An improved rotary concentrator separates the desorption gas flow into two flow portions. The first flow portion is sent to a final processing system. The second portion is recycled to the rotary concentrator. In a first embodiment, gas is recycled to the process gas inlet. In a second embodiment, the recycled gas is reused as desorption inlet gas. Most preferably, the recirculated gas is relatively clean compared to the gas in the first portion which is sent to the final processing system. In this way, the improved rotary concentrator is more efficient and reduces the amount of gas which must be processed by the final processing system.