GB2471771A

GB2471771A - Heat recovery steam generator with heat pipes and distributed water inlet

Info

Publication number: GB2471771A
Application number: GB201011398A
Authority: GB
Inventors: Dumitru Fetcu
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-07-07
Filing date: 2010-07-07
Publication date: 2011-01-12
Anticipated expiration: 2030-07-07
Also published as: GB201011398D0; GB2471666A; GB0911680D0; GB2471771B

Abstract

A heat exchanger of steam generator has two chambers 11,12 separated by a plate 23 through which an array of finned heat pipes 27 are supported to pass, the heat pipes 27 having one end in an gas flow in chamber 12 and the other end in water 39 in chamber 11, each heat pipe drawing in heat from the gas and transferring it to the water, and the water chamber having a distributed inlet 17. Gas inlet 25 of chamber 12 and outlet 24 are on the same vertical axis, with exhaust gas flow radially through the heat pipes 27 being controlled by a baffle 33 and butterfly valve 36. The water inlet 17 has a circular tube 18 with nozzles or apertures above the heat pipes. Panels of the heat exchanger may be removable.

Description

Heat Exchanger The present invention relates to.a heat exôhanger.ahd particularly, but not sxclusively to a heat exchanger comprising heat pipes.

A heat pipe is a bet metically sealed evacuated tube typically comprising a mesh or sintered powder wick and a working fluid in both the liquid and vapor phase When one end of the tube is heated the liquid turns to vapor upon absorbing the latent heat of vaporization. The hot vapor subsequently passes to the cooler end of the tube where it condenses and gives out the latent heat to the tube The condensed liquid then flows back tO the hot end of the tube and thö vaporization-condensation cycle repeats. Since the latent heat of vaponzation is usually very large considerable quantities of heat can be transported along the tube and a substantially uniform temperature distribution can be achieved along the heat pipe.

It is known to utilize a heat exchanger comprising separated chambers and a plurality of heat pipes which extend between the chambers such that heat can become transferred from one chamber tO the other. in this respect, by passing a heated fluid through one chamber, the heat pipes can transfer the heat absorbed from the heated fluid to the other chamber wherein a cooled fluid may pass to subsequently absorb the heat from the heat pipes.

Heat exchangers are known for recovering heat from exhaust gases generated by industrial processes, and this heat is typibally used to generate steam for driving a steam.

turbine, for example. In this respect, the heat pipes are arranged to extend from a position within, an exhaust gas Outlet to within a water chamber, such that the heat transferred along the heat pipes can be used to produce steam in the water chamber. It is found however that the heat, extracted from the heat pipes within the chamber varies between heat pipes which can thus reduce the efficiency of the heat exchanger.and cause an early failure of one or more of the heat pipes Moreover it is found that the variation in heat extraction between heat pipes can lead to a dangerous build up of heat within the heat exchanger.

We have now devised an improved heat exchanger which alleviates the above-mentioned problems.

In accordance with the present invention, there is provided a heat exchanger for generating steam from water, the exchanger comprising a first heat exchanging chamber, a second heat exchanging chamber and an array of heat pipes which are arranged to extend from within the first heat exchanging chamber to within the second heat exchanging chamber; the first heat exchanging chamber comprising an inlet for receiving the water into the chamber and an outlet through which the steam can exit the first chamber, the water being arranged to pass over the portion of the heat pipes which extend within the first chamber; the second heat exchanging chamber comprising an inlet for receiving a gas into the chamber and an outlet through which the gas can exit the second chamber, the gas being arranged to pass over the portion of the heat pipes which extend within the second chamber; wherein the inlet to the first chamber comprises a distributed inlet for passing the water into the first chamber from a distributed position around the first chamber.

The distributed inlet ensures a uniform cooling of the portion of the heat pipes within the first chamber and thus a uniform extraction of heat from the heat pipes. The distributed inlet minimises any localized heating within the first chamber, which is typically associated with a localized inlet for the water.

The distributed inlet preferably comprises a distributed nozzle arrangement and is preferably arranged to extend above the portion of heat pipes which extend within the first chamber. The distributed nozzle arrangement preferably comprises a tube which extends around the first chamber and which comprises a plurality of apertures formed therein though which the water can pass.

The first heat exchanging chamber preferably further comprises a sensor for monitoring the level of water therein.

Preferably, the portion of at least one of the heat pipes within the first heat exchanging chamber comprises a fin arranged in contact therewith which is arranged to increase thermal transfer between said portion of the heat pipe and the water. The provision of at ieast one fin increases thermal transfer between said portion of the heat pipe and the water to provide for a more efficient heat transfer.

The portion of each of the heat pipes within the first heat exchanging chamber comprises a fin. Preferably, the or each fin is arranged to extend in a substantially helical path around the portion of the at least one or each heat pipe within the second heat exchanging chamber.

The portion of at least one of the heat pipes within the second heat exchanging chamber comprises a fin arranged in contact therewith, which is arranged to increase thermal transfer between said portion of heat pipe and the gas. Alternatively, each of the heat pipes within the second heat exchanging chamber comprises a fin arranged in contact therewith which is arranged to increase thermal transfer between said portion of the heat pipe and the gas. Preferably, the or each fin is arranged to extend in a substantially helical path around the portion of the at least one or each heat pipe within the second heat exchanging chamber.

Preferably, the number of turns of the or each fin per unit length around the or each heat pipe in the first heat exchanging chamber is greater than number of turns of the or each fin per unit length around the or each heat pipe in the second heat exchanging chamber.

The first and second heat exchanging chambers are preferably separated by a separation plate. The plurality of heat pipes are preferably supported within the heat exchanger by the separation plate which is coupled to the heat pipes at a position intermediate opposite ends of the heat pipes. Accordingly, the separation plate obviates the requirement to support the heat pipes at their free end and as such the free ends of the heat pipes can be left uncoupled. This therefore enables the heat pipes to expand and contract along their length during use thereby minimizing thermal stresses upon the heat pipes.

The second heat exchanging chamber preferably further comprises at least one baffle for directing the flow of gas over the respective portions of the heat pipes. The baffle preferably further comprises a valve to control the passage of gas direct from the inlet to the outlet of the second chamber. The baffle preferably comprises a butterfly valve.

An embodiment of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 is a longitudinal sectional view through a heat exchanger according to an embodiment of the present invention; Figure 2 is a top view of the heat exchanger illustrated in figure 1; Figure 3 is a view from the underside of the heat exchanger illustrated in figure 1 and, Figure 4 is a magnified longitudinal sectional view of a heat pipe disposed within a separation plate.

Referring to figures 1 to 3 of the drawings, there is illustrated a heat exchanger 10 according to an embodiment of the present invention for generating steam from water, The heat exchanger 10 compriaea a first heat exchanging chamber 11 and a second heat exchanging chamber 12. Each chamber 11, 12 comprises a substantially cylindrical housing 13, 14, which are mounted one on top of the other such that a longitudinal axis of the first chamber 11 extends in a substantiafly collinear relationship with a longitudinal axis of the second chamber 12 and thus the heat exchanger 10. The housing of the first and second chambers 11, 12 further comprises removable side panels (not shown) which enable the interior of the respective chambers 11, 12 to be accessed for cleaning and maintenance, for example.

The first chamber 11 of the heat exchanger 10 is disposed above the second chamber 12 and comprises an inlet 15 for passing water into the first chamber 11, and an outlet 16 through which the steam, which is generated from the heating of the water, can pass out from the first chamber 11. The inlet 15 comprises a duct 1 5a having a proximal end disposed outside of the chamber 11 for coupling with a source of water (not shown), and a distal end disposed within the chamber 11, which is arranged to couple with a distributed nozzle arrangement 17. The nozzle arrangement 17 comprises a substantially circular tube 18 which extends around an upper region of the first chamber 11, and comprises a plurality of apertures or nozzles (not shown) disposed therein which S are arranged to spray water into the chamber 11 from a distributed position around the tube 18.

The first chamber 11 further comprises a passage 19 which extends along the first chamber 11 substantially along the longitudinal axis thereof The passage 19 is defined by a substantially cylindrical wall 20 which seals the interior of the first chamber 11 from the passage l9 and extends from an opening 21 disposed in an upper end wall 22 of the first chamber 11 to an upper region of a separation plate 23.

The separation plate 23 comprises a first aperture 24 disposed substantially at the centre thereof which is arranged to align with the cylindrical wall 20 defining the passage 19, such that the wall 20 extends substantially around a periphery of the first aperture 24, The second chamber 12 is secured to the underside of the separation plate 23 and thus the first chamber 11, and comprises an inlet 25 disposed substantially upon the longitudinal axis of the chamber 12, within a lower end wall 26 thereof The first aperture 24 disposed within the separation plate 23 selves as an outlet from the second chamber 12, such that heated gas from an industrial process (not shown) for example, can pass into the second chamber 12 through the inlet 25 disposed in the lower end wall 26 of the second chamber 12, through the first aperture 24 in the separation plate, namely the outlet to the second chamber 12, into the passage 19 and out from the heat exchanger 10 via the opening 21 disposed in the upper end wall 22 of the first chamber 11.

The heat exchanger 10 further comprises a plurality of substantially linear heat pipes 27 which extend from within the first chamber 11, through an array of second apertures 28 disposed within the plate 23 around the first aperture 24, and terminate in the second chamber 12 so as to enable heat to be transferred between the chambers 11, 12. The heat pipes 27 extend substantially parallel to the longitudinal axis of the first and second chambers 11, 12 and are configured in a substantially arcuate arrangement of rows of heat pipes 27, the radius of curvature of each arcuate row being centered substantially on the longitudinal axis. In this manner each chamber 11, 12 comprises a plurality of arcuate rows of heat pipes 27, having different radii of curvature.

Referring to figure 4 of the drawings, the heat pipes 27 are supported within the heat S exchanger 10 by the separation plate 23 by a series of collars 29 which separately extend within each of the second apertures 28 and which further serve to seal the heat pipes 27 to the separation plate 23. The collars 29 are bonded to the heat pipes 27, for example by a weld, and a nut 30 is then screwed upon the collar 29 to compress a sealing ring 31 to the separation plate 23 and thus ensure that the interior of the first and second chambers 11, 12 remain isolated from each other. The longitudinal ends of the heat pipes 27 are uncoupled and spaced from the upper end wall 22 of the first chamber 11 and the lower end wall 26 of the second chamber 12, such that the heat pipes 27 are free to expand and contract and thus relieve any thermal stresses which would otherwise develop during use of the heat exchanger 10.

The portion of each of the heat pipes 27 which extend in the first chamber 11 comprise a helical fin 32a disposed around the outer surface thereof which extend substantially along the length of the portion of the respective heat pipe 27 within the first chamber 11.

The fins 32a comprise a metallic strip which extends away from the outer surface of the respective heat pipe 27 in direction which is substantially perpendicular to the longitudinal axis of the respective heat pipe 25. The fins 32a are found. to increase the transfer of heat between said portion of the heat pipes 27 and the water tc provide for a more efficient heating of the water within the first chamber 11.

The portion of each of the heat pipes 27 which extend in the second chamber 12 similarly comprise a helical fin 32b disposed around the outer surface thereof which extend substantially along the length of the portion of the respective heat pipe 27 within the second chamber 12. The fins 32b similarly comprises a metallic strip which extends away from the outer surface of the respective heat pipe 27, in direction which is substantially perpendicular to the longitudinal axis of the respective heat pipe 27.

The second chamber 12 of the heat exchanger 10 further comprises a baffle 33 which extends across the second chamber 12, substantially transverse to the longitudinal axis of the heat exchanger 10, and serves to direct the flow of gas from an industrial process for example, across the portion of the heat pipes 27 within the second chamber 12, to ensure that the heat associated with the gas is given up to the portion of the heat pipes 27 within the second chamber 12. The baffle 33 comprises an annular disc 34 centered substantially upon a longitudinal axis of the heat exchanger 10, having an aperture 36 disposed substantially centrally thereof. The baffle 33 further comprises a closure 36 which is sized to substantially match the aperture 35 within the annular disc 34, and which is rotatable about a diameter thereof, to open and close the aperture 35 within the annular diac 34.

The outer periphery of the annular disc 34 is spaced from the housing 14 of the second chamber 12 to define an annular passage 37. The heat pipes 27 are arranged to extend through apertures 38 in the annular disc 34 in sealing relation therewith, such that the gas is arranged to pass across the heat pipes 27, through the annular passage 37, and back across the heat pipes 27, in moving from the inlet 25 to the outlet 24 of the second chamber 12.

The annular disc 34 and closure 36 cooperatively define a valve, such as a butterfly valve, which can be configured between a fully open state in which the gas is arranged to pass direct from the inlet 25 to the outlet 24 without substantially passing through the annular passage 37, a closed state in which the majority of the gas is arranged to pass through the annular passage 37 in passing from the inlet 25 to the outlet 24 of the second chamber 12, and various intermediate states in which a portion of the gas is arranged to pass through the aperture 35 and a portion of the gas is arranged to pass through the annular passage 37.

In use, hot gas from an industrial process (not shown) for example, is passed into the second chamber 12 through the inlet 25, and caused to pass radially outwardly across the heat pipes 27 due to the baffle 33 and through the annular passage 37. The gas is then caused to pass radially inwardly of the second chamber 12, back across the heat pipes 27 toward the outlet 24 thereof. As the gas passes across the heat pipes 27, the heat associated with the gas becomes transferred tO the heat pipes 27, causing the gas to become cooled. The heat transferred to the heat pipes 27 is then communicated along the heat pipes 27 to the first chamber 11 and becomes extracted therefrom by the water within the first chamber 11. a

The heat extracted by the water causes the water temperature to incréasé and this heat is allowed to increase to convert the water into steam in the first chamber 11. The steam generated is then passed out from the outlet 16 of the first chamber 11 and may be used to drive a steam turbine (not shown) for example. The distributed nozzle arrangement 17 in the first chamber 11 ensures that each heat pipe portion within the first chamber 11 receives a uniform cooling and thus minimises any localised heating of the heat pipes 27.

The water level 39 within the first chamber is maintained above an upper region of the portion of heat pipes 27 therein to maximize the heat transfer area between the portion of the heat pipes 27 and the water This water level is maintained by a sensor 40 the output from which is arranged to selectively open and close the water supply into the first chamber 11. In this manner, as the water becomes converted to steam, the water level 39 withIn the first chamber 11 will fall. This change in water level 39 will become sensed by the sensor 40, which in turn will open the inlet 15 to the first chamber 11 causing water to become sprayed into the chamber 11 until the desired water level 39 is abhieved.

The intimate contact and increased surface area Of the portion of the heat pipes 27 in the first chamber 11, due to the presence of the fins 32a, provides an efficient removal of heat from the heat pipes 27, such that the portion of the heat pipes 27 in the second chamber 12 can further absorb the heat from the gas and thus coolS the gas. This increased surface area provides for an increased effective thermal coefficient and thus a reduced length of the portion of the heat pipe 25 in the first chamber 11 compared with cohventionai heat exchangers. Moreover, in the event that a condensate (riot shown) of the industi-iàl gas forms in the second chamber 12, then the fins 32b associated with the portion of the heat pipes 27 in the second chamber 12, enable the condensate (not shown) to develop thereon as opposed to the pipe itself, which would otherwise insulate pipe from cooling further industrial gas.

Claims

Claims I A heat exchanger for generating steam from water the exchanger compnsing a first heat exchanging chamber, a second heat exchanging chamber and an array of heat pipes which are arranged to extend from within the first heat exchanging chamber to within the second heat exchanging chamber; the first heat exchanging chamber comprising an inlet for receiving water into the chamber and an outlet through which the steam can exit the first chamber, the water being arranged to pass over the portion of the heat pipes which extend within the first chamber; the second heat exchanging chamber compnsing an inlet for receiving a gas into the chamber and an outlet through which the gas can exit the second chamber, the gas being arranged to pass over the portion of the heat pipes which extend within the second chamber; wherein the inlet to the first chamber comprises a distributed inlet for passing the water into the first chamber from a distributed position around the first chamber.
2 A heat exchanger according to claim 1 wherein the distnbuted inlet is arranged to extend above the portion of heat pipes which extend within the first chamber.
3 A heat exchanger according to claim 1 or 2 wherein the distiibuted inlet comprises a distributed nozzte arrangement.
4 A heat exchanger according to claim 3 wherein the distnbuted nozzle arrangement comprises a tube which extends around the first chamber and which comprises a plurality of apertures formed therein though which the water can pass.
5. A heat exchanger according to any preceding claim, Wherein the first heat exchanging chamber further comprises a sensor for monitoring the level of water therein.
6. A heat exchanger according to any preceding claim, wherein the portion of at least one of the heat pipes within the first heat exchanging chamber compnses a fin arranged in contact therewith which is arranged to increase thermal transfer between said portion of the heat pipe and the water.
7. A heat exchanger according to any preceding claim, wherein the portion of each of the heat pipes within the first heat exchanging chamber cOmprises a fin.
8. A heat exchanger according to claim 6 or 7, wherein the or each fin is arranged to extend in a substantially helical path around the portion of the at least one or each heat pipe within the second heat exchanging chamber
9. A heat exchanger according to any preceding claim wherein the portion of at least one of the heat pipes within the second heat exchanging chamber comprises a fin arranged in contact therewith, which is arranged to increase thermal transfer between said portion of heat pipe and the gas.A heat exchanger according to any preceding claim, wherein the portion of each of the heat pipes within the second heat exchanging chamber comprises a fin arranged in contact therewith which is arranged to increase thermal transfer between said portion of the heat pipe and the gas.11. A heat exchanger according to claim 9 or 10, wherein the or each fin is arranged to extend in a substantially helical path around the portion of the at least one or each heat pipe within the second heat exchanging chamber.ia A heat exchanger according to any of claims 8 or 11, wherein the ilumber of turns of the or each fin per unit length around the or each heat pipe in the first heat exchanging chamber is greater than number of turns of the or esch tin per unit length around the or each heat pipe in the second heat exchanging chamber.13. A heat exchanger according to any preceding dlaim wherein the first and second heat exchanging chambers are separated by a separation plate.14. A heat exchanger according to claim 13, wherein the plurality of heat pipes are supported within the heat exchanger by the separation plate which is coupled to the heat pipes at a position intermediate opposite ends of the heat pipes.15. A heat exchanger according to any preceding wherein the second heat exchanging chamber further comprises at least one baffle for directing the flow of gas over the portion of the heat pipes within the second chamber.16. A heat exchanger according to claim 15, wherein the at!east one baffle comprises a valve to control the passage of gas direct from the inlet to the outlet of the second chanter.