The present invention relates generally to liquefied natural gas and, more particularly, to systems and methods for capturing refrigeration from gasification or vaporization of liquefied natural gas.
Liquefied Natural Gas (LNG) is a clean, viable source of heat and power. When natural gas is cooled and liquefied, the density increases about 600 times. In other words, LNG occupies about 1/600th the volume or space than the same volume of natural gas vapor. LNG is, accordingly, easier to transport, and far more energy dense than natural gas in a vapor form. Liquefying natural gas into LNG, however, requires a significant amount of energy and special cryogenic tanks are needed to prevent rapid heat gain after the natural gas is liquefied.
When natural gas is liquefied into LNG, the energy content becomes more comparable to other liquid fuels. Nonetheless, as illustrated below, LNG generally provides less energy per gallon as compared to other fuels (measured in British Thermal Units (Btu)):
One gallon diesel=135,000 Btu
One gallon gasoline=125,000 Btu
One gallon Liquefied Petroleum Gas (LPG)=91,000 Btu
One gallon Liquefied Natural Gas (LNG)=83,000 Btu
These other fuels, including, for example, diesel, gasoline, kerosene, and propane, may be used in applications similar to LNG. However, as described below with respect to embodiments of the disclosed invention, unlike LNG, these other fuels do not provide significant “cold energy.”
As a fuel, LNG is versatile and can be used in just about any way other fuels are used. These uses may be, for example, in boilers, dryers, power generation, marine fuel, locomotives, drilling rigs, asphalt plants, port operations, and over-the-road trucks. Once LNG arrives at an industrial site, it is vaporized or gasified into a gas for consumption. Prior to vaporization or gasification, LNG is not flammable and will not combust unless it is in a mixture with air where the natural gas is between 5% to 15% mixture with air. Vaporizing or gasifying LNG theoretically requires the same amount of energy from the environment as compared to the energy required to liquefy natural gas.
The amount of energy required to liquefy natural gas tends to vary with, for example, gas composition, gas pressure, product purity, product pressure, and refrigeration technology. With respect to liquefaction, for example, small scale liquefiers of less than about 500,000 gallons per day may require about 0.7 to 0.9 kWh/gallon of LNG, not including energy associated with inlet gas compressions, pretreatment, and other processes.
Conventional vaporization or gasification LNG systems and methods use various heat exchangers. The NFPA-59A Standard for Production, Storage, and Handling of Liquefied Natural Gas lists five options: (1) Ambient vaporizer, (2) Heated Vaporizer, (3) Integral Heated Vaporizer, (4) Remote Heated Vaporizer, and (5) Process Vaporizer. However, with the conventional vaporization or gasification LNG systems and methods, the cooled process fluid used to vaporize or gasify the LNG is discharged to the environment and/or the “cold energy” is not otherwise utilized.
According to an embodiment, a method for capturing refrigeration is disclosed comprising providing a predetermined flowrate of liquefied natural gas to a first heat exchanger; providing a process fluid to the first heat exchanger, wherein the process fluid is warmer than the liquefied natural gas; heating at least a portion of the liquefied natural gas with at least a portion of the process fluid; calculating an amount of energy transferred in the first heat exchanger from the process fluid to the liquefied natural gas; and utilizing the process fluid for cooling.
According to another embodiment, a skid for capturing refrigeration from liquefied natural gas vaporization is disclosed comprising: a first heat exchanger mounted on the skid, the first heat exchanger having a natural gas inlet, a natural gas outlet, a process fluid inlet, and a process fluid outlet; wherein process fluid is configured to flow from the process fluid inlet through the first heat exchanger to the process fluid outlet and then to the process fluid inlet.
The features and advantages of the invention will be apparent from the following drawings wherein like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements.
Embodiments of the invention are discussed in detail below. In describing embodiments, specific terminology is employed for the sake of clarity. However, the invention is not intended to be limited to the specific terminology so selected. A person skilled in the relevant art will recognize that other equivalent parts can be employed and other methods developed without departing from the spirit and scope of the invention.
As used herein, the term “about” or “approximately” when referring to a measurable value such as an amount, a temporal duration, and the like, is meant to encompass variations of ±20% or ±10%, more preferably ±5%, even more preferably ±1%, and still more preferably ±0.1% from the specified value, as such variations are appropriate to perform the disclosed methods.
Referring now to
According to an embodiment, the heat exchanger or vaporizer 103 may be a remote heated vaporizer. For example, in remote heated vaporizers, the primary heat source (e.g., heat exchangers, industrial equipment, heaters, etc.) is separated from the actual vaporizing heat exchanger, and an intermediate or process fluid is used as the heat transport medium from the primary heat source or sources to the heat exchanger or vaporizer. According to various embodiments, the process fluid may be, for example, but not limited to water, steam, isopentane, glycol, mixtures thereof or other fluids known to one of ordinary skill in the art.
As illustrated in
According to still another embodiment, the heat exchanger or vaporizer 103 may comprise a counter-flow shell and tube heat exchanger where flow in the shell-side is counter to, or opposite, the flow in the tube-side. Such a flow configuration provides efficient heat transfer between, for example, LNG flowing through the tube-side and process fluid flowing through the shell-side of the heat exchanger.
As illustrated at
The connecting piping may generally comprise piping 123 for fluidly connecting the LNG inlet 105 of the heat exchanger or vaporizer 103 to a position near or adjacent to an edge of the platform or skid 121, piping 125 for fluidly connecting the natural gas outlet 107 of the heat exchanger or vaporizer 103 to another position near or adjacent to an edge of the platform or skid 121, piping 127 for fluidly connecting the warm process fluid inlet 109 of the heat exchanger or vaporizer 103 to another position near or adjacent to an edge of the platform or skid 121, and piping 129 for fluidly connecting the cold process fluid outlet 111 of the heat exchanger or vaporizer 103 to another position near or adjacent to an edge of the platform or skid 121. For example, the connecting piping 123, 125, 127, 129 may be provided at positions near or adjacent to edges of the platform or skids 121 so that the platform or skid 121 may be easily placed on a site for installation with on-site or existing piping and equipment. Such a configuration may avoid damage to both on-site piping and equipment and piping and equipment located on the platform or skid 121. According to other embodiments, the connecting piping 123, 125, 127, 129 may extend past the edges of the skid or platform 121. According to still other embodiments, the connecting piping 123, 125, 127, 129 may not extend past the edges of the skid or platform 121.
The connecting piping 123, 125, 127, 129 may include various sizes of piping, tubing, flanges or threaded connections, valves, regulators, vents or pressure relief valves, and other types of pipes, valves, and fittings as known to one of ordinary skill in the art. Pipe and equipment supports 131 may be further included on the skid or platform 121 to support the connecting piping 123, 125, 127, 129 and other equipment located on the skid or platform (including the heat exchanger or vaporizer 103). The pipe and equipment supports 131 may raise the connecting piping 123, 125, 127, 129 and other equipment located on the skid or platform (including the heat exchanger or vaporizer 103) above the surface of the skid or platform 121 for operator access to the equipment.
According to an embodiment, the LNG vaporization or gasification system 101 may be configured to vaporize or gasify approximately 40,000 to 100,000 standard cubic feet per hour (scfh) of natural gas in approximately 10,000 scfh increments. According to other embodiments, the LNG vaporization or gasification system 101 may be configured to vaporize or gasify in approximately up to 40,000 scfh, up to 60,000 scfh, up to 80,000 scfh, up to 100,000 scfh flow rates. For example, for such embodiments, such natural gas flow rates allow for the heat exchanger 103 and other piping and equipment, further explained below, to be placed on one skid or platform 121, or a skid or platform 121 having multiple pieces. For example, the skid or platform 121 including the heat exchanger 103 and the other piping and equipment may be factory assembled so that the assembly can be quality tested in a controlled environment and then delivered to and installed on a site.
Referring still to
According to an embodiment, the connecting piping 123, 125, 127, 129 may include temperature sensors and/or transmitters 143, pressure sensors and/or transmitters 145, and flow meters and/or transmitters 147. As explained in more detail below, the various sensors and transmitters may be used to control the LNG gasification or vaporization system 101 and optimize captured refrigeration capacity.
According to an embodiment, the connecting piping 125 may also include a regulator 149 to reduce the pressure of the natural gas to a predetermined pressure after it exits the heat exchanger or vaporizer 103. For example, the regulator may reduce the pressure to less than a maximum allowable operating pressure of boilers, dryers, power generation equipment, marine fuel equipment, locomotives, drilling rigs, asphalt plants, port operation equipment, over-the-road trucks, or other equipment requiring natural gas.
Referring now to
As illustrated in
As described above, the natural gas changes phase, from liquid to vapor, in the heat exchanger or vaporizer 103 by heat transfer with the process fluid. As the liquid natural gas changes to vapor, the natural gas undergoes a temperature increase, which is characterized herein as providing “Cold Energy,” which is based on the change in enthalpy of the natural gas between the liquid phase and the vapor phase. According to embodiments, this Cold Energy can be captured and used in other processes.
According to embodiments illustrated at
From a thermodynamic perspective, enthalpy is calculated as follows in equation (1):
H=U+pV (1)
Where
H=enthalpy
U=internal energy
p=pressure exerted by the natural gas
V=volume occupied by the natural gas
The Cold Energy (in Btu) captured by the process fluid is expressed in equation (2):
Cold Energy=ρV*(ĥsat−ĥvapor) (2)
Where
ĥsat=enthalpy of saturated liquid
ĥvapor=enthalpy of vapor
V=volume occupied by the saturated liquid
ρ=density of saturated liquid
As illustrated by equation (2), the total difference in enthalpy is the total Cold Energy generated by the phase change of the natural gas, which depends on saturation conditions (i.e. temperature and pressure).
Refrigeration can be further calculated based on the change in enthalpy and the mass flowrate of LNG, according to equation (3):
1 ton of refrigeration=12,000 Btu/hr (3)
According to embodiments, approximately half of the energy required to liquefy natural gas may be recovered upon vaporization or gasification, such as at a customer site. For example, Table 1 illustrates the Cold Energy recovered by embodiments of the present invention:
As a first illustrative example of an embodiment, the LNG storage tank 151 is configured to hold 14,000 gallons of LNG at 60 psig and natural gas vapor exits the heat exchanger or vaporizer 103 at 60 psig and 60° F., where the following conditions are met:
ĥsat=380.60 Btu/lbm
ĥvapor=31.443 Btu/lbm
ρ=24.391 lbm/ft3
V=1871.53 ft3
Accordingly, the Cold Energy generated by Example 1 is 15.9*106 Btu or 15.9 million Btu (mmBtu). In other words, 15.9 mmBtu is required to vaporize 14,000 gallons of LNG.
As a second illustrative example of an embodiment, LNG is vaporized at the same conditions as Example 1 and the mass flowrate of LNG is 15 gallons per minute (gpm). According to Equations (2) and (3), the refrigeration capacity generated by vaporizing 15 gallons per minute of LNG is about 94 tons.
As described above, the Cold Energy can be extracted during the gasification or vaporization process and captured by the process fluid in the heat exchanger or vaporizer 103. In other words, the process fluid releases heat to the LNG. For example, based on an energy balance of the heat exchanger, the required flow rate to achieve a desired temperature of the process fluid at the cold process fluid outlet 111 of the heat exchanger or vaporizer 103 can be calculated by the following equations (4) and (5):
Heat transfer of process fluid=qw={dot over (m)}w*cp*(Tw out−Tw in) (4)
Heat transfer of LNG=qLNG={dot over (m)}LNG*(hLNG out−hLNG in) (5)
Where:
{dot over (m)}w=mass flowrate of process fluid
cp=heat capacity of process fluid
Tw out=temperature of process fluid exiting the heat exchanger
Tw in=temperature of process fluid entering the heat exchanger
hLNG out=enthalpy of natural gas exiting the heat exchanger
hLNG in=enthalpy of natural gas entering the heat exchanger
Assuming an adiabatic process (i.e. no heat loss or gain from the environment), the required flow rate of the process fluid can be calculated as follows by the following equations (6) and (7):
qw=qLNG={dot over (m)}LNG*(Tw out−Tw in)={dot over (m)}wcp*(hLNG out−hLNG in) (6)
{dot over (m)}w=qLNG/(cp*(Tw out−Twin)) (7)
According to an embodiment, the process fluid may be, for example, but not limited to, water, glycol, or a water/glycol mixture. For purposes of a third illustrative example of an embodiment, LNG is vaporized at the same conditions as Example 1 and the mass flowrate of LNG is 15 gallons per minute and the process fluid is water with an inlet temperature of 60° F. with a desired outlet temperature of 32° F. Assuming an adiabatic process, the required flowrate of water at 1 atm can be calculated by Equation (7) as 73.1 gallons per minute where: cp=heat capacity of water=1 Btu/lbm° F.
Referring now to
The display 201 indicates readings, such as real-time transmissions, from various sensors and/or transmitters located throughout the illustrated embodiment. On the process fluid piping, a temperature sensor/transmitter 143 and flow meter/transmitter 147 is located on the process fluid inlet piping to the heat exchanger or vaporizer 103. Another temperature sensor/transmitter 143 is located on the process fluid outlet piping from the heat exchanger or vaporizer 103, and may additionally include a flow meter/transmitter. A differential pressure sensor/transmitter 145 is located between the process fluid inlet and outlet piping. This differential pressure sensor/transmitter 145 may indicate, for example, freezing process fluid or other fouling in the heat exchanger or vaporizer 103. On the natural gas piping, other temperature and pressure sensors/transmitters 143, 147 may be located on the piping.
The display 201 indicates different flow paths of the LNG. From the LNG storage tank 151, the LNG may flow to either the heat exchanger or vaporizer 103, to the ambient vaporizers 161, or to a sump used, for example, for blowdown or recycle to the LNG storage tank 151. The flow of LNG may be controlled by various valves 171 to control LNG flow to either the heat exchanger or vaporizer 103, one or more ambient vaporizers 161, sump, or any combination thereof.
Referring now to
According to an embodiment, the controller or PLC 203 may also track use of the ambient vaporizers 161 according to a predetermined length of time for using the ambient vaporizers 161. For example, at a predetermined length of flowing LNG through the ambient vaporizers 161, the controller 203 may divert LNG flow from one ambient vaporizer 161 to another in order to prevent freezing in the ambient vaporizers 161.
According to an embodiment, the controller or PLC 203 may further control the valves 171 in order to adjust the flow of LNG to prevent freezing in one or more of the ambient vaporizers 161. Further, the controller or PLC 203 may control the valves 171 to divert LNG flow to or away from the heat exchanger or vaporizer 103 according to refrigeration requirements of other equipment.
According to an embodiment, the controller or PLC 203 may control the flow of LNG to the heat exchanger or vaporizer 103 to be a predetermined flow rate. The controller or PLC 203 may adjust the predetermined flow rate of LNG to the heat exchanger or vaporizer 103 based on, for example, temperature of process fluid entering or exiting the heat exchanger or vaporizer 103. Further, the controller or PLC 203 may adjust the predetermined flow rate of LNG to the heat exchanger or vaporizer 103 based on, for example, flow rate of process fluid through the heat exchanger or vaporizer 103.
Referring to
Referring now to
The embodiments illustrated and discussed in this specification are intended only to teach those skilled in the art the best way known to the inventors to make and use the invention. Nothing in this specification should be considered as limiting the scope of the present invention. All examples presented are representative and non-limiting. The above-described embodiments of the invention may be modified or varied, without departing from the invention, as appreciated by those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the claims and their equivalents, the invention may be practiced otherwise than as specifically described.
This application claims priority to U.S. Nonprovisional application Ser. No. 15/285,965, filed Oct. 5, 2016, which claims priority to U.S. Provisional Application Ser. No. 62/237,223, filed on Oct. 5, 2015, the content of which are hereby incorporated herein by reference in their entirety.
Number | Name | Date | Kind |
---|---|---|---|
4224802 | Ooka | Sep 1980 | A |
5288312 | Payne | Feb 1994 | A |
5394704 | Johnson | Mar 1995 | A |
7726874 | Kirchberg | Jun 2010 | B2 |
20020170297 | Quine | Nov 2002 | A1 |
20050126220 | Ward | Jun 2005 | A1 |
20070079617 | Farmer et al. | Apr 2007 | A1 |
20080178611 | Ding | Jul 2008 | A1 |
20080302519 | Franklin et al. | Dec 2008 | A1 |
20090211263 | Coyle | Aug 2009 | A1 |
20100229573 | Ehrstrom | Sep 2010 | A1 |
20100263389 | Bryngelson et al. | Oct 2010 | A1 |
20110297346 | Minta et al. | Dec 2011 | A1 |
20120222430 | Madsen | Sep 2012 | A1 |
20120234024 | Street | Sep 2012 | A1 |
20130025306 | Matsukura | Jan 2013 | A1 |
20130291567 | Bohra et al. | Nov 2013 | A1 |
20140174122 | Cooper | Jun 2014 | A1 |
20140245779 | Bohra et al. | Sep 2014 | A1 |
20140338371 | Nierenberg | Nov 2014 | A1 |
20150252948 | Schmidt-Lussmann | Sep 2015 | A1 |
Number | Date | Country |
---|---|---|
2682666 | Jan 2014 | EP |
2012-021837 | Feb 2012 | JP |
10-0678852 | Feb 2007 | KR |
10-2015-0052980 | May 2015 | KR |
03085317 | Oct 2003 | WO |
Entry |
---|
International Search Report dated Dec. 22, 2016 in International Patent Application No. PCT/US2016/055503. [Cited in Parent]. |
Written Opinion dated Dec. 22, 2016 in International Patent Application No. PCT/US2016/055503. [Cited in Parent]. |
Number | Date | Country | |
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20180045441 A1 | Feb 2018 | US |
Number | Date | Country | |
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62237223 | Oct 2015 | US |
Number | Date | Country | |
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Parent | 15285965 | Oct 2016 | US |
Child | 15669395 | US |