5/3/2015New Challenges for Indian Coals1 A n Experience of Third Party Sampling of Coal A. Choudhury, Kalyan Sen C.F.R.I, Dhanbad (India)

5/3/2015New Challenges for Indian Coals2 Quality Monitoring (QM) of Coal is an essential requirement for process control, plant performance or for any commercial transaction between Consumer and Producer QM requires proper implementation of standard sampling, preparation and test procedures

5/3/2015New Challenges for Indian Coals3 Sampling methods depend on < mechanical or manual sampling < sampling from moving belt < sampling from stationary lot (wagon, stockpile, etc.)

5/3/2015New Challenges for Indian Coals4 Nos of increments of sample is to be optimized in such a manner that whole volume of the lot is repesented, thus minimising the variance About 80% of the error comes from collection of samples because

5/3/2015New Challenges for Indian Coals5 Sampling variance is a function of product variability i.e. different results can be obtained from u same increments for different coal u different increments for same coal

5/3/2015New Challenges for Indian Coals6 The objective is to reduce the sampling variance as far as practicable

5/3/2015New Challenges for Indian Coals7 Any Sampling scheme normally conforms with the national or international standards (BIS/ISO/ASTM, etc.) Constraint - technical, cost and time Thus modifications in sampling procedures are necessary with mutual agreement between parties

5/3/2015New Challenges for Indian Coals8 Precision u measures the closeness of data in given condition u indicates the reproducibility of the results u measures the chance error as expressed by variance SMALLER THE RANDOM ERROR, PRECISE IS THE METHOD A commonly accepted index of precision is twice the population standard deviation

5/3/2015New Challenges for Indian Coals9 Precision depends on u Variability of coal u number of samples from a lot u number of increments comprising each sample u mass of sample related to the nominal top size

5/3/2015New Challenges for Indian Coals10 Bias Systematic error which leads to the average value of a series of results being persistently higher or lower than those which are obtained using a reference sampling method which is intrinsically unbiased

5/3/2015New Challenges for Indian Coals11 Reference method of sampling is ‘Stop Belt Method’ (free of Bias) (free of Bias)

5/3/2015New Challenges for Indian Coals12 General principle of Sampling u Primary increments should account for the Variability u Equal probability to all particles to be selected and included in the sample u Largest particle of the lot should pass freely through the sample device u Sufficient mass of the sample to enable particles to be present in the same ratio as in the lot

5/3/2015New Challenges for Indian Coals13 General Scheme for Sampling

5/3/2015New Challenges for Indian Coals14 General scheme for sampling... u Decide purpose of sampling e.g. plant performance, process control, commercial transaction u Identify the quality parameters, viz., general analysis, TM, size, washability, etc. u Define the lot u Define the precision required u Decide whether continuous or intermittent sampling is required

5/3/2015New Challenges for Indian Coals15 u Determine the number of sub-lots, increments to achieve the required precision. u Determine the nominal top size of the coal u Determine the min. mass/ increment and the min. mass of the total sample u Decide on the method of combining the different increments for gross sample u Decide on drawing common or separate samples, for analysis General scheme for sampling.. contd..

5/3/2015New Challenges for Indian Coals16 Design of sampling scheme u Division of lots u Basis of sampling u Time basis u Mass basis  Precision

5/3/2015New Challenges for Indian Coals17 SAMPLING FOR COMMERCIAL TRANSACTION Joint Sampling Joint Sampling Washed coking coal Washed coking coal Power coal Power coal

5/3/2015New Challenges for Indian Coals18 Joint sampling u at loading point - by customer and producer on mutually agreed methods u at both ends - mean value u bonus/penalty to producer for values beyond agreed tolerance limits u requires periodic testing... Unfortunately rarely practiced in India

5/3/2015New Challenges for Indian Coals19 Reasons for discrepancies in results u level of precision not defined u Non-identical procedures for sampling at both ends u manual sampling results in large human error u deviation in procedures from agreed one

5/3/2015New Challenges for Indian Coals20 Primary requirements for development of a methodology u testing for estimation of the variances, V i and V pt u decision on level of precision of the ash value u calculation for no. of sub-lot and increment /sublot at desired precision from known values of variances u estimation of precision for the existing procedure u estimation of min. mass/ sub-lot form the std. Table u estimation of min. mass/ increment

5/3/2015New Challenges for Indian Coals21 SAMPLING SCHEME is designed based on the above test The procedure can significantly reduce the discrepancies in the results at both ends

5/3/2015New Challenges for Indian Coals22 Sampling of washed coking coal Samples are drawn from the u Automatic mechanical Sampler (AMS) u Conveyor Belt For day to day quality monitoring, samples are reduced by offline and/or manual means to analyze ASH & TOTAL MOISTURE

5/3/2015New Challenges for Indian Coals23 Sampling of Power Coal Best option: AMS at loading/ unloading point AMS for coal x200mm or above is not a proper choice to ascertain quality parameter Suggestion: sampling on crushed coal below 50mm or preferably at 20mm

5/3/2015New Challenges for Indian Coals24 Where AMS is non-existing/ non-functioning, sampling may be done for the time being, at loading point from the wagon by manual means Wagon top sampling is difficult, because segregation occurs because of large size segregation occurs because of large size impractical to collect sample from the full depth impractical to collect sample from the full depth introduces bias due to manual operation introduces bias due to manual operation Suggestion: smaller size (< 50mm) of the sample

5/3/2015New Challenges for Indian Coals25 Conclusion: Choice of Sampling methodology depending on the purpose Choice of Sampling methodology depending on the purpose Efforts to reduce the sampling variance to a min. possible limit Efforts to reduce the sampling variance to a min. possible limit Sampling on mechanically crushed coal below 50mm Sampling on mechanically crushed coal below 50mm Preferable size is 20mm ( feed to most power plants) Preferable size is 20mm ( feed to most power plants)

5/3/2015New Challenges for Indian Coals26 Replacement of manual sampling method by AMSReplacement of manual sampling method by AMS In absence of AMS, manual wagon top sampling of this size would give better resultsIn absence of AMS, manual wagon top sampling of this size would give better results In absence of AMS, manual sampling from wagon top can be done as an temporary option, following the prescribed methodology In absence of AMS, manual sampling from wagon top can be done as an temporary option, following the prescribed methodology Conclusion…………contd.

5/3/2015New Challenges for Indian Coals27 THANKS