Light Product Pressurisation

Light product pressurisation (LPP) re-pressurises a bed using purified light product (the weakly-adsorbed gas) taken from a bed that is producing. Because the pressurising gas is already clean, LPP raises product purity compared with feed-end pressurisation, and it recovers product that would otherwise be spent on pressurisation.

LPP is built as a connection between a producing step and a pressurisation step.

Setting it up

The two steps run for the same duration.

Producing step — on the light-product end (usually the Top), add a Flow boundary, direction Outlet, with a stream that carries the product. This is the gas that will be diverted to pressurise the other bed.

Pressurisation step (LPP) — on the same (light-product) end of the receiving bed:

1. Set the boundary to Pressure, direction Inlet.
2. Give it a Linear (or Exponential) pressure profile that ramps from the low pressure up to the high pressure over the step. This drives the pressurisation.
3. Enter a temperature and composition — these are used only as the first-cycle assumption.

Connect them: on the Cycle Design → Interacting Steps tab, connect the producing outlet to the LPP inlet. Once connected, the LPP inlet takes its temperature and composition from the producing stream, so the bed is genuinely pressurised with light product rather than with the placeholder composition you typed.

Notes

• The receiving bed follows the pressure ramp you set; the connection supplies the quality (composition and temperature) of the gas, while the pressure profile supplies the driving force. Match the ramp to the step time so the bed reaches the target pressure by the end of the step.
• LPP is included in the built-in 4-Step VPSA with LPP example cycle — load it from Cycle Design → Load Example Cycle to see a complete working setup.
• To account for the light product consumed by pressurisation, classify the LPP step appropriately in the KPI Configuration so recovery is computed correctly.