Expert Speak
GCV-based pricing: Some apprehensions J.P. Panda
G
rading of coal was conceived in India in the year 1917. It was, however, in the year 1944 that a systematic grading of coal was started after promulgation of the colliery control order. Ash content of low moisture coal and the ash plus moisture content of high moisture coals remains the basis of the present system of grading of non-
coking coals. It was in the year 1962 that a committee was set up by the government, which recommended a grading system based on gross calorific value as the parameter. This, however, was not implemented. In the same year, the government again constituted a study group to examine whether the ash plus moisture or the heat value would be a better measure for coal grading. The study group while considering the suitability of gross calorific value also viewed with concern the heat losses arising out of high ash content and evolved a concept of Useful Heat Value (UHV). The UHV was obtained by subtracting ‘ash penalty’ from gross calorific value. The gross calorific value (GCV) was obtained by using Central Fuel Research I nstitute (CFRI) formulae, namely; For low moisture coal: 1.8Q = 165F + 136 ( V- 0.1A ) – 108 M; and For high moisture coal: 1.8Q = 154 [100 – ( 1.1A + M ) ]-108M; where, Q = Heat value Kilo Calories per Kilogram; F = Fixed carbon%; V = Volatile Matter%; A = Ash%; M = Equilibrated Moisture % at 60% relative humidity and temperature 40 degrees Centigrade for high moisture coal and “ analysed basis” for low moisture coal. This system of UHV was approved by the erstwhile tariff commission, Government of India in the year 1966-67 but was adopted only in the year1975 for grading and pricing. In the year 1976, CFRI put forward a formula for UHV, which avoided the need to calculate GCV by an empirical formula by deducting Ash + Moisture penalty. UHV (K Cal/Kg) = 8900 - 138 (A+M), where A & M represent the equilibrated ash and moisture percentage of coal. This formula was applicable to high moisture coal only. However a modified formula was given by CFRI for low moisture and low volatile coal which is as follows: UHV (K Cal/Kg) = 8900 – 138(A+M) – 150(19 – VM) where A, M, VM are percentages of ash, moisture and volatile matter respectively.
Based on the above two UHV formulae adopted by the government, Grades A to G were specified in the UHV span of 6200 to 1300 Kilo Cal/Kg. Currently the UHV system is still in vogue in this country for both pricing and grading. UHV introduction In the sixties most of the boilers of the thermal power houses were designed for low ash coal and were imported and, had fixed bed and moving grate stokers. Use of high ash Indian coal in these boilers resulted in loss of sensible heat in the ash as well as loss due to unburnt carbon lost along with the ash. The other probable reason for introduction of UHV concept was probably the incentive provided to the consumers using high ash coal and low cost of oil at that time. Drawbacks In the UHV concept, the variation in each grade slab is between 600 to 1100 K Cal/Kg. For example the variation between upper and lower limit of grade B is 600 K cal/Kg and it increases to 1100 K cal/Kg between the upper and lower limit of grade G. Most of the grade declarations conform to the lower limit only, and if by chance at some places it conforms to the higher limit, there is a tendency on the part of the producer to blend it with lower grades to bring it to the lower limit. Therefore by and large there is dissatisfaction amongst the coal consumers. These wide variations between the upper and lower limits in a particular grade does not provide any incentive to the producer to improve the quality by any means of coal beneficiation methods as the grade does not improve. The UHV currently in use is a notional formula arrived from the statistical average of coal samples in the sixties and at present does not represent the actual utilisation of heat in the coal. It is not an accepted global concept. All over the world coal is transacted only in GCV.The ash penalty benefits to consumer were relevant to the combustion technologies in use in the 60’s. With the improvement in the boiler efficiency now with newly designed boilers capable of burning high ash coal efficiently, the ash penalty bonus is no longer relevant as compared to the earlier decades. Low moisture coals having less than 35 percent ash are mature and high ranking coals but due to the penalty for low volatile content in the UHV concept, its heat value is reduced considerably against the more realistic value of the GCV. This results in loss to the producers of low ash and low volatile coal even though the heat value is much more.The present combustion technology of the boilers for utilising high ash coal with high efficiency has no place to still rely on the UHV which included an ash penalty for loss of sensible heat in the ash and poor combustion of o the older type boilers.
COAL INSIGHTS 54 January 2012