Method and apparatus for maintaining product availability during a disturbance in an air separation unit

Abstract

A method for operating an air separation unit during an unexpected disturbance is provided. The method can include the steps of: determining that a process disturbance has occurred; starting-up a liquid back-up system that is configured to deliver a product gas at a desired product pressure; and introducing compressed air from an air accumulator into the air separation unit at a location that is downstream a main air compressor and upstream a cold box, wherein the compressed air is introduced in an amount that is effective for maintaining nominal operation of the air separation unit during the process disturbance and until the liquid back-up system is delivering the product gas at the desired product pressure.

Description

TECHNICAL FIELD[0001]The present invention generally relates to a method for providing an air gas stream in the event of a disturbance in an air separation unit. The method is particularly useful for maintaining product purity of air gas streams (e.g., nitrogen, oxygen, argon, etc. . . . ) during the transient phase from normal production until a liquid backup system can be brought online in the event of a trip of the plant or reduced flows of incoming air feed.BACKGROUND OF THE INVENTION[0002]A typical air separation unit (ASU) may include use of 1) Main Air Compression (MAC) to medium pressure ˜6 bar, 2) purification unit, 3) Booster Air Compression (BAC) to high pressure ˜50-60 bar, 4) main heat exchanger, and 5) medium pressure, low pressure and argon distillation columns for the production of oxygen, nitrogen, and argon. Various arrangements for the MAC include a single large machine (1×100%), two half-sized machines (2×50%), or combination of the MAC and BAC into a single mach...

AI Technical Summary

Benefits of technology

The patent text describes a system that allows air to be accumulated and blended with air from a compressor in a way that minimizes the impact on the process in case of a sudden loss of airflow from the compressor. This system also allows for temporary production while a customer system is shutdown and reduces energy costs by turning down one of the main air compressors. The technical effects of this system include improved stability of the process, reduced energy costs, and the ability to maintain normal operation of downstream air separation units.

Problems solved by technology

GOX backup systems are also available; however, they are less used than the LOX backup system for economic reasons.

Process upsets can greatly affect the operation of the distillation column, since the purity profile inside the column changes, which ultimately affects the final product purity.

One example of such a process upset is a sudden change in airflow to the cold box (e.g., trip of the 1×20% MAC), which disrupts the purity profiles in the various distillation columns followed by the loss of product purities.

A complete ASU trip or one of multiple MAC trips inevitably leads to either a complete outage of product or rapid reduction of production capacity.

As the product stream is likely being fed either directly to a downstream user or to a pipeline, a change in product purity and / or flow rate can have dire consequences for the downstream user.

As noted above, liquid backup systems have an inherent delay, and therefore, cannot be the only design used in instances where the product purity and pressure must be maintained at all times. In those instances, an additional costly online gas buffer is often required.

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