New plant helps meet increased demand for specialized asphalts
Foster Yeoman, one of the UK’s leading producers of asphalt, have a manufacturing capacity of over 2 million tonnes a year from nine production plants located at seven sites across southern England.
The need to increase flexibility and offer an enhanced service to customers has led to the recent installation of a new Benninghoven ‘Concept TBA 240’ asphalt plant at the company’s Theale depot, near Reading, Berkshire.
A high-volume drum-mix-type plant is already in operation at the depot but Foster Yeoman decided to supplement this with a new asphalt plant to help meet the ever-increasing demand for specialized asphalts and to have the ability to respond to specific individual customer requirements.
The new plant, which has an output of up to 240 tonnes/h, has been built inside an existing building at the Theale depot, a task which involved stringed restrictions on roof removal during erection.
With the acquisition of the new plant, Foster Yeoman, in effect, have an ‘asphalt supermarket’ with the ability to supply a wide range of products in both large and small quantities.
To achieve their requirements of high-volume, flexible production, including the use of pigments, latex, granulate, flux, wet-fix and recycled materials, together with their emphasis on the environment, low-noise operation and fuel efficiency, Foster Yeoman selected the Concept TBA 240 asphalt plant – one of an extensive range of 40-500 tonnes/h fixed, transportable and mobile asphalt plants available from Benninghoven.
The cold-feed system comprises 17 flange-mounted variable-speed belt feeders located below existing concrete storage bunkers. These feed into parallel collecting conveyors (77m and 59m in length) which deliver aggregate materials to the dryer unit.
In addition, three 10m3 capacity cold-feed bins equipped with belt feeders are used to feed special imported aggregates to the dryer unit via a third collecting conveyor.
Aggregates are introduced to the 2.4m diameter x 9.0m long rotary dryer via a reversible slinger conveyor. The dryer is fully insulated and clad for fuel efficiency and noise reduction.
The heat source for the friction-driven dryer is the well proven Benninghoven Rax-Jet turbo burner, which is capable of running on gas oil or natural gas and is equipped with a silencer unit.
A twin-chain elevator transports the dried aggregates from the dryer to a six-deck screen equipped with a bypass facility. The screen drive is mounted outside the screen enclosure, thereby allowing high-temperature materials to be screened.
Six hot-stone bins and one bypass bin mounted below the screen offer a total capacity of 50 tonnes.
The weighing of ingredients is performed by a series of load-cell-mounted weigh hoppers (aggregates: 3,000kg capacity; filler: 400kg capacity; bitumen: 478 litres capacity).
An injection pump delivers the bitumen from the bitumen weigh hopper to the mixer, where it is sprayed under pressure for better coating.
The mixer unit itself comprises a 3,000kg capacity Benninghoven twin-shaft paddle mixer.
A 58,000m3/h dust-collection system with pre-skimmer unit for coarse-dust separation achieves particulate emissions of less than 20mg/m3.
Collected fine dust is transferred, via a filler elevator, to a screw conveyor feeding two 40m3 capacity reclaimed filler silos or a 50m3 reclaimed/imported filler silo.
The bitumen system comprises three electrically heated 90m3 vertical tanks and two electrically heated 60m3 vertical tanks, the latter equipped with stirrer mechanisms for the storage of polymer-modified bitumens.
All five vessels are the latest Benninghoven ‘high-efficiency’ bitumen tanks with maximum insulation to minimize heat loss, resulting in significant energy savings.
Each tank has its own dedicated pump and delivery pipework to the bitumen weigh kettle.
A 3,000kg capacity inclined skip transports the mixed material to one of four load-cell-mounted, 50-tonne capacity mixed-material storage hoppers. Each hopper is fully insulated and fitted with electro/thermal oil-heated discharge doors.
Foster Yeoman required a range of additional equipment to cater for the supply of various specialized asphalt products to their customers. This included:
- a gravimetric granulate additive arrangement with 30m3 storage silo, weigh hopper and pneumatic delivery system
- a pigment additive system with hopper designed to accept ‘Big Bags’ raised by a 1.5-tonne hoist, the pigment being delivered to the mixer via a flexible screw
- a wet-fix dosing system with pump and pipework from the supply vessel
- a 40,000-litre flux-oil tank with flux-oil pump and flowmeter
- a latex system with special pump and pipework to the mixer from the supply vessel
- a cold RAP system comprising a 10m3 capacity, steep-sided feed hopper with belt feeder and transfer conveyor to a vertical elevator feeding a weigh conveyor which discharges into the mixer, complete with a steam-extraction system.
The entire plant is controlled by a Benninghoven Online Batcher 2002 computer system with touch-screen controls, fault diagnostics and 1,000-recipe capacity. An additional mix computer system was also supplied to allow operation of the plant from a second location.
The plant layout was specifically designed to suit Foster Yeoman’s operational requirements, while taking into consideration the restrictive parameters of the existing building in terms of area and height. All equipment was supplied and installed to exacting safety requirements and in accordance with CDM directives.