DK170607B1 - Apparatus for catalytic removal of nitrogen oxides from power plant flue gases - Google Patents

Abstract

Apparatus for denitrifying power station excess gases (crude gas) which come from a flue gas desulphurisation unit and are heated to the requisite catalyst temperature before the injection of ammonia by heat exchange with the denitrified gases (pure gas) and by supplying additional heat. Known denitrification devices fitted with regenerative heat exchangers operate with large gap and leakage losses, which leads to restrictions in the achievable degree of denitrification and hence the efficiency. Moreover, known denitrification devices have a large space requirement, which makes expensive heat insulation measures necessary due to the free surfaces, in order to prevent a deterioration in efficiency due to heat losses. It is proposed to use, for the heat exchange between crude gas and pure gas, a plate heat exchanger (4) which operates in cross-counterflow, the additional heat being supplied and the ammonia being injected (14) to the outlet duct (9) of the plate heat exchanger. At the end of the outlet duct (9) is arranged a deflection hood (16), with the catalysts (9a, 9b) being arranged between its outlet and the re-entry of the denitrified gases into the plate heat exchanger (4). <IMAGE>

Description

in DK 170607 B1

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an apparatus for catalytic removal of nitrogen oxide (NO) from power plant flue gases (raw gases), preferably coming from a flue gas desulfurization plant, where the flue gases have been heated to the temperature required for a catalyst process for heat exchange before injection of ammonia. nitrogen stove 1st purified gases (purified gas) and through an additional heat supply.

In a known apparatus for removing nitrogen from power plant flue gases, the heating gases are heated in a regeneration heat exchanger whose heat transferring surfaces are heated by the clean gases which have passed the catalyst. The purified crude gases exiting the regeneration heat exchanger through a connection nozzle are fed via a crude gas line to an additional heating apparatus in which the flue gases are brought to the required temperature to operate the catalyst.

After flowing through the heater, ammonia is added to the raw gases, after which the gases, after the corresponding mixture with the ammonia, reach the catalyst. The purified nitrogen-purified gases are then passed through a purge line to the regeneration heat exchanger, which they pass through while heating the heating surfaces.

The disadvantages of this known apparatus are that gap and leakage losses occur in the regeneration heat exchanger, which leads to limitations in the attainable nitrogen dust filtration rate (NO purity) and thus in the efficiency of the apparatus. Furthermore, the known apparatus requires that the required start-up energy for the regeneration mass and the additional energy to operate a shut-off fan are present. The space requirement for the NO purifier is large, which is mainly due to a diverse and therefore a countervailing temperature profile over the gas flow cross section at the output of the regeneration heat exchanger. In addition, the raw gas lines leading from the regeneration heat exchanger and the purge lines leading back to the catalyst also require a lot of space. Finally, the free surfaces of the NO purification plant require similar thermal insulation ratios, so that no loss of efficiency occurs through heat loss.

It is therefore the object of the invention to provide an energy-saving apparatus for catalytic removal of nitrogenous substances from power plant flue gases, which possess a good NO purification rate and which, with a small space requirement, allow easy access to the plant parts requiring maintenance work.

5 For the technical solution of this task, it is proposed that the apparatus for the heat exchange between raw gas and purified gas is provided with a plate heat exchanger, which is activated, in combination with each other, next to each other and in turn, in cross-counter current, the outlet channel of the plate heat exchanger with devices. 10, the additional heat is supplied and the ammonia injection then follows, and at the end of this outlet duct a bypass cap is placed, between the outlet of the duct and the re-inlet of dfe NO-purified gases in the plate heat exchanger in ducts formed in the hood. .

15

An apparatus of this construction has the advantage that, despite a low build volume and short wires for raw and clean gas, it provides easy access to the plant parts that require maintenance work. Due to the small building volume, the appliance has only small 20 free surfaces, thus avoiding heat loss and thus improving the energy efficiency. To this end also contributes the use of a plate heat exchanger which requires no start-up energy and which, in addition to a regeneration preheater, has no slits, and thus leaks, so that an improved NO purity and thus an improved efficiency of the apparatus are obtained.

The wear and tear of the known regeneration preheater and the noise emission known from corresponding heat exchangers are avoided; moreover, 30 the need for energy for a blocking air fan lapses.

The temperature profile, which is plotted at the output of the plate heat exchanger, is substantially equalized, which means that extra mixing lines can be discontinued, and a redirection of the gas flow within a small space is therefore possible. *

The plate heat exchanger used in the apparatus can be made up of individual modules, which allows a simple adaptation to the required performance and size of the NO purification plant at all times. Due to DK 170607 B1 3, the compact design of the NO purification plant, it is not necessary to incorporate this in a special housing, so that the whole system can be installed outdoors.

5 in a further embodiment of the invention, the apparatus is divided into several building groups which can be individually switched on and off. In this way, the NO purification system, when shut down individual chambers, also becomes applicable with only some areas of the apparatus in use. The blocking of individual chambers also facilitates the execution of repairs, 1 ° maintenance and cleaning work.

According to a further feature of the invention, the raw gas is supplied with additional heat by means of a steam-heated gas preheater located in front of the ammonia injection in the plate heat exchanger outlet duct. Thereby, a uniform temperature profile over the flow cross-section is obtained at the end of the output channel and before the introduction into the catalyst. Unlike the use of extra burners, no additional exhaust gases are generated, thereby improving the NO purification rate.

In addition, for homogenizing the rerouted raw gas stream, it is advantageous to place mixing devices in the rerout cap, for example by incorporating vortex guide surfaces.

Particularly good access to the individual appliance parts is obtained, for example, by means of a common working platform at the same height, the steam heated gas preheater and the catalysts according to a further embodiment of the invention being arranged at the same level.

In yet another embodiment of the invention, the bypass cap is formed 30 having a cross section corresponding to the flow cross section of the catalysts and having at least one length corresponding to the double inlet width. In this way, despite the compact structure, a sufficiently long mixing distance is obtained, and the pressure losses due to the narrowing are reduced.

35

Finally, according to the invention, it is proposed that the return lines from clean gas inside the plate heat exchanger are designed for rectilinear passage. This makes the cleaning pipes easier to clean, especially for the occasional removal of ammonia carbonate.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates, in partial section, a perspective view of an apparatus for removing nitrogen oxides (NO) from power plant flue gases in a first embodiment; and FIG. partly in section, a perspective view of an apparatus for removing nitrogen oxides from power plant flue gases in a second embodiment.

The apparatus depicted in Figure 1 is intended for the removal of nitrogen oxides from power plant flue gases, which mainly come from a flue gas desulphurisation plant, and consists of two building groups: a heating part 1 15 and a NO-cleaning part 2 located above it. Both the heating part 1 and NO-cleaning part 2 In the exemplary embodiment, each consists of four building groups, whereby two building groups, as seen on the lower part of figure 1, are supplied through a common studs 3 from a power plant to produce raw gas which must be purified for nitrogen oxides. To the two two studs 3, each distributor is coupled 11. Via a further two in the drawing, only partially shown collection units 12 with the studs formed on the back of the apparatus, the NO-purified gas, hereinafter referred to as "cleaned", leaves the heating part 1 of the apparatus.

25 Corresponding to the four building groups of the apparatus, the heating element 1 is constituted by four plate heat exchangers 4. For simplification of the figure description, the reference numerals used in the following are indicated only for the building group shown in Figure 1 on the right; however, they apply in the same way to the other three building groups.

30

Each plate heat exchanger 4 consists of 3 superimposed heat exchanger stages 5 ', 5 ", 5'". Each heat exchanger stage 5 ', 5 ", 5"' consists of two heat exchanger elements 6a, 6b, each of which is mounted in pairs at the same height and spaced apart. For the sake of clarity, only heat exchanger elements 6a, 6b in the upper heat exchanger stage 5 '"are shown in FIG.

The plate heat exchanger 4 is flowed in cross-mode flow, whereby the vertical, downward-flowing heat is cleaned rectilinearly through the heat exchanger elements 6a and 6b, respectively, at the same time as the raw gas 6 in the heat exchanger 6 is used for heating. angle in relation thereto. The raw gas flowing through the plug 3 first reaches 5 to the outside of the lower heat exchanger stage 5 ', flows its heat exchanger element inwardly to a common collection chamber 7, rises upwardly in this collecting chamber 7 to reach the gas at the middle heat exchanger stage 5 ", and flows through it. The flue gas exiting the middle heat exchanger-10 stage 5 "heat exchanger element extends into the externally placed, subsequent collection chambers 8a, 8b, in which the flue gas rises upwardly to the region of the upper heat exchanger stage 5 '" and whose heat exchanger elements 6 The heated flue gas then passes through an exit duct 9, which in the exemplary embodiment is designed as a narrowing trapezoid, to the NO-cleaning part 2 of the apparatus.

Similarly, on both sides of the outlet duct 9 are connected reflux ducts 10a, 10b through which the purge gas flowing back from the NO purification part 20 2 into the plate heat exchanger 4 to heat the crude gas in cross mode. The reflux ducts 10a, 10b are located at the same height, in which also the heat exchanger elements on the various heat exchanger stages 5 ', 5 ", 5'" are located, so that the NO-purified gas flows without heat through the heat exchangers in the vertical direction. The purge gas emanating from the lower heat exchanger stage 5 'is fed into a common assembly unit 12 arranged for every two building groups and from it via a chimney into the open.

The temperature of the gas flowing back from the NO-cleaning part 2 in the plate heat exchanger 4 is approx. 320 ° C and at the outlet approx. 85 to 90 ° C. Similarly, the crude gas supplied from the flue gas desulphurisation plant is heated in a cross-mode flow from an input temperature of approx. 55 to 60 ° C to a temperature of approx. 290eC in the 35 outlet duct 9.

The NO cleaning part 2 in each of the four building groups consists of three channels running parallel to one another. The middle, upper open channel forms an extension of the outlet channel 9 and is provided, among other things, with a heating device 13 formed by two superimposed heating surfaces, by means of which the heating device the plate heat exchanger 4 heats it approximately. 290 ° C hot exhaust flue gas to the temperature required for a catalyst operation of approx. 320eC. Above 5 the heating device 13 is arranged an ammonia supply line 14 with single-mounted injection nozzles through which the rising flue gas is added with ammonia. The ammonia supply can also be made below or inside the heater 13. Above each of the output nozzles of the ammonia supply line 14, there are also 10 mounted vortex housings 15 for a good distribution of the ammonia over the flow cross-section.

The upper end of the NO purge portion 2 in each building group individually forms a bypass cap 16. The circumferentially designed bypass 16 is formed approximately as a downwardly open U 15 at a certain distance, the upper opening 17 of the outlet duct 9, so that the flue gas exiting of the outlet channel 9, approx. 180 * in a downward direction and inserted into two exteriors, in extension of the reflux channels 10a, 10b, formed NO purification channels 18a, 18b, externally bounded by the sidewalls of the bypass 16.

Catalysts 19a, 19b are provided for NO purification of the hot ammonia-enriched flue gas catalysts 19a, 18b. To enhance the effect of the vortex housings 15, additional mixing devices may be provided above the catalysts 19a, 19b to achieve a homogenization of the flue gas flow in the bypass cap 16. The NO-purified flue gas coming out of catalysts 19a and 19b is then fed back through the reflux ducts 10a, 10b to the heat exchanger 4.

30

The heaters 13 are preferably designed as steam heated gas heaters and positioned at the level of the catalysts 19a, 19b. In this way, these maintenance-intensive construction parts are made readily accessible, especially when work platforms 35 molds 20 are mounted around the circulation caps 13. *

The flow cross-section determined by the width of the bypass 16 of the NO purification channels 18a, 18b is aligned with the cross-section of the catalysts 19a, 19b, whereby the length of the bypass cap 16 corresponds at least to the double cross-section of the upper opening 9 of the outlet channel obtain a sufficiently long mixing distance before the catalysts 19a, 19b and to keep a pressure drop due to constriction low.

In the further embodiment of an apparatus for removing nitrogen from FIG. 2 shown in FIG. 2, the heating portion 1 is constructed in a manner similar to the previous embodiment of FIG. 1. However, the flue gas flow in the NO purification portion 2 occurs in a different way. , the crucial difference of which is that each of the two building groups in the heating part 1 is connected to a common NO-cleaning part 2 with each a by-pass cap 16. The distribution of the raw gas rising from the plate heat exchanger 4 into a heating duct 21 provided with a heating device 13 as the return of the NO-cleaned gas coming from the catalysts 19 to the plate heat exchanger 4 is effected through a flow distributor 22 introduced between the heating part 1 and the NO-cleaning part 2. The flow distributor 22 consists of a system of mostly tetrahedral distributor caps 23, whose outward surfaces guide the raw gas into the NO purification portion 20 2, and if inward f lets the NO-purified clean gas return to the heating part 1.

It can be seen from Figure 2 that each bypass cap 16 encloses a heating duct 21 provided with the heating device 13 and with the ammonia supply line 14 and the catalysts 19. Separated therefrom through a vertical wall 24 To improve the 180 # of the duct between the duct 21 and NO. In the circulation hood 16, circulation guide surfaces 25, which are designed as angles of 90e in addition to a flue gas flow overflow, also cause its homogenisation over the cross-section of the catalysts 19. As in the exemplary embodiment of FIG. 1, it is heated as steam-heated gas. 13 placed at the same level as the catalysts 19.

35 DK 170607 B1 8

Refer to: Circuit cap 17 Upper opening 18a Dust cloth cleaning channel 18b Dust cloth cleaning duct 19 Catalyst 19a Catalyst 19b Catalyst 20 Work platform 21 Heating duct 22 Flow distributor 23 Distributor cap 24 Wall 25 Circulation control surface?

Claims (8)

1. Nitrogen (NO) catalytic removal device from power plant flue gases (raw gas), which preferably comes from a flue gas desulfurization plant and which is heated by heat exchange with the nitrogen-purified (NO) purified gases before injection of ammonia and by supplying additional heat to the temperature required for the catalyst process, the clean gas being returned from the catalyst to the heat exchange, characterized in that a plate heat exchanger (4) is provided for the heat exchange between raw gas and gas, as well as one another, as one after another, interconnected heat exchanger elements (6a, 6b) are activated in cross-counter current, that the outlet channel (9) of the plate heat exchanger (4) with devices (13) therein is supplied with the extra heat, and that the ammonia injection then follows, and that an end cap (16) is provided at the end of this outlet duct (9), between the outlet of the duct (9) and the re-inlet of the NO-purified gas The catalysts (19, 19a, 19b) are arranged in the plate heat exchanger (4) in channels (18, 18a, 18b) formed in the cap (16). 20 Apparatus according to claim 1, characterized by a division into several building groups which can be individually switched on and off. Apparatus according to claim 1 or 2, characterized in that the raw gas is supplied with extra heat by means of a steam-heated gas preheater (13) arranged in front of the ammonia injection (14) in the outlet duct (9, 21) of the plate heat exchanger (4). Apparatus according to claims 1-3, characterized in that mixing housings (15, 25) are arranged in the orifice cap (16) for homogenization of the controlled raw gas stream. Apparatus according to claim 4, characterized in that the mixing housing (15) is made up of swirl forming surfaces. 35 Apparatus according to at least one of claims 1-5, characterized in that the steam heated gas preheater (13) and the catalysts (19, 19a, 19b) are arranged at the same height. DK 170607 B1 10 Apparatus according to at least one of claims 1-6, characterized in that the by-pass cap (16) has a cross-section corresponding to the flow cross-section of the catalysts (19a, 19b) and has a length corresponding to at least twice the inlet width. 5 Apparatus according to at least one of claims 1-7, characterized in that the reflux pipes (10a, 10b) for cleaning gas inside the plate heat exchanger (4) are designed for a rectilinear gas flow in extension of the ducts (18a, 18b). 10 15 20 25 30 4. 35 *