EP1610081A1 - Heat exchange process and heat exchanger - Google Patents
Heat exchange process and heat exchanger Download PDFInfo
- Publication number
- EP1610081A1 EP1610081A1 EP05013053A EP05013053A EP1610081A1 EP 1610081 A1 EP1610081 A1 EP 1610081A1 EP 05013053 A EP05013053 A EP 05013053A EP 05013053 A EP05013053 A EP 05013053A EP 1610081 A1 EP1610081 A1 EP 1610081A1
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- EP
- European Patent Office
- Prior art keywords
- fluid
- heating zone
- heat exchanger
- zone
- heat exchange
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- 238000000034 method Methods 0.000 title claims abstract description 13
- 238000010438 heat treatment Methods 0.000 claims abstract description 74
- 239000012530 fluid Substances 0.000 claims abstract description 62
- 239000000956 alloy Substances 0.000 claims abstract description 17
- 229910045601 alloy Inorganic materials 0.000 claims abstract description 16
- 238000005260 corrosion Methods 0.000 claims abstract description 16
- 230000007797 corrosion Effects 0.000 claims abstract description 16
- 229910000851 Alloy steel Inorganic materials 0.000 claims abstract description 12
- 238000001816 cooling Methods 0.000 claims abstract description 4
- 229910052751 metal Inorganic materials 0.000 claims description 18
- 239000002184 metal Substances 0.000 claims description 18
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims description 14
- 229910052759 nickel Inorganic materials 0.000 claims description 7
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims description 4
- 239000011651 chromium Substances 0.000 claims description 4
- 229910000599 Cr alloy Inorganic materials 0.000 claims description 3
- 229910000640 Fe alloy Inorganic materials 0.000 claims description 3
- 235000012489 doughnuts Nutrition 0.000 claims description 3
- 239000007789 gas Substances 0.000 description 17
- 238000010410 dusting Methods 0.000 description 14
- 230000015572 biosynthetic process Effects 0.000 description 8
- 238000003786 synthesis reaction Methods 0.000 description 8
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 5
- 229910002091 carbon monoxide Inorganic materials 0.000 description 5
- 238000006243 chemical reaction Methods 0.000 description 5
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 4
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 4
- 239000000463 material Substances 0.000 description 3
- 238000000629 steam reforming Methods 0.000 description 3
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- 229910000831 Steel Inorganic materials 0.000 description 2
- 229910001026 inconel Inorganic materials 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- 238000002407 reforming Methods 0.000 description 2
- 239000010959 steel Substances 0.000 description 2
- 239000002918 waste heat Substances 0.000 description 2
- 229910000975 Carbon steel Inorganic materials 0.000 description 1
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 1
- 238000009835 boiling Methods 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 239000010962 carbon steel Substances 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 230000002542 deteriorative effect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 125000004435 hydrogen atom Chemical class [H]* 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 229910001092 metal group alloy Inorganic materials 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 239000011733 molybdenum Substances 0.000 description 1
- 230000002093 peripheral effect Effects 0.000 description 1
- 238000006722 reduction reaction Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Images
Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
- F28D7/00—Heat-exchange apparatus having stationary tubular conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
- F28F21/00—Constructions of heat-exchange apparatus characterised by the selection of particular materials
- F28F21/08—Constructions of heat-exchange apparatus characterised by the selection of particular materials of metal
- F28F21/081—Heat exchange elements made from metals or metal alloys
- F28F21/082—Heat exchange elements made from metals or metal alloys from steel or ferrous alloys
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
- F28D7/00—Heat-exchange apparatus having stationary tubular conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall
- F28D7/06—Heat-exchange apparatus having stationary tubular conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall the conduits having a single U-bend
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
- F28D7/00—Heat-exchange apparatus having stationary tubular conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall
- F28D7/10—Heat-exchange apparatus having stationary tubular conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall the conduits being arranged one within the other, e.g. concentrically
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
- F28D7/00—Heat-exchange apparatus having stationary tubular conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall
- F28D7/16—Heat-exchange apparatus having stationary tubular conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall the conduits being arranged in parallel spaced relation
- F28D7/163—Heat-exchange apparatus having stationary tubular conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall the conduits being arranged in parallel spaced relation with conduit assemblies having a particular shape, e.g. square or annular; with assemblies of conduits having different geometrical features; with multiple groups of conduits connected in series or parallel and arranged inside common casing
- F28D7/1669—Heat-exchange apparatus having stationary tubular conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall the conduits being arranged in parallel spaced relation with conduit assemblies having a particular shape, e.g. square or annular; with assemblies of conduits having different geometrical features; with multiple groups of conduits connected in series or parallel and arranged inside common casing the conduit assemblies having an annular shape; the conduits being assembled around a central distribution tube
- F28D7/1676—Heat-exchange apparatus having stationary tubular conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall the conduits being arranged in parallel spaced relation with conduit assemblies having a particular shape, e.g. square or annular; with assemblies of conduits having different geometrical features; with multiple groups of conduits connected in series or parallel and arranged inside common casing the conduit assemblies having an annular shape; the conduits being assembled around a central distribution tube with particular pattern of flow of the heat exchange media, e.g. change of flow direction
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
- F28F21/00—Constructions of heat-exchange apparatus characterised by the selection of particular materials
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
- F28F9/00—Casings; Header boxes; Auxiliary supports for elements; Auxiliary members within casings
- F28F9/22—Arrangements for directing heat-exchange media into successive compartments, e.g. arrangements of guide plates
Definitions
- the invention concerns a heat exchanger and a process for heat exchange in which the heat exchanger is applicable.
- the invention relates to a heat exchanger useful as a steam super heater and having improved resistance to metal dusting and stress corrosion.
- Steam reforming is most often an essential step in the production of carbon monoxide rich synthesis gas.
- methane and steam is hereby converted under supply of heat to a gas composition comprising hydrogen, carbon dioxide, carbon monoxide, steam and methane.
- the temperature of the synthesis gas after reforming is most often between 750°C and 1050°C.
- the hot synthesis gas is subsequently cooled in a boiler or in a boiler and a super heater.
- Metal dusting is a deteriorating attack of the carbon monoxide rich gas on alloys based on iron and/or nickel.
- a basic reaction by metal dusting is the decomposition of carbon monoxide in a reduction reaction or the bouduard-reaction.
- Metal dusting only takes place when the metal surface temperature is below the equilibrium temperature of these reactions. That will typically be between 750°C and 850°C. However, if the temperature is lower, typically below 450°C, the reaction will not take place at a significant rate. This means that there is a metal temperature surface intermediate, which should be avoided for contact with gas in reformed gas coolers. These temperature ranges are between 450-800°C for nickel based high alloys and 400-800°C for low alloy steels.
- waste heat boilers are cooled by the effective heat transfer to the boiling water and can therefore normally be designed to avoid conditions of metal dusting.
- super heaters when applied as coolers for synthesis gasses have to be considered as subject to metal dusting attack.
- Nickel based alloys are very sensitive to stress corrosion, whereas low alloy steels are not. Nickel based alloys should therefore only be in contact with dry steam.
- the invention provides a heat exchange process comprising sequentially cooling of a first fluid by indirect heat exchange with a second fluid and comprising the following steps:
- the invention also provides a heat exchanger for use in the above process, the heat exchanger for use in the above heat exchange process, the heat exchanger comprising a plurality of U-tubes securing a heat exchange surface for allowing heat transfer between a first and a second fluid, the U-tubes arranged in at least two sequential concentric tube bundles, the tube bundles defining at least a first and second heating zone respectively, each heating zone partially separated from the other by a wall, the first heating zone being a colder zone and the second heating zone being a hotter zone, the tube bundle of the first colder heating zone being made of a low alloy steel and the tube bundle of the second hotter heating zone being made of a temperature and corrosion resistant alloy.
- the invention concerns a heat exchanger which is useful as a super heater and is designed to avoid metal dusting and stress corrosion by a proper selection of a combination of metal alloys and gas/steam flow through a pre-defined pattern of heat exchange tube bundles.
- the heat exchanger is suitable for heat exchange between a first and a second fluid.
- An example of such fluids is steam (first fluid) and synthesis gas (second fluid).
- the hot synthesis gas from a steam reforming reactor is cooled by steam in the heat exchanger.
- the heat exchanger is of the U-tube type with a thick tube sheet.
- a plurality of U-tubes for transfer of the first fluid are arranged parallel and spaced apart with a central inlet and a peripheral outlet for the second fluid.
- the shell side heat exchange is enhanced by disc and doughnut baffles.
- the plurality of tubes is arranged in tube bundles, each tube bundle corresponding to a particular heating zone.
- the first fluid for instance steam
- the second fluid for instance reformed gas
- the essential principle of the invention is that at least two tube bundles are present in the heat exchanger and they are connected to one tube sheet in concentric rings.
- the compartments for each tube bundle are separated by metallic walls with openings in their middle or at their ends through which the second fluid passes and is divided into several streams when flowing from one compartment to the other.
- the second fluid flows both countercurrent- and concurrent to the first fluid within each tube bundle compartment, as shown by the arrows in figures 1 and 3.
- Figure 1 relates to an embodiment of the invention having two heating zones separated by a wall.
- the first fluid for instance steam, enters the heat exchanger through inlet 1.
- the first fluid then enters a compartment comprising U-tubes in a first tube bundle and defining a first heating zone 2.
- the first fluid After passing through the U-tubes in the first heating zone in indirect heat exchange with the second fluid, the first fluid enters a second compartment comprising the U-tubes in a second tube bundle and defining a second heating zone 3.
- the U-tubes of the second tube bundle are placed sequentially after the U-tubes of the first tube bundle.
- the tube bundle defining the second heating zone 3 is placed innermost in the heat exchanger while the tube bundle defining the first heating zone 2 is placed outermost and the two tube bundles are separated by a wall 12.
- the wall 12 can be of metal and it is positioned and constructed to provide openings 15 and 16 allowing division of the flow of the second fluid into several streams, when flowing from one compartment to the other.
- the first fluid passes through the U-tubes in the second heating zone 3 in indirect heat exchange with the second fluid. After passing through the second heating zone 3 the first fluid is now heated and it leaves the heat exchanger through the outlet 4.
- the second fluid for instance synthesis gas, or any other hot gas that requires cooling, enters the heat exchanger through inlet 5.
- Inlet 5 leads to a central pipe 13 placed in the middle of the innermost tube bundle.
- This central pipe 13 has openings 14 allowing the second fluid to leave the central pipe 13 and enter the second heating zone 3 on the shell side of the tube bundles defining this heating zone. It is preferable that the openings 14 are not located at the ends of the central pipe 13, in order to ensure both concurrent and countercurrent flow.
- the second fluid enters the middle of heating zone 3 through the openings 14 and the fluid is then divided to flow towards the two ends of the tube bundle.
- the second fluid thus contacts the external surfaces i.e. the shell side of the U-tubes of the innermost tube bundle and is cooled in indirect heat exchange with the first fluid.
- the second fluid thereafter passes through end openings 15 and 16 in the wall 12 separating the two tube bundles defining the first and second heating zones 2 and 3.
- the opening 15 is at the lower end of the wall 12 and the opening 16 is at the upper end of the wall 12.
- the second fluid then passes across the shell side of the tube bundles defining the first heating zone 2, which surrounds the innermost bundle defining the second heating zone 3.
- the gas then flows in the tube bundle from the end openings 15 and 16 towards the middle of the heating zone 2.
- the further cooled second fluid then leaves the first heating zone 2 and the heat exchanger through outlet 6.
- Figure 2 shows the placement of the tube bundles relative to each other in the heat exchanger.
- the wall 12 divides the heating zones into two compartments resulting in heating zones 2 and 3.
- the tube bundles are placed in the heat exchanger with the tube bundle of heating zone 2 placed outermost and the tube bundles of heating zone 3 placed innermost.
- the heat exchanger can have three heating zones, as shown in figure 3.
- the third bundle also defines a heating zone 11 allowing further heat exchange of the first fluid with the second.
- the second fluid enters the middle of this heating zone through a central opening 17 in the wall 18 separating the outermost tube bundle from the two innermost tube bundles.
- the wall 18 separates thereby heating zone 11 from heating zones 2 and 3.
- the fluid is then divided into streams flowing towards the two ends of the tube bundle.
- the walls separating the compartments can therefore have openings at either their ends (15 and 16) or in their middle (17).
- the openings in each subsequent wall therefore alternate by being either at the end of the wall or in its middle. This ensures that the flow of the second fluid is both concurrent and counter current to the flow of the first fluid in each heating zone. Effective heat exchange is thereby realised.
- the second fluid is in this way cooled by subsequent flow (divided flow) through the two or three tube bundles.
- first fluid is heated by subsequent flow through the tubes, starting in the outermost bundle, which is coldest and has the lowest temperature and leaving after flow through the innermost bundle, which is hottest and therefore has the highest temperature.
- the outmost tube bundle defining the heating zone 2 therefore corresponds to a cold zone (a low temperature zone) and the innermost bundle defining the heating zone 3 therefore corresponds to a hot zone (a high temperature zone).
- the heating zone 2 in the middle between heating zones 3 and 11 has intermediate temperatures between the hottest (high temperature zone) and the coldest (low temperature zone) zones.
- Baffles can be placed in the heating zones in order to improve the heat distribution.
- Baffles particularly suitable for the heat exchanger are of the disc and doughnut type. These have the effect of allowing the second fluid to travel through the heating zones in a zig-zag movement and additionally they assist in positioning the U-tubes.
- the baffles 7, 8 and 9 shown in figure 1 are held in place by rods.
- Baffle 7 is hot i.e. experiences high temperature
- baffle 8 is cold i.e. experiences low temperature.
- the baffles 10 in the central pipe are hot baffles.
- Baffles can also be placed in the embodiment shown in figure 3.
- the hot (high temperature) tube bundle defining heating zone 3 must be made of a material resistant to metal dusting. This could for example be a high alloy such as austenitic nickel/chromium/iron alloy, for instance Inconel®.
- the baffles, rods and walls defining the channels in which the tube bundles are situated must also be resistant to metal dusting.
- the cold (low temperature) tube bundle defining heating zone 2 may be of low alloy steel and in most cases the baffles and rods may also be of low alloy material. If a third bundle of tubes are present as shown in figure 3, the tubes of the middle/intermediate bundle may be of low alloy steel, whereas the rods, baffles and walls/channels may be of Inconel®.
- the low alloy steel could for example be a ferritic iron, chromium, molybdenum, carbon steel.
- Characteristic for the heat exchanger of the invention is that the U-tubes are of materials resistant to metal dusting when the material surface is hot enough to give a risk of metal dusting.
- the U-tubes can be of cheaper low alloy steel when situated in colder zones. Low alloy steel is not sensitive to wet stress corrosion. When the first fluid is steam, it enters U-tubes of low alloy steel, and the steam will not come in contact with the U-tubes of high alloys before it is completely dry.
- the heat exchanger of the invention shows an improvement in its heat exchange performance due to it enhanced resistance towards metal dusting and stress corrosion.
- a typical process in which the heat exchanger is useful is in a steam reforming process as described in the following:
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- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Geometry (AREA)
- Heat-Exchange Devices With Radiators And Conduit Assemblies (AREA)
Abstract
- introducing the first fluid sequentially into at least two concentric U-tube bundles defining at least a first heating zone and a second heating zone respectively,
- introducing a second fluid onto the shell side of the U-tube bundles, each heating zone partially separated from the other by a wall, the first heating zone being a colder zone and the second heating zone being a hotter zone, the tube bundle of the first colder heating zone being made of a low alloy steel and the tube bundle of the second hotter heating zone being made of a temperature and corrosion resistant alloy,
- withdrawing the cooled second fluid and the heated first fluid.
Description
- The invention concerns a heat exchanger and a process for heat exchange in which the heat exchanger is applicable. In particular the invention relates to a heat exchanger useful as a steam super heater and having improved resistance to metal dusting and stress corrosion.
- Steam reforming is most often an essential step in the production of carbon monoxide rich synthesis gas. In this reaction methane and steam is hereby converted under supply of heat to a gas composition comprising hydrogen, carbon dioxide, carbon monoxide, steam and methane. The temperature of the synthesis gas after reforming is most often between 750°C and 1050°C. The hot synthesis gas is subsequently cooled in a boiler or in a boiler and a super heater.
- One of the severe conditions related to coolers for reformed gas is the corrosion known as metal dusting. Metal dusting is a deteriorating attack of the carbon monoxide rich gas on alloys based on iron and/or nickel. A basic reaction by metal dusting is the decomposition of carbon monoxide in a reduction reaction or the bouduard-reaction. Metal dusting only takes place when the metal surface temperature is below the equilibrium temperature of these reactions. That will typically be between 750°C and 850°C. However, if the temperature is lower, typically below 450°C, the reaction will not take place at a significant rate. This means that there is a metal temperature surface intermediate, which should be avoided for contact with gas in reformed gas coolers. These temperature ranges are between 450-800°C for nickel based high alloys and 400-800°C for low alloy steels.
- The heat transfer surfaces of waste heat boilers are cooled by the effective heat transfer to the boiling water and can therefore normally be designed to avoid conditions of metal dusting. However, super heaters when applied as coolers for synthesis gasses have to be considered as subject to metal dusting attack.
- Another severe condition to consider in the design of super heaters is the possibility of stress corrosion from the wet steam which is to be superheated. Nickel based alloys are very sensitive to stress corrosion, whereas low alloy steels are not. Nickel based alloys should therefore only be in contact with dry steam.
- It is therefore an objective of the invention to provide a heat exchanger which shows improved resistance to metal dusting and stress corrosion.
- The invention provides a heat exchange process comprising sequentially cooling of a first fluid by indirect heat exchange with a second fluid and comprising the following steps:
- introducing the first fluid sequentially into at least two concentric U-tube bundles defining at least a first heating zone and a second heating zone respectively,
- introducing a second fluid onto the shell side of the U-tube bundles, each heating zone partially separated from the other by a wall, the first heating zone being a colder zone and the second heating zone being a hotter zone, the tube bundle of the first colder heating zone being made of a low alloy steel and the tube bundle of the second hotter heating zone being made of a temperature and corrosion resistant alloy,
- withdrawing the cooled second fluid and the heated first fluid.
- The invention also provides a heat exchanger for use in the above process, the heat exchanger for use in the above heat exchange process, the heat exchanger comprising a plurality of U-tubes securing a heat exchange surface for allowing heat transfer between a first and a second fluid, the U-tubes arranged in at least two sequential concentric tube bundles, the tube bundles defining at least a first and second heating zone respectively, each heating zone partially separated from the other by a wall, the first heating zone being a colder zone and the second heating zone being a hotter zone, the tube bundle of the first colder heating zone being made of a low alloy steel and the tube bundle of the second hotter heating zone being made of a temperature and corrosion resistant alloy.
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- Figure 1 shows a heat exchanger with two heating zones.
- Figure 2 shows a horizontal section through a heat exchanger.
- Figure 3 shows a heat exchanger with three heating zones.
-
- The invention concerns a heat exchanger which is useful as a super heater and is designed to avoid metal dusting and stress corrosion by a proper selection of a combination of metal alloys and gas/steam flow through a pre-defined pattern of heat exchange tube bundles. The heat exchanger is suitable for heat exchange between a first and a second fluid. An example of such fluids is steam (first fluid) and synthesis gas (second fluid). The hot synthesis gas from a steam reforming reactor is cooled by steam in the heat exchanger.
- The heat exchanger is of the U-tube type with a thick tube sheet. A plurality of U-tubes for transfer of the first fluid are arranged parallel and spaced apart with a central inlet and a peripheral outlet for the second fluid. The shell side heat exchange is enhanced by disc and doughnut baffles. The plurality of tubes is arranged in tube bundles, each tube bundle corresponding to a particular heating zone.
- The first fluid, for instance steam, flows in the tubes and the second fluid, for instance reformed gas, flows around these tubes, i.e. on their shell side, thereby securing a heat transfer surface.
- The essential principle of the invention is that at least two tube bundles are present in the heat exchanger and they are connected to one tube sheet in concentric rings. The compartments for each tube bundle are separated by metallic walls with openings in their middle or at their ends through which the second fluid passes and is divided into several streams when flowing from one compartment to the other.
- The second fluid flows both countercurrent- and concurrent to the first fluid within each tube bundle compartment, as shown by the arrows in figures 1 and 3.
- The heat exchanger of the invention will be described in more detail in the following:
- In figures 1 and 3 the flow directions of the first and second fluids are indicated by curved arrows.
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- Figure 1 relates to an embodiment of the invention having two heating zones separated by a wall. The first fluid, for instance steam, enters the heat exchanger through inlet 1. The first fluid then enters a compartment comprising U-tubes in a first tube bundle and defining a
first heating zone 2. After passing through the U-tubes in the first heating zone in indirect heat exchange with the second fluid, the first fluid enters a second compartment comprising the U-tubes in a second tube bundle and defining asecond heating zone 3. - The U-tubes of the second tube bundle are placed sequentially after the U-tubes of the first tube bundle. In figure 1 the tube bundle defining the
second heating zone 3 is placed innermost in the heat exchanger while the tube bundle defining thefirst heating zone 2 is placed outermost and the two tube bundles are separated by awall 12. Thewall 12 can be of metal and it is positioned and constructed to provideopenings second heating zone 3 in indirect heat exchange with the second fluid. After passing through thesecond heating zone 3 the first fluid is now heated and it leaves the heat exchanger through theoutlet 4. - The second fluid, for instance synthesis gas, or any other hot gas that requires cooling, enters the heat exchanger through
inlet 5.Inlet 5 leads to acentral pipe 13 placed in the middle of the innermost tube bundle. Thiscentral pipe 13 hasopenings 14 allowing the second fluid to leave thecentral pipe 13 and enter thesecond heating zone 3 on the shell side of the tube bundles defining this heating zone. It is preferable that theopenings 14 are not located at the ends of thecentral pipe 13, in order to ensure both concurrent and countercurrent flow. - The second fluid enters the middle of
heating zone 3 through theopenings 14 and the fluid is then divided to flow towards the two ends of the tube bundle. The second fluid thus contacts the external surfaces i.e. the shell side of the U-tubes of the innermost tube bundle and is cooled in indirect heat exchange with the first fluid. The second fluid thereafter passes throughend openings wall 12 separating the two tube bundles defining the first andsecond heating zones wall 12 and the opening 16 is at the upper end of thewall 12. The second fluid then passes across the shell side of the tube bundles defining thefirst heating zone 2, which surrounds the innermost bundle defining thesecond heating zone 3. The gas then flows in the tube bundle from theend openings heating zone 2. The further cooled second fluid then leaves thefirst heating zone 2 and the heat exchanger throughoutlet 6. - Figure 2 shows the placement of the tube bundles relative to each other in the heat exchanger. The
wall 12 divides the heating zones into two compartments resulting inheating zones heating zone 2 placed outermost and the tube bundles ofheating zone 3 placed innermost. - In an embodiment of the invention, the heat exchanger can have three heating zones, as shown in figure 3. In this case there is a third bundle of U-tubes surrounding the second bundle. The third bundle also defines a heating zone 11 allowing further heat exchange of the first fluid with the second. The second fluid enters the middle of this heating zone through a
central opening 17 in thewall 18 separating the outermost tube bundle from the two innermost tube bundles. Thewall 18 separates thereby heating zone 11 fromheating zones - The walls separating the compartments can therefore have openings at either their ends (15 and 16) or in their middle (17). When several heating zones are at present the openings in each subsequent wall therefore alternate by being either at the end of the wall or in its middle. This ensures that the flow of the second fluid is both concurrent and counter current to the flow of the first fluid in each heating zone. Effective heat exchange is thereby realised.
- The second fluid is in this way cooled by subsequent flow (divided flow) through the two or three tube bundles. When two heating zones are present as shown in figure 1, the first fluid is heated by subsequent flow through the tubes, starting in the outermost bundle, which is coldest and has the lowest temperature and leaving after flow through the innermost bundle, which is hottest and therefore has the highest temperature. The outmost tube bundle defining the
heating zone 2 therefore corresponds to a cold zone (a low temperature zone) and the innermost bundle defining theheating zone 3 therefore corresponds to a hot zone (a high temperature zone). - When three heating zones are present as shown in figure 3, the
heating zone 2 in the middle betweenheating zones 3 and 11, has intermediate temperatures between the hottest (high temperature zone) and the coldest (low temperature zone) zones. - Baffles can be placed in the heating zones in order to improve the heat distribution. Baffles particularly suitable for the heat exchanger are of the disc and doughnut type. These have the effect of allowing the second fluid to travel through the heating zones in a zig-zag movement and additionally they assist in positioning the U-tubes. The
baffles Baffle 7 is hot i.e. experiences high temperature, andbaffle 8 is cold i.e. experiences low temperature. Thebaffles 10 in the central pipe are hot baffles. Baffles can also be placed in the embodiment shown in figure 3. - The hot (high temperature) tube bundle defining
heating zone 3 must be made of a material resistant to metal dusting. This could for example be a high alloy such as austenitic nickel/chromium/iron alloy, for instance Inconel®. The baffles, rods and walls defining the channels in which the tube bundles are situated must also be resistant to metal dusting. The cold (low temperature) tube bundle definingheating zone 2 may be of low alloy steel and in most cases the baffles and rods may also be of low alloy material. If a third bundle of tubes are present as shown in figure 3, the tubes of the middle/intermediate bundle may be of low alloy steel, whereas the rods, baffles and walls/channels may be of Inconel®. The low alloy steel could for example be a ferritic iron, chromium, molybdenum, carbon steel. - Characteristic for the heat exchanger of the invention is that the U-tubes are of materials resistant to metal dusting when the material surface is hot enough to give a risk of metal dusting. The U-tubes can be of cheaper low alloy steel when situated in colder zones. Low alloy steel is not sensitive to wet stress corrosion. When the first fluid is steam, it enters U-tubes of low alloy steel, and the steam will not come in contact with the U-tubes of high alloys before it is completely dry.
- The heat exchanger of the invention shows an improvement in its heat exchange performance due to it enhanced resistance towards metal dusting and stress corrosion.
- A typical process in which the heat exchanger is useful is in a steam reforming process as described in the following:
- Hot effluent, for instance a carbon monoxide containing reformed gas such as synthesis gas from a reforming reactor, is passed to a waste heat boiler where the temperature of the effluent is reduced from, for instance 1050°C to 475°C, using steam supplied from a steam drum. The cooled effluent is then sent to a heat exchanger of the invention where the temperature is further reduced to 360°C by heat exchange with steam. The heat exchanger functions as a steam super heater. The steam used can be supplied from the steam drum and it is thereby heated from a temperature of for instance 320°C to 400°C.
-
Claims (10)
- Heat exchange process comprising sequentially cooling a first fluid by indirect heat exchange with a second fluid and comprising the following steps:introducing the first fluid sequentially into at least two concentric U-tube bundles defining at least a first heating zone and a second heating zone respectively,introducing a second fluid onto the shell side of the U-tube bundles, each heating zone partially separated from the other by a wall, the first heating zone being a colder zone and the second heating zone being a hotter zone, the tube bundle of the first colder heating zone being made of a low alloy steel and the tube bundle of the second hotter heating zone being made of a temperature and corrosion resistant alloy,withdrawing the cooled second fluid and the heated first fluid.
- Heat exchange process according to claim 1, wherein the first fluid is steam and the second fluid is reformed gas.
- Heat exchange process according to claim 1, wherein the temperature and corrosion resistant alloy is austenitic nickel/chromium/iron alloy.
- Heat exchange process according to claim 2, wherein the heated first fluid is superheated steam.
- Heat exchanger for use in the process of claim 1, comprising a plurality of U-tubes securing a heat exchange surface for allowing heat transfer between a first and a second fluid, the U-tubes arranged in at least two sequential concentric tube bundles, the tube bundles defining at least a first and second heating zone respectively, each heating zone partially separated from the other by a wall, the first heating zone being a colder zone and the second heating zone being a hotter zone, the tube bundle of the first colder heating zone being made of a low alloy steel and the tube bundle of the second hotter heating zone being made of a temperature and corrosion resistant alloy.
- Heat exchanger according to claim 5, wherein the heat exchanger has three tube bundles, the third bundle being placed in the middle between the first and the second bundles.
- Heat exchanger according to claim 5, wherein the temperature and corrosion resistant alloy is austenitic nickel/chromium/iron alloy.
- Heat exchanger according to claim 5, wherein the heat exchanger has baffles of the disc and doughnut type.
- Heat Exchanger according to claim 6, wherein the tubes of the third bundle placed in the middle are of low alloy steel and the baffles and rods holding the baffles in place and the walls of the middle bundle are of temperature and corrosion resistant alloy.
- Heat exchanger according to claim 5, wherein the wall separating the heating zones is of metal and is positioned to divide the flow of the second fluid into several streams by passage through openings in the wall.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DK200400998 | 2004-06-25 | ||
DKPA200400998 | 2004-06-25 |
Publications (1)
Publication Number | Publication Date |
---|---|
EP1610081A1 true EP1610081A1 (en) | 2005-12-28 |
Family
ID=34937511
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP05013053A Withdrawn EP1610081A1 (en) | 2004-06-25 | 2005-06-16 | Heat exchange process and heat exchanger |
Country Status (9)
Country | Link |
---|---|
US (2) | US20050284606A1 (en) |
EP (1) | EP1610081A1 (en) |
JP (1) | JP2006010309A (en) |
KR (1) | KR101175993B1 (en) |
CN (1) | CN1715743A (en) |
AU (1) | AU2005202782B2 (en) |
CA (1) | CA2510916C (en) |
RU (1) | RU2374587C2 (en) |
ZA (1) | ZA200505145B (en) |
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DE102010040278A1 (en) * | 2010-09-06 | 2012-03-08 | Siemens Aktiengesellschaft | Heat exchanger e.g. steam generator used in nuclear plant, has perforated plate whose surface is divided into hot and cold regions, such that heat transfer medium flows through passages in opposite directions |
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EP3406999A1 (en) | 2017-05-26 | 2018-11-28 | ALFA LAVAL OLMI S.p.A. | Shell-and-tube heat exchanger |
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Also Published As
Publication number | Publication date |
---|---|
RU2005119478A (en) | 2006-12-27 |
CN1715743A (en) | 2006-01-04 |
CA2510916C (en) | 2013-08-13 |
US20100218931A1 (en) | 2010-09-02 |
US20050284606A1 (en) | 2005-12-29 |
JP2006010309A (en) | 2006-01-12 |
AU2005202782A1 (en) | 2006-01-12 |
ZA200505145B (en) | 2006-04-26 |
AU2005202782B2 (en) | 2009-12-10 |
KR20060049684A (en) | 2006-05-19 |
KR101175993B1 (en) | 2012-08-23 |
RU2374587C2 (en) | 2009-11-27 |
CA2510916A1 (en) | 2005-12-25 |
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