Reducing fluctuations in tail gas flow from an adsorption unit

A process for producing a product gas and a by-product gas from a feed gas mixture in an adsorption separation unit comprising a plurality of adsorption beds, the feed gas mixture comprising a primary gas component and secondary gas components, each adsorption bed containing an adsorbent selective for the secondary gas components, the product gas enriched with the primary gas component, the by-product gas depleted of the primary gas component, where each of the plurality of adsorption beds is subjected to a repetitive cycle of steps, the process comprising:

• a production step, which comprises introducing a stream of the feed gas mixture into an adsorption bed undergoing the production step and adsorbing the secondary gas components on the adsorbent in the adsorption bed undergoing the production step while simultaneously withdrawing a product gas stream from the adsorption bed undergoing the production step;
• a supply purge gas step, which comprises co-currently withdrawing a stream of purge gas from an adsorption bed undergoing the supply purge gas step, and passing the stream of purge gas from the adsorption bed undergoing the supply purge gas step to an adsorption bed undergoing a purge step;
• a blowdown step, which comprises counter-currently withdrawing a stream of blowdown gas from an adsorption bed undergoing the blowdown step;
• the purge step, which comprises counter-currently introducing the stream of purge gas from the adsorption bed undergoing the supply purge gas step into an adsorption bed undergoing the purge step and counter-currently withdrawing a stream of purge gas effluent from the adsorption bed undergoing the purge step;
• a repressurization step, which comprises increasing the pressure in an adsorption bed undergoing the repressurization step by at least one of (i) co-currently introducing a second stream of the feed gas mixture into the adsorption bed undergoing the repressurization step, or (ii) counter-currently introducing a portion of the product gas stream from the adsorption bed undergoing the production step into the adsorption bed undergoing the repressurization step;
• wherein at least one adsorption bed undergoes at least part of the purge step simultaneously with at least one other adsorption bed undergoing at least part of the blowdown step, and the stream of purge gas effluent from the adsorption bed undergoing the purge step is combined with the stream of blowdown gas from the adsorption bed undergoing the blowdown step to form a by-product gas stream;
• introducing the by-product gas stream into a surge vessel;
• withdrawing the by-product gas stream from the surge vessel;
• periodically obtaining signals from a sensor operatively disposed to sense a pressure and/or a flow rate of the by-product gas stream before the by-product gas stream is introduced into the surge vessel;
• regulating the flow rate of the stream of blowdown gas that is combined with the stream of purge gas effluent during at least a portion of the blowdown step, where the flow rate of the stream of blowdown gas is regulated responsive to the signals from the sensor, wherein regulating the flow rate of the stream of blowdown gas comprises
• increasing the flow rate of the stream of blowdown gas when it is determined from the signals from the sensor to increase the pressure or flow rate of the by-product gas stream;
• and
• decreasing the flow rate of the stream of blowdown gas when it is determined from the signals from the sensor to decrease the pressure or flow rate of the by-product gas stream.