[BS 1016-105-1992] -- Methods for analysis and testing of coal and coke. Determination of gross calorific value.pdf

BRITISH STANDARD BS 1016-105:1992

Methods for

Analysis and testing of coal and coke —

Part 105: Determination of gross calorific value

BS 1016-105:1992

This British Standard, having been prepared under the direction of the Solid Mineral Fuels Standards Policy Committee, was published under the authority of the Standards Board and comes into effect on15 August 1992

© BSI 04-1999

The following BSI references relate to the work on this standard:Committee reference SFC/3Draft for comment 91/56592 DC

ISBN 0 580 20903 2

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.)Institute of PetroleumPower Generation Contractors’ Association (BEAMA Ltd.)

Amendments issued since publication

Amd. No. Date Comments

BS 1016-105:1992

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Contents

PageCommittees responsible Inside front coverForeword iiIntroduction 1

1 Scope 12 References 13 Definitions 14 Principle 15 Reagents and materials 16 Apparatus 27 Preparation of test sample 38 Procedure 39 Corrections 5

10 Expression of results 611 Precision 612 Test report 6Annex A (normative) Determination of the effective heat capacity of the calorimeter system and the standard interval for adiabatic calorimeters 7Annex B (informative) Checking the average deviation of the rate of change of temperature 8Annex C (informative) Examples to illustrate the method ofcalculating results 9Table B.1 — Acceptable difference sequences 8Table B.2 — Example of how to obtain coded differences 9Table C.1 — Temperature readings 10List of references Inside back cover

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Foreword

This Part of BS 1016 has been prepared under the direction of the Solid Mineral Fuels Standards Policy Committee. Part 105 is a revision of the 1977 edition of BS 1016-5, which is withdrawn. The principal change is that stainless steel or nickel-chromium crucibles are now specified for all purposes (see 6.6), instead of silica, nickel-chromium or platinum crucibles; lining of the crucible is now recommended whenever complete combustion cannot otherwise be achieved.Part 105 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 earlier series of Parts is 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 for 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.

This Part is related to ISO 1928:1976, published by the International Organization for Standardization (ISO). The principal differences are as follows.

a) ISO 1928 specifies the use of silica, nickel-chromium or platinum crucibles, depending on the nature of the test portion.b) ISO 1928 describes the calculation of other calorific values: in this Part of BS 1016 reference is made to BS 1016-16 instead.

WARNING NOTE. 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.

BS 1016-105:1992

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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 12, 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

BS 1016-105:1992

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IntroductionThe result obtained by the method described in this Part of BS 1016 is the gross calorific value of the general analysis sample at constant volume, the water formed during combustion being condensed to liquid at the calorimeter temperature. In practice, fuel is burned at constant (atmospheric) pressure and the water is not condensed but is removed, as vapour, with the flue gases. Under these conditions, the heat available to the system is the net calorific value of the fuel at constant pressure; the net calorific value at constant volume may also be used. The calculation of other calorific values, i.e. gross calorific value at constant pressure, net calorific value at constant volume and net calorific value at constant pressure, from the gross calorific value determined at constant volume is described in BS 1016-16 and discussed in fuller detail in BS 7420.

1 ScopeThis Part of BS 1016 describes a method for the determination of the gross calorific value of coal and coke at a constant volume in a bomb calorimeter. The determination of the effective heat capacity of the calorimeter system and the standard interval for adiabatic calorimeters is described in Annex A.

2 References2.1 Normative referencesThis Part of BS 1016 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 Part of BS 1016 only when incorporated in it by updating or revision.2.2 Informative referencesThis Part of BS 1016 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 DefinitionsFor the purposes of this Part of BS 1016 the following definitions apply.

3.1 gross calorific value at constant volume

the amount of heat liberated per unit mass of a solid mineral fuel when it is burned in oxygen saturated with water vapour in a bomb calorimeter under specified conditions

3.2 effective heat capacity of the system

the amount of heat required to cause unit rise of temperature in the calorimeter system under specified conditions

4 PrincipleA test portion is burned in oxygen in a bomb calorimeter under standard conditions. The gross calorific value is calculated from the temperature rise of the water in the calorimeter vessel and the effective heat capacity of the system. Allowances are made for the heat released by the ignition fuse, for thermochemical corrections and, if appropriate, for heat losses from the calorimeter vessel to the water jacket.

5 Reagents and materials5.1 General. During the test, unless otherwise specified, use only reagents of recognized analytical grade and only water conforming to grade 3 of BS 3978:1987. Test sieves used for the preparation of reagents and materials shall conform to BS 410:1986.5.2 Oxygen, industrial grade, at a pressure such that it can be used to fill the pressure vessel (6.1) to a pressure of 3 MPa.5.3 Firing wire, of nickel-chromium 0.16 mm to 0.20 mm in diameter, or of platinum 0.06 mm to 0.10 mm in diameter.5.4 Cotton fuse, of white cellulose cotton.5.5 Paste, of fused aluminosilicate cement, passing a 63 4m test sieve and suitable for use up to a temperature of 1 400 °C, mixed with water.5.6 Aluminium oxide, fused, passing a 180 4m test sieve and retained on a 106 4m test sieve.

5.7 Standard volumetric solutions

5.7.1 Barium hydroxide solution, c(Ba(OH)2) = 0.05 mol/l.5.7.2 Sodium carbonate solution, c(Na2CO3) = 0.05 mol/l.5.7.3 Sodium hydroxide solution, c(NaOH) = 0.1 mol/l.5.7.4 Hydrochloric acid solution, c(HCl) = 0.1 mol/l.

5.8 Indicators

5.8.1 Screened methyl orange, 1 g/l solution.Dissolve 0.25 g of methyl orange and 0.15 g of xylene cyanol in 50 ml of 95 % (V/V) ethanol and dilute to 250 ml with water.5.8.2 Phenolphthalein, 10 g/l solution.Dissolve 2.5 g of phenolphthalein in 250 ml of 95 % (V/V) ethanol.

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5.9 Benzoic acid, thermochemical standard, certified reference material, in pellet form.NOTE The benzoic acid should be used in the condition as certified. Drying or any treatment other than pelleting should not be carried out.

6 ApparatusNOTE The apparatus should be designed so that the combustion of 1.2 g of benzoic acid produces a temperature rise of approximately 2.5 K (see Annex A).

6.1 Pressure vessel (bomb), conforming to BS 4791:1985, designed to allow the complete recovery of all liquid products.NOTE Bomb parts should be inspected regularly for wear and corrosion. Particular attention should be paid to the condition of the threads of the main closure.

6.2 Calorimeter vessel, made of metal, highly polished on the outside and capable of holding sufficient water to cover completely the flat upper surface of the bomb (6.1) while the water is being stirred.6.3 Stirrer, capable of being driven at constant speed. The stirrer shaft shall include anon-conducting section below the cover of the water jacket to minimize the transmission of heat to or from the system. If a cover is used for the calorimeter vessel, the non-conducting section shall be above this cover.NOTE For isothermal and static bomb calorimeters the rate of stirring should ensure that the length of the chief period (see 8.5.4) in determinations of the effective heat capacity of the system (see Annex A) does not exceed 10 min.

6.4 Water jackets

6.4.1 General. The water jacket shall be one of the types described in 6.4.2 to 6.4.4. The water jacket shall enclose the calorimeter vessel with an air gap of approximately 10 mm separating the vessel and the water jacket.6.4.2 Adiabatic water jacket, having either electrode or immersion heaters capable of supplying energy at a rate sufficient to maintain the temperature of the water in the jacket within 0.1 K of that of the calorimeter vessel after the charge has been fired. At 25 °C, the temperature drift of the calorimeter vessel should not exceed 0.0005 K/min.NOTE It is essential to check the stability of the system periodically by taking additional readings at the end of a determination. If the temperature drift is greater than 0.005 K over a period of 10 min, a new balance point should be established in accordance with the manufacturer’s instructions.

6.4.3 Isothermal water jacket, capable of maintaining the temperature constant to ± 0.1 K.

6.4.4 Static water jacket, having a thermal capacity great enough to restrict changes of temperature of the water in it. From the time of firing the charge to the end of the after-period or during a period of 15 min, whichever is the greater, with a cooling constant d of 0.0020 (see 9.3), the rise in temperature of the water in the jacket shall be less than 0.16 K; with a cooling constant d of 0.0030, the rise in temperature shall be less than 0.11 K.6.5 Temperature measuring device, capable of measuring temperatures which, when corrected, have an accuracy of 0.002 K, so that temperature intervals of 2 K to 3 K can be determined to an accuracy of 0.004 K.NOTE 1 The device should be calibrated against a known standard by a testing authority, at intervals not greater than 0.5 K over the range of use or, for mercury-in-glass thermometers, over the whole graduated scale.NOTE 2 The following types of temperature measuring device are suitable.

a) A platinum resistance thermometer.b) A mercury-in-glass thermometer, conforming to BS 791, with a viewer of about × 5 magnification for reading the temperature to the required accuracy.c) A thermistor and quartz crystal resonator which, together with a suitable resistance bridge, null detector, frequency counter or other electronic equipment, will give the required accuracy.

6.6 Crucible, of stainless steel or nickel-chromium, about 25 mm in diameter, flat based, not more than 20 mm deep and about 0.5 mm thick.NOTE If complete combustion cannot be achieved it may be necessary to line the crucible (see note 1 to 8.6).

6.7 Ignition circuit, supplied with a 6 V to 12 V alternating or direct current.NOTE It is desirable to include some form of indicator in the circuit to show when current is flowing.

The firing switch shall be of the spring-loaded, normally open type.WARNING. Do not mount the firing switch on the calorimeter. Place it in a remote, safe location.

6.8 Ancillary pressure equipment

6.8.1 Pressure regulator, to control the filling of the bomb with oxygen.6.8.2 Pressure gauge, with a range of 0 MPa to 6 MPa (0 bar to 60 bar), of the safety pattern conforming to BS 1780:1985, to indicate the pressure in the bomb.6.8.3 Relief valve or bursting disc, operating at 3.5 MPa, installed in the filling line, to prevent over-filling of the bomb.NOTE If a relief valve is used, its functioning should be checked once a year.

WARNING. Keep the equipment for high pressure oxygen free from oil and grease. Do not test or calibrate the pressure gauge with hydrocarbon fluid.

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6.9 Timer, indicating minutes and seconds, accurate to the nearest 1 s.NOTE A timer which gives audible signals may be useful.

6.10 Balance, capable of weighing to the nearest 0.1 mg.

7 Preparation of test sampleThe sample used for the determination of calorific value is the general analysis sample taken in accordance with BS 1017-1:1989 or BS 1017-2:1960, as appropriate, ground to pass a 212 4m test sieve conforming to BS 410:1986. Expose the sample in a thin layer for the minimum time required for the moisture content to reach approximate equilibrium with the laboratory atmosphere.Immediately before weighing out the test portion (see 8.1), mix the test sample for at least 1 min, preferably by mechanical means.

8 Procedure8.1 Test portion

Weigh the crucible (6.6) to the nearest 0.1 mg using the balance (6.10). Add sufficient of the test sample to cause a temperature rise of 2 K to 3 K during the test and reweigh to the nearest 0.1 mg.NOTE Normally about 1 g of the test sample is appropriate.

8.2 Preparation of the bomb

Connect a piece of the firing wire (5.3) tautly across the terminals of the bomb (6.1). Tie a known mass of the cotton fuse (5.4) to the firing wire. Arrange the ends of the cotton fuse so that they will touch the test portion when the bomb is assembled.NOTE For convenience, a measured length of cotton of known mass per unit length may be used. The length used in each determination of calorific value should be the same as that used in the determination of the effective heat capacity of the system (see Annex A).

Put 5 ml of water into the bomb. Assemble the bomb, with the crucible containing the test portion (see 8.1) inside, connect the ancillary pressure equipment (6.8), and charge the bomb slowly with the oxygen (5.2) to a pressure of 3 MPa without displacing the original air. If the bomb is inadvertently charged with oxygen to a pressure above 3.3 MPa, discontinue the test and repeat the procedure.

8.3 Calorimetry

Depending on the type of calorimeter used, proceed as described in 8.4 or 8.5. Carry out all timings to the nearest 1 s using the timer (6.9).

8.4 Use of adiabatic calorimeters

Put sufficient water into the calorimeter vessel (6.2) to cover the flat upper surface of the bomb cap to such a depth that it does not break the surface of the water during stirring. The mass of water shall be the same, to within ± 1 g, as that used in determining the effective heat capacity of the system (see Annex A). The temperature of the water in the calorimeter vessel shall be such that it is still higher than that of the water jacket after assembly of the calorimeter.NOTE 1 A temperature difference of 1 K to 2 K between the water in the calorimeter vessel and the water jacket, after assembly, is usually adequate.

Transfer the calorimeter vessel to the water jacket (6.4), lower the bomb (6.1) carefully into the calorimeter vessel and check that the bomb isgas-tight. If gas escapes from the bomb, discontinue the test, eliminate the cause of the leakage and repeat the procedure. Assemble the stirrer (6.3) and the temperature measuring device (6.5) and connect the ignition circuit (6.7).NOTE 2 The depth of immersion of the temperature measuring device should be the same for all determinations and as far as possible all determinations should register over the same part of the temperature scale.

Start the stirrer (6.3) and the pump for the water jacket (if any). Use a constant rate of stirring such that the duration of the standard interval (see A.5) does not exceed 10 min. Select the setting of the bridge circuit that will result in the minimum drift in the temperature of the calorimeter vessel at the final temperature.After 10 min read the temperature measuring device to 0.001 K (the “firing temperature” Ú0).NOTE 3 If using a mercury-in-glass thermometer, it should be tapped lightly before reading it and care should be taken to avoid parallax errors when using the viewer to take the reading.

Fire the charge by means of the ignition circuit (6.7), holding the switch closed only long enough to ignite the fuse.WARNING. Do not approach the calorimeter for 20 s after firing.After the standard interval (see A.5) read the temperature to 0.001 K (the “final temperature” Ún) as before.

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8.5 Use of isothermal and static calorimeters

8.5.1 Assembly of apparatus

Put sufficient water into the calorimeter vessel (6.2) to cover the flat upper surface of the bomb cap to such a depth that it does not break the surface of the water during stirring and ensure that the temperature of the water is about 2.5 K lower than that of the water jacket. The mass of water shall be the same, to within ± 1 g, as that used in determining the effective heat capacity of the system (see Annex A). Transfer the calorimeter vessel to the water jacket (6.4), lower the bomb (6.1) carefully into the calorimeter vessel and check that the bomb is gas-tight. If gas escapes from the bomb, discontinue the test, eliminate the cause of the leakage and repeat the procedure. Assemble the stirrer (6.3) and the temperature measuring device (6.5) and connect the ignition circuit (6.7).NOTE The depth of immersion of the temperature measuring device should be the same for all determinations and as far as possible all determinations should register over the same part of the temperature scale.

8.5.2 Preliminary period

Start the stirrer (6.3) and maintain a constant speed throughout the determination. Stir for at least 10 min before starting to read the temperature. Read the temperature to 0.001 K and continue to do so at intervals of 1 min for a period of 5 min.NOTE 1 If using a mercury-in-glass thermometer, it should be tapped lightly, by means of a mechanical vibrator or manually, for about 10 s before each reading and care should be taken to avoid parallax errors when using the viewer to take the reading.

If the average deviation of the values of the rate of change of temperature during the 5 min period exceeds 0.001 K/min (see Annex B) continue to read the temperature at 1 min intervals until the average deviation is less than 0.001 K/min for a period of 5 min.NOTE 2 The final temperature of the preliminary period is the “firing temperature” Ú0.

8.5.3 Firing

Fire the charge, by means of the ignition circuit (6.7), immediately after reading the final temperature in the preliminary period (see 8.5.2). Hold the switch closed only long enough to ignite the fuse.WARNING. Do not approach the calorimeter for 20 s after firing.

8.5.4 Chief period

During the first minutes of the chief period it will not be possible to read the thermometer to 0.001 K but resume readings to this precision as soon as possible and continue them to the end of the test. The chief period ends when, for a subsequent 5 min period (the “after-period”), the average deviation of the individual values of change of temperature per minute is not more than 0.001 K (see Annex B).

8.6 Conclusion

Remove the bomb from the calorimeter vessel, release the pressure and dismantle the bomb. Examine the bomb interior. If unburned sample or a sooty deposit is visible, discontinue the test and repeat the procedure.NOTE 1 If complete combustion cannot be achieved, i.e. if there are traces of unburnt carbon at the end of a test, the crucible should be lined with the paste of fused aluminosilicate cement (5.5). After drying at 50 °C to 60 °C, scrape off the excess cement to leave a smooth lining about 1.5 mm thick.Then heat the crucible at 1 000 °C for 2 h. Before use, spread 0.3 g of the aluminium oxide (5.6) over the base of the lined crucible and compact it with the flat end of a metal rod.NOTE 2 When certain unreactive cokes are tested, the residue in the bomb frequently contains detectable unburned sample. A correction to be applied for such persistently incomplete combustion may be calculated (see 9.6) from the amount of unburned carbon estimated as follows.Transfer the contents of the crucible (not the lining) to a silica or porcelain dish and dry for 1 h at 320 °C. Cool, weigh the dish and its contents to the nearest 0.1 mg, heat at 815 °C for 1 h, cool and reweigh to determine the loss in mass. The loss in mass is taken to be unburned carbon. Alternatively the unburned carbon may be determined by one of the methods described in BS 1016-6:1977 or BS 1016-7:1977. If more than 6 mg of unburned carbon is found, the correction is invalid and the determination of calorific value should be repeated.

Wash the contents of the bomb into a beaker with water. Wash the underside of the bomb cap and the outside of the crucible with water and add the washings to the beaker. Dilute to approximately 100 ml and boil to expel carbon dioxide. While still hot, titrate with the barium hydroxide solution (5.7.1), using the phenolphthalein solution (5.8.2) as indicator. Add 20 ml of the sodium carbonate solution (5.7.2), filter the warm solution and wash the precipitate with water. When cold, titrate the filtrate with the hydrochloric acid solution (5.7.4), using the screened methyl orange solution (5.8.1) as indicator, ignoring the phenolphthalein colour change.

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NOTE 3 For any given bomb, under constant conditions of heat release, the quantity of nitric acid formed, and therefore the consequent correction, is relatively constant. For hard coals in general, a typical value would be 33 J and for anthracite 25 J. After the value has been firmly established it may be applied in subsequent tests instead of being determined each time. The determination of the sulfuric acid correction may then be shortened by titrating the warm (not boiling) bomb washings with the sodium hydroxide solution (5.7.3), using the screened methyl orange solution (5.8.1) as indicator, to determine the total acidity. Deduct from this titre (in millilitres) 0.17 times the nitric acid correction (in joules), to obtain the volume of sulfuric acid, c(H2SO4) = 0.05 mol/l, present.NOTE 4 If the sulfur content of the sample and the appropriate nitric acid correction are both known, the titration of the acids in the bomb washings is unnecessary. The sulfuric acid correction is equal to 9.5 J/mg of sulfur in the test portion.

9 Corrections9.1 General

The corrections given in 9.2 to 9.6 shall be applied, as appropriate, to the observations made during the test.

9.2 Thermometer corrections

If a mercury-in-glass thermometer is used, the corrections prescribed in the certificate issued with the thermometer shall be applied to the observed firing temperature Ú0 and to the observed final temperature Ún.

9.3 Cooling correction

The heat loss to the water jacket of an adiabatic calorimeter, as described in 6.4, is negligible and a cooling correction is not necessary.The heat loss to the water jacket of an isothermal or static calorimeter shall be compensated by an addition to the temperature rise, calculated from the following formula (the Regnault-Pfaundler formula):

where

NOTE If the temperature is rising in the preliminary period, Ý9 is negative.

9.4 Heat of ignition

The heat release from the cotton fuse and the firing wire shall be subtracted from the total heat released. The heat release from the cotton fuse shall be calculated from its mass (after drying at 100 °C) and the calorific value of cellulose (17 500 J/g). The heat release from the firing wire shall be calculated from the mass of a piece of wire equal in length to the distance between the poles of the bomb, allowing 1 400 J/g for nickel-chromium wire or 420 J/g for platinum wire.

9.5 Correction for heat of formation of acids

The heat gain due to the formation of sulfuric acid and nitric acid shall be subtracted from the total heat released. These corrections amountto 15.1 J/ml of sulfuric acid solution (c(H2SO4) = 0.05 mol/l) and 6.0 J/ml of nitric acid solution (c(HNO3 = 0.1 mol/l) present in the bomb washings (see 8.6 notes 3 and 4).The sulfuric acid correction, in joules, is given by the formula:

15.1(V1 + V2 – 20)where

n is the duration of the chief period (in min);

Ý9 is the rate of fall of temperature in the preliminary period (in K/min);

Ý99 is the rate of fall of temperature in the after-period (in K/min);

Ú9 is the average temperature during the preliminary period (in °C);

Ú99 is the average temperature during the after-period (in °C);

Ú0 is the firing temperature (in °C);

Úi are the successive temperatures (Ú1, Ú2, Ú3 ... Ún) recorded during the chief period (in °C);

Ún is the first temperature after which the rate of change of temperature is constant within the defined limits (see 8.5.4);

is the sum of Ú1, Ú2, Ú3 ... Ún-1;

d is the cooling constant of the calorimeter, which has to be determined for each set of conditions

(in min–1) and is equal to

Z is equal to

V1 is the volume of the standard volumetric hydrochloric acid solution (5.7.4) used (in ml);

V2 is the volume of the standard volumetric barium hydroxide solution (5.7.1) used (in ml).

Úii 1=

n 1–

∑

I″ I′–Ú″ Ú′–-----------------

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The nitric acid correction, in joules, is given by the formula:

6.0(20 – V1)The sum of these two corrections, in joules, may be calculated directly from the formula:

9.1 V1 + 15.1 V2 – 182

9.6 Correction for unburned carbon (certain cokes only)

If the amount of unburned carbon has been estimated (see 8.6 note 2), its heat equivalent shall be calculated on the basis of 33.5 J/mg and added to the determined heat release.

10 Expression of resultsThe gross calorific value at constant volume Q gr, v, in J/g, is given by the equation:

where

NOTE 1 The corrected temperature rise is calculated by subtracting the observed firing temperature Ú0, corrected for thermometer error, from the observed final temperature Ún, corrected for thermometer error, and adding the cooling correction for an isothermal or static calorimeter (see 9.3).

Examples illustrating the method of calculating the results are given in Annex C.Report the result to the nearest 10 J/g.NOTE 2 It is recommended that the result is calculated as the mean of duplicate determinations.

The results of the test described in this Part of BS 1016 are reported on the “air-dried” basis. Calculation of the results to other bases and calculation of other calorific values are dealt with in BS 1016-16.

11 Precision11.1 Repeatability

The results of duplicate determinations, carried out at different times in the same laboratory by the same operator using the same apparatus on representative portions taken from the same test sample, should not differ by more than 120 J/g.

11.2 Reproducibility

The means of the results of duplicate determinations, carried out in each of two different laboratories, calculated on a dry basis, on representative portions taken from the same sample after the final stage of sample preparation, should not differ by more than 300 J/g.

12 Test reportThe test report shall include the following:

a) the identification of the sample;b) the reference to the method used,i.e. BS 1016-105:1992;c) the results expressed in accordance with clause 10;d) any unusual features noted during the determination;e) any operations not specified in this standard or regarded as optional.

%Ú is the corrected temperature rise (in K);

Cm is the mean value of five determinations of the effective heat capacity (Annex A describes the determination of the effective heat capacity) of the system (in J/K);

e1 is the correction for heat of combustion of the cotton fuse (in J);

e2 is the correction for heat of combustion of the firing wire (in J);

e3 is the correction for heat of formation of sulfuric acid (in J);

e4 is the correction for heat of formation of nitric acid (in J);

m is the mass of the test portion (in g).

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Annex A (normative)Determination of the effective heat capacity of the calorimeter system and the standard interval for adiabatic calorimeters

A.1 PrincipleA known mass of benzoic acid of certified calorific value is burned in oxygen in the bomb calorimeter. To the heat of combustion of the benzoic acid are added the heats of combustion of the cotton fuse and the firing wire and the heat of formation of nitric acid.A.2 GeneralCarry out five complete determinations of the effective heat capacity. Provided that their range does not exceed 55 J/K, the mean of these five values, Cm, is taken for calculation of the calorific value of the fuel (see clause 10).NOTE 1 A range of 55 J/K corresponds to a standard deviation about the mean of 15 J/K and to a precision of the mean of ± 18 J/K at the 95 % probability level.

If the range of the five results exceeds 55 J/K, carry out one more determination. If any five of the results lie within the range, their mean is taken as the effective heat capacity and the other result is rejected.NOTE 2 If these conditions are not fulfilled, the series should be repeated after careful examination of the experimental technique.NOTE 3 When any part of the system is changed, the mean effective heat capacity should be redetermined. It should also be redetermined at intervals of not greater than six months.If a change to the system is not involved, the redetermined mean should be within 20 J/K of that previously determined. If the difference is greater than 20 J/K, experimental procedures should be examined and carefully checked.

During the determination of effective heat capacity of adiabatic calorimeters, the standard interval is also determined (see A.5).A.3 ProcedureProceed as described in clause 8 taking about 1.2 g of the benzoic acid (5.9), weighed to the nearest 0.1 mg using the balance (6.10), as the test portion.When determining the effective heat capacity of an adiabatic calorimeter, read the temperature at 1 min intervals over a period of 10 min, commencing 5 min after firing the charge (see A.5).Dilute the bomb washings to approximately 50 ml with water. Titrate the nitric acid directly with the sodium hydroxide solution (5.7.3) or the sodium carbonate solution (5.7.2), using the screened methyl orange solution (5.8.1) as indicator.A.4 Calculation of effective heat capacityCalculate the effective heat capacity of the system C, in J/K, from the equation:

where

The corrections for the heat of combustion of the cotton fuse and the heat of combustion of the firing wire are calculated as described in 9.4. The correction for the heat of formation of nitric acid, in joules, is six times the volume, in millilitres, of the sodium hydroxide solution or the sodium carbonate solution used in titrating the bomb washings.An example illustrating the method of calculating the effective heat capacity is given in C.3.

mb is the mass of benzoic acid used (in g);

Qb is the certified gross calorific value of the benzoic acid at constant volume (in J/g);

e1 is the correction for heat of combustion of the cotton fuse (in J);

e2 is the correction for heat of combustion of the firing wire (in J);

e4 is the correction for heat of formation of nitric acid (in J);

%Ú is the corrected temperature rise (in K).

C mbQb e1 e2 e4+ + +

%Ú------------------------------------------------------=

BS 1016-105:1992

8 © BSI 04-1999

A.5 Calculation of standard interval for adiabatic calorimetersThe standard interval is the period between the firing of the charge and the reading of the final temperature. It is calculated from the temperature readings taken at intervals of 1 min in each valid determination of effective heat capacity (see A.2).From the recorded observations of each determination, note the shortest time in minutes from the firing of the charge to reaching the second of three consecutive readings which do not differ by more than 0.001 K. Calculate, to the nearest whole minute, the mean of the five values to obtain the length of the standard interval. If this value exceeds 10 min, adjust the rate of stirring and repeat the determinations.Use the standard interval for all determinations of calorific value until a new value is established.NOTE The standard interval should be re-established when commissioning a new calorimeter and checked after changing any component.

Annex B (informative)Checking the average deviation of the rate of change of temperature

A convenient method of checking that the average deviation of the rate of change of temperature during the preliminary period (see 8.5.2) and the after-period (see 8.5.4) is less than the specified limit is to list the five differences as units without the decimal place, code them by subtracting the smallest and arrange the coded differences in descending sequence. If the sequence is one of those listed in Table B.1, the average deviation is less than the specified limit.

Table B.1 — Acceptable difference sequences

An example showing how the coded differences are obtained is given in Table B.2. In this example the sequence 33220 appears in Table B.1 and the average deviation of the rate of change of temperature is therefore acceptable.

Coded difference

Average deviation × 103

Coded difference

Average deviation × 103

10000 0.32 22210 0.72

11000 0.48 22220 0.64

11100 0.48 30000 0.96

11110 0.32 31000 0.96

20000 0.64 31100 0.80

21000 0.72 31110 0.72

21100 0.64 32110 0.88

21110 0.40 32210 0.88

22000 0.96 32220 0.72

22100 0.80 33220 0.80

22110 0.64 33320 0.96

22200 0.96 33330 0.96

BS 1016-105:1992

© BSI 04-1999 9

Table B.2 — Example of how to obtain coded differences

Annex C (informative)Examples to illustrate the method of calculating results

C.1 Adiabatic calorimeter

C.2 Isothermal calorimeter

Time Temperature Difference (units)

Coded Difference

min °C

0 24.1577 2

1 24.1645 0

2 24.1698 3

3 24.1778 3

4 24.1857 2

5 24.192

Mass of test portion = 0.9992 g

Volume V1 of hydrochloric acid solution (5.7.4) used = 13.0 ml

Volume V2 of barium hydroxide solution (5.7.1) used = 10.9 ml

Observed final temperature (Ún) = 25.416 °C

Thermometer correction = + 0.011 K

Observed firing temperature (Úo) = 22.793 °C

Thermometer correction = + 0.017 K

Temperature rise (Ún – Úo) corrected for thermometer inaccuracies

= 2.617 K

Mean effective heat capacity = 10 370 J/K

Heat liberated (2.617 × 10 370) = 27 138 J

Subtract:

sulfuric acid correction = 15.1(13.0 + 10.9 – 20) = 59

nitric acid correction = 6.0(20 – 13.0) = 42

correction for cotton fuse and firing wire = 84

correction for unburned carbon = Nil

– 185 J

Heat from 0.9992 g of coal = 26 953 J

Gross calorific value at constant volume = 26 975 J/g

= 26.98 GJ/t

Temperature of water jacket = 25 °CMean effective heat capacity = 10 370 J/KMass of test portion = 0.9992 gVolume Ý1 of hydrochloric acid solution (5.7.4) used = 13.0 ml

Volume Ý2 of barium hydroxide solution (5.7.1) used = 10.9 ml

BS 1016-105:1992

10 © BSI 04-1999

The temperature readings for this example are given in Table C.1.Table C.1 — Temperature readings

Cooling correction (Regnault-Pfaundler formula):

Time Temperature Time Temperature Time Temperature

min °C min °C min °C

0 22.771 6 23.99 13 25.407 (Ún)

1 22.775 7 25.00 14 25.405

2 22.780 8 25.295 15 25.403

3 22.785 9 25.373 16 25.400

4 22.789 10 25.400 17 25.398

5 22.793 (Úo) 11 25.407 18 25.396

12 25.408

n = 8Ý9 = – 0.0044Ý99 = 0.0022Ú9 = 22.782Ú99 = 25.402

d = = 0.00252

= 175.873

"(Úo + Ún) = 24.100– ÝÚ9 = – 182.256therefore Z = 17.717

dZ = 0.0446nÝ9 = – 0.0352

Cooling correction = dZ + nÝ9 = 0.009 KOberserved final temperature (Ún) = 25.407 °C

Thermometer correction = + 0.011 KObserved firing temperature (Úo) = 22.793 °C

Thermometer correction = + 0.017 KTemperature rise (Ún – Úo) corrected for thermometerinaccuracies

= 2.608 K

Cooling correction = + 0.009 KCorrected temperature rise = 2.617 KHeat liberated (2.617 × 10 370) = 27.138 JSubtract:

sulfuric acid correction = 15.1(13.0 + 10.9 – 20) = 59nitric acid correction = 6.0(20 – 13.0) = 42correction for cotton fuse and firing wire = 84correction for unburned carbon = Nil

= – 185 JHeat from 0.9992 g of coal = 26 953 JGross calorific value at constant volume = 26 975 J/g

= 26.98 GJ/t

0.00662.620------------------

Ú ii 1=

n 1–

∑

BS 1016-105:1992

© BSI 04-1999 11

C.3 A single determination of effective heat capacity

NOTE The temperature rise in this example is the difference between the observed final temperature Ún and the observed firing temperature Úo, corrected for thermometer inaccuracies; for isothermal or static calorimeters it will also include the cooling correction.

Mass of benzoic acid (5.9) used = 1.1833 g

Volume of sodium hydroxide solution (5.7.3) used = 7.0 ml

Temperature rise (see note) = 3.036 K

Final calorimeter temperature = 25.5 °C

Gross calorific value of the benzoic acid at 25.5 °C = 26 467 J/g

Heat liberated from the benzoic acid (1.1833 × 26 467) = 31 318 J

Add:

nitric acid correction = 7.0 × 6.0 = 42

correction for cotton fuse and firing wire = 84

126 J

total heat release = 31 444 J

effective heat capacity = = 10 357 J/K31 444

3.036-------------------

12 blank

BS 1016-105:1992

© BSI 04-1999

List of references

Normative references

BSI standards publicationsBRITISH STANDARD INSTITUTION, London

BS 410:1986, Specification for test sieves. 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. BS 1780:1985, Specification for bourdon tube pressure and vacuum gauges. BS 3978:1987, Specification for water for laboratory use. BS 4791:1985, Specification for calorimeter bombs.

Informative references

BSI standards publicationsBRITISH STANDARD INSTITUTION, London

BS 791:1990, Specification for solid-stem calorimeter thermometers. 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. BS 1016-16:1981, Methods for reporting results. BS 7420:1991, Guide for determination of calorific values of solid, liquid and gaseous fuels (including definitions).

ISO standards publications

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

ISO 1928:1976, Solid mineral fuels — Determination of gross calorific value by the calorimeter bomb method, and calculation of net calorific value.

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.

BS 1016-105:1992

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