Abstract:
A combined compressor and dehydrator apparatus including a gas compressor unit with an exhaust through which exhaust gas is expelled from said gas compressor unit; a glycol dehydrator unit with a glycol reboiler; a means of transferring heat from said exhaust of said gas compressor unit to said glycol reboiler of said glycol dehydrator unit; and a skid; wherein said gas compressor unit, said glycol dehydrator unit and said means of transferring heat are fixedly attached to said skid.

Description:
FIELD OF THE INVENTION 
       [0001]    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 
       [0002]    Gas compressors are commonly used to pressurize natural gas in order to facilitate the gas&#39;s movement through pipelines and other facilities. 
         [0003]    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. 
         [0004]    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 installation and makes it expensive to transport or move the units from place to place. 
       SUMMARY 
       [0005]    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. 
         [0006]    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. 
         [0007]    According to the present invention then there is provided a combined compressor and dehydrator apparatus comprising a gas compressor unit, said gas compressor unit comprising at least an exhaust through which exhaust gas is expelled from said gas compressor unit; a glycol dehydrator unit, said dehydrator unit comprising at least a glycol reboiler; a means of transferring heat from said exhaust of said gas compressor unit to said glycol reboiler of said glycol dehydrator unit; and a skid; wherein said gas compressor unit, said glycol dehydrator unit and said means of transferring heat are fixedly attached to said skid. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    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: 
           [0009]      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; 
           [0010]      FIG. 2  is a diagrammatic view of the exhaust gas heat exchanger forming part of the apparatus of  FIG. 1 ; and 
           [0011]      FIG. 3  is a schematical flow diagram of a modified apparatus comprising another aspect of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0012]    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, a retrofit or as a temporary replacement. 
         [0013]    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 a skid  110  which can be a transportable or permanently installed platform for these major components of the system. 
         [0014]    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 . 
         [0015]    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 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 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 . 
         [0016]    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 . 
         [0017]    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 can be opened and closed manually, 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. 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 . 
         [0018]    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. 
         [0019]    A description of the operation of compressor skid  100  according to an embodiment of the present invention follows. 
         [0020]    Fluid circuit  200  is filled with a heat-transfer fluid such as Dowtherm™ RP or Q to approximately 300° C. Pump  204  circulates the heat-transfer fluid around fluid circuit  200  at a preferred rate of 9.7 gallons per minute or approximately 2125 kg per hour. Other rates are contemplated as well. 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 . 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 temperatures ideally in the range of 390° to 405° F. Other temperatures are contemplated depending upon the particular application. 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 . 
         [0021]    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 . 
         [0022]    Compressor skid  100  maintains the temperature in glycol reboiler  402  within a preset range: greater than the boiling point of water but less than the boiling point of glycol. 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 . 
         [0023]    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 range in glycol 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 computerized system as will be known in the art. 
         [0024]    Reference is made to  FIG. 3  which is a more detailed flow diagram of the present system wherein like numerals have been used to denote like elements. Notable differences between this system and that shown in  FIG. 1  include placement of heat exchanger  216 , including a fan  217 , between heat exchanger  222  and reservoir  224  instead of between heat exchanger  208  and exchanger  222  for improved thermal efficiency. Also shown are additional controls, by-passes, filters, re-cycle separators, sensors, gauges, valves and inlets for heat from possible additional external sources that can be added to the heat transfer fluid. 
         [0025]    The above-described embodiments of the present invention are meant to be illustrative of preferred embodiments and are not intended to limit the scope of the present invention. Various modifications, which would be readily apparent to one skilled in the art, are intended to be within the scope of the present invention. The only limitations to the scope of the present invention are set forth in the following claims appended hereto.