FR2614284A1 - Device for transferring a pulverulent material - Google Patents

Abstract

This device for transferring pulverulent material between an entry conduit 3 and an exit conduit 5 consists of a centrifugal turbomachine 1 including a movable wheel equipped with straight fins rotating in a spiral stator, the entry conduit 3 injecting the material into the central hole of the wheel, the spiral ejecting the material into the exit conduit 5, at least one conduit 22 injecting a stream of gas into the spiral, the said injection conduit or one 22 of the said injection conduits being substantially in line with the exit conduit 5.

Description

Device for transferring pulverulent material
The invention relates to the transfer of porous material, in particular dry cement powder.

 By powdery materials is meant here powdered materials with a high solid concentration: the solid / gas ratio (generally air) is typically 100: 1 or. more.

 It is known to transfer pulverulent materials between an inlet pipe and an outlet pipe using, for example, rotary screw pumps, rotary vane pumps or the like. A drawback of these pumps is their size and their relatively high cost price, both during construction and in use due to their energy consumption.

 The object of the invention is to propose a new transfer device which is simpler, less bulky and more economical than the above-mentioned devices.

 The invention achieves its object by means of a device which comprises a centrifugal turbomachine of the type comprising a movable wheel provided with fins rotating in a scroll stator, the material entering the device by the eye of the wheel and leaving by the outlet. of the scroll. there is provided on the volute at least one gas injection pipe -generally air aidant in particular in the transport of the powder in the outlet pipe following the transfer device. The or one of the injection pipes is substantially aligned with the outlet pipe.

 The turbomachine used is of known type and is used, under the names of centrifugal pump, blower, fan, exclusively for the transfer of liquid or gaseous fluids. Such machi neg are also used when the liquid or gas stream contains a solid material in suspension, but in all cases the maximum possible solid / gas concentration remains very low.

 The principle underlying the use of these turbomachines is based on the transformation of the kinetic energy of the fluid into potential energy inside the device.

This transformation is only recognized by the skilled person as possible for fluids. As AJ Stepanoff, ddn writes; his book "Centrifueal and Axial FLow Pumps" (John Wilen G Sons,
Inc., USA, 1957) which is authoritative in the matter: "suspended solids cannot absorb, store, or transmit potential energy, which is a property of fluids (p.11, 1.6.) And "not playing any. role in the conservation or transmission of potential energy, suspended solids cannot convert their kinetic energy into potential energy "[p.12,1 6.). This is a unanimously recognized physical principle and admitted, and which is therefore completely opposed to the use of turbomachines of this type for the transfer of pulverulent material with almost no carrier fluid, that is to say at high solid concentration.

 However, it has been discovered according to the invention that, contrary to all expectations, such a transfer was possible.

 It seems that a bed of centrifugal fluidized particles is established in the device, and that this fluidized state gives the material a behavior similar to that of a true fluid vis-à-vis a centrifugal turbomachine. This behavior is maintained in the outlet pipe over a distance which can be a few meters. it is possible to prolong this behavior by placing several similar devices in series along the pipe.

 The advantages of the invention are obvious. The technology of these turbomachines is simple and well known. Their size is small. Average energy consumption is reduced significantly to a quarter or a third of that of a positive displacement screw pump, at equal flow.

 Other characteristics and advantages will emerge from the following description of a particular embodiment.

reference will be made to the accompanying drawings on which
FIG. 1 is a schematic side view of the device of the invention installed under a cement hopper,
FIG. 2 is a schematic top view of the device of the invention showing the location of the lateral air jets,
FIG. 3 is a top view of an embodiment of the wheel of the device of the invention,
FIG. 4 is a section IV-IV of FIG. 3,
FIG. 5 is a section VV of FIG. 3.

 FIG. 1 shows the transfer device 1 installed under the vertical discharge pipe 3 of a powdered cement hopper 2. The bottom of the hopper 2 may include a section 4 for fluidizing the cement intended to facilitate the evacuation of the latter. ci by opposing obstructions by agglomeration or vaulting.

 The device 1 returns the cement in a lateral horizontal evacuation pipe 5, to a network of use not described. If the distance from the network is too great and leads to pressure drops opposing the correct transfer of the cement, other devices such as device 1 can be installed along pipe 5.

 The device 1 has an axial inlet 6, provided with a flange 7 for connection to the discharge line 3, and leading the material towards the eye of a movable wheel 8 provided with fins 8 ′ imparting kinetic energy to the material and sending it radially towards the spiral cover or volute 9. This ends with a tangential outlet 10 provided with a flange 11 for connection to the discharge pipe 5.

 The wheel 8 is rotated by a motor housed in a casing 12, and the assembly is supported by a frame 12.

Figures 3, 4 and 5 show a particular embodiment of the wheel 8, quite conventional for a turbomachine wheel: the hub 14 has a central hole 15 where the engine shaft is keyed; the fins S1 radiate around the hub 14 by bending in the intended direction of rotation (but the fins could as well be straight), the central region of the wheel forming the eyelet 16
The device 1 has hitherto been of conventional design in the field of centrifugal turbomachines for transporting fluids and a more detailed description is unnecessary for those skilled in the art. As we have seen, it is essentially the adaptation of this conventional device, for the transfer of a pulverulent material which constitutes the content of the invention.

 FIG. 2 illustrates an example of installation of the air jets decisively improving the efficiency of the system.

 First, a main air jet 7 is injected through a pipe 22 located on the volute 9, in its final section, in the axis 18 of the lateral outlet 5. This air jet is essential for transporting the powdery cement in the pipe 5. The pipe 22 is connected to a main distributor 23 itself connected to a source of compressed air not shown.

 These secondary air jets can be provided along the volute 9. Thus, three inclined jets 19, 20, 21 have been shown in the first three quarters of the volute. Each air jet is injected through a pipe, not shown, connected to the distributor 23: regulating valves 19 ′, 20 ′, 21 ′ allow the flow rate to be adjusted.

 According to a particular embodiment, the main air jet 17 represents half of the total flow of injected air, the three secondary jets 9,20,21 being equally distributed the other half.

 Without an attempt at scientific explanation to limit the scope of the invention, it seems that we can analyze the phenomena involved as well.

 The rotation of the wheel cooperates with the air injected to establish a centrifugal fluidized bed, the main jet 17 transporting the fluidized material to the outlet pipe.

The establishment of this fluidized bed inside the volume defined by the paralt wheel possible even because of the high solid concentration of the material: everything happens in fact count if the particles were sufficiently numerous and dense to "trap" them air and force it with them when these particles are subjected to the centrifugal action of the wheel. On the contrary, for a lower concentration, the air would pass through the particles and would not be entrained it would result in a solid aggregate which would quickly clog the system. Thus, while in known centrifugal transfer systems, it is the fluid which entrains the solid in suspension, according to the invention, it is the solid which entails air.

 It also seems that the different air injections cause a vacuum effect quite similar to the Venturi effect, favoring the setting in motion of the particulate unit.

 Different experiments with various types of equipment have been carried out. In all the tests, the device was used under a hopper loaded with 5 tonnes of cement from the Compagnie des Ciments Belges, class G (in accordance with American Petroleum Institute standards).

Experience nl
The device comprises a turbomachine, the wheel of which is fitted with fins curved in the opposite direction to that of rotation.

 Air is injected via the main main line, aligned with the volute outlet, at a flow rate of 9.5 m3 / min.

 Five rotational speeds were tested and the output flows were measured. The results are as follows.

Tests nO Speed (rpm) Flow rate (kg / min)
1.1 0 98
1.2 500 190 1.3 1000 130
1.4 2000 110
1.5 3000 132
it seems that the output flow does not follow a progression law directly related to the rotation of the turbomachine, but goes through a maximum (test 1-2) for a relatively low rotation speed.

Experiment n02
The device includes the same machine as for experiment nO.

 It rotates at a constant speed of 2000 trslmin. In the first eight tests, air is injected at a total flow rate of 9.5 M3 / min, but distributed according to the tests between the pipes 19,20,21,22 (see Fig. 2); for the last two tests, the total flow was reduced to 42 X of the initial spite.

The output flow rate was measured, as a function of the distribution of the injected air. The results are as follows:
Tests n Injection pipe Flow rate (kg / min)
2.1 19,20,21,22 120
2.2 19.20, 21.22 115
2.3 20.21.22 117
2.4 21.22 95
2.5 20.22 97
2.6 22 136
2.7 19.22 92
2.8 19,20,22 106
2.9 22 86
2.10 19.20, 21.22 95
the usefulness of the secondary injection lines seems to depend on the total air flow. At high air flow, primary injection alone gives the best bladder results 2.6).

 Other tests have shown that an insufficient air flow (less than 20X of the initial flow) no longer allows the device to operate.

Experiment 3
We have repeated, in the same general conditions, of experiment n 1, but with a turbomachine whose wheel is equipped with straight blades. The results are as follows:
Tests n Speed (rpm) Flow rate (kglmin)
3.1 1000 190
3.2 2000 197
3.3 2000 235
3.4 2500 278
3.5 2500 178
Tests 3.2 to 3.5 were carried out one or two days apart, in the open air, and seem to indicate fluctuations of which the changing humidity conditions can undoubtedly account.

 it seems that the following operating conditions for a straight-bladed wheel can be used as the best embodiment (which is unusual for transfer devices). rotation speed 2500 trsimin.

 air flow of 9.5 m3 / min injected into the main line 22.

 The flow of cement transferred is then of the order of 280 kg / min.

Claims (4)

1. Device for transferring pulverulent material between an inlet pipe (3) and an outlet pipe (5), characterized in that it consists of a centrifugal turbomachine (1) comprising a mobile wheel (B) provided fins (B ') rotating in a scroll stator (9t, the inlet pipe (3) injecting the material into the eye (8) of the wheel (8), the scroll (9) ejecting the material into the outlet pipe (5t, and in that it comprises at least one pipe (22) injecting into the volute (9) a jet (17,19,20,21) of gas, the or one (22) said injection pipes being substantially aligned with the outlet pipe (S). 2. Device according to claim 1, characterized in that the wheel has straight fins. 3. Device according to claim 1, characterized in that the wheel has fins curved in the opposite direction to that of rotation.  4 Device according to any one of claims 1 to 3, characterized in that the speed of rotation of the wheel is between 0 and about 3000 rpm.  8. Device according to any one of claims 1 to 4, characterized in that the flow rate of injected gas is between 2 and @, 5 m / min and is preferably of the order of 9.5 m3 / min. 6. Device according to claim 1, characterized in that the wheel has straight fins and is driven at a speed of about 2500 rpm, the injected gas being air introduced by the line (22) aligned on the outlet pipe with a flow rate of approximately 9, S m3 / min.