GB/T 19494.2-2023 PDF in English
GB/T 19494.2-2023 (GB/T19494.2-2023, GBT 19494.2-2023, GBT19494.2-2023)
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Mechanical sampling of coal - Part 2: Method for sample preparation
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Mechanical sampling of coal -- Part 2: Method for sample preparation
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Standards related to (historical): GB/T 19494.2-2023
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GB/T 19494.2-2023: PDF in English (GBT 19494.2-2023) GB/T 19494.2-2023
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
Mechanical Sampling of Coal - Part 2: Method for Sample
Preparation
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.
NOTE: sample preparation includes mixing, reduction and division, and sometimes air-drying. It
can be carried out in several stages.
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.
Where,
PL---the precision estimated (absolute) value of the determination results;
V1---the primary sub-sample variance;
n---the number of sub-samples in each sampling unit;
VPT---the sample preparation and assay variance;
m---the number of sampling units.
The precision of coal sample preparation is the total precision of sample preparation and assay
of a batch of coal under a confidence probability of 95%, which is recorded as VPT when
expressed as the sample preparation and assay variance. A relatively small sample preparation
and assay variance can improve sampling precision or reduce the number of primary sub-
samples.
Sample preparation and assay error almost entirely arises from the process of division and
extraction of several grams of coal sample from the analyzed coal sample. The most important
factors affecting the precision of sample preparation are the uniformity of coal sample before
division and the amount of coal sample retained after division, as well as the number of cuts,
the size of the cut and all particles of the divided coal sample, which have an equal probability
of being cut during the mechanical division. The sample preparation procedures specified in
this document can make the sample preparation and assay variance VPT expressed in ash content
or moisture less than 0.2. If mechanical sample preparation equipment is used, the sample
preparation and assay precision may be better.
For some sample preparation schemes, the limitations of actual conditions may prevent the
sample preparation and assay variance from reaching such a low level. Under this circumstance,
the user shall improve the sampling schemes or divide the coal batch into more sampling units
to achieve the expected total precision of sampling and preparation.
The target value of the sample preparation and assay variance VPT expressed in ash content or
moisture is 0.05PL2. The total error of sample preparation and assay, as well as the error
(expressed as variance) generated in each stage can be inspected by the method specified in
GB/T 19494.3.
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-
(see Chapter 6).
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.
The mechanical divider removes a part or several parts from the coal sample by cutting the coal
sample. When the mass of the coal sample after one division is greater than the required amount,
the divided coal sample can be further divided using the original divider or the next divider.
When the coal sample is obviously wet and cannot smoothly pass through the divider or sticks
to the surface of the divider, before division, it shall be air-dried in accordance with the
stipulations of 10.2.2.
When mechanical division causes the integrity of the coal sample to be compromised, such as:
moisture loss and particle size reduction, etc., the method of manual division shall be adopted.
However, care shall be taken because the manual method itself may cause bias, especially when
the amount of the divided coal sample is relatively large.
Regularly or under the following circumstances, in accordance with the method specified in
GB/T 19494.3, the off-line dividing machinery or reduction - division combined machinery
shall be subject to the precision inspection and bias test:
a) When a new design is put into production;
the reduction opening (jaw type and roller type) or speed (hammer type and ball type). The
crusher requires the particle size of reduction to be accurate. During reduction, the loss of
specimens and the residue from previous specimens shall be as small as possible. For crushers
used to prepare total moisture coal samples with calorific value and cohesiveness, it is required
that the heat generation and air flow shall be as small as possible. Therefore, there shall be no
contact between the metal surfaces of the reduced parts of the crushers used to prepare these
coal samples, and disc mills, and hammer crushers and high-speed ball mills (greater than 20
Hz) with a rotation speed greater than 950 r/min should not be used. When preparing special
test specimens with requirements for the particle size range, a jaw crusher or roller crusher shall
be used, and the step-by-step reduction method shall be adopted.
The reduction equipment shall be regularly screened to check the nominal maximum particle
size of its discharging.
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.
In the final stage of sample preparation, the mixing of specimens by the mechanical methods
can improve the precision of division.
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).
Table 2 provides the time required for coal samples to reach a balance with the atmospheric
humidity when the ambient temperature is less than 40 C. Under normal circumstances, this
time is sufficient. If necessary, it can be appropriately extended, but the extension time shall be
as short as possible, especially for easily oxidized coal.
Table 2 -- Drying Time under Different Ambient Temperatures
sealed crushers and riffles with a low air flow shall be used for sample preparation.
10.2.2 Air-drying
The purpose of air-drying is primarily to determine external moisture and minimize moisture
loss during the subsequent sample preparation.
Generally, air-drying shall be carried out before the reduction and division of specimens. Under
the following circumstances, air-drying is not required in advance:
a) When the moisture content of coal sample is relatively low, and no substantial bias of
moisture is generated during the sample preparation process;
b) When the amount of specimens is too large and it is difficult to air-dry all the
specimens, the specimens can be reduced - divided to a certain stage first, then, air-
dried. However, the reduction - division process shall be tested and verified that there
are no substantial bias;
c) When the particle size of the specimen is too large and it is difficult to conduct air-
drying, the specimen can be reduced to a certain particle size, then air-dried. However,
the substantial bias of total moisture shall not be generated during the reduction.
When the coal sample is too wet and moisture seeps out of the coal or touches the container,
the container and coal sample shall be air-dried together.
Air-drying is carried out, until the mass change of the coal sample does not exceed 0.1% after
1 h of continuous drying. The mass loss of the coal sample is regarded as its external moisture
and included in the total moisture.
10.2.3 Reduction and division
Reduction shall be carried out using equipment that does not generate significant heat and has
very little air flow inside the machine, so as to avoid moisture loss during the reduction. In
addition, unless it is proved by test that reduction will not generate substantial bias of moisture,
the specimen cannot be reduced before air-drying.
Division shall generally be carried out after air-drying. If division is conducted before air-drying,
then, a dividing machine with very little air flow shall be used and operated rapidly, so as to
minimize moisture changes. If the coal sample is too wet and cannot smoothly pass through the
dividing machine, then, the specimen shall either be air-dried first, and then, divided, or be
divided through the artificial chessboard method, the strip method or the nine-point method.
10.2.4 Storage
Coal samples shall be stored in non-absorbent and air-tight sealed containers in a cool place
before, after and in any intermediate stage of sample preparation.
When the sampling process and the specimen placement time are excessively long, the number
10.3.2 Air-drying
The purpose of air-drying is, firstly, to make the coal sample smoothly pass through the
reduction and division equipment, and secondly, to avoid changes in the moisture content of
the coal sample during the analysis test.
Air-drying can be performed in any stage of sample preparation. Drying before the final sample
preparation stage is not required to reach the air-dried state. If the coal sample can smoothly
pass through the reduction and division equipment, it does not need to be dried. However, the
air-drying in the final sample preparation stage shall reach the air-dried state.
10.3.3 Reduction and division
Under general circumstances, each sub-sample shall firstly be divided to less than 3 mm in
accordance with the requirements of Chapter 6 and Chapter 7, then, merged into a total
specimen. When possible, it is best to reduce the coal sample to less than 3 mm in the first stage,
so as to reduce the amount of retained specimen in the next stage, and meanwhile, minimize
the division error; when the particle size of the coal sample is too large or the moisture content
is too high, a sample preparation stage can be added before 3 mm.
Mechanical methods shall be used for reduction. If the initial particle size of the coal sample is
too large, then, it is allowed to use manual methods to reduce the large pieces to below the
maximum particle size of feeding of the crusher.
Mechanical methods shall be used for division. If manual methods are used, then, when the
particle size is less than 13 mm, a riffle should be used. If the chessboard method and strip
method are used, then, at least 20 sub-samples shall be taken.
Before reducing to a coal sample smaller than 0.2 mm, magnets shall be used to absorb the iron
filings in the coal sample, then, reduce it to a size that can all pass through a sieve with an
aperture of 0.2 mm. After the coal sample reaches an air-dried state, put it into a coal sample
bottle (the amount of sample filled shall not exceed 3/4 of the volume of the coal sample bottle,
and shall be convenient for the mixing and weighing of specimens).
10.4 Shared Coal Samples
10.4.1 Sample preparation procedures
Under most circumstances, for convenience, during sampling, shared coal samples for the total
moisture determination and general analysis test are simultaneously taken. When preparing a
shared coal sample, it shall satisfy the requirements of GB/T 211 and the national standards on
general analysis test items. The preparation procedures are shown in Figure 11.
It is best to extract total moisture coal samples from shared coal samples by mechanical methods.
When the moisture is too large and it is impossible to air-dry the entire coal sample, manual
methods can be used.
11 Coal Sample for Back-check
The coal sample for back-check is taken in a certain sample preparation stage using the same
procedures at the same time as the original coal sample preparation.
The coal sample for back-check shall be divided as little as possible, only to the maximum
storage capacity; it shall not be reduced too much either, only to the nominal maximum particle
size corresponding to the maximum storage mass found in Table 1.
The storage time of the coal sample for back-check can be determined as needed. In terms of
commercial coal, the coal sample for back-check shall generally be retained for 2 months for
review, from the date of reporting the results.
12 Design Requirements for Sample Preparation Equipment
12.1 Divider
The dividing equipment shall satisfy the following requirements:
a) It shall have sufficient capacity and be able to completely retain or completely pass
through the entire specimen without loss or spillage;
b) No substantial bias shall be generated, for example, selective collection (or discarding)
of coal particles or moisture loss. In some cases, it shall be fully enclosed to prevent
moisture loss;
c) The feeding mode shall minimize particle size segregation;
d) The coal flow fed into the equipment in each division stage shall be uniform;
e) For online dividing machines, the cutting frequency of the latter divider shall not be
the same as that of the previous divider.
In addition, the divider shall preferably be able to randomly conduct sampling within the first
division interval, and the dividing machine shall be actuated before the feeding starts.
12.2 Cutter of Falling Flow Dividing Machine
12.2.1 Basic requirements
In addition to satisfying the requirements specified in 12.1, the cutter of falling flow dividing
machine shall also satisfy the following requirements:
a) The cutter can cut a complete cross-section of the coal flow;
b) The front edge and trailing edge of the cutter shall be on the same plane or cylindrical
surface, and the plane or cylindrical surface shall preferably be perpendicular to the
The cross-belt cutter used for division is generally a fixed-type, and the basic requirements are
as follows:
a) The cutter shall cut the coal flow along a plane perpendicular to the centerline of the
belt;
b) The cutter shall cut a complete cross-section of the coal flow;
c) The cutter shall pass through the coal flow at a uniform speed (the speed difference
at each point is not more than 10%);
d) The cutter opening size shall be more than 3 times the nominal maximum particle size
of coal;
e) The cutter shall have sufficient capacity to accommodate the entire sub-sample cut
under the maximum coal flow rate;
f) The radian of the edge of the cutter shall match the curvature of the belt. The side
plate and back plate shall maintain a minimum distance from the belt surface and not
directly contact the belt. The back plate is equipped with a cleaning brush or elastic
scraper.
12.3.2 Cutting speed
There are no rigorous stipulations on the speed of the cross-belt cutter. Generally speaking, the
larger the speed ratio of the cutter to the belt, the larger the effective opening size of the cutter,
the shorter the time to block the coal flow, and the more conductive to division. However, the
speed shall not be too fast, otherwise, it will cause unacceptable damage to the coal.
12.4 Sample Preparation System
The sample collection (preparation) mechanical system should be designed, constructed and
put into operation at the same time as related projects, so as to ensure the optimum operating
conditions of the mechanized sampling system. If a sampling system is added to an already
constructed factory, then, there shall be no circumstances in the engineering design that would
cause errors in the sampling system.
The design of the sampling and sample preparation system shall be based on the type of coal,
the parameters to be determined, the expected number of sub-samples, the mass and sampling
frequency, and in accordance with the stipulations of Chapter 6.
The design and processing of the sample preparation system shall satisfy the following
requirements:
a) The sample preparation has no substantial bias, and the precision complies with the
requirements (see GB/T 19494.3);
b) Able to maintain the operational capability under specified conditions;
c) The operation is safe, and the safety complies with the requirements of on-site safety
regulations;
d) Robust enough to withstand the worst expected working conditions;
e) The entire system, including dividers, chutes, feeders, reducers and other equipment,
is self-cleaning and non-blocking, and rarely requires maintenance during operation;
f) Able to avoid specimen contamination, for example, contamination by specimens left
in the machine during the previous sample preparation;
g) When preparing particle size analysis specimens, the particle size is reduced to the
minimum;
h) Changes in moisture and chemical and physical properties, and loss of fine coal are
minimized.
12.5 Fully Automatic Sample Preparation System
12.5.1 Overview
A sample preparation system that can directly prepares coal samples that comply with the
stipulations of total moisture test coal samples, coal samples for back-check and test coal
samples with a particle size less than 0.2 mm from coal samples manually collected or by a
mechanized sampling machine, without manual intervention throughout the process, and
equipped with functions, such as: coal sample weighing, reduction, division, drying, packaging,
coal sample transshipment in each stage and sample preparation process control, etc. is called
fully automatic sample preparation system.
NOTE 1: depending on the control modes of the sample preparation process, some sample
preparation systems are also called intelligent sample preparation systems and other
similar names.
NOTE 2: coal samples are transshipped in each stage by belts, chained hoppers and robots, etc.
NOTE 3: if the fully automatic sample preparation system has measures to make the test coal
sample with a particle size less than 0.2 mm reach the air-dried state, then, the specimen
is a general analysis test coal sample.
12.5.2 Basic requirements
12.5.2.1 In addition to satisfying the corresponding stipulations of this document, the fully
automatic sample preparation system shall satisfy the following requirements:
a) Adjust the subsequent sample preparation procedures in accordance with the mass of
the feeding coal sample and the nominal maximum particle size, so that the mass of
the prepared total moisture test coal samples, coal samples for back-check and test
coal samples with a particle size less than 0.2 mm satisfies the stipulations of this
document;
b) The discharging particle size of each stage (except the 0.2 mm stage) shall satisfy the
stipulations of the nominal maximum particle size, and all 0.2 mm test coal samples
shall pass the 0.2 mm standard sieve;
NOTE 1: excessively large particle size will affect the precision of division, while excessively
small particle size will increase moisture loss and affect the total moisture determination
results.
c) During the entire sample preparation process, the loss and remaining of moisture and
mass of the coal sample shall not affect the representativeness of the coal samples
prepared this time or the coal samples subsequently prepared;
d) After the bias test and precision test, the system shall satisfy the following
requirements:
---The system shall have no substantial bias and pass the precision inspection;
---The bias test parameters shall at least include total moisture and ash content;
---The target value of sample preparation and assay variance VPT expressed in ash
content or moisture is 0.05PL2, the acceptable bias range shall be determined
through consultation among all relevant parties using the system; when the coal
sample prepared by the sample preparation system is a staged coal sample after
online sample preparation by the sampling machine, the bias and precision
inspection shall assess the entire sample preparation process of online sample
preparation and sample preparation by the automatic sample preparation system;
NOTE 2: if the acceptable bias range cannot be determined through negotiation, then, the absolute
value of the upper and lower limits of the range should not be greater than 0.15PL.
---The bias test and precision inspection shall be carried out in accordance with GB/T
19494.3.
12.5.2.2 Precision verification and bias test shall be performed on the fully automatic sample
preparation system regularly or under the following circumstances:
a) When a new system is put into use;
b) When the sample preparation procedures of the system are changed;
c) When key components of the system are replaced;
d) When there is doubt about the bias or precision of sample preparation;
e) When it is considered necessary to inspect the bias or precision of sample preparation.
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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