“Heathrow asphalt” ready for take off!

The family company F.M. Conway, based in Dartford, is boosting its coated products and recycling capacity by developing an advanced state of the art asphalt facility near Heathrow airport. With this high efficiency plant, F.M Conway will provide materials for their own paving division as well as supplying other local companies. Due to the highest level of quality standards, additional business growth is anticipated.

The new multi million pound “Heathrow Depot”, which is strategically located inside the M4-M25 motorways hub, will enable the company to efficiently serve its customers in West London with the added security of on-demand access to high quality materials around the clock and the capacity to produce over 300,000 tonnes of asphalt per annum. Plant type “BA 5000” with a mixing capacity of 400 t/h incl. Recycling parallel drum system.

The new asphalt coating plant, has been specially designed to meet the high number of required mix specifications, together with all the necessary London specific high environmental criteria.

The plant has a drying capacity output rated at 240 t/h of dense base course, at 5 % initial moisture, with an additional 180 t/h recycling capability at 3 % moisture.The technical concept of the plant is designed to provide significant energy, operational and other important cost saving factors. With the new plant a broad range of the latest specification coated materials can be achieved and produced efficiently. This also includes a wide variety of new specialised mix recipes.

Michael Conway, CEO of F.M Conway, commenting on the development said,”This new facility will boost our existing BENNINGHOVEN asphalt plant at Erith, which is now producing over 400,000 tonnes per year. This plant sets the benchmark for asphalt recycling and with the new ”Heathrow” plant we will adopt the same operating model in delivering high quality asphalt to our customers“.

Asphalt Plant under construction

When completed and all components of the asphalt plant are in place the complete plant will be housed in a fully sheeted, factory style building to aid both insulation and noise reduction levels.The aggregate cold feed system consists of nine units, each of 14m³ capacity and fitted with a frequency controlled belt feeder for accurate blending of the aggregates. Two of the hoppers are for fines, and are supplied with hopper wall vibrators to ease material flow. All hoppers are sheeted on their sides, ends and roof to avoid water entry.

A 61m long collecting conveyor moves the mineral onto a 20m long inclined conveyor followed by a 6m long reversible slinger conveyor from which material is fed directly into the dryer drum.The aggregate dryer drum, which is 2.4m diameter x 9m long, is fully insulated and aluminium clad for heat retention and noise reduction .The drum is indirectly friction driven by a cardan shaft arrangement by four support rollers through individual geared motor units. To ensure a wide range of various product temperatures the rotation speed of the dryer can be regulated by an inverter.

The combination burner is the new type “EVO JET Oil-NG 4-FU”, which burns gas oil and natural gas. A change over to the other fuel can be realised without a re-start of the burner. The burner is equipped with a full range of additional operating and safety devices to deliver high efficiency fuel usage. An optimised air inlet silencer is connected to the burner for effective reduction of noise emission levels.

The “PURE-Air” dust collection system, achieves emission levels of less than 20mg/m³. A spezial designed primary knock out box separates any coarse dust from the airstream. Over 1500 cassette bag filters collects any remaining dust and transfers it via two screw conveyors to a filler 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. Elevator drive is by a 37kW soft start operated geared motor and toothed chain wheels at the elevator head. A double link chain ensures the perfect positioning of the elevator bucket and provides a longer operational life for the buckets as they are fixed stable to both sides when compared with a single chain arrangement. Further elevator features are outside located bearings and a safety backstop facility. A wide platform provides access for maintenance.

The six-deck screen machine features a twin drive via two low maintenance vibrating motors. Wide access doors, together with a rollaway chute, provide perfect access.The hot aggregate storage section has a total capacity of 160 tonnes and comprises seven bins. Mixing takes place in an insulated, 5,000kg capacity, twin shaft paddle mixer.The mixed material silo has a total capacity of 540 tonnes. Arranged in four compartments of 100 tonnes each and two at 70 tonnes. All bins are mounted on load cells to ensure accurate material loading of vehicles.

Bitumen is stored adjacent to the plant in two vertical 110m³ and additional one double compartment type 110m³ capacity tanks. Filler is stored in a three-compartment silo tower arrangement. A bagged additive pallet crane system is also incorporated in the plant to feed granulated material to be fed directly into the paddle mixer.

Recycling section

The heart of the recycling system is the parallel flow drum, which both dries and heats the recycled asphalt. The design of the drum internals ensures the burner flame makes no direct contact with the moving reclaimed material inside the drum. The combustion zone of the drum is fitted with special heavy-duty, self-cleaning finger lifters that vibrate during the production process to prevent clogging of the material.

Graded and tested RAP material fed to the recycling drum comes from one of three hoppers, depending on the mix. This ensures a high flexibility to match the mix recipe. Hot recycled material is discharged from the drum and held in a 20 tonne electrically heated buffer silo prior to being discharged into the load cell mounted weigh hopper, where it is batch weighed before entering the mixing cycle. The plant is controlled by the BENNINGHOVEN recently developed management BLS 3000 computer system which displays all plant functions, generates all operation data of production, consumption and energy. The data can be sent on-line to the head office in order to ensure a perfect production and cost control over the operation. By a GSM modem, on-line support can be given at any time.