CA1260441A

CA1260441A - Apparatus for discharging fine-grained solids

Info

Publication number: CA1260441A
Application number: CA000478837A
Authority: CA
Inventors: Egon Ackermann; Rudiger Gartner
Original assignee: Metallgesellschaft AG
Current assignee: GEA Group AG
Priority date: 1984-04-12
Filing date: 1985-04-11
Publication date: 1989-09-26
Also published as: BR8501710A; DE3413750A1; JPS60228324A; AU568930B2; EP0159751A1; IN159579B; GR850906B; AU4104585A

Abstract

ABSTRACT OF THE DISCLOSURE

An apparatus for discharging fine-grained solids from a system which is under a high pressure into a re-ceiving space which is under a lower pressure. The appa-ratus comprises means forming a U-shaped siphon having a vertical entrance leg, a vertical discharge leg, and a connection at a bottom of the siphon between the legs;
a solid supply line leading from the system under a higher pressure to the entrance leg of the U-shaped siphon; means forming a solids outlet on the discharge leg for connecting the discharge leg of the U-shaped siphon to the receiving space; and a supply line for supplying entraining gas to solids contained in a lower portion of the siphon.
The discharge leg is shorter than the entrance leg. A
shut-off device for opening and closing the solids outlet of the discharge leg is biased opposite to the direction of flow by a force which slightly exceeds a force which is exerted on the shut-off device in the direction of flow by pressure in the discharge leg.

Description

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The present invention relates to an apparatus for discharging fine-grained solids.
In particular, the present invention relates to apparatus for discharging fine-grained solids from a system which is under a higher pressure into a receiving space which is under a lower pressure.
It is often necessary to discharge fine-grained solids from a system in such a manner that reaction gases cannot escape from the system and that gases cannot enter the system. If the fine-grained solids have an exactly defined angle of repose, said solids can substantially seal the discharge apparatus if the discharge apparatus always contains a sufficient amount of solids. Flowable solids may fail to provide a seal even if they are con-lS tained in the discharge apparatus. In both cases the solids will not provide a seal if the discharge apparatus contains no solids or only an inadequate quantity of solids. Flow-able solids often cannot be discharged in a controlled quantity or at a controlled rate.
German patent specification 915,199 discloses a discharge apparatus in which a passage which is rela-tively small in diameter is provided between two chambers, which are under different pressures, and the passage is closed at its outlet end by a weight-biased flap. A feeding plunger is provided for forcing solids in a compacted state into the passage so that the flap will be opened by the solids as they are advanced and a corresponding quantity of solids will fall out of the outlet end, which is subsequently closed by the flap.
Germain patent publication 11 21 545 discloses discharge apparatus in which the sealing means consist of a lock chamber provided with a star feeder, which discharges the solids through a supply line to a lifting tube, in which the solids are pneumatically conveyed.

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U.S. patent 2,833,622 discloses discharge apparatus which comprises a U-shaped siphon, one leg of which is connected to a duct for supplying solids from a cyclone, which is connected to fluidized bed equipment.
The other leg is provided in its top part with an opening for discharging the solids, which drop into a container.
A line for supplying an entraining gas opens above the bottom of the U-shaped siphon. The entraining gas entrains the solids upwardly in the discharge leg and through the outlet opening out of the siphon. That discharge apparatus will not provide a seal if no solids are contained in the siphon and if the higher pressure in the system is sufficient for a discharge of flowable solids. In the latter case the discharge rate will highly depend on the lS pressure in the system.
It is an object of the invention to provide apparatus for the discharge of fine-grained solids, in-clusive of flowable solids, from a system that is under a higher pressure to a receiving space which is under a lower pressure, which discharge apparatus does not tend to be clogged and has only a small wear and permits a simple and accurate control of the discharge rate and will prevent an escape of gases from the system even when no solids are contained in the discharge apparatus.
According to the present invention, there is provided an apparatus for discharging fine-grained solids from a system which is under a high pressure into a re-ceiving space which is under a lower pressure, comprising:
means forming a U-shaped siphon having a vertical entrance leg, a vertical discharge leg, and a connection at a bottom of the siphon between said legs;
a solid supply line leading from the system under a higher pressure to said entrance leg of the U-shaped siphon;
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1;~60441 means forming a solids outlet on said discharge leg for connecting sald discharge leg of the U-shaped siphon to said receiving space;
a supply line for supplying entraining gas to solids contained in a lower portion of the siphon, said discharge leg being shorter than said entrance leg; and a shut-off device for opening and closing said solids outlet of the discharge leg and biased opposite to the direction of flow by a force which slightly exceeds a force which is exerted on said shut-off device in the direction of flow by pressure in said discharge leg.
The expression "system which is under a higher pressure" covers any equipment in which fine-grained solids are treated and which is under a pressure that is higher than the pressure in the space which receives the treated solids. Such equipement is used, e.g., in fluidized bed processes. The expression "receiving space" covers any equipment which is under a lower pressure than the system, and includes, e.g., a bin, a belt conveyor, a handling vessel etc.. The pressure difference between the system and the receiving space may be very small, e.g., 0.5 mbars, or may be much higher, e.g., 10 mbars or more. The line for supplying the entraining gas is so arranged that in an inoperative condition of the apparatus said line opens in the bed of solids in the lower portion of the siphon and that it is directed toward or directly into the dis-charge leg. The discharge leg is about 10 to 40~ shorter than the entrance leg. The height of the column of solids in the entrance leg connected to the solids supply line should be so large that said column will seal the system from the receiving space. The magnitude of the force which biases the shut-off device opposite to the direction of flow is so selected that it will just seal the solids lZ6044~

outlet against the action of the pressure in the system.
When the siphon contains no solids or only a small amount of solids, the valve will seal the solids outlet so that no gas can escape from the system. In that case the valve will be closed even when entraining gas is being supplied because this will virtually result in no increase of the pressure. If the entrance leg of the siphon is filled with solids, the solids outlet will be closed too as long as no entraining gas is supplied. When entraining gas is being supplied, the valve will be opened by the pressure in the discharge leg and solids will be entrained by the entraining gas through the solids outlet. The force which biases the valve opposite to the direction of flow may be exerted pneumatically, mechanically or electrically.
The solids outlet may be provided at the top or on the side.
Preferably, the shut-off device consists of a plate, which closes the solids outlet and which is se-cured to a movable piston rod. The plate may constitute a planar surface or may have the shape of a cone having an apex facing opposite to the direction of flow. The conical shape will be particularly desirable if the solids outlet faces vertically upwardly. That end of the discharge leg where the solids outlet is provided is preferably formed with a bead because this will improve the seal.
The provision of the shut-off device comprising a plate and a piston rod will ensure a good guidance of the shut-off device.
Preferably, the piston rod is secured to a dia-phragm, which is accomodated in a pressure vessel, anda fluid is supplied to the outer chamber of the pressure vessel. The fluid may consist of a gas or a liquid. In this manner the required force can easily be exerted on the plate.

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lZ60441 Preferably, a supply line Eor a gaseous fluid and a discharge line for a gaseous fluid open in the outer chamber of the pressure vessel. In that case the required force can be exerted on the plate in a particularly simple manner.
Preferably, the discharge line for the gaseous fluid leads from the outer chamber of the pressure vessel to the system. A flow of gas at a low rate from the pres-sure vessel through the discharge line into the system will ensure that the force by which the plate is biased opposite to the direction of flow will exceed the pressure acting from the system on the plate in the direction of flow. The area of the diaphragm must slightly exceed that area of the plate which can be subjected to the pressure in the system. In that case the required backpressure force can be produced and controlled in a very simple manner.
Preferably, the solids outlet of the discharge leg communicates with a coaxial tube which has an aperture, the piston rod extends through said aperture, and the aperture is sealed by a sealing element which surrounds the piston rod. The coaxial tube extends somewhat above the solids outlet of the discharge leg and is sealed at that end by a diaphragm. The solids entrained by the entraining gas are entrained downwardly through the annular gap which is defined between the discharge leg and the coaxial tube. This design results in a particularly simple and reliable structure.
A preferred embodiment of the invention will now be explained in more detail as example without limita-tive manner with reference to the drawings, wherein:
Figure 1 is a transverse sectional view showing discharge apparatus in which the solids outlet faces up-wardly; the connection to the system and the receiving ~ .
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space are not shown.
Figure 2 is a diagrammatic view showing discharge apparatus which is provided with a lateral solids outlet and is connected to the system and the receiving space.
The dischar~e apparatus comprises a U-shaped siphon 1, which has an entrance leg 3. The latter is con-nected to a system 17 (figure 2) by a solids supply line

2 (which is indicated only by an arrow in figure 1). The discharge leg 5 is provided with a solids outlet 4, which faces upwardly in figure 1 and laterally in figure 2.
In accordance with figure 1 the solids are entrained by the entraining gas into the annular gap between the dis-charge leg 5 and the coaxial tube 15. In accordance with figure 2 the solids are entrained by the entraining gas into the laterally disposed space 18. Thereafter the solids enter the receiving space l9, which is provided in ac-cordance with figure 2 by a belt conveyor and which is under a lower pressure than the system 17. A nozzle pro-vided in the bottom of the siphon constitutes a supply line 6 for entraining gas. The shut-off device 7 associated with the solids outlet 4 consilsts of a plate 8, which is secured to a movable piston rod 9. The piston rod 9 is secured to a diaphragm 10, which is contained in a pressure vessel 11. A supply line 13 and a discharge line 14 for a gaseous fluid open in the outer chamber 12 of the pressure vessel 11.
In accordance with figure 1 the top opening of the coaxial tube 15 is sealed by a diaphragm seal 16, which surrounds the piston rod 9 in gastight contact there-with. The piston rod 9 extends through the bearing 20.
The solids outlet 4 is closed by the plate 8. When en-training air is supplied through the nozzle 6, as is indicated by a dotted line, the plate 8 will be lifted so that solids are entrained by the entraining air through A

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the solids outlet 4 into the annular gap between the dis-charge leg S and the coaxial tube 15 (dotted line arrows).
In accordance with figure 2, the rate at which air is supplied through the supply line 13 into the outer part 12 of the pressure vessel 11 is sufficient to result in a flow of air at a low rate through the discharge line 14 into the system.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An apparatus for discharging fine-grained solids from a system which is under a high pressure into a receiving space which is under a lower pressure, com-prising:
means forming a U-shaped siphon having a vertical entrance leg, a vertical discharge leg, and a connection at a bottom of the siphon between said legs;
a solid supply line leading from the system under a higher pressure to said entrance leg of the U-shaped siphon;
means forming a solids outlet on said discharge leg for connecting said discharge leg of the U-shaped si-phon to said receiving space;
a supply line for supplying entraining gas to solids contained in a lower portion of the siphon, said discharge leg being shorter than said entrance leg; and a shut-off device for opening and closing said solids outlet of the discharge leg and biased opposite to the direction of flow by a force which slightly exceeds a force which is exerted on said shut-off device in the direction of flow by pressure in said discharge leg.

2. The apparatus defined in claim 1, wherein said shut-off device comprises a plate which closes the solids outlet and which is secured to a movable piston rod.

3. The apparatus defined in claim 2, wherein said piston rod is secured to a diaphragm which is received in a pressure vessel, and means is provided for supplying a fluid to an outer chamber of said pressure vessel.

4. The apparatus defined in claim 3, wherein a supply line for a gaseous fluid and a discharge line for a gaseous fluid open in said outer chamber of said pressure vessel.

5. The apparatus defined in claim 4, wherein the discharge line for the gaseous fluid leads from said outer chamber of said pressure vessel to said system under higher pressure.

6. The apparatus defined in claim 2, wherein the solids outlet of the discharge leg communicates with a coaxial tube which has an aperture, the piston rod extends through said aperture, and the aperture is sealed by a sealing element which surrounds the piston rod.

7. The apparatus defined in claim 6, wherein said supply line for supplying entraining gas includes a nozzle opening upwardly into said discharge leg at the bottom thereof.

8. The apparatus defined in claim 7, wherein said shut-off device further comprises means for applying a biasing force to said rod acting against the pressure in said discharge leg.

9. The apparatus defined in claim 6, wherein said means for applying said discharge force includes a diaphragm connected to said rod and having a diameter greater than the diameter of contact of said plate with said solids outlet.

10. The apparatus defined in claim 9, further comprising means defining a pressure vessel receiving said diaphragm and having an outer chamber, and means for pres-surizing said outer chamber.