Pressure Equalisation

Pressure equalisation recovers work and gas by connecting a bed that is finishing a high-pressure step to a bed that is at low pressure, so gas flows from one to the other until their pressures approach each other. It improves recovery and reduces compression duty, and is a standard feature of multi-bed PSA cycles.

There is no dedicated "equalisation" object — you build it from a valve on each bed connected together. The valve turns the flow into a pressure-driven exchange: gas moves from the higher-pressure endpoint to the lower-pressure one at a rate set by the valve coefficient.

Setting it up

You need two steps, running for the same duration (they represent the two beds equalising at the same time):

Equalisation-down step (the bed releasing gas):

1. On the end that connects to the other bed, set the boundary to Flow, direction Outlet, and add a stream with Boundary Device Type = Valve.
2. Enter a Valve Flow Coefficient (Cv) and a target pressure.
3. Set the opposite end to Closed.

Equalisation-up step (the bed receiving gas):

1. Mirror the setup: a Valve stream, direction Inlet, on the connecting end.
2. Set the opposite end to Closed.

Connect them: connect the two valve endpoints. Once connected, each valve uses the other bed's pressure as its driving pressure, so gas flows down the pressure gradient between them.

Tuning

• The valve coefficient (Cv) controls how quickly the beds equalise. A small Cv throttles the exchange so the pressures approach gently over the step; a large Cv equalises almost immediately. Choose Cv together with the step time so the beds reach the intended intermediate pressure by the end of the step.
• For multiple equalisation stages, repeat the pattern with additional step pairs, each equalising to a successively lower pressure level.

Remember the coupling is lagged by one cycle: the two beds converge on the true shared equalisation pressure as the simulation approaches cyclic steady state, not on the very first cycle.