There is a reference in the book
Grand Opportunity: The Gaelic Revival and Irish Society, 1893 - 1910 saying that O'Shaughnessy purchased the
out-of-date woollen mill at Dripsey, that description suggesting it had been a woollen mill for some time.
In terms of how long, I suspect some time after 1837, since in Lewis' TOPOGRAPHICAL DICTIONARY OF IRELAND, there are only mention of paper mills and flour mills:
http://www.libraryireland.com/topog/I/Inniscarra-Barretts-Cork.phpI can get you back to the 1880s, for example, Guy's Topographical Directory for 1889 says "At Dripsey is an extensive woollen mill" and Guy's Cork Almanac for 1884 mentions "Lynch, D & Co., Dripsey mills, Woollen manufacturers".
Both of these references found here (there are other directories listed, you may be able to get further back):
http://www.corkpastandpresent.ie/places/streetandtradedirectories/Edited to add: I suspect that the previous reference to "Lynch, D & Co" relates to Daniel Lynch in the following reference:
"Leemount House, Coachford was, c1895, the residence of Albert Beamish, who held the post of managing director of the Dripsey Woollen Mills under the ownership of Messrs. Daniel Lynch & Co. Ltd. "
That being so, there are newspaper and other references suggesting this Lynch operating in the area back to the 1860s, albeit most references to a drapery business, but that would fit in well.