Pressure Swing Adsorption Unit
Summary
Pressure swing adsorption (Under is PSA) is a technology used to separate some gas species from a mixture of gases under pressure according to the species' molecular characteristics and affinity for an adsorbent material. It operates at near-ambient temperatures and differs significantly from cryogenic distillation techniques of gas separation. Specific adsorptive materials (e.g., zeolites, activated carbon, molecular sieves, etc.) are used as a trap, preferentially adsorbing the target gas species at high pressure. The process then swings to low pressure to desorb the adsorbed material.
Features
The proven high performance PSA units are designed for the recovery and purification of pure hydrogen from different hydro-gen-rich streams, such as synthesis gases from Steam reforming process, partial oxidation or gasification, as well as from various off-gases in refineries or petrochemical processes, e.g. ethylene off-gas, coke oven gas, methanol and ammonia purge gas. Capacities range from a few hundred Nm³/h to large scale plants with more than 400,000 Nm³/h.
The hydrogen product meets every purity requirement up to 99.9999 mol-% and is achieved at highest recovery rates. Main hydrogen consumers are refineries requiring this valuable gas for example for their cracking, dearomatization or desulphurization processes. As a second group of users in the petrochemical industry has a demand for hydrogen for its methanol and ammonia synthesis, MTBE processes, etc.
Composite of PSA
A PSA plant consists basically of the adsorber vessels containing the adsorbent material, tail gas drum(s), valve skid(s) with interconnecting piping, control valves and instrumentation and a control system for control of the unit.
The pressure swing adsorption process has four basic process steps:
▪ adsorption
▪ de-pressurization
▪ regeneration
▪ re-pressurization
To provide continuous hydrogen supply, minimum 4 adsorber vessels are required.
The figure in below shows the combination of the sequences of four adsorber vessels as a pressure-time-diagram.
Flow Diagram
