LU92978B1 - Installation for distribution of granular or powder material via pneumatic transport comprising a device for pressurizing and depressurizing a dispensing hopper for storage of said material - Google Patents

Abstract

An installation (10) for distribution of granular or powder material via pneumatic transport comprising at least one dispensing hopper (12) for temporary storage of the granular or powder material, the dispensing hopper (12) being suited for being, alternately, pressurized for emptying the dispensing hopper (12) and depressurized to permit filling thereof. The installation (10) comprises a device for pressurizing and depressurizing the dispensing hopper (12) with a pressurizing duct (14) associated with the dispensing hopper (12) for feeding pressurizing gas into the dispensing hopper (12) through at least one pressurizing nozzle (40), the pressurizing duct (14) being fluidly connected to a feed line (16) for receiving pressurizing gas from a gas source. The device further comprises a depressurizing duct (18) associated with the dispensing hopper (12) for evacuating pressurizing gas from the dispensing hopper (12). The depressurizing duct (18) is fluidly connected to the at least one pressurizing nozzle (40), wherein the at least one pressurizing nozzle (40) comprises a filter element. (Fig. 1) 92978

Description

Installation for distribution of granular or powder material via pneumatic transport comprising a device for pressurizing and depressurizing a dispensing hopper for storage of said material

Technical Field [0001] The present invention relates to an installation for distribution of granular or powder material via pneumatic transport, such as for example an installation for injecting coal into a blast furnace, comprising at least one dispensing hopper for temporary storage of the granular or powder material. The dispensing hopper is pressurized for emptying and must be depressurized to permit filling thereof. The present invention more particularly relates to the depressurizing of such a dispensing hopper. The present invention also relates to a method for operating such an installation.

Background Art [0002] It is well-known, for example from EP 0 079 444 or EP 0 212 296 to inject granular or powder materials, in particular powdered coal, into a blast furnace. These materials are conventionally transported pneumatically. Typically, in a blast furnace, powdered coal may be injected at the level of each tuyere or at least into a plurality of tuyeres. The coal is supplied from a main storage hopper, which is maintained at atmospheric pressure, and distributed towards each injection point via a pneumatic dispensing line which, in the vicinity of the blast furnace, divides into a plurality of injection lines, each connected to an injection point. The coal may also be transported via the dispensing line towards another vessel maintained under constant pressure, then known as injection hopper, located in the vicinity of the blast furnace. The injection lines are then connected to the injection hopper. Transport and injection installations conventionally comprise pressurized temporary storage vessels, or dispensing hoppers, which are suited to containing the material and are pressurized by a transport gas, for example nitrogen. This gas makes it possible to fluidize the powder material and to transport it to its point of use, conventionally located in the tuyere.

[0003] Transport and injection installations are intended, on the one hand, to enable control of the flow rate of injected material and, on the other hand, a continuous supply of powder material. To this end a set of at least two dispensing hoppers are often located in parallel in the transport line and provided with closing valves enabling control of filling and emptying of each hopper is conventionally used for each transport line. The dispensing hoppers are used alternately, with one being emptied for supplying coal to the blast furnace tuyeres, while the other one is being filled from the main storage hopper. Furthermore, each dispensing hopper is provided with a weighing means which makes it possible to determine the quantity of powdered coal introduced on each filling, so enabling control of the quantity of coal injected.

[0004] When filling a dispensing hopper from the main hopper, in order to avoid excess pressure which could prevent the coal from flowing well, the gas present in the dispensing hopper is discharged towards the upper part of the main hopper by a pressure-equalizing duct equipped with an isolation valve which is open during the filling. Since the duct is closed by the valve once filling of the dispensing hopper is complete, it therefore remains filled with moist gas containing powdered coal. In order to avoid the risks of condensation and clogging of the coal, or even blockage of the line, which may arise, these ducts are insulated and heated.

[0005] In order to empty each dispensing hopper via pneumatic transport of the powdered coal, these hoppers are supplied with pressurized gas via a duct equipped with a valve, which makes it possible to maintain the pressure required for transport during the entire duration of emptying. These dispensing hoppers, which are maintained under pressure when in use, must therefore periodically be depressurized each time before being refilled from the main storage hopper. The gas escaping from the hopper during depressurization inevitably entrains some powder product still present in the hopper. Bag filters are conventionally used in order to avoid discharging significant quantities of powdered coal into the atmosphere together with the pressurized gas during depressurization. Typically, each dispensing hopper is connected via a depressurizing duct equipped with a valve to a bag filter located on the main storage hopper, which makes it possible to recover the powdered coal retained by the bag filter directly into the main hopper, the gas being discharged into the atmosphere or recovered elsewhere. Since the main hopper is at atmospheric pressure, the filter too is therefore also under atmospheric pressure, the drop in pressure arising from the loss of load between the dispensing hopper and the bag filter and being controllable by the depressurizing valve located on the duct connecting the hopper and filter.

[0006] During depressurization, the pressure in the dispensing hopper declines gradually. Furthermore, the bag filters permit a maximum volumetric flow rate which is determined by the area of the filter's filtration surface. In order to optimize depressurization, it is therefore desired to maintain a maximally constant volumetric flow rate through the filter throughout depressurization, which makes it possible to minimize the necessary filtration surface and hence the overall size of the filters and the cost thereof. The flow rate control provided by the valve located on the duct between the dispensing hopper and the bag filter makes it possible to ensure the desired constancy of flow rate.

[0007] One drawback of these systems resides in the fact that the control valve therefore necessarily acts on gas streams laden with powder material. Another drawback arises from the fact that, in a typical blast furnace installation, two, or even three, dispensing hoppers are connected to a single low pressure bag filter and, consequently, variations in pressure in a duct connecting a dispensing hopper to the filter during depressurization may have a disruptive effect on the weighing equipment of the other dispensing hoppers, and in particular on the dispensing hopper currently carrying out injection.

[0008] Another drawback arises from the fact that, during depressurization, a certain quantity of powdered coal is returned with the depressurization gas stream towards the bag filter and then onwards towards the main storage hopper. It is not possible to determine this quantity with precision. As a result, not only is the true quantity of coal injected into the tuyeres less than the quantity detected by the dispensing hopper weighing operations, but the quantity is also not known with precision.

[0009] Still another drawback originates from the fact that the duct between the depressurizing valves and the bag filter are relatively long and of large diameter, so resulting in elevated equipment costs.

[0010] It is suggested in WO 2014/006073 to provide a pressurized bag filter for each dispensing hopper and to place the pressurized bag filter in direct fluid communication with the associated dispensing hopper. Any valves or control means regulating the flow of pressurizing gas evacuated from the dispensing hopper is placed downstream of the pressurized bag filter.

Technical Problem [0011] It is an object of the present invention to provide an improved installation for distribution of granular or powder material, wherein pressurizing and depressurizing of the dispensing hopper is enhanced. This object is achieved by an installation as claimed in claim 1. In particular, the present invention seeks to avoid having to install a pressurized bag filter on each dispensing hopper. It is a further object of the present invention to provide an improved method for distribution of granular or powder material. This object is achieved by a method as claimed in claim 12.

General Description of the Invention [0012] In the light of these aims, the invention provides an installation for distribution of granular or powder material via pneumatic transport comprising at least one dispensing hopper for temporary storage of the granular or powder material, the dispensing hoppers being suited for being, alternately, pressurized for emptying the dispensing hopper and depressurized to permit filling thereof.

[0013] The installation further comprises a device for pressurizing and depressurizing the dispensing hopper with a pressurizing duct associated with the dispensing hopper for feeding pressurizing gas into the dispensing hopper through at least one pressurizing nozzle, the pressurizing duct being fluidly connected to a feed line for receiving pressurizing gas from a gas source. The device further comprises a depressurizing duct associated with the dispensing hopper for evacuating pressurizing gas from the dispensing hopper.

[0014] According to an aspect of the invention, the depressurizing duct is fluidly connected to the at least one pressurizing nozzle, wherein the at least one pressurizing nozzle comprises a filter element, preferably a sintered metal filter. Thus, the pressurizing nozzles serve for the pressurizing of the dispensing hopper as well as for the depressurizing thereof. No dedicated depressurizing nozzles need be provided. The filter element arranged in the pressurizing nozzle retains a large quantity of the granular or powder material and prevents the latter from flowing through the depressurizing duct. As the pressurizing gas exiting the dispensing hopper is at least partially “dedusted”, the wear on any downstream valves is limited. There is no need to provide a bag filter between the dispensing hopper and the valves. Also, in case of a multi-hopper arrangement, there is no need to provide a bag filter associated with each of the dispensing hopper. A single, common bag filter may be arranged downstream of the valves in the depressurizing duct, i.e. shortly before the pressurizing gas exits the installation, either into the atmosphere or for use elsewhere.

[0015] The filter element preferably has a pore size distribution adapted to the bulk material used in the dispensing hopper. The pore size is indeed chosen such that the filter element retains a large portion of the granular or powder material without however creating too high a pressure loss of pressurizing gas passing therethrough, in either direction.

[0016] The depressurizing duct comprises a first de Laval nozzle for controlling the flow of pressurizing gas out of the dispensing hopper, a first shut-off valve being preferably arranged upstream of the first de Laval nozzle. Such a de Laval nozzle is used to produce a roughly constant gas volume flow rate.

[0017] A first bypass branch bypassing the first de Laval nozzle may be provided for shortening a final depressurizing time when the pressure level in the dispensing hopper is close to the downstream pressure level. The first bypass branch comprises a second shut-off valve to open or close the first bypass branch.

[0018] A second bypass branch bypassing the first de Laval nozzle may be provided for emergency depressurizing of the dispensing hopper at reduced flow rate. Such a second bypass branch would comprise an orifice plate and a third shut-off valve to open or close the second bypass branch.

[0019] By means of the first, second and third shut-off valves, the flow of pressurizing gas out of the dispensing hopper through the depressurizing duct can be controlled depending on the requirements of different circumstances.

[0020] It should be noted that other valve arrangements may also be envisaged such as e.g. described in LU 92 534 or LU 92 813, both herewith incorporated by reference.

[0021] The pressurizing duct may comprise an auxiliary pressurizing branch for feeding pressurizing gas into the dispensing hopper through at least one auxiliary pressurizing gas nozzle, the at least one auxiliary pressurizing gas nozzle being arranged at a level below the at least one pressurizing gas nozzle. Such an auxiliary pressurizing branch preferably comprises a fourth shut-off valve in order to isolate the auxiliary pressurizing branch from the pressurizing duct. The auxiliary pressurizing branch allows feeding pressurizing gas into the dispensing hopper on two separate levels. However, during the depressurizing of the dispensing hopper, it may not be desired to extract pressurizing gas though the lower level. This is in particular the case in installations with parallel hopper arrangement, wherein the dispensing hoppers are generally not fully emptied and the auxiliary pressurizing gas nozzles may still be covered with material. It is then more advantageous to close off the auxiliary pressurizing branch.

[0022] The pressurizing duct may comprise a second de Laval nozzle for controlling the flow of pressurizing gas into the dispensing hopper, a fifth shut-off valve being preferably arranged upstream of the second de Laval nozzle.

[0023] The installation may comprise two or more dispensing hoppers, each dispensing hopper having a depressurizing duct with a first de Laval nozzle for controlling the flow of pressurizing gas out of the dispensing hopper, each depressurizing duct feeding pressurizing gas to a common bag filter.

[0024] The present invention also relates to a method for operating an installation according to any of claims 1 to 11. The method comprises: feeding granular or powder material into the dispensing hopper; operating the device for pressurizing and depressurizing the dispensing hopper in a pressurizing mode; evacuating the granular or powder material from the dispensing hopper; operating the device for pressurizing and depressurizing the dispensing hopper in a depressurizing mode.

[0025] In the pressurizing mode, all shut-off valves in the depressurizing duct are closed, while the fifth shut-off valve in the pressurizing duct is open. Pressurizing gas is fed from the feed line through the pressurizing duct into the dispensing hopper. The auxiliary pressurizing branch may also be opened to feed pressurizing gas into the dispensing hopper on two separate levels if so desired.

[0026] In the depressurizing mode, the fifth shut-off valve in the pressurizing duct is closed, while one of the first, second or third shut-off valves is open. Generally, at the beginning of the depressurizing, the first shut-off valve is open and the gas flow through the depressurizing duct is controlled by the first de Laval nozzle. As the pressure level in the dispensing hopper approaches the downstream pressure level, the second shut-off valve is in addition opened to allow further gas evacuation.

[0027] While depressurizing, the fourth shut-off valve may also be closed. This is of particular interest if the associated auxiliary pressurizing nozzles are below the level of material still left in the dispensing hopper.

[0028] The above installation is preferably used for injecting powdered coal into a blast furnace.

Brief Description of the Drawings [0029] A preferred embodiment of the invention will now be described, by way of example, with reference to Fig. 1, which is a simplified schematic view of an installation according to an embodiment of the invention.

Description of Preferred Embodiments [0030] Figure 1 shows an installation 10 for distribution of granular or powder material via pneumatic transport comprising at least one dispensing hopper 12 (generally, two or more dispensing hoppers are used) for temporary storage of the granular or powder material, the dispensing hopper being suited for being, alternately, pressurized for emptying the dispensing hopper and depressurized to permit filling thereof, and a device for pressurizing and depressurizing the dispensing hopper. The device for pressurizing and depressurizing comprises a pressurizing duct 14 associated with the dispensing hopper 12 for feeding pressurizing gas into the dispensing hopper, the pressurizing duct 14 being fluidly connected to a feed line 16 for receiving pressurizing gas from a gas source.

[0031] A depressurizing duct 18 is also associated with the dispensing hopper 12 for evacuating pressurizing gas from the dispensing hopper. The depressurizing duct 18 feeds pressurizing gas from the dispensing hopper 12 to a bag filter 20. In the bag filter 20, granular or powder material is removed from the pressurizing gas before the latter is fed to the atmosphere ore used elsewhere.

[0032] The depressurizing duct 18 shown in Figure 1 is provided with a first valve arrangement 22 for controlling the flow of pressurizing gas out of the dispensing hopper 12. The depicted first valve arrangement 22 comprises main branch 24 with a first de Laval nozzle 26 and a first shut-off valve 28. A first bypass branch 30, in arranged parallel to the main branch 24, comprises a second shut-off valve 32. A second bypass branch 30, in arranged parallel to the main branch 24, comprises a third shut-off valve 36 upstream an orifice plate.

[0033] Generally, during the depressurizing of the dispensing hopper only one of the shut-off valves 28, 32, 36 is open. A combination of open valves may however also be envisaged.

[0034] Typically, the flow is controlled by the first de Laval nozzle 26 after opening the first shut-off valve 28. In order to shorten the final depressurizing time, i.e. when the pressure level in the dispensing hopper is close to the downstream pressure and the depressurizing flow rate through the de Laval nozzle 26 is strongly decreasing, the second shut-off valve 32 is opened. The third automatic valve 36, upstream the orifice plate, may be opened for the purpose of emergency depressurizing of the dispensing hopper, at reduced flow rate.

[0035] In order to avoid compacting of pulverized coal in the dispensing hopper 12, pressurizing gas is generally not injected into the upper part of the dispensing hopper. Instead, pressurizing gas nozzles 40 are usually located in the lower part, i.e. the lower conical part 42, of the dispensing hopper 12.

[0036] The pressurizing duct 14 feeding pressurizing gas to the pressurizing gas nozzles 40 may comprise, as shown in the embodiment of Figi, an auxiliary pressurizing branch 44 for feeding pressurizing gas into the dispensing hopper 12 at a separate, lower level through auxiliary pressurizing gas nozzles 46. The auxiliary pressurizing branch 44 comprises a fourth shut-off valve 48 for isolating the auxiliary pressurizing branch 44 from the pressurizing duct 14.

[0037] The pressurizing duct 14 comprises a second valve arrangement 50 comprising a second de Laval nozzle 52 and a fifth shut-off valve 54 associated therewith.

[0038] In order to shorten the pressurizing time duration and thus increase the time duration for depressurizing at a reduced flow rate, an alternative second valve arrangement may be used, switching from a pressurizing gas flow rate control by means of a de Laval nozzle, as shown in Figure 1, producing roughly a constant gas mass flow rate, to a control by means of a pressurizing gas flow rate control valve, producing roughly a constant volume flow rate, as described in LU 92 534 or LU 92 813, both herewith incorporated by reference. The constant volume flow rate pressurizing has the advantage of minimizing the required pressurizing time duration, while limiting as well the pressure loss in the sintered metal filters, resulting from the fact that the gas flow in the filter is primarily laminar.

[0039] Similarly, the depressurizing time duration may be shortened by replacing the first de Laval nozzle 26 of the first valve arrangement 22 with an arrangement as described in LU 92 534or LU 92 813.

[0040] According to the present invention, the depressurizing duct 18 is fluidly connected to the pressurizing gas nozzles 40. In other words, the nozzles used to feed pressurized gas into the dispensing hopper 12 during the pressurizing cycle are also used to evacuate pressurized gas from the dispensing hopper 12 during the depressurizing cycle. To this effect, the depressurizing duct 18 is connected to the pressurizing duct 14 somewhere between the second valve arrangement 50 and the pressurizing gas nozzles 40.

[0041] The pressurizing gas nozzles 40 are each fitted with a filter element, preferably a sintered metal filter adapted to the grain size distribution of the bulk material fed into the dispensing hopper 12. The pore size distribution of the sintered metal filter conditions the gas pressure losses caused in the filters, during pressurizing as well as during depressurizing. For a common pulverized coal grain size distribution, a commercially available sintered metal filter having an indicated 98 % separation efficiency at 9 pm would retain about 93 % of that pulverized coal, when assuming that the grain size distribution of the entrained material is the same as the grain size distribution of whole of that pulverized coal, while the pressure losses in the pressurizing gas would remain acceptable, during both the pressurizing and depressurizing cycles.

[0042] During depressurizing of the dispensing hopper 12, pulverized material is trapped in the sintered metal filters inside the pressurizing gas nozzles, thus preventing a substantial amount of pulverized material from escaping the dispensing hopper 12 and being fed through the depressurizing duct 18 towards the bag filter 20. Reducing the amount of pulverized material in the pressurizing gas in the depressurizing duct 18 prevents excessive wear to the various components in the first valve arrangement 22. The reduced amount of pulverized material in the evacuated pressurizing gas also reduces the amount of pulverized material that would have to be caught in the bag filter 20. Due to the reduced solid material concentration in the evacuated pressurizing gas, the load of the filter bags can be increased and thus the filtering surface area decreased. In case the evacuated pressurizing gas is to be recovered, the bag filter is preferably a pressurized bag filter, as described in patent application WO 2014/006073 or LU 92 944, both herewith incorporated by reference.

[0043] During the subsequent pressurizing cycle, pressurizing gas is again fed into the dispensing hopper through the same pressurizing gas nozzles 40. Generally, the pressurizing gas flow rate is larger than the depressurizing gas flow rate. Thus, the particles trapped in the filters of the pressurizing gas nozzles 40 are blown back into the dispensing hopper 12. This does not only return the trapped particles to the dispensing hopper, but also clears the filter ready for the next depressurizing cycle.

[0044] With respect to the auxiliary pressurizing branch 44, it may be noted that this branch is generally used during the pressurizing cycle, not however during the depressurizing cycle. The use of the auxiliary pressurizing branch 44 is controlled by means of the fourth shut-off valve 48. Indeed, in particular in the case of a parallel hopper arrangement, i.e. of dispensing hoppers feeding pulverized coal into a conveying line, dispensing hoppers are not completely emptied when bulk material is fed into the conveying line, but a minimum filling level is maintained at the end of the emptying. This may result in that the auxiliary pressurizing gas nozzles 46 remain covered with bulk material contained in the hopper when the depressurizing of the lock hopper is to be performed. It is preferred not to involve the auxiliary pressurizing gas nozzles 46 covered with bulk material into the depressurizing process and isolate them by means of the fourth shut-off valve 48.

[0045] It should be noted that the bag filter 20, as shown in Fig.1, is preferably an atmospheric bag filter. Alternatively, a bag filter suited to operating under pressure may be provided. In an installation with such a pressurized bag filter, the shut-off valves 28, 32, 36 should be installed downstream the bag filter. In this case, an additional shut-off valve should be provided between the dispensing hopper and the bag filter.

[0046] The invention is not restricted to the above embodiments and to the specific application relating to injecting coal into a blast furnace. It may also be applied to other installations comprising pressurized hoppers containing granular or powder materials and requiring periodic pressurization and depressurization of the hoppers through bag filters.

Legend of Reference Numbers: 10 installation for distribution 32 second shut-off valve 12 dispensing hopper 36 third shut-off valve 14 pressurizing duct 40 pressurizing gas nozzle 16 feed line 42 lower conical part 18 depressurizing duct 44 auxiliary pressurizing branch 20 bag filter 46 auxiliary pressurizing gas nozzle 22 first valve arrangement 48 fourth shut-off valve 24 main branch 50 second valve arrangement 26 first de Laval nozzle 52 second de Laval nozzle 28 first shut-off valve 54 fifth shut-off valve 30 first bypass branch

Claims (15)

1. Installation for dispensing granular or powdery material via a pneumatic transport comprising at least one distribution hopper for temporary storage of said granular or powdery material, the distribution hopper being suitable for being, alternately, pressurized for emptying the dispensing hopper and depressurized to allow filling thereof, and a device for pressurizing and depressurizing said dispensing hopper, said device for pressurizing and depressurizing comprising - a pressurizing line associated with said dispensing hopper for feeding a pressurizing gas in said dispensing hopper via at least one pressurizing gas nozzle, said pressurizing conduit being fluidly connected to a supply line for receiving a pressurizing gas from a gas source; a depressurizing line associated with said distribution hopper for evacuating a pressurizing gas from said dispensing hopper; characterized in that - said depressurizing conduit is fluidly connected to said at least one pressurizing nozzle, wherein said at least one pressurizing nozzle comprises a filter element. 2. Installation according to claim 1, wherein said filter element comprises a sintered metal filter. 3. Installation according to claim 1 or 2, wherein said filter element has a pore size distribution adapted to the bulk material used in the distribution hopper. 4. Installation according to any one of the preceding claims, wherein said depressurizing pipe comprises a first nozzle Laval to control the flow of pressurizing gas out of the hopper distribution, a first stop valve being preferably arranged upstream said first nozzle Laval. 5. Installation according to claim 4, wherein said depressurizing pipe comprises a first bypass branch bypassing said first Laval nozzle, said first bypass branch comprising a second stop valve. 6. Installation according to claim 4 or 5, wherein said depressurizing pipe comprises a second bypass branch bypassing said first Laval nozzle, said second bypass branch comprising an orifice plate and a third stop valve arranged upstream of said orifice plate. 7. Installation according to any one of the preceding claims, wherein said depressurizing pipe comprises a bag filter. An apparatus according to any one of the preceding claims, wherein said pressurizing conduit comprises an auxiliary pressurizing branch for supplying a pressurizing gas to said dispensing hopper via at least one auxiliary pressurizing gas nozzle. said at least one auxiliary pressurizing gas nozzle being arranged at a lower level than said pressurizing gas nozzle. 9. Installation according to claim 8, wherein said auxiliary pressurizing branch comprises a fourth stop valve. 10. Installation according to any one of the preceding claims, wherein said pressurizing pipe comprises a second nozzle Laval to control the flow of pressurizing gas in the distribution hopper, a fifth stop valve being preferably arranged upstream of said second nozzle Laval. 11. Installation according to any one of the preceding claims, comprising two or more distribution hoppers, each distribution hopper comprising a depressurization pipe with a first nozzle Laval to control the flow of pressurizing gas out of the hopper distribution, each depressurization line supplying a pressurizing gas to a common bag filter, preferably a pressurized bag filter. 12. A method of using an installation according to any one of claims 1 to 11, said method comprising: • feeding a granular material or powder in said distribution hopper; • use of said device for pressurizing and depressurizing said dispensing hopper in a pressurization mode; • evacuation of said granular or powder material from said distribution hopper; The use of said device for pressurizing and depressurizing said dispensing hopper in a depressurization mode. The method of claim 12, wherein: in said pressurization mode, any shutoff valves in said depressurization pipe are closed, while said fifth shutoff valve in said pressurization pipe is open, thereby supplying a pressurizing gas of said feed line, via said second Laval nozzle, into said distribution hopper via said at least one pressurizing gas nozzle. The method of claim 12, wherein: in said depressurization mode, said fifth stop valve in said pressurizing line is closed, while at least one stop valve in said depressurizing line is open, thereby supplying a pressurizing gas of said dispensing hopper via said at least one pressurizing gas nozzle via said depressurizing line to said bag filter. The method of claim 13 or 14, wherein: in said pressurization mode, said fourth stop valve in said auxiliary pressurizing branch is open; and in said depressurization mode, said fourth stop valve in said auxiliary pressurization branch is closed.