Real-Time Measurement Required
The first solution approach was to install a dual gamma ash gauge with an associated microwave moisture meter to monitor the coal quality. This system, installed in late April 2002, produced early results that were encouraging. Unfortunately, operators soon discovered that disparity in the ash and moisture results was caused by variation in lignite flow rate, changes in conveyor belt loading, or lignite mined from multiple sources or seams. In addition, the microwave moisture meters do not work well when the lignite moisture content exceeds 30%. The dual gamma ash gauge was subsequently removed from service.
According to mine and plant operators, they did learn two lessons from this experiment: Real-time lignite quality data is extremely valuable, and incorrect real-time data is worse than no real-time data at all.
Their next approach was to experiment with Prompt Gamma Neutron Activation (PGNA) instrumentation. PGNA nuclear elemental analysis is a real-time measurement technology with a long track record in the coal and cement industries. It has a number of advantages:
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The PGNA can determine the percentage of ash in the lignite by measuring the elemental constituents of the lignite.
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The PGNA directly measures ash, sulfur, and moisture.
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The PGNA directly measures SiO2, Al2O3, Fe2O3, Na2O, CaO, TiO2, K2O, N, and Cl.
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The PGNA can directly calculate the energy content in the supplied fuel in Btus, SO2 /mmBtu, and the like.
Once the technology was selected, the best supplier was chosen. Red Hills Mine had several key specifications for the supplier beyond first cost and experience with coal. For example, the interface with the PGNA should be through a web browser to minimize operator training. After closely comparing three different vendor offerings, Red Hills Mine selected SABIA’s PGNA analyzer (Figure 5). SABIA’s willingness to do a demonstration project and put a unit on-site for a six-month trial lease was one of the deciding factors for its selection. In addition, SABIA’s experimental moisture meter also promised improved measurement results in the future. The six-month trial run with a PGNA analyzer on conveyor 5A was a success, and Red Hills Mine subsequently leased three PGNA analyzers for five years: one each for conveyors C5A and C5B and a third on the C2 belt just downstream of the truck dump/primary crusher (Figure 6).
5. PGNA plays a key role. Three SABIA PGNA instrumentation packages were installed at the Red Hills Power Plant to provide real-time lignite fuel quality measurements. Source: SABIA
6. Sharing real-time data. Data collected by the PGNA systems are fed back directly to the Red Hills Mine operators’ computers through their intranet, so all the information from the analyzers is available in real time, enabling operators to quickly change fuel collection locations when fuel quality drops. Source: SABIA
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