US3765664A

US3765664A - Construction of heating surface of waste heat boiler for metal refining furnace

Info

Publication number: US3765664A
Application number: US00169910A
Authority: US
Inventors: M Ojima; R Otoyo; T Shiraishi
Original assignee: Kawasaki Heavy Industries Ltd
Current assignee: Kawasaki Heavy Industries Ltd; Kawasaki Motors Ltd
Priority date: 1971-08-09
Filing date: 1971-08-09
Publication date: 1973-10-16
Anticipated expiration: 1990-10-16

Abstract

A waste heat collecting water wall in which boiler tubes are placed close together to absorb the waste heat from a metal refining furnace in which filler rods fill the space between the adjacent tubes and provide a substantially flat wall on which dust collects and can easily be removed because there are no deep indentations in the wall surface in which the dust from the furnace can collect and the wall is sufficiently flexible so that collected dust can be removed by vibration and/or by rapidly moving air.

Description

United States Patent [191 Ojima et al.

[ CONSTRUCTION OF HEATING SURFACE OF WASTE HEAT BOILER FOR METAL REFINING FURNACE [75] Inventors: MasakiOjima, Akashi City;

Ryouichi Otoyo; Tomohiko Shiraishi,

both of Kobe City, all of Japan 73] Ass i gnee: Kawasaki Jukogyo Kabushiki Kaisha, Kobe, Japan [22 Filed: Aug. 9, 1971 T 21 Appl. No.: 169,910

[52] U.S. C1. 266/43, 266/35 [51] Int. Cl. C21c 5/46 [58] Field of Search 266/35, 31, 15, 16, 266/43; 122/6 A [56] References Cited UNITED STATES PATENTS 2,660,155 11/1953 Chapman 122/6 A 1,770,928 7/1930 .Iacobus 122/6 A 1,791,064 2/1931 Murray 122/6 A 2,552,830 5/1951 Witzke 122/6 A Oct. 16, 1973 3,303,876 2/1967 Berman et a1. 122/6 A 3,545,409 12/1970 Young 3,320,931 5/1967 Durham 3,323,495 6/1967 Blaskowski 3,380,728 4/1968 Baillie 266/35 FOREIGN PATENTS OR APPLICATIONS 1,041,452 9/1966 Great Britain 122/6 A 1,110,439 4/1968 Great Britain 122/6 A Primary Examiner-Gerald A. Dost Attorney-Milford A. Juten [5 7] ABSTRACT A waste heat collecting water wall in which boiler tubes are placed close together to absorb the waste heat from a metal refining furnace in which filler rods fill the space between the adjacent tubes and provide a substantially flat wall on which dust collects and can easily be removed because there are no deep indentations in the wall surface in which the dust from the furnace can collect and the wall is sufficiently flexible so that collected dust can be removed by vibration and/or by rapidly moving air.

1 Claim, 9 Drawing Figures Patented Oct. 16, 1973 3,765,664

FIE-2 H97 1i h 11 f1 {i ii 1 1-1) 7 "A GE @6965 NVENTOR.

CONSTRUCTION OF HEATING SURFACE OF WASTE HEAT BOILER FOR METAL REFINING FURNACE This invention is regarding to the construction of the heating surface of the waste heat boiler, to be installed following the refining furnace for iron or non-ferrous metal.

High temperature gas, coming out from the refining furnace such as smelter, converter and etc., generally contains considerable amount of dusts, but usually the furnace is provided with the waste heat boiler for the purpose both for gas cooling and heat recovery.

Such waste heat boiler is always designed to be consisted of the radiation heating surface (water wall) and the convection heating surface, so that at first molten dusts carried over from the furnace can be cooled down to be solidized, then brought into convection heating surface to prevent fouling of its surface.

But because often times removal of stuck dusts on the water wall is not satisfactory, the gas temperature of the convection heating surface inlet goes up over the solidizing temperature of dusts, that causes sticking and accumulation of dusts in considerable amount on the convection heating surface, and the drop of heat transfer coefficient makes a rise of boiler outlet gas temperature and draft loss through the boiler, eventually it necessiate to stop the boiler operation for cleaning, which makes the main cause of lowering of the overall plant operation rate.

For this, the mechanical cleanings by means of the soot blowers, the hammering equipments (method to remove stuck dusts by knocking from outside of the boiler) or the hand lancing, are often performed during the operation both in the radiation and convection heating surfaces.

However, on the conventional membrane type water wall after mentioned, such methods of cleaning are rather difficult to be performed satisfactorily. This invention is intended to faciliate the cleaning of stuck dusts on the water wall and maintaining the clean condition of the water wall, beside with many fabrication advantages.

This invention, on the basis of above-mentioned point, is to make almost flat surface at inner side of the water wall using special filler rods welded continuously to boiler tubes, or using tangentially arranged fin tubes, of which fin position is deviated to inner side of the water wall, welded continuously at the each fin end.

By means of the feature of these water wall structure, the defects of aftermentioned conventional water wall can be removed.

To make further explanations and to make clear of these points, the following drawings shall be referred:

FIG. 1 shows a part of section of the water wall, actually adopted under this invention.

FIG. 2 shows a part of section of the water wall, slightly modified of FIG. 1.

FIG. 3 shows a part of section of the water wall using fin tubes under this invention.

FIG. 4, 5 and 6 show a part of sections of the conventional water walls.

FIG. 7, 8 and 9 show a part of sections of the water walls in order to explain of this invention.

FIG. 4 shows the conventional tangential tube arranged water wall, insulated with skin refractory mate rial (a) and covered with skin casing (12), or continuously welded between each boiler tube.

If the molten carried over dusts touch on this water wall, the dusts become solid by rapid cooling, but the adhesive force of the dusts on the water wall is comparatively weak.

In this stage, the removal of the stuck dusts is rather easy. However, it is practically impossible to operate the dust removal equipments always all over the water wall.

In the case, some of the stuck dusts on the water wall stay for a while, the best conductivity of the dusts is normally very low, therefore the temperature of the stuck dusts surface rises very high.

The molten dusts coming out from the furnace are apt to stick on the stuck dusts surface due to its high temperature and finally all the surface of the water wall is covered with the stuck dust layer firmly.

Under such conditions, the mechanical cleaning as above mentioned becomes very difficult.

Even if the cleaning is possible to be carried out, the stuck dusts of the grooved space, shown by dotted lines on the boiler tubes, are very difficult to be removed and are apt to remain.

For example, in the case that the dusts blown off by the soot blower, it is not only almost impossible to remove the dusts of the grooved space by blowing in the direction of an arrow mark (R), crossing to the axis of the tube and almost parallel to the water wall surface, but also much power is necessary to crack or break off the stuck dusts by shearing.

So if the dusts remain at any small parts on the water wall as described above, the dust sticking starts from these parts and again the whole water wall is covered with the stuck dusts in a short period.

FIG. 5 shows a well known membrane type water wall comprised with continuously welded of the flat bar between boiler tubes.

FIG. 6 shows another well known membrane type water wall comprised with fin tubes, of which fin position is at the center of the tubes and continuously welded at the each fin end.

These conventional water walls have unevenness at the inner side surface of the water wall in cross direction to the axis of the tubes, therefore these both have defect that the stuck dusts of the grooved space shown by dotted lines on the tubes are difficult to be removed and are apt to remain.

In this invention, considering the defect of above mentioned conventional water walls, the water wall is constituted of inserting filler rods (12) shaped with a surface (b1) and (b2) as shown in FIG. 1, between each space of two adjoining tubes and welded both ends of the surface (b-l) and (b-2) to the adjoining surface of tubes, provided that the above mentioned surface (b-l) is a plane parallel and adjacent to the common contact plane of adjoining tubes and the above mentioned surface (b-2) is a narrow plane close to the straight line connecting the assumed centre of each adjoining tubes.

According to the construction of this invention, there is no grooved parts between the tubes of the water wall, which are shown by dotted lines in FIG. 4, 5 and 6, making nearly flat heating surface, so that the stuck dusts are easy to remove off and expose the whole water wall surface by mechanical cleaning, and there is no place liable to have the remnant dusts.

That is to say, in the case that the stuck dusts are blown off by a soot blower, its blowing direction is almost parallel to the water wall, the same effects of the stuck dusts removal are expected in spite of the blowing direction is parallel to the axis of the boiler tube or crossing to the same axis, and also there is less need to break off the stuck dusts by shearing.

Also, if the water wall is knocked from outside of the water wall shown an arrow mark (S) in FIG. 1 by a hammering equipment, the water wall deflects and vibrates in the vertical direction g-h to the water wall surface due to the elasticity of the water wall.

In the case that the stuck dusts are removed by means of acceleration of this vibration, it is evident that the removal of the stuck dusts is much easier if the water wall surface is almost flat.

Furthermore, if the deformation of the water wall is larger, some cracks take place in the stuck dusts and easier to remove the dusts.

As has been described, this structure of the water wall is easy to keep the water wall surface in clean conditiondue to easiness of removal of the stuck dusts and is difficult for carry over molten dusts sticks and accummulates.

The tube arrangement pitch (f), the distance (e) between common contact plane of the tubes and the filler rod surface (b-l) is decided considering the heat load, the gas temperature, the dust quantity,the dust components and etc.. If the operating conditions is severe, the value (e) will be nearly zero.

Here, as modified cases, are shown in FIG. 2 and 3.

FIG. 2 shows the case of which surface (b-l) of the filler rod is not flat plane but hollow arc surface, and FIG. 3 shows the case of which fins substitute the above mentioned filler rod.

Each fin end (fi) of the fin tube (a) is welded continuosuly.

Also, the construction of this invention has outstanding advantages in technical problem regarding to the thermal distortion at the time of welding of the tubes.

In the case of FIG. 1, if a filler rod (b) is placed between two tubes, the tube pitch can be definitely set and ensured, furthermore, the welding can be applied to the surface (b-2) close to the straight line between the centres of adjoining two tubes, then carry out the welding of the both ends of a surface (b-l).

This results gives greater rigidity by the previous welding of (b-2) and makes the welding distortion of (b-l) surface smaller at the time of welding, so subsequent correction is rather easy.

FIG. 7, 8 and 9 are similar to this construction examples but they have following defects:

FIG. 7 shows the water wall with boiler tubes (a) and continuosuly welded small rods (T).

FIG. 8 shows the water wall with boiler tubes (a) and continuously welded flat fins (f-b) of which fln position is deviated to the water wall inside from the tube centre.

In these structures, there is a probability to cause disorder in tube pitches, and also decision of the position of the rod and flat bar is difficult even after the tubes are properly arranged.

In the case of a rod, there is a limit to make it flat at the water wall inner side surface, and in the case of flat bar, when the heat load is high, the temperature of the flat bar also goes up and there is a danger of the dust sticking.

Furthermore, there is an enough worry to have the thermal distortion due to the welding heat.

FIG. 9 shows the water wall with boiler tubes (a) and continuously welded symmetrical filler rods (3).

In the case FIG. 9, there is a defect that the thermal distortion gets greater on account of the welding heat from the primary welding side.

Also in the case that heat applying side is limited to only one side such as water wall, it has disadvantage in the waste of the welding and materials, and still further disadvantage is that the effect of the hammering is reduced due to the more rigidity of the water wall.

This invention not only facilitates the cleaning the stuck dusts on the water wall, but also facilitates maintenance of the cleaned condition together with other fabrication advantages.

We claim:

1. A water wall heating surface for a waste heat boiler for waste heat from a metal refining furnace comprising a plurality of closely spaced substantially parallel tubes, long filler strips having a generally flat smooth surface extending between the tubes closely adjacent the heat and dust engaging surface of the tubes providing with the tubes a generally flat water wall, the generally flat surfaces of the strips being substantially spaced from the axis of the tubes and closely adjacent the heat and dust engaging surface of the tubes and being substantially tangent with the curvature of the tubes to increase the area of contact with the gases the strips being rods of generally triangular cross section and have arcurate surfaces corresponding to the 'arcuate surface of the tubes and abutting the tubes to obtain maximum heat transfer between the rods and tubes, and the rods being welded to the tubes at each dihedral angle thereof.

Claims

1. A water wall heating surface for a waste heat boiler for waste heat from a metal refining furnace comprising a plurality of closely spaced substantially parallel tubes, long filler strips having a generally flat smooth surface extending between the tubes closely adjacent the heat and dust engaging surface of the tubes providing with the tubes a generally flat water wall, the generally flat surfaces of the strips being substantially spaced from the axis of the tubes and closely adjacent the heat and dust engaging surface of the tubes and being substantially tangent with the curvature of the tubes to increase the area of contact with the gases the strips being rods of generally triangular cross section and have arcurate surfaces corresponding to the arcuate surface of the tubes and abutting the tubes to obtain maximum heat transfer between the rods and tubes, and the rods being welded to the tubes at each dihedral angle thereof.