ISO 923:2000 pdf download

ISO 923:2000 pdf download.Coal cleaning equipment-Performance evaluation.
B.1 Description of the tables
Two sets of tables are required (see clauses B.4 to B.7):
a) for three-product separation (cleaned coal, middlings and reject);
b) for two-product separation (cleaned coal and reject).
For convenience, an identical layout has been adopted for both sets of tables but, in those intended for use with two-product separations, the columns that relate only to three-product separation have been left blank to avoid confusion.
Each set of tables is presented in two ways.
a) Blank tables, to show the method of printing (see Form 1 and Form 3 in clauses B.4 and B.6, respectively).
b) Tables completed by filling in the figures relating to test results. For example, Form 2 and Form 4 shown in clauses B.5 and B.7 give the results of a test using a Baum jig washer.
NOTE The example described in this annex was carried out prior to the publication of ISO 7936. The particle sizes used therefore are not in accordance with those specified in that International Standard.
For the test described in this example, the washer was supplied with coal sized from 152 mm to 0 mm. The figures used refer to the fraction sized between 12,7mm and 0,5 mm. The fine material below 0,5 mm was removed from the samples before carrying out float and sink tests, because this fine material presents difficulties in testing. Moreover, the jig is not expected to clean material smaller than 0,5 mm.
For a full analysis of the test, tables similar to those given for the 12,7 mm to 0,5 mm size would be required for the other sizes of the raw coal, in this instance 152 mm to 51 mm, 51 mm to 25,4 mm, and 25,4mm to 12,7 mm. Such tables would enable the performance on the different sizes to be compared. By adding together the results on the four individual sizes, a further set of tables could be constructed giving cumulative data for the whole of the 152 mm to 0,5 mm coal.
In this test, three products were made: cleaned coal, middlings and reject. The reject is the material removed by the primary reject elevator and the middlings is the reject from the secondary reject elevator. The tables headed “threeproduct separation” are built up from float and sink tests at various relative densities from 1,30 to 2,20 on samples of each of these three products. Although intervals of 0,1 relative density have been used for the example, different ranges and intervals may be required in other cases.
The figures in the tables headed “two-product separation” have been calculated from these same figures on the assumption that the products from both elevators (i.e. the middlings and the reject) were combined so that there were two products only: cleaned coal and a single reject.
Although for Method A the formulae are identical for diagrams 2 and 3, in the latter case there is no sharp dividing line between the first and second cuts. The first (high-density) cut separates the reject R from the combination of the cleaned coal C and middlings M, and it is this combination that becomes the feed to the second stage of the separation.
Method A enables the efficiency of each of the two separations to be studied individually, because only the material actually admitted to the separation is included in the calculation. This is of advantage when considering the performance of each machine or stage in the separation process.
Method B does not show up so emphatically the actual performance of the second machine or stage, but by referring each separation back to the reconstituted raw feed it facilitates comparisons of the efficiency of the whole separation process in terms of the results on the original raw coal. (The sequence of operations included in this complete process may include steps not shown in diagrams 1 to 3, for example crushing of the middlings and its recirculation to the feed, which is common in jig washing and may also occur in dense-medium separation.)
It is essential, whenever the efficiency of a three-product separation is expressed (for example, in descriptions of plant and efficiency statements and guarantees), that it be clearly stated which of these two bases has been used for the calculation. To facilitate this, it is proposed that Method A be described as the equipment performance basis, and Method B as the coal performance basis.
Tables B.1 to B.1O for the three-product separations are drawn up on the coal performance basis. When calculations are made on the equipment performance basis, it is recommended that two-product tables be used (one for each stage). It is possible, however, to deduce the results from the three-product table; thus, partition coefficients for the second cut would be calculated on the equipment performance basis as follows:
a) for diagram 1 (see Figure B.1 in clause B.2), column (12) would be calculated from (7)1(9) instead of (7)/(10) in Table B.7;
b) for diagrams 2 and 3 (see Figure B.1 in clause B.2), column (13) would be calculated from (6)/(8) instead of (9)1(10) in Table B.7.