COMPRESSED AIR DRYER

DESCRIPTION Technical field

The present invention relates to a compressed air dryer of the type comprising the characteristic features set out in the preamble of the main claim.

Technological background

In the technical field of compressed air treatment plant, refrigerated dryers are known in which the compressed air is brought into contact with heat exchangers cooled so as to separate the dry air from the water vapour by condensation. These dryers normally comprise a device for discharging the condensed water.

Use is normally made of simple direct expansion dryers or dryers provided with a thermal mass heat accumulator. In a direct expansion air dryer, the cooling circuit is regulated by means of a valve disposed between the compressor inlet and outlet. When the opening of the valve is varied, it is possible to recycle, bypassing the condenser and evaporator, part of the flow of compressed cooling fluid output from the compressor, regulating it as a function of the flow and/or temperature of the air to be dried.

The main drawback of this solution lies in the fact that this regulation method is not very efficient as it entails high energy consumption even when a low flow of air is required as output from the dryer. In practice, the cooling circuit continues to operate in all operating conditions, functioning at a constant speed, irrespective of the actual operative thermal load

requirements.

In thermal mass air dryers this drawback is partially remedied by means of a mass able to accumulate heat in which calories surplus with respect to instantaneous consumption are temporarily accumulated for future use. This clearly improves the efficiency of the plant and also reduces energy consumption.

The main drawback of this solution lies in the fact that the thermal mass is typically confined in a chamber, in thermal contact with the air to be dried, bringing about a substantial increase in the overall dimensions of the dryer. Description of the invention

The main object of the present invention is to provide a compressed air dryer which is structurally and functionally designed to remedy all the drawbacks discussed with respect to the prior art. This object and further objects to be discussed below are met by the invention which relates to a dryer embodied in accordance with the accompanying claims. Brief description of the drawings

The characteristic features and advantages of the invention are described in the following detailed description of a preferred embodiment shown, by way of non-limiting example, in the accompanying drawings, in which : Fig. 1 is a diagrammatic view of a dryer of the invention; Fig. 2 is a perspective view of a component of the dryer of Fig. 1; Figs. 3 and 4 are perspective views, partly in section, in opposite directions, of the component of Fig. 2; Figs. 5 and 6 are views, on an enlarged scale, of two respective

details of Fig. 3;

Fig. 7 is a perspective view of a section, with some parts removed, of a constructional variant of the component of Fig. 2;

Fig. 8 is a view, on an enlarged scale, of a detail of Fig. 7. Preferred embodiment of the invention

A compressed air dryer is shown diagrammatically in Fig. 1. With reference to Figs. 2 to 6, the dryer 1 comprises a pressure vessel 2, provided with a cylindrical jacket 2a of axis X, whose axially opposing ends are closed by respective bases 3a, 3b. The vessel 2 is supported by support feet 4a, 4b, 4c.

At the location of the base 3a, the jacket 2a is provided with two openings 5, 6 spaced longitudinally along the axis X, for the inlet of moist air and the outlet of dry air respectively. In the non-limiting embodiment of Figs. 1 and 2, the opening 5 is disposed on the apex of the jacket 2a, while the opening 6 is disposed laterally at an angular distance of approximately 90° with respect to the opening 5.

At the location of the openings 5, 6, the dryer 1 is provided with two respective sections of flanged tubing 7, 8. A separator baffle 11 divides the pressure vessel 2 into two chambers 12a, 12b communicating with the outside via a respective opening 5, 6. The moist air to be dried is introduced into the chamber 12a via the opening 5 while the dried air is removed from the chamber 12b via the opening 6. The baffle 11 is provided with a screen 13 which faces the inlet section of a heat pre-exchange circuit 9 extending along the axis X from the baffle 11 up to an end section 32.

A finned pack exchanger 10 is adjacent to the heat pre-exchange circuit 9.

The finned pack exchanger 10 extends along the axis X from the section 32 to an end section 14 close to the base 3b.

The pre-exchange circuit 9 comprises a shell and tube exchanger 15 whose tubes are interconnected and supported by finning 16 comprising a plurality of equally spaced fins 16a extending along the axis X from the opening 13 to the section 32.

The dry air from the exchanger 10 passes through the shell and tube exchanger 15 receiving heat from the moist compressed air from the chamber 12a, which passes through the pre-exchange circuit 9, striking the outer surface of the shell and tube exchanger 15 and the finning 16.

The dry air is supplied at the output of the shell and tube exchanger 15 to the consumer units via the opening 6 of the pressure vessel 2.

The finned pack exchanger 10 comprises a first tube bundle 20 in which a cooling fluid is circulated, and a second tube bundle 21 in which a thermal mass in the fluid state is circulated.

The tube bundles 20, 21 are orthogonal to the axis X and disposed in respective alternate rows, so that each row of each tube bundle is interposed between two successive rows of the other tube bundle. The mutual arrangement of the tubes of the tube bundles 20, 21, is shown in particular in Fig. 5 by means of the graphical representation of a surface mesh on the drawing of the tubes of the tube bundle 21.

The tube bundles 20, 21 are interconnected by a plurality of fins 22 acting as a heat exchanger member between the tube bundles 20, 21. The pre-cooled moist air from the pre-exchange circuit 9 passes through the

exchanger 10 striking the outer walls of the tube bundles 20, 21 and the fins 22, ceding their heat until reaching dew point.

In the vicinity of the base 3b, the dryer 1 comprises a condensate recovery device 33 which is known per se. The tube bundles 20, 21 are supplied by means of respective inlet tubes 23,

24 and outlet tubes 25, 26. The tubes 23, 24, 25, 26 pass through the respective holes provided on the base 3b of the dryer.

The inlet tubes 23, 24 are provided, at one end, with two respective collector tubes 27, 28 orthogonal to the axis X and the tube bundles 20, 21. The tubes of the tube bundles 20, 21 start from the collector tubes 27, 28 respectively.

The outlet tubes 25, 26 are provided, at one end, with two respective collector tubes 29, 30 orthogonal to the axis X and the tube bundles 20, 21.

The tubes of the tube bundles 20, 21 converge into the collector tubes 29, 30 respectively.

The tube bundle 20 is part of a cooling circuit which makes it possible to cool both the air to be dried and, via the finning 22, the thermal mass within the tube bundle 21.

The exchanger 10 comprises means (not shown) for circulating the thermal mass in the second tube bundle 21. According to a non-limiting embodiment of the invention, these circulation means include a heat accumulator.

Any fluid with a high thermal capacity could conveniently be used within the tube bundle 21, for instance a mixture of water and glycols. In a possible variant of the invention, this mixture is recycled within a closed circuit dedicated exclusively to the supply of the tube bundle 21.

In a further application of the invention, the tube bundle 21 is supplied by means of a circuit comprising one or a plurality of consumer units external to the compressed air dryer 1.

According to a constructional variant of the invention, shown in Figs. 7 and 8, a portion 21a of the second tube bundle 21 extends in a heat exchange conditions, at least partially, into the pre-exchange circuit 9. The portion 21a of the tube bundle is interposed with respect to the tubes 15 of the pre- exchange circuit 9 and makes it possible further to reduce the temperature of the moist air inlet into the exchanger 10. In cases in which the consumer units require a relatively low flow of dry air, the cold accumulated in the thermal mass is sufficient to ensure the operation of the dryer 1. In these cases the cooling circuit may therefore be turned off. The mutual arrangement of the tube bundles 20, 21 in the exchanger 10 makes it possible to increase the efficiency of the dryer, in particular when operating at low speed, without substantially modifying its dimensions. The present invention thus resolves the problems discussed with respect to the cited prior art as it is able to dry compressed air much more efficiently and with much smaller operating costs, without at the same time modifying the basic structure and the maximum bulk of the dryer.