Page 110 - Hub-4 Issue 55

Bulk Handling
Anhydrite
An evaporate mineral used as a soil treatment and to produce construction materials
What is Anhydrite?
Anhydrite is an evaporate mineral that occurs in extensive layered deposits in sedimentary basins where large volumes of seawater have been evaporated. It is typically interbedded with halite, gypsum, and limestone in accumulations that can be up to hundreds of feet thick. On a much smaller scale, anhydrite can form in shoreline or tidal flat sediments from the evaporation of seawater.
Anhydrite also occurs as a vein-filling mineral in hydrothermal deposits. It is deposited from solution, often along with calcite and halite, as gangue in sulphide mineral deposits. Anhydrite is also found in the cap rock of salt domes and in cavities of trap rock.
Anhydrite is an anhydrous calcium sulphate with a composition of CaSO4. It is closely related to gypsum, which has a chemical composition of CaSO4.2H2O.
The worldwide abundance of gypsum greatly exceeds the abundance of anhydrite.
Anhydrite receives its name from the Greek "anhydrous" which means "without water." It readily converts to gypsum under humid conditions or in contact with groundwater. This transition involves the absorption of water and a significant change in volume. That expansion can cause deformation in the rock units. If gypsum is heated to about 200oC, it will yield water and be converted to anhydrite.
This reaction occurs much less often.
Uses of Anhydrite
Anhydrite can be substituted for gypsum in some of its uses. Both minerals are crushed for use as a soil treatment, and in this purpose anhydrite is superior. One ton of anhydrite has more calcium than one ton of gypsum - because gypsum is about 21% water by weight. This yields more calcium per ton in a soil application. Anhydrite also has a higher solubility, which helps it benefit the soil quickly.
Small amounts of anhydrite are used as drying agents in plaster, paint, and varnish. It is also used along with gypsum to produce plaster, joint compound, wallboard, and other products for the construction industry. Anhydrite has also been used as a source of sulphur in the production of sulfuric acid.
The Brief !
Client brief was for some c 1000Te additional storage with direct, dust free, tanker loading to compliment their existing facility.
An agreed location was determined, adjacent to existing, thus ensuring their existing traffic management system could be adhered to as this large plant has a high volume of traffic movements therefore site safety was paramount.
SN Engineering initiated a design, in conjunction with clients preferred civil contractor, utilising 2 No SP490 ( 490m3 ) series sectional bolted silos from their 7.6mØ range c/w raised super structure for direct drive under loading.
As previously, due to the exposed site location, the silos & structures were designed for 45m/sec peak wind loads. This exposed environment also meant the steelwork had to be finished to ‘C5’—Marine spec for enhanced longevity. An
element of future proofing was also catered for within the initial design such that possible future use of these silos for direct offloading from ship was also built in to the design.
At the beginning of May, civil contractors commenced removing an old weighbridge, which was to be recycled & extended for this new facility, and making good the ground adjacent to the clients existing & very busy facility. Fortunately, for CDM compliance, a relatively easy site works demarcation could be achieved and a dedicated site ingress / egress system could be employed thus zero hindrance to the clients working site could be achieved.
At this point, SNE installed a time-lapse, high definition, camera to the bottom of the site—this allowed for the whole project site to be captured for future reference, but more importantly for live continual monitoring throughout the various project phases.
During this initial civil works, SNE could complete the 3D modelling—having already agreed the design principle & loadings for passing to civil & piling contractors - ensuring the tight manufacturing timeline could be achieved.
SNE’s in-house 3D modelling not only enables our engineers to check finite detail, thus ensuring everything is covered before manufacture commences & more importantly a trouble free site installation.
The obvious added benefit is to the client who can view these 3D drawings, with colleagues &/or stakeholders, to assist better in visualising what they are getting from their investment.
The design also had to cater for 2 wrap around high level platforms, for accessing silo outlet components, and had to be combined with ease of operator access to tanker hatches at a lower level. A unique 1 piece, twin deck, design allowed for both easy access to silo outlet components, including easy access to the loading bellows, combined with integral step down to a suitable tanker access height where a pair of specially commissioned counter balanced drop down stairs could be fitted. These balanced drop down stairs c/w integral perimeter hand railing allow for operators to safely access the top of the tankers whilst being fully protected by the hand railing, which is hinged to work in unison with the up / down action of the drop down stairs. These can be easily & safely locked in desired position thus caters for variations in tanker heights.
Late August saw the deployment to site of the initial crew of 4, this would be increased to 6 as the project naturally evolved. This coincided with the 1st 3 ( of 7 ) artic deliveries to site. All our silos, even our 12.5mØ range are fully transportable via standard road haulage &/or shipping containers, thus can be shipped to any part of the globe.
The silos were each 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 silos each having a working capacity of approximately 500m3, stock inventory is maintained via a continuous level device; utilising the latest radar technology available to constantly feedback data to the clients existing 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.
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www.hub-4.com March 2019 - Issue 55