GB2032597A

GB2032597A - A method and an apparatus for the introduction of pulverised material into the hearth of a shaft furnace

Info

Publication number: GB2032597A
Application number: GB7933410A
Authority: GB
Original assignee: MAXHUETTE UNTERWELLENBORN
Current assignee: MAXHUETTE UNTERWELLENBORN
Priority date: 1978-09-28
Filing date: 1979-09-26
Publication date: 1980-05-08
Also published as: DD139271A1; DE2934130A1; CS241953B1; BG34843A1

Abstract

The apparatus comprises a batching container (3) having an upper portion, and a lower portion (4) open towards the upper portion. The lower portion has a porous inner bottom (7) and an outer bottom which is spaced from the latter and has connections for pipes (10) for supplying carrier gas below the inner bottom. Carrier pipelines (5) extend into the lower portion of the container above the inner bottom and have outlets to the furnace hearth (1). The pulverised material is deposited by gravity feed in to the lower portion of the container which is sealed and carrier gas from the pipes (10) is forced into the material and forms in the region above the inner bottom a fluidised layer. The carrier gas loaded with the powder enters the carrier pipelines (5) and travels therethrough to the furnace. <IMAGE>

Description

SPECIFICATION A method and an apparatus for the introduction of pulverised material into the hearth of a shaft furnace The invention relates to a method and an apparatus for the introduction of pulverised material into the hearth of a shaft furnace, more particularly the introduction of pulverised lignite into the hearth of a blast furnace for the production of pig-iron.

Pulverised materials, especially pulverised coal, are injected through the tuyères into the hearth of shaft furnaces in order to be substituted for highgrade gaseous, liquid or solid fuels and/or reduce the specific -consumption of metallurgical coke.

An apparatus for the introduction of liquid, gaseous or pulverised fuels into the hearth of shaft furnaces is described in the Federal German Offenlegungsschrift 1 433 317. It merely discloses the:introduction of the additional fuel into the tuyère without solving the problem of generating a carrier-gas/dust suspension, of conveying it with the effect of little wear, and of its uniform distribution.

In the Federal German Offenlegungsschrift 22 43 439, a method and an apparatus are described for the transport of pulverised coal into a blast furnace, the primary object of which is the saving of metallurgical coke.

In accordance with said method and said apparatus, the pulverised coal is introduced via several alternately operating, pressure vessels into a pneumatic forwarding pipe through which conveyance to the blast furnace, or the blast furnace tuyères, takes place.

The quoted publication gives a detailed account of the technological sequence and the necessary control processes for the introduction of the dust into the pneumatic forwarding pipe, but is does not solve the technical problems arising from the requirements of avoiding any fluctuations in the flow of the pulverised coal to the blast furnace during alternating operation of the pressure vessel system, of reliable operation of the pneumatic forwarding pipe with little wear and with as small as possible a quantity of the forwarding gas, and of uniform distribution to the individual blast furnace inlets.

Finally, a method is described in the Federal German Offenlegungsschrift 1 433 327 for the introduction of a solid material into a reaction zone, that of a blast furnace for instance, which, while avoiding some of the disadvantages of the prevously described solution, retains the introduction of the dust from a batching and distribution system into a conventional pneumatic forwarding pipe to carry the dust to the blast furnace, and therefore fails to achieve any substantial reduction in the amount of forwarding gas required for the pneumatic transport of the dust to the blast furnace nor, as would otherwise be associated therewith, any improvement in the economy of this transport nor reduced wear.The Offenlegungsschrift 1 433 327 is characterised in that it explicitly recommends a cyclone extractor to be arranged at the end of the pneumatic forwarding pipe, immediately above the point of entry into the blast furnace, in order to reduce the amount of carrier gas entering the blast furnace. It is obvious that this arrangement necessitates substantial additional expenditure for the control of pressure within this cyclone and the removal of dust from the waste gas.

Object of the invention are a method and an apparatus for the introduction of pulverised material into the hearth of a shaft furnace, especially that of a blast furnace, by means of a continuous system operating with high uniformity and high reliability, requiring but little carrier gas, which ensures feeding, batching and forwarding of the pulverised material to the shaft furnace.

The aim of the invention is for the introduction of pulverised material into the hearth of a shaft furnace, especially that of a blast furnace for the production of pig iron, to achieve a high accuracy of batching, to make it possible for the distribution of the pulverised material, or materials, to the blast inlets to be controllable within given limits, to maintain at a low level the amount of energy required for the feeding and conveyance of the pulverised materials and to suffice with a relatively small quantity of carrier agents for suspending and forwarding the pulverised material, i.e. to achieve a high solid-matter-to-carrier-gas loading ratio (more than 300 kg/m3 of carrier gas in operating conditions), also to maintain at a low level the amount of wear occurring during batching, distribution and forwarding of the pulverised reagents.

The previously proposed technical solutions for the batching, forwarding and distribution of pulverised fuels, to be injected into blast furnaces, employ as a rule the known process principles of pneumatic conveyance.

The pulverised fuel is fed by mechanical metering devices, e.g. variable bucket-wheel feeders, or feeder screws, or compartment gates under gas pressure, into a pneumatic forwarding pipe in which it is transported by a carrier gas current to the shaft furnace. Although there are peak values quoted up to 192 kg/m3, as in the Federal German Offenlegungsschrift 1433 327 for example, with this technology loading of the carrier gas with pulverised material does not as a rule exceed a ratio between 15 and 20 kg/m3; To move large quantities of pulverised material, there are thus required considerable carrier gas volumes, i.e. high gas flow rates that have the disadvantage of giving rise to heavy wear and tear.

With the high flow rates of the dust/carrier gas suspension there are also problems in respect of a uniform distribution of the pulverised~materíal to the individual tuyères, and in respect of the wear suffered by the distribution device.

The given problem is solved by the invention as follows: The pulverised material intended for injection into the hearth of the shaft furnace is transferred from a storage bunker to a pressure vessel, hereinafter referred to as batching container. A gaseous agent, hereinafter referred to as carrier gas, is blown into the lower portion of this batching container, and the pulverised charge contained therein is loosened to a degree such as to enable the pulverised material, together with the injected carrier gas, to be directly forwarded to the shaft furnace through a delivery pipe that extends into, and begins within, the batching container, whereupon the said material is injected through a lance, for example, into the hot air current of the tuyère of a blast furnace.In accordance with the invention, the velocity of the carrier gas current in the lower portion of the batching container is so selected as to correspond to a quantity 0.2 to 10 times, preferably 1 to 6 times, the fluidising speed of the pulverised material which can be measured by known methods.

In accordance with the invention, the ratio between the internal cross-section of the conveyor pipe line and the internal cross-section of the batching container lower portion is approximately between 1:50 and 1:300.

The above mentioned loosening of the pulverised fuel in the batching container lower portion may be intensified to such a degree as to result in what could be described as a fluidised layer (confined to the lower portion). It is characteristic of the invention that the pulverised fuel charge above the lower portion of the batching container assumes the nature of a static bulk, which slides slowly downwards as and when pulverised fuel is discharged to the shaft furnace, and through which flows, as a rule, only the small amount of gas that is equivalent to the solid matter volume of the quantity of dust removed from the batching container.

With the method proposed by the invention, the achieved loading of the carrier gas current with pulverised fuel may for example be 600 kg powder per m3 carrier gas in operating conditions, if the net density of the powder is 1 500 kg/m3.

It was found that the flow of powder to the shaft furnace can be controlled very accurately (in kg of pulverised fuel per unit of time) by variation of the carrier gas quantity injected into the lower portion of the batching container, while the powder to-carrier-gas ratio remains constant within a wide range. It is, therefore, another characteristic of the method proposed by the invention that the control of fuel supply to the shaft furnace is effected by corresponding variation of The carrier gas flow into the lower portion of the batching container. The control puises employed for this purpose may be obtained, for example, by direct measurement of the powder flow in the conveyor pipe line to the shaft furnace, or by differential measurement of the batching container filling level.

With the method proposed by the invention, the conveyor pipe line for the discharge of the powder/ carrier-gas flow, which extends into the batching container lower portion, may enter the loosened zone of the charge, horizontally, or vertically from the top or the bottom. Continuity of supply to the shaft furnace is not affected by changes of direction in the conveyor pipe line, if the bending radii selected are sufficiently large. Various arrangements are therefore possible for the geometric layout of batching container and supply to the shaft furnace.

It was found that, the fewer the fluctuations to which the batching container bulk filling level is subjected, the higher is the accuracy with which the pulverised fuel can be metered. Therefore, it proved desirable to arrange for a coarse adjustment of the supply of powder to the batching container by means of simple devices that undergo little wear and demand little maintenance, e.g. bucket-wheels or slide valves, in which case the control pulse transmitter may be any known level detecting device designed for use with pulverised materials.

It was furthermore found to be an advantage that the lower portion of the batching container, in which the fludised layer is maintained, is smaller in diameter than the upper portion of the aforementioned batching container.

Homogeneity of the powder/carrier-gas suspension in the conveyor pipe line to the blast tuyère and accuracy of the powder flow control were found to improve when utmost uniformity is achieved in the distribution of the supplied carrier gas over the entire cross section of the lower portion of the batching container. The carrier gas is therefore forced into the bulk charge through a bottom of a porous material, which, in the case of the invention, lead in normal operating conditions to a reduction in pressure that is at least equivaient to the weight of the bulk charge per unit of cross-section area. Possible materials for these baffles are, for example, sintered metal plates or felt pads.To ensure a uniform distribution of the pulverised fuel over the circumference of the shaft furnace hearth, it is useful to install several, identical, batching and delivery systems in accordance with the present invention.

It is, however, equally possible with the present invention, for a single batching container to have several lower portions, or a lower portion that is subdivided into a number of separate sections.

For each of these lower portions or sections it is possible to have a separate carrier gas flow injected, as described above, so as to generate a fluidised layer therein, and to forward the powder th;ough a conveyor pipeline, extending into the respective lower portion or section, to a specific point of the circumference of the shaft furnace hearth.

There is as a rule at the blast inlet of the shaft furnace a higher pressure than atmospheric. To overcome this pressure as well as the pressure difference arising from the resistance of the conveyor pipeline, there is a build-up of increased pressure in the batching container. Therefore it is as a rule necessary also to apply increased gas pressure to the storage bunker or to install in a known manner one or several parallel pressure compensation vessels, operating in an alternating cycle, between storage bunker and batching container.

Various inert gases, such as nitrogen, CO2 or flue gas, may be employed to charge the storage bunker or pressure compensation vessel, also as carrier gas. It is also possible to use gas from the production process such as blast-furnace gas.

Air may also be added to the filling and carrier gas where slow-reacting pulverised fuels, such as pulverised coke, are used, also where quickreacting pulverised fuels, such as pulverised opencast coal, are used, provided in the latter case due consideration is given to the explosion hazard in confined pressure spaces, and the temperatures are below 600 C.

The preferred application of the invention, as has been shown, is the introduction of pulverised lignite into the hearth of shaft furnaces. The predominant grain size of the pulverised lignite is in this case 0.5 mm, and has been dried as a rule to a water content of between 8% and 12%. The velocity of the carrier gas flow in the batching container lower portion, when related to the internal cross section, is then 0.005 to 0.025 m/s, and the velocity of the powder/carrier-gas mixture in the delivery pipe from the batching container lower portion to the inlet of the shaft furnace hearth is 1 to 12 m/s.

The invention may also be employed for the injection of other carboniferous solid substances having similar grain sizes. Depending on the hygroscopic properties of such substances, it is advisable to maintain as low as possible a water content, also 12%, as a rule.

Finally, the invention may also be used for the injection of slag-forming or ferrous, fine-grain, substances into shaft furnaces, and, depending on grain size and density of the substance, the velocity of the carrier gas flow in the lower portion of the batching container, may be up to 0.1 m/s, whereas the velocity of the powder/carrier-gas mixture in the delivery pipe remains within 1 to 12 m/s.

The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which: Figure 1 shows in section along C-D in Figure 2 a batching container the lower portion of which is subdivided into three separate sectors for supplying three separate inlet points at the shaft furnace.

Figure 2 is a section along line AB in Figure 1, and Figure 3 is a diagrammatic representation of the pulverised fuel feed and batching system in the embodiment shown in Figures 1 and 2 and showing the three conveyor pipelines.

In the illustrated embodiment the pulverised material (hereinafter: powder) intended for feeding the shaft furnace hearth 1 arrives from a storage bunker (not shown) which may be followed by two alternately operating pressure compensation vessels (not shown), and is then forwarded through a coarse metering device 2 (or variable restrictor device) into a pressure vessel, hereinafter referred to as batching container, which is of circular cross-section, has a lower portion 4 and an upper portion, and is sealed against the atmosphere. The lower portion 4 of the batching container 3, which is closed by an outer bottom 8 and has a porous inner bottom 7 parallel to the bottom 8, is of a diameter which is smaller than that of the upper portion.

In the illustrated embodiment the batching container 3 is designed to supply three individually controllable conveyor pipelines 5 with the powder.

The lower portion 4 of the batching container 3 is for this purpose subdivided by three radially arranged partitions 6 into three equal sectors 9. These sectors are open towards the other portion of the batching container 3 so that the powder may freely enter from the upper portion. The partitions 16 also subdivide the bottom 7 and the space between the bottoms 7 and 8. Each of the sectors 9 has beneath the bottom 7 a connection for a separately controllable carrier gas supply pipe 10, from which the carrier gas flows into the space between the bottoms 7 and 8 and from there through the bottom 7 into the respective sector 9 and penetrates into the powder therein and loosens and expands it while forming a local fluidised layer of the powder. A conveyor pipeline 5 enters vertically from the top each of the sectors 9 to forward a stream of carrier gas and powder to the respective inlet at the shaft furnace 1.

The preferred manner of control of the powder flow to the shaft furnace 1 is in this embodiment by means of a powder flow measuring point 11 in each of the conveyor pipelines 5. Each of the points 11 acts on a control valve 1 2 on the carrier gas supply pipe 10 which is associated with that sector 9 from which the pipeline 5 controlled by that measuring point 11 is supplied.

The batching container 3 is filled with powder up to a predetermined level in the upper portion thereof. This level is monitored by a level detector 13 which controls the device 2.

Claims

1. A method for the introduction of pulverised material (hereinafter: powder) into the hearth of a shaft furnace, such as for the introduction of pulverised lignite into the hearth of a blast furnace for pig-iron production, wherein the powder is deposited by gravity feed in the lower portion of a batching container, sealed against the atmosphere, as a quasi static batch, a gaseous medium acting as carrier gas is forced into the lower portion of the batching container at a velocity between 0.2 and 10 times the fluidising velocity of the powder, thereby locally loosening or expanding the batch into a fluidised layer, the carrier gas heavily loaded with the powder enters a carrier pipeline, the inlet end of which extends into the loosened or expanded layer or fluidised layer, and the thus loaded carrier gas is forwarded through said pipeline to the hearth, the stream of powder to the hearth being controlled by variation of the amount of the carrier gas forced into the lower portion of the batching container.

2. A method according to Claim 1 wherein the ratio of the internal cross-sectional area of the said conveyor pipeline and the free cross-sectional area of the loosened or expanded part of the batch orfluidised layer is between 1 :50 and 1:300.

3. A method according to Claim 1 wherein the velocity of the carrier gas forced into the lower portion of the batching container is between 1 and 6 times the fluidising velocity of the powder.

4. A method according to anyone of the preceding claims wherein the powder is crushed or ground lignite, or other carboniferous material, or slag-forming or fine-grain ferrous material, and the velocity of the carrier gas stream entering the lower portion of the batching container is set to between 0.005 and 0.1 m/s, while the velocity of the mixture of carrier gas and powder in the conveyor pipeline from the lower portion of the batching container to the discharge point at the shaft furnace is set to between 1 and 12 m/s.

5. A method according to Claim 4 wherein the lignite or other carboniferous material has a grain size of up to 0.5 mm and water content of up to 12%.

6. A method for the introduction of pulverised material into the hearth of a shaft furnace substantially as herein described with reference to the accompanying drawings.

7. An apparatus for carrying out the method according to any one of the preceding claims comprising a batching container having an upper portion in the form of a shaft and at least one lower portion open towards the upper portion, the or each lower portion having an inner bottom, made of a material allowing the passage of gas therethrough, and an outer bottom, spaced from the inner bottom and provided with at least one connection for the flow-controlled introduction of a gaseous medium, a carrier pipeline extending with its inlet into the or each lower portion and with its outlet to the hearth.

8. An apparatus according to Claim 7 comprising one lower portion subdivided into sectors open towards the upper portion, at least one said carrier pipelines extending into each of the sectors.

9. An apparatus according to Claim 7 or 8 wherein the ratio of the internal cross-sectional area of the conveyor pipeline and of the internal cross-sectional area of the lower portion, or the ratio of the internal cross-sectional area of each conveyor pipeline and the associated lower portion or sector is between 1:50 and 1:300.

10. An apparatus according to any one of Claims 7 to 9 wherein the carrier pipelines extend into the apparatus through a side wall thereof, through the bottoms or through the-upper portion.

11. An apparatus according to any one of Claims 7 to 10 wherein the apparatus or at least its upper part is of circular cross-section.

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12. An apparatus according to any one of Claims 7 to 11 wherein the cross-section of the lower portion of the batching container is smaller than that of the upper portion, and the transition from the cross-section of the upper portion of the cross-section of the lower portion or lower portions or sectors of the lower portion, is so designed as to ensure that the batch of powder, held in the upper portion of the batching container, is uniformly distributed over the crosssection without any cavities when it slides downwards into the lower portion orportions or sectors of the lower portion of the batching container.

13. An apparatus for carrying out the method according to any one of Claims 1 to 6 constructed, arranged and adapted to operate substantially as herein described with reference to, and as shown in, the accompanying drawings.