Device for direct detection of solid formation

Abstract

A device for directly detecting solid formation in a fluid under known pressure and temperature conditions is disclosed. The device includes a container having an electromagnetic resonant cavity defined by an upper portion, a lower portion, and a gap defined between the upper portion and the lower portion, the gap having a resonant property sensitive to the presence of a solid phase therein. The upper portion or the lower portion may be provided with a channel extending therethrough, the channel being in communication with an inlet fluid so that a fluid flow enters the gap to remove solids from the cavity after solid formation. The device also includes one or more probes, one or more sensors, and a signal processor operably connected to the sensors and the one or more probes to directly detect solid formation in a fluid within a cavity by responding to changes in the resonant properties of the cavity being detected.

Description

Technical Field

[0001] The present invention relates to a device for directly detecting the formation of solids in a fluid under known pressure and temperature conditions.

[0002] The present invention also relates to systems and methods for preventing or repairing plugging of cryogenic heat exchangers used in LNG production. Background Art

[0003] Liquefied natural gas (LNG) is essential in the global natural gas trade. Liquefaction increases the energy density of natural gas, allowing it to be transported economically over long distances. Natural gas processing and liquefaction are technically demanding, as the complexity and variability of the composition make the prediction and understanding of phase equilibria very difficult. The low temperatures and high pressures required for liquefaction are favorable conditions for freezing heavy hydrocarbons. Even at very low concentrations, the accumulation of solids resulting from trace amounts of heavy hydrocarbons can pose a risk to the efficient operation of LNG facilities. Therefore, methods are needed to quantify and remediate the risk of solids formation.

[0004] Natural gas and gas condensate fluids are mainly composed of lower alkanes, including methane, ethane and propane (C1, C2 and C3). In addition to these components, there are also small amounts of butane (nC4, iC4) and heavier hydrocarbons (C 5+ ), which has a higher risk of freezing (Table 1). 5+ The specific composition of the group strongly affects the effective freezing temperature. In particular, aromatic compounds have a greater impact on the freezing temperature of the fluid. Conventional analytical methods are unable to effectively resolve the composition, resulting in inaccurate detection (C 5+ ) impurities when operating too conservatively.

[0005] The risk of solids shedding during the liquefaction stage is usually reduced by using a heavy hydrocarbon (HHC) removal unit that produces a lean natural gas product and heavy waste. 5+ Concentration limit (<0.1 mol%). 5+ The location of the monitoring device is usually after the HHC removal unit and before the liquefaction unit. Concentration limits have two benefits: (1) the LNG product will meet sales specifications; (2) freezing in the downstream main cryogenic heat exchanger (MCHE) will be avoided. Monitoring C 5+ The concentration of the group is a measure that allows online monitoring of the heavy hydrocarbon content in dynamic LNG systems, but it is limited by the lack of transparency of the compositional breakdown of the group, which may adversely affect the prediction of the freezing temperature.

[0006] Table 1: Freezing temperatures of paraffinic and aromatic impurities that are critical to natural gas processing

[0007] Components Pure freezing temperature (℃) Components Pure freezing temperature(℃) <![CDATA[Butane (C4)]]> -140 benzene 5.5 <![CDATA[Pentane (C5)]]> -129.8 p-Xylene 13.2 <![CDATA[Hexane (C6)]]> -93.5 Neopentane -16.6 <![CDATA[Heptane (C7)]]> -90.6 Cyclohexane 6.5

[0008] Inefficient operation of the HHC unit or dynamic compositional changes in the reservoir fluid may result in HHC carryover into the MCHE. Due to the large difference between the freezing points of aromatic / cyclic compounds and alkanes, carryover of about 15 ppm of benzene (67 times less than 0.1 mol%) can cause serious solidification risks downstream. Figure 1 The sensitivity of the solid phase equilibrium temperature to small ppm concentration increases of benzene in a standard MCHE feed is depicted. In this figure, the temperature of the MCHE effluent is shown to illustrate the risk of large solids shedding if HHC (especially benzene) residues are considered. An increase in benzene concentration from 10 ppm to 50 ppm raises the freezing temperature (solid phase equilibrium line) by 15 K, which is well within the operating conditions of MCHE. This relationship between HHC concentration and freezing temperature is consistent across all trace heavy components. The ability to resolve the composition of complex mixtures at the ppm level is an increasingly difficult task that is both time consuming and expensive.

[0009] For reliable and efficient operation of MCHE, it is essential to be able to accurately predict the behavior of hydrocarbon fluids under steady-state and transient conditions. In addition to predicting the vapor-liquid equilibrium for optimizing LNG production, predicting the solid-liquid equilibrium is also essential to avoid plugging of the MCHE. Even if a small amount of solids is deposited in the MCHE tubes, such as during a temporary increase in C 5+ During the concentration period, the risk of subsequent plugging also increases because the presence of crystals and surface defects increases the rate of solid formation and other impurities accumulation. Even when the LNG feed specification is met, the accumulation of impurities will gradually affect the operation of the MCHE over a long period of operation.

[0010] Initially, the deposited solid layer reduces the thermal efficiency of the heat exchanger, increasing the refrigerant load and pressure drop required to operate the entire unit. Eventually, the pressure drop may become insurmountable and affect the productivity of the entire plant, requiring shutdown. Figure 2a and Figure 2b A case study illustrating this phenomenon shows plant data for Plant 4 at the Las Vegas facility in Qatar over a period of 9 months (2014). The figures depict the pressure drop curves before the liquefaction unit and the C 5+ Composition specification and moisture specification. It should be noted that there is only one C 5+ An incident where the composition was out of specification and there was no evidence of water leakage. Although this was a seemingly harmless event, the MCHE needed to be shut down for the next several months. This period of unplanned downtime can negatively impact contract supply requirements and therefore result in significant financial penalties.

[0011] The discussion of the background to the invention is intended to facilitate understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of the invention. Summary of the invention

[0012] The present invention provides a device for directly detecting solids formation in a fluid under known pressure and temperature conditions. The present invention also relates to a system and method for repairing solids blockage in a cryogenic heat exchanger.

[0013] One aspect of the present invention provides a device for directly detecting solid formation in a fluid under known pressure and temperature conditions, the device comprising:

[0014] a container for receiving a fluid, wherein the container is provided with means for changing the temperature of the fluid in the container,

[0015] The container defines an electromagnetic resonant cavity operating at frequencies up to and including microwave frequencies and having resonant properties sensitive to the presence of a solid phase;

[0016] one or more probes for exciting and monitoring electromagnetic resonance of the cavity;

[0017] a pressure sensor and a temperature sensor, wherein the pressure sensor and the temperature sensor are used to sense the pressure and temperature of the fluid in the cavity, respectively; and

[0018] a signal processor operably connected to the pressure and temperature sensors and the one or more probes to directly detect solids formation in the fluid within the cavity in response to detected changes in the cavity resonant properties;

[0019] Wherein, the electromagnetic resonant cavity is defined by:

[0020] an upper portion and a lower portion defining a gap therebetween, the gap having resonant properties that are sensitive to the presence of a solid phase,

[0021] The upper or lower portion may be provided with a passage extending therethrough, the passage being in fluid communication with the inlet to allow a fluid flow into the gap to clear solids from the cavity after they have been formed.

[0022] In one embodiment, the lower portion is configured to define a well and facilitate solid formation in the well.

[0023] In one embodiment, the well is integrated with a coaxially aligned spigot extending through the lower portion, the spigot being made of a material having a higher thermal conductivity than the surrounding region of the lower portion, so that the spigot is able to provide a thermal gradient between the well and the surrounding region, thereby facilitating solid formation in the well.

[0024] In one embodiment, the lower portion defines a cylindrical sidewall terminating in an inclined bottom wall within a well, wherein the well is coaxially aligned with the cylindrical sidewall, and

[0025] The upper portion defines an annular top wall and a projection coaxially aligned with the well, wherein the gap is defined between the projection and the well.

[0026] In one embodiment, the protrusion may include a conical protrusion or a cylindrical protrusion.

[0027] In one embodiment, the channel may extend through the protrusion. In another embodiment, the channel may extend through the well. The channel extending through the protrusion or well may be a coaxial channel.

[0028] In one embodiment, the channels may be sized such that the fluid flow is directed to the gap.

[0029] In one embodiment, the resonant frequency of the cavity can be tuned by varying the size of the gap. In various embodiments, the gap can be less than 2 mm.

[0030] In one embodiment, the annular top wall may be provided with a plurality of apertures defining outlets for the outflow of fluid streams and ports for receiving one or more probes for exciting and monitoring the electromagnetic response of the cavity.

[0031] In one embodiment, the lower portion may be in heat exchange communication with a heat exchanger and / or a thermoelectric cooler to cool the resonant cavity.

[0032] In another embodiment, the plug may be in heat exchange communication with a second heat exchanger and / or a thermoelectric cooler.In use, the second heat exchanger may be arranged to cool the well to a temperature lower than the surrounding area of ​​the lower portion.

[0033] In one embodiment, the signal processor may be configured to directly detect solid formation in the fluid within the cavity by responding to a detected change in the dielectric constant (Δε) of the fluid within the cavity.

[0034] In one embodiment, the dielectric constant change (Δε) of the fluid can be calculated according to formula (1):

[0035] Δε=ε 测量 -ε 计算 , (1)

[0036] where, for known temperature and pressure, ε 计算 is the theoretical dielectric constant of the bulk fluid, ε 测量 Calculate according to formula (2):

[0037] ε测量 =(f 真空 / f 测量 ) 2 (2)

[0038] where, for known temperature and pressure, f 真空 is the electromagnetic resonance frequency of the cavity under vacuum, f 测量 is the electromagnetic resonant frequency of the cavity in the presence of fluid.

[0039] In one embodiment, the device may be capable of directly detecting the presence of solids in a cavity, wherein the solids comprise about 0.01 vol / vol % of the cavity. In particular, the device may be capable of directly detecting the presence of solids in a cavity, wherein the solids comprise about 0.001 vol / vol % of the cavity.

[0040]

[0013] In various aspects, the present invention also provides a system for preventing or repairing solids deposition in a cryogenic heat exchanger.

[0041] In one embodiment, the system comprises:

[0042] A low temperature heat exchanger is used to cool the fluid to a working temperature (T 液体 )

[0043] A sensor for directly detecting solid formation, wherein the sensor is configured to receive a fluid sample cooled or intended to be cooled by a cryogenic heat exchanger and to determine a temperature (T) corresponding to the temperature at which solids are formed in the fluid. 冻结 ) and ΔT 冻结 , where ΔT 冻结 =T 液体 -T 冻结 ;as well as

[0044] A controller is in operative communication with the cryogenic heat exchanger, whereby, in use, the controller is arranged to 冻结 When the temperature falls below a predetermined operating temperature margin, corrective measures are initiated to avoid solid deposits in the low temperature heat exchanger.

[0045] In one embodiment, the controller can be configured to increase or decrease the operating temperature (T 液体 ) or by initiating corrective action by introducing a repair fluid in a cryogenic heat exchanger.

[0046] In one embodiment, the system further comprises:

[0047] means for determining the composition of the fluid; and

[0048] A thermodynamic simulation program for solid-liquid equilibrium (SLE) calculations, which is set up to use T 冻结 and the fluid composition determined by the device to calculate the repair temperature (T 修复 );as well as

[0049] a temperature controller in operative communication with the controller to increase or decrease the operating temperature of the cryogenic heat exchanger to a repair temperature (T 修复 ).

[0050] In one embodiment, a temperature controller may be in operative communication with the cryogenic heat exchanger to vary the refrigeration load at one or more locations in the cryogenic heat exchanger to raise or lower the operating temperature to the repair temperature (T 修复 ).

[0051] In an alternative embodiment, the system further comprises:

[0052] means for determining the composition of the fluid; and

[0053] A thermodynamic simulation program for solid-liquid equilibrium (SLE) calculations, the program being configured to use (T 冻结 ) and the fluid composition determined by the device to calculate a repair composition capable of removing solids deposited in the cryogenic heat exchanger; and

[0054] A fluid metering device is in operative communication with the controller to introduce a remediation fluid into the cryogenic heat exchanger in an amount sufficient to obtain the remediation composition.

[0055] In various embodiments, as described above, a sensor that directly detects solid formation can include a device that includes an electromagnetic resonant cavity that operates at frequencies up to and including microwave frequencies and has resonant properties that are sensitive to the presence of a solid phase.

[0056] In one embodiment, the means for determining the composition of a fluid comprises a gas chromatograph.

[0057] In one embodiment, the system further comprises a second sensor as described above for directly detecting solids formation.The second sensor may be placed in fluid communication with the outlet of the cryogenic heat exchanger to monitor the effectiveness of the remediation.

[0058] In some embodiments, a second sensor is configured to receive a sample of the production fluid from an outlet of the cryogenic heat exchanger.

[0059] In another aspect, the present invention provides a method of preventing or repairing solid deposits in a cryogenic heat exchanger, the cryogenic heat exchanger being arranged to cool a fluid to an operating temperature (T液体 ) under the condition of liquid, the method comprising the following steps:

[0060] Directly detecting solid formation in a fluid sample cooled or intended to be cooled by a cryogenic heat exchanger and determining a temperature (T) corresponding to the temperature at which solids are formed in the fluid 冻结 ) and ΔT 冻结 , where ΔT 冻结 =T 液体 -T 冻结 ;and

[0061] When ΔT 冻结 When the temperature is less than a predetermined operating temperature margin, corrective measures for operating the cryogenic heat exchanger are initiated.

[0062] In one embodiment, initiating corrective action includes increasing or decreasing the operating temperature (T 液体 ).

[0063] In an alternative embodiment, initiating corrective measures includes introducing a repair fluid into the cryogenic heat exchanger.

[0064] In one embodiment, the method further comprises the following steps:

[0065] Determine the composition of the fluid;

[0066] Use (T 冻结 ) and the determined fluid composition to perform a solid-liquid equilibrium (SLE) calculation to calculate the repair temperature (T 修复 );as well as,

[0067] Increase or decrease the operating temperature of the low temperature heat exchanger to the repair temperature (T 修复 ).

[0068] In an alternative embodiment, the method further comprises the following steps:

[0069] Determine the composition of the fluid;

[0070] Use (T 冻结 ) and the determined fluid composition to perform a solid-liquid equilibrium (SLE) calculation to calculate a repair composition capable of dissolving solids deposited in the cryogenic heat exchanger; and,

[0071] The composition of the fluid in the cryogenic heat exchanger is adjusted to the repair composition.

[0072] In one embodiment, the step of detecting solid formation may be performed using a device for detecting solid formation as defined above.

[0073] In one embodiment, adjusting the composition of the fluid includes injecting an amount of a repair fluid into the fluid. In one embodiment, the repair fluid may include one or more hydrocarbon compounds that are capable of increasing the solubility of solids deposited in the cryogenic heat exchanger.

[0074] In one embodiment, the method further comprises monitoring the effectiveness of the remediation by sampling the produced fluid from the cryogenic heat exchanger and testing the produced fluid for solids formation.

[0075] In another embodiment, the process includes raising or lowering the operating temperature of the low temperature heat exchanger to the repair temperature T 修复 and / or prior to the remediation step of adjusting the composition of the fluid in the cryogenic heat exchanger to a remediation composition, the method comprises testing the remediation step in a device for detecting solids formation as defined above. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] Although any other forms may fall within the scope of the methods described in the Summary of the Invention, specific embodiments will now be described with reference to the following drawings:

[0077] Figure 1 The solid-liquid equilibrium phase diagram for changing the molar concentration of benzene in the natural gas fluid under the temperature conditions of a conventional low-temperature heat exchanger.

[0078] Figure 2a and Figure 2b The moisture content and C respectively were recorded in Las Vegas Plant 4 over a period of nine (9) months. 5+ content, and a graphical representation of the pressure drop.

[0079] Figure 3a and Figure 3b is an orthogonal cross-sectional representation of one embodiment of an apparatus for direct detection of solid formation, Figure 3c and Figure 3d A cross-sectional representation of an alternative embodiment of an apparatus for directly detecting solid formation.

[0080] Figure 4 Graph representation of a finite element analysis (FEA) simulation of the frequency response of one embodiment of the apparatus described herein with respect to varying amounts of benzene solids formation in LNG.

[0081] Figure 5a and Figure 5b Graph representation of the measured resonant frequency and fluid dielectric constant changes with temperature for a mixture of 100 ppm CO2 in methane, respectively.

[0082] Figure 6a and Figure 6b] are graphical representations of the measured changes in resonant frequency and fluid dielectric constant, respectively, as a function of temperature for a mixture of 100 ppm benzene in methane.

[0083] Figure 7 According to various embodiments of the present invention, the heat exchanger is configured relative to the low temperature heat exchanger. Figure 3a and Figure 3b Schematic partial representation of the apparatus described in .

[0084] Figure 8 is a schematic representation of an LNG processing plant integrated with a remediation system according to various embodiments of the present invention.

[0085] Fig. 9 A graphical representation of the resonant frequency measured versus temperature for a 4% solution of p-xylene in ethane.

[0086] Fig.10a ) is a graphical representation of the time to remove benzene solids as a function of the injected volume of three different repair fluids (mixed refrigerant (MR); isobutane (iC4); and n-pentane (n-C5)).

[0087] Fig.10b ) is a graphical representation of the variation of benzene solubility with injected volume of three different repair fluids (mixed refrigerant (MR); isobutane (iC4); and n-pentane (n-C5)). DETAILED DESCRIPTION

[0088] The present invention relates to an apparatus and method for detecting solids formation, particularly in a cryogenic heat exchanger, such as a cryogenic heat exchanger used in LNG production. The present invention also relates to a system and method for repairing a blockage in a cryogenic heat exchanger.

[0089] General terms

[0090] In this specification, unless otherwise expressly stated or the context requires otherwise, references to individual steps, compositions of matter, combinations of steps, or combinations of material ingredients shall be deemed to include both one and multiple (i.e., one or more) of these steps, compositions of matter, combinations of steps, or combinations of material ingredients. Therefore, as used herein, the singular forms "a", "an", and "the" include plural aspects unless otherwise expressly stated. For example, reference to "a" includes one and two or more; reference to "an" includes one and two or more; reference to "the" includes one and two or more, etc.

[0091] Unless expressly stated otherwise, each embodiment of the invention described herein is applicable to each other embodiment, mutatis mutandis. The scope of the invention is not limited by the specific embodiments described herein, which are intended for illustrative purposes only. Functionally equivalent products, compositions and methods are clearly within the scope of the invention described herein.

[0092] The term "and / or", such as "X and / or Y", should be understood to mean "X and Y" or "X or Y", and should be considered to provide clear support for both or either meanings.

[0093] In the present specification, the term "comprise" or variations thereof such as "include" or "comprising" will be understood to imply the inclusion of stated elements, integers or steps, or a combination of elements, integers or steps, but not the exclusion of any other elements, integers or steps, or a combination of elements, integers or steps.

[0094] Unless otherwise defined, all technical terms and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present invention belongs. Although methods and materials similar or equivalent to the methods or materials described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. In the event of a conflict, this specification (including definitions) shall prevail. In addition, materials, methods and embodiments are illustrative only and are not intended to be limiting.

[0095] As used herein, the term "about" means within 5%, more preferably within 1%, of a given value or range. For example, "about 3.7%" means 3.5% to 3.9%, preferably 3.66% to 3.74%. When the term "about" is associated with a numerical range, such as "about X% to Y%, the term "about" is intended to modify both the lower (X) value and the upper (Y) value of the range. For example, "about 20% to 40%" is equivalent to "about 20% to about 40%".

[0096] Specific terms

[0097] Solid is a fundamental state of matter in which atoms or molecules are closely packed together in a regular geometric lattice (crystalline solid) or irregularly (amorphous solid) and contain a minimum amount of kinetic energy. The term "solid formation" as used herein refers to a solid produced by a phase transition, such as a gas to solid phase transition or a liquid to solid phase transition, wherein the phase transition is caused by a change in pressure and / or temperature (particularly a decrease in temperature).

[0098] As used herein, the phrase "directly detect solid formation" refers to the ability to sense or measure a change in a physical property resulting from the presence of a solid resulting from a phase transition. Direct detection of solid formation can be distinguished from indirect detection of solid formation, where a device, instrument, or sensor is able to measure or sense a physical property, such as temperature or pressure, at which the formation of a solid due to a phase transition can be predicted or anticipated.

[0099] The term "cryogenic" used herein to describe heat exchangers refers to heat exchangers that are configured to operate at extremely low temperatures (about -140°C and lower) to liquefy one or more gases. Such cryogenic heat exchangers are commonly used in liquefied natural gas (LNG) production and the production of liquefied gases such as liquid nitrogen, liquid oxygen, liquid hydrogen, liquid helium, and liquid argon.

[0100] As used herein, the term "fluid" refers to a homogeneous gas mixture or a homogeneous liquid mixture, optionally with one or more trace impurities. A "trace impurity" is a compound present in a fluid at a concentration less than or equal to 3000 ppm.

[0101] Trace impurities may be "freezable compounds", in other words, compounds that are capable of forming solids at a temperature above the phase transition temperature of the fluid. Examples of "freezable compounds" in a fluid (e.g., natural gas) include, but are not limited to, water, acid gases (e.g., carbon dioxide and hydrogen sulfide), carbon disulfide, carbon oxysulfide, mercaptans (R-SH, where R is an alkyl group having 1 to 20 carbon atoms), sulfur dioxide, sulfur-containing aromatic compounds, and heavy hydrocarbons including aromatic hydrocarbons (e.g., benzene, toluene, xylene, naphthalene, etc.). The term 'heavy hydrocarbons' as used herein may be represented by the symbol 'C 5+ ', and refers to a hydrocarbon having a carbon chain or carbon backbone containing five (5) or more carbon atoms. Other examples of freezable compounds may include waxes.

[0102] It will also be understood by those skilled in the art that two or more compounds may potentially combine to form a clathrate, which may also be a "freezable compound." For example, methane hydrate is a clathrate comprising methane and water that solidifies at a temperature higher than the solid formation temperature of either methane or water.

[0103] The term "bulk fluid," used alone or in combination with "composition" or "property," refers to the fluid excluding one or more trace impurities, or the composition or property of the fluid in the absence of one or more trace impurities.

[0104] The term "operating temperature margin" used herein in relation to a cryogenic heat exchanger means the allowable difference in the temperature at which the cryogenic heat exchanger can operate. The allowable difference may vary depending on the size and type of the cryogenic heat exchanger and the bulk fluid composition of the fluid cooled in the cryogenic heat exchanger, and may be predetermined using a thermodynamic simulation program (described below) for solid-liquid equilibrium (SLE) calculations.

[0105] The term 'repair fluid' as used herein may refer to a gas or liquid comprising a compound or a mixture of two or more compounds capable of removing solids deposited in a cryogenic heat exchanger. The one or more compounds in the repair fluid may be capable of increasing the solubility of solids in a fluid passing through a cryogenic heat exchanger by changing the composition of the fluid. Alternatively, the one or more compounds in the repair fluid may be capable of changing the conditions of solid-liquid equilibrium in the cryogenic heat exchanger so that the solid undergoes a solid-liquid phase transition or a solid-gas phase transition. In some embodiments, the one or more compounds may be hydrocarbon compounds.

[0106] Device for direct detection of solid formation

[0107] Embodiments described herein generally relate to a device for directly detecting solid formation in a fluid. In particular, various embodiments relate to a device configured to detect solid formation in a fluid containing a freezable compound.

[0108] Although the present invention is made in the context of LNG production, it will be appreciated that the present invention has general application in the cryogenic production of other gases and liquids where it is undesirable for impurities in the fluid to form solids. Other examples of general application principles to which the apparatus described herein may have include, but are not limited to, the production of liquefied gases (e.g., nitrogen, argon, hydrogen, or helium); determination of hydrate formation temperatures in gas (and oil) production systems; determination of wax formation temperatures in gas (and oil) production, etc.

[0109] refer to Figure 3a-3d (wherein like numbers refer to like features throughout), various embodiments of an apparatus 10 for directly detecting solid formation are shown. The apparatus 10 includes a cylindrical pressure vessel 12, which includes a lower portion 14, which is sealingly coupled to an upper portion 16 by a plurality of fasteners 18 and seals 20 (e.g., O-rings). In use, the lower portion 14 and the upper portion 16 define an electromagnetic resonant cavity 22. The electromagnetic resonant cavity 22 operates at frequencies up to and including microwave frequencies and has a resonant property that is sensitive to the presence of a solid phase (described below).

[0110] With respect to the electromagnetic resonant cavity 22, the lower portion 14 defines a cylindrical sidewall 24 and an inclined bottom wall 26, which terminates in a coaxially aligned flat bottom well 28. The upper portion 16 defines an annular top wall 30 and a conical protrusion 32, which extends to the cavity 22 and terminates in a plane 34 coaxially aligned with the flat bottom well 28, and the gap 36 between the plane 34 and the flat bottom well 28 is 2 mm or less. It should be understood that the size of the gap 36 is selected to obtain a balance between sensitivity in operation (which is enhanced by a smaller gap) and robustness. A gap that is too small may be contaminated or blocked by small solid metal particles that can pass through an upstream filter. In addition, the stability of the baseline frequency (i.e., the frequency under vacuum conditions) of the resonant cavity 22 may be adversely affected by vibration or displacement of the gap size over time. In one embodiment, the gap 36 can be 0.1 mm to 2 mm.

[0111] Freezing is a random phenomenon that can be manifested by thermal and compositional driving forces and the presence of favorable nucleation sites. In various embodiments, the resonant cavity 22 is configured to facilitate solid formation in the well 28. For example, the respective inclination angles of the inclined bottom wall 26 and the tapered protrusion 32 are set to promote fluid flow toward the well 28. Similarly, the respective joints between the cylindrical side wall 24 and the inclined bottom wall 26 of the lower portion 14 and the annular top wall 30 and the tapered protrusion 32 of the upper portion 16 can be curved or inclined to avoid stagnant areas and promote flushing of the resonant cavity 22. It should also be understood that the respective surfaces of the inclined bottom wall 26 and the tapered protrusion 32 can be highly polished to prevent solid formation thereon.

[0112] Furthermore, the lower portion 14 may be made of a thermally conductive material, such as stainless steel or aluminum. It may be advantageous for the thermally conductive material of the well 28 or its vicinity to have the same or similar material properties as the associated portions of the cryogenic equipment, such as the cryogenic heat exchanger. Figure 3a In the illustrated embodiment, for example, the lower portion 14 is provided with a plug 28a extending through the lower portion 14 in coaxial alignment with the tapered protrusion 32, wherein the front surface of the cylindrical plug 28a defines the well 28. The plug 28a may be made of a thermally conductive material different from that of the lower portion 14, such as copper. In particular, the plug 28a may be made of a material having a higher thermal conductivity than the lower portion 14 (particularly, higher than the portion of the lower portion 14 surrounding the well 28). The difference in thermal conductivity between the lower portion 14 and the plug 28a amplifies the temperature gradient therebetween, thereby creating a local "cold spot" in the well 28 where solids are preferentially formed. In other words, a thermal gradient may be established between the well 28 and the surrounding area to favor the formation of solids in the well 28.

[0113] The lower portion 14 may also be provided with a device for controlling its temperature, thereby facilitating solid formation in the trap 28. For example, the lower portion 14 may be in heat exchange communication with a liquid nitrogen heat exchanger (not shown). Such liquid nitrogen cooling allows the resonant cavity 22 to be cooled to temperature conditions comparable to cryogenic gas processing conditions (e.g., 90-130K). In some embodiments, the liquid nitrogen heat exchanger may be combined with resistive heating to control the temperature of the electromagnetic resonant cavity 22.

[0114] Additionally, or alternatively, the device 10 may be provided with a thermoelectric cooler (eg, a Peltier device) to cool the lower portion 14 (particularly near the well 28) to a desired temperature range.

[0115] The plug may also be arranged in heat exchange communication with a second heat exchanger and / or thermoelectric cooler (not shown). In use, the second heat exchanger and / or thermoelectric cooler may be arranged to cool the well 28 to a temperature lower than that of the portion of the lower portion 14 surrounding the well 28.

[0116] In some embodiments, resistive heating may also be provided to the cylindrical sidewall 24 of the cavity 22 to establish a thermal gradient therein and ensure that the well 28 is "colder" than any other area of ​​the cavity 22. The arrangements described in these specific embodiments are equally useful in the absence of the plug 28a as described above.

[0117] The lower portion 14 may be provided with a plurality of calibrated thermometers or thermistors, such as platinum probes, which may be positioned relative to the resonant cavity to monitor the temperature therein. For example, a first thermistor 38 may be provided in the lower portion 14 near the well 28 and may be used to infer the temperature (T ) at which the solid is formed. 冻结 ). A second thermistor 40 may be disposed proximate the cylindrical sidewall 24 to measure the magnitude of the temperature gradient present in the resonant cavity 22. Another thermistor 42 may also be disposed in the base of the lower portion 14 to monitor the control temperature of the device 10.

[0118] In one embodiment, if Figure 3a As shown, the conical protrusion 32 of the upper portion 16 is provided with an inlet 44 in fluid communication with a coaxial passage 46 extending through the conical protrusion 32 to allow a fluid sample to enter the electromagnetic resonant cavity 22 to study its phase behavior and measure T 冻结 The size of the passage 46 allows the fluid to flow directly to the gap 36 without affecting the electromagnetic field distribution in the cavity 22 .

[0119] In an alternative embodiment, Figure 3c and 3d As shown, an inlet 44 is disposed in the lower portion 14. A passage 46 is disposed in fluid communication with the inlet 44 and extends through the lower portion 14. Figure 3cIn the embodiment shown, the channel 46 extends coaxially with respect to the well 28 .

[0120] Advantageously, passage 46 terminates in gap 36 between well 28 and flat surface 34 of conical protrusion 32, thereby allowing fluid flow to enter to clear solids from gap 36 after solids formation. In this manner, cavity 22 can be effectively restored to baseline conditions after a solids formation detection event.

[0121] The annular top wall 30 of the upper part 16 is also provided with a plurality of holes defining outlets 48 for fluid outflow and a port 50 for receiving one or more microwave probes 52 for exciting and monitoring the electromagnetic response of the cavity 22. The microwave probe 52 may include any suitable electromagnetic resonance sensor or network analyzer, and the electromagnetic resonance sensor includes but is not limited to a frequency discriminator circuit (separated or integrated with an oscillator circuit), a radio frequency (RF) source, and a power detector. The electromagnetic signal may be transmitted through the resonant cavity 22 or reflected from the resonant cavity 22 via a position located in an appropriate field strength region. Therefore, the resonant frequency may be measured by a transmission or reflection operation mode. In a preferred embodiment, the resonant frequency is measured by transmission because the signal quality is better. However, it should be noted that the transmission mode requires two seals, while the reflection mode requires one seal. Therefore, from the perspective of reducing the possibility of leakage of high-pressure fluid that may occur in the cavity 22, the reflection mode is more robust.

[0122] The device 10 may be in operative communication with a processor and controller (not shown) for data acquisition, resonant frequency measurement, thermal control, flow control, and generating real-time data analysis of key parameters including, but not limited to, resonant frequency, temperature, and pressure.

[0123] The gap 36 between the plane 34 of the conical protrusion 32 and the well 28 defines a capacitive region to concentrate the electric field therein, thereby making the resonant frequency of the cavity 22 highly sensitive to the dielectric constant (ε) of the material in the gap 36. Those skilled in the art will appreciate that the frequency of the resonant cavity 22 can be tuned by varying the size of the gap 36.

[0124] The measured resonant frequency (f0) is related to ε according to the following equation:

[0125]

[0126] The vacuum frequency (f 真空 ).

[0127] Various electromagnetic models, analytical and / or numerical methods may be used to predict the resonant modes of cavity 22. For example, in this particular embodiment, finite element analysis (FEA) may be used to solve the electromagnetic field equations so that the frequency response of dielectric constant changes (e.g., changes associated with fluid phase transitions) is accurately modeled.

[0128] The geometry of the embodiment described with reference to the drawings shows a first resonant mode at ~2.6 GHz in a vacuum. The electric field distribution of this mode exhibits high electric field strength in the gap 36 between the conical protrusion 32 and the well 28. The frequency measured with this mode is almost entirely determined by the dielectric properties of the fluid (or solid) in this region. FEA shows that the presence of a small amount of solid in the gap 36 can produce a signal response that can be resolved and detected.

[0129] For example, FEA simulations of benzene freezing in LNG can predict the minimum detectable solid volume in the trap 28 . Figure 4 The expected frequency shift is shown as a function of the amount of benzene present in the gas sample when cooling in the well 28 of the cavity 22 until the benzene solidifies. Extrapolation of the trend line shows that the presence of only 1 ppm of benzene can cause a detectable 50 kHz shift in the resonant frequency. Example 1 (described later) shows the ability to detect solids occupying only 0.0001 vol / vol % of the volume of the cavity 22.

[0130] In use, a fluid flow may enter the electromagnetic resonant cavity 22 via the inlet 44 through the passage 46. The electromagnetic resonant cavity 22 is then cooled at a constant pressure within a temperature range that includes the solid-liquid equilibrium region or the solid-gas equilibrium region to directly detect solid formation.

[0131] At the same time, the electromagnetic resonant cavity 22 is excited by the microwave radiation of the microwave probe 52, and the response (ie, the resonant frequency) of the cavity 22 is measured.

[0132] Typically, the resonant frequency of the cavity 22 responds approximately linearly to temperature, with changes in the slope indicating solid formation in the cavity 22, and particularly in the well 28. Frequency signatures representative of solid formation generally result in a rapid decrease in frequency, although exceptions to this trend may occur depending on the composition and morphology of the solid formed. The measurement of the resonant frequency allows relatively small changes in the resonant behavior of the cavity to be detected.

[0133] After a solids formation event, solids may be cleared from trap 28 and cavity 22 by directing fluid flow through inlet 44 through passage 46. Fluid flows out of cavity 22 through outlet 48.

[0134] It will be appreciated by those skilled in the art that the solidification temperature (T) of a fluid or bulk fluid component can be determined using thermodynamic simulation programs for solid-liquid equilibrium (SLE) calculations.冻结 ). Such thermodynamic simulation programs include, but are not limited to, multi-flash or thermodynamic calculation programs implemented in the multiphase flow simulation programs OLGA, LedaFlow, HyFAST, and CryoFAST. Particularly suitable examples include ThermoFAST, which was developed specifically for predicting solid-liquid transitions in hydrocarbon mixtures. This thermodynamic simulation program has been recognized by the Gas Processor Association Midstream organization as a useful prediction tool for thermodynamic properties of natural gas and LNG systems containing solid-liquid equilibrium.

[0135] Advantageously, the curing temperature (T 冻结 ), the apparatus 10 for directly detecting solid formation as described above can be easily used to more accurately determine the solidification temperature (T 冻结 ).

[0136] However, in some dynamic systems where the bulk fluid is cooled, potential changes in the dielectric properties of the bulk fluid may mask the deviations in the resonant frequency caused by the solid formation of the freezable compound. This is particularly applicable to fluids with trace impurities, where the amount and rate of solid formation may be low. Although not wishing to be bound by theory, the inventors also believe that the crystal morphology of certain freezable compounds may also play a role in this "masking phenomenon".

[0137] The inventors have found that according to the following formula (1), the dielectric constant change (Δε) of the fluid can be measured (which is the theoretical dielectric constant (ε) of the bulk fluid). 计算 ) and the dielectric constant of the measured fluid (ε 测量 ) to overcome this "masking phenomenon" bulk fluid:

[0138] Δε=ε 测量 -ε 计算 , (1)

[0139] According to the following formula (2), the dielectric constant (ε 测量 ) can be calculated based on the electromagnetic resonance frequency (f 测量 ) relative to the electromagnetic resonance frequency of the cavity measured under vacuum (f 真空 ) to calculate.

[0140] ε 测量 =(f 真空 / f 测量 ) 2 (2)

[0141] The theoretical dielectric constant (ε) of the bulk fluid can be calculated under known conditions of temperature and pressure using thermodynamic simulation programs for solid-liquid equilibrium calculations as described above (particularly ThermoFAST software). 计算 ).

[0142] By directly measuring the dielectric constant (ε 测量 ) minus the theoretical dielectric constant (ε) of the bulk fluid 计算 ), the measurement of the dielectric constant change (Δε) of the fluid eliminates the systematic effect of changing the dielectric properties of the bulk fluid, and the theoretical dielectric constant (ε 计算 ) is calculated using fluid property software and the measured temperature and pressure. The directly measured dielectric constant (ε 测量 ) is calculated from the frequency shift of the cavity resonance measured under vacuum from the cavity's baseline frequency. Using this zeroing measurement algorithm, the presence of solids is identified as a deviation from the zero or baseline value.

[0143] Curing temperature T 冻结 It can be determined as the temperature at which the dielectric constant change (Δε) of the fluid deviates from the baseline value. This determination T 冻结 The method is also more accurate than the above thermodynamic simulation program. In particular, the solidification temperature T is determined by measuring the change in the dielectric constant (Δε) of the fluid. 冻结 The curing temperature T is determined by measuring the resonance frequency of the cavity. 冻结 Consistent.

[0144] Now refer to Figure 5a , Figure 5b , Figure 6a and Figure 6b The method of cooling a fluid containing a freezable solid in an apparatus 10 as described above and determining T by measuring the resonant frequency of the cavity or the change in the dielectric constant (Δε) of the fluid is described. 冻结 .

[0145] refer to Figure 5a and Figure 5b , the liquefaction temperature of pure methane at 9.5 MPa and the solidification temperature T of a mixture of 100 ppm CO2 in methane predicted by SLE calculation using ThermoFAST 冻结 They are 90.9K and 103.5K respectively.

[0146] The mixture was cooled from 110 K to 96 K at a rate of 1 K / min and then kept constant. Figure 5a shows a deviation from the linear relationship between temperature and the measured resonant frequency of the cavity at 97 K, which shows that at T 冻结 = 97.0 K, a clear signal of solid formation (indicated by the asterisk). Similarly, Figure 5bThe change in the dielectric constant (Δε) of the fluid at 97.0K deviates from the baseline value, which shows that the T 冻结 = 97.0 K, a clear signal of solid formation (indicated by the asterisk). Both measurements agree with the visual identification of solid formation at 95.5 K for the same mixture at 10 MPa. In particular, the T determined by both methods 冻结 The same as and higher than the T predicted by ThermoFAST 冻结 6.5K low.

[0147] refer to Figure 6a and Figure 6b , the liquefaction temperature of pure methane at 9.5 MPa and the solidification temperature T of a mixture of 100 ppm benzene in methane predicted by SLE calculation using ThermoFAST 冻结 They are 90.9K and 149.7K respectively.

[0148] The mixture was cooled from 148 K to 134 K at a rate of 1 K / min and then kept constant. Figure 6a It is shown that even in the presence of solids, there is no deviation from the linear relationship between temperature and the resonant frequency of the cavity measured over the temperature range, making it impossible to identify T 冻结 .on the other hand, Figure 6b The change in the dielectric constant (Δε) of the fluid at 140.1K deviates from the baseline value, which shows that at T 冻结 = 140.1 K, a clear signal of solid formation (indicated by an asterisk). The measured T 冻结 T than predicted by ThermoFAST 冻结 9.6K low.

[0149] The device 10 can be generally used to determine the pressure and / or temperature at which solids are formed in a fluid of uncertain composition. In particular, the device can be used to determine the temperature at which solids are formed when contaminated natural gas passes through a cryogenic heat exchanger, thereby determining the operating temperature to avoid solid blockage in the cryogenic heat exchanger.

[0150] For example, the apparatus 10 can be conveniently configured relative to a cryogenic heat exchanger to provide real-time measurement of a feed fluid sample and detect solid formation and determine the solidification temperature (T) directly before the feed fluid enters the cryogenic heat exchanger. 冻结 ). Figure 7 The discharge tube shown (described below) directs the feed fluid sample to the device 10. Measurements can be made intermittently or nearly continuously to determine (T 冻结 ) in absolute terms, or in relative terms to compare multiple samples studied over a predetermined period of time. For example, (T 冻结) over time may indicate changes in feed fluid composition or inefficiencies in upstream units (e.g., heavy hydrocarbon removal units). In addition, the magnitude of the signal response to solidification can also provide operators with qualitative indications related to the severity of downstream solids formation.

[0151] System and method for preventing or repairing solid deposits in cryogenic heat exchangers

[0152] In LNG production, there are practical difficulties in measuring the specific composition of heavy hydrocarbons in the natural gas entering the main cryogenic heat exchanger ('MCHE'), and therefore determining whether the fluid contains significant amounts of freezable compounds. As a result, LNG plants are typically operated with a large safety margin to avoid potential solids deposition on the MCHE. This safety margin is of an 'open loop' nature.

[0153] The disclosed apparatus for direct detection of solids formation in fluids enables measurement and control of previously inaccessible operating parameters: ΔT 冻结 . Solid formation temperature T 冻结 It can be obtained by taking a sample of a fluid cooled or intended to be cooled by a cryogenic heat exchanger and then gradually reducing the temperature of said sample until solid formation is detected. Parameter ΔT 冻结 is the operating temperature T of the low temperature heat exchanger 液体 and T 冻结 The difference between 冻结 =T 液体 -T 冻结 ).

[0154] Integration of the device described in this article into an LNG plant can reduce the ΔT 冻结 Monitor the ΔT 冻结 Corrective measures are initiated when a predetermined operating margin is deviated from. The predetermined operating margin may be 1K to 20K, or 1K to 10K, or even 2K to 5K. The margin may vary depending on the historical stability of the cryogenic process. In this way, ΔT may be controlled in a closed loop manner. 冻结 .

[0155] ΔT 冻结 Reliable knowledge of the variation relative to predetermined operating margins and the likelihood of solids deposition in the MCHE enables the operation of various units in the LNG plant that remove impurities prior to the MCHE (e.g., the heavy hydrocarbon removal unit) to be less conservative. This means that less gas is burned to provide the energy required to remove the impurities, thus improving the overall efficiency of the plant, and a greater proportion of the gas entering the plant can be liquefied.

[0156] refer to Figure 7 and Figure 8, in accordance with various aspects of the present invention, a system 100 for remediating solid deposits in a cryogenic heat exchanger integrated with a natural gas liquefaction system 200 ("remediation system 100") is shown. The natural gas liquefaction system 200 described herein is for illustrative purposes only, and it should be understood that various embodiments of the remediation system 100 may be similarly integrated into an alternative natural gas liquefaction system 200 to facilitate remediation of solid deposits. Furthermore, it should be understood that the remediation system 100 may be similarly integrated into a cryogenic gas liquefaction system for gases other than natural gas (e.g., hydrogen) where the concentration of impurities (e.g., water, carbon dioxide, carbon monoxide, or nitrogen) may be high enough to present a risk of solids forming within the cryogenic heat exchanger.

[0157] The raw gas is introduced into the compressor 202 of the natural gas liquefaction system 200 via pipeline 1, where the raw gas is compressed and then cooled with propane refrigerant. Then, the cooled compressed raw gas is fed to a compressor 202 for separating and removing condensed heavy hydrocarbons (C 5+ ) of the washing tower 204. The depleted C 5+ The overhead vapor product is sent to compressor 206, where it is compressed and then cooled with propane refrigerant. The compressed overhead vapor product is sent to separator 208 via line 7 to remove any condensed liquid hydrocarbons, which are then returned to scrubber 204 via line 9.

[0158] The overhead vapor product ("gas stream") of separator 208 is then passed via line 11 to C 5+ Analyzer 110. C 5+ Analyzer 110 may be a gas chromatograph or any other suitable analyzer capable of determining the cumulative content of heavy hydrocarbon compounds in a gas stream. Additional analyzers (not shown) may also be provided to monitor the concentration of other freezable compounds (e.g., water) that may freeze at low temperatures but cannot be monitored by a gas chromatograph. It should be understood that C 5+ The analyzer 110 may not be able to determine any specific C 5+ However, it should be understood by those skilled in the art that this C 5+ The analyzer 110 may be capable of providing an estimate of the content of freezable hydrocarbon compounds (eg, benzene content) and providing information about the composition of the gas stream.

[0159] The gas stream may then be sent via line 11 to a cryogenic heat exchanger 210 where cooling is provided by one or more refrigerants (including a mixed refrigerant) where the gas stream is cooled to an operating temperature (T ) equal to or lower than the temperature at which hydrocarbons in the overhead vapor product condense. 液体). Preferably, the gas stream is cooled to a temperature below the boiling point of methane under pressure, for example, a temperature between about -140°C and -150°C. The liquefied stream may be further expanded and cooled to about -162°C and atmospheric pressure for storage purposes.

[0160] In addition, before entering the low temperature heat exchanger 210, a small amount of gas flow can be sent to the device 10 for detecting solid formation in the fluid via the side pipeline 13. As mentioned above, the device 10 can be used to directly detect solid formation and determine the solidification temperature (T 冻结 ).

[0161] The detection of solids in the sample may indicate that solids have formed (or will form) in the cryogenic heat exchanger 210. Thus, the formation of solids in the apparatus 10 may be correlated to the formation of solids in the cryogenic heat exchanger 210.

[0162] The system 100 of the present invention may also include a thermodynamic simulation program for solid-liquid equilibrium (SLE) calculations. Such thermodynamic simulation programs will be well understood by those skilled in the art, and include, but are not limited to, multi-flash or thermodynamic calculation programs implemented in multiphase flow simulation programs OLGA, LedaFlow, HyFAST, and CryoFAST. Particularly suitable examples include ThermoFAST, which was developed specifically for predicting solid-liquid transitions in hydrocarbon mixtures. This thermodynamic simulation program has been recognized by the Gas Processor Association Midstream organization as a useful prediction tool for thermodynamic properties of natural gas and LNG systems containing solid-liquid equilibrium.

[0163] The composition of the gas stream measured by gas chromatography (including C 5+ The content) can be used in a thermodynamic simulation program to determine the repair composition that can remove the solids deposited in the cryogenic heat exchanger 210. In other words, the thermodynamic simulation program will determine the characteristics of the solvent that can dissolve the freezable compound of interest or cause a change in the fluid composition, thereby changing the conditions of the SLE to cause the deposited solids to undergo a solid-liquid phase transition or a solid-gas phase transition.

[0164] The solidification temperature (T 冻结 ) can be used in a thermodynamic simulation program to determine the repair temperature (T 修复 ).

[0165] The repair system 100 may further include a temperature controller (not shown) for the low temperature heat exchanger 210 to increase or decrease the operating temperature of the low temperature heat exchanger 210 to a repair temperature (T 修复The temperature controller may be operatively connected to the cryogenic heat exchanger 210 to change the refrigeration load at one or more locations in the cryogenic heat exchanger 210, thereby raising or lowering the operating temperature to the repair temperature (T 修复 ). Counterintuitively, in some embodiments, lowering the operating temperature of the cryogenic heat exchanger 210 may help remove solids within the cryogenic heat exchanger 210 (i.e., "reverse" melting) rather than increase solid deposition, because the solubility of deposited solids in the fluid in the cryogenic heat exchanger 210 may increase as the temperature decreases.

[0166] Alternatively, or in addition, the remediation system 100 may also include a remediation fluid metering device 120 to adjust the composition of the fluid in the cryogenic heat exchanger to the remediation composition. The composition of the fluid may be adjusted to the remediation composition by injecting a certain amount of remediation fluid into the gas stream before entering the cryogenic heat exchanger 210. The remediation fluid may be injected continuously or intermittently or periodically until the solids have been removed from the cryogenic heat exchanger 210.

[0167] The repair fluid may include one or more hydrocarbon compounds that, when added to the gas stream, will increase the solubility of the freezable compound. It should be understood that the composition of the repair fluid will vary depending on the composition of the gas stream and the operating conditions of the cryogenic heat exchanger 210. However, it is contemplated that the repair fluid may be derived from a hydrocarbon fluid that is readily available on site, including but not limited to a refrigerant (e.g., propane refrigerant, heavy mixed refrigerant, light mixed refrigerant) or a product fluid (e.g., ethane, LPG, and light condensate, etc.).

[0168] The introduction of the repair fluid into the gas stream will inherently temporarily change the composition, and therefore the energetic properties, of the LNG produced in the cryogenic heat exchanger 210. Significant changes in the composition of the LNG (particularly if the LNG composition is "out of specification") may require the recovery or flaring of the LNG. It is expected that the economic losses associated with flaring will be insignificant compared to the losses incurred by a complete plant shutdown to remove the solids plug (which may take several days).

[0169] The remediation system 100 may optionally include another device 10' for detecting solid formation, the device 10' being in fluid communication with the outlet 212 of the cryogenic heat exchanger 210 to monitor the effectiveness of the remediation process. A sample of the output fluid from the outlet 212 of the cryogenic heat exchanger 210 may pass through the device 10', and the behavior of the output fluid with respect to solid formation may be studied within the operating temperature range of the cryogenic heat exchanger 210. The presence (or absence) of solid formation in the device 10' may be related to the progress of the remediation process within the cryogenic heat exchanger 210, the presence of solid formation in the device 10' indicating the need to continue the remediation process, and the absence (or abortion) of solid formation in the device 10' indicating the success or completion of the remediation process.

[0170] The effectiveness of the remediation process may also be monitored by measuring the pressure drop within the cryogenic heat exchanger 210, whereby a reduction in the pressure drop may indicate the removal of solids deposited therein.

[0171] It should be understood that when adjusting the raw gas composition to the repair composition or raising or lowering the working temperature to the repair temperature (T 修复 ), before implementing repair measures on the low-temperature heat exchanger 210, such repair measures can first be tested in the device 10 for detecting solid formation to ensure the effectiveness of such repair measures.

[0172] Various embodiments can be illustrated by the following examples. The examples are provided for illustrative purposes only and should not be construed as limiting the scope or content of the present invention in any way.

[0173] Example 1

[0174] The electromagnetic resonant cavity 22 of the apparatus 10 described herein was filled with a sample of a 4% p-xylene, 96% ethane fluid and then cooled from -60°C to -82°C at a constant pressure while the resonant frequency response of the cavity was measured.

[0175] Fig. 9 Shown in T 冻结 A shift of 76 MHz was observed at -76°C at the onset of solid formation, which is consistent with the FEA simulation. The minimum frequency shift that can be resolved is about 25 kHz, which, by extrapolation, indicates a sensitivity to ~3 ppm molar p-xylene solids. The FEA modeling of the cavity 22 can be combined with this data to estimate the minimum solid volume that the apparatus 10 can unambiguously detect. For the ethane p-xylene system, the apparatus 10 can detect a solid volume equivalent to 0.0001 vol / vol % of the volume of the cavity 20. This is important considering the relatively small differences in the dielectric properties of hydrocarbon liquids and solids.

[0176] Example 2

[0177] Example 2 illustrates a case study of the remediation of benzene solid deposition after the addition of three different remediation fluids (mixed refrigerant (MR), isobutane (iC4) and neopentane (n-C5)) to the gas stream of a cryogenic heat exchanger. The results are based on the solubility of benzene in the remediation composition predicted by the thermodynamic simulation tool ThermoFAST. The case study involved the deposition of 1 kg of benzene solids in the cryogenic heat exchanger, and the composition and flow rate of the gas stream were similar to the composition and flow rate experienced by the Las Vegas 4 plant before the blockage event in November 2014. Table 2 provides the composition of the gas stream under normal operating conditions of the LNG plant. The average mass flow rate through the cryogenic heat exchanger was 146 kg / s and the coldest effluent temperature was 124K.

[0178] Table 2: Estimation of the molar composition of the natural gas components in the gas stream fed to the main cryogenic heat exchanger during normal operation of the Las Vegas plant.

[0179]

[0180]

[0181] Fig.10a ) shows the time of repair fluid addition required to remove benzene deposits per volume percent of each component added. It can be seen that some repair fluids perform better in dissolving benzene per unit volume, however, the best choice will depend on the price and availability of the repair fluid. Despite the worst performance on a volume basis, mixed refrigerant fluids are readily available and stored in large quantities in LNG plants.

[0182] Fig.10b ) graphically represents the solubility of benzene in the components of the conditioned gas stream after the addition of the repair fluid. Intuitively, the solubility of benzene increases with the amount of repair fluid added, however, the amount added by the operator will be limited by the plant's ability to handle the additional mass flow through its unit operations.

[0183] It will be appreciated by those skilled in the art that various modifications and / or changes may be made to the above embodiments without departing from the general scope of the invention. Therefore, the present embodiments are to be considered in all aspects as illustrative and not restrictive.

[0184] In the following claims and the foregoing description, unless the context requires otherwise due to express language or necessary implication, the term "comprise" or variations such as "include" or "contains" are used in an open manner, meaning the presence of the features described in various embodiments of the invention, but not excluding the presence or addition of other features.

Claims

1. A device for directly detecting solid formation in a fluid under known pressure and temperature conditions, the device comprising: a container for receiving a fluid, wherein the container is provided with means for changing the temperature of the fluid in the container, The container defines an electromagnetic resonant cavity operating at frequencies up to and including microwave frequencies and having resonant properties sensitive to the presence of a solid phase; one or more probes for exciting and monitoring electromagnetic resonance of the cavity; A pressure sensor and a temperature sensor, wherein the pressure sensor and the temperature sensor are used to sense the pressure and temperature of the fluid in the cavity respectively; as well as a signal processor operably connected to the pressure sensor and the temperature sensor and the one or more probes to directly detect solid formation in the fluid within the cavity by responding to the detected change in dielectric constant Δε of the fluid within the cavity; The dielectric constant change Δε of the fluid is calculated according to the following formula: No = yes 测量 -e 计算 , (1) where, for known temperature and pressure, ε 计算 is the theoretical dielectric constant of the bulk fluid, ε 测量 Calculate according to formula (2): e 测量 =(f 真空 / f 测量 ) 2 (2) where, for known temperature and pressure, f 真空 is the electromagnetic resonance frequency of the cavity under vacuum, f 测量 is the electromagnetic resonance frequency of the cavity in the presence of fluid; Wherein, the electromagnetic resonant cavity is defined by: The upper and lower portions define a gap therebetween, the gap having resonant properties sensitive to the presence of a solid phase, wherein the upper or lower portion is provided with a channel extending therethrough, the channel being in fluid communication with the inlet for allowing a fluid flow to enter the gap to purge solids from the cavity after they are formed.

2. The device as defined in claim 1, wherein: The lower portion is configured to define a well and facilitate solid formation in the well.

3. The device as defined in claim 2, wherein: The well is integrated with a coaxially aligned plug extending through the lower portion, the plug being made of a material having a higher thermal conductivity than the surrounding region of the lower portion so that the plug is able to provide a thermal gradient between the well and the surrounding region to facilitate solid formation in the well.

4. The device as defined in claim 2, wherein: The lower portion defines a cylindrical sidewall and an inclined bottom wall terminating in a well, wherein the well is coaxially aligned with the cylindrical sidewall, and The upper portion defines an annular top wall and a projection coaxially aligned with the well, wherein the gap is defined between the projection and the well.

5. The device as defined in claim 1, wherein: The dimensions of the channel are such that the fluid flow is directed to the gap.

6. The device as defined in claim 4, wherein: A channel extends through the protrusion or a channel extends through the well.

7. The device as defined in claim 1, wherein: The resonant frequency of the cavity is tuned by varying the size of the gap.

8. The device as defined in claim 3, wherein: The lower portion is in heat exchange communication with a heat exchanger and / or a thermoelectric cooler to cool the resonant cavity.

9. The device as defined in claim 8, wherein: The plug is in heat exchange communication with a second heat exchanger and / or a thermoelectric cooler which, in use, is arranged to cool the well to a temperature below that of the lower surrounding region.

10. A system for preventing or repairing solid deposits in a cryogenic heat exchanger, the system comprising: A low temperature heat exchanger is used to cool the fluid to a working temperature T 液体 Liquid under A device for directly detecting the formation of solids in a fluid as defined in claim 1, wherein the device is configured to receive a fluid sample cooled or intended to be cooled by a cryogenic heat exchanger and to determine a temperature T corresponding to the temperature at which solids are formed in the fluid. 冻结 and ΔT 冻结 , where ΔT 冻结 =T 液体 -T 冻结 ; as well as A controller is in operative communication with the cryogenic heat exchanger, whereby, in use, the controller is arranged to 冻结 Initiate corrective action when temperature falls below a predetermined operating temperature margin.

11. A system as defined in claim 10, wherein: The controller is configured to increase or decrease the operating temperature T of the low temperature heat exchanger by 液体 Or initiate corrective action by introducing repair fluid in the cryogenic heat exchanger.

12. The system as defined in claim 10, further comprising: a device for determining the composition of a fluid; Thermodynamic simulation program for solid-liquid equilibrium (SLE) calculations, the program is set up to use T 冻结 and the fluid composition determined by the device to calculate the repair temperature T for removing the solids deposited in the low-temperature heat exchanger 修复 ; as well as A temperature controller is in operative communication with the controller to increase or decrease the operating temperature of the low temperature heat exchanger to a repair temperature T 修复 .

13. A system as defined in claim 12, wherein: The temperature controller is in operative communication with the low temperature heat exchanger to change the refrigeration load at one or more locations in the low temperature heat exchanger to increase or decrease the operating temperature to the repair temperature T 修复 .

14. The system as defined in claim 10, further comprising: a device for determining the composition of a fluid; Thermodynamic simulation program for solid-liquid equilibrium (SLE) calculations, the program is set up to use T 冻结 and calculating a repair composition capable of dissolving solids deposited in the cryogenic heat exchanger from the composition of the fluid determined by the apparatus; as well as A fluid metering device is in operative communication with the controller to introduce a remediation fluid into the cryogenic heat exchanger in an amount sufficient to obtain the remediation composition.

15. The system as defined in claim 10, wherein: The system further comprises another device for directly detecting solids formation in the fluid as defined in claim 1, which is arranged to be in fluid communication with the outlet of the cryogenic heat exchanger to monitor the effectiveness of the repair.

16. A method of preventing or repairing solid deposits in a cryogenic heat exchanger, the cryogenic heat exchanger being arranged, in use, to cool a fluid to an operating temperature T 液体 The method comprises the following steps: Direct detection of solid formation in a fluid sample cooled or intended to be cooled by a cryogenic heat exchanger and determination of the temperature T corresponding to the temperature at which the solid is formed in the fluid 冻结 and ΔT 冻结 , where ΔT 冻结 =T 液体 -T 冻结 , the step of detecting solid formation is performed by using an apparatus for detecting solid formation as defined in claim 1; and When ΔT 冻结 When the temperature is less than a predetermined operating temperature margin, corrective measures for operating the cryogenic heat exchanger are initiated.

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