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Show Counter Spin Versus Parallel The basic approach to the impeller testing performed at Ashtabula was to check the performance of different styles of blade type impellers installed in both applications of counter and parallel flow arrangements. The objective was to reduce flame intensity and slagging tendencies. The two impellers of most interest were the flat blade 30 0 angle and the Rieley Stoker curved blade 45 0 impeller (see photo, Figure No. 11). Specific burner performance was judged solely on visual observations. The results of each case were recorded with the use of VHS video equipment in order to make reliable comparisons after the testing was complete. Numerical data was taken during each test to assure that consistent conditions were maintained during all of the testing. However, final judgments to make flame performance evaluations were essentially made using the knowledge gained from the· video tapes. This proved to be a real asset in meeting the objectives of the testing program. The visual observations and video tape show that the turbine blade type impeller installed in an opposed relationship to the air register spin produces a flame pattern · which departs from the normal distribution of the secondary airflow path. This phenomenon is basically caused by the interaction of the opposed secondary air and the primary air spin. In the case of the two test burners seen in the photo, Figure No. 12, the bulk of the flame pattern is directed in a skewed direction towards the center of the furnace. The secondary air distribution for both of these burners rotates towards the side walls of the furnace, thus the counterflow impellers were installed with their effective rotation being towards the center of the setting. The counterflow arrangement produces an extremely wide angle flare type pattern which totally fills the burner throat and generally moves straight away from the burner opening. However, the flame pattern proper, when viewed from the rear of the furnace, can be seen to have high velocity spike tails on the outboard side and the majority of flame is traveling towards the center of the furnace. This results in most of the combustion process of a burner taking place beyond the boundary of the path of secondary air coming from that burner and to depend on air being supplied by an adjacent burner to support complete combustion. In reality, the adjacent burner might also be in operation or it might be out of service at any given time. This impeller set-up produced flames that had good ignition, stayed close to the tip of the burner nozzle and looked excellent when viewed from the side of the burner next to the burner throat opening. The negative aspect of the flame travel towards the center of the furnace was obvious when looking towards the front from the rear and by observations made looking down from the upper elevations. The flame pattern generally caused a wide body of fire that filled the lower furnace region before the movement approached the rear wall. Both the 30 0 and 45 0 curved impellers create a similar flame shape, except the 45 0 curved impeller generated a slightly wider flare and more intense looking flame. The photos shown in Figur~ No. 12 were taken from video tapes of these flames. The turbine blade type impeller installed in a parallel relationship produces a flame pattern which is confined to the distribution of the secondary airflow path. This feature is basically due to the complementary action caused by the |
