SN Engineering completes one of the largest single silo facilities in the UK

Bulk materials handling specialists, SN Engineering, have recently completed a project to construct the largest single silo storage facility it had ever worked on, thought to be the biggest silo of its type in the UK. The silo has a capacity of 3000m3 and was erected to increase product availability for Francis Flower at its Runcorn Docks site in Cheshire.

Established in 1953, Francis Flower reclaims and processes mineral by-products from industry to supply sustainable construction, agricultural, food and pharmaceutical products across the UK. In 2015 the business expanded its product portfolio to include GGBS, a by-product of the iron and steel making process, and has quickly invested in this business to meet the growing demand of its existing customers.

What is GGBS?
‘GGBS’ stands for Ground Granulated Blastfurnace Slag and is made from a by-product of the iron manufacturing process. It is used to make durable concrete structures in combination with Ordinary Portland Cement (OPC) and/or other pozzolanic materials. The product is already widely used in Europe, and increasingly in the United States and Asia, for its superiority in concrete durability, extending the lifespan of buildings from fifty years to a hundred years.

The use of GGBS significantly reduces the potential risk of damage caused by alkali–silica reaction (ASR), provides higher resistance to chloride ingress (reducing the risk of reinforcement corrosion) and provides higher resistance to attacks by sulphate and other chemicals. This makes GGBS suitable for structures immersed in water such as sea defences, or bridges where foundations are set into the river bed. For example, Blackpool’s sea defence and many others are now using GGBS in subsurface concrete for sulphate resistance.

GGBS is also routinely used to limit the temperature rise in large concrete pours. The more gradual hydration of GGBS cement generates both lower peak and less total overall heat than Portland cement. This reduces thermal gradients in the concrete, which prevents the occurrence of micro cracking which can weaken the concrete and reduce its durability, and was used for this purpose in the construction of many high profile UK civil projects, such as the Channel Tunnel Rail, the Second Severn Crossing road bridge and the Spinnaker Tower.

Concrete made with GGBS cement sets more slowly than concrete made with ordinary Portland cement, depending on the amount of GGBS in the cementitious material, but also continues to gain strength over a longer period in production conditions. This results in lower heat of hydration and lower temperature rises, and makes avoiding cold joints easier, but can affect construction schedules where quick setting is required. Concrete containing GGBS has a higher ultimate strength than concrete made with Portland cement. It has a higher proportion of the strength-enhancing calcium silicate hydrates than concrete made with Portland cement only, and a reduced content of free lime, which does not contribute to concrete strength. Concrete made with GGBS continues to gain strength over time, and has been shown to double its 28-day strength over periods of 10 to 12 years.

Environmentally, the product has many positive attributes too, as the manufacture of GGBS requires less than 20% of the energy and produces less than 10% of the C02 emissions compared to Portland Cement production.

With GGBS able to replace more than 70% of the Portland Cement content in a concrete mix, it has the ability to significantly improve the environmental credentials of a mix, without compromising on quality.

Increasing capacity for Francis Flower GGBS
Francis Flower is one of only two GGBS producers manufacturing this product in the UK at their plant in Scunthorpe, which is located on the site of the newly formed British Steel production facility, (formally owned by Tata).

Shortly after acquiring the GGBS business in August 2015, Francis Flower was approached by its customers to supply additional volumes of GGBS. This was primarily as a result of the accelerated reduction in the availability of PFA, an alternative cementitious by-product derived from coal-fired power stations, following Government environmental legislation changes.

Despite a capacity in excess of 600,000 tonnes per annum at its Scunthorpe plant, Francis Flower knew that to meet growing customer needs in the timescales requested, further investment in its GGBS business was a must.

With this in mind, plans were quickly made to expand the Francis Flower national supply capability by more than 200,000 tonnes per annum via the expansion of its pre-existing North West distribution terminal in Cheshire to facilitate the importation of GGBS from its strategic partners. This strategically important project would enhance the Francis Flower GGBS supply offering to over 800,000 tonnes per annum to ensure sustainable product availability on time and in line with its customers’ requests.

Located on the Manchester Ship Canal, Francis Flower already had in operation a 5,000 tonne GGBS importation and distribution facility, the first of its kind in Runcorn, which would provide the basis for its expansion project. The project itself was designed to increase storage capacity by more than 70 per cent via the installation of an additional silo facility, whilst also improving the established site infrastructure and logistics capability.

The newly expanded site would also need the capability of operating on a 24/7 basis to provide the certainty of supply that the Francis Flower customers demand.

In order to achieve this aim, Francis Flower recognised that partnering with the right engineering provider would be vital if safety, equipment specification, cost and tight deadlines were to be achieved. The engineering provider of choice was SN Engineering, based in Gloucester.

A challenging project
SN Engineering’s brief was to design a facility that would accept and store an additional 3,000 tonnes of GGBS delivered via self-discharging ships, and then onward convey the bulk material from this storage facility into Francis Flower’s existing road tanker load out silos, via a lean phase conveying system. This plan would increase the overall Francis Flower storage capability at Runcorn to 8,000 tonnes and had to be delivered in eight months!

Francis Flower Group Operations Director, Rowan Elliott commented: “The Francis Flower business prides itself upon having the ability to deliver value and sustainability to its customers. As project lead, I knew that safely delivering a time bound engineering solution would be both exciting and challenging in equal measure.”

The main project restriction was the actual site area. After carrying out an intensive site survey the chosen location for the new facility was a narrow strip of land between the dockside and the estuary. The challenges that this narrow site posed were further compounded by the small proportion of land actually available for development, with the remaining area requiring 24/7 access for the Port Authority’s day to day bulk cargo offloading and the existing supply of the Francis Flower GGBS customers.

Director at SN Engineering (SNE), Mark Osborne, explained the scale of the project: “Having analysed the various options open to Francis Flower, it soon became apparent that with such a restricted site area for final location and, more importantly, lay down and sub assembly areas, the only real option was for one large silo facility. Having already supplied various 2600m³ x 12.5mØ silos in the past and with an all new 3000m³ silo added to our range, a proposal was put forward utilising this new, larger silo model. This would represent the largest silo of this type undertaken by SNE and quite possibly the largest of its type in the UK.”

Francis Flower awarded the contract to SNE for the design, supply and installation of the silo, and under CDM requirements and a tight timeline, the task was set. SNE rose to the challenge and completed in just eight months - from initial conception and design, through to manufacture, delivery to site and final installation. Actual installation time for the silo took only seven weeks, including fully cladding the structure. Alongside this, the delivery of requisite site civil engineering and additional works were delivered by the Francis Flower engineering team, working in partnership with specialist contractors and supported by in-house electrical and mechanical expertise.

The exposed location on the docks led SNE to specify additional protection for the silo: “With the Manchester Ship Canal being totally exposed to the full force of UK weather, the design catered for higher than normal wind speeds (45m/sec) for that extra peace of mind. Again, for extra weather protection, all the roof-mounted equipment – such as the pair of dust filtration units – were enclosed within a roof-mounted ‘penthouse’. Further enhancements, for field longevity, included marine painting the structure and all the external surfaces of the silo. Even the bolts were Geomet® treated, and to give you a sense of the size of the project, we used 7.5 tonnes of bolts! One request that made us all smile was that of seeking a NOTAM (Notice to Airmen) approval from the Civil Aviation Authority, because we were erecting the 35 metre tall silo on the direct flight path of an international airport three miles away – this made for some very interesting photographs throughout the build!”

“The silo was equipped with a pair of high capacity, high efficiency, fan assisted dust plants to ensure all introduced dust laden air is safely managed, with only pre-filtered air being released to atmosphere. With the silo having a working capacity of approximately 3000 cubic metres, stock inventory is maintained via a dual system of weigh indication: strain gauges fitted to each of the 16 x 2.25 tonne legs and a continuous level device; utilising the latest radar technology available to constantly feedback data to the Francis Flower system via a 4-20mA interface. Pressure relief valves and mechanical high, and ultimate high levels, complete with continuous ground testing capabilities, have also been installed as additional safety devices as part of our ‘belt & braces’ approach.”

To ensure the GGBS discharges freely, the whole of the silo cone has been fitted out with air pads and the lower units have anti wear discs installed to counter the abrasive sliding friction of the product as it reaches the outlet of the silo. This is serviced by its own dedicated ring main, ensuring that the area within the cone can be aerated as and when required. In addition, the silo aeration system is fed by its own dedicated low pressure-high volume blower unit, with the aforementioned blower being enclosed within its own acoustic cabinet to minimise noise pollution.

Once the new bulk silo has been charged with the GGBS, the product is discharged through an electro pneumatic, extra heavy-duty cast iron slide valve. Onward discharge occurs via a special heavy-duty, rotary valve-lean phase blowing system, to Francis Flowers’ loading silos, feeding their road tankers for onward shipment to end clients.

The first ship arrives
Mark said: “In early August we welcomed the first ship into the docks and the first 2000 tonnes of GGBS was successfully blown into the silo with ease, and more importantly with zero dust being emitted to atmosphere. Discharge to client’s day silos also proved uneventful and met the client’s design brief in full. Francis Flower can now turnaround ships in 24 hours rather than the 36-45 hours it took previously, as they have the facility to fill both the new silo and the existing ones simultaneously.

The whole site construction process was captured on a time-lapse camera, which allowed Mark and the team at SN Engineering to view the project remotely at the time. “Using a time lapse camera worked really well, said Mark”. It was fixed onto one of the existing silos and could capture the whole construction site in high definition. I found it really useful to check in on progress or visualise an issue when I couldn’t be up at Runcorn, as it took pictures every quarter of an hour during each day of construction. Now at the end of the build, the photos have been linked together as a time-lapse video and we have a really good record of the project that we can look back on with pride.”

Rowan Elliott, further remarked: “Getting this project off the ground as soon as possible to meet our customer needs was crucial in order to enhance our GGBS offering. SN Engineering delivered this project on time, on target cost, and most importantly, with zero harm and in compliance with UK CDM requirements. The completion of this project is the culmination of many months of hard work by the Francis Flower Runcorn-based team, SN Engineering and a set of highly skilled contractors. Expanding our GGBS offering is great news for us, and more importantly, great news for our customers too as we can further ensure continuity of supply of our quality assured product.”

For further information on SN Engineering including project evaluation or a site survey – contact:
For further information on Francis Flower GGBS or to view the time lapse video of the new silo construction – visit:

Associated Businesses

  • SN Engineering, a leading UK manufacturer of Dry Bulk Material Handling Equipment, offer in-house design, manufacture & supply of a wide range of Bulk Storage Silos & solutions; Dust Filtration units & systems; Screw conveyor...