1、INTERNATIONAL STANDARD IS0 609 Second edition 1996-02-I 5 AN251 IBPntemat Dot se!c Solid mineral fuels - Determination of carbon and hydrogen - High temperature combustion method Combustibles minkaux solides - Dosage du carbone et de Ihydrogene - MBthode par combustion B haute tempkrature - - 1 gffi
2、 1 k sodium hydroxide on an inert base (4.2) for ab- sorbing dioxide; magnesium perchlorate for absorbing the water evolved in the reaction between carbon dioxide and sodium hydroxide. The purification trains shall be large enough to render frequent recharging unnecessary, even with continu- ous use
3、. NOTE 1 Midvale tubes that have been freshly packed with absorbent and used in the purification train are thereby conditioned for subsequent use in the absorption train. 5.4 Combustion assembly 5.4.1 Heating unit, an electrically heated furnace or furnaces, designed to carry a combustion tube (5.4.
4、2) and heat it to 1 350 “C over a distance of 125 mm in the hot zone, and yield a temperature-distribution profile similar to that shown in figure 1. The heating unit normally requires an auxiliary furnace to ensure that the silver gauze roll (5.9) is maintained at the correct temperature (approxima
5、tely 600 “C to 800 “C). Suitable furnaces are, for example: a) molybdenum or tungsten wire wound; b) platinum or platinum-rhodium wire wound; c) heated by silicon carbide rods. , IS0 609:1996(E) NOTES 0 100 200 300 400 500 600 Distance from inlet end. mm 75 mm Combustion tube / / /% Silver gauze rol
6、l Heat-resistant mineral fibre / Figure 1 - Typical temperature-distribution curve for furnace deep for brown coal and lignite, capable of with- 2 Type c) has the lowest initial cost and has proved satis- factory in use. 3 Furnaces of the type normally used for the determi- nation of carbon or sulfu
7、r in steel are not suitable because of the absence of the auxiliary section required to maintain the silver gauze roll at the correct temperature. 5.4.2 Combustion tube, of approximately 28 mm external diameter, 3 mm wall thickness and 650 mm length, made of refractory aluminous porcelain which is i
8、mpervious to gases up to a temperature of 1 400 “C. The end of the combustion tube shall be lagged with a suitable heat-resistant mineral fibre to prevent condensation in the tube. 5.4.3 Combustion boat, of iron-free, unglazed porcelain, approximately 60 mm long, 12,5 mm wide and 10 mm deep, for har
9、d coal and coke samples and approximately 75 mm long, 15 mm wide and 10 mm standing a temperature of 1 350 “C. NOTE 4 Combustion boats should not blister, discolour or change in mass on heating in oxygen at 1 350 “C for 3 h. A suitable boat lasts for about IO to 20 determinations and should then be
10、discarded because of the accumulation of fused ash. For coals with a high ash content, it may be convenient to line the boat with alumina before adding the sample, in order to prevent fusion of the ash to the boat. 5.5 Absorption train, for absorbing the water and carbon dioxide evolved by the combu
11、stion of the sample. Midvale tubes (figure21, which provide a large area of reaction, are used in order to reduce the back-pressure in the apparatus, and so obviate the danger of leakage through the rubber sleeve carrying the pusher. Assemble the train using the following reagents in the order state
12、d, in the direction of flow: a) magnesium perchlorate (4.1) for absorbing the water evolved during the combustion; 3 IS0 609:1996(E) 0 IS0 Dimensions in millimetres Indicator spot - 0 ext. 5.5 to 6 0 ext. 33 to 34 Wall thickness 1 to 1.25 .5 to 6 Figure 2 - Midvale tube b) sodium hydroxide on an ine
13、rt base (4.2) for ab- sorbing carbon dioxide; c) magnesium perchlorate for absorbing the water evolved in the reaction between carbon dioxide and sodium hydroxide. Place glass wool (4.101, previously dried at 105 “C for 1 h, above and below the absorbents to prevent the carry-over of dust by the flo
14、w of oxygen, and to pre- vent the cracking of the Midvale tube by the heat of reaction. A typical absorption train with details of the packing is shown in figure3. A is the absorber for water; B and C are the absorbers for carbon dioxide, C serving as a control to indicate when the packing in B is i
15、n need of replacement. Any water released in B by the reaction between sodium hydroxide and car- bon dioxide is absorbed in C. The inlet of the water-absorption tube shall be in- serted through the heat-resistant stopper so that it is flush with the inner end of the stopper. All con- nections betwee
16、n the tubes shall be made of glass- to-glass, using the rubber connecting sleeves merely as seals. 4 IS0 609:1996(E) 4- 3- Key 1 Glass wool 3 Magnesium perchlorate, I,2 mm to 0.7 mm size 2 Sodium hydroxide (see 4.2) 4 Inlet Figure 3 - Absorption train 5.6 Two flowmeters, both capable of measuring ra
17、tes of flow up to 300 ml/min of air. 5.7 Heat-resistant stopper (acrylonitrile or chloroprene) for connecting the absorption train to the combustion tube. 5.8 Silica or steel pusher, made from rod or sealed tube, approximately 6 mm in diameter and 450 mm long, with a disc end, 12 mm in diameter, for
18、 pushing the boat into the hot zone of the combustion tube. The pusher passes loosely through a glass or metal T-piece, one end of which fits into the stopper which closes the inlet end of the combustion tube, the other being sealed by a rubber sleeve (see note 61, through which the pusher slides. T
19、he sleeve prevents the es- cape of oxygen which enters at the stem of the T-piece. The pusher is usually marked from the disc end, for convenience in ascertaining the position of the boat in the combustion tube during pushing. NOTE 5 The rubber sleeve should be changed period- ically to avoid leakag
20、e. 5.9 Silver gauze roll, for absorbing chlorine and oxides of sulfur. Roll the pure silver gauze (4.6) to form a plug, 75 mm long and of sufficient diameter to ensure a close sliding fit in the combustion tube (5.4.2). A stout, pure silver wire is passed through the centre of the roll to facilitate
21、 its removal from the tube. 5.10 Bubbler, for use when determining the correct location for the silver gauze roll (see 6.2). It may be a large boiling tube, wide-necked bottle, or Dreschel bottle, containing a sintered glass disc of 0,015 mm to 0,040 mm maximum pore size in the gas distri- bution tu
22、be. The diameter of the absorber shall be such that the disc is covered to a depth of at least 90 mm by the absorbing solution; a vessel 35 mm in diameter and 150 mm deep is suitable. A silica adapter, or the combustion tube fitted with a tubulure, is connected to the bubbler. To avoid leakage at th
23、e rubber sleeve of the inlet end due to the resistance of the sintered glass bubbler, the bubbler is connected to a suction-pump through a pressure regulator adjusted to maintain slight suction at the inlet end of the combustion tube. 5 IS0 609:1996(E) 0 IS0 A convenient assembly of the apparatus fo
24、r this pur- oxides of sulfur by the silver gauze roll. Use this exact pose is illustrated in figure4. location in all subsequent determinations. 5.11 Heat-resistant wire, approximately 2,5 mm thick and 450 mm long, with a bent end to transfer the used boat from the combustion tube onto a rigid refra
25、ctory sheet. 6 Preparation of the apparatus 6.1 Preparation of the combustion tube Insert the combustion tube (5.4.2) into the furnace (see 5.4.1) so that it projects 75 mm at the exit end. Wrap this projecting portion with mineral fibre to pre- vent condensation of water in the tube. Insert the rub
26、ber stopper carrying the silica or steel pusher (5.8) at the inlet end of the combustion tube and connect the purified oxygen supply (see 4.7 and 5.3) to the limb of the glass or steel T-piece. NOTE 6 The distance the combustion tube projects from the furnace may be reduced to about 40 mm if an auxi
27、liary furnace is fitted. 6.2 Location of the silver gauze roll Insert the silver gauze roll (5.9) into the exit end of the combustion tube (5.4.2) to a distance of about 75 mm. With the main furnace at its working tem- perature of 1 350 “C and the auxiliary furnace (if fitted) at the temperature req
28、uired to give a temperature- distribution curve as shown in figure 1, connect the bubbler (5.10) containing a 3 % (m/m) solution of the hydrogen peroxide (4.5) to the exit end of the com- bustion tube using a heat-resistant stopper (5.7), and switch on the suction-pump (see figure4). Burn 0,5 g of a
29、 coal containing 1 % (m/m) to 2 % (m/m) of sulfur using the procedure described in 8.2 (but excluding the absorption train). Wash the silica adapter (see 5.10) and the contents of the bubbler into a 250 ml conical filtration beaker, add 2 to 3 drops of the mixed indicator solution (4.8) and measure
30、the amount of chlorine and oxides of sulfur passing through the silver gauze roll by titration of the hydrogen peroxide with the sodium tetraborate sol- ution (4.4) to a neutral steel-grey colour. Move the silver gauze roll forward in 5 mm stages and repeat the test until a position is found where t
31、he volume of the sodium tetraborate solution corre- sponding to the end point is not more than 0,2 ml, which will represent at least 99 % retention of the Disconnect the bubbler, pressure regulator (see 5.10) and suction-pump. Using the bent heat-resistant wire (5.111, withdraw the used combustion b
32、oat onto a thick sheet of suitable refractory material. The roll tends to shrink with continual use and it is important to check its diameter to ensure a close sliding fit in the combustion tube. When the combustion tube is not in use, protect the silver gauze roll from atmospheric contamination by
33、sealing both ends of the tube. NOTE 7 The silver gauze roll can absorb sulfur equivalent to 7 % (m/m) of the sample; for higher sulfur contents, the mass of the test portion should be proportionally reduced. The roll should be periodically cleaned by boiling in water (to remove silver sulfate), in c
34、oncentrated ammonia solution (to remove silver chloride) and finally in water, after which it should be dried. The total sulfur content of samples exam- ined between two cleanings of the roll should not exceed 0,035 g. 6.3 Conditioning the absorption train At the start of each working day, the Midva
35、le tubes should be conditioned by purging them with purified air for 10 min whilst connected to the apparatus. After purging, the Midvale tubes should be sealed, cooled for about 20 min in a draught-free enclosure, wiped carefully with a lint-free cloth and weighed with the minimum of handling. Repe
36、at this procedure until the change in mass of each tube is less than 1 mg. 7 Preparation of test sample Prepare the test sample for general analysis in ac- cordance with IS0 1988, IS0 2309 or IS0 5069-2, as appropriate. Ensure that the moisture content of the sample is in equilibrium with the labora
37、tory atmos- phere, exposing it, if necessary, in a thin layer for the minimum time required to achieve equilibrium. Before commencing the determination, thoroughly mix the test sample for at least 1 min, preferably by mechanical means. After weighing the test portion (see clause 81, deter- mine the moisture content using a further portion of the test sample by the method described in IS0 331, IS0 687, IS0 1015 or IS0 5068, as appropriate. A further portion should be set aside if the determi- nation of carbon dioxide (IS0 925) is required. 6
