Heat exchanger, combination with heat exchanger and method of manufacturing the heat exchanger
A heat exchanger for heat exchange between a first and a second fluid and comprising a cylindrical casing 2, a cylindrical fluid conduit 5 arranged inside the casing such that an axially extending tubular space 8 is defined, at least one helical coil 9, 10 of a finned or corrugated tube being arranged inside the tubular space, and adjustable throttle means 17, 17a, 18 adapted and arranged for adjustably throttling flow of the first fluid through the conduit 5 to adjust the flow of the first fluid through the conduit and the first tubular space for adjusting the heat exchange between the first fluid and the second fluid flowing through the helical coils 9, 10.
Latest Aalborg Industries A/S Patents:
The present invention relates to a heat exchanger for heat exchange between a first fluid and a second fluid and comprising a generally cylindrical casing with a first inlet and a first outlet for allowing said first fluid to flow through said casing in a generally axial direction, and at least one helical coil of a finned or corrugated tube arranged inside said casing.
Heat exchangers of this type are known where the first fluid is forced to flow from inside the coil or coils outwards or vice versa. The transfer of heat from the first fluid to the second fluid in the coils is not very well controlled and therefore not as efficient as possible.
It is an object of the invention to provide a heat exchanger of the type in reference where the flow of first fluid, for instance exhaust gas from a natural gas fired turbine, an internal combustion engine, an incinerator, a furnace, a burner or the like, takes place around the finned tube in a well controlled and efficient manner affording a highly efficient heat transfer from the first fluid to the second fluid, for instance water.
According to the invention this object is obtained by providing a generally cylindrical fluid conduit inside said casing generally coaxial therewith so that an axially extending first tubular space is defined between said conduit and said casing, said conduit having a second inlet and a second outlet for allowing said first fluid to flow through said conduit in a generally axial direction, and said first tubular space having a third inlet and a third outlet for allowing said first fluid to flow through said first tubular space in a generally axial direction, the at least one helical coil of a finned or corrugated tube being arranged inside said first tubular space generally coaxial therewith and having a fourth inlet and a fourth outlet for allowing said second fluid to flow through said finned tube.
Hereby, the first fluid is forced to flow around the finned tube coil windings in a very efficient manner for heat exchange. This also reduces the space requirements for the heat exchanger, the so-called “footprint”.
According to the invention, the heat exchanger further comprises first adjustable throttle means for adjustably throttling said flow of said first fluid through said conduit and/or second adjustable throttle means for adjustably throttling said flow of said first fluid through said first tubular space.
Hereby, the flow of first fluid may by-pass the finned tube coils so that the heat transfer to the second fluid may be reduced according to the demand for heated second fluid. Furthermore, the pressure loss from the inlet of the casing to the outlet thereof may be reduced by by-passing the finned tube coils which is desirable during start up of for instance a gas fired turbine generating the first fluid in the form of exhaust gas from the gas combustion.
In one of the currently preferred embodiments of the heat exchanger according to the invention, said first throttle means comprise a first butterfly valve, preferably arranged adjacent said second inlet or said second outlet, and said second throttle means comprise a second butterfly valve, preferably arranged adjacent said third inlet or said third outlet. Hereby, rather simple mechanisms that are simple to adjust and regulate are provided.
In an alternative embodiment, said first throttle means comprise a first butterfly valve, preferably arranged adjacent said second inlet or said second outlet, and said second throttle means comprise a ring having planar dimensions corresponding to the cross section of said first tubular space and being arranged for being displaced from a heating position wherein said flow of first fluid through said tubular space is substantially unhindered to a bypass position wherein said flow is substantially obstructed. In this embodiment, the space requirements are reduced.
In another currently preferred embodiment, said first and second throttle means comprise a fixedly arranged stationary plate with first and second apertures provided therein arranged such that said second and third inlets or outlets are obstructed by said plate such that the flow of first fluid through said conduit and said first tubular space takes place through said first and second apertures, respectively, in said stationary plate, and one or two movable plates with third and fourth apertures provided therein and arranged displaceable, preferably rotatably displaceable, from a bypass position overlying said stationary plate, wherein said third apertures coincide with said first apertures and said fourth apertures do not coincide with said second apertures, to a heating position overlying said stationary plate wherein said fourth apertures coincide with said second apertures and said third apertures do not coincide with said first apertures. This embodiment of the first and second throttle means requires a minimum of space and is particularly well suited for precise adjustment of the by-pass flow through the conduit relative to the heat transfer flow through the tubular space.
In the currently preferred embodiment, the heat exchanger according to the invention further comprises preferably motorized actuating means for adjusting the throttling effect of said first and second throttle means, and said throttling means and said actuating means are preferably adapted such that substantially any rate of flow between a maximum and minimum rate of flow of said first fluid through said second inlet and said third inlet may be obtained. Said minimum rate is substantially equal to zero. Hereby, any distribution of fluid flow between the by-pass conduit and the tubular space may obtained which allows simple and precise regulation of the output of the heat exchanger according to the requirements for heat transfer from the first fluid. By allowing substantially total by-pass, no heat is transferred to the second fluid which is advantageous in case no heat transfer is needed to means exterior of the heat exchanger and therefore no temperature increase with consequent steam formation will take place in the finned coil or coils.
The currently preferred embodiment of a heat exchanger according to the invention comprises two or more of said helical coils arranged concentrically and such that mutually adjacent coils are radially spaced such that an axially extending second tubular space is provided between said mutually adjacent coils, and the outer surface of said conduit is spaced radially from the coil adjacent said surface such that an axially extending third tubular space is provided between said surface and said adjacent coil, the radial dimensions of said second and third tubular spaces being adapted so as to achieve a certain pressure loss for a given rate of flow of said first fluid through said first tubular space.
Hereby, the pressure loss from said first inlet to said first outlet for a given flow of first fluid may be kept at a minimum while not substantially reducing the efficiency of the heat exchanger. This is particularly of importance in connection with gas fired turbines being the origin of said first fluid because gas turbines are particularly sensitive to the back pressure at the exhaust outlet thereof.
Preferably, the mutually adjacent individual windings of a coil are mutually axially spaced such that a helically extending space is provided between said adjacent windings. Hereby any differential thermal expansion or contraction of the casing and/or conduit relative to the coils in the axial direction will be taken up by said helically extending space.
In a currently preferred embodiment of a heat exchanger according to the invention and comprising three or more of said helical coils arranged concentrically and the interior diameter of the finned tubes constituting the coils preferably being the same, third throttling means are provided in the tubes constituting the coils located radially inwards of the outermost coil for increasing the pressure loss through the tubes of said inner coils so as to compensate for the shorter length of said tubes relative to the length of the tubes of the outermost coil such that the rate of flow of said second fluid through the tubes of all the coils is substantially the same for a given uniform pressure in said second fluid at said fourth inlets. Hereby, the heat transfer efficiency of each coil will be substantially the same without having to vary the diameter of the tubes of each coil to achieve this effect.
In the currently preferred embodiment of a heat exchanger according to the invention said third throttling means are constituted by a reduction of the cross sectional area of the flow of said second fluid relative to the internal cross sectional area of said tubes, the heat exchanger preferably further comprising an inlet header tube and an outlet header tube in fluid communication with said fourth inlets and fourth outlets, respectively, of all said tubes through corresponding communication apertures in said header tubes, said reduction of flow cross sectional area being constituted by reduced size of said communication apertures in said inlet header tube and/or in said outlet header tube. This is a particularly simple and inexpensive way of compensating for the different lengths of the different coils.
In case the heat exchanger according to the invention is to be used for generating steam, then according to the invention each helical coil may advantageously comprise two or more helically wound finned tubes extending adjacent one another with the same pitch. Hereby the number of flow paths is increased which is advantageous in connection with the large volume expansion of the water in the coil tubes resulting from the steam generation.
In another aspect, the present invention relates to a combination of a heat exchanger according to the invention and an exhaust gas generating combustion means such as a natural gas fired turbine, an internal combustion engine based on gasoline, diesel oil or natural gas, a furnace, a burner, an incinerator and the like, the combination comprising interconnection means for interconnecting an exhaust gas outlet of the combustion means with said second and third inlets of the heat exchanger such that said exhaust gas constitutes said first fluid.
The currently preferred embodiment of the combination according to the invention may further comprise heat exchanging means for heat exchange between said second fluid and a third fluid and/or the surroundings of said heat exchanging means, said heat exchanging means being in fluid communication with said fourth outlet, measuring means for measuring the rate of heat exchange of said heat exchanging means, signal output means for emitting a signal representing the result of a measurement carried out by said measuring means, and first control means for controlling the adjustment of said first and second throttle means and adapted for receiving said signal.
Preferably, the combination according to the invention further comprises second control means for controlling the adjustment of said first throttle means such that the throttling effect thereof is at a minimum during the start up phase of the combustion means.
In yet another aspect, the present invention relates to a method of manufacturing a heat exchanger according to the invention and comprising the steps of providing a first length of finned or corrugated tube, providing a body having a substantially circular cylindrical surface, providing rotating means for causing relative rotation of said tube and said surface, arranging a lead portion of said tube abutting against said surface, and causing relative rotation of said surface and said lead portion such that said first length of tube is helically wound on said surface to form a first helical coil. Hereby, a particularly simple, precise and inexpensive method of manufacturing a heat exchanger according to the invention is achieved.
In connection with heat exchangers according to the invention having two or more concentric coils, the method according to the invention preferably comprises the further steps of providing spacing means, attaching said spacing means to said first helical coil, providing a second length of finned or corrugated tube, arranging a lead portion of said second length of finned tube abutting against said spacing means, causing relative rotation of first helical coil and said lead portion of said second length of tube such that said second length of tube is helically wound on said spacing means to form a second helical coil radially spaced from said first helical coil.
So as to avoid inaccuracies in the diameter of the coils and other disadvantages, the method according to the invention preferably comprises the further steps of fixating said helical coil relative to said body, and subjecting said body and said coil to annealing heat treatment and/or fixating said second helical coil relative to said body and/or said first helical coil, and subjecting said body and said first and second coils to annealing heat treatment. Hereby the diameter alteration of the coils because of elasticity and stresses in the steel of the coil tubes is avoided in a simple and cost efficient manner.
In the following the invention will be explained more in detail with reference to different embodiments thereof shown, solely by way of example, in the accompanying drawings where:
Referring first to
The finned tube coils 9 and 10 are arranged mutually concentric and coaxially with the outer and inner casings 2 and 5. A flanged outlet header tube 13 and a flanged inlet header tube 14 communicate with the interior of the tubes 11 of the coils 9 and 10 through apertures 15 and 16, respectively.
A butterfly valve 17 (by-pass valve) is pivotably arranged on a shaft 18 at the outlet 7 of the conduit 5, a position wherein the valve 17 is in an intermediate position between fully closing the outlet 7 and fully opening said outlet 7 being shown with dotted lines at 17a. Semicircular rings 19 and 20 are arranged for abutting the rim of the butterfly valve 17 in the closed position thereof thereby ensuring a good closing function of the valve 17.
The heat exchanger 1 is primarily intended for use in combination with a natural gas fired turbine for recuperating and utilizing the heat of the exhaust gases thereof, but may in principle be used in combination with any means producing a heated gas such as internal combustion engines, furnaces, burners, incinerators and the like.
During maximum output operation of the heat exchanger 1, the butterfly by-pass valve 17 is in the closed position shown in full lines in
The heated water is transported to not shown exterior heat exchange means for transmitting some of the heat of the water to some other fluid or to the surroundings, typically radiators in a building heating system or a district heating system.
Either during start up of the gas turbine (when the pressure loss through the heat exchanger 1 should be at a minimum to facilitate the turbine start up) or when the exterior heat exchange means do not require the full heating capacity of the heat exchanger 1, then the butterfly valve 17 is pivoted on shaft 18 so as to allow some or all the exhaust gas from the gas turbine to flow through the internal conduit 5 as indicated with dotted arrows thereby by-passing the tubular space 8 and the coils 9 and 10.
Hereby, the pressure loss through the heat exchanger 1 is decreased and the heat transmission to the water in the tubes 9 and 10 is decreased. The butterfly valve 7 can also be described as a throttling means and may be substituted by other throttling means as described in the following in connection with
Referring now to
Referring now to
Referring now to
The innermost coil 10 is spaced from the outermost coil 9 by a tubular space having a thickness or radial dimension t1, while the innermost coil 10 is spaced from the outer surface of the conduit 5 by a tubular space having a thickness or radial dimension t3. The outermost coil 9 is not spaced from the inner surface of the outer casing 2, i.e. the coil 9 abuts the casing 2.
The spacings t1 and t3 are chosen such that the loss of pressure through the tubular space 8 is maintained at a level acceptable for the optimal operation of the gas turbine (or other hot exhaust gas generating means) delivering exhaust gas to the heat exchanger 1. The heat exchange efficiency of the heat exchanger 1 is not substantially affected by the spacings t1 and t3. On the other hand, operational tests show that if a spacing were present between the outer casing 2 and the outermost coil 9, then the efficiency of the heat exchanger 1 would be considerably reduced. These two phenomena are at least to a certain degree owing to, on one hand, turbulent flow between the coils 9 and 10 and between the conduit 5 and the coil 10 and, on the other hand, laminar flow in a tubular space between the outer coil 9 and the casing 2.
There are several parameters determining the spacings ti and t3 between the coils and between the innermost coil and the conduit 5. The two most important considerations or parameters are:
Exhaust Gas Pressure Drop
The exhaust gas pressure drop or loss is very dependent on the exhaust gas velocity and the geometry of the heating surface of the coil windings. The velocity is dependent on the free gas flow cross sectional area (total area for the gas flow between the tubes and fins in a cross section).
-
- Δp=ξ·½·ρ·w2, where
- Δp: exhaust gas pressure drop [Pa]
- ξ: pressure drop coefficient, dependent on geometry (fin shapes, tube diameter, inline/staggered configuration, number of windings etc),
- ρ: Density of the gas at mean temperature between inlet 3 and outlet 4 [kg/m3]
- w: exhaust gas velocity [m/s]
In most cases, the allowable exhaust gas pressure drop in heat exchangers and boilers after gas turbines (and engines as well) is quite limited. For gas turbines it is extremely important to minimize the exhaust gas pressure drop as the power production on the turbine (and thus the efficiency of the turbine) is very dependent on the back pressure. In connection with the heat exchanger according to the invention the allowable exhaust gas pressure drop is preferably limited to be below 500 Pa (50 mm water column), giving very low exhaust gas velocities and thus large distance between the coils (alternatively more coils giving larger gas cross section area and larger diameter of the unit).
Heat Transfer Coefficient
In general the heat transfer coefficient should be as high as possible to minimize the heating surface area. The heat transfer coefficient is increased with higher exhaust gas velocities and more turbulent flow. For the heating surface chosen (serrated spiral wound fin tubes) the turbulence of the flow is very good, in general giving high heat transfer coefficient even for low exhaust gas velocities.
Designing the heat exchanger according to the invention with the spacings t1 and t3 is also advantageous from a production point of view because it allows the coils to be inserted in the casing individually as compared with coils designed to abut one another or to be nested in one another that must be handled and inserted as a unit comprising several coils.
Still referring to
In the following, the basic technical specifications for a combination according to the invention of a two coil heat exchanger according to the invention and a gas fired turbine are listed as a non-limiting example:
Dimensions of the Heat Exchanger
Process Data
Referring now to
As the length of the tubes 11 of the different coils 32-34 are different and all the coils are interconnected at the outlet header 38 and at the inlet header 39, a flow distribution will be established in the coils giving the same pressure loss through each of the coils.
Thus, the inner coils 33 and 34 [where the second fluid (typically water) have shorter flow paths than in the outermost coil 32] can transport more water than the outer coil 32. The water in the coils 33, 34 and 35 will then not be heated to the same temperature and will result in a skewed and reduced recuperation of the heat contained in the first fluid (for instance exhaust gas from a gas fired turbine).
It is therefore desirable that the flow rate through the coils be regulated so that best possible heat recuperation is obtained with best possible temperature distribution both in the water and in the exhaust gas. This is achieved by creating an extra pressure loss in the inner coils 33 and 34 relative to the outer coil 35 and each other.
This can be achieved in two manners:
-
- By providing the tubes of the coils with different diameters. From a practical point of view this is not desirable except in case a large number of concentric coils are involved in which case 2-3 different tube diameters may be acceptable.
- By installing throttle or baffle means in the tubes or at the inlet or outlet thereof. As can be seen in
FIG. 5 andFIG. 6 , this can be achieved by providing the outlet header tube 38 with apertures 35-37 and 40-43, respectively, having different diameters. The diameters of the individual apertures are determined based on the tube diameter and tube length in the individual coils of a heat exchanger. As an example of diameters for the four apertures shown inFIG. 6 for an inner diameter of 56 mm of all four coil tubes, aperture 40 is 56 mm, aperture 41 is 13 mm, aperture 42 is 11 mm and aperture 43 is 9 mm. Other throttle or baffle means well known in the art may also be used to achieve the different pressure loss coefficients for the individual coil tubes.
Referring now to
This embodiment is intended for use for steam generation where it is necessary to take into consideration the large volume expansion of the mass inside the tubes (at the transition from liquid to vapour, water to steam) with corresponding increase in flow rate and velocity as well as pressure loss at the inner surface of the tubes. So as to provide sufficient inner flow cross sectional area in the tubes it will therefore often be necessary to use a larger tube diameter, a larger number of coils or provide for a larger number of flow paths in other ways.
Apart from providing many coils, more flow paths may be obtained by having several parallel extending windings in the same coil as shown in
Referring now to
In the embodiment of
In the situation shown with full lines, the butterfly valve 17 is closed and does not allow any exhaust gas to flow through conduit 5 while the ring 52 is in its highest position in which it does not throttle the flow of exhaust gas through the tubular space 8.
In the situation shown with dotted lines, the butterfly valve 17a functions as a by-pass valve and allows unthrottled flow of exhaust gas through the conduit 5 while the ring 52a is in its full throttle position supported on tightening rings 55 thereby preventing flow of exhaust gas through the tubular space 8.
The shaft 18 may be actuated manually, by an electric motor or a pneumatic or hydraulic mechanism. In the simplest version, the wires are wound onto and off not shown pulleys arranged on the shaft 18 such that rotation of the shaft 18 for opening of the butterfly valve 17 automatically entails lowering of the ring 52 and vice versa.
When no heat is required by the external heat consumption means connected to the heat exchanger 31, then the butterfly valve 17 is in its fully open position (17a) and the ring 52 is in its lowered fully closed position (52a) so that all the exhaust gas is by-passed through the conduit 5. Hereby, the water in the finned tube coils is not heated so that external cooling means to avoid overheating of this water are not necessary.
A very simple means for regulating the heat output of the heat exchanger 31 is thus provided. A temperature sensor and transmitter (not shown) may be provided in the outlet header 38 for transmitting a signal to the not shown actuator (electric motor) for the shaft 18 so that if the temperature measured at the outlet header does not conform to the required temperature, then the shaft rotates in the corresponding direction to either open or shut the by-pass valve 17. Many different regulating circuits are conceivable depending on the requirements of the end user and the configuration of the external heat consumption devices connected to the heat exchanger 31.
Referring now to
The tubular space 8 communicates with a space 60 defined by an extension of the outer casing 2, said space communicating with the outlet 4 through an aperture 61 in a plate 62. A butterfly valve 63 is mounted in said aperture 61 on the shaft 59 such that rotation of the shaft 59 rotates the butterfly valve 63 from the shown fully open position in which flow of exhaust gas from the tubular space 8 through the space 60 and through the aperture 61 is unhindered to a fully closed position in which flow of exhaust gas through the aperture 61 is totally obstructed. The shaft 59 is connected to an electric motor 64 for being rotated in opposite directions so as to rotate the valves 58 and 63 between the two positions described above and to any intermediate position.
Referring now to
Referring now to
A rotatably arranged circular plate 73 is arranged on top of plate 70 on a pivot 74. The plate 73 is provided with apertures 75 identical in shape and distribution to apertures 72 in plate 70 and with apertures 76 identical in shape and distribution to apertures 71 in plate 70. An electrical motor 77 is arranged for rotating the rotatable plate 73 in both directions.
In the position of the rotatable plate shown in
The lower plate 70 may instead be the rotatable one whereby the pressure from the exhaust gas will press the plate 70 against the stationary plate 73 and enhance the sealing effect of abutment of the plates 70 and 73 against each other. Sealing between the plates may also be achieved in many other ways obvious to those skilled in the art.
Referring now to
A cylindrical body 80 is constituted by a steel plate 81 with a thickness of 10 mm, a steel rod 82 inserted between the free axially extending edges of the plate 81, and not shown circumferentially extending tightening straps or wires for holding the plate 81 and rod 82 in the shown cylindrical configuration.
The inner coil 34 is wound helically around the body or core 80, the leading end (not shown) and the trailing end 11a of the pipe 11 of the coil 34 being attached to the body by means of brackets or rods 83 welded to said ends and to the body 80. The tightening straps mentioned above are located outside the area of the body 80 to be covered by the coil 34.
Four cylindrical plates 84 having a quarter circle cross section and a thickness equal to the required radial dimension t1 (see
The next coil 33 is wound helically around the plates 84 and rods 85 with the leading and trailing ends of the coil 33 being welded to one of the plates 84 by means of brackets or rods 83 in a manner very similar to the winding and attachment of the inner coil 34.
The process is repeated for the next coil 32. If more coils than three are required, the process described above may be repeated for any such further coils.
The unit comprising the body 80, the coils 32-34 and the plates 84 with rods 85 is thereafter subjected to annealing heat treatment for avoiding elastic diameter expansion of the coils and to remove potentially damaging stresses.
After annealing, the attachments by means of brackets 83 are removed, the rods 85 are rotated such that the major dimension of the oval or elliptical cross section is oriented radially whereby the coils 32-34 are forced to expand slightly such that the cylindrical plates 84 may be removed. Finally rod 82 is removed such that the body 80 may be removed. The coils 32-34 are now ready for being inserted in a casing 2 with a conduit 5 placed inside the inner coil 34.
A heat exchanger according to the invention is particularly well suited for use in a combination or system comprising a gas fired turbine (or an internal combustion engine utilizing natural gas as fuel). Such a system is furthermore particularly well suited for (but not in any way limited to) for use in a system for small scale combined production of electricity and heat, for instance for large buildings, hospitals, small district heating systems and the like.
Referring now to
The system can comprise other exhaust gas generating devices, and the regulation of the heat exchanger's by-pass valve (and the heat exchanger's throttle valve for throttling fluid flow through the tubular space containing the finned tube coils) can be provided for in many different manners depending on the configuration of the end user's heat consuming devices.
Claims
1. A heat exchanger for heat exchange between a first fluid and a second fluid and comprising:
- a generally cylindrical casing with a first inlet and a first outlet for allowing said first fluid to flow through said casing in a generally axial direction,
- a generally cylindrical fluid conduit arranged inside said casing generally coaxial therewith so that an axially extending first tubular space is defined between said conduit and said casing, said conduit having a second inlet and a second outlet for allowing said first fluid to flow through said conduit in a generally axial direction, and said first tubular space having a third inlet and a third outlet for allowing said first fluid to flow through said tubular space in a generally axial direction,
- at least one helical coil comprising a tube selected from the group consisting of a finned tube and a corrugated tube arranged inside said first tubular space generally coaxial therewith and having a fourth inlet and a fourth outlet for allowing said second fluid to flow through said tube.
2. A heat exchanger according to claim 1 further comprising first adjustable throttle means for adjustably throttling said flow of said first fluid through said conduit and second adjustable throttle means for adjustably throttling said flow of said first fluid through said first tubular space.
3. A heat exchanger according to claim 2, wherein said first throttle means comprise a first butterfly valve, arranged adjacent one of said second inlet and said second outlet, and said second throttle means comprise a second butterfly valve, arranged adjacent one of said third inlet and said third outlet.
4. A heat exchanger according to claim 2, wherein said first throttle means comprise a first butterfly valve, arranged adjacent one of said second inlet and said second outlet, and said second throttle means comprise a ring having planar dimensions corresponding to the cross section of said first tubular space and being arranged for being displaced from a heating position wherein said flow of first fluid through said tubular space is substantially unhindered to a bypass position wherein said flow is substantially obstructed.
5. A heat exchanger according to claim 2, wherein said first and second throttle means comprise:
- a fixedly arranged stationary plate with first and second apertures provided therein arranged such that said second and third inlets or outlets are obstructed by said plate such that the flow of first fluid through said conduit and said first tubular space takes place through said first and second apertures, respectively, in said stationary plate, and
- at least one movable plate with third and fourth apertures provided therein and arranged so as to be displaceable from a bypass position overlying said stationary plate, wherein said third apertures coincide with said first apertures and said fourth apertures do not coincide with said second apertures, to a heating position overlying said stationary plate wherein said fourth apertures coincide with said second apertures and said third apertures do not coincide with said first apertures.
6. A heat exchanger according to any of the claims 2-5 and further comprising actuating means for adjusting the throttling effect of said first and second throttle means.
7. A heat exchanger according to claim 6, wherein said throttling means and said actuating means are adapted such that substantially any rate of flow between a maximum and minimum rate of flow of said first fluid through said second inlet and said third inlet may be obtained.
8. A heat exchanger according to claim 7, wherein said minimum rate is substantially equal to zero.
9. A heat exchanger according to claim 1 and comprising at least two coil arranged concentrically and such that mutually adjacent coils are radially spaced such that an axially extending second tubular space is provided between said mutually adjacent coils.
10. A heat exchanger according to claim 1, wherein the outer surface of said conduit is spaced radially from the coil adjacent said surface such that an axially extending third tubular space is provided between said surface and said adjacent coil.
11. A heat exchanger according to claim 9 or 10, wherein the radial dimensions of said second and third tubular spaces are adapted so as to achieve a certain pressure loss for a given rate of flow of said first fluid through said first tubular space.
12. A heat exchanger according to claim 1, wherein the coil has mutually adjacent individual windings that are mutually axially spaced such that a helically extending space is provided between said adjacent windings.
13. A heat exchanger according to claim 1 and comprising three or more helical coils arranged concentrically, each comprising a finned tube one of the coils being an innermost coil and another of the coils being an outermost coil, the interior diameter of the finned tubes constituting the coils being the same, wherein third throttling means are provided in the tubes constituting the coils located radially inwards of the outermost coil for increasing the pressure loss through the tubes of the remaining coils so as to compensate for the shorter length of said tubes relative to the length of the tubes of the outermost coil such that the rate of low of said second fluid through the tubes of all the coils is substantially the same for a given uniform pressure in said second fluid at said fourth inlets.
14. A heat exchanger according to claim 13, wherein said third throttling means are constituted by a reduction of the cross sectional area of the flow of said second fluid relative to the internal cross sectional area of said tubes.
15. A heat exchanger according to claim 14 and further comprising an inlet header tube and an outlet header tube in fluid communication with said fourth inlets and fourth outlets, respectively, of all said tubes through corresponding communication apertures in said header tubes, said reduction of flow cross sectional area being constituted by reduced size of said communication apertures in one of said inlet header tube and said outlet header tube.
16. A heat exchanger according to claim 1, wherein the helical coil comprises two or more helically wound finned tubes extending adjacent one another with the same pitch.
17. A combination of a heat exchanger according to claim 1 and an exhaust gas generating combustion means selected from the group consisting of at least one of a natural gas fired turbine, an internal combustion engine, a furnace, a burner, an incinerator, the combination comprising interconnection means for interconnecting an exhaust gas outlet of the combustion means with said second and third inlets of the heat exchanger such that said exhaust gas constitutes said first fluid.
18. A combination according to claim 17 and further comprising
- heat exchanging means for heat exchange between said second fluid and at least one of a third fluid and the surroundings of said heat exchanging means, said heat exchanging means being in fluid communication with said fourth outlet,
- measuring means for measuring the rate of heat exchange of said heat exchanging means,
- signal output means for emitting a signal representing the result of a measurement carried out by said measuring means, and
- first control means for controlling the adjustment of said first and second throttle means and adapted for receiving said signal.
19. A combination according to claim 17 or 18 and further comprising second control means for controlling the adjustment of said first throttle means such that the throttling effect thereof is at a minimum during the start up phase of the combustion means.
20. A combination of a heat exchanger for heat exchange between a first fluid and a second fluid and an exhaust gas generating combustion means, the heat exchanger comprising:
- a generally cylindrical casing with a first inlet and a first outlet for allowing said first fluid to flow through said casing in a generally axial direction,
- a generally cylindrical fluid conduit arranged inside said casing generally coaxial therewith so that a axially extending first tubular space is defined between said conduit and said casing, said conduit having a second inlet and a second outlet for allowing said first fluid to flow through said conduit in a generally axial direction, and said first tubular space having a third inlet and a third outlet for allowing said first fluid to flow through said tubular space in a generally axial direction, and
- at least one helical coil comprising a tube selected from the group consisting of a finned tube and a corrugated tube arranged inside said first tubular space generally coaxial therewith and having a fourth inlet and a fourth outlet for allowing said second fluid to flow through said finned tube,
- the combination comprising interconnection means for interconnecting an exhaust gas outlet of the combustion means with said second and third inlets of the heat exchanger such that said exhaust gas constitutes said first fluid.
21. A combination according to claim 20 further comprising first adjustable throttle means for adjustably throttling said flow of said first fluid through at least one of said conduit and second adjustable throttle means for adjustably throttling said flow of said first fluid through said first tubular space.
22. A combination according to claim 21, wherein said first throttle means comprise a first butterfly valve, arranged adjacent one of said second inlet and said second outlet, and said second throttle means comprise a second butterfly valve, arranged adjacent one of said third inlet and said third outlet.
23. A combination according to claim 21, wherein said first throttle means comprise a first butterfly valve, arranged adjacent said one of second inlet and said second outlet, and said second throttle means comprise a ring having planar dimensions corresponding to the cross section of said first tubular space and being arranged for being displaced from a heating position wherein said flow of first fluid through said tubular space is substantially unhindered to a bypass position wherein said flow is substantially obstructed.
24. A combination according to claim 21, wherein said first and second throttle means comprise:
- a fixedly arranged stationary plate with first and second apertures provided therein arranged such that either said second and third inlets or said second and third outlets are obstructed by said plate such that the flow of first fluid through said conduit and said first tubular space takes place through said first and second apertures, respectively, in said stationary plate, and
- at least one movable plate with third and fourth apertures provided therein and arranged displaceable from a bypass position overlying said stationary plate, wherein said third apertures coincide with said first apertures and said fourth apertures do not coincide with said second apertures, to a heating position overlying said stationary plate wherein said fourth apertures coincide with said second apertures and said third apertures do not coincide with said first apertures.
25. A combination according to claim 21 and further comprising actuating means for adjusting the throttling effect of said first and second throttle means.
26. A combination according to claims 21, wherein said throttling means and said actuating means are adapted such that substantially any rate of flow between a maximum and minimum rate of flow of said first fluid through said second inlet and said third inlet may be obtained.
27. A combination according to claim 26, wherein said minimum rate is substantially equal to zero.
28. A combination according to claim 21 and comprising two or more helical coils arranged concentrically and such that mutually adjacent coils are radially spaced such that an axially extending second tubular space is provided between said mutually adjacent coils.
29. A combination according to claim 21, wherein the outer surface of said conduit is spaced radially from the coil adjacent said surface such that an axially extending third tubular space is provided between said surface and said adjacent coil.
30. A combination according to claim 28, wherein the radial dimension of said second tubular space is adapted so as to achieve a certain pressure loss for a given rate of flow of said first fluid through said first tubular space.
31. A combination according to claim 29, wherein the radial dimension of said third tubular space is adapted so as to achieve a certain pressure loss for a given rate of flow of said first fluid through said first tubular space.
32. A combination according to claim 21, wherein the mutually adjacent individual windings of a coil are mutually axially spaced such that a helically extending space is provided between said adjacent windings.
33. A combination according to claim 21 and comprising three or more helical coils arranged concentrically, one of said coils being an outermost coil, each of the coils comprising a finned tube, the interior diameter of the finned tubes being the same, wherein third throttling means are provided in the tubes of the coils located radially inward of the outermost coil for increasing the pressure loss through the tubes of said radially inward located coils so as to compensate for the shorter length of said tubes of said radially inward located coils relative to the length of the tubes of the outermost coil such that the rate of low of said second fluid through the tubes of all the coils is substantially the same for a given uniform pressure in said second fluid at said fourth inlets.
34. A combination according to claim 33, wherein said third throttling means are constituted by a reduction of the cross sectional area of the flow of said second fluid relative to the internal cross sectional area of said tubes.
35. A combination according to claim 34 and further comprising an inlet header tube and an outlet header tube in fluid communication with said fourth inlets and fourth outlets, respectively, of all said tubes through corresponding communication apertures in said header tubes, said reduction of flow cross sectional area being constituted by reduced size of said communication apertures in one of said inlet header tube and said outlet header tube.
36. A combination according to claim 21, wherein a helical coil comprises two or more helically wound finned tubes extending adjacent one another with the same pitch.
37. A combination according to claim 21 and further comprising
- heat exchanging means for heat exchange between said second fluid and at least one of a third fluid and the surroundings of said heat exchanging means, said heat exchanging means being in fluid communication with said fourth outlet,
- measuring means for measuring the rate of heat exchange of said heat exchanging means,
- signal output means for emitting a signal representing the result of a measurement carried out by said measuring means, and
- first control means for controlling the adjustment of said first and second throttle means and adapted for receiving said signal.
38. A combination according to claim 21 and further comprising second control means for controlling the adjustment of said first throttle means such that the throttling effect thereof is at a minimum during the start up phase of said combustion means.
39. A combination according to claim 20, wherein said exhaust gas generating combustion means is chosen from the group comprising a natural gas fired turbine, an internal combustion engine, a burner, a furnace and an incinerator.
40. A method of manufacturing a heat exchanger according to claim 1 and comprising the steps of:
- providing a first length of tube selected from the group consisting of a finned tube and a corrugated tube,
- providing a body having a substantially circular cylindrical surface,
- providing rotating means for causing relative rotation of said tube and said surface,
- arranging a lead portion of said tube abutting against said surface,
- causing relative rotation of said surface and said lead portion such that said first length of tube is helically wound on said surface to form a first helical coil.
41. A method according to claim 40 and comprising the further steps of:
- providing spacing means,
- attaching said spacing means to said first helical coil,
- providing a second length of tube selected from the group consisting of a finned tube and a corrugated tube,
- arranging a lead portion of said second length of tube abutting against said spacing means,
- causing relative rotation of first helical coil and said lead portion of said second length of tube such that said second length of tube is helically wound on said spacing means to form a second helical coil radially spaced from said first helical coil.
42. A method according to claim 40 and comprising the further steps of:
- fixating said helical coil relative to said body, and
- subjecting said body and said coil to annealing heat treatment.
43. A method according to claim 41 and comprising the further steps of:
- fixating said second helical coil relative to at least one of said body and said first helical coil, and
- subjecting said body and said first and second coils to annealing heat treatment.
Type: Application
Filed: May 7, 2004
Publication Date: Jun 23, 2005
Applicant: Aalborg Industries A/S (Aalborg)
Inventors: Lars Jorgensen (Gandrup), Niels Spender-Andersen (Stovring), Mosekaer Nielsen (Aalborg Ost)
Application Number: 10/840,952