Golden Bay Cement’s new $45 million bulk storage and distribution centre on the Auckland waterfront is now fully operational. The Eastport facility replaces the old depot located at the ‘Tank Farm’ on Wynyard Point, where Golden Bay leased the land for 51 years. Following a two month transition phase, the Tank Farm depot was decommissioned in February 2010.
Golden Bay Cement contracted Fletcher Construction Engineering to manage the design, building, and commissioning of the two structures on the Eastport site. Golden Bay Cement logistics manager Petar Misic says the storage and service structures and their highly automated handling facilities were designed and built specifically to minimise noise and visual impact.
In addition, Fletcher’s structural design partner Beca applied existing technology in a novel manner to create the 30 metre wide by 90 metre deep by 18 metre tall low-profile bulk store. Beca also successfully addressed several other challenges, arising in part from the facility’s location on reclaimed land, to secure its integrity.
Golden Bay’s lease on the Tank Farm land has five years to run, but Misic says the move has only upsides. He says the complex, situated on the Bledisloe B1 Wharf just metres off Quay Street, has ten times the level of dust control the system at the Tank Farm had, and it operates at a decibel level quieter than Quay Street traffic noise.
The distinctive series of seven Tank Farm silos, the tallest standing 30 metres high, could store 12,000 tonnes of cement. The new bulk store at Eastport holds 25,000 tonnes and its 2,700 square metre floor area is divided into six bays. The bays are enclosed in an elegant 18 metre high, ship-like concrete structure. In addition, Golden Bay now has long term access to a deep water port in its single biggest domestic market.
“Our aim was to design and build a world-class facility that would meet our customers’ demands for the foreseeable future, have a high level of environmental performance, and would fit in with the CBD. The facility utilises 20 dust collectors, contemporary valving and sealing equipment for its sealed cement handling system, and noise attenuation throughout. These, as well as certain design factors, keep our activities out of eye and out of earshot in two enclosed, unobtrusive buildings,” Misic says.
Misic explains how the cement travels in a sealed off system from ship to truck, how the team controls and monitors the operation, and how the storage system’s silos can function despite their unconventional design. Sophisticated software, developed, installed and maintained by Australian Current Consulting, drives the highly automated process.
First, either the 2,000 tonnes capacity barge CB Marsden Bay or the 4,000 tonnes capacity ship MV Golden Bay berths opposite the bulk store twice or three times a week, carrying cement from Golden Bay’s cement making factory in Whangarei.
Then, equipment on the discharging vessel aerates the cement powder to make it more fluid, then pumps the almost liquefied mixture to the bulk store through either one 250 millimetre diameter or one of two 400 millimetre diameter discharge pipelines. The discharge pipeline distance is 230 metres, of which 115 metres is underground.
The cement enters the bulk store at a rate of over 300 tonnes per hour and a temperature of around 65 degrees Celsius, the result of friction generated by the pumping action and heat generated by compressing the transport air.
Fletcher’s technology partner, Australian Ammermann Partners, designed and supplied the centre’s cement handling equipment. Ammermann, in turn, sourced its choices chiefly from German technology partners Luhr and IBAU. Luhr built the dust filters and IBAU the handling equipment including air slides, pneumatic pumps, and truck loading spouts.
The cement enters the bulk storage area on its top level. Next, a Luhr filter separates the transport from the cement using. In total, five large filters are fitted in strategic locations on the bulk store roof. The system has been designed so that only one filter needs to run at any one time. The other four filters are available on standby.
The Luhr filters work as follows. A large fan draws the transport air through a series of custom designed filter bags. The bags are made from a special material designed for cement and cement handling operating conditions. The material’s fine weave allows only air to pass through the material. The filtered air then exhausts through a vent.
The filter units incorporate performance and emission monitoring equipment that provides information to the supervisory control system. The control system will automatically stop cement transfer and start up a different dust collector if the system detects any anomalies.
A high pressure pulse cleans the filter bags by agitating their surfaces. The cement then drops into the storage bay. Each of these five filters has a filter area of 207 square metres and air capacity of 250 cubic metres per minute.
The dust filters in both the bulk store and service area do their job well.
“We designed for a dust free operation, and there is no visible dust. Performance tests we did during commissioning showed dust emission levels below 10 milligrams per normal cubic metres (mg/Nm3), well below the 20 mg/Nm3 guarantee from the supplier,” Misic says.
Three storage bays have a capacity of 6,250 tonnes, one has a capacity of 3,125 tonnes, and two have a capacity of 1,560 tonnes. Misic says the technology used in marine bulk cement ships was applied to achieve the store’s low profile and ensure its integrity on its reclaimed land site.
Low noise, low visual impact
A combination of in-situ concrete with precast rib elements, the Eastport structure rests on 692 H piles, varying in depth from 12 metres to 20 metres. The external fins are an integral part of the structure, transferring the forces the stored cement exerts on the vertical walls to the foundation raft and piles below it.
A key design constraint was that noise measured at the neighbours’ boundaries had to comply with the City of Auckland District Plan for the area. The architects incorporated noise attenuation into all aspects of the design and build processes to ensure that the measured noise level would be less than 55 decibels (dBA). Marshall Day Consultants from Auckland did the acoustic and noise attenuation design.
Next, the cement transfers from the storage bays to the service centre. The system automatically selects a source bay in the bulk store and a destination silo in the service centre. Air pads that enable the cement to be fluidised cover the entire 1,800 square metres base of the bulk store. Five blowers provide the approximately 30 cubic metres per minute at 500 millibar (mBar) aeration air required to fluidise the cement and extract it from the main storage bays into the cement pumps. The control system automatically controls the sequence of air pad activation to ensure continuous cement flow and avoid dead stock. It also automatically selects one of two transport lines to transfer the cement to the service centre’s six 150 tonne silos, via a Luhr filter per silo. It then starts the corresponding transfer equipment and set of two pneumatic pumps per transport line, using a pre-determined sequence. One of three Aerzen VML95 compressors make a set of pumps work, at 315kW and 1.75 bar each capable of providing 109 cubic metres per minute transport air.
The fluidised cement exits the silo through the discharge outlet. All the extraction and transfer equipment is housed in a large triangle shaped tunnel located at the base of the structure. The tunnel runs the full length of the bulk store.
Inside the fully enclosed 24m x 34m x 24m structure are three bulk tanker loading lanes, each serviced by two silos. It also contains an automated blending plant, the only one in New Zealand, where up to four components can be mixed simultaneously at 95 tonnes per hour.
The loading system is also fully automated, managed by the sophisticated Citect SCADA supervisory computer control system. A loading cycle, from driving in to driving out, takes 15 minutes. Entry and exit for the tankers are via high speed roller doors, designed and made by Flexible Door Technology.
Finally, cement loads by gravity via an airtight loading spout into a loading opening on the tanker’s roof. The spout contains an outer ring for venting, with the centre part feeding cement into the tanker and the outside section taking away displaced air. The displaced air is also fed through a Luhr filter per loading lane. The service centre’s dispatch capacity is 750,000 tonnes per annum.
The Golden Bay-Fletcher team started work on the green field site in June 2008. All construction and commission work was completed in 18 months, with Fletcher handing over the site to Golden Bay on December 22 last year. Misic says Golden Bay has a 35 year lease on the new property.
Looking ahead, Auckland’s city fathers plan to transform the Tank Farm into a retail, housing and tourism hub. The six Tank Farm silos will remain as a feature of Wynyard Quarter for many years to come.