Method for expanding a chemical recovery boiler

Abstract

In a boiler, a space is reserved to expand the boiler by increasing the front and rear walls. To expand the boiler, wall additions are added to increase the width of the front and rear walls. After the expansion, the distance between the front and rear walls is substantially the same distance between the front and rear walls before the expansion.

Claims

1. A method for expanding a chemical recovery boiler having a front wall, a rear wall and a pair of side walls between the front and rear walls, the method comprises: operating the chemical recovery boiler in a first capacity range wherein the front wall, the rear wall and the pair of sidewalls define a combustion zone and the pair of sidewalls is separated by a first distance and the front wall and the rear wall are separated by a third distance, wherein at least one of the front wall and rear wall includes a secondary air nozzle; positioning at least one sidewall such that the pair of sidewalls is separated by a second distance greater than the first distance; attaching the at least one sidewall to the front wall and the rear wall, wherein the pair of sidewalls is separated by a second distance greater than the first distance and the combustion zone has an increased volume due to the greater distance between the pair of sidewalls and wherein the front wall and the rear wall remains separated by the third distance after attaching the at least one sidewall; in cooperation with attaching the at least one sidewall to the front wall and the rear wall, increasing a width of the front wall and the rear wall such that the third distance between the front wall and the rear wall when the boiler operates in the first capacity range is substantially equal to the third distance between the front wall and the rear wall when the boiler operates at a capacity greater the first capacity range; adding at least one secondary air nozzle to at least one of the front wall and the rear wall, wherein the added secondary air nozzle is on a section of the front wall or rear wall added in conjunction with the increase of the width of the front wall and the rear wall, and after attaching the at least one sidewall, increasing the width of the front wall and the rear wall and adding the at least one secondary air nozzle, operating the chemical recovery boiler at the capacity greater than the first capacity range.

2. A method as in claim 1 wherein positioning the at least one sidewall includes moving the sidewall from a first position to a second position.

3. A method as in claim 1 wherein modifying the boiler includes providing additional air capacity by adding the secondary air nozzle and a tertiary air nozzle arranged on the added section of the front wall.

4. A method as in claim 1 wherein adding at least one air nozzle includes adding at least one tertiary air nozzle and at least one secondary air nozzle.

5. The method of claim 1 wherein the pair of sidewalls lack a secondary air nozzle before and after the extension of the front wall and the rear wall.

6. A method as in claim 1 further comprising adding at least one tertiary air nozzle to at least one of the front wall and the rear wall.

7. A method as in claim 6 wherein the added tertiary air nozzle is on a section of the front wall or rear wall added in modifying the boiler.

8. A method to expand a chemical recovery boiler having a front wall, a rear wall and a pair of side walls defining a combustion zone, the method comprises: operating the chemical recovery boiler in a first capacity range wherein the front wall, the rear wall and the pair of sidewalls define a combustion zone and the pair of sidewalls is separated by a first distance and the front wall and the rear wall are separated by a third distance, wherein at least one of the front wall and rear wall includes a secondary air nozzle; removing a sidewall of the pair of sidewalls from between the front wall and rear wall; positioning the removed sidewall a distance from the opposite sidewall greater than the first distance; extending the front wall and the rear wall; connecting the extended front wall and extended rear wall to the pair of the side walls after the positioning of the removed sidewall , wherein the extended front wall and the extended rear wall remain separated by the third distance after being connected to the pair of the side walls; adding at least one air nozzle to an extended portion of the front wall or the rear wall, and after the connection of the extended front wall and the extended rear wall to the pair of the side walls and after the addition of the at least one air nozzle, operating the chemical recovery boiler at a capacity greater than the first capacity range.

9. A method as in claim 8 wherein positioning the sidewall includes moving the sidewall from a first position to a second position.

10. A method as in claim 8 wherein extending the front wall and rear wall includes extending by substantially equal distances the front wall and the rear wall.

11. A method as in claim 8 wherein adding at least one air nozzle includes adding at least one tertiary air nozzle.

12. The method of claim 8 wherein the pair of sidewalls lack a secondary air nozzle before and after the extension of the front wall and the rear wall.

Description

(1) The present invention is described in more detail with reference to the appended figures, of which

(2) FIG. 1 illustrates schematically a typical chemical recovery boiler in side view, in connection with which boiler the present invention may be applied, and

(3) FIG. 2 illustrates a schematical cross-section of the bottom of the furnace according to the invention from an air level.

(4) FIG. 1 illustrates a chemical recovery boiler construction with a furnace 1 defined by water tube walls: front wall 2, sidewalls 3 and rear wall 4, and a bottom 5 also formed of water tubes. Combustion air is fed into the furnace from several different levels as primary, secondary and tertiary airs. There may be other air levels as well. Spent liquor, such as black liquor, is introduced via nozzles 6 between the secondary and tertiary air zones. In the combustion process, a melt bed from the effluent is formed on the bottom 5 of the furnace, wherefrom the melt is discharged via a melt spout 7 fitted in the bottom of the furnace.

(5) Heat recovery surfaces of the boiler, i.e. superheaters 8, are located above the furnace, and the rear wall 4 side of the furnace accommodates the heat surfaces following the superheaters above the furnace, the boiler bank 9 and the economizers 10, wherein the heat of the flue gas generated in the furnace is recovered in form of steam. In the superheaters the saturated steam is converted to a higher-temperature steam. On the boiler banks 9 of the boiler the water in a saturated temperature is boiled partly into steam and in the feed water preheaters 10 the water is heated by means of flue gas prior to leading the water into the vaporizing part 9 of the boiler and into the superheating parts 8. The so-called nose is shown with reference numeral 14.

(6) The water/steam circulation of the boiler is effected by means of natural circulation, whereby the water/steam mixture generated in the water tubes of the boiler walls and bottom flows upwards via collection tubes into a steam drum 11 arranged crosswise in relation to the boiler, i.e. in the direction of the front wall 2. Hot water flows from the steam drum via drain tubes 12 into the bottom manifold 13, wherefrom the water is distributed into the bottom water tubes and further into the water tube walls.

(7) FIG. 2 illustrates the enlargement zone reserved in the boiler for the relocation of one sidewall 3 when an enlargement to the boiler is desired. The sidewall is moved to the extent of the length of the elongation 2a, 4a of the front/rear wall. FIG. 2 further shows schematically air jets 15 via air ports 16, the number of air jets in this arrangement comprising with a lower boiler capacity two jets on the rear wall 4 and three jets on the front wall 2. The required additional air is received into the enlargement by arranging more air ports 16a and via them air jets 15a in the elongation 2a, 4a of the front and rear wall. During the enlargement, there is no need to change the operation of the existing air ports and the air jets flowing therethrough.

(8) The measures connected to the boiler enlargement are as such known to a person skilled in the art, and thus have not been more widely described in this connection.

(9) Though the present invention has been described in the connection, which at present is considered the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the presented embodiment, but in the opposite it is intended to cover various modifications and corresponding arrangements in the spirit and scope of the appended claims. For example, the application of the invention is not limited to a certain air arrangement, although the advantages of the invention become especially obvious when the main portion of the air on certain levels is fed in via the front and rear wall.