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Batch Hot Mixture Asphalt Plant (PART 1)

Posted by aditya | 3:50 PM | highway materials | 5 comments »

A comparison of the first two or three components in the batch and drum mix facilities shows that the cold feed proportioning systems for both types are similar.

◊ The primary difference up to the drying operation, is the automatic weighing system on the cold feed conveyor of the drum facility. The proportioned material is fed by the cold feed conveyor into the dryer.

◊ The dryer in a batch facility is typically of counter flow design in which the aggregates flow in the drum in opposition to (counter to) the flow of exhaust gases.

◊ The drier consists primarily of a large (from 0.9 to 3m in diameter and 6 to 12m long) rotating cylinder that is equipped with a heating unit at one end, usually a low pressure air atomization system using fuel oil.

◊ The drier is mounted at an angle to the horizontal, with the heating element being located at the lower end. Hot gases, from the burner pass from the lower end up the cylinder and out at the upper end.

◊ The so-called cold aggregate is fed into the upper end of the drier, picked up by steel angles or blades set on the inside face of the cylinder, and dropped in “veils’’ through the burner flame and hot 8 gases, and it moves down the cylinder because of the rotating action and force of gravity.

◊ The hot aggregate then discharges from the lower end of the drier, generally onto an open conveyor or enclosed “hot elevator’’ that transports it to the screens and storage bins mounted at the top of the power plant in conjunction with the mixing unit.

◊ the temperature of the aggregates may be raised to 160 °C or more, and practically all the moisture in them removed. In the preparation of “cold’’ mixtures such complete drying may be neither necessary nor particularly desirable.

◊ The hot, dust laden exhaust gases from the dryer are passed through a dust collection system to remove dust particles so that emission standards are met. The collected dust is returned to the hot material elevator or filler silo and is reintroduced into the mixture as required.

◊ Mineral filler that is added to the mixture is not normally passed through the aggregate drier, this material being fed by a separate device directly into the mixing unit in some cases or into the aggregate batching unit.

◊ Separate feeder units are also used in the preparation of cold mixtures to supply liquefier, other fluxes, or hydrated lime to the mix.

◊ The tower unit contains a series of components that screen, store, proportion by weight, mix, and discharge the bituminous mixture into a truck or storage silo.

◊ After the aggregates exit the hot elevator at the top of the tower, they are discharged onto vibrating screens that are designed to separate the material into a number of sizes.