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storage and recirculatory systems which utilize the storage at- 

 mosphere as part of the system. The basis for the nitrogen 

 purge and inert gas generating systems is to dilute the initial 

 storage oxygen by displacing it with the nitrogen-rich atmosphere. 

 The recirculatory system removes oxygen directly by converting it 

 to carbon dioxide. Each system will be described. 



Nitrogen Purge System 



Liquid or gaseous nitrogen is bled into the storage room where 

 it displaces an equal volume of storage atmosphere. It is basic- 

 ally inefficient because at the start each cubic foot of pure 

 nitrogen introduced pushes out 1 cubic foot of air which contains 

 19% nitrogen and 21?; oxygen. As the oxygen level is reduced the 

 inefficiency becomes more pronounced. Some improvement can be 

 made by connecting several rooms in series. No one in Michigan 

 employs this system. 



Inert Gas Generators 



There are three basic types. Tectrol System : This was intro- 

 duced in the early 1960 's which combusts propane or natural gas 

 with fresh air in a flame and uses a catalytic burner to ensure 

 clean combustion. The storage room is purged with this low oxygen 

 atmosphere (about 2% oxygen) at a flow rate of 700 to 1200 cubic 

 feet per hour until the storage room has been lowered to the desired 

 low level, e.g., 2 to 3% oxygen. A minimum of 11% oxygen is required 

 to support a flame with propane so this type of generator can not 

 be used in a recirculatory system. The carbon dioxide produced is 

 removed with an activated carbon adsorber. This is now known as 

 the Gen-o-Fresh system of the Samifi Transfresh Corporation. When 

 operating properly with propane with an effective catalyst the 

 atmosphere introduced into the storage room contains about 2% oxygen 

 and 971 nitrogen with less than 1 ppm of carbon monoxide, ethylene 

 and other hydrocarbons. If the catalyst is functioning poorly the 

 effluent from the burner can contain several hundred ppm of carbon 

 monoxide and ethylene and if the air fuel mixture is not adjusted 

 properly, several thousand ppm of carbon monoxide and ethylene 

 along with other hydrocarbons. One thousand ppm equals 0.1%. It 

 is important to supply fresh make-up air to this type of generator. 

 If the make-up air becomes contaminated with the refrigerant freon, 

 the catalyst can become poisoned by hydrofluoric and hydrochloric 

 acids formed as freon is decomposed on the hot catalyst. This is 

 the reason that these units should not be located near the refriger- 

 ation compressors. The catalyst can also be damaged by over heating 

 which causes it to agglomerate and fuse which reduces the effective 

 calalytic surface area. This is one reason the catalyst on these 

 units has a cooling jacket. 



Open Flame Burner 



This is known variously as the Eaves, Australian, Anderson 

 and Wilde system. Propane or natural gas in combusted with fresh 

 air in a flame. And, as with Tectrol, a minimum of 11% oxygen is 



