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Coal Sampling Procedures Overview

Coal sampling is the first step before ordering the bulk coal material and generating power by coal. As we know, the purpose of coal sampling and preparation is to get a precision sample which can represent the entire lot.

The coal sampling procedure seems like a simple procedure, but it has many rules in the sampling industry. The fundamental sampling process has three main steps. Firstly, getting a coal sample from the entire coal lot, we call these coal briquettes as a primary increment. Then combining all primary increments which are divided and the non-divided primary increments together, which calls the gross sample. The gross sample will be tested and analyzed to ascertain the entire coal lot characters. The basic requirement of sampling is, each coal particles can be sampled, and each coal particles can be made to the test sample.

In order to ensure the precision of test sample meets the ASTM D7430 Standard and the GBT-19494.1-2004, we should consider these elements when sampling:

  1. The variability of coal;
  2. The number of the gross sample;
  3. The number of sub-samples per gross sample;
  4. The quality of test sample;

In order to meet the requirements of coal sampling standards, it is better to use the moving stream coal conveyor belt. In according with the coal moving stream, the cross belt sampling system is the best choice. Of course, the auger sampling system is the best sampling method for the coal trucks and coal wagons. Whatever sampling methods you choose, the sampling system machine must be tested and meets the sampling standard.

General sampling procedures

How to make the sample? The general coal sampling procedures must include these procedures:

  1. Get the basic information of the coal including the source of coal (like China coal, India coal), the coal amount and the nominal top size.
  2. Ensuring the text parameters and the test-sample type;
  3. Determining the sampling method is continuous sampling or the intermittent sampling.
  4. Ensuring or presuming the required precision;
  5. Determining how to combine the primary increment to the gross sample;
  6. Presuming the coal variability;
  7. Ensuring the number of sampling unit and sub-sample;
  8. Ensuring the gross sample minimum quality according to the nominal top size;
  9. Ensuring the sampling methods: auger sampling, cross belt sampling;

Moving Coal stream sampling method


The moving coal stream is common in the sampling industry. The suitable sampling methods are stratified random sampling method, mass-basis sampling, and time-basis sampling. The sub-sample should take from a complete coal stream, and the sub-sample should not be filled with a sampler or overflow of the sample collector. The test sample should be sampled from the uniform velocity and load moving coal stream.

For the moving coal stream, we suggest the mechanical cross belt sampling system. TOP SAMPLER cross belt sampling system has complied with the essential conditions:

  • Our cross belt sampling system has passed the bias test by SGS.
  • Hard-wearing material, the cross belt sampling system can work under the worse working condition;
  • The sample collector has enough capacity to collect the primary increment and ensure the primary increment is not overflowed;
  • The cross belt sampling system has a self-washing function;

Furthermore, the cross belt sampling system has two main types that are head cross belt sampler and central belt sampler.

Head cross belt sampler, we also call the falling-stream sampler. We have introduced the head belt sampler in the cross belt sampling system selection, so we list some tips we need to pay more attention.

The speed of the coal sampler is crucial for the sampling procedure. According to some researches, the suggested sampler collector size is three times than the coal nominal top size, and the speed of the coal sampler should less than 1.5m/s.

Central cross belt sampler is used to the coal moving stream which is installed on the coal conveyor belt. The working principle of central cross belt sampler is sampler rotates along the axis of the center line of the conveyor belt. The primary sampler size must more than 30mm.

Stationary sampling method


The stationary sampling is suited for the coal railcar, coal trucks, coal vessel. The stationary sampling method must be a full- depth sampling method. The sampling unit can be a coal truck, a carriage or a ship. An auger sampler will enter the coal material to sample the primary increment.

Auger sampling system for railcar


Auger sampling system’s crucial element is the auger sampler. TOP SAMPLER auger sampling system is suited for various wagons. The depth of sampling is 0 to 3000mm. the sampling points are chosen by the PLC controlled system automatically. Generally, the auger sampling system has two main types. The picture shows the crane type auger sampling system for the railcar. Of course, there are some differences. the biggest difference is the left auger sampling system has two lanes, it samples independently and simultaneously. You can get more details on what is auger sampling system.


Above all, we have said the main coal sampling procedures and the moving coal stream sampling method and stationary sampling method. How to guarantee the coal sample precision? First, we need to know what the mean of coal sample precision is.

Coal sample Precision

top sampler provides coal sample analytics machines

All the coal sampling methods have errors whatever you choose. The test result will have a bias. The precision refers to a degree of coincidences among the test results which are calculated by a series of tests. Theoretically, TOP SAMPLER can design the sampling projects with any precision. This is the precision estimation formula:



PL: the precision of a coal lot;

V1: the variance of primary increment;

n: the sub-sample number of each sample unit;

u: the actual number of sampling unit;

m: the number of sampling units;

Vm: the variance of each sampling unit;

VPT: the variance of sample preparation and analytics;

For the coal sample, we pay more attention to the coal sample precision. How to determine the sampling precision? The sampling precision is decided by the sampling purpose, test sample type, and the client’s requirements. Generally, the coal sample precision like the table shown.

                                                    Coal sample precision
Coal varietyCoal precision
Clean coal±0.8%
Other types coal


All in all, this article we choose to introduce the coal sampling procedures and the main sampling methods. We have introduced much information about the coal sampling system machines.Welcome to contact us to get the free inquiry!