Cement terminal system cost study

Customising dome storage to suit a particular project is a normal part of the project development service that Dome Technology is involved with. Owners have many options to choose from as they develop the project scope. We are often asked to compare two or more storage concepts which inherently involve a customised dome shape. Because we can model costs along with mechanical supply cost, mechanical and electrical installation, we can develop a side-by-side comparison.

In order to focus the comparison, we will concentrate on the core terminal, which consists of just the central storage and loadout system costs. We will compare mechanical arrangements with similar features and functions. Our core system will vary in storage capacity. The mechanical process system requirement, sometimes called throughput, will be the same for all. We will use a day bin system, with one truck loading position. The usual capacity calculation for this system would be:

200 sTons/hour = 8 trucks @ 25 sTons per truck per hour 8 trucks x 8 hrs x 180 days per year = 288,000 sTons throughput per year

To develop a suitable storage size for a particular site that can handle the calculated annual throughput, the owner will balance storage capacity against the practical logistics of filling the terminal. For example, if a 25,000 sTon ship is used to fill the system, an expected shipping frequency would be about 12 shiploads per year (288,000 ÷ 25,000). In order to create a comfort level for the shipper, the dome storage size should be about 35,000 sTons.

Reclaim system configurations can vary between projects. Typical configurations include Cambelt screw-style reclaimers, dihedral pneumatic floors, conical pneumatic floors, and drivethrough pneumatic floors. For each of these reclaim system configurations, our core cost comparison begins with the pneumatic inlet piping at grade and ends with a customer truck fully loaded.
 

Cambelt reclaim system

The Cambelt mechanical system is shown in Figure 1 is a popular choice. The installed system includes the pipe support stair tower and bridge, headhouse, dust collector and loading system. Gap engineering, day bin, electrical wiring and control room complete the system.
 

Dihedral pneumatic floor

The dihedral pneumatic floor dome, Figure 2, is competitive over a wide range of storage capacities. The cost of the pipe support stair tower is eliminated, as is a large headhouse. Because weight on the dome apex is reduced, the added cost of strengthening the dome shell is also eliminated. This configuration entails installing the pneumatic floor, bracing the bucket elevator and providing a day bin structure and truck loadout. Gap engineering, electrical wiring and control room complete the system.
 

Conical pneumatic floor

The conical pneumatic floor dome, Figure 3, includes a tunnel wide enough for a cement pump. The vertical chase functions as a secondary egress and eliminates the pipe support costs. The system includes installation of the pneumatic floor, mechanical systems and provision of a similar day bin structure with truck loading. Gap engineering, electrical wiring and control room complete the system.
 

Drive-through pneumatic floor

The drive-through pneumatic floor dome, Figure 4, consolidates the mechanical systems, and structures to within the dome footprint. Cement is piped though the vertical chase to fill the dome. A portion of the cement (live storage) directly flows into the day bin. The remaining cement is fluidised by the fully fluidised sloping floors, to an air-lift conveyor then pumped to the surge bin. The through tunnel is integrated with the surge bin and the control room, mechanical room and electrical room are located above the customer’s truck. Gap engineering, electrical wiring and mechanical systems complete the system.
 

Cost approach

Figure 5 compares the construction costs of the various reclaim systems as a function of total storage capacity using optimised costs for excavation, fill, soil compaction, stemwall height, required ring beam variations, headhouse weights, tunnels, vaults, day bin foundations, office, mechanical room and electrical room as well installed PLC, MCC, and electrical wiring. Commissioning costs are also included. This tabulation was done from the perspective of a supervising plant engineer responsible for administrating the purchasing and installation contracts. Costing includes a modest allocation for a consulting engineer to provide gap engineering and to define sub-contracts such as the electrical and mechanical installation packages.

Thomas W. Hedrick, Managing Engineer, Dome Technology, Inc, Missouri, USA
Edition: Edition 29

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