Abstract:
A gas compressor refrigeration system including a chiller for cooling gas, a separator for separating condensate from the gas, and a reheater for heating the gas. The system also includes a closed refrigerant system which passes a charge of refrigerant in series, through a compression unit, then through the reheater in which the refrigerant exchanges heat with the gas, then through a condenser in which the refrigerant exchanges heat with ambient air, and then through the chiller.

Description:
FIELD OF INVENTION 
     The present invention relates generally to gas compressors, and more particularly to refrigeration systems for gas compressors. 
     BACKGROUND OF INVENTION 
     A common problem when using a gas in an enclosed system is removing condensable material from the gas. Condensable material may lead to a variety of problems within the closed system if the material is left in the gas. A common method to remove condensable material from a gas is to cool the gas to a temperature below the condensation temperature of the condensable material, and then separate the condensed material from the gas. The substantially condensate free gas may then proceed through the system to its final application. 
     Removing condensable material from a gas is especially important for air compressors that must remove water vapors from the compressed air. Compressed air may experience several temperature changes within compressed air lines, and water vapors may form a liquid within the lines. Water vapors and liquid within compressed air lines may cause corrosion, reduce air pressure, clog filters, and lead to inconsistent air output. These problems can be substantially eliminated by removing the water from the compressed air before using the air in the final application. 
     Air compressors typically have a refrigerant system to lower the temperature of the compressed air to a temperature below the condensation temperature of water, such that condensed water can be removed from the compressed air. The refrigerant system passes a charge of refrigerant through an enclosed circuit that transfers heat from the compressed air to the refrigerant, and reduces the compressed air temperature. Elements of the refrigerant system generally include a chiller, a compression unit, a condenser, and a reheater. The chiller uses the refrigerant to lower the compressed air temperature to a temperature below the condensation temperature of water. The compression unit adds energy to the refrigerant. The condenser transfers heat from the refrigerant to ambient air, and lowers the temperature of the refrigerant. The reheater transfers heat from the refrigerant to the compressed air to warm the compressed air before it is discharged. 
     Prior art devices pass the refrigerant through a compression unit, condenser, reheater, and then a chiller in series. This arrangement adds energy to the refrigerant in the compression unit, and then removes that energy in the condenser soon afterwards. 
     SUMMARY OF INVENTION 
     The present invention includes an improved and efficient gas compressor cooling system for removing condensable material from a compressed gas. The cooling system comprises a gas system and a closed refrigerant system. The gas system includes a chiller for cooling the gas and forming a condensate, a separator for separating the condensate from the gas, and a reheater for reheating the gas. In the preferred embodiment, the compressed gas is air, and the condensate being removed from the air is water. 
     The gas system passes compressed air through a chiller, separator, and reheater in series to remove water from the compressed air. The chiller lowers the temperature of the compressed air to a temperature below the condensation temperature of water, and a condensate forms. The separator separates the condensed water from the compressed air. Finally, the reheater increases the temperature of the compressed air. In the preferred embodiment, the temperature of the compressed air exiting the reheater is higher than the inlet temperature of compressed air entering the chiller. 
     The refrigerant system preferably includes the chiller, a compression unit, the reheater, a condenser, a filter dryer, and an expansion device. A charge of refrigerant is passed through the compression unit, the reheater, the condenser, and the chiller in series. The compression unit adds energy to the refrigerant, and increases the pressure and temperature of the refrigerant. The reheater transfers heat from the refrigerant to the compressed air, and the condenser transfers heat from the refrigerant to ambient air. Preferably, the filter/dryer removes water and particulate matter from the refrigerant, and the expansion device lowers the pressure of the refrigerant. The chiller transfers heat from the compressed air to the refrigerant, and lowers the compressed air temperature below the condensation level of water. 
     The refrigerant passes through the reheater directly after passing through the compression unit, and before passing through the condenser. This arrangement utilizes the energy added to the refrigerant from the compression unit to maintain a high temperature for the refrigerant entering the reheater. The high refrigerant temperature increases the difference in temperature between the refrigerant and the compressed air entering the reheater. The large temperature difference creates a large heat exchange potential in the reheater, which improves the reheater efficiency, and allows a high compressed air discharge temperature. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a schematic diagram of a refrigeration system embodying the present invention. 
    
    
     Before a preferred embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
     DETAILED DESCRIPTION 
     FIG. 1 illustrates a refrigerant system  10  for an air compressor embodying the invention. As illustrated in FIG. 1, the refrigerant system  10  is a closed cycle that is used to remove condensable material from compressed air in an air compressor. The air compressor includes two separate systems: a compressed air system  14 , and the refrigerant system  10 . Compressed air  18  passes through the compressed air system  14 , and a refrigerant  22  flows through the refrigerant system  10 . Heat exchangers are used to transfer heat between the compressed air  18  and the refrigerant  22 . The refrigerant  22  is preferably R-134a when the refrigerant system  10  is used to remove water from compressed air  18 . 
     The compressed air system  14  shown in FIG. 1 represents only a portion of an entire air compressor. The compressed air  18  passes through a chiller  26 , a separator  30 , and a reheater  34  in series. The chiller  26  is a heat exchanger that reduces the temperature of the compressed air  18 . The compressed air  18  generally contains condensable material, such as water, and the water condenses and forms a condensate when the temperature decreases below the condensation temperature of the water. The compressed air  18  then enters a separator  30  in which the condensate is separated and drained from the compressed air  18 . Finally, the compressed air  18  passes through the reheater  34  before continuing through the air compressor to a final application. The reheater  34  is a heat exchanger that transfers heat from the refrigerant  22  to the compressed air  18 . 
     The refrigerant system  10  is a closed cycle in which the refrigerant  22  passes through the chiller  26 , a compression unit  38 , the reheater  34 , and a condenser  42  in series. The refrigerant  22  first passes through the chiller  26  in which heat is transferred from the compressed air  18  to the refrigerant  22 . The compressed air  18  typically enters the chiller  26  at approximately 100 degrees Fahrenheit, 100% RH, and 100 psig, and the temperature of the refrigerant  22  is substantially lower than the temperature of the compressed air  18 . The chiller  26  condenses the condensable material in the compressed air  18 , and may evaporate the refrigerant  22 . Preferably, a relatively cool and low pressure gas refrigerant  22  exits the chiller  26  and proceeds to the compression unit  38 . 
     The compression unit  38  adds energy to the refrigerant  22 , and increases the temperature and pressure of the refrigerant  22 . The compression unit  38  is preferably a conventional compressor, and may include a motor and piston or scroll compressor. Once the refrigerant  22  exits the compression unit  38 , the refrigerant system  10  may have a potential hot gas bypass  46  that bypasses the remainder of the refrigerant system  10  and delivers the refrigerant  22  back to the chiller  26 . However, the refrigerant  22  normally exits the compression unit  38  and proceeds to the reheater  34 . 
     In the reheater  34 , the hot, high pressure refrigerant  22  transfers heat to the dry compressed air  18 . The temperature of the refrigerant  22  is reduced as it passes through the reheater  34 , although the pressure remains substantially the same. The refrigerant  22  is preferably still a gas when it exits the reheater  34 . Typically, the temperature of the compressed air  18  exiting the reheater  34  is approximately 140 degrees Fahrenheit. The refrigerant system  10  of the present invention will normally produce a reheater  34  discharge temperature of the compressed air  18  that is greater than the chiller  26  inlet temperature of the compressed air  18 . 
     It should be noted that the refrigerant  22  passes through the reheater  34  before passing through the condenser  42 . In prior art, the refrigerant  22  generally passes through a condenser  42  before passing through a reheater  34 . The condenser  42  generally cools the refrigerant  22  by transferring heat from the refrigerant  22  to ambient air. 
     The thermodynamic effectiveness and efficiency of the reheating is maximized by increasing the temperature difference in the reheater  34  between the hot refrigerant  22  and the cold compressed air  18 . The temperature of the refrigerant  22  is highest after flowing through the compression unit  38 . Passing the refrigerant  22  through the reheater  34  directly after the compression unit  38 , and before the condenser  42 , provides a relatively high refrigerant  22  temperature entering the reheater  34 . Having a high refrigerant  22  temperature also provides a large temperature difference between the refrigerant  22  and compressed air  18 , which increases the heat exchange potential and improves heat transfer efficiency. In addition, having a high entering temperature for the refrigerant  22  at the reheater  34  also provides a high discharge temperature for the compressed air  18 . 
     After exiting the reheater  34 , the refrigerant  22  proceeds to the condenser  42 . The condenser  42  is preferably a wire-on-tube or fin-on-tube heat exchanger that transfers heat from the refrigerant  22  to ambient air. The performance of the condenser  42  may depend on the load conditions of the compressed air  18 . Under normal load conditions, the condenser  42  condenses the refrigerant  22  and exchanges heat with ambient air. Under lower than normal loads, the condenser  42  functions mainly as a refrigerant  22  cooler to greatly reduce the temperature of the refrigerant  22 . Generally, the condenser  42  cools the refrigerant  22 , and may condense the refrigerant  22  to create a liquid and gas mixture that exits the condenser  42 . 
     The refrigerant system  10  preferably has a filter/dryer  50  and an expansion device  54  disposed between the condenser  42  and the chiller  26 . The filter/dryer  50  removes water and particulate matter from the refrigerant  22 . The refrigerant  22  is still at a relatively high pressure as it exits the filter/dryer  50  and continues to the expansion device  54 . The expansion device  54  lowers the pressure of the refrigerant  22  to create a cold, low pressure, liquid and gas mixture before the refrigerant  22  returns to the chiller  26 . Once the refrigerant  22  reaches the chiller  26 , the cycle is complete, and the refrigerant system  10  is then repeated. 
     The refrigerant system  10  may have multiple bypass circuits to regulate the conditions within the refrigerant system  10 . A reheater bypass circuit  58  may bypass refrigerant  22  around the reheater  34 , and divert flow directly from the compression unit  38  to the condenser  42 . A condenser bypass circuit  62  may bypass refrigerant  22  flow around the condenser  42 , and divert flow directly from the reheater  34  to the filter/dryer  50 . As mentioned above, the potential hot gas bypass circuit  46  may divert refrigerant flow directly from the compression unit  38  to the chiller  26 , and bypass the reheater  34 , condenser  42 , filter/dryer  50 , and expansion device  54 . These bypass circuits may not be necessary for the present invention, but may be incorporated into the refrigerant system  10  to accommodate various conditions.