VACUUM INSTALLATION FOR A STEEL TREATMENT VESSEL AND ITS OPERATION

Abstract: The present invention relates to a vacuuming process and installation for the in-ladle treatment of steel, applicable to iron metallurgy within the degassing and/or decarburation processes as well as to other similar processes. According to the invention, the process consists in providing a rough vacuuming achieved by summing more rough suction points, parallely connected through a single path to the ladle, thereby a pressure ranging from 100 to 150 mbar being obtained. In the second step, the direct connection of the rough suction points to the ladle is closed and they are serially connected to another row of points for medium suction which are also parallely and directly connected to the ladle, by summing the effect, a pressure in the range of 10 to 20 bars being reached. In the last step, the direct connection of the medium suction points to the ladle is closed, followed by serially connecting these points to another row of high suction points also parallely connected and through a single path to the ladle, wherein a pressure ranging from 0.1 to 0.5 mbar is obtained by summing the effect. According to the invention, the installation is provided with a rough vacuum stage (A), followed by a medium level vacuum stage (B) and a high vacuum stage (C) serially connected by some valves (1 and 2) and parallely connected by other valves (15, 16 and 17) to a connecting pipe (18).

Description: VACUUM INSTALLATION FOR A STEEL TREATMENT VESSEL AND ITS OPERATION The present invention relates to a vacuuming process and installation for the treatment of steel, applicable to the secondary metallurgy of steel, within the degassing and/or decarburation processes as well as to other similar processes. Upon generating the vacuum in the ferrous metallurgy there is known a vacuuming process by the ejection of fluids (steam) , the vacuum being generated by the suction effect of the steam jet, the gases from inside the ladle being thereby eliminated. The disadvantages of this process lie in the necessity of preparing the steam at the required pressures and temperatures, and in the high steam consumption, which leads to increasing the steel cost. For the purpose of in-ladle generation of vacuum there is known an installation provided with ejectors which operate with steam and which, serially connected in more steps and connected to the ladle, provide the required vacuum inside the ladle. The disadvantage of said installation is in conjunction with the presence of water on the suction path of the ejectors, which may cause the contamination of the remanent atmosphere inside the ladle. The invention solves the problem of providing a vacuuming process and installation for the treatment of steel, which enables the lowering of the operational costs by the use of dry mechanical pumps located in a specific parallel and serial configuration. According to the invention, the vacuuming process for the treatment of steel, consists, in a first step, in providing a rough vacuum stage achieved by summing more rough suction points, parallelly connected through a single path to the ladle, thereby a pressure ranging from 100 ... 150 mbar being obtained. In the second step, the direct connection of the rough suction points to the ladle is closed and they are serially connected to another row of points for medium suction which are parallelly connected and directly connected to the ladle, a pressure ranging from 10 to 20 bars being reached inside the ladle by summing the effect of the two rows of rough and medium suction points. Finally, in the third step, the direct connection of the medium suction points to the ladle is closed, followed by serially connecting these points to another row of high suction- points also parallelly connected and through a single path to the ladle. Thus, the effect of the three rows of points for rough, medium and high suction is summed, thereby a pressure ranging from 0.1 to 0.5 mbar being reached inside the ladle. The installation according to the invention is provided with a rough vacuum stage, followed by a medium level vacuum stage and a high vacuum stage, serially connected by means of some valves and parallelly connected through other valves to a connecting pipe, whereon some by-pass valves are interposed between the rough and medium level vacuum stages and the medium level and high vacuum stages. The rough vacuum stage is provided with mechanical vacuum pumps parallelly connected to a manifold through some valves, and to the environment through the purge valves. The medium level vacuum stage and the high vacuum stage are provided with mechanical vacuum pumps parallelly connected to some manifolds through some valves. The following advantages are obtained by the application of the invention: - decrease of the operational costs relating to the thermal and electric energy consumed; - increase of the steel quality due to the high vacuum obtained and the purity of the residual atmosphere; - improvement of the process efficiency; - simplification of the installation construction; - automation of the installation; - reduction of the volume occupied by the installation; - elimination of the water pollution; - decrease of the industrial water consumption. There is given hereinafter an embodiment of the invention in connection with the only figure, which represents the pneumatic diagram of the vacuuming installation for the treatment of steel. The vacuuming process for the treatment of steel, according to the invention is based on a dry vacuuming principle and consists, in a first step, in a rough vacuuming obtained by summing more coarse suction points which are parallelly connected to a single path, whereby, the pressure in the ladle is lowered from the initial atmospheric pressure to 100 ... 150 mbar. In the second step, after having reached the pressure specified above, the direct connection of the rough suction points to the ladle is closed and the suction points are serially connected to another row of medium suction points which are also parallelly connected, and connected directly to the ladle. By summing the effect of the two rows of points for rough and medium suction - a pressure ranging from 10 to 20 mbar is obtained inside the ladle. In the third and last step, after having reached the mentioned pressure inside the ladle, the direct connection of the medium suction points to the ladle is closed, and these points are serially connected with another row of high suction points, which are also connected parallelly and through a single path to the ladle. Thus, the effect of the three rows of points for rough, medium and high suction is summed and makes possible to obtain a pressure between 0.1 ... 0.5 mbar inside the ladle. According to the invention, the vacuuming installation for the treatment of steel comprises more stages of generating the vacuum, namely: a rough vacuum stage A, a medium level vacuum stage B and a high vacuum stage C, connected in series and separated by means of some valves 1 and 2, respectively. The rough vacuum stage A is provided with mechanical vacuum pumps 3, manufactured in the dry lubrication technology, with the suction parallelly connected through some' valves 4, to a manifold 5. The vacuum pumps 3 may also be connected to the environment by means of some purge valves 6. The medium level vacuum stage B is provided with mechanical vacuum pumps 7, manufactured in the dry technology, parallelly connected with the discharge to a duct 8 connected to the valve 1, on one hand, and with the suction to some valves 9 which are connected to a manifold 10, on the other hand. Similarly to the vacuum stages A and B explained above, the high vacuum stage C is also provided with some mechanical dry vacuum pumps 11, connected parallelly and connected with the discharge to a pipe 12 which is connected to the valve 2 and with the suction to some valves 13 connected to a manifold 14. Each of the manifolds 5, 10 and 14 of the vacuum stages A, B and C, respectively, are pneumatically connected through some valves 15, 16 and 17 to a pipe 18 connecting with an inner chamber to be vacuumed, which is not represented in the figure. On the pipe 18, between the connections of valves 16 and 17 of the stages B and C there is interposed another valve 19. As already shown before, the installation described by the invention uses mechanical vacuum pumps manufactured in the "dry" technology, ROOTS-type pumps or other equivalent ones and which do not use sealing fluids, thus being capable of taking over extremely heavy dust loads - which are the reaction products specific to the iron metallurgy processes. The number of vacuum pumps 3, 7 and 11, respectively, used in each of the vacuum stages A, B, and C is selected depending on the steel quantity to be subjected to the treatment, consequently, on the capacity of the chamber to be vacuumed, on the gas flow rate to be sucked and on the time required for obtaining the vacuum level necessary for carrying out the process, said number ranging from 1 to n . As a rule, the number of the vacuum pumps on each stage must be selected so as to obtain the following values achieved by the vacuum stages in steps : - with the rough vacuum stage A, from the atmospheric pressure to 100 mbar; - with the medium level vacuum stage B, from the pressure of 100 mbar to the pressure of 10 mbar; - with the high vacuum stage C, from the pressure of 10 mbar to the pressure of 0.1 mbar. During the operation, corresponding to the technological process to be carried out and to the vacuum level to be obtained, there may be selected a working configuration, whereby one, two or all stages are set into operation. The working configuration may be obtained by automatic programming of the valves which are opened or of those which are closed. Thus, for example, by opening the valve 15, the medium level vacuum stage B is excluded from the vacuuming circuit even if the valve 16 is open. In the same way, by opening valve 19 the high vacuum stage C may be excluded. The valves 16 and 17 are meant for introducing the vacuum stage B and vacuum stage C, respectively, into the circuit and operate in phase opposition with the valves 15 and 19, or in other words, if the valve 15 is opened, the valve 16 must be closed and reversely, and if the valve 19 is opened, valve 17 must be closed and reversely. The valves 4 are intended to close the access to the vacuum pumps 3 in the rough vacuum stage A, the valves 9 close the access to the vacuum pumps 7 in the medium level vacuum stage B, and the valves 13 close the access to the vacuum pumps 11 from the high vacuum stage C. The valves 1 and 2 close the access between the vacuum stages A, B and C, but they are not absolutely necessary for the functioning of the installation according to the invention. According to the invention, the installation operates in the following manner in the case of the vacuum oxygen decarburation process - VOD: in the initial vacuuming step, the vacuum pumps 3 in the rough vacuum stage A are started and the valves 4 to which they are connected will be opened, thereafter, the valves 15 and 19 will be opened, all the other valves being closed. When reaching a pressure of 100 ... 150 mbar within the working chamber, the valve 15 will be closed and the valves 9 will be opened at the same time with starting the vacuum pumps 7 in the medium level vacuum stage B. Both stages A and B are in operation until reaching a vacuum level of 100 ... 110 mbar in the chamber, then the medium vacuum stage B is separated by closing the valve 16 and opening the valves 15, the valve 1 remaining open and the vacuum pumps 7 in the medium vacuum stage B being maintained in operation. The oxygen insufflation is started and the suction of gases from the chamber is continued with this working configuration as long as necessary. During the oxygen insufflation, the vacuum pumps 3 in the rough vacuum stage A must be purged periodically in order to remove the dust collected therein by the suction of gases from the ladle. The operation is started with pump 3 (1) by closing the valve 4(1) and opening the valve 6(1) for one second. Then the valve 6(1) is closed and valve 4(1) is opened, this connection of the pump 3 (1) suction to the environment being sufficient for cleaning the same from dust. This manner of purging is continued uninterruptedly for the vacuum pump 3(2), too, by closing the valve 4(2) and opening the valve 6(2) for one second, then the valve 4 is closed. The purging of all pumps 3 in the rough vacuum stage A is continued successively and uninterruptedly, in the same manner. After purging all vacuum pumps 3 in the stage A, the suction from the working chamber is continued. The frequency of starting the purging sequence of the vacuum pumps 3 is established depending on the technological and constructive parameters of the installation for the treatment of steel and is continued during the whole oxygen insufflation time. At the end of the oxygen insufflation step, the purging frequency of pumps 3 may be decreased. Also, at the end of this step the medium level vacuum stage B is reintroduced into the circuit by closing the valve 15 and opening the valve 16. When a pressure in the range of 10 ... 20 mbar is reached, the high vacuum stage C is introduced into the circuit by opening the valve 17 and the valves 13, simultaneously with starting the vacuum pumps 11 and closing the valve 19. The suction is continued, the three vacuum stages A, B and C being maintained in operation simultaneously until the maximum required vacuum level is obtained. According to the invention, the operation is stopped in a reverse order by closing the valves 17, 13, 2, 16, 9, 1, and then by closing the valves 4. The working diagram for operating within the VD (vacuum degassing) processes, RH (reducing hydrogen) and DH (degassing hydrogen) is the following: the vacuum pumps 3 in the rough vacuum stage A are started; the valves 4, 15 and 19 are opened. When a pressure ranging from 100 to 150 mbar is reached within the working chamber, the valve 15 is opened, the vacuum pumps 7 in the medium level vacuum stage B are started and the valves 16, 9 and 1 are opened. After having reached a pressure ranging from 10 to 20 mbar, the valve 19 is closed, the vacuum pumps 11, 13 and valve 2 are started. Similarly to the VOD process diagram, the suction operation within VD, RH and DH processes is performed in a reverse order as compared to the starting operation shown in the previous paragraphs. The vacuum pumps 3 will be purged at intervals of about 3 minutes in the above described manner.

Claims: CLAIMS 1. Vacuuming process for the treatment of steel, characterized in that it is based on a dry vacuuming principle, consisting, in the first step, in providing a rough vacuuming achieved by summing more rough suction points, parallelly connected through a single path to the ladle, there obtaining a pressure ranging from 100 to 150 mbar followed by the second step, wherein the direct connection of the rough suction points to the ladle is closed and they are serially connected to another row of points for medium suction which are also parallelly connected and directly connected to the ladle, by summing the effect of the two rows of rough and medium suction points there being obtained a pressure ranging from 10 to 20 mbar inside the ladle, and finally, followed by a third step wherein the direct connection of the medium suction points to the ladle is closed, then the suction points are serially connected to another row of high suction points also parallelly connected and through a single path to the ladle, thereby the effect of the three rows of points for rough, medium and high suction being summed , and a pressure ranging from 0.1 to 0.5 mbar being reached inside the ladle. 2. Vacuuming installation for the treatment of steel, characterized in that comprises a rough vacuum stage (A) , followed by a medium level vacuum stage (B) and by a high vacuum stage (C) , serially connected by means of some valves (1 and 2) and parallelly connected by the valves (15, 16 and 17) to a connecting pipe (18) , whereon a valve (19) is interposed between the vacuum stages (B and C) . 3. Vacuuming installation for the treatment of steel, according to claim 2, characterized in that the rough vacuum stage (A) is provided with some mechanical vacuum pumps (3) parallelly connected through some valves (4) to a manifold (5) , and through the purge valves (6) to the environment. 4. Vacuuming installation for the treatment of steel, according to claim 2, characterized in that the vacuum stages (B and C) are provided with some mechanical vacuum pumps (7 and 11, respectively) parallelly connected with some valves (9 and 13, respectively) to the manifolds (10 and 14, respectively) .

Inventors: BODEA ADRIAN, BODEA, ADRIAN
Applicants: BODEA ADRIAN, BODEA, ADRIAN
Application year: 2001
Main classification: C21C7
IPC codes: C21C7