-60째C Blast Freezer in a 40 foot hi-cube insulated ocean-going ISO container
Left Front View loading through the front door
Left Rear View The Machine Compartment
Available with a wide variety of refrigerating concepts to suit virtually any application
Self-contained - easily movable between worksites -
xLow Temperature Applications Refrigerants R23 and R404A - Cascaded The Block Diagram below shows the refrigerating concept for a Blast Freezer capable of freezing gutted but otherwise whole fish of 30 kg average weight to below -60째C in the core in 14 to 16 hours. The plant works with refrigerant R23 in a low temperature circuit, which is cascaded through a plate heat exchanger (intermediate cooler) to a high temperature circuit that works with refrigerant R404A. Heat is rejected to the atmosphere through an air cooled condenser, which makes the plant self-contained.
The refrigerating equipment is assembled into a compact package shown in the picture (right) and placed in a machine compartment in the rear end of the container (below). The compressors are semi-hermetic, operating with frequency converters (green) for starting and to control the capacity. The package is accessible from all sides for convenient service and maintenance. The condenser block (blue) is inserted into the rear end (gavel) of the container; two powerful propeller fans, fitted in the walls of the machine compartment, draw air from outside and push it out through the condenser block in a forced draft manner, using the machine compartment as plenum (below).
The air cooler and the three airfoil propeller fans in the freezing compartment operate in an induced draft fashion, recirculating air back and forth through the goods; the baffle in the center of the compartment guides the air. The low temperature liquid separator must not be insulated since it is located in the cold area.
Low Temperature and Conventional Applications Refrigerants R410A or R404A - Two-stage The Block Diagram further down on this page shows a twostage refrigerating concept for the Blast Freezer, with three separate and totally independent refrigerant cuicuits. Charged with refrigerant R410A, this system can freeze whole gutted fish with an average weight of 30 kg down to -60°C in the core in 16 to 18 hours.
Replacing the refrigerant (R410A) with R404A will turn the container into a conventional facility, freezing the goods to only -18°C in the core, but capable of handling larger quantities. Thinner goods––such as parts for IQF freezing and common fish cartons––reaching the core temperature of -18°C in ten hours or less, can be loaded twice in 24 hours, thus further boosting the capacity (for indication of capacities; see page 6).
The Two-stage Low Temperature and Conventional Application (above) is equipped with plate heat exchangers as condensers. Usually, the heat rejection takes place through a remote cooling tower (Block Diagram above), which can be stored inside the container while it is being transferred between sites (the end of the baffle is on hinges to make room for the cooling tower). Where conditions permit, the plate heat exchangers can be cooled with seawater, which, however, must be treated with filtering and UV bacteria killing to prevent accumulative growth of algae and other organisms in the system. The xLow Temperature Application on page 2 is equipped with an air cooled condenser inserted into the gavel of the container and two powerful propeller fans in the side walls. This set-up could, of course, also be made water cooled, thus causing less damage to the structural strength of the container.
The refrigerating equipment for Low Temperature and Conventional Applications (page 3) is assembled into two compact packages (pictures, left and below) and placed against the walls on either side of the machine compartment in the rear end of the container. The air cooler and three airfoil propeller fans in the freezing compartment operate in an induced draft fashion, recirculating air back and forth through the goods; the baffle in the center of the compartment guides the air. The three low temperature liquid separators need not be insulated since they are located in the cold area. Three plate heat exchangers (condensers), together with three vertical liquid receivers and three water pumps, including related automatic controls and accessories (picture right), are assembled into a compact package on a welded steel base frame and placed against the right wall in the machine compartment in the rear end of the container. Three semi-hermetic two-stage compressors (picture left), three frequency converters for starting and capacity control (green, below the compressors) and three oil separators (red, mounted on a steel bar ...
... above the compressor motors), including automatic controls and accessories, are assembled into a compact package on a welded steel frame and placed up against the left wall in the machine compartment in the rear end of the container. The refrigerating package is easily accessible for convenient service and maintenance.
The Refrigerating Package in the picture on the right is installed in a containerised IQF Freezer on board a fishing vessel operating in the Barents Sea. The package is built up from a belt driven two-stage Compressor-Motor Unit (left in picture), a seawater cooled Condenser (plate heat exchanger, blue, behind in picture) and a Horizontal Receiver (off-white, below the condenser). A Twin Liquid Separator (blue, front-right) and an Oil Separator (blue, behind the condenser) rest on a support on top of the receiver together with the condenser. The package rests on vibration eliminators in three points and is connected to an induced draft air cooler (behind the partition wall, not visible) over flexible joints. The Control Panel (grey, mounted on the partition wall behind the package) contains all starting gear and automatic controls for the freezer.
Conventional Applications Refrigerant R717 (ammonia) - Two-stage Conventional Applications––freezing goods to -18°C in the core only––can sometimes with preference be refrigerated with two-stage ammonia (R717) systems. Compared to the halocarbons, ammonia offers a simple and user-friendly mechanical arrangement, responds faster to variations in the loads and is undisputedly an environment-friendly 'natural' product. However, clients' preference for concepts and refrigerants is usually guided by designs employed in their existing facilities, but also to some extent by the skill and experience of their machine minders. Internally compounded two-stage reciprocating compressors––the semi-hermetic types as proposed on pages 3 and 4 for Low Temperature and Conventional Applications in particular, but also the open types as shown below under 'Alternative Prime Movers - RPE'––are more compact than compound packages built up from two or more separate machines. However, two compressors, one booster and one high stage machine, primed directly with one and the same two-shaft electric motor (picture right), are rather compact and sometimes quite competitive in the price also. Intermediate cooling can be effected through direct injection of liquid refrigerant, subcooling the liquid in a plate heat exchanger at the same time. It is important that atmospheric conditions prevailing on the worksites and the availability of public services––electric power, water, sewage––be thoroughly investigated before decisions are made on the concepts and subsequent selection of equipment.
Alternative Prime Movers - RPE Units There can be many reasons for someone wanting to prime his refrigerating compressor directly with a combustion engine (pictures below); the electric power supply may be insufficient or unreliable, it may be too expensive, or there may be no electric power available on the site. In applications of industrial magnitude, diesel or gas prime movers can offer substantial savings in operating cost and sometimes mean the difference between a company being competitive or not. The RPE Unit in the picture below is built up from a GRASSO Model RC69 reciprocating compressor operating on refrigerant R717, directly coupled through a Twin Disc disengaging clutch to the flywheel end of a Daimler Benz Model OM355 diesel engine developing 120 kW on the shaft.
At the back, a 35 kVA Brush electric alternator––driven off the engine's front end––powers other electric consumers, such as pumps, fans, conveyors, lights etc. This particular unit was delivered to Central Java, Indonesia. It has a capacity to produce twenty-five (25) metric tonnes of block ice in twenty-four hours under tropical conditions.
RPE is an abbreviation for Refrigeration-Power-Electricity 5
Capacities The figures below indicate performance to be expected from Blast Freezers based on concepts and design features outlined on pages 2 through 5.
xLow Temperature Applications Refrigerating Concept: Cascade Refrigerants: R23 and R404A Heat Rejection: Air Cooled Capacity: 5 to 6 mTon Freezing Time: 14 to 16 hours Core Temperature: < -60째C
Low Temperature Applications Refrigerating Concept: Two-stage Refrigerant: R410A Heat Rejection: Water Cooled Capacity: 5 to 6 mTon Freezing Time: 16 to 18 hours Core Temperature: -60째C
Conventional Applications Refrigerating Concept: Two-stage Refrigerant: R404A Heat Rejection: Water or Air Cooled Capacity: 2 X 6 mTon Freezing Time: 2 X 10 hours Core Temperature: -18째C
Conventional Applications Refrigerating Concept: Two-stage Refrigerant: R717 Heat Rejection: Water Cooled Capacity: 2 X 6 mTon Freezing Time: 2 X 10 hours Core Temperature: -18째C
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Published on Mar 1, 2011