DE102004059360A1 - Method for burning fossil fuels in power stations operating using oxyfuel system comprises combustion in pure oxygen, known melt-firing method being used, in which ash melts and is removed from firing system - Google Patents

Abstract

The method for burning fossil fuels in power stations operating using the oxyfuel system comprises combustion in pure oxygen (7). The known melt-firing method is used, in which ash melts and is removed from the firing system.

Description

The The invention relates to a method of burning fossil fuel in power plants operating after the oxyfuel process.

When Oxyfuel process is referred to as a process of combustion a carbonaceous fuel as a final product largely pure carbon dioxide stream among others produced by the fact that Combustion with pure oxygen is performed.

The Separation of largely pure carbon dioxide is often sought about using carbon dioxide in other processes or around it store or deposit.

In order to be able to separate off carbon dioxide more easily, a high CO ₂ partial pressure in the flue gas flow is advantageous. In addition to the CO ₂ is usually nitrogen to a high proportion in the flue gases contained, which was introduced with the combustion air and to a small extent by the fuel in the process. On the way to a nearly pure CO ₂ stream as a flue gas, it would be helpful if the nitrogen is eliminated first.

At the Oxyfuel process is by means of an air separation plant from the Combustion air extracts the nitrogen and only one oxygen flow with a high purity goes into the combustion process. This leads to a smaller by about 75% flue gas mass flow, the standard volume flow is reduced to about one sixth of the original value (Combustion bill).

Thus, the flue gas stream to be treated is substantially reduced, which in itself leads to a reduction and simplification of the plants for carbon dioxide enrichment. Furthermore, the separation of most impurities from CO _{2 is} easier than the separation of CO ₂ from a nitrogen-dominated flue gas. Water can be condensed out, after a few further purification steps highly concentrated carbon dioxide is available.

When burning only with oxygen in the combustion chamber of conventionally miteingetragene nitrogen is by definition not registered, that is, with the same heat release a much lower mass flow or heat capacity flow of the flue gases, which the flue gas temperature level (including the adiabatic combustion temperature) significantly increased (see 3 ).

at the usual Dry firing, in which a melting of the ash avoided must be, are the permissible Temperatures, however, limited by that they are well below the Ash melting point must lie for slagging in the combustion chamber and in the subsequent heating surfaces of the To avoid steam generator.

Around too high adiabatic combustion temperatures in this type of firing It is usually necessary to avoid this a big part the flue gases leaving the steam generator (of the order of magnitude 70%) are recirculated.

• – Aufwand (Anlagentechnik, Energie) für Rezirkulation,
• – verhältnismäßig großer Dampferzeuger,
• – Ascheanfall in schwer verwertbarer Form,
• – Aus technischen Gründen muss der Rezirkulationsstrom kalt und staubfrei dem Rauchgasstrom entnommen werden, sollte aber so warm wie möglich in den Dampferzeuger wieder eingeführt werden, damit ist ein Rezirkulationsvorwärmer erforderlich, der um so größer sein muss je größer die rezirkulierte Rauchgasmenge ist.
• – Aufwendige und große Entstaubungsanlage, da die Rauchgas einer Trockenfeuerung besonders viel Staub enthalten (Großteil der Asche) und die Rezirkulation in der Regel mit entstaubten Rauchgas erfolgt, und die rezirkulierte Gasmenge jedes Mal mit entstaubt werden muss,

This procedure is burdened with some significant problems:

• - effort (equipment, energy) for recirculation,
• - relatively large steam generator,
• Ash accumulation in difficult to use form,
• - For technical reasons, the recirculation must be cold and dust-free removed from the flue gas stream, but should be reintroduced as warm as possible in the steam generator, so a Rezirkulationsvorwärmer is required, which must be greater the larger the recirculated flue gas.
• - Elaborate and large dedusting plant, since the flue gas of a dry fire contain a lot of dust (most of the ash) and the recirculation is usually done with dedusted flue gas, and the recirculated gas must be dedusted with each time,

Of the Invention is based on the object by limiting the Firing temperature to reduce problems in the oxyfuel process.

According to the invention Task by a method having the features mentioned in claim 1 solved. Advantageous variants of the method are the subject of dependent claims.

With such a furnace operating temperatures well above the ash melting point, for example, those between 1500 ° C and 1800 ° C are possible. As a result, the Required Rezirkulationsgasmenge is significantly reduced, as from 3 seen.

As in 3 Through the use of melt firing, a significant reduction in the amount of recirculation is possible. As a result, the plant technical and energy cost of recirculation is reduced, dedusting and Rezirkulationsvorwärmer can be significantly reduced. A considerable proportion of the ash falls as a liquid Schla on. This proportion does not pollute the dedusting.

in the Contrary to the difficult to use ashes from dry firing is the slag granules from Schmelzfeuerungen a popular raw material, about for the road construction. By returning the Fly ash from the dedusting into the combustion chamber can be achieved that all ash as slag granules leaves the plant. By higher Temperatures, especially in the radiation part, can be the steam generator be built much smaller.

Possible versions of a smelting furnace are open melt firing, melting chamber firing, Cyclone firing or cycloid firing.

By The oxygen burning will be undried even when used Brown coal temperatures reached the use of a smelting furnace possible do.

By Oxygen combustion is the formation of thermal and prompt nitrogen oxides as good as impossible. This eliminates the Main disadvantage of known melting furnaces for burns with air.

The problem solving according to the invention with the melting chamber kettle is obviously not close. For example, the publication Large Scale CO ₂ Capture - Applying the Concept of O ₂ / CO ₂ Combustion to Commercial Process Data "(Andersson, Johnsson, Strömberg) VGB Power Tech 10, 2003 is based on a dry-desiccant system that is currently mostly built become.

Attachments with melting chamber become over it In addition, not very frequently built in recent years. Furthermore There are hardly any examples where melting chamber plants for lignite were used. The reason is that at usual conventional firing in lignite is not sufficient high furnace temperatures or adiabatic temperatures arise (because the calorific value is lower, so the slag flow is not always guaranteed can be). One had therefore in the cases, where one lignite in Schmelzkammerfeuerungen began, for example, the brown coal pre-dry accordingly. In Effenberger, H .: steam generation. Springer publishing: Berlin Heidelberg New York 1999 will therefore be pointed out that melting furnaces for Lignite is not useful and generally not with new applications is expected. For example, in Germany in recent years Years ago rather brown coal block power plants were rebuilt as hard coal blocks and these all doused dry are, obviously, this idea of liquid ash removal for the Oxyfuel principle not close.

Certain Disadvantages are then awarded to the melting chamber firing if The fiber content, ie the ash content, is high, since the ash to a greater extent in the combustion chamber to the outside dissipated is with high temperatures and therefore with higher heat loss as the filter ash removed becomes. For hard coal with low ash content, however, this is not Disadvantage and just the German brown coal both in the Rhineland than in the new federal states are characterized by low ash content.

As well decrease due to the lower total amount of flue gas (including Recirculation), the cross sections of the steam generator, for example by a factor of 2 in the flues. The convection train dissipated amounts of heat are significantly lower, for example by the same factor 2 and the convection trains Build accordingly cheaper. The design will also be compared to previous Schmelzkammerkesseln to the effect that the heating surfaces be placed in the burner area so that one in contrast to the previous plants desired Cooling the flame temperature is achieved. This is possible, for example, by introduction of individual sub-chambers, between which partitions are arranged are.

The The invention will be explained in more detail below with reference to an embodiment. In the Drawings show:

1 a representation of the oxyfuel process with a smelting furnace

2 a schematic representation of the oxyfuel process

3 a representation of the influence of the recirculation amount on the adiabatic combustion temperature

In the 1 is an oxyfuel process with a Schmelzfeuerung shown. The furnace of the plant is designed as a double U-stage melting furnace.

The Combustion chamber temperature is 1700 ° C. It results an ash inclusion in the slag of about 60% and a reduced recirculation amount.

The recirculation can be made smaller. The dedusting is loaded with only 40% of the dust. By returning the dust to the combustion chamber, it is possible to melt almost 100% of the ash and remove it as building material with proceeds put.

2 shows a schematic diagram of the oxyfuel process.

In the 3 the influence of the recirculation amount on the adiabatic combustion temperature with classification of dry and melt firing is shown, using Central German Lignite (TBR) / dry lignite (TBK, 12% water) and the following parameters were obtained: fuel temperature 60 ° C, inlet temperature air or oxygen (95% purity): 300 ° C, temperature of recirculated flue gases: 350 ° C.

1

steam generator with melting firing

2

capacitor

3

condensate

4

Niederdruckvorwärmersäule

5

Hochdruckvorwärmersäule

6

fuel

7

oxygen

8th

flue gas

9

Sauerstoffvorwärmer

10

turbine

11

recirculation

12

slag runoff

101

Air separation plant

102

steam generator

103

gas cleaning

104

air

105

nitrogen

106

oxygen

107

fossil fuel

108

Heat (steam)

109

flue gas Rezierkulation

110

CO ₂ -rich flue gas

111

condensate (Water)

112

other separated contaminants

113

purified CO ₂

Claims (4)

A method of burning fossil fuel in power plants operating according to the oxyfuel process, wherein the combustion of a carbonaceous fuel as the end product, a substantially pure carbon dioxide flow is generated by the combustion is carried out with pure oxygen, characterized in that as firing a known per se Welding is used, wherein the furnace is designed and operated at such temperatures that at least a portion of the ash is obtained molten and is discharged in this state from the furnace. Method according to claim 1, characterized in that that the furnace operated at a temperature between 1500 ° C and 2000 ° C becomes. Method according to claim 1 or 2, characterized that as firing an open melt firing, a Schmelzkammerfeuerung, a Cyclone combustion or a Zykloidfeuerung is used. Method according to one of claims 1 to 3, characterized that used as fuel not technically pre-dried coal becomes.