plug-gage and coal void signaling devices. lubrication piping and electric wiring, microprocessor control cabinet.
• The feeder frame is comprised of casing, inlet and discharge end doors, side doors and internal feeder light. The casing is an enclosed weldment that can resist explosive pressure up to 0.34 MPa to meet requirements specified in NFPA Code 85F by National Fire Protection Association of the U.S.A. Guide plate and skirt are provided in the inlet to form fixed section of coal flow on the belt after coal is dropped into the feeder. All parts contacting coal are made of OCr18Ni9Ti stainless steel. Inlet and discharge end doors are firmly bolted to the casing to ensure perfect seal. All doors are optional to open leftward or rightward. sight glasses are provided on all doors and nozzles are equipped interior of sight glasses to clear off accumulated coal dust by pressurized air or water. Internal feeder light of sealed construction enables observation of internal feeder operation.
• The feeder belt assembly is comprised of motor, reducer, drive pulley, take-up pulley, tension roll, belt supporting plate and the belt. The belt is rimmed and provided with a v-guide at the inner belt center to engage with grooves on rollers to keep good belt tracking. At the end of drive pulley scraper is equipped to clear off coal adhered on the outer surface of belt. The tension roll is located at the midpoint of bell travel, it keeps the belt under a fixed tension to obtain optimum weighing effect. The belt tension varies with different temperature and with temperature variation. Intensive observations should be frequently done and make tension adjustment by means of the take-up screws. Scaled indicator is equipped interior of side door to the feeder, the tension roll should be regulated to locate its center at the midpoint of the indicator. Totally enclosed, variable frequency motor is used to drive the belt. Which is comprised of a 3-phase ac motor, a tacho-generator. A variable frequency driver and variable frequency motor provide an ac stepless speed regulation .It can provide a smooth and stepless speed regulation within a rather broad range. The feeder belt reducer is a two-stage reducer, comprised of cylindrical gears and worm wheel. The worm wheel is oil bath lubricated while a cycloidal pump in the reducer pumps oil via a hole in the worm shaft to 3 lubricate the gears. The drive pulley is driven through a pin type coupling which is mounted on the worm wheel shaft.
• The coal void signaling device is located above the belt. When there is no coal on the belt, the paddle of signaling device deflects and causes cam on the axle of device to turn and actuate the limit switch, either to control the belt drive motor, or to initiate the coal bunker vibrator, or to output a signal back to control room to signify no coal on the belt. The customer may determine, according to operating system requirements, which of these functions shall be performed. The coal void signal can also deactivate integrated weight and can prevent feeder calibration with coal on the belt. The coal plug-gage signaling device locates at the feeder discharge and is of identical construction to the coal void signaling device. The limit switch outputs signal signifying coal flow plug-gage at discharge and stops the feeder operation.
• The weighing system is located between feeder inlet and drive pulley. All of the three roller surfaces are finely finished, of which two rollers are fixed on the feeder casing to form a weigh span and the third roller hangs on a pair of load cells. Coal weight on the belt acts on load cells to output a signal. Output signal from the calibrated load cells signifies unit length coal weight and frequency signal from the tacho-generator signifies belt speed. The microprocessor controls integrates both signals to obtain the feedrate. Test weights are located below the load cells and the weigh roller. During feeder operation, test weights are supported by the weigh arm and the eccentric disc to part from the weigh roller. On calibration, turn the ratchet handle so that the eccentric disc is turned to make test weights hang on the load cells to check if the weight signal is correct.
• Cleanout conveyor is used to clean off coal accumulated on inner floor of the feeder. During feeder operation, coal adhered on the belt is cleaned off by a scraper and dirt accumulated on inner belt is dropped off from both ends of the self-cleansing type tension roll. As seat air also generates dirt, dirt will deposit on the inner floor to cause self-ignition if it is not timely cleaned off. Cleanout chain is driven by a motor via a reducer, wing type chain scrapes off the dirt to the feeder discharge. It is recommended that the cleanout conveyor is synchronously operated with the feed bell operation so that coal accumulation interior of the feeder is minimized. Furthermore, continue clean off is also of advantage both to reduce feedrate error and to prevent chain pin from adhesion and rustiness. The cleanout conveyor reducer is comprised of cylindrical gears and worm wheel. Electric overload protection is provided for the cleanout conveyor drive motor, when overload the cleanout conveyor motor’s power is automatically turn off by electronic overload relay to stop reducer.
• Seal air inlet is located below the feeder inlet with a flange-type connection for the customer to supply seal air into the feeder. Under pressure operation status, the feeder needs sear air to prevent pulverizer heat air from reversing into the feeder through the inlet. The seal air pressure is 60～245 Pa higher than the pulverizer inlet pressure. The required seal air delivery is the sum of air leakage from hopper of downspout and the amount required to form a pressure difference between inlets of the feeder and of the pulverizer. The feeder itself is construed as of reliable sealed with no leak. A threaded hole is provided near the feeder inlet for adapting a pressure gauge to test the feeder internal pressure. The hole must be plugged if a pressure gauge is not equipped. If the seal air pressure is too low, it will cause the pulverizer heat air reverse back to the feeder so that coal dusts will stagnate at the door frames and at protrusion parts to induce self-ignition. If either the seal air pressure or its flow rate is too high, it will blow coal particles off the belt to degrade weighing accuracy and to increase the load on clean out scrapers. 4 Furthermore, if the seal air flow rate is too large, dustiness is prone to be formed interior of the sight glass to hamper observation. Therefore, suitable seal air pressure has to be adjusted.
• Except that the reducer is oil bath lubricated, grease lubrication is used for all other parts. All lubricating points within the feeder are connected with hoses that extend outside the feeder so that, lubrication can be performed without opening doors to the feeder. Flexible tubes are used for electric wiring, cables are led into the feeder through the tubes so that casing seal is kept.
• Control cabinet is installed on the body of the feeder. Power supply switch is located in cabinet. It can turn on or turn off the power.
• Microprocessor control board, power supply board signal converting board, variable frequency driver disconnect switch, transformers, fuses and relays are installed within the microprocessor control cabinet which is mounted on the feeder casing. On the panel of cabinet microprocessor display keyboard and switches SSC and FLS are equipped. For their functions.
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