Method and apparatus for improving start-up for an air separation apparatus

Abstract

A method for operating an air separation unit having both a startup phase and a steady-state operating phase is provided. The method can include the steps of: introducing a plurality of air streams into a cold box, wherein each stream is cooled in a heat exchanger and then sent to a system of distillation columns for separation therein by cryogenic distillation; producing a plurality of air gas streams from the system of distillation columns and warming said plurality of air gas streams in the heat exchanger; determining whether each stream of the plurality of air streams is a net cold producing stream or net cold consuming streams; and adjusting a flow rate of each stream of the plurality of air streams during the startup phase such that each stream that is a net cold producing stream has a higher flow rate during the startup phase as compared to the steady-state operating phase, and wherein each stream that is a net cold consuming stream has a lower flow rate during the startup phase as compared to the steady-state operating phase.

Description

TECHNICAL FIELD[0001]The present invention generally relates to a method for shortening the cool down process for an air separation unit (ASU).BACKGROUND OF THE INVENTION[0002]A typical 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.[0003]During normal operation of the ASU, it is common to feed the cold box multiple air streams at various flow rates, pressures and temperatures. These process conditions are optimized based on the overall design and in an effort to produce particular product fluid mixes at specific pressures, temperatures, and concentrations.[0004]Prior to running at normal operation, the ASU must first undergo a startup operation in which the equipment within the cold box is cooled down to process temperatures th...

AI Technical Summary

Benefits of technology

The present invention aims to reduce the time needed to bring an ASU from ambient conditions to cryogenic operating temperatures. This is achieved by increasing the flow ratio between net cold producing and consuming streams during the startup phase as compared to the steady-state operating phase by increasing the flow rate of net cold producing air streams and decreasing the flow rate of net cold consuming air streams. Additionally, the apparatus includes a system of distillation columns and means for determining which air streams are net cold producing or consuming and increasing the flow ratio between them during startup.

Problems solved by technology

However, use of liquid nitrogen, which is at very low temperatures can cause thermal stresses on the equipment that is originally at ambient temperatures.

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