外文翻譯--袋式除塵器在dap裝置中的應(yīng)用-其他專業(yè)-在線瀏覽
2025-03-24 00:39本頁(yè)面
【正文】 oins the other. We prefer one long, wedgeshaped hopper with any stiffeners that are required placed on the outside walls. Depending on the condition of the air being handled (temperature, humidity etc.) we may remend steam tracing of the hopper. Build up on the walls of the hopper has also proven to be a problem. The use of sonic horns, however, has proved useful in ensuring that hopper walls are kept clean. Dust Collection / Airlock The dust collected in the hopper is removed by screw conveyor for recovery as part of the recycle to the granulator. Since the bag filter is under suction, an airlock is required to minimize or eliminate leakage of the surrounding air into the process airstream. The traditional airlock used in this duty has been a rotary valve. We do not, however, have good experience with rotary valves in fertilizer duty, mainly from a maintenance standpoint: – blockages, wear on the vanes etc. Shutdown Precautions Most problems that are encountered with build up occur on shutdown when the temperature of the process air drops causing humidity to rise. We therefore remend installing a small shutdown heater with recirculation fan. 15 A shutdown timer shuts down the main fan and closes its inlet damper. The heater fan starts and the heater is brought on line. The fan circulates the air through the hopper and the bags to the outlet air plenum and back again. The temperature inside the bag filter unit is maintained at the desired set point by a thermostat. The entire bag filter unit, of course, is insulated Bag Breakage Detection In cases where the plan is to recycle the warm, clean gases from the bag filter to the dryer as dilution air in the bustion chamber, we remend the installation of a dust monitor to detect any increase in dust loading in the airstream leaving the filter. In case high levels of dust are detected, the airstream is diverted to atmosphere temporarily until the bag can be replaced or plugged. 3. DAP plant airstreams The airstreams from the dryer, cooler and general plant dedusting (equipment vents) are potential candidates for dust recovery using bag filters. Typical operating conditions for each of those airstreams in a DAP plant are given below in Table 1. Table 1 Dryer Cooler Equipment Vents Temperature, o C 88 58 72 Humidity,kg/kg Relative Humidity,% 11 15 7 Dust Loading,g/m 3 30 3 50 Ammonia Loading,g/m3 4 Negligible 1 The dryer is not generally considered as a suitable candidate for a bag filter due to its high humidity and the fact that the airstream ultimately needs to be scrubbed, in any case, due to its relatively high 16 ammonia concentration. Either the cooler or equipment vent’s airstreams could be considered. The very low ammonia concentration in the cooler airstream is an advantage as is the low dust concentration. The cooler airflow matches or exceeds that of the dryer so that all the dilution air requirements would be provided by recycled cooler air. In the equipment vents case, only part of the dilution air requirements would be provided. Table 2 below provides details of the heat that can be recovered by recycling either the equipment vents or the cooler airstreams to the dryer. The ammonia concentration in the equipment vents system means that some scrubbing would probably also be required to bring the concentration down within proper limits, unless the clean air from the bag filter is recycled through the dryer as dilution air in the bustion chamber. 4. Economics The impact on capital cost of replacing dry cyclones and wet scrubbing with a bag filter is pared below for each of the two options. Cooler The cooler airstream is
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