WASTE HEAT RECOVERY

Abstract

There is provided a method for pre-heating a fluid (140, 240, 340) by heat transfer from combustion gases (101) flowing through an exhaust duct (100) of a furnace, wherein the fluid (140, 240, 340) is supplied to a heat transfer device (120, 200, 300) which is in heat transfer contact with the combustion gases (101). At least a portion of the heat transfer device (120, 200, 300) is movably arranged relative to the exhaust duct (100) such that it can be moved into and out of the exhaust duct.

Claims

1-12. (canceled)

13. In a method for pro-heating a fluid (140, 240, 340) by heat transfer from combustion gases (101) flowing through an exhaust duct (100) of a furnace, wherein the fluid (140, 240, 340) is supplied to a heat transfer device (120, 200, 300) in heat transfer contact with the combustion gases (101), the improvement comprising: the heat transfer device (120, 200, 300) comprising a double pipe (200) having an inner pipe (201, 301) and an outer pipe (202, 302); passing the fluid (240) first through the inner pipe (201) and subsequently through the outer pipe (202); and arranging at least a portion of the heat transfer device (120, 200, 300) relative to the exhaust duct (100) for moving that at least a portion of the heat transfer device into and out of the exhaust duct (100).

14. The method of claim 13, wherein the fluid (140, 240, 340) comprises a substance selected from the group consisting of an oxygen-containing gas, an oxygen-containing gas comprising at least 90% by volume oxygen, a fuel, and a gaseous fuel.

15. The method of claim 13, wherein the furnace comprises a glass furnace.

16. In a furnace having an exhaust duct (100) to exhaust combustion gases (101) from the furnace, and a heat transfer device (120, 200, 300) for pre-heating a fluid (140, 240, 340) by heat transfer from the combustion gases (101), the heat transfer device (120, 200, 300) including an inlet (204, 304) for the fluid (140, 240, 340) to be pre-heated and an outlet (206) for pre-heated fluid, the improvement comprising: the heat transfer device (200, 300) comprising at least one double pipe (200, 300), and at least a portion of the heat transfer device (120, 200, 300) is arranged relative to the exhaust duct (100) and movable for movement into and out of the exhaust duct (100).

17. The furnace of claim 16, further comprising an automated retraction system for moving at least a portion of the heat transfer device (120, 200, 300) into and out of the exhaust duct (100).

18. The furnace of claim 16, further comprising the heat transfer device (120, 200) being oriented vertically with respect to the exhaust duct (100).

19. The furnace of claim 16, wherein a portion of the double pipe (200, 300) movable into the exhaust duct (100) has a length selected from the group consisting of at least 0.25 m, at least 1.0 m, and at least 1.5 m.

20. The furnace of claim 16, wherein a portion of the double pipe (200, 300) movable into the exhaust duct (100) has a maximum length selected from the group consisting of a maximum of 1.0 m, a maximum of 1.5 m, and a maximum of 2.0 m.

21. The furnace of claim 16, wherein the double pipe (200, 300) comprises: an inner pipe (201, 301); and an outer pipe (202, 302) closed at one end (303), wherein the inner pipe (301) is reset with respect to the closed end (303) of the outer pipe (302).

22. The furnace of claim 16, further comprising an inert gas supply line (245) connected to the heat transfer device (120, 200, 300).

23. The furnace of claim 16, further comprising at least one additional heat transfer device (120, 200, 300), and at least one burner, wherein the outlet of each of the heat transfer devices (120, 200, 300) is connected to a corresponding same one of the at least one burner.

24. The furnace of claim 23, wherein the at least one additional heat transfer device (100, 200, 300) is an amount selected from the group consisting of between 1 and 30 heat transfer devices per burner, and less than 20 heat transfer devices per burner.

25. The furnace of claim 16, further comprising the heat transfer device (120, 200, 300) being located upstream of other waste heat recovery devices and emission control devices of the furnace.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The invention as well as further details of the invention shall now be explained with reference to the accompanying schematic drawings.

[0036] FIGS. 1a and b show a heat transfer device according to the invention,

[0037] FIG. 2 shows another embodiment of the invention, and

[0038] FIG. 3 shows an alternative design of a waste heat transfer device of the double pipe design.

DETAILED DESCRIPTION OF THE INVENTION

[0039] In FIGS. 1a and 1b, a heat exchanging system according to a preferred embodiment of the invention is schematically shown in a sectional side view. FIGS. 1a and 1b show an exhaust duct 100 through which combustion gas 101 emerging from the combustion in a furnace (not shown) is exhausted.

[0040] At one end 102, the exhaust duct can especially be connected with an appropriate furnace. At another end 103, the exhaust duct can be provided with exhaust treatment components, further waste heat recovery devices and it can especially be connected with an appropriate chimney.

[0041] The exhaust duct 100 comprises a refractory element 110. The refractory element 110 is especially embodied as a wall of the exhaust duct 100. This wall 110 of the exhaust duct 100 is for example constructed by a multitude of bricks.

[0042] The exhaust duct 100 is provided with an opening 111 at its top side. A heat transfer device 120 can be inserted into the opening 111 and moved into the exhaust duct 100. The heat transfer device 120 is oriented vertically and fixed to an automated retraction mechanism (not shown) which allows to lift up and lower down the heat transfer device 120. When inserted into the exhaust duct 100, the combustion gases 101 flow around the lower portion 121 of the heat transfer device 120 and heat it up. The combustion gases typically have a temperature between 300 C. and 1800 C. The heat is transferred from the combustion gases to the gas flowing through the heat transfer device 120.

[0043] In this example, the heat transfer device 120 is used to preheat oxygen. Gaseous oxygen 140 is passed through the heat transfer device 120 and heated up. The pre-heated oxygen gas 141 is then transferred to a burner for heating the furnace.

[0044] The heat transfer device 120 may be provided with a collar 123 which fits into the opening 111 in the wall of the exhaust duct 100 and which seals the heat transfer device 120 in its seat in the opening 111.

[0045] The oxygen flow 140 into the heat transfer device 120 is controlled by flow control means 150.

[0046] Additional heat transfer devices may be used to pre-heat additional oxygen streams or to pre-heat a gaseous fuel stream.

[0047] For maintenance the heat transfer device 120 can be lifted up and retracted from the exhaust duct 100 (see FIG. 1b). The opening 111 in the wall of the exhaust pipe 100 is closed by a plug 112 to avoid the escape of combustion gases 101. The oxygen flow 140 continues to flow through heat transfer device 120 even if it is no more pre-heated. It is also possible to have a bypass around the heat transfer device 120. Thus, maintenance of the heat transfer device 120 can be done during continuous operation of the furnace.

[0048] FIG. 2 shows a more detailed view of an embodiment of the invention wherein the heat transfer device is designed as a double pipe 200.

[0049] A double pipe 200 is oriented with its axis in a vertical direction. The double pipe 200 comprises an inner pipe 201 and an outer pipe 202 coaxially arranged to each other. The outer pipe 202 has an outer diameter of between 30 mm and 100 mm. The inner pipe 201 has an outer diameter between 10 mm and 70 mm. The length of the outer pipe which is located inside the exhaust duct, that is the active heat transfer length is for example between 0.25 m and 2.5 m.

[0050] The outer pipe 202 is closed at its bottom end 203. The top end 204 of the inner pipe 201 is designed as inlet for the fluid to be pre-heated, for example for a cold or room-temperature oxygen stream. The bottom end 205 of the inner pipe 201 is open and terminates at a distance of for example 10 mm to 200 mm from the closed bottom end 203 of the outer pipe 202. In the side wall of the upper portion of the outer pipe 202 there is provided an outlet 206 for the pre-heated fluid.

[0051] Spacers 207 are provided in the annular gap between the outer pipe 202 and the inner pipe 201. The spacers 207 are preferably provided at a location in the lower third of the outer pipe 202. It is further advantageous to design the spacers 207 as swirling elements which cause a turbulent flow of the fluid passing the spacers 207.

[0052] As already explained with reference to FIGS. 1a and 1b the double pipe 200 is movably arranged in the wall 110 of the exhaust duct 100 such that it can be inserted into the exhaust duct 100 or be retracted from the exhaust duct 100.

[0053] In operation of the waste heat recovery system of FIG. 2 an oxygen stream 240 at ambient temperature is introduced into inlet 204 of the inner pipe 201. The oxygen stream flows down (241) the inner pipe 201, leaves (242) the inner pipe 201 at its bottom end 205, turns upwards and flows back (243) through the annular gap between the outer pipe 202 and the inner pipe 201. When having reached the top of the outer pipe 202 the oxygen stream 244 leaves the double pipe 200 through outlet 206.

[0054] During its flow down through the inner pipe 201 the oxygen stream 241 is in heat transfer contact with the oxygen stream 243 flowing upwards through the annular gap. Thereby, oxygen stream 243 is pre-heated to a temperature between 80 C. and 150 C. The oxygen stream then returns through the annular gap between the outer pipe 202 and the inner pipe 201. During this upward passage the oxygen stream 243 is in heat transfer contact with the combustion gases 101 flowing through the exhaust duct 100. Thereby, the oxygen stream 243 is further heated up to a temperature between 200 C. and 600 C. The so pre-heated oxygen 244 leaves the double pipe 200 via outlet 206 and is passed to a burner.

[0055] Since the cold or room-temperature oxygen stream 240 does not come into direct contact with the wall of the outer pipe 202, that wall remains always at a high enough temperature so that water vapour as a component of the combustion gases does not condense at the wall. For example, the temperature of the wall of the outer pipe 202 is between 200 C. and 1100 C. close to the bottom end 203 of the outer pipe 202 and between 300 C. and 1100 C. at the upper end of the outer pipe 202.

[0056] An inert gas supply 245, such as a gaseous nitrogen storage, is also connected to the inlet of the inner pipe 201. In normal operation valve 246 is closed and only the fluid 240 to be pre-heated is passed to the inner pipe 201. If the flow of the fluid 240 is too low or if it is stopped at all, there is a considerable risk that the double pipe 200 is heated up too much and damaged. In this case valve 246 is opened and gaseous nitrogen is introduced into the inner pipe 201 and passed through the outer pipe 202 whereby the double pipe 200 is cooled.

[0057] The inert gas supply 245 can also be used together with the embodiments of FIGS. 1a, 1b and 3.

[0058] FIG. 3 shows another design of a double pipe heat transfer device.

[0059] The outer pipe 302 of the double pipe 300 is of U-shape closed at one end 303.

[0060] The inner pipe 301 is designed as inlet for the fluid 340 to be pre-heated, for example for a cold or room-temperature oxygen stream. The inner pipe enters the outer pipe 302 through the closed end 303. The inner pipe 301 is arranged in the vertical arm of the U-shaped outer pipe 302. The inner pipe 301 is also of U-type with its outlet 305 close to the closed end 303 of the outer pipe 302.

[0061] As explained with reference to FIGS. 1a, 1b and 2 the double pipe 300 is also movably arranged in the wall 110 of the exhaust duct 100 such that it can be inserted into the exhaust duct 100 or be retracted from the exhaust duct 100. The refractory is provided with a removable cutout 307 in order to retract the double pipe 300 from the exhaust duct 100.

[0062] The operation of the waste heat recovery system of FIG. 3 is very similar to the one of FIG. 2. An oxygen stream at ambient temperature is introduced into inlet 304 of the inner pipe 301. The oxygen stream flows through the inner pipe 301, leaves the inner pipe 301 at its end 305, turns downwards and flows through the outer pipe 302.

[0063] The embodiment of FIG. 3 may in particular be used for pre-heating fluids, such as oxygen or fuel, if the exhaust duct has a small diameter only. The heat transfer length of the embodiment of FIG. 3 is not limited by the diameter of the exhaust duct 100 but can be simply increased by increasing the length of the basis 306 of the U-shaped outer pipe 302.

[0064] The invention has been described with respect to pre-heating oxygen. One skilled in the art will understand that the above examples can also be used to pre-heat fuel, air or any other fluid.