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Calorific values of Greek lignites
Fuel 89 (2010) 3610
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Fuel journal homepage: www.elsevier.com/locate/fuel
Letter to the Editor Calorific values of Greek lignites
Ref. [1] is concerned with the use of lignite (brown coal) in the electricity industry in Greece. On reading it the following issues arose in my mind. We are told on page 477 that moisture contents of the lignites under review varied in the range 9–60%, the mean being 38%. Such moisture contents are described as appertaining to the ‘area of extraction’ so presumably these are values in the bed-moist state. Not only the spread is very surprising but also the suggestion that any lignite when bed-moist would have a moisture content below 10%. In Fig. 4 of Ref. [1] average calorific values over a 12 year period are shown to be in the approximate range 1150–1350 kcal kg 1. The mean of these values is 1250 kcal kg 1, equivalent to 5.25 MJ kg 1. Now in Victoria, Australia brown coal has been used to make electricity since 1924 and at this time such use is as extensive as it ever was, partly because of the failure of an ‘alternative’ means of power generation to come to fruition. These brown coals in the bed-moist state have moisture contents of about 65% and calorific values of 7–8 MJ kg 1, yet the Greek lignites under discussion in Ref. [1] with 38% moisture have calorific values in the neighbourhood of 5 MJ kg 1. The Greek and Victorian coals will of course differ in structure and composition but not to a degree which can explain these differences, and clarification is required. Thirty-five years ago NY Kirov [2] in promoting the fuel use of municipal waste gave calorific values for such waste in the range 7.6–10.5 MJ kg 1 and went onto state:
‘...in heating value such wastes are some 15–20% higher than that of Victorian brown coal which provides most of the electricity in the State.’ The middle of the range of calorific values he gives for municipal waste is 9.0 MJ kg 1, and to reduce that by 15% gives 7.7 MJ kg 1 which is totally consistent with the value for the brown coal given in the previous paragraph. Had Kirov based his argument on Greek lignite it would, according to [1], have been even more convincing! In order not to misrepresent the comparison quoted above it must be made clear that Kirov was not asserting superiority in every respect of municipal waste. It has many disadvantages including high ash yield, variation in composition and possible presence of harmful bacteria. References [1] Kaldellis JK, Zafirakis D, Kondili E. Contribution of lignite in the Greek electricity generation: review and future prospects. Fuel 2010;88:475–89. [2] Kirov NY. Principles of waste management: unit operations and processes UNSW, Sydney; 1975.
J.C. Jones School of Engineering, University of Aberdeen, AB24 3UE, United Kingdom Tel.: +44 1224 272793; fax: +44 1224 272497 E-mail address: [email protected] Available online 20 March 2010
0016-2361/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2010.03.023
Contents lists available at ScienceDirect
Fuel journal homepage: www.elsevier.com/locate/fuel
Letter to the Editor Calorific values of Greek lignites
Ref. [1] is concerned with the use of lignite (brown coal) in the electricity industry in Greece. On reading it the following issues arose in my mind. We are told on page 477 that moisture contents of the lignites under review varied in the range 9–60%, the mean being 38%. Such moisture contents are described as appertaining to the ‘area of extraction’ so presumably these are values in the bed-moist state. Not only the spread is very surprising but also the suggestion that any lignite when bed-moist would have a moisture content below 10%. In Fig. 4 of Ref. [1] average calorific values over a 12 year period are shown to be in the approximate range 1150–1350 kcal kg 1. The mean of these values is 1250 kcal kg 1, equivalent to 5.25 MJ kg 1. Now in Victoria, Australia brown coal has been used to make electricity since 1924 and at this time such use is as extensive as it ever was, partly because of the failure of an ‘alternative’ means of power generation to come to fruition. These brown coals in the bed-moist state have moisture contents of about 65% and calorific values of 7–8 MJ kg 1, yet the Greek lignites under discussion in Ref. [1] with 38% moisture have calorific values in the neighbourhood of 5 MJ kg 1. The Greek and Victorian coals will of course differ in structure and composition but not to a degree which can explain these differences, and clarification is required. Thirty-five years ago NY Kirov [2] in promoting the fuel use of municipal waste gave calorific values for such waste in the range 7.6–10.5 MJ kg 1 and went onto state:
‘...in heating value such wastes are some 15–20% higher than that of Victorian brown coal which provides most of the electricity in the State.’ The middle of the range of calorific values he gives for municipal waste is 9.0 MJ kg 1, and to reduce that by 15% gives 7.7 MJ kg 1 which is totally consistent with the value for the brown coal given in the previous paragraph. Had Kirov based his argument on Greek lignite it would, according to [1], have been even more convincing! In order not to misrepresent the comparison quoted above it must be made clear that Kirov was not asserting superiority in every respect of municipal waste. It has many disadvantages including high ash yield, variation in composition and possible presence of harmful bacteria. References [1] Kaldellis JK, Zafirakis D, Kondili E. Contribution of lignite in the Greek electricity generation: review and future prospects. Fuel 2010;88:475–89. [2] Kirov NY. Principles of waste management: unit operations and processes UNSW, Sydney; 1975.
J.C. Jones School of Engineering, University of Aberdeen, AB24 3UE, United Kingdom Tel.: +44 1224 272793; fax: +44 1224 272497 E-mail address: [email protected] Available online 20 March 2010
0016-2361/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2010.03.023