Title:
COMBUSTION SYSTEM OF A STEAM GENERATOR DESIGNED FOR OXYFUEL OPERATION
Kind Code:
A1


Abstract:
For a steam generator comprising a combustion chamber fired with a fossil fuel and/or with particulate fuel containing carbon and at least one burner level comprising several burners (1) and/or at least one level comprising nozzles in the form of upper air nozzles and/or side wall nozzles, each having connected feed means (9, 10, 11, 12) and/or feed lines (2, 4, 5, 9a-9d, 10a-10d, 11a-11d, 12a-12d) through which/by means of which gas flows conveying combustion and/or oxidation oxygen can be fed to burners (1) and/or the nozzles (13) and/or the combustion chamber, a solution should be created by means of which undesired oxygen contents in the flue gas can be avoided during oxyfuel operation of the steam generator in the partial-load range. This is achieved in that the feed means (9, 10, 11, 12) and/or the feed lines (2, 2a-2d, 4, 5, 9a-9d, 10a-10d, 11a-11d, 12a-12d) are designed in such a way that at least one burner (1) or some of the burners (1) independently of the other burners (1) and/or a nozzle (13) or some of the nozzles (13) independently of the other nozzles (13) can be exposed to a gas flow providing the desired oxygen content or the desired oxygen concentration and/or the desired oxygen mass flow.



Inventors:
Bergins, Christian (Datteln, DE)
Niesbach, Jürgen (Bochum, DE)
Gwosdz, Alfred (Mulheim a. d. Ruhr, DE)
Application Number:
13/259792
Publication Date:
05/10/2012
Filing Date:
03/25/2010
Assignee:
HITACHI POWER EUROPE GMBH (Duisburg, DE)
Primary Class:
Other Classes:
110/263, 110/297, 110/347, 110/348, 431/174, 110/205
International Classes:
F23N1/02; F23C5/00; F23C9/00; F23D1/00; F23L7/00
View Patent Images:



Primary Examiner:
PEREIRO, JORGE ANDRES
Attorney, Agent or Firm:
KNOBBE MARTENS OLSON & BEAR LLP (2040 MAIN STREET FOURTEENTH FLOOR, IRVINE, CA, 92614, US)
Claims:
1. A steam generator comprising a combustion chamber fired with a fossil fuel and/or with particulate fuel containing carbon, and at least one burner level comprising a plurality of burners and/or at least one level comprising nozzles in the form of upper air nozzles and/or side wall nozzles, each having connected feed means and/or feed lines through which/by means of which gas flows which make available combustion oxygen and/or oxidation oxygen can be fed to the burners and/or to the nozzles and/or to the combustion chamber, wherein the feed means and/or the feed lines are configured such that in each case at least one burner or some of the burners can be provided, independent of the respective other burners, and/or in each case one nozzle or some of the nozzles can be provided, independent of the respective other nozzles, with a gas flow which makes available the respectively desired oxygen content or the desired oxygen concentration and/or the respectively desired oxygen mass flow.

2. The steam generator as claimed in claim 1, wherein at least one burner or some of the burners can be provided, individually and/or separately from the other burners of the respective burner level, and/or one nozzle or some of the nozzles can be provided, individually and/or separately from the other nozzles of a respective nozzle level, with a gas flow which can be adjusted individually in terms of its oxygen content or its oxygen concentration and/or the oxygen mass flow which it carries.

3. The steam generator as claimed in claim 1, wherein at least some of these gas flows which are respectively fed to one or more burner levels or nozzle levels and/or respectively fed to one or more burners and/or one or more nozzles, and are of one type or category that can be respectively provided with oxygen individually and/or separately from the other gas flows of this type or category, and/or can be adjusted, individually and/or separately from these other gas flows of the same type or category, in terms of their oxygen content or their oxygen concentration and/or the oxygen mass flow conveyed with them.

4. The steam generator as claimed in claim 1, wherein at least a part of the burner level or nozzle level and/or some of the burners or nozzles which is/are provided with an oxygen-containing gas flow, in particular for the purpose of cooling, during partial loading of the steam generator, has/have such a feed means and/or such a feed line.

5. The steam generator as claimed in claim 1, wherein the secondary gas supply and/or tertiary gas supply of each burner level and/or of each burner can be provided with oxygen individually and/or separately from other gas flows of this type or category and/or can be adjusted individually and/or separately from these other gas flows, in terms of their oxygen content.

6. The steam generator as claimed in claim 1, wherein the core gas supply of each burner level and/or of each burner can be provided with oxygen individually and/or separately from other gas flows of this type or category, and/or can be adjusted individually and/or separately in terms of its oxygen content.

7. The steam generator as claimed in claim 1, wherein the primary gas supply of each burner level and/or of each burner can be provided with oxygen individually and/or separately from other gas flows of this type or category, and/or can be adjusted individually and/or separately in terms of its oxygen content.

8. The steam generator as claimed in claim 1, wherein the upper air nozzle supply and/or the side wall nozzle supply of each nozzle level and/or of each nozzle can be provided with oxygen individually and/or separately from other gas flows of this type or category, and/or can be adjusted individually and/or separately in terms of its oxygen content.

9. The steam generator as claimed in claim 1, wherein all the gas flows, feeding combustion oxygen and/or oxidation oxygen to the combustion chamber, of each burner level and/or of each burner and/or of each nozzle level and/or of each nozzle can be provided with oxygen individually and/or separately from other gas flows of the respective type or category, and/or can be adjusted individually and/or separately in terms of their oxygen content.

10. The steam generator as claimed in claim 1, wherein each burner level or nozzle level and/or each burner or each nozzle is connected to at least one feed line feeding an oxygen-containing gas flow, wherein the oxygen content of the gas flow, respectively fed therein, of one type or category can be adjusted independently of the gas flows of this type or category which are respectively fed to the other burner levels or nozzle levels and/or other burners and/or nozzles.

11. The steam generator as claimed in claim 1, wherein the oxygen content in the respective gas flow can be adjusted between 0 and 100% by weight or % by volume.

12. The steam generator as claimed in claim 1, wherein at least in some of the feed lines, a mixture of fed-back CO2-containing flue gas and added oxygen is fed to the respective burner level or nozzle level and/or to the respective burner or to the respective nozzle as a gas flow.

13. The steam generator as claimed in claim 1, wherein the steam generator is operated at least at certain times in an oxyfuel operating mode.

14. A method for feeding combustion oxygen and/or oxidation oxygen to burners and/or nozzles of a combustion chamber of a steam generator which is fired with a fossil fuel and/or with particulate fuel containing carbon and which has at least one burner level comprising a plurality of burners and/or at least one level having nozzles, in particular in the form of upper air nozzles and/or side wall nozzles, wherein in each case at least one burner or some of the burners is/are provided, independently of the respective other burners, and/or in each case one nozzle or some of the nozzles is/are provided, independently of the respective other nozzles, with a gas flow which makes available the respectively desired oxygen content or the respectively desired oxygen concentration and/or the respectively desired oxygen mass flow.

15. The method as claimed in claim 14, wherein at least one burner or some of the burners are provided, individually and/or separately from the other burners of the respective burner level, and/or one nozzle or some of the nozzles is/are provided, individually and/or separately from the other nozzles of a respective nozzle level, with a gas flow which can be adjusted individually in terms of its oxygen content or its oxygen concentration and/or the oxygen mass flow which is carried by it.

16. The method as claimed in claim 14, wherein at least some of the gas flows of one type or category, which are fed to in each case one or more burner levels or nozzle levels and/or to in each case one or more burners and/or one or more nozzles, are provided with oxygen, in each case individually and/or separately from the other gas flows of this type or category, and/or are adjusted individually and/or separately from these other gas flows of the same type or category, in terms of their oxygen content or their oxygen concentration and/or the oxygen mass flow conveyed with them.

17. The method as claimed in claim 14, wherein said method is carried out in a steam generator as claimed in claim 1.

18. The steam generator as claimed in claim 1, wherein the oxygen content in the respective gas flow can be adjusted to less than 21% by volume.

Description:

The invention is directed to a steam generator comprising a combustion chamber fired with a fossil fuel and/or with particulate fuel containing carbon, and at least one burner level comprising a plurality of burners and/or at least one level comprising nozzles in the form of upper air nozzles and/or side wall nozzles, each having connected feed means and/or feed lines through which/by means of which gas flows which make available combustion oxygen and/or oxidation oxygen can be fed to the burners and/or to the nozzles and/or to the combustion chamber.

Furthermore, the invention is directed to a method for feeding combustion oxygen and/or oxidation oxygen to burners and/or nozzles of a combustion chamber of a steam generator which is fired with a fossil fuel or with particulate fuel containing carbon and which has at least one burner level comprising a plurality of burners and/or at least one level having nozzles in the form of upper air nozzles and/or side wall nozzles.

Conventional large-scale steam generators which are fired with a fossil fuel, in particular with coal, have a combustion chamber in which the fossil fuel is burnt. These combustion systems are composed of a plurality of burner levels, arranged one on top of the other, and further nozzle levels through which, for example, upper air, curtain air or other air is fed to the combustion chamber. The burner levels per se are composed of a multiplicity of burners which have a conveying cross section through which, in the case of coal-fired burners, a coal mass flow which is conveyed with carrying air is conveyed through the burner and is fired at its outlet-side mouth end. In order to promote the combustion, a burner has further flow cross sections and conveying cross sections through which core air, secondary air or tertiary air is fed through the burner to its mouth-side outlet end in order to assist the combustion process and, for example, combustion which is particularly low in nitrogen oxide. The number of flow cross section openings is dependent here on the type of burner and differs depending on the type of burner, with the result that conveying cross sections for conveying carrying air, secondary air and tertiary air do not have to be present in all cases.

However, it is a basic principle that, in addition to the cross section which conveys the fuel, further conveying cross sections which convey combustion oxygen and/or oxidation oxygen into the combustion chamber are also present. The burner levels and/or levels having upper air nozzles or side wall nozzles, respectively formed in a steam generator, are then provided with connected feed means and/or feed lines, through which or by means of which combustion oxygen and/or oxidation oxygen is fed to the combustion chamber. In this context, with respect to the piping it has previously been the practice that a pulverizer which pulverizes the coal as a fossil fuel respectively supplies all the burners of a burner level or at least all the burners of one side of a burner level with the fossil fuel (coal) and the gas flow (carrying air) conveying the latter, jointly via a pulverizer outlet line which subsequently branches. Furthermore, in such large-scale steam generators it has in practice been customary hitherto for the supply of the other flow cross sections and/or conveying cross sections which are present to occur in the individual burner levels or the levels having the additional upper air nozzles or side wall nozzles, by means of feed lines which branch off from a common feed line which conveys heated combustion air. As a result, the oxygen content of the gas flow which is conveyed in these feed lines is defined once on the basis of the branching of all the lines from an original line, and is the same at all the flow cross sections and/or conveying cross sections which open into the combustion chamber. Only the quantity of the respectively conveyed gas flow is regulated by flaps or similar devices. In these known large-scale steam generators, the oxygen content in the conveying flow which starts from the pulverizer is also the same for all the burners which are connected to the respective pulverizer.

If such a system is then operated in the partial load range, individual burner levels or individual burners are switched off, while the remaining number of burners or burner levels continues to operate. In order that damage of the switched-off burners does not occur owing to the high temperatures which continue to occur in the combustion chamber, the latter must be cooled. This cooling is brought about by virtue of the fact that oxygen-containing gas flows continue to be conveyed through at least some of the flow cross sections and/or conveying cross sections or line cross sections or opening cross sections which are present in the respective burner, and, if appropriate, are also conveyed into the combustion chamber through existing upper air nozzles or side wall nozzles. In addition to the cooling, it is also necessary to convey oxygen-containing gas flows in such a way in order to maintain a necessary minimum quantity of flue gas in the steam generator, i.e. in the boiler, in order to reach the temperatures which are necessary in the steam generator, in particular in the high pressure range and in the intermediate superheater range. This quantity of oxygen which is fed to the combustion chamber in the partial load range even when burners are switched off, then leads to a situation in which the total oxygen offer which is made available is significantly higher than is necessary and required in terms of processing technology for complete combustion of the fuel which is made available in the active burners.

Furthermore, it is known from specialist publications that power plants with large-scale steam generators are operated in what is referred to as the oxyfuel operating mode in order to reduce the emission of CO2. In the oxyfuel operating mode, only pure oxygen is then fed as “combustion air” to the burners, and CO2-containing flue gas, which is produced, is fed back to the burners and also to the pulverizers, and the required steam parameters are set, in particular, by corresponding setting of CO2/O2 mixtures in the combustion chamber in order to be able to operate such a power plant in an optimum way. In these power plants which are operated in the oxyfuel operating mode, the reduction in CO2 in the exhaust gas which is subsequently emitted is achieved by virtue of the fact that the CO2 is removed from the flue gas and compressed, in particular, for subsequent storage. However, for this concluding flue gas treatment process it is necessary that the oxygen content in the flue gas be as low as possible. At this point, oxygen constitutes an undesired impurity in the flue gas and makes direct storage of the compressed CO2 impossible.

Such large-scale steam generators are configured in such a way that a quantity of oxygen/oxygen concentration is made available such as is necessary for complete, low-NOx combustion of the fuel according to the requirements of the burner process technology. The quantity of oxygen which is necessary for complete low-CO combustion is to be added here, if appropriate, as what is referred to as burnoff air at the end of the combustion chamber at the transition to the actual steam generator. In the oxyfuel operating mode, the problem then occurs in the partial load range that when a burner level is switched off when maintaining the necessary cooling of the individual burners of this switched-off burner level as described above, an oxygen offer is present in the combustion chamber by virtue of the oxygen content of the respective gas flow/gas flows which is defined for all the similar flow cross sections and/or opening cross sections of the burners of this burner level by recourse to a single common original conveying line, which goes beyond the amount necessary for stoichiometric combustion of the fed-in fuel. This leads to a situation in which oxygen occurs as an impurity in the flue gas, which adversely affects the envisaged CO2 precipitation or even makes it impossible. A conceivable reduction in all the relevant oxygen-containing gas flows of one burner or of all the burners, i.e. the core air and/or secondary air and/or tertiary air, with respect to its oxygen content or its oxygen concentration, in order then to produce, when viewed globally, the overall permitted total quantity of oxygen in the combustion chamber in order to avoid O2 components in the exhaust gas, leads, however, to a situation in which, owing to the existing line connection, an excessively low oxygen concentration is made available at the burners which continue to be active in a partial load operating mode and as a result stable combustion of the fuel at these burners cannot be ensured in the partial load operating mode. It is therefore problematic according to realizations made hitherto to operate customary large-scale steam generators known from the prior art according to the oxyfuel process if a partial load range is reached which requires or would permit switching-off of a burner level or part of a burner level. In order to avoid placing the envisaged CO2 precipitation at risk, such power plants must therefore always be operated in such a way that all the burners are in operation even if it is not necessary for this entire load to be made available. Consequently, in the power plants which are known from the prior art the partial load capability of such a large-scale steam generator which is operated in the oxyfuel process is highly restricted by the fact that the CO2 purity in the exhaust gas which is required for the CO2 precipitation is no longer provided below a load range in which a burner level can or should be switched off, because owing to the cooling of the burners oxygen is inevitably fed into the combustion chamber as an impurity in the exhaust gas.

The invention is based on the object of making available a solution to the problematic situation described above. In particular, a solution is to be provided by means of which undesired oxygen contents in the flue gas can be avoided in the partial load range in the oxyfuel operating mode of the steam generator.

In a steam generator of the type described in more detail at the beginning, this object is achieved according to the invention in that the feed means and/or the feed lines are embodied in such a way that in each case at least one burner or some of the burners can be provided, independently of the respective other burners, and/or in each case one nozzle or some of the nozzles can be provided, independently of the respective other nozzles, with a gas flow which makes available the respectively desired oxygen content or the desired oxygen concentration and/or the respectively desired oxygen mass flow.

According to the invention there is therefore now provision that one or more of a multiplicity of burners or nozzles are in each case connected by lines, individually and separately in respect of the oxygen content required for the respectively desired function of the burner or nozzle, to a gas flow which makes available precisely this desired oxygen content or this desired oxygen concentration or this desired oxygen mass flow. For example, each burner of a burner level is therefore provided with a separate feed line. However, it is also possible to connect in each case all the burners of a level with a separate line which feeds in combustion oxygen or oxidation oxygen. Likewise, individual nozzles or all the nozzles of a respective nozzle level can be connected to a line which feeds in the oxidation oxygen or combustion oxygen which is desired or necessary for the respectively desired function.

The same advantages and the same method of operation can also be achieved in a method according to the invention. The object above is achieved according to the invention in a method of the type described in more detail at the beginning by virtue of the fact that in each case at least one burner or some of the burners can be supplied, independently of the respective other burners, and/or in each case one nozzle or some of the nozzles can be provided, independently of the respective other nozzles, with a gas flow which makes available the respectively desired oxygen content or the respectively desired oxygen concentration and/or the respectively desired oxygen mass flow.

In a refinement of the steam generator, the invention provides that at least one burner or some of the burners can be provided, individually and/or separately from the other burners of the respective burner level, and/or one nozzle or some of the nozzles can be provided, individually and/or separately from the other nozzles of a respective nozzle level, with a gas flow which can be adjusted individually in terms of its oxygen content or its oxygen concentration and/or the oxygen mass flow which it carries. There is therefore not only provision that each burner or each nozzle or each burner level or each nozzle level can be supplied with oxygen separately from other burners or nozzles, but there is also provision that in these lines the oxygen concentration or the oxygen content or the oxygen mass flow which is made available can also be adjusted or regulated individually and separately. This advantage is also characterized by the inventive refinement of the method according to which at least one burner or some of the burners can be provided, individually and/or separately from the other burners of the respective burner level, and/or one nozzle or some of the nozzles can be provided, individually and/or separately from the other nozzles of a respective nozzle level, with a gas flow which can be adjusted individually in terms of its oxygen content or its oxygen concentration and/or the oxygen mass flow which carried by it.

Furthermore, the invention is defined in that the feed means and/or feed lines are embodied in such a way that at least some of these gas flows which are respectively fed to one burner level or nozzle level and/or respectively fed to one burner or one nozzle, and are of one type or category can be respectively provided with oxygen individually and/or separately from the other gas flows of this type or category, and/or can be adjusted, individually and/or separately from these other gas flows of the same type or category, in terms of their oxygen content or their oxygen concentration and/or the oxygen mass flow conveyed with them.

In the same way, at least some of these gas flows which are respectively fed to a burner level or a nozzle level and/or respectively fed to a burner and/or a nozzle, and are of one type or category are respectively provided with oxygen individually and/or separately from the other gas flows of this type or category, and/or are adjusted, individually and/or separately from these other gas flows of the same type or category, in terms of their oxygen content or their oxygen concentration and/or the oxygen mass flow conveyed with them.

Furthermore, expedient refinements and advantageous developments of the invention are the subject matter of the respective further dependent claims.

The invention therefore departs from the customary design principle and the method principle of feeding all the gas flows of a respective category or type, for example carrying “air” or core “air”, secondary “air”, tertiary “air”, curtain “air”, what is referred to as overfire “air”, etc., which respectively make available combustion oxygen and/or oxidation oxygen for the combustion process, from in each case one common original line for the respective “air” type or “air” category in which the oxygen content is determined by the gas flow conveyed therein. Instead, the invention provides for at least some of the burners and/or nozzles and/or some of the flow cross sections and/or opening cross sections of the burners or nozzles to be provided with a gas flow individually and separately and therefore independently of other gas flows of the same type or category. At the simplest, this can be implemented by a separate feed line which is individually assigned to each flow cross section and/or opening cross section and into which a gas which has the desired conditions with respect to the oxygen content and/or the oxygen concentration and/or the quantity of oxygen conveyed with the gas flow (oxygen mass flow) with respect to the flow cross section or opening cross section of a burner or of a nozzle, which is respectively connected to this line, is respectively introduced in a controllable fashion, for example downstream of an air fractionator and a device which heats oxygen formed in the air fractionator.

On the basis of this inventive measure it is possible, even when burner levels are switched off in the partial load range, to continue to make available in the active burner levels the quantity of oxygen and oxygen concentration which is respectively necessary for stable, low-NOx combustion in said levels, at different points at which the oxygen-containing gas flow serves only for cooling, but to reduce the oxygen content and the oxygen concentration to such an extent that, viewed globally over the entire combustion chamber, such a processing equilibrium is established that no O2 content which can be detected or measured or evaluated as an impurity is contained anymore in the flue gas which leaves the steam generator and is fed to the CO2 precipitation.

Since this problematic situation arises in particular in switched-off burners when said burners continue to be provided with a gas flow or a plurality of gas flows for the purpose of cooling, the invention provides, in a refinement, that at least a part of the burner level or nozzle level and/or some of the burners or nozzles which is/are provided with an oxygen-containing gas flow, in particular for the purpose of cooling, during partial loading of the steam generator, has/have such a feed means and/or such a feed line.

Depending on the application, it is possible that, in order to cool burners, the secondary gas flow and/or the tertiary gas flow of each burner are provided individually, separately and independently of one another, or at least the secondary gas flows and/or tertiary gas flows of the burners are provided per burner level, with the then necessary oxygen, but with the minimum required amount of oxygen. The invention therefore provides, in a refinement, that the secondary gas supply and/or tertiary gas supply of each burner level and/or of each burner can be provided with oxygen individually and/or separately from other gas flows of this type or category and/or can be adjusted individually and/or separately from these other gas flows, in terms of their oxygen content.

Likewise, it is possible that the core air flows or core gas flows are used for cooling. For this to be possible, the invention is also defined in that the core gas supply of each burner level and/or of each burner can be provided with oxygen individually and/or separately from other gas flows of this type or category, and/or can be adjusted individually and/or separately in terms of its oxygen content.

Since the fuel for a burner level is usually fed by a pulverizer using a conveying gas flow or carrying gas flow, it is also possible to provide that when this burner level is switched off, exclusively an oxygen-containing gas flow is conveyed through the corresponding conveying cross section. The invention therefore also provides that the primary gas supply of each burner level and/or of each burner can be provided with oxygen individually and/or separately from other gas flows of this type or category, and/or can be adjusted individually and/or separately in terms of its oxygen content.

Furthermore, in this context, it is expedient also to provide the oxygen regulating facility for the upper air supply and/or the supply of side wall nozzles. A further refinement of the invention therefore consists in the fact that the upper air nozzle supply and/or the side wall nozzle supply of each nozzle level and/or of each nozzle can be provided with oxygen individually and/or separately from other gas flows of this type or category and/or can be adjusted individually and/or separately in terms of its oxygen content.

In order to be able to vary over a particularly large range the adjustment and distribution of the various gas flows which convey combustion oxygen and/or oxidation oxygen, it is then advantageous according to a further refinement of the invention if all the gas flows, feeding combustion oxygen and/or oxidation oxygen to the combustion chamber, of each burner level and/or of each burner and/or of each nozzle level and/or of each nozzle can be provided with oxygen individually and/or separately from other gas flows of the respective type or category and/or can be adjusted individually and/or separately in terms of their oxygen content.

The separate and individual adjustability of the respective gas flows and the supplying of the individual burners or burner levels or nozzles or nozzle levels can be implemented in a structurally particularly favorable way in that each burner level or nozzle level and/or each burner or each nozzle is connected to at least one feed line feeding an oxygen-containing gas flow, wherein the oxygen content of the gas flow, respectively fed therein, of one type or category can be adjusted independently of the gas flows of this type or category which are respectively fed to the other burner levels or nozzle levels and/or other burners and/or other nozzles.

On the basis of the inventive refinement of a steam generator it is possible to adjust the oxygen content in the respective gas flow in the individual burners or burner levels or nozzles or nozzle levels between 0 and 100% by weight or % by volume, in particular to less than 21% by volume, which also defines the invention.

One refinement of the steam generator according to the invention then also consists here in the fact that, at least in some of the feed lines, a mixture of fed-back CO2-containing flue gas and added oxygen is fed to the respective burner level or nozzle level and/or to the respective burner or to the respective nozzle as a gas flow.

Since the inventive refinement of a steam generator is appropriate and advantageous in particular when CO2 precipitation from the flue gas which is produced is to be carried out in a steam generator operated in the oxyfuel operating mode, the invention is also defined by the fact that the steam generator is operated at least at certain times in an oxyfuel operating mode.

Finally, in one refinement of the method, the invention provides that the method is carried out in a steam generator as claimed in one of claims 1-13.

If the primary tube is also provided with cooling gas in the partial load range, separate supply and control with oxygen is also to be provided individually or on a level basis for this gas flow or the primary gas supply is to be provided with a valve with which gas can be deflected from another gas flow (secondary air, tertiary air or other air) on to the primary gas cross section. Such a design is known for the air operation from EP 1 369 640 B1. If upper air nozzles and side wall nozzles are present and if they are provided with cooling gas in the partial load operating mode, these gas flows are also to be provided individually or on a level basis with their own supply of oxygen and a corresponding control.

Overall, the invention therefore provides that at least the secondary gas, tertiary gas and core air flows of each burner are supplied with the necessary or desired oxygen individually or at least on a level basis in so far as said flows are also provided for cooling the respective burners, so that in the partial load range of the steam generator the oxygen content of these gas flows can be reduced to a value which is lower than the full load situation and normal load situation, and in an extreme case can be reduced as far as zero. The installation of the ducts, feed means and/or feed lines which are necessary for this was previously not considered when configuring fossil fired large-scale steam generators of power plants. However, if an overall excess of oxygen which is to be maintained is not to be exceeded in the oxyfuel operating mode of such a large-scale steam generator in the partial load, the inventive embodiment of a steam generator is, however, a relatively easily implemented measure for avoiding oxygen contamination in the exhaust gas, which would be damaging for the precipitation of CO2.

The gas flows which are referred to above in each case as “gas flow of one type or category” are therefore respectively the core “air”, secondary “air” or tertiary “air” flows of a burner or of a burner level or the upper “air” or side wall “air” flows of the respective nozzles or nozzle levels.

The core idea on which the invention is based can therefore be summarized as follows:

The oxygen content and therefore the quantity of oxygen of at least one gas flow, some of the gas flows or all of the gas flows which are fed to all the burners of a burner level and/or the oxygen content of at least one gas flow, some of the gas flows or all of the gas flows fed to one or more or all of the plurality of burners of a combustion chamber of a steam generator is independent of, and in particular can be regulated and adjusted individually and separately with respect to, the oxygen content of the respectively remaining other gas flows, in particular the remaining other gas flows of the same type and category, in such an individual fashion, in particular in the range from 0-100% by weight or % by volume, in particular ≦21% by volume, that the overall oxygen content which is introduced into the combustion chamber or the overall quantity of oxygen which is introduced or the excess of oxygen which is set in the combustion chamber does not exceed the desired amount in the respectively currently set operating state or operating state which is to be set, preferably during the operation of the steam generator in the oxyfuel operating mode. Likewise, if desired, the oxygen content and therefore the quantity of oxygen of at least one gas flow, some of the gas flows or all of the gas flows fed to all the nozzles of a nozzle level and/or the oxygen content of at least one gas flow or some of the gas flows or all of the gas flows fed to one or more or to all of the plurality of nozzles of a combustion chamber of a steam generator can be adjusted and regulated in an analogous fashion. In particular, in this context the oxygen or excess of oxygen which is introduced overall via the burner or burners and/or via the nozzle or nozzles is then set in such a way that the amount which is respectively desired as a function of the operating state is not exceeded and, in particular, is set.

It is possible here that each of the individual gas flows of core “air”, primary “air”, secondary “air”, tertiary “air”, upper “air”, side wall “air”, overfire “air”, etc. which are fed to a burner or to a nozzle is embodied in such a way that it can be adjusted in terms of its respective oxygen content individually and separately, as a gas flow of the same type, from the respective other gas flows of this type. However, it is also possible to configure in each case just one of these gas flows such that it can be adjusted individually in terms of its oxygen content.

The invention is explained in more detail by way of example below with reference to a drawing. Said drawing shows, in a schematic illustration in the single FIGURE, a burner level, comprising four burners 1, of a fossil fuel fired combustion chamber of a steam generator. The burners 1 are each connected to a coal pulverizer 3 in a line connection via a feed line 2 which branches into component lines 2a-2d. In the configuration of the system illustrated in the FIGURE, in particular of the combustion system for an oxyfuel operating mode of the steam generator, CO2-containing recirculated flue gas is fed to the coal pulverizer 3 via a line 4, said flue gas also reaching the burners 1 via the line 2. The gas flow which is fed via the feed line 4 then conveys the coal which has been pulverized in the pulverizer 3, via the feed line 2 and the branches 2a-2d of this flue gas as a primary gas or carrying gas and coal dust to the respective burners 1. In the partial load operating mode of the steam generator it is possible to switch off the primary gas supply or carrying gas/coal supply to the individual burners 1, in particular to all the burners 1 of the illustrated level, and therefore to deactivate the burners 1. In order to adjust the oxygen content in the recirculated flue gas flow which is fed through the feed line 4, a feed line 5 (illustrated by dashed lines) is provided which has a line connection to an oxygen heater 6, to which an oxygen gas flow is fed via a line 8 from an air fractionator 7. Oxygen can then be fed into the line 4 via the line 5, with the result that pure flue gas, a mixture of flue gas and oxygen or pure oxygen or even no gas at all can be fed to the burners 1. By means of a branch line 5b, it is also possible to feed an oxygen-containing gas flow to the lines 2a-2c by bypassing the pulverizer 3. The oxygen mass flow which is carried in the gas flow in the lines 5 and 5b and 2 and 2a-2d can be adjusted by means of devices or apparatuses which are not illustrated.

For the purpose of individually and separately supplying the further gas flow cross sections, provided in the burners 1, with core “air”, secondary “air” and tertiary “air”, wherein the term “air” denotes within the scope of this application essentially nitrogen-free, oxygen-containing gas flows and does not in fact denote atmospheric air but rather if appropriate pure oxygen, said gas flow cross sections on each burner 1 are also connected to a separate feed line. In this way, core “air” as a gas flow of this type or category is fed to the burners 1 via the feed lines 9a-9d, secondary “air” as a gas flow of this type or category is fed to the burners 1 via the feed lines 10a-10d, and tertiary “air” as a gas flow of this type or category is fed to the burners 1 via the lines 11a-11d. An essentially nitrogen-free, oxygen-containing gas flow of a further type or category is fed to nozzles 13, for example upper “air” gas nozzles, of a nozzle level via the lines 12a-12d. The oxygen heater 6 is, moreover, operatively connected to feed means 9, 10, 11 and 12 which ensure, through interaction with the respectively assigned feed lines 9a-9d, 10a-10d, 11a-11d and 12a-12d, that each of the feed lines can be respectively provided with oxygen individually and/or separately from the other gas flows in the respective other feed lines, in particular of the same type or category. Overall, the oxygen content of the gas flow of one type or category which is respectively conveyed in the respective line and the oxygen concentration of this gas flow and/or the oxygen mass flow which is conveyed with the gas flow can therefore be adjusted selectively, with the result that this respective oxygen-containing gas flow which is, if appropriate, necessary for the combustion or in the case of desired cooling, and is fed to the (gas) nozzles 13 and/or a respective burner 1, can be regulated and adjusted in such a way that the overall oxygen which is introduced into the combustion chamber or the excess of oxygen does not exceed the respectively desired amount. The feed means 9, 10, 11 and 12 also include the possibility of feeding and adding fed-back, CO2-containing flue gas as well as the possibility of measuring and controlling the respective oxygen concentration in the individual flows in the feed lines 9a-9d, 10a-10d, 11a-11d and 12a-12d, with the result that the oxygen/flue gas mixtures which characterize the oxyfuel operating mode can be fed to the burners 1 and/or the nozzles 13 in the feed lines 9a-9d, 10a-10d, 11a-11d and 12a-12d as well as 2 and 2a-2d. In particular, what is referred to as the air factor can as a result be set selectively and can be adapted to the respective load situation.

As a result of this refinement, it is possible not only to avoid undesired O2 contents or oxygen contents in the flue gas in the partial load range as a result of the individually adjustable O2 contents or oxygen contents. In the full load range it is also possible to selectively set oxygen ratios which are desired as a result. It is therefore possible for a different or at least the respectively desired supply with an oxygen concentration to be respectively individually fed to the various burner cross sections of a burner 1 or of the burners of a burner level, with the result that a flame pattern or temperature pattern or combustion can be set in a way which is analogous with the customary air operating mode (non-oxyfuel operating mode). Likewise, it is possible to carry out trimming with respect to the oxygen content/the oxygen concentration between burner levels.