the existing compressor to provide the pressure and 

 volume of air needed to operator the N^ generator 

 efficiently. 



In September, 1988, two 600-bushel CA rooms 

 filled with Mcintosh apples were sealed. One was 

 pulled down with liquid N2, and the other one was 

 pulled down with the Nj generator. With liquid Nj the 

 room was at 3% O2 in 1 hour. With the generator, the 

 other room reached 5% O^ in 26 hours, although at that 

 time the unit was being powered by only the new air 

 compressor. 



After the two air compressors were operating to- 

 gether, the Nj generator was used to pull down a 2500- 

 bushel CA room filled with a mixture of "hard" culti- 

 vars. The generator pulled the room down to 13% O^ in 

 6 hours, and to 3% O^ in a total of 30 hours. 



At various times, the generator was used to purge 

 O, from the storage atmosphere, to observe its opera- 

 tion. For example, at one point it reduced O2 from 3.7% 

 to 3.4% in 4 hours. The unit is effective for scrubbing 

 COj, since COj diffuses rapidly through the plastic 

 tubes, but in our system we maintain constant CO^ 

 levels by adjusting continual flow through lime boxes, 

 so we did not use the generator for COj scrubbing. 



In January, 1989, the 2500-bu room was opened, 

 800 bushels were removed, the room was resealed, and 

 the generator was used to pull down O^. In this partly 

 empty room, the unit required 24 hours to reduce O^ to 

 11%, and a total of 48 hours to reduce it to 7%. It then 

 took an additional 48 hours to reach 3% O2. 



The hollow-fiber N^ generator exhibited a number 

 of attractive features during these operations. Once 

 the operator becomes familiar with its operation, the 

 unit requires Uttle "tinkering" and does not have to be 

 watched, so the operator is free to attend to other 



duties. The unit has no moving parts, so it should 

 require very little maintenance and have a very long 

 operating life. It can maintain both O^ and COj in an 

 atmosphere as well as generate an atmosphere, al- 

 though we chose to use it for little more than genera- 

 tion. Also, it wiU combine with a computer-operated 

 CA system very easily, although we chose not to do this 

 due to other research objectives. 



The two problems we encountered were first, the 

 high initial cost of the unit, and second, the absolute 

 need for adequate air compressor capacity. Operating 

 costs are limited to the power needed to operate the 

 compressor and to maintain the temperature of the 

 generator at 110°F. 



The hollow-fiber generator will not pull down a CA 

 room as fast as can be done with liquid N2. However, 

 the pull-down rate is sufficient to optimize CA condi- 

 tions for apples, and the fact that the unit is always 

 ready to operate as soon as the room is sealed may save 

 time that would be spent obtaining liquid N, or prepar- 

 ing for its use. In the short-run, use of liquid N^ is the 

 less expensive method, but since the N2 generator 

 should have a long, trouble-free life, in the long-run the 

 costs may be comparable. 



In summary, while our experience with the hol- 

 low-fiber, N2-generating system is not extensive, it has 

 been very positive. These units should have a secure 

 place in CA storage operations. While we have had no 

 experience with a pressure-swing adsorption unit, a 

 number of these are in use throughout the United 

 States and in other countries, and experiences with 

 them also have been positive. Thus, it appears that CA 

 storage operators have a number of effective options for 

 achieving CA atmospheres rapidly. The choice from 

 among these options will depend on personal and local 

 considerations. 



•i^ ftf# «fA «f# 9S3 



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10 



Fruit Notes, Summer, 1989 



