Engine suddenly sounds like a diesel.

[Prairiemaster1]

I have a 1997 Volvo 850 T5. Ok, so the serpentine belt started shredding late at night while my wife was driving home. No safe place to stop, she was about 5 miles from home, she didn't really know what was wrong until she didn't have any power steering. By then she was almost home. The belt never totally broke entirely but the broken strands wrapped around the pulleys. When she got home none of the pulleys where moving. I replace the serpentine belt the next day and untangled the pieces wrapped around the pulleys. No problems, drove fine. She drove to work the next day, about 20 miles (mostly interstate), no problems. When she went to leave, about 10 min. after starting, while sitting at the light the engine just started making a "knocking/tapping", like there was no oil in the engine at all. Checked the fluids, only a half quart low. Not the problem. When she drove it on the interstate it doesn't want to go past 60mph, the engine literally sounds like a diesel engine at idle. I have checked some things that I thought it could be but came up empty. Any suggestions or a direction would be greatly appreciated.
Thanks for your help.

[oragex]

Maybe have another look at the serp belt pulleys, maybe some piece got stuck into the alternator?

Also, on some engines the serpentine belt can get to the crank pulley and mangle with the timing belt. IMaybe remove the tb lower cover and have a look.

[FLXC90]

+1 on checking your TB
you say pulleys weren't moving, you mean they weren't being driven, or they were bound up?
If the belt had a sudden stoppage, or sharp pull from the serp getting jammed, it could have skipped a couple teeth, or maybe torn some loose that didn't give way completely.
Definitely a significant event warranting further investigation.

[Prairiemaster1]

Thanks for the direction. Will definitely check your suggestions.