5. ICE STORAGE

5.1 Block Ice
5.2 Flake Ice
5.3 Plate Ice
5.4 Tube Ice
5.5 Simple Bin Stores Using Manual Discharge
5.6 Ice Store Costs
5.7 Ice Crushers

The type and size of an ice store will depend upon the type of ice, the demand for ice and the patterns of demands. It is common for ice stores to be 2-4 times the daily production. Physical dimensions of stores of given capacities are included under the description of each type of store and are based on manufacturers published information. As a comparison Table 11 lists the volume and area requirements of different types of stores with the forms of ice commonly stored in them.

Table 11 Volume requirements of ice stores

Table 12 compares the area requirements of the types of store with different forms of ice commonly stored in them.

Table 12 Area requirements of ice stores

a/ Inclusive of the air jacket space surrounding the silo

5.1. Block Ice

Block ice is usually stored in block form and crushed on demand. It is stored at temperatures between -4 �C and -2 �C and can be stacked one block upon another. Wooden battens can be used to separate blocks to prevent fusion but this is not normally a problem. Care should be taken when stacking tapered blocks which should be stacked to a maximum height of 2.2 m depending on block size or crushing of the lower blocks may result with danger to workers. The smaller sizes of block (e.g., 25 kg) may be stacked manually but larger sizes normally require some kind of lift or inclined conveyor to raise blocks one above another to a height at which they can be dragged using tongs. It is normal to base capacity upon a storage volume of 2-3 m�/t of ice stored.

5.2 Flake Ice

Flake ice is usually stored in silo or bin with the ice-maker located over the store The silo system which is shown in Figure 14 usually requires slightly less ground area for a given storage capacity but will usually be taller than a bin system and will have a greater capital cost due to the civil work involved, particularly if the site has an exposed location where windage is an important design factor. The silo shown in Figure 14 is contained within an insulated jacket and cooled air passed between the jacket and silo to keep the ice in a subcooled and dry condition. To prevent bridging of the ice and to assist the flow of ice on discharge, an agitator rotates within the silo driven by an electric motor from above. The silo works on the first in-first out principle of storage but ice build-up can occur on the walls and requires occasional removal either by blows to the outside of the silo or by removal from the inside manually. Normally a trap door is provided in the top of the silo for access. The trap door is connected to a safety mechanism that isolates the agitator mechanism. The dimensions of the silo and building for given storage capacities are shown in Figure 14. The capital cost of the smaller capacities (40 t and below) are expensive compared with simple bin systems. For capacities much in excess of 100 t it is usual to install multiple units.

Bin store capacities and sizes are given in Figure 15. Many patented systems of handling and discharge exist but the mechanical rake and end gate system is common. The system operates on the first in-last out principle and requires emptying occasionally to remove stale and packed ice build-up at the bottom. To help overcome this problem the double bin system was developed which employs two bins and which enables one bin to be emptied while the other is filled. The triangular configuration shown in Figure 15 is less mechanically complicated than the rectangular system as the drive-end of the rake is fixed. It also discharges at a height convenient for loading but requires nearly twice the ground area of the rectangular bin and for this reason is rarely used for stores of large capacity. Other bin systems exist that operate on a first in-first out principle by removal of ice at the bottom of the store but the systems are expensive compared to the rake and end-gate systems and are more commonly used on large industrial application. Discharge of flake ice is usually by screw and/or belt conveyor. Pneumatic discharge systems need very careful design for application with flake ice or a pulverized soft and wet product will result

5.3 Plate Ice

Plate ice is usually stored in a bin system similar to that described above for flake and shown in Figure 15. The storage capacities given in Figure 15 which are for flake ice will be increased slightly for plate due to the higher packing density of plate compared to flake ice. A factor of 1.2 should be applied to the stated capacities when used for plate ice. Plate ice is commonly discharged by screw and pneumatic systems.

5.4 Tube Ice

Tube ice is commonly stored in bin systems similar to that shown in Figure 16 using a scraping bucket or grab device to handle the ice in the store. The operation is controlled from an observation platform with a view through a window into the store. The walls and sometimes the floor are usually protected by timber planking to prevent damage by the bucket. The observation window is also suitably protected by a guard. The bucket or grab transfers the ice via a screw discharge conveyor to an automatic weighing device which can be read from the observation and control platform. Usually only small packaged units of up to 15 t/d (production) are located above the store and it is usual that the ice is delivered from the ice-maker at ground level to the store by vertical and horizontal screw conveyors. The ice is distributed within the store by a centrifugal or gated belt device. Storage capacities and dimensions of stores are given in Figure 16.

5.5 Simple Bin Stores Using Manual Discharge

Simple bin stores of capacity up to 50 t are available or can be made, without expensive weighing or automatic discharge systems, suitable for manual discharge. Figure 17. shows a timber framed and clad store suitable for small flake or plate ice-makers.

Figure 14. Flake ice silo plant

Figure 15. Ice storage bins

Figure 16. Tube ice bin with scraping bucket discharge system

Figure 17. Simple bin store

Other bin stores are available that use modified insulated transport containers that require a minimum of site preparation and civil works. The stores can be purchased with ice-maker as a packaged unit. The plant can be considered as semi-permanent and should need arise it is possible to relocate it.

5.6 Ice Store Costs

The capital cost of ice stores will depend upon the type and capacity of the store, location and the specification or otherwise of associated equipment for refrigeration, handling, discharge and weighing, etc. The costs given in Section 4.6 for ice plants include stores but as a guide the following costs given in Table 13 apply to the store only. The costs are inclusive of steelwork, cladding, refrigeration plant (silo), piling and civil works, insulation, erection, automatic discharge (where stated) and weighing (where stated).

Table 13 Ice store costs

5.7 Ice Crushers

Mechanical ice crushers are available suitable for crushing block ice to a desired particle size within given limits. The loss on crushing is minimal (a fractional percentage), but loss on delivery will depend upon the distance involved and methods of delivery and may amount to more. If the factory is located some distance from the quay or from the point of usage then delivery in block form from the plant to a remote crusher may reduce loss during transit as loss is dependent on a surface heat transfer effect.

Crushing by hand, by ice pick and/or mallet is a laborious process that often leads to losses as high as 15-20 percent and larger particle sizes which are less efficient for the rapid cooling of fish.

Table 14 gives details of capacity, size of blocks, particle size, installed power and costs for electrically driven mechanical crushers.

Table 14 Ice crushers