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Unit for the Recovery and Storage of Oxygen (URASO) Disclosure Number: IPCOM000022445D
Publication Date: 2004-Mar-15
Document File: 4 page(s) / 36K

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Unit for the Recovery and Storage of Oxygen (URASO)


The URASO (Unit for the Recovery and Storage of Oxygen ) is a process and device for handling variable oxygen demand. It may be operated in either condensation mode to recover oxygen during periods of low demand or vaporization mode to utilize the stored oxygen during periods of high demand. A supply of nitrogen is compressed and condensed when operating in oxygen-vaporization mode. This liquid nitrogen is vaporized when operating in oxygen-condensing mode. An expander provides supplemental refrigeration in condensing mode. A master controller determines whether oxygen demand exceeds supply or whether excess supply may be recovered for later use. Based on the selected operating mode, and the desired rate of recovery or vaporization, certain controllers are enabled and others are disabled. The oxygen flow is specified either by the master controller or by the operator. Other controller setpoints are then calculated automatically based on the desired oxygen flowrate. The basis for the design is that during periods of low oxygen demand, the pipeline pressure will be near the upper end of its operating range, since without the URASO, oxygen gas would be vented on pressure control. It is also assumed that during periods of high oxygen demand, the pipeline pressure will be at the low end of its operating range, since without the URASO, liquid oxygen would be vaporized from the backup system in order to meet the total oxygen demand. It is normal practice for the oxygen vent and the oxygen backup system to work based on pipeline pressure, with the vent pressure being the maximum oxygen pipeline pressure, and the vaporization system setpoint being the lowest oxygen pipeline system. The URASO is designed to operate between these two pressure extremes. This design basis allows the URASO liquid oxygen tank to operate at a pressure between the vent and backup system settings, avoiding the need for any oxygen pressure increasing components (such as a pump), with obvious reliability and operability benefits.

The operation of URASO in these two modes will now be detailed with reference to the attached figures.

Oxygen-Vaporization Mode

Refer to Figure 1. When operating in vaporization mode the expander does not run. Liquid oxygen is withdrawn from the LOX Storage tank and warmed against compressed nitrogen in the Main Exchanger. The GAN compressor (C/A) takes low pressure dry waste nitrogen from the ASU (Air Separation Unit). The compressor inlet guidevanes automatically maintain the discharge pressure at a setpoint that is determined based on the oxygen vaporization pressure. The nitrogen is cooled and condensed in the Main Exchanger against the boiling oxygen. The cold nitrogen is flashed into the LIN Storage tank. Flash vapor is recovered and warmed in the Main Exchanger to recover its refrigeration, before being vented to the atmosphere. While operating in this mode, the level in LOX...