EP0745807B1 - Steam boiler - Google Patents

Abstract

The steam generator (1) is inserted into a circuit for the direct, selective catalytic reduction of nitrogen oxide in flue gas (19). The economiser is in two parts between which (2a,2b) is the nitrogen oxide catalytic converter (5). The economiser (2a) positioned in front of the catalytic converter in the flow direction of the gas is divided into at least two sections (10a,10b) through which flow in parallel flue gas and heatable working substances. At least one section (10a) is constantly connected to a drum (13) by a pipe (11a,12). The other sections are sealed off from the water circulation by pipes (11b) which can be blocked by shut-off devices (14).

Description

Technical field

The invention relates to a steam generator with a Furnace downstream radiation part and one adjoining convective part, the latter essentially Consisting of cascaded flue gas side Touch heat exchanger, superheater and economizer, which for direct selective catalytic reduction (SCR process) of nitrogen oxides (NOx) in the waste gas from waste incineration plants (KVA) is used, the NOx catalyst is fed directly with the hot smoke gases, so is arranged in the circuit before the scrubber.

State of the art

The NOx emissions from thermal waste incineration plants must not exceed legally prescribed values. To reduce NOx emissions, which are generally between 300 and 450 mg / m ³ , it is known that primary firing measures and / or more effective exhaust-side secondary measures are used, the secondary measures being the SNCR process (selective non-catalytic reduction) and the SCR -Procedures (selective catalytic reduction) are available.

In the SNCR process, the NOx reduction takes place thermally by the reducing agent (ammonia or urea) in one Temperature range from about 900 to 1100 ° C in the furnace or Boiler part is injected.

With the SCR process, however, the nitrogen oxides are converted to nitrogen and water vapor at a much lower temperature with the addition of ammonia water on a catalyst. According to the current state of the art, it is only possible with a catalytic process to reduce the NOx emissions to values <100 mg / m ³ .

For switching the catalyst stage exist according to the known State of the art different options. So be e.g. Boiler for waste incineration plants with NOx catalysts equipped, usually after the washer be used. On the one hand, this has the advantage that the risk of catalyst poisoning or blocking by Dust and sulfur dioxide is reduced, but on the other hand the Disadvantage that the flue gases enter the catalytic converter must be heated again.

Therefore, the NOx catalyst is provided in front of the scrubber in newer circuits. It is then fed directly with the hot flue gases, so that the exhaust gas does not have to be reheated after washing. With prior dedusting ("direct low dust" switching) to residual dust contents below 10 mg / Nm ³ , the catalytic converters achieve a service life similar to that in the switching systems after exhaust gas scrubbing. The electric filter (e-filter) for dedusting can also be arranged after the NOx catalyst ("direct high dust" circuit).

For an optimal working of the catalyst and one as possible long life it is necessary the gas temperature in front of the NOx catalytic converter as constant as possible on a predetermined one Value, for example 350 ° C. The optimal operating temperature the catalyst is at 320 to 350 ° C. (K.J. Thomé-Kozmiensky: Thermal waste treatment. EF publishing house für Energie- und Umwelttechnik GmbH, 2nd edition, 1994, p. 555-557). This bandwidth can be used depending on the Catalyst even larger, e.g. is one at one Operating temperature of 280 ° C working catalyst in one Waste incinerator known.

Without a control device, however, an approximately constant gas temperature is not possible in the various operating states (see, among others, Leibacher and R. Walder: "NOx elimination according to the SCR process in raw gas switching during waste incineration", MÜLL and ABFALL 1995 (9), p 619-625). For example, the gas temperature in a conventional KVA boiler has the following values in two different operating cases: Operating case Gas temperature in ° C after Superheater Evaporator Economizer Dirty at full load 461 343 237 Part load clean 370 290 190

So there are considerable differences in height the flue gas temperature (here approx. 50 ° C after the economizer), what happens when the NOx catalyst is fed directly with the hot smoke gases.

Control devices are also from the prior art known, with which an almost constant Gas temperature can be reached. DE 42 18 016 A1 for example, a multi-part economizer described, the Heating surfaces are connected in series, and the shut-off devices which has water side at the entrance of the individual switchable heating surfaces are arranged. The heating surfaces water flows through one after the other. With this device it is possible to lower the flue gas temperature safe at a minimum value at the outlet of the steam generator to avoid. A disadvantage of this device is that the Water at low temperatures flows through heat exchanger surfaces become. The flue gas temperature is therefore in the control heating surface necessarily less than the evaporation temperature of the water, evaporation of the water is not possible (Water hammer).

In the steam generator disclosed in DE 33 44 712 C1, in which a three-way valve in the to an inlet manifold of the Feed water preheater leading feed water line arranged is the temperature of the flue gases before they enter limited in the catalyst to a narrow temperature range. The control heat exchanger is always with this solution Flows through with water and produces hot water, water / steam mixture or superheater steam.

Finally, a steam generator is known from US 4 160 009, in which a catalyst is arranged between two economizers is. These economizers each have constant, unchangeable heating surfaces. To control the flue gas temperature a gas bypass is used in front of the NOx catalytic converter, which is relatively expensive.

Presentation of the invention

The invention tries to avoid all these disadvantages. you is based on the task of developing a steam generator, for SCR process circuits in which the NOx catalyst in front of the washer directly with the hot smoke gases is loaded, can be used, with relatively little effort the gas temperature in front of the catalyst on an approximate constant, predetermined value can be kept.

According to the invention, this is according to a steam generator Preamble of claim 1 achieved in that the in the flow direction of the gas in front of the catalytic converter is divided into at least two sections, which on the one hand one after the other on the flue gas side and on the other hand from Work equipment to be heated flows in parallel, whereby at least one section over a line with the Drum is connected and the other section (s) Can be optionally locked from the water circuit via lockable lines are.

According to the invention, this is the case with a method of operation of the steam generator in that the temperature of the Flue gases immediately before they enter the NOx catalytic converter is measured and a dependent on the level of this temperature Number of lines (11b) that can be shut off from the water circuit is completed. This creates one or more sections of the economizer completed before the catalyst from the water cycle and part of the heating surface becomes inactive.

The advantages of the invention include that regulating the gas temperature upstream of the NOx catalyst is relatively easy to use and is guaranteed an approximately constant admission temperature of the NOx catalytic converter works optimally and has a long service life. The invention can be used both in "direct-low dust" direct high dust circuits are also used, i.e. the e-filter can be arranged either before or after the economizer be.

It is particularly useful if the economizer is in front of the catalyst is so large that "full load dirty "the inlet temperature of the flue gas in the catalytic converter is less than or equal to the operating temperature of the catalytic converter is.

It is also advantageous if the economizer in the boiler components upstream of the catalytic converter, such as superheaters, Protection bundles, empty trains, are designed so that during operation "Part load clean" the inlet temperature of the flue gas in the economizer upstream of the catalytic converter greater than / equal to the operating temperature of the catalyst.

Brief description of the drawing

Exemplary embodiments of the invention are shown in the drawing of a boiler for a waste incineration plant.

Fig. 1

drei Schaltungssschemata von Kehrrichtverbrennungsanlagen mit SCR-Verfahren nach dem Stand der Technik

I: konventionell

II: direkt-low dust

III: direkt-high dust;

Fig. 2

das erfindungsgemässe Schaltungsschema einer Kehrrichtverbrennungsanlage mit SCR-Verfahren (direkt-high dust);

Fig. 3

eine detailliertere Darstellung eines Teils von Fig. 2 im Bereich des Kessels, des NOx-Katalysators und des Economizers;

Fig. 4

eine schematische Darstellung der Erfindung im Bereich des Kessels, des E-Filters, des NOx-Katalysators und des Economizers (direkt-low dust-SCR-Verfahren).

Show it:

Fig. 1

three circuit diagrams of waste incineration plants with SCR processes according to the prior art

I: conventional

II: direct-low dust

III: direct-high dust;

Fig. 2

the circuit diagram according to the invention of a waste incineration plant with SCR (direct high dust) method;

Fig. 3

a detailed representation of a part of Figure 2 in the area of the boiler, the NOx catalyst and the economizer.

Fig. 4

a schematic representation of the invention in the area of the boiler, the e-filter, the NOx catalyst and the economizer (direct-low dust SCR method).

It is only essential for understanding the invention Elements shown. The system is not shown for example the loading of the boiler, the firing system and the wet laundry facility. The flow direction of the work equipment is marked with arrows.

Way of carrying out the invention

The invention is described below using exemplary embodiments and Figures 1 to 4 explained in more detail.

For a better understanding of the invention are first in Fig. 1 three SCR circuits known from the prior art that which can be achieved after the individual treatment steps Temperature level of the gas shown. Part I shows a circuit in which the apparatus boiler 1 / economizer 2, e-filter 3, scrubber 4, NOx catalyst 5 and cooler 6 in the Order of their flow are arranged, because of the low temperature of the flue gas after the scrubber 4 (e.g. 70 ° C) the gas before entering the NOx catalyst 5 must be heated again (e.g. to 350 ° C). This heating up does not apply to the "low dust" circuit shown in Part II, where the units are arranged in the order boiler 1, Electric filter 3, NOx catalyst 5, economizer 2 and scrubber 4 are arranged, as well as that shown in part III "High dust" circuit with an arrangement in the order Boiler 1, NOx catalyst 5, economizer 2, e-filter 3 and scrubber 4th

Because in the latter two cases for different Operating conditions no constant gas temperature before NOx catalyst 5 can be ensured, the inventive Solution, of which an embodiment variant in Fig. 2 and 3 is applied. The basis is that the Steam generator 1 has a two-part economizer 2. This consists of part 2a, which is on the gas side in front of the NOx catalyst 5 is arranged and a part 2b, which is arranged after the NOx catalyst 5. According to circuit arrangement 2 are then in the order of A filter 3 and then a scrubber flow through the gases 4 arranged. The temperature in front of the NOx catalytic converter is approximately constant for different operating states (in Embodiment shown 350 ° C), it can be +/- 10 ° C differ.

Fig. 3 shows a more detailed schematic representation of the Steam generator according to the invention, as in the high dust circuit 2 is used. Above a firebox 7, two vertical empty trains 8 are arranged, which Form the radiation part of the steam generator. In the following horizontal part of the steam generator are in a superheater 9 and a in the order of their flow economizer 2 divided into two main parts 2a and 2b, with the NOx catalyst between the two parts 2a, 2b 5, which is used for the selective catalytic reduction of the Nitrogen oxides is needed is housed.

The economizer in front of the NOx catalyst 2a is divided into several Sections 10 (here 4 sections) divided, the gas side are flowed through one after the other while they are i.e. water parallel from bottom to top be flowed through. These parallel connecting lines 11 finally open into a line 12 with the drum 13 communicates. With one exception, all are parallel switched lines 11 a shut-off device 14, for example a valve, according to the individual sections 10 of the Economizers arranged in front of the NOx catalytic converter 2a so that these sections are optionally completed by the water cycle can be seen during a section 10 of the economizer the catalyst in any case, i.e. also when shutting off all other sections 10, is connected to the drum 13.

The economizer in front of the catalytic converter 2a is designed in such a way that Partial evaporation can occur. It’s so big that in the "full load dirty" operating condition the inlet temperature of the flue gas 19 in the catalytic converter 5 is less than or equal to is the operating temperature of the catalyst 5.

The economizer in front of the catalytic converter 2a in the steam generator 1 upstream components, such as superheater 9, contact heat generator 18 ("protective bundle", which is first acted upon by the flue gas 19 ), empty trains 8, are designed so that during operation "Part load clean" the inlet temperature of the Flue gas 19 in the economizer in front of the catalyst greater than / equal is the operating temperature of the catalyst.

After the last section 10 in the gas flow direction is a Temperature measuring element 15 arranged. The gas side after the second part of the economizer 2b located on the catalytic converter 5 is essentially realized in countercurrent circuit. A Pump 16 pumps water via line 17 into part 2b of the Economizers, which is arranged after the NOx catalyst 5. The water cools the denoxified smoke gases 19 from the catalytic converter 5 emerge further before they are not shown here Filter 3 dedusted and fed to the scrubber 4 become. The water then passes parallel to the catalyst 5 passed into the sections 10, which flows from bottom to top be taking another heat exchange with here even hotter flue gas 19 takes place. To an almost constant Entry temperature of the flue gases 19 in the NOx catalyst to ensure, is by means of the temperature measuring element 15 measured the flue gas temperature. Depending on the The level of this temperature can influence the flue gas temperature be by closing or opening the respective Shut-off devices 14 individual sections 10 of the economizer upstream of the catalytic converter 2a from the water cycle or be reconnected. This causes a change the active heating surface. The SCR process itself then runs according to the known prior art.

Of course, the invention is not limited to that just described Embodiment limited. For example, it can even in a steam generator with a vertical convective train can be realized.

4 schematically shows a steam generator according to the invention shown for the SCR low dust process. The difference 3 is here between the economizer before Catalyst 2a and the NOx catalyst 5 an E-filter 3 arranged. In addition, this embodiment shows that the economizer after the catalyst 2b also with vertical Gas flow can be carried out. In another, not shown Variant is the economizer after the catalyst 2b even at a greater spatial distance from the NOx catalyst arranged.

Reference list

1

boiler

2nd

Economizer

2a

Part of the economizer in front of the NOx catalytic converter

2 B

Part of the economizer after the NOx catalyst

3rd

E filter

4th

washer

5

NOx catalyst

6

Cooler

7

Firebox

8th

Empty train

9

Superheater

10th

Sections from item 2a

10a

Section not lockable from the water cycle

10b

Section lockable from the water cycle

11

parallel connection lines

11a

Connection line without shut-off device

11b

Connection line with shut-off device

12th

management

13

drum

14

Shut-off device

15

Temperature measuring element

16

pump

17th

management

18th

Touch heat generator

19th

Flue gas

Claims (9)

1. Steam generator (1) having, downstream of the firebox (7), a radiant part and, subsequent thereto, a convective part, the latter essentially comprising, connected in series on the flue-gas side, contact heat exchanger (18), superheater (9) and economizer (2), the steam generator (1) being used in a circuit for the direct selective catalytic reduction (SCR process) of the nitrogen oxides in the flue gas (19), the economizer (2) consisting of two parts and an NOx catalyst (5) being arranged between the two parts (2a, 2b), characterized in that the economizer (2a) arranged upstream of the catalyst (5) in the direction of flow of the flue gas (19) is subdivided into at least two sections (10a, 10b), through which, on the one hand, the flow passes in series on the flue-gas side and, on the other hand, the working medium to be heated flows in parallel, at least one section (10a) always being connected via a line (11a, 12) to the drum (13) and the other section(s) (10b) being able to be shut off as desired from the water circulation via lines (11b) which can be shut off.
2. Steam generator according to Claim 1, characterized in that a shut-off element (14) is arranged in each of the lines (11b) which lead from the sections (10b) of the pre-catalyst economizer (2a), which can be shut off from the water circulation, into the line (12) to the drum.
3. Steam generator according to claim 1 or 2, characterized in that the pre-catalyst economizer (2b [sic]) is designed to be of a size such that, in the operating case "full load, dirty", the entry temperature of the flue gas (19) into the catalyst (5) is less than or equal to the operating temperature of the catalyst (5).
4. Steam generator according to claim 1 or 2, characterized in that the components, such as superheater (9), contact heat generator (18), outlet flues (8), in the steam generator (1) which are upstream of the pre-catalyst economizer (2a) are designed so that in the operating case "partial load, clean", the entry temperature of the flue gas (19) into the pre-catalyst economizer (2a) is greater than or equal to the operating temperature of the catalyst (5).
5. Steam generator according to Claim 1, characterized in that an electrostatic precipitator (3) is arranged between the pre-catalyst economizer (2a) and the NOx catalyst (5).
6. Steam generator according to Claim 1, characterized in that the flow passes through the post-catalyst economizer (2b) essentially in a countercurrent circuit.
7. Steam generator according to Claim 1, characterized in that the flue gas (19) flows vertically through the post-catalyst economizer (2b).
8. Steam generator according to Claim 1, 6 or 7, characterized in that the post-NOx-catalyst economizer (2b) is arranged spatially separated from the NOx catalyst (5).
9. Process for operating a steam generator according to one of Claims 1 to 8, characterized in that the temperature of the flue gases (19) is measured immediately before their entry into the NOx catalyst (5) and a number, which is dependent on this temperature, of the lines (11b) which can be shut off are shut off from the water circulation.

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