Does the desiccant used in R-134a refrigerant receiver-driers irreversibly bind water?

If not, can the water load in a drier be reduced by the application of a vacuum to the system... can a drier that has been exposed to air be salvaged by means of applying a vacuum for a sufficient duration to allow the water to boil off?

I've seen where people will pull vacuum on a system for several hours with a heat lamp shining on the filter/dryer to accelerate the process, however if the system was exposed to air for a long time, or if you're resurrecting a system that has been dead for a while, you're better off flushing the lines and replacing the filter/dryer.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Desiccant needs to be baked at 150 *F or so to dry it out. I'd say to just replace it as the heat lamp is probably not hot enough and there is no way to tell if it is actually working.