Conventional PSA Schematic
Xebec's core technology makes advancements on a simple and long-standing gas separation and purification process, pressure swing adsorption (PSA).
PSA is a commonly used technology for purifying gases. PSA technology was introduced commercially in the 1960's and today PSA is used extensively in the production and purification of oxygen, nitrogen and hydrogen for industrial uses. PSA is based on the capacity of certain materials, such as activated carbon and zeolites, to adsorb and desorb particular gases as the gas pressure is raised and lowered. PSA can be used to separate a single gas from a mixture of gases. A typical PSA system involves a cyclic process where a number of connected vessels containing adsorbent material undergo successive pressurization and depressurization steps in order to produce a continuous stream of purified product gas.
The operation of a simplified PSA process to separate hydrogen from a feedstock gas containing impurities, such as carbon dioxide, carbon monoxide or water is
illustrated in the diagram on the right.
- The contaminated feedstock gas is pumped into a cylinder at pressure. The cylinder contains beads of adsorbent material.
- The impurities in the feedstock gas, such as carbon dioxide, are adsorbed onto the internal surfaces of the adsorbent beads, leaving hydrogen in the vessel,
most of which is removed as purified hydrogen product.
- Pressure in the cylinder is reduced, releasing the impurities from the adsorbent material.
- A small amount of product hydrogen is used to flush the waste gas through an exhaust port, preparing the vessel for another production cycle.
Conventional PSA systems used today in industry are made up of four to 16 large vessels, connected by a complex network of piping and valves to switch the gas flows between the vessels. Despite their widespread use in industry, we believe that large scale PSA systems suffer from a number of inherent disadvantages. These PSA systems typically operate at slow cycle speeds of 0.05-0.5 cycles/minute since faster cycle speeds would cause the adsorbent beads to float or "fluidize" in the vessel, causing the beads to wear and ultimately fail. To meet customer demands for capacity, conventional PSA systems must utilize large vessels to compensate for the slow cycle speeds, leading to higher costs and a large equipment footprint. The use of large vessels also means that these PSA systems are typically erected in the field, increasing installation costs. The network of piping and valves used in large scale PSA systems, with the associated instrumentation and process control equipment, also adds cost to the overall system.