Patent Application
20250065261
The present invention generally relates to separation of substances in a fluid, and more particularly to an apparatus for separating liquids from a gas stream such as removing natural gas liquids or water during gas well extraction.
Fluid processing is an important part of oil and gas well production. For gas wells in particular it is often necessary to remove substances such as contaminants or liquids that might otherwise damage downstream processing equipment. Gas scrubbers are a common solution for this problem.
There are many different types of gas scrubbers including wet scrubbers, dry scrubbers and precipitators. Wet scrubbers typically use a liquid of some sort to filter out contaminants whereas dry scrubbers use dry sorbent materials. Electrostatic precipitators are filterless devices and use an electric field to attract contaminants and trap them.
One class of scrubbers uses what is known as the Joule-Thompson effect to separate liquids from a wet gas stream. According to this principle, when a gas expands from higher pressure to lower pressure it also cools, which can lower the temperature sufficiently to collect atomized liquids as well as condense some of the gaseous components to a liquid state. In particular natural gas liquids can be recovered in various amounts depending on gas composition, pressures, and temperatures involved.
The present invention in at least one embodiment is generally directed to an apparatus for separating liquids from a gas stream comprising a vertically-disposed elongate hollow main body, a top cover attached to a top end of the main body, a bottom cover attached to a bottom end of the main body, an inlet attached to the main body, an outlet attached to the top cover, a baffle interposed between the inlet and the outlet which diverts the gas stream, and a drain attached to the bottom cover. In the illustrative embodiment, the inlet is attached to a side of the main body along an upper portion thereof proximate the top end, the outlet includes a perforated pipe section extending through the top cover, and the baffle divides an interior of the main body into at a first chamber and a second chamber, so the baffle forces the gas stream from the upper portion of the main body downwardly along the first chamber to a lower portion and thence upwardly along the second chamber to the upper portion. A differential control valve can be connected to the inlet to automatically maintain an exit pressure of the gas stream as it is fed to the inlet. The baffle is preferably constructed of a top diverter plate, an intermediate diverter plate, and a bottom diverter plate generally forming a Z-shape, with the top diverter plate being proximate the top cover, the intermediate diverter plate spanning the upper portion of the main body to the lower portion, and the bottom diverter plate located along the lower portion, with the inlet entering the main body below the top diverter plate A side edge of the top diverter plate is affixed to a top edge of the intermediate diverter plate, a bottom edge of the intermediate diverter plate is affixed to a side edge of the bottom diverter plate, and the bottom diverter plate has a plurality of holes therein, such that the baffle forms a complete seal between the first chamber and the second chamber except for the holes. The holes in the bottom diverter plate are preferably formed along a periphery thereof but not in a central area.
The above as well as additional objectives, features, and advantages in the various embodiments of the present invention will become apparent in the following detailed written description.
The present invention may be better understood, and its numerous objects, features, and advantages of its various embodiments made apparent to those skilled in the art by referencing the accompanying drawings.
The use of the same reference symbols in different drawings indicates similar or identical items.
There are still many problems with conventional scrubbers for wet gas. One of the biggest is efficiency in terms of liquids removal. Most systems leave a significant amount of suspended liquid or near-liquid in the exit stream, which can create all kinds of issues for downstream equipment, resulting in increased maintenance costs and downtime in the extraction process. Attempts to remedy these inefficiencies merely result in greater expense or require constant chemicals injection.
Another problem relates to the gas compressors used in these systems, which may be necessary in order to raise the pressure of the incoming gas stream and induce the Joule-Thompson effect in the expansion bottle. The compressors can require excessive repairs due to the high pressures, temperatures and load requirements involved to achieve successful liquids elimination, particularly when some of the gas product is rerouted to the compressor as fuel. Detonation, intake manifold air temperature (IMAT) and emissions errors often arise in the compressors. Detonation, sometimes called pre-ignition or knock, is when the fuel gas ignites prematurely due the presence of natural gas liquids and water. It can cause serious damage to the engine components such as melted spark plugs, blown head gaskets, hammered bearings, cracked pistons and cracked piston rings. Detonation is also affected by the IMAT. In the heat of the summer the air, fuel gas can be too hot. IMAT error codes can only be removed if the temperature is lowered. There are a variety of other problems that can arise as well. For example, the gas compression also results in a higher entry temperature of the raw gas stream which can contribute to expansion bottle failures.
It would, therefore, be desirable to devise an improved wet gas scrubber that more efficiently separates liquids from the gas stream. It would be further advantageous if the method could allow for a cooler exit stream to mitigate errors in compressor engines. These and other advantages are achieved in various implementations of the present invention by providing an expansion bottle design that allows for a more complete separation of liquids and an increased pressure differential for the bottle resulting in a cooler exit stream. The bottle design includes a unique layout for the inlet and outlet locations, an enhanced baffle construction using multiple diverter plates, and a perforated outlet pipe. While each of these design components individually offer performance improvement, the combination in particular creates a superior expansion chamber which cools the gas causing nearly all liquids to drop out into the expansion tank, creating a lean and cool fuel gas stream. Natural gas compression engines have to pass a standards requirement (40 C.F.R. 60, Subpart JJJJ), and the cooler, leaner fuel gas produced in accordance with the present invention helps the engine pass that test.
With reference now to the figures, and in particular with reference to
Liquids formed in scrubber bottle 12 during the process are removed with a drain line at the bottom via dump valve 18. While the exact nature of the liquids will depend upon the gas source, for a natural gas well the composition of the liquid is mostly water and natural gas liquids (e.g., ethane, propane, butane, isobutane, pentane) in various ratios. A pneumatic level control sensor (not shown) may be used for automatic control of the dump valve, or field operators can manually dump the liquids. The liquids are sent to heater/treater 22 for processing such as breaking down emulsions and removing water.
The outlet of scrubber bottle 12 can direct the processed gas to a number of different lines, particularly a sales line 30 that leads to collection and/or storage facilities to provide the processed gas as a commodity. The gas may be separated further into different gas constituents for this purpose. A fuel line 32 can siphon off a portion of the gas to power the engine for gas compressor 14 or any other local equipment. In some embodiments, if the bottle is overpressured a valve dumps excess outlet gas into a suction line 34 for gas compressor 14 (i.e., recirculated). In other embodiments excess gas is sent to a flare line 36 or to a pressure relief valve 38 that vents to the atmosphere.
With the exception of scrubber bottle 12, most of the components of scrubbing system 10 can be obtained off-the-shelf. Appropriate parts include the stem-guided high-pressure control valve available from Kimray Inc. of Oklahoma City, Oklahoma, as part number CVS1S4TW08L2S, with the diaphragm-controlled high-pressure controller part number PDHND1S. Those skilled in the art will appreciate, however, that this overall configuration for scrubbing system 10 may change considerably depending on the application, and may include other components as well. Every customer and/or location can be different. For example, the wellhead gas may be treated prior to entering gas compressor 14 as is known in the art. The entire system can further be mounted on an oil field skid (not shown) whose design and function is based on the particular oilfield in which the skid is employed.
Exterior features of scrubber bottle 12 can be seen in the front elevational view of
For typical operational parameters of scrubber bottle 12, the piping and valves generally do not need to be heated to prevent freezing but the inlet and drain line can be heat traced and insulated to prevent freezing in colder climates.
Interior features of scrubber bottle 12 can be further seen in
Diverter plates 60a, 60b and 60c are all generally flat, and plates 60a and 60c are disposed horizontally while plate 60b is disposed vertically, with the top edge of intermediate diverter plate 60b being affixed to the right side edge of top diverter plate 60a, and the bottom edge of intermediate diverter plate 60b being affixed to the left side edge of bottom diverter plate 60c. In this manner, the baffle created by these three diverter plates forms a complete seal between the two interior chambers except for the holes in bottom diverter plate 60c, i.e., all of the gas coming into scrubber bottle 12 via inlet 46 must pass through the holes in bottom diverter plate 60c before exiting the bottle via outlet 48. In the preferred embodiment top diverter plate 60a is located at the seam between main body 40 and top cover 42 (i.e., the upper half), and bottom diverter plate 60c is located roughly two-thirds down the length of main body 40 (i.e., the lower half).
As mentioned above, outlet 48 has a pipe section 62 that extends downwardly through top cover 42 and into the upper portion of main body 40. The perforations in pipe section 62 enhance the bottle inlet/outlet pressure differential by allowing further expansion of the gas right after it passes through the perforations. Pipe section 62 is perforated but the terminal end is capped to force all of the gas through the perforations.
One possible construction of bottom diverter plate 60c is seen in
The exact materials and dimensions of the components of scrubber bottle 12 are generally a function of desired performance factors such as pressure rating or liquid volume, as well as cost, so can vary widely according to specifications and application. The components can be constructed of any durable material such as a metal or metal alloy, particularly carbon steel, and can be attached via a combination of welding and screw pipe. Approximate dimensions for an exemplary embodiment are as follows. Cylindrical main body 40 is 48″ long with a 8.65″ outer diameter. Top cover 42 and bottom cover 44 also have a 8.65″ outer diameter. The length of intermediate diverter plate 60b is 24″. The width of intermediate diverter plate 60b is 6.875″ long (this is also the length of the chord defining the minor/major segment boundary for top diverter plate 60a and bottom diverter plate 60c). These components can all have the same thickness of ⅜″, resulting in a segment radius of 3.775″ for the top and bottom diverter plates 60a, 60c. The holes in bottom diverter plate 60c are preferably 0.875″ in diameter, and have a combined surface area that is about 13% of the total area defined by the plate segment. Inlet 46 is 2″ diameter and enters main body 40 4″ underneath top diverter plate 60a. Outlet 48 and pipe section 62 have a diameter of 2″. The wall of pipe section 62 is 0.237″ thick, and the perforations in pipe section 62 are circular, having a diameter of 0.1875″ and occupying about 3% of the outer surface area of pipe section 62 (excluding the capped bottom).
Many of the foregoing features offer individual performance improvements over conventional wet gas scrubbers. These include the overall configuration for the inlet and outlet in a vertical scrubber, the baffle design to optimize gas expansion, and the perforated outlet to further enhance the expansion. These features together provide superior performance as experienced in the field. Systems constructed in accordance with the present invention have a cooler exit gas resulting in cooler valves, cooler (and leaner) fuel for the gas compressor, and cooler off suction, all of which contribute to better runtime. This also eliminates hotter temperature on the driver cylinders and eliminates detonation with little to no cylinder failures. It is also easier to adjust the temperature of the fuel via recirculation and bypass, and provides a cleaner exhaust by-product. Testing has shown that a system such as that described herein lowers engine load 15% on average, and up to 20%.
Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. For example, the main body of the bottle does not need to cylindrical (i.e., it may have other cross-sectional shapes besides circular), the outlet and attached pipe section could be off center or inclined rather than perfectly vertical, or the drain line could be at a side of the bottom cover rather than at the very bottom. Also, the diverter plates do not have to be perfectly orthogonal or flat (or exactly vertical/horizontal), they could be curved or have any general Z-shape that forces the gas to move downwardly from the upper half of main body 40 (along the left side) to the lower half thereof before returning back upwardly to the upper half (along the right side). Rather than being composed of several plates, the baffle could be integrally formed in one piece such as by casting. The bottom diverter plate 60c could also be completely absent in some embodiments in which case the baffle would still force the gas stream downward before it returns upward. Also, embodiments still offers significant performance improvement without using a perforated pipe. It is therefore contemplated that such modifications can be made without departing from the spirit or scope of the present invention as defined in the appended claims.
