Mobile asphalt plant commissioned for road surfacing work

The new plant was manufactured and supplied by Benninghoven of Germany, a specialist in asphalt plant technology. It has produced over 10,000 tonnes of PMB asphalt for the surfacing work around the ski centres in the Snowy Mountains.

Founded in 1989, Tropic Asphalts is a family business, run today by father and son team Norman and John Fletcher, who together with another director, Geoff Cox, bring a wealth of knowledge and experience to the business.


The design parameters for the new plant called for a compact, mobile, easily relocated plant, simple to operate, yet providing a high flexibility of mix specifications, together with on-demand volume production. Due to the plant?s location, the particular emphasis for planning was placed on its low profile image, together with low noise and dust emissions.

The mixing tower comprises individual pre-built and wired modules, installed in set positions to form the tower. This configuration of ISO standard container sizes gives a standardisation of components and provides high reliability with the minimum of maintenance and reduces on-site erection times. All other units are supplied in mobile-road towable form, reducing transport costs for the contractor.

The aggregate cold feed system consists of a six bin unit converted to sit on support landing legs. Variable speed belt feeders beneath the hoppers are fitted with frequency controllers for accurate blending of the aggregates. Two of the hoppers are for sand and are supplied with hopper wall vibrators to ease material flow.

A 9.5m long by 650m wide inclined dryer feed conveyor, which feeds directly onto a 3.5m reversible slinger conveyor, transports materials into the dryer.

The aggregate dryer drum, which is 1.8m in diameter by 8m long, and fully insulated and clad for heat retention and noise reduction, is fitted with high efficiency lifters. The drum is chain-driven through a 30kW geared motor unit and chain ring on the outside of the cylinder.

The oil burner is the proven Benninghoven model, Rax Turbo 2 FUO. This is equipped with a full range of operating and safety devices to deliver high efficiency fuel usage. An air inlet silencer is connected to the burner to suppress noise levels. The burner and silencer are mounted on a track to allow the unit to slide back from the dryer for routine servicing. The design of the unit gives high operating efficiency coupled to high reliability.

The plant?s dust collection system, sized for the dryer unit and mixing section scavenging, is rated at 64,000Nm3/h and achieves emission levels of less than 20mg/m3. The filter is of the cassette type-bags being fitted horizontally for ease of access. A cleaning mechanism ensures efficient cleaning down of the bags. Dust is also collected from nuisance points at the screen, weigh hoppers and elevator. A dust monitor mounted on the exhaust stack provides a remote readout in the operator?s cabin. As a result, the plant meets the most stringent dust control regulations.

Hot aggregates are transported from the dryer up to the screen by a vertical bucket-type elevator. This is totally enclosed and features a heavy duty double strand chain and wear-resistant steel buckets with replaceable liner plates at impact points.

The elevator is driven by a 15kW geared motor and toothed chain wheels at the elevator head. The elevator features external bearings to minimise wear and a safety backstop facility. A platform and wide inspection doors allow for easy maintenance.

Material discharged from the elevator passes into a five-deck screen that operates with two 8kW low maintenance bolt-on external drives, to allow for high temperature mixes, when the plant is using recycled materials. The screen is fitted with a by-pass facility arranged to feed material into the sand bin of the plant.

The hot storage section has a total capacity of 55 tonnes and comprises five bins. The bins are all insulated and clad and each is fitted with continuous level indicators and overflow chute. Discharge is by a pneumatically operated radial door fitted with a limit switch to allow coarse and fine dosing, thereby maintaining accurate regulation of material flow to the aggregate weigh hopper.

The accurate weighing out of ingredients is achieved by separate load cell-mounted weigh hoppers, comprising a 2700kg capacity aggregate, 300kg filler weigh hopper, and a 350 litre capacity weigh vessel for bitumen. A 460 litres per minute injection pump forces the bitumen into the mixer. Mixing takes place in an insulated 2000kg capacity, twin-shaft paddle mixer, with drive provided by two 22kW geared motor units, through synchronised gears. A rapid and thorough mixing cycle is achieved by the mixer?s efficient paddle arrangement.

All lubrication points are centrally located to aid routine maintenance. A radiation pyrometer is situated at the mixer discharge to indicate mix temperature. A chute is fitted beneath the mixer door to avoid any spillage when loading directly into trucks.
Imported and reclaimed filler is stored in a 50m3 capacity twin compartment horizontal mobile silo. A double filler elevator, built into the unit discharges direct into the plant?s weigh hopper.

The bitumen system consists of a mobile electrically heated tank mounted on an articulated trailer. This is fitted with all the necessary control and safety devices and is insulated and clad.

The plant is controlled by a Benninghoven on-line Batcher 3000 computer system that displays all plant functions via colour graphics. This advanced and operator-friendly system is housed in an air-conditioned control cabin overlooking the plant. A modem-linked system provides storage for up to 500 asphalt mix recipes.

Commenting on the new plant, the owners, Norman and John Fletcher, said that they ?wanted a quality built plant for project work that would produce a wide range of mixes and have the flexibility that a batch plant provides. It had to be mobile, highly productive, reliable, easy to operate, and produce a quality product. The Benninghoven plant has met all of these requirements.?

The new asphalt plant, because of its speedy relocation capabilities, will give Tropic Asphalts more operating flexibility in taking on contracts over a wider area.

Source: NMC Media

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