Abstract
To study the effects of inherent and external alkali and alkaline earth metallic species (AAEMs, i.e., K, Ca and Mg) on the behavior of N-containing species release during rice straw (RS) pyrolysis, different pretreatments were applied in numerous experiments. Results indicate that ammonia (NH3) and hydrogen cyanide (HCN) are the major N-containing species and that the yields of isocyanic acid (HNCO) and nitric oxide (NO) are relatively low. The removal of inhert AAEMs shifts N-containing species release to a high-temperature zone according to volatile release behavior because of the increase in activation energy. The formation selectivity of NH3, HNCO, and NO increases by demineralized pretreatment, whereas HCN selectivity decreases. The formation of HNCO is mainly affected by alkaline earth metal. N-containing species release occurs in low temperatures with the addition of external AAEMs. The activation energy of samples impregnated with CaCl2 and MgCl2 sharply decreases compared to the original RS. The total yields of N-containing species are reduced significantly in the presence of KCl, CaCl2, and MgCl2 as additives. The inhibition ability of AAEMs follows the sequence MgCl2 > CaCl2 > KCl. The inhibition effect of MgCl2 can be improved by solution immersion compared with solid powder mixing. The clean biomass pyrolysis and gasification technology with low N-containing species content may be developed according to the results.
Highlights
As an alternative fuel, biomass has drawn a significant attention in the past decades
Traditional Selective Catalytic Reduction (SCR) denitrification technology is unsuitable for biomass power plants because high alkali content in biomass leads to rapid catalyst deactivation [4]
Pyrolysis kinetic parameters were estimated by the method of distributed activation energy model (DAEM) [20]
Summary
Biomass has drawn a significant attention in the past decades. Most previous studies focus on the effects of pyrolysis conditions, such as temperature, particle size, biomass type, and atmosphere on N-containing species formation [8,9,10,11] Model compounds such as amino acids, proteins, and 6-disubstituted-2,5-diketopiperazines have been selected to study N conversion during biomass pyrolysis [6,7,12]. The release characteristics of volatile compounds and the distributions of N-containing species during RS pyrolysis have been studied with water washing and acid washing to remove inherent AAEMs. The nitrogen contents of samples with different pretreatments were investigated by element analysis. KCl, CaCl2, and MgCl2 were added into the sample pretreated by acid washing, and the effects of external AAEMs on N-containing species release were studied. Two additional methods for external AAEMs, namely, solution impregnation and solid phase physical mixing were studied and compared
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