Patent Application
20070295249
In the following, the invention will be described in more detail with reference to the appended drawings, in which
In order to burn the liquor so that the resulting flue gases contain as little nitrogen oxides as possible, combustion air is fed into the furnace from nozzles placed at several different levels with respect to the height of the furnace. Primary air nozzles 4 are placed closest to the bottom of the furnace, at a distance from it. Secondary air nozzles 5 are placed above the primary air nozzles 4 but still below the liquor nozzles 6a and 6b in the height direction of the furnace. As can be seen from the figure, the secondary air 5 is divided into two parts to be fed from different levels into the furnace 2. Part of the secondary air is fed into the furnace 2 via so-called lower secondary air nozzles 5a, and the rest is fed into the furnace 2 via upper secondary air nozzles 5b. Above the secondary air nozzles 5, liquor nozzles 6a and 6b are provided for feeding liquor into the furnace. Above the liquor nozzles, tertiary air nozzles 7 are provided for feeding tertiary air into the furnace. Above the tertiary air nozzles, quaternary air nozzles 8 are provided for feeding quaternary air into the furnace.
By feeding the combustion air from different levels into the furnace 2, different combustion zones are formed in the furnace, whereby the quantity of combustion air to be fed into them can be adjusted. Approximately at the level of the primary air nozzles 4 there is a reducing zone A with substoichiometric, reducing conditions. Into this zone, air is fed from the primary air nozzles 4. The combustion of coke formed of liquor takes place here. Approximately at the level of the secondary air nozzles 5, or slightly above them but still underneath the liquor nozzles 6a and 6b, there is a combustion zone B where the air coefficient is slightly greater than 1. The purpose of this zone is to secure the complete combustion of the liquor. Air is fed from the secondary air nozzles 5 into the combustion zone B.
Approximately at the level of the tertiary air nozzles 7 or slightly above them there is an afterburning zone C with substoichiometric, reducing conditions. Combustion air is fed from the tertiary air nozzles 7 into the afterburning zone C. Uppermost in the furnace 2 there is a burning-out zone D which is placed approximately at the level of the quaternary air nozzles 8 or above them. Combustion air is fed from the quaternary air nozzles 8 into the burning-out zone. The zone D has an air coefficient well above 1, and its purpose is the afterburning of pyrolysis gases still left in the furnace by means of excess air.
Black liquor is fed into the furnace from one level so that two combustion zones are generated. The first and second liquor nozzles 6a and 6b are provided between the secondary air nozzles 5 and the tertiary air nozzles 7. The liquor nozzles 6a and 6b are placed substantially on the same level with respect to the height of the furnace. There are two different types of liquor nozzles, producing liquor droplets of different sizes. The larger liquor droplets fed from the first liquor nozzles 6a fly downwards, and the liquor and the pyrolysis gases formed thereof are burnt in the reducing zone A and the combustion zone B prevailing underneath the liquor nozzles 6a and 6b.
The second nozzles 6b produce a liquor jet consisting of liquor droplets that are are substantially smaller than the liquor droplets generated by the first nozzles 6a. The liquor droplets generated by the second liquor nozzles 6b and the pyrolysis gases formed of them are burnt in the afterburning zone C and the burning-out zone D prevailing at the level of the liquor nozzles and higher than them.
The first liquor nozzles may be spoon-shaped nozzles that are commonly used and which generate liquor droplets in the size of some millimetres. The aim is that the formed droplets fall downwards, dry on their way down and are burnt as low down as possible in the furnace.
The second liquor nozzles are nozzles which are capable of generating substantially smaller liquor droplets than the first liquor nozzles. The size of the liquor droplets is some hundreds of microns. The droplet size is adjusted such that the liquor to be fed from the second nozzles forms a “liquor cloud” in the centre of the boiler, at the level of the liquor nozzles or slightly above them. However, the droplet size is adjusted to be so large that the droplets travel to the centre of the cross-sectional area of the boiler. A carrier gas can be utilized for feeding the liquor. The second liquor nozzles may be, for example, nozzles provided with a carrier gas channel surrounding the liquor channel in the nozzle and thereby forming a curtain of gas around the liquor. The carrier gas improves the penetrability of the liquor in the centre of the furnace and prevents the formation of a liquor cloud in the vicinity of the walls of the furnace.
If necessary, the liquor to be fed from the second nozzles can be heated or treated to make the formation of small droplets easier. However, the liquor to be fed from the nozzles is the same liquor as the liquor fed from the first nozzles.
The first and the second liquor nozzles can be arranged in different ways to the walls 9 of the furnace.
The invention is not intended to be limited to the embodiments presented as examples above, but the invention is intended to be applied widely within the scope of the inventive idea as defined in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20065429 | Jun 2006 | FI | national |
