The present invention relates generally to systems for injecting chemicals into pipelines and, more specifically, to an improved system for adding odorant to natural gas or liquefied petroleum gas flowing in a pipeline.
There are many instances in which it is desirable to inject chemicals of various types into fluids (gas and liquids) flowing in pipelines. One such example is in the area of natural gas pipelines. In addition to such substances as corrosion inhibitors and alcohol to inhibit freezing, odorants are commonly injected into natural gas pipelines. Natural gas is odorless. Odorant is injected into natural gas in order to provide a warning smell for consumers. Commonly used odorants include tertiary butyl mercaptan (TBM). Such odorants are typically injected in relatively small volumes normally ranging from about 0.5 to 1.0 lbs/mmscf.
The odorants are typically provided in liquid form and are typically added to the gas at a location where distribution gas is taken from a main gas pipeline and provided to a distribution pipeline. In such circumstances, the gas pressure may be stepped down through a regulator from, for example, 600 psi or more, to a lower pressure in the range of 100 psi or less. The odorants can also be added to the main transmission pipeline in some situations.
As can be seen above, the odorants which are added to natural gas are extremely concentrated. Odorants such as TBM and other blends are mildly corrosive and are also very noxious. If the job of injecting odorant is not performed accurately, lives are sometimes endangered. It would be possible for a homeowner to have a gas leak without it being realized until an explosion had resulted if the proper amount of odorant was not present. Also, if a leak of odorant occurs at an injection site, people in the surrounding area will assume that a gas leak has occurred with areas being evacuated and commerce being interrupted. Contrarily, if such mistakes become common, people in the surrounding area will become desensitized to the smell of a potential gas leak and will fail to report legitimate leaks.
Two techniques are commonly used for providing odorization to natural gas in a main distribution pipeline. One technique involves bypassing a small amount of natural gas at a slightly higher pressure than the pressure of the main distribution pipeline, through a tank containing liquid odorant. This bypass gas absorbs relatively high concentrations of odorant while it is in the tank. This heavily odorized bypass gas is then placed back into the main pipeline. The odorant, now volatilized, is placed back into the main pipeline and diffuses throughout the pipeline. However, there are a number of disadvantages associated with the bypass system for odorizing pipelines. One disadvantage of the bypass system is the fact that the bypass gas picks up large and inconsistent amounts of odorant from the liquid in the tank and becomes completely saturated with odorant gas. As a result it is necessary to carefully monitor the small amounts of bypass gas which are used. Also, natural gas streams typically have contaminates such as compressor oils or condensates which can fall out into the odorant vessel in bypass systems. These contaminates create a layer that reduces the contact area between the liquid and the bypass stream. This necessarily degrades the absorption rate of the stream failing to accurately measure and control the amount of odorant being added to the stream. This absorption amount can change as condensates and other contaminates fall out and change the absorption boundary layer.
Another technique involves the injection of liquid odorant directly into the pipeline through the use of a high-pressure injection pump. High-volume odorizers have depended on a traditional positive-displacement pump or solenoid valve to deliver discrete doses of odorant to natural gas or liquid propane gas (LPG) streams for the purpose of bringing these streams to safe perception levels. However, injecting discrete doses in this manner results in higher pressure drops due to the higher piston speed. The higher the piston speed, the more likely the odorant will vaporize and the more likely entrainment of gas. Such vapor lock is detrimental to the performance and accuracy of odorant injection systems. These methods can leave dangerous dead time between doses. Because odorant is extremely volatile, drops injected to the pipeline immediately disperse and spread throughout the gas in the pipeline. In this way, within a few seconds, the drops of liquid odorant are dispersed in gaseous form.
There are also several disadvantages with this prior art technique. As mentioned above, the odorant liquid is extremely noxious. The injection pump must therefor be designed so that no odorant can leak. This requires a pump design which is relatively expensive and complex in order to meet the required operating conditions. Even in such sophisticated systems, there is an unpleasant odor present when working on the pump which can make people think that there is a natural gas leak. There continues to be a need for improvements in odorization systems of the above described types.
The present invention relates to an improved system, apparatus and method for injecting chemical into a pipeline which prevents escape of odorant, nearly eliminates dead time between doses and provides a reliable, uniform injection rate over a wide variety of rate requirements.
It is an object of the present invention to provide an improved chemical injection system for metering odorant into pipelines overcoming some of the problems and shortcomings of the prior art, including those referred to above.
Another object of the invention is to provide a chemical injection system which allows precise metering of chemical injected into a pipeline.
Another object of the invention is to provide a chemical injection system which provides continuous flow of odorant.
Another object of the invention is to provide a chemical injection system which allows a wide range of chemical dosing.
Another object of the invention is to provide a self-priming chemical injection system which is low-maintenance.
Another object of the invention is to provide a chemical injection system which allows maintenance of the power unit without exposure to the chemical.
Another object of the invention is to provide a chemical injection system which prevents flashing of odorant and vapor lock.
Still another object of the invention is to allow use of low pressure blanket gas which inhibits gas entrainment.
How these and other objects are accomplished will become apparent from the following descriptions and drawing figures.
The instant invention overcomes the above-noted problems and satisfies the objects of the invention. A system, apparatus and method for injecting a chemical from a storage tank into a natural gas or LPG pipeline at a flow-controlled injection rate is provided. The chemical injection system, apparatus and method includes a pair of positive-displacement pumps, the pair having a first positive-displacement pump and a second positive-displacement pump, each having substantially similar displacement and driven in complementary fashion by a driver. The chemical injection system, apparatus and method also includes a controller for controlling the driver, with each pump being fed from the storage tank and injecting chemical into the pipeline.
Accordingly, a preferred embodiment of the present invention provides a chemical injection system, apparatus and method which utilizes a positive-displacement pump to pump odorant from a liquid storage tank into a small pipe which empties directly into the main gas pipeline. The pump is operated by a power unit or motor which is responsive to a controller which, in turn, calculates the necessary amount of chemical to be dosed based on the flow rate of the natural gas or LPG in a pipeline. A flow-rate meter is connected to the pipeline and provides a signal to the controller. As the flow rate within the pipeline fluctuates, the controller will increase or decrease the speed of the power unit, which in turn increases or decreases the speed of the positive-displacement pumps and, consequently, the rate of chemical injection into the pipeline. A second flow-rate meter may be provided in the pump discharge line which measures the rate of chemical being pumped and generates a signal to the controller. The controller then compares the pipeline flow rate to the pump discharge flow rate to assure that the proper amount of chemical is being injected into the pipeline. In the event that the controller determines that the flow rate of the chemical being discharged from the pumps is deficient or excessive with respect to the desired rate, the controller will adjust the speed of the power unit accordingly to correspond with the pipeline gas flow rate requirement.
Another preferred embodiment of the present invention provides a chemical injection system, apparatus and method which includes a second pair of positive-displacement pumps having substantially similar displacement and operatively connected to the first pair of positive-displacement pumps. The first pair of positive-displacement pumps being driven in a substantially complementary fashion with the second pair of pumps by the driver. A controller is provided which controls the driver with each pump being fed from the storage tank and discharging chemical into the pipeline. An additional preferred embodiment may include pumps which are substantially similar bellows-type pumps. Another preferred embodiment may include a pair of substantially similar hydraulic actuators, one of each hydraulic actuator being operatively connected to one of each first pump and second pump of the pair of positive-displacement pumps and driven by the driver.
Another preferred embodiment of the present invention provides a chemical injection system, apparatus and method which includes a first and second pair of positive-displacement pumps being driven in a substantially complementary fashion with a first and a second driver. Another preferred embodiment may include a first and a second pair of substantially similar hydraulic actuators. The first pair of hydraulic actuators being operatively connected to the first pair of pumps and driven by the first driver. The second pair of hydraulic actuators being operatively connected to the second pair of positive-displacement pumps and driven by the second driver.
In yet other preferred embodiments, the driver may include a rotary motor and a rotary-to-linear transmission driving the pistons of the hydraulic actuators in complementary linear fashion. The driver may be an electric motor. The transmission may preferably include a scotch yoke.
In order that the advantages of the invention will be readily understood, a more detailed description of the invention briefly described above will be rendered by reference to specific embodiments that are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings, in which:
The present invention utilizes a positive-displacement pump. An advantage of using a positive-displacement pump is that the pressure of the blanket gas in the chemical supply tank can be lower than that associated with the use of a centrifugal pump. Limiting how much gas is dissolved in the odorant inhibits vaporization, vapor lock, and gas entrainment. Another key advantage is that a positive-displacement pump system can be designed to provide exacting accuracy of chemical at slower speeds thereby minimizing maintenance of the system. The preferred embodiment of the present invention includes the use of a bellows-type positive-displacement pump. Bellows-type pumps offer key advantages such as a design which reduces system stress and provides an infinite life versus other types of positive-displacement pumps commonly used in chemical systems such as a diaphragm pump. Despite shortcomings of other positive-displacement pumps, any such type may nonetheless be substituted.
As shown in
As seen in
Seal housings 44A, 44B seal actuators 32A, 32B from yoke box 46 by use of a glide ring seals 48A, 48B. Also provided in actuator seal housings are glide rings 50A, 50B which assist in maintaining axial alignment of the actuators. Yoke 40 includes cam bearing 52 which is operatively attached to pistons 34A, 34B. A linear guide 54 is also provided in yoke box 46 which is in contact with cam bearing 52 and pistons 34A, 34B to maintain axial alignment of the actuators during operation.
In operation, as shown in
As best seen in
The volume of displacement of each of the actuators is substantially equal. It will be understood that the larger the displacement of the actuators, the slower the speed of the power unit may be. As piston speeds increase, pressure drops increase. By keeping piston speeds slow, pressure drops in the pump are minimized, and “flashing” or vaporization of the fluids is prevented. Flashing or vaporization may be a cause of vapor lock and gas entrainment which are both detrimental to performance and accuracy of odorant injection systems.
As seen in
A second flow-rate meter 68 may be utilized in the pump discharge line 70. Second flow-rate meter 68 measures the pump discharge rate and sends a signal to controller 58. Controller 58 compares the flow rate of pipeline 57 to the flow rate of the pump discharge line 70 and regulates the speed of power unit 60. If the actual pump discharge flow rate does not match the desired flow rate as calculated from the flow-rate sensor 56 of pipeline 57, controller 58 adjusts the power unit 60 accordingly. The faster power unit 60 turns, the faster actuator pistons 34A, 34B displace hydraulic fluid into bellows hydraulic chambers 20A, 20B, and the faster odorant is discharged from bellows odorant capsules 22A, 22B. Although many types of flow-rate meters exist, positive-displacement flow-rate meters are preferred due to their cost versus performance benefit.
Second flow-rate meter 68 can be located in pump discharge line 70 to measure the pump discharge flow-rate and provide a signal to controller 58 at 80. Controller 58 compares the signal generated by the pump discharge flow-rate meter 80 to the signal generated by the pipeline flow-rate meter 56 at 82. Upon comparison of the signals generated at 80 and 82, the controller 58 generates an adjustment signal 84 which adjusts power unit 60 so that the actual flow of chemical matches the desired flow of chemical injected into the pipeline.
Second flow-rate meter 68 can be located in pump discharge line 70 to measure the pump discharge flow-rate and provide a signal to controller 58 at 80. Controller 58 compares the signal generated by the pump discharge flow-rate meter 80 to the signal generated by the pipeline flow-rate meter 56 at 82. Upon comparison of the signals generated at 80 and 82, the controller 58 generates an adjustment signal 84 which adjusts power unit 60 so that the actual flow of chemical matches the desired flow of chemical injected into the pipeline.
Second flow-rate meter 68 can be located in pump discharge line 70 to measure the pump discharge flow-rate and provide a signal to controller 58 at 80, 80′. Controller 58 compares the signal generated by the pump discharge flow-rate meter 80, 80′ to the signal generated by the pipeline flow-rate meter 56 at 82. Upon comparison of the signals generated at 80, 80′ and 82, the controller 58 generates an adjustment signal 84 which adjusts power units 60, 60′ so that the actual flow of chemical matches the desired flow of chemical injected into the pipeline.
Reference throughout this specification to “the embodiment,” “this embodiment,” “the previous embodiment,” “one embodiment,” “an embodiment,” “a preferred embodiment” “another preferred embodiment” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in the embodiment,” “in this embodiment,” “in the previous embodiment,” “in one embodiment,” “in an embodiment,” “in a preferred embodiment,” “in another preferred embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
Furthermore, the described features, advantages, and characteristics of the invention may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize that the invention may be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the invention.
While the present invention has been described in connection with certain exemplary or specific embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications, alternatives and equivalent arrangements as will be apparent to those skilled in the art. Any such changes, modifications, alternatives, modifications, equivalents and the like may be made without departing from the spirit and scope of the invention.
Number | Name | Date | Kind |
---|---|---|---|
1301485 | Mueller | Apr 1919 | A |
2856857 | Saalfrank | Oct 1958 | A |
2871789 | Kiffer | Feb 1959 | A |
2946488 | Kraft | Jul 1960 | A |
3134508 | Bayer et al. | May 1964 | A |
3216434 | Lovendahl | Nov 1965 | A |
3257952 | McCormick | Jun 1966 | A |
3304870 | Growall et al. | Feb 1967 | A |
3338170 | Swartz | Aug 1967 | A |
3471079 | Myers | Oct 1969 | A |
3796516 | McCormick | Mar 1974 | A |
3917531 | Magnussen | Nov 1975 | A |
4540346 | Davies | Sep 1985 | A |
4775481 | Allington | Oct 1988 | A |
5141412 | Meinz | Aug 1992 | A |
5406970 | Marshall et al. | Apr 1995 | A |
5490766 | Zeck | Feb 1996 | A |
6142162 | Arnold | Nov 2000 | A |
6162030 | Pierrat | Dec 2000 | A |
6208913 | Marshall et al. | Mar 2001 | B1 |
8349038 | Zeck | Jan 2013 | B2 |
20010014840 | Marshall et al. | Aug 2001 | A1 |
20010047621 | Arnold | Dec 2001 | A1 |
20090242035 | Zeck | Oct 2009 | A1 |
20120167465 | Zeck | Jul 2012 | A1 |
Number | Date | Country | |
---|---|---|---|
20140060651 A1 | Mar 2014 | US |