Coal sampling is very important because about 85% of coal quality determination errors come from sampling while another 15% comes from sample preparation and laboratory testing.
Adequate manpower, competence, and also the standard sampling equipment is also required. If sampling is done in the shipping process then the sample should be able to represent the overall amount of cargo in the vessel.
Therefore, ASTM provides the rules of the number of side increments according to the total cargo load.
Sampling should be done randomly or if using a conveyor then you should know about the sampling time interval. Don't do sampling at one point only. Do it at a random point. Keep sampling done evenly. Coal in the field can have various sizes. From small to large-sized particles. Therefore, the representative sampling of each size is also very important.
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| Coal sampling process in Vessel |
Each sample that has been collected should be identified. Plastic bags that have been marked can be used in this process.
Make sure the sample is tightly closed to prevent water evaporation and also coal oxidation during the trip to the test site.
Signs of Coal Sampling Errors
One indication of an error in sampling is if the coal has a significant difference in the analysis results of each parameter. This difference occurs in every lot in sampling. Whereas, in reality, there is no blending done in the shipping process.
One other sign is the unreasonable analysis result, as if the calorie value of the coal is lower-grade you get a higher-grade result or vice versa. However, the feasibility of laboratory equipment, as well as the sample preparation process, should also be verified beforehand.
Yes, the result difference always occurs in the analysis, but if you know the characteristics of the product quality of a coal mine then it can be used as a reference, though not always the case. Other errors on sampling can be viewed visually.
If you find the size of the coal in sampling is only large or small only. In fact, the coalfield has a particle size that is not the same. So, the sampling is not representative and the possibility of error will be greater. To compare it, you can check the report of the sampling team how real coal conditions are in the field.
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| Coal with size about 50 mm |
This is due to uneven sampling. For example coal sampling with a certain quality at one point, when in fact the part is only a small part of the larger part. With a large enough shipload, it can reach 30,000-80,000 metric tons then the correct sampling technique should be applied.
The correct way of sampling is that it can represent the quality of coal from the whole of the charge.
Error in sampling always happens. However, by following standard procedures, such as from ASTM, ISO or other recognized standards, the error can be minimized as much as possible.
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