I have a projection TV that I'm tearing apart because it is broken and I was thinking of building a lumenlab replacement. Thinking I'd do the frankenstein thing and salvage some of the parts, I found out that these lenses could be removed from the CRTs. They are huge, and have "Delta Digital 240" as the only marking. I'm assuming the 240 is for 240mm focal length, but I dont know how to test this.

It also has about 1/2" adjustment for focusing, so this might help a little.

Would it be possible to use this in the projection system?

240 is a little small for the focal length. If you use a 15" LCD, the picture will be too big. It would work great for a 5-8" LCD though.

Actually that lens is designed to sit directly on top of a little high output CRT. The only way to use it is to find a panel the same size as the lens.

Actually it doesnt sit right on top of the CRT, there is another concave lens under it. Between this lens and the CRT is a bath of glycol. The convex lens is a half sphere and I believe it focuses the CRT image to the focal point of this lens.

I assume the gycol is there to keep the plastic optics from melting. What is the distance betweem CRT and lens? The additional lens might be there to compensate for the distance (hack job). You can easily test the lens in a darkened room with your crt computer monitor. Mask off the monitor down to the lens aperture. Hold the lens in front of the monitor and focus it on a screen about 4' away.

the field of view for the delta lens is way to small for the 15" lcd, i have three of them taken out of a RPTV and they are for 4" CRT's

Yep, you tend to see those lenses in rear projection TVs and CRT projectors.