freezing food
freezing food
ENGINEERING REPORT

The energy required to produce liquid nitrogen and liquid carbon dioxide is not the only costeffecting the total price of the delivered product.. Liquid carbon dioxide is normally delvered by trailer in an insulated tank designed to operate at 350psig (-10 degree F) Liquid nitrogen is delvered in a simailr way at atmospheric pressure (-250 degree F) Liquid nitrogen trailers and customer stations usually cost twice that of comparable liquid carbon dioxide equipment, The cost of transportation exceeded the cost of liquid carbon dioxide production some 7 to 10 years ago - before the price of fuel started to rise.

Liquid carbon dioxide is selling at priced ranging from -2.5 cents to 4.0 cents/ pound delivered, depending upon the plant location and amount of freezant being used. Liquid nitrogen prices vary in a similar manner from 3,0 cents/pound to 7.0 cents/pound. This varied quite drastically white the "users" plant is Adjacent to the liquid nitrogen manufacturing facility, Thus with the cost of electrical energy, gasoline and diesel fuel riding at A rapid rate, both liquid nitrogen and liquid carbon dioxide will increase in price at a much more rapid rate than mechanical systems.

Relevant physical characteristics of carbon dioxide are:

  1. Normal transportation and storage 250 psig (-10 degree F).
  2. Triple point 60 psig (-70 degree F). The element 'in a solid liquid and/or gas at this condition.
  3. At atmospheric pressure carbon dioxide exists as a vapor or solid only at -10 degree F. When used in a freezing system there are about 140 Btu/pound available for freezing a product if the carbon dioxide is exhausted at about 0 degree F.

Nitrogen at atmospheric pressure exists As a liquid at -320 degree F. When used in a freezing system there is Approximately 160 Btu/pound available for useful work if the Vapors are exhausted at 0 degree F.

The selection of a freezing system for many products is relatively simple. Vegetable products such peas, , corn, lima beans, carrots, and other "staples" are normally frozen in an "IQF." mechanical System. These systems usually consist of one or two mesh belts which convey the product through an enclosure while being gently agitated by high velocity cold air (-20 to -25 degree F.) directed from beneath the belt.

Cryogenics are seldom used for such products as their use is generally limited to the following:

  1. High cost items
  2. Freezers for small quantities
  3. Freezers for test markets
  4. Quality considerations
  5. Advertising and/or sales advantages
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