GB/T 19494.2-2004 English PDF (GBT19494.2-2004)
GB/T 19494.2-2004 English PDF (GBT19494.2-2004)
GB/T 19494.2-2004: Mechanical sampling of coal -- Part 2: Method for sample preparation
NATIONAL STANDARD OF THE
PEOPLE REPUBLIC OF CHINA
Mechanical sampling of coal -
Part 2: Method for sample preparation
(ISO 13909-1:2001 Hard coal and coke - Mechanical sampling - Part 1:
General introduction, ISO 13909-4:2001 Hard coal and coke - Mechanical
sampling - Part 4: Coal - Preparation of test samples, NEQ)
ISSUED ON: APRIL 30, 2004
IMPLEMENTED ON: OCTOBER 01, 2004
Issued by: General Administration of Quality Supervision, Inspection and Quarantine;
Standardization Administration of PRC;
Table of Contents
Foreword ... 3
1 Scope ... 5
2 Normative references ... 5
3 Terms and definitions ... 6
4 Precision of sample preparation ... 7
5 Composition of samples ... 8
6 Division ... 9
7 Reduction ... 23
8 Mixing ... 24
9 Air drying ... 24
10 Preparation of various coal samples ... 25
11 Coal samples retained for reference ... 32
12 Design of sample preparation equipment ... 32
Mechanical sampling of coal -
Part 2: Method for sample preparation
This part of GB/T 19494 specifies the terms and definitions for coal sample preparation; the composition, division, reduction, mixing, air drying of samples; the preparation of various coal samples; the design of reference coal samples and sample preparation equipment.
This part applies to lignite, bituminous and anthracite.
2 Normative references
The provisions in following documents become the provisions of this part through reference in this part of GB/T 19494. For the dated references, the subsequent amendments (excluding corrections) or revisions do not apply to this part; however, parties who reach an agreement based on this part are encouraged to study if the latest versions of these documents are applicable. For undated references, the latest edition of the referenced document applies. GB/T 211 Determination of full moisture in coal (GB/T 211-1996, eqv ISO 589:1981)
GB/T 19494.1 Mechanical sampling of coal - Part 1: Method for sampling
(GB/T 19494.1-2004, ISO13909-1:2001 Hard coal and coke - Mechanical
sampling -Part 1: General introduction, ISO 13909-2:2001 Hard coal and
coke -Mechanical sampling - Part 2: Coal - Sampling from moving streams, ISO 13909-3:2001 Hard coal and coke - Mechanical sampling - Part 3: Coal -Sampling from stationary lots, NEQ)
GB/T 19494.3 Mechanical sampling of coal - Part 3: Determination of
precision and bias test (GB/T 19494.3-2004, ISO 13909-7:2001 Hard coal
and coke - Mechanical sampling - Part 7: Methods for determining the
precision of sampling, sample preparation and testing, ISO 13909-8:2001 Hard coal and coke - Mechanical sampling - Part 8: Methods of testing for bias, NEQ)
3 Terms and definitions
The terms and definitions as specified in GB/T 19494.1 and the following terms and definitions apply to this part.
The process of bringing a coal sample to an analytical or experimental state. Note: Sample preparation includes mixing, reduction, division, and
sometimes air drying. It can be done in several stages.
On-line sample preparation
Samples are prepared using equipment integrated into the sampling system. 3.3
Off-line sample preparation
The coal sample taken by the mechanical sampling system is manually or
mechanically prepared by the use of equipment that is not integrated with the mechanical sampling system.
Sample preparation process of dividing the sample into representative,
Fixed mass division
Division method with constant retained sample mass and independent of the mass of the divided sample.
Fixed ratio division
A method of division with a certain division ratio, that is, the amount of samples retained is proportional to the amount of samples to be divided. samples. The most important factors affecting the precision of sample
preparation are the homogeneity of the coal sample before the division and the remaining amount of the coal sample after the division. The sample preparation procedures specified in this standard can make the variance of sample
preparation and assay VPT as expressed by ash or moisture be below 0.2. If mechanical sample preparation equipment is used, sample preparation and assay precision may be better.
The errors (represented by variance) at each stage of sample preparation and assay can be tested by the method specified in GB/T 19494.3.
5 Composition of samples
A sample is generally composed of many single sub-samples, or synthesized from all the sub-samples of the entire sampling unit, or synthesized from a part of the sub-samples of a sampling unit. In some cases, such as particle size analysis and bias test, a sub-sample constitutes a specimen.
The subsample merging procedure varies depending on the sampling method - time-based sampling or mass-based sampling (see 5.2).
A specimen may also be a combination of several smaller specimens (see 5.3). 5.2 Merging of subsamples
5.2.1 Time-based sampling
The mass of the sub-samples in time-based sampling is proportional to the coal flow during sampling. At this time, the sample can be directly combined from the primary sub-samples, or can be combined from the post-division sub- samples that have been prepared to a certain stage by the fixed ratio division method (see 6).
5.2.2 Mass-based sampling
If the mass of the primary sub-samples is nearly uniform (that is, the coefficient of variation of the mass of the sub-samples is less than 20%, meanwhile there is no correlation between the mass of the sub-samples and the coal flow rate - see GB/T 19494.1 Appendix B), the primary sub-samples can be combined into a sample, or combined directly, or combine the primary sub-samples after dividing it into a certain stage by using the fixed ratio division method (see 6). If the mass of the primary sub-samples is not uniform, they shall be divided to a certain mass according to the fixed mass division method and then combined into a specimen (see 7).
mSO - The mass of the specimen after division at a given nominal maximum particle size as specified in Table 1, in kilogram (kg);
PO - The precision of a given division stage as specified in Table 1;
PR - Precision required for a given division stage.
When a coal is routinely sampled in the same environment, the precision of all required quality parameters shall be checked as much as possible (see GB/T 19494.3), meanwhile the mass of the specimen after division shall be adjusted, but its mass must not be less than the minimum required by the relevant analytical method standard.
When preparing coal samples for various purposes, the required mass and particle size composition of each sample shall be fully considered.
6.3 Artificial division method
The riffle is a simple and effective divider (the structure is shown in Figure 4). It consists of two sets of oppositely arranged grid slots and receivers. The number of slots on both sides is equal, at least 8 on each side. The size of the cell opening is at least 3 times the nominal maximum particle size of the specimen. The inclination of the slot to the horizontal plane is at least 60??. In order to prevent the loss of pulverized coal and moisture, the receiver and the main body of the riffle shall be closely matched, preferably closed.
When division, the specimen shall be swing back and forth along the length of the riffle into the slot. The feeding shall be uniform and the feeding speed shall be controlled. Do not concentrate the specimen on one end; do not block the grid.
When the division needs to pass through the riffle in several steps or several times, after each step or each pass, it shall collect the retained sample from the receivers at both sides, alternately.
an air circulation device at a temperature not exceeding 50 ??C. But after drying, the dried coal sample must be cooled at ambient temperature before weighing and allowed to reach equilibrium with atmospheric humidity. The cooling time depends on the drying temperature. If it is dried at 40 ??C, cooling for 3 hours is usually sufficient. However, for easily oxidized coal and the following coal samples for analysis and testing, they cannot be dried at temperatures higher than 40 ??C:
a) Heat generation;
d) Air drying as part of the full moisture determination.
10 Preparation of various coal samples
10.1 Types of coal samples
Coal samples for coal analysis test may be divided into the following types: a) Coal sample for determination of full moisture;
b) Coal sample for general analysis test;
c) Coal samples for both full moisture and general analysis tests;
d) Coal sample for particle size analysis;
e) Coal samples for other tests, such as the determination of Hastelloy index, determination of carbon dioxide chemical reactivity, etc.
10.2 Coal sample for determination of full moisture
10.2.1 Sample preparation procedure
Coal samples for determination of full moisture shall meet the requirements of GB/T 211. The general preparation procedure is as shown in Figure 8.
external moisture, and then reduce it to the appropriate particle size to measure the internal moisture. However, a sealed, small air flow reducer and a riffle shall be used for sample preparation.
10.2.2 Air drying
The purpose of air drying is mainly to determine the external moisture and to minimize the loss of moisture during the subsequent sample preparation
Air drying shall generally be performed before the sample is reduced and divided. In the following cases, air drying may not be performed in advance: a) Coal samples have low moisture content and no substantial moisture bias during sample preparation;
b) When the volume of the sample is too large and it is difficult to air-dry all, it can be reduced and divided first to a certain stage, then air-dried, but the reduction-division process shall be tested without substantial bias; c) The specimen?€?s particle size is too large for air drying. It can be reduced to a certain particle size and then dried, but there shall be no substantial bias during the reduction process.
When the coal sample is too wet and the water seeps out of the coal or sticks to the container, the container and the coal sample shall be air-dried together. After the air drying is continued for 1 hour, the mass of the coal sample does not change up to 0.1%; the mass loss of the coal sample is taken as its external moisture and counted as the full moisture.
10.2.3 Reduction and division
Reduction shall be performed by the use of equipment that does not generate obvious heat and little air movement in the machine, to avoid water loss during the reduction process. Unless the test proves that reduction does not produce substantial bias of moisture, the specimen cannot be reduced before air drying. Division shall generally be performed after air drying. If division before air drying, a division machine with small air flow shall be used and operated quickly to minimize the degree of moisture change. If the coal sample is too wet and cannot pass the division machine smoothly, then the sample is first air-dried and then divided, or the artificial checkerboard method, strip method or nine- point method is used for division.
Coal samples shall be stored in non-absorbent, air-tight sealed containers and The preparation of coal sample for general analysis test is usually performed in 2 ~ 3 stages; each stage consists of drying (when needed), reduction, mixing (when needed), division. If necessary, the reduction stage can be increased or decreased according to the specific situation. The particle size of the coal sample and the mass of the divided coal sample at each stage shall meet the requirements of 22.214.171.124.
10.3.2 Air drying
The purpose of air drying is to make the coal sample pass through the reduction and division equipment smoothly; to prevent the moisture change of the coal sample during the analysis test.
Air drying can be performed at any sample preparation stage. Drying before the final sample preparation stage is not required to achieve a humidity equilibrium. If the coal sample can pass through the reduction and division equipment smoothly, it may not be dried. However, the air drying in the final sample preparation stage must reach a humidity equilibrium state.
10.3.3 Reduction and division
In general, each sub-sample shall be reduced to less than 3 mm in accordance with the requirements of Chapter 6 and Chapter 7; then combined into a total sample. When possible, it is best to reduce it below 3 mm in the first stage to reduce the amount of sample retained in the next stage, while minimizing the division error. When the coal sample?€?s particle size is too large or the moisture is too high, it may add one sample preparation stage before it reaches 3 mm. Mechanical methods shall be used for reduction. If the original particle size of the coal sample is too large, it allows to use artificial methods to reduce the large pieces below the maximum feed particle size of the reducer.
Division shall be done by mechanical methods. If manual method is used, when the particle size is less than 13 mm, it is better to use a riffle. If using the chessboard method and the strip method, take at least 20 sub-samples.
10.4 Shared coal sample
10.4.1 Sample preparation procedure
In most cases, for the sake of convenience, the shared coal sample used for full moisture determination and general analysis test is taken at the same time. When preparing shared coal samples, it shall meet the requirements of GB/T 211 and national standards for general analysis and test items at the same time. The preparation procedure is as shown in Figure 10.
The coal samples for other tests are prepared as described in 10.3 and 10.4, but their particle size and mass shall meet the requirements of relevant test methods. The sample preparation procedure is as shown in Figure 11.
11 Coal samples retained for reference
At the same time as the original coal sample is prepared, the coal sample retained for reference is prepared at certain preparation stage by the same procedure.
The coal sample retained for reference shall be divided as little as possible; it may be divided to the maximum possible storage amount. It shall not be
reduced too much. It shall be reduced to the nominal maximum particle size corresponding to the maximum storage mass as found in Table 1.
12 Design of sample preparation equipment
The division equipment shall meet the following requirements:
a) There is sufficient capacity to completely retain or pass the entire specimen without loss or overflow;
b) It does not create substantial bias, such as not selectively collecting (or discarding) particulate coal or losing moisture. In some cases, it shall be fully enclosed to prevent moisture loss;
c) The feeding method shall minimize particle size segregation.
d) The coal flow as fed into the equipment shall be uniform at each stage of division;
e) For online divider, the cutting frequency of the latter divider shall be out of phase with that of the previous divider.
In addition, the divider shall preferably be able to sample randomly during the first division interval, meanwhile the divider shall be started before starting the feed.
12.2 Design of downflow divider?€?s cutter
12.2.1 Basic requirements
In addition to the requirements described in 12.1, the downflow divider?€?s cutter shall also meet the following requirements:
12.3.1 Basic requirements
The cross-belt division cutter for division is generally fixed; its 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 coal flow;
c) The cutter shall pass through the coal flow at a uniform speed (the speed difference between each point is not greater than 10%);
d) The size of the cutter?€?s opening shall be more than 3 times the nominal maximum particle size of the coal;
e) The cutter shall have sufficient capacity to accommodate the entire sub- sample taken at the maximum coal flow;
f) The arc of the edge of the cutter shall match the curvature of the belt; the side plate and the rear plate shall be kept at a minimum distance from the surface of the belt. They shall not be in direct contact with the belt. The rear plate is equipped with cleaning brush or elastic scraper.
12.3.2 Cutting speed
The speed of the cross-belt cutter is not strictly regulated. In general, 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 better it is for division. But the speed shall not be too fast, otherwise it will cause unacceptable damage to the coal block.
12.4 Sample preparation system
The sampling (manufacturing) mechanical system should be designed,
constructed and put into operation at the same time as related projects, to ensure that the mechanized sampling system has the best operating conditions. If the sampling system is added to the completed factory, there must not be any situation in the engineering design that causes the sampling system error. 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 subsamples, the mass and the sampling frequency as described in Chapter 6. The design and processing of the sample preparation system shall meet the following requirements:
a) The sample preparation has no substantial bias and the precision meets