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COMBINED EVAPORATIVE AND CONVECTIVE COOLER

IP.com Disclosure Number: IPCOM000019378D
Publication Date: 2003-Sep-12
Document File: 6 page(s) / 1M

Publishing Venue

The IP.com Prior Art Database

Abstract

The waste chiller unit and the top of the DCAC (Direct Contact After Cooler) in an air separation plant are integrated into a novel heat exchanger called a Combined Evaporative and Convective Cooler (CECC). The bottom section of the DCAC is replaced with a conventional aftercooler. In a CECC, which is a modified shell and tube type heat exchanger, incoming air cools by flowing inside the tubes in down flow, while a returning process waste stream and water flow in counter current directions on the shell side with the waste flowing upwards. Such process integration can lead to a more cost effective design. Also, the CECC eliminates a mode of failure of the DCAC by water overflow into downstream adsorption beds which can be disruptive and expensive to repair.

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COMBINED EVAPORATIVE AND CONVECTIVE COOLER

Summary

The waste chiller unit and the top of the DCAC (Direct Contact After Cooler) in an air separation plant are integrated into a novel heat exchanger called a Combined Evaporative and Convective Cooler (CECC). The bottom section of the DCAC is replaced with a conventional aftercooler. In a CECC, which is a modified shell and tube type heat exchanger, incoming air cools by flowing inside the tubes in down flow, while a returning process waste stream and water flow in counter current directions on the shell side with the waste flowing upwards. Such process integration can lead to a more cost effective design. Also, the CECC eliminates a mode of failure of the DCAC by water overflow into downstream adsorption beds which can be disruptive and expensive to repair.

Background and Prior Art

A cryogenic air separation plant produces oxygen and nitrogen by distillation which is carried out at pressures of 6-10 atmospheres and temperatures that are in the range of minus 250° to minus 320°F. In this process, prior to cooling the incoming air the contaminants such as water, carbon dioxide, and hydrocarbons are removed by front end adsorption. While some of the nitrogen and most of the oxygen are recovered as products, a portion of the incoming air is returned as a waste nitrogen stream which is used to regenerate the adsorption beds in a cyclical fashion and rejected to the atmosphere.

When a cryogenic air separation plant produces more waste than is necessary just to regenerate the front end adsorption beds, this flow of very dry gas can be used to produce chilled water by evaporative cooling. Further, the chilled water so produced can be used to precool the incoming air stream to temperatures far below normal cooling water temperatures. The general idea of using a waste stream to produce chilled water by evaporative cooling and to further use the chilled water to pre cool the feed to a plant such as an air plant is discussed in the US Patent # 5,306,331 by Auvil, Allam, Webley and Young. Not only does this recover the refrigeration from the waste stream, but it also reduces the amount of saturated water that will be in the air. The result is a lowering of the water load on the front end adsorption system. The common synthesis of this process scheme utilizes a packed column chill tower which uses cooling water and waste nitrogen and a two section DCAC which uses the chilled water from the chill tower in the top section of the DCAC and normal cooling water in the bottom section of the DCAC both against compressed air flowing upwards. Both the chill tower and the DCAC are typically packed with structured or random packing. This conventional process is described in more detail below.

The compression of the incoming air to process pressures is achieved in multistage units with inter cooling. After the final stage of compression the final cooling is done with a DCAC which uses ambient as well as chilled water...