WO2001028900A1 - Pneumatic device for controlling the flow of granular solids - Google Patents

Abstract

The pneumatic device for controlling the flow of granular solids is chiefly characterized in that it consists of a non-mechanical valve (that is, it has no mobile elements) which is based on combinations of vertical and slanted tubular sections. It is operated with compressed air or another aeration gas in such a way that the flow of solids passing through the device can be controlled, whereby said flow can be modified in a given interval or can be even closed completely if desired. The device comprises automatic control systems to regulate the flow of the solid and the aeration flow volumes used in the handling of said flow and during self-cleaning cycles. The device can be used in managing, dosing and controlling the flow of granular solids in hoppers, silos, mobile and fluidized beds.

Description

Title

Pneumatic device to control the flow of granular solids State of the art

The transport of granular solids is a very common operation in various industrial sectors in which it is necessary to empty or fill containers, either to control the level in them, control the passage of solid from one container to another or dose a certain amount of solid in containers for packaging and distribution. In any case, it is necessary to control the flow of the solid through a conduit to maintain the level or dosage variables in required values. There are many devices used for this purpose. Some are mechanical, such as chopping or butterfly valves, worm screws, pistons, conveyor belts and rotary cylinders; others are pneumatic, with no moving or non-mechanical parts, such as L valves in vertical pipes and fluidized beds attached to inclined pipes.

Various configurations, geometric shapes and applications of these devices have been described in scientific and technical publications and patents. The works of Trees and Sarkar et al. on transport systems based on inclined pipes finished in fluidized beds (J. Trees, '"A Practical Investigation of the Flow of Particulate Solids Through Sloping Pipes", Trans. Instn. Chem. Engrs. 40 _^ 1962, pp. 286-296 ; M. Sarkar, SK Gupta and MK Sarkar, "An Experimental Investigation of the Flow of Solids from a Fluidized Bed Through an Inclined Pipe", Powder Technology 64 _> 1991, pp. 221-231) and the work of Knowlton and Hirsan on L valves (TM Knowlton and I. Hirsan, "L-Valves Characterized for Solids Flow", Hydrocarbon Processing, Marchl978, pp. 149-156). Five patents on different types of L valves used as regulating element of the flow of granular solids in loads, discharges and level control of fluidized systems are also highlighted (US 4500231, US 4538549, US 4687382, JP6074418A, JP8134520A). The main advantages of pneumatic type valves and devices derive from the fact that they are non-mechanical devices, that is, they do not have moving parts such as conventional valves used with fluids, and are of relatively simple construction and reduced cost.

On the other hand, the most important problems that arise when designing and using L valves, devices based on inclined or vertical tubular elements terminated in a fluidized bed and similar pneumatic devices are the following:

• The balance of pressures inside pneumatic devices with solid circulation is very complicated and it is difficult to design and manage devices that can control the flow of granular solids over a wide range of flows and for different types of solid. This means that it is necessary to make a large number of studies, tests and adjustments for each type of application. Practically, each device must be designed for each particular case, type of solid (density, particle size, shape and irregularities of the granules), operating conditions (differences in pressure between different parts of the device, flow range of solid to be controlled ). Frequently, a valve thus designed will hardly work well by varying, sometimes only slightly, some of the conditions or properties assumed in the design.

• The appearance of agglomerations that produce solid blockages in different parts of the system is frequent. In devices based on an inclined or vertical duct terminated in a small fluidized bed that controls the flow of the solid, defluidization phenomena occur (the bed stops fluidizing, remains fixed and blocks the passage of the solid). In the vertical or inclined ducts a circulation regime of the descending solid called udder circulation can occur, in which a solid-free, high-flow and uncontrolled transport occurs. • The transport and flow control operations of solids that have certain rheological and dynamic fluid properties are especially complicated, sometimes impossible, on many occasions. For example, when handling irregularly shaped granule solids (similar to needles, plates, discs), sticky materials (resinous wood sawdust, certain plastics and synthetic rubbers), very small particle size materials that can be electrified by friction ( fine particles of plastic, glass, cloth, paper), fine and hygroscopic materials (flours, certain drugs, paints, dyes and pigments), mixtures of different nature (metals and plastics, two or more solids of different density or particle size) .

Explanation of the invention.

The pneumatic device for controlling the flow of granular solids object of the present invention solves three fundamental problems of those indicated above: it allows to control the flow of solid in a wide range of values, by means of an adequate rhythm of pulses of air or other compressed gas, allows to control the flow of very diverse solids, when using these impulses and avoids or eliminates agglomerations and clogging by means of a special self-cleaning cycle.

The pneumatic device is a combination of areas of circulation and pneumatic transport by impulses of air or other compressed gas. The geometry and construction mode are based on combinations of tubular, quadrangular or rectangular sections of vertical and inclined arrangement. The device operates with an aeration gas, usually compressed air, but any other gas such as nitrogen can be used in case of explosion-proof conditions or inert atmosphere. By sequentially applying pulses of the injection gas, control can be exercised on the flow of solid that passes through it, modifying it within a given interval, and even completely closing the solid passage if it is of interest. The pneumatic device, object of the invention, has the advantage of being able to have a self-cleaning cycle, which can be imposed periodically or by an appropriate control criterion (for example, depending on pressure variations that indicate the start of agglomeration formation or clogging, or depending on certain cycles of sampling or changes in the type of solid to be controlled).

In the pneumatic device there are no moving parts that can be subject to damage due to wear, seizing, deformations, obstructions, etc., which implies a reduced maintenance and repair cost. On the other hand, the number of emergency stops and start-up delays caused by the low efficiency of other systems is reduced.

Also this pneumatic device is very versatile; the diversity of solids that can be handled is wide and the range of flows of solid to be controlled, temperatures and pressures. It is constructed with standard materials (for example, stainless steel AISI 304 and AISI 316, iron, plastic, metal coated with vitreous or ceramic layers, etc.) and is simple to mechanize, compact structure and easy transport and installation. In addition, it is simple to clean since it can be washed with water since there is no electrical part.

The pneumatic device for controlling the flow of granular solids is a pneumatic system, that is, all its operation is based on air or other compressed gas. For this reason it is anti-flammable and, with respect to similar pneumatic devices, drastic reductions in the consumption of aeration gas necessary to achieve large mass flows of solid are achieved while mastering said flow very effectively.

The applications of the pneumatic device to control the flow of granular solids are varied, presenting special efficiency when used as a system of feeding or discharge to fluidized, fixed, mobile and combined bed systems. The device can be manufactured and arranged practically airtightly or with a conduit outlet, which means that dispersion of fines and suspended solids in the working environment (toxicity, allergies, etc.) is avoided and applications can be easily made to solids that require inert atmospheres.

Finally, the pneumatic device for controlling the flow of granular solids is equipped with an advanced control system that allows to increase the effectiveness of the operation, safety at work, reduce operating costs, save energy and minimize environmental impact.

Description of the drawings

To facilitate the understanding of the features of the invention and as part of this specification, a figure is attached that illustrates the following:

Figure 1. Figure 1 represents an elevation view of the pneumatic device assembly for controlling the flow of granular solids, consisting of the following parts: a storage hopper, fluidized bed, moving bed or any other type of container (1) that it contains a granular solid; a tubular, cylindrical or quadrangular section (2) equipped with air or other compressed gas inlets (12, 13, 14); a tubular, cylindrical or quadrangular section (3) equipped with air or other compressed gas inlets (7, 8, 9, 10, 11); a zone for reconduction of the solid of cylindrical or quadrangular section (4) provided with a rounded dome (5) to avoid violent collision of the solid with the upper part of the aforementioned reconduction zone; an outlet of the solid (6) that communicates with a second container where the solid from (1) wants to be sent or dosed; a valve (15) for gas outlet in cases where the outlet (6) is airtight and to avoid overpressures within the system. Embodiment of the invention

Referring to the numbering indicated in the figure, it can be seen that the pneumatic device for controlling the flow of granular solids, carried out at a precise scale for the required flow range, consists of an inclined conduit (2) connected with a container that It contains the solid and from which you want to transport it (1). This duct can have an inclination angle between 40 ° and 90 ° to avoid accumulations of solid and facilitate its circulation; on the other hand, this inclined duct is provided with a certain number of air injection points or other compressed gas (for example, the ducts 12, 13 and 14 indicated in the figure). These injection points are circular section tubes with a sigmoidal shape to prevent the exit or return of solid through it when the compressed air or gas does not circulate through them. The inclined duct ends in a vertical duct (3) also provided with a certain number of injection points of air or other compressed gas (for example, ducts 7, 8, 9, 10 and 11 indicated in the figure). These injection points are also circular section tubes with a sigmoidal shape to prevent the exit or return of solid through them when the compressed air or gas does not circulate through them. The vertical conduit is surrounded by another vertical conduit (4) whose purpose is to prevent the solid from dispersing through the environment and causing all the solid to be redirected towards the bottom and mouth or outlet flange (6). Through the injection points of air or other compressed gas, the correct functioning of the system is achieved. It can be operated in three types or modes of operation: solid flow rate control, complete solid step closure and self-cleaning. Each of these modes of operation requires that the sequence of injections of air or other compressed gas through the different injection points (7-14) be different. This sequence is regulated by the appropriate control system equipped with timers and sequencers that allow injections of air or other compressed gas of a certain duration through each injection duct. During normal operation the device functions as a control device for a given flow of solid through the device or as a dosing device that is feeding a dose of solid from time to time to fill vials or other types of containers. In this mode of operation, the sequence of injections through the injectors is downstream of the conduit 3, that is, an injection is first made through point 11, then through point 10, then through point 9 , and so on. This allows a very accurate dosage of solid packets and a wide range of flow rates. For example, for low flow rates or small doses, only injection point 11 is used, so that with each injection of air or other compressed gas through 11 only a small amount of solid is displaced upwards. The small range of flows can in turn be adjusted by setting the time during which the injection of air or other compressed gas lasts through point 11 and the downtime left between injection and injection. Similarly, for a larger range of flow rates or doses, successive injections are used at points 11 and 10. Similarly, in order to control large flow rates, successive injections are used at all injection points provided by the vertical conduit ( 4).

During the shutdown operation mode, air or other compressed gas is simply stopped injected through the injection ducts (7-14). In this way, the rheological properties of the granular solid cause the circulation of the solid through the conduits 2 and 3 to be completely interrupted, in this case the device functioning as a non-mechanical valve for closing the solid passage.

During the self-cleaning operation mode the pneumatic device to control the flow of granular solids can be completely emptied of solid. This self-cleaning is done from time to time to ensure that there are no agglomerations, deposits or portions of solid adhered to the walls of pipes 2 and 3, or to renew completely the content of these areas for analysis, equipment cleaning, total emptying before changing the type of solid to be transported, etc. The way to carry out this self-cleaning is as follows: with the injection points 7-13 closed, that is to say without injection of air or other compressed gas through them, one proceeds to inject impulses of air or other compressed gas by point 14 This will empty the upper part of the inclined duct (2), successive injections through points 13 and 12 will empty the rest of the inclined duct. Finally, successive injections through points 11, 10, 9, 8 and 7 will empty the vertical duct (3).

There is an outlet duct (15) that serves to vent gases in case of excessive overpressure within the system, if used as a dispenser or flow controller in an airtight system, that is, with the solids outlet (6) connected by flanges or systems similar to another closed conduit or vessel. The arrangement of the outlet (15) just below the duct (3) reduces the probability of solids coming out of said gas outlet (15) which, independently, can be provided with filters, cyclones or other similar devices to collect the possible particles fine that leave improperly through said exit.

The solid finally has its exit from the bottom of the conduit (4) through a simple mouth or a suitable connection element (6) from where it is directed to any other storage, transport or destination device that is coming.

All the main ducts of the pneumatic device to control the flow of granular solids (2, 3, 4, 5) are manufactured in materials suitable for the conditions of pressure, temperature and physicochemical aggressiveness of the solid to be treated (to minimize the wear of the equipment and of the solid itself, corrosion problems, etc.) and can be made of tubular or quadrangular section, depending on the size and scale required.

Claims

1. Pneumatic device for controlling the flow of granular solids, characterized by the integration in a single apparatus of a circulation zone, inclined or vertical, of a vertical zone of pneumatic transport of granular solids and an adequate number of tubes for injection of air or other gas impulses, fully pneumatic operation and characterized by the absence of moving or electrical parts. 2. Pneumatic device for controlling the flow of granular solids, according to the preceding claim, characterized in that by applying an adequate rhythm of pulses of air or other compressed gas, a control is exercised on the flow of granular solids and allows dosing over a wide range of values. 3. Pneumatic device for controlling the flow of granular solids, according to claim 1, characterized by the sigmoidal shape of the injection tubes to avoid losses of solid by them and by the shape and location of the vent tube to also prevent the exit of solid through said conduit. 4. Pneumatic device for controlling the flow of granular solids, according to previous claims, which has a self-cleaning cycle to eliminate agglomerations, portions of solid adhered to the walls of the device or completely empty it 5. Pneumatic device for controlling the flow of granular solids, according to previous claims, characterized in that air or any other gas or gaseous mixture can be used as an injection and discharge gas for its operation. 6. Pneumatic device for controlling the flow of granular solids, according to previous claims, characterized in that it comprises a control system for the impulses of air or other compressed gas that regulates the periodic or aperiodic sequence of the impulses in each and every one of the different device injection points 7.. Pneumatic device for controlling the flow of granular soils, according to previous claims, which can be used as a feed and discharge control system for fluidized systems, fixed beds, moving beds and combinations between them and as a dosing system for containers or containers. 8. Pneumatic device for controlling the flow of granular solids, according to claim 7, which can be manufactured and arranged in a hermetic or driven manner to avoid contact of the solid transported inside with the environment. MODIFIED CLAIMS [received by the International Office on February 1, 2001 (01.02.01); original claims of 1-8 replaced by modified claims of 1-6 (1 page)] 1. Pneumatic device for controlling the flow of granular solids, characterized by the integration in a single device of an inclined circulation area and of 5 a vertical area of pneumatic transport of granular solids with a number of tubes for the injection of pulses of air or other gas. 2. Pneumatic device for controlling the flow of granular solids, according to the preceding claim, characterized in that the control of the flow of solids is carried out by applying an adequate succession of pulses of air or other gas. 0 3. Pneumatic device for controlling the flow of granular solids, according to claim 1, characterized by the sigmoidal shape of the injection tubes to avoid losses of solid by them and by the shape and location of the vent tube to also prevent the exit of solid through said conduit. 4. Pneumatic device for controlling the flow of granular solids, according to 5 previous claims, which has a self-cleaning cycle to eliminate agglomerations, portions of solid adhered to the walls of the device or completely empty it. 5. Pneumatic device for controlling the flow of granular solids, according to previous claims, characterized in that it comprises a system of 0 control of the pulses of air or other gas that regulates the sequence of the pulses in each and every one of the different injection points Of the device. 6. Pneumatic device for controlling the flow of granular solids, according to previous claims, which can be manufactured and arranged in a hermetic manner or driven outlet to avoid contact of the transported solid 5 inside with the environment.