Claims
- 1. Process for vitrifying environmentally hazardous waste material in a glass melting furnace, comprising:
- forming a glass melt having a surface in the furnace;
- forming a batch containing the waste material and an additive consisting of at least one compound selected from the group consisting of phonolite and SiO.sub.2 containing materials;
- adding the batch to the furnace so that a batch layer is formed on the molten glass;
- heating the molten glass after the batch layer is formed thereon, solely by devices in the molten glass;
- producing a gall layer of glass gall on the surface of the glass melt between the glass melt and the batch layer, said glass gall consisting essentially of at least one of an alkali salt and an alkaline earth salt;
- withdrawing glass gall from the gall layer as necessary and controlling the composition, supply, and distribution of the batch so that the gall layer and the batch layer are maintained at respective thicknesses which are sufficient to maintain the furnace atmosphere above the batch layer at a sufficiently low temperature so that substantially all of the condensable components which emerge from the molten glass and the gall layer condense in the batch layer; and
- withdrawing the molten glass from the furnace via a first outlet means.
- 2. Process in accordance with claim 1 wherein said glass gall consists essentially of at least one compound selected from the group consisting of
- CaSO.sub.4, CaCl.sub.2, MgSO.sub.4, and MgCl.sub.2 added during the melting process with said waste and/or as a separate additive, and
- Na.sub.2 SO.sub.4, NaCl, K.sub.2 SO.sub.4, KCl, Li.sub.2 SO.sub.4, and LiCl produced by reaction with said CaSO.sub.4, CaCl.sub.2, MgSO.sub.4, and MgCl.sub.2.
- 3. Process in accordance with claim 1 characterized in that the thickness of the gall layer is from 2 cm to 5 cm.
- 4. Process in accordance with claim 1 wherein the thickness of the batch layer is more than 5 cm.
- 5. Process in accordance with claim 1 wherein during operation of the glass melting furnace, the required thermal energy is generated exclusively electrically by means of heating electrodes which extend into the glass melt.
- 6. Process in accordance with claim 1 wherein the necessary withdrawal of gall is carried out on a essentially horizontal plane and that the melted glass is separately withdrawn from the furnace while maintaining a constant level of the glass melt.
- 7. Process in accordance with claim 1 wherein the glass is withdrawn directly from inside the furnace from the depth of the melt.
- 8. Process in accordance with claim 7 wherein the first outlet means is a bottom outlet means.
- 9. Process in accordance with claim 1 wherein a second outlet means is provided for withdrawing the gall.
- 10. Process in accordance with claim 9 wherein the amount of withdrawn gall and, hence, gall layer thickness in the glass melting furnace are controlled by applying a strong vacuum at the second outlet means.
- 11. Process in accordance with claim 9 wherein the amount of withdrawn glass and, hence, the height of the glass melt level in the glass melting furnace are controlled by applying a strong vacuum at the first outlet means.
- 12. Process in accordance with claim 9 wherein the necessary withdrawal of gall from the second outlet means of the glass melting furnace is carried out discontinuously by means of tapping the furnace.
- 13. Process in accordance with claim 9 wherein the first and second outlet means are heated.
- 14. Process in accordance with claim 11 wherein the furnace has a bottom where a heavy metal melt gathers, and from time to time, the heavy metal melt is withdrawn from the furnace.
- 15. Process in accordance with claim 1 wherein exhaust gas emerging from the furnace falls within the range of 80.degree. to 400.degree. C.
- 16. Process as in claim 15 exhaust gas emerging from the furnace falls within the range from 100.degree. to 200.degree. C.
Priority Claims (3)
| Number |
Date |
Country |
Kind |
| 3841918 |
Dec 1988 |
DEX |
|
| 3903194 |
Feb 1989 |
DEX |
|
| 3912311 |
Apr 1989 |
DEX |
|
SUMMARY OF THE INVENTION
This application is a continuation-in-part of U.S. application Ser. No. 303,841, filed Jan. 30, 1989 and now U.S. Pat. No. 4,948,411 which is incorporated herein by reference.
The invention relates to a process for operating a glass melting furnace, particularly for vitrifying environmentally hazardous waste material such as asbestos or asbestos containing demolition material, sewage sludge, varnish sludge, ashes, and filter dust. During operation, batch including the waste material and additives containing SiO.sub.2 is fed into the furnace and forms a batch layer on top of the molten glass, which is heated by electrodes therein.
It is known to convert waste material which occurs in the form of toxic or radioactive sludge or suspensions, for example, into glass by means of melting after adding additives and after mixing into batch. Some of the waste material is dissolved in the melt, i.e., it is chemically decomposed, and the rest is firmly incorporated in the glass when the latter solidifies after withdrawal from the furnace. It is advantageous that glass is difficult to leach out, so that release of components contained in the glass can occur only to a very small extent. This permits a disposal without problems or further manufacture of bodies made from this glass. Processes of this kind are known, for example, from German patent 26 31 220 or from U.S. Pat. No. 4,666,490.
A problem which often occurs when vitrifying waste materials is that these waste materials often contain a high percentage of chlorides and sulfates; these are absorbed by the melt only to a small extent during melting, even when the glass melt is fully saturated with chlorides and sulfates. This leads to the disadvantageous formation of large amounts of exhaust gas which develop from the chlorides and sulfates, particularly Cl, HCl, SO.sub.2, and SO.sub.3. Further, it is disadvantageous that evaporation causes heavy metals and alkali metals to enter the exhaust gas from the glass melt. This requires a purification which involves a great amount of labor and cost which in connection with the high energy consumption negatively affects the cost-effectiveness ratio of the process.
It is hence an object of the invention to find a process of the aforesaid kind wherein the amount of exhaust gas and the energy consumption are reduced and wherein the cost-effectiveness ratio is improved.
The object is accomplished by a process wherein a liquid alkali salt or alkaline earth salt gall layer (a layer of glass gall) is produced on the surface of the glass melt. The layer is maintained at a thickness corresponding to the respective operational conditions of the furnace by withdrawing a respectively required amount. Alternatively or supplementally, the object is accomplished by maintaining the batch layer at a thickness which corresponds to the respective operational conditions of the furnace, by controlled supply and distribution of a suitably composed batch.
The gall layer permits a substantially improved heat transfer into the batch to be molten, which reduces the amount of energy required for the working of the process and increases the throughput which can be achieved with the process. Moreover, large percentages of the substances emerging from the melting process, particularly the chlorides and sulfates, are incorporated in the gall layer so that the amount of exhaust gas which develops is substantially reduced. Labor and cost for the purification of the exhaust gas are thus significantly reduced. After cooling and solidification the gall which was withdrawn from the glass melting furnace can easily be treated to form dry and clean salts and then be subject to further manufacture or be deposited on a waste disposal site. The metal oxides which develop during the melting are practically completely absorbed in the glass melt with no particular measures required and are thus firmly incorporated in the glass body to be formed. Finally, in the new process the gall layer and/or the defined batch layer avoid an evaporation of heavy metals and alkali components at the surface of the glass melt. The amounts of exhaust gas and the harmfulness are thus further reduced.
US Referenced Citations (8)
Continuation in Parts (1)
|
Number |
Date |
Country |
| Parent |
303841 |
Jan 1989 |
|
Patent Grant
5035735
