Do you know the size and structure of kitchen flue? Can you modify it a little by yourself? My gas pipeline is very close to this flue, so we can't tile it. Look at the flue

I advise you not to change this flue. The structure of kitchen flue is as follows:

There is a fork in the middle and upper part of the pipe height between floors. This fork is independent of a single floor, and the lower part of the fork is closed, which can better control the smoke from other residents downstairs to flow back to your home. If you knock it off and turn it into a flue, although it can be connected, smoke from other homes is likely to enter your home.