EP0858495B1 - Use of a process operating a combustion plant of a coal-fired power station for the accelerated coal combustion in a smelt chamber - Google Patents

Abstract

A method of operating a combustion unit of a coal-fired power plant operating according to a slag tap furnace firing method, which includes supplying a titanium-containing material in addition to coal to a melting chamber for accelerating coal burn-up, burning the titanium-containing material together with the coal in the melting chamber at a temperature above 1500 DEG C., and generating fly ash and molten ash as a result of combustion in the melting chamber. Additionally, a combustion unit for a coal-fired power plant, including a melting chamber that has a combustion zone for receiving coal. The combustion zone produces fly ash. The combustion unit also includes a separate feed line for supplying a titanium-containing material to the combustion zone for accelerating burn-up of the coal and a second separate feed line first to supply a titanium-containing material to the fly ash and then supply the titanium-containing material and fly ash combination to the combustion zone for accelerating burn-up of the coal and fly ash.

Description

The invention relates to the use of a method for operating a combustion plant of a coal-fired power plant with smelting chamber firing.

To operate an incineration plant in coal-fired power plants there are essentially two different firing techniques, namely the process of dry firing and the process the melting chamber firing. With dry firing the temperature in the combustion chamber is below Melting temperature of the ashes. The resulting ash is therefore almost completely swept away by the flue gas flow and settles as fly ash in downstream separation systems, such as. Electrostatic precipitators. The fly ash or the Fly dust can be used as an additive in the construction industry are. According to DE 31 28 903 A1 has already been proposed has been used to improve combustion in dry firing to use various metal oxides as an additive.

In melting chamber firing, the combustion temperature in the combustion chamber, which in this case is also referred to as the melting chamber, is above the melting temperature of the ash. Under normal operating conditions, this is approx. 1500 ° C. The ash melting temperature of the coal used for firing can vary widely and is essentially dependent on the content of aluminum oxide Al ₂ O ₃ and silicate SiO ₂ . The majority of the ashes combine to form a melt flow at the bottom of the combustion chamber and are supplied to wet slag removers below through outlet openings. These are pools of water in which the leaking liquid ash is caught and quenched. The resulting granulate (= melting chamber granulate), which essentially consists of aluminum silicate, has a rough structure. The granulate is a popular material in road construction and is used, for example, as a bulk material but also as a grit or blasting agent. The fly ash entrained by the flue gas flow, which can consist of up to 50% combustible material (carbon and / or semi-burned hydrocarbons), is separated in the electrostatic precipitators.

The temperature of the combustion or melting chamber and the melting temperature of the ash must be coordinated for particularly effective melting chamber operation, ie complete burnout, rapid fuel conversion and avoidance of NO _x formation. The composition of the coal (depending on the composition, the ash melting temperature varies between 1300 ° C and 1700 ° C) determines the design of the coal-fired power plant, such as the size of the combustion chamber. By adding limestone, however, it is possible to lower the melting temperature of the ash. Experience shows that by adding approx. 2% limestone to coal, the melting temperature of the ash can be reduced by approx. 100 ° C. This procedure provides a regulation for the operation of the furnace.

To achieve a high level of efficiency through complete burnout of the Obtaining fuel is used in modern coal-fired power plants, which work according to the melting chamber firing method, the fly ash again via a separate fly ash return blown into the combustion chamber. In this case, the entire falls Ash from the combustion or melting chamber as slag and can be disposed of in the usual way.

The fly ash return makes it a perfect one Burnout of the fuel achieved, however, the increases average residence time of a coal or ash particle in the Feuerungskreislauf. The disadvantage is the maximum Throughput of coal and thus the possible performance of the Power plant limited.

The invention is therefore based on the object of an inexpensive Method for operating a coal-fired power plant, which according to the process of melting chamber firing works, with which the throughput of fuel and thus the performance of the power plant can be increased. This is supposed to be with a incinerator suitable for carrying out the method can be achieved with particularly simple means.

With regard to the method, this object is achieved according to the invention solved by the features of claim 1. Titanium dioxide, at most in a titanium dioxide: coal ratio of 3:97.

The invention is based on the observation that titanium dioxide the burning out of the coal in the combustion chamber and thus can increase the throughput of coal, which in turn Performance increase of the power plant leads.

For effective firing operation, the viscosity and the melting temperature of the ash, as mentioned at the beginning, by the addition amount of titanium-containing materials is not essential to be changed. In particular, the addition of titanium, the is present as titanium dioxide under the conditions of the melting chamber, slag-like approaches behind the combustion chamber, that stick to pipes and walls, do not favor. It has been shown that titanium dioxide has the melting point of Ash or slag lowers. From a sand-like, not melted and non-sticking dust could result in a viscous, flowing and sticky melt become the higher Cleaning costs and financial losses during maintenance of the coal-fired power plant. However, it was found that the titanium dioxide is largely found in the liquid ash. With titanium dioxide levels below about 3% in the total amount of coal and titanium dioxide Material is achieved that the consistency of the slag-like approaches do not change since the titanium dioxide now practically only in the liquid bag. In In an advantageous embodiment, the titanium dioxide content is in the total amount of coal and materials containing titanium dioxide added at most 2.25%.

This finding is surprising, because the titanium dioxide content is also lower in the mixture of coal and materials containing titanium dioxide lead at a coal-fired power plant with dry combustion system already to a considerable intensification of the slagging behind the combustion chamber and to a flowing Slag consistency. Such additives are titanium dioxide therefore especially for the operation of a coal-fired power plant Melting chamber firing suitable.

The supplied titanium dioxide-containing material is advantageous more than 50% from titanium dioxide. This can even with a small additions an acceleration of coal burnout be achieved. A titanium dioxide: carbon ratio is advantageous here of at least 1:99.

In a power plant without fly ash return to the Melting chamber is made according to an embodiment of the invention the added titanium as titanium dioxide to a low Partly excreted via fly ash, but mostly via liquid ash. Since titanium dioxide is not toxic, it cannot only the liquid ash, but also the fly ash as usual continue to be used. The coal-fired power plant works with one Fly ash return, the resulting fly ash is in the furnace returned so that the titanium is practically exclusively as titanium dioxide together with the resulting Liquid ash is excreted.

The material containing titanium dioxide advantageously becomes coal added, then it can be used in a coal mill of the power plant and ground over a coal belt the burners are inserted into the combustion chamber of the power plant. However, the material containing titanium dioxide can be particularly simple also pneumatically into the combustion chamber, preferably via the Fly ash return, to be blown in.

In many cases it can also be beneficial to use the liquid ash to pass into a wet slag remover at the bottom of the combustion chamber and process it into granules. This allows aggregates in the admixed titanium dioxide-containing material safely into the resulting Granules are melted down.

A danger to the environment when using the granulate as There is no building material because the melted aggregates, such as. Heavy metals, insoluble in the granules are involved.

In a particularly advantageous variant of the process used as titanium dioxide-containing material, ie to be disposed of DeNO _x catalysts or waste products, eg. B. the titanium processing industry used. For used DeNO _x catalysts, this creates a cheaper, environmentally friendly disposal route, since otherwise costs are incurred through landfilling or expensive reprocessing measures. Only for certain catalysts, which consist largely of titanium dioxide and contain 10% molybdenum or more, has it been shown that heavy metals (in particular arsenic) can be leached out of a granulate produced in this way to a detectable extent. However, such leaching was not found in a DeNO _x catalyst with 4.5% molybdenum, so that restrictions can only arise for catalysts with such a high molybdenum content.

Also for the titanium processing industry - in the FRG approx. 300,000 to 400,000 tons of titanium dioxide are produced annually - The process offers itself as an inexpensive disposal route for the waste products, e.g. Titanium slag.

FIG 1

eine schematische Darstellung einer Verbrennungsanlage eines Kohlekraftwerks mit einer Schmelzkammer, einer Kohlemühle, einer DeNO_x-Anlage und einer Granulaterzeugung;

FIG 2

ein Kohlekraftwerk gemäß Figur 1 mit einer Flugasche-Rückführung;

FIG 3

in einem ersten Diagramm die Masse an Flugasche bei steigender Zugabe von verbrauchtem Katalysatormaterial;

FIG 4

in einem zweiten Diagramm den brennbaren Anteil in der Flugasche als Funktion des Katalysatoranteils in der Kohlemischung; und

FIG 5 - 7

in einem dritten, vierten bzw. fünften Diagramm den Gehalt an Katalysatorbestandteilen (TiO₂, V₂O₅, WO₃) eines DeNO_x-Katalysators in der Schlacke, in der Flugasche bzw. in den schlackeartigen Abscheidungen an der Brennkammer nachgeordneten Bauteilen, jeweils als Funktion des Katalysatoranteils in der Kohlemischung.

Exemplary embodiments are explained in more detail with reference to a drawing. In it show:

FIG. 1

a schematic representation of a combustion plant of a coal-fired power plant with a melting chamber, a coal mill, a DeNO _x plant and a granulate production;

FIG 2

a coal-fired power plant according to Figure 1 with a fly ash return;

FIG 3

in a first diagram the mass of fly ash with increasing addition of spent catalyst material;

FIG 4

in a second diagram, the combustible fraction in the fly ash as a function of the catalyst fraction in the coal mixture; and

FIG 5-7

in a third, fourth or fifth diagram the content of catalyst components (TiO ₂ , V ₂ O ₅ , WO ₃ ) of a DeNO _x catalyst in the slag, in the fly ash or in the slag-like deposits on the components downstream of the combustion chamber, in each case as a function of the proportion of catalyst in the coal mixture.

The incinerator 1 shown in Figure 1 is part of a coal-fired power plant, not shown. It comprises a high-temperature combustion chamber designed as a melting chamber 2 with at least one burner 2a, and with a feed 2b, for example a conveyor belt for the coal K, and a fresh air line 4 guided over a compressor 3. It further comprises a discharge line 5 for liquid ash F with one on it connected wet purifier 6. It also comprises a flue gas line 7 and in the flue gas line 7 connected in series a dust filter system 8 with a fly ash collector 9, a flue gas desulfurization system 10 and a catalytic denitrification system 11. The flue gas line 7 opens into a chimney 12. The feed 2b is connected to a Coal mill 13 connected, which is connected to a feed shaft 14 of a coal store 15 and to a separate feed line 16 for adding material M containing titanium dioxide. The burnout acceleration of the coal K in the combustion chamber 2 is set via the amount of titanium dioxide-containing material M. During the operation of the coal-fired power plant, the coal K is conveyed from the coal store 15 via the feed shaft 14 into the coal mill 13. The titanium dioxide-containing material M is either introduced via the feed line 16 and the feed shaft 14 or directly into the coal mill 13 and there, together with the coal K, is ground very finely. Fuel B prepared in this way reaches the combustion chamber 2 via the feed 2b and the burner 2a, where it is burned with compressed air L supplied via the fresh air line 4. The resulting flue gas RG flows via the flue gas line 7 into the dust filter system 8, where fly ash or fly dust S entrained by the flue gas is intercepted and discharged via the fly ash collector 9. The now practically dust-free flue gas RG arrives at the flue gas desulfurization system 10 and into the chimney 12 via the denoxification system 11, which is generally referred to as a DeNO _x system.

The liquid ash F collecting on the combustion chamber bottom 2c becomes via the discharge line 5 to the wet slag remover 6 and processed into granules G.

The fly ash S collected at the collector 9 can be recycled as usual become. Up to 3% material containing titanium dioxide is advantageous M used with a titanium dioxide content of more than 50%. Additives contained in this material M or Impurities such as Heavy metals, become insoluble in the granules G melted down. This melting chamber granulate G can be used as a building material as usual.

According to Figure 2, the incinerator 1 with Melting chamber firing a fly ash return 20 on. This opens directly into the combustion chamber 2 of the melting chamber furnace. The in the dust filter system 8 via the collector 9 restrained fly ash S is pneumatically using a additional compressor 21 blown into the combustion chamber 2. Via a separate feed line 22, titanium dioxide-containing Dust-finely ground material M is added to the fly ash S. and gets into the combustion chamber 2 by adding Titanium dioxide-containing material M in the combustion chamber 2 of the coal-fired power plant with melting chamber firing in combination with a Fly ash return 20 becomes particularly effective burnout with a simultaneous acceleration of the throughput Coal K achieved in the power plant. This increases the performance of the Power plant.

Additives contained in the fly ash S, which are contaminated with heavy metal, and titanium dioxide are insolubly incorporated into the resulting melting chamber granules G. In this way, used DeNO _x catalysts with more than 50% TiO ₂ can be disposed of without any problems.

Test results are explained below. In this parts mean parts by mass.

Example 1: Used DeNO _x catalysts are used as the titanium dioxide-containing material M and mixed with coal K. A highly decarburized, high-ballast hard coal is used as coal K, which, according to its degree of decarburization and the proportion of volatile constituents, belongs to lean coal and lies on the border between lean coal and anthracite coal. The ashes of this coal show normal melting behavior. The catalyst used consists of approximately 75% TiO ₂ and contains further catalytic components (approx. 11% SiO ₂ , approx. 8% WO ₃ and approx. 1.8% V ₂ O ₅ ).

With a catalyst fraction M _K of 0%, 1% and 3% in the mixture of catalyst material and coal, combustion tests are carried out in a combustion chamber 2. The combustion chamber 2 is designed as a laboratory combustion chamber, each with a liquid ash extractor and a dry ash extractor. The composition of the ash, the influence of the slagging behavior of the coal by adding used catalyst, the influence of the catalyst fraction M _K on the slagging intensity of the heating surfaces behind the combustion chamber and the distribution of the catalyst material in the combustion residues are examined. An X-ray fluorescence analysis of these combustion residues is carried out.

FIGS. 3 to 7 show the test results as an example for the combustion chamber with liquid ash extraction. FIG. 3 shows the mass of fly ash S _{M produced} per kilogram of coal as a function of the catalyst fraction M _K supplied. It can be seen that the mass of the fly ash S _M does not change up to a catalyst fraction M _K of 3% (curve a). Surprisingly, however, it can be seen very clearly that the catalyst fraction improves the burnout of the coal (measured in terms of the fraction B _S of combustibles in the fly ash) (curve b in FIG. 4). With a catalyst proportion M _K of 3% in the mixture of coal and catalyst, the proportion B _S of combustibles in the fly ash is reduced from 50% to 30% compared to M _K = 0%.

Curves c, d and e of FIGS. 5 to 7 show the percentage of active catalyst substances TiO ₂ (FIG. 5), V ₂ O ₅ (FIG. 6) and WO ₃ (FIG. 7) in the slag F, in the fly ash S. or in the slag-like approaches. Another surprising result is that the catalyst is found primarily in the slag or liquid ash F (curve c, FIGS. 5 to 7) and partly in the fly ash S (curve d, FIGS. 5 to 7), but hardly in the slag-like approaches ( Curve e, Figures 5 to 7) takes place. With increasing catalyst proportion M _K (0 to 3%) in the fuel, only the proportions of TiO ₂ (FIG. 5), V ₂ O ₅ (FIG. 6) and WO ₃ (FIG. 7) in the slag F and in the fly ash S become clear to. In the slag-like approaches behind the combustion chamber, however, they remain practically unchanged.

In the cooling area, there is never a more intense one Slagging found behind the combustion chamber (Table 1). The small amounts of slag-like approaches behind the combustion chamber are definitely not soft melted and not sticky. The fact that the additional Catalyst share up to 3% behind the combustion chamber liquid ash removal no change in slagging behavior is caused by the fact that the catalyst can hardly be found in the beginning.

The investigations, which are carried out in the laboratory combustion chamber with dry ash extraction (dry firing), clearly show that the formation of deposits is intensified with increasing catalyst content (Table 1). The approaches behind the combustion chamber with dry ash extraction have a hard, melted structure and already show a clear flow behavior in the combustion chamber. Approaches behind a melting furnace a dry fire Intensity of education very weak (regardless of the amount of catalyst) weak (when burning a pure coal) to strong (with a 3% addition of catalyst material) structure light, not melted slightly to heavily melted Catalyst fraction M _K in the fuel Approaches behind the combustion chamber 0% 1 % 3% 0% 1 % 3% Share of TiO ₂ 1.15 1.25 1.33 1.88 5.04 10.8 Share in V ₂ O ₅ 0.06 0.06 0.05 0.09 0.15 0.35 Share in WO ₃ 0.04 0.05 0.05 0.06 0.26 0.63

Example 2: Fly ash from an electrostatic precipitator of a coal-fired power plant with smelting chamber firing is mixed with calcium carbonate (CaCO ₃ ) in a mass ratio of 100: 5. As a result, a melt can be obtained directly ("zero test"). The same mixture is mixed for comparison with dust-finely ground, used DeNO _x catalyst in such a way that the catalyst content is 1%. The mixture is melted at 1550 ° C for 20 minutes and quenched in water ("comparative sample"). 5 g of the granules G obtained are eluted with 50 g of H ₂ O for 24 hours and the eluate is examined for traces of vanadium V, tungsten W and arsenic as.

The amount of active washed out from the comparative sample Catalyst substances (V, W) are below the detection limit (<0.1 mg / l). The arsenic content is in both samples in the same area.

Claims (13)

1. Use of a process for operating a combustion plant of a coal-fired power station working according to the smelt chamber firing process, in order to accelerate coal combustion in a smelt chamber (2) with coal (K), wherein a titanium dioxide-containing material (M) is added and is combusted together with the coal (K) as a fuel (B), so that the acceleration of the combustion of the coal (K) in the smelt chamber (2) is adjusted by the added amount of titanium dioxide-containing material (M).
2. Use according to claim 1, characterised in that titanium dioxide TiO₂ is present at most in a titanium dioxide:coal ratio of 3:97.
3. Use according to claim 1 or 2, characterised in that the titanium dioxide mass fraction in the added total amount of coal (K) and titanium dioxide-containing material (M) is at most 2.25%.
4. Use according to claims 1 to 3, characterised in that the titanium dioxide-containing material (M) consists of more than 50% by mass of titanium dioxide.
5. Use according to claim 4, characterised in that the mass ratio of the predominantly titanium dioxide-containing material to coal is below 3:97.
6. Use according to one of claims 1 to 5, characterised in that the titanium dioxide:coal mass ratio is at least 1:99.
7. Use according to claims 1 to 6, characterised in that the titanium dioxide is separated on the one hand through flue ash (S) and on the other hand through molten ash (F).
8. Use according to claims 1 to 7, characterised in that flue ash (S) formed in the combustion is returned to the smelt chamber (2) and the titanium dioxide is separated together with molten ash (F).
9. Use according to claims 1 to 8, characterised in that the titanium dioxide-containing material (M) is mixed with the coal (K).
10. Use according to claims 1 to 8, characterised in that the titanium dioxide-containing material (M) is blown pneumatically into the smelt chamber (2), preferably through a flue ash recycling line (20).
11. Use according to claims 7 to 10, characterised in that the molten ash (F) is processed in a wet slag removal means (6) to form granular material (G), in which the titanium dioxide is fused.
12. Use according to claims 1 to 11, characterised in that DeNO_x catalysts to be disposed of are used as titanium dioxide-containing material (M).
13. Use according to claims 1 to 11, characterised in that titanium dioxide-containing waste products are used as titanium dioxide-containing material (M).

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