NITROGEN FIXATION — LOF 213 



have been proposed and patented, but none except the above-men- 

 tioned types have come into any general use. With the exception of 

 the above-mentioned large plants in Norway, the process has had a 

 very limited use. One plant of moderate size has been in operation 

 in France, and the activities in this country have so far been con- 

 fined to two small installations, one in the West and one in the South 



THE CTANAMID PROCESS 



The cyanamid process is based on the ability of calcium carbide 

 to absorb free nitrogen, forming a nitrogen compound known as 

 calcium cyanamid, or more generally under its commercial name of 

 simply cyanamid. 



The calcium carbide is produced in huge electric electrode fur- 

 naces in capacities up to as high as 20,000 electrical horsepower each. 

 The furnaces are kept filled with a mixture of calcined lime and coke, 

 and the electric current passing through the mixture between the 

 electrodes melts the lime to a liquid which then combines with the 

 coke in the interior of the furnace, forming calcium carbide, the 

 reaction being as follows : CaO+3C=CaC 2 +CO. 



The furnace is tapped every 15 to 20 minutes into chill cars, the 

 carbide when leaving the furnace having a temperature of about 

 4,000° F. 



A supply of pure nitrogen free from oxygen is essential with the 

 cyanamid process. It is obtained by liquefying air under intense 

 cooling and high pressure. Such liquid air machines work under 

 pressures of 500 pounds per square inch, and with cooling by ex- 

 pansion the air is reduced to liquid form at 380° F. below zero. By 

 then allowing this liquid air to warm up slightly, pure nitrogen gas 

 boils off first, leaving the oxygen behind in the liquid. The nitrogen 

 is then pumped to the fixation building. 



After the carbide has cooled in the cars, it is crushed and pow- 

 dered. It is then placed in cylindrical perforated paper cylinders in 

 the fixation ovens, and nitrogen from the liquid-air plant is ad- 

 mitted. The ovens are then heated by passing an electric current 

 through a carbon rod which extends through the center of the charge. 

 Due to this heat and the heat from the exothermic reaction, a tem- 

 perature of about 2,000° F. is reached in the ovens. The carbide 

 absorbs the nitrogen, forming a new chemical compound, calcium 

 cyanamid. The nitrogen fixation is represented by the equation: 

 CaC 2 +N 2 =CaCN 2 +C. 



When the absorption is complete, the charge is removed from the 

 oven, allowed to cool, and crushed to a powder. It is then hydrated 

 or treated with a small quantity of water to remove the last traces 



1454—25 15 



