I have successfully added freichat to our elgg website and it works without any problem. But it seems that if a user isn't active on the elgg website, he gets log out automatically. Can this be disabled? The user should always be online as long he is logged in at elgg no matter if he is active or not.

We had added that feature so that idle users don't waste server resources .

You can increase this in FreiChat backend under general settings .