NEW XRF ELEMENTAL ANALYZER USED FOR CONTROL OF SO_2 AND HEAT RATE

摘要

The Tennessee Valley Authority (WA) incollaboration with the Electric Power Research Institute (EPRI)has installed and tested a new elemental analyzer at theirParadise Plant in Drakesboro, Kentucky. Using X-RayFluorescence (XRF) to measure sulfur and the major ashforming oxides in coa4 the analyzer provides an elementalanalysis of feed coal to the plant, when coupled with amicrowave moisture analyzer, a measurement of moisture,calorific value and lb. SO_2/mmbtu is available every 5-10minutes (depending on coal flow through the as-fired samplingsystem). Designed by Process Control Inc. the XRF ElementalAnalyzer uses detector technology developed for NASA for soilanalysis on Mars. Using only low energy (<7.5 KeV) X-rays,measurements of At, Si, S, C4 K Ca, Ti, and Fe are possiblewithout radioisotopes and a NRC license. The system is designto mount on a mechanical sampling system and much smallerand less costly than Prompt Gamma Neutron ActivationAnalysis (PGNAA) analyzers now in use. Because ofdifferences in mineralogy in WA's eastern and western coals, theblend can be identified from the calcium content measured bythe analyzer and changed in response to SO_2 trends in the feedplant feed. A fuzzy logic controller has been developed for feedforward control of blends to an SO_2 target Calorific value inthe feed coal is also inferred and used in a heat rate balancearound the plant. The coal quality data is output to the plant datahighway (ethernet network) and used in the plc program. TheXRF technology was also tested for its ability to monitormercury and arsenic in coal. A summary of the performance testconducted in accordance with a new draft standard forevaluating the measurement performance of on-line analyzers(ISO/DIS 15239) is presented in this paper