On Belt Coal Quantity and Quality Analyzers (BCA)

A new generation of on-belt radioisotope ash-meters and scales is designed by Analix, Bulgaria. Accuracy, reliability, and stability are improved by a new high-tech electronics design and software.

    BCA-6 in TPP                    BCA-5 on the excavator boom 

BCA-5 on belt conveyor in open pit

The mane benefit of using BCA is reducing the production costs

Production costs reducing by using BCA in Coal mines comes from:

• improving coal/overburden ratio;
• better meeting customer requirements;
• on-line control and optimizing the mining processes.

Production costs reducing by using BCA in Coal TPP is due to:

• effective on-line control of the quantity and quality of the incoming coal;
• optimizing burning process trough on-line quantity and quality control of the coal feeding the boilers;
• avoiding critical situations caused by out of limits coal caloricity.

The pay back period for BCA instruments is about one year of operation.

Accuracy of BCA

The standard error for ash content:

• 0.5% for the range 5.0 ÷ 15.0%
• 1.0% for the range 15.0 ÷ 25.0%
• 1.5% for the range 25.0 ÷ 35.0%
• 2.0% for the range 35.0 ÷ 50.0%

For total weight the accuracy is about 2 % for quantities more than 500 t.

Radiation safety of BCA

Our instruments are permanently checked and licenzed by the Bulgarian Agency for Nuclear Regulation.

All measurements done by all kind of regulatory officials (Agency for Nuclear Regulation, Ministry of Health, Ministry of Internal Affairs, etc.) confirm the complete radiation safety of our radioisotope on-belt ash-analyzers.

The staff passing by, or working around as closed as possible, do not obtain any irradiation.

There is no one case the radiation for people working there or passing by to be higher then the native radioactive background for that area.

Construction and installing of BCA

The Ash Analyzers are mounted directly on the Belt-Conveyors without changing the construction of the Conveyor.

The supporting structure of the on-belt ash analyzer is a rectangular frame vertically mounted and embracing the belt. On the top crossbeam is mounted the detector unit registering irradiation cross passing the coal.

 Supporting frames of BCA in TPP               and in Open Pit Mine         

Under the belt is mounted the shielded container with two sources of radiation. Due to а heavy lead protection covering sources no radiation could be obtained at any point around the instrument. There is only one narrow collimator letting a pencil type beam to go out vertically across the coal to the detector where this beam is totally absorbed. You can see the mechanics of this unit opening and closing the collimator. It could be made automatically, or by remote control, or locally during the service works.

Radioisotope containers with automatic and with manual shutter

In waterproof side mounted boxes are housed supplying units for low and high voltage, specialized electronics processing the detector signal, high speed spectral analyzer controlled by a local processor, and the computer. The computer controls the measurements, calculates the load and the ash content and supports the connection with the server.

Side mounted control boxes in TPP and in Open Pit Mine

The on-belt radioisotope ash-content analyzers BCА operate fully automatically and operator service is not required, except in case of failure or damage. They are designed and built in such way that they do not require adjustments and service during normal operation. The current maintenance includes only periodical status check and empty belt normalization.

The construction of the instrument is module-based and allows service and maintenance works in almost any conditions and usually without stopping the belt.

Principal block scheme of BCA

Theory

Analix’ Belt-Conveyor Ash-analyzers (BCA) use the well-known and common physical principle – attenuation of two gamma-energies (low and high), crosspassing the coal.

The attenuation of the gamma-energy is calculating by the formula:

or :

,where:

• I - intensity of the passed radiation, sec-1;
• Io - intensity at empty belt, sec-1;
• ρ - specific weight of the coal, g/cm3;
• d - thickness of the coal layer, cm;
• µ(Eγ,Z) - the factor characterizing the attenuation of a γ-radiation depending on its energy, cm2/g.

When we have two different energies and divide their attenuations the specific weight and the thickness are canceled:

Here Zeff is the “effective” atomic number of the coal, which is determined by the ratio between two components of the coal or lignite: organic (Zeff ≅ 6) and mineral (Zeff ≅ 12) – i.e. by the ash content.

But in theory as well as in the practice the things are not so simple as it could seems. There are a lot of factors, influencing this dependence:

• the variable chemical composition of the coal ash – we could obtain the same Zeff when the ash content is different;
• the variable moisture and grain size could cause significant mistakes, if not accounted;
• climate changes;
• electrical and electro-magnetic interferences, etc.

What helps us to account all these factors?

It is our high speed Gamma-spectrum Multichannel Analyzer that makes possible on-line registration and developing of the full gamma-spectrum of the passed-trough radiation.

Gamma – Spectrum of the Analix Ash Analyzer

We use five spectral areas for accounting the varying chemical composition of the coal mineral phase (so called “ash”) and the varying physical parameters of the coal. Trough an original algorithm and respective mathematical mode we achieve results with highest reliability regardless changes in the coal origin, chemical composition, humidity and size.

Our software for spectrum stabilization was proved as the best by practice.

In the generally applied way for gamma spectrum registration the intensities of the lines of Cs-137 and Am-241 are measured in fixed regions. We changed this routine approach and significantly improved the sensitivity and the precision of the method.

Our on-belt ash-meters were the first instruments of this type using on-line full spectrum processing and respectively software determination of the line edges in the spectrum. The exact localization of these edges allows applying of the background subtraction and respective improving of the signal-noise ratio. We also solved another problem following from the great variety of the spectrum depending on the quantity of the material over the belt. The spectrum line areas change up to 1000 times from empty belt to fully loaded belt. Respectively the amplitude and wide changes all the time and the edges don’t stay at one place. Our software enables current fixing of the line edges and exact calculation of the background in every single second.

Together with changing the lines shape the great variety of the intensity during changing of the loaded coal causes a total change of the detector non-linearity. The dependence between the energy of the gamma-quanta and the height of scintillation detector outgoing pulses changes in different way for the low and for the high energy. We developed an independent localization of the low-energy pick also. So we account the “breathing” of the spectrum in wide as well as in height.

These innovations introduced by Analix allow our on-belt ash-analyzers to become the most successfully working directly at the coal excavators TPP and in the open pit coal mines. The large and very variable size of the coal, the hard meteorological conditions, the vibrations and the dust are not problem anymore due to our new design and software.