You are currently viewing Coal Sample Preparation Procedures Overview (1)

Coal Sample Preparation Procedures Overview (1)

As we know, sampling is the most important part in the characteristics detection of commercial coal and is a prerequisite for obtaining reliable test results. A large number of experiments show that if the bias is represented by percentage, the coal sampling accounts for 80% and the coal sample preparation occupies 16%. Obviously, in addition to sampling, the sample preparation is also a crucial part before coal sample analysis. As an experienced manufacturer, TopSampler manufactures automatic sample analytics system which merges sampling system, sample preparation system, inspection system, and analytics system into a single. We also have some research on sample preparation system. Next, we will make an introduction to the procedures of coal sample preparation.

Under normal conditions, the size and mass of coal samples we collected from the raw material are too large for the subsequent chemical and physical test. The purpose of sample preparation is to reduce and divide the original samples into test samples which have suitable size and represent the characteristics of the original samples. The size and mass of test samples depend on what kind of analysis you performed. The procedures of coal sample preparation mainly include reduction, division, mixing, sieving and drying. In article  Coal Sample Preparation Procedures Overview (2), we introduce the sample division, mixing and sieving.  We’ll walk through coal sample drying and reduction in detail in an upcoming section.

Coal Sample Drying

Drying is the process of removing large amounts of water from coal. If the water content of coal is too high, it will be hard to get through or adhere to the surface of the sample reduction and sample division machine. Therefore, the first purpose of drying is making the coal sample pass through the crushing and dividing equipment smoothly and the second one is avoiding water content changes in coal samples during analysis and testing.

Drying should normally take place before the sample is reduced and divided, but the air drying procedure should be changed under the following circumstances:

  1.  If the coal sample is low in moisture, it has no need to be dried in advance.
  2.  When the sample quantity is too large, it is difficult to be completely dried. It could be reduced and divided firstly to a certain stage, then drying.
  3.  If the sample size is too large to be dried, it can be reduced and divided to a certain size before drying.

In another word, drying can be carried out at any stage during the procedures but be careful not to oxidize the sample during drying.


drying time
Drying Time

Normally, coal sample drying should not exceed 50 degrees centigrade and dry on the floor will take much longer than in the drying oven. After continuous drying, the mass change of coal samples should not exceed 0.1%, and we should cool coal samples at ambient temperature and balance them with atmospheric humidity. The cooling time depends on the drying temperature. If it is dried at 40℃, it is enough to cool normally for 3 hours, while, the oxidizing coal should not be dried at a temperature above 40 degrees centigrade.

Coal Sample Reduction

Coal sample reduction is the process of reducing the size of coal samples, aiming at increasing the number of sample particles and decreasing the sample division bias. Samples which have the same quality, the size is smaller and the number is larger, the bias of sample division will be lesser. However, crushing consumes time and energy, especially lead to water loss. Therefore, a mess of large size coal samples should not be crushed at one time to the size required by the test sample. The method of multi- class crushing and division is better than it, but the division stages should not be too much.

Crushing should be used with mechanical equipment. The size of coal samples depends on the type of crusher, crushing speed and port. On this basis, we divide it into three categories:


Particles size <25mm-6mm

Machines: Jaw Crusher and Hammer Crusher


The jaw crusher has a strong crushing ability, high water adaptability and simple structure. It is easy to clean and good at crushing raw materials with high rigidity, such as limestone and coal. We can control the sample size by adjusting the space between the jaw plates. Jaw crusher XDEP-A TYPE produced by TopSampler is a good choice.


The hammer crusher has high working efficiency and good sealing, but it is difficult to clean and it has bad water adaptability. Thus, the coal samples which have high water content should not be put into it directly. The sample size is controlled by replacing sieve plates with different apertures. Hammer crusher XDSP-600 from TopSampler is made up of crusher hammer, crusher cavity, sample divider system and electric controlling system. It is applied to various auger sampling system and sample analytics system.


Particles size <3mm-1mm

Machines:  Roller Crusher and Hammer Crusher


The coal samples processed by roller crusher will not be excessively crushed or overheated. The sample size is controlled by adjusting the clearance of the rolls. XDSP-300 is a kind of roller crusher produced by TopSampler. It has no noise and no dust, and it is convenient to move and clean. The cavity is weld by high-quality steel to avoid cracks and breakage. If you are interested, feel free to contact us.


Particles size <0.2 mm

Machines:  Sealed Crusher

The sealed crusher is a new type of equipment which has been developed successfully in recent years. It has high efficiency. The coal samples can be reduced to less than 2mm in 1-2 minutes, no powder pollution.

With the development of technology and the updating of products, some manufacturers have upgraded the traditional sample making equipment in recent years. They assemble single crushing and division equipment into a reliable sample preparation system which called crushing-dividing machine and multi-functional crushing-dividing combined sample preparation unit, making work simple and easy. The working efficiency is greatly improved.

All in all, above content is the introduction of the coal sample drying and reduction. Hope this article is helpful to you.