To the OP
It sounds like this may have been the procedure used when Nacelle Anti Ice is used in icing conditions.
On the type I’m familiar with we used the 60/30/30 rule. 60 percent N1 for 30 seconds every 30 minutes. That was on a CF6. it sounds quite dramatic so I’d always make a PA to inform the passengers in advance what was happening.
edited to add: agree with Wiggy and TB above. Hadn’t seen their replies when I posted.