EP0021222B1 - Process and apparatus for dosing and for pneumatically conveying and feeding solid materials to a vessel maintained under pressure - Google Patents

Description

The invention relates to a process for metering and transporting solid materials pneumatically between a storage tank being under substantially atmospheric pressure and a pressure vessel, as well as an installation for carrying out such a process.

Although not limited thereto, the invention relates to the handling of pulverulent materials in the steel industry, such as, for example, lignite powder for injection into blast furnaces, or even powdered ore, or powdered coal for injection into a reactor of a direct reduction installation and will be described, by way of illustration, with reference to such steel applications.

The use of lignite as fuel for the maintenance of the reduction process in blast furnaces is a very recent technique, the control of which is of particular importance insofar as it allows the replacement of petroleum products by lignite , which is a cheap product and of which there are still large reserves. Unfortunately, this technique has remained at the theoretical stage or at most, at the experimental stage. The reason is precisely that we did not have, to date, the technical means necessary for the injection of large quantities and metered into pressure vessels, such as a blast furnace.

The problem of transporting coal powder and ore powder in the case of direct reduction plants, although slightly different, is nonetheless comparable in so far as such plants already exist, but the use of expensive and cumbersome mechanical transport systems for horizontal and vertical transport and which have not yet been able to take advantage of the advantages offered by pneumatic transport systems, well known per se. The reason is again that it involves injecting large quantities into a pressure vessel and this, in a controlled manner and in metered quantities. However, pneumatic systems do not simultaneously meet all these criteria at the same time, a prerequisite, however, sine qua non for implementation on an industrial scale in the applications concerned. Application DE-A 2 703 736 describes an installation and a method for metering and transporting solid materials by pneumatic route between a storage tank at atmospheric pressure and a pressurized enclosure, which consists of extracts the material from the reservoir, that it is introduced into a metering container at atmospheric pressure until the latter contains a predetermined quantity of material, the content of the container being continuously measured during filling, which is isolated then the dosing container storage tank, which is pressurized yesterday, that a communication is established between the dosing container and an intermediate container, that the contents of the dosing container are transferred to the intermediate container by gravity, isolate the dosing container from the intermediate container after this transfer, pressurize the intermediate container, ventilate the dosing container and start again the filling operation thereof, that the content of the intermediate container is transferred to a supply tank under the same pressure by gravity, and that the material is extracted from this supply tank to transfer it in the enclosure in a controlled manner.

In application DE-A 2 703 736, the metering tank is therefore under pressure during weighing, which complicates the latter. In addition, the dosing tank cannot be weighed separately since it is integral with the other downstream tanks.

Consequently, the object of the present invention is to fill this gap and to provide a new process allowing controlled injection and metered against pressure in an enclosure, as well as an installation for the implementation of such a process.

This object is achieved by the method as set out in claim 1 and by the installation as set out in claim 8.

The propulsion fluid is preferably air at a temperature below 80 ° C and circulating at a speed of about 20 meters / second.

The solid matter can be either lignite, iron ore or coal dust, in powder form.

The intermediate container and the supply tank are fitted with level sensors to measure the minimum and maximum filling.

Other particularities and characteristics will emerge from the detailed description of an embodiment, presented below, by way of illustration, with reference to the single figure which shows a block diagram of an installation according to the present invention.

The pulverulent material is stored in a storage tank 2 into which it is brought directly from a means of transport such as, for example, the railway. In the figure, only one storage tank has been shown, but in general, two are provided, in order to be able to work continuously.

The pulverulent material is discharged through the bottom of the storage tank through a pipe 6 provided with an automatic valve 10. A second pipe 4 provided with an automatic valve 8 is used for emptying the storage tank 2. From the pipe 6 the pulverulent material is conveyed by means of a conveyor propeller 12 into a metering container 14 provided with two automatic valves 16 and 18 for the isolation upstream respectively downstream.

The dosing container 14 rests on several, for example three, pressure sensors intended to continuously measure the weight of the dosing container 14 and more particularly the weight of its contents. This weight measuring device is used, as will be explained later, for the automatic control of the installation. A supply line for pressurized air is indicated by the reference 20. Assuming that the overpressure in the enclosure into which the pulverulent material is to be injected is 2.5 bars, it is necessary to provide an overpressure of approximately 3 , 5 bars in line 20. This supply line is divided into three branches, each comprising an automatic valve 22, 24, 26, a manual valve 28, 30, 32 and a non-return valve 34, 36 and 38. The automatic valves 22, 24 and 26 are intended for automatic adjustment of the pressurized air flow as required, while the manual valves 28, 30 and 32 are used for an initial manual adjustment fixing the maximum flow in each of the pipes. The metering container 14 is further provided with an automatic valve 40 for aeration of the container.

From the metering container 14 the pulverulent material is pneumatically conveyed through a line 42 using the pressurized air as propulsion fluid introduced by the valve 26. The line 42 brings the pulverulent material into an intermediate container 44. This container being alternately under pressure and at atmospheric pressure, also comprises two automatic valves 46 and 48 for the insulation downstream and upstream. Downstream of this intermediate container 44 is a supply tank 50 also isolated upstream and downstream by automatic valves 52 respectively 54. To the tank 50 is associated a filtering device 56 with which; is connected a self-regulating pressure valve 58 intended to maintain a uniform pressure in the tank 50, for example, an overpressure of 3 bars when the initial overpressure in the pipe 20 is 3.5 bars. The reservoir 50 is also connected to a pressurized air line 62 intended to increase the pressure inside the reservoir 50 when the latter falls below the set pressure on which the self-regulating valve is calibrated. 58,

The reference 66 schematically indicates the transfer of the pulverulent material from the reservoir 50 to the pressure enclosure 64. This enclosure 64 can be constituted by the reactor of a direct reduction installation which is connected to two installations of the type described above. , one being for transporting coal powder and the other for iron ore powder.

The enclosure 64 can also designate a blast furnace and the installation described will be used for the injection of lignite into this blast furnace 64. In this case, the lignite will be extracted from the tank 50 and propelled pneumatically to be injected into each nozzles. While in the case of the transport of coal powder and iron ore, the transfer 66 may consist of a single pipe, in the case of lignite, it is necessary to provide a certain number of pipes depending on the number of nozzles, preferably one line for each pair of nozzles.

We will now describe a method of using the installation described above for injecting lignite into a blast furnace with a back pressure of 2.5 bars. We will refer, for example, to an oven provided with a series of nineteen nozzles, with an hourly consumption of 27 tonnes of lignite. For such an installation, two storage tanks 2 with a capacity of 500 m ³ each will be provided.

At the start of the cycle, the valves 18, 22, 24 and 26 are closed, while the valves 10, 16 and 40 are open. The lignite powder flows by gravity from the tank 2 and is introduced by the propeller 12 into the metering container 14. When the content of the metering container reaches the target weight, detected by the load cells 19, a signal of command is triggered which stops the action of the propeller 12, closes the valves 16 and 40 and opens the valves 18, 22 and 26. The valve 24 remains, in principle, closed and will only be opened when necessary to increase the degree of fluidity of the content of the dosing container 14. The valve 22 controls the admission of pressurized air into the upper part of the dosing container 14 in order to cause the flow of lignite powder through the bottom of this container. The pressure of the air admitted into the container 14 is substantially equal to that of the supply line 20, that is to say 3.5 bars.

The valve 18 will be adjusted automatically according to the content of the metering container so that it is emptied in a predetermined time. The valve 26 will be adjusted as a function of the valve 18 in order to have an optimal proportion between the lignite and the propellant air in the pipe 42, this proportion being general err of 100 kilos of solid matter per kilo of fresh air.

While the lignite is propelled pneumatically into the intermediate container 44, the latter _is' occurs under substantially atmospheric pressure; that is to say that the valve 48 is open. The transport speed in line 42 is approximately 20 meters / second. This speed is determined according to two criteria, namely to avoid deposits (lower limit: 18 meters / second) and for safety reasons, that is to say to avoid backfire.

During filling of the container 44, the valve 48 remains open. When the contents of the metering container 14 have been transferred to the intermediate container 44, the valves 18, 22, 26 and 48 will be closed. It is preferable to operate in the enclosure 44 with an overpressure of 3.5 bars and for this purpose, it is possible to close the valve 26 only a few moments after the others in order to inject into the container 44 a supplement of pressurized air to reach the overpressure of 3.5 bars. Instead of using propellant fluid sion to achieve the desired pressure in the enclosure 44, one can also use a pressure source specially provided for this purpose such as, for example, an inert gas such as nitrogen.

When the level in the supply tank 50 reaches the minimum, as noted by the level probes which, in general, are gamma radiation probes, the valves 46 and 52 are open for the transfer of the contents of the container 44 into the tank 50. This obviously implies that the operating program is such that the container 44 must be full and under pressure before the minimum is reached in the tank 50. The flow from the container 44 to the tank 50 is stopped by closing the valves 46 and 52 when the minimum level is reached in the container 44. This minimum level is also determined, for example by means of a gamma-ray probe.

It is understood that the filling operation of the metering container 14 begins again immediately after closing the valve 18 and after aerating the container by opening the valve 40, so that the filling of the metering container 14 is generally performed in parallel with the filling of the reservoir 50.

One of the essential attractions of the installation described is that it allows exact control of the quantity of solid material injected into the pressure vessel 64. Since the requirements for lignite are fixed by weight, it is necessary to '' carry out a weight dosage instead of a volumetric dosage, because the specific weight of lignite or other pulverulent materials is not constant. However, it is not possible to carry out a weighing of the reservoir 50 with a view to metering, since this reservoir is constantly under pressure. On the other hand, the container 14, specially provided for this purpose, can be depressurized for weighing and be pressurized for supply. Consequently, the metering is carried out as required at the level of the enclosure 64 and the signals resulting from the weighing of the container 14 allow, in association with the signals from the level probes, automatic control of the various valves. '' ensure an optimal sequence of different successive operations. The merit of the invention is therefore to have made possible a compatibility between a pneumatic transport and the metering by weight of the transported materials.

It should be emphasized that the values of the pressures cited above have been given only by way of example. If one operates with another pressure in the enclosure 64, it is obvious that the operating pressures will increase accordingly.

Finally, it should be noted that the pressure of the pneumatic propulsion fluid does not necessarily have to be greater than the pressure in the enclosure 64. This is only the case if this propulsion fluid also serves to pressurize the enclosure 64.

Claims (11)

1. Process for dosing and pneumatically conveying solid materials from a vessel (2) at substantially atmospheric pressure to a pressurized chamber (64) consisting in that the solid material is extracted from the storage container (2) and introduced into an atmospherically pressurized dosing receptacle (14) until the latter contains a predetermined quantity of solid, this receptacle (14) and its contents being weighed as and when it is filled, in that the storage container (2) is then isolated from the dosing receptacle (14), in that the latter is pressurized, in that communication is established between the dosing receptacle (14) and an intermediate receptacle (44) which, at the moment in question, is at subtantially atmospheric pressure, in that the contents are transferred from the dosing receptacle (14) into the intermediate receptacle (44) by means of a pneumatic propulsion fluid, in that the dosing receptacle (14) is isolated from the intermediate receptacle (44) when the contents of the dosing receptacle (14) have been completely transferred into the intermediate receptacle (44), in that the intermediate receptacle (44) is pressurized, in that the dosing receptacle (44) is ventilated and the operation of filling the latter recommenced, in that the content of the intermediate receptacle (44) are transferred into a feed tank (50) in which an intermediate pressure is maintained between the pressure in the said chamber (64) and the pressure in the intermediate receptacle (44), in that the solid material is extracted from this feed tank (50) as required and in that it is transferred into the interior of the said chamber (64) and that from the said weighing of the dosing receptacle (14) signals are derived which are intended for the automatic control of the commencement and termination of the filling phase of the dosing receptacle (14) of the opening and closing of valves (16, 18; 22, 24, 26, 40), associated with the said receptacle for the purpose of pressurizing and ventilating it, and also the operation of establishing communication between the said receptacle and the intermediate receptacle (44).

2. Process in accordance with Claim 1, characterized in that the propulsion fluid is air, at a temperature lower than 80 °C, and circulating at a speed of approx. 20 metres per second.

3. Process in accordance with one of Claim 1 and 2 characterized in that the pressurization of the intermediate receptacle (44) is carried out by means of the propulsion fluid and in that the pressure of this receptacle is greater than the pressure in the said chamber (64).

4. Process In accordance with one of Claims 1-3, characterized in that the minimum level of filling of the intermediate receptacle (44) and the feed tank (50) is determined continuously, as well as the maximum level of the said feed tank and in that the transfer of the contents of the intermediate receptacle (44) into the feed tank (50) is effected when the level in the latter reaches the minimum, this transfer being stopped either when the level in the intermediate receptacle (44) reaches the minimum of when the level in the feed tank (50) reaches the maximum.

5. Process in accordance with one of Claims 1-4, characterized in that the solid material is lignite in powdered form.

6. Process in accordance with one of Claims 1-4, characterized in that the solid material is coal powder.

7. Process in accordance with one of Claims 1-4, characterized in that the solid material is iron or powder.

8. Installation for the performance of the process in accordance with Claims 1-7, wherein the dosing receptacle (41) is suspended by pressure pick-ups (19) for continuously determining the weight of the contents of this receptacle (14) wherein the intermediate receptacle (44) is installed downstream from the dosing receptacle (14) and the feed tank (50) installed « downstream from the intermediate receptacle (44) the sets of valves being associated respectively with the said receptacles (14, 44) and with the said tank (50) in order to isolate them in the « upstream * and/or « downstream direction, characterized by the fact that only the dosing receptacle is suspended from the pressure pick-ups and that an admission pipe (20) for a pneumatic propulsion fluid is provided which is subdivided into three branches of which the first penetrates the upper part of the dosing receptacle (14) in order to drain the latter automatically, while the second penetrates the lower part of the dosing receptacle (14) in order to fluidize its contents and the third communicates with a pipe (42) connecting the dosing receptacle (14) to the intermediate receptacle (44) in order to transfer material pneumatically from the dosing receptacle (14) to the intermediate receptacle (44).

9. Installation in accordance with Claim 8, characterized by the fact that each of the three branches comprises an automatic regulating valve (22, 24, 26), a manual valve (28, 30, 32) for the initial regulating action, and a non-return valve (34, 36, 38) respectively.

10. Installation in accordance with Claim 9, characterized in that the intermediate receptacle (44) and the feed tank (50) are equipped with level probes (60) to measure the minimum and maximum filling levels of this intermediate receptacle (44) and of the feed tank (50) and that these level probes (60) are designed to emit signals for the operation of the valves regulating the passage between the intermediate receptacle (44) and the feed tank (50).

11. Installation in accordance with Claim 9, characterized In that the feed tank (50) is equipped with a pressure governor to maintain a constant pressure slightly higher than the pressure of the saidchamber.

Images