EP0373450A1 - Process and regenerative heat exchange apparatus for gas heating - Google Patents

Abstract

A process and regenerative heat exchange apparatus for heating gases, it being the case that, in turn, the heat carrier, preferably a bed of heat-carrying bodies, is firstly heated and subsequently this energy, stored by the heat carriers, is used to heat cold gases. Located between two gratings (2, 4) arranged coaxially and equidistantly from the regenerative heat exchanger apparatus is a loose bed of heat carriers (6), and this bed is traversed in the heating phase of the regenerative heat exchange apparatus by the hot gas from inside to outside, and vice versa in the gas heating phase by the cold gas from outside to inside. …<IMAGE>…

Description

The invention relates to a method and a regenerator for heating gases, the heat carrier being alternately first heated and then this energy stored by the heat carriers being used to heat cold gases.

The principle of regenerative gas heating is known and is used in various fields in industry. For example, the hot wind for the blast furnace operation in winder heaters (Cowpern) is heated to a temperature of approx. 1200 ° C using this method. The heat energy from the combustion of blast furnace gas is transferred to the grate of its refractory trim in the chimney of the gas heater, and after the heating-up phase has been completed, cold air is blown through the heated grille and heated with the stored heat. The lattice chambers for Siemens Martin and glass trough ovens also use the same method.

For the continuous heating of cold gases, at least two regenerators are required, in accordance with the method of operation described, one of which is heated and thus stores heat, while the second gives off the stored heat to the blown-in, cold gases and thereby heats them up.

When designing and building regenerators, there is always a compromise between thermal requirements and structural possibilities. For example, the well-known wind heaters in cylindrical form with a diameter-to-height ratio of approximately 1: 5 have been introduced for wind heating in blast furnace operation. When designing the lattice masonry, which is flowed through from top to bottom in the heating phase and vice versa from bottom to top in the gas heating phase, in addition to the requirements for heat transfer between gas and lattice masonry, the prerequisites for a tolerable pressure loss of the gases when flowing through the refractory trimmings. While a large surface area and narrow channels are favorable for heat transfer, the free flow cross section can only be restricted to a certain extent in order to maintain an acceptable pressure loss for the gas flow. Because of the larger free cross-section of the flow channels, the heat transfer deteriorates, and accordingly the temperature rise of the combustion gases for heating the heat storage masonry increases compared to the attainable wind temperature. To reach the blast furnace wind temperature of 1200 ° C, a flame temperature of around 150 ° C is required in the heating phase. This flame temperature can no longer be reached with the blast furnace gas emitted by the blast furnace, and therefore an additional combustion of rich gas, e.g. Natural gas, necessary and common.

A known way to improve the thermal efficiency of the regenerators is to significantly increase the surface of the heat storage body. There are a number of proposals for this. With a particular The effective way to get closer to this goal is to replace the grid wall with a suitable bulk material with an approximately uniform grain size. For example, pellets made of refractory materials can be used. A regenerator with a corresponding bed of heat storage bodies with an egg-shaped or spherical shape in a diameter range of 5 to 15 mm allows the surface area that is effective for heat exchange to be increased compared to a lattice wall to such an extent that the temperature difference between the flame or the Exhaust gas in the heating phase and the heated gas in the gas heating phase is only low and is around 10 ° C.

However, for example, the usual grating of a hot air heater for blast furnace operation cannot be replaced by a bed of the type mentioned, since an unacceptably high pressure drop would occur when gas was passed through due to the large bed height.

Known proposals which avoid the pressure loss by considerably increasing the diameter of the hot-water heater and achieving an inverse diameter-height ratio compared to the previous design, show a considerably better heat transfer with approximately the same pressure loss, but have other disadvantages. The dome above the heat transfer bed poses problems during construction and proves to be disadvantageous when operating such a hot water heater. Mainly the considerable dome volume when switching from the heating phase to the gas heating phase leads to a relatively high gas loss, and secondly the dome with its large surface area significantly increases the heat losses in this hot area of the hot water heater. Furthermore, it is difficult to to produce a bed of uniform thickness in cross-section, which is large and relatively thin, and in particular to maintain it during operation.

The invention is therefore based on the object to provide a method for heating gases, and a corresponding regenerator that allows gas heating without the disadvantages of the known systems, and in particular the advantages of lower heat losses with increased heat transfer through large heat exchange surfaces in a uniform bed of Has heat transfer media with a relatively low pressure drop for the gases flowing through.

This object is achieved according to the invention in that there is a loose bed of the heat transfer medium between at least two coaxially and equidistantly arranged grates, and that this bed in the heating phase of the regenerator with the hot gas from the inside out and in the gas heating phase vice versa with the cold Gas flows from outside to inside.

The method according to the invention has a number of advantages over the known processes in regenerative hot gas generation, both in terms of heat technology and in the construction of corresponding systems. In particular, the heat loss due to the significantly smaller heat flow to the outer wall of the regenerator is reduced, since the high temperature areas are in its center and the outer wall only comes into contact with cold gases. On the one hand, this results in improved thermal efficiency and, on the other hand, significant advantages in the construction of the regenerator through savings in steel requirements and the refractory lining due to reduced dimensions and lower temperature bean compared to the known systems with the same heating output, ie gas throughput and gas temperature.

The method according to the invention surprisingly produces very uniform hot gas temperatures and consequently renders appropriate temperature control superfluous in many applications. For example, when generating hot wind for blast furnace operation with a wind temperature of 1200 ° C and a changeover time in the gas heating phase after 30 minutes, the flue gas temperature can be expected to vary between 20 ° C and 40 ° C.

According to the invention, a relatively small temperature difference between the heat carriers and the gases is required. This applies both to the heating of the heat transfer medium itself and to the final temperature of the gases to be heated, for example air. When heating the heat transfer medium, you only need fuel gases with a flame temperature that is slightly above the heating temperature of the cold gases. For example, in the case of wind heating for blast furnace operation, it is possible to work with blast furnace gas from the blast furnace or with only slightly enriched blast furnace gas.

When using the method according to the invention for preheating the wind to 1150 ° C., the heat transfer media in the regenerator could be heated with blast furnace gas, which has a calorific value of approx. 750 kcal / Nm³, and a resulting flame temperature of approx. 1200 ° C. Practically the same heating temperatures can be achieved with the operating values mentioned when heating other gases, for example nitrogen, argon, with oxygen-enriched air, oxygen and fuel gases.

The regenerator according to the invention, in which heat carriers are first alternately heated and then this energy stored by the heat carriers is used to heat cold gases, is distinguished by the fact that it has a hot gas collecting space centrally around the axis of symmetry, which is formed by a first inner grate , and at least one further outer grate arranged equidistant from the inner grate, a gas collecting space being located between this outer grate and the regenerator outer wall, and the gases flowing radially through the bed of the heat transfer medium arranged between the grates.

This regenerator according to the invention has some clear advantages over the known comparable devices. For example, the heat transfer media, similar to the trim on a hot water heater, consist of loose bodies with an approximately uniform grain size. By pouring these heat transfer media between the equidistant grates, the layer thickness in the flow direction of the gases is uniformly thick. In the regenerator according to the invention, the heat transfer media cannot move even under the influence of the flow, and thus there is no risk of gas breakthrough, for example caused by locally exceeding the swirl point.

In the regenerator according to the invention, the free volume between the heat carriers and also in the hot gas and gas collecting space is relatively small, and accordingly there are only slight gas losses when switching from the heating phase to the gas heating phase.

In the regenerator according to the invention, the heat transfer media can be replaced during operation. Through appropriate sockets or flanges on the top and bottom On the other side of the bed, it is possible to refill the heat transfer medium on one side and remove it on the opposite side.

The regenerator often has only a uniform bed of one type of heat transfer medium, which is arranged between an inner and an outer grate. However, it is also within the scope of the invention to use more than two coaxial grids and thus to produce a plurality of coaxial annular spaces. The same heat transfer medium is preferably used between two adjacent grates. However, it is possible to use different fillings of heat transfer media from annulus to annulus. For example, between two grates on the hot inner side of the regenerator, high-temperature-resistant ceramic balls, for example made of corundum, and less expensive heat carriers made of, for example, mullite and / or chamotte can be used on the colder side. The total fill can be divided into two or more layers not only from a cost point of view, but also for operational, especially thermal, reasons. Both the material and the size and shape of the heat transfer medium can be varied according to the invention.

The grids of the regenerator according to the invention can be made of the same, but preferably different, materials. For example, the inner, hot-side grate can be made of refractory material, such as refractory bricks with corresponding gas channels, and the outer, cold-side grate can be made of metal, such as steel, scale-resistant steel or cast iron. When using additional grids between the inner and the outer grate, the material must be selected according to the temperature load. head Ceramic or metal materials are mainly used.

An essential feature of the invention is to build up the bulk of the heat transfer medium with a uniform thickness and to allow the gases to flow through it in the radial direction. This characteristic also applies when the heat transfer bed is divided into several layers.

Ceramic materials of different qualities, for example based on corundum, mullite, fireclay, magnesia, chromium oxide, zirconium oxide, silicon carbide and any mixtures thereof, have proven themselves as materials for the heat transfer medium, as have metal materials. Of course, the heat transfer materials should be selected according to their temperature stress. In principle, the shape of the heat transfer medium according to the invention is arbitrary, but shapes corresponding to the economical and expedient production, such as are produced, for example, when pelletizing and briquetting, in particular for ceramic materials, can be preferred. Geometrically, these are essentially egg shapes or spheres. However, fillings from any gap and fracture structures can also be used.

The method according to the invention and the regenerator according to the invention are particularly suitable for use in the smelting reduction of iron ore, the electric melt and the blast furnace.

The invention will now be explained in more detail using an exemplary embodiment and an illustration.

Figure 1 shows schematically the cross section through a regenerator according to the invention.

This regenerator consists of an outer sheet metal jacket 1 of approximately spherical shape. Although the external shape of the regenerator is insignificant and can therefore take any shape, in practice, more for manufacturing reasons, shapes such as standing cylinders, balls or superimposed double-cone frustum with and without a cylindrical intermediate piece have proven their worth.

In the steel sheet jacket 1 there is the cylindrical outer grate 2 with circular and / or slit-shaped openings. Between this grate 2 and the outer sheet steel casing 1 there is the annular gas collecting space 3 for the cold gas.

The inner grate 4 is made of refractory stones with corresponding gas passage channels. The coaxial arrangement of the two gratings 2 and 4 ensures the same distance between these two grids for the intermediate space 5 over the entire circumference. This space 5 with an annular cross section receives the heat transfer medium 6, for example pellets made of ceramic material.

The hot gas chamber 7 with a circular cross section is located in the center of the regenerator. At the lower end of this hot gas space 7, the hot exhaust gases generated in the burner 8 flow in during the heating phase of the regenerator. The burner 8 is accessible via the vessel lid 9.

The hot combustion gases flow from the hot gas space 7 through the grate 4 and through the bed from the heat carriers 6 into the room 5, further through the grate 2 into the gas collecting space 3. On their way through the bed of the heat carriers 6, the gases have cooled and reach the gas collecting space 3 approximately at normal temperature. they leave the gas collecting space and thus the regenerator through the connector 10.
During the gas heating phase, compressed gas flows through the nozzle 11 into the gas collecting space 3, further through the grate 2 and the bed of heat carriers 6 in the space 5, over the inner grate 4 into the hot gas space 7. In this way, the gases on the heated ones Heat carriers 6 are heated and leave the regenerator via the connector 12.
Furthermore, the openings 13 and 14, which can be closed with flanges, can be seen on the regenerator vessel. The heat transfer medium 6 can be drained from the space 5 and simultaneously refilled through the openings 13 via the connecting piece 14 during operation or maintenance and repair times. It is accordingly possible to replace the entire filling of the heat transfer medium 6 in space 5 discontinuously or continuously.

It is within the meaning of the invention to adapt the method and the regenerator to the various conditions in industrial use. As previously explained, the grate and heat transfer materials can be tailored to the temperature requirements. The shape of the regenerator can also be modified according to its use, but the principle of radial flow through the heat transfer medium should be retained.

Claims (11)

1) Method for heating gases in a regenerator, in which the heat carriers are first alternately heated and then this energy stored by the heat carriers is used to heat cold gases, characterized in that there is a loose bed of the at least two coaxially and equidistantly arranged grids Is heat transfer medium and that this bed in the heating phase of the regenerator with the hot gas from the inside to the outside and vice versa in the gas heating phase with the cold gas from the outside to the inside. 2) Regenerator for heating gases, in which the heat carrier is first alternately heated and then this energy stored by the heat carriers is used to heat cold gases, characterized in that the regenerator has a hot gas collecting space (7) centrally around the axis of symmetry, through which a first inner grate (4) is formed and consists of at least one further outer grate (2) arranged equidistant from the inner grate (4), a gas collecting space (3) being located between this outer grate (2) and the regenerator outer wall (1) , and the gases the bed of the heat transfer medium (6) arranged between the grates flow through radially. 3) regenerator according to claim (1) or (2), characterized in that the grids (2,4) are made of different materials. 4) regenerator according to one or more of claims (1) to (3), characterized in that the inner hot-side grate (4) consists of refractory material, for example refractory stones with gas channels. 5) regenerator according to one or more of claims (1) to (4), characterized in that the outer cold grate (2) consists of metal, for example steel. 6) regenerator according to one or more of claims (1) to (5), characterized in that further gratings are provided, according to their temperature stress, made of ceramic material or metal materials. 7) regenerator according to one or more of claims (1) to (6), characterized in that the bed of the heat transfer medium (6) can be replaced in whole or in part at any operating or idle times of the regenerator. 8) regenerator according to one or more of claims (1) to (7), characterized in that the heat transfer medium (6) can have any shape. 9) regenerator according to one or more of claims (1) to (8), characterized in that the heat transfer medium (6) made of briquetted, sintered, ceramic Materials in egg or spherical form exist. 10) regenerator according to one or more of claims (1) to (9), characterized in that heat transfer media (6) made of different materials are used. 11) Regenerator according to claim 1, characterized in that the gas collecting space (3) has an annular shape.

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