EP0651058A1 - Process for introducing a second flow of powdered materials into a pneumatic transport system conveying powdered materials with adjustable flow rate - Google Patents

Abstract

The second flow of pulverulent materials is introduced at a controlled flow rate and the control of the first flow rate is rendered insensitive to the perturbations generated by the introduction of the second flow by controlling the first flow rate directly or indirectly upstream of the point of injection of the second flow. <IMAGE>

Description

The present invention relates to a method for introducing a second flow of pulverulent materials into a transport pipe conveying a first adjustable flow rate of pulverulent materials.

Although not limited thereto, the present invention relates to the introduction of dust extracted from blast furnace gas in a pulverulent coal flow.

In blast furnace gas cleaning plants, solid pollutants are separated from the gas phase using dry separators such as dust bags, cyclones, bag filters and electrostatic precipitators. These solid residues are collected in hoppers installed directly below the dry separators.

These hoppers, which must be emptied regularly, freely discharge, via extraction equipment, solid residues, either directly into wagons or trucks, or simply on a heap below the hoppers. The solid residues are then loaded by mechanical shovels onto wagons or trucks and then evacuated to a landfill. It will be noted that the solid residues separated from the blast furnace gases mainly consist of iron and coke dust.

The operation of evacuating solid residues from the separator hoppers is a very dusty operation, which undoubtedly leads to problems from the point of view of healthiness of the workplace and environmental protection. Then the discharge into the open air of solid residues also uncontrollably releases harmful or toxic gases and vapors which are entrained by solid residues outside the purification plant. gas when unloading the hopper. These gases and vapors released in an uncontrolled manner undoubtedly represent a significant safety problem. It is obvious that this discontinuous handling of solid residues is an unsanitary, polluting and costly practice. In order to avoid having to landfill these solid residues, we thought of reintroducing them into the blast furnace. A suitable means of introduction is obviously the installation for injecting pulverulent coal into the blast furnace via the nozzles of the blower. In fact, here we have an installation for injecting large quantities of pulverulent materials into the blast furnace. If we knew how to use this installation to reinject the dust into the blast furnace, we would have an elegant way to recycle the materials contained in the dust and we would avoid the costs of landfilling this dust.

The simplest way would obviously be to mix the coal dust in the storage silos and inject a mixture of coal and dust into the blast furnace. However, this solution has several disadvantages. In fact, coal storage silos are normally quite far from the blast furnace and gas purification installations. It would therefore be necessary to transport the dust from the purification installation to the storage silos and then bring it back to the blast furnace. As dust is much more abrasive than carbon particles, this method could quickly wear down the coal transport lines. In addition, the quantity of carbon injected cannot be precisely controlled because the carbon concentration is not known and is not constant.

Another potential solution consists in injecting the dust, near the blast furnace, into the main pneumatic transport pipe conveying the pulverulent coal. This solution avoids unnecessary transport of dust and minimizes wear on the pipes due to dust abrasion.

However, coal injection is an important parameter in the operation of a blast furnace. It is therefore essential to be able to exactly control the flow of coal injected at all times and care must be taken not to disturb the coal injection regime by the introduction of a second product flow into the flow of powdered coal.

The object of the present invention is to provide a method which makes it possible to introduce, in a controlled manner, a second flow of pulverulent materials into a pipe conveying a first regulated flow rate of pulverulent materials without disturbing this first flow rate.

To achieve this objective, the present invention provides a method of introducing pulverulent materials into a pneumatic conveying line conveying a first adjustable flow rate of pulverulent materials characterized in that the second flow of pulverulent materials is introduced at a controlled flow rate and in that the regulation of the first pneumatic transport flow is made insensitive to disturbances caused by the introduction of the second flow by adjusting the first flow directly or indirectly upstream of the injection point of the second flow.

The method according to the present invention has the advantage that a second flow of pulverulent materials can be injected into a pneumatic system without disturbing the regulation of the first flow. In fact, the first flow rate depends among other things on conditions such as the pressure in the pipe at the point of discharge. If the flow is adjusted - either directly or indirectly - no longer at the discharge point but at a point upstream from the injection point of the second flow, the first flow is regulated as if a fictitious discharge point was at the regulation point located upstream of second injection site. It is enough to take into account, in the parameters used to adjust the flow at this point, the influence of the pipe end lying between the regulation point and the actual discharge point.

According to a first advantageous embodiment, the first flow rate is adjusted by measuring and adjusting the first flow rate of pulverulent materials to a predetermined value upstream of the injection point of the second flow.

According to a preferred embodiment, the first flow is adjusted by measuring the pressure and adjusting it inside the pipe to a predetermined value upstream of the injection point of the second flow.

Preferably, the second flow of pulverulent materials is injected at the injection point in the middle of the first flow of pulverulent materials. This protects the walls of the pipes against abrasion due to the particles injected.

Advantageously, the second flow of pulverulent materials is injected vertically in the direction of flow of the first flow. This keeps the injected particles in the middle of the first flow of pulverulent materials and minimizes abrasion.

According to yet another advantageous embodiment, the second flow of pulverulent materials is maintained at a constant value. The advantage of controlling the second flow, is that the disturbances caused in the system by this injection are less significant and the regulation of the first flow therefore becomes less difficult.

It is important to note that the present method makes it possible to introduce the two different materials at a predetermined ratio. It is therefore possible to know at all times the quantity of coal injected.

• la Figure 1 représente un schéma général d'une installation d'injection de charbon pulvérulent et de poussières et
• la Figure 2 représente un schéma des pressions en fonction des différents points d'un circuit comprenant un point d'injection pour un deuxième flux de matériaux pulvérulents.

Other features and characteristics will emerge from the description of an embodiment advantageous, presented below, by way of illustration with reference to the appended figures, in which:

• FIG. 1 represents a general diagram of an installation for injecting powdered coal and dust and
• FIG. 2 represents a diagram of the pressures as a function of the different points of a circuit comprising an injection point for a second flow of pulverulent materials.

Figure 1 shows two silos 10, respectively 14 injection for powdered coal. These two silos alternately feed an evacuation pipe 18 and are each equipped with a weighing system 22 making it possible to control, at all times, the weight of the silo and thus to deduce therefrom the quantity of pulverulent coal evacuated per unit of time . The discharge line 18 is equipped with a device for direct measurement of the flow 23 and with a device for direct adjustment of the flow 24 or alternatively with a device for measuring the pressure 26 and with an adjustment device of the pressure 28 located upstream of an injection device 30 of a second flow of pulverulent products. The control device 23 and flow adjustment 24 respectively the control device 26 and pressure adjustment 28 make it possible to regulate, effectively and simply, the coal flow as a function of the pressure prevailing in the injection silos powdered coal. At the regulation point, the pressure inside the pipe 18 is maintained at a higher level than the injection pressure of the second product at the injection device 30. In this way, the injection of the second product will not disturb the flow of powdered carbon. The coal flow thus becomes independent of the pressure at the point of discharge.

The injection device 30 is preferably located in a vertical section of the pipe 18 to facilitate the introduction of the second product.

The device 30 consists of an enlarged section of the pipe 18 into which the second product is injected by means of an injection nozzle 34 preferably located in the middle of the enlarged section of the said pipe 18. In this way, the second product, more abrasive than coal, is maintained in the middle of the coal flow which protects the pipes against abrasion by the injected particles.

Line 18 leads to a device 38 for distributing powdered products as described, for example, in US Pat. No. 5,123,632. In this device, the product flow is divided and led to the different blast-holders and is finally injected into the blast furnace.

The system for supplying pulverulent materials injected through the nozzle 34 into the pneumatic line, consists of a hopper 110 installed below a solid particle separator (not shown) of an installation for purifying gas from blast furnace. This hopper 110 receives the solid residues separated by the separator of the blast furnace gas. It should be noted that these blast furnace gases include toxic gases such as CO and more or less significant quantities of water vapor. Solid residues mainly consist of coke dust, coal and iron ores.

A discharge line 112, fitted upstream of a closure member 114 for solid residues and downstream of a gas-tight isolation valve 116, connects the hopper 110 to a closed vessel 118. The closed vessel 118 constitutes a thermally insulated pressure vessel, into which the discharge line 112 opens at its upper part. At its lower part, the vessel 118 is equipped with a fluidization device making it possible to inject a gas from below, through the solid residues discharged in the closed vessel 118. The fluidization device is, for example, constituted by a peripheral surface permeable to gases and delimiting on the lower part of the vessel 118 the space for storing solid residues.

From the upper part of the closed vessel also leaves a purge and decompression line 124. This purge and decompression line 124 is advantageously connected to a separator 128. A hopper below the separator filter 128 discharges through a discharge pipe 130, fitted with a gas-tight isolation valve (not shown), in the vessel 118. The purge and decompression gases filtered by the separator 128 are discharged through a discharge pipe 134 fitted with a gas-tight isolation valve (not shown).

The gas supply to the fluidization device 120 is via a line 136 connected to a gas supply (not shown).

The lower end of the vessel 118 opens out through an isolation valve 140 into a pneumatic conveying line 144.

The operation of the device described in the foregoing can be summarized as follows:

The discharge line 112 makes it possible, by opening the isolation valve 116 then the closure member 114, to discharge by gravity said solid residues from the hopper 110 into the closed vessel 118. When the closed vessel is filled to a certain height, which is detected by a level detector, the shutter member 114 is closed first, interrupting the discharge flow before closing the gas-tight isolation valve 116. When loading the vessel 118, the purge valves and the isolation valve are open to allow evacuation of the gaseous content of the vessel 118.

Then the fluidization device 120 is supplied with a constant flow of inert gas. This gas flow is blown from below through the solid residue to create a static or fluidized bed of solid particles.

The inert gas, entraining the gases and vapors contained in the vessel 118 and trapped in the solid residues, is evacuated through the line 124, and the filter 128 in the purge line 134. In the separator 128 the gas mixture is separated entrained solid particles.

The closed vessel 118 is connected to a buffer silo 210 by the line 144. Said silo 210 is also equipped at its upper part with a decompression 214. This decompression 214 is advantageously connected to a separator 218. A hopper in the lower part of the separator 218 discharges the solid particles retained by the filter through a discharge pipe 222, provided with a shut-off valve (not shown) gas tight, in the silo 210. The decompression gases filtered by the separator 218, are evacuated through an evacuation pipe 226 provided with a gas-tight isolation valve 230. This valve 230 is connected to a pressure regulating device 234 controlled by a pressure measuring device 238 permanently monitoring the pressure prevailing inside the silo 210. A gas supply source (not shown) supplies the silo 210 with gas by means of a pipe 242. A first branch 246, comprising a gas-tight valve 250, supplies a fluidization device as described above, located in the lower part of the silo 210. A second branch 254 supplies the upper part of the gas silo 210. This supply is regulated by a valve 258 provided with a regulating device 262, controlled by the pressure measuring device 238.

This equipment makes it possible to control and adjust the pressure inside the silo 210 at all times. In fact, when filling the silo 210, the overpressure is evacuated via the decompression 214. The regulating device 234 controlled by the pressure measuring device 238 only lets out the quantity of gas necessary to maintain the pressure inside the silo 210 at a predetermined value. When the silo is unloaded, gas is injected into the fluidization member and if necessary via line 254, the valve of which is open if the pressure falls below a set value. This silo 210, thanks to this pressure regulation, can be loaded and unloaded simultaneously without varying the unloading rate.

The silo 210 is also equipped with a weighing system 266 so as to be able to determine the weight of the silo 210 at any time and to deduce the flow during unloading.

The pulverulent materials, fluidized inside the silo 210 are discharged through the lower part of the silo 210 equipped with a shutter member 270 which is controlled by a device for determining the flow rate 274 connected to the weighing system 266.

The material flow is fluidized in a fluidization chamber 278 located at the outlet of the silo 210 before the flow is injected into the discharge line 18 via the injection device 30. This way of proceeding makes it possible to inject in continues a controlled flow of powdery materials in line 18.

One of the great advantages of this system is that the dust is injected back into the blast furnace without contact with the open air. Dust pollution of the environment and the workplace is therefore eliminated.

FIG. 2 schematically shows a pneumatic circuit comprising an injection device for a second flow of pulverulent materials and the pressures prevailing in this circuit.

Curve A shows a pressure diagram of a pipe not including an injection device for a second flow of powdery materials.

Curve B shows a pressure diagram of a circuit comprising a device for injecting a second flow of pulverulent materials without an adjusting device. The vertical arrows indicate the variations of pressure over time in this circuit. Without regulation, the pressures and consequently the flow rates vary greatly and the first flow of materials, that of pulverulent coal, in this case, varies very strongly as a function of the pressure variations induced by the injection of the second flow. Under these conditions, it becomes very difficult to control the conduct of the blast furnace because we can no longer effectively control the amount of coal injected over time.

Finally, curve C represents the variations in pressure in the regulated circuit as described above. The regulating member 24 plays an important role in adjusting the pressure and therefore the flow of injected carbon. Indeed, the regulating member 24 makes it possible to work with a higher supply pressure for the same flow rate of pulverulent coal and this pressure is independent of the variations of the pressure prevailing in the remainder of the circuit. By opening or closing the advantage regulating member, a more or less large pressure drop is created, so as to adjust the pressure before said member to the pressure variations created by the device for injecting the second material flow. powdery. If the pressure increased downstream of the regulating member, it would be opened more so as to create a lesser pressure drop. If, on the contrary, the pressure decreased downstream of the regulating member, that would be closed a little more so as to create a greater pressure drop. It is important to underline that this artificial and adjustable pressure drop does not influence the flow of injected carbon, because the pressure in the tank is not influenced by the regulator.

Claims (6)

Method for introducing a second flow of pulverulent materials into a pneumatic transport pipe conveying a first adjustable flow of pulverulent materials characterized in that the second flow of pulverulent materials is introduced at a controlled flow and in that makes the regulation of the first pneumatic transport flow insensitive to disturbances caused by the introduction of the second flow by adjusting the first flow directly or indirectly upstream of the injection point of the second flow. Method according to claim 1, characterized in that the first flow rate is adjusted by measuring and adjusting the first flow rate of pulverulent materials to a predetermined value upstream of the injection point of the second flow. Method according to claim 1, characterized in that the first flow rate is adjusted by measuring the pressure and adjusting it inside the pneumatic conveying line to a predetermined value upstream of the injection point of the second flow. Process according to any one of Claims 1 to 3, characterized in that the second flow of pulverulent materials is injected at an injection point situated in the middle of the first flow of pulverulent materials. Method according to claim 4, characterized in that the second flow of pulverulent materials is injected vertically into the pneumatic line in the direction of flow. Method according to any one of Claims 1 to 5, characterized in that the second flow rate of pulverulent materials is maintained at a constant value.

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