Research On Nitrogen Conversion In Co-pyrolysis Of Raw And Torrefied Biomass With Coal

Utilizing the existing power equipment to realize the co-combustion,co-gasification and co-pyrolysis of biomass or terrified biomass and pulverized coal will be the main way to realize the large-scale energy utilization of biomass in the future.Then it will alleviate the energy crisis and be an important technical routes to reduce environnental pollution and achieve carbon emission reduction.The forms of fuel nitrogen in primary biomass,torrefied biomass and pulverized coal are different.It is important to provide theoretical guidance for the conversion of fuel nitrogen and the synergistic effect of fuel in the process.In this paper,three kinds of biomass and two coals were selected for separate/mixed pyrolysis experiments on a fixed bed reactor.The effects of material type,pyrolysis temperature and blending ratio on fuel nitrogen conversion during pyrolysis were investigated.In order to improve the fuel quality of biomass,wheat straw was used as the typical representative of crop straw.The effects of torrefaction temperature and torrefaction atmosphere on the characteristics of wheat straw fuel were researched.The pyrolysis of torrefied straw and the co-pyrolysis of torrefied straw and bituminous coal were carried out.to study the nitrogen conversion in process.Results are summarized as follows:When the three biomasses were pyrolyzed separately,the conversion rate of NH3-N increased at first and then decreased with the increasing temperature,while the conversion rate of HCN-N increased monotonously with the increasing temperature.Product(NH3+HCN)yields of wheat straw>Arundo donax>cotton stalk NH3 is the main nitrogen-containing phase product in the rapid pyrolysis of bituminous coal and anthracite.The yields of bituminous coal HCN was higher than that of anthracite.In the range of pyrolysis temperature 600-1000℃,when the mass ratio of blending is 1:4 when the wheat straw and the bituminous coal are mixed and pyrolyzed,the release of the nitrogenous product in the gas phase has only a weak synergistic effect.The release rule of gas nitrogenous products in the mixed pyrolysis of Arundo donax and cotton stalk and bituminous coal changed significantly.The blending of Arundo donax inhibited the formation of NH3 and promoted the formation of HCN,while the blending of cotton stalk promoted the NH3 and HCN.generation.With the increase of biomass blending ratio,the synergistic effect in the co-pyrolysis process was more obvious.The synergistic effect of the conversion of nitrogen-containing products in the co-pyrolysis process of biomass and anthracite was stronger than the co-pyrolysis of biomass and bituminous coal.The torrefaction temperature was the most important factor affecting the volatile contents of the biomass sample after torrefaction.The mass yields and energy yields of the torrefied straw at 250℃ was the highest.When the torrefaction temperature was 300℃,the yields of wheat straw torrefied under CO2 atmosphere was the highest,and the energy yields of torrefied straw under 5%O2 atmosphere was the highest As the pyrolysis temperature increased,the yields of char-N decreased,and more fuel-N converted to harmless N2.As the torrefied temperature increased,the conversion of NH3-N and HCN-N decreased,torrefied straw samples under CO2 and 5%O2 atmosphere at torrefaction temperature of 300 ℃,the NH3 and HCN generated from rapid pyrolysis were less than under the Ar atmosphere.The co-pyrolysis experiments were carried out by mixing the straw sample obtained by Ar atmosphere at the mass ratio of bituminous coal 1:1.It was found that the conversion rates of NH3-N and HCN-N were inhibited to some extent.And the higher the torrefaction temperature of wheat straw was,the more significant the inhibition effect.The torrefaction atmosphere had an effect on the conversion of wheat straw torrefied sample and nitrogen conversion in the co-pyrolysis process of bituminous coal.The co-pyrolysis of wheat straw and bituminous coal obtained in three torrefied atmospheres can inhibit the conversion of fuel-N to NH3-N,while the conversion rate of HCN-N was not same.The torrefied straw in Ar and CO2 atmosphere had almost no effect on the conversion of HCN-N in the co-pyrolysis,and the conversion of torrefied straw to HCN-N under 5%O2 atmosphere were promoted.At 800℃,the torrefied wheat straw at 250℃ under Ar and bituminous coal were blended at mass ratios of 1:3,1:1 and 3:1.The difference between the theoretical value and experimental values of NH3-N conversion was 4.57%.However,the conversion rate of HCN-N was within 1%,indicating that changing the blending ratio of torrefied straw had no significant effect on the conversion of NH3-N and HCN-N.