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 3D 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.
StarMix 2000 Overview
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 rest of the plant on the quarry floor.
The plant consists of 8 x feed hoppers complete with low level indicators with a visual alarm above each bin and indication in the cabin. Mounted under each feed hopper is a 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 horizontal collecting conveyor, scalping screen and slinger conveyor discharges the feed aggregates direct into the dryer. The conveyors and screen are covered to minimise air borne dust and provide weather protection.
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 and all of the open walkways, handrails and stair treads are galvanised and the whole plant is located on 30mm thick galvanised blocks.
The dryer features nylon support and thrust rollers, minimising wear on the roller paths and reducing the noise levels. The dryer is friction driven by 4 geared motors via soft starters and 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 also equipped with a silencer for further noise attenuation.
A hot stone bucket elevator lifts the hot aggregates to a 6 deck vibrating screen which is enclosed in a fully insulated housing. The screen separates the feed into six sizes plus rejects and a screen by-pass chute can transfer material direct into bin 1 of the hot stone bins if selected. The hot stone bins have 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 above the paddle mixer.
The paddle mixer is driven by 2 geared motors with a timing shaft and soft starters are used to reduce the starting current. An infrared pyrometer is mounted in the mixer discharge housing to monitor and record the discharge temperatures.
The mixer discharges into a horizontal skip and the whole mixing tower is mounted over a 200 tonne mixed material facility which is loadcell mounted for automatic load out into trucks. The storage is split into 4 x 50 tonne silos with a direct lorry loading hopper situated directly under the paddle mixer for small orders.
The reverse air cleaning bag filter dust collector extracts 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. An inverter controlled exhaust fan varies the air flow and 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.
Reclaimed dust from the bag filter is transferred to a buffer hopper. 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. A purge system is fitted to the reclaimed filler silo via a sealed transfer assembly with extending bellows. Additionally, an imported filler silo provides extra filler storage.
There are 3 high thermal efficiency electrically heated bitumen storage tanks 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 system has been designed so that the computer monitors the status of all tanks and 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 plant also features a loadcell mounted SMA fibre additive system 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 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 above ground level on ladder cable trays and 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 control cabin sits above the switch room and houses a PC based system with two large computer screens. One of the screens shows the production data, whilst the other screen has a live animated mimic of the plant. 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 plant was opened 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”.