TREATMENT FOR TEXTILE INSULATION 241 



allowed to get between approximately 2.5 per cent and 13 per cent by 

 volume and at the concentration of 5 per cent an explosive force of as 

 high as 75 pounds per square inch might result. To eliminate the 

 possibility of a vapor explosion, enough of the mixture is constantly 

 drawn away through an exhaust duct so that the concentration of 

 acetone will not exceed 1.5 per cent. The vapors are conducted back 

 to the building in which the mixing was performed and the acetone is 

 recovered. 



The acetone recovery system shown in Figs. 9 and 10 consists of 

 activated carbon adsorbers, a condensing tower, and a dehydrating 

 plant. The air and acetone mixture coming through the exhaust 

 header from the coating machines passes through a water cooler to 

 the carbon adsorbers where the acetone is adsorbed and the air is 

 exhausted through the roof. After about an hour's operation, the car- 

 bon in one of the tanks has adsorbed as much acetone as it can without 

 allowing a portion of it to pass through and the air valves are switched 

 to pass the acetone air mixture through the other adsorber. Steam 

 at low pressure is then admitted to the first adsorber and the acetone 

 is driven off. The steam and acetone vapors are condensed, giving a 

 condensate that averages about half water and half acetone. This 

 flows by gravity to one of the outside underground storage tanks where 

 it is held until it can be dehydrated. When a supply of water-acetone 

 has accumulated, it is pumped to the evaporator and the dehydrating 

 is performed in the usual way. The recovered acetone flows by grav- 

 ity to another of the underground tanks for reuse. Samples are taken 

 at intervals to insure that the dehydration is complete, that no foreign 

 materials are present and that no breakdown of the acetone has oc- 

 curred. More than 85 per cent of the acetone purchased is recovered. 



There were, of course, other types of recovery systems available, but 

 for our purpose the carbon adsorption process was most economical. 

 Scrubbing with water or other absorbing mediums would not give as 

 high a percentage of recovery and would be more expensive to install 

 and operate. Freezing out the acetone would not be as economical 

 with the low concentration of acetone-air mixture that it was felt must 

 be maintained to afford safety from explosion. 



Precautions Against Fire 

 Throughout the engineering of this installation, the greatest pre- 

 cautions were taken against possible fire and explosion. Double forty- 

 mesh screens were installed close to the junction of the vent pipes with 

 the underground tanks. The mixing tanks were equipped with explo- 

 sion reliefs consisting of .002 inch thick sheet aluminum. The tanks 



