FI86474C - Metallic, heat accumulating body and heat accumulator - Google Patents

Description

1 86474

Metal, heat accumulating body and heat accumulator

The invention relates to a metallic, heat-storing body. The invention also relates to a heat accumulator comprising a heat accumulating body, one surface of which forms a contact surface with a heat transfer fluid.

Heat storage bodies are commonly used in a wide variety of applications where the purpose is to transfer the heat supplied to and stored in the body to a destination where it is needed. In this case, a liquid, typically water, is often used as the heat transfer or transfer medium, but the gas can also act as a heat transfer medium. The present invention can be applied to objects in which the heat transfer medium is either a liquid or a gas.

It is natural that heat-accumulating bodies are made of materials with good heat-storage capacity. In this case, there is often also a wish-20 way that the heat storage capacity of the material per unit volume is high. The use of soapstone as a heat storage material is well known because of its good heat storage capacity compared to other stone materials. Ceramic and fire-resistant materials, as well as mineral materials such as * · · 25 ferrosilicate, are commonly used in the cores of heat accumulators *. However, compared to the above-mentioned materials, the metals even have a multiple heat transfer capacity per unit volume. For this reason, efforts have been made to use metals in heat accumulators. For example, the use of cast iron is known in heat accumulators, where heat is stored in a large mass, i.e. in so-called mass - ## · ρ limbs. However, the use of cast iron is limited by the fact that: * its chemical resistance at high temperatures is very limited. In addition, it swells at high temperatures when heated intermittently. The exception is 2 86474 alloyed cast irons, but they are very expensive materials for bulk storage use because the weight of bulk storage is generally high. Another problem with cast irons is that it is difficult or impossible to produce non-porous Kap-5 pieces from them. Welding them is also difficult.

The high heat storage capacity of steel per unit volume, as well as its many advantages over cast iron (weldability, non-porosity, etc.), have led to attempts to make heat accumulator cores from steel. 10 The problem in this case is the poor fire resistance of the steel: the surface of the steel has flaked at high temperatures, approx. 600 - 800 ° C, i.e. it has reacted with the surrounding oxygen so strongly that the use of steel has been abandoned. By using high-alloy steels, it is possible to obtain good resistance to flaking; however, the use of high-alloy steels does not make sense in heat accumulators due to their high cost. In addition, the weldability of high-alloy steels is generally problematic compared to conventional steels 20.

The object of the present invention is to eliminate. the problems mentioned above. To achieve this, the metallic heat storage body according to the invention is characterized in that it comprises a steel core 25 on the surface of which an alloy with good fire resistance is sprayed. Preferably, the core is a common structural steel. The composition of the alloy used as a coating preferably corresponds substantially to the composition of low carbon austenitic stainless steel. Large heat storage bodies used in mass accumulators are used; In this case, it is generally very advantageous for the core to be formed of steel pieces which are fastened to each other by welding, since then the core is easy to manufacture and can be manufactured on site.

The heat accumulators according to the invention are mainly characterized in that the heat accumulating body comprises a steel core with an alloy with good fire resistance sprayed on the surface in contact with the oxidizing environment. Preferred embodiments of the heat accumulator are set out in the appended claims 6-10.

The present invention is based on the idea of using cheap "ordinary" steel having very good heat storage properties as the core of the heat storage body, whereby the steel is protected from oxidation and other chemical reactions by an alloy sprayed on the steel surface.

The main advantages of the invention are that it enables the cheap production of a compact, heat-storing body with a high heat storage capacity per unit volume. The use of general structural steel as the core material ensures the good availability of the material in different moldings and dimensions to meet the size and shape requirements set by the application; in addition, it is possible to manufacture or assemble the steel cores by welding, which is particularly advantageous in the manufacture of very large cores. By choosing the composition of the alloy used as a coating to substantially correspond to the composition of austenitic low carbon, its stainless steel, sufficient fire resistance and a tendency to sensitize the coating in the normal environment of use are ensured at low cost.

The invention will now be described, by way of a preferred embodiment, with reference to the accompanying drawing, in which Figure 1 shows an overview of the heat accumulator, / Figure 2 shows the heat accumulator of Figure 1 from behind, Figure 3 shows a sectional view along lines III-III and I of Figure 1. Fig. 4 shows 4 86474 cassettes for thermal resistors used in the heat accumulator of Fig. 1.

Figure 1 shows a heat accumulator typically associated with a heat exchanger (not shown) for heat recovery. The heat accumulator comprises a heat accumulating body 5, generally indicated by reference numeral 1. The heat accumulating body 1 is obtained by juxtaposing four substantially rectangular steel pieces 2 to 5. Steel pieces 2-5 are common structural steels, for example Fe 52-c (St 52-3), because the price of such steel 10 is low and the availability is good, in addition, it is easily weldable. A space for an electric heating resistor 6, 7 is formed in the contact surface between the steel pieces 2 and 3 and 4 and 5 arranged in the side sections. The heat storage body 1 is thus heated by electric resistors raising the temperature to about 550 to 750 ° C, with a typical operating temperature of about 600 ° C. It is noted that the temperature of the body 1 can be clearly higher than 750 ° C and naturally lower than 550 ° C, above the latter temperature of which the alloy-20 non-alloy steel has a high tendency to flake. The heating resistors 6 and 7 are arranged in their own cassettes 8 and 9, which act as their holders. Cassettes 8, 9 with ra - ;;; returning to the field in connection with Fig. 4, are in good thermal contact with the steel pieces 2 and 3 and 4 and 5 25 and the heating resistors 6, 7 are in good thermal contact with the cassettes 8, 9. This ensures that the heat transfer from the heating resistors 6, 7 to the steel pieces 2 to 5 is efficient. The passage of the heating resistors 6, 7 in the heat accumulator 1 is indicated by broken lines.

A lid 10 is tightly fitted to the surface of the heat accumulator 1 which forms the contact surface with the heat transfer medium which is water, whereby a heat transfer space is formed between the lid and the contact surface. The cover 10 is provided with an inlet 11 for water and an outlet 12 for water. 35 for removing steam. Since the surface 10 of the cover 10 of the heat accumulator 1 and 5 86474 is surrounded by air and the surface is heated to a temperature at which the general structural steel oxidizes and flakes, an alloy having good fire resistance is sprayed on the surface of the heat accumulating body. The lid 10 must also be coated if it is made of steel which flakes at the operating temperature. Since the cover 10 forms a relatively small part of the heat accumulator in terms of material consumption, it is conceivable that it is made of a material which has inherently good fire resistance, so that it is not naturally coated. A wire material or powder having a composition substantially similar to that of low carbon austenitic stainless steel type 18-8 is well suited as a starting material for the coating material. Low carbon content has been found to be important for the adhesion of pin-15 weft. The carbon content of the well-functioning mixture was about 0.03%. Even a lower carbon content is not known to be a disadvantage. The availability of said steel is good and its price is quite reasonable compared to many other stainless ter-20 alloys or superalloys. If the operating temperature is very high and / or the environment is corrosive, Kanthal coating is used instead of stainless steel. The walls bounded by the heat transfer space are left uncoated because an oxygen-free environment prevails in the heat transfer space.

·· '- 25 Figure 2 shows the heat accumulator from the back, i.e. from the side of the cover 10.

Figure 3 shows a section along the line III-III in Figure 1. In the figure, reference numerals 13 to 15 indicate welding seams connecting the steel pieces 2-5. In this connection, it is mentioned that the steel pieces 2 to 5 are welded to each other only on the contact surface side, i.e. the heat storage body 1 is not welded from above, below or in front, i.e. on the heating resistors 6, 7 side. This is done so that the seams 35 between the steel pieces 2-5 are slightly opened for insertion of the heating resistor cassettes 8, 9 6 86474 so that they are in close contact with the steel pieces. Fig. 1 shows a locking member indicated by reference numeral 17 ', which is bolted to the steel pieces 2-5 to prevent the latter from moving away from each other.

It can also be seen from Figure 3 that water guide plates 17 to 20 are arranged one below the other in the heat transfer space, the purpose of which is to distribute water and water vapor over the entire contact surface of the charging body 1. For this purpose, the guide plates 17 to 20 are arranged to be inclined alternately in the opposite direction. The baffles 17 to 20 are preferably attached to the steel pieces 2-5 by welding.

Figure 4 shows a cassette 8 to be inserted between the steel pieces 2 and 3. The cassette 8 comprises two plate-like parts 21 and 22. The parts 21, 22 are shaped so that the removal of the inner part 22 is sufficient to remove the heating resistor 6 from the heat accumulating body 1. The outer part 21 then remains in place in the body 1. The two-piece cassette 8 is advantageous for maintenance.

The invention has been described above with reference to only one of its preferred embodiments. It is therefore to be understood that the invention may be practiced in detail in many ways within the scope of the appended claims. It is thus conceivable that the heat accumulating body is formed, for example, by a ingot or brick-shaped body which is heated, for example, by heat generated in a storage fireplace, which heat storage body is built inside the storage fireplace. In this case, there is no electric heating involved in the heat storage body at all, and the heat transfer medium is not water but air or gas. Instead of electric heating, heating can take place with an oil or gas flame. It is further understood that instead of the conventional general structural steel, various low-alloy steels and 35 annealing steels which are coated can be used as the core material; however, such steels 7 86474 are more expensive than ordinary structural steels, so their use is less meaningful - especially considering the object of the invention, i.e. to provide a cheap body with good heat storage capacity and suitable for high temperatures. Instead of the austenitic stainless steel and Kanthal alloy shown, the coating material may be another material suitable for high temperatures: it is conceivable that, for example, austenitic-ferritic steel is suitable for use.

10 The condition for the suitability of a material is that it has sufficient fire resistance and adhesion.

Claims (10)

1. A metallic, heat accumulating body (1), characterized in that it comprises a core (2 - 5) of steel on which the surface of the core is sprayed a metal alloy whose refractory is high. 2. A body according to claim 1, characterized in that the core is a general structure. 3. A body according to claim 1 or 2, characterized in that the composition of the alloy used as a coating substantially corresponds to the composition of a low carbon content austenitic stainless steel. 4. A body according to any of the preceding claims, characterized in that the core is formed of frame parts (2-5) which are attached to each other by means of welding. A heat exchanger comprising a heat accumulating body (1) having a surface forming contact surface with a heat transferring fluid, characterized in that the heat accumulating body consists of a ground core (2 - 5), the surface of which comes into contact with it. oxidizing environment, has been sprayed with a metal alloy whose refractory is high. 6. A heat exchanger according to claim 5, characterized in that the contact surface is covered by a cover (10), such that a heat transferring space is formed between the cover and the contact surface, which includes an entrance opening (11) and an exit opening (12) for supply and removal. taking the heat transfer fluid. 7. A heat exchanger according to claim 6, characterized in that the walls defining the heat transfer space are uncoated. 35 8. A heat exchanger according to claim 7, characterized in that the heat transfer space comprises mutually arranged water control discs (17-20) arranged to tilt alternately in the opposite direction. 5 9. A heat exchanger according to any one of claims 4-8, characterized in that the core is formed of rectangular shaped parts (2 - 5) which are fastened together by welding, whereby at the contact surface between at least two adjacent steel parts (2, 3 and 4, 5) a space for electrical resistance (6, 7). 10. A heat exchanger according to claim 9, characterized in that the space formed at the contact surface between the actuating elements (2, 3 and 4, 5) is intended to receive a cassette (8, 9) which is in good thermal contact with the set pieces and the electrical resistor (6, 7) and acts as a holder for the latter.