Search

The formation of NO x precursors (mainly HCN and NH 3 ) from the pyrolysis of Pingshuo coal with or without minerals was studied in a quartz fixed bed reactor. The coal sample in the reactor was heated in two kinds of fashion: at a slow heating rate by temperature-programmed and at a fast heating rate than constant temperature. The experimental results revealed that demineralization by acid washing drastically decreases nitrogen conversion to NH 3 at a fast heating rate and at a slow heating rate, but for HCN, its formation is different at fast heating and slow heating rates. The yield of HCN from demineralized coal is slightly lower than that from raw coal at a fast heating rate and it is the reverse at a slow heating rate. On the other hand, the pyrolysis experiments data of demineralized coal and raw coal added with ash from Pingshuo coal combustion also indicated that minerals in coal play an important role in gaseous-N formation, but the reaction mechanism is different for raw coal and demineralized coal. [ABSTRACT FROM AUTHOR]

Three coal macerals with high purities were separated from Pingshuo gas coal. The formation rules of HCN and NH3 during macerals pyrolysis and gasification were investigated. Experiments were carried out in a tubular quartz reactor at atmospheric pressure. The reactor allowed coal particles to be heated up rapidly and held for a prespecified period of time at a peak temperature. The amount of HCN and NH3 were quantified by ion chromatography. The influence of temperature and macerals type on the formation rules of HCN and NH3 was discussed. Results showed that the formation of HCN was mainly due to the thermal cracking of volatile, and NH3 formed both from the thermal cracking of volatile and the cracking of nascent char. The HCN yield increased with an increase in pyrolysis temperature. For three coal macerals (liptinite, vitrinite and inertinite), the yield of HCN depended not only on their volatile contents but also nitrogen-containing functional groups, in which more pyrrole-type nitrogens would form more amount of HCN at lower temperature. The yield of NH3 depended on the ability of forming ‘H’ radical. Under the experiment condition in this study, inertinite could convert more nitrogen into NH3 than vitrinite and liptinite. The yield of HCN during gasification was almost the same as that during pyrolysis, the yield of NH3 during gasification was little higher than that during pyrolysis. [Copyright &y& Elsevier]

Formation of NH3, HCN, NO and NO2 from the gasification of a Chinese coal (Shenmu) in a fluidised-bed/fixed-bed reactor in 4.1% O2 in argon was investigated. The presence of O2 even at 673 or 773 K could lead to the gradual gasification of char to form HCN and NH3. The yields of NH3 and HCN showed maxima at about 773 K, amounting to 40% of coal-N. In the presence of O2, the H radicals required for the formation of NH3 and HCN may be generated from the reactions in the gas phase and within the solid particles. The yields of NOx increased from 773 to 973 K. A non-negligible proportion (∼5%) of coal-N was converted into NO2 at 773 K through homogeneous and heterogeneous reactions. The yield of NO2 diminished with increasing temperature. At 1173 K, the reactions between char-N and H2O (or O/H-containing radicals) formed from the oxidation of char and volatiles led to the formation of NH3 but not HCN. This route of NH3 formation is believed to be an important pathway for the formation of NH3 in an air-blown gasifier. [Copyright &y& Elsevier]

Coal conversion in arc plasma with an initial temperature of 3700 K is complex; a new conversion mechanism is put forward in this article. The functions of pyrolysis and the interaction of active species containing plasma jets are the main factors for coal conversion under these conditions. This study indicates that when the coal feed rate is lower than 2.0 g/s, both pyrolysis and active species have evident contribution to coal conversion; the pyrolysis controls the coal conversion and the function of active species is very weak. It is also found that the coal feed rate has a large influence on coal conversion and the production of gas components. [ABSTRACT FROM AUTHOR]

Point of Ayr coal has been extracted using three solvents, tetralin, quinoline and 1-methyl-2-pyrrolidinone (NMP) at two temperatures 350 and 450 °C, corresponding approximately to before and after the onset of massive covalent bond scission by pyrolysis. The three solvents differ in solvent power and the ability to donate hydrogen atoms to stabilise free radicals produced by pyrolysis of the coal. The extracts were prepared in a flowing solvent reactor to minimise secondary thermal degradation of the primary extracts. Analysis of the pentane-insoluble fractions of the extracts was achieved by size exclusion chromatography, UV-fluorescence spectroscopy in NMP solvent and probe mass. With increasing extraction temperature, the ratio of the amount having big molecular weight to that having small molecular weight in tetralin extracts was increased; the tetralin extract yield increased from 12.8% to 75.9%; in quinoline, increasing extraction temperature didn''t have an effect on the molecular weight of products but there was a big increase in extract yield. The extracts in NMP showed the enhanced solvent extraction power at both temperatures, with a shift in the ratio of larger molecules to smaller molecules with increasing extraction temperature and with the highest conversion of Point of Ayr coal among these three solvents at both temperatures. Solvent adducts were detected in the tetralin and quinoline extracts by probe mass spectrometry; solvent products were formed from NMP at both temperatures. [Copyright &y& Elsevier]

Our results indicate that the gas atmosphere surrounding coal/char particles can greatly affect the formation of NH3 and HCN through its influence on the availability of H radicals. Based on our results, it is believed that the chemisorption of CO2 on the nascent char surface can consume H radicals or block the access of N-sites by H radicals for the formation of NH3 and HCN. For the chars whose thermal cracking generates little H radicals, the gasification of char by CO2 can also generate additional H radicals, enhancing the formation of NH3. However, even gasification of char in CO2 at 950 °C does not lead to the formation of HCN. The oxidation of coal with 4% O2 at low temperatures (400–600 °C) leads to the formation of HCN as well as NH3 due to the enhanced formation of (H) radicals. The gasification of coal with 15% H2O drastically enhances the formation of NH3 due to the greatly enhanced availability of H as an intermediate between the reactions of H2O and char. These results support our reaction mechanisms proposed previously, emphasising the importance of H on the formation of NH3 and HCN during pyrolysis, which can also be extended to the conversion of coal-N during gasification. [Copyright &y& Elsevier]

Abstract: The migration of sulfur resulting in the formation of CS, H2S and thiophene during benzenethiol pyrolysis has been investigated using the density functional theory method with PW91 functional and DND basis set. The lowest energy path is that H of the thiol group transfers to the ipso C and S radical is eliminated by beta scission reaction, and then the S radical combines with H radical formed during coal pyrolysis and eventually results in the formation of H2S. The formation of H2S via benzenthiol pyrolysis is easier than via thiophene by comparing with the kinetic data. [Copyright &y& Elsevier]

Abstract: The pyrolysis mechanism of thiophene in coal has been investigated with a density functional theory method. Three intramolecular hydrogen migration reaction paths leading to the formation of H2S were designed. It can be concluded that the favorable energy path by the kinetic analysis is that the α-H migrates to S firstly; then the β-H migrates to the α-C followed by a concerted C–S bond cleavage resulting in the cyclic structure of thiophene turning into a chain structure; finally H2S and butadiyne are formed via H migrating twice. In the favorable energy path, the rate determining step is the α-H migration to S, and the activation energy is about 351.63kJmol−1 at 298.15K. [Copyright &y& Elsevier]

Abstract: Vitrinite- and inertinite-rich samples separated from Shenfu-Dongsheng (SD) and Pingshuo (PS) coals were extracted with CS2 and the extraction solutions were analyzed with GC/MS. The results show that extract yields of the two maceral-rich samples (MRSs) from PS coal are much higher than those from SD coal; for MRSs from the same coal, the yield of vitrinite-rich sample is larger than that of inertinite-rich sample; there is no remarkable difference in chemical composition from the extraction solutions between the two MRSs separated from PS coal, whereas the difference between those separated from SF coal is significant. [Copyright &y& Elsevier]