Parker Plant continues to serve the Isle of Wight with a new Starmix 2000 Asphalt Plant supplied to Wight Building Materials
In November 2013 Wight Building Materials Ltd awarded the contract for its new asphalt plant to Parker Plant Ltd. Wight Building Materials Ltd is a Joint Venture between Eurovia and Aggregate Industries and the new plant is part of a capital investment exceeding £3.5million in the Blackwater Quarry at St Georges Down on the Isle of Wight.
The new Parker StarMix 2000 high level asphalt batch plant will meet the requirements of the 25 year Isle of Wight Highways PFI (Private Finance Initiative) and it will also be available to supply a variety of projects across the island. The Parker StarMix replaces a Parker Blackmix 1500 supplied in 1986 and recently decommissioned after approximately 1.2 million tonnes of production. The replacement plant offers high thermal efficiency, low energy consumption and reduced environmental emissions with the added reliability afforded by the latest technology.
The new plant was a phased installation and was installed and commissioned whilst the old Blackmix plant was still operational. This was a necessity for Wight Building Materials as this is the only asphalt plant on the island.
As with all new Parker equipment the StarMix plant was completely designed using the latest three-dimensional engineering technology. The new plant is a modular design allowing the larger sections of the plant to be shipped in during the night and delivered to site before 7 am to minimise local traffic disruption on the island. The StarMix plant started full production in early May 2014, mixing day and night from day one.
To ensure long life of the plant the dryer is made from type P265GH boiler plate with Hardox lifters, the complete top section of the bag filter along with the filter bag cages are made from stainless steel. All of the open walkways, handrails and stair treads are galvanised and the whole plant is located on 30mm thick galvanised blocks.
The StarMix 2000 is a 160 tonne/hr high level static asphalt mixing plant designed specifically to be fitted into a restricted site with the feed hoppers mounted at an elevated level on a bank and the dryer, bag filter, mixing tower and mixed material silos mounted on the quarry floor.
The plant consists of 8 x 11.5m³ feed hoppers complete with 100mm grids, low level indicators with a visual alarm above each bin and indication in the cabin. A canopy is fitted to three sides of the feed hoppers with a roof to minimise airborne dust generated when feeding the plant and for weather protection. Mounted under each feed hopper is a 500mm wide x 1800mm centres variable speed belt feeder with 20:1 turndown ratio. The feeders are fitted with starvation switches to indicate a no flow situation. The sand and the dust hoppers are equipped with vibrators and UHMW polyethylene liners to minimise sticking feed materials.
A 650mm wide horizontal collecting conveyor discharges on to a 650mm wide declined scalping screen feed conveyor. The 1m wide x 1.5m long vibrating scalping screen removes the plus 50mm material from the plant feed and the minus 50mm material is fed to the reversible dryer slinger conveyor. The slinger conveyor discharges the feed aggregates direct into the dryer. Alternatively when reversed it is used to calibrate the belt feeders or it can be used to provide a blended mix to trucks. The conveyors and screen are covered to minimise air borne dust and provide weather protection. Stairways and walkways are provided on both sides of the conveyors and the vibrating scalping screen for access and maintenance purposes.
The dryer is a 2.2m diameter x 8m long drum with nylon support and thrust rollers, minimising wear on the roller paths and reducing the noise levels. The dryer has friction drive with 4 x 15kw geared motors via soft starters. A 2m high fence with an electric interlock gate guards the dryer. The multi fuel burner is capable of burning gas oil, CFO and natural gas. The burner blower is variable speed to attain optimum air to fuel ratio and to minimise noise. An infrared pyrometer is located in the dryer discharge to monitor the temperature and automatically control the burner. The burner is equipped with a silencer for further noise attenuation.
The hot stone bucket elevator is 500mm wide x 26m centres and has twin strand chain. This lifts the hot aggregates to a 1.8m wide x 3.3m long 6 deck vibrating screen which is enclosed in a fully insulated housing. The screen separates the feed into six sizes plus rejects. The hot stone elevator has a local inching facility and is equipped with an inverter and safety interlocks for maintenance purposes. A screen by-pass chute is incorporated in the elevator discharge chute to transfer material direct into bin 1 of the hot stone bins if selected. The 36 tonne hot stone bins are split into 6 compartments and integral overflow chutes direct the overflow and rejects to a 5 tonne holding hopper. Each bin compartment has continuous level indication for display on the controls screen and a sampling chute for test purposes.
The aggregate, bitumen and filler weigh hoppers are all loadcell mounted. The bitumen weigh hopper is electrically heated and insulated, with an agitator mounted on top for bitumen blending during production. The bitumen discharges via a spray bar across the paddle mixer.
The 2250 kg paddle mixer is driven by 2 x 22kw geared motors with a timing shaft and soft starters are used to reduce the starting current. Two sides of the paddle mixer are hinged for internal maintenance purposes. Lifting beams are fitted throughout the plant including over the elevator, the vibrating screen and the paddle mixer. An infrared pyrometer is mounted in the mixer discharge housing to monitor and record the discharge temperatures.
The mixer discharges into a horizontal 2250kg skip controlled by an inverter. The whole mixing tower is mounted over a 200 tonne mixed material facility which is loadcell mounted for automatic load out into trucks. The 200 tonne storage is split into 4 x 50 tonne silos. There is also an 8 tonne direct lorry loading hopper situated directly under the paddle mixer for small orders.
The TC340 reverse air cleaning bag filter dust collector has an air volume capacity of 72,590m³/hr, extracting air from the dryer and the nuisance dust points on the plant. A primary skimmer is used to separate the coarse dust from the dryer exhaust. The coarse dust is continually fed to the hot stone elevator via a screw conveyor. A 90kw backward inclined exhaust fan, controlled by an inverter to vary the air flow, extracts the air through the system discharging into a 30m high exhaust stack. The speed of the fan is varied according to a transducer monitoring the pressure at the dryer discharge end. Particulate emission levels of less than 20mg/m³ are guaranteed. Special safety features included in the bag filter are a cold air door which automatically activates if a pre-set temperature is exceeded and a fire door which isolates the filter if a pre-set temperature is detected, or if activated by an emergency stop.
A screw conveyor delivers the collected reclaimed dust from the bag filter to a vertical filler elevator which discharges into a buffer hopper. The buffer hopper stores hot filler and discharges into an inclined screw conveyor which feeds the plant mounted filler weigh hopper. The buffer hopper also incorporates an overflow chute to a 70 tonne reclaimed filler storage silo mounted at ground level. At the end of production the buffer hopper can discharge any stored filler back into the reclaimed silo, therefore allowing hot filler to be used upon starting the next scheduled production. At the base of the 70 tonne reclaimed silo an inclined screw conveyor feeds the vertical filler elevator. A purge system is fitted to the reclaimed filler silo, this includes three screw conveyors and a sealed purge transfer assembly featuring extending bellows and a local pendant operated controller. A 50 tonne imported filler silo is mounted directly above the reclaimed filler silo making a total of 120 tonnes filler storage.
There are 3 high thermal efficiency electrically heated bitumen storage tanks with a nominal capacity of 94.4 tonnes each. The bitumen tanks are compliant with current RBA recommendations. Each tank is fitted with a stainless steel overflow/vent, radar level indication and a control panel at the fill point with contents gauge and light indicators for safe to fill (green), high level warning (amber) and ultimate high level warning (red). One of the tanks is fitted with a motorised stirrer for agitating all types of modified bitumen.
The electrically heated bitumen pumps and piping between the bitumen tanks and the bitumen weigh hopper are configured to automatically provide from the computer system:
- recipe controlled bitumen supply from any tank to the weigh hopper
- recipe controlled bitumen blending from any tank to the weigh hopper
- bitumen tanker filling to any tank
- transfer of bitumen from tank to tank
- bitumen tank to bitumen tanker transfer
- bitumen tanker transfer direct to weigh hopper
The system has been designed so that the computer monitors the status of all tanks and valves. A sampling valve is also incorporated in the system to allow safe sampling during bitumen delivery to the plant.
The fuel tanks, one for CFO and the other for gas oil, consist of two 60,000 litres vertical self bunded cylindrical tanks, complete with piping to the dryer burner.
An SMA fibre additive system is positioned at ground level consisting of a 28m³ silo and a spiral screw conveyor to a loadcell mounted weighing unit with transfer to the paddle mixer via a pneumatic conveying system.
A recycled asphalt pavement (RAP) feed system allows for the addition of up to 20% recycled material. The system consists of 2 x 12m³ steep angled RAP feed hoppers with 100mm grids. The hoppers are positioned adjacent to the high level cold aggregate feed hoppers. A three sided canopy and roof is positioned around the feed hoppers. Two 650mm wide x 4m centres variable speed belt feeders with 20:1 turndown ratio feed a 650mm wide collecting conveyor which discharges the RAP onto an inclined conveyor.
This in turn transports the material to a vertical RAP elevator. A by-pass chute at the inclined conveyor discharge enables the RAP feeders to be calibrated, or the feeder hoppers to be emptied direct to a truck. A 300mm wide x 14m centres vertical elevator, mounted at the mixed material discharge level, transfers the RAP to the weigh feeder.
The RAP feed conveyors and the RAP elevator are positioned at high level to facilitate site vehicle movement. The 650mm wide x 2.8m centres variable speed weigh feeder is supported on 4 loadcells and discharges the RAP into the paddle mixer. An extraction fan removes the steam created when the RAP is added to the mix from the mixer housing to the bag filter. A cut off door isolates the vent duct when the RAP is not being processed.
All of the wiring for the plant is positioned at 2.2m above ground level on ladder cable trays. The plant wiring is separated from the control wiring. There are no cables underground. The motor control panels are situated inside a switch room. The panels have manual motor start/stop buttons located on the outside for plant maintenance purposes only.
The control cabin is positioned above the switch room and houses a desk with two large computer screens complete with keyboards. There are no further controls inside the cabin; all of the plant is controlled from these computers. There is limitless recipe storage. One of the PC screens shows the production data, whilst the other PC screen has a live animated mimic of the plant showing the running and tripped status of each unit plus the plant monitoring functions. The information on the two PC screens can be interchanged if required. The system incorporates a production scheduler, a plant monitor, plant diagnostics, alarm reporting and a recipe editor. The control system has automatic sequenced plant start-up, full plant control and automatic load-out to trucks from each of the mixed material silos. The controls also have special features for asphalt plant operation such as concurrent weighing with top-up, and over and under weigh checking. There is also an energy consumption monitor included to establish the kWh rating at any one time during the plant operation. The whole plant has the ability to be able to be operated from the control cabin, or alternatively from the weighbridge.
The plant was officially opened on 1st August 2014 by Mr Andrew Turner MP, the local Member of Parliament for the Isle of Wight. During his speech he said “It was important we reached this point because this plant is absolutely vital to the future success of the PFI”. During the opening ceremony Mr Simon Willis the Chairman of Wight Building Materials Ltd added “Wight Building Materials now has a modern, low emission plant capable of providing quality high performance products to meet the needs of our customers”.
The Parker team wishes to thank Wight Building Materials for this valued order and their assistance throughout the design, manufacture and installation process which contributed greatly to the success of the project.