Device with a heat exchanger and method for operating a heat exchanger of a steam generating plant

Abstract

A device with a heat exchanger with a feed pipe for a medium leading from a medium inlet to the heat exchanger entrance and with a discharge pipe leading away from the heat exchanger exit is characterized in that it has a first bypass from the medium inlet to the discharge pipe and a second bypass from the feed pipe to the medium outlet and valves, so that the medium can also flow from the heat exchanger exit to the heat exchanger entrance.

Claims

1. A process for cooling firing system exhaust gas having a temperature above 100 C. in a heat exchanger of a steam generating plant, the process comprising the steps of: providing a heat exchanger comprising a plurality of pipes; initially flowing cooling water or steam having a temperature above 130 C. through the pipes of the heat exchanger in a concurrent flow operation mode; lowering a temperature of the firing system exhaust gas flowing outside the pipes of the heat exchanger by switching a flow of the cooling water or steam flowing through the pipes of the heat exchanger from the concurrent flow operation mode to a countercurrent flow operation mode by adjusting a plurality of three-way valves when an efficiency of the heat exchanger drops due to deposits produced by the firing system exhaust gas on an outside of the pipes of the heat exchanger; and actuating the plurality of three-way valves such that no pipe of the plurality of pipes of the heat exchanger containing the cooling water or steam is closed on both sides.

2. The process for cooling firing system exhaust gas in a heat exchanger of a steam generating plant according to claim 1, wherein the heat exchanger comprises: a heat exchanger entrance; a heat exchanger exit; a feed pipe for the cooling water leading from a medium inlet to the heat exchanger entrance; a discharge pipe leading away from the heat exchanger exit to a medium outlet; a first bypass leading from the medium inlet to the discharge pipe; and a second bypass leading from the feed pipe to the medium outlet; and wherein the plurality of three-way valves comprises: a first three-way bypass valve coupling the medium inlet to the first bypass and to the feed pipe; and a second three-way bypass valve coupling the medium outlet to the second bypass and to the discharge pipe.

3. The process for cooling firing system exhaust gas in a heat exchanger of a steam generating plant according to claim 2, wherein the step of initially flowing the cooling water or steam through the heat exchanger in the concurrent flow operation mode comprises the steps of configuring the first three-way bypass valve to convey the cooling water or steam from the medium inlet to the feed pipe and configuring the second three-way bypass valve to convey the cooling water or steam from the discharge pipe to the medium outlet and to prevent the cooling water or steam from flowing from the second bypass to the medium outlet, thereby causing the cooling water or steam to flow from the heat exchanger entrance to the heat exchanger exit in a concurrent flow.

4. The process for cooling firing system exhaust gas in a heat exchanger of a steam generating plant according to claim 2, wherein the step of lowering a temperature of the firing system exhaust gas by switching the flow of the cooling water or steam through the heat exchanger from the concurrent flow operation mode to countercurrent flow operation mode comprises the steps of configuring the first three-way bypass valve to convey the cooling water or steam from the medium inlet to the first bypass and configuring the second three-way bypass valve to convey the cooling water or steam from the second bypass to the medium outlet and to prevent the cooling water or steam from flowing from the discharge pipe to the medium outlet, thereby causing the cooling water or steam to flow from the heat exchanger exit to the heat exchanger entrance in a countercurrent flow.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the device and of the method are shown in the figures and are further explained in the following. In the drawing:

(2) FIG. 1 shows a heat exchanger switching mechanism with four valves in concurrent flow operation mode,

(3) FIG. 2 shows a heat exchanger switching mechanism with four valves in countercurrent flow operation mode,

(4) FIG. 3 shows a heat exchanger switching mechanism with two valves in concurrent flow operation mode,

(5) FIG. 4 shows a heat exchanger switching mechanism with two valves in countercurrent flow operation mode,

(6) FIG. 5 shows a steam generating plant with an economizer in concurrent flow operation mode and

(7) FIG. 6 shows a steam generating plant with an economizer in countercurrent flow operation mode.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(8) The device 1 shown in FIG. 1 consists substantially of a heat exchanger 2, which is supplied with a medium 16 via a feed pipe 3. This feed pipe 3 leads from a medium inlet 4 to the heat exchanger entrance 5. A discharge pipe 6 from the heat exchanger exit 7 is provided on the side facing away from the heat exchanger entrance. A first bypass 8 thereby leads from the medium inlet 4 to the discharge pipe 6 and a second bypass 9 leads from the feed pipe 3 to the medium outlet 10.

(9) A first bypass valve 11 is provided between the medium inlet and the first bypass 8 and a second bypass valve 12 is provided between the second bypass 9 and the medium outlet 10. A feed pipe valve 13 is disposed in the feed pipe 3 and a discharge pipe valve 14 is provided in the discharge pipe 6.

(10) In the present case, the second medium is a gas, the flow of which is indicated by the arrows 15. In the example shown in FIG. 1, the heat exchanger 2 thus operates in concurrent flow.

(11) To this end, the feed pipe valve 13 and the discharge pipe valve 14 are open, so that the medium 16 flows concurrently with the gas 15 through the heat exchanger 2. The first bypass 8 thereby makes it possible to adjust the heat exchanger output and the temperature of the medium at the medium outlet 10 via the first bypass valve 11. In this setting, the second bypass valve 12 is closed, so that no medium flows through the second bypass 9.

(12) In the setting shown in FIG. 2, the medium 16 flows through the first bypass valve 11 and the first bypass 8, through the heat exchanger 2 to the second bypass valve 12 and from there to the medium outlet 10. Since the gas still flows in the direction of the arrows 15, the heat exchanger 2 is operated in countercurrent flow with this valve setting. Adjusting the medium temperature at the medium outlet 10 is possible by switching the feed pipe valve 13, thus achieving a bypass flow from the medium inlet 4 directly to the medium outlet 10. The route from the medium inlet via the discharge pipe 6 to the medium outlet 10 is closed by the discharge pipe valve 14.

(13) In FIGS. 3 and 4 however, the switching mechanisms shown in FIGS. 1 and 2 are correspondingly described with respectively 2 two-way valves. The bypass valve 11 and the feed pipe valve 13 have thereby been merged into a first three-way valve 17 while the bypass valve 12 and the discharge pipe valve 14 are merged into a second three-way valve 18. The first bypass valve 17 thus distributes the medium 16 coming from the medium inlet 4 to the feed pipe 3 and the first bypass 8. The second three-way valve 18 correspondingly conducts the medium carried in the discharge pipe 6 together with the medium coming from the second bypass 9 to the medium outlet 10.

(14) The heat exchanger 2 can thus be switched from the concurrent flow operation mode shown in FIG. 3 to the countercurrent flow operation mode shown in FIG. 4. Whereas during the concurrent flow operation mode the second bypass 9 is closed by the setting of the second three-way valve 18, in the countercurrent operation mode the second three-way valve 18 closes the discharge pipe 6 while the second bypass 9 is open.

(15) In the steam generating plant 20 shown in FIG. 5, the firing system, in which combustible material, more specifically such as waste, is burnt with preheated combustion air, is not shown. The exhaust gases generated during combustion are indicated by arrows 21, 22 and 23.

(16) These exhaust gases first flow through the evaporator 24 and then through three superheaters 25, 26, 27. The exhaust gases eventually flow through an economizer 28 before being fed to a catalytic denitrogenization plant (SCR) not shown in the drawing.

(17) The water 29 serving as a cooling medium is evaporated in the evaporator 24 and is fed as steam via the first superheater 25, then via the third superheater 27 and lastly via the second superheater 26 to a turbine 30 which drives a generator 31. It then flows through a condenser 32 and is conveyed to the economizer 28 via a pump 33. The first three-way valve 34 is thereby open in accordance with the setting shown in FIG. 3 and the second three-way valve 35 is switched in such a manner that the second bypass 36 is closed.

(18) The medium thus flows from the medium inlet 37 via the first three-way valve 34 and the feed pipe 38 to the economizer 28 and from the economizer 28 via the discharge pipe 39 and the second two-way valve 35 to the boiler drum 40. Controlling the medium temperature is thereby possible via the first bypass 41 between the first bypass valve 34 and the discharge pipe 39.

(19) FIG. 6 shows that the economizer 28 can be switched from the concurrent flow operation mode shown in FIG. 5 to a countercurrent flow operation mode shown in FIG. 6 by a mere switching of the second bypass valve 35. In this setting, the water 29 flows from the medium inlet 37 via the first two-way valve 34 and the first bypass 41 to the economizer 28. From there, the water gets to the second three-way valve 35 via the second bypass 36 and back to the boiler drum 40.

(20) In this setting, the feed pipe 38 assumes the function of a possible bypass, in order to conduct the water, under control by the first three-way valve 34, past the economizer 28 directly to the first three-way valve 35 and from there to the boiler drum 40. The water 29 serving as a cooling medium is evaporated in the evaporator 24 and is fed as steam first via the first superheater 25, then via the second superheater 26 and finally via the third superheater 27 to the turbine 30 which drives the generator 31. This makes it possible in this setting also to provide a regulation of the medium temperature on the gas and the water side in a simple manner without further expenses in pipes and valves. It is furthermore possible during operation to switch from concurrent flow operation mode to countercurrent flow operation mode and back.