Refrigeration and atmosphere control
Page 50
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The recent swing to containerisation and an increasing awareness of the way better food quality and freshness lead to increased profits, has brought refrigeration methods under close scrutiny. In the past mechanical refrigerators have had a virtual monopoly in this field, but many users are now moving to the liquid nitrogen system. Although the latter has unquestionable advantages in terms of refrigeration efficiency and food quality, operators have been prejudiced against it by supposedly high running costs.
THE COST
There is no one solution for all users. When assessing liquid nitrogen in relation to mechanical refrigeration, it is necessary to evaluate a number of factors, including interest charges on the capital, depreciation, maintenance, downtime losses, load factors and nett cargo capacity. Virtually the only operating cost with liquid nitrogen is the consumption of the liquid.
The diagram below shows two typical cases where users reduced costs by converting from mechanical systems to Air Products Cryo-guard liquid nitrogen system.
LIQUID NITROGEN
Air Products Cryo-guard provides an oxygen-reduced atmosphere for all types of fresh food, together with all the necessary refrigeration for maintaining temperatures at any desired level, from ambient to sub-zero, in insulated containers and vans. The system is non-mechanical and uses liquid nitrogen as a refrigerating agent that is sprayed into the cargo space. In all instances it has a much faster pull-down time than mechanical systems. No auxiliary power is required, so that all types of insulated vehicles, including the largest ISO road and rail containers, can be equipped with Cryo-guard.
With Air Products Cryo-guard the chosen temperature is automatically controlled to an accuracy of 1°F and the system can be guaranteed to maintain the cargo space at virtually any desired temperature below ambient, even with frequent door openings and in the hottest weather.
Another distinct advantage of Cryo-guard is the substantial increase in pay-load offered to the operator. This is partly because of the compactness and light weight of the equipment, but more significantly because negligible air circulation space is required: this means that Cryo-guard enables the operator to pack his cargo from wall to wall, front to rear and from the floor almost to the ceiling. Even if the cargo has been packed tightly the liquid nitrogen system will ensure a uniform temperature throughout, because nitrogen increases its volume about 700 times when changing from liquid at — 320°F to gas at about 0°F and this creates a gas velocity which results in the penetration of every crevice no matter how tightly the cargo has been packed. Should an operator wish to carry a mixed load different temperatures can be maintained by partitioning the container and installing a separate thermostatic controller for each section.
Cryo-guard is an entirely automatic refrigeration system and goes into operation as soon as the vehicle doors are closed. For ordinary transport vehicles the control panel, with its overall on-off switch and temperature regulators, can be mounted at the front of the vehicle so that it is readily visible to the driver, but for ISO containers the panel can be fitted into the container-wall with a suitable access door on the outside so that it is free from any danger of damage in transit.
FOOD QUALITY
Cryo-guard's oxygen-reduced atmosphere is particu larly beneficial for fresh foods, which can be delivered in the same condition as when the produce was loaded. With Cryo-guard there is no frosting up, ice formation or food dehydration and hence no loss of saleable cargo. To the user Cryo-guard means better quality in terms of freshness, flavour, texture, sugar content and colour.
Cryo-guard is the liquid nitrogen refrigeration system fitted to all leading makes of refrigerated vehicle including Bonallack Coldsaver, Mickleover and Crane Fruehof. For full details and cost evaluation please contact Air Products Limited, Coombe House, St. George's Square, New Malden, Surrey. Telephone 01-942 2424.