PROCESS FOR DETECTING WATER LEAKS FROM SMELTING FURNACES IN METAL OR ALLOY PRODUCTION PLANTS AND RELATED PLANT

Abstract

The invention concerns a process for detecting water leaks in smelting furnaces (2; 4) or in metal or alloy treatment plants, comprising the following steps: (i) providing at least one smelting furnace (2; 4), or at least one metal or alloy treatment plant provided with a water cooling system (5) and being connected to a process fume exhaust system; (ii) mixing in the cooling water a tracer chemical which is volatile in the event of water leakage together with the exhaust gases and which is suitable to be detected by an analysis system of the exhaust gases; and (iii) detecting said tracer chemical contained in the exhaust gases by said analysis system comprised in said process fume exhaust plant, wherein said tracer chemical is deuterated water. The invention further refers to a Plant for the production of metals or alloys.

Claims

1. A process for detecting water leaks in smelting furnaces or in metal or alloy treatment plants, comprising the following steps: (i) providing at least one smelting furnace or at least one metal or alloy treatment plant provided with a water cooling system and connected to a process fume exhaust system; (ii) mixing in the cooling water a tracer chemical which is volatile in the event of water leakage together with the exhaust gases from the smelting furnace or metal or alloy treatment plant and which is suitable to be detected by an analysis system of the exhaust gases produced in said at least one smelting furnace or in said at least one metal or alloy treatment plant; and (iii) detecting said tracer chemical contained in the exhaust gases by said analysis system comprised in said process fume exhaust plant, wherein said tracer chemical is deuterated water.

2. The process according to claim 1, wherein said analysis system is a mass spectrometer.

3. The process according to claim 1, wherein said cooling system is a closed circuit system.

4. The process according to claim 3, wherein said closed circuit of cooling H.sub.2O contains at least 0.1% by mass of D.sub.2O.

5. The process according to claim 1, wherein said cooling system comprises cooling panels provided with water pipes.

6. The process according to claim 1, wherein said process fume exhaust plant comprises at least one deduster device and that said analysis system is located downstream of the device.

7. A plant for the production of metals or alloys comprising: (a) at least one smelting furnace, or at least one metal or alloy treatment plant, provided with a water cooling system; and (b) a process fume exhaust plant adapted to extract and remove the exhaust gases produced by said at least one smelting furnace or by said metal or alloy treatment plant; wherein (c) said cooling water is admixed with a tracer chemical, which is deuterated water, which is volatile together with the exhaust gases from the smelting furnace or metal or alloy treatment plant, and is adapted to be detected in the exhaust gases produced in said at least one smelting furnace or in said metal or alloy treatment plant by an analysis system; and (d) said analysis system is located in said process fume exhaust plant.

8. The plant according to claim 7, wherein said analysis system is a mass spectrometer.

9. The plant according to claim 7, wherein said cooling system comprises cooling panels provided with water pipes and in that said cooling system.

10. The plant according to claim 7, wherein said process fume exhaust plant comprises at least one deduster device and that said analysis system is located downstream of this/these device(s).

11. The process according to claim 1, wherein the at least one smelting furnace is an electric arc furnace.

12. The process according to claim 6, wherein said process fume exhaust plant further comprises an exhaust gas cooling device.

13. The process according to claim 7, wherein the at least one smelting furnace is an electric arc furnace.

14. The process according to claim 7, wherein the cooling system is a closed circuit system.

15. The process according to claim 10, wherein said process fume exhaust plant further comprises an exhaust gas cooling device.

Description

DESCRIPTION OF PREFERRED EMBODIMENT EXAMPLES

[0033] FIG. 1 illustrates a steel production plant and the relative fume extraction system according to the invention.

[0034] FIG. 2 schematically illustrates a prior art electric arc furnace to which the inventive concept is applicable.

[0035] FIG. 3 illustrates in a graph (molar fractions of H.sub.2O, D.sub.2O and HDO as a function of the isotopic fraction D/(D+H)) the exchange equilibrium between H.sub.2O/D.sub.2O and HDO.

[0036] FIG. 4 illustrates the detection of traces of D.sub.2O for the ratio 18:19 of the atomic mass for a simulation of water leakage.

[0037] FIG. 1 illustrates a steel production plant according to the invention. The plant depicted is composed of two furnaces, an electric arc smelting furnace 2 and a ladle furnace 4 for refining treatments. The exhaust gases produced inside the arc furnace 2 are extracted from a fume extraction system, which can comprise the most varied treatment element components in various combinations and sizes, ranging from different forms of cooling of the fumes or exhaust gases, to different types of separators of solid and liquid components from the fumes, such as hoods, filters, cyclones, combustion devices, sedimentation chambers. Other typical elements of such plants are valves and fans to direct the flows.

[0038] In an exemplary form the fume system line is composed of a cooled conduit 6 which includes a sedimentation chamber 8 which removes heavy particles while cooling the fumes. Downstream of this chamber is a cyclone 10 for extracting further dust from the exhaust gases, which subsequently pass through a heat exchanger 12. This exhaust gas line deriving directly from the inside of the electric arc furnace 2 is the primary branch 14 of the plant and contains any water deriving from leaks in the faulty cooling panels of the electric furnace. The exhaust gases exiting the ladle furnace 4 and the gases extracted by a hood 16 above the electric arc furnace 2 comprise any water leaks outside the arc furnace 2 and deriving from the cooled and panelled vault of the ladle furnace 4 and form the secondary branch 18 of the exhaust gas plant of the steel production plant. The primary branch 14 and the secondary branch 18 join and the total exhaust gases are conveyed through a sleeve filter 20 to further purify the gas and then exit the plant through a stack 22. The entire extraction line is under vacuum by fans generally arranged at the base of the stack, which have the task of extracting the fumes. As mentioned, the plant depicted is only one example of a plant comprising an electric furnace in which the present invention can be applied and in which the analysis system can be integrated at various points to determine the presence of tracer added to the cooling water detectable in the exhaust gases in case of water leakage. The analysis system can preferably be located in the flue of the stack 22 (variant 11c), but alternatively also in the primary branch 14, clearly downstream of the electric arc furnace 2, such as for example immediately after the electric furnace (variant 11a) or before the filter 20 (variant 11b). If only the cooling water of the arc furnace 2 is provided with additional D.sub.2O, but not the cooling water of the ladle furnace 4, a detection of the tracer is a sure indication of a leak in the arc furnace 2.

[0039] A steel production plant may comprise one or more furnaces or different types of furnaces in various combinations. If it is necessary to determine any water leakage in their respective cooling circuits, it is sufficient to arrange one or more analysers in the section of the fumes extraction system downstream of each furnace of interest (namely one for each furnace provided with deuterated water). To detect water leaks from the ladle furnace 4, it is advisable to have an analysis system (not shown) in the line 18 before encountering other lines which could contain tracers deriving from water leaks which do not derive from the ladle furnace 4. Usually the detection of leaks from the arc furnace 2 is of the most interest, and only the cooling water of this furnace is admixed with a tracer. In this case the analysis system can be arranged in the stack 22 (variant 11c) after the joining of the two branches 18 and 14 since the tracer can only derive from the arc furnace 2. If both arc furnace 2 and ladle furnace 4 leakage are to be monitored, two separate analysis systems must be provided downstream of the respective furnace before the related exhaust fume/gas lines meet.

[0040] The invention is applicable to all variants of process fume exhaust systems and combinations of furnaces mentioned above, with the only variation being the need to adapt the amount of tracer added to the size of the plant and the position of the analysis system and include a positioning of analysers at the appropriate points.

[0041] FIG. 2 schematically illustrates a prior art electric arc furnace 2 to which the inventive concept is applicable. A furnace as depicted is divided into a lower part 1 with the bottom and the vat for collecting the molten metal 15 covered by slag 17 and an upper part 3 covered with cooling panels 5 and covered by a panelled vault 9, which are often subject to water leakage from the respective cooling panels. The wall of the upper vat 3 has openings through which injectors 7 can be inserted to provide oxygen (for combustion), coal, lime and auxiliary fusion materials and to confer certain chemical, mechanical or physical features to the metal produced. An electric arc is produced with the electrodes 11 which melts the metal. The exhaust gases or fumes can be extracted from the furnace through an extraction mouth 13, which are then extracted by a pipe 6. The molten metal can instead be discharged from a hole 19 in the bottom of the furnace 2. The furnace can tilt on curved racks (not shown), to the right to spill through the hole 19, to the left to output the excess slag from the slag door 21. For scrap loading in general (in the case of basket feeding) the vault 9 opens, moving sideways around a pin. Alternatively, another side door (not shown) is arranged in the middle between the door 21 and the hole 19 for feeding scrap by means of a so-called continuous loading conveyor belt. There may be traces of water in the furnace, usually deriving from the humidity of the loaded material, the humidity of air, and the water sprays which cool the electrodes, however according to the invention only the water leaks coming from the cooling panels are provided with deuterium concentrations greater than the natural concentration, the D.sub.2O being added only to the water fed to the cooled panels.

[0042] FIG. 3 illustrates in a graph (molar fractions of H.sub.2O, D.sub.2O and HDO as a function of the isotopic fraction D/(D+H)) the exchange equilibrium between H.sub.2O/D.sub.2O and HDO. Due to this equilibrium, the concentration of HDO in the concentration range concerned is higher than the concentration of D.sub.2O and it is therefore preferable to measure the peak of HDO (19) instead of D.sub.2O (20).

[0043] The mass spectrometer measures the mass of atoms or molecules. In this regard, the gaseous material to be analysed is inserted into an empty ionization chamber. An accelerated electron beam transforms what is introduced into positive ions which are pushed out of the chamber by an intense electric field. The speed reached by the ions depends on the mass, the lighter ions precisely reaching higher speeds than the heavy ones. In passing through a magnetic field, each ion deviates from its original trajectory because of its velocity and thus its mass. The magnetic field strength is slightly varied and a signal is obtained when the field is strong enough to deflect the ion beam enough to direct it into the detector. The mass of the ion type formed is calculated based on the accelerating voltage and magnetic field strength applied to obtain the signal. The mass spectrum is the diagram of the signal detected as a function of the magnetic field. The position of the peaks is used to calculate the mass of the accelerated ions, while their relative height indicates the proportion of the various types of ions. Mass spectrometers are known in the art and need not be described in more detail. The market offers a wide range of instruments useful for this purpose. Suitable spectrometers are for example systems for continuous smoke and steam analysis based on a mass spectrometer with a quadrupole mass analyser with a double detection system: SEM (secondary electron multiplier) and Faraday. The mass range is 0 to 50 amu (atomic mass unit) with a sensitivity of 100% at 100 ppb. The speed is advantageously more than 500 measurements per second and the response time <300 ms. An ultra high vacuum (UHV) turbomolecular pump with a flow rate of 60 l/s with an integrated membrane pump for sample foreline and bypass-type pumping can be provided as a vacuum system. The inlet for the capillary gas sampling is suitable for continuous sampling with a sample pressure between 100 mbar and 2 bar. Components may be a molecular leak manifold bypass, a 2 metre long heated quartz capillary sampling line, an inlet heating system ranging from room temperature to 200° C., and a bypass pumping line with a sample bypass control valve.

[0044] The measurement system can be improved by reducing system vibrations, minimizing cold spots, optimizing capillary diameter and the dilution of fumes or exhaust gases.

[0045] To demonstrate the functionality of the principle of the invention, in a system as depicted in FIG. 1, injections of deuterated water were carried out within the furnace and the sedimentation chamber at various concentrations and at various frequencies in a limited period of time.

[0046] FIG. 4 illustrates in exemplary form the detection of traces of D.sub.2O for the ratio 18 amu:19 amu for a simulation of water leakage with two injections within one minute. The diagram clearly distinguishes two peaks spaced apart over time, which correspond to the two injections made and express the variation in the H.sub.2O/D.sub.2O ratio caused by the presence of high concentrations of D.sub.2O. The graph shows a temporary simulation of leaks, in the case of continuous leaks the trend detected would obviously be different.

[0047] During operation further embodiment modifications or variants of the process and the plant object of the invention may be implemented. If such modifications or such variants should fall within the scope of the following claims, they should all be considered protected by the present patent.