EP0839301A1

EP0839301A1 - Method of incinerating material

Info

Publication number: EP0839301A1
Application number: EP96926373A
Authority: EP
Inventors: Albert Merz; Hubert Vogg; Roland Walter
Original assignee: Forschungszentrum Karlsruhe GmbH; EVT Energie und Verfahrenstechnick GmbH
Current assignee: Forschungszentrum Karlsruhe GmbH
Priority date: 1995-07-20
Filing date: 1996-07-19
Publication date: 1998-05-06
Anticipated expiration: 2016-07-19
Also published as: DE59604896D1; JPH10508371A; EP0839301B1; DK0839301T3; JP3121840B2; DE19629216C2; US6038988A; DE19629216A1; WO1997004274A1; ATE191552T1

Abstract

In a method of incinerating waste material in a parallel flow process wherein hot exhaust gases are conducted above a combustion chamber grate in the same direction as the material is moved on the grate, different temperatures zones are maintained to which air is admitted from the bottom through the grate such that a temperature of less than 900 DEG C. is maintained in a first zone which is a drying zone, a temperature of about 1000 DEG C. is maintained in a second zone which is an evaporization and vaporizing zone, a temperature of about 900 DEG C. is maintained to in a third zone, which is the final combustion zone and a temperature less than 900 DEG C. is maintained in a fourth zone which is a sintering zone. Additional air is supplied to the combustion zones 1 through the side walls of the combustion chamber. A dividing wall is disposed above the grate over which the hot combustion gases are conducted to a discharge opening so that heat is transferred to the dividing wall for radiation back onto the waste material on the grate.

Description

Process for the combustion of materials to be thermally treated

The present invention relates to a method for combusting materials to be treated thermally, for example domestic waste according to the principle of direct current firing on a grate of an incineration plant with supply of primary air from below through the grate according to the preamble of claim 1, and a combustion system for exercising of the procedure.

The thermal treatment of residual waste is an indispensable cornerstone in the context of integrated waste management concepts. B. residual waste is burned as waste with a relatively large amount of excess air. Theoretically, a little more than 3 Nm ^{3 of} air is required per kg of fuel with a calorific value of approx. 8 MJ / kg. In fact, 6 Nm ^{3 was} used until recently. To date, the specific air consumption figure has been reduced to approx. 5 Nm ³ .

The development of cost-optimized waste incineration plants is an obstacle to the fact that it has so far not been possible to counteract the formation of NO _x on the primary side to such an extent that the subsequent flue gas cleaning technology used today in the exhaust system can do without DeNOX measures. Although there is a limit value of 200 mg NO _x / Nm ³ for waste incineration, less than half the limit value is expected from the public, primarily because of the ozone problem. 100 mg NO _x / Nm ^{3 is} thus to be specified as the development goal for NO _x reduction measures on the primary side.

From US Pat. No. 3,808,986 a method for the incineration of waste and an installation therefor are known. Purpose and conception

ORIGINAL DOCUMENTS This system aims to increase the combustion temperatures in order to reduce the amount of the otherwise non-combustible components. However, this leads to exhaust gas temperatures in the range of well over 1000 ° C and thus to a strong NO _x formation in the exhaust gas, a measure that is no longer tolerable due to the constantly tightened exhaust gas regulations. Other systems according to the prior art, which operate in medium and countercurrent mode, generally have high NO _x values in the range from 200 to over 400 mg / Nm ³ .

From DE 42 19 231 Cl and from Thome-Kozmiensky: Thermal waste treatment, Berlin, EF-Verlag für Energie- und Umwelttechnik, 1994, pp. 160 to 163, a further combustion process according to the direct current principle for waste and a plant for it are known. This process, in which secondary air or flue gas is blown into the combustion chamber from above, creates a temperature profile in the firing zone above the grate, which continuously increases flue gas temperatures from 700 ° C at the beginning of the grate to 1300 ° C at the end of the firing zone before the flue gas flue behind Combustion chamber geometry. This also leads to the aforementioned unwanted high N0 _X - values, a finding that was, however, not made here and in the vor¬ standing reference and therefore no measures were getröffen to eliminate them.

In contrast, the object of the present invention is to provide a method which, by means of purely firebox-side measures, enables the NO _x components in the exhaust gas of the system to be reduced. The invention is based on the knowledge that this can be achieved by reducing the temperatures in the range below 900 ° C. at the end of the combustion chamber in the outflowing flue gas. This task is new.

To achieve the object, the present invention proposes the method steps in a method according to the preamble before, which are specified in the characterizing part of claim 1.

Further advantageous features of the invention as well as the solution to the problem with regard to an incineration plant for the method are set out in the features of the subclaims.

With the method according to the invention, by means of purely firebox-side measures, the zone-by-zone temperature reduction, not only a reduction in the specific amount of combustion air but also a flue gas-side temperature of considerably below 900 ° C can be achieved and thus subsequent thermal NO _x formation can be prevented in a particularly advantageous manner . A secondary air addition for post-combustion, which would increase the flue gas temperatures, is not necessary. It is essential that the invention specifies a controlled temperature field or profile that must be generated in the combustion chamber.

With the help of the special fittings in the combustion chamber, the exhaust gas is guided through the zones in precisely defined temperature ranges by the addition of air into the co-current with the movement of solids on the grate, redirected upwards and back again. Due to the forced guidance of the hot combustion gases, the internals assume the temperature of the gases and additionally act as infrared emitters, similar to the hot gas body located above the drying zone in a countercurrent combustion. The fire situation in the DC configuration here is identical to that of countercurrent firing without any further measures. In addition to the already mentioned improvements with regard to the exhaust gas composition, the system therefore combines the favorable properties of both combustion processes in a particularly advantageous manner.

Details of the new method are explained in more detail below and with reference to FIGS. 1 to 4: It shows 1 shows a schematic section through a waste incineration plant,

2 shows an enlarged section of the combustion chamber area of FIG

3 shows graphical representations of the temperature profiles according to the method and

4 shows a schematic section through the side wall at the level of primary region I of FIGS. 1 and 2.

In the diagram shown schematically in FIG. 1 as a possible exemplary embodiment for such a system, waste is burned on a grate 1 according to the principle of direct current firing. The primary air is supplied to the grate from below underwind zones a to d. The hot exhaust gas or flue gas 2a-2e is released by means of later-described heat-conducting and - storing internals 3, 4 arranged above the grate 1, which can have approximately the same length as the combustion zone 5 of the primary region I, in cocurrent with the movement of solids the grate 1 positively guided over this in the combustion direction 6. The combustion takes place in successively defined zones in their temperatures, which will be described in more detail later with reference to FIGS. 2 and 3. Subsequently, the hot exhaust gas in the area of the grate end 7 is directed upward around the end of the internals 4 and above the internals 3 in the secondary region II in the opposite direction 2d, 2e over the grate 1, in the embodiment of the system shown in FIG. 1 up to its initial area 8, again forcibly returned. As a result, the heat transferred to the internals 3, 4 by this gas recirculation can be radiated again from these internals 3, 4 over their entire length in the direction of the grate 1 onto the combustion material and can thus be used. A shorter one Transmission length over only part of the internals is also possible by moving the outflow opening 12.

The central element of an exemplary waste incineration plant in which the method is carried out is the combustion chamber 10 consisting of the primary area I and the secondary area II, which is closed off at the top by a heat-insulating wall 9 and which is shown enlarged in FIG. The details shown in FIG. 2 correspond to those in FIG. 1, with the same elements having the same position numbers as in FIG. 1, even if these are not shown separately. In the lower part of the firing chamber, primary area I, is the firing grate 1, above which the entire combustion zone 5, consisting of individual zones, is also shown in FIG. 2. The combustion of the firing material 11 into the initial area 8 of the grate 1 brought in garbage takes place according to the principle of direct current combustion, whereby the combustible material moves in the direction of combustion 6 or with the combustion up to the ash discharge 14. The resulting smoke or exhaust gas 2 flows in the direction of the arrows 2a to 2e in the secondary region II from the combustion zone 5 to the outflow opening 12 into the flue gas duct 13. The outflow opening 12 is in the system form shown by way of example in FIG Combustion direction 6 seen - approximately above the beginning of the combustion zone 5 on the grate 1 in the upper wall 9 of the combustion chamber 10 behind the secondary area II and leads through this into the flue gas flue 13 above it. However, the outflow opening to the flue gas flue can also - against the combustion direction seen - be located further forward in secondary area II.

As a special measure, above the grate 1 and below the upper wall 9 of the combustion chamber 10, a heat-conducting and -saving intermediate wall of approximately the same length as the combustion zone 5 is used, which consists of individual ceramic plates 3 and 4 lying one behind the other, which are attached to the side - tenwanden 17 of the combustion chamber 10 attached ledges 15 are placed and which separates the primary area I from the secondary area II. The last ceramic plate 4, as seen in the direction of combustion 6, is inclined towards the grate 1. The intermediate wall 3, 4 sits tightly between the side walls 17 and the front wall 16 of the combustion chamber 10 and, viewed in the direction of combustion 6, extends up to approximately the area of the grate end 7 or the combustion zone 5. The lower part of the side walls 17, which is assigned to primary area I or combustion zone 5, is designated by 18.

Behind the intermediate wall 3, 4, now - again seen in the direction of combustion 6 - is the deflection area 2c for the deflection of the flue gases 2a, 2b in the opposite direction 2d and 2e via the intermediate wall 3, 4 to the outflow opening 12. Above it, starting in the deflection area 2c, the secondary area II. B. from an Al oxide ceramic and have a thickness of 25 to 35 mm with a grate width of 80 cm. They have a high heat transfer coefficient in order to ensure good heat transfer through them from the exhaust gas area 2d, 2e and then further by means of heat radiation back into the combustion zone 5.

In the present method, the combustion takes place in primary area I in four successive zones A, B, C and D, which are each located approximately above the corresponding underwind zones a, b, c and d, as shown in FIG. There are three mechanisms for NO _x formation:

1. From the nitrogen contained in the fuel, whereby about 1% chemically bound nitrogen is contained in common waste.

2. Prompt Nθ _x formation takes place, the nitrogen coming from the combustion air. 3. Is thermal NO _x as under 2. by nitrogen from the

Air in the flue gas duct behind the combustion chamber at higher

Temperatures formed under the formation of flames. This NO _x -

Education is at the forefront of what is here

Process, i.e. the aim is to achieve lower temperatures there.

For this purpose, the temperatures in the individual zones A, B, C and D are driven or set according to the method in a very special way, as shown in the curve in FIG. 3:

In a first zone A of the combustion chamber 10 above the grate 1, the drying and pyrolysis zone of the fuel in the primary region I, to an average temperature in the range of below 900 ° C.

In a second zone B, the degassing and gasification zone of the fuel, a precisely controlled average temperature in the range of a maximum of 1000 ° C, which is higher than that in zone A.

- As an important step, a third zone C, the burnout zone of the fuel, is then used to lower the mean temperature in the range from 950 ° C. to below 900 ° C., which is lower than that of the second zone B, while thereafter

in a fourth zone D, the sintering zone, even lower temperatures of below 900 ° C. to below 700 ° C.

This means falling temperatures in the direction of flow of the flue gases over the bed. The desired temperature profiles are achieved in that the primary air is fed zone by zone from the underwind zones a, b, c, and d through the grate, the air quantities for zones A and B being metered in such a way that a substoichiometric Ver¬ in the material bed burning takes place. Due to the primary acid In this area, material deficiency during combustion releases considerable quantities of CO in the order of 100 g / Nm ³ from the material bed, which in turn have a reducing effect on N0 _X which has already formed, as a result of which elemental nitrogen is formed. In addition, a large number of radical reactions can occur, which in turn can influence the NO _x reduction. The substoichiometric fire control can be carried out either by increasing the fuel addition or by throttling the amount of air from the underwind zones.

Furthermore, the side wall or walls of the combustion chamber predominantly or only in the area of zones A and B of the combustion chamber 10 below the internals 3 and 4, i.e. in the combustion chamber above the grate 1, additional air, the so-called curtain air 20 of lower or approximately the same temperature as compared to the combustion chamber temperature, is added to the combustion chamber. This additional air thus forms an air curtain in the wall area. The fog air supports the gas phase reaction in zones A and B. It is important that in the area above the internals 3 and 4, in the secondary area II i.e. no further secondary air is added after the fourth zone D.

To explain the addition of the veil air 20, a section through a side wall of the system at the level of the furnace 10 is shown in FIG. 4. A cooling air duct 19 runs in the side wall 17, through which cooling air 22 is guided to the combustion direction 6 by means of fans, no longer shown, for cooling the side walls with a certain cooling air overpressure in direct current. This side wall 17 is air-permeable in the partial area 18 located between the primary area I and the channel 19 in the sub-area 18, so that veil air 20 can escape from the channel 19 into the primary area I. The air permeability can be achieved through porosities, small channels or other passages 21. The portion 18 of the side wall 17 with the Porosity or the openings is preferably or predominantly only in the area of zones A and B.

By presetting the air permeability and / or varying the cooling air pressure, the fog air 20 can be metered as desired. The temperature of the curtain air is determined by its heating up in the wall.

The primary area I is bounded at the bottom by the grate 1, at the top by the ceramic plate internals 3 and 4, and on the sides by the lower side walls 18 in the form of the firebox lining. This side wall 18 in the primary area I has, as already described, a defined air permeability for the passage of the air 20 in whole or in part. The air permeability can be achieved by a uniform, certain and adjustable air passage rate of the wall itself or of individual wall parts. This is particularly favorable in the case mentioned, in which the veil air 20 is taken from the cooling air 22 cooling the side wall 17 from the outside, but the veil air 20 can also be supplied from other sources through one or more openings in the wall.

In FIG. 3, the temperature curves of the new method are graphically represented in the lower part over the individual zones and in the upper part further characteristic values of the combustion. These are measured values from a test that was carried out in a waste incineration plant. The curves with the round measuring points show the temperature profile in the primary area I, ie in zones A, B, C and D at the measuring points T70 to T75, the curves with the square points at the measuring points T105 to T107 in the exhaust gas flue. The full points show the temperature profile without the addition of the fog air 20, the hollow points show the profile desired with the addition of the fog air 20 in the process according to the invention. It clearly shows that the required temperature reduction the rear zones C and D is reached. Doing this

Volume ratios of about 1/5 (about ie 14-17% haze air proportion of the total air) to 1/6 of fog air to primary air DERS been shown in the illustrated combustion temperatures and curtain air temperatures of about 500 ° C to 750 ^β C as beson¬ low.

In zones A, B, C and D of primary area I, as already described above, all processes such as drying, degassing, gasification, sintering reactions and gas phase reactions take place above the material bed. A usual gradation of the primary air addition from the underwind zones a, b, c and d in the tests according to FIG. 3 is at a fuel throughput of approximately 170 kg / h: 100 Nm ³ / h in zones A and D and each 200 Nm ³ / h in zones B and C. To support the gas phase reactions in zones A and B above the material bed on the grate 1, the aforementioned Schleier¬ air of 100-120 Nm ³ / h is now passed through the combustion chamber longitudinally limiting side wall 18 mainly fed to zones A and B. Due to the way of guiding through the hot walls, the veil air enters the primary room I at the desired temperatures of 500 ° C. to 750 ° C., the temperature in this area being specifiable by air-side measures.

The secondary room II directly adjoins the primary room I. As already stated, no further combustion air is fed into this secondary space II. For the chemical reactions taking place there, e.g. B. the remaining CO conversion, the oxygen offered by primary and fog air is sufficient.

In the experiments with the described system in direct current, ie with the internals 3 and 4, by adding primary air from the four underwind zones a, b, c, and d of the grate in connection with the addition of fog air 20 from the side wall cooling realizes a complete combustion with CO values <5 mg / Nm ³ . The special addition of air to zones A, B, C and D allows the temperature distribution in the gas duct to be influenced in a targeted manner. If the process according to the invention is used on the combustion chamber side, the desired temperatures over long distances of 870 to 930 ° C. result down the flow, which in addition to the NO _x reduction in the exhaust gas flue are also responsible for a very good burnout of the exhaust gas.

Experiments showed the following results, which are listed in the upper part of the table in FIG. 3:

Combustion without veil air: approx. 170 mg / Nm ³ NO _x in the flue gas duct,

(Temperature curve full points) Combustion with veil air: approx. 55 mg / Nm ³ NO _x in the flue gas duct,

(Temperature curve hollow points),

at a mass flow _rate of 171 kg / h and oxygen _additions of 9.0 or 10.8% and each without exhaust gas denitrification measures. As already explained, systems according to the prior art, which operate in medium and countercurrent operation, generally have high NO _x values in the range from 200 to over 400 mg / Nm ³ .

It was thus possible to show that the new method allows emission limit values of possibly considerably less than 200 mg / Nm ³ NO _x to be expected by measures purely on the combustion chamber side, without further denitrification in the exhaust system. Reference symbol list:

I primary area

II secondary area

a - d underwind zones

1 moving grate

2 exhaust gas (2a - 2e flow arrows)

3 plates

4 inclined plate

5 combustion zone

A drying and pyrolysis zone B degassing and gasification zone C burnout zone D sintering zone

6 Direction of combustion

7 rust end

8 initial area

9 top wall

10 combustion chamber

11 Firing material entry

12 discharge opening

13 flue gas flue

14 ash discharge

15 ledges

16 end wall

17 side walls

18 side wall primary area

19 cooling air duct

20 fog air

21 porosity or channels

22 cooling air

T70 - T75 temperature measuring points in the combustion chamber area T105 - 107 temperature measuring points in the flue gas duct

Claims

Claims:

l. Process for the combustion of materials to be thermally treated, e.g. of domestic waste according to the principle of direct current firing on the grate of an incinerator with primary air being supplied from below through the grate, in which the hot exhaust gas by means of internals arranged above the grate in primary area I over part of the grate length with the movement of solids on the Grate is guided over this in the direction of combustion, then in the area of the grate end upwards around the end of the internals and above the internals in the secondary area II or at least partially returned via the internals in the opposite direction and then diverted, characterized. that

in a first zone (A) of the combustion chamber (10) above the grate (1), the drying and pyrolysis zone in primary area I, an average temperature in the range below 900 ° C,

in a second zone (B), the degassing and gasification zone, an average temperature in the range of approximately 1000 ° C.,

in a third zone (C), the burnout zone, an average temperature in the range from 950 ° C. to below 900 ° C. and lower than that of the second zone (B)

- In a fourth zone (D), the sintering zone, a temperature of below 900 ° C to below 700 ° C is set and that

for this purpose the primary air is fed in zones from the underwind zones (a, b, c and d) through the grate, the air being quantities for zones A and B are dosed so that substoichiometric combustion takes place there in the material bed and that

- predominantly through the side wall or walls of the combustion chamber or only in the area of zones A and B of the combustion chamber (10) below the internals, i.e. in the combustion chamber above the grate additional air of the same or lower temperature than the combustion chamber temperature is added as fog air in the combustion chamber and that

-in the area above the internals, in secondary area II i.e. after the fourth zone (D) no more air is added as secondary air.

2. The method according to claim 1, characterized in that the additional fog air is in a temperature range of about 500 ° C to 750 ° C.

3. The method according to claim 1 or 2, characterized in that the volume ratio of fog air to primary air is about 1/5 to 1/6.

4. The method according to claim 1, 2 or 3, characterized. that the veil air is taken from the cooling air cooling the side wall of the combustion chamber.

5. Incinerators for performing a method according to one of claims 1 to 4, characterized by the further features: a) above the grate (1) and below the upper wall (9) of the furnace (10) is an intermediate wall (3, 4) about the same length as the zones (A, B, C, D) set which limits the primary area (I) upwards and the secondary area (II) above it downwards,

b) the intermediate wall (3, 4) sits tightly between the side walls (17) and the front wall (16) of the combustion chamber and extends, viewed in the direction of combustion (6), up to approximately the area of the grate end (7) or the combustion zone (5), c) behind the end of the partition (3, 4), - seen in the direction of combustion (6) - there is a deflection area for the deflection of the flue gases (2) upwards around the partition (3, 4) from the primary (I) into the secondary area (II) and to the outflow opening (12), d) in the side wall (17) there is a cooling air duct (19) through which cooling air (22 ) is blown, e) the side wall (17) has a defined air permeability for the cooling air in the partial area (18) located next to the primary area (I) between the primary area (I) and the channel (19) ( 22) so that veil air (20) can emerge from the channel (19) into the primary region (I).

5. Incinerator according to claim 4, characterized in that the partial area (18) of the side wall (17) has uniformly or unevenly distributed porosity.

6. Incinerator according to claim 4, characterized. that openings or channels lead through the partial area (18) of the side wall (17).

7. Incinerator according to one of claims 5 or 6, characterized by, the partial area (18) of the side wall (17) with the porosity or the openings is only or predominantly in the area of zones A and B.

8. Incinerator according to one of claims 4 to 7, da¬ characterized in that the intermediate wall consists of individual ceramic plates (3, 4) lying one behind the other, which are placed on the side walls (17) of the combustion chamber (10) attached ledges (15) .

9. Incinerator according to claim 8, characterized in that the last ceramic plate (4), seen in the direction of combustion (6), is inclined towards the grate (1).