DEVELOPMENT AND UTILIZATION OF TEST FACILITY FOR THE STUDY OF CANDLE FILTER SURFACE REGENERATION

Hot gas particulate filtration is a basic component in advanced power generation systems such as Integrated Gasification Combined Cycle (IGCC) and Pressurized Fluidized Bed Combustion (PFBC). These systems require effective particulate removal to protect the downstream gas turbine and also to meet environmental emission requirements. The ceramic barrier filter is one of the options for hot gas filtration. Hot gases flow through ceramic candle filters leaving ash deposited on the outer surface of the filter. A process known as surface regeneration removes the deposited ash periodically by using a high pressure pulse of gas to back flush the filter. After this cleaning process has been completed there may be some residual ash on the filter surface. This residual ash may grow and this may then lead to mechanical failure of the filter. A Room Temperature Test Facility (RTTF) and a High Temperature Test Facility (HTTF) were built to investigate the ash characteristics during surface regeneration at room and selected high temperatures. The RTTF system was used to gain experience with the selected instrumentation and develop an operating procedure to be used later at elevated temperatures. The HTTF system is capable of conducting surface regeneration tests of a single candle filter at temperatures up to 1500 F. In order to obtain sequential digital images of ash particle distribution during the surface regeneration process, a high resolution, high speed image acquisition system was integrated into the HTTF system. The regeneration pressure and the transient pressure difference between the inside of the candle filter and the chamber during regeneration were measured using a high speed PC data acquisition system. The control variables for the high temperature regeneration tests were (1) face velocity, (2) pressure of the back pulse, and (3) cyclic ash built-up time. Coal ash sample obtained from the Power System Development Facility (PSDF) at Wilsonville, AL was used at the elevated temperatures regeneration tests. The basic test conditions were (1) Face velocity: 5 cm/s or 7 cm/sec (2) Regeneration pressure: 95 psi, and (3) Build-up time: 20 minutes. A number of cyclic regeneration tests were conducted at 1,100, 1,200, 1,300, and 1,400 F. The surface regeneration tests indicated no temperature dependence from room temperature tests up to 1,200 F. Above 1300 F, the ash layer showed greater cohesive strength and only the loose particles were removed during the initial few cycles of surface regeneration. It appears that the ash cake can continue to grow as the pressure difference between the chamber and filter pressure increases slowly. This may then lead to the inevitable candle filter failure due to bridging between filters