Combined furnace

Abstract

Installation including an industrial glass furnace (1) including a tank (2) for molten glass (3), a combustion heating chamber (4) situated above the tank (2), and a duct for evacuation of flue gases in communication with said heating chamber (4), and a stone furnace including a firing zone (21) for stone to be fired, the flue gas evacuation duct including a flue gas outlet that is connected to the firing zone (21) of stone to be fired and supplying the firing zone (21) of stone to be fired with flue gases at high temperature.

Claims

1. An installation including an industrial glass furnace (1) comprising a tank (2) for molten glass (3), a combustion heating chamber (4) situated above the tank (2), and a duct for evacuation of flue gases in communication with said heating chamber (4), and a stone furnace (11) comprising a firing zone (21) for stone to be fired, and a cooling zone (22) situated under the firing zone (21), wherein ambient air enters at a bottom portion of the stone furnace (11), passing upwardly through the cooling zone (22), the duct comprising a flue gas outlet that is connected to the firing zone (21) of stone to be fired and supplying the firing zone (21) of stone to be fired with flue gases at a temperature greater than 900° C.

2. The installation as claimed in claim 1, wherein the flue gases outlet is in a duct (10) of the flue gases evacuation duct.

3. The installation as claimed in claim 1 wherein the fuel is gas and/or fuel oil, the oxidizer is oxygen and/or air and the daily capacity of the glass furnace is greater than 10 tons of glass per day.

4. The installation as claimed in claim 1, wherein the firing zone (21) is tubular, a stone to be fired feeding zone being disposed above and a fired stone extraction zone being disposed below.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features, details and advantages of the invention will become apparent on reading the following detailed description and from the appended drawings, in which:

(2) FIG. 1 is a sectional view of a combined installation according to one aspect of the invention;

(3) FIG. 2 is a sectional view of a combined installation according to another aspect of the invention;

(4) FIG. 3 shows a variant of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) The following description and drawings essentially contain elements of a certain character. They may therefore not only serve to explain the present invention better but also contribute to its definition if necessary.

(6) The Applicant has carried out trial calcination of limestone in the duct of an operating industrial glass furnace. The mass of the samples of limestone was from 396 to 633 grams. The temperature at the start of calcination was between 1240 and 1340° C. inclusive. The temperature at the end of calcination was between 1290 and 1380° C. inclusive. The calcination reaction CaCO.sub.3.fwdarw.CaO+CO.sub.2 leads to a theoretical loss of mass of 43%. Calcination times less than 1 hour produce losses of mass that are too low, indicative of incomplete calcination. One hour of calcination produces a loss of mass of 42.1%. 1.75 to 2.25 hours of calcination produces a loss of mass 43.7 to 44% reflecting complete calcination and a slight loss of material on recovering the sample. The loss is linked to the test conditions and may be prevented in an industrial process. The flue gases leaving the glass furnace enable calcination of the limestone. The other stones to be fired may include dolomite, flint, hydrated alumina.

(7) The glass furnace 1 includes a tank 2 containing molten glass 3 for batch production. The glass furnace 1 includes a combustion chamber 4 situated above the bath of molten glass 3 and an upper wall 5 made up of a vault 5a and vertical parts 5b termed side walls (length) or gables (width) delimiting the combustion chamber 4. The glass furnace 1 includes at least one burner 6 fed with fuel oil or gas and an oxidizer inlet 7. The oxidizer may be air, see FIG. 1, or oxygen, see FIG. 2.

(8) The tank 2 and the upper wall 5 are made of refractory materials reinforced by an external metal structure away from zones of high temperature. The burner 6 produces a flame oriented horizontally in the combustion chamber 4. The glass furnace 1 includes a flue gases outlet 8 in one of the vertical walls 5b above the bath of molten glass. The burner 6 and the flue gases outlet 8 may be on the same shorter side so that the flame and the flue gases follow a U shaped path in the combustion chamber 4. The glass furnace 1 may be a loop furnace.

(9) Downstream of the glass furnace 1 in the direction of movement of the flue gases the installation includes a duct 10. The duct 10 is a substantially horizontal flue gases duct. The duct 10 is in fluid communication with the combustion chamber 4 via the flue gases outlet 8. The duct 10 is made of refractory materials reinforced by an external metal structure away from the zones of high temperature. The duct 10 is provided with a fork and has two outlets. The duct 10 does not include valves.

(10) Downstream of the glass furnace 1 in the direction of movement of the flue gases the installation includes a stone furnace 11. The stone furnace 11 may be a lime furnace. The stone furnace 11 has a vertically oriented structure. The stone furnace 11 is circular. The stone furnace 11 is made of refractory materials reinforced by an external metal structure away from the zones of high temperature. The stone furnace 11 may have a height of 25 m and a diameter of 4 m for example. The stone furnace 11 includes a chamber 12 with a vertical axis, a bottom opening 13 and a top opening 14 or throat. The bottom opening 13 enables extraction of the fired stone and introduction of sufficient air to prevent flue gases exiting via said bottom opening 13.

(11) The top opening 14 enables the introduction of the stone to be fired, for example via a hatch 15, and the flue gases to exit. The top opening 14 may be fitted with a separator for on the one hand treating the flue gases, in particular extraction of dust in a filter 16, and on the other hand feeding the stone furnace 11 with stone to be fired. Downstream of the filter 16 a chimney 17 is adapted to evacuate the cooled flue gases from which the dust has been removed. Downstream of the filter 16 the flue gases can be released into the atmosphere whereas the filter receives directly the flue gases coming from the stone furnace 11 or from an energy recovery device.

(12) The structure of the chamber 12 is generally airtight. The chamber 12 includes a preheating zone 20 adjacent to the top opening 14, a firing zone 21 situated under the preheating zone 20, and a cooling zone 22 situated under the firing zone 21 and adjacent to the bottom opening 13. Between the firing zone 21 and the cooling zone 22 the chamber includes an opening 23 in fluid communication with one of the outlets of the duct 10. The cooling zone 22 has a height of 55 to 75% of the height of the chamber 12. The firing zone 21 has a height of 5 to 20% of the height of the chamber 12. The preheating zone 20 has a height of 10 to 25% of the height of the chamber 12.

(13) The installation also includes a heat exchanger 25 in fluid communication with the other outlet of the duct 10. The heat exchanger 25 transfers thermal energy from the flue gases to the air feeding the glass furnace 1. The transfer may be via heat conducting plates in the case of a recovery device. The transfer may be via intermediate thermo storage in materials of high calorific capacity in the case of a regenerator device. The flows of flue gases and oxidizer air alternate, one heating and the other cooling the regenerator device, by means of mobile flaps.

(14) The heat exchanger 25 has an ambient air inlet 26 and a hot air outlet 27. The hot air outlet 27 is connected by a duct 28 to the oxidizer inlet 7. The heat exchanger 25 has a hot flue gases inlet 29 fed by the other outlet of the duct 10 and a cooled flue gases outlet 30 leading to the filter 16.

(15) In the embodiment shown in FIG. 2 the glass furnace is an oxygas furnace, that is to say it uses a fuel gas, generally methane, and oxygen as the oxidizer. The inlet and outlet gas flow rates are then reduced, in particular by 80%, at the oxidizer inlet because of the absence of nitrogen in the air. Because of this, the NOx content can be divided by 3. The flue gases are made up essentially of water vapor coming from the combustion of the gas and carbon dioxide from the combustion of the gas and the degassing of the glass, together with other degassing gases. The flue gases flow rate being lower than in the previous embodiments, at least two glass furnaces 1 and one stone furnace 11 may be coupled up.

(16) In the embodiment shown in FIG. 3 a top up burner 35 is provided in the stone furnace 11 and consumes air rising in the cooling zone 22 or alongside the stone furnace 11 supplying a supplementary flow rate of flue gases at high temperature.

(17) In the above embodiments the flue gases exit the stone furnace at low temperature, having lost a large part of the chlorides and sulfates that said flue gas contains on leaving the glass furnace. The flue gases are therefore neutralized and cleaned to the point where neutralization of the flue gases further downstream becomes of no utility. Neutralization produces CaCl.sub.2 and CaSO.sub.4 in the case of lime, MgCl.sub.2 and MgSO.sub.4 in the case of dolomite, remaining in the fired stone. These compounds add chlorides and sulfides to the bath of glass.

(18) The invention is of greater interest if the glass furnace produces a grade of glass necessitating a high temperature, in particular borosilicate glass, for example Pyrex®, or vitroceramic.

(19) In other words, the stone to be fired includes at least one of the following: limestone, dolomite, flint or hydrated alumina. The stone to be fired is introduced into the stone furnace from the top and begins a descent leading it after firing to exit via the bottom of the stone furnace, having passed through the chamber thereof. The chamber includes a preheating zone, a firing zone and a cooling zone in that order in the direction in which the stone descends.

(20) The gases pass upwards through the chamber. Said gases may include ambient air entering at the bottom and leaving either at the top of the stone furnace or at the top of the cooling zone. Said gases include combustion flue gases. The combustion flue gases enter at the bottom of the firing zone of stone to be fired. The combustion flue gases travel through the firing zone and the preheating zone. The combustion flue gases come from a flue gases evacuation duct downstream of a combustion heating chamber of an industrial glass furnace. The industrial glass furnace includes a molten glass tank and said flue gases evacuation duct at the outlet of the heating chamber during heating of the glass furnace. The combustion flue gases are at a temperature between 1300 and 1500° C. inclusive at the outlet of the heating chamber. The flue gases at the outlet of the stone furnace are at a temperature between 100 and 200° C. inclusive, preferably between 100 and 150° C. inclusive.

(21) The invention is not limited to the examples of processes and containers described hereinabove by way of example only and encompasses all variants that the person skilled in the art might envisage that are within the scope of the following claims.