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.
Gas compressors are commonly used to pressurize natural gas in order to facilitate the gas's movement through pipelines and other facilities.
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.
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.
The present invention is directed toward a combination gas compressor unit and a glycol dehydrator unit wherein exhaust heat from the compressor'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.
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'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.
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.
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.
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:
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.
Referring to
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'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.
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.
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.
Reference is made to
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.
A description of the operation of compressor skid 100 according to an embodiment of the present invention follows.
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.
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.
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
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.
Reference is now made to
As in the embodiment of
In the embodiment of
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.
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.
Number | Date | Country | Kind |
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2,555,905 | Aug 2006 | CA | national |
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.
Number | Date | Country | |
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Parent | 11604017 | Nov 2006 | US |
Child | 11891653 | US |