RU2729679C1 - Straight-flow-counterflow furnace for calcination of carbonate materials - Google Patents

Abstract

FIELD: furnaces.

SUBSTANCE: invention relates to shaft furnaces for calcination of carbonate materials and can be used in metallurgical, construction, chemical, food and other industries. Furnace contains two wells with heating zones with heat regeneration, burning and cooling of the ready product. Shafts are connected by a transition channel arranged on the boundary of the roasting and cooling zones with a cross-section at the level of the arch of the transition channel in the form of a segment, the base of which is directed towards the transition channel, the peripheral part in the form of a semicircle and the inner part in the form of a rectangle. At that, shafts up to lower part of annealing zone are made with round section, and in lower part of annealing zone with smooth transition from round section to cross section at level of arch of transition channel, at that angle of inclination to horizon of walls in lower part of annealing zone is 75–90°, and at level of arch of transition channel section width of inner part is equal to radius of semicircular section of part periphery.

EFFECT: technical result consists in reduction of capital costs and improvement of quality of calcined lime.

1 cl, 7 dwg

Description

The invention relates to shaft furnaces for calcining carbonate materials and can be used in metallurgical, chemical, construction, food and other industries where slaked lime is used.

Currently, the most effective for producing lime are furnaces consisting of two cylindrical shafts, interconnected by a transition channel for passing a periodically changing direction of exhaust gases and operating using a direct-flow counter-flow principle of heat exchange. The leading designer of such furnaces is the Swiss company Maerz-Ofenbau AG. The kilns are designed for the production of burnt lime up to 800 tons per day. For production in the amount of 400 to 800 tons of lime per day, circular kilns with annular collecting channels connected by a narrow transition channel are used. For the production of up to 400 tons per day, furnaces with rectangular shafts and a straight transition channel connecting the shafts along their long side are used. The ratio between long and short sides of mines in practice is on average 2: 1. Depending on the productivity of the furnaces, the long side of the shafts has a size of 2.0 to 5.4 m, and the short side of the shafts is from 1.0 to 2.7 m. It is very problematic to ensure a uniform loading of carbonate materials in rectangular mines. Usually, in such furnaces, the material is loaded using stationary inclined streams, which does not allow evenly, as in round furnaces, to distribute raw materials and fuel over the cross section of mines and to obtain a uniformly fired product. Dead zones are often formed in the corners of rectangular shafts. With the same cross-sectional area, the lining of rectangular shafts requires a larger volume of refractory lining than circular shafts. In addition, the resistance of straight walls made of refractory bricks is significantly lower than that of semicircular ones.

So known is a direct-flow counter-current furnace for roasting carbonate materials with rectangular shafts interconnected by a transition channel for exhaust gases passing in a periodically changing direction. In addition, the furnace is equipped with a combustion system for natural gas, process blowers, hydraulic equipment, a skip winch, an exhaust gas filter, including related electrical and control equipment. Natural gas is used as fuel. Kiln capacity up to 150 tons of burnt lime per day, (see the Internet: "Maerz Ofenbau AG-The world leader in lime kilns, 2019. Section" KALSTIL Bulgaria, as well as the site: PFR Kilns for soft-burnt lime ", in general the address www.maerz.com in the search engine GOOGLE. ") As noted above, due to the uneven distribution of lump material over the cross section of the mines, the firing is uneven, and the quality of lime is lower than in kilns with round mines.

Also known is a direct-flow counter-current furnace for roasting carbonate materials, divided in height into heating zones with heat recovery, roasting and cooling. At the border of the firing and cooling zones, the shafts are connected by a transition channel for exhaust gases passing in a periodically changing direction from one furnace shaft to another. The section of the shafts in the peripheral part is made of a segment-like shape with the base directed towards the transition channel. The peripheral part of the section of the shafts can be made in the form of a semicircle, and the inner part in the form of a rectangle. In these furnaces, better heat distribution over the cross section is ensured by reducing stagnant zones, which leads to an improvement in the quality of the finished product. This furnace was adopted as a prototype for its functional purpose and the achieved result (see USSR inventor's certificate No. 1663353 F27B 1/02, published on July 15, 1991, "Direct-flow counter-current furnace for roasting carbonate rocks.") But this direct-flow counter-current furnace for firing carbonate materials (hereinafter referred to as the kiln) does not completely solve the problem of the quality of the finished lime, since two right angles remain in the heating and firing zones of each mine, in which, as in the above analogue, stagnant zones are formed, causing uneven heat distribution, and therefore there is not enough high quality of finished products. In addition, with the same cross-sectional area, the lining of this furnace will require a larger volume of refractories than round shafts.

The object of the present invention is to provide a compact and economical two-shaft kiln for obtaining lime of a higher quality.

The technical result is a decrease in the volume of refractories for the lining of the furnace and an increase in the quality of fired lime while maintaining high productivity is achieved by the fact that the shafts at the top to the bottom of the firing zone are made with a circular cross-section, and in the lower part of the firing zone with a smooth transition from a circular cross-section to a cross-section at the level the arch of the transition channel in the form of a semicircle in the peripheral part and in the form of a rectangle in the inner part, and the angle of inclination of the walls in the lower part of the firing zone is 75 ... 90 degrees to the horizon, and at the level of the arch of the transition channel, the cross-sectional width of the inner part is equal to the radius of the semicircular section of the peripheral part ...

To ensure smooth material flow and lining stability in the section of a smooth transition from a circular section to a rectangular section of the inner part at the level of the arch of the transition channel, the angle of inclination of the walls α should be within 75-90 °.

An increase in the angle α of the inclination of the walls more than 90 ° will cause the formation of an obstacle for the descent of material and can cause the formation of stagnant zones, and a decrease in the angle of inclination of the walls α less than 75 ° is impractical due to the complication of the design with the use of anchors and a decrease in the resistance of the furnace lining in this section of the smooth transition.

The equality of the cross-sectional width of the inner part to the radius of the semicircular cross-section of the peripheral part at the level of the transition channel provides the highest durability and the minimum volume of the lining without the formation of obstacles for material escape.

The proposed design of the furnace for roasting carbonate material has a novelty, since the totality of the features of the claims in information and patent sources has not been found.

The technical solution declared as an invention, in our opinion, also has an inventive level, since the execution of shafts from the top to the bottom of the firing zone with a circular cross-section, and in the lower part of the firing zone with a smooth transition from a circular cross-section to a cross-section at the level of the arch of the transition channel in the form a semicircle in the peripheral part and in the inner part in the form of a rectangle is not obvious, and this leads to the achievement of a higher level of quality of the burnt lime.

The proposed invention is at the stage of preliminary design, but in general its use is not in doubt in view of the fact that a change in the design of the shaft furnace does not change the principle of its construction, since known equipment and materials are used.

The claimed invention is illustrated in the drawings, where FIG. 1 shows a schematic cutaway view of a two-shaft furnace; FIG. 2, 3, 4, 5 and 6 show the cross-sections of the furnace shafts along A-A, B-B, C-C, G-G and D-D in their various places, and Fig. 7 shows, for clarity of the essence of the invention, a general view of a furnace with two shafts in axonometric projection showing the location of a smooth transition in the area between sections BB and B-C.

The direct-flow counter-current furnace for roasting carbonate materials contains two shafts of the same type 1 and 2 with zones 3,4 and 5, respectively, heating with heat recovery, roasting and cooling of the finished product, connected by a transition channel 6 located at the border of zone 4 of roasting and zone 5 cooling. To prevent the formation of stagnant zones, reduce the volume of refractory materials and ensure high uniformity of the loaded carbonate material over the entire inner section of shafts 1 and 2, they are made from above in section 7 of preheating zone 3 and the upper part of firing zone 4 with circular section 8, and in the lower part of the same firing zone 4, the circular section 8 of each shaft 1 and 2 smoothly passes in section 9 to the level of the arch 10 of the transition channel 6 into section 11 in the form of a semicircle 12 with a radius R in the peripheral part 13 and the inner part 14 in the form of a rectangle 15. To prevent the formation of stagnant zones and guaranteeing the stability of the lining, the angle α of inclination of the walls inside the smooth transition 16 in the section 9 of shafts 1 and 2 is in the range of 75-90 °. The profile 17 of shafts 1 and 2 in the cooling zone 5 may be the same as in the end part of the firing zone 4, namely, in the form of a semicircle in the peripheral part and in their inner part in the form of a rectangle (Fig. 5). The equality of the cross-sectional width of the inner part 14 to the radius R of the semicircular cross-section of the peripheral part 13 at the level of the arch 10 of the transition channel 6 provides the highest durability and the minimum volume of the lining without the formation of obstacles for material flow.

Direct-flow counter-current furnace for roasting carbonate material works as follows.

The carbonate material to be fired, preferably limestone, is fed and evenly distributed in the upper section of the round shafts 1 and 2, which is then preheated in the heating zone 3 to the dissociation temperature, then in the firing zone 4 the heated limestone is dissociated to obtain the finished calcined lime, after which it is cooled in the cooling zone 5 by air supplied from the bottom of shafts 1 and 2. Gaseous fuel is supplied to the material to be fired into a direct-flow shaft 1 at the border of heating zones 3 and firing 4 through a series of burners (not shown in the figures). Combustion air is also fed from above through a bed of heated limestone where it is heated. Combustion products pass through the firing zone 4 of the direct-flow shaft 1 and, mixing with the cooling air from the cooling zone 5, enter through the transition channel 6 from the direct-flow shaft 1 into the counter-current shaft 2, in which the furnace gases with the cooling air pass upward, giving off heat to the limestone in the heating zone 4. Switching the supply of fuel and air from mine 1 to mine 2 is performed after 12-15 minutes. Burnt and cooled lime is discharged from the bottom from two shafts 1 and 2.

The execution of shafts up to the lower part of zone 4 with a circular cross-section, the absence of stagnant zones and the presence of a smooth transition 16 in the lower part of the firing zone with wall slopes of 75-90 ° ensures the minimum use of refractory materials for the lining of the furnace and the achievement of a higher level of quality of the fired material.

The proposed design is recommended for the construction of furnaces with a capacity of up to 300 tons of lime per day with an inner diameter in the upper part of up to 2.7 m.

Sources of information

1. USSR author's certificate No. 1330430 F27B 1/02 published on August 15, 1987.

2. USSR author's certificate No. 1529027 F27B 1/02 published on 15.12.1989.

3. USSR author's certificate No. 1663353 F27B 1/02 published on 15.07.1991.

4. RF patent No. 2353595 С04В 2/12 published on April 27, 2009.

5. US patent No. 6453831 F23D 17/00, F27B 1/02 published on February 27, 1999.

6. US patent No. 5460517 С04В 2/12, F27B 1/04 published on 10.24.1995.

7. Patent DE No. 2927834 F27B 1/02 published on January 27, 2011.

Claims (1)

Direct-flow counter-current furnace for roasting carbonate materials, containing two shafts with heating zones with heat recovery, roasting and cooling of the finished product, connected by a transition channel located at the border of the roasting and cooling zones with a cross-section of the shafts at the level of the arch of the transition channel in the form of a semicircle in their peripheral part and the inner part in the form of a rectangle directed towards the transition channel, characterized in that the shafts in the top to the lower part of the firing zone are made inside with a circular cross-section, and in the lower part of the firing zone with a smooth transition from a circular cross-section to a cross-section at the level of the arch of the transition channel, and the angle of inclination of the walls inside the lower part of the firing zone is 75-90 degrees to the horizon, and at the level of the transition channel, the width of the inner part of the section is equal to the radius of the semicircular section of the peripheral part.

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