Fly Ash Sampling Success
Sentry Inc. of Texas and J W Industrial Instruments Australia have achieved a significant success with the installations of 8 type R 90 degree automatic samplers handling fly ash. Various types of Sentry Sampling Systems are used throughout Australia and the world but this installation is believed to be the first in a Power generating industry.
The first R 90 degree sampler was installed about 3 ½ years ago to be thoroughly checked and evaluated over a period of 12 to 18 months. The sampler was found to meet their exacting requirements with the result that 7 more units were installed and now relied exclusively on Sentry for the important job of sampling fly ash for over 18 months.
The R 90 degree units replace samplers of a different type which had been found to be unreliable and which were fitted upstream of the air heaters.
The power station operates four 500-megawatt generators. Two dust discharge lines are fitted to the combustions side of each generator and convey the fly ash pneumatically to the dust silos. One Sentry Sampler is fitted at right angles to each of the eight discharge lines. Sampling is therefore representative, as all the fly ash produced by the combustion of the fuel, in this case pulverized bituminous coal, must pass through these eight lines.
The type R 90 degree sampler is operated pneumatically. A tubular stainless-steel probe is pushed into the flow of PFA at regular, predetermined intervals and remains in the material stream for a predetermined time during each sampling cycle. The whole operation is automatically controlled. The stainless steel auger, which conveys the sample from the sampling orifice in the top of the probe to the discharge point, which is connected to a 2 litre collecting jar placed below the sampler, at the conclusion of each sampling cycle the probe is withdrawn leaving the PFA discharge line completely free of obstruction. 1.25 to 1.5kg of sample is collected by each of the eight units every 24 hours. The samples are analyzed to determine the carbon content of the fly ash , this being a reliable and definitive indicator of the efficiency of combustion of the fuel.
Combustion efficiency is, of course, a vital control factor in power stations operations, as it has a direct and highly significant effect on the economics of the plant. A further consideration is the control of the quality of the fly ash, which is sold for admixing into clay in brick manufacture, for use in the production of lightweight aggregate and as an additive in some types of cement..
Environmental factors such as fuel conservation and the recycling of materials form an important part of the business of responsible power generation. The power company is very sensitive to these issues, which go hand in hand with its current major investment in flue gas desulphurisation plant.
The importance of fly ash sampling and analysis in power station operations cannot be overstated. It is essential therefore, that such sampling be representative, regular, consistent and mechanically reliable. The equipments used must require little maintenance in spite of being continuously exposed to the very aggressive conditions imposed by hot, abrasive dust. The Sentry Samplers installed are reported to fulfill these requirements quite satisfactorily.
