Abstract:
A method and apparatus for the dehydration of glycol, comprising a gas compressor unit including an engine which produces a flow of hot exhaust gas; a glycol dehydrator unit including a reboiler for heating and dehydrating the glycol; transferring heat from the exhaust gas to the reboiler to heat the glycol; and a support platform, wherein the gas compressor unit, the glycol dehydrator unit and the circuit for transferring heat are all supported on the support platform.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. application Ser. No. 11/604,017, filed on Nov. 22, 2006, the disclosure of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to heat transfer systems and more specifically to the transfer of heat generated by a compressor motor for use in a dehydrator to remove water dissolved in a carrier fluid such as glycol. 
       BACKGROUND OF THE INVENTION 
       [0003]    Gas compressors are commonly used to pressurize natural gas in order to facilitate the gas&#39;s movement through pipelines and other facilities. 
         [0004]    Glycol dehydration is a process that removes naturally occurring water, usually in the form of vapour, from natural gas, thereby preventing hydrate formation in and corrosion of gas pipelines. A glycol dehydration unit exposes natural gas to glycol. When natural gas comes in contact with glycol, the glycol removes water vapour from the natural gas. However, the glycol itself eventually becomes saturated with water and ineffective at removing water vapour from natural gas. At this point, the glycol and water mixture is moved to a glycol reboiler forming part of a glycol dehydration unit. The glycol reboiler separates the water from the glycol by raising the temperature of the mixture to a level that will cause the water to evaporate but is below the boiling point of glycol. After the water has been evaporated, the glycol may again be used to remove water vapour from natural gas. 
         [0005]    Conventional glycol dehydration units are gas-fired to generate the necessary heat to flash off the water dissolved in the glycol. There are several drawbacks associated with these units: safety issues; the cost of the fuel they consume; the negative environmental impact caused by their burning of fuel. With respect to safety issues, a conventional glycol dehydration unit cannot even be placed on the same skid as a gas compressor unit because of the explosion hazards. This greatly increases the cost of manufacturing and installation and makes it expensive to transport or move the units from place to place. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention is directed toward a combination gas compressor unit and a glycol dehydrator unit wherein exhaust heat from the compressor&#39;s prime mover is transferred and used in the glycol dehydrator unit. One objective of the present invention is to provide an easy to manufacture and mobile apparatus that combines a gas compressor and a glycol dehydrator on one skid. Another objective of the present invention is to provide an apparatus that transfers the heat generated by a gas compressor unit to the glycol reboiler of the glycol dehydrator. Another objective of the present invention is to provide a glycol reboiler that does not burn fuel to achieve its requisite temperature. Yet another objective of the present invention is to provide a glycol dehydrator that is safer than fuel-fired dehydrators. 
         [0007]    The stated objectives are accomplished by a novel apparatus wherein a gas compressor and a glycol dehydrator are manufactured together on a single skid. A closed fluid circuit connects a heat exchanger in the exhaust of the compressor unit with a heat exchanger in the glycol reboiler of the glycol dehydrator. A heat transfer fluid is pumped through the closed circuit. Heat is transferred to the heat transfer fluid as it passes through the heat exchanger in the exhaust of the compressor&#39;s prime mover. As the heat transfer fluid flows through the heat exchanger in the reboiler, heat is transferred to the glycol and water mixture in the glycol reboiler to boil off the water content. The flow and/or temperature of the heat transfer fluid is regulated to maintain the requisite temperature in the glycol reboiler. 
         [0008]    According to the present invention then there is provided an apparatus for the dehydration of glycol, comprising a gas compressor unit including an engine which produces a flow of hot exhaust gas; a glycol dehydrator unit including a reboiler for heating and dehydrating the glycol; means for transferring heat from said exhaust gas to said reboiler for heating the glycol; and a support platform, wherein said gas compressor unit, said glycol dehydrator unit and said means for transferring heat are all supported on said support platform. 
         [0009]    According to another aspect of the present invention, there is also provided a method for the dehydration of glycol, comprising the steps of operating a gas compressor unit having an engine to produce a flow of hot exhaust gas; operating a glycol dehydrator unit having a reboiler to heat and thereby dehydrate the glycol; transferring heat from said hot exhaust gas to said reboiler through a heat transfer circuit to heat the glycol; and supporting said gas compressor unit, said glycol dehydrator unit and said heat transfer circuit on a single supporting platform. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Preferred embodiments of the present invention will now be described in greater detail and will be better understood when read in conjunction with the following drawings in which: 
           [0011]      FIG. 1  is a schematical flow diagram of the of the combined compressor unit and dehydrator unit apparatus according to an embodiment of the invention; 
           [0012]      FIG. 2  is a diagrammatic view of the exhaust gas heat exchanger forming part of the apparatus of  FIG. 1 ; and 
           [0013]      FIG. 3  is a schematical flow diagram of a modified apparatus in accordance with another aspect of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    The construction and operation of both gas compressors and glycol dehydration units is well known in the art and a detailed description of how they function and are used is therefore omitted from the present description. There are many commercially available units in the market today and the skilled technician will be familiar with the selection of units having a size, capacity and throughput appropriate to any particular installation. The present invention is intended to be adapted for use in most if not all such installations either as original equipment, as a retrofit or as a temporary replacement. 
         [0015]    Referring to  FIG. 1 , the combined dehydration and compressor skid  100  of the present invention generally comprises a mounting skid  110 , a closed loop fluid circuit  200  for a heat transfer fluid (also called “hot oil”), a gas compressor unit  300 , and a glycol dehydrator unit  400 . Compressor unit  300 , glycol dehydrator  400  and fluid circuit  200  are mounted onto skid  110  which can be a transportable or permanently installed platform for these major components of the system. 
         [0016]    Fluid circuit  200  comprises piping or tubing  202 , a circulation pump  204 , a pump controller  206 , a first heat exchanger  208  in the exhaust stream from the compressor&#39;s prime mover  302 , a first temperature gauge  210 , a three way-valve  212 , a three way valve controller  214 , a third heat exchanger  216 , a one way check valve  218 , a three way connector  220 , a second heat exchanger  222  disposed within the glycol reboiler  402  of glycol dehydrator  400  and a heat transfer fluid reservoir  224 . 
         [0017]    To complete closed loop fluid circuit  200 , tubing  202  connects pump  204  to first heat exchanger  208 ; first heat exchanger to three way valve  212 ; three way valve  212  to third heat exchanger  216  and to three way connector  220 ; third heat exchanger  216  to three way connector  220 ; three way connector to second heat exchanger  222 , second heat exchanger  222  to heat transfer fluid reservoir  224  and heat transfer fluid reservoir  224  back to pump  204  to close the loop. Third heat exchanger  216  is in contact with ambient air for shedding excess heat in the transfer fluid to atmosphere. First temperature gauge  210  is disposed in fluid piping  202  between first heat exchanger  208  and three way valve  212  to monitor the temperature of the transfer fluid leaving first heat exchanger. The check valve  218 , disposed in fluid piping  202  between third heat exchanger  216  and three way connector  220 , permits one-way flow only of heat transfer fluid from third heat exchanger  216  to three way connector  220 . 
         [0018]    Gas compressor  300  includes prime mover  302  and an exhaust manifold  304  that will typically also include a muffler for noise abatement. Prime mover  302  is a commercially available internal combustion engine or gas turbine manufactured by companies such as Caterpillar Corporation that can generate a thousand or more horsepower and produce exhaust stack temperatures that can exceed 400° C. First heat exchanger  208  is disposed in manifold  304  so that exhaust gas produced by compressor motor  302  heats the transfer fluid being pumped through first heat exchanger  208 . 
         [0019]    Reference is made to  FIG. 2 , wherein like numerals have been used to identify like elements, which illustrates an exemplary arrangement of heat exchanger  208  relative to manifold  304 . Exhaust gas from motor  302  flows into a duct  308  and through a diverter  309  into heat exchanger  208 . Inside the exchanger are a series of baffles  310  to cause the gas to circulate inside the exchanger and around the coils or loops (not shown) of tubing  202  for the heat transfer fluid. The cooled exhaust exits exchanger  208  through outlet  305  and back into duct  308  for eventual discharge to the atmosphere. Diverter  309  preferably includes a diverter valve  320  which is operable to direct the flow of gas into the heat exchanger by simultaneously closing duct  308  and opening the diverter, or closing the diverter and opening the duct by means of movable dampers  324  and  326 . Valve  320  can also be partially opened to split the flow of exhaust gas for additional control over the temperature of the transfer fluid flowing through exchanger  208 . Valve  320  can be manually operated but more preferably its operation is automated using an actuator  327  drivingly connected to valve  320  and dampers  324  and  326  that is responsive to the temperature of the heat transfer fluid monitored by fluid temperature gauge  210 . The actuator  327  will route the exhaust flow as needed through heat exchanger  208  to maintain the temperature of the heat transfer fluid at a predetermined temperature. This temperature will be approximately 290° C. This temperature is however exemplary and it may be different or varied as required depending on operating conditions. If temperature gauge  210  detects a temperature lower than 290° C., actuator  327  will route more exhaust gas through exchanger  208 , and conversely, if the temperature of the heat transfer fluid exceeds the preset value, actuator  327  will adjust valve  320  as needed to direct less exhaust gas through exchanger  208 . 
         [0020]    As mentioned above, glycol dehydrator  400  includes a glycol reboiler  402 . Glycol reboiler  402  includes its own temperature gauge  404  to monitor the temperature of the glycol being heated inside the reboiler by second heat exchanger  222 . As is known in the art, glycol dehydrator unit  400  circulates hydrated glycol to glycol reboiler  402  where the water is boiled off and the escaping vapour is exhausted to the atmosphere. 
         [0021]    A description of the operation of compressor skid  100  according to an embodiment of the present invention follows. 
         [0022]    Fluid circuit  200  is filled with a heat transfer fluid such as Dowtherm™ RP or Q or Sun™ 21. These products are rated for heating to at least 290° to 300° C. Pump  204  circulates the heat transfer fluid around fluid circuit  200  at a predetermined rate which will be controlled by pump controller  206 . Controller  206  can be manually or automatically controlled as known in the art for fine tuning the rate at which the heat transfer fluid is pumped. In one embodiment constructed by the applicant, the predetermined rate is 9.7 gallons per minute or approximately 2125 kg per hour. This rate is exemplary only and other rates are contemplated as required or depending upon system capacity, operating conditions and the like. The heat transfer fluid flows initially from pump  204 , through piping  202  to first heat exchanger  208  where its heated by exhaust gas from manifold  304  as described below. Next, the heat transfer fluid flows to three way valve  212 . Three way valve  212  is operable to permit heat transfer fluid to flow either to third heat exchanger  216  or to second heat exchanger  222  or both. Heat transfer fluid directed by three way valve  212  to third heat exchanger  216  is cooled by ambient air as it passes through the exchanger and then flows through check-valve  218  and on to second heat exchanger  222 . The heat transfer fluid flowing through second heat exchanger  222  heats the glycol in glycol reboiler  402  to a predetermined temperature. This preset temperature will be approximately 190° C., but as will be apparent to those skilled in the art, the temperature can be higher or lower as desired or required. From second heat exchanger  222 , the heat transfer fluid then flows to heat transfer fluid reservoir  224  and back to pump  204 , completing fluid circuit  200 . 
         [0023]    First temperature gauge  210  monitors the temperature of heat transfer fluid after it has passed through first heat exchanger  208 . Second temperature gauge  404  monitors the temperature of glycol in the glycol reboiler  402 . 
         [0024]    As mentioned above, the present system maintains the temperature of the glycol in reboiler  402  in the approximate range of 190° C. which is greater than the boiling point of water but less than the boiling point of glycol. In the embodiment of  FIG. 1 , the temperature in glycol reboiler  402  is regulated by up to three mechanisms. First, pump controller  206  controls the rate of flow of heat transfer fluid through fluid circuit  200  by adjusting the speed of pump  204 . Second, the three way valve controller  214  operates three way valve  212  to direct the heat transfer fluid either directly to second heat exchanger  222  in whole or in part or to third heat exchanger  216 , where the heat transfer fluid will be cooled prior to its arrival at second heat exchanger  222 . Third, the amount of exhaust gas flowing through first exchanger  208  can be regulated by diverter valve  320 . 
         [0025]    The temperature at first temperature gauge  210  and second temperature gauge  404  is analyzed to determine if the heat transfer fluid is too hot or too cold to maintain the preset temperature of the glycol in reboiler  402 . If the heat transfer fluid is too hot or too cold, one or more of the three temperature regulation mechanisms described above is used to adjust the temperature and/or flow rate of the heat transfer fluid appropriately. This process can of course be automated using conventional thermostatic controls or a computerized system as will be known in the art. 
         [0026]    Reference is now made to  FIG. 3  showing another embodiment of a combined dehydrator and compressor skid  100  in which like numerals have been used to identify like elements. As in the embodiment of  FIG. 1 , the system includes a closed loop fluid circuit  200  for the heat transfer fluid, gas compressor unit  300  and a glycol dehydrator unit  400 , all of which are supported by skid or platform  110 . The primary difference between this system and that shown in  FIG. 1  includes an additional three way valve  223  and associated controller  225  that can be used to control the flow of hot oil through second heat exchanger  222 , and the placement of heat exchanger  216 , including a fan  217  as required, between heat exchanger  222  and fluid reservoir  224  instead of between heat exchanger  208  and heat exchanger  222 . 
         [0027]    As in the embodiment of  FIG. 1 , tubing  202  connects pump  204  to first exchanger  208 . But then tubing  202  connects first heat exchanger  208  to three way valve  223 . Three way valve  223  is connected by tubing  202   a  to second heat exchanger  222  and by tubing  202   b  to three way valve  212  via three way connector  220 . Three way valve  212  is connected by tubing  202   c  to third heat exchanger  216  and by tubing  202   d  to reservoir  224  via another three way connector  220 . Check valves  218  and  219  are included in the tubing to prevent reverse flow of heat transfer fluid through heat exchangers  216  and  222  respectively. Additional tubing  202  connects reservoir  224  back to pump  204  to complete the loop. 
         [0028]    In the embodiment of  FIG. 3 , the temperature in glycol reboiler  402  is controlled primarily by the amount of hot oil routed through heat exchanger  222  which in turn is controlled by controller  225  that opens and closes three way valve  223  in response to the temperature of the glycol in the reboiler as monitored by temperature sensor  404 . Assuming a predetermined or preset glycol temperature of 190° C., if sensor  404  detects a lower temperature, controller  225  is actuated to deviate additional hot oil through heat exchanger  222 . If sensor  404  detects a higher glycol temperature, more of the hot oil will be routed through tubing  202   b  to bypass heat exchanger  216  or back to reservoir  224  or both. 
         [0029]    Third heat exchanger  216  is actually optional. As mentioned above, it can be used to exhaust excess heat to the atmosphere. But it is also possible to make use of any excess heat not required by the glycol reboiler. For example, the heat available from third exchanger  216  can be used to boil water by means of an evaporator, to transfer the heat to air that can be used to heat buildings or rooms within buildings or even to create steam that can run a turbine to generate electricity. As will be appreciated by those skilled in the art, other uses of excess waste heat can be found. Actuator  214  is programmed to operate valve  16  to direct heat transfer fluid to third exchanger  216  only if there is a threshold amount of heat remaining in the heat transfer fluid after flowing through or past the glycol reboiler. 
         [0030]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.