US20220290916A1

US20220290916A1 - Heat exchanger system and method

Info

Publication number: US20220290916A1
Application number: US17/631,953
Authority: US
Inventors: Uma Shankar PAL; Himanshu Madhav JOSHI
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 2019-08-14
Filing date: 2020-08-14
Publication date: 2022-09-15
Also published as: WO2021030648A1; CA3150438A1; AU2020329293B2; AU2020329293A1

Abstract

The present disclosure provides a heat exchanger system and a method of using the heat exchanger system for heating, cooling or condensing a gaseous multiple component process stream comprising at least one hydrocarbon. The heat exchanger system comprises: —a shell having at least one first inlet and at least one first outlet defining a flow path for a first process fluid, and at least one second inlet and at least one second outlet defining a flow path for a second process fluid; —a number of parallel tubes arranged in the shell between the first inlet and the first outlet, each tube having an outer surface being provided with a multitude of plate fins extending radially outward from the outer surface; the first flow path extending along the outer surface of the tubes, and the second flow path extending through the tubes. The multiple component process stream may comprise two or more components selected from the group of methane, ethane, propane, and nitrogen. The heat exchanger may be used to cool or condense a mixed refrigerant, comprising one or more hydrocarbons, in a process for the liquefaction of natural gas.

Description

FIELD OF THE INVENTION

The disclosure relates to a heat exchanger system and method. The system and method may be included in a process for the liquefaction of gases, such as natural gas. The system is for instance a heat exchanger included in the liquefaction process, for instance in the pre-cool or main cooling loops of a liquefaction process for liquefied natural gas. The system and method can be used to condense a mixed or multicomponent refrigerant.

BACKGROUND TO THE INVENTION

Natural gas can be liquefied for purposes of storage and transportation, as the gas occupies a smaller volume as a liquid than in the gaseous state. Liquefaction takes place in an LNG (liquified natural gas) plant, in which a natural gas feed stream is typically first treated (including for instance the removal of contaminants) and subsequently liquefied. The section for liquefaction typically includes one or more heat exchangers to cool the (natural) gas by heat exchange with a refrigerant. Of these heat exchangers, the last heat exchanger for cooling the natural gas to the liquid state is typically referred to as the main cryogenic heat exchanger (MCHE).
Indirect heat exchangers are heat exchangers in which two fluid flows can exchange heat without being in direct contact as the fluids are separated by one or more heat exchange surfaces. The fluid flows may be liquid, vapor, gaseous or multiphase flows. Indirect heat exchangers may be used for different purposes. For instance, indirect heat exchangers can be used in refrigeration cycles to allow a refrigerant to exchange heat with the ambient air or cooling water (e.g. a condenser, cooling down the refrigerant) and to allow the refrigerant to exchange heat with a process stream (cooling down the process stream) in a further indirect heat exchanger. Such refrigerant cycles are for instance used in liquid natural gas plants to cool down and liquefy a natural gas process stream as well as in regasifying plants in which liquid natural gas is heated up to be regasified/vaporized.
The LNG liquefaction process typically includes various types of heat exchangers for gases (for instance mixed refrigerant, natural gas, etc.) at various locations in the liquefaction process. The heat exchangers may function for condensing, cooling or heating. For instance, the liquestion process may include one or more mixed refrigerant (MR) condensers, gas coolers, and gas heaters. Some of these are generally designed as cross flow (so-called TEMA type X-shell) shell and tube heat exchangers. Herein, for some applications an allowable shell side pressure drop may be limited to a set threshold. Herein, TEMA refers to the Standards of the Tubular Exchanger Manufacturer's Association. TEMA has designated a naming system for shell types based on various shell side flow arrangements.
Well-known types of indirect heat exchangers currently used in the oil and gas industry are plate fin heat exchangers, and shell and tube heat exchangers. These heat exchangers are typically relatively large. The most compact heat exchangers currently used in the oil and gas industry are printed circuit heat exchangers (PCHE). In an LNG liquefaction process, one of these types of heat exchangers are typically used for condensing and liquefying the natural gas process stream. Such heat exchangers may be referred to as main cryogenic heat exchanger and pre-cool heat exchanger.
Conventionally, the condensers and gas coolers and heaters included in the refrigerant loops have been low finned tube type heat exchangers. A low finned tube (also referred to as an Integral Finned Tube) is a finned tube, wherein the fins on the tube are recessions or a relief. The recessions have a smaller outer diameter than an outer diameter of the base material of the tube. The recessions may be grooves arranged in a particular pattern, for instance helical or circular. The recessions may be formed through plastic deformation of the tube. This plastic deformation causes an increment of heat transfer area and allows to reduce the heat exchanger size. Finned tube heat exchangers are heat exchangers wherein one process fluid flows through a tube, and another process fluid flows on the outside of said tube.
The concern with low finned tube heat exchangers is that the design is suspetible to differential condensation of components of a mixture comprising multiple components. Differential condensation of respective components is for instance relatively likely when the mixture moves with very low velocity in a large shell. Very low herein may refer to a velocity between 0 and 1 m/s.
Mixtures of components may for instance be used as refrigerant for the liquefaction of natural gas. Such refrigerant may be referred to as a mixed refrigerant. In a heat exchanger for condensing the mixed refrigerant (called a condenser), differential condensation arises when vapor and condensate parts of the mixed refrigerant are separated within the condenser. Such separation causes the condensing process to depart from overall equilibrium. It is preferred to avoid differential condensation, because of the required correction of the condensing process. The vapor becomes richer in the more volatile component(s) with a fall in saturation temperature and driving force. As a result, a larger heat exchange area is required for a given condensation rate. On the other hand, for a given size of the heat exchanger, the heat exchange performance will decrease, resulting in reduced heat exchanger performance. The risk of differential condensation increases at lower velocity of the refrigerant in relatively large industrial applications, including LNG production. Consequently, it is relativey difficult to design heat exchangers for the sections of an LNG liquefaction process using a mixed refrigerant.
In view of the above, there is demand for an improved heat exchanger to avoid at least some of the disadvantages referenced above.

SUMMARY OF THE INVENTION

In one aspect the disclosure provides a method of using a heat exchanger system for heating, cooling or condensing a gaseous multiple component process stream comprising at least one hydrocarbon, the heat exchanger system comprising:

- a shell having at least one first inlet and at least one first outlet defining a flow path for a first process fluid, and at least one second inlet and at least one second outlet defining a flow path for a second process fluid;
- a number of parallel tubes arranged in the shell between the first inlet and the first outlet, each tube having an outer surface being provided with a multitude of plate fins extending radially outward from the outer surface;

the first flow path extending along the outer surface of the tubes, and the second flow path extending through the tubes.
In an embodiment, the heat exchanger system comprising a distributor plate arranged in the shell between the at least one inlet and the number of parallel tubes.
In another embodiment, the first process fluid is the gaseous multiple component process stream.
In yet another embodiment, the multiple component process stream comprises two or more components selected from the group of methane, ethane, propane, and nitrogen.
In an embodiment, the multiple component process stream is a mixed refrigerant comprising two or more components, at least one of the components being a hydrocarbon.
The method may comprise the step of using the heat exchanger for cooling or condensing the mixed refrigerant in a process for the liquefaction of natural gas.
The method may comprise the step of condensing the gaseous multiple component process stream from a fully gaseous state at the first inlet to a fully liquid state at the first outlet.
In an embodiment, the gaseous multiple component process stream comprises natural gas, the method comprising the step of using the heat exchanger for heating the natural gas.
According to another aspect, the disclosure provides a heat exchanger system for heating, cooling, or condensing a gaseous multiple component process stream comprising at least one hydrocarbon, the heat exchanger system comprising:

- a shell having at least one first inlet and at least one first outlet defining a flow path for a first process fluid, and at least one second inlet and at least one second outlet defining a flow path for a second process fluid;
- a number of parallel tubes arranged in the shell between the at least one first inlet and the at least one first outlet, each tube having an outer surface being provided with a multitude of plate fins extending radially outward from the outer surface;

the first flow path extending along the outer surface of the tubes, and the second flow path extending through the tubes.
In an embodiment, the heat exchanger comprises a distributor plate arranged in the shell between the at least one first inlet and the number of parallel tubes.
In another embodiment, the multiple component process stream is a mixed refrigerant comprising two or more components, at least one of the components being a hydrocarbon.
In yet another embodiment, the multiple component process stream comprises two or more components selected from the group of methane, ethane, propane, and nitrogen.
In the design according to the disclosure, a heat exchanger comprises a relatively high finned tube inside a shell. The heat exchanger concept can be extended to medium and large size business applications. The use of high fin tube in shell heat exchangers for liquefaction of natural gas provides better mixing for multi component mixtures in two phase flow. The latter may occur, for instance, when using a mixed refrigerant (MR) for cooling of natural gas. Herein, one of the components of the MR may condense relatively early on in the heat exchanger, limiting the efficiency of the heat exchange. The high finned design of the present disclosure promotes integral condensation and enhances heat exchange performance, when using a mixed refrigerant. For instance, the design of the disclosure can handle turn down cases better than a plain tube or low fin tube design. Turn down herein relates to a situation wherein production is reduced for a while and subsequently returned to normal operation. This is due to, for instance, a higher velocity of the process stream in the heat exchanger and improved phase mixing of respective components of a process stream in the shell. As a result, differential condensation is obviated. High finned tubes in the shell will create more flow turbulence and will, for instance, promote and improve condensation.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawing figures depict one or more implementations in accord with the present teachings, by way of example only, not by way of limitation. In the figures, like reference numerals refer to the same or similar elements. Herein,

FIG. 1 schematically depicts an examplary process for liquefying a gas stream using a mixed refrigerant for cooling;

FIG. 1A shows a diagram indicating another option for a section of the process of FIG. 1;

FIG. 1B shows a diagram indicating yet another option for a section of the process of FIG. 1;

FIG. 2 shows a front view in cross section of an embodiment of a heat exchanger according to the present disclosure;

FIG. 3 shows a perspective view of an examplary embodiment of high finned tubes for the heat exchanger of FIG. 2;

FIG. 4 shows a perpendicular view of a cross section of an embodiment of the heat exchanger of FIG. 2, including the high finned tubes of FIG. 3;

FIG. 5 shows a perspective view of another examplary embodiment of high finned tubes for the heat exchanger of FIG. 2;

FIG. 6 shows a perpendicular view of a cross section of an embodiment of the heat exchanger of FIG. 2, including the high finned tubes of FIG. 5;

FIG. 7 shows a part open perspective view of an embodiment of the heat exchanger of the present disclosure, indicating view points A and B;

FIGS. 7A and 7B show exemplary results of modelling of a liquid volume fraction on a scale of 0 to 1, in front view (along line A) and side view (along line B) in cross section, when using the heat exchanger of FIG. 7 for condensation of a process stream using a multicomponent refrigerant;

FIGS. 8A and 8B show exemplary results of modelling of a pressure distribution across the heat exchanger of FIG. 7, during condensation of a process stream using a multicomponent refrigerant, in front view (along line A) and side view (along line B) respectively;

FIGS. 9A and 9B show exemplary results of modelling of velocity vectors of the refrigerant, in cross section in front view (FIG. 9A) and side view (FIG. 9B), when using the heat exchanger of FIG. 7 for heating of cooling a process stream using a multicomponent refrigerant; and

FIGS. 10A and 10B shows exemplary results of modelling of a pressure distribution across the heat exchanger of FIG. 7, in cross section in front view (FIG. 10A) and side view (FIG. 10B), during heating or cooling of a process stream using a multicomponent refrigerant.

DETAILED DESCRIPTION OF THE INVENTION

Certain terms used herein are defined as follows:
“NG” refers to natural gas. Natural gas is a naturally occurring hydrocarbon gas mixture primarily comprising methane, but commonly including varying amounts of other higher alkanes, and sometimes a small percentage of carbon dioxide, nitrogen, hydrogen sulfide, or helium;
“LNG” refers to liquefied natural gas, which is typically cooled to at least a temperature whereat the gas can be in the liquid phase at about 1 bar pressure; for liquefied methane this temperature is about −162° C.;
“Mixed refrigerant”, “MR” or “multicomponent refrigerant” refers to a refrigerant comprising two or more components. For liquefaction of natural gas, the mixed refrigerant may include at least two components, such as methane, ethane, propane, and nitrogen.
“PMR” may refer to a pre-cool mixed refrigerant. This may be a mixed refrigerant used in a precool circuit for liquefying natural gas. The precool circuit typically preceeds a main cooling circuit, comprising a main cryogenic heat exchanger.
“HMR” and “LMR” refer to “heavy mixed refrigerant” and “light mixed refrigerant” respectively, indicating mixed refrigerant separated into light and heavy mixed refrigerant streams, wherein the terms “light” and “heavy” indicate average component weight of each stream relative to each other;
“Bar” is a metric unit of pressure, defined as equal to 100 kPa. “Bar(a)” and “bara” are sometimes used to indicate absolute pressures and “bar(g)” and “barg” for gauge pressures. Herein, “2 barg” is similar to fuller descriptions such as “gauge pressure of 2 bar” or “2-bar gauge”.
Different liquefaction schemes are known, such as C3MR, SMR (single mixed refrigerant) or DMR (double mixed refrigerant). Many of these schemes comprise a coil wound heat exchanger, typically the main cryogenic heat exchanger, in which a substantial part of the cooling of the natural gas takes place. Suitable coil wound heat exchangers are commercially available from a variety of vendors, including Air Products and Chemicals Inc. (APCI), Pennsylvania (USA), and Linde AG (Germany).
FIG. 1 schematically depicts an examplary system and method for liquefying a gas. The present disclosure allows to replace some heat exchangers in said system and method, or in similar systems and methods.
In the system of FIG. 1, a natural gas stream 1 is supplied at a predetermined, elevated pressure to scrub column 5 or similar treatment equipment. In the scrub column 5, hydrocarbons heavier than methane are removed from the natural gas stream 1. The heavier hydrocarbons 7 may be withdrawn from the bottom of the scrub column 5. Gaseous overhead stream 8 typically has a higher methane concentration than the natural gas feed stream 1. The gaseous overhead stream 8 may be withdrawn from the top of the scrub column 5 through a conduit.
The gaseous overhead stream 8 is at least partly condensed in pre-cool heat exchanger 35. Herein, the gaseous overhead stream 8 is guided through tube 83 inside the pre-cool heat exchanger 35. Inside the heat exchanger 35, the gaseous stream in gas tube 83 exchanges heat with respect to a refrigerant. The refrigerant may be a mixed refrigerant.
The condensed gas stream is guided from upper end of the tube 83 to a separator 90. A condensate stream is removed in separator 90. Condensate stream 91 may be directed to the scrub column 5.
A methane enrichted stream 10 may be passed, at elevated pressure, through a conduit to a first tube 15 arranged in main heat exchanger 17. In the main heat exchanger 17, said methane enriched stream 10 is liquefied. The stream enriched in methane 10 may be liquefied at elevated pressure in the first tube 15 arranged in the main heat exchanger 17 by indirect heat exchange. The indirect heat exchange may be with respect to a multicomponent refrigerant (mixed refrigerant) evaporating at relatively low refrigerant pressure in the shell side 19 of the main heat exchanger 17. Liquefied gas is removed at elevated pressure from the main heat exchanger 17 through a conduit 20 for further treatment downstream (not shown).
The main cryogenic heat exchanger 17 has a corresponding first refrigerant loop. In use, evaporated multicomponent refrigerant is withdrawn from warm end of the shell side 19 of the main heat exchanger 17 through conduit 25. Compressor 27 receives the evaporated multicomponent refrigerant and compresses the multicomponent refrigerant to elevated refrigerant pressure. Heat of compression is removed from the compressed refrigerant stream using a heat exchanger 30, for instance an air cooler or a water cooler.
The cooled compressed multicomponent refrigerant 32 may be passed to the pre-cool heat exchanger 35. In a first tube 38 of the pre-cool heat exchanger 35, the multicomponent refrigerant may be partly condensed at elevated refrigerant pressure by indirect heat exchange with a second multicomponent refrigerant evaporating at low second refrigerant pressure in the shell side 39 of the pre-cool heat exchanger 35. Condensed multicomponent refrigerant 42 is subsequently passed from an end of the tube 38 to the main heat exchanger 17.
The condensed first multicomponent refrigerant 42 may be passed to a separator 45. In the separator, the first refrigerant is separated into a gaseous overhead stream (light mixed refrigerant) 47 and a liquid bottom stream (heavy mixed refrigerant) 57. The gaseous overhead stream 47 is passed to a second tube 49 arranged in the main heat exchanger 17. In tube 49, the light mixed refrigerant stream 47 is cooled, liquefied and sub-cooled at elevated refrigerant pressure. The liquefied and sub-cooled light mixed refrigerant stream is passed through an expansion device, for instance an expansion valve 51. The expanded light mixed refrigerant 50 is passed to a cold end of the shell side 19 of the main heat exchanger 17. Inside the heat exchanger 17, the light mixed refrigerant evaporates at low refrigerant pressure.
The liquid bottom stream or heavy mixed refrigerant 57 is passed through a conduit to a third tube 59 arranged in the main heat exchanger 17. In the third tube 59, the heavy mixed refrigerant stream 57 is cooled at elevated refrigerant pressure. The liquefied heavy mixed refrigerant stream is passed through an expansion device, for instance in the form of expansion valve 61. Expanded liquefied heavy mixed refrigerant stream 60 is provided to a middle section of the shell side 19 of the main heat exchanger 17. In the heat exchanger 17, the expanded liquefied heavy mixed refrigerant stream 60 can evaporate at low refrigerant pressure. In the heat exchanger 17, the evaporating multicomponent refrigerant, i.e. light and heavy mixed refrigerant streams 50 and 60, extracts heat from the fluid passing through the first tube 15 to liquefy it, but also from the light and heavy mixed refrigerant streams 47 and 57 passing through the second and the third tube 49 and 59 respectively.
The pre-cool heat exchanger 35 has a corresponding second refrigerant loop. In use, evaporated second multicomponent refrigerant 65, evaporated at low pressure in the shell side 39 of the auxiliary heat exchanger 35, is removed from a lower end or warm end of the pre-cool heat exchanger 35 through a conduit. Compressor 67 receives the evaporated second multicomponent refrigerant 65 and compresses the second multicomponent refrigerant to an elevated pressure. Heat of compression can be removed using a heat exchanger 70, for instance an air cooler or water cooler.
The cooled and compressed second mixed refrigerant 72 is passed to one or more second tubes 78 arranged in the pre-cool heat exchanger 35. In said second tubes 78, the second mixed refrigerant is cooled. The cooled second refrigerant is passed through an expansion device 81, for instance in the form of expansion valve. The expanded cooled second refrigerant 80 is supplied to a cold end of the shell side 39 of the pre-cool heat exchanger 35. Herein, the expanded second refrigerant 80 can evaporate at low second refrigerant pressure.
The gaseous overhead stream 8 withdrawn from the top of the scrub column 5 can be partly condensed. For instance, the gaseous overhead stream 8 can be supplied to a third tube 83 arranged in the pre-cool heat exchanger 35. In this third tube 83, the gaseous overhead stream 8 is partly condensed. A partly condensed gaseous overhead stream 85 is removed from the third tube 83 and may be provided to separator 90. In separator 90, a condensate stream 91 is removed to obtain stream 10 enriched in methane at elevated pressure. Said methane enrichted stream 10 is passed to the first tube 15 arranged in the main cryogenic heat exchanger 17. The condensate stream 91 can be returned to an upper part of the scrub column 5 as reflux.
As an example, the gaseous overhead stream 8 from the top of the scrub column 5 can be partly condensed. Stream 8 may have a temperature of about −50° C.
The natural gas stream 1 can be pre-cooled and/or dried before it enters the scrub column 5. Pre-cooling can be affected, for instance, by indirect heat exchange with a bleed stream from the second mixed refrigerant. For instance, the compressed second mixed refrigerant 72 downstream of the cooler 70. As an example, the second mixed refrigerant can be passed through conduit 93 provided with expansion valve 95 to a heat exchanger 97 to heat exchange with respect to the natural gas feed stream 1 (indicated schematically). Please note that—for the sake of simplicity—the heat exchanger 97 is shown twice (in stream 1 and between stresm 72 and 65 as well). However, it is the same heat exchanger.
FIGS. 1A and 1B schematically show alternatives for the refrigerant loop of the pre-cool section of the process of FIG. 1. Basically, the diagrams of FIGS. 1A and 1B provide alternative setups with respect to the compressor 67 and heat exchanger 70 in FIG. 1.
In the embodiment of FIG. 1A, a mixed refrigerant vapor stream 65 is provided from the heat exchanger 35 to a first separator 165. From the separator, a mixed refrigerant vapor 166 is provided to first refrigerant compressor 167. A first compressed refrigerant vapor 168 is provided to a first refrigerant cooler 170. The first refrigerant cooler 170 may also be referred to as interstage cooler. A first cooled compressed refrigerant vapor stream 171 is provided to a second refrigerant compressor 172. The first compressor 167 herein may be referred to as low pressure compressor. The second compressor 172 may be referred to as high pressure compressor. A second compressed refrigerant vapor stream 173 may be provided to a second heat exchanger 174 for cooling. The second heat exchanger 174 may be referred to as (MR or PMR) de-superheater. A cooled compressed refrigerant stream 175 may be provided to a third heat exchanger 176 for further cooling and typically for condensing the refrigerant. The third heat exchanger 176 may be referred to as refrigerant condenser, MR condenser or PMR condenser. A condensed refrigerant stream 177 may be provided to a separator or accumulator 178. A compressed cooled and condensed refrigerant stream 72 is provided to the heat exchanger 35.
In the embodiment of FIG. 1B, the first heat exchanger 170 partially condenses the first compressed refrigerant vapor 168. Herein, the first heat exchanger 170 can be referred to as partial condenser, MR partial condenser or PMR partial condenser. A partially condensed refrigerant stream 180 is provided to a separator 182. A vapor stream 184 is provided to the second compressor 172 for compression, and subsequent condensation. A liquid stream 186 is provided to a pump 188. The pump 188 provides a pressurized liquid stream 190. The pressurized liquid refrigerant stream 190 can be combined with, for instance, the condensed refrigerant stream 177, wherein the combined refrigerant liquid stream 192 is provided to, for instance, the separator 178.
In the exemplary liquefaction schemes for liquefying gas of FIGS. 1, 1A and 1B, for instance the heat exchangers 30, 70, 97, 170, 174, and/or 176 can be replaced with a heat exchanger according to the present disclosure. Examples of heat exchangers suitable to be replaced with the heat exchanger and method of the present disclosure are, for instance, the (PMR) de-super heater, (MR) condenser, (MR) Inter stage cooler and (MR) after stage cooler, etc.
In another embodiment, a heat exchanger as disclosed herein may be used for heating a natural gas feed stream in a treatment process. A treatment process for instance cleans the natural gas and removes unwanted contaminants, such as CO2, water, H2S, mercaptans and hydrocarbon components heavier than methane. The step of heating of natural gas using a heat exchanger as disclosed herein may be included, for instance, before the gas is provided to an acid gas removal unit (AGRU). See WO2016150827 for an example of an AGRU.
FIG. 2 shows a heat exchanger 100 comprising a housing or shell 102. The shell may be substantially cilindrical, as shown in FIG. 2. The shell may be provided with one or more inlets 104 and one or more outlets 106 for a first medium. The first medium may be a (mixed) refrigerant. The shell may be provided with at least one second inlet 108 and at least one second outlet 110 for a second medium. The second medium may be coolant for cooling the first medium. FIG. 2 shows a typical 4 tube pass X shell (cross flow) heat exchanger arrangement. Tube passes can be 2, 4, 6 and more depending upon tube side flow and process flow data.
The heat exchanger 100 may be referred to as a cross flow heat exchanger, or TEMA X-shell. Herein, flow of a first process fluid (indicated by first arrows 112) is generally perpendicular to the flow of a second process fluid (indicated by second arrows 114). The first arrows 112 indicate flow through the inside of the shell 102. The second arrows 114 indicate flow guided through the inside of finned tubes 116.
The tubes 116 are typically straight tubes. Opposite ends of the tubes 116 can be arranged in connector plates or tubesheets 118, 120 respectively. The tubes 116 are provided with fins 122 extending substantially perpendicular to a length direction of the tubes 116. The fins 122 may be provided on an outer surface of the tubes 116, typically between the tubesheets 118, 120. A distributor plate 124 may be provided inside the shell 102 between the at least one inlet 104 and the tubes 116. The distributor plate 124 is provided with openings 126 for the first process fluid. The distributor plate 124 defines a distribution space 128 between the plate 124 on one side and the shell 102 and the inlet 104 on the other. The openings 126 and the distribution space 128 allow the first flow 112 of the first process fluid to distribute evenly across the inner shell space 129 between the flange plates 118, 120. Said space 129 may be referred to as the shell side of the heat exchanger 100.
The tubesheets 118, 120 seal the inner space of the shell substantially gas-tight, keeping the first process fluid inside the shell and guiding the first flow between the first inlet 104 and the first outlet 106. Opposite first end 130 and second end 132 of the shell may be provided with separation or partition plates 134, 136, 138 respectively. The partition plates 134, 136, 138 guide the second flow 114 towards corresponding sets of tubes 116.
The partition plates 134, 136, 138 determine the number of times that the second fluid flow 114 passes through the tube sideheader. Said number may be any number. In practice, said number of passages is a multiple of two passages, typically 2, 4 or 6 and higher even passages. In some specific cases it may be odd passes. In the embodiment of FIG. 2, the second fluid flow 114 passes from the second inlet 108 to inlet header or channel space 140, and subsequently through a first set of tubes 116A (FIG. 4) to return header space 142. Subsequently, the second fluid flow 114 passes from the return header space 142 through a second set of tubes 116B to channel space 144. Subsequently, the second fluid flow 114 passes from the channel space 144 through a third set of tubes 116C to return header space 146. A finally, the second fluid flow 114 passes from the return header space 146 through a fourth set of tubes 116D to channel space 148 and towards the second outlet 110.
As shown in FIGS. 3 and 4, the fins 122 may be substantially circular.
As shown in FIGS. 5 and 6, the fins 122 may be substantially rectangular.
The tubes 116 provided with the fins 122 may be referred to as high-finned tubes. “High-finned”, as opposed to “low finned”, may refer to the diameter of the fins relative to an outer diameter of the tube. Alternatively, high-finned may include a reference to the method of production. Low finned typically refers to structures applied in the material of a base tube or pipe. The low fin diameter is smaller than or equal to the outer diameter of the base tube. High finned typically refers to fins which may be fabricated as separate structure or of another material material with respect to the base tube or pipe. Said structures may have been subsequently connected to the outer surface of the tube. Said connection may be, for instance, by welding, brazing, (hard) soldering, or any other suitable means to create a robust and durable connection between the pipe and the fins. The outer diameter or dimension of the high fins exceeds the outer diameter of the base tube. The high finned tubes can be termed as wrapped on, embedded, extruded, plate fin, wire wound etc. depending on fin shape and manufacturing method.
High-finned tubes have a much greater outer surface area than plain or low-finned tubes. This allows for particularly compact designs with an increased heat transfer area. Thanks to their relatively high, thin fins, these tubes perform particularly well in the heating and cooling of liquids and gases. High fins may have a diameter exceeding the diameter of the tube diameter with a factor in the order of 25 to 150%. High fins, for instance, may have a height of up to 5 to 40 mm with respect to the outer surface of the tubes 116. Alternatively, the fins may be plates, each plate fin connected to multiple tubes (see FIG. 5).
Due to difficulty and unpredictability in the design, the use of high fin or high-finned tubes 116 in a shell 102 in a process for the liquefaction of natural gas is uncommon. A close example may be an air/nitrogen (N2) compressor intercoolers or compressor aftercooler, comprising finned tubes in a shell. However, a thermal sizing calculation for air and N2 is relatively easy. There is a standard calculation method and proven software available on the market to design heat exchangers for such applications, for instance to calculate sizes and throughputs of respective process fluids. On the other hand, calculating sizes and throughputs for high-finned heat exchangers used for the cooling, heating or condensing of mixtures of multiple (gaseous) hydrocarbons is relatively difficult. At present, the market lacks any software tool or calculation method to design a heat exchanger comprising high-finned tubes in a shell for application in combination with a multiple component gaseous hydrocarbon mixture. Consequently, such heat exchangers are currently unavailable. The Applicant has used heat transfer knowledge, judgement, experience and testing to come up with the design of the present disclosure.
The design and fabrication of a high fin tube heat exchanger differs from conventional shell and tube heat exchangers. For instance, the sequence of tube insertion, tube supporting and leakage path sealing arrangement is different with respect to conventional heat exchangers. For instance, for a plain or low finned tube, the outer diameter of the tubes including the fins is equal to smaller than the openings for the tubes in the respective tubesheet. For high finned tubes, the outer fin diameter is (much) larger than the openings for tubes in the tubesheets. Accordingly, a fabrication sequence and method vary depending on selection and type of high finned tubes.
FIG. 7 shows a schematic version of the heat exchanger 100 of the present disclosure. FIGS. 7A and 7B show results of computer simulations done by Applicant, indicating the liquid volume fraction (from 0 to 1; 0 being 100% gaseous and 1 being 100% liquid) when condensing a multiple component gaseous mixture, such as a mixed refrigerant. Said simulations indicate that Applicant can design a high-finned tube heat exchanger for condensing a mixed refrigerant, wherein the mixed refrigerant is fully gaseous at the first inlet 104 and is fully condensed (liquid) at the first outlet 106.
FIGS. 8A and 8B indicate examples of a typical pressure distribution (top to bottom) when using the heat exchanger 100 for condensing a multiple component gaseous mixture, such as a mixed refrigerant. Pressure drop across the perforated distribution plate 124 may be in the range of −100 to −200 Pa. As indicated, the pressure distribution in the heat exchanger can be controlled to be relatively even, obviating pressure drops below a set design threshold.
FIGS. 9A and 9B indicate examples of a typical velocity vector (top to bottom) for gas cooling or heating applications. Herein, the heat exchanger 100 may be used for heating or cooling a multiple component gaseous mixture, such as a mixed refrigerant. In an embodiment, the heat exchanger may be provided with two or more first inlets 104, and/or two or more first outlets 106. Herein, the first fluid flow 112 may arrive at first inlet 104 at a velocity of about 4 to 7 m/s. At and beyond the distributor plate 124, the velocity drops in the range of 0.05 to 1 m/s. After the distributor plate, the fluid velocity increases when the fluid enters the tube bundle, due to the net free area of the section. Although slightly different, similar results were obtained for gas cooling and heating application.
FIGS. 10A and 10B indicate examples of a typical pressure distribution (top to bottom) when using the heat exchanger 100 for heating or cooling a multiple component gaseous mixture, such as a mixed refrigerant. Applicant has been able to design the heat exchanger 100 wherein the pressures across the shell side 129 remain within a predetermined range, without exceeding a higher threshold or dropping below a lower threshold. In the example, said range is about 2500 to 6500 Pa.
Results of tests and simulations indicated that shell side velocity increase can be a factor of 1.3 and higher, with respect to conventional heat exchangers used in the industry. Design margin can be about 15 to 25% higher for the same size of heat exchanger, with respect to conventional heat exchangers used in the industry. The latter means that a heat exchanger 100 can condense, heat or cool 15 to 25% more mixed refrigerant than a conventional heat exchanger. The tests indicated an overall size reduction of the heat exchanger 100 for the same heat duty compared to the conventional low fin tube design. The number of tubes 116 can be reduced compared to the conventional low fin tube design. Also, the total weight of the heat exchanger 100 and of the tube bundle of combined tubes 116 can be reduced, providing an overall weight reduction of the heat exchanger 100 compared to conventional designs.
As indicated above, Applicant has demonstrated that a shell and high fin tube heat exchanger design is suitable for use in combination with mixed refrigerant. The high-finned tube design is more efficient and cost effective than a conventional (shell and low fin tube) design for LNG service heat exchangers. This provides benefits for, for instance, X-shell type heat exchangers using cross flow. The X shell designation is defined for fluid cross flow arrangement in shell as per Standards of Tubular Heat Exchanger Manufacturers Association (TEMA).
Applicant has reviewed some of the LNG service heat exchangers (for instance for gas cooling, condensing and heating applications) using a high-finned tube in shell design. The review observations and findings are as follows:
High confidence (>−85%) on predicted benefits using shell and high fin tubes.
The gas flow pattern in the shell around the high finned tube is like a gas flow in an economizer with finned tubes in a duct. The use of a high fin tube has shown improved results for LNG cooling, condensation and heating applications. For cooling and condensing applications, the gas or gas mixture cross flow from top to bottom. For heating applications, gas flow will from bottom to top.
The design can have a distributor plate 124 above the bundle of tubes 116. The uniform flow distribution (evaluated with Computational Flow Dynamics analysis) using the distributor plate 124 will ensure equal distribution of vapor along the length of the tube bundle. The distributor plate resistance will enable uniform distribution of vapor prior to flow through the tube bundle for vapor cooling, condensation and heating applications.
X shell heat exchangers according to the present disclosure can replace, for instance, a PMR condenser, PMR de-super heater, MR inter-stage cooler, MR after-stage cooler and natural gas pre-cooler. Evaluated for comparative design benefits, these deliver about 15% to 25% additional heat duty for the same size of heat exchanger.
Tests and computer modelling have indicated the following advantages of using high finned tubes in shell-and-tube heat exchangers for application in a liquefaction process for natural gas. The evaluation findings indicated, for instance:
1) Use of high finned tubes can increase the cooling duty up to 25% for the same size of heat exchanger (based on a typical PMR condenser design case). Engineering simulation checks have confirmed approximately a 2% increased LNG production with only PMR condenser design optimization.
2) Use of high finned tube heat exchangers (in liquefaction of NG) can reduce size and cost of heat exchangers for given duty of heat exchanger;
3) Use of high finned tubes will reduce weight of heat exchangers, resulting in an associated cost reduction for equipment, support structure and foundation (resulting in overall reducting of capital expenditure);
4) LNG liquefaction leaves heat exchangers relatively clean, so that the use of aluminum high finned tubes is considered appropriate for these applications. The base tube thickness can be reduced. This will enable a substantial cost reduction along with a reduction of the number of tubes with respect to conventional heat exchangers.
In general, the system and method of the present disclosure can be applied to any heat exchanger in a mixed refrigerant circuit. For example, a mixed refrigerant process may include a precooling circuit as well as a main cooling circuit, both cooling circuits comprising one or more heat exchangers. A similar approach as described in the present disclosure can be applied to all heat exchangers in a liquefaction process carrying both mixed refrigerant and a gas stream to be liquefied, to improve the flow of mixed refrigerant. Examples of mixed refrigerant processes include, for instance, a single mixed refrigerant process (see for instance U.S. Pat. No. 6,658,891), a dual mixed refrigerant process (see for instance U.S. Pat. No. 6,370,910), a parallel mixed refrigerant process (see for instance US20080156037), or a C3MR process (see for instance US20090301131).
The heat exchanger according to the present disclosure can also be applied in Chemical Plants, including but not limited to refineries. Applications may include using the heat exchanger for CO₂absorber gas cooling, CO₂absorber feed heater, ethylene oxide (EO) concentrator overhead cooling, CO₂compressor recycle coolers, EG-1/EG-2 Reactor top condensers. There can be other applications on upstream or downstream businesses.
For completeness sake, some other examples of heat exchangers are mentioned. For instance, WO2008079593 describes a method of using a minimal surface or a minimal skeleton to make a heat exchanger component and describes relatively complicated structures. US20150007969 describes a heat exchanger comprising ribs and slits, which can for example be formed using ultrasonic additive manufacturing (UAM). Reference to additive manufacturing is for instance made in US20160108814, GB2521913A, US20160114439, WO2013163398A1 and CN204830955.
The present disclosure is not limited to the embodiments as described above and in the appended claims. Many modifications are conceivable therein and features of respective embodiments may be combined.

Claims

1. A method comprising:

providing a heat exchanger system comprising:

a shell having at least one first inlet and at least one first outlet defining a first flow path for a first process fluid, and at least one second inlet and at least one second outlet defining a second flow path for a second process fluid;

a number of parallel tubes arranged in the shell between the first inlet and the first outlet, each tube having an outer surface being provided with a multitude of high fins extending radially outward from the outer surface;

wherein the first flow path extending along the outer surface of the tubes, and the second flow path extending through the tubes; and

using the heat exchanger system for heating, cooling or condensing a gaseous multiple component process stream comprising at least one hydrocarbon.

2. The method of claim 1, wherein the heat exchanger system comprising a distributor plate arranged in the shell between the at least one inlet and the number of parallel tubes.

3. The method of claim 1, wherein the first process fluid being the gaseous multiple component process stream.

4. The method of claim 1, wherein the multiple component process stream comprising two or more components selected from the group of methane, ethane, propane, and nitrogen.

5. The method of claim 1, wherein the multiple component process stream being a mixed refrigerant comprising two or more components, at least one of the components being a hydrocarbon.

6. The method of claim 5, wherein the step of using the heat exchanger system for heating, cooling or condensing comprises using the heat exchanger system for cooling and condensing the mixed refrigerant in a process for the liquefaction of natural gas.

7. The method of claim 1, wherein the step of using the heat exchanger system for heating, cooling or condensing comprises using the heat exchanger system for condensing the gaseous multiple component process stream from a fully gaseous state at the first inlet to a fully liquid state at the first outlet.

8. The method of claim 1, wherein the gaseous multiple component process stream comprises natural gas and the step of using the heat exchanger system for heating, cooling or condensing comprises using the heat exchanger system for heating the natural gas.

9. A heat exchanger system for heating, cooling, or condensing a gaseous multiple component process stream comprising at least one hydrocarbon, the heat exchanger system comprising:

a number of parallel tubes arranged in the shell between the at least one first inlet and the at least one first outlet, each tube having an outer surface being provided with a multitude of high fins extending radially outward from the outer surface;

the first flow path extending along the outer surface of the tubes, and the second flow path extending through the tubes.

10. The heat exchanger system of claim 9 further comprising a distributor plate arranged in the shell between the at least one first inlet and the number of parallel tubes.

11. The heat exchanger system of claim 9, wherein the multiple component process stream being a mixed refrigerant comprising two or more components, at least one of the components being a hydrocarbon.

12. The heat exchanger system of claim 9, wherein the multiple component process stream comprising two or more components selected from the group of methane, ethane, propane, and nitrogen.

13. The heat exchanger system of claim 9, wherein the parallel tubes has a diameter and wherein the high fins comprise a diameter greater than the diameter of the diameter of the parallel tubes by about 25% to 150%.

14. The exchanger system of claim 9, wherein the high fins has a height of 5 to 40 mm with respect to the outer surface of the parallel tubes.

15. The heat exchanger system of claim 9, wherein the high fins are plate fins.

16. The heat exchanger system of claim 9, wherein the heat exchanger system is a cross flow heat exchanger system with the first flow path being generally perpendicular to the second flow path.

17. The method of claim 1, wherein the parallel tubes has a diameter and wherein the high fins comprise a diameter greater than the diameter of the diameter of the parallel tubes by about 25% to 150%.

18. The method of claim 1, wherein the high fins has a height of 5 to 40 mm with respect to the outer surface of the parallel tubes.

19. The method of claim 1, wherein the high fins are plate fins.

20. The method of claim 1, wherein the heat exchanger system is a cross flow heat exchanger system with the first flow path being generally perpendicular to the second flow path.