The invention relates to a steam generating boiler and to a method for operating a steam generating boiler.
In boilers with linear or tangential firing two gas flows are generated which in addition to the axially orientated flow components include radially orientated flow components. These radially orientated flow components may be caused both by different pressure conditions in the boiler space as well as by mutual influences of the flow paths of mutually opposite burners with simultaneous influences of the circulation regions in the combustion chamber and bring about a greater or lesser flue gas flow towards the side walls of the boiler vessel including fuel products which are still in part capable of reacting.
A result of this is the formation of regions of oxygen starvation which due to geometrical conditions spread out preferentially towards the center of the boiler walls but which, caused by pressure differences, may frequently change their positions and in the long term result in damage to material due to corrosion of the pipe walls. The phenomenon of the formation of such oxygen starvation regions will in the following be elucidated with reference to the diagrammatic illustrations in
A quantitative illustration of the above described conditions involving the formation of oxygen starvation regions in a combustion chamber operated by means of linear or boxer firing is illustrated in
For the avoidance of oxygen starvation regions and thereby for protection against corrosive attack it is known to integrate wall air nozzles into burner groups (e.g. in the case of tangential firing) by way of which a partial air flow, deflected from the burner flow axis is conducted in the direction of the combustion chamber wall. Furthermore, it is known to install lateral air nozzles besides burners close to the wall by way of which an air flow is injected at high velocity parallel to the burner flow axis into the combustion chamber in the immediate vicinity of the wall. However, these expedients suffer from the disadvantage that, on the one hand by the high ejection velocity of the air flow introduced from the side air nozzles new vortexes are formed which conduct the oxygen depleted flue gas towards the boiler walls and that on the other hand frequently the depth of penetration of these air flows into the more viscous flue gas flow is inadequate such that an oxygen enrichment in the endangered boiler regions cannot be attained, which has been simulated in numerous experiments with variations of the side and burner air quantities in a variety of boiler installations and in numerous simulation models.
By way of example in
From WO 98/16779 it is known to fit wall air nozzles in the endangered combustion chamber side walls in order to protect the side walls against corrosion. These wall air nozzles are arranged in one or more horizontal rows or in an arcuate pattern over the entire wall width in order to form on the side walls a corrosion protective layer in the combustion chamber flow by means of the wall air fed into the wall air nozzles and by utilizing vertical flow components.
These expedients as well suffer from the drawback, however, that viewed over the height covered by the string of burners and, where applicable, between the plurality of horizontal nozzle rows, regions of oxygen starvation are still formed. This is apparent from the illustration according to
To summarize, according to known attempts at creating a corrosion protection, wall air nozzles are integrated either as side air nozzles adjoining the burners (e.g. in the case of tangential firing) or integrated into one or more essentially horizontal rows on the side walls (which are not equipped with burners). Any corrosion protection in those arrangements is either inadequate or can only be attained employing amounts of wall air which for economic as well as thermal and emission technological reasons are unacceptable.
It is accordingly an object of the present invention to provide a steam generating boiler and a process for operating a steam generating boiler by means of which damage to the boiler wall in particular by corrosion is effectively avoided.
This object is attained according to the features of the independent patent claims.
A method according to the invention for operating a steam generating boiler in which a combustion chamber defined by boiler walls is fired by combustion of fuel causing the formation of a flue gas flow by means of a plurality of burners, includes the following steps:
The present invention is based on the realization that when firing a steam generating boiler the flow component which in relation to the combustion chamber bottom is horizontal, particularly in the region of the string of burners, dominates as compared with the vertical component. Due to the feeding of the insulating gas according to the invention (e.g. the wall air) in the source region of this horizontal component of the combustion chamber basic flow along the combustion chamber wall, this flow is effectively utilized for distributing the insulating gas along the combustion chamber wall to be protected, so that the formation of oxygen starvation regions and of resultant corrosion is effectively counteracted.
Within the meaning of the invention, the expression “insulating gas layer” is to be understood to denote a gas layer which in relation to the flue gas flow exhibits a feed impulse flow into the combustion chamber so low that, due to the lack of mixing energy in the insulating gas layer, a mixing of the insulating gas layer with the flue gas either does not take place at all or in any event with so much delay that compared with the flue gas flow present in the immediate vicinity of the boiler wall region a protective layer is formed which counteracts the effects on the atmosphere in the immediate vicinity of the boiler wall and which accordingly, in this sense, “insulates” the boiler wall region against the flue gas flow.
The term “source region” within the meaning of the invention denotes a region from which the respective wall flow or its horizontal component respectively issues and in which the resultant flow velocity amounts essentially to zero.
According to a preferred embodiment the feeding of the insulating gas proceeds by way of a gas feed nozzle arrangement provided in at least one combustion chamber wall which in each of a plurality of mutually adjoining planes, horizontal in respect of the bottom of the combustion chamber, includes exactly one gas feed zone which is arranged in the source region above the horizontal component of the combustion chamber wall flow associated with this plane.
The combustion chamber may comprise a symmetrical burner arrangement and the gas feed nozzles may be arranged in a line vertical in relation to the respective combustion chamber wall and extending along the vertical center line of the respective combustion chamber wall.
Preferably the gas feed nozzle arrangement extends essentially along the burner string level of the combustion chamber.
According to an alternative embodiment the combustion chamber includes an intermediate wall between opposite walls of the boiler and the gas feed nozzles provided in the source region of the combustion chamber flow are provided in the intermediate wall.
According to a preferred embodiment the feeding of the insulating gas proceeds by way of a gas feed slot, vertical in relation to the combustion chamber bottom provided on at least one combustion chamber wall and extending more or less continuously essentially along the level of the burner string.
Preferably air is used as the insulating gas which is fed from the combustion gas supply of the combustion chamber.
The content by volume of the air used as the insulating gas preferably amounts to maximally 10% more preferably maximally 5% of the total amount of air required for the conversion of the fuel.
It is also possible to employ an oxidizing gas or an inert gas as the insulating gas.
According to a preferred embodiment the insulating gas flow is generated independently in individual sectors of the boiler wall so that variations in the strength of the flue gas flows which may arise in the boiler wall sectors due to geometrical circumstances and the arising pressure differences may, depending on conditions prevailing in the respective sector, may be taken into account by a locality dependent variation of the insulating gas flow.
According to a preferred embodiment the steam generating boiler includes analysis means for the determination of contents by volume of flue gas components in the gas atmosphere prevailing, adjoining the boiler wall, and a regulating means for regulating the insulating gas flow as a function of the volume proportions so determined. The flue gas components so determined include preferably oxygen and carbon monoxide but may also, depending on requirements, include further flue gas components, in particular HCl and/or H2S.
The determination of proportions by volume of the flue gas components and/or regulating the insulating gas flow in this context is preferably performable independently from one another in individual sectors of the boiler wall.
According to a preferred embodiment the determination of the volume proportions of the flue gas components and/or the regulating of the insulating gas flow can be performed repeatedly in independent measuring cycles. In this manner it becomes possible to take into account variations in time of the conditions prevailing on the boiler wall surface or in the individual boiler wall sectors by appropriately regulating the insulating gas flow, whereby the protection attained according to the invention against damage of the boiler wall by corrosion is improved even further.
According to a preferred embodiment the insulating gas flow is fed from the combustion gas supply of the combustion chamber which thereby attains a dual functionality.
According to a preferred embodiment the gas feed means in each boiler wall sector includes a gas feed unit (e.g. air box) for the feeding of insulating gas to the surface of the boiler wall into the combustion chamber.
Preferably in this context the gas feed units associated with a boiler wall are each connected to a main line coupled separately to the combustion gas supply. Preferably in this context each main line includes a regulating element for regulating the gas flow there through so that a selective feed to the individual boiler walls can take place by way of the associated main line.
According to a preferred embodiment each gas feed unit is moreover adapted to be selectively coupled by way of a closure element to the associated main line so that also a selective feed to the individual boiler wall sectors can take place.
Preferably in this context the regulating element of the particular main line and/or the closure element of the respective air box is operated as a function of the volume ratios of flue gas components determined in the gas atmosphere adjoining the boiler wall.
In this context the burners may more particularly be arranged both for linear firing as well as for tangential firing of the combustion chamber.
A steam generating boiler according to the present invention includes:
Further embodiments of the invention may be derived from the following description and the subsidiary claims.
In what follows the invention will be further elucidated with reference to a working example illustrated in the accompanying illustrations.
There is shown in:
According to the invention, for the distribution of an insulating gas flow in the combustion chamber region to be protected, flow conditions are utilized which are characterized in that along the side walls to be protected of the combustion chamber a horizontal basic flow exists. For this basic flow which is horizontal in relation to the bottom of the combustion chamber there exists along the side walls a “source region” starting from where the horizontal expansion of the flow in the direction of the corners of the combustion chamber proceeds. This situation is illustrated in
In
From the simulation illustrated in
The source points constituting the source region accordingly form an array extending in vertical direction (in particular along the so-called burner string) which in a final analysis depends on the specific parameters (combustion chamber geometry, arrangement of side as well as possible intermediate walls, burner array, burner operation etc.) and which according to the process according to the invention is determined first.
The detection according to the invention of the source region of a horizontal base flow can be performed either according to
Once according to the invention, as described above, the source region of the horizontal basic flow has been determined, a nozzle system is provided in each side wall of the combustion chamber such that the wall air nozzles are each provided in the source region as determined above. Thus, for example, in the working example as shown in
In
As appears from
Along the outer combustion chamber walls it is for example also possible to select the more simple arrangement illustrated in
The spacing and the aperture size of the wall air nozzles in the vertical nozzle arrangement according to the invention may be selected appropriately as a function of the static conditions. In this context the insulating gas protective layer is as a rule generated with increasing effectiveness, the closer is the spacing of adjoining wall air nozzles, i.e. the more effectively the respective wall surface is fed with insulating gas in the source region of the horizontal wall flow. In principle therefore when designing the vertical nozzle arrangement—depending on the concrete design and construction limitations—the ideal of a continuous vertical slot in the source region of the horizontal wall flow should be aimed at as far as possible.
In the following a preferred embodiment of the invention will be elucidated in which the insulating gas flow can be regulated in individual boiler wall sectors independently from one another and in dependency of the conditions actually prevailing there.
The nozzle arrangement according to the invention proceeds not necessarily along a straight vertical line, because the configuration in the source region of the horizontal wall flow may also follow a non-linear pattern depending on the concrete flow conditions in which in the vertical direction adjoining nozzles are in horizontally staggered mutual interrelationship in order each to optimally utilize the prevailing horizontal wall flow.
In accordance with
The steam generating boiler according to the invention in accordance with the illustrated working example moreover includes a plurality (six in the working example) of air boxes 109-114, each air box 109-114 being individually associated with one boiler wall region sector each. By means of each such air box the insulating air is fed as explained above into the previously determined source region of the horizontal component of the combustion chamber flow.
The air boxes 109-114 according to the illustrated preferred embodiment provided along a side wall 103 or 104 respectively are each individually connected by way of an associated individual duct 115-120 to a common main duct 121 or 122, each main duct 121 or 122 respectively providing air to an entire boiler side wall 103 and 104 respectively. The main ducts 121 and 122 are jointly connected to a combustion gas supply system 123 by means of which the air boxes 109-114 as well as the burners are supplied with air. The respective air flow is represented by broken lines drawn alongside the ducts.
Each of the individual ducts 115-120 includes a closure element 124 by means of which when required the air supply of the particular air box can be switched on or off. Furthermore, each main duct 121 or 122 respectively includes a regulator element 125 for regulating the amount of air flowing through the respective main duct, which in turn is quantitatively determined by a measuring device 126 connected upstream or downstream of a regulating element 125.
Each of the air boxes 109-114 includes a plurality (eight each in accordance with the working example) of gas withdrawal localities 127, each gas withdrawal locality 127 being individually connected by way of a measuring duct 128 to a measuring point reversing device 129. From the measuring point reversing device 129 the gas withdrawn is passed to an analyzer 130 which sucks in the gas from the region of the combustion chamber 100 close to the wall by way of the above described route and analyses the composition of the atmosphere in the respective boiler wall region. The analyzer 130 is preferably designed for the determination of proportions by volume of (O2) and carbon monoxide (CO), but may in addition and as required also be suitable for the determination of the contents by volume of further flue gas components such as HCl or H2S.
The respectively measured volumetric proportions (in particular oxygen and carbon monoxide proportions) in the atmosphere of the particular boiler wall region measured in any particular run (measuring cycle) are stored in the memory of a evaluation unit 131 and compared with predetermined index values, whereafter the evaluation unit 131 issues an appropriate output signal according to which the closure element 124 in the individual duct 115-120 associated with the corresponding air box 109-114, is actuated. Preferably in doing so the corresponding closure element for increasing the insulating gas feed flow to the respective air box 109-114 is actuated whenever the determined oxygen content by volume decreases or whenever the determined content by volume of carbon monoxide (or HCl or H2S) increases.
Simultaneously, as apparent from
After the conclusion of a measuring cycle within any one sector of a boiler wall region the stored measuring data are deleted and the cycle of locality dependent measurements of the atmosphere of the boiler wall region at successive measuring points 127, corresponding actuation of closure elements 124 in the individual ducts 115-120 leading to the respective air boxes 109-114, recalculation of air feed index values for the entire boiler wall and appropriate actuation of the regulating element 125 in the respective main duct 121 or 122 respectively is again resumed.
During the operation of the steam generating boiler according to the invention the air feed rushing in from the combustion gas supply means by way of the main duct and the individual ducts into the air boxes enters approximately in the central region of the boiler wall at a plurality of localities (not illustrated) arranged vertically in the source region of the horizontal component of the combustion chamber wall flow enters at a very low velocity into the combustion chamber and expands utilizing the basic flow of the combustion chamber essentially blanket-like in the area close to the tube wall with the formation of an insulating gas layer. This expansion proceeds at a flow velocity which by comparison with the flue gas flow is so low that a mixing with the flue gas due to the lack of mixing energy in the gas layer proceeds only at a greatly retarded rate, if at all. The oxygen enriched air insulation layer thus formed in the immediate vicinity of the boiler wall region in that manner prevents the formation of oxygen starvation regions in the respectively endangered regions 108 and 109.
In accordance with the above described preferred embodiment a concerted regulation of the protective gas layer formed in the boiler wall region can take place, more particularly both for an entire side wall 103 or 104 outlining the combustion chamber (by regulating the air flow through the main duct 121 or 122) as well as also of the air supply to individual sectors (by way of the respective closure elements 124), the respective index values for regulating in independent measuring cycles being newly fixed on the basis of a repeated locality dependent measurement of the atmosphere in the boiler wall region. In that manner a variation in terms of time and locality of the flow conditions in the combustion chamber and a variation of the oxygen starvation regions resulting there from can be taken into account by appropriately regulating the protective gas layer according to the invention.
Even though the above described selective regulation is advantageous, it is not an absolute precondition for the realization of the invention. In particular, it is also possible to omit the above mentioned measuring and regulating devices and to provide a constant air feed, more particularly either for an entire boiler wall or alternatively with different feed rates in the individual boiler wall region sectors.
The air boxes used with the system according to the invention need not be connected by way of main or individual ducts jointly to the combustion gas supply means. Alternatively, (even though less preferred) it is also possible to provide a supply to the air boxes from a separate air feed system. Moreover, the number of air boxes is optional, such that in particular even a single box only for each wall of the combustion chamber may be provided.
Furthermore, the invention is not limited to the feeding of air for the insulating gas layer. In principle, it is also possible to use a different inert or oxidizing gas mixture which is suitable for corrosion protection.
Even though the invention has been elucidated through the example of a steam generating boiler with boxer firing, it is likewise applicable also to a steam generating boiler with tangential firing.
Number | Date | Country | Kind |
---|---|---|---|
10 2004 022 514.1 | May 2004 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/DE2005/000850 | 5/4/2005 | WO | 00 | 11/6/2006 |