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Title:
APPARATUSES AND METHODS FOR USING RESIDUAL HEAT IN GAS COMPRESSION SYSTEMS
Document Type and Number:
WIPO Patent Application WO/2020/104949
Kind Code:
A1
Abstract:
Apparatuses and methods for enhancing efficiency of air compressor are disclosed. The apparatus comprises a pre-cooler though which ambient air is cooled before entering the compressor using coolant fluid and an after-cooler receiving compressed cooled air from the compressor. An economizer for exchanging heat is provided wherein the economizer receives a first stream of the compressed air from the after-cooler and a second stream from the pre-cooler, wherein the second stream is of heated air that was heated in the pre-cooler by exchanging heat with the ambient air. The economizer outlets a third stream of the compressed air heated by the first stream and a fourth stream of cooled air. The apparatus further comprises a cooling dryer receiving the fourth stream from the economizer, and configured to further cool the fourth stream and direct it to the pre-cooler, wherein the fourth stream that passed through the dryer acts as the coolant fluid. Heat is exchanged in the pre-cooler and the economizer by residual heat.

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Inventors:
DAGAN OFER (IL)
Application Number:
PCT/IB2019/059946
Publication Date:
May 28, 2020
Filing Date:
November 19, 2019
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
DAGAN OFER (IL)
International Classes:
F25B25/00; F25D27/00
Foreign References:
US6895774B12005-05-24
US4936109A1990-06-26
US2632315A1953-03-24
Attorney, Agent or Firm:
GOLD-PATENTS & FINANCIAL SERVICES LTD. et al. (IL)
Download PDF:
Claims:
CLAIMS

1. An apparatus for enhancing efficiency of an air compressor comprising:

a pre-cooler though which ambient air is cooled before entering the compressor using a coolant fluid;

an after-cooler receiving compressed air from the compressor, wherein the compressed air is cooled;

an economizer for exchanging heat receiving a first stream of the compressed air from the after-cooler and a second stream from the pre-cooler, wherein the second stream is of heated air that was heated in the pre-cooler by exchanging heat with the ambient air, and wherein said economizer outlets a third stream of the compressed air heated by the first stream and a fourth stream of cooled air; and a cooling dryer receiving the fourth stream from the economizer, configured to further cool the fourth stream and direct it to said pre-cooler, wherein said forth stream passed through the dryer acts as the coolant fluid,

wherein heat is exchanged in the pre-cooler and the economizer by residual heat.

2. The apparatus for enhancing efficiency according to claim 1, wherein the pre-cooler cools the ambient air to approximately 9-11°C.

3. The apparatus for enhancing efficiency according to claim 1, wherein energy that is used for cooling the ambient air in the pre-cooler is harvested from residual energy of the cooling dryer. 4. The apparatus for enhancing efficiency according to claim 1, wherein the compressed air exiting the compressor and enters the after-cooler is cooled by a regulator.

5. The apparatus for enhancing efficiency according to claim 4, wherein the regulator is selected from a group of a fan, a blower, a heat-sink, and any combination thereof.

6. The apparatus for enhancing efficiency according to claim 1, wherein the cooling dryer is configured to reduce the compressed air temperature to a dew point of 2-3°C that is used as the coolant.

7. The apparatus for enhancing efficiency according to claim 1, wherein the after-cooler and the economizer are combined to a single unit.

8. The apparatus for enhancing efficiency according to claim 7, wherein the single unit is regulated by a regulator selected from a group of a fan, a blower, a heat-sink, and any combination thereof.

9. The apparatus for enhancing efficiency according to claim 1, wherein the third stream of compressed air can be stored within a tank for later use.

10. The apparatus for enhancing efficiency according to claim 1, wherein the ambient air is filtered by a filter before entering the pre-cooler.

11. The apparatus for enhancing efficiency according to claim 1, wherein an auxiliary cooling unit is adjunct to the cooling dryer to facilitate cooling.

12. The apparatus for enhancing efficiency according to claim 11, wherein the pre-cooler is combined with the auxiliary cooling unit to a single unit. 13. The apparatus for enhancing efficiency according to claim 1, wherein the pre-cooler combined with the auxiliary cooling unit cools the ambient air to approximately 6°C.

14. A method of using residual heat to increase efficiency of air compression process comprising: cooling the atmospheric air in a pre-cooler before entering the compression process using the compressed air from the compression process that is dried and cooled; and

heating an outlet stream from the compression process using residual heat that was taken from an after-cooler that receives the compressed air from the compression process.

15. The method of using residual heat according to claim 14, further comprising cooling the compressed air that leaves the compressing process by a regulator.

16. The method of using residual heat according to claim 15, the regulator is controlling a temperature in which the compressed air enters an economizer, wherein the economizer produces a stream of compressed air that is heated. 17. The method of using residual heat according to claim 14, further comprising filtering the atmospheric air.

18. The method of using residual heat according to claim 14, further comprising storing the compressed air after it was heated in a tank.

Description:
APPARATUSES AND METHODS FOR USING RESIDUAL HEAT

IN GAS COMPRESSION SYSTEMS

TECHNICAL FIELD

[0001] The present subject matter relates to compressed air systems. More particularly, the present disclosed subject matter relates to systems and methods of using waste heat in compressed systems; thus, improving the systems efficiency.

BACKGROUND

[0002] According to CAGI (Compressed Air & Gas Institute), compressed air in industry is often referred to, as the fourth utility after electricity, natural gas and water. Compressed air is energy of choice. It is used widely throughout the world. Almost every industrial plant has some type of compressed air system. The compressed air systems are used in thousands of applications and are vital to the productivity of industries around the globe. According to D.O.E. (U.S.A. Department of Energy), 10 percent of the global electrical bill is compressed air. The efficiency of producing compressed air is very low. Only 4% converts to useful energy (compressed dry air), the rest 96% is wasted as heat to the surrounding. Energy savings by system improvements is therefore required. All the compressed air experts (as describe in the literature, master works, symposiums and patents), claim that cooling the inlet air to the compressor and heating the air to the load, increase the efficiency of the compression prosses.

[0003] Along the history of compressed air, many patents describe solutions to cool the inlet air to the compressor, and heat the compressed air sent to the load. There are two popular compression technologies that are used in the industrial world:

1. Positive displacement compressor, and

2. Dynamic compressor

[0004] Rotary screw compressor is in a type of positive displacement compressor, in which a given quantity of air or gas is trapped in a compression chamber and the occupied space is mechanically reduced, causing a corresponding rise in pressure prior to discharge.

[0005] The compression principle of the rotary screw compressor consists of two rotors in a stator house have an inlet port at one end and a discharge port at the other. The male has helical lobes shape and the female screw has helical grooves shape. The air that flows into the inlet port, fills the spaces between the screws. As rotation advances, a lobe on one screw rolls into a groove on the other screw and the point of intermeshing moves progressively along the axial length of the screws, reducing the space occupied by the air, resulting in increased pressure. Compression continues until the trap spaces exposed to the discharge port. Every rotation of the screws causes the same amount of volume to be compressed. Cooling the air that enters the compressor increases the number of molecules in this volume. On the other hand, lowering the air temperature reduces air volume while in order to compress this volume of air, the screw compressor needs fewer rotations. In positive displacement compressors, electric power is proportional to the flow. When the flow of air goes down, the electric energy reduces and efficiency is increase.

[0006] Centrifugal compressors are the most popular dynamic compressors. They are used in industry were stable supply of compressed air in massive amount is needed.

[0007] The compression principle: ambient air enters the center (eye) of an impeller and accelerates radially by the rotating wings. When leaving the impellers wing, the flow has kinetic energy. After leaving the impeller the flow enters a volute canal that expands and the air to slow down. As a result, the air pressure goes up (potential energy). Half of the pressure comes from the kinetic energy and half of it comes from the potential energy.

[0008] Cooling the intake air that enters the compressor, increases the power to accelerate the air in the impeller (the need to overcome higher air density) and decrease the power to rotate the impeller (less volume to compress, less impeller rotations).

According to“Bernoulli’s law”, the power increase is linear with increase in density and density increase with pressure.

[0009] According to the "affinity laws”, the power decrease is proportional to the cube of impeller speed and flow is proportional to the impeller speed. The result of the two is less energy and higher efficiency. BRIEF SUMMARY

[0010] The present disclosed subject matter relates to energy efficiency improvements in compressed air systems. According to an aspect of the present disclosure, improving the efficiency is performed by recovering the“wasted energy” in the compressed air energy streams produced by the compressor and the cooling dryer.

[0011] It is therefore provided in accordance with a preferred embodiment an apparatus for enhancing efficiency of an air compressor comprising:

a pre-cooler though which ambient air is cooled before entering the compressor using a coolant fluid;

an after-cooler receiving compressed air from the compressor, wherein the compressed air is cooled;

an economizer for exchanging heat receiving a first stream of the compressed air from the after-cooler and a second stream from the pre-cooler, wherein the second stream is of heated air that was heated in the pre-cooler by exchanging heat with the ambient air, and wherein said economizer outlets a third stream of the compressed air heated by the first stream and a fourth stream of cooled air; and a cooling dryer receiving the fourth stream from the economizer, configured to further cool the fourth stream and direct it to said pre-cooler, wherein said forth stream passed through the dryer acts as the coolant fluid,

wherein heat is exchanged in the pre-cooler and the economizer by residual heat.

[0012] In accordance with another preferred embodiment, the pre-cooler cools the ambient air to approximately 9-11°C.

[0013] In accordance with another preferred embodiment, energy that is used for cooling the ambient air in the pre-cooler is harvested from residual energy of the cooling dryer.

[0014] In accordance with another preferred embodiment, the compressed air exiting the compressor and enters the after-cooler is cooled by a regulator.

[0015] In accordance with another preferred embodiment, the regulator is selected from a group of a fan, a blower, a heat-sink, and any combination thereof. [0016] In accordance with another preferred embodiment, the cooling dryer is configured to reduce the compressed air temperature to a dew point of 2-3 °C that is used as the coolant.

[0017] In accordance with another preferred embodiment, the after-cooler and the economizer are combined to a single unit.

[0018] In accordance with another preferred embodiment, the single unit is regulated by a regulator selected from a group of a fan, a blower, a heat-sink, and any combination thereof.

[0019] In accordance with another preferred embodiment, the third stream of compressed air can be stored within a tank for later use.

[0020] In accordance with another preferred embodiment, the ambient air is filtered by a filter before entering the pre-cooler.

[0021] In accordance with another preferred embodiment, an auxiliary cooling unit is adjunct to the cooling dryer to facilitate cooling.

[0022] In accordance with another preferred embodiment, the pre-cooler is combined with the auxiliary cooling unit to a single unit.

[0023] In accordance with another preferred embodiment, the pre-cooler combined with the auxiliary cooling unit cools the ambient air to approximately 6°C.

[0024] It is also provided in accordance with yet another preferred embodiment of the present subject matter, a method of using residual heat to increase efficiency of air compression process comprising:

cooling the atmospheric air in a pre-cooler before entering the compression process using the compressed air from the compression process that is dried and cooled; and

heating an outlet stream from the compression process using residual heat that was taken from an after-cooler that receives the compressed air from the compression process.

[0025] In accordance with another preferred embodiment, the method further comprising cooling the compressed air that leaves the compressing process by a regulator. [0026] In accordance with another preferred embodiment, the regulator is controlling a temperature in which the compressed air enters an economizer, wherein the economizer produces a stream of compressed air that is heated.

[0027] In accordance with another preferred embodiment, the method further comprising filtering the atmospheric air.

[0028] In accordance with another preferred embodiment, the method further comprising storing the compressed air after it was heated in a tank.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Some embodiments of the disclosed subject matter described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present disclosed subject matter only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the disclosed subject matter. In this regard, no attempt is made to show structural details of the disclosed subject matter in more detail than is necessary for a fundamental understanding of the disclosed subject matter, the description taken with the drawings making apparent to those skilled in the art how the several forms of the disclosed subject matter may be embodied in practice.

In the drawings:

[0030] Figure 1 illustrates a block diagram of a gas compression system as used in the prior art.

[0031] Figure 2 illustrates a block diagram of a an apparatus that effectively uses waste energy in gas compression system, in accordance with some exemplary embodiments of the disclosed subject matter;

[0032] Figure 3 illustrates a block diagram of another configuration of an improved apparatus of air compression, in accordance with some exemplary embodiments of the disclosed subject matter;

[0033] Figure 4 illustrates a block diagram of another apparatus that effectively uses waste energy in gas compression system, in accordance with some exemplary embodiments of the disclosed subject matter; and [0034] Figure 5 illustrates yet another improved apparatus of air compression in accordance with some exemplary embodiments of the disclosed subject matter.

DETAILED DESCRIPTION

[0035] Before explaining at least one embodiment of the disclosed subject matter in detail, it is to be understood that the disclosed subject matter is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The disclosed subject matter is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting. The drawings are generally not to scale. For clarity, non-essential elements were omitted from some of the drawings.

[0036] One technical problem dealt with by the disclosed subject matter is the low efficiency of generating compressed air by commercially available air compressors. The efficiency of compressed air production can be calculated by a ratio between the energy in the compressed air and the electrical energy to produce this amount of compressed air.

[0037] The technical object of the present disclosure is improving the energy efficiency of a gas compressing apparatus by utilizing residual energy produced in the apparatus for cooling the air prior to its entering a compressor unit of the apparatus as well as heating the pressurized air just before exiting the apparatus and doing that using the residual heat in the air stream itself. In one exemplary embodiment as will be shown herein after, the efficiency can be increased by 10.8% at pressure 8.5 bar and outlet temperature of 30 degrees Celsius. In yet another exemplary embodiment, the efficiency can be increased by 17.5% at the same pressure and outlet temperature of 50 degrees Celsius.

[0038] As mentioned herein before, the purpose of the disclosed subject matter is to increase the efficiency of the compressed air system and particularly, the efficiency of the air compressor and cooling dryer using several possible actions:

• First, cooling the intake ambient air stream that enters the compressor with the cold compressed air stream that comes from the cooling dryer, or other air-cooling aperture. This can be performed with a radiator type heat exchanger or the like. As a result of cooling the intake air, its "mass flow rate” increases.

• Heating the compressed air that is sent to the load with the hot compressed air that leaves the after-cooler heat exchanger or the like. As a result, "volumetric flow rate" increases.

• Regulating the temperature of the hot compressed air that is sent to the load by regulating the ambient air flow that removes heat from the hot compressed air that flows in the after-cooler heat exchanger.

• Decreasing the temperature of the compressed air stream that enters the cooling dryer evaporator. The air cools first in the after-cooler and second, in the economizer. As a result of lowering the temperature before entering the evaporator, the dryer cooling energy is reduced.

[0039] Reference is now made to Figure 1 illustrating block diagram of a gas compression system as used in the prior art. Gas compression system 10 comprises an inlet 12 through which air enters several units until it outputs while first, it enters the compressor 14, where the air is compressed, its volume is decreased, and the temperature of the compressed air that outlets the compressor 15 is increased to a relatively high temperature. The compressed and hot air is then being cooled in an after-cooler 16 that can optionally be regulated by a regulator 18. After being cooled within the after-cooler 16, the cooled air is being transferred to a cooling dryer 20 that reduce the air temperature to a dew point close to zero Celsius and removes extra water vapor from the flowing air. The compressed and cooled air that flow through the output 24 is being used for industrial purposes, as desired. As mentioned herein before, the efficiency of the compression process is very low.

In the disclosed subject matter, there are several units aimed at increasing the efficiency of the compression process as follows:

• In order to cool down the atmospheric air that enters the compressor; an action that assists the compressor, a pre-cooler is provided before the compressor to cool the air. In order to effectively cool the air, compressed cold air from the apparatus is being used, in this case from the cooling dryer. The results are higher“Mass Flow Rate” and in case of high humidity, smaller amount of water vapor in the air that enters the compressor.

• The compressed air that leaves the compressor is being heated and sent to the load. As a result, the“Volumetric Flow Rete” is increased. The cooling rate of the hot air stream is controlled by regulating the cooling fan speed. Regulating the cooling rate of the hot air, results in a controlled temperature of the air that flows to the load.

[0040] According an embodiment of the present disclosure, an apparatus for enhancing efficiency of an air compressor is provided that comprises the following units:

• A pre-cooler though which ambient air is cooled before entering the compressor using a coolant fluid.

• An after-cooler that receives the compressed air from the compressor, wherein the compressed air is cooled.

• An economizer for exchanging heat. The economizer receives a first stream of the compressed air from the after-cooler and a second stream from the pre-cooler, wherein the second stream is of heated air that was heated in the pre-cooler by exchanging heat with the ambient air. The economizer outlets a third stream of the compressed air heated by the first stream to be used in industry or stored for a later use and a fourth stream of cooled air.

• A cooling dryer that receives the fourth stream from the economizer, configured to further cool the fourth stream and direct it to the pre-cooler. The forth stream passed through the dryer is used as the coolant fluid in the pre-cooler unit.

[0041] Referring now to Fig. 2, illustrates a block diagram of an apparatus that effectively uses waste energy in gas compression system, in accordance with some exemplary embodiments of the disclosed subject matter. The block diagram illustrates a gas compression apparatus 100 having a cooling system, wherein the apparatus comprising an inlet 101 a pre-cooler 103, a compressor 105, an after-cooler 104 couples with a regulator 102, an economizer 106, a cooling dryer 107 and an outlet 109. In addition, the units are connected by a set of conductors depicted in solid lines, through which gas flows in the direction shown by an arrow. The conductors can be pipelines that conduct pressurized air, wherein the type of pipelines is dictated by pressure temperature and gas type that the apparatus 100 is set for. The pressure in the conductors that connect inlet 101 to compressor 105 via pre-cooler 103 is atmospheric pressure. [0042] In some exemplary embodiments of the disclosed subject matter, pre-cooler 103, after cooler 104, economizer 106 and dryer 107 are heat-exchangers used for a process of transferring heat in different stages of processing the pressurized air. The heat-exchangers used in the present disclosure can be counter-flow heat-exchangers; parallel-flow, cross-flow and any combination of flow. In the present disclosure, the heat-exchangers are based on two fluid circuits mutually transferring heat generated, between one another. In some exemplary embodiments, a coolant fluid of the cooling dryer 107 (shown in dotted lines) is used for cooling the pressurized air that flows in dryer 107.

[0043] In some exemplary embodiments, atmospheric air at ambient temperature enters the pre cooler 103 via inlet 101, where it is cooled down to approximately 9-11°C prior to entering compressor 105. Compressor 105 raises the pressure of the atmospheric air at its input, to a pressurized air at its output. The value of the pressurized air is a preset value typically derived by the application in which apparatus 100 is used for. It should be noted that the compressor 105 also raises the temperature of the pressurized air. In screw compressors, the temperature can be elevated to approximately 65°C above ambient temperature. Without the pre-cooler 103 unit (Figure 1), and inlet air temperature is about 27°C, the outlet temperature of the pressurized air would have been approximately 95°C. With the pre-cooler 103 unit and inlet air temperature of 10°C, the outlet temperature of the pressurized air would have been approximately 75°C. It should also be noted that the energy used for cooling the atmospheric air at the entrance to compressor 105, in the pre-cooler, is harvested from residual energy from the cooling dryer 107, as will be explained herein after.

[0044] It should be noted that cooling the air temperature before entering the compressor, increases the“mass flow rate” to the compressor, e.g. increasing the number of molecules in unit of volume, and increasing the volume to the load with the same amount of energy to compress the original volume.

[0045] In some exemplary embodiments, pressurized hot air exiting compressor 105 enters an after-cooler 104, cool down by a regulator as rotating fan 102 in order to control the gas outlet temperature, as explained herein before. Optionally, the compressed air from the after-cooler 104 enters an economizer 106 where it shall be further cooled, prior to entering the cooling dryer 107 while another stream of output 109 flows for use in industries. In some exemplary embodiments, the cooling dryer 107 is used to reduce the compressed air temperature to a dew point of 2-3°C, and drain the condensate that purges from the air. In some exemplary embodiments, the cooling technology is implemented with compression cooling, absorption cooling or any other type of cooling system. The cooling dryer 107 can be powered by residual energy.

[0046] As mentioned herein before, pressurized air exiting cooling dryer 107, enters pre-cooler 103 for cooling the atmospheric air that is flowing through pre-cooler 103.

[0047] It should be noted that, heating the pressurized air at the economizer 106 increases the air flow-rate to a load.

[0048] In some exemplary embodiments, regulator 102 can be activated to cool the pressurized air stream in the after-cooler 104, if lower temperature required at the load.

[0049] It should be noted that, evaluation the apparatus 100 of the present disclosure exhibits the following efficiency increase:

a. Up to 17.5% at 8.5 bar and outlet temperature of 50°C.

b. Up to 14.2% at 8.5 bar and outlet temperature of 40°C.

c. Up to 10.8% at 8.5 bar and outlet temperature of 30°C.

[0050] In some exemplary embodiments, regulator 102 is a fan, a blower, a heat-sink, and any combination thereof, or any known in the art device that is capable of removing heat from after cooler 104.

[0051] It will be understood that heat-exchanger components of the present disclosure (pre cooler 103, after cooler 104, economizer 106 and cooling dryer 107) are optionally comprised of at least two circuits, wherein the circuits of each heat-exchanger are mutually thermally coupled. That is to say that while a cold circuit cools other circuit, the other circuit heats the cold one. . Furthermore, components disclosed herein are designed, integrated, and connected to one another in a way that maximizes harvesting of residual energy.

[0052] Reference is now made to Figure 3 illustrating a block diagram of another configuration of an improved apparatus of air compression, in accordance with some exemplary embodiments of the disclosed subject matter. Air compressing apparatus 300 is similar to the apparatus shown in Figure 2, however, two of the units or components are combined into a single unit. The apparatus comprises an inlet 301 through which atmospheric air flows into a pre-cooler 303, in which the air is cooled by a cold stream of compressed air coming from a cooling dryer 307 and into a compressor 305. From the compressor 305, the compressed air is flowing to a combined after-cooler and economizer 306 that is regulated by regulator 302.

[0053] Two streams of compressed air flow through the after-cooler and economizer 306. The first is hot air stream from the compressor 305 to the cooling dryer 307 and the second is cold air stream from the pre-cooler 303 to the outlet 309. The two streams exchange heat. As a result, the hot stream gets cooler and the cold stream is being heated. The temperature of the heated stream to the outlet 309 is regulated by regulator 302 that removes heat from the hot stream coming from the compressor 305, The compressed heated air sent to the outlet 309 is used in industry. The compressed cooled air is sent to the dryer 307 for further cooling. The cold air that leaves the cooling dryer 307, flow through the pre-cooler 303.

[0054] To emphasize again the features in the embodiments shown herein, there are two main features in which residual and waste energy is used in order to increase the efficiency of the compression process: cooling the inlet atmospheric air that enters the compressor. As a result, the "mass flow rate" is increased. Heating the outlet compressed air to the load causes an increase in "volume flow rate", which means higher volume at the outlet. Cooling the atmospheric air stream that enters the compressor, causes few consequences. First, increase "mass flow rate". Second, when the air temperature goes below“Dew Point”, extra water vapor will condense. The volume of air with the rest of the water vapor to be compressed is decreased, and the energy to compress the air to be sent to the load is reduced. Third, condensing the moisture reduces the enthalpy (internal energy) of the air and decreases the cooling energy of an auxiliary cooling unit ACU 308 that is adjunct to the cooling dryer. Cooling the atmospheric air is done with the cold compressed air stream from the cooling dryer by the pre-cooler or by the combined pre-cooler and cooling dryer- ACU unit.

[0055] As for the outlet heating - by heating the compressed air sent to the load, the volume flow rate is increased. The thermal energy to heat the outlet compressed air stream, coming from the compressed hot air that leaves the compressor.

[0056] Reference is now made to Figure 4 illustrating a block diagram of another apparatus that effectively uses waste energy in gas compression system, in accordance with some exemplary embodiments of the disclosed subject matter. The apparatus for gas compression 400 is similar to the system that was shown in Figure 3, wherein the units through which the air flows, compressed, and going through temperature changes are the same - an inlet 401 through which air flows into a pre-cooler 403, in which the air is cooled by a cool stream of air coming from within the apparatus, and into a compressor 405. From the compressor 405, the compressed air is flowing to a combined after-cooler and economizer 406 that is regulated by regulator 402. Compressed air flows from the combined after-cooler and economizer 406 to the output 409 to be used in industry. Additional features are introduced to apparatus 400: 1. Air that enters to the compressor 405 through the pre-cooler 403 are filtered in filter 404; 2. Compressed air from the combined after cooler and economizer 406 that are outgoing through outlet 409 are transferred into a tank 402. The compressed air is held in the tank until called into use.

[0057] Reference is now made to Figure 5 illustrating yet another improved apparatus of air compression in accordance with some exemplary embodiments of the disclosed subject matter. Air compressing apparatus 500 comprises an inlet 501 through which atmospheric air flows into a pre-cooler 503 that is now combined with an ACU 508 as part of the dryer 507. As shown in the previous embodiments, the pre-cooler and the ACU are located in the stream line of the atmospheric air. The pre-cooler is cooled by the cold air that is supplied by the dryer 507, and the ACU 508 is cooled by the cooling process. The atmospheric air stream that flows through the pre cooler 503 and then through the ACU 508, cools down and then directed to the compressor 505. The two units, pre-cooler 503 and the ACU 508 can be combined to a single unit. The pre-cooler cools the atmospheric air to around 10 degree Celsius. The ACU 508 cools the atmospheric air to around 6 degree Celsius. The atmospheric cold air enters the compressor 505., Two streams of compressed air flow from the compressor 505 through the after-cooler 504 and economizer 506. The first is hot air stream from the compressor 505 to the cooling dryer 507 and the second is cold air stream from the pre-cooler 503 to the outlet 509. The two streams exchange heat. As a result, the hot stream gets cooler and the cold stream is being heated. The temperature of the heated stream to the outlet 309 is regulated by regulator 502 that removes heat from the hot stream coming from the compressor 505, The compressed heated air sent to the outlet 509 is used in industry The cold compressed air stream, leaves the pre-cooler with a lower temperature than the ambient air, enters the economizer and reduces the compressor compressed air temperature before entering the dryer for further cooling. The combined after-cooler and economizer 506 is regulated by regulator 502 so as to produce compressed air in a controlled temperature. It should be noted that the efficiency of centrifugal compressor operated in hot and humid climate areas, is dramatically reduced. In some cases when the ambient temperature is getting relatively high, the compressor stops its operation automatically in order to protect it from surge and damage. Cooling the air to the compressor expands the centrifugal compressors limits.

[0058] It should also be noted that heating the compressed air after it leaves the compressor raises the air's volume, increases its flow, and consequently, improve its efficiency.

[0059] Although the subject matter has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present subject matter.