generate gaseous nitrogen-containing substances with the char gasification.Therefore,the migration and transformation of nitrogen during the brown coal hydropyrolysis and char gasification were studied,which can provide theoretical and technical support for the efficient and clean utilization of brown coal and the clean utilization of char.In this study,Shengli brown coal was used as the experimental coal sample.The Shengli brown coal hydropyrolysis experiment was carried out in the metal and quartz fixed bed reactor.The effects of pyrolysis conditions(temperature,pressure,residence time,heating rate,and gas flow rate)and minerals and reactor characteristics on the formation of NH₃,HCN,N₂,tar nitrogen(Tar-N)and char nitrogen(Char-N)were studied systematically,and the effects of these factors on nitrogen functional groups transferred to chars and the conversion of nitrogen-containing compounds in tars were studied systematically.The experiment of the steam and carbon dioxide(CO₂)gasification of char prepared by hydropyrolysis were carried out in the quartz fixed bed reactor.The effects of gasification temperature,gasification time,and gasifier concentration on the formation of NH₃,HCN,N₂,and ash nitrogen(Ash-N)were systematically studied.And the effects of pyrolysis conditions(temperature,pressure,and residence time)and minerals on the formation of NH₃,HCN,N₂,and Ash-N during char gasification under the same gasification conditions were also systematically studied.The conclusions were as following:(1)During hydropyrolysis,Char-N and quaternary nitrogen(N-Q)are the main nitrogen-containing products after pyrolysis and the main nitrogen functional groups in the pyrolysis char,respectively.Increasing temperature hinders the formation of Char-N and the generation of pyrrolic nitrogen(N-5)and nitrogen oxide(N-X)in the char,while,promotes the formation of Tar-N,NH₃,HCN and N₂ and the generation of pyridinic nitrogen(N-6)and N-Q in the char,however,the contents of Tar-N,N-6 and NH₃reaches the maximum at 600°C and 800°C,respectively,further increase in temperature inhibites the formation of Tar-N,N-6 and NH₃.The increase of pressure facilitates the generation of NH₃ and N₂and the formation of N-6 and N-Q in the char,while,inhibits the generation of Char-N,Tar-N and HCN,however,the content of N-6 has maximum value at the pressure of 0.5 MPa,while,there is a minimum generation of HCN at the pressure of 1MPa,further increase in pressure inhibits N-6 formation,while,does not influence the HCN formation.When pyrolyzed under helium atmosphere,the increase of pressure suppresses NH₃ release,which indicates that hydrogen plays key role in NH₃ generation.Prolonged residence time promotes the formation of NH₃,N₂,HCN and Tar-N and the generation of N-Q in the char,while,inhibites Char-N generation and the formation of N-5 and N-6 in the char,however,the yields of Tar-N and HCN reach maximum when residence time is 30min,further extension of residence time hinders Tar-N formation,while without affecting HCN generation.Increasing heating rate facilitates the release of NH₃ and HCN and the formation of N-6 in the char,while inhibits the formation of Char-N,Tar-N and N₂ and the generation of N-Q in the char.The increase of gas flow rate promotes the formation of NH₃,HCN and Tar-N,and the generation of N-5 and N-6 in the char,while hinderes the formation of Char-N and N₂ and the generation of N-Q in the char,however,when the gas flow rate is 300m L/min,the content of Tar-N,N-5 and N-6 have maximum values,while,the content of char-N and N-Q have minmum values,continuing to increase the gas flow have no effect on the formation of Char-N,Tar-N,N-5,N-6 and N-Q.The highest contents of six-membered ring nitrogen compounds in tars obtained at high temperature,high pressure,long residence time,and high gas flow rates,while the highest contents of five-membered ring nitrogen compounds in tar obtained at high heating rates.(2)In process of hydropyrolysis,minerals inhibit nitrogen in coal conversion to Char-N,Tar-N and HCN,while catalyze nitrogen in coal conversion to NH₃ and N₂.Minerals promote the formation of pyridinic nitrogen in char,however,inhibit the generationof quaternary nitrogen.Minerals only catalyze five-membered ring nitrogen compounds formation in tars.(3)During hydropyrolysis,compared with the nitrogen-containing species generation in the metal reactor,Char-N,Tar-N,and N₂ are not easily formation in the quartz reactor.However,NH₃ is very conducive to formation in the quartz reactor.At low temperatures,HCN is conducive to formation in the quartz reactor.The chars produced in the quartz reactor have a higher content of pyridinic nitrogen and a lower content of quaternary nitrogen.The tar produced in the quartz reactor contains more six-membered ring nitrogen compounds.(4)During the steam gasification of char,the increase of gasification temperature enhances the formation of NH₃ and N₂,while hinders Ash-N formation,however,when the gasification temperature is too high,the increase of gasification temperature suppresses the generation of NH₃.During the gasification of chars containing pyrrolic nitrogen(N-5),HCN formation increased with the gasification temperature increasted.However,during the gasification of char without containing N-5,with the increase of gasification temperature,the increase in the yield of HCN has an inflection point.Both the increase of gasification time and steam concentration facilitates the release of NH₃,HCN and N₂,while inhibites Ash-N formation.NH₃ and N₂ are the main gaseous nitrogen-containing species generated during the steam gasification of char.the contents of the N-5 and pyridinic nitrogen(N-6)in the char prepared at high temperature are lower,while the quaternary nitrogen(N-Q)content is higher,when the char is gasification,the release of NH₃,HCN and N₂ are lower,while,the yield of Ash-N is higher.The N-6 content in the char prepared at high pressure is lower,while the N-Q content is higher,when the char is gasification,the generated of NH₃,HCN and Ash-N are higher,while,the release of N₂ is lower.The N-5 content in the char prepared at long residence time is lower,while the N-Q content is higher,when the char is gasification,the yield of N₂ is higher,while,the yields of NH₃,HCN and Ash-N are unchanged.During char steam gasification,minerals enhance the formation of NH₃ and N₂,while suppress Ash-N formation.(5)In the process of CO₂ gasification of char,the increase of gasification temperature promotes the formation of NH₃,N₂ and HCN,while hinders Ash-N formation,however,the release of NH₃ and HCN have inflection point with the increase of gasification temperature,both reaching maximum values at 900°C.Increasing gasification time enhance the formation of NH₃,HCN and N₂,however inhibtes Ash-N generation.Increasing CO₂ concentration facilitates HCN and N₂ generaiton,while suppresses Ash-N formation.With the increase of CO₂ concentration,the amount of NH₃ release increased,however,during the gasification of char containing pyridinic nitrogen(N-6),there is an inflection poin in the release of NH₃,while,During the gasification of char without N-6 this phenomenon did not occur.N₂ is the main gaseous nitrogen-containing species generated during CO₂ gasification.The contents of the pyrrolic nitrogen(N-5)and N-6 in the char prepared at high temperature are lower,while the quaternary nitrogen(N-Q)content is higher,when the char is gasification,the release of NH₃ and HCN are lower,while,the yields of N₂ and Ash-N are higher.The N-6 content in the char prepared at high pressure is lower,while the N-Q content is higher.When the char is gasification,the generated of NH₃,HCN and Ash-N are higher,while,the release of N₂ is lower.The N-5 content in the char prepared at long residence time is lower,while the N-Q content is higher,when the char is gasification,the yield of Ash-N is higher,while,the yields of N₂ is lower.During CO₂ gasification,minerals promotes the release of NH₃,HCN and N₂,while inhibit Ash-N formation.