Ignoramus31221 wrote:
Despite this name, it seems to be a vacuum pump. Has anyone seen these
installed anywhere?

We used liquid ring pumps to withdraw and compress
digester gas (wet dirty methane). The pumps will
draw a vacuum on the intake side and discharge to
a pressure higher than atmosphere on the outlet.
They work with dirty corrosive gases and don't
complain.

Here's a pretty good description...

http://www.fluidcompressor.com/products/