There are several reasons for dehydrating gas before compressing and exporting it
1/ Reduce corrosion in the export lines as a result of condensation of water in the pipelines.
2/ Prevention of hydrate formation as the gas cools down in the export pipeline.
3/ Reduction in the formation of a liquid phase in the pipeline and therefore a reduction in the possibility of slugging (depends upon a lot of other factors as well i.e. flowrate, length and diameter of pipeline, total cooling etc.)
4/ Reduce the corrosion experienced by the export compressor by passing warm, wet gas into it.
As for handling significant percentages of CO2, I would expect that corrosion issues would be foremost in your mind so you would have to be very careful with your materials selection for the pipeline. I assume that the plant you are exporting this gas to will be able to cope with a high CO2 concentration.
I hope that this is of use to you.
For further information refer to Gas Conditioning and Processing Volume 2 by JM Campbell & Co. (currently in it's 8th Edition)
