EP0235562B1 - Process and device for the measured supply of fine solid particles to an industrial furnace - Google Patents

Abstract

A process and apparatus for the metered introduction of fine-grain materials, particularly pulverulent solid substances (i.e., coal dust) from a pressurized metering container which contains a supply of solid material, into an industrial furnace having a plurality of feed locations such as a blast furnace or cupola furnace is presented. The solid material is fed to the individual feed locations in a carrier gas stream through a conveying duct, the gas stream being highly charged with the solid material. The carrier gas is fed to the lower end section of the metering container in a flow which causes a local loosening in the lower section of the supply of solid material with the conveying ducts opening into the loosening region. The apparatus includes a metering container, which is designed as a pressure vessel and which is adapted to be filled at its upper end section with solid material to be fed to the furnace. The metering container includes at its lower end section a plurality of upwardly open chambers. At least one conveying duct leading to a feed location opens into each of the chambers. The conveying ducts are provided in each instance with a gas-permeable incident flow floor. Also, on the side of each conveying duct remote from the metering container a carrier gas duct for the carrier gas feed communicates therewith.

Description

The invention relates to a method for the metered introduction of fine-grained, in particular dust-like solids, in particular coal dust, from a metering container containing a solid supply and under pressure into an industrial furnace having several feed points, in particular a shaft furnace such as a blast furnace or a cupola furnace, in which the solids are fed to the individual feed points in a carrier gas stream with a high solids load, each through a conveying line, the carrier gas being fed to the lower end section of the metering container in a flow causing local loosening in the lower section of the solids supply and the delivery lines open into the loosening area.

The invention further relates to a device for carrying out the aforementioned method with a metering container designed as a pressure vessel, which is to be filled with solid to be fed to the furnace at its upper section and which has a plurality of open-topped chambers at its lower end section, in each of which at least one to a supply point leading delivery line opens, and which are each provided with a gas-permeable inflow base, on the side facing away from the solid column, a carrier gas line for supplying carrier gas opens.

To save high-quality fuels such as Oil or coke can replace part of the fuel with coal dust, which can be obtained from raw coal in a grinding and drying plant, the coal dust being fed to the industrial furnace by means of a corresponding device by pneumatic conveying.

The most important metallurgical requirement is that the metering of the coal dust, ie the amount of coal dust supplied to the furnace per unit of time, is carried out with the greatest possible accuracy, so that the metallurgical As far as possible, processes in the furnace are subject to as little fluctuation as possible.

Since the coal dust, for example in a blast furnace, is not supplied at one point but has to be fed to each blow mold, industrial furnaces generally have several feed points, a further requirement being that the coal dust must be fed evenly to the individual feed points.

Different solids or types of solids generally have different fluid mechanical properties under the same conditions and accordingly show different delivery behavior, which can be determined empirically. The carrier gas flow to be fed to the chambers of the dosing container below the inflow bottoms must (at least) be dimensioned such that it always leads to sufficient loosening of the solid in the local loosening zone in the case of the type of solid to be conveyed - that is to say also at the highest operating pressure occurring in the dosing container that the so-called loosening point of the solid bed in the metering container is reached or exceeded in every operating state. In the case of a fine-grained solid, this loosening point is only insignificantly dependent on the pressure under which the solid bed is.

Various proposals have already been made in the literature for solving the problem at hand, and some have already been tried out, at least on an experimental basis, but the solutions available so far have failed the requirements to be placed on such a method and a device for carrying out the method have so far not been optimally satisfied.

For example, according to DE-OS 29 34 130, it is provided that both the regulation of the total solid conveying capacity to be supplied to the furnace (all the conveying lines) and the regulation of the solid conveying capacities of the individual conveying lines by changing the amount of carrier gas supplied to the lower end section of the metering container he follows. This is done by means of dust flow measuring points which are assigned to each individual delivery line, the dust flow measuring points each acting on a control valve which is arranged in each carrier gas supply line. However, such regulation of the delivery rate via the carrier gas flow does not always lead to the desired results. Regarding this technology, it should be noted, among other things, that a quantitative measurement of the solids content of such two-component flows is relatively imprecise even with great effort if absolute values are to be determined with such a measurement. In addition, with the method of operation proposed in DE-OS 29 34 130, it is difficult to achieve fine regulation of the delivery rates of the individual delivery lines, since the changes in the carrier gas supply triggered by the dust flow measuring points greatly change the fluidization state of the solid at the beginning of the delivery lines can.

The present invention has for its object to provide a method and a device suitable for performing the method of the types described above, by means of which, with the least possible investment, an accurate, operationally reliable and robust, largely independent of the inevitably fluctuating respective properties of the solid Dosage of the predetermined total amount of solids fed to the furnace is to be ensured, the total amount of the solid also being to be largely uniformly fed to the individual feed points of the furnace and the largest possible control range for the respective solids delivery capacity should be present in the individual delivery lines, and furthermore the wear of the delivery lines should be as small as possible or limited to a small section.

As a solution to the procedural part of this task it is provided according to the invention that to regulate the total delivery rate of the furnace all the delivery lines, the dosing container containing the solids supply is continuously weighed, so that the actual weight of the dosing container (including its contents) with which the initial weight is the target -Delivery capacity and the target weight that has elapsed since the start of the discharge are compared and the pressure in the metering container is increased or decreased when the target weight is exceeded or undershot, and that regulation of the delivery capacity of each delivery line is independent of the other delivery lines in in a manner known per se by adding secondary gas, the secondary gas being fed to the feed lines in each case adjacent to the relevant feed point of the industrial furnace upstream to a throttle point or narrowing of the cross-section.

In the method according to the invention, the above-described gravimetric metering of the total amount of solids supplied to the furnace per unit of time and its regulation via the pressure difference between the pressure in the metering container and the furnace or the end of the delivery lines achieve an extraordinarily high degree of accuracy within the scope of the requirements , which is usually so large that the pressure regulating the total discharge rate in the dosing container is generally only changed at intervals of the order of 5 to 10 minutes, this accuracy being able to be achieved with comparatively little effort. The differential pressure is preferably regulated in a manner known per se by supplying or removing pressurized top gas which is supplied through the metering container of the solid supply. The amount of top gas supplied is preferably such that not only is the amount of solids discharged from the metering container replaced by top gas, and the gap volume between the solid parts corresponding to the respective operating pressure is filled by gas, but also that part of the top gas supplied is always up to the local loosening area flows and is discharged through the delivery lines together with the solids and the carrier gas supplied to the metering vessel at the lower end section. The latter has proven to be extremely useful for ensuring a steady flow of solids into the chambers and for the desired high solids loading.

In contrast to the previously known method described above, the amount of carrier gas supplied to the lower end section of the metering vessel (based on the standard state) is preferably kept constant for a particular type of solid in the method according to the invention, the amount of carrier gas being dimensioned such that it falls below the respective type of solid the highest operating pressure in the dosing tank leads to a loosening of the solid in the local loosening zone.

The device-related part of the above object is achieved in that the metering vessel is designed in a manner known per se as a weighing vessel, in the upper end section of which a top gas line provided with a control valve for supplying top gas under excess pressure opens out, that a (first) control device is present by means of which the actual weight of the metering vessel (together with its contents) is to be compared with its target weight at predetermined intervals and if the target weight is exceeded or undershot, the pressure in the metering container is increased or regulated by regulating the top gas pressure. is to be reduced and, if the target weight corresponds to the actual weight, it is to be kept constant that the cross section of the delivery lines is in each case in that of the feed point in question upstream immediately upstream section is significantly reduced that a bypass line carrying secondary gas leads upstream to the cross-sectional constriction in each delivery line, that in each delivery line there is a measuring device by means of which the relative actual delivery rate of the delivery line in question is to be determined, that an averager is present, by means of which the calculated average delivery rate per delivery line is to be determined, and that in each delivery line there is a (second) control device by means of which the amount of secondary gas supplied to the delivery line can be increased or decreased if the actual value determined by the measuring device is - Delivery rate of the delivery line is greater or less than the average delivery rate per delivery line determined by the averager.

In addition to the described gravimetric dosing of the total amount of solids fed to the furnace and its regulation via the differential pressure between the pressure in the dosing container and in the furnace or at the end of the delivery lines, another essential feature of the present invention is the cross-sectional narrowing of the delivery lines at their end section and the supply of Secondary gas to the delivery lines more or less immediately adjacent to the cross-sectional constriction. Due to the cross-sectional constriction of the delivery lines, there is a considerable pressure difference to the pressure in the dosing tank at the constriction point due to the pressure drop in the delivery lines and, on the other hand, due to the throttling associated with the cross-sectional constriction to the pressure in the furnace, so that a relatively large amount of gas enters the bypass lines with the secondary gas Delivery lines are to be introduced and accordingly a relatively large one Control range for the amount of solids flowing into the furnace from the individual delivery lines results, since secondary gas introduced into a delivery line dilutes the two-substance mixture accordingly and accordingly, with a greater addition of secondary gas, the furnace receives less solid per unit time from the line in question.

The large cross-sectional constriction at the end of the delivery lines also gives the great advantage that the non-narrowed part of the delivery lines, the length of which can be 100 to 200 meters, is driven at a relatively low delivery speed of, for example, 0.8 to 3 m / sec can be, which only causes a correspondingly low wear, while only the flow velocity in the narrowed part is relatively high (e.g. 18 to 30 m / sec) and only in this short section of the delivery line there is more wear, these short sections according to Wear can be exchanged.

The cross-sectional constriction in the delivery lines is preferably continuous, with a conical and the like between the section of the delivery line having the larger cross section and its section having the smaller cross section. trained intermediate section may be present.

The cross-sectional ratio between the non-constricted and the constricted part of a delivery line can, according to the invention, be approximately 10: 1 - 25: 1, it being preferably provided that the non-restricted cross-section of the delivery lines each has a diameter of approximately 25 to 40 mm, while the constricted Cross section has a diameter of 6 to 8 mm.

Electrical load cells, on which the dosing vessel is supported, and whose measurement signals are to be fed to the first control device, are preferably provided as weight measuring devices for the weight measurements of the metering container, together with their contents. Such load cells are not only extremely robust and relatively inexpensive, but also have a level of accuracy that is sufficiently high for gravimetric dosing within the framework of the circumstances described above.

The measuring devices for determining the relative actual delivery rate in the delivery lines do not need to be highly complex measuring devices which measure the flow rate in the delivery lines with a relatively high degree of accuracy, since according to the invention only a relative measurement of the delivery rate in the individual delivery lines to one another needs to take place because with these measuring devices, in contrast to previously known devices such as the device described above according to DE-OS 29 34 130, no absolute values have to be measured. Accordingly, it is preferably provided that these measuring devices are capacitively operating measuring devices, with impairments in the measuring results due to changes in moisture etc. not playing a role in this relative measurement, since the properties of the conveyed material in the individual delivery lines are essentially the same at the same time are.

Further preferred embodiments of the present invention are described in the subclaims.

Fig. 1

eine vereinfachte schematische Darstellung einer erfindungsgemäßen Vorrichtung; und

Fig. 2

eine vereinfachte Darstellung einer Verengungsstelle einer Förderleitung.

The invention is explained below using an exemplary embodiment with reference to a schematic drawing. It shows:

Fig. 1

a simplified schematic representation of a device according to the invention; and

Fig. 2

a simplified representation of a constriction of a delivery line.

Fig. 1 shows a highly schematic and simplified representation of a device for the metered introduction of coal dust into a blast furnace, not shown, of which only one blow mold 2 is indicated, of which there are several distributed over the circumference of the blast furnace, each in one Wind tunnel 3 open.

The coal dust to be blown into the blast furnace 1 is put into a storage silo 4 after its production in a grinding and drying system, in which a quantity of coal can be stored under an inert atmosphere, which is sufficient to bridge a production loss of the grinding and drying system that lasts several hours can. The ground coal passes from the storage silo 4 via a cellular wheel sluice 5 into a sluice vessel 6, which after filling is closed by a valve 7 to the storage silo 4. Thereafter, the sluice vessel 6 is strung at its lower end section via a line 8 with sluice gas originating from a wind boiler 9 until the predetermined working pressure of a metering container 10 arranged below the sluice vessel 6, also designed as a pressure vessel, is reached and that in the sluice vessel 6 located coal dust reaches the metering container 10 after opening valves 11. After filling the metering container 10, the valves 11 are closed again.

The gas line 12 leading from the wind boiler 9 to line 8 for the lock gas is continued via the connection point of line 8 and connected to an upper gas line 13 which leads to the upper section of the metering container 10 and in which a control valve 14 is arranged.

At the lower end of the metering container 10, a plurality of chambers 15 are arranged which are open at the top, that is to say into the metering container 10, the maximum number of which corresponds to the number of blow molds 2 of the blast furnace 1 to be charged with coal dust. Each chamber 15 is provided with a gas-permeable inflow base 16 in its lower region. A carrier gas line 17 opens into each chamber 15 below the inflow bottoms 16, the carrier gas lines 17 being connected to the gas line 12 via a valve 18.

A delivery line 19 is led out of each chamber 15, the delivery lines 19, of which only one line is shown for the sake of clarity, each end in the chambers 15 somewhat above the inflow floor 16, where the coal dust is loosened or fluidized by the introduced carrier gas is.

The conveyor lines 19, the length of which is between 100 and 200 meters, have a free cross section of 25 mm over their entire length. The cross section of the delivery lines 19 is in each case significantly reduced downstream of the feed point 20 in question and adjacent to it, to a diameter of 6 mm. As can be seen from FIG. 2, this considerable reduction in cross-section does not occur suddenly, but essentially continuously via a conical intermediate piece 21.

The gas line 12 coming from the air boiler 9 is continued via the connection point of the carrier gas lines 17 with a bypass line 22, via which secondary gas is to be conducted into the relevant delivery line 19. A control valve 23 is arranged in each bypass line 22 and is used to regulate the amount of secondary gas supplied to the relevant delivery line 19.

The connection point 24 for the bypass line 22 is preceded by a capacitive measuring device 25 upstream in each delivery line 19, by means of which the relative delivery rate of the relevant delivery line 19 can be determined. The measuring devices 25 each give their measured values to a u.a. a control device 26 containing a computer, with which the control valves 23 in the bypass lines 22 are to be controlled.

The dosing container 10 is supported on load cells 27, by means of which its weight (together with its content) can be measured continuously, the measured values being fed to a control device 28, which is also connected to the control valve 14 of the upper gas line 13.

Since the filling of the dosing container 10 is of no particular interest in the present context, in addition to the comments already made above, the following description of the mode of operation of the device is limited to the operational sequence after the dosing container 10 has been filled.

Depending on the respective conveying properties of the coal dust and the operationally specified delivery rate, the required operating pressure is set in the dosing tank 10 via the upper gas line 13, the differential pressure between the pressure in the dosing tank 10 and the pressure prevailing in the blast furnace 1 or that prevailing at the end of the delivery lines 19 Pressure is basically kept constant during the emptying of the metering container 10.

The actual weight of the dosing container 10 (including its contents) is constantly compared by the control device 28 with the target weight of the dosing container 10, that is to say with the weight which the dosing container has after the time that has elapsed since emptying, taking into account the specified discharge rate ought to. If the actual weight of the metering container 10 corresponds to its target weight, this indicates that the specified discharge quantity has actually been discharged and fed to the blast furnace 1 in the relevant time interval, so that the operating conditions are not changed. If, on the other hand, the actual weight of the metering container 10 is greater than its target weight at the relevant time, this means that too little coal dust has been discharged from the metering container 10. In such a case, the control device operates 28 that the previously constant pressure in the metering container 10 is increased by the control device 28 acting accordingly on the control valve 14 of the upper gas line 13. If, on the other hand, the actual weight is smaller than the target weight of the metering container 10 and accordingly too much coal dust has been discharged from the metering container at the time of measurement, the control device 28 brings about a reduction in the previously constant pressure in the metering container 10 and thus a corresponding reduction in the discharge capacity.

In this way it can be ensured with relatively simple, robust and operationally reliable means that the predetermined amount of coal dust per unit time is actually supplied to the blast furnace 1 within the required accuracy.

During the charging of the blast furnace 1 with coal dust, the amount of carrier gas supplied to the dosing container 10 via the chambers 15 via the carrier gas lines 17 is kept constant. so that the conditions determined during or before start of operation, adapted to the respective properties of the coal dust and adjusted to the predetermined throughput, remain essentially unchanged. This obviously also applies in an advantageous manner to the fluidization conditions at the beginning of the delivery lines 19.

However, since - as stated above - a further operational requirement consists in the fact that the coal dust is also largely uniformly fed to the individual feed points 20 of the blast furnace 1, a corresponding relative regulation of the delivery rates takes place during the discharge of the individual delivery lines 19, in that the solids flow rates determined by the capacitive measuring devices 25 of the delivery lines 19 are supplied to the measuring device 25 as signals and a calculated average value of the delivery rate per delivery line 19 is determined in an averager of the control device 26. If the control device 26 detects that the measured delivery capacity of a particular delivery line 19 is greater than the determined mean value and must therefore be reduced for the purpose of equalization, the control device 26 acts on the control valve 23 of the relevant bypass line 22 in such a way that that of the relevant delivery line 19 at the connection point 24 supplied secondary gas is increased in quantity, so that there is a corresponding dilution of the two-component flow and thus a reduction in the discharge capacity of the delivery line 19 in question of solid matter (coal dust). If, on the other hand, the delivery rate determined in a delivery line 19 is less than the mean value, the reverse process takes place, ie the secondary gas flow supplied to the delivery line 19 is reduced accordingly.

Since the connection points 24 of the bypass lines 22 are each arranged adjacent to the constriction point 21, there is therefore a considerable pressure drop due to the pressure drop during delivery in the delivery line 19 to the metering container 10 and also due to the cross-sectional constriction to the blast furnace 1, so that there is a large control range of the order of 1: 3 - 1: 4 can be achieved in the individual delivery lines 19.

Despite the high solids loading, which, depending on the properties of the coal, the line dimensions etc., and depending on the back pressure in the industrial furnace, is in the range from 20: 1 to greater than 100: 1 kg coal / kg gas, the wear on the delivery lines 19 is extremely low, since you can get under normal conditions with conveyor speeds in the range of about 0.8 to 3 m / sec and only in the area of the lance-shaped constriction section 19 'speeds in the range of 18 to 30 m / sec can be achieved, which, however, not as a negative side effect of Cross-sectional narrowing of the delivery lines 19 to be considered, but in view of the high wind speeds in the wind tunnel 3 or in the blow molds 2 and the internal pressure prevailing in the furnace are necessary in order to be able to blow the two-component flow into the blast furnace. Here, due to the narrowing of the cross-section, the relatively small diameter at the narrowed end section 19 'of the conveyor lines 19 also proves to be advantageous when it is introduced into the blast furnace 1, since such dimensions allow manual insertion even with the high internal pressures of the blast furnace.

REFERENCE SIGN LIST (LIST OF REFERENCE NUMERALS)

1

Blast furnace

2nd

Blow mold

3rd

Wind tunnel

4th

Storage silo

5

Cell wheel lock

6

Lock vessel

7

Valve

8th

management

9

Air boiler

10th

Dosing container

11

Valves

12

Gas pipe

13

Upper gas line

14

Control valve (in 13)

15

Chambers

16

Inflow floor (from 15)

17th

Carrier gas line

18th

Valve

19th

Conveyor lines

20th

Feed point

21

Conical adapter (from 19)

22

Bypass line

23

Control valve

24th

Connection (for 22 to 19)

25th

Measuring device (in 19)

26

Control device

27th

Load cells

28

Control device

Claims (12)

1. A process for a metered introduction of fine-granular solid, particularly dusty substances, particularly cole dust, from a metering container, which contains a supply of solid substance and which is pressurized, into an industrial furnace having a plurality of feed locations, particularly into a pit furnace as a black furnace or a cupola furnace, in which the solid substance is fed to the individual feed locations in a highly charged carrier gas stream through a conveying duct, whereby the carrier gas is fed to the lower end section of the metering container in a flow causing a local loosening in the lower section of the supply of solid substance, and the conveying ducts open into the loosening region, characterized in that the metering container containing the supply of solid substance is continuously weighed; that the actual weight of the metering container is compared with its theoretical weight; and the pressure in the metering container is regulated by increasing or decreasing the pressure in the event the actual weight exceeds or falls below the theoretical weight, respectively; and that the conveying capacity of each conveying duct is regulated independently of the other conveying ducts in a known per se manner by an addition of secondary gas, whereby said secondary gas is fed to said conveying ducts adjacent each feed location at a position upstream in relation to a throttling position or restriction of the cross section.
2. The process of claim 1, characterized in that the quantity of carrier gas related to standardized condition, which is fed as a function of time to the lower end section of the metering container is maintained constant for a specified type of solid substance, whereby the quantity of carrier gas being selected so that, in the case of a specified type of solid substance under the greatest operating pressure occuring in the metering container, it still leads to a loosening of the solid substance in the local loosening zone.
3. The process of claim 1 or 2, characterized in that the regulation of the pressure in the metering container takes place by the step of supplying or withdrawing of pressurized top gas, which is supplied or withdrawn above the supply of solid substance in said metering container.
4. The process of claim 3, characterized in that the quantity of top gas fed to the metering container is measured so that not only the quantity of solid substance discharged from the metering container is replaced in each instance by top gas, and that the gap volume, corresponding to the respective operating pressure, between the solid substance components filled out by gas, but also a portion of the fed top gas flows into the local loosening region and is discharged through said conveying ducts together with the solid substance as well as the carrier gas supplied to the metering vessel at the lower end section.
5. An apparatus for conducting the method in accordance with one or more of the preceding claims, including a metering container having an upper end section and a lower end section defining a pressure vessel, and which is adapted to be filled with solid substance at its upper section, said metering container having a plurality of upwardly open chambers communicating with its lower end section, into which at least one conveying duct communicates leading to a feed location for feeding an industrial furnace; a gas-permeable incident flow floor provided in each chamber, whereby on the side thereof remote from said solid material in said metering a carrier gas duct for the supply of carrier gas communicates, characterized in that said metering container (10) is provided as a weighing means in a known per se manner, whereby a top gas duct (13) connected to said upper end section of said metering container (10) being provided with a regulating valve (14) for feeding top gas under excess pressure; (first) regulating means (28) for comparing the actual weight of the metering container (10), after specified time intervals, with its theoretical weight, and for increasing or decreasing the pressure in the metering container (10) by regulation of the top gas pressure in the event of the actual weight exceeding or falling below the theoretical weight, respectively, and wherein the pressure is kept constant in the event of agreement between the theoretical weight and the actual weight; said conveying ducts (19) having a cross-section which is substantially reduced defining a constriction (21) in an area (19') disposed upstream of a selected feed location (20); bypass duct means (22) for guiding secondary gas into each conveying duct (19), said bypass duct means (22) being upstream adjacent said constriction (21); measuring means (25) associated with each of said conveying ducts (19) for determining the actual conveying capacity of each conveying duct (19); mean value former means for determining the mean conveying capacity for each conveying duct (19); and (second) regulating means (26) associated with each of said conveying ducts (19) for increasing or decreasing the quantity of secondary gas fed to the conveying duct (19) if the actual conveying capacity of the conveying duct (19), as determined by said measuring means (25) is greater or smaller, respectively, than the mean conveying capacity of each of said conveying ducts (19) as determined by said mean value former means.
6. The apparatus of claim 5, characterized in that said metering container (10) is supported on electrical load cells (27), the measurement signals of which are fed to said first regulating means (28).
7. The apparatus of claim 5 or 6, characterized in that said constriction (21) in said conveying ducts (19) is substantially gradual.
8. The apparatus of claim 7, characterized in that said gradual constriction (21) comprises: a conical intermediate section (21) in each of said conveying ducts (19) located between said section having the greater cross section of a conveying duct (19), and said section (19') having the smaller cross section.
9. The apparatus of claim 7, characterized in that the cross-sectional ratio on opposed ends of said constriction (21) is about 10:1 to about 25:1.
10. The apparatus of one ore more of claims 5 - 9, characterized in that the cross section of the conveying ducts (19) is reduced from about 25 to 40 mm prior to said constriction (21) to about 6 to 8 mm subsequent to said constriction (21).
11. The apparatus of one or more of claims 5 - 10, characterized in that said measureing means (25) for the determination of the relative actual conveying capacity in said conveying ducts (19) are capacitive measuring means.
12. The apparatus of one or more of claims 5 - 10, characterized in that said chambers (15) disposed at said lower end section of said metering container (10) have pot shaped extensions communicating with a conveying duct (19) each.

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