page 1 of 3 Writer：Wei ZHOU, senior engineer Translator: Thomas Newman
Batch type asphalt mixing plant is the most choice for the Chinese road contractors, almost 98% asphalt mixing plant working for China highway projects are batch type, and it is well known for compact structure, precise batching, high-degree measure accuracy ,good quality of hot mix asphalt, easy operation and control. To assess the quality of an asphalt mixing plant, we mainly consider into factors like technical performance, structure, reliability, stability, failure occurrences etc. The following is what I want to share with you, the reader, about my experiences through 20years work in the field of asphalt mixing plant design, installation, commissioning.
1. Cold feed system: to feed and primarily measure aggregates. Normally 4-6 compartments, adjustable according to the project requests.
1.1 Loading height should not higher than 3.5meters; otherwise, oil consumption of the loaders will be increased. Loading width should be wider than 3.5meters particularly for asphalt mixing plants bigger than LBJ2000 facilities (160tph)
1.2 Bar grizzly should cover every compartment of cold feed bins. Platform should be available for maintaining cold feed bins.
1.3 Conveyers under cold feed bins usually are belt conveyers. Its belt is sided belt. Discharge gate in every outlet of the hopper is adjustable, the quantity of aggregates are controlled through adjusting the gate openness and the belt revolving speed. Frequency inverter is better to adjust the belt speed. The belt conveyer is to guarantee a stable and even aggregates supply. Bin wall vibrators should be installed in the sand bin and fine-graded aggregate bin. Announciator installed at the outlet of the aggregate feed bins, will flash and signal to computer when the aggregate runs out or stick and block the outlet.
1.4The self-relieving bottom of cold bins should be made in trapezia shape, and aggregates flows the length from the smaller width to the bigger width; meanwhile, spaces between belt and outlet become bigger and bigger, this structure efficiently decreases the resistance and abrasion to belts in the aggregate feeding process, runs even aggregate flows and thus to a longer service time.
1.5 Collecting belt conveyors and slant belt conveyors should have built-in calibration device to calibrate and modify belt run deviations(automatically will be better); should have emergency Shut-Down device(Pull-wire switches will be better); Protection fences should be encircled the belt conveyors to protect the safety of persons nearby; When aggregates go from collecting belt conveyor to slant belt conveyor, there should be one partition screen (together with a cold vibrator will be better).
2、Drying system
2.1Dryer drum encircled by more than 50mm mineral wool, energy effectively; Dryer drum clad plate uses steel plate particularly used for boiler; abrasion-resistant materials like HARDOX400 is recommended for the material of flights in dryer drum.
2.2 Dryer drum is rotated by chain drive, gear ring drive and friction drive etc, friction drive often used in plants bigger sizes than LBJ2000,chain drive and gear ring drive rotate dryer drum in smaller size plants. Drive device should adopt good quality products.。
2.3 Port Seal mode of dryer drum: plane seal, ring seal,friction seal and labyrinth seal etc. One reliable port seal mode will decrease leaking airs from dryer drum, while abnormal leak airs would not only increase exhaust airs and also decrease heat-effectiveness. Heat-sensitive or infrared ray temperature meter should installed at the hot aggregate discharge port of dryer drum.
2.4 Burner:
a) Low pressure atomize burner, famous brand air compressor, together with air reservoir tank.
b) Burner should be fired mainly on heavy oil, and can switch to burn diesel automatically. A heavy oil preheater is necessary, and also one diesel tank no less than 10ton and one heavy oil tank no less than 30ton.
c) Adjust proportion: must bigger than 1:6
d) Burner must ignite before finishing self test process; remote control, burning process completed through automatic control and visible monitoring.
e) In coal abundant areas, burner can be fired on both coal powder or oils is recommended, that is, you need not replace the burning jet mouth in case you turn to another fuel.
f) Low fuel consumption, complete combustion, that is, dried aggregates and reclaimed fillers will not have black color or other changed surface colors.
g) Complete combustion, energy effectiveness, small pollution, short flame and low noise level are important, when you choose one burner.
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