EP0839301B1 - Method of incinerating material - Google Patents

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

The present invention relates to a method for the combustion of materials to be thermally treated, for example household 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 plant for carrying out the method . Such a method and such a system are known from document A Merz "Industrial furnaces and boilers - Proceedings of the 3rd European Conference", April 18-21, 1995, Lisbon, Portugal, pages 454 to 466.

The thermal treatment of residual waste is an indispensable cornerstone within the framework 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 that to date it has not been possible to counteract the formation of NO _x on the primary side to an extent that the subsequent flue gas cleaning technology in the exhaust system, which is generally used today, can do without DeNOX measures. Although there is a limit value of 200 mg NO _x / Nm ³ for waste incineration, the public expects less than half the limit value, primarily because of the ozone problem. This means that 100 mg NO _x / Nm ³ must 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 of this The aim of the plant is to increase the combustion temperatures in order to reduce the amount of the otherwise non-combustible parts. 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 which is no longer tolerable due to the constantly tightened exhaust gas regulations. Other systems according to the state of the 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 C1 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 undesirable high NO _x values mentioned above, a finding which, however, as in the above literature reference, was not made here and therefore no measures have been taken to eliminate it.

In contrast, the object of the present invention is to provide a method which, by means of purely combustion chamber-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 and 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 a precisely defined temperature range 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 take on the temperature of the gases and also act as infrared emitters, similar to the hot gas body located above the drying zone during 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.

die Fig. 1

einen schematischen Schnitt durch eine Müllverbrennungsanlage,

die Fig. 2

einen vergrößerten Schnitt des Brennraumbereiches der Fig.1

die Fig. 3

graphische Darstellungen der Temperaturverläufe nach dem Verfahren und

die Fig. 4

einen schematischen Schnitt durch die Seitenwand in Höhe des Primärbereiches I der Fig. 1 und 2.

Details of the new method are explained in more detail below and with reference to FIGS. 1 to 4: It shows

1

a schematic section through a waste incineration plant,

2

an enlarged section of the combustion chamber area of Fig.1

3

graphic representations of the temperature profiles according to the method and

4

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

In the figure 1 schematically as a possible embodiment for such a system shown, 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 described later, above the firing grate 1, arranged heat-conducting and - storing internals 3, 4, which can have approximately the same length as the combustion zone 5 of the primary area I, in cocurrent with the movement of solids on 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 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 to its initial area 8, forcibly returned. As a result, the heat transferred to the internals 3, 4 by this gas recirculation can be radiated from these internals 3, 4 over their entire length in the direction of the grate 1 onto the combustion material and 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 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, the same elements being intended to have the same position numbers as in FIG. 1, even if these are not shown separately. In the lower part of the firing chamber, the primary area I, is the firing grate 1, over which the entire combustion zone 5, consisting of individual zones, is also shown in FIG. 2. The combustion of the fired material 11 introduced into the initial area 8 of the grate 1 Refuse is carried out according to the principle of direct current firing, the fired material migrating in the combustion direction 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 flue 13. The outflow opening 12 lies in the system form shown by way of example in FIG 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 - seen against the direction of combustion - 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 on the side walls 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 end wall 16 of the combustion chamber 10 and extends, as seen in the combustion direction 6, to approximately the area of the grate end 7 or the combustion zone 5. The lower part of the side walls 17, the Primary area I or the combustion zone 5 is assigned, is designated 18.

Behind the intermediate wall 3, 4, the deflection region 2c for the deflection of the flue gases 2a, 2b in the opposite direction 2d and 2e is now - again seen in the combustion direction 6 - via the intermediate wall 3, 4 to the outflow opening 12. Above it, yes beginning 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.

• 1. Aus dem im Brennstoff enthaltenen Stickstoff, wobei in gängigem Müll etwa 1% chemisch gebundener Stickstoff enthalten ist.
• 2. findet eine prompte NO_x-Bildung statt, wobei der Stickstoff aus der Verbrennungsluft stammt.
• 3. Wird thermisches NO_x wie unter 2. durch Stickstoff aus der Luft im Abgaszug hinter dem Feuerungsraum bei höheren Temperaturen unter Flammenbildung gebildet. Diese NO_x-Bildung steht im Vordergrund des hier vorliegenden Verfahrens, d.h. es wird mit ihm angestrebt, dort niedrigere Temperaturen zu erreichen.

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 NO _x formation takes place, the nitrogen coming from the combustion air.
• 3. Thermal NO _{x is formed} as in 2. by nitrogen from the air in the flue gas duct behind the combustion chamber at higher temperatures with the formation of flames. This NO _x formation is at the forefront of the method at hand here, ie the aim is to achieve lower temperatures there.

• In einer ersten Zone A des Feuerungsraumes 10 über dem Rost 1, der Trocknungs- und Pyrolysezone des Brennstoffes im Primärbereich I, auf eine mittlere Temperatur im Bereich von unter 900°C.
• In einer zweiten Zone B, der Entgasungs- und Vergasungszone des Brennstoffes, eine genau kontrollierte mittlere Temperatur im Bereich von maximal 1000°C, die höher ist als die in der Zone A.
• Als wichtiger Schritt wird danach in einer dritten Zone C, der Ausbrandzone des Brennstoffes, eine gegenüber der zweiten Zone B wieder niedrigere mittlere Temperatur im Bereich von 950°C bis unter 900°C gefahren, während danach
• in einer vierten Zone D, der Sinterzone, noch niedrigere Temperatur von unter 900°C bis unter 700°C gefahren werden.

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 medium zone in the third zone C, the burnout zone of the fuel, is then again lower than the second zone B in the range from 950 ° C. to below 900 ° C., 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 substoichiometric combustion takes place in the material bed . Due to the lack of oxygen on the primary side During combustion, considerable amounts of CO in the order of 100 g / Nm ^{3 are} released from the material bed in this area, which in turn have a reducing effect on NO _x that 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 sub-stoichiometric fire control can be carried out either by increasing the fuel addition or by throttling the air volume 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 fog air 20 of lower or approximately the same temperature is added to the combustion chamber temperature in 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 through the side wall 17, through which cooling air 22 is guided in a direct current to the combustion direction 6 by means of fans, which are no longer shown, for cooling the side walls with a certain excess cooling air pressure. This side wall 17 is designed to be air-permeable in the partial area 18 located next to the primary area I between the primary area I and the channel 19, so that fog 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 dosed 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 combustion chamber 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, specific and adjustable air passage rate of the wall itself or individual wall parts. This is particularly favorable in the case in which the veil air 20 is taken from the cooling air 22 cooling the side wall 17 from the outside. however, the fog air 20 can also be supplied through one or more openings in the wall from other sources.

In FIG. 3, the temperature profiles of the new method are shown graphically over the individual zones in the lower part and further characteristic values of the combustion in the upper part. 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 primary area I, ie in zones A, B, C and D at measuring points T70 to T75, the curves with square points at 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 is clearly shown that the required temperature reduction the rear zones C and D is reached. Volume ratios of approximately 1/5 to 1/6 of air to primary air (ie approximately 14-17% of air in the total air) have proven to be particularly favorable at the combustion temperatures and air temperatures of approximately 500 ° C. to 750 ° C. shown.

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 zone A and D and 200 Nm each 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 air of 100-120 Nm ³ / h is now passed through the side wall 18 that delimits the combustion chamber lengthways mainly fed into 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 conjunction with the addition of fog air 20 from the side wall cooling complete combustion with CO values <5 mg / Nm ³ . The special addition of air to zones A, B, C and D can be used to influence the temperature distribution in the gas duct. 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.

Verbrennung ohne Schleierluft:

ca.170 mg/Nm³ NO_x im Abgaszug, (Temperaturverlauf volle Punkte)

Verbrennung mit Schleierluft:

ca.55 mg/Nm³ NO_x im Abgaszug, (Temperaturverlauf hohle Punkte),

bei einem Massenstrom m_Br von 171 kg/h und Sauerstoffzugaben von 9.0 bzw. 10,8 % und jeweils ohne abgasseitige Entstickungmaßnahmen. Wie bereits ausgeführt, weisen Anlagen nach dem Stand der Technik, die im Mittel- und Gegenstrombetrieb arbeiten, generell hohe NO_x-Werte im Bereich von 200 bis über 400 mg/Nm³ auf.Experiments showed the following results, which are listed in the upper part of the table in FIG. 3:

Combustion without air curtain:

approx. 170 mg / Nm ³ NO _x in the flue gas flue, (temperature curve full points)

Combustion with fog air:

approx. 55 mg / Nm ³ NO _x in the flue gas duct, (temperature curve hollow points),

at a mass flow m _Br of 171 kg / h and oxygen additions of 9.0 or 10.8% and without any denoxing measures on the exhaust gas side. 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 can be used to significantly undercut emission limit values that may be considerably below 200 mg / Nm ³ NO _x without further denitrification in the exhaust system.

Reference symbol list:

I.

Primary area

II

Secondary area

a -

d underwind zones

1

Moving grate

2nd

Exhaust gas (2a - 2e flow arrows)

3rd

plates

4th

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

Rusting

8th

Initial area

9

top wall

10th

Combustion chamber

11

Firing material entry

12th

Discharge opening

13

Flue gas flue

14

Ash discharge

15

Ledges

16

Front wall

17th

side walls

18th

Sidewall primary area

19th

Cooling air duct

20th

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 (10)

1. Process of incinerating materials to be treated thermally, e.g. domestic waste, in the co-current mode on the grate (1) of an incineration plant with primary air (a-d) being passed through the grate (1) from below and the hot exhaust gas (2) being led in incineration direction (6) over part of the movable grate by means of internal structures (3, 4) located above the grate (1) in the primary zone I and, in the range of the grate end (7), passed upwards around the internal structures (3, 4) and discharged above these structures (3, 4) in the secondary zone II or returned in counterdirection at least partially above the internal structures (3, 4) and discharged afterwards, characterized by

   - a mean temperature of less than 900°C in the first zone (A) of the incineration chamber (10) above the grate (1), i.e. the drying and pyrolysis area in the primary zone I;

   - the mean temperature amounting to about 1000°C in the secondary zone (B), i.e. the degasification and gasification zone;

   - a mean temperature, smaller than that of the secondary zone (B), of 950°C down to below 900°C prevailing in a third zone (C), i.e. the burn-out zone;

   - a temperature of less than 900°C to below 700°C being set in a fourth zone (D), i.e. the sintering zone;

   - the primary air being supplied from the underblast zones (a, b, c, and d) through the grate with the amounts of air in the zones A and B being metered such that a sub-stoichiometric incineration takes place in the waste bed;

   - additional air of a temperature identical to or smaller than the furnace chamber temperature as veiling air being fed into the furnace chamber above the grate through the side wall or walls of the burning chamber, mainly or only in the zones A and B of the furnace chamber (10) below the internal structures;

   - no further air being supplied above the internal structures in the secondary zone II, i.e. downstream of the fourth zone (D).
2. Process according to claim 1, characterized by the additional veiling air having a temperature of about 500°C to 750°C.
3. Process according to claims 1 or 2, characterized by the volume ratio of veiling air to primary air amounting to 1/5 - 1/6.
4. Process according to claims 1, 2, or 3, characterized by the veiling air being taken from the air cooling the side wall of the furnace chamber.
5. Incineration plant for incinerating materials to be treated thermally, e.g. domestic waste, in the co-current mode on the grate of an incineration plant with primary air being passed through the grate from below and the hot exhaust gas being led in incineration direction over part of the movable grate by means of internal structures located above the grate in the primary zone I and, in the range of the grate end, passed upwards around the internal structures and discharged above these structures in the secondary zone II or returned in counterdirection at least partially above the internal structures and discharged afterwards with

   - a mean temperature of less than 900°C in the first zone (A) of the incineration chamber (10) above the grate (1), i.e. the drying and pyrolysis area in the primary zone I;

   - the mean temperature amounting to about 1000°C in the secondary zone (B), i.e. the degasification and gasification zone;

   - a mean temperature, smaller than that of the secondary zone (B), of 950°C down to below 900°C prevailing in a third zone (C), i.e. the burn-out zone;

   - a temperature of less than 900°C to below 700°C being set in a fourth zone (D), i.e. the sintering zone;

   - the primary air being supplied from the underblast zones (a, b, c, and d) through the grate with the amounts of air in the zones A and B being metered such that a sub-stoichiometric incineration takes place in the waste bed;

   - additional air of a temperature identical to or smaller than the furnace chamber temperature as veiling air being fed into the furnace chamber above the grate through the side wall or walls of the burning chamber, mainly or only in the zones A and B of the furnace chamber (10) below the internal structures;

   - no further air being supplied above the internal structures in the secondary zone II, i.e. downstream of the fourth zone (D), and with this plant having the following features:

   a) Above the grate (1) and below the upper wall (9) of the furnace chamber (10), an intermediate wall (3, 4) of about the same length as the zones (A, B, C, D) is located, which delimitates the primary zone (I) to the top and the above secondary zone (II) to the bottom;

   b) This intermediate wall (3, 4) is located close between the side walls (17) and the front wall (16) of the furnace chamber and reaches - in incineration direction (6) - down to the end of the grate (7) or beyond the incineration zone (5);

   c) Behind the intermediate wall (3, 4) - in incineration direction (6) -, a deflection area for the deflection of the flue gases (2) from the primary (I) to the secondary zone (II) in upward direction around the intermediate wall (3, 4) to the outlet (12) is located, which is characterized by

   d) a cooling air channel (19) existing in the side wall (17), through which cooling air (22) is blown;

   e) the side wall (17) having a defined permeability for the cooling air (22) in the partial area (18) between the primary zone (I) and the channel (19), which is adjacent to the primary zone (I), such that veiling air (20) may enter the primary zone (I) from the channel (19).
6. Incineration plant according to claim 4, characterized by the partial area (18) of the side wall (17) having a homogeneously or heterogeneously distributed porosity.
7. Incineration plant according to claim 4, characterized by openings or channels being passed through the partial area (18) of the side wall (17).
8. Incineration plant according to one of the claims 5 or 6, characterized by the partial area (18) of the side wall (17) having the porosity or the openings located only or predominantly in the range of the zones A and B.
9. Incineration plant according to one of the claims 4 through 7, characterized by the intermediate wall consisting of single ceramic plates (3, 4) arranged in series, which are supported by the ledges (15) at the side walls (17) of the furnace chamber (10).
10. Incineration plant according to claim 8, characterized by the last ceramic plate (4) in incineration direction (6) being inclined towards the grate (1).