-11- 



required to support a flame so a recirculatory system can not be 

 used safely. No catalyst is employed to ensure removal of incom- 

 pletely combusted fuel so proper adjustment of the air/fuel mix- 

 ture is essential. The storage room is purged with the low oxygen 

 effluent from the burner and the carbon dioxide produced is gener- 

 ally removed by dry lime in the storage room or by adsorbers or 

 absorbers. It is not uncommon for these systems to introduce at- 

 mospheres into the storage room containing several thousand ppm 

 of carbon monoxide and ethylene I And, carbon monoxide can permeate 

 the storage room walls and enter work areas where it is a hazard 

 to workers. 



Ammonia Cracking 



This system is known as the Smit Oxydrain process and converts 

 ammonia to nitrogen and water vapor at high temperature and the room 

 is purged as with the other inert generators. We have no experience 

 with this system in Michigan. It is being used to a limited extent 

 in the U.S. but more widely in Europe where it was developed. 

 Since no hydrocarbon fuel is used only the carbon dioxide produced 

 by the fruit needs to be scrubbed from the room. There seems to be 

 no danger of ammonia leaking into the CA room and damaging the fruit, 



Recirculatory Systems 



These include the Arcat and COB units already widely in use 

 and the Acotec unit under development by Atmosphere Control Tech- 

 nology, Inc. of Grand Rapids. Unlike the inert gas generators 

 such as Tectrol, Gen-o-Fresh or Wilde which rely on flame combustion 

 to convert oxygen to carbon dioxide, the recirculatory system oxi- 

 dizes the fuel on a catalyst surface without a flame. Catalytic 

 oxidation of the fuel will occur, without flame down to as low as 

 0.51 oxygen. It is necessary to maintain the proper balance of 

 fuel and oxygen to ensure there is sufficient oxygen to combine 

 with all the fuel introduced. As the oxygen supply becomes limit- 

 ing with propane as fuel, the propane is 'cracked' to carbon mon- 

 oxide and ethylene. 



The recirculatory systems consist of an air blower, pre-heater, 

 catalyst and cooler. Air from the storage room is heated to a 

 temperature of about 450° to 600°F to initiate the catalytic oxi- 

 dation of fuel. Propane is then introduced and as it undergoes 

 catalytic oxidation the heat of combustion increases the operating 

 temperature of the catalyst to 1000 to 1200 F. This high temper- 

 ature will be maintained as long as the fuel and air flow remain 

 at the proper setting and the catalyst remains functional. The 

 catalyst allows the fuel to be completely oxidized to carbon dio- 

 xide and water at temperature as low as 900 F which is about half 

 the temperature of a flame. 



The oxidation of propane becomes prggress ively poorer as the 

 catalyst temperature decreases below 900 F. If a minimum operating 

 temperature of 900° can not be achieved at the recommended fuel 

 and air flow rate the catalyst many need renewal. Over-heating and 

 freon from a leak in the refrigeration system in the storage room 



