It is understandable why refiners would want to filter on the rich amine side as that is where most of the crud is coming from. The lean/rich exchangers tend to be the most effected equipment when deposits foul the tubes and you can no longer cool your lean amine. As SRS mentions, rich amine has PSM issues due to the entrained H2S. It is a lot simpler to deal with lean amine filter cake without the H2S and fresh air handling. We run a 10% slipstream off the lean amine side through a precoat filter with diatomaceous earth and have decent results with run length in the system. We have had issues with excessive corrosion of the carbon steel lean amine piping and equipment when it is operated above 140F, but cooling or upgrading to stainless seems to take care of the problem.