US3550918A - Heat regenerator,particularly a regenerative air preheater for a blast furnace - Google Patents

Description

United States Patent [72] Inventor Jacobus Van Laar ABSTRACT: A regenerative heater such as for preheating air Santpoort, Netherlands to be fed to a blast furnace, having a brick-lined single vertical 211 Appl. No. 841,663 he lamima amen? s de viaa tqatsssr rstirs we" [22] Filed Aug. 5, 1969 therein, a burner stack and a regenerating chamber filled with [45] Patented Dec. 29, 1970 checkerwork, with an insulating layer and a vertical slide joint [73] Assignee Koninklijke Nederlandsche l-loogovens En in the separating wall, is provided, separately and in various Staalfabrieken N. V. combinations, with: (l) a sliding joint in the shell wall of the ljmuiden, Netherlands burner stack; (2) a location of the heat insulating layer at the [32] Priority Aug. 9, 1968 side of the sliding joint remote from the burner stack; (3) an [33] Netherlands extension of the heat insulating layer entirely around the [31] No. 6811373 burner stack at the side of the sliding joint remote from the burner stack; (4) an extension of the heat insulating layer at least over the lower half ofthe height of the burner stack; (5) HEAT REGENERATOR, PARTICULARLY A a sliding joint of a width which is exactly closed in the hot con- REGENERATIVE AIR PREHEATER FOR A BLAST dition of the heater; (6) an extension of the bricks on the outer FURNACE side of the separating wall into a recess in the inner brick 11 claimsi3nl'awingfigslayers of the shell with a sliding joint therebetween; (7) a 52 us. c1 263/19 metal Plate the dividing wall Outside the insulating layers; [51] Int Cl n F23 15/02 (8) a metal plate in such location of heat resistant metal con- 50 Field ofSearch 263/19,5I; mining silicon, chromium and molybdemum; (9) an inner- HO/(CMSOIY) most layer of tire brick extending continuously around substantially the lower half of the burner stack, itself uninter- [56] Referen e Cited rupted by any sliding joint and separated from the next layer UNITED STATES PATENTS by a continuous slidingljgint; (10) a division of said next layer into two portions by si ing joints where the separating wall meets the shell; (1 a dome covering the shell and resting on 2,420,373 5/1947 H0 beg... 263/19 only thelayers of the shell outside said sliding joints; and (12) 3'l20380 2/1964 f fg 'g 263/19 a ceramic burner In the burner stack with the sliding joint in the shell extending down to the burner, and the sliding joint in Primary Examiner-Edward G. Favors the separating wall extending downwardly past the top of the Attorney-Hall and Houghton burner.

(Ill t. 7* r 1 II II 12 20 HEAT REGENERATOR, PARTICULARLY A REGENERATIVE AIR PREHEATER FOR-A BLAST FURNACE This invention relates to a regenerative heater, in particular to an air preheater for preheating the air to be fed to a blast furnace, being of the type having within a single vertical shell covered interiorly by bricks, a flame funnel or burner stack and a space filled with piles of heat absorbing refractory bricks, in which a heat insulating layer is provided in aseparating wall between the burner stack and the piled bricks, the brick work showing vertical sliding joints where the bricks to both sides of the vertical joint face are allowed to move, slide, expand and contract with respect to the bricks at the other side of the joint.

Heat regenerators are known in several fields of engineering for regenerating heat or combustible components liberated in some process.

One of the best known applications of such heat regeneration is the application of air preheaters (Cowpers) for preheating the air to be fed to a blast furnace.

Therein the energy present or remaining in for instance coke oven gas or blast furnace gas isturned to heat by burning in the burner stack, of such a preheater this heat being accumulated in the piled refractory bricks leaving spaces between them allowing the gas to pass through said space with piled bricks. In a following phase of operation air for combustion in .the blast furnace is preheated by feeding it through the heated the highest possibletemperatures of the preheated air. It will be clear in this respect that such a high airpreheating temperature is a necessity for the economy of the blast furnace process, instead of only ameans to apply the remaining energy in the blast furnace gas to advantage. In fact other fuels are also used quite often in practice for heating such a heat regenerator, such as natural gas or oil. However, for such higher temperatures the serious problem arises that the temperature of the air preheater is restricted by the danger of cracking, bending and crushing or pulverizing of parts of the interior masonry as a result of high thermal stresses in the structure. Particularly for air preheaters of the type with a burner stack within the same outer shell as the piled bricks the thermal stresses could become very high as a result of con: siderable differences in temperature over short distances, particularly transverse distances.

The separating wall between the burner stack and the piled bricks is, particularly in the lower part of the regenerator, heated to temperatures which vary considerably between the burner stack side and the other side of said wall, where the space for the piled bricks is. Thus this wall has the tendency to take up a curved. position, concavely with respect to the burner stack. This could easily bring on the formation of 'cracks in the separating wall itself andin the zones where this wall contacts the masonry on the inner side of the outer shell of the preheater.

Moreover the shell itself with its inner masonry will be subject to mutually different thermal expansions at the side of the burner stack and at the parts surrounding the piles of heat absorbing bricks, which cannot only cause cracks between these parts of the shell masonry, but also between the shell and its masonry on the one hand and the dome resting thereon on the other hand and between the shell and its masonry on the one hand and the separating wall on the other hand. Such cracks and deformations could in their turn destroy the piles of refractory heat absorbing bricks and could cause a short circuiting of gases and air through the separating wall. The above considerations are the main reasons for the fact that with regenerative air preheaters with an interior burner stack as indicated above it was not possible to realize air temperatures of preheating higher than l,l C. for larger plants and than l,200 C. for smaller, less efficient plants.

However, at present air preheating temperatures of l,300

- C. to 1,500" C. are considered necessary for an efficient blast .nace increases. For this reason the aim atpresent is to obtain;

furnace operation with large air preheaters. This means that the structure should be resistant against temperatures in the dome of the air preheater up to about l,700 C.

It is remarked that it is possible to obtain such high temperatures in regenerative air preheaters if they are made of a different structure. This is possible if such preheaters in known manner, have a burner stack outside the outer shell surrounding the piles of heat absorbing bricks. Such a exterior burner stack is in such structures connected to the cylinder contain ing the piles of bricks by a special design of the dome structure. Thus such air preheaters with exterior burner stack solve the problems in essence, as seen from anengineering point of view, but they require very much higher capital costs than an air preheater with an interior burner stack, so that in total exploitation they are not substantially more profitable than regenerative air preheaters with interior burner stack and lower air preheating temperatures. Moreover, such air preheaters with exterior burner stack require much more, space than air preheaters with interior burner stack.

It is a purpose of the present invention to'obtain an air preheater with an interior burnerv stack, which is in its technological possibilities as favourable and reliable as the described air preheaters with exterior burner stack'while avoiding the very much higher costs of said latter type of air preheater, and v without underlying the described disadvantages of damage to the structure by thermal expansions etc.

It is remarked here that it was tried before to avoid damage to the structure of regenerative air preheaters with interior burner stack for high air'preheating temperatures. Thus it was tried for a regenerator as given in the preamble of this specification Ito apply a heat insulating layer in the separatingwall. Also experiments were made with vertical dilatation (sliding) joints, along which the bricks to both sides could move differently. It was assumed when designing such structures that the insulating layer in the separating wall could prevent that the piled heat absorbing bricks neighboring the separating wall would be heated to, a too-high temperature. Moreover it was assumed that the dilatation joints could take up the shear in the masonry sufficiently. g

- However, all these former attempts did not lead to sufficient success, so that up to now .the air preheaters with interior burner stack are never suited for high air preheating temperatures up to l,500 C. t

According to the invention a good result is obtained in that v in a regenerative heater as given in the preamble of this than one layer of bricks, at least in the cold condition of the regenerator, are separated by a vertical sliding dilatation joint from the remainder of the masonry of the shell and of the separating wall, and that the said heat insulating layer is provided at that side of the sliding joint which is farthest away from the burner stack.

Thanks to the sliding joint extending all around the burner stack it is possible that the inner layers of the wall of the stack, which have the highest temperature difference with the remainder of the structure, can show thermal expansions, quite independently upon the remainder of the structure. This is, however, only possible as a result of the presence of the insulating layer at the outer side of the sliding joint in the separating wall. This insulating layer ensures that the layers of the separatingwall to both sides of the sliding joint each are about homogeneous in temperature in any of the cross sections through said layer. Thus the separating wall as a whole and the several brick layers therein do not have the tendency to warping, bending or curving.

It is preferred that the insulating layer according to the invention extends entirely around the burner stack at the side of the sliding joint remote from the interior of the burner stack, and that said insulating layer extends at least over the lower half of the height of the burner stack.

, Thus it is obtained that also the outer layers of the shell with its masonry, in the region of the burner stack, in the average differ only very little in temperature from the remainder of the shell masonry and from the layers of the separating wall at the side bordering the space containing the piles of heat absorbing bricks. This prevents cracking in the shell masonry and in the separating wall in the region of the transition between the burner stack and the piles of heat absorbing bricks. Moreover this entrains that the upper edge of the shell both in cold and in hot condition maintains a substantially horizontal position, so that there are no thermal stresses between the shell and the dome.

A further advantage of the fact that the separating wall and theshell remain straight without curving, consists in the fact that it is now possible to calculate the shape of the structure in hot condition exactly, starting from the shape in cold condition.

According to the invention this could be applied to ad vantage in that the width of the sliding joint and the heat expansion characteristics of the materials used for the several layers can be chosen so that said sliding joint is exactly closed inthe hot condition of the eater.

This gives a very elegant method to obtain a structure, which does not show cracks and which in operation in gastight. According to the invention it is even possible to improve this further by having the brick layers outside the sliding joint in the separating wall extend into a recess in the inner brick layers layers of the shell masonry and are separated therefrom by a second sliding joint. The lower half of the separating wall in the burner stack is subjected to the highest loads by the flames, while by the high difference in temperature across the separating wall in said zone the danger of cracking and leakage of gas is highest in said zone. Thus it is according to the invention preferable, in order to keep the separating wall gastight also after a long period of operation, to apply a metal plate in at least the lower half of the separating wall at that side of the insulating layer which is directed towards the piles of heat absorbing bricks, said metal plate preferably consisting of a heat-resistant steel containing sil-,

icon, chromium and molybdenum.

Among others in view of the fact stated above that in the lower part of the burner stack the highest loads by the flames occur in the wall of the burner stack, in combination with greater differences in temperature in different places across the thickness of the walls, it is desirable to take additional measures in said zone to adapt mutually the thermal dilatations of several wall parts.

In this respect it is according to the invention preferable that the innermost layer of the layers present at the inside of the first sliding joint extend as a continuous layer without any sliding joint all around the burner stack over substantially the lower half of the burner stack, that this layer is separated from the remainder of the layers present at the inside of the first sliding joint by a third continuous sliding joint all around and that this remainder is divided into two shells by sliding joints present in the zones where the separating wall merges into the shell masonry.

it is described above in what manner the inner part of the burner stack wall could become longer upwardly with respect to parts of this wall more to the outside. Thus it is according to the invention preferable to have the dome rest only on those layers of the shell masonry, which are outside the sliding joints.

It is remarked that this structure does not bring on the danger of cracks, contrary to a direct merging of the dome masonry into the masonry of the shell as in the known air preheaters, where the dome masonry rests on the masonry of the shell. It has been suggested in the prior art to solve-this problem in another way, namely to support the dome separately from the shell with dome parts protruding outside the shell, resting on a separate supporting structure, which was not very attractive from a structural point of view and entrained high costs for the external supporting structure. In

such structures the shell could move vertically somewhat with respect to the dome. Such structural complications can be avoided when applying the present invention. I

The best results are obtained with regenerative heaters according to this invention when applying a so-called ceramic burner in the lower part of the burner stack. Such ceramic burners are known as such. If they are used together with the invention it is preferable to have the first sliding joint in the shell masonry extend downwards to the burner and in the separating wall extend downwardly past the top ofthe burner.

This invention will now be explained-inmore detail with reference to the enclosed drawings which give a preferable embodiment ofa regenerative air preheatenfor preheating the air for a blast furnace, according to this invention, without, however, limiting the scope ofthe invention.

In said drawings:

FIG. 1 gives a vertical cross section through said preheater;

FIG. 2 gives one half of a partial cross section on an new larged scale along the line II-ll in FIG. 1 on an enlarged scale;

FIG. 3 shows the detail in circle Ill from FIG. 1 on an enlarged scale.

In FIG. 1 the reference numeral 1 indicates the shell of the air preheater, forming together with the bottom 2, on which it rests, a unitary structure of masonry. The masonry of the shell is surrounded by a steel jacket 27 (FIG. 2). A number .of

columns 3 protruding upwardly from the bottom 2, support a grid 4 serving to support piles of perforated bricks for heat absorption, which bricks are not shown and between which piles alternatively hot combustion gases flow downwardly and air to be preheated flows upwardly. This piled brickwork is separated by a separating wall 5 from the burner stack, which in its turn is limited or bordered by a segment of shell 1. The air preheater at the upper end is closed by a dome 6 of refractory bricks and by a steel dome 7.

Gaseous fuel and air required to generate the hot combustion gases necessary for heating the heat absorbing bricks are supplied by passage 8 and annular duct 9 respectively towards burner 10. This burner, a so-called ceramic burner, has been shown only diagrammatically in FIG. 1, but such burners are known as such and this burner is not essential for understanding the invention.

Above the burner 10 fuel and air are mixed intimately and fuel is burnt in the burner stack. The hot combustion gases are guide over the top of the separating wall 5 to and through the space within the dome and then downwardly through the piles of heat absorbing bricks and they leave the preheater at the bottom through one or more openings not shown in the shell 1. After these bricks have been heated sufficiently the supply 8, 9 of fuel and combustion air are closed and air to be preheated is fed by opening 11 in the opposite direction through the device, said air leaving the regenerator through port 12.

In the upper part of the shell 1 there is an interiorly protruding supporting edge 13 in the brickwork thereof, the dome 6 resting on said edge 13.

As is seen in FIG. 1 and, on an enlarged scale, also in FIG. 2, a sliding joint 14 extends from the upper part of shell 1 through the segment of this shell, which is defined by the separating wall 5, down to a zone close to the upper surface of burner 10.

A sliding joint 15 (vide also FIG. 3) extends from the upper edge of the separating wall 5 along the whole width thereof, down to a position somewhat below burner 10. Sliding joints 14 and 15 form a continuous slot extending all around the burner stack. If the part 17, 18 of the burner stack wall within said continuous slot increases in length by the heat, this part is able to displace freely with respect to the dome 6 and with respect to the remainder l6, 19 of the shell 1 and of the separating wall 5. 1

In order to make the outer layer 19 of separating wall 5 sufficiently strong and gastight, it is coated at the inner (concave) side of its curvature with a set of steel plates 20. These plates 20 consist of a heat-resistant steel which contains silicon, chromium and molybdenum.

lnorder to keep the average temperature of shell part 16 and separating wall part 19 as nearly as possible equal to the average temperature of the part of shell 1 surrounding the piles of heat absorbing bricks, shell part 16 and separating wall part 19 are, at the convex sides of the sliding joints l4and 15, covered or coated with layers of heat insulating material 22 and 23.

The layer 22 extends from a position near to the burner up to a position at or nearly at the upper edge of the shell. The layer 23 extends from a position shortly below the upper part of the burner to about three-fourths of the height of the separating wall 5. A sliding joint prevents the occurence of stresses between the burner stack wall parts 17 and 18 if these parts would undergo different thermal expansions.

Corresponding considerations have brought on that a sliding joint 26 is left open between separating wall part 19 and, shell 1.

Along the lower half of the burner stack the wall thereof is provided with an additional protecting wall 21 (FIG. 2 and 3). This in its turn is arranged freely with re'spectto the remainder j of the stack wall, thanks to the presence of a continuous sliding joint 24 extending all around the burner stack.

The wall 21 protects the burner stack additionally in the zone where the influence of the flames on the wall of the burner stack is highest.

With the described structure of the air preheater it is possible to apply operating temperatures in the dome up to l,700 C. Curving or bending of the separating wall, cracks in the masonry or the occurence of other known harmful phenomena due to too high thermal loads 6tC.0f the device did not occur in practice.

As insulating material known refractory bricks could be used, which, as is known to the expert, are much'more porous than the normal refractory bricks used in such structures and not intended for insulating purposes.

if in this specification and in the attachedclaims reference is made to a burner stack the assumption is made when speaking about the height thereof that this is the part of the space between separating wall and shell, whichextends above the burnerlO.

The invention could also be applied with known burners positioned outside the shell 1 and connected to an opening like8inFlG. l. j

The term checkerwork is'u sed herein in its conventional meaning in the field of metallurgy, i.e. to designate the piles of heat absorbing bricks, which may constitute a structure of fire bricks so built up that the bricks alternate with open spaces, permitting the passage of heated gases.

lclaim:

1. A regenerative heater of the type employed, for preheating air to be fed to a blast furnace, said heater being of the type which comprises: a single vertical shell covered internally with refractory brick work, wall means separating the space within said brick work into a burner stack and a space filled with checkerwork, means establishing communication between the upperends of said stack and space, openings through said shell communicating with the lower ends of said stack and space; said separating wall means comprising a vertical sliding joint between layers of brick, whereby the bricks on one side of the vertical sliding joint may move, slide, expand, and contract with respect to those on the other side of the joint, and, said separating wall means also comprising a heat insulating layer therein, characterized in that: over at least the upperhalf of the burner stack both the masonry of the shell and that of the separating wall means comprise layers closest to the burner stack which, at least in the cold condition of the regenerator, are separated by a vertical sliding dilation joint from the remainder of the masonry of the shell and of the wall means, and in that said heat insulating layer is located at that side of the sliding joint which is furthest away from the burner stack.

2. A heater according to claim 1, further characterized in that: the width of the vertical sliding joint is so related to the furthest away from the burner stack, and in that said insulating layer extends at least over the lower half of the height of the burner stack.

4. A heater according to claim 1, further characterized in that: the insulating layer extends entirely around the burner stack at the side of the sliding joint in the masonry of the shell and in the masonry of the separating wall means which is furthest away from the burner stack, and in that said insulating layer extends at least over the lower half of the height of the burner stack.

5. A- heater according to claim 4, further characterized in that: a metal plate is located in at least the lower half of the separating wall at that side of the insulating layer which is directed toward the checkerwork.

6. A heater according to claim 5, further characterized in that: said metal plate consists of a heat resistant metal containing silicon, chromium and molybdenum.

7. A heater according to claim 1, further characterized in that: the bricks on the outer side of the vertical sliding joint in said separating wall means extend into a recess in the inner brick layers of the masonry of the shell and are separated therefrom by a second sliding joint.

.layer, while the said remainder of the layers present at the inner side of said vertical sliding joint is divided into two portions by sliding joints present in the regions where the separating wall merges into the shell masonry.

9 A heater according to claim 1, further characterized in that: the means (c comprises a dome covering the shell, and in that said dome rests on only the layers of the shell outside said sliding joints.

10. A heater according to claim 1, further characterized in that: a so-called ceramic burner is positioned in the lower part of the burner stack, and in that the sliding joint in the shell extends down to the burner, and the sliding joint in the separating wall means extends downwardly past the top of the burner.

11. A heater according to claim 1, further characterized in that: the bricks on the outer side of the vertical sliding joint in saidseparating wall means extend into a recess in the inner brick layers of the masonary of the shell and are separated therefrom by a second sliding joint, a metal plate is located in at least the lower half of the separating wall at that side of the insulating layer which is directed toward the checkerwork,

said metal plate consists of a heat resistant metal containing silicon, chromium and molybdenum, the innermost layer of the layers present at the inside of said vertical sliding joint, extends as a continuous layer uninterrupted by any sliding joint all around the burner stack over substantially the lower half of the burner stack, said innermost layer is separated from the remainder of the layers present at the inner side of said vertical sliding joint by another continuous sliding joint all around said innermost layer, the said remainder of the layers present at the inner side of said vertical sliding joint is divided into two portions by sliding joints present in the regions where the separating wall mergesinto the shell masonry, the means (c) comprises a dome covering the shell, said dome rests on only the layers of the shell outside said sliding joints, a so-called ceramic burner is positioned in the lower part of the burner stack, the sliding joint in the shell extends down to the burner,

of the height of the burner stack, and the width of a sliding joint proximate to the said separating wall is so related tothe heat expansion characteristics of the materials used for the several layers that said sliding joint is exactly closed in the hot condition of the heater.

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