Overview 1. 1. 1
The sampling of moving coal flow can be carried out in the coal flow or on the belt. For the sake of safety, this standard is not recommended to be used in coal flow belt.
Sampling can be done on a time basis or a quality basis in a systematic sampling mode or a stratified random sampling mode. From the point of view of convenience and economy, timing sampling is better.
When sampling, try to intercept a complete coal flow section as a sub-sample, and the sub-sample cannot fill the sampler or overflow from the sampler.
As far as possible, samples should be taken from the coal flow with uniform velocity and load. The load and quality change cycle of coal flow should avoid overlapping with the operation cycle of sampler as far as possible to avoid sampling deviation. If unavoidable, stratified random sampling should be adopted.
1. 1.2 Downflow sampling method
This method is not suitable for systems with coal flow above 400 t/h.
At the transfer point of the conveyor belt, coal samples are collected from the falling coal flow.
When sampling, the sampling device should cut the coal flow at a constant speed of less than 0.6/s as much as possible. The opening of the sampler should be at least 3 times the nominal maximum particle size of coal and not less than 30mm, and the capacity of the sampler should be large enough so that the subsamples will not fill the sampler. There should be no inappropriate physical loss in the extracted sub-samples.
When sampling, make the sampling funnel intercept one sub-sample at a time through the coal flow along the length or thickness direction of the coal flow. For safety and convenience, the sampling funnel can be placed on a bracket, and the sampling can move from left to right (or vice versa) or from front to back (or vice versa) along the crossbar of the bracket.
1. 1.2. 1 system sampling
1. 1.2. 1 subsample distribution
The main sub-samples should be evenly distributed throughout the sampling unit. The sub-samples are acquired at a preset time interval (time-based sampling) or quality interval (quality-based sampling), the 1 th sub-sample is randomly acquired at the 1 time/quality interval, and the remaining sub-samples are acquired at equal time/quality intervals. During the whole sampling process, the speed of the sampler through the coal flow should be kept constant. If enough pre-calculated number of sub-samples have been collected, but the coal in the sampling unit has not flowed out, sampling should continue at the same time/quality interval until the coal flow ends.
In order to ensure that the actually acquired number of sub-samples is not less than the specified minimum number of sub-samples, the actual sub-sample time/quality interval should be equal to or less than the calculated sub-sample interval.
1. 1.2. 1.2 subsample interval
When sampling the system, determine the sub-sampling interval as follows:
A) time-based sampling
1. 1.2. 1.3 sub-sample quality
The quality of the subsample is directly proportional to the coal flow.
1. 1.2.2 stratified random sampling
Overview 1. 1.2.2. 1
The coal quality may change periodically during the sampling process, so it should be avoided that the change period coincides with the sampling period, otherwise it will bring unacceptable sampling deviation. Therefore, stratified random sampling method can be adopted.
Stratified random sampling does not sample in equal time or quality intervals, but randomly samples in pre-divided time or quality intervals.
In stratified random sampling, two sub-samples belonging to different time or quality intervals are likely to be very close, so the coal unloading box of a sampler should be able to accommodate at least two sub-samples.
1. 1.2.2 sub-sample distribution
Sampling sub-samples randomly in each preset time interval (time-based sampling) or quality interval (quality-based sampling).
1. 1.2.2.3 subsampling interval
Determine the sub-sampling interval of stratified random sampling, as follows:
A) time-based sampling
Calculate the sampling interval according to the formula (1).
The time (s or min) from 0 to the end of each time interval is divided into several segments, and then the sampling period in each time interval is determined by a random method, such as drawing lots, and sub-samples are taken at this time.
B) quality-based sampling
Calculate the sampling quality interval according to formula (2).
The quality (T) number of each quality interval from 0 to the end of the interval is divided into several sections, and then the coal quality analysis instrument determines the sampling quality section in each quality interval by random methods such as drawing lots, and samples are taken when the quality number is reached.
1. 1.3 Stop the belt sampling method.
Overview 1. 1.3. 1
Some sampling methods tend to collect too much large or small coal, so it is likely to introduce deviation. The most ideal sampling method is stop sampling method. It takes a complete cross section from the stopped belt as a sub-sample. It is the only way to ensure that all particles can be collected, and the sulfur analyzer of coal quality instrument has no deviation. It is also a reference method for checking other methods. In the case of routine sampling, it is not practical to stop belt sampling operation, so this method is only used as a reference method in deviation test.
1. 1.3.2 sub-sample collection
Stop the strip sample at a fixed position and use a special sampling frame for sampling.
The sampling frame consists of two parallel side plates, the distance between the plates is at least 3 times of the nominal maximum particle size of the sampled coal and not less than 30mm, and the radian of the bottom edge of the side plate is similar to that of the belt. When sampling, put the sampling frame on the coal flow of the stationary belt so that the two side plates are perpendicular to the center line of the belt. Insert the side plates into the coal flow, contact the belt at the bottom edge, and then collect all the coal between the two plates. Left-handed or reverse-handed treatment shall be carried out on the coal particles inserted by the baffle, that is, the coal particles inserted on the left side of the baffle shall not enter the coal sample, and the coal particles inserted on the right side of the baffle shall not be discarded, and vice versa. How to choose between the initial sampling and the whole sampling process? The coal stuck on the sampling frame should be scraped into the sample.