DE19808146A1 - Demisting and heat recovery from flue gas e.g. gas-fired plant flue gas having high aggressive acid component content - Google Patents

Abstract

A flue gas demisting and heat recovery process involves initially cooling the flue gas to below the dew point of sulfuric acid but above that of water prior to sharply reversing the flow direction to separate the condensate. Flue gas demisting and heat content recovery are effected by passing the flue gas downwards through a heat exchanger for aggressive acid condensation and cooling to below the sulfuric acid dew point but above the water dew point, sharply reversing the flow direction to separate the condensate, passing the cooled flue gas upwards through another heat exchanger for cooling below the water dew point and a scrubber for acid and condensate removal and finally heating the cooled flue gas to a safe temperature for release into the environment. An Independent claim is also included for a flue gas demisting and heat recovery apparatus comprising a U-shaped flow channel (1), a first heat exchanger (7) in the downward inlet portion (2) of the channel, a second heat exchanger (10) and a scrubber in the upward outlet portion (4) of the channel, a demister (16) above the second heat exchanger, and a heater (17) and a controller above the demister.

Description

The invention is based on a prior art, such as it is formed by DE 689 14 784 T2. In the known Fall becomes a hot flue gas in a U-shaped stream channel cooled down first and finally opened again heated such a temperature that the necessary Ka min train guaranteed.

The flue gas enters a falling one from above Inlet strand of the flow channel and is in this by means of two successively arranged heat exchangers cools. The condensate is in the trough-like Deflection area of the flow channel collected and after un deducted. With the sharp deflection of the flue gas from the inlet line leading down the flue gas  the rising exit leading the flue gas upwards lassstrang is further condensate from the flue gas hurls.

After the sharp deflection, the flue gas passes through third heat exchanger, on which there are failures of Condensate is cooled further. Then it flows through a droplet separator and ultimately a fourth heat exchanger, in which it is based on the necessary ca minzug required temperature is reheated.

That removes the flue gas from the cooling heat exchangers Heat is used to generate feed water for steam heating up. So although it is possible in the known case is to dehumidify the flue gas and thereby heat content of the flue gas for steam generation use, the proposal has the peculiarity that the Flue gas already in the falling inlet branch of the U-shaped flow channel to a temperature below the Water dew point is cooled. In principle, therefore only low-sulfur flue gases are used to control their Use heat content. In any case, must in the known Case should be avoided that the temperature below the Sulfuric acid dew point falls. As a result, this means that not all of the flue gases produced in industry in the system belonging to the state of the art can be.

The invention is based on the prior art Task based on a method and an apparatus create which also smoke gases with even large ones Amounts of aggressive components can be dehumidified and their heat content can be used.

The procedural solution to this task exists of the invention in the features of claim 1.  

An essential aspect of this method is that the z. B. flue gas originating from a gas firing is specifically cooled during its downward movement to below the sulfuric acid dew point, but above the water dew point. Sensitive heat is obtained below the sulfuric acid dew point, but above the water dew point, whereby the highly concentrated acid condensates generated are safely controlled. The SO ₃ content is reduced by condensing out H ₂ SO ₄ . For this purpose, according to the invention, the U-shaped flow channel and the heat exchanger coming into contact with the flue gas and the corrosion-resistant coating and / or lining on their devices by appropriate techniques. This can be done, for example, with enamelling or with suitable plastics.

That when cooling below the sulfuric acid dew point, however Acid condensates occurring above the water dew point are together with other condensates on the bottom of the Deflection area of the flow channel collected and from there deducted.

Which is a temperature below the sulfuric acid dew point, however, flue gas exhibiting above the water dew point is then sharply deflected in the course of the flow, whereby further accruing during the cooling of the flue gas Condensates are flung out of the flue gas.

The flue gas has passed the deflection area and is flowing now in the upward outlet line of the Flow channel, it will continue to below the water dew point cooled. The flue gas becomes countercurrent the condensate falling down and on this Way achieved a cleaning of the flue gas.  

In the lower region of the outlet line, a further SO ₃ reduction takes place by condensing out H ₂ SO ₃ below the water dew point. At the same time, the HCl content is reduced by absorption on the surface of the water condensate drops.

In the inlet line is above the temperature of the Flue gas below the sulfuric acid dew point, but above half of the water dew point lowering the heat exchanger Cleaning system provided, especially in Beauf with water the heat exchanger underneath cleans from time to time and makes it fully functional holds.

In the outlet line is useful between which the flue gas under the water dew point cooling heat exchanger and the flue gas re-heating a trop fenabscheider provided.

According to claim 2 can to minimize the steam plume the chimney mouth the temperature and humidity of the exhaust gas depending on the environment exercise conditions are regulated.

Furthermore, it is enough to ensure one the chimney draft possible according to claim 3, dehumidify reheated and cooled flue gas.

This heating can also be avoided according to claim 4 condensation on the chimney walls.

In further development of the basic idea according to the invention can un according to claim 5 in the cooling of the flue gas an additional washing liquid at the water dew point be sprayed into the flue gas. This is then the purpose moderate between which the flue gas below the water dew point  lowering heat exchanger and the droplet separator a ge suitable flushing system is provided. This will make the further Advantage achieved that the flue gas in the exhaust line counter-flowing large amounts of water also dusts and absorb other particles, so that here the Dust separation effect is achieved.

As a washing liquid in the lower height range of the Aus lassstrangs can according to claim 6 at least subsets of the cooling and deflection of the flue gas from the strands of mixture of condensate and Acid can be used. This will make the economy increased because comparatively little freshness quantities of water must also be introduced.

It is further in accordance with the features of claim 7 an advantage if this is used as a washing liquid mixture entering the Aus before reintroduction first let free strand of solid components and then this washing liquid promoting the washing effect Chemicals are added. This can be especially lime milk.

It is advantageous according to the invention if, according to claim 8 the portions of the Mixture added to the wastewater after a pH dosage become. In this way it can cause wastewater mixture can be neutralized safely.

That in the lower level of the exhaust line in the heat exchangers provided there are used Cooling fluid can according to claim 9 in various ways be recooled to ensure the desired cooling effect to deliver. Effective recooling makes it possible large amounts of water in the lower height range of the Aus  condensate letstrands. The is preferred Air cooling used.

The recooling of the in the lower height range of the off coolant fluid used with the characteristics of claim 10 can be used specifically to Depending on the environmental conditions a freedom from steam at the chimney outlet (avoidance a steam flag). For this, the recooling cooling fluid depending on the temperature and the moisture content of the ambient air. For example, if the recooling from an air condenser sation with fans can be achieved by targeted Control of the fans depending on the temperature temperature and the moisture content of the ambient air of the water content of the flue gas can be controlled so that optimal Results for steam plume minimization at the fireplace mouth also under widely varying environmental conditions gene can be achieved.

As for the solution of the objective part of the task meets, this consists in the features of the claim 11.

Further advantageous embodiments are the subject of claims 12 to 15.

The invention is based on in the drawings gene illustrated embodiments explained in more detail. Show it:

Fig. 1 to 3 each in schematic vertical cross-sectional arrangements for dehumidifying flue gas and for using the heat content of the flue gas.

In Figs. 1 to 3 with 1 each denotes a U-shaped flow passage composed of a falling inlet line 2, a trough-like deflection region 3 and a rising outlet leg. 4

In the inlet line 2 , a nozzle 5 is arranged, which can be acted upon via a line 6 with a cleaning fluid, in particular in the form of water. The Dü senstock 5 sprays the cleaning fluid onto a heat exchanger 7 arranged in an inlet strand 2 . This heat exchanger 7 can be acted upon via a line 8 with cold feed water. A line 9 leading from the heat exchanger 7 with heated feed water leads to a steam generation, not shown in detail.

In the outlet line 4 , a heat exchanger 10 is arranged in the lower height range, which can be acted upon via a line 11 with a cooling fluid. A outgoing from the Wärmetau shear 10 line 12 can lead to a recooling system 13 explained in more detail below with reference to FIG. 3.

Above the heat exchanger 10 is in the outlet strand 4 from a nozzle assembly 14 which can be acted upon with a washing liquid via a line 15 .

A droplet separator 16 is incorporated into the outlet line 4 above the nozzle assembly 14 .

Above the droplet separator 16 there is a heat exchanger 17 in the upper region of the outlet line 4 which can be beaten with a heating medium via a line 18 . The cooled in the heat exchanger 17 Heizme medium is discharged via a line 19 .

At the top of the inlet line 2 , a flue gas RG is introduced from a gas firing (not shown in more detail) at a temperature of about 175 ° C., which is particularly loaded with SO ₂ , SO ₃ and HCl. This flue gas RG is initially cooled in the course of its flow path via the inlet branch 2 , the deflection region 3 and the outlet branch 4 and ultimately heated again to a temperature of approximately 90 ° C., which ensures the desired chimney draft. Since the proportions of the flue gas RG are aggressive components, all areas of the flow channel 1 and the heat exchangers 7 , 10 , 17 , the nozzle assemblies 5 , 14 and the droplet separator 16 are designed to be corrosion-resistant accordingly. These can be enamel coatings or plastic linings or coatings.

In the arrangement of FIG. 1, the flue gas RG enters the inlet line 2 at a temperature of approximately 175 ° C., passes through the nozzle assembly 5 and, in the area of the heat exchanger 7 , comes into heat-exchanging contact with the feed water which is positively guided in the heat exchanger 7 . This feed water has, for example, a temperature of about 70 ° C. when it enters the heat exchanger 7 . Due to the temperature difference, the flue gas RG in the area of the heat exchanger 7 is specifically cooled to a temperature below the sulfuric acid dew point, but above the water dew point. The feed water leaves the heat exchanger 7 at a temperature of about 120 ° C. As a result, the flue gas RG then has a temperature of approximately 100 ° C. below the heat exchanger 7 . The SO ₃ content of the flue gas RG is reduced by condensing out H ₂ SO ₄ . This acid and other condensate fall down and collect as a mixture 20 on the bottom side of the trough-like deflection area 3 . From here, the Ge mixture 20 can be withdrawn via a nozzle 21 .

In the deflection area 3 , the flue gas RG is sharply deflected from the inlet line 2 into the outlet line 4 , further condensates being thrown out, which then likewise collect as a mixture 20 .

After the deflection, the flue gas RG enters the outlet strand 4 and comes here into a heat-thawing contact with the heat exchanger 10 . The flue gas RG is selectively cooled to a temperature of approximately 60 ° C. below the water dew point by the cooling fluid (inlet temperature approximately 40 ° C., outlet temperature approximately 60 ° C.) which is forced into the heat exchanger 10 . During its upward movement, the flue gas RG is in countercurrent to the condensate flowing down, which leads to a purification of the flue gas RG in the sense that HCl is reduced, by absorption on the surface of the water condensate drops. Furthermore, a further reduction of SO ₃ takes place by condensing out H ₂ SO ₃ below the water dew point. The large condensed by the deep cooling of the flue gas RG against flowing water also cause absorption of dusts and other particles, so that a certain dust separation is achieved.

The rising amount of flue gas RG What water quantities can be increased if additional washing liquid is sprayed into the flue gas RG via the nozzle half 14 located above the heat exchanger 10 .

Moist constituents of the flue gas RG are separated off at the droplet separator 16 and can fall down into the mixture 20 .

After passing through the droplet separator 16 , the flue gas RG on the heat exchanger 17 is brought to a temperature of 70 ° C., which ensures the necessary chimney draft. The heating medium enters the heat exchanger 17 at approximately 120 ° C. and leaves it at a temperature of approximately 100 ° C.

The illustrated in the FIG. 2 embodiment, it laubt it, the ren zuzudosie out of the deflection region 3 via the Stut zen 21 withdrawn mixture 20 29 chemicals which promote the washing effect in the exhaust manifold 4 with respect to HCl and SO _2.

For this purpose, the mixture 20 is first fed to a separator 23 by means of a pump 22 incorporated in a line 24 , in which solid constituents are removed from the mixture 20 and drawn off via a line 25 . If necessary, water can be added to the mixture 20 via a line 26 for dilution.

After removal of the solid constituents, a chemical 29 in the form of lime milk is metered into the mixture 20 flowing in the line 15 via a line 27 with a pump 28 incorporated therein, and this washing liquid is then sprayed through the nozzle assembly 14 into the rising flue gas RG.

Portions of the mixture 20 , which are not used as cleaning liquid after cleaning and metering in with chemicals 29 , can be fed to the waste water via a line 30 . Before this, however, these subsets of the mixture 20 from a container 31 are subjected to a pH metering by a pump 33 integrated into a line 32 and thus neutralized.

In the line 30 , a blocking member 34 is incorporated before the mouth of the line 32 .

In the scope of the embodiment shown in FIG. 3, the steam lug can be controlled in a more targeted manner at a chimney mouth which is not shown in more detail.

For this purpose, the heat exchanger 10 through-flowing cooling fluid is guided through a recooling system 13 with valves 35 . The drives of the fans 35 are connected via control lines 36 to a control and regulating unit 37 , which is assigned a sensor 38 for measuring the moisture content and a sensor 39 for measuring the temperature of the ambient air. Depending on the moisture content and the temperature, the speed of the fans 35 can then be controlled and thereby the cooling fluid entering the heat exchanger 10 can be tempered in such a way that a corresponding heat exchange with the flue gas RG takes place in the sense of a reduction of the steam plume at the chimney mouth.

With a 40 in the heat exchanger 10 with the return cooling system 13 connecting line 12 is referred to pump.

In addition, the temperature of the heating medium introduced into the heat exchanger 17 can be controlled with the aim of reducing or even eliminating the steam plume at the chimney opening via the control and regulating unit 37 depending on the ambient conditions. For this purpose, the control and regulating unit 37 is connected via a control line 41 with a switching element 42 into which the heating medium leads the heat exchanger 17 line 18 and via the temperature and humidity-determining measuring lines 43 , 44 to the upper end of the outlet line 4 .

Of course, the embodiments of FIGS. 2 and 3 can also be used together.

Reference list

1

Flow channel

2nd

Inlet line v.

1

3rd

Deflection area v.

1

4th

Exhaust line v.

1

5

Nozzle assembly

6

management

7

Heat exchanger

8th

management

9

management

10th

Heat exchanger

11

management

12th

management

13

Recooling system

14

Nozzle assembly

15

management

16

Droplet separator

17th

Heat exchanger

18th

management

19th

management

20th

mixture

21

Support

22

pump

23

Separator

24th

management

25th

management

26

management

27

management

28

pump

29

chemical

30th

management

31

container

32

management

33

pump

34

Blocking organ

35

Fans

36

Control lines

37

Control and regulation unit

38

sensor

39

sensor

40

pump

41

Control line

42

Switching element

43

Measurement line

44

Measurement line
RG flue gas

Claims (15)

1. Processes for dehumidifying flue gas (RG) as well to use the heat content of such a flue gas (RG), in which the flue gas (RG) initially from above led downwards, with condensation of aggressive acid and release of heat to a rope shear fluid targeted below the sulfuric acid dew point, however cooled above the water dew point and there after separating condensate in its flow course is sharply deflected, whereupon the abge cooled flue gas (RG) from bottom to top and while washing out acid by the after following cooling below the water dew point the condensate when heat is given off to a cooling fluid is further lowered in temperature, and that ultimately the so cooled flue gas (RG) under Absorption of heat on the smoke gases ensuring temperature in the environment is brought. 2. The method of claim 1, in which to minimize the temperature and the humidity activity of the emitted flue gas (RG) in dependency be regulated by the ambient conditions. 3. The method according to claim 1 or 2, in which the Si dehumidification tied and cooled flue gas (RG) reheated becomes.   4. The method according to any one of claims 1 to 3, in which chem to avoid condensation on the chimney dehumidified and cooled flue gas (RG) like which is heated up. 5. The method according to any one of claims 1 to 4, in which chem when cooling the flue gas (RG) among the Water dew point also a washing liquid in the flue gas (RG) is sprayed. 6. The method according to claim 5, in which at least partial amounts of the mixture ( 20 ) of condensate and acid obtained during the cooling and deflection of the flue gas (RG) are used as the washing liquid. 7. The method according to claim 6, wherein the mixture ( 20 ) is freed of solid components and then the washing liquid, the washing effect promoting chemicals ( 29 ) are added. 8. The method according to claim 6 or 7, wherein the portions of the mixture ( 20 ) not used as washing liquid are fed to the waste water after a pH metering. 9. The method according to any one of claims 1 to 8, in which chem that for cooling the flue gas (RG) among the Water dew point used cooling fluid recooled becomes. 10. The method of claim 9, wherein the recooling cooling fluid depending on the temperature structure and the moisture content of the ambient air leads.   11. Device for the recovery of heat while removing aggressive components from flue gas (RG), consisting of:

• - A U-shaped flow channel ( 1 ) with a downward inlet line ( 2 ), a downward outlet line ( 4 ) and an inlet line ( 2 ) with the outlet line ( 4 ) ver binding deflection area ( 3 );
• - In the inlet line ( 2 ) incorporated first heat exchanger ( 7 ) to lower the temperature of the flue gas (RG) below the sulfuric acid dew point;
• - A in the outlet line ( 4 ) incorporated second heat exchanger ( 10 ) and a first cleaning arrangement to reduce the temperature of the flue gas (RG) below the water dew point using water as the cleaning fluid:
• - Above the second heat exchanger ( 10 ) in the outlet line ( 4 ) incorporated drop separator ( 16 );
• - Above the droplet separator ( 16 ) arranged reheating means ( 17 ) and control means to regulate the temperature and humidity of the expelled flue gas (RG) and the reheating depending on the ambient air.

12. The apparatus of claim 11, wherein the control means control the operation of the second heat exchanger ( 10 ) for influencing the moisture of the exhausted flue gas (RG). 13. The apparatus of claim 11 or 12, wherein above the second heat exchanger ( 10 ) a cleaning fluid on the surfaces of the second heat exchanger ( 10 ) spraying additional cleaning arrangement is provided. 14. Device according to one of claims 11 to 13, in which a recooling system ( 13 ) outside the flow channel ( 1 ) for the second heat exchanger ( 10 ) acting on the exchanger fluid is provided, at least a partial amount of the exchanger fluid again through the second Heat exchanger ( 10 ) is feasible. 15. The device according to one of claims 11 to 14, in which cleaning agents for the first heat exchanger ( 7 ) and / or the second heat exchanger ( 10 ) and / or the droplet separator ( 16 ) and / or the reheater ( 17 ) are provided, wherein the cleaning means in each case have spraying means to spray cleaning fluid onto the surfaces of the respective heat exchanger ( 7 , 10 , 17 ) or the droplet separator ( 16 ).