6. Ice plants
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The first step in planning is to confirm whether an ice plant is actually required. Other ice plants in the area may be a reliable source of suitable ice and, even with the additional transport costs and the manufacturer's profit, they may be able to supply ice cheaper than it can be made by the user. A large installation has many economic advantages over a small unit and it is not unreasonable to expect that it can produce cheaper ice. Other factors, such as being self sufficient, may over-ride an economic disadvantage.
The most important stage in planning is to consider the site of the ice plant, both in relation to the services required for the manufacture of the ice and, to the ease of distribution to the consumer. Ice plants require a power source, and suitable water supplies for both ice manufacture and refrigeration plant condenser cooling. In addition, some plants require a further supply of water for defrosting purposes. The cost of transporting ice is substantial, particularly in heavy traffic areas, and may be the biggest cost to the consumer. Ice plant should therefore be located where the ice is required, or sited to keep transport requirements to a minimum. Advice on layout is usually given by the manufacturer, but this information is only applicable to the type of plant he supplies. For instance, traditional block ice plants require a much larger floor space than modern automatic ice makers. Other ice makers, like the tube ice machine, require a good deal of headroom and are seldom located above the ice storage space, whereas with flake ice machines this arrangement is usual. Silo storage also requires a relatively high building structure, whereas large storage bins need plenty of floor space because of limitations on the storage depth. Space and building height limitations should therefore be considered at an early stage of planning, since any restrictions may preclude the use of some types of plant. For instance, on some sites tall buildings are undesirable for aesthetic reasons.
Most ice machine manufacturers produce a range of standard unit sizes. Since each unit has a variable capacity, depending on the operating conditions, it is usually possible to meet the requirements of each customer under the most favourable conditions.
Some manufacturers produce dual units in which the unit capacity range is apparently extended upwards. However, higher icemaking capacities are usually achieved by using multiple units which may operate with a centralised refrigeration plant or each ice maker may be a self contained unit. Since the system used will have a bearing on the service provided, the choice will depend on the operational requirements. For instance, if the demand for ice is widely variable a number of individual self contained units may be selected in order to accurately match supply and demand.
Space. Modern ice makers are compact compared with conventional block ice plants, but a direct comparison of the space requirements of the various types cannot readily be made. The capacity varies with the operating conditions and it is usual to quote a capacity range when referring to its ice manufacturing capabilities. Some types of plants are more suited to high rates of production and are made in large units whereas others are made in small unit sizes only. Table 8 gives some typical figures for the space requirements for a number of the more widely used types of ice maker, producing 50 t of ice per day.
Table 8. Space requirements of ice makers
|Type of icemaker||Capacity (t/24 h)||Floor space (m²)||Height (m)|
|Rapid block ice||50||30||3.5|
The space requirements given in Table 8 are for the icemaker only. Since the ice maker is comparatively compact in modern types of plants (plate, tube and flake ice), the requirements for refrigeration machinery and handling and storage space are far in excess of the figures in Table 8. Like most machinery of this type there is an effect of scale, with larger sizes generally requiring less space per unit of ice making capacity. In some plants it is also possible to stack the units, therefore, both floor space and height can be varied to suit individual requirements. Self-contained units with a rating of up to 10 to 20 tonnes/24 hours can be located within the floor space required for storage, with the icemaker and refrigeration equipment on top. Some guidance on ice storage space requirements is given later in this chapter.
Power. Two aspects of power requirement have to be considered. The energy consumed in making a tonne of ice is important, since it influences the ice manufacturing costs. The installed power is also of interest since this will determine the power supply equipment required by the plant.
The energy required to produce a tonne of ice is not a constant; it varies with the type of plant and the operating conditions. Plants which operate with low temperatures in the ice maker, such as flake ice plants, will have a higher energy consumption. Plants operating with high condenser cooling temperatures and warm ice make-up water will also have a higher energy consumption. Thus, a plant will be more expensive to operate in the tropics than in temperate climates. Defrost procedures also add to the refrigeration load and hence the energy requirement. Tube ice and plate ice plants will therefore have an additional requirement over plants using flake ice machines which harvest the ice without a defrost. This factor is the main reason why an ice plant with a defrost process cannot economically make ice with a thickness much less than 10 mm; below this ice thickness the proportion of energy attributed to the defrost process becomes excessive. Large units tend to operate more efficiently than small units, and an ice plant fully utilised will operate more efficiently than plant operated intermittently or with a light refrigeration load. Other factors, such as the choice of refrigerant and the type of refrigeration system used, also govern the energy requirement. In climates where the ice make-up water is excessively warm, prechilling in a separate cooler can reduce energy requirements. It is therefore difficult to be precise about the energy requirements of an ice plant when it depends not only on the type of plant, but also on its environmental conditions and mode of operation. Care should therefore be taken when using manufacturer's energy consumption figures without a clear indication of the operating conditions to which they apply.
For the purpose of initial planning, the following figures may be helpful, which give the energy consumption in kWh per tonne of ice produced:
|Temperate area||Tropical area|
These figures are for the ice maker and associated refrigeration machinery only. There may be additional energy requirements for conveyors, ice breakers and a separate cooling system for the ice storage space. These additional requirements are unlikely to be large and, since most of them are operated intermittently, the energy requirements will be small compared with the figures for the ice maker. However, all electrical equipment should be taken into account in calculating the peak power demand, which will nominally be 1.5 to 3.8 kW (2 to 5 hp) for every tonne made each day. Ice making is usually a service industry and continuity of supply is essential. A suitable storage capacity will take care of short breakdowns, maintenance requirements and interruptions to the power supply but, in areas where the local supply is unreliable, the plant may require its own generator. Alternatively, the essential refrigeration machinery may be operated by a direct coupled engine with a small generator for auxiliary power requirements. In these cases, careful planning is required to avoid situations where large generators are used uneconomically to maintain a supply well below their rated capacity.
Water. The quantity of water required for a shell and tube condenser which rejects water to waste depends on the design temperature rise of the cooling water. This may vary, depending on the temperature of the supply water and other factors. A rise of 5°C is a widely used design value and this will result in a water requirement of about 30 to 40 tonnes per tonne of ice.This figure is only quoted in order to indicate the likely quantities of water that need to be available for the operation of a shell and tube condenser. The manufacturer or a qualified engineer should be consulted for more accurate figures.
For small plants, air-cooled condensers may be used. With commercialsized ice plants evaporative condensers or shell and tube condensers with acooling tower are normally used. An evaporative condenser or a cooling towersystem will use less than 0.5 tonnes of water per tonne of ice produced. This figure will increase slightly if a greater overspill is necessary to ensure that the concentration of solids in the reservoir does not build up to an excessive level.
Defrost water for plate ice machines must be of the same quality as the ice make-up water, since they are mixed in the process. The quantity required is roughly 2 tonnes for each tonne of ice produced. This requirement is reduced to only a nominal value if a closed circuit system with reheating is used for the defrost water.
Only water which satisfies the requirements for drinking water, or clean seawater, can be used for manufacturing ice for the chilling and storage of fish. Clean seawater can be defined as seawater which meets the same micro- biological standards as drinking water and is free from objectionable substances. Ice made from water that does not satisfy these requirements may contaminate fish with waterborne micro-organisms. These can reduce the keeping time of fish and may also create a health hazard. Water which may be polluted must therefore be suitably treated. Standards for drinking water can be obtained from the local health or sanitary authorities, and internationally recommended standards and methods for determining the impurities are given in the book "International Standards for Drinking Water" published by the World Health Organization, Geneva (1963).
In addition to hygienic quality, ice make-up water has to meet the requirements of the ice plant manufacturer in terms of its chemical properties. Excessive solids or hardness may result in the fouling of the ice-forming surfaces of some types of icemaker and may also affect the physical properties of the ice, because excessive solids in the water tend to give a soft wet ice. On the other hand, ice made from pure water gives problems, especially with flake ice machines. Ice from pure water sticks to the drum and a salt dosing device is required to overcome this difficulty; 200 to 500 9 of sodium chloride in a tonne of ice is sufficient to improve the physical properties of the ice. At this level the salt cannot be tasted and it does not affect the quality of the fish in any way. Information about the ice make-up water should therefore be supplied to the ice plant manufacturer; he will advise on any treatment necessary to make the water suitable for the efficient operation of the plant. Other than in extreme cases, all that may be required is a simple chemical treatment of the water in a storage reservoir.
Storage of ice
Ice manufacture and demand rates are seldom in phase, therefore storage is necessary to ensure that the plant caters for peak demand. Storage allows the ice maker to be operated 24 hours per day. It also acts as a buffer against any interruption to the ice supply due to minor breakdowns and routine maintenance procedures. Therefore, the potential buyer should calculate the storage capacity necessary to satisfy the above requirements. Account should be taken of both short-term and seasonal variations and also variations in the capacity of the icemaker. Peak demand for ice in the warmer seasons also coincides with adverse plant operating conditions when make-up water and condenser cooling water temperatures are higher. There is no general rule for estimating ice storage capacity requirements. Usually this is done by plotting the likely pattern of ice production and ice usage over a period of time, and selecting a storage capacity which will ensure that ice will be available at all times. In most cases, ice storage capacity is never less than twice the daily rate of production and more usually it is 4 or 5 times this value.
Storage space requirements for different types of ice vary in relation to their bulk density, Table 9. Although flake ice requires more storage space for a given weight, this subcooled ice can be stored to a greater depth in a silo, thus floor space requirements will be much the same as for more compact types of ice.
Table 9. Storage requirements for various types of ice
|Type of ice||Storage
|Flake||2.2 - 2.3|
|Tube||1.6 - 2.0|
|Crushed block||1.4 -1 .5|
Silo storage. Silo storage is generally used with a free-flowing subcooled ice such as flake ice and, in order to be effective, it must have an independent cooling system to maintain the ice in this subcooled condition. The cooling is usually by means of an air cooler in the jacket space between the silo and the outer insulated structure. The air cooler is normally placed at the top of the jacket space adjacent to the ice maker and the air space is cooled by gravity or fan circulation (Fig 14).
Ice is collected by gravity flow with the aid of a chain agitator which scrapes the ice from the walls of the silo. The silo allows for a first-in- first-out (FIFO) system of storage but, if the storage space is not cleared periodically, only the central core of ice is used, leaving a permanent outer wall of compacted ice. An access hatch should therefore be provided at the top of the silo so that a pole can be inserted to collapse the outer wall of ice into the central core at least once daily.
Silo storage is expensive for small quantities of ice and although units are made for as little as 10 tonne, this method of storage is more suited for storing 40 to 100 tonnes of ice.
Fig. 14. Silo ice store
Bin storage. Bin storage may mean anything from a box holding no more than 500 kg to a large installation of 1,000 tonnes or more. Bin storage can be used for any type of ice and may incorporate a separate cooling system. Whatever the size of system used, ice storage should always be within an insulated structure since the saving made by reducing ice meltage, particularly in warmer climates, is always worth the extra cost of the insulation. An insulation thickness of 50 to 75 mm of polystyrene or its equivalent in one of the many other suitable types of insulation, is suggested. Small bins may be arranged with the icemaker above the storage space; the bin is filled by gravity and a FIFO system is operated by removing the ice at a low level. This simple bin system is suitable for processors making and using their own ice. When the ice has to be distributed, the bin arrangement is such that the unloading system is at a level suitable for filling road vehicles or for cross-quay transportation to fishing vessels (Fig. 15). Bins of up to about 50 tonnes capacity can be constructed without a mechanical unloading system. This type of storage would usually be a high structure with a sloping base and access to dislodge compacted ice. Any ice left undisturbed for a few days will compact and fuse together. Ice which is free flowing when used daily may require a mechanical unloading system if used infrequently.
Large bins require considerable floor space because the recommended maximum depth of storage is limited to about 5 m, due to the fact that excessive storage depth increases pressure and results in fusion of the ice. A large capacity storage bin will require a mechanical unloading system. Some of the systems are discussed below.
Block ice storage. Block ice cannot be stored in silos or bins unless the ice is crushed beforehand. This type of ice is therefore stored in block form in refrigerated rooms. A conventional block ice plant also has a considerable amount of extra storage in the ice making unit, since it is usual to maintain the ice cans filled, even when demand has fallen below the plant's rated capacity.
Ice handling and conveying
Some types of ice maker can be sited above the storage space and new ice is therefore added directly by gravity flow. This arrangement can only be used when the ice maker produces a dry subcooled ice. With other types of ice it is necessary to drain excess water, usually in the conveyor system, before storage. Silos, and the smaller size of vertical bin, require no ice distribution system within the storage space to ensure uniform loading. Larger bins, however, require a means of distributing the ice uniformly, irrespective of whether they have the ice maker situated above the storage space or the ice is supplied by conveyor. A variety of harvesting methods can be used with bin storage and some of these are also used to distribute the ice uniformly over the store area. One system of unloading uses a combined rake and scraper arrangement, which breaks up the surface ice and then conveys it to the end of the bin, where an adjustable gate regulates the flow into a discharge conveyor (Fig 16). Another system uses a scraper bucket to move the ice to the discharge conveyor. Both these systems can operate as ice distributors, but have the disadvantage of discharging the newly-made ice first. Since long-term storage of ice is undesirable, these bins should be emptied periodically. This can be more readily accomplished in larger installations if two bins are used.
Fig. 15. Bin ice store
Another method of harvesting from large bins ensures a FIFO operation by removing the ice from the bottom of the bin. A travailing screw conveyor moves along the length of the bin, undermining the ice and discharging it to another conveyor running alongside. This is a heavy piece of expensive mechanical equipment requiring additional floor space outside the bin area. It also requires a good deal of power to operate and special structural work is necessary to support the bin wall on the side the ice is discharged. This system also requires additional mechanical equipment for uniform distribution of the ice, usually a conveyor running the length of the bin along its central line with means of off-loading the ice on both sides.
Both dished belt conveyors and screw conveyors are used extensively for transporting ice. Screw conveyors allow both horizontal and vertical movement of the ice but are limited in the distance over which they can operate; there is also some breakdown in the size of ice particle due to agitation. Belt conveyors are generally used for long distances and special belts with a ribbed flange arrangement can be used on an incline to raise the ice. The final discharge to the lorry or fishing vessel is usually by gravity with a mobile tube to direct the ice.
Pneumatic systems are also used for moving ice but their use should be restricted. A good deal of energy is required to move ice at velocities of about 20 m/s and this energy, along with the heat introduced by the transporting air, will cause meltage. In addition, the ice is fragmented by impact on the ducting walls with the result that a good percentage of the ice appears as "wet snow" at the point of discharge. This ice is unsuitable for further storage. The use of pneumatic systems is therefore confined to filling boxes at sea or in fish processing factories.
When small quantities of ice are involved, measurements are usually made by volume; the weight being ascertained by filling a standard container such as a bag, bin or hopper. With block ice, delivery weights are calculated by counting the number of blocks before they are discharged through the ice- breaker.
In larger installations, ice can be weighed automatically on the supply conveyor belt by using electronic weighing devices which have an accuracy of + /-2 percent. This method can be used with a system which allows remote control of the discharge operation. It can also be integrated with an automatic accounting system which identifies individual customers and allows a self-service operation. The complete system simplifies delivery control, bookkeeping and invoicing procedures.
Fig. 16. Large bin ice store with rake discharge system
Transport of ice
One of the main advantages of the compact modern ice plant is that it can usually be located at the place where the ice is to be used, therefore transport distances are kept to a minimum. Transport to distribution points or to the consumer is usually done in bulk and, for short journeys in temperate climates, this may be in a covered uninsulated vehicles. However, if long journeys are made, the ice should at least be covered and, in warmer climates, insulated transport or even refrigerated transport may be economical.
Ordering ice plant
The general rule in ordering ice plant is that the buyer should supply as much information as possible. The more facts the buyer supplies, the easier it will be for ice plant manufacturers to submit competitive tenders which can be compared on a common basis. At this stage of planning, some decisions should have been made and specific instructions given on such things as type of ice required, site location, building layout and services available.
The following is a check list of the information the buyer should provide when ordering an ice plant:
Main purpose for which ice is intended Type of ice required (block, flake, tube, plate, freshwater, seawater ice, etc) Ice production capacity (tonnes of ice/24 h) Local maximum ambient temperature and humidity or exact location of plant
Information on ice make-up water:
Purity (details of hygienic quality, hardness, etc.)
Temperature range (°C) Pressure (kg/cm²)
Information on condenser cooling water:
Type available (tap, well, river, sea, etc. with details of quality) Quantity available Cost Temperature range Pressure
Information on electricity supply:
Maximum installed power (kW)
Maximum starting current allowable
Details of separate power source if required (generator, direct drive, engine, etc.)
Refrigerant preferred (R12, R22, R502, ammonia, etc.)
Ice storage capacity (tonnes of ice or m³)
Type of storage preferred (silo, bin, bin with mechanical unloading of ice)
Whether a prefabricated or site-built store is required
Preferred method of discharging ice (gravity, rake, bucket or screw)
Rate of discharge required (tonnes of ice/in)
Details, with sketch, of any existing plant and store buildings
Details of site if the plant is to be built inclusive of
building, services, etc Details of the discharge requirements (to
lorry or over quay to fishing vessel, etc.) Details of
ice-weighing equipment preferred (continuous belt weighing,
standard bin, etc.) Details of local maintenance facilities
Details of local skill available for installing and servicing the
plant Spare parts and refrigerant supply requirements Technical
instructions, specifications, drawings, etc. for installation and
maintenance required and in what language.
The above list is extensive but it may not have exhausted the information available which may influence the choice of the plant and the layout. Additional information such as building rules and regulations are important, and as much detail as possible should be given to the potential supplier.
Finance of ice making
Cost. An accurate cost can be made of an installation only at the time of purchase. If an ice plant is planned from the start, the costs to be taken into account are numerous and varied and depend very much on local conditions. For example, they may include cost of land, buildings, roads, electrical and water supply services and drainage. Annual fixed costs will take into consideration depreciation, maintenance, interest on capital, insurance, taxes and overheads. The main operating costs to be considered are power, labour, water and, if applicable, delivery costs. A number of 1990 prices for equipment are given in Table 10 in order to give the reader some idea of the capital required for the ice plant machinery only. The prices are the figures at the port of dispatch and the total cost will have to be increased to include transportation and other delivery charges.
It cannot be emphasized too strongly that all costs and coatings in this document may not apply to any particular country or situation and they therefore must not be used other than as a guide. Local costs should be ascertained and related to local conditions when making calculations which involve any financial commitment.
Table 10. Approximate f.o.b. prices of ice-making equipment (as per 1990)
|Cost (US $)|
|Flake icemaker only||1-100||9,000 - 150,000|
|1-100||14,000 - 322,000|
|Rapid block ice,
equipment for 25 kg blocks
|1-50||30,000 - 578,000|
ice maker for tropics
complete equipment for 25 kg blocks
|0.5-50||15,000 - 318,000|
|Plate ice plant,
|5-100||75,000 - 400,000|
|Silo with agitator end conveyor||2-10||37,000 - 95,000|
|Bin ice store||1-10||12,500 - 26,000|
|Rake system for bin store||300||60,000|
plant complete with
compressor, condenser, cooling
fans, pumps, etc (add 25% if two
compressors are supplied)
|0.5-100||8,000 - 180,000|
generation system for
typical power requirements
|Block ice store equipment||5-50||3,500 - 7,500|
Costing. An early costing may influence the size of plant to be installed, since many costs are virtually independent of the plant size and ice is therefore cheaper to produce in larger installations. The potential user of ice may also decide to become a supplier of ice by installing a plant larger than is necessary for his own requirements. Labour costs are much the same whatever the size of a modern automatic plant; also space and power requirements get less for each tonne of ice produced as the size of the installation increases.
Maintenance costs may be a major consideration in remote areas. Although modern plants operate with the minimum of attention, they require routine expert maintenance, and this attention may be costly if suitably qualified labour is unavailable locally. Capital and running cost of the different types of ice plant vary, but the comparison often depends on the site of the installation and the choice of operating conditions. Any direct comparison of costs would therefore, either cover a wide range of conditions or, include so many controlling factors that the comparison will have little value for general use. Some plants require high capital costs, but have comparatively low running costs, for others it is the reverse. Therefore individual circumstances must be considered in this respect, when making a decision on a cost basis on the type of plant to be installed.
In order to give some idea of the method used to determine the manufacturing cost of ice, an investment analysis for a 20 t/24 hour block ice plant is given below. The figures used are 1990 UK costs converted to US dollars and, since costs and conversion rates may change rapidly and also differ from costs in other countries, the values used may have little relevance to any other situation. It is the method of costing that is of primary interest. Where possible local costs and other factors should be used even to give a rough estimate for guidance purposes.
|Ice plant, installed||150,000|
|Annual fixed charges:|
|Depreciation (10 % )||34,700|
|Insurance and taxes (4%)||13,800|
|Capital maintenance (2 % )||6,900|
|Power -||Assume 5-day week full capacity: 5 x 52 x 20 = 5200 t/year|
|Power at 45 kWh/t + 15% for auxiliaries: 45 x 1.15 = 51.7 kWh/t;|
|at US$ 0.08/kWh: 51.7 x 5200 x 0.08 = US$ 21507/year|
|Water-||For ice||5,200 t|
|For evaporative condenser losses||2,600 t|
|Add 20% for other wastage||1,560 t|
|9,360 t at US$ 0.30/t|
|= US$ 2,808/year|
in/year for day labour
8,760 in/year for shift labour
|Operating engineer- 8,760 x US$ 6.50/h||=US$ 56,940|
|Office manager and accountant - 2,000 x US$ 6.50/h||=US$ 13,000|
|Day labourer- 2,000 x US$ 5.0/h||=US$ 10,000|
Note: Administrative costs may be shared with several other
services or operations.
|Refrigerant, salt, oil, office supplies, etc.||US$ 4,000/year|
|2 drivers + 2 helpers - 4 x 2,000 x US$ 5.0||40,000|
|Parts, repair, fuel, etc||6,500|
|Rental and depreciation||5,000|
|Summary of annual operating costs:|
|Total annual charges:|
|Total charges||US$ 249,755|
|Cost of ice:||249,755/5,200 US$ 48.03/t|
|Based on selling price of US$ 60/t:|
|Income US$ 60 x 5,200 = US$ 312,000/year||312,000|
|Less Total annual charges||249,755|
|Annual profit||US$ 62,245|
Analysis of the above costing shows that manufacturing and
delivery costs in this particular case are made up as follows:
|Electricity, water, supplies||11.4%|
This pattern can change considerably from plant to plant, but it is clear that many of the costs are fixed and independent of ice production. Therefore, in order to keep the cost per tonne of ice down, the plant should be fully utilized.
Selling price. The 1990 selling price of the ice in the United Kingdom varied between US$ 30 and US$ 45 per tonne. Whether these figures reflect real differences in the manufacturing costs, or merely indicate differences in the marketable price of ice between different areas is difficult to ascertain. However, the lowest prices are often charged by manufacturers with old plant supplying large quantities of ice throughout the year, hence there is little depreciation and overhead costs are widely spread. On the other hand, manufacturers with small plants supplying fluctuating seasonal markets often charge comparatively high prices, as also do manufacturers operating plants at a level well below their rated capacity, perhaps due to reduced demand in the area. It is therefore important to ensure that the proposed plant matches the anticipated demand for the future. It is often the practice to cater for present requirements but plan a layout with the possibility that more ice-making units may be added at a future date. The delivery costs above are only 20% of the total. Where transport times are longer delivery costs may rise to 50% of the total.
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