外文翻譯--維多利亞褐煤的熱解過程中堿金屬和堿土金屬的作用（原文）

1、Fates and roles of alkali and alkaline earth metals during the pyrolysis of a Victorian brown coalC.-Z. Li*, C. Sathe, J.R. Kershaw, Y. PangCRC for New Technologies for Power Generation from Low-Rank Coal, Department of

2、Chemical Engineering, Monash University, Clayton, Victoria 3168, AustraliaAbstractH-, Na- and Ca-form coal samples were prepared from a sample of Loy Yang brown coal and pyrolysed in a wire-mesh reactor. The tars were ch

3、aracterised with UV-absorption and UV-fluorescence spectroscopies. Increases in heating rate (1 to 2000 K s?1) and temperature (up to 700?C) were found to facilitate the release of larger (“equivalently” larger than naph

4、thalene) aromatic ring systems from coal during pyrolysis. The presence of alkali and alkaline earth metallic (AAEM) species in the coal samples greatly hindered the release of the larger aromatic ring systems during pyr

5、olysis. The AAEM species also reduced the effects of heating rate on the release on aromatic ring systems at lower temperatures. However, the hindering effect was not proportional to the contents of AAEM species in the c

6、oal. In addition, the ion- exchange processes caused irreversible changes to coal structure. Significant proportions of the AAEM species in the coal samples were volatilised during pyrolysis even at temperatures as low a

7、s 300?C. The volatilisation of AAEM species was not sensitive to changes in heating rate but was intensified with increasing temperature. The monovalent species (Na) was always volatilised to a much larger extent that th

8、e divalent species (Mg and Ca) under similar pyrolysis conditions. At high temperatures (900–1200?C), the drastic volatilisation of Na (up to 80%) and of Ca (up to 40%) was accompanied by the increases in tar yield durin

9、g the pyrolysis of the Na-form and Ca-form samples. The fates and roles of the AAEM species during pyrolysis are thought to be related to their transformation during pyrolysis. The AAEM species might have been involved i

10、n a repeated bond-forming and bond-breaking process between the AAEM species and the coal/char matrix. During this process, tar precursors were repeatedly linked to the coal/char matrix and were thermally cracked. Some o

11、f the more aliphatic components and/or smaller aromatic ring systems in a tar precursor were cracked to gas and some of the larger aromatic ring systems were charred. ? 2000 Elsevier Science Ltd. All rights reserved.Keyw

12、ords: Brown coal; Pyrolysis; UV-absorption spectroscopy; UV-fluorescence spectroscopy; Ion-exchangeable cations; Alkali and alkaline earth metals in coal; Aromatic ring systems1. IntroductionOne of the most prominent fea

13、tures of the Victorian brown coals is the presence of significant amounts of alkali and alkaline earth metals (AAEM) associated with the carboxylic and phenolic functionalities in the coal structure [1–3]. These AAEM met

14、allic cations in the brown coals can be removed by washing with acid. Individual cations (e.g. Na? or Ca2?) can then be ion-exchanged onto the coal structure [4]. Although the AAEM species generally account for less than

15、 1% of the raw coal, they play very important roles in the utilisation of the brown coals [3–5]. For example, they are largely responsible for the particular fouling/slagging problems encountered during the pulverised-fu

16、el combustion of the brown coals [3]. When the brown coals are used in the future to generate electricitywith advanced technologies such as advanced pressurised fluidised-bed combustion (APFBC), the roles of the AAEM spe

17、cies are two-fold. The volatilisation of the AAEM species, either during pyrolysis or during gasification/ combustion, will probably cause severe problems for the operation of gas turbines due to the corrosion/erosion of

18、 the turbine blades. On the other hand, if these metallic species are retained in the char after pyrolysis, they can act as good catalysts for the subsequent gasification/ combustion of the char. Therefore, the future su

19、ccess of the potentially highly efficient and environmentally friendly technologies such as APFBC will to a large extent depend on our understanding on the fates and roles of these AAEM species under the conditions perti

20、nent to those in the APFBC process. A large number of researchers have examined the roles of these AAEM metallic species and experimental conditions on the yields of light hydrocarbons [1,6–11] oxygen- containing species

21、 [8,10–14], char [6,7,10,11,14,15] andFuel 79 (2000) 427–4380016-2361/00/$ - see front matter ? 2000 Elsevier Science Ltd. All rights reserved. PII: S0016-2361(99)00178-7www.elsevier.com/locate/fuel* Corresponding author

22、. Tel.: ?61-3-9905-9623; fax: ?61-3-9905-5686. E-mail address: lic@itsengl.eng.monash.edu.au (C.-Z. Li).the air that would take place if a dry coal sample was used. The weighing of the char sample after pyrolysis was als

23、o carried out after the char sample was considered to have reached equilibrium with ambient air. The moisture contents of the coal and the char were considered in the calculation of pyrolysis yields. At the end of a pyro

24、lysis experiment, tar was recovered by washing the tar trap with HPLC grade CHCl3:CH3OH (80:20) [32–34]. Tar yield was then determined [29] through quantifying concen- tration of tar in the solution.2.3. Characterisation

25、 of tarUV-fluorescence spectra were recorded with a Perkin– Elmer LS50B luminescence spectrometer. The tar solution obtained by washing the tar trap (see above) was diluted with SpectrosoL grade CH3OH (BDH) to a concentr

26、ation of the order of magnitude of 10?6 g ml?1 where the effects of self-absorption were minimal. A visible cell of 1 cm light pathlength was used. Slit widths for both excitation and emission monochromators were 3.0 nm.

27、 Spectra were recorded using a scan speed of 200 nm min?1. The instru- ment features the automatic correction of source intensity variation. The emission intensity was not further corrected. Spectra in Figs. 1–5 and thos

28、e in Figs. 7 and 8 were recorded on different occasions using different detectors. Thus, these spectra may not be compared directly. UV- absorption spectra were recorded with a GBC 918 double beam UV/VIS spectrometer. UV

29、–Visible cells of 20 mm light pathlength were used. Both the fluorescence intensity and absorbance signals were multiplied by a factorin order to facilitate comparison of the signals of different tars on the basis of “pe

30、r g of substrate coal”.2.4. Quantification of AAEM species in coal/char samplesLess than 4 mg of coal/char sample was ashed in O2 in a thermogravimetric analyser–differential thermal analyser (TGA–DTA). Care was taken to

31、 control the conditions in the TGA to ensure that particles were not ignited and that all organic matters were fully oxidised. The final ashing temperature was 600?C with 30 min holding time. At the end of a TGA ashing e

32、xperiment, the ash sample together with the Pt crucible was placed in a Teflon vial for acid digestion with a hot mixture of HNO3:HF (1:1) solution for at least 16 h. HNO3 and HF were then evaporated on a hot plate and t

33、he residue was re-dissolved in 20 mM CH3SO3H. Quantification of Na, K, Mg and Ca was carried out using a Dionex DX 500 ion chromatograph with a suppressed conductivity detection system. Separation was carried out on a Di

34、onex CS12 column using 20 mM CH3SO3H aqueous solution as eluent.Retention of an AAEM species in char was calculated by comparing the content of the AAEM species in the char with that in the raw substrate coal sample, con

35、- sidering the weight loss of the coal sample during pyrolysis.3. Results and discussion3.1. Effects of temperature, heating rate and AAEM species on the release of aromatic ring systems during pyrolysis at lower tempera

36、turesA fuller account of the tar and total volatile yields from the pyrolysis of raw, H-form-1, Na-form, Ca-form, H-form- 2 and H-form-3 Loy Yang coal samples at temperatures up to 900 or 1000?C has been given elsewhere

37、[29]. For the raw coal and H-form coal samples, the increases in heating rate resulted in large increases in tar yield while the correspond- ing increases in total volatile yield, if any, were small [29]. The presence of

38、 AAEM cations in coal tended to reduce the tar (and to a lesser extent the total volatile) yields, and, more importantly, reduced the heating rate sensitivity of the tar yield [29]. As was discussed elsewhere [29], the l

39、oss of the humic materials might have caused the widening of pores due to the extraction of the humic materials originally present in the pores. It was also possible that some humic materials, extracted out of the pores

40、but not lost during filtration, might also have blocked some pores at the exter- nal particle surface when the samples were dried. However, more importantly, the ion-exchange processes, particularlywith divalent ions (e.

41、g. Ca??), might have caused changes to the coal macromolecular network [25,29] due to the ionic forces. The same sets of tar samples have been characterised with UV-absorption and UV-fluorescence spectroscopies in this s

42、tudy. Fig. 1 shows the synchronous spectra of the tars produced from the pyrolysis of the Loy Yang raw coal with a heating rate of 100 K s?1. A constant energy differ- ence of ?2800 cm?1 between the emission and excitati

43、on monochromators was used in recording these spectra. Simi- lar trends were also observed when a constant energy differ- ence of ?1400 cm?1 was used. In agreement with the previous UV-fluorescence spectroscopic study [3

44、5] on a set of tars from the pyrolysis of a set of rank-ordered coals in a wire-mesh reactor, the synchronous spectra in Fig. 1 show two broad peaks centred around 340 and 380 nm respectively. The tars from the pyrolysis

45、 of the same raw coal are seen to become progressively more fluor- escent (Fig. 1a) with increasing temperature, although the shapes of the spectra do not seem to change very much. The fluorescence intensities expressed