Balancing Flow Rate Distribution Between Separate Devices in Plate-Fin Heat Exchanger Units

Abstract

The non-uniformity of fl ow rate distribution between separate devices of the plate-fi n heat exchanger units working as a part of air separation plant, exceeding 2% of the nominal value, signifi cantly reduces integral characteristics of the unit. Shortcomings of the method for regulating uniformity of fl ow rate distribution in the plate-fi n heat exchanger units by means of regulating valves are considered. It is suggested to use a different approach allowing to avoid the use of expensive regulating valves and to specify the conditions to provide the required uniformity of fl ow rate distribution between separate heat exchangers already at the preliminary design stage. Keywords: plate-fi n heat exchangers unit, air separation plant, hydraulic resistance, characteristics of the double-type manifold, fl ow rate distribution uniformity.Currently, high performance air separation plants (ASP) are complexed with sets of identical plate-fi n heat exchangers operating in parallel. The number of such devices, combined into a single unit, may be signifi cant in a single unit. For example, in an ONAr (oxygen, nitrogen, argon) type ASP in a plate-fi n heat exchanger (PFHE) unit up to eight main heat exchangers operate in parallel [1].The PFHE unit in the ASP includes units with distributing manifolds (which distribute streams for all the heat exchangers in the unit) operating in parallel, and gathering manifolds (gathering streams divided between the heat exchangers into a general stream), as well as pipelines.In the scientifi c literature, the distributing and gathering manifolds working together are called double-type manifolds [2, 3]. The number of double-type manifolds in the PFHE unit is equal to the number of streams involved in heat exchange. The number of streams in each device of the PFHE unit in a large capacity plant usually ranges between six and nine. The supply and output pipes differ in length and, consequently, hydraulic resistance values. As a result of inequalities in hydraulic resistance values, conditions arise for maldistribution of fl ow rates through individual devices of the heat exchanger unit, and, correspondingly, for their operation under conditions different from the calculated (on the basis of which the necessary heat exchange surface area is determined for each stream).The practice of exploitation of large ASPs, in which the main heat exchanger unit consists of a number of PFHE operating in parallel, showed that in the case of uneven distribution of streams between the individual devices of the PFHE unit there is a reduction in the integral characteristics of the entire unit [1,4]. This leads to an increase in under-recovery on the warm side of the production streams, an increase in the exit temperature of the expander fl ow, and some increase in the temperature of the direct stream of air at the outlet of the unit.

Optimization of a compressed gaseous CO2 energy recovery dry ice pelletizer

“…Since the conversion factor is approximately 0.5 [17,18], let us take the equal portions of the formed CO2 snow ( ) and compressed gaseous CO2 ( г ) at throttling, then:…”