1、INTERNATIONAL STANDARD IS0 728 Third edition 1995-l l-01 ANSI Internrat Dot ec Coke (nominal top size greater than 20 mm) - Size analysis by sieving Coke (dimension suphieure nominale supbrieure ti 20 mm) - Analyse granulom 100 mm; 80 mm; 71 mm; 63 mm; 50 mm; 40 mm; 31,5 mm; 20 mm and 10 mm may be s
2、uitable. For samples containing pieces with a particle size greater than 125 mm, single-hole gauges may be used instead of test sieves. For graded coke, a series of test sieves of nominal hole sizes 50 mm; 45 mm; 40 mm; 35,5 mm; 31,5 mm; 25 mm; 20 mm; 16 mm; 10 mm; 5,6 mm and 2,8 mm may be suitable.
3、 It is important to check the sieves from time to time, using the methods described in IS0 3310-2, to ensure that the hole dimensions are within the specified tolerances. Worn or damaged sieves can give rise to serious errors in size analysis and should be discarded. 4.2 Weighing machine, capable of
4、 measuring the mass of the sample to be sieved to the nearest 0.1 %. 5 Sampling and preparation of test sample Take two gross samples for physical testing in ac- cordance with IS0 2309). Prepare one of these sam- ples for the determination of moisture content in I) In due course, IS0 2309 will be re
5、placed by IS0 13909-6, Hard coal and coke - Sampling - Part 6: Coke - Preparation of test samples. 1 IS0 728:1995(E) 0 IS0 accordance with IS0 2309 and carry out the determi- nation in accordance with IS0 579. If the moisture content is higher than 5 % (m/m), dry the other sample sufficiently to red
6、uce the moisture content to lower than 5 % (m/m). Use this second sample for the remainder of the test. 6 Procedure 6.1 Arrange the set of sieves (4.1) in a stack in order of nominal hole sizes, with the smallest size at the bottom. Weigh the test sample, in several portions if necess- ary, using th
7、e weighing machine (4.2). 6.2 Place on the top sieve a portion of the test sample small enough that not more than 75 % of the sieve area is covered, and shake to allow most of the undersize to pass. Manually place the remaining coke on the sieve and transfer the oversize to a suitable container. Rem
8、ove the top sieve and repeat these operations for sieves of nominal hole sizes down to and including 40 mm. 6.3 Continue the process described in 6.2 for sieves of nominal hole sizes less than 40 mm, but using manual shaking. Carry out manual shaking by holding the sieve in the hands, or suspending
9、it freely, and moving. it horizontally to and fro with a displacement of about 75 mm. Complete fifty such oscillations (each consisting of one movement to and fro) in a period of about 30 s. If the amount of coke remaining on the sieve is then such that it covers more than 75 % of the sieve area, di
10、vide it into two or more portions and manually shake each portion separately. Otherwise, transfer the oversize to a suitable con- tainer. NOTE 2 Mechanical sieving may be carried out if it can be demonstrated that the method is free from bias when compared to the manual sieving method described in t
11、his International Standard. 6.4 If necessary, re-stack the sieves and repeat the steps described in 6.2 and 6.3 for successive portions until the entire test sample has been sized and each size fraction has been collected in a separate con- tainer. 6.5 Either weigh each container separately with its
12、 size fraction and subtract the respective tare mass, or, after weighing the first fraction, successively add the other fractions and note the cumulative mass after each addition. NOTE 3 Cumulative weighing is preferable because it reduces the weighing error for the cumulative fractions. Depending o
13、n how the results are to be expressed (see clause 71, cumulative weighing should be in descending order of size fractions (cumulative oversize) or in ascending order of size fractions (cumulative undersize). 7 Expression of results If necessary, calculate the cumulative mass on each sieve starting w
14、ith the sieve with the largest size of holes, or the cumulative mass passing through each sieve starting with the sieve with the smallest size of holes, from the masses of the individual size fractions. Calculate the apparent loss, i.e. the difference be- tween the total mass of the test sample befo
15、re sieving and the total mass of coke collected after- wards. If the loss is greater than 0,4 % of the original mass of the test sample, reject the results and carry out a further test. Otherwise, add the apparent loss to the mass of the smallest size fraction. Convert each cumulative mass to a perc
16、entage of the total mass of the test sample. Report the cumulative masses to the nearest 0,l kg and the cumulative percentages to the nearest 0,l %. NOTES 4 An example of the calculation of the results of a size analysis of coke, in terms of the cumulative oversize, is given in table 1. 5 If the mea
17、n size is required, it may be determined in accordance with annex A. 2 0 IS0 IS0 728:1995(E) Table 1 - Example of size analysis of coke Nominal size of hole (round hole) Mass of fraction Cumulative mass Cumulative percentage oversize mm kl kc3 % 140 4.9 49 I,1 125 34 14,3 32 100 41,3 55,6 12,4 80 11
18、3.4 169,0 37,7 71 78,5 247,5 55,2 63 67,7 315,2 70,3 50 51,5 366,7 81.8 40 37,2 403.9 90.1 31,5 17,9 421.8 94.1 20 989 431.7 96,3 10 8,1 439.8 98,l passing 10 7,4 + I,1 = 8.5 448,3 100,o Sum 447.2 Original mass 448,3 Loss in mass L.i 0,4 % of original mass 13 The loss in mass, being less than 0,4 %
19、of the original mass, is added to the fraction of smallest size ( 10 mm). 8 Test report d) the date of the test; The test report shall include the following: a) the method used by reference to this International Standard; e) the results expressed in accordance with clause 7; f) any unusual features
20、noted during the determi- nation; b) a complete identification of the sample; c) whether the sieves used had round or square holes; g) any operation not included in this International Standard, or regarded as optional. 3 IS0 728:1995(E) Annex A (informative) Determination of mean size The mean size
21、of the coke may be calculated from the following formula: B(a-c)+C(b-d)+.+J(h-k)+lOOj 200 where a, b, c, d , h, j, k are the hole sizes, in milli- metres, of successive sieves; A, B, C, D . . H, J, K are the cumulative per- centage oversizes for each of the sieves. NOTE 6 The sieve with hole size a
22、is the smallest size through which all the coke passes (i.e. A = 0 %). The sieve with hole size k is a hypothetical sieve through which no coke will pass (i.e. k = 0 mm, K = 100 %I. Alternative methods of calculation or graphical methods of determination may lead to slightly differ- ent results and
23、the same method should, therefore, be used for comparative tests. The precision of a determination of mean size can be expressed in terms of the repeatability limit, as fol- lows. The results of duplicate determinations of mean size, carried out at different times in the same laboratory, by the same
24、 operator with the same apparatus, on representative test samples taken from the same lot of coke, should not differ by more than 2,5 mm. No value for reproducibility can be quoted for deter- minations carried out in different laboratories, since the transport of coke samples involves the risk of breakage and thus alteration of the size distribution. 4 IS0 728:1995(E) ICS 75.160.10 Descriptors: solid fuels, coke, tests, grain size analysis, sieve analysis. Price based on 4 pages .
