DE3323937A1 - Improved process for the preparation of water-soluble alkali metal silicates and of silicate glass - Google Patents

Abstract

The invention relates to an improved process for the preparation of water-soluble alkali metal silicates and of silicate glass from a homogeneous batch of silicon dioxide and suitable metal compounds by the melt process, which is characterised in that the principal batch components are subjected separately to prewarming with the aid of the energy present in the process offgases before the batch is introduced into the melter. <IMAGE>

Description

Improved Process for Making

water-soluble alkali metal silicates and of silicate glass The invention relates to an improved process for the preparation of water-soluble alkali metal silicates and of silicate glass from a homogeneous mixture of silicon dioxide and suitable Metal compounds in the melting process, which is characterized in that the main batch components separate from each other a preheating process before being introduced into the melting tank with the help of the energy contained in the process exhaust gases.

The manufacture of water-soluble alkali metal silicates, commonly called Designated water glasses, is usually carried out on an industrial scale by melting of silicon dioxide, for example in the form of sand, quartz powder, silica or the like. and suitable alkali metal compounds, preferably the alkali metal carbonates and, if appropriate, the hydrogen carbonates or hydroxides, in suitable for this purpose Furnaces at temperatures in the range of 1000 to 1600 "C.

Silicate glass is produced in an analogous manner; generally referred to as glass, at temperatures in the range of about 1200 to 18000C, where the metal compounds in the form of salts of sodium, potassium, calcium, magnesium, Aluminum, barium, zinc, lead or other metals can be added.

Due to the high temperatures involved in the process, such a device is required Melting process requires a correspondingly high amount of energy, the costs of which are increasing Take measurements into account.

The heating of a melting furnace takes place in a technically common way Way with the help of burners in which e.g. heavy fuel oil or natural gas in open Flame burned and so the heat energy necessary to melt the reaction components is produced. To at least some of the entrained in the hot process exhaust gases Recover thermal energy and in order to - the necessary high flame temperatures reach, these exhaust gases are usually through periodically operated heat exchangers, Called regenerators, directed to the fresh air required for combustion to heat up. In this way it is possible to - in the process exhaust gases ("flue gases") at least partially to supply the thermal energy contained in the melting process again.

The recovery rates that can be achieved with the aid of the regenerator system. however, are on average only 50 to 60 Z; based on the total energy content the flue gases. The rest of the energy goes into the actual melting process lost, since the flue gases generally after passing through the regenerators in a Exhaust chimney.

From DE-OSs 30 12 073 and 30 12 074 a method is now known with which there is also a further amount of the heat potential contained in the flue gases can be used for the melting process. This is done by having one main component of the raw mixture, the sand, utilizing that contained in the process exhaust gases Heat energy, then the sand is mixed homogeneously with the other components and then the heated mixture is fed into the melting process.

A major disadvantage of this process is that it requires temperature control the preheated component must be done before this with the other components of the total mixture mixed homogeneously.

The temperature of the preheated sand must be well below the Melting point of the quantitatively essential metal salt component lie around caking or clumping of these components and the associated inhomogeneities of the mixture to prevent.

A preheating of the metal salt component of the mixture with the flue gases was generally considered to be disadvantageous, as that in the flue gases is usually sulfur compounds, e.g. SO2 or SO3, lead to undesirable reactions with the metal salt components of the mixture and the sulfates formed in remain in the molten glass and thus result in undesirable properties. Therefore, in the procedure according to the above-mentioned German Offenlegungsschrift with the process exhaust gases only the component that does not react with SO2 or SO3, namely the sand, heated.

In DE-OS 31 16 755 a method and a device to carry out this process described in the Glasrohgemenge, cullet or a mixture of the two prior to introduction into the glass furnace in an exhaust gas stream exposed at low speed and thus gently heated. One Segregation of the raw batch and consequent inhomogeneities in the products keep within reasonable limits. This - for the production of industrial glass Applicable processes cannot, however, be transferred to the production of glasses, due to their special use, high demands are placed on the homogeneity of the Material and the uniformity of the products are made.

A method of recovering the heat from. a pan glass oven escaping combustion gases. describes DE-OS 26 42 947. The aim of this process it is a powdery substance in a suspension or floating state to be heated by the hot combustion gases released from a furnace glass furnace and the fresh combustion air necessary for the process with the so heated preheat powdery substance. The powdery substance has the function a heat exchanger and can be part of the basic glass materials, which is then fed to the melting furnace together with the combustion air.

Apart from the high demands on the homogeneity of the material and uniformity of the products, there is also a need for a process., - in which the heat energy necessary for the melting process from in ste-i-.

- The fuels used to a certain extent have a high sulfur content have without that also the emission of sulfuric acid exhaust gases increases beyond the permissible level.

Surprisingly, it has now been found that both components, sand and aggregates, can be heated to a shear temperature with the process exhaust gases than with one component with subsequent admixture of a second, not heated one Component is possible if the exhaust gas flow in a corresponding to the requirements Ratio is divided and with the two partial flows both main components of the raw mixture are heated separately. In addition, it turned out that with one Such an approach not only controls the sulfur content in the emitted into the atmosphere Exhaust gases, based on the amount of glass produced, by recirculating individual gas components can be reduced in the melting or preheating process, but by the different Process parameters also control the sulfur content in the product as desired Limits is possible.

The invention relates to an improved method. for the production of water-soluble alkali detail silicates and of silicate glass from a homogeneous Mixture of silicon dioxide and suitable metal compounds in the melting process, which is characterized in that the main batch components prior to introduction into the melting tub separately from each other in a preheating process with the aid of the in the process exhaust gases contained in the energy content are subjected.

The improvement over the after. Process known from the prior art thus consists in, in addition to the main constituent dc; Mixtures, the sand, including the second component, the metal oxides or metal salts, are heated in a separate preheating system with a partial flow of the exhaust gases. It is necessary to divide the process exhaust gas flow according to the respective requirements (required amount of heat, desired sulfur content in the product, exhaust gas composition). As part of this process, the acidic components of the exhaust gases, preferably SO2 and SO3, are bound by the metal oxides or metal salts, for example according to the following reaction equation, and fed back into the furnace: Na20 + SO3 2 4 In the course of the melting process, the acidic fractions are then released again from the salts formed, in accordance with the inverse of the above reaction equation, and the process gases are enriched in SO2 or S03.

However, they are partly used by the heat exchanger for the plant Batch components supplied again; some of it leaves after the sand has been preheated the plant, during which the heat exchanger for the metal.lverbindungen supplied Share recirculated.

For preheating the batch for water glass or silicate glass production 60 to 75% of the heat is used to heat the sand, the rest from 40 to 25% required to heat up the metal oxides or metal salts. There-.

both components are at the same final temperature.

heated up. Correspondingly, the process exhaust gas flow is in parts of 3/5 to 3/4 on the one hand and 2/5 to 1/4 on the other hand to divide up the sand and separately to heat the aggregates in known apparatus.

An example. of the method according to the invention in the operating state shows the flow diagram in FIG. 1.

The flame of the heavy oil burner heats the material to be melted in the melting tank 1. From the combustion of e.g.

Heating oil containing 1.5% sulfur feeds the combustion air into a Amount of e.g. 50 kg / h SO2, 2, with.

The SO2 concentration in the total exhaust gas flow is still enriched by 25 kg / h of S02, 3, the thermal decomposition of the bound in the aggregates S02 or SO3 quantities are released again.

The total exhaust gas stream 4, which now contains 75 kg / h SO2, is divided into two substreams 5 and 10 divided, of which one, i.e. partial flow 5, 2/3 of the exhaust gas, and thus also of sulfur dioxide, carries with it and in a heat exchanger (schematized, 6) heats the sand 7; afterwards the exhaust gases leave and with them the accumulated ones 50 kg / h SO2 via the exhaust air chimney 8 the system.

The heated sand 9 is fed to the melting furnace.

The remaining third 10 of the total exhaust gas flow 4, and with it 25 kg / h 502, heat the supplements in a second heat exchanger (schematized, 11) 12, in this case soda, on; the acidic SO2 is bound to and on the soda Paths 13 of the melting tank 1 are fed back. This amount becomes during the melting process of 25 kg / n S02 is released again, 3, and thus temporarily increases the amount from the combustion of the sulfur-containing oil resulting in the amount of SO2 supplied to the furnace 1 2 Uberraschezoci When carrying out the method according to the invention it was that by the separate Heating of the two fouling mixture components of the glass tube mixture with two substreams .the process exhaust gases when starting up the smelting plant into the Amount of sulfur dioxide emitted in the atmosphere per hour of operating time of the system increases to an ever lesser extent and after reaching the operating state the system adjusts to a certain level. In the above case, that the combustion air at 2 when the system starts up a quantity of 50 kg / h SO2 and the exhaust gas flow is divided in the ratio 2/3: 1/3, this goes out the table below.

Process table Al) BI) C1) D1) E1) stage (kg / h) (kg / h) (kg / h) (kg / h) (%) Start of the system 50 33.3 16.7 66.7 -2 66.7, 44.5 22.2 72.2 33.6 3 72.2 48.1 24.1 74.1 8.1 4 74.1 49.4 24.7 74.4 2.7 5 74.4 49.8 24.9 - 74.9 0.8 6 74.9 49.9 25.0 75.0> 0.2 7 75.0 50.0 25.0 75.0 X 0f2 operating status 75.0 50.0 25.0 75.0 0.0 5) Comments: A: SO2 supply at 2 (see Fiq.l) B: SO2 emissions at 8 C: SO2 amount tied to surcharge for 13 or 3 D: - SO2 supply for 2 in the following Procedural stage.

E: Increase in SO2 emissions compared to the preliminary stage.

As can be seen from column B of the table, the S02 emission increases in the exhaust air chimney 8 from 33.3 kg / h when starting up the system to 50 kg / h after reaching of the operating state, whereby the rate of increase is getting smaller. Since the Glass output due to a reduced dwell time of the melting material in the melting furnace 1 can be increased due to the method according to the invention, the emission decreases of S02 per ton of glass or water glass emitted.

Surprisingly, the sulfur content in the glass increases when the Process according to the present procedure only slightly; he can also get through Change of the process parameters, such as the heating temperature for the aggregates, being controlled. In addition, part of the addition of sodium sulfate can be used as a refining agent, which is added to the raw batch in order to obtain bubble-free, clear glass, can be saved.

The use of waste heat from the process for additional separate heating the main constituents of the batch lead to extensive utilization of the exhaust gas heat except for the temperatures necessary to avoid falling below the dew point in the chimney. This reduces energy costs for heating the components in the melting tank reduced. In addition, the regenerative chambers can be smaller designed and thus saved part of the investment costs for the construction of the chambers because their waste heat is still used to heat the feed material. Of course there is the option of using additional firing or external heat to feed the feed material heating up and thereby also reducing fuel costs. As the components of the raw glass mix on a higher level Temperature level than with conventional methods, the. Time of heat absorption in the actual melting tank, and with the same heat load on the melting tank leads - this leads to an increase in capacity.

Despite the different particle sizes and bulk weights of the Raw material components, carries out the separate continuous heating of the batch components with the hot process exhaust gases and the subsequent combining of the heated components to a homogeneous one with regard to the melting behavior in the subsequent melting process Mixture which later results in a uniform glass. Segregation phenomena of the Components before the melting process, as feared in the prior art, are avoided.

In the example below, the implementation of the erfindunsgemäße Method explained in more detail using a water glass melting process.

In a water glass tub with a melting power. of 12 t / h with regenerative preheating of the combustion air, the amount of Abyas fell to 19,000 m3 / h (under normal conditions) with a temperature of 600 ° C. The exhaust gas flow was. divided in a ratio of 70 g to 30%. The greater part dried the sand and heated it to 4500C; the exhaust gas was cooled to 200 ° C. in the process. The smaller one Part of the gas flow also heated the soda to 450 "C.

The furnace output increased due to the batch preheating of 12 t / h to 18 t / h, which corresponds to an increase in the melting capacity of 50%.

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Claims (3)

Claims. Improved Process for Making Water Soluble Alkali metal i 3. ikaten and of silicate glass. from a homogeneous mixture of silicon dioxide and suitable metal compounds in the melting process, characterized in that the egg main batch components before Introduce into the melting tank separately from each other with the help of a preheating process of the energy contained in the process exhaust gases. 2. The method according to claim 1, characterized in that the process exhaust gases in two different sizes. Partial streams are divided, with the greater proportion of the silicon dioxide, the smaller part heats the metal compounds to the same temperature level, before the preheated glass raw materials are mixed with one another and a pan glass melting point, fen are fed. 3. The method according to claims 1 and, characterized in that the two partial flows are divided in a volume ratio of 60:40 to 75:25.