GB/T 19494.2-2023 PDF English
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| GB/T 19494.2-2023 | English | 430 |
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Mechanical sampling of coal - Part 2: Method for sample preparation
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| GB/T 19494.2-2004 | English | 145 |
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Mechanical sampling of coal -- Part 2: Method for sample preparation
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GB/T 19494.2-2023: Mechanical sampling of coal - Part 2: Method for sample preparation---This is an excerpt. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.), auto-downloaded/delivered in 9 seconds, can be purchased online: https://www.ChineseStandard.net/PDF.aspx/GBT19494.2-2023
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 73.040
CCS D 21
Replacing GB/T 19494.2-2004
Mechanical Sampling of Coal - Part 2.Method for Sample
Preparation
(ISO 13909-1.2016, Hard coal and coke - Mechanical sampling - Part 1.
General introduction; ISO 13909-4.2016, Hard coal and coke - Mechanical
Sampling - Part 4.Coal - Preparation of Test Sample, NEQ)
Issued on. NOVEMBER 27, 2023
Implemented on. MARCH 1, 2024
Issued by. State Administration for Market Regulation;
Standardization Administration of the People’s Republic of China.
Table of Contents
Foreword... 3
Introduction... 5
1 Scope... 6
2 Normative References... 6
3 Terms and Definitions... 6
4 Precision of Coal Sample Preparation... 7
5 Specimen Composition... 8
6 Division... 10
7 Reduction... 27
8 Mixing... 28
9 Air-drying... 28
10 Preparation of Various Coal Samples... 29
11 Coal Sample for Back-check... 38
12 Design Requirements for Sample Preparation Equipment... 38
1 Scope
This document specifies the precision of coal sample preparation, specimen composition,
division, reduction, mixing and air-drying, as well as the preparation of various coal samples,
coal sample for back-check and the design requirements for sample preparation equipment.
This document is applicable to lignite, bituminous coal and anthracite coal.
2 Normative References
The contents of the following documents constitute indispensable clauses of this document
through the normative references in the text. In terms of references with a specified date, only
versions with a specified date are applicable to this document. In terms of references without a
specified date, the latest version (including all the modifications) is applicable to this document.
GB/T 211 Determination of Total Moisture in Coal
GB/T 19494.1 Mechanical Sampling of Coal - Part 1.Method for Sampling
GB/T 19494.3 Mechanical Sampling of Coal - Part 3.Determination of Precision and Bias Test
3 Terms and Definitions
What is defined in GB/T 19494.1, and the following terms and definitions are applicable to this
document.
3.1 sample preparation
The process of bringing coal samples to analysis or testing status.
3.2 on-line sample preparation
Samples are prepared using equipment integrated into the sampling system.
3.3 off-line sample preparation
Use equipment that is not integrated with the mechanized sampling system to prepare coal
samples taken by the mechanical sampling system by manual or mechanized methods.
3.4 sample division
The sample preparation process that divides a specimen into representative and discrete parts.
3.5 fixed mass division
A division method, in which, the mass of the retained specimen is fixed and has nothing to do
with the mass of the specimen being divided.
3.6 fixed ratio division
A division method with a certain division ratio, that is, the retained specimen amount is in a
certain proportion to the divided specimen amount.
4 Precision of Coal Sample Preparation
In accordance with the description in GB/T 19494.3, under continuous sampling, the precision
estimated (absolute) value PL of the determination results of a batch of coal under a confidence
probability of 95% is calculated in accordance with Formula (1).
5 Specimen Composition
5.1 Overview
A specimen is generally merged by many individual sub-samples, or all sub-samples of the
entire sampling unit, or a part of sub-samples of a sampling unit. Under certain circumstances,
such as. particle size analysis and bias test, a sub-sample constitutes a specimen.
Sub-sample merging procedures vary with the sampling mode---time-based sampling or mass-
based sampling (see 5.2).
5.2 Merging of Sub-samples
5.2.1 Time-based sampling
The mass of sub-samples of time-based sampling is proportional to the coal flow rate at the
time of sampling. At this time, the specimen can be directly merged by primary sub-samples or
merged by divided sub-samples prepared by the fixed ratio division method to a certain stage
5.2.2 Mass-based sampling
If the mass of the primary sub-samples is close to uniform (that is, the coefficient of variation
of the sub-sample mass is less than 20%, and there is no correlation between the sub-sample
mass and the coal flow rate, see GB/T 19494.1), then, the primary sub-samples can be merged
into a specimen, or directly merged, or merged after the primary sub-samples are divided by
the fixed ratio division method to a certain stage (see Chapter 6).
If the mass of the primary sub-samples is non-uniform, then, they shall be divided by the fixed
mass division method to a certain mass, then, merged into a specimen.
5.3 Specimen Merging
During specimen merging, the mass of each specimen shall be proportional to the mass of each
sampled coal, so that the quality parameter value of the merged specimen is the weighted
average value of the quality parameter value of each merged specimen. The division of each
specimen before merging shall adopt the fixed ratio division method (see Chapter 6).
6 Division
6.1 Basic Requirements
Division is the most critical procedure in sample preparation, and its purpose is to reduce the
amount of coal sample. The division of coal sample can be carried out online or offline using
mechanical methods, or manually. Whenever the conditions permit, mechanical division shall
be applied, so as to minimize human error.
6.2 Mechanical Division Method
6.2.1 Division and dividing machinery
Mechanical division can be performed on individual sub-samples or total specimens that have
not been reduced, or on specimens that have been reduced to a certain particle size. Division
can be carried out by the mode of fixed mass division or fixed ratio division, but it shall comply
with the requirements specified in 6.2.3.Specifically speaking, the fixed ratio division is
relatively simple and easy to implement.
6.2.3 Cutting interval
In order to minimize the bias, when dividing, the first cutting shall be performed randomly
within the first cutting interval. For the second and third dividers, the cutting cycle of the latter
cutter shall not coincide with the cycle of the previous cutter.
6.2.4 Division of single sub-sample
6.2.4.1 Number of cuttings
The number of cuttings for one sub-sample.
a) For fixed mass division, the minimum number of cuttings for primary sub-sample is
4, and the number of cuttings for each primary sub-sample of the same sampling unit
shall be equal;
b) For fixed ratio division, the minimum number of cuttings for primary sub-sample with
an average mass is 4;
c) When the divided primary sub-sample is further divided, each cut shall be cut again
at least once.
The division and re-division procedures of a single sub-sample are shown in Figure 3.
a) Stage 1 division of a single sub-sample
6.2.4.2 Minimum mass of divided sub-sample
The minimum mass of the divided sub-sample shall satisfy the following requirements. the
mass of the total specimen merged by all the divided sub-samples in each division stage shall
be greater than the mass under the corresponding sample purpose and the nominal maximum
particle size specified in Table 1, and satisfy the requirements of Formula (2); if the sub-sample
mass is too small to satisfy the two requirements, then, it shall be further reduced, then, divided.
Specimen division
(at least 60 cuttings)
6.2.5 Division of coal sample
6.2.5.1 Number of cuttings
The minimum number of cuttings for the division of coal sample merged by all sub-samples or
divided sub-samples is 60.
If the mass of the coal sample is too small, then, the manual methods shall be used for division.
6.2.5.2 Minimum mass of divided specimens
The minimum mass of the divided specimens (see Table 1) depends on the nominal maximum
particle size of the divided coal sample, the precision required for relevant parameters and the
relations between this parameter and particle size. However, just meeting the requirement for
the minimum mass of divided specimens does not guarantee that the precision meets the
requirement, because the latter also depends on the number of cuttings of division (see 6.2.4.1
and 6.2.5.1).
6.3 Manual Division Method
6.3.1 Riffle method
Riffle is a simple and effective divider (the structure is shown in Figure 4). It consists of two
sets of cells and receivers arranged oppositely across each other. The number of cells on both
sides is equal, with at least 8 on each side. The cell opening size is at least 3 times the nominal
maximum particle size of the coal sample.
6.3.2 Chessboard method
The division by the chessboard method is shown in Figure 5.
After the coal sample is thoroughly mixed, pave it into a uniform rectangular block with a
thickness not greater than 3 times the nominal maximum particle size of the coal sample [see
Figure 5a)]. If the amount of the coal sample is large, and the paved rectangular block is larger
than 2 m 2.5 m, then, 2 or more rectangular blocks of equal mass shall be paved, and each
rectangular block shall be divided into more than 20 small pieces [see Figure 5b)]. Then,
respectively conduct sampling from each small piece.
6.3.3 Strip cutting method
The division by the strip cutting method is shown in Figure 6.
After the coal sample is thoroughly mixed, randomly lay it along one direction into a long strip,
with the length of the strip being at least 10 times the width. When laying the strip, block baffles
at both ends of the strip, so that particle size segregation occurs only on both sides of the strip.
Then, use a sampling frame with a width at least 3 times the nominal maximum particle size of
the coal sample and a side height greater than the thickness of the coal sample strip to cut a
section of coal sample at a certain distance along the length of the sample strip as a sub-sample.
Merge all the sub-samples into the divided coal sample.
6.3.4 Coning and quartering method
The coning and quartering method is a relatively convenient method, but it may lead to particle
size segregation and moisture loss, and improper operation may cause bias.
In order to guarantee the precision of division, during coning, the coal sample shall be scattered
from the top of the sample pile in small portions to form a regular particle size distribution from
the top to the bottom, and from the center to the outer edge, and the pile shall be turned over at
least 3 times; when spreading the cake, gradually level or flatten it from top to bottom; during
sample division, draw two vertical intersecting lines from the center of the cake, then, separate
the coal sample along the lines. It is best to use a cross dividing template. In order to reduce
moisture loss, the operation shall be rapid.
6.3.5 Nine-point sampling method
This method is specially used to take total moisture specimens from total moisture coal samples
or shared coal samples.
7 Reduction
The purpose of reduction is to increase the number of specimen particles and reduce the division
error. For specimens of the same mass, the smaller the particle size, the larger the number of
particles, and the smaller the division error. However, reduction consumes time, physical
strength and energy, and will cause the loss of specimens, especially moisture. Therefore, during
sample preparation, a large number of large-particle-sized specimens shall not be reduced to
the required particle size as test specimens at one time. Instead, the method of step-by-step
reduction and division shall be adopted to gradually reduce the particle size and the amount of
specimen.
8 Mixing
Theoretically speaking, thorough mixing before division will reduce the errors of sample
preparation. However, in practice, this is not entirely the case. Some artificial mixing methods
may have the opposite effect, for example, the coning and blending method will cause particle
size segregation; when using a mechanical divider, mixing before division is not necessary in
guaranteeing the precision of division, and mixing will also cause moisture loss.
A feasible mixing method is to pass the specimen through a riffle (see 6.3.1) or a multi-container
divider [see Figure 2c)] for multiple times (3 times or above), and merge all samples after each
pass, then, feed them into the divider.
9 Air-drying
Air-drying is to spread the coal sample into a uniform thin layer and balance it with the
atmospheric humidity at ambient temperature. The thickness of the coal layer cannot exceed
1.5 times the nominal maximum particle size of the coal sample or the surface load is 1 g/cm2
(whichever is larger).
......
Source: Above contents are excerpted from the full-copy PDF -- translated/reviewed by: www.ChineseStandard.net / Wayne Zheng et al.
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