Patent Grant
10982843
This application is the U.S. national phase of International Application No. PCT/FI2017/050488 filed 29 Jun. 2017, which designated the U.S. and claims priority to FI Patent Application No. 20165555 filed 1 Jul. 2016, the entire contents of each of which are hereby incorporated by reference.
The present invention relates to an over fire air arrangement and more particularly to an over fire air arrangement according to the preamble of claim 1. The present invention also relates to a method for supplying over fire air into a furnace, and more particularly to a method according to the preamble of claim 12.
Nitrogen oxides (NOx) are unwanted byproducts of combustion processes, such as combusting fossil fuels. NOx emissions from combustion processes have negative effects on environment by causing acid rains. In the prior art NOx emissions have been reduced by staged combustion of fuels in the furnace or staged air supply into the furnace. This means that the fuel is burned in stages. In principle, increasing the staging of the combustion process the NOx emissions may be decreased. However, increasing the staging of the combustion process increases the amount of unburns, including carbon monoxide (CO). Increased unburns decrease the combustion efficiency and also cause emissions. The increase of unburns may be prevented by using over fire air arrangement in which air is supplied to the upper furnace for good burn-out of the fuel after staged combustion.
In prior art over fire air arrangements there are usually one or two levels of over fire air ports provided to furnace walls in upper furnace and in vertical direction over the lower furnace in which the staged combustion is carried out. In these prior art over fire air arrangements the over fire air is supplied from one furnace wall or two opposing furnace walls towards the centre of the furnace. Thus the over fire air improves burn-out of fuel when the staged combustion is used.
However, one of the disadvantages of prior art over fire air arrangements is that the mixing of the over fire air and coverage of the whole upper furnace is inadequate for achieving good burn-out of fuel in the whole upper furnace area. This compromises the combustion efficiency and also generates unwanted unburn emissions.
An object of the present invention is therefore to provide an over fire air arrangement and method for supplying over fire air into a furnace so as to overcome or at least alleviate the prior art disadvantages. The objects of the invention are achieved by an over fire arrangement according to the characterizing portion of claim 1. The objects of the invention are further achieved by a method according to the characterizing portion of claim 12.
The preferred embodiments of the invention are disclosed in the dependent claims.
The invention is based on the idea of providing an over fire air arrangement for a furnace having opposing first wall and second wall and opposing first side wall and second side wall between the first and second walls for forming a furnace enclosure. The over fire air arrangement comprises at least one first over fire air port provided to the first wall for supplying a first over fire air flow into the furnace and at least one first additional over fire air port provided to at least one of the first and second side walls in the vicinity of the first wall, the at least one first additional over fire air port being arranged to supplying a first additional over fire air flow into the furnace transversely to the first over fire air flow.
In an alternative embodiment the over fire air arrangement further comprises at least one second over fire air port provided to the second wall for supplying a second over fire air flow into the furnace and at least one second additional over fire air port provided to at least one of the first and second side walls in the vicinity of the second wall, the at least one second additional over fire air port being arranged to supplying a second additional over fire air flow into the furnace transversely to the second over fire air flow.
In one embodiment of the invention the first and second additional over fire air ports are arranged to supply the first and second additional over fire air flows along and in vicinity of the first and second walls respectively.
In one embodiment of the invention the invention the first and second additional over fire air ports are arranged to supply the first and second additional over fire air flows parallel the first and second walls respectively, or parallel and along the first and second walls, respectively.
In yet another embodiment of the invention the invention the first and second additional over fire air ports are arranged to supply the first and second additional over fire air flows perpendicularly to the first and second over fire air flows, or parallel and along the first and second walls, respectively, and perpendicularly to the first and second additional over fire air flows.
The first and second over fire air ports provided to the first and second wall, respectively, are arranged to provide together with the first and second additional over fire air ports a crossflow of over fire air into the furnace.
The invention is further based on the idea of supplying over fire air into a furnace, the furnace having opposing first wall and second wall and opposing first side wall and second side wall between the first and second walls for forming a furnace enclosure. The method comprises supplying a first over fire air flow from the first wall into the furnace and supplying a first additional over fire air flow from at least one of the first and second side walls in the vicinity of the first wall and transversely to the first over fire air flow.
In one embodiment of the invention the method further comprises supplying a second over fire air flow from the second wall into the furnace and supplying a second additional over fire air flow from at least one of the first and second side walls in the vicinity of the second wall and transversely to the second over fire air flow.
When air is supplied from the over fire air ports provided to the first and second opposing walls of the furnace, the over fire air flows are directed towards the centre or opposite wall of the furnace. Thus an oxygen rich area is formed in the centre of the furnace or towards the opposite wall of the furnace. At the same time on oxygen lean area is formed in the vicinity of the first and second walls via which over fire air is supplied in to the furnace. This is due to the fact that the over fire air flows flow away from the first and second walls via which they are supplied and start to rise upwards in the furnace. According to the present invention additional over fire flows are supplied from at least one of the side walls of the furnace in the vicinity of the first and second walls and substantially along the first and second wall. Thus additional over fire air is supplied into the oxygen lean area.
The additional over fire air flows provide oxygen to the oxygen lean area in vicinity of the first and second walls via which the over fire air is supplied. The additional over fire air enhances the burn-out of fuel and thus decreases the amount of unburns in the combustion process. The additional over fire air flows may also provide shield flows and decrease corrosion tendency of the first and second walls of the furnace.
In the following the invention will be described in greater detail by means of preferred embodiments with reference to the attached [accompanying] drawings, in which
It should be noted that the furnace 1 may comprise at least one primary burner 14, 15 and at least one secondary burner 12, 13 in vertical direction above the at least one primary burner 14, 15 for providing staged combustion. The furnace 1 may also comprise tertiary or further burner levels for forming more than two combustion stages. Furthermore, burners may also be provided only on one wall of the furnace 1.
The furnace further comprises an over fire air arrangement comprises one or more over fire air ports 20, 21 provided to the upper furnace 110 above the lower furnace 100. In the embodiment of
In the context of this application the over fire air ports 20, 21 may be provided on the same wall with the burners 14, 12, 15, 13 or alternatively on adjacent walls. Therefore, the arrangement of the over fire air ports 20, 21 is not dependent on the arrangement of burners 14, 12, 15, 13 combustion air ports provided to the lower furnace 100.
The over fire air ports 20, 21 supply over fire air flows in the direction of arrows 26 such that on oxygen rich over fire air area 42 is formed in the centre of the upper furnace 110.
The additional over air ports 50, 51 are provided to the first and second side walls 5, 7 as shown in
It should be noted that also in single wall combustion furnace the over fire air ports may be provided on two opposite walls of furnace in the same way as shown in context of
Furthermore, it should be noted that the present invention is not restricted to any special type on furnace, but the over fire arrangement according to the present invention may be utilized in any type of furnaces. For example, the furnace may be single wall combustion furnace, opposite wall fired furnace, corner fired furnace, a grate furnace, bubbling fluidized bed furnace or even a circulating fluidized bed furnace. The present invention is not restricted to any particular fuel, but fuel used in the furnace may be any known fuel.
According to the above mentioned, the over fire air arrangement of the present invention comprises at least one first over fire air port 20 on the first wall 4 and at least one first additional over fire air port 50 provided to at least one of the first and second side walls 5, 7 in the vicinity of the first wall 4. The at least one first additional over fire air port 50 is arranged to supplying the first additional over fire air flow 60 into the furnace 1 transversely to the first over fire air flow 40 of the at least one first over fire air port 2. Alternatively the upper furnace 110 may also comprise at least one second over fire air port 21 provided to the second wall 6 and at least one second additional over fire air port 51 provided to at least one of the first and second side walls 5, 7 in the vicinity of the second wall 6. The at least one second additional over fire air port 51 being arranged to supplying a second additional over fire air flow 61 into the furnace 1 transversely to the second over fire air flow 41 of the at least one second over fire air port 21.
As described above and shown in
the first and second additional over fire air ports (50, 51) are arranged such that:
As described above the first and second additional over fire air ports 50, 51 are arranged in the vicinity of the first and second walls 4, 6, respectively. The term in the vicinity means that the first and second additional over fire air ports 50, 51 are arranged such that the a first distance z between the first and second additional air port 50, 51 and the first and second wall 4, 6, respectively, is smaller than a second distance y between the first and second additional air port 50, 51 and a vertical centre line A-A′ of the furnace enclosure 2, as shown in all
In one embodiment the first and second additional over fire air ports 50, 51 are arranged such that first distance z between the first and second additional air port 50, 51 and the first and second wall 4, 6, respectively, is smaller than or equal to one third of a third distance x between the a vertical centre line A-A′ of the furnace enclosure 2 and the first and second wall 4, 6, respectively.
In an alternative embodiment the first and second additional over fire air ports 50, 51 are arranged such that the first distance z between the first and second additional air port 50, 51 and the first and second wall 4, 6, respectively, is smaller than a second distance y between the first and second additional air port 50, 51 and a vertical centre line A-A′ of the furnace enclosure 2, and that the first distance z is smaller than 2.0 m, or preferably the first distance z is between 0.3-1.0 m.
According to the present invention the first and second additional over fire air ports 50, 51 are arranged above the over fire air ports 20, 21 in the vertical direction of the furnace 1. The first and second additional over fire air ports 50, 51 may also be arranged even below the over fire air ports 20, 21 in the vertical direction of the furnace 1.
The over fire air arrangement may also comprise at least one first primary over fire air port 20 and at least one first secondary over fire air port 22 provided to the first wall 4. The first secondary over fire air port 22 is arranged in vertical direction above the first primary over fire air port 20.
In the embodiment of
In the embodiment of
The over fire air arrangement may also comprise at least one first primary additional over fire air port 50 and at least one first secondary additional over fire air port 52. The at least one first secondary additional air port 52 is arranged in vertical direction above the at least one first primary additional air port 50.
The furnace of
It should be noted that in some embodiments of a grate furnace, the secondary and tertiary air ports 72, 73 and 74, 75 may be omitted and there is only primary air ports 72 and the over fire air arrangement.
This configuration of the over fire air arrangement may be utilized when there are at least one first primary over fire air port 20 and at least one first secondary over fire air port 22 provided to the first wall 4 and at least one second primary over fire air port 21 and at least one second secondary over fire air port 23 provided to the second wall 6. This enables increasing the height of the additional over fire air supply to the first and second oxygen lean over fire air areas 44, 46, as shown in
The first primary and secondary and second primary and secondary additional over fire air ports 50, 51, 52, 53 may be arranged such that both the first primary and secondary and second primary and secondary additional over fire air ports 50, 51, 52, 53 are in vertical direction above the first and second over fire air ports 20, 21, 22, 23 (not shown) or below the first and second secondary over fire air ports 22, 23, as in
The a fourth distance q between the first and second secondary additional air port 52, 53 and the first and second wall 4, 6, respectively, is smaller than or equal to one third of a third distance x between the a vertical centre line A-A′ of the furnace enclosure 2 and the first and second wall 4, 6, respectively. In an alternative embodiment the first and second secondary additional over fire air ports 52, 53 are arranged such that the fourth distance q between the first and second secondary additional air port 52, 53 and the first and second wall 4, 6, respectively, is smaller than 2.0 m, or preferably the first distance z is between 0.3-1.0 m.
In an alternative embodiment the both the first primary and secondary and second primary and secondary additional over fire air ports 50, 51, 52, 53 may be in vertical direction between the first and second primary over fire air ports 20, 21 and the first and second secondary over fire air ports 22, 23. In another alternative embodiment the first and second primary additional over fire air ports 50, 51 may be in vertical direction between the first and second primary over fire air ports 20, 21 and the first and second secondary over fire air ports 22, 23, and the first and second secondary additional over fire air ports 52, 53 are in vertical direction above the first and second secondary over fire air ports 22, 23.
When the over fire air arrangement comprises the first primary and secondary and second primary and secondary additional over fire air ports 50, 51, 52, 53, the momentum of the additional over fire air flows 62, 63 of the first and second secondary over fire air ports 52, 53 is lower than the momentum of the additional over fire air flows 60, 61 of the first and second secondary over fire air ports 50, 51, arranged below the first and second secondary over fire air ports 52, 53. Momentum means product of mass flow of the air and air velocity from the additional over fire air ports.
The present invention further provides a furnace 1 for combustion of fuels. The furnace comprises a bottom 3, first and second opposing walls 4, 6 extending in vertical direction from the bottom 3 and first and second opposing side walls 5, 7 between the first and second opposing walls 4, 6. The first and second opposing walls 4, 6 form together with the first and second opposing side walls 5, 7 a furnace enclosure 2. The furnace 1 further comprises a lower furnace 100 comprising
a) at least one primary combustion air supply port 71 and at least one secondary combustion air supply port 74, 73 in vertical direction above the at least one primary combustion air supply port 71 for providing staged combustion, the at least one primary combustion air supply port 71 and the at least one secondary combustion air supply port 74, 73 being arranged to the first wall 4 or the first and second wall 4, 6, or
b) at least one primary burner 14, 15 and at least one secondary burner 12, 13 in vertical direction above the at least one primary burner 14, 15 for providing staged combustion, the at least one primary burner 14, 15 and the at least one secondary burner 12, 13 being arranged to the first wall 4 or the first and second wall 4, 6.
The furnace 1 further comprises an the over fire arrangement according to present invention. The furnace 1 may be a bubbling fluidized bed furnace, a grate furnace or a pulverized fuel furnace, such as pulverized coal or peat furnace.
The present invention also provides a method for supplying over fire air into a furnace 1. The method comprises supplying a first over fire air flow 40 from the first wall 4 into the furnace 1 and supplying a first additional over fire air flow 60 from at least one of the first and second side walls 5, 7 in the vicinity of the first wall 4 and transversely to the first over fire air flow 40.
In an alternative embodiment the method further comprises supplying a second over fire air flow 41 from the second wall 6 into the furnace 1 and supplying a second additional over fire air flow 61 from at least one of the first and second side walls 5, 7 in the vicinity of the second wall 4 and transversely to the second over fire air flow 41.
The first and second additional over fire air flows 60, 61 may be supplied along the first and second walls 4, 6 respectively, and/or parallel the first and second walls 4, 6 respectively. In one embodiment the first and second additional over fire air flows 60, 61 may be supplied perpendicularly to the first and second over fire air flows 40, 41. In another embodiment the first and second additional over fire air flows 60, 61 from the first and second side walls 5, 7, respectively, at a first distance z from the first and second walls 4, 6, respectively. The first distance z is smaller than a second distance y between the first and second additional over fire air flows 60, 61 and a vertical centre line A-A′ of the furnace enclosure 2.
The method also comprises supplying 10-35%, preferably 20 to 35%, of total amount of over fire air with the first and second additional over fire air flows 60, 61.
It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20165555 | Jul 2016 | FI | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FI2017/050488 | 6/29/2017 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2018/002441 | 1/4/2018 | WO | A |
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| Entry |
|---|
| Office Action issued in China Appln. No. 201780047671.5 dated Dec. 23, 2019 (with translation). |
| International Search Report for PCT/FI2017/050488, dated Oct. 20, 2017, 4 pages. |
| Written Opinion of the ISA for PCT/FI2017/050488, dated Oct. 20, 2017, 6 pages. |
| Search Report for FI20165555, dated Jan. 19, 2017, 2 pages. |
| Office Action for FI20165555, dated Dec. 17, 2018, 6 pages. |
| Number | Date | Country | |
|---|---|---|---|
| 20190323705 A1 | Oct 2019 | US |
