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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.

Comparisons are made between different materials (basalt, quartzite, quartz, dolomite, gravel, pebbles, carborundum, heat-resistant glass, high-temperature ceramics, steel, and aluminum) and different types of packings (granulated materials, spherical particles, Raschig rings, and twisted rings) for their possible use as packings in heat accumulators. It is found that within the chosen temperature range nearly all of the above materials have roughly the same average volumetric heat capacity as the granulated basalt currently used in heat accumulators and, based on existing specifications, can also be recommended for use as such packings.Heat accumulators are part of the heat recovery loop in the integrated cleaning systems (ICSs) of medium-and highcapacity air separators (ASPs).The function of the heat accumulators is to accumulate heat as the processes of cooling, pressurization, and depressurization take place in one of two alternately operating adsorbers; the stored-up heat is then removed from the accumulator as heating and regeneration take place inside the adsorber. The heat is stored in a heat-absorbing packing made of a material such as granulated basalt. The packing is heated by a regenerating gas -waste nitrogen that has first been passed through an electric heater (with a temperature 20-25°C higher than the regeneration temperature of the adsorbers). The packing is cooled by cold regenerating gas. The heat-storing packing is thus continually subjected to temperatures that fluctuate within a wide range of values (from 280 to 490 K), which means that it must meet certain service requirements.Due to the cyclic alternation of regimes involving the accumulation and removal of heat, the packing is subjected to appreciable dynamic mechanical and thermal loads. Also, most of the packing must operate at high temperatures -up to 490 K. The velocity of the gas flow in the accumulator can change by a factor ranging from three to four as the operating regime changes, while the packing's temperature can fluctuate by 160-180 K.The packing cannot be allowed to wear and break down during the operation of the ICS because the resulting dust and small pieces of packing material will enter the adsorbers during the heat-removal regime and disrupt their normal operation.In accordance with the above, the packing that is used in heat accumulators should have the following properties: high strength under dynamic mechanical loads; low abradability, depending on the material's hardness; high resistance to thermal loads. The material should also have a fairly high volumetric heat capacity in order to keep the size of the accumulator acceptable.

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