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Lower cost inert gas packaging with VPSA.

Lower cost inert gas packaging with VPSA

Many coffee roasters are packing ground coffee in an atmosphere of inert gas such as nitrogen and carbon dioxide to prolong shelf life. A new process has been commercially developed by a major chemical company for separating air into its chief components, oxygen and nitrogen. This carries the possibility of reducing the cost of these gases by up to 50 percent and merits investigation by packers who use inert gas.

It has long been recognized that oxygen is the major enemy of freshness in ground roasted coffee. oxygen, even in the small amount left in atmospheric packing of coffee has a two-fold deleterious effect; (1) in a short time it oxidizes several key aroma components to an odorless state, and this results in the coffee flavor's becoming dull; (2) during a somewhat longer period, it initates oxidation of the natural oils in coffee and promotes rancidation. Between the two oxidative effects, after about six months, even though the container has been hermetically sealed, sensitive public tasters detect an unattractive staleness from coffe stored too long in warehouses and on supermarket shelves before sale.

Tea packers have yet to discover the benefits of inert gas packaging. Tea contains a negligible quantity of oil so that rancidity is not a problem. However, the aroma is impaired by oxidation upon prolonged shelf storage. With the recent trend to a wider variety of flavors, each having its individual sensitivity to oxidation and each having a different rate of sale with varying shelf residence, staling may become a problem. Ordinary paper packaging is not viable for inert gas usages, as it is porous to oxygen. However, plastic films available which prevent oxygen transit can be used to wrap the paper and maintain an inert gas atmosphere, and prolong shelf life by retarding flavor deterioration.

The plastic method for the manufacture of industrial pure nitrogen is the distillation of liquid air. To liquidfy air requires compressing the air to over 700 per square inch. When this compressed air is refrigerated to minus 150[Degrees]C, the air becomes a free flowing liquid. This is then separated into its components by allowing the oxygen to distill off first, since it has a slightly higher boiling point. This leaves pure nitrogen.

Pure liquid nitrogen has wide industrial purposes. It is used in metal working for annealing, brazing, carburizins and hardening of the metal; also in the manufacture of aluminun and fabrication of aluminun products. In petroleum refining and chemical manufacture, it is used for blanketing and purging of reactors; drying of reactive chemicals; improving and maintaining color and viscosity standards; regenerating catalysts; and as a safety for the prevention of fires and explosions.

This liquid nitrogen is manufactured in a specialized plant, then is shipped and stored in large thermos tanks. It is fairly expensive to produce, requiring heavy duty compressors and costly refrigeration. The user must then supply heat to convert the liquid to its gaseous usable state.

The new process requires much less expensive equipment. It is a non-refrigeration system which generates nitrogen in ready-to-use gaseous form. Essentially it is two tank adsorption system. Each tank is filled with a newly patended synthetic mineral, Zeolite, which has the property of adsorbing nitrogen from the air and emitting a stream of pure oxygen. Air under moderate pressure is blown through this Zeolite bed in one tank which soaks up nitrogen like a sponge. When the Zeolite is saturated, the air is automatically switched to the other tank, while pure nitrogen is removed from the first tank by vacuum. The tanks are alternated, assuring a continuous supply of both gases.

This system has been designated a Vacuum Pressure Swing Adsorption (VPSA) system. For medium and large volume users, it can save 20 to 50 percent of gas cost. Energy requirements are 20 to 35 percent less, and capital equipment costs and space requirements are significantly reduced.

Major components of a typical VPSA system include a feed air compressor, a vacuum pump, two adsorption vessels, a product compressor and electrical equipment, piping and controls. All components are skid mounted for ease of installation.

A chemical plant in Illinois recently installed this system. It produces 18,000 cubic feet per hour of 99.5 percent nitrogen. The plant had previously used liquid nitrogen and a vaporizer to convert the liquid to gas. "Our nitrogen cost at full capacity is approximately 50 percent lower than our previous liquid nitrogen costs," reported the plant manager.

There is another non-refrigerating method, using a membrane to separate the two air components by filtration. This meets requirements of 10,000 to 50,000 cubic feet per hour at purities of 95 percent to 99.5 percent. Users who also require pure oxygen for boiler combustion or other purposes get pure oxygen practically free.

Each system for use in packaging should be investigated in the light of quantity required, purity, and cost. Further information may be obtained from the process developer: Union Carbide Industrial Gases, Danbury, CT 06817.
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Title Annotation:vacuum pressure swing adsorption
Author:Lee, Samual
Publication:Tea & Coffee Trade Journal
Article Type:column
Date:Nov 1, 1989
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