Simple Solutions That Work! Issue 11

58 electric-resistance heaters is that the membrane becomes clogged with moisture, oil, particulate, or rust from the compressed-air piping. The normal solution to this is to install a simple, bowl-type compressed-air filter. While these filters collect most of the moisture and particulate, they are only about 80% efficient. The Palmer design incorporates both a bowl filter and a 99% high- efficiency, cartridge-type filtration unit right after it. This ensures all the air going into the pressure chamber and then through the fluidizing membrane is completely dry and completely clean. This will extend the service life of the membrane much beyond the effect of a bowl filter alone. 2. Pressure-chamber pressure gage. The pressure gage in the pressure chamber under the fluidizing membrane usually is a 0-5-psi instrument; if the scale is higher it is impossible to be sure the pressure is set correctly. Normally, the pressure is increased “until the needle bounces,” typically at 2-3 psi, depending on heater size and type of aggregate. The bouncing needle means the sand is bubbling around within the housing, but not excessively. If the gage is fixed at 4 psi, or higher, it means that the compressed-air pressure is set so high that air is escaping as quickly as possible, which fluidizes the sand to the point that it is not contacting the elements as efficiently as it should be. If the fluid bed becomes clogged, the common response to sand not exiting the heater is to turn up the fluidizing pressure. This will increase the sand flow, but it will over-fluidize the sand so that it will not have intimate contact with the heating elements, and there will be wide swings in temperature consistency. The first fix is to make sure the fluidizing membrane is in good condition. 3. Exhaust. The exhaust from the fluid bed must be free-flowing at all times. Many times, this exhaust is connected right back to the top of the silo, into a bin vent, or tied into the plant dust-collection system. If there is a restriction in the piping this will affect the fluidizing pressure, which will affect the accuracy and consistency of the sand-discharge temperature and, in the case of extremely plugged exhaust, sand flow.