Regenerative heater

The regenerative heater comprises the brickwork of the walls and checker of refractory materials with different coefficients of linear expansion enclosed within a jacket also included are superimposed horizontal sections corresponding to the distribution of the internal operating temperatures. Each of the horizontal sections consists of a homogeneous refractory material. Arranged between the horizontal sections are transition sections, each consisting of the refractory materials of the contiguous sections, the materials being uniformly distributed in each course and superimposed so that the content of the material in one of the contiguous section gradually diminishes from course to course toward the other section.

FIELD OF THE INVENTION 
The present invention relates to heaters and, in particular, to 
regenerative heaters. 
The present invention can also be utilized in heat exchangers in which 
gases are conducted through the open brickwork of regenerative chambers. 
This permits the brickwork to heat. Then, another gas is passed through 
the brickwork to raise the gas temperature due to its contact with the 
heated bricks. 
The present invention is of particular advantage in ironmaking for heating 
the blast. Therefore it will be described in terms of this specific 
embodiment. However, it is not intended that the invention be limited to 
the disclosed embodiment. 
DESCRIPTION OF THE PRIOR ART 
The heaters in the category of high-temperature hot air stoves for blast 
furnaces are well known in ironmaking. These heaters comprise, a wall and 
checker brickwork of refractory materials having different coefficients of 
linear expansion. The wall and checker brickwork are encased within a 
jacket. Also included are superimposed horizontal sections corresponding 
to the distribution of internal operating temperatures of the regenerative 
heater, each of the sections consisting of a homogeneous refractory 
material. 
The checkers of commonly used regenerative heaters are made of bricks in 
such a way that vertical channels are formed throughout the entire height 
of the checkers. 
The cycle of blast heating in the regenerative heaters consists of two 
stages. During the first stage a mixture of gas with air is burnt and the 
hot combustion products are conducted through the checkers chamber, 
thereby heating the brickwork to a high temperature. During the second 
stage, in order to heat the air the required temperature, it is passed 
through the heated checker brickwork. 
In conventional regenerative heaters the temperature under the dome reaches 
1600.degree. C. and the temperature gradient in hot blast heating is of 
the order of 150.degree. C. in the upper zones and of the order of 
300.degree. C. in the lower zones. In accordance with the distribution of 
the internal operating temperature by zones, the brickwork of the walls 
and checker in conventional heaters is made of various refractories, such 
as dinas brick, high-alumina and fireclay materials. Thus, in the 
high-temperature zone the brickwork is made of hard-burnt high-strength 
dinas brick, whereas in the lower zones, relatively low temperature 
kaolin, high-alumina and fireclay refractories are used. Thus, in each 
temperature zone characterized by a certain temperature range, the 
horizontal section is made from the refractory best suitable by its 
strength characteristics for the operating conditions of the given zone. 
In heating, the contiguous areas of the horizontal sections develop 
relative radial shifts of the brickwork due to the difference in the 
coefficients of linear expansion of the refractories. For example, for 
dinas brick the coefficient of linear expansion is on the average 
12.multidot.10.sup.-6 1/deg, and for kaolin refractories it is 
6.multidot.10.sup.-6 1/deg. When heating to 1000.degree. C. brickwork of a 
radius of 500 cm there is a relative shift of the contiguous horizontal 
section .DELTA.R = .alpha..sub.1 TR - .alpha..sub.2 TR, in which 
.alpha..sub.1 = coefficient of linear expansion of dinas brick 
.alpha..sub.2 = coefficient of linear expansion of kaolin refractories 
T = temperature in the area of conjugation of horizontal sections 
R = average brickwork radius, 
which is about 20-30 mm. 
As a result of such shift the peripheral flues of a 40 mm diameter in the 
checker brickwork in the plane of conjugation of the horizontal sections 
will be overlapped up to 50-75%, and on the average in the brickwork 
section by 30-40%, which will cause a respective loss of efficiency of the 
regenerative heater, and hence, of the blast furnace. 
The relative shift of the brickwork in the areas of conjugation of the 
horizontal sections increases in direct proportion to the increase in the 
brickwork diameter and heating temperature. 
The contemporary stage of blast furnace construction is characterized by a 
substantial increase in the volume of blast furnaces (up to 5000 m.sup.3) 
and hot blast temperature above 1400.degree. C. The dimensions of heaters 
increase to 14 m in diameter and 50 m in height, while dome heating 
increases to 1600.degree. C. All this entails the need to employ new 
materials possessing higher refractories, whose coefficient of linear 
expansion significantly differs from that of commonly used refractory 
materials. Thus, the danger of reduction in the efficiency of modern large 
heaters for the above reasons considerably increases. 
SUMMARY OF THE INVENTION 
The principal object of the present invention is to provide a regenerative 
heater with an arrangement of the brickwork of the walls and checkers that 
would substantially reduce radial shifts between conjugated horizontal 
sections. 
Another object of the invention is to provide a regenerative heater with a 
substantially constant clear opening of the vertical gas flues. 
Still another object of the invention is to provide a regenerative heater 
with increased supporting power of the brickwork of the walls and 
checkers. 
A further object of the invention is to provide a regenerative heater with 
uniform distribution of tensile and compression strains caused by 
alternate heating and cooling. 
These and other objects are attained in a regenerative heater comprising a 
wall and checker brickwork of refractory materials having different 
coefficients of linear expansion. The wall and checker brickwork are 
encased within a jacket. Also included are superimposed horizontal 
sections corresponding to the distribution of internal operating 
temperatures of the regenerative heater. Each of the sections consists of 
a homogeneous refractory material. According to the invention, between the 
horizontal sections there are transition sections, each being formed by at 
least one course of refractory materials of contiguous horizontal 
sections, the material of one section being uniformly distributed within 
that of the other section. 
Such a construction of the regnerative heater is considerably less 
susceptible to radial shifts in each course between the contiguous 
horizontal sections, due to which the clear opening of the vertical flues 
changes less, which, in turn, makes it possible to increase the efficiency 
of the heaters, and hence, the furnaces they serve. Additionally, the 
uniform distribution of refractories of two contiguous horizontal sections 
in each course of the walls and checker provides a uniform distribution of 
strains over the entire cross-sectional area of the transition section and 
for a smaller specific shift of the courses. The reduction in the shift 
between the horizontal sections also contributes to the strength of the 
brickwork of the walls and checker, since the refractory materials will be 
characterized by a longer service life and the strained state of the 
jacket of the regenerative heater will be improved in the areas of 
conjugation of the horizontal sections. 
It is especially advantageous to lay each transition section of several 
courses of both contiguous horizontal sections with a gradual reduction 
therein of the refractory material of one horizontal section towards the 
other, which will contribute to smoothing the profile of the gas flues, 
i.e., to equalizing the clear opening of the flues throughout the entire 
height of each transition section. 
It has been established that the optimum height of the transition section 
of the regenerative heater is about 0.15 to 5% of the total height of the 
regenerative heater.

DETAILED DESCRIPTION OF THE DRAWING 
As it is evident from FIG. 1, the regenerative heater comprises a jacket 1 
made as a steel cylinder with a dome at the top. It encloses the brickwork 
of walls 2 and checker 3 made of refractory materials with different 
coefficients of linear expansion and formed by superimposed horizontal 
sections corresponding to the distribution of the heater internal 
operating temperatures, each of the horizontal sections consisting of a 
homogeneous refractory material. 
The brickwork of the walls and checker consists of a plurality of 
superimposed courses so that vertical flues 4, shown in FIGS. 2 and 3, are 
formed in the checker 3 for passage of gases. 
In accordance with the distribution of the heater internal operating 
temperatures, several superimposed courses of homogeneous material form 
horizontal sections 5, 6, 7, 8. For example, the top section 5 is made of 
dinas brick, the next one of high-alumina refractories and the last one of 
fireclay. 
Disposed between the contiguous sections are transition sections 9 which, 
according to the invention, contain at least one course from the 
refractory materials of the contiguous horizontal sections with a uniform 
distribution therein of one material among the other. 
FIG. 2 shows a portion of the brickwork of the wall and checker of the 
regenerative heater prior to operation. Vertical flues 4 of checker 3 are 
rectilinear along the entire height both in the horizontal and transition 
sections. 
Each transition section 9, according to the preferred embodiment of the 
invention, comprises, as shown in FIG. 2, several courses consisting of 
bricks of the contiguous sections. 
The bricks in each course are distributed uniformly over the entire radial 
sectional area of the brickwork (FIGS. 4 and 5) in such a way that the 
number of bricks of material M, for instance of the horizontal section 5, 
gradually diminishes from course to course towards the horizontal section 
6, whereas the number of bricks of material N of the contiguous horizontal 
section 6 increases respectively. That is, the total number of bricks in 
each of the courses is constant, whereas the ratio of bricks made from the 
material of the contiguous sections varies as stated above. The above 
condition is valid for all the horizontal sections. 
In the course of operation of the heater the brickwork of the walls 2 and 
the checker 3 sustains tension and compression strains resulting in a 
shift of each course. With K courses in the transition sections, the 
relative shift of each course diminishes K times with respect to the 
common brickwork construction. Therefore, the overlapping of the vertical 
flues 4 caused by the shift of the courses will be K times less. By 
increasing K, it is possible to bring the overlapping to an acceptible 
magnitude at which only some bending of the vertical flues will occur 
without reduction in the cross sectional area of the latter within the 
transition sections 9 (FIG. 3). This causes the rated efficiency of the 
regenerative heater will be assured. 
The height of each of the transition sections 9 is selected with due 
account to the planned efficiency, thermal characteristics, and design 
features of the regenerative heaters and will amount to 0.15 to 5% of the 
total height of the heater, i.e., a value dependent on the brick height 
and the number of courses in each transition section. 
Thus, due to the transition sections a gradual bending of the vertical 
flues occurs at the conjugating areas of the horizontal sections without 
diminishing the cross sectional areas of the flues which provides for the 
rated efficiency of the heaters, increased brickwork strength and service 
life. The brickwork of the walls, bending gradually, improves the strained 
state of the jacket in the areas of conjugation of the horizontal 
sections, eliminates the appearance of large cracks in the brickwork and 
enhances the operational reliability of the regenerative heater.