US20180045460A1

US20180045460A1 - Systems and methods for capturing natural gas liquids from oil tank vapors

Info

Publication number: US20180045460A1
Application number: US15/670,202
Authority: US
Inventors: Robert M. Zubrin; Gevorg Sargsyan; Andrew C. Young; Kevin Hotton; Matthew Lewis
Original assignee: Pioneer Energy Inc
Current assignee: Pioneer Energy Inc
Priority date: 2016-08-09
Filing date: 2017-08-07
Publication date: 2018-02-15
Also published as: CA2975751A1

Abstract

A hydrocarbon vapor capture and processing system is disclosed to reduce both carbon emissions and conventional pollution, while producing financial returns by turning waste vapors into high quality NGLs. In one embodiment, the hydrocarbon vapor is sent to a compressor for compression. Compressed vapor is then cooled via an air cooler, before being condensed by a refrigerator to form a liquid. The resulting two-phase flow is then separated into a dry gas stream and a liquid stream using a cyclonic separator. The dry gas stream may be transmitted as a light gas to sales line. The resulting liquid stream is passed to a stripping column to produce NGLs. The system offers great benefits to the environment and public health, by providing a technology that drastically cuts carbon emissions and noxious pollution, while incentivizing drillers to implement such measures through its ability to produce revenue.

Description

REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Ser. No. 62/372,711, filed on Aug. 9, 2016, entitled “VAPORCATCHER System for Capturing Natural Gas Liquids from Oil Tank Vapors,” the entirety of which is hereby incorporated by reference herein.

NOTICE OF COPYRIGHTS AND TRADEDRESS

A portion of the disclosure of this patent document contains material which is subject to copyright protection. This patent document may show and/or describe matter which is or may become tradedress of the owner. The copyright and tradedress owner has no objection to the facsimile reproduction by anyone of the patent disclosure as it appears in the U.S. Patent and Trademark Office files or records, but otherwise reserves all copyright and tradedress rights whatsoever.

FIELD OF THE INVENTION

The present invention relates to systems and methods for enabling the utilization of oil vapors such as those emitted by oil tanks.

BACKGROUND OF THE INVENTION

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Oil tanks at well sites emit large quantities of vapors that are very rich in natural gas liquids, with typical compositions being over 70% C3+ hydrocarbons. Currently these vapors are either flared, causing considerable environmental pollution, or compressed at some cost into a sales line using a Vapor Recovery Unit. In either case, little or no financial return is achieved.
Accordingly, as recognized by the inventors, there is an unsolved need for novel methods, apparatuses, and systems for capturing and utilizing oil tank vapors. In addition, it would be an advancement in the state of the art to provide an apparatus, system, and method for cost-effective control, monitoring, and management of oil vapors at remote oil and gas fields.
It is against this background that various embodiments of the present invention were developed.

BRIEF SUMMARY OF THE INVENTION

In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the invention. It will be apparent, however, to one skilled in the art that the invention can be practiced without these specific details. In other instances, structures, devices, activities, and methods are shown using schematic, use case, and/or flow diagrams in order to avoid obscuring the invention. Although the following description contains many specifics for the purposes of illustration, anyone skilled in the art will appreciate that many variations and/or alterations to suggested details are within the scope of the present invention. Similarly, although many of the features of the present invention are described in terms of each other, or in conjunction with each other, one skilled in the art will appreciate that many of these features can be provided independently of other features. Accordingly, this description of the invention is set forth without any loss of generality to, and without imposing limitations upon, the invention.
In one aspect, embodiments of the present invention include an apparatus to capture natural gas liquids (NGLs) from oil tanks, comprising a compressor to withdraw hydrocarbon vapors from the oil tanks; and a cooling system to condense liquids from said hydrocarbon vapors resulting in a natural gas liquids (NGLs) stream and a light gas stream.
In one embodiment, the compressor is connected to a refrigerated evaporator to condense liquid components of the hydrocarbon vapors.
In one embodiment, the refrigerated evaporator is connected to a cyclonic separator.
In one embodiment, liquid product from the cyclonic separator connects into a stripping column warmed from below by a reboiler.
In one embodiment, the stripping column and the reboiler remove dissolved air, methane, and excess ethane from the hydrocarbon vapors.
In one embodiment, the cyclonic separator, the stripping column and the reboiler are integrated into a single unit.
In one embodiment, the compressor is powered by the light gas stream taken from the cyclonic separator.
In one embodiment, the light gas stream produced by the cyclonic separator has a Caterpillar methane number above 40, making it suitable for powering compressors and onsite generators.
In one embodiment, the apparatus further comprises one or more electrical motors powered by electricity produced by an electric grid or by onsite power generators.
In one embodiment, the cooling system is a two-stage refrigerator.
In one embodiment, the cooling system is a one-stage refrigerator.
In one embodiment, the light gas stream produced is sufficient to meet a power requirement of the apparatus (gas-powered), without any reliance of power on an electric grid.
In one embodiment, the apparatus operates autonomously with the capacity to be remotely monitored and controlled.
In one embodiment, the apparatus further comprises hardware and software capable of operating completely autonomously within defined operating ranges.
Some embodiments of the present invention include a method for capturing natural gas liquids (NGLs) from hydrocarbon vapors in reservoirs, comprising drawing the hydrocarbon vapors from a reservoir; compressing the drawn hydrocarbon vapors to a pressure between 15 to 500 psia; cooling the compressed hydrocarbon vapors to a temperature between −30 and +20° C. from the compressing step; condensing liquids from the cooled hydrocarbon vapors from the cooling step; separating two-phase flow from the condensing step using a cyclonic separator, to produce a liquid stream and a dry gas stream; passing the liquid stream into a stripping column to produce natural gas liquids (NGLs); and pumping the natural gas liquids (NGLs) to a collection tank.
In one embodiment, the hydrocarbon vapors are compressed to a pressure between 100 and 200 psia.
In one embodiment, the hydrocarbon vapors are cooled to a temperature between −10 and +10° C. above ambient temperature.
In one embodiment, the hydrocarbon vapors are cooled to a temperature of approximately 5° C.
In one embodiment, the hydrocarbon vapors are cooled to a temperature of about −4° C. to achieve 70% propane capture.
In one embodiment, at least a portion of the dry gas stream is injected into a sales line for disposal.
In one embodiment, the dry gas stream extracted from the cyclonic separator is used to produce power and/or to drive pneumatic devices.
In one embodiment, a reboiler is used with some ethane and propane rejected downstream.
In one embodiment, an exhaust gas stream from the reboiler is used to provide process cooling. That is, in one embodiment, the reboiler exhaust gas travels up through the stripping column and leaves as B gas, which is cold, and is used to cool the inlet gas in the feed-exhaust heat exchanger.
In one embodiment, the reboiler's temperature is brought to between 30 and 50° C.
In one embodiment, the temperature is below −50° C., and the method is operated at 1 bara.
In one embodiment, the pressure is 3 bar to operate the method at temperatures in the −20° C. range.
In one embodiment, the pressure is 10 bar or higher to operate the method at temperatures of 5° C. or more.
In one embodiment, high pressures are employed to operate the method with minimal cooling to eliminate ice formation.
Some embodiments of the present invention include an apparatus to capture natural gas liquids (NGLs) from an oil tank, comprising a compressor to withdraw and compress hydrocarbon vapors from the oil tank; an air-cooler to cool the compressed vapors; a refrigerated evaporator to condense liquids from the air-cooled hydrocarbon vapors, resulting in a two-phase fluid; and a cyclonic separator to separate the two-phase fluid into a liquid stream comprising NGLs and a gaseous stream.
In one embodiment, the apparatus further comprises a stripping column to further separate the liquid stream into a natural gas liquids (NGLs) stream and an additional gaseous stream.
In one embodiment, the apparatus further comprises a reboiler connected to the stripping column, the reboiler comprising a reboiler controller to control the ethane content in the NGLs stream by controlling the reboiler temperature.
In another aspect, embodiments of the present invention operate using vapor recovery units (VRUs) or other high-pressure compressors to boost tank or VRT or other gas sources, comprising mixtures with more than 50% C3+ hydrocarbons, from near atmospheric pressure to pressures of 100 to 200 psia, after which natural gas liquids (NGLs) comprising largely of propane, butane, pentane, and heptane can be liquefied by cooling to temperatures typically between −20 and +20° C. using a single-stage refrigerator.
In yet another aspect, other embodiments of the present invention operate to capture vapors rich in natural gas liquids, comprising mixtures with more than 50% C3+ hydrocarbons, using low-pressure compressors to boost the vapors from near atmospheric pressure to pressures of less than 100 psia, after which NGLs may be liquefied using a two-stage or auto-cascade refrigerator capable of cooling to temperatures below −20° C.
Other features, utilities, and advantages of the various embodiments of the invention will be apparent from the following more particular description of various embodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, in which:

FIG. 1 shows a block diagram of a hydrocarbon vapor capturing and processing unit, according to one embodiment of the present invention.

FIG. 2 is a system diagram illustrating the operations of a hydrocarbon vapor capturing and processing unit, according to one embodiment of the present invention.

FIG. 3 shows potential operating parameters for hydrocarbon vapor capturing and processing, according to one embodiment of the present invention.

FIG. 4 is a flow diagram illustrating steps for hydrocarbon vapor capturing and processing, according to one embodiment of the present invention.

FIG. 5 shows exemplary use cases of captured and processed hydrocarbon vapors, according to one embodiment of the present invention.

FIG. 6A shows a perspective view of a hydrocarbon vapor capturing and processing unit, according to one embodiment of the present invention.

FIGS. 6B, 6C, 6D, and 6E show respective front, right, back, and left elevation views of the hydrocarbon vapor capturing and processing unit in FIG. 6A.

DETAILED DESCRIPTION OF THE INVENTION

Commonly overlooked, tank vapors can be a big environmental problem. Some oil producers vent or combust oil vapors, ignoring environmental regulations while trying to minimize operating cost. Some use Vapor Recover Units (VRUs) to compress oil vapors into sales lines.
To cut oil vapor emission and carbon emission, reduce operating expenses, while capitalizing on natural gas liquids (NGLs) present in tank vapors, embodiments of the present invention capture and liquefy tank hydrocarbon vapors, and actively reject oxygen from the liquid hydrocarbon product, so that instead of being flared or disposed of at minimal return as sales-line gas, they can be shipped off to the market and sold as high-quality, valuable liquid fuels. In addition to drastically cutting environmental impacts, low pressure NGL-rich vapors from oil tank batteries can thus be monetized, providing a much better economic return than using a Vapor Recovery Unit (VRU) alone. Oil vapor or gas processing units implemented according to embodiments of the present invention provide extremely high NGL yield. The economics of deploying such systems are far superior to those for deploying a VRU alone and injecting into a gathering system.
More specially, tank vapors are hydrocarbon vapors rich in NGLs. Instead of just being dumped directly into a sales line for little or no return, such tank vapors may be processed to obtain NGLs, which in turn ay be liquefied and shipped to market for sale. Applied to a typical tank vapor emission with a volumetric flow rate of 400 thousand-cubic-feet-per-day (MCFD), embodiments of the present invention may produce 8,000 gallons (˜30,000 liters) of valuable natural gas liquids per day and raise the non-condensable gases to sufficient pressure to be sent into a sales line.
If deployed to a site where tank battery vapors are currently being flared or combusted, embodiments of the present invention may cut carbon emissions by a factor of 4, and the polluting C4+ combustion emission by more than a factor of 12, while providing cash returns at the same time.
VAPORCATCHER is a trademark name carrying embodiments of the present invention, and hence, the aforementioned trademark name may be interchangeably used in the specification and drawing to refer to the products/services offered by embodiments of the present invention. In particular, the term VAPORCATCHER may be used in this specification to describe methods, processors, systems, and apparatuses for natural gas liquids capturing and compression and oxygen removal form oil vapors. With reference to the figures, embodiments of the present invention are now described in detail.
FIG. 1 shows a block diagram 100 for a hydrocarbon vapor capturing and processing unit, according to one embodiment of the present invention. In this embodiment, a VAPORCATCHER system 105 may receive tank vapors 115 from a reservoir such as one or more oil tanks 110. Tank vapor 115 is sent to compressor 120 for compression until a desired pressure is achieved. Compressed vapor is then cooled via air cooler 130, before being condensed by refrigerator 140 to form a liquid. The resulting two-phase flow is then separated into a dry gas stream and a liquid stream using a cyclonic separator 150. The dry gas stream may be transmitted as a light gas to sales line 155. On the other hand, the resulting liquid stream may be passed to a stripping column (not shown) to produce natural gas liquids 157, which in turn may be pumped into an NGLs collection tank 160. In another embodiment, compressor 120 and air cooler 130 may be optional, and the VAPORCATCHER system may receive compressed and air-cooled oil vapor directly from an external VRU.
FIG. 2 is a system diagram illustrating the operations of a VAPORCATCHER system, according to one embodiment of the present invention. Tank vapors or gas 205 enter the process at a compressor suction inlet location 206. Compressor 210 then raises the vapor or gas pressure to a desired pressure and discharges at location 213. The desired pressure may be configured to between 15 to 500 psia, for example 200 psia. Gas 215 may then be air-cooled by air cooler 220 to a temperature of about 5 to 50° C. above ambient, or to a temperature between −30° C. and +20° C., for example, 10° C. above ambient temperature. Next, air-cooled gas 225 may flow through a refrigerated evaporator 230 (refrigerator not shown) where it is cooled further to a temperature between about −30° C. and +30° C., for example about 5° C., thereby condensing the large majority (typically over 75%), of the entering mass flow to liquid. To separate the now two-phase flow 235 into gas and liquid streams, a cyclonic separator 240 may be used. The gaseous stream 246, sometimes termed the A gas, can be used for fuel in electric generators or to provide motive gas for pneumatic valves. The separated liquid stream 245 then flows into a stripping column 250. The stripping column may utilize a reboiler 252 to provide heat to drive the stripping process to produce high-quality NGLs (natural gas liquids) 255 with ethane composition reduced below transportation pressure limits or to meet customer requirements. NGLs stream 255 may be pumped to a collection tank (not shown) by use of pump 260. Reboiler gas exhaust gas stream 256, sometimes termed the B gas, may be used to provide process heat, for example, to power the reboiler. Those portions of the A gas and/or B gas not utilized on-site for the purposes identified above, or for other purposes, may be injected into a sales line for disposal, or, if no sales line is available, can also be combusted or flared.
Table 1 shows typical results for a VAPORCATCHER system implemented according to one embodiment of the present invention, processing 200 MCF of tank gas per day, with a compression pressure of 190 psia and a cooling temperature of 5° C.

TABLE 1

VAPORCATCHER performance using 200 MCF per day of tank gas

								NGL
			Carbon	Carbon	Fraction			captures
			weight of	weight	carbon	Inlet mass	NGL mass	(5%	“A” gas	“B” gas
	Mole % of	Carbon	feed	captured	captured	flow	flow	ethane)	flow	flow
Gas	tank gas	number	kg/hr.	kg/hr.	%	kg/hr.	kg/hr.	gals/day	MCFD	MCFD

Methane	7.60%	1	9.13	0.00	0.0%	12.17	0.00	0.0	9.55	5.65
Ethane	18.18%	2	43.65	7.57	17.3%	54.56	9.46	167.3	7.81	22.25
Propane	33.48%	3	120.55	88.43	73.4%	147.34	108.08	1342.8	4.69	13.15
i-Butane	6.7%	4	32.16	28.67	89.1%	38.87	34.64	387.8	0.38	1.07
n-Butane	18.78%	4	90.16	82.99	92.1%	108.94	100.28	1082.2	0.76	2.22
i-Pentane	4.65%	5	27.90	26.97	96.6%	33.48	32.36	326.8	0.08	0.24
n-Pentane	4.78%	5	28.68	27.86	97.1%	34.42	33.43	334.2	0.06	0.21
Hexane+	2.94%	6	22.31	22.18	99.4%	26.64	26.49	248.6	0.01	0.03
Nitrogen	1.62%	0	0	0	0.0%	4.53	0.00	0.0	2.73	0.51
CO₂	0.53%	1	0.63	0.00	0.6%	2.33	0.01	0.0	0.44	0.60
Water	0.74%	0	0	0	0.0%	1.33	0.02	0.4	0.02	0.02
Total	100.00%		375.17	284.67	75.9%	464.60	344.79	3890	26.52	45.95

The VAPORCATCHER system shown in Table 1 may capture almost 4,000 gallons of natural gas liquid product per day, providing a substantial financial return. In situations where there is no sales line, and so un-liquefied vapors must be combusted or flared, the VAPORCATCHER system may reduce carbon emissions by 75%, or more than a factor of 4, and smoky C4+ combustion emissions by more than a factor of 12. These are very powerful environmental benefits. In addition, the quality of natural gas liquids thus produced may be very high, being less than 5% ethane in the example shown above. In fact, by adjusting the temperature of the reboiler unit and the stripping column pressure, the ethane content of the NGLs product can be adjusted to meet virtually any specification. In one embodiment of the present invention, a control system is implemented to control the temperature of the reboiler unit to meet a desired ethane content specification in the NGLs stream.
In various embodiments, the VAPORCATCHER system may be designed to operate across a range of temperature and pressure combinations, as illustrated in FIG. 3, which assumes the same tank gas composition shown in Table 1.
FIG. 3 is a graph 300 showing potential operating parameters of a VAPORCATCHER system. The horizontal axis 310 represents pressure in bar absolute, and the vertical axis 320 represents fluid temperature in degrees C. The lower curve 330 indicates a VAPORCATCHER system achieving initial liquefaction of 90% of the propane in the tank vapors. The upper curve 340 indicates a VAPORCATCHER system with 70% initial propane liquefaction. In general, the higher the pressure, the higher the temperature may be allowed for the fluid after cooling, while still achieving satisfactory capture of the C3+ liquids. For example, in FIG. 3, at 5 bara, a temperature of the fluid may be cooled to about −25° C. to achieve 90% initial liquefaction of the tank vapor propane, or −4° C. to achieve 70% propane capture. If the pressure is raised to 15 bara, then a fluid temperature of 16° C. may allow 90% initial capture of the tank gas propane, while at 35° C., 70% of the propane may still be captured. FIG. 3 shows initial liquefaction fractions of the propane. If a reboiler is used, some propane may be rejected downstream, reducing the overall propane capture rate of the system, as for example, as reported in Table 1. Propane capture rates are a useful way to characterize the overall NGLs capture rate of the VAPORCATCHER system, because propane has the highest vapor pressure of all the NGLs of interest, and thus is hardest to capture. If propane capture is satisfactory, capture of C4+ NGLs would be excellent as well. This may be seen in Table 1, where an overall system propane capture of 73% corresponds to a C4+ NGLs capture rate of 92%.
In one embodiment, at a fluid temperature below −50° C., the VAPORCATCHER system may be operated at 1 bara. Such a design may require a two-stage refrigerator but may eliminate the need for a compressor.
In another embodiment, at a pressure of 3 bara, satisfactory operation may be achieved with temperatures in the −20° C. range. Such a design may require a modest compressor but allow the use of a one-stage refrigerator.
In yet other embodiments, at pressures of 10 bara or higher, satisfactory operation may be achieved with fluid temperatures of 10° C. or more, requiring a substantial compressor but imposing minimal requirements on the cooling system. Furthermore, since the fluid does not need to be cooled below 0° C., operating with such system parameters eliminates concerns about water freezing in the system. This corresponds to another embodiment of the VAPORCATCHER system.
In one embodiment, the VAPORCATCHER system may operate above the freezing point of water, and thus avoids freezing and delivers any captured water in liquid form to the NGL tank. As water is heavier than the NGLs and is not miscible in them, it will sink to the bottom of the NGLs tank, where it may be drained off.
In another embodiment, the VAPORCATCHER system may operate below the freezing point of water where freezing may be avoided by adding an antifreeze, such as methanol or ethanol, to the fluid upstream of the refrigeration system. The antifreeze-water product may then be drained from the NGLs tank downstream.
In another embodiment, water may be removed from the tank gas stream by a dehydration system, either upstream of the VAPORCATCHER or upstream of the VAPORCATCHER cooling system.
In some embodiments, the VAPORCATCHER system may use a stripping column and a reboiler, as shown in FIG. 2, to produce high-quality NGLs and an A gas product. In some embodiments, the stripping column and/or the reboiler may be optional to lower capital cost and system complexity. In other embodiments, the cyclonic separator, stripping column, and reboiler may be combined into a single unit. In still other embodiments, the cyclonic separator and stripping column may be combined into one unit, with the reboiler separate. In still other embodiments, the stripping column and reboiler may be combined into one unit, with the cyclonic separator separate.
In some embodiments, the VAPORCATCHER system may utilize electrical motors powered by electricity produced by the grid, or by onsite power generators. In another embodiment, the VAPORCATCHER compressor may be powered by gas. The A gas produced in the example shown in Table 1 typically has a Caterpillar methane number above 40, such as 48.5, making it suitable for powering compressors and onsite generators. The amount of A gas shown in Table 1 may be sufficient to provide 112 kWe of power, while the entire system may have a power requirement of 88 kWe. The A gas produced would thus be more than sufficient to meet the power requirements of a gas-powered VAPORCATCHER, without any reliance of power on an electric grid, making the system especially portable and usable in a wide variety of environments.
FIG. 4 is a flow diagram 400 illustrating steps for hydrocarbon vapor capturing and processing, according to one embodiment of the present invention. Upon initiation at step 410, hydrocarbon vapors are drawn from a reservoir and compressed to a pressure between about 15 to 5000 psia at step 420. The compressed hydrocarbon vapors are then cooled at step 430 to a temperature of between −30° C. and +20° C. Resulting liquids from the cooling step are then condensed at step 440 to form a two-phase flow. This two-phase flow is separated at step 450 into a dry gas stream and a liquid stream using a cyclonic separator. The separated liquid stream is passed into a stripping column at step 460 to produce NGLs, which are in turn pumped into a collection tank at step 470. The overall process terminates at step 480.
FIG. 5 shows an exemplary use case of captured and processed hydrocarbon vapors, in which a portion of the processed stream is used as liquid fuel, transported, or used to power remote vehicle fleets. As shown, oil vapor is obtained as it “boils” off oil tank 510. The oil vapor is taken to VAPORCATCHER unit 520, where it is turned into NGLs 525 and used to fill storage vessels 530. The stored NGLs may be off-loaded directly to tankers 550 and/or 555 for transportation to remote locations (for example, to fuel remote vehicle fleets). Light gas processed from the oil vapors may also be transmitted as light gas to sales pipeline 540.
To further illustrate the portability of embodiments of the present invention as disclosed herein, FIG. 6A shows a perspective view of an exemplary VAPORCATCHER system 600, according to one embodiment of the present invention. In this embodiment, VAPORCATCHER system 600 may receive compressed and air-cooled gas from a VRU (not shown), and perform liquefaction and cyclonic separation steps to obtain NGLs for further storage and/or transmission. FIGS. 6B, 6C, 6D, and 6E show respective front, right, back, and left elevation views 620, 640, 660, and 680 of system 600.

VAPORCATCHER Control and Monitoring System

The VAPORCATCHER system is designed to be operated autonomously, with the capacity to be remotely monitored and controlled, allowing a large number of dispersed units to be overseen by a small centrally located staff with minimal labor costs. This is accomplished by a layered hardware, software, and communications architecture. The essential feature to maximize the hardware-to-human ratio is encapsulating relevant logic at appropriate layers.
The total complement system of installed VAPORCATCHER units may be connected in a distributed, sparse network. This network may be designed to be highly available with minimal site-specific configurations required. To minimize configuration but maintain security, private point-to-point VPN tunnels may be deployed over public networks in a hub-and-spoke topology. Each VAPORCATCHER system may represent a spoke. The hub may be configured to forward packets, enabling machine-to-machine communication between both local and remote installations.
Each VAPORCATCHER unit may contain hardware and software capable of operating completely autonomously within known operating ranges. This logic may be completely self-contained and may provide safe operating and shutdown instructions in the case of a network loss. In the event of unforeseen operating conditions, remote monitoring and control intervention by a human operator may be made available and may be requested by the machine.
Industrial programmable logic controllers (PLCs) are good at handling I/O requests and implementing local logic, but often are very poor in networking and communication features. To bypass this restriction, a real-time publish/subscribe messaging framework may be installed as a software layer on remote servers. This framework may be cluster-aware and may aggregate and dispatch messages to and from machines as they enter and leave the network. This opportunistic approach benefits from using open communication protocols which allows it to be both vendor agnostic and very lightweight. This allows advanced metrics and analytics to be performed on a high-powered centralized server with decisions relayed back to the field machines.
The final layer to implementing a multilayered network of autonomous VAPORCATCHER machines with intervention ability is an efficient high-level interface, such as a human-machine interface (HMI). This layer may represent access to machines as well as comprehensive access to historical data, calculated values, trends over time, and predictive analytics generated from asynchronous machine learning algorithms.
In some embodiments, all of the above control and monitoring systems may be implemented. In some embodiments, several of these systems may be optional to help reduce capital costs.

Illustrative VAPORCATCHER Economics

To illustrate the environmental and financial benefits of the VAPORCATCHER system, Table 2 compares the total income that may be generated by a conventional VRU and a VAPORCATCHER system as disclosed herein. When a midstream connection is provided, without loss of generality on pricing, assuming a unit price of $0.40/gal net, with 40/60 split of proceeds between the oil producer and the VAPORCATCHER service provider, and $2/MCF sold, the VAPORCATCHER system may provide a monthly income that is eight times that produced by a VRU. When no midstream connection is provided, Table 3 compares the total amount of gas and C4+ flared per day, and total incomes that may be generated per month. The VAPORCATCHER system is clearly advantageous in both scenarios.

TABLE 2

Financial benefit of the VAPORCATCHER system, with midstream
connection, assuming $0.40/gal net, 40/60 split of proceeds,
and $2/MCF sold

	VRU	VAPORCATCHER

Rental Fee	$6,250	$0
NGLs Revenue	$0	$38,400
Sales of Gas to Line	$12,000	$8,600
Total Income Per Month	$5,750	$47,000

TABLE 3

Environmental and financial benefits of the VAPORCATCHER system,
without midstream connection, assuming $0.40/gal net, and 40/60
split of proceeds

	Flaring	VAPORCATCHER

Total Gas Flared (kg/d)	22,300	5,750
C4+ Flared (kg/day)	11,630	724
Total Income Per Month	$0	$38,400

In summary, the VAPORCATCHER system offers many benefits. It redirects oxygen-contaminated rich hydrocarbon streams away from flaring towards a revenue-generating stream, and reduces liquid content in gas transmission pipelines by removing liquids from gas streams. The VAPORCATCHER system may provide a large financial return from a gas stream that today produces little or no income, and in many cases is a substantial source of both carbon emissions and conventional pollution. In some cases, the reduction of such pollution may be a requirement for allowing oil field operations to proceed, making the financial return of the VAPORCATCHER system even greater than that offered by its own product, as it could make the very large capital expense and project delays required to build a sales line unnecessary.
In addition, the VAPORCATCHER system offers great benefits to the environment and public health, by providing a technology that drastically cuts carbon emissions and noxious pollution, while incentivizing drillers to implement such measures through its ability to produce revenue. In short, the VAPORCATCHER system takes what is now a source of pollution and turns it into a useful energy resource.

VAPORCATCHER Field Deployment Case Study

A commercial deployment of a VAPORCATCHER from the summer of 2017 in Colorado (US) is presented here to illustrate exemplary performance of the system and a preferred embodiment of operating parameters. This VAPORCATCHER was installed on a producing oil site containing five horizontal wells and two vertical wells. A VRU screw compressor is connected to the combined head space of all crude oil and waste water tanks on site. The VRU operates on suction pressure control and is able to maintain tank pressures anywhere from 1-16 ounces of pressure per square inch, gauge (osig). A preferred operating range for tank pressures is from 2-8 osig, with an optimum value of 4 osig. The VRU can provide anywhere from 0-500 MCFD flow of tank vapors to the cooling system of the VAPORCATCHER. Higher flow is preferred due to economic and performance reasons. The VRU can provide a discharge pressure anywhere from 25-200 psig, with a preferred range of 100-170 psig, an even better range of 120-140 psig, and an optimal range of about 130 psig.
The refrigeration system of the VAPORCATCHER can be adjusted to operate at temperatures from −20 to 20° C., with a preferred value just above 0° C. to minimize water freezing and maximize hydrocarbon liquefaction. The temperature of the reboiler can be adjusted from 0 to 100° C., with a preferable range of 30-50° C., depending on the system pressure. Adjusting the reboiler temperature in relation to the system operating pressure allows the ethane content in the NGL liquid product to be specified anywhere from 1-20% by volume, with a preferred range from 3-10% by volume, and an ideal value of about 5% by volume. This parameter is determined by purchaser requirements and NGL market conditions.
Tank vapors are not available at a constant rate from the production tanks due to a variety of reasons, including manual level gauging of tanks, oil and wastewater deliveries into transport trucks, well maintenance and shut ins, diurnal temperature cycles, and ambient weather conditions. The installed VAPORCATCHER system processes as much of the tank vapors that are available at any given time as a function of production tank pressure. This has resulted in instantaneous NGL production from 0 to 7,000 GPD (gallons per day). Total NGL production for the month of July 2017 was about 90,000 gallons.
The VAPORCATCHER employed in this field deployment utilized a system that combined the cyclonic separator, the stripping column, and the reboiler in a single unit.
A typical composition of the tank vapor gas feed being processed by the VAPORCATCHER is shown in Table 4. The composition is reported in mole percent (mole %).

TABLE 4

Typical composition of tank vapor gas for VAPORCATCHER commercial
deployment

	Component	Composition (mole %)

	O₂+ Ar	2.07%
	N₂	8.15%
	CH₄	8.24%
	CO₂	1.40%
	Ethane	28.46%
	Propane	35.44%
	iso-Butane	3.94%
	n-Butane	8.86%
	iso-Pentane	1.21%
	n-Pentane	1.34%
	Hexanes+	0.55%
	H₂O	0.35%
	Total
	100%

A typical composition for the liquefied NGL product is shown in Table 5. Nine 10,000 gallon shipments with compositions similar to the one in Table 5 were produced in July of 2017. Composition is reported in volume percent (volume %).

TABLE 5

Typical composition of NGL liquefied product produced and sold by a
commercial deployment of a VAPORCATCHER

	Component	Composition (volume %)

	Inerts (N₂, CO₂, CH₄)	0.018%
	Ethane	7.76%
	Propane	39.85%
	iso-Butane	8.04%
	n-Butane	24.27%
	Pentanes+	20.06%
	Total
	100%

CONCLUSIONS

Although the present invention has been described with reference to specific exemplary embodiments, it will be evident that the various modification and changes can be made to these embodiments without departing from the broader scope of the invention. Accordingly, the specification and drawings are to be regarded in an illustrative sense rather than in a restrictive sense. It will also be apparent to the skilled artisan that the embodiments described above are specific examples of a single broader invention which may have greater scope than any of the singular descriptions taught. There may be many alterations made in the descriptions without departing from the spirit and scope of the present invention.
While the methods disclosed herein have been described and shown with reference to particular operations performed in a particular order, it will be understood that these operations may be combined, sub-divided, or re-ordered to form equivalent methods without departing from the teachings of the present invention. Accordingly, unless specifically indicated herein, the order and grouping of the operations is not a limitation of the present invention.
While the present invention has been particularly shown and described with reference to embodiments thereof, it will be understood by those skilled in the art that various other changes in the form and details may be made without departing from the spirit and scope of the present invention.

Claims

What is claimed is:

1. An apparatus to capture natural gas liquids (NGLs) from oil tanks, comprising:

a compressor to withdraw hydrocarbon vapors from the oil tanks; and

a cooling system to condense liquids from said hydrocarbon vapors resulting in a natural gas liquids (NGLs) stream and a light gas stream.

2. The apparatus of claim 1, wherein the compressor is connected to a refrigerated evaporator to condense liquid components of the hydrocarbon vapors.

3. The apparatus of claim 2, wherein the refrigerated evaporator is connected to a cyclonic separator.

4. The apparatus of claim 3, wherein liquid product from the cyclonic separator connects into a stripping column warmed from below by a reboiler.

5. The apparatus of claim 4, wherein the stripping column and the reboiler remove dissolved air, methane, and excess ethane from the hydrocarbon vapors.

6. The apparatus of claim 5, wherein the cyclonic separator, the stripping column and the reboiler are integrated into a single unit.

7. The apparatus of claim 6, wherein the compressor is powered by the light gas stream taken from the cyclonic separator.

8. The apparatus of claim 7, wherein the light gas stream produced by the cyclonic separator has a Caterpillar methane number above 40, making it suitable for powering compressors and onsite generators.

9. The apparatus of claim 1, further comprising one or more electrical motors powered by electricity produced by an electric grid or by onsite power generators.

10. The apparatus of claim 1, wherein the cooling system is a two-stage refrigerator.

11. The apparatus of claim 1, wherein the cooling system is a one-stage refrigerator.

12. The apparatus of claim 1, wherein the light gas stream produced is sufficient to meet a power requirement of the apparatus, without any reliance of power on an electric grid.

13. The apparatus of claim 1, wherein the apparatus operates autonomously with capacity to be remotely monitored and controlled.

14. The apparatus of claim 13, further comprising hardware and software capable of operating completely autonomously within defined operating ranges.

15. A method for capturing natural gas liquids (NGLs) from hydrocarbon vapors in reservoirs, comprising:

drawing the hydrocarbon vapors from a reservoir;

compressing the hydrocarbon vapors to a pressure between 15 to 500 psia;

cooling the hydrocarbon vapors to a temperature between −30 and +20° C.;

condensing liquids from the hydrocarbon vapors from the cooling step;

separating two-phase flow from the condensing step using a cyclonic separator, to produce a liquid stream and a dry gas stream;

passing the liquid stream into a stripping column to produce natural gas liquids (NGLs); and

pumping the natural gas liquids (NGLs) to a collection tank.

16. The method of claim 15, wherein the pressure is between 100 and 200 psia.

17. The method of claim 15, wherein the temperature is between −10 and +10° C. above ambient temperature.

18. The method of claim 15, wherein the temperature is approximately 5° C.

19. The method of claim 15, wherein the temperature is approximately −4° C. to achieve 70% propane capture.

20. The method of claim 15, wherein at least a portion of the dry gas stream is injected into a sales line for disposal.

21. The method of claim 15, wherein the dry gas stream extracted from the cyclonic separator is used to produce power and/or to drive pneumatic devices.

22. The method of claim 15, wherein a reboiler is used with some ethane and propane rejected downstream.

23. The method of claim 22, wherein an exhaust gas stream from the reboiler is used to provide process cooling.

24. The method of claim 22, wherein the reboiler's temperature is brought to between 30 and 50° C.

25. The method of claim 15, wherein the temperature is below about −50° C., and the method is operated at 1 bara.

26. The method of claim 15, wherein the pressure is 3 bar to operate the method at temperatures in the −20° C. range.

27. The method of claim 15, wherein the pressure is 10 bar or higher to operate the method at temperatures of 5° C. or more.

28. The method of claim 15, wherein high pressures are employed to operate the method with minimal cooling to eliminate ice formation.