灰份仪 进口灰份仪 灰份在线测量装置    

广州瑞发公司供应高质量灰份仪、灰份在线测量装置。进口灰份仪其精度和稳定性均表现十分优越。同时提供相似的国产灰分仪，品质好，价格低。灰份仪其主要原理特点用英文介绍如下：

Continuous determination of ash in coal and in coal turbid

MEASURING PRINCIPLE 灰份仪测量原理

Electro-magnetic waves like X-rays or gamma-rays are absorbed in material by different ways. Therefore it depends on the energy of the radiation and on the material itself in which way it is absorbed. High energy waves and low atomic numbers are absorbed according to the density (or bulk density) of the material. Of course the absorption  also is depending on the layer thickness. That means the absorption is depending on the weight of the material  the radiation has passed through ( The weight increases if the way becomes longer or if the density becomes higher). Density and thickness can be measured by means of radiations: If one is constant the other can be calculated.

Lower energy radiation and higher atomic numbers are absorbed in the same way but additional according to the  atomic weight. As higher the atomic weight and as lower the energy as higher the absorption.

For analysis purposes a weak energy is needed to determine the atomic composition. But also the weight is influencing  the absorption. So a higher energy radiation also must be applied to get a signal which is influenced by the weight only but not by the atomic composition. Both signals can be used mathematically to determine the composition.

THE TECHNIC 灰份仪技术要点

To measure radiation it must be absorbed. The absorption is higher as more dens the absorber material is. There  are gas filled ionisation chambers or Geiger tubes available but the most sensitive is a crystal of NaJ with a  density of 3.7 g/cm3. This crystal produces a small light flashes when exposed to radiation which must  be detected by a light amplifier called photo-multiplier. The whole detector must be build in a mechanical protection and light tight housing and also stabelized against any changes.

The two sources of radiation have to be shielded in lead containers to prevent the rays to travell in all directions. By a thin channel it is ensured that only in one direction the working beam is allowed to come out. The radiation is measured by a scintillation counter which is the most sensitive detector available for industrial applications.  Both, source and detector, is called measuring path. Two measuring pathes are necessary for ash determination.  It would be possible to use only one detector for both radiations but because physically in the detector each radiations  influences the other it is more reliable to use separate ones.

Either source or detector can be installed above or underneeth the belt. The measuring pathes should have a distance of 1 m minimum to each other. A firm mechnical frame is needed to prevent changes of the distance between source and detector: It must be absolutelly constant to avoid measuring errors.

PRACTICAL APPLICATION 灰份仪实际应用

A radiation source with Caesium-137 is an emitter of relatively high energy radiation. The energy is high enough  to be independent on the composition and low enough to handle it in a secure way. It is able to detemine the weight of the material which it has passed through with a high precition so that for instance radiometric belt scales  are using it.

Another material emmiting radiation is Americium-241. This energy is quiete low: A sheet of steel of 0.8mm thickness  is weakening the intensity to the half. In coal the part which is called ash absorbs the radiation of the Am-241  much more then the carbon. So a higher ash content gives an relativly strong increase of the absorption. Unfortunatelly there is no practical way that this absorption is not influenced by density or layer thickness e.g. loading on a belt. Therefore both signals are needed together to calculate mathematically the percentage of ash.

THE EVALUATION

A program just using highly sophisticated mathematics is not helping the user: It must be appliable. The ash analyser must be able to be calibrated without extended mathematical background. Therfor a table is stored in the  evakuation unit where laboratory values can be stored and used as comparison. A automatical routine for determination  of the calibration curve finds the coeffcients and shows immidiatelly how good the fit was.

But not only the simple display of the measuring results is important. The allready mentioned table can be used  as a data storage. All measuring values are shown over a time period of 1 hour, 1 shift and 1day back for 30 days.

In the service menu the soft ware is able to change the wiring terminals so that a relay or an analogue output  can be switched from one terminal to another.

Therefore the evakuation unit is not only an display of ash but fits into the process and can help tho controll  it.

ACCURACY 灰份仪精度

A few influences are responsible for possible errors and good or bad accuracy.

The coal comming from one mine only normally an accuracy of better then ± 0.5% standard error for about 10% ash also with corse coal . For ash contents lower then 10% even better results are achieved. For higher ash contents the error is bigger but not because of the principle but related to the higher error of the laboratories.  The system must be calibrated with an error of 0.3% caused by the laboratoties and therefore has a restricted accuracy.

The most important possible error is caused by the coal itself: The measuring principle is based on distinguishing two components. In reality it is something like ten. Any change of the composition of the ash causes a slight error. Because the two main components do have nearly the same absorption coefficient this ratio does not cause a wrong  indication. The attention must be put on changes like such in iron content. The theoretical error can be very big but is not very important in practice. Nevertheless it has to be considered.

Another error can be caused by the moisture content. Only when the ash content is about 5 - 10 % is does not cause an error because water is measured as coal. For higher contents is can cause an error. Fortunatelly this can be compensated for with an RGI micro wave moisture meter.