Automatic Sampler success
Sentry Equipment USA and J W Industrial Instruments Australia have achieved significant success with the installations of RX 90 degree automatic samplers handling pulverized fly ash (PFA). Various types of Sentry Sampling Systems are used throughout Australia but this installation is the first in the power generating industry.
Installation in Pulverised Fly Ash
The first RX 90 degree sampler was installed 3 years ago to be thoroughly checked and evaluated over a period of 12 to 18 months. The sampler was found to meet the requirements with the result that 7 more units were installed and now the plant relies exclusively on Sentry for the important job of sampling PFA.
Replacement of manual sampling
The RX 90 degree units replaced manual samplers which had been unreliable, not representative and difficult to operate. The RX90 is now giving representative samples upstream of the air heaters and collecting composite samples over a set period with precisely timed intervals between activation. This provides the client a complete overview of the product over a 24 hour period.
Sampler installation
The power station operates four 500-megawatt generators. Two dust discharge lines are fitted to the combustion side of each generator and convey the PFA 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 PFA produced by the combustion of the fuel, in this case pulverized bituminous coal, must pass through these eight lines.
Automatic sampler operation
The type RX 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connected to a 2 liter collecting jar placed below the sampler, at the conclusion of each sampling cycle the probe is withdrawn leaving the PFA discharge line completely free of obstruction.
Sampler controller
The RX90 sampler can be controlled via the Sentry SBC Controllerwhich allows the user to set the sample interval and duration. The controller has a quick start screen for easy set up via an intuitive interface. The controller also supports ModBus, CAN, AB DF1, GE Fanuc SNP communication protocols without any additional hardware. This makes integration with existing plant systems simple and easy.
Representative sample for further analysis
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 PFA , this being a reliable and definitive indicator of the efficiency of combustion of the fuel.
Combustion efficiency metrics
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.
Quality of the by-product
A further consideration is the control of the quality of the PFA, 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.
Environment and sustainability
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 plants.
Conclusion
PFA sampling and analysis in power station operations is extremely important. One of the key criteria is that the sampling equipment must provide representative samples. Throughout this case study we found composite samples over a 12 or 24 hour period are the most effective. It was also determined the samplers must be mechanically reliable and require little maintenance as in this application samplers are continuously exposed to the very aggressive conditions imposed by hot, abrasive dust. The Sentry samplers supplied by JWII coped extremely well in those conditions.
