US1992620A - Furnace wall - Google Patents

Description

Feb. 26, 1935.

B, M. JoHNsoN FURNACE WALL 2 Sheets-Sheet 1 Filed Feb. 5, 1932 INVENTOR BoYD M. JQHNSON BY @QM ATTORNEY Feb. 26, 1935. B. M. .JoHNsQNv 1,992,620

FURNACE WALL Filed Feb. 5, 1932 2 Sheets-Sheet 2 INVENTOR BOYD M. JOHNSON ATTORNEY 6l. OWE@ Patented Feb. 26, 1935 UNITED STES PATENT orrlcl:

FURNACE WALL Application February 5, 1932, Serial No. 591,118

'1 Claims.

This invention relates to the structure of furl nace walls which are subjected to extreme and uneven temperatures, and more particularly to the construction and support of the front, back and side walls of combustion chambers which have large areas exposed-to large temperature gradients.

In the case of powdered coal furnaces which are used to supply steam to large manufacturing plants each of the four walls of the combustion chamber may cover an area of more than one hundred square feet and may reach a height of twenty feet. In such furnacesthe problem of support of walls subjected to uneven temperatures (which may reach 1300 C. -to 1400 C. in parts) is diicult. Air-cooled blocks have been proposed for use in the inner lining of the combustion chamber, the blocks having openings therethrough from front to back and channels at the back, which openings and channels permit ventilation of each block and permit the passage of air into the combustion chamber to form cooling currents along the. exposed surface. Such extensive ventilation of the surface portions of the wall of the combustion chamber results in inefcient operation of furnaces of the kind above described. My improved structure has been designed to overcome these diiiiculties. I have accordingly designed an air-cooled furnace wall structure having an inner wall composed of conducting blocks with rearward projections and an outer wall of non-conducting blocks with inwardly extending complementary projections. The rearwardly extending projections are supported on the projections from the non-conducting blocks in such a manner that the inner exposed wall can expand vertically with respect `to the outer wall, while the outer wall supports the inner wall horizontally. This improved structure is illustrated in the accompanying drawings in which:

Figure 1 is a horizontal section of a portion of my improved furnace wall;

Figure 2 is a section on the line II-lI of Fig. 1;

Figure 2A is a fragmentary sectional elevation illustrating a modification of the facing shown in Fig. 2;

Figure 3 is a perspective view of one yof the blocks used in the inner `wall of the combustion chamber, the block having rearwardly extending lugs for supporting connection with the outer.

Wall

Figure 4 is a perspective view of another form of block used in the inner wall of the combustion chamber;

Figure 4A is a view similar to Fig. 4 of a facing block adapted to interlock with other facing blocks;

Figure 5 is a perspective view of one of the blocks used in the outer wall of the furnace;

Figure 6 is a perspective view of another of the blocks used in the outer wall;

Figure 7 is a section of a modified wall struc. p ture which is particularly adapted for 'the'roof of the combustion chamber; and y Figure 8 is a perspective view of one of the facing blocks shown in Figure '1. I

Referring to the drawings in detail theportion of the wall which is nearest, to the, combustion chamber (and which will hereafter be referred l5 to as the inner wall) is indicated in Fig. 1 as being made of blocks 2 which forma thin facing backed by air spaces 3. 'These facing blocks are shown in Figures 3 and 4, the blocks illustrated by Fig. 3 being provided with lugs or projections 20 4 which are hooked on to complementary lugs or projections 5 on blocks 6, which last-'mentioned blocks are used to form the outer wall. The `outer blocks 6 are provided with recess 7 designed to receive steel I-beams, which in turn 25 are secured to a steel frame work 9. The blocks 2 which are used in the inner wall are composed of a material having high thermal conductivity and great mechanical strength at high temperatures.

Silicon carbide is particularly adapted (by reason of its high thermal conductivity and great mechanical strength at high temperatures) for use in facing blocks which form the inner wall. The projections 4 for example evidently need to 35 be able to withstand large mechanical stresses in spite of their small area of cross-section. These projections 4 are surrounded onall sides (except at their contacting surfaces) ,by air spaces through which a current of cooling air isy .40 kept flowing. The thermal drop along the projection 4 (in a direction toward the outer wall) is therefore quite rapid. The blocks 6 and 6' which compose the outer wall are made of a poorly conducting refractory such as fire-clay. 45 Theseblocks are much thicker than the 4blocks 2 and 2 which are used to form the inner wall.

In consequence of the poor thermal conductivity and great thickness ofthe blocks 6 and 6 the steel I-beams 8 are kept at a comparatively low 50 temperature.` The projections 5 on the blocks 6 project upwardly and are strongly supported by the portion of the block underneath as will readily be seen by an inspection of the design ofthe vblock shown in Fig'. 5r.` The'connection between 5 the projections 4 from the blocks 2 of the inner wall and the lugs 5 of the blocks 6 of the outer wall is such that the inner wall or portions thereof can expand upwardly without producing additional strain on the outer wall. The inner wall can evidently lift itself away from the outer wall in a vertical direction without losing the protection afforded against substantial horizontal displacement, this protection resulting from .the interengagement of the projecting lugs 4 and 5.

It is not necessary that each of the blocks that go to make up the inner wall should be provided with rearwardly extending lugs. 'I'he blocks 2' are shown in Fig. 2 as placed between the blocks 2 in such a way that they cannot move outwardly toward the combustion chamber. 'I'he facing block 2' (like the other facing blocks) is made of a material having a thermal conductivity several times greater than thatof re-clay, such as silicon carbide. 'I'his material has also a low coefficient of expansion and is highly refractory.

These properties make silicon carbide a suitable material for the facing blocks. The blocks 2' (as shown in Figures 4 and 4A) have the exposed face toward the observer, the longer dimension being horizontal and the shorter dimension vertical. In both Fig. 4 and Fig. 4A the back portion of the block is shown as projecting above and below the front portion of the block. 'I'hese projections enable the blocks 2 to interlock with the alternately arranged blocks 2 in any given vertical column. 'Ihe blocks 2' are thus held from movement in the direction of the combustion chamber, the blocks 2 being held by the interlocking of the projections 4 with the projections 5 on the backing brick. As shown in Fig. 1 the front portions, that is the exposed portions adjacent to the combustion chamber are 'alternately longer and shorter. 'I'he blocks 2 are made so that they can be arranged in a similar manner as will be seen from Figures 4 and 4A, that is the horizontal rows containing facing blocks of the 2' type have the forms shown in Figures 4 and 4A in alternate arrangement. In order to penetrate the furnace walls combustion gases would have to follow a tortuous path on account of the various flange arrangements which have been disclosed for the facing blocks. The blocks 2' may also be interconnected with the blocks 2 by means of a groove and tongue arrangement which will afford as much protection against outward movement of the block 2 as against inward movement. The main support of the inner wall against movement toward or away from the combustion chamber is therefore provided by the interengagement ofthe lugs 4 and 5. 'Ihese lugs are protected from the direct action of the flames by means of the plates 2 and are subjected to the cooling action of the air currents which ow between the outer and inner wall.

The block shown in Figure 5 may be undercut below the projection 5 to permit larger air spaces between the blocks 6 and 2.

The facing block 2" (shown in Figures 7 and 8) is provided with a rearwardly extending lug 11 of rectangular lor other cross-section; and this lug is suiliciently long to extend through the outer Vwall and beyond the outer surface of the outer means of the long projecting lugs 11. These lugs do not conduct much heat from the furnace because of their small area of cross-section and because of the cooling to which they are subjected from currents of-air owing in the spaces 12.

While a number of modications of my improved furnace structure have been shown, there may be considerable variation in the wall structure and in the materials used in constructing the walls without departure from the scope of my invention which is defined in the following claims.

I claim:

1. A furnace wall structure comprising an inner exposed wall composed of a plurality of thin plates of highly conducting refractory, an outer thick wall substantially spaced from said inner wall by means of an air chamber, said outer wall being composed of aplurality of blocks of poorly conducting refractory, and supporting connections between said inner wall and said outer.

wall, said connections comprising lugs extending rearwardly from certain of said highly conducting blocks and having downwardly extending projections which fit into depressions in certain of said poorly conducting blocks, thereby allowing expansion of the inner wall in a vertical direction.

2. The furnace wall described in claim 1 in which the inner wail is composed of silicon carbide and the outer wall is composed of flreclay.

3. A pair of ounits for use in constructing a wall of a combustion chamber comprising a thin plate of highly conducting refractory, a thick block of poorly conducting refractory, eand complementary lugs integral with the plate and block respectively, said platelugs having each a downwardly extending projection which flts loosely behind an upwardly extending projection of a complementary block lug, whereby the plate can expand vertically with respect to the block while substantial separation of the two units in a horizontal direction is prevented.

4. A furnace wall structure comprising an inner wall composed of a plurality of thin plates of highly conducting refractory, an outer wall substantially spaced from said inner wall for the most part by air chambers, said outer wall being composed of a plurality of blocks of poorly conducting refractory, rigid steel supports extending into the outer surfaces of certain of said outer blocks and interlocking therewith, interlocking connections between the inner wall and outer wall comprising lugs extending from the inner wall and having downwardly extending projections which t into depressions in certain of said poorly conducting blocks, thereby allowing expansion of the inner wall in a vertical direction, and means for supplying a current of cooling air between the inner and outer' walls.

5. A furnace wall comprising in combination an inner wall adjacent to the combustion chamber and composed of highly `conducting refractory plates having interlocking flanges in the adjoining portions of the plates, an outer wall composed of blocks of poorly conducting refractory and having a slot extending through a plurality of said poorly conducting blocks, a steel mem-I ber adapted to pass through corresponding slots to lock said poorly conducting blocks against movement perpendicular to said member, a steel frame for supporting a pluralityof such members and the attached blocks in substantially ilxed position to form an outer furnace wall, and lugs integral with certain of said inner wall plates and extending through the outer wall, said lugs having slots outside of the outer wall whereby the inner wall plates are locked in position with respect to the outer wall while separated from the latter for the most part by means of air ducts.

6. A furnace wall structure comprising an inner wall composed of a plurality of thin plates of highly conducting refractory, an outer wall substantially spaced from said inner wall for the most part by air chambers, said outer wall being composed of a plurality of backing blocks of poorly conducting refractory, rigid steelsupports having tongue andgroove locking connectionsl with certain of said outer blocks, and interlocking extensions projecting rearwardly from said inner wall and having downwardly projecting lugs which contact loosely with complementary surfaces of portions of said outer wall, whereby the interlocking extensions provide support between the walls in a horizontal direction.

'1. A furnace wall comprising in combination an inner wall adjacent to the combustion cham. ber and composed of highly conducting refractory plates having interlocking flanges in the adjoining portions of the plates, an outer wall composed of blocks `of poorly conducting refractory and having a slot extending through a plurality of said poorly conducting blocks, a steel member adapted to pass through said slot to lock a number. of said poorly conducting blocks against movement perpendicular to said-y member, a steel frame for supporting a, plurality of such members and the attached blocksto form an outer furnace wall, and rearwardly extending projections from certain of said face plates which projections interlock with certain of said poorly conducting blocks in a direction to prevent relative movement of the plates and blocks perpendicular to the furnace wall while the inner and outer walls are separated for the most part by means of air ducts.

BOYD M. JOHNSON.

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