GB/T 19494.1-2023Mechanical sampling of coal - Part 1: Method for sampling (English PDF)

3.1 coal sample

A representative portion of coal taken for the purpose of determining certain properties.

3.2 test sample of coal

Sample prepared to satisfy specific test requirements.

3.3 common sample of coal

Coal sample taken for multiple tests.

3.4 moisture sample of coal

Coal sample specially taken for the determination of total moisture.

3.6 size analysis sample of coal

Coal sample taken specifically for particle size analysis.

3.7 sampling

The process of taking a representative portion of coal from a large amount of coal.

3.8 increment

A sample taken by operating the sampling device once or intercepting a full cross-section of the coal flow.

3.9 primary increment

An increment taken during the first stage of sampling, before any reduction or division.

3.14 lot

An independent quantity of coal, for which, bulk properties need to be determined.

3.15 continuous sampling

Take a gross sample from each sampling unit in a lot of coal. During sampling, the increment points are distributed at even intervals.

3.16 systematic sampling

Take increments at the same time, space or mass intervals, but the first increment is taken randomly within the first interval, and the remaining increments are taken at selected intervals.

3.31 relevant bias

A bias that is of practical importance or agreed by all parties to the contract.

4.1 General Requirements for Sampling

The purpose of coal sampling and sample preparation is to obtain a test sample of coal whose test results can represent the entire lot of sampled coal.

4.2 Precision

In principle, sampling schemes can be designed to achieve any level of precision.

Formula (1) is the precision estimation formula during continuous sampling, and its relevant theory is described in GB/T 19494.3.

5.1 Basic Procedures of Establishing Sampling Schemes

The basic procedures of establishing sampling schemes are as follows.

5.2 Design of Sampling Procedures

5.2.1 Determination of sampling object and type of specimen

The first step in designing a sampling scheme is to determine the coal to be sampled, including the source, variety, original production (or use) coal / new production (or use) coal, lot size of sampled coal, nominal top size and quality history.

5.2.2 Determination of Sampling Precision

The sampling precision is determined based on the purpose of sampling, the type of specimens and the requirements of all parties to the contract. In the absence of agreement, the precision can be determined with reference to Table 1.

5.2.3 Determination of coal variability

5.2.3.1 Determination of variance of primary increments

The variance of primary increments depends on the variety of coal, the nominal top size, the degree of processing and mixing, the absolute value of the parameter to be measured and the mass of increments.

5.2.3.2 Sample preparation and assay variance

The variance of sample preparation and assay VPT is obtained through one of the following methods.

5.2.4 Number of sampling units and number of increments

5.2.4.1 Overview

Theoretically speaking, the number of increments taken from a lot of coal to obtain a specific sampling precision is a function of the quality variability of that lot of coal, which has nothing to do with the size of that lot of coal. However, in practice, due to the serial correlation of coal, it is related to the quantity of coal.

5.2.4.2 Determination of number of sampling units and number of increments with known

VI and VPT

6.1 General Rules

The moving coal flow sampling is carried out in a time-basis or mass-basis systematic sampling mode or a stratified random sampling mode. From the perspective of operational convenience and economy, time-basis sampling is preferred.

6.2 Systematic Sampling

6.2.1 Time-basis sampling

6.2.1.3 Mass of increment

The mass of the increment is proportional to the coal flow rate. The average mass of primary increments and the absolute mass of primary increments shall be greater than the values calculated through Formula (12) and Formula (13).

6.2.2 Mass-basis sampling

6.2.2.1 Primary increment collection method

The primary increments are collected at preset mass intervals. The first increment is randomly taken within the first mass interval, and the remaining increments are taken at equal mass intervals. Variable-velocity or fixed-velocity samplers can be used for sampling. If the pre-calculated number of increments has been collected, but the coal flow in the sampling unit has not finished, then, sampling shall continue at the same mass interval, until the coal flow finishes.

6.3 Stratified Random Sampling

6.3.1 Basic requirements

The quality of coal may periodically change during the sampling, and its change period shall not coincide with the increment collection period, otherwise, it may cause unacceptable sampling bias. For this purpose, stratified random sampling can be adopted.

6.3.2 Time-basis stratified random sampling

In accordance with the stipulations of 6.2.1.2 and 6.2.1.3, respectively calculate the sampling time interval and increment mass.

6.4 Reference Sampling

The reference method for coal flow sampling is the stop-belt sampling method, which is only used when conducting sampling system error tests. This method shall comply with the stipulations of GB/T 19494.3.

6.5 Moving Coal Flow Sampling Machinery

6.5.1 Basic requirements

The basic conditions for mechanized samplers are as follows.

6.5.2 Design of downflow samplers

6.5.2.1 Basic requirements

The sample cutter shall satisfy the following requirements.

7.1 Overview

This clause mainly applies to full depth and deep stratified sampling of coal carried by trains, cars and shallow barges. A sampling unit can be a train, one or several carriages, one or several barges.

7.2 Collection of Increments

The increments are collected using the sampler specified in 7.4.During sampling, the sampler shall be inserted into the coal to take a full-depth coal pillar of increment from the top to the bottom, or it shall be inserted into the coal to a certain depth and take out a stratified increment when it can ensure that the quality of coal in the carrier is uniform and there is no stratified loading of coal with different qualities; during sampling, large blocks of coal, hard coal or rocks that shall be collected shall not be pushed away, and wet coal shall not stick to the sampler.

7.3 Distribution of Increments

7.3.1 Sampling on trains

7.3.2.2 Selection of increment position

The selection of increment position is the same as sampling on trains (see 7.3.1.2).

7.3.3 Sampling on barges

The increment distribution of sampling on barges is, in principle, the same as that of sampling on trains (see 7.3.1). Sampling on barges can be carried out in accordance with the stipulations of 7.2 and 7.3.

7.3.6 Random collection method of increments

7.3.6.1 Selection of carriages / barges for sampling

Number the carriages / barges of the entire sampling unit, make and number the number of plates equal to the total number of carriages / barges, and one plate corresponds to one carriage / barge.

7.4 Stationary Coal Sampling Machinery

7.4.1 Basic requirements

Any stationary coal sampling machinery that satisfies the stipulations of 6.5.1 can be used.

Before using the stationary coal sampling machinery, a bias test shall be carried out in accordance with the method specified in GB/T 19494.3, and it can only be used after it is proved that there is no relevant bias.

7.4.2 Example

Commercial sampling machinery, to which, stationary coal sampling applies, is shown in Figure

4 and Figure 5.