BRITISH STANDARD BS 1016-106.4.1: 1993

Methods for

Analysis and testing of coal and coke —

Part 106: Ultimate analysis of coal and coke —

Section 106.4 Determination of total sulfur content —

Subsection 106.4.1 Eschka method

BS 1016-106.4.1:1993

This British Standard, having been prepared under thedirection of the Solid Mineral Fuels Standards Policy Committee, was publishedunder the authority of the Standards Board and comesinto effect on15 May 1993

© BSI 06-1999

The following BSI references relate to the work on this standard:Committee reference SFC/3Draft for comment 91/54102 DC

ISBN 0 580 21715 9

Committees responsible for this British Standard

The preparation of this British Standard was entrusted by the Solid Mineral Fuels Standards Policy Committee (SFC/-) to Technical Committee SFC/3, upon which the following bodies were represented:

British Cement AssociationBritish Coal CorporationBritish Gas plcBritish Steel IndustryElectricity Industry in United KingdomGAMBICA (BEAMA Ltd.)Power Generation Contractors’ Association (BEAMA Ltd.)

Amendments issued since publication

Amd. No. Date Comments

BS 1016-106.4.1:1993

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Contents

PageCommittees responsible Inside front coverForeword iiIntroduction 1

1 Scope 12 References 13 Principle 14 Reagents 15 Apparatus 16 Preparation of test sample 17 Procedure 28 Expression of results 39 Precision 3

10 Test report 4Annex A (informative) Derivation of factors used in the expression of results 5Table 1 — Test portion for coal 2Table A.1 — Relative atomic masses 5List of references Inside back cover

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Foreword

This Subsection of BS 1016 has been prepared under the direction of the Solid Mineral Fuels Standards Policy Committee. Part 106 will form a revision of Part 6 to Part 11 of BS 1016. This Subsection supersedes 8.2 in bothBS 1016-6:1977 and BS 1016-7:1977 which are to be deleted by amendment, from which the principle changes are as follows.

a) When charging the crucible, some of the 4 g of Eschka mixture is now used to form a bottom layer in the crucible.b) A further alternative means, using a Gooch crucible, of filtering the solution after precipitation of the barium sulfate has been added.

Part 106 is a further Part numbered under a scheme for rationalizing and restructuring BS 1016. The new series, when complete, will begin with Part 100, which will include a general introduction. The current Parts are as follows, with the new Part numbers (which will be given to revisions when they are published) in parentheses.

— Part 1: Total moisture of coal (Part 101);— Part 2: Total moisture of coke (Part 102);— Part 6: Ultimate analysis of coal (Part 106);— Part 7: Ultimate analysis of coke (Part 106);— Part 8: Chlorine in coal and coke (Part 106);— Part 9: Phosphorus in coal and coke (Part 106);— Part 10: Arsenic in coal and coke (Part 106);— Part 11: Forms of sulphur in coal (Part 106);— Part 14: Analysis of coal ash and coke ash (Part 114);— Part 15: Fusibility of coal ash and coke ash (Part 113);— Part 16: Methods of reporting results (Part 100);— Part 17: Size analysis of coal (Part 109);— Part 18: Size analysis of coke (Part 110);— Part 20: Determination of Hardgrove grindability index of hard coal (Part 112);— Part 21: Determination of moisture-holding capacity of hard coal (Part 103).

The following Parts in the new series have been published.— Part 104: Proximate analysis;— Part 105: Determination of gross calorific value;— Part 107: Caking and swelling properties of coal;— Part 108: Tests special to coke;— Part 111: Determination of abrasion index of coal.

Part 106 will be divided into a number of Sections and Subsections, including the following.

— Section 106.1: Determination of carbon and hydrogen content;— Section 106.2: Determination of nitrogen content;— Section 106.3: Determination of oxygen content;— Section 106.4: Determination of total sulfur content;— Subsection 106.4.1: Eschka method;— Subsection 106.4.2: High temperature combustion method;— Section 106.5: Determination of forms of sulfur;— Section 106.6: Determination of chlorine content;— Subsection 106.6.1: Eschka method;— Subsection 106.6.2: High temperature combustion method;

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— Section 106.7: Determination of carbon dioxide content;— Section 106.8: Determination of phosphorus content;— Section 106.9: Determination of arsenic content.

This Subsection is based on ISO 334:1992, published by the International Organization for Standardization (ISO). It is technically equivalent except for the following changes.

a) References to the application of the method to brown coals and lignites have been removed from the main text.NOTE The method as described for hard coal may also be applied to brown coals and lignites but in such cases the test sample (see clause 6) should be prepared in accordance withISO 5069-2 and, if required, its moisture content should be determined in accordance with ISO 1015 or ISO 5068.

b) References to British Standards, which are not exactly technically equivalent to the international standards referred to in ISO 334, have been substituted.

WARNING. This British Standard does not necessarily detail all the precautions necessary to comply with the requirements of the Health and Safety at Work etc. Act 1974 [1] or the Control of Substances Hazardous to Health Regulations 1988 [2]. Attention should be paid to any appropriate precautions and the method should be operated only by trained personnel.A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application.

Compliance with a British Standard does not of itself confer immunity from legal obligations.

Summary of pagesThis document comprises a front cover, an inside front cover, pages i to iv, pages 1 to 6, an inside back cover and a back cover.This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.

iv blank

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IntroductionAn alternative reference method to that specified in this Subsection of BS 1016 is given in 8.3 of BS 1016-6:1977 and 8.3 of BS 1016-7:1977.Instrumental methods for a more rapid determination of total sulfur are now available. If such a method is to be used, it is important to demonstrate that the method is free from bias, when compared to this reference method, and will give levels of repeatability and reproducibility which are the same as, or better than, those quoted for the reference method (see clause 9).

1 ScopeThis Subsection of BS 1016 specifies a reference method for determining the total sulfur content of hard coal and coke by the Eschka method.

2 References2.1 Normative referencesThis British Standard incorporates, by reference, provisions from specific editions of other publications. These normative references are cited at the appropriate points in the text and the publications are listed on the inside back cover. Subsequent amendments to, or revisions of, any of these publications apply to this British Standard only when incorporated in it by updating or revision.2.2 Informative referencesThis British Standard refers to other publications that provide information or guidance. Editions of these publications current at the time of issue of this standard are listed on the inside back cover, but reference should be made to the latest editions.

3 PrincipleA test portion is ignited in intimate contact with Eschka mixture in an oxidizing atmosphere, to remove combustible matter and to convert the sulfur to sulfate. This is then extracted with hydrochloric acid solution and determined gravimetrically by precipitation with barium chloride.

4 ReagentsWARNING. Care should be exercised when handling the reagents, many of which are toxic and corrosive.NOTE During the analysis, unless otherwise stated, use only reagents of recognized analytical grade and only distilled water or water of equivalent purity.

4.1 Eschka mixture. Mix two parts by mass of light, calcined magnesium oxide with one part by mass of anhydrous sodium (or potassium) carbonate. The mixture shall entirely pass a test sieve of 212 4m nominal size of openings.4.2 Hydrochloric acid, concentrated, Ô approximately 1.18 g/ml,approximately 36 % (m/m).4.3 Potassium sulfate, solution. Weigh, to the nearest 0.1 mg, about 2 g of potassium sulfate, previously dried at a temperature of 105 °C to 110 °C. Dissolve in water and dilute to 1 l.4.4 Barium chloride, approximately 85 g/l solution. Dissolve 100 g of barium chloride dihydrate in water and dilute to 1 l. Filter before use through aclose-textured, doubly acid-washed filter-paper of filter-paper pad.4.5 Methyl red, indicator solution. Dissolve 1 gof 2-(4-dimethylaminophenylazo)benzoic acid, sodium salt (methyl red) in 1 l of water.4.6 Ammonia, concentrated solution, not less than 25 % (m/m).4.7 Silver nitrate, 17 g/l solution. Dissolve 17 g of silver nitrate in water and dilute to 1 l. Store in a dark glass bottle.

5 Apparatus5.1 Analytical balance, capable of weighing to the nearest 0.1 mg.5.2 Graduated glassware, conforming to the requirements for class A in the appropriate British Standards.5.3 Electrically heated muffle furnace, capable of being maintained at a temperature of 800 °C ± 25 °C. The ventilation through the muffle furnace shall be such as to give about 5 air changes per minute.5.4 Crucible, of platinum, silica or glazed porcelain, of capacity approximately 25 ml.5.5 Flat plate, 6 mm thick, of silica (or other suitable refractory material), which fits easily into the muffle furnace (5.3).5.6 Gooch crucible, of glazed porcelain or sintered glass.5.7 Air oven, capable of being maintained at a temperature of 130 °C ± 10 °C.

6 Preparation of test sampleThe test sample is the general analysis test sample prepared in accordance with BS 1017-1:1989 or BS 1017-2:1960, as appropriate. Expose the sample, in a thin layer, for the minimim time required for the moisture content to reach approximate equilibrium with the laboratory atmosphere.

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Before commencing the determination, thoroughly mix the test sample for at least 1 min, preferably by mechanical means.If the results are to be calculated other than on an “air-dried” basis (see clause 8), then, after weighing the test portion (see 7.1), determine the moisture content using a further portion of the test sample by the method described in BS 1016-104.1:1991 or BS 1016-104.2:1991, as appropriate.

7 Procedure7.1 Test portion

7.1.1 For coal

Take a test portion of the mass given in Table 1 (for the expected total sulfur content), weighing to the nearest 0.1 mg.

Table 1 — Test portion for coal

7.1.2 For coke

Take a test portion of 1 g, weighing to the nearest 0.1 mg.

7.2 Charging the crucible

Cover the bottom of the crucible (5.4) uniformly with 0.5 g of the Eschka mixture (4.1), weighed to the nearest 0.1 mg. Mix the test portion intimately with 2.5 g of the Eschka mixture, weighed to the nearest 0.1 mg, in a suitable vessel. Transfer the mixture to the 25 ml crucible. Level the contents by tapping the crucible gently on the bench and cover the contents uniformly with 1.0 g of the Eschka mixture, weighed to the nearest 0.1 mg.NOTE The entire 4 g of the Eschka mixture should be weighed out and the 0.5 g and 1 g portions, required for the bottom and top layers, should be extracted from this. For this purpose, it is convenient to calibrate a small glass tube for each batch of Eschka mixture, to deliver 0.5 g and 1 g without weighing. The bottom layer of Eschka mixture below the test portion mixture reduces attack on the porcelain surface, so that the extraction of sulfate with hot water is complete even when the surface deteriorates.

7.3 Ignition

7.3.1 For coal

Place the charged crucible (and any others up to the limit of the muffle furnace capacity) in the cold muffle furnace (5.3) and raise the temperature to 800 °C ± 25 °C in about 1 h, maintaining this temperature for at least a further 1.5 h. Withdrawn the crucible (or crucibles) and allow to cool.

NOTE The cracking of porcelain crucibles can be prevented, if they are slowly cooled by insertion in supports of light porous firebrick on removal from the muffle furnace.

7.3.2 For coke

Place the charged crucible (or crucibles) on the cold insulating plate (5.5) and insert into the muffle furnace (5.3) at a temperature of 800 °C ± 25 °C, maintaining this temperature for at least a further 1.5 h. Withdraw the crucible (or crucibles) and allow to cool (see note to 7.3.1).

7.4 Recovering the residue

Transfer the ignited mixture from the crucible to a 400 ml beaker containing 25 ml to 30 ml of water. If unburnt particles are present, the determination shall be stopped and the test repeated. Wash the crucible thoroughly with about 50 ml of hot water, and add the washings to the contents of the beaker.

7.5 Extraction

Place a watch-glass on the beaker and then, while tilting the watch-glass, carefully add enough hydrochloric acid (4.2) to dissolve the solid matter (17 ml will normally be required), warming the contents of the beaker to effect solution. Boil for 5 min to expel carbon dioxide and filter, collecting the filtrate in a 400 ml conical beaker.NOTE A medium-textured, doubly acid-washed filter-paper or a filter-paper pad is recommended for speed of filtration.To prepare the filter-paper pad, shake doubly acid-washedfilter-paper clippings, in pieces with areas of approximately 1 cm2, with water in a bottle until the paper is thoroughly disintegrated. Place a porcelain filter cone of 25 mm diameter in a 75 mm funnel, close the stem of the funnel with a finger and add water until the cone is immersed and the funnel stem is full. Shake, onto the cone, sufficient paper pulp to form a pad 5 mm thick, and level it with a fiat-ended glass rod. Allow the excess water to drain away by removing the finger from the stem and as drainage ceases, lightly tamp the pad round the edges with the glass rod. A final wash with water renders the filter ready for use.

Wash the filter with five 20 ml portions of hot water.Add 2 or 3 drops of the methyl red indicator solution (4.5) to the combined filtrate and washings, and then cautiously add the ammonia solution (4.6) until the colour of the indicator changes and a trace of precipitate is formed. Add enough hydrochloric acid (4.2) to just redissolve the precipitate and then add 1 ml in excess.

Expected total sulfur content

Mass of test portion

% (m/m) g

< 5 1.05 to 10 0.5> 10 0.25

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7.6 Precipitation of barium sulfate

After extraction, dilute the solution, if necessary, to approximately 200 ml and cover the beaker containing the solution with a watch-glass. Heat the covered beaker until the solution boils and then reduce the heating slightly until ebullition of the solution ceases. Then add 10 ml of the cold barium chloride solution (4.4) from a pipette with a delivery time of approximately 20 s, so that the barium chloride solution falls into the centre of the hot solution, while it is being agitated. Keep the solution just below boiling point for 30 min.Filter the solution using one of the following techniques.

a) By gravity through an ashless, close-textured, doubly acid-washed filter-paper of diameter 100 mm to 125 mm. Carefully fold thefilter-paper and fit it into a fluted,long-stemmed 60° funnel, so that the stem remains full of liquid during the filtration.b) By gravity through a filter-paper pad prepared from ashless, doubly acid-washedfilter-paper (see note to 7.5).c) By suction through a pad of filtration mineral fibre in a Gooch crucible (5.6). Before commencing the filtration, dry the Gooch crucible and pad for 1 h at a temperature of 130 °C ± 10 °C and weigh, to the nearest 0.1 mg.

Wash the precipitate with hot water, using not more than 250 ml, until the last 20 ml of the washings give not more than a faint opalescence with the silver nitrate solution (4.7).If technique a) or b) is used, place the wetfilter-paper or pad in the previously ignited and weighed crucible (5.4) on the cold flat plate (5.5).If technique b) is used, after transferring thefilter-paper pad to the crucible, wipe the funnel successively with two halves of an ashlessfilter-paper and place this paper in the crucible with the pad. Insert the crucible slowly into the muffle furnace (5.3), at a temperature of 800 °C ± 25 °C, and then heat for 15 min. Cool in a desiccator and reweigh, to the nearest 0.1 mg.If technique c) is used, dry the Gooch crucible (5.6) and pad for 1 h at a temperature of 130 °C ± 10 °C, cool in a desiccator and reweigh, to the nearest 0.1 mg.

7.7 Blank test

Carry out a blank test using the same procedure as for the determination, but omitting the test portion (as described in 7.2 to 7.6). Using a one-mark pipette, add 25.0 ml of the potassium sulfate solution (4.3) to the filtrate before adding the methyl red indicator solution (4.5), as described in 7.5.

8 Expression of resultsThe sulfur content, ws, of the sample, expressed as a percentage by mass, is given by the equation

where

NOTE The derivation of the factors used in the equation is given in Annex A.

Report the result, as the mean of duplicate determinations, to the nearest 0.1 % (m/m).The results of the determination described in this standard are reported on the “air-dried” basis. Calculation of the results to other bases is dealt with in BS 1016-16:1981.

9 Precision9.1 Repeatability limit

The results of duplicate determinations, carried out at different times, in the same laboratory, by the same operator with the same apparatus on representative portions taken from the same test sample, should not differ by more than 0.05 % absolute.

9.2 Reproducibility critical difference

The means of the results of duplicate determinations, carried out in each of two laboratories on representative portions taken from the same sample after the last stage of sample preparation, should not differ by more than 0.1 % absolute, at a 95 % confidence level.

m1 is the mass, expressed in grams, of the test portion;

m2 is the mass, expressed in grams, of barium sulfate found in the determination;

m3 is the mass, expressed in grams, of barium sulfate found in the blank test;is the mass concentration expressed in grams per litre, of the potassium sulfate solution (4.3).

Ôk2so4

BS 1016-106.4.1:1993

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10 Test reportThe test report shall include the following particulars:

a) the identification of the sample;b) the method used, i.e. BS 1016-106.4.1:1993;c) the date of the test;

d) the results expressed in accordance with clause 8;e) any unusual features noted during the determination;f) any operation not included in this standard or regarded as optional.

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Annex A (informative)Derivation of factors used in the expression of results

In this annex, relative atomic masses and relative molecular masses are represented by the chemical formulae in square brackets. The relative atomic masses given in Table A.1 were used in the calculations.

Table A.1 — Relative atomic masses

The mass, expressed in grams, of barium sulfate equivalent to 25 ml of potassium sulfate solution is given by the formula

where is the mass concentration, expressed in grams per litre, of the potassium sulfate solution.

Thus, the sulfur content ws of the sample, expressed as a percentage by mass, is given by the equation

where

Hence

Element Symbol Relative atomic mass

Barium Ba 137.33

Oxygen O 15.999

Potassium K 39.098

Sulfur S 32.06

m1 is the mass, expressed in grams, of the test portion.;

m2 is the mass, expressed in grams, of barium sulfate found in the determination;

m3 is the mass, expressed in grams, of barium sulfate found in the blank test.

Ôk2so4

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List of references (see clause 2)

Normative references

BSI standards publicationsBRITISH STANDARDS INSTITUTION, London

BS 1016, Methods for analysis and testing of coal and coke. BS 1016-16:1981, Methods for reporting results. BS 1016-104, Proximate analysis. BS 1016-104.1:1991, Determination of moisture content of the general analysis sample of coal. BS 1016-104.2:1991, Determination of moisture content of the general analysis sample of coke. BS 1017, Sampling of coal and coke. BS 1017-1:1989, Methods for sampling of coal. BS 1017-2:1960, Methods for sampling of coke.

Informative references

BSI standards publicationsBRITISH STANDARDS INSTITUTION, London

BS 1016, Methods for analysis and testing of coal and coke. BS 1016-6:1977, Ultimate analysis of coal. BS 1016-7:1977, Ultimate analysis of coke.

ISO standards publicationsINTERNATIONAL ORGANIZATION FOR STANDARDIZATION (ISO) , Geneva. (All publications are available from BSI Sales.)

ISO 334:1992, Solid mineral fuels — Determination of total sulfur — Eschka method1). ISO 1015:1992, Brown coals and lignites — Determination of moisture content — Direct volumetric method1). ISO 5068:1983, Brown coals and lignites — Determination of moisture content — Indirect gravimetric method1). ISO 5069-2:1983, Brown coals and lignites— Principles of sampling — Part 2: Sample preparation for determination of moisture content and for general analysis1).

Other references[1] GREAT BRITAIN. Health and Safety at Work etc. Act 1974. London: HMSO[2] GREAT BRITAIN. Control of Substances Hazardous to Health Regulations, 1988. London: HMSO

1) Referred to in the foreword only.

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