Why removing noise increases my audio file size?
This is has nothing to do with the noise removal process but with your encoding. In order to do any type of processing with an encoded audio file you need to

Decode the input file to PCM
Process PCM data
Encode the PCM into the desired output format

Please note that steps and 1 and 3 are completely independent. The decode is determined by the input file format and the encode by the desired output file format. If you want those to be the same, you need to capture all encoding parameters from the input file and pass them to the encoding process.
In your case, you are probably using a different bitrate for input and output.