DE1279939B - Use of ferrosilicon as a material for heat storage cores - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int α .:

C22c

German KI .: 40 b -37/10

Number: File number: Registration date: Display day:

P 12 79 939.2-24 (K 58346)

5th February 1966

October 10, 1968

The present invention relates to the use of ferrosilicon as a material for storing Heat as it is used in heat storage tanks, preferably in electric storage stoves.

In storage stoves, a storage core or block made of a suitable material is closed heated for certain times and returns the heat as required to a suitable heat exchanger Medium, e.g. air or water. The storage core or block is heated up up to temperatures of 500 to 800 ° C. It is usually carried out by electrical heating elements, which are installed in a suitable place in storage stoves and from which the heat is transferred to the Memory core passes.

Various materials have already been proposed as storage ceramic material, e.g. B. magnesite, Olivine and other refractory oxides or compounds of several oxides. These ceramic fabrics have a relatively high specific heat, which allows a relatively large heat per unit weight To store the amount of heat. They are also up to the stated temperatures of 500 to 800 ° C chemically resistant. In the construction of storage stoves, especially those for use in households are determined, it is primarily important that the units are as compact as possible can be produced, which can be set up in a suitable location without taking up excessive space.

The decisive factor is therefore not the specific heat per se, but the heat capacity per Unit of volume. This is in the case of an oxide that is in a temperature range of, for example, 0 to 600 ° C has an average specific heat of 0.25 kcal / kg grad, with a density of 2.5 kg / 1 at most only the same 0.625 kcal / 1 degree A significant disadvantage of such oxides is also their poor thermal conductivity. The heating of the storage core and the heat dissipation to the heat exchanger is thereby very deteriorated.

Furthermore, the possibilities for processing such refractory ceramic masses are suitable Shaped bodies limited. Processing is only possible by pressing the shredded material into suitable forms and subsequent firing or sintering at high temperatures or a Pressing with a binder, e.g. B. refractory cement or so-called rammed earth. After these Methods, however, will only get those memory cores or blocks whose density is always lower is than the true density of the storage material, so that the heat capacity of e.g.

Use of ferrosilicon as a material for heat storage cores

Applicant:

Knapsack Aktiengesellschaft,

5030 Huerth-Knapsack

Named as inventor:
Dr. Hellmut Gabler, 5033 Knapsack;
Dr. Joachim Kandier,
Hans-Dieter Thiel, 5030 Huerth

0.625 kcal / 1 degree only a theoretical upper limit Represents a limit value that is practically not reached. The heat storage capacity is maximum only about 80 to 90% of this value, e.g. B. 0.50 to 0.55 kcal / 1 degree, but is usually still there.

ao under.

Such a reduction in heat capacity could be avoided if the material melted and poured into appropriate molds, since it is then compact and with maximum Density would arise. However, this method is practically inapplicable for oxidic materials Question, because the melting points are extraordinarily high.

It has therefore already been proposed, instead of oxidic materials with relatively high specific heat, but low density and the other disadvantages described, substances with something use lower specific heat, but high density, which in terms of heat capacity per Unit of volume are superior to the previously known oxidic materials. As such a storage material cast iron has already been proposed. The specific heat of cast iron lies in that temperature range of interest from 0 to 600 ° C on average at about 0.14 to 0.15 kcal / kg grd. the The density of cast iron is about 7.2 kg / l, so that there is a heat capacity of about 1.05 kcal / 1 degree. Cast iron is therefore superior to oxides in terms of heat capacity per unit volume. aside from that it has the advantage that its heat capacity can be better used because you melt it and can be poured into molds in the molten state. The fittings can be used directly as storage cores or blocks can be used. In addition, cast iron points towards ceramic or oxidic Materials have better thermal conductivity, which is also desirable.

S09 620/348

However, the general application of cast iron as storage materials for heat is available The disadvantage is that it is not resistant to chemically aggressive substances at elevated temperatures is enough. In the temperature range under consideration, up to 500 are considered to be chemically aggressive Up to 800 ° G practically all known heat exchangers, i.e. in particular air and water, are to be considered. Since the storage core or block for the purpose of dissipating heat to the heat exchanger with this must be in direct connection, occurs in this way on cast-iron storage cores at increased Temperature a corrosion, which leads to a gradual destruction of the surface and a Change of shape leads. You must therefore in a complex manner by expensive corrosion-resistant Isolate materials from the heat exchanger, making the storage heater in undesirable Way is made more expensive.

It has now surprisingly been found that ao ferrosilicon, even at these elevated temperatures, chemically compared to the media preferably used as heat exchangers, air and water is constant. The ferrosilicon is covered with an oxidic skin that protects it from another Attack protects. It was not foreseeable that in this case ferrosilicon would be different from cast iron behaves. According to the invention, therefore, a ferrosilicon consisting of 8 to 50%, preferably 10 to 30% silicon, the remainder iron, and the production-related impurities are used. One increases If the silicon content exceeds the specified limits, the specific heat increases, however, since the density decreases at the same time, the heat capacity decreases in turn. Also more expensive a high silicon content the material. Also for reasons of corrosion resistance is a silicon content not necessary beyond the above-mentioned limits. The following figures clarify the relationship between density, specific heat and heat capacity of various Ferrosilicon grades.

Ferrosilicon 10% Si
Ferrosilicon 20% Si
Ferrosilicon 30% Si

density
kg / 1

7.26
6.72
6.19

Specific

warmth
kcal / kg grd

0.161
0.167
0.172

Heat capacity kcal / 1 degree

1.17
1 _S 12
1.06

The specified heat and heat capacities are mean values for a temperature range from 0 to 600 ° C. Ferrosilicon is understood to mean alloys which, in addition to the Silicon essentially contain iron.

The thermal conductivity of ferrosilicon is also very good, and besides, it can also be very good easily potted and thereby brought into compact form, so that the listed heat capacities, which are higher than those of the already known materials, come into their own.

Although it is particularly beneficial to first melt the ferrosilicon and then mold it used potted, it can also be crushed in a conventional manner, for. B. ground or granulated, advantageously atomized, pressed and sintered, optionally with the addition of a temperature-resistant binder. It is also possible to use the crushed ferrosilicon in the form of a To accommodate bulk in a suitable container, which then serves as a storage element. How nice mentioned, the crushing of the ferrosilicon can be done mechanically. However, it is particularly advantageous its crushing from the molten state by atomization with the aid of a liquid or a gas or by granulation with a mechanical device, because doing the individual Grains of ferrosilicon occur in a rounded form, whereby one has a granulate with a special high bulk density. This direct comminution takes place from the melt flow in the presence or with the help of bound or free oxygen, so z. B. water or air, so are the granules particularly resistant to corrosion, as they form the protective oxide skin during manufacture bring with you, which is the case in the case of ferrosilicon used in cast or broken form only forms when the heat storage tank is put into operation.

Claims (1)

Claim: Use of ferrosilicon, consisting of 8 to 50%, preferably 10 to 30% silicon, Remainder iron with manufacturing-related impurities, in cast, ground, granulated, atomized, poured with or without the addition of a temperature-resistant binding agent, pressed or sintered state as a material for heat storage cores.