Sulphur transformation during pyrolysis of an Australian lignite

Abstract

Sulphur Transformation during Pyrolysis of an Australian Lignite v moisture, very high ash, low fixed carbon and thus they have low calorific value, except for L1. The lignites contain considerable amount of total sulphur, except for L1. Mineralogy of the lignites showed that the lignites contain extremely high sodium and chlorine. FTIR and solid state 13 C NMR spectroscopy confirmed that oxygenated functional structures are significantly present in the lignites. Transformation of pyrite in the lignite during pyrolysis was studied using samples of a lignite with pyrite-free lignite (L1), a high pyrite lignite (L2), acid-washed lignites (AW L1 and AW L2), a pyrite mineral, and AW L1 blended with various amounts of the pyrite minerals. It was shown that in nitrogen the pyrite mineral (S/Fe = 2) decomposes to troilite (S/Fe =1) at ca 1200K and above this temperature, the troilite further decomposes to form elemental iron (S/Fe <1). However, when blended with the demineralised lignite, the pyrite mineral can be completely decomposed to troilite at 873 K as confirmed by FTIR, SEM-EDS and XRD analyses on the resulting chars. Using TGA-MS, it was revealed that hydrogen sulphide and a small quantity of sulphur dioxide were released during the pyrolysis of the pyrite-lignite blends. However, only sulphur dioxide was detected during the pyrolysis of the lignite with high pyrite content. By assuming that the pyrolysis follows the first-order reactions, kinetic parameters of the pyrolysis of the lignite samples and the pyrite-lignite blends were obtained. The activation energy values of the lignite samples decreased with increasing temperature. The transformation of sulphate during pyrolysis of the lignite was studied using pure sulphates (CaSO 4, FeSO 4 and Fe 2 (SO 4) 3), L1 and L4, and acid washed L1 doped with sulphates (CaSO 4 +L1 and FeSO 4 +L1), respectively. The TGA experiments showed that CaSO 4 decomposes between 1400-1700 K in nitrogen and a 50/50 N 2 /CO 2 mixture, while in air CaSO 4 decomposes between 1500-1700 K. Using a TGA-MS it was found that only a small fraction of CaSO 4 in CaSO 4 +L1 decomposed at 653 K, releasing SO 2 .

Nitrogen and sulfur conversion during pressurized pyrolysis under CO 2 atmosphere in fluidized bed

“…Sulfur-containing functional groups in coal decompose and release during pyrolysis process, and at the same time the interactions between pyrite, sulfate and organic sulfur also affect the distribution and speciation of sulfur in the final products. Zhang et al [42] proposed a schematic of the sulfur conversion mechanisms during coal pyrolysis, as shown in Fig. 10, to illustrate the complex series of reactions.…”

Following the structure and reactivity of Tuncbilek lignite during pyrolysis and hydrogenation

“…6. Pyrolysis is accepted to be an important desulfurization step [22,[70][71][72], with the major desulfurization reaction being pyrite-organic coal matrix interactions resulting in hydrogen sulfide evolution. Pyrite may also be converted to SO 2 when the oxygen content of coal is high.…”

“…Inorganic compounds, including Na and dolomite, do not improve either organic or inorganic sulfur removal. On the other hand, they prevent sulfur decomposition [71,72].…”

Pyrolysis of Low-Rank Coal: From Research to Practice

“…As to element constitutes of organic matters, LRC has relatively high hydrogen and oxygen content. Table 2 lists the results of proximate and ultimate analysis of some typical LRC [2][3][4][5].…”